مدیریت فناوری نانو

Nano management

Self-perfection in nanomanufacturing

Posted: May 2, 2008

(Nanowerk Spotlight) In the past, random defects caused by particle contamination were the dominant reason for yield loss in the semiconductor industry - defects occur in the patterning process (so-called process defects) when contaminants become lodged in or on the wafer surface. Another problem are mask defects, where particle contamination on the photomask used in the lithography process end up on the wafer as defects or pattern distortions. Trying to prevent such fabrication defects, chip manufacturers have spent much effort and money to improve the fabrication process, for instance by installing ultra-clean fabrication facilities. 'Class One' cleanrooms, the cleanest of all, keep the number of particles that are larger than 500 nanometers to less than 3000 per cubic meter. It takes an incredible amount of technology to achieve and maintain such cleanliness and that's what makes these facilities so expensive to build and maintain.

With the semiconductor industry's move to advanced nanometer nodes, and feature sizes approaches the limitation of the fabrication method used, particles are no longer the only problem for chip manufacturers. In a nanoscale feature-size fabrication environment, systematic variations, such as metal width and thickness variations or mask misalignment, are also major contributors to yield loss.

Rather than perfecting a nanostructure by improving its original fabrication method, researchers at Princeton University have demonstrated a new method, known as self-perfection by liquefaction (SPEL), which removes nanostructure fabrication defects and improves nanostructures after fabrication.

nanoscale silicon lines improved by SPEL
SEM images of nanoscale silicon lines before (left) and after (right) treatment with open-SPEL with a single excimer laser pulse. (Reprinted with permission from Nature Publishing Group)

"When feature sizes in a device are small enough, the fabrication defects in many nanofabrication methods can become a dominant factor that determines the actual shape of the nanostructure" Dr. Stephen Y. Chou explains to Nanowerk. "Although extrinsic defects can be removed by improving the process, intrinsic defects caused by the fundamental statistical nature of a fabrication process – for example, noise in photon, electron or ion generation, scattering, and variations in chemical reaction – cannot be removed within the process regardless of improvements to it. The minimum line width and line height are often determined by the fundamental working principle of a fabrication, and are fixed once a fabrication method is selected."

"Our process removes defects after fabrication rather than in the fabrication. As structures become very small, conventional fabrications will be limited by intrinsic noise, and improving the fabrication technology becomes fruitless."

Chou, the Joseph C. Elgin Professor of Engineering at Princeton University and head of the university's Nanostructures Laboratory, developed the method along with graduate student Qiangfei Xia. Chou's lab has previously pioneered a number of innovative chip making techniques, including a revolutionary method for imprinting of nanopatterns on wafers. The scientists published their method in the May 4 online issue of Nature Nanotechnology ("Improved nanofabrication through guided transient liquefaction"), showing a technique that could lead to more precise shaping of microchip components beyond the current technology limits, potentially allowing them to be smaller, better and more powerful computers and other devices.

"SPEL is a paradigm shift in nanofabrication," says Chou. "We are able achieve a precision far beyond what was previously thought possible (e.g. ITRS – The International Technology Roadmap for Semiconductors). Using this method we reduced the line-edge roughness of 70-nm-wide chromium grating lines from 8.4 nm to less than 1.5 nm, which is well below the 'red-zone limit' of 3 nm discussed in ITRS. We also reduced the width of a silicon line from 285 nm to 175 nm, while increasing its height from 50 nm to 90 nm."

Rather than struggle to improve fabrication methods, Chou's solution would fix the defects after fabrication. Even more, the fixing is a 'self-perfection' – it automatically corrects the defects. The process is not only capable of removing both intrinsic and extrinsic defects but also of forming new shapes that may not be achievable using conventional fabrication techniques.

Chou's SPEL method achieves this by selectively melting the structures on a chip momentarily (hundreds of nanoseconds) while guiding the liquid flow into a desired shape before re-solidification. Natural forces acting on the molten structures, such as surface tension – the force that allows some insects to walk on water – smooth the structures into geometrically more accurate shapes. Lines, for instance, become straighter, and dots become rounder. The method has three basic forms: open-SPEL, capped-SPEL and guided SPEL:

Working principle of three forms of self-perfection by liquefaction
Working principle of three forms of self-perfection by liquefaction (SPEL). a–c, Open-SPEL (a), capped-SPEL (b) and guided-SPEL (c) for lines and squares (or dots). SPEL selectively melts nanostructures (for example, silicon or chromium) for a short period of time (hundreds of nanoseconds) while applying a set of boundary conditions (for example, one or more plates placed in contact or a gap above) to guide the flow of the molten material into a desired geometry before solidification. SPEL can significantly reduce the LER, can increase the sidewall slope and flatten the top surface (capped- and guided-SPEL), and, moreover, narrow the width while increasing the height (guided-SPEL). (Reprinted with permission from Nature Publishing Group)

A simple straight melting was tried to smooth out the defects in plastic previously, but cannot apply to nanostructures on a chip, because of two obstacles. First, the key structures on chips are not made of plastic which can be melt at temperature close to boiling water, but rather the materials with a high melting temperature that will melt nearly everything, including other parts of the chip. Secondly, melting itself will widen the structures and round their top and side surfaces – all detrimental to the chip's integrity.

Chou overcame the first obstacle by using a light pulse from an excimer laser which melts only semiconductors and metals and only the tiny surface layer, in a similar fashion to laser eye surgery. Only 10 millionth of a second of melting is sufficient for this process since molten metal and semiconductors can flow as easily as water and have high surface tension, which allows them to smooth out even during that extremely short time frame.

The researchers overcame the second obstacle by adding a guiding to direct the flow. They placed a plate on top of the melting structure, which prevents widening of the molten structure and keeps the structure top flat and side surface straight. In one experiment, it made the edges of 70 nanometer-wide chromium lines more than five times smoother. The resulting line smoothness was far more precise than what semiconductor researchers believe to be attainable with existing technology.

Chou points out that the working principle behind SPEL is fundamentally different from conventional fabrication methods. "SPEL puts a structure into liquid phase and uses surface tensions and other guiding to change its existing shape to a desired one – this process involves different physics from conventional nanofabrication and it opens up new directions in nanomanufacturing approaches and sciences."

While SPEL can be scaled to large-area wafers (more than 8 inch diameter), Chou points out that the process does have limitations: "For example, it cannot be applied when the dimensions of the defect are comparable with the dimensions of the nanostructure, and it cannot fix defects where the total materials are insufficient" he says.

Nevertheless, several leading semiconductor manufacturers have expressed keen interest in the technique, according to Chou.

By Michael Berger. Copyright 2008 Nanowerk LLC

+ نوشته شده در  87/02/13ساعت 21:38  توسط مهندس محمدرضا فروغی  | 

UT Dallas and Brazilian Researchers Discover New Properties for Nanotube Sheets

A team of nanotechnologists at The University of Texas at Dallas, along with Brazilian collaborators, have discovered that sheets of carbon nanotubes can produce bizarre mechanical properties when stretched or uniformly compressed.

These unexpected but highly useful properties could be used for such applications as making composites, artificial muscles, gaskets or sensors. The team’s findings are reported in the April 25 issue of the journal Science.

When most materials are pulled in one direction, they get thinner in the other direction, similar to how a rubber band behaves when it is stretched. However, specially designed carbon nanotube sheets, dubbed “buckypaper,” can increase in width when stretched. The buckypaper can also increase in both length and width when uniformly compressed.

Ordinary materials contract laterally when stretched — a phenomenon that can be quantified by Poisson’s ratio, which is the ratio of the percent lateral contraction to the percent applied stretch.

Dr. Ray H. Baughman, Robert A. Welch Professor of Chemistry and director of UT Dallas’ NanoTech Institute, and his colleagues created their nanotube sheets, or buckypaper, by drying a fibre slurry. The slurry has a mixture of carbon single-walled nanotubes (SWNTs) and multi-walled nanotubes (MWNTs). The researchers found that increasing the amount of MWNTs in the paper produced a sharp transition from a positive Poisson’s ratio of about 0.06 to a much larger magnitude negative value of about -0.20.

As described by the team in Science, this transition can be understood by relating the deformation modes of the nanotube sheets to those of a collapsible wine rack. If two neighbouring nanotube layers are coupled like the struts in a compressible wine rack, Poisson’s ratio is positive and the rack becomes narrower when stretched. In contrast, if the rack is blocked so that it can no longer be collapsed but the struts are stretchable, increases in strut length produce a negative Poisson’s ratio.

“This abrupt switching of the sign of Poisson’s ratio is so surprising and the structure of the nanotube sheets is so complicated that we initially believed that quantitative explanation was impossible using state-of-art theoretical capabilities,” said Baughman, the article’s corresponding author. “Distant daily teaming with our Brazilian colleagues through the Internet enabled us to jointly extract essential features from a structure that was much too complex for complete analysis, leading to our successful wine-rack-like model.”

Baughman and his team subsequently found that the nanotube sheets containing both single-walled and multi-walled nanotubes had a 1.6 times higher strength-to-weight ratio, 1.4 times higher modulus-to-weight ratio and a 2.4 times higher toughness than sheets made of SWNTs or MWNTs alone.

According to Baughman, the implications of the discovery that properties can be enhanced by mixing nanotube types can likely be extended from nanotube sheets to other nanotube arrays, like the twisted nanotube yarns Baughman and colleagues invented in 2005.

Publication Date: 30/04/2008

+ نوشته شده در  87/02/12ساعت 10:23  توسط مهندس محمدرضا فروغی  | 

Speeding up catalytic nanomotors with carbon nanotubes

Posted: May 1, 2008

(Nanowerk Spotlight) Sophisticated molecular-size motors have evolved in nature, where they are used in virtually every important biological process. In contrast, the development of synthetic nanomotors that mimic the function of these amazing natural systems and could be used in man-made nanodevices is in its infancy. Building nanoscale motors is not just an exercise in scaling down the design of a macroworld engine to nanoscale dimensions. Many factors such as friction, heat dissipation and many other mechanical behaviors are just very different at this scale – everything is constantly moving (under kinetic energy supplied by the heat of the surroundings) and being buffeted by other atoms and molecules (Brownian motion).

In nature, biological motors use catalytic reactions to create forces based on chemical changes. These motors do not require external energy sources such as electric or magnetic fields. Instead, the input energy is supplied locally and chemically. Despite impressive progress over the past years, man-made nanomachines lack the efficiency and speed of their biological counterparts. New research has demonstrated that the incorporation of carbon nanotubes (CNT) into the platinum component of asymmetric metal nanowire motors leads to dramatically accelerated movement in hydrogen peroxide solutions, with average speeds of 50-60 micrometers per second.

"Our study demonstrates dramatically faster and more powerful synthetic nanomotors" Dr. Joseph Wang tells Nanowerk. "Unlike existing bimetal nanowires which are slow and weak, we illustrates that the incorporation of carbon nanotubes into such motors results in dramatic acceleration and higher efficiency. These new capabilities offer great promise to the use of synthetic nanomachines, approaching those of biological nanomotors."

CNT-induced high speed catalytic nanomotors

CNT-induced high speed catalytic nanomotors: (a, b) Tracking lines illustrating a typical motion and moving distances of Au/Pt (a) and Au/Pt-CNT (0.50 mg/ml) (b) nanomotors during a period of 4 s in the presence of 15 wt % hydrogen peroxide fuel. Scale bar is 45 µm. (c) Histograms of average speeds of Au/Pt (red) and Au/Pt-CNT (blue) nanomotors measured from the movement of the nanomotors in a 15 wt % hydrogen-peroxide fuel over a 10 s period. Bar graphs with Y error bars (inset) represent the mean of average speeds (µm/s) and the error limit at 90% confidence interval of the corresponding nanomotors, respectively. (d) A schematic representation of the self-electrophoresis mechanism of Au/Pt (top) and Au/Pt-CNT (bottom) bipolar nanomotors. Hydrogen peroxide fuel is preferentially consumed/oxidized on the Pt (top, blue) or Pt-CNT (bottom, patterned blue) ends while oxygen is catalytically reduced on the Au (yellow) segment. The flux of electrons inside the nanomotors proceeds from one end to the other generating a local electric field, as well as the migration of protons and surrounding fluid outside the nanomotors resulting in the movement of the nanomotor in the opposite direction. The higher electrocatalytic activity of Pt-CNT compared with Pt provides a faster reaction rate, and hence a higher proton and fluid flow corresponding to an increased flux of electrons inside the nanomotors as indicated by the vectors. (Reprinted with permission from American Chemical Society)

Wang is a professor with a joint appointment in the departments of Chemical & Material Engineering in the Ira A. Fulton School of Engineering and Chemistry and Biochemistry in the College of Liberal Arts and Science at Arizona State University (ASU). He is the Director of ASU's Center for Bioelectronics and Biosensors - The Biodesign Institute.

He and his team have demonstrated a dramatic acceleration of self-powered bimetal nanomotors based on the incorporation of CNT into the platinum segment of gold/platinum nanowires. They reported their findings in the April 24, 2008 online edition of ACS Nano "Carbon-Nanotube-Induced Acceleration of Catalytic Nanomotors".

"Such CNT-induced acceleration of catalytic nanomotors reflects the enhanced oxidation of the hydrogen peroxide fuel" Wang explains. "We also illustrated that the speed of nanomotors can be further increased upon adding hydrazine to the peroxide fuel and that this efficient movement can be manipulated magnetically."

carbon nanotube accelerated nanomotors
Movie showing the typical motion of nanomotors without (left) and with (right) carbon nanotubes.

The researchers were able to observe further acceleration to 94 µm/s – with some motors moving above 200 µm/s – upon adding hydrazine to the peroxide fuel.

Wang notes that current studies in his laboratory aim at understanding the underlying mechanisms and forces involved in these accelerated nanomotors and exploring new energy-rich chemical reactions based on different choices of fuels and a variety of motor compositions.

"For example, recent experiments indicate a similar acceleration upon doping the CNT into a palladium (anodic) segment instead of a platinum one" he says. "We expect that these studies will lead to even more energy-efficient nanomotors and will open up new opportunities for nanoscale vehicle systems."

Such high-performance nanomotors should allow transport and release of 'heavy' loads, locomotion in physiological conditions, and the design of more sophisticated nanosystems performing multiple complex tasks.

Preliminary data compiled by the ASU team indicate that the new CNT-doped nanomotors are still self-motile when loaded with particles more than 10 times their size.

Wang's team has also accomplished controlled motion in microfluidic channels (these results will be reported separately). "Currently, we are designing nanomotor-based sensing systems for monitoring the levels of fuels, including the biosensing of glucose based on the direct speed-concentration correlation" Wang describes the team's next steps.

By Michael Berger. Copyright 2008 Nanowerk LLC

+ نوشته شده در  87/02/12ساعت 10:19  توسط مهندس محمدرضا فروغی  | 

Why don't we have a nanotechnology Apollo Program for clean energy?

Posted: April 30, 2008

(Nanowerk Spotlight) It wasn't market forces that landed a man on the moon; and It wasn't market forces that led France to build a nuclear energy infrastructure that now enables it to generate some 75% of its entire energy needs from nuclear power (just an example of what energy policy can do; let's not get into a discussion here of nuclear energy, though). But somehow, the leading political and industrial forces in the United States – together with China the largest emitter of greenhouse gases on the planet – think that a task so fundamental and massive as fighting global warming and environmental pollution should mostly be left 'to the market'. Unfortunately, it’s just a matter of economic reality that 'the market' will not invest in new energy technologies on a large scale until existing ways of producing energy become more expensive than producing alternative energies – which at the moment they aren't.

As is the case with almost all emerging technologies, government initially lends a helping hand before the technology becomes a viable commercial proposition and the market takes over (remember how the Internet got created?). In the case of future clean energy technologies, it appears that this 'helping hand' needs to be massive and swift. It's not so much that clean/green tech wouldn't develop over time on its own. But it's against the backdrop of accelerating global warming that it becomes a top priority that requires massive public resources.

A government's energy policy makes all the difference - not the market

Of course there are some government-initiated efforts in the U.S. like the FreedomCAR (how is that going, by the way?), or the Department of Energy’s (DOE) announcement last year to select 13 industry-led solar technology development projects for up to $168 million in public funding.

The most promising effort appears to be the DOE's Energy Frontier Research Centers (EFRC) initiative, a comprehensive effort to accelerate the rate of scientific breakthroughs needed to create advanced energy technologies for the 21st century. Unfortunately, the program has been set up as a typical government program – a timid effort, ridiculously underfunded (given the challenge), glacially slow (commissions and committees have kept themselves busy since the beginning of the decade "establishing the energy research directions"), and controlled by a bureaucratic federal apparatus.

Rather than a massive, Apollo Program type effort that would be justified by the scope of the challenge, the EFRC initiative gets a paltry $100 million for a five-year effort starting only in 2009. To put this amount in perspective, $100 million is what the U.S. is spending for 6.5 hours of the Iraq war. Or consider this chart:

Change in Petroleum Consumption for G7 Countries 1980-2007
Change in Petroleum Consumption for G7 Countries 1980-2007
Change in petroleum consumption for G7 countries on the basis of million barrels per day (G8 couldn't be compiled because data for Russia is only available from 1992, after breakup of the Soviet Union); All of Europe also shown in comparison. Data source: U.S. Department of Energy, Energy Information Administration. Compilation and chart: Nanowerk)

Due to a deliberate energy policy away from oil, petroleum consumption actually fell from 1980 to 2007 in the largest EU countries (with the exception of the UK). This was due to an increase in renewable energy sources (for example, in 2007, renewable energy already accounted for over 14% percent of total gross electricity consumption in Germany) and in efficiency gains. For instance, gasoline in most European countries costs twice as much as in the U.S., even today with average prices in the US approaching $4 per gallon – the difference is caused by massively higher taxes on petrol – which led to cars in Europe having much better gas mileage than in America. Given the current hysterical reaction in the U.S. to higher gas prices, with pandering politicians talking of even reducing the tax on gas or introducing a "summer tax holiday", a responsible energy policy in this country seems to be more remote than ever.

While rising oil prices will lead to reduced consumption eventually, the problem is that we might not have the time from an ecological perspective to sit this one out. Without going into the ideological discussion as to whether global warming is man-made or not – shouldn't we be doing anything humanly possible anyway to reduce the amount of greenhouse gases in the atmosphere to reduce the catastrophic effects of a warming planet?

There are basically four ideological camps that compete with each other in proposing the best solutions: At one end of the extreme are environmental groups that argue that we need stringent environmental laws and heavily tax all greenhouse gas emissions. At the other end are free-market proponents who believe that an unregulated capitalist system will self-correct and that industry will develop the necessary technologies and become 'green' over time because it’s in their own interest. In between there is a smorgasbord of – mostly uncoordinated – activities by state and local governments, grassroots campaigns, investors and entrepreneurs to provide small, local and partial solutions. And finally, there is a broad but loose coalition of scientists, interest groups and governments who propose that the best way out of our climate problems is massive international agreements (such as the Kyoto protocol) where governments voluntarily agree (or not, as is the case with the U.S. and China) to reduce harmful gas emissions by certain amounts within specified timeframes.

While European countries have shown that a mix of all of the above works in moving their societies away from oil and towards renewable and clean energy sources, it is far from being enough to slow down the carbon dioxide increase in the atmosphere.

Realizing that existing solutions are not good enough, there is a small but growing number of voices that, in contrast to heavy regulations or the hope for self-regulating markets, propose a third way out of the energy crisis. Akin to the Apollo Program that landed a man on the moon, they put forward the idea of a massive, publicly-funded and technology-led project that will result in breakthrough technological solutions that can be implemented on a large scale and in a relatively short time. (For some thought-provoking ideas on a technology-driven way out of the climate and energy crisis read Break Through: From the Death of Environmentalism to the Politics of Possibility)

Nanotechnology's major role in tomorrow's clean energy

In a 2005 report, the Basic Energy Sciences Advisory Committee (BESAC) within the DOE published a report which examined the roadblocks to progress, and the opportunities for truly transformational new understanding of future energy systems ("Directing Matter and Energy: Five Challenges for Science and the Imagination" – pdf download, 29.6 MB). The report concludes that a new era of energy science poses five challenges:

  • How do we control materials processes at the level of electrons?
  • How do we design and perfect atom- and energy-efficient syntheses of revolutionary new forms of matter with tailored properties?
  • How do remarkable properties of matter emerge from the complex correlations of atomic or electronic constituents and how can we control these properties?
  • How can we master energy and information on the nanoscale to create new technologies with capabilities rivaling those of living things?
  • How do we characterize and control matter away – especially very far away – from equilibrium?
  • Based on a series of 10 "Basic Research Needs" workshops, the DOE hopes that research proposals from the scientific community will lead to the establishment of EFRCs that will address all the issues that have been raised in the workshops.

    To give a brief overview of nanotechnology's key role in our future energy supply, it makes sense to broadly group potential applications into three main areas (energy production; energy transport and storage; energy consumption). This compilation provides an – by no means complete – overview from the EFRC brochure and makes snapshot references to some exemplary research:

    Nanotechnology in energy production

    Direct conversion of solar energy to electricity and chemical fuels will benefit from powerful new methods of nanoscale fabrication, characterization, and simulation – using physical, chemical and biological tools that were not available as few as five years ago – to create new opportunities for understanding and manipulating the molecular and electronic pathways of solar energy conversion. A lot of research in this area today is on carbon nanotubes (Carbon nanotubes can double the efficiency of photoelectrochemical solar cells) and quantum dots (Catching a rainbow - quantum dot nanotechnology brightens the prospects for solar energy).

    Understanding of how biological feedstocks are converted into portable fuels – biological systems are the proof-of-concept for what can be physically achieved by nanotechnology (Nanotechnology's role in next generation biofuel production). The way in which energy, entropy, and information are manipulated within the nanosystems of life provide lessons on how to develop similarly sophisticated energy technologies. This entails research in light harvesting, exciton transfer, charge separation, transfer of reductant to carbon dioxide as well as carbon fixation, storage and conversion.

    Catalysis – the essential technology for accelerating and directing chemical transformation – is key to realizing environmentally friendly, efficient and economical processes for the conversion of fossil and renewable or alternative energy feedstocks. The grand challenge at the core of all of these areas is to achieve detailed mechanistic understanding of catalytic dynamics for complex heavy molecular mixtures, bio-derived species, and solid nanostructures and interfaces (Nanotechnology optimizes catalyst systems).

    In a smaller way, nanotechnology materials and processes will generally benefit most areas of renewable energy production. For instance, the use of nanocomposite materials that provide lighter and substantially stronger turbine blades may be the most promising short-term contribution nanotechnology will make in next generation wind turbines. Improving turbine performance and reliability will allow for longer lifetime, less fatigue failure, and thus lower costs of energy generation.

    Nanotechnology in energy transport and storage

    Fundamental performance limitations of energy storage systems are rooted in the constituent materials making up an electrical energy storage device (batteries and fuel cells), and novel approaches are needed to develop multifunctional energy storage materials that offer new self-healing, self-regulating, failure-tolerant, impurity-sequestering, and sustainable characteristics (A new promising class of non-precious metal catalysts for fuel cells). The discovery of novel nanoscale materials with architectures tailored for specific performance offer particularly exciting possibilities for the development of revolutionary architectures that simultaneously optimize ion and electron transport and capacity (Converting conventional nanotubes into superior carbon for batteries).

    As an energy carrier, electricity so far has no rival with regard to its environmental cleanliness, flexibility in interfacing with multiple production sources and end uses, and efficiency of delivery. However, the challenge facing the electricity grid will soon grow to crisis proportions. Incremental advances in existing grid technology are not capable of solving the bottlenecks to power transmission. Revolutionary new power transmission and control solutions based on superconductors can solve this crisis. Advancing the state-of-the-art in superconductivity presents a formidable research challenge. One of the primary scientific opportunities here is rooted in nanoscale phenomena as superconductivity’s two composite building blocks have dimensions ranging from a tenth of a nanometer to a hundred nanometers. Unraveling superconductivity’s mechanism with the promise of nanoscale fabrication, characterization, and simulation will provide a pathway for the rational design of and production of functional superconducting materials required for next-generation grid technology (Where's the glue? Scientists find a surprise when they look for what binds in superconductivity).

    Safe, efficient and compact hydrogen storage is a major challenge in order to realize hydrogen powered transport. Nanotechnology plays an important role here. Nanomaterials have diverse tunable physical properties as a function of their size and shape due to strong quantum confinement effects and large surface to volume ratios. These properties are useful for designing hydrogen storage materials. For instance, researchers are now investigating nanostructured polymeric materials as hydrogen storage adsorbents. Due to their large surface areas with relatively small mass, single-walled carbon nanotubes have been considered very promising potential materials for high capacity hydrogen storage. However, there is some skepticism on carbon nanotube hydrogen storage due to early mistakes in experimental publications and a rational basis for high capacity hydrogen storage materials is now being developed (New carbon nanotube hydrogen storage results surpass Freedom Car requirements).

    Nanotechnology in energy consumption

    Transforming energy utilization and transmission – at the heart of nanoscale behavior, one often finds emergent phenomena, in which a complex outcome emerges from the correlated interactions of many simple constituents. By understanding the fundamental rules of correlations and emergence and then by learning how to control them, we could produce, for example, an entirely new generation of energy utilization and transmission processes, such as in phase change materials for thermal energy conversion, strong light-matter interaction and collective charge behavior for light emission nearing theoretical efficiency, and radically different combustion chemistry of alternative fuels. Understanding the emergent behavior of materials and chemical reactivity at the nanoscale offers remarkable opportunities in a broad arena of applications including solid-state lighting, electrical generators, clean and efficient combustion of 21st century transportation fuels, catalytic processes for efficient production and utilization of chemical fuels, and superconductivity for resistance-less electricity transmission.

    In 2001, twenty-two percent of electricity used in the U.S., equivalent to eight percent of the nation’s total energy, was used for artificial light. Solid state lighting (SSL) modalities present an opportunity to achieve tremendous advances in energy efficiency (Nanocomposite solid-state lighting). By discovering and controlling the materials and nanostructure properties that mediate the competing conversion of electrons to light and heat, nanotechnology will address the challenge of converting every injected electron into useful photons. The anticipated results are ultra-high-efficiency light-emitting materials and nanostructures, and a deep scientific understanding of how light interacts with matter, with broad impact on science and technology areas beyond SSL.

    There are other, more indirect – and only incremental – impacts that nanotechnology could have on energy usage. For instance, by using high-performance nanocomposite materials, cars and airplanes could be made much lighter, thereby improving fuel efficiencies. But the major improvement in the transportation sector will come once nanotechnology-enabled fuel cells have become commercially viable alternatives to the internal combustion engine.

    The solution: Change the shotgun approach to nanotechnology funding

    Nanotechnologies will have a major role to play in almost all future clean energy applications and that's why the scope – but not the scale – of the DOE's Energy Frontier Research Centers initiative seems such a good starting point. Add three zeroes to the current funding and you have the beginning of a promising energy initiative.

    There is no doubt that nanotechnologies could provide the solutions to our energy problems, not today, and not tomorrow, but with a massive, coordinated and international effort a 10-20 year timeframe seems not unrealistic. Today's various national nanotechnology programs fund their vast hodgepodge of research initiatives more from a viewpoint of basic research (or, in the case of the U.S., military wish lists) than with a focus on commercial implementation – in the process scattering funding resources by trying to cover each and every potential application.

    Instead, the leading dozen or so nanotechnology nations should get together and commit to a concerted and massively funded 10-year program to develop commercially viable, clean energy solutions based on nanotechnology. Rather than have bureaucratic government departments oversee the effort there should be a new agency – much like the can-do organization that NASA was in the 1960s – to drive this effort forward in close cooperation with academia and industry.

    Not only would this provide a way out of the energy and climate crisis, it would finally provide the much-needed, large-scale commercialization of nanotechnologies that will lead to entirely new industries. The funding can be found, the technology can be developed, all it takes is political will...

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/02/11ساعت 9:48  توسط مهندس محمدرضا فروغی  | 

    Converting conventional nanotubes into superior carbon for batteries

    Posted: April 29, 2008

    (Nanowerk Spotlight) The race is on to develop the next generation of nanotechnology-enabled electrochemical energy storage devices, also knows as batteries. Lithium of course has long been recognized as an ideal material for energy storage due to its light weight and high electrochemical energy potential, as witnessed by the ubiquitous use of Li-ion batteries. There still seems to be considerable potential to further improve the performance characteristics of these Li-ion batteries (see our recent Spotlight: Using nanotechnology to improve Li-ion battery performance and this previous article: Nanotechnology batteries - the end of exploding batteries?). There have been many design approaches to creating lithium ion batteries but they usually share common features: The positive electrode is typically a lithium metal oxide, with various metals used such as cobalt, nickel, and manganese. The negative electrode is typically a carbon compound or natural or synthetic graphite. Researchers in Germany have now demonstrated a simple route for transforming cheap commercial carbon nanotubes into highly efficient carbon for electrochemical energy storage applications. When tested as electrode materials for lithium batteries, this composite material exhibits excellent performance over long test cycles.

    "We were able to demonstrate, for the first time, the template-free synthesis of carbon nanotube (CNT) encapsulated carbon nanofibers (CNFs@CNTs), where cheap and low-quality commercial carbon nanotubes are transformed into high-performance electrode materials" Dr. Dangsheng Su tells Nanowerk. "Compared to single-walled CNTs, the CNTs used in our study had a lower surface area, bigger outer diameter (50–200 nm), and thicker walls (50–100 walls). Large-scale production reduced their price to as little as $50 per kilogram."

    Su, who heads the Electron Microscopy & Microstructure Group in the Department of Inorganic Chemistry at the Fritz Haber Institute of the Max Planck Society in Berlin, Germany, together with colleagues from his institute and the Max Planck Institute for Solid State Research in Stuttgart, has found that this new class of carbon materials exhibits unique structural properties; which give it significant potential for applications in the field of gas adsorption, environmental protection, fuel cells, catalysis, hydrogen storage, etc.

    These results have been reported in the March 28, 2008 online edition of Advanced Materials ("CNFs@CNTs: Superior Carbon for Electrochemical Energy Storage")

    Su explains that the CNFs@CNTs were synthesized via selective deposition of an active metal on the inner walls of CNTs, which was followed by the growth of carbon nanofibers (CNFs) by means of catalytic chemical vapor deposition (CCVD).

    "The Co@CNTs precursor, containing 0.5 wt% cobalt, was produced using a capillary force based incipient wetness impregnation methods, whereby a thin layer of cobalt nitrate solution is preferentially dispersed onto the inner surface of the CNTs. This causes the generation of metallic cobalt nanoparticles (average size: 6.6 nm) primarily on the inner wall of the CNTs during the subsequently performed H2 reduction step. These then act as active phase for CNF growth in the tubular chamber during the CCVD process."

    Synthesis route to carbon-nanotube-encapsulated carbon nanofibers
    Synthesis route to carbon-nanotube-encapsulated carbon nanofibers (CNFs@CNTs). (Reprinted with permission from Wiley-VCH Verlag)

    The researchers found that the CNFs@CNTs with a novel structure possessed a much better porosity than the pristine nanotubes. "Nitrogen physisorption tests showed that the specific surface area and the pore volume increased from 82 m2 per gram and 0.17 cm3 per gram to 347 m2 per gram and 0.61 cm3 per gram, respectively" says Dr. Jian Zhang from the Fritz Haber Institute. " The total increase in weight was 25% as measured after the CCVD process; which suggests a greatly improved utilization of space inside the hollow channels of the CNTs, thus an increase in their bulk density. This arises primarily from the formation of secondary pores between the CNFs and CNTs as well as the extremely close stacking of CNFs inside the CNTs, because the produced CNFs alone could not contribute to such a great extent."

    Su also notes that In terms of permanence of the high lithium storage capacity, CNFs@CNTs are superior to pristine CNTs. "During 120 cycles the reversible capacity of the CNFs@CNTs electrode stayed at around 410 mAh per gram while it gradually decreased to 258 mAh per gram when the electrode was formed from commercial CNTs."

    The researchers hypothesize that the superior stability of these CNFs@CNTs probably arises from a steric hindrance effect of their compact structure which suppresses the diffusion of big electrolyte molecules through wall defects. The confinement of CNTs suppresses the exfoliation of CNFs during intercalation/de-intercalation of lithium ions, give the long time stability they observed.

    Su points out that their outstanding cycling performance in combination with their high storage capacity makes CNFs@CNTs much more attractive than other carbon materials previously reported in the literature, such as for instance multi-walled CNTs, hard carbon, and CNFs.

    "Our fabrication method can be extended to other carbon materials (mesoporous carbon, activated carbon, carbon nanocones, etc.) as well as one-dimensional inorganic nanotubes and nanofibers" he says.

    For now, the scientists are working on the challenge of increasing the graphitization degree of carbon nanofibers inside CNTs. Eventually this could lead to much better performing Li-ion batteries. Another intriguing question is if this novel carbon composite material is suitable for hydrogen storage and at what performance.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/02/11ساعت 0:40  توسط مهندس محمدرضا فروغی  | 

    Molecular delivery system could lead to blood tests using a cell phone

    Posted: April 28, 2008

    (Nanowerk Spotlight) In case you haven't seen the absolutely amazing animation Cellular Visions: The Inner Life of a Cell yet, go watch it now. In it, there is a sequence where a motor protein is sort of 'walking' along a filament, dragging this round sphere of lipids behind it. This kind of nanoscale biological motor is able to load/unload particular types of cargo without external stimuli, and transport them along cytoskeletal filaments by using the energy of adenosine triphosphate (ATP) hydrolysis within cells. Nanotechnology researchers are fascinated by the various molecular delivery systems that have evolved in nature and they are receiving increasing attention as blueprints for nanoscale actuators and building blocks to construct artificially-engineered bio-hybrid systems. Some researchers expect that artificial molecular transport systems which utilize microtubules motility (like the cytoskeletal filament the motor protein in the animation was walking along) will be an alternative way to pressure-driven or electrokinetic flow-based microfluidic devices.

    Researchers in Japan propose a molecular transport system that can achieve autonomous loading/unloading of specified cargoes. This system loads a cargo molecule through DNA hybridization (DNA hybridization: The complementary bases – adenine and thymine, guanine and cytosine – of two single-stranded DNAs bind together to form a double-helix structure) between single-stranded DNAs attached to a cargo molecule and a cargo transporter (step I in diagram below; the schematic runs from right to left). It transports the loaded cargo molecule by using motor proteins to move (glide) the cargo transporter (step II). It then unloads the transported cargo molecule (step III) through DNA hybridization between single-stranded DNAs attached to the cargo molecule and a glass substrate – the DNA strand exchange (upon untwisting a double-stranded DNA, one of the resulting single-stranded DNA and a third single-stranded DNA bind together to form a new double-stranded DNA).

    molecular delivery system
    Schematic diagram of a proposed molecular transport system. (Image: NTT DoCoMo)

    "We believe that our results may help create highly miniaturized on-chip-systems – such as molecular sorters, molecular sensors, and molecular communication systems – because our molecular delivery system can autonomously load, transport and unload cargoes by exploiting DNA hybridization and a biological motor system," Satoshi Hiyama explains to Nanowerk.

    Hiyama, a member of the Frontier Technology Research Group at NTT DoCoMo's Research Labs in Kanagawa, Japan, is first author of a recent paper in Small titled "Autonomous Loading, Transport, and Unloading of Specified Cargoes by Using DNA Hybridization and Biological Motor-Based Motility". The NTT DoCoMo team, in experiments carried out jointly with Professor Kazuo Sutoh of the Department of Life Sciences, The University of Tokyo, and Associate Professor Shoji Takeuchi of the Institute of Industrial Science, The University of Tokyo, has successfully demonstrated the world's first molecular delivery system for molecular communication.

    DoCoMo has been pioneering research into the field of molecular communication, a new communication paradigm in which molecules are used as a communication medium. By combining communication technology and biochemistry, DoCoMo aims to develop systems that could transmit information about the biochemical conditions of living organisms, such as excitement, emotion, stress or disease.

    The idea is to construct a controllable, biochemically engineered communication system using cell-to-cell communication and other biological signal-transduction mechanisms in which living organisms transmit/control biochemical information and reactions, such as excitement and emotions, that are hard to encode/transmit using electromagnetic waves.

    molecular communication technology
    Schematic diagram of a molecular communication technology that complements, rather than competes with, existing communication systems. (Image: NTT DoCoMo)

    The experiment by the Japanese research group has confirmed the feasibility of a proposed delivery system to transport specific molecules using artificially synthesized DNAs and chemically energized motor proteins, typically found in muscles and nerve cells, which are capable of moving autonomously by converting chemical energy into mechanical work.

    Hiyama explains that, in order to exploit the highly selective hybridization and strand-exchange reactions for reliable loading and unloading of cargoes, they need to further suppress nonspecific loading and unloading of cargoes, which results mainly from nonspecific interactions of cargoes with gliding microtubules or with an unloading surface, but not from mismatched hybridization. "This could be achieved by using other types of cargoes with less affinity to microtubules or to a glass surface" he says. "With such an improvement, these autonomous operations may help create highly miniaturized on-chip systems such as molecular sorters, sensors, and communication systems. This may also be an alternative way to realize pressure-driven or electrokinetic flow-based microfluidic devices."

    The system, which functions on its own because it does not require external power supply or control, could help lead to the realization of a biochemical analyzer, or biochip, a fingertip-sized microchip for biological and chemical analysis.

    The envisioned molecular delivery system could have many applications in medicine and healthcare. For instance, it may be possible to diagnose diseases or stress by directly analyzing biomolecules in a drop of sweat or blood using a mobile phone equipped with a biochip.

    mobile phone with biochip
    Schematic diagram of remote medical diagnosis by mobile phone with biochip. (Image: NTT DoCoMo)

    The molecular delivery system would be packaged in the biochip, and the data generated in the biochemical analysis would be transmitted to a medical specialist via a mobile phone using traditional wireless technology (not surprisingly, this research was sponsored by a telephone company, after all). The system could be used, for example, for remote health checks or preventive medicine. A mobile phone with a biochip could also have applications beyond healthcare, for instance in environmental monitoring, e.g. water analysis.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/02/11ساعت 0:38  توسط مهندس محمدرضا فروغی  | 

    A gripping tale for nanomanufacturing

    Posted: April 25, 2008

    (Nanowerk Spotlight) Future nanomanufacturing processes will rely on two basic principles: a combination of chemical synthesis and self-assembly on one hand and robotic nanofabrication on the other. While the former is a controlled 'natural' process relying on chemistry and self-organization principles of nature (read more: How falling spaghettis could lead to more complex nanotechnology self-assembly), the latter will be an industrial process similar in concept to today's automated manufacturing assembly lines.

    Robotic assembly lines in modern factories have come a long way since the early 20th century when Henry Ford first used an assembly line on an industrial scale for his Model T automobile. Nevertheless, the principle is the same. Rather than having a single craftsman or team of craftsmen create each part of a product individually and assemble them together into a single item, an assembly line is a (often completely automated) manufacturing process in which interchangeable parts are added to a product in a sequential manner to create a finished product.

    While sporadic automation of certain tasks has already begun (for instance, automated microrobotic injection of foreign materials into biological cells), nanotechnology techniques today are pretty much where the industrial world was before Ford's assembly line – a domain of highly skilled artisans and not of automated mass production. It has long been a dream for nanotechnologists that robots could one day be used in an assembly line type of process to manufacture nanodevices. Researchers are beginning to develop the first rudimentary nanomanipulation devices that could lead to future automated manufacturing systems. Now, a team of scientists in Canada have reported the first demonstration of closed-loop force-controlled grasping at the nanonewton level.

    MEMS-based microgripper with integrated two-axis force sensor
    MEMS-based microgripper with integrated two-axis force sensor. (Image: Dr. Sun)

    "We have demonstrated force-controlled micrograsping of highly deformable cells at a 20 nanonewton force level" Dr. Yu Sun tells Nanowerk. "The contact force feedback of the MEMS-based microgripper enables the micromanipulation system to conduct rapid contact detection at a nanonewton force level and protects the microgripper from breakage. The work clearly explains the importance of the availability of force feedback along multiple directions. The implication is that these microgrippers get us closer to reliable, autonomous micromanipulation."

    Sun, an Assistant Professor in the Department of Mechanical and Industrial Engineering, Institute of Biomaterials and Biomedical Engineering, and Department of Electrical and Computer Engineering at the University of Toronto in Canada, reports his team's findings in the April 1, 2008 online issue of Journal of Micromechanics and Microengineering ("Nanonewton force-controlled manipulation of biological cells using a monolithic MEMS microgripper with two-axis force feedback").

    "We are currently applying these force-feedback microgrippers to characterize elastic and viscoelastic properties of polymeric microcapsules (∼20 microns) used for drug delivery and cell encapsulation" Sun explains. "We are also further improving the force sensing resolutions of these microgrippers for sub-nanonewton force measurements, which will enable a new, easy-to-operate technique for our fundamental cell mechanics studies, such as for distinguishing malignant cells from benign cells and for correlating mechanical properties of cells to disease states."

    Cell manipulation and alignment with force-controlled micrograsping
    Cell manipulation and alignment with force-controlled micrograsping. (a) After contact detection, the microgripper grasps a first cell. (b) The microgripper transfers the cell to a new position and releases the cell. (c) The microgripper grasps a second cell. (d) Transferring and releasing the second cell. (e) The microgripper approaches a third cell. (f) Transferring and releasing the third cell. Three cells of different sizes are transferred to desired positions and aligned. (Reprinted with permission from IOP Publishing)

    In order to facilitate the maneuvering of nanoscale materials (e.g., pick-transport-place), Sun's group is further miniaturizing these microgrippers, not so much on the overall device size, but more on reducing the gripping tip thickness and integrating novel mechanisms to facilitate nano-object release by counteracting undesired adhesion forces.

    "These nanogripping devices under development will promise highly reproducible pick-place of nanoscale objects, a capability the nanorobotics community has been striving for" says Sun.

    For their microgripper design, the researchers used a V-beam electrothermal actuator to control the opening of the active gripping arm for object grasping. With an applied voltage, the V-beams are heated and thus, expand to produce motion. The microgripper used is a commonly closed type with an initial opening of 5 µm. When actuated, the active gripping arm is pulled open. In order to prevent a high temperature at the gripping arm tips, electrical and thermal isolation on the device silicon layer is implemented, and many heat sink beams are used. The temperature rise at the gripping arm tips caused by the integrated electrothermal microactuator was determined to be tolerable by biological cells.

    To verify the effectiveness of their force-controlled manipulation system, the team selected biological cells for manipulation due to their high delicacy, high deformability, variations in sizes and mechanical properties. The two key steps in the process is contact detection as the gripper approaches a cell, and the grasping of the cell.

    "Contact detection is important to protect both the microgripper and the cell from damage" says Sun. "Without the integrated contact force sensor, this process would be extremely time consuming and operator skill dependent. When the monitored contact force level reaches a pre-set threshold value, it indicates that contact between the gripping arm tips and the substrate is established. Subsequently, the microrobot stops lowering the microgripper further and moves the microgripper upward until the contact force returns to zero. After the initial contact position is detected, the microgripper is positioned a few micrometers above the detected contact position."

    Sun explains that, in order to achieve reliable micrograsping, a closed-loop control system was implemented by using gripping force signals as feedback to form a closed loop. "Enabled by the monolithic microgripper with two-axis force feedback, our system demonstrates the capability of rapidly detecting contact, accurately tracking nanonewton gripping forces, and performing reliable force-controlled micrograsping to accommodate size and mechanical property variations of objects" he says.

    Besides force-controlled manipulation of biomaterials in liquid, these grippers can also find important applications in biomaterial mechanical characterization and in electronic component handling as well as the assembly of micro objects.

    By Michael Berger, Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/02/06ساعت 12:49  توسط مهندس محمدرضا فروغی  | 

    LCDs might be graphene's first realistic commercial application

    Posted: April 24, 2008

    (Nanowerk Spotlight) Following up on yesterday's Spotlight about graphene quantum dots, today we look at what might be the first realistic application of this revolutionary material. Back in December we reported on the development of transparent and conductive graphene-based composites for use as window electrodes in solid-state dye sensitized solar cells ("Ultrathin transparent graphene films as alternative to metal oxide electrodes"). While the researchers who conducted this work produced graphene by chemical oxidation of graphite, a multi-step process, new results from the University of Manchester group that discovered graphene in 2004 show a simpler route to producing graphene films that cannot only be used for solar cells but might be well suited for liquid crystal displays.

    "There are already several technologies that potentially allow mass production of thin graphene-based transparent conductors – besides the chemical exfoliation of graphite described in our most recent work, one can also think of epitaxial growth of graphene on top of a metal surface, followed by a transfer of such a layer onto a transparent substrate" Dr. Kostya Novoselov explains to Nanowerk. "These techniques are capable of producing continuous graphene films of thickness below five monolayers, which is required for realistic applications."

    Novoselov, The Royal Society Research Fellow, and a member of the Mesoscopic Physics Group at the University of Manchester, is one of the original team, led by Professor Andre Geim, that discovered graphene in 2004. In a recent article in Nano Letters ("Graphene-Based Liquid Crystal Device") the University of Manchester scientists, together with collaborators from the Institute for Microelectronics Technology in Chernogolovka, Russia, demonstrate the use of graphene as a transparent conductive coating for photonic devices and show that its high transparency and low resistivity make this two-dimensional crystal ideally suitable for electrodes in liquid crystal devices.

    "Graphene is only one atom thick, optically transparent, chemically inert, and an excellent conductor," says Novoselov. "These properties seem to make this material an excellent candidate for applications in various electro-optical devices that require conducting but transparent thin films. We believe graphene should improve the durability and simplify the technology of potential electronic devices that interact with light."

    Geim points out that transparent conducting films are an essential part of many gadgets including common LCD displays for computers, TVs and mobile phones. "The technology behind these devices uses thin metal-oxide films based on indium. But indium is becoming an increasingly expensive commodity and, moreover, its supply is expected to be exhausted within just 10 years. Forget about oil – our civilization is first to run out of indium. Scientists have this urgent task on their hands to find new types of conductive transparent films."

    LCD with electrodes made of graphene
    Liquid Crystal Device with electrodes made of graphene with different voltages applied. The overall width of the insert image is 30 microns. (Image: Mesoscopic Physics Group, University of Manchester)

    Although it is important to demonstrate the possibility and advantages of using graphene as a transparent conductive coating, the feasibility of its mass production is essential when considering realistic applications. Novoselov notes that no industrial technology can rely on the micromechanical cleavage technique that allows only minute quantities of graphene and, although sufficient for fundamental research and proof-of-concept devices, is unlikely to become commercially viable.

    "Recently, large-area conductive films have been demonstrated by using chemical exfoliation of graphite oxide and then reducing it to graphene" he says. "This could lead to a viable way of making thin graphene-based films, however, so far this technique has not demonstrated the ability to fully recover the excellent conductive properties of graphene. We propose an alternative approach. It involves making a graphene suspension by direct chemical exfoliation of graphite (rather than graphite oxide), which is subsequently used to obtain transparent conductive films on top of glass by spin- or spray-coating."

    The Manchester research team has now demonstrated highly-transparent and highly-conductive ultra-thin films that can be produced cheaply by this technique – basically "dissolving" graphite chunks into graphene and then spraying the suspension onto a glass surface. These resulting graphene-based films can be used in LCDs and, to prove the concept, the researchers demonstrate the first liquid crystal devices with graphene electrodes (see figure above).

    Novoselov believes that only a few small, incremental steps remain for this technology to reach mass production stage. "Graphene-based LCD products can appear in shops as soon as in a few years," he says.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/02/05ساعت 9:48  توسط مهندس محمدرضا فروغی  | 

    Graphene quantum dots as single-electron transistors

    Posted: April 23, 2008

    Nanowerk Spotlight) We have written about scientists' fascination with graphene - the flat one-atom thick sheet of carbon - before ("Nanotechnology researchers go ballistic over graphene"). Over the past couple of years, graphene has become a new model system for condensed-matter physics - the branch of physics that deals with the physical properties of solid materials - because it enables table-top experimental tests of quantum relativistic phenomena, some of which are unobservable in high-energy physics.

    The behavior of electrons in graphene is very different from their behavior in typical semiconductors. In the latter, they possess a mass, and a finite energy (called the energy gap) is necessary to move the electrons from the valence to the conductance band and they move like regular particles, increasing their speed as they get accelerated. In graphene, electrons move with a constant speed - much faster than electrons in other semiconductors - independent of their kinetic energy (similar to the behavior of photons), and there is no energy gap.

    Graphene, which basically is an unrolled, planar form of a carbon nanotube therefore has become an extremely interesting candidate material for nanoscale electronics. Researchers in the UK have now, for the first time, shown that it is possible to carve out nanoscale transistors from a single graphene crystal. Unlike all other known materials, graphene remains highly stable and conductive even when it is cut into devices one nanometer wide.

    "Our recent work demonstrates electron transport in quantum dot devices carved entirely from graphene" Dr. Kostya Novoselov tells Nanowerk. "At large sizes (>100 nanometers), they behave as conventional single-electron transistors, exhibiting periodic Coulomb blockade peaks. For quantum dots smaller than 100 nanometers, the peaks become strongly nonperiodic, indicating a major contribution of quantum confinement."

    Quantum dot carved from a graphene sheet
    Quantum dot carved from a graphene sheet. (Image: Mesoscopic Physics Group, University of Manchester)

    Novoselov, The Royal Society Research Fellow, and a member of the Mesoscopic Physics Group at the University of Manchester, is one of the original team, led by Professor Andre Geim, that discovered graphene in 2004. In a recent progress article in Science ("Chaotic Dirac Billiard in Graphene Quantum Dots") Novoselov and Geim show that graphene can be carved into tiny electronic circuits with individual transistors having a size not much larger than that of a molecule.

    The University of Manchester group has developed an approach that lets them reliably fabricate graphene quantum dots with features as small as 10 nanometers. They found three basic operational regimes for these quantum dots, depending on their size.

    Devices larger than 100 nm exhibit nearly periodic Coulomb blockade resonances. "In general, the behavior we observed is in agreement with the one exhibited by conventional single-electron transistors (SET)" says Novoselov. " The all-graphene SETs we fabricated are technologically simple, reliable, and robust and can operate well above liquid-helium temperatures, making them attractive candidates for use in various charge-detector schemes."

    For devices smaller than 100 nm, the scientists observed a qualitative change in behavior: Coulomb blockade peaks were no longer a periodic function of the back-gate voltage but varied strongly in their spacing. "This is a clear indication that the size quantization becomes an important factor even for such a modest confinement" says Novoselov.

    He notes that for even smaller devices (<30nm), the experimental behavior is completely dominated by quantum confinement. "However, because even the state-of-the-art lithography does not allow one to control features <10 nm in size, the experimental behavior varies widely. Some of the devices become overetched and stop conducting, but in other cases we have narrowed them down to a few nanometers so that they exhibit the transistor action even at room temperature."

    Unlike any other material, graphene remains mechanically and chemically stable and highly conductive at the scale of a few benzene rings, which makes it uniquely suitable for the top-down approach to molecular-scale electronics.

    "Previously, researchers tried to use large molecules as individual transistors to create a new kind of electronic circuits. It is like a bit of chemistry added to computer engineering," says Novoselov. "Now one can think of designer molecules acting as transistors connected into designer computer architecture on the basis of the same material – graphene – and use the same fabrication approach that is currently used by the semiconductor industry".

    "It is too early to promise graphene supercomputers," adds Geim. "In our work, we relied on chance when making such small transistors. Unfortunately, no existing technology allows cutting materials with true nanometer precision. But this is exactly the same challenge that every post-silicon electronics has to face. At least we now have a material that can meet such a challenge."

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/02/04ساعت 10:56  توسط مهندس محمدرضا فروغی  | 

    Pilot toxicology study of intravenously injected carbon nanotubes

    (Nanowerk Spotlight) The toxicity issues surrounding carbon nanotubes (CNTs) are highly relevant for two reasons: Firstly, as more and more products containing CNTs come to market, there is a chance that free CNTs get released during their life cycles, most likely during production or disposal, and find their way through the environment into the body. Secondly, and much more pertinent with regard to potential health risks, is the use of CNTs in biological and medical settings. CNTs interesting structural, chemical, electrical, and optical properties are explored by numerous research groups around the world with the goal of drastically improving performance and efficacy of biological detection, imaging, and therapy applications. In many of these envisaged applications, CNTs would be deliberately injected or implanted in the body. For instance, CNT-based intercellular molecular delivery vehicles have been developed for intracellular gene and drug delivery in vitro.

    What these CNTs do once inside the body and after they discharge their medical payloads is not well understood. Cell culture studies have shown evidence of cytotoxicity and oxidative stress induced by single-walled carbon nanotubes (SWCNTs), depending on whether and to what degree they are functionalized or oxidized. A recent report also found that inhaled single-walled CNTs can cause damage to the lungs in animal studies. On the other hand, another study (New nanotube findings give boost to potential biomedical applications) reported that the CNTs leave the body without accumulating in organs and without observable toxic effects (read more about this ongoing debate in The detection of carbon nanotubes and workplace safety).

    So of course you need to take these results with a grain of salt (see Comparing apples with oranges - the problem of nanotubes risk assessment).

    For most medical applications like drug delivery, the most relevant route into and through the body for CNTs would be in the circulatory system. However, close to nothing is known about the acute and chronic toxicity of SCWNTs when they enter the bloodstream. A new study at Stanford University tested non-covalently pegylated SWCNTs as a 'least toxic scenario', and oxidized, covalently functionalized nanotubes as a 'most toxic scenario' in a study on mice. It was found that SWCNTs injected intravenously into nude mice do not appear to have any significant toxicity during an observation period of four months following injection.

    "Our study demonstrates the first systematic toxicity evaluation of functionalized SWCNTs following intravenous injection" Dr. Sanjiv Sam Gambhir tells Nanowerk. "Single administrations of high doses did not lead to acute or chronic toxicity, but we observed some changes in red blood cells. Because of the small number of animals used in the tests, our findings must be considered a pilot study. Although more extensive series are needed to confirm our results and show equivalence in other mouse strains, they do encourage further exploration of functionalized SWCNTs in biomedical applications in living animals."

    Liver and spleen histology of injected carbon nanotubes
    Liver and spleen histology. a–f, Haematoxylin and eosin stains of liver (a–c) and spleen (d–f) tissues of mice injected with phosphate buffered saline (PBS) (a,d), non-covalently pegylated SWCNTs (SWCNT PEG) (b,e) or covalently functionalized nanotubes (SWCNT O PEG) (c,f). Finely granular brown-black pigments were seen in sinusoidal liver cells of SWCNT PEG (b, arrows) and SWCNT O PEG (c, arrows), as well as a golden-brown pigment in spleen macrophages of SWCNT PEG and SWCNT O PEG (e,f), without signs of cellular or tissue damage. (Reprinted with permission from Nature Publishing Group)

    Gambhir, a professor in Stanford University's Departments of Radiology and Bioengineering, and Director, Molecular Imaging Program at Stanford (MIPS) as well as Head, Stanford Nuclear Medicine, collaborated on this project with Stanford researchers from MIPS, Hongjie Dai's group in the Department of Chemistry, and the Department of Comparative Medicine. The scientists published their findings in the March 30, 2008 online edition of Nature Nanotechnology ("A pilot toxicology study of single-walled carbon nanotubes in a small sample of mice"). This work was funded in part by the National Cancer Institute's (NCI) Center for Cancer Nanotechnology Excellence (CCNE).

    All aspects of toxicity, including EKG, blood pressure, temperature, cell blood count, electrolytes, etc were monitored repeatedly during the 4-months study period. Gambhir says that, although minor changes occurred, no statistically significant changes occurred between mice given SWCNTs and those not given them.

    "At the end of the monitoring period of 4 months all mice were sacrificed and a full tissue histology was done to look for signs of organ toxicity; but there was none." he says. "The Kupfer cells in the liver (a special type of cell that sits within the sinusoids, which are the phagocytes of the liver) had eaten up the nanotubes and they were found in these cells within the liver."

    Gambhir and his group were motivated to do this study because they are developing imaging agents for cancer detection that rely on carbon nanotubes. Of course, before these technologies can be moved to a human trial stage the question of toxicity must be much better understood than it is today. Although preliminary, this recent study gives some hope in at least not finding any obvious toxicity problems.

    By Michael Berger, Copyright 2008 Nanowerk LLC

    Posted: April 22, 2008

    + نوشته شده در  87/02/03ساعت 11:44  توسط مهندس محمدرضا فروغی  | 

    Silicon nanotubes could exceed their carbon counterparts in hydrogen storage efficiency

    Posted: April 21, 2008

    Nanowerk Spotlight) Safe, efficient and compact hydrogen storage is a major challenge in order to realize hydrogen powered transport. According to the U.S. Department of Energy's Freedom CAR program roadmap, the on-board hydrogen storage system should provide a gravimetric density of 6 wt% at room temperature to be considered for technological implementation. Currently, the storage of hydrogen in the absorbed form is considered as the most appropriate way to solve this problem. Research groups worldwide are seeking and experimenting with materials capable of absorbing and releasing large quantities of hydrogen easily, reliably, and safely. One candidate material that is being considered as a candidate for hydrogen storage media is single-walled carbon nanotubes (SWCNT).

    So far, carbon nanotubes have been unable to meet the DOE's hydrogen storage target. This even has led to a decision by the DOE to discontinue future applied research and development investment in pure, undoped SWCNTs for vehicular hydrogen storage applications. Although most of the previous studies have focused on hydrogen storage through physisorption, recent Density Functional Theory calculations for SWCNT indicate the potential for up to 7.5 wt% hydrogen storage capacity for this material through chemisorption (see our Spotlight: "New carbon nanotube hydrogen storage results surpass Freedom Car requirements").

    New theoretical work from China suggests that silicon nanotubes can store hydrogen more efficiently than their carbon nanotube counterparts. This raises the possibility that, after powering the micro-electronics revolution, silicon could also become a key material for the future hydrogen economy.

    "Compared to carbon, silicon has more electrons in the outer shells, which leads to higher polarizability and a stronger dispersion force" Dr. Dapeng Cao explains to Nanowerk. "Motivated by this observation, we employ a multiscale theoretical method, which combines the first-principle calculation and a grand canonical Monte Carlo simulation, to predict the adsorption capacity of hydrogen in silicon nanotube (SiNT) arrays at a temperature of 298°K (25°C) and pressure range from 1 to 10 MPa. Our calculations show that silicon nanotubes can adsorb hydrogen molecules more efficiently than carbon nanotubes under normal fuel cell operating conditions."

    Cao, is a professor and vice director of the Lab of Molecular and Materials Simulation at the Beijing University of Chemical Technology. Together with other members of the Lab he published their recent findings in the March 19, 2008 online edition of The Journal of Physical Chemistry (Silicon Nanotube as a Promising Candidate for Hydrogen Storage: From the First Principle Calculations to Grand Canonical Monte Carlo Simulations).

    carbon nanotube serpentines carbon nanotube serpentines
    Left: Schematic representations of a (5,5) SiNT cluster model, where all the terminals are saturated with H atoms and the brown yellow and gray spheres represent Si and H atoms, respectively. Right: Gravimetric adsorption capacity of hydrogen in the rhombic SiNT array at T=298°K and P=10 MPa, resulting in 2.88 wt%. A comparative simulation with CNTs results in gravimetric density of 1.96 wt%. (Images: Dr. Cao)

    Following the successful synthesis of silicon nanotubes by the chemical vapor deposition method in 2002, researchers developed numerous other methods to fabricate these SiNTs and well-aligned SiNT arrays. Because silicon has more electrons in the outer shells than carbon – which leads to higher polarizability and a stronger dispersion force – scientists theorized that SiNTs may exhibit a stronger van der Waals attraction to hydrogen than CNTs.

    "Our multiscale theoretical method combines the first-principle calculations to obtain the binding energy between hydrogen and the SiNT and a grand canonical Monte Carlo simulation to evaluate the hydrogen adsorption capacity in the SiNT arrays, where the calculated binding energy is provided as an input in the Monte Carlo simulation" Cao explains.

    The researchers found that geometrical arrangement of the tubes as well as the diameter and curvature of the tube affect the adsorption of hydrogen in the SiNT array.

    Since SiNTs are a novel material, there is no experimental data available yet with regard to their hydrogen storage capability. Experimental work needs to be conducted to confirm this theoretical findings. Cao points out that the separation between silicon nanotubes affects the capacity of hydrogen storage significantly. Therefore one of the challenges for conducting practical experiments will be control of the optimal separation between SiNTs in the preparation of well-aligned arrays.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/02/02ساعت 19:20  توسط مهندس محمدرضا فروغی  | 

    Single-crystal semiconductor wire built into an optical fiber

    Single-crystal semiconductor wires integrated into microstructored optical wires. Credit: Penn State University

    Single-crystal semiconductor wires integrated into microstructored optical wires. Credit: Penn State University

    An international science team from Penn State University in the United States and the University of Southampton in the United Kingdom has developed a process for growing a single-crystal semiconductor inside the tunnel of a hollow optical fiber. The device adds new electronic capabilities to optical fibers, whose performance in electronic devices such as computers typically is degraded by the interface between the fiber and the device.
    The research is important because optical fibers -- which are used in a wide range of technologies that employ light, including telecommunications, medicine, computing, and remote-sensing devices -- are ideal media for transmitting many types of signals.

    The development of the single-crystal device, which will be described in a paper to be published later this month in the journal Advanced Materials, builds on research reported in 2006, in which the team first combined optical fibers with polycrystalline and amorphous semiconductor materials in order to create an optical fiber that also has electronic characteristics. The group's latest finding -- that a single-crystal semiconductor also can be integrated into an optical fiber -- is expected to lead to even further improvements in the characteristics of optical fibers used in many areas of science and technology.

    "For most applications, single-crystal semiconductor materials have better performance than polycrystalline and amorphous materials," said John Badding, associate professor of chemistry at Penn State. "We have now shown that our technique of encasing a single-crystal semiconductor within an optical fiber results in greater functionality of the optical fiber, as well."
    The team used a high-pressure fluid-liquid-solid approach to build the crystal inside the fiber. First, the scientists deposited a tiny plug of gold inside the fiber by exposing a gold compound to laser light. Next, they introduced silane, a compound of silicon and hydrogen, in a stream of high-pressure helium. When the fiber was heated, the gold acted as a catalyst, decomposing the silane and thus allowing silicon to deposit as a single crystal behind the moving gold catalyst particle, forming a single-crystal wire inside the fiber.

    "The key to joining two technologies lies not only in the materials, but also in how the functions are built in," said Pier Sazio, senior research fellow in the Optoelectronics Research Centre at the University of Southampton. "We were able to embed a nanostructured crystal into the hollow tube of an optical fiber to create a completely new type of composite device."

    The research team sees potential to carry the application to the next level. "At present, we still have electrical switches at both ends of the optical fiber," said Badding. "If we can get to the point where the electrical signal never leaves the fiber, it will be faster and more efficient."

    Source: Penn State
    + نوشته شده در  87/02/02ساعت 0:22  توسط مهندس محمدرضا فروغی  | 

    Nanotechnology funding strategy in Germany shows a growing focus on sustainability aspects

    (Nanowerk Spotlight) The European Union currently spends about 740 million Euros (roughly $1.2 billion) annually in public funding on nanotechnology research. This is almost on par with the U.S. National Nanotechnology Initiative (NNI) budget of $1.28 billion (2007). Almost 40% of public EU nanotechnology funding takes place in Germany and it is estimated that about half of the European companies active in nanotechnology are based in Germany, making the country the clear nanotechnology leader in Europe. Germany’s strengths include a well structured R&D infrastructure and a high level of research in the various subfields of nanotechnology. The industrial base for utilizing the results of this research is also in place. About 700 companies are currently involved in the development, application, and sales and marketing of nanotechnological products. 130 of these are large companies, and 570 are small or medium sized enterprises. The VDI Technologiezentrum maintains a database with over 1130 links to nanotechnology companies, university labs, networks and research centers. Click the map below to explore the database.

    nanotechnology in Germany

    What sets public nanotechnology policy in Germany and other European countries apart from the U.S. is a more deliberate attempt to create, and evolve over time, an integrated approach in the development of nanotechnology research, trying to link sustainability questions and technology development.

    A recent report analyzes the relationship between innovation and sustainability in light of the development of the nanotechnology funding strategy in Germany. This strategy has been guided by an integrated approach of technology management activities. The report, titled "Nanotechnology in Germany: from forecasting to technological assessment to sustainability studies", describes how this led from technological forecasting activities, the definition of application fields and market surveys to early technological assessment activities and sustainability studies combined with communication measures. The importance of sustainability aspects grew steadily throughout this process, and the integrated approach facilitated the early detection of relevant sustainability issues to be dealt with in the future.

    The report has been authored by researchers from the Future Technologies Division of the VDI Technologiezentrum in Düsseldorf, Germany. VDI is the Association of German Engineers and its two technology centers are providing support, planning and forecasting expertise to decision-makers in academics, politics, and industry. The VDI experts argue that the experience with the evolving nanotechnology funding strategy in Germany underlines the importance of integrating innovation measures in research funding with work on systematically assessing the sustainability potential of the new technologies.

    But they also acknowledge that "certainly, the potential of nanotechnology to contribute to sustainability has not been fully exploited by these activities. It remains interesting to ask how this potential could be fully exploited and used as early as possible."

    Both nanotechnology and environment/sustainability have been on the research agenda in Germany since the early 1990s. As is often the case, both research agendas frequently were set up in different programs, divisions or thematic sections, usually with minimal overlap. Consequently, it required deliberate efforts and strategies to build linkages between the two areas, requiring systematic approaches that integrate both views.

    The main federal funding agency in Germany tasked with promoting pre-commercial nanotechnology R&D is the Ministry for Education and Research (BMBF). Starting its nanotechnology activities in the early 1990s, the Ministry's strategic orientation of its nanotechnology funding policy has seen a a substantial shift in the last decade, with sustainability aspects playing an increasing role.

    Broadly defined, sustainability is economic development that takes full account of the environmental consequences of economic activity and is based on the use of resources that can be replaced or renewed and therefore are not depleted. Sustainability has been on the political agenda in Germany for the past 20 years and the German Government has recognized sustainability as a cross-sectional task and has made it a fundamental principle of its policy.

    In 2001, the German government launched launched a national sustainability strategy (pdf download, 2.1 MB) which defines four guiding principles (generational equity, quality of life, social cohesion, and international responsibility), six areas of activity and 21 indicators for monitoring progress in these areas. As part of implementing the strategy, the German Council for Sustainable Development was established in 2001. The Council makes recommendations to experts in a variety of fields and fosters an informed public debate.

    The VDI's overview shows that nanotechnology funding activities address 11 of the 21 criteria of the national sustainability strategy in three of the four guiding principles. Besides contributions in ecological indicators such as resource productivity and energy efficiency, social and economic indicators like employment and gender issues are also addressed by the programs.

    The integrated approach followed by the BMBF resulted in a very quick switch from a mere technology push to a market pull strategy, since a high level of involvement of companies in the research programs was achieved. As the focus switched early from curiosity-driven research to applied research, the VDI authors point out that early orientation towards industry interests had two (maybe adverse) effects on the role of sustainability in the development of nanotechnology:

    "On the one hand, the strong focus on industry interests and marketable solutions fostered a concentration on potential future lead markets like the automobile sector, the chemical industry or ICT technologies. This did not preclude sustainable solutions, but the main focus and the main criterion for project and funding decisions was the perspective of opening up new emerging markets as opposed to pointing to sustainability effects produced by these technology fields. The concentration on lead innovations and lead markets may have neglected other fields where nanotechnology could contribute to sustainability, e.g. soil remediation, and water purification or pollution control.

    "On the other hand, the market assessments and patent analyses served to define the application fields for the new technology at a very early stage during the process. This in turn paved the road for an early launch of the innovation and technology analysis. The insights gained from the technology forecasting process and the market analyses could be used directly and without time delays for a substantiated first innovation and technology analysis (ITA) study. Thus, the relevant fields for further ITA questions (like toxicity of nanoparticles, behavior in the environment) could be identified and decisions on rewarding issues for first quantitative life cycle assessments of nanotechnology products could be made."

    In stark contrast to the U.S., where a large part of nanotechnology R&D funding comes from the military – with a resulting focus on deliverables and applications – the identification of relevant issues for ITA in Germany has helped design a communication and education process at a time when the debate was still open and fixed pro- and contra groups had not yet formed within society. The authors point out that "from the very beginning, critical issues such as health, toxicity and environmental effects were integrated into the communication measures such as the NanoTruck and built a knowledge base for the discussion on the acceptance of the new technology."

    The German approach to developing nanotechnologies, taking into consideration all societal aspects, is clearly documented in the Nano Initiative - Action Plan 2010 (pdf download, 1.9 MB) where, for the first time, a unified framework across seven key federal ministries has been presented. The Federal Ministries for Labor and Social Affairs (BMAS), Environment, Nature Conservation and Nuclear Safety (BMU), Food, Agriculture and Consumer Protection (BMELV), Defense (BMVg), Health (BMG) and Commerce and Technology (BMWi) together with the BMBF have laid the foundations to, among other things, lead an intensive dialogue with the public on the chances of nanotechnology including its risks. To this end, possible effects on health and nature will be analyzed, a common strategy on environmental risks of insoluble nanoparticles developed, and modern means of information and participation of the public applied.

    In general terms, the activities described by the VDI paper – integrating sustainability issues in technology development as early as possible – can be seen as complementary and supportive to approaches that focus more on the sustainability challenges (e.g. climate change, water purification) and then derive the activities and technology developments necessary to achieve progress in these fields. However, as the authors point out, "the main challenge in this context remains how to merge the different research cultures of innovation/technology and sustainability research."

    What this report nicely lays out is that technology development and sustainability issues cannot be seen as two different, even opposite, policy goals but have to go hand in hand. While technology development clearly is in the self-interest of industry, sustainability is not, at least not until it results in negative factors (such as oil prices spiking well over $100 a barrel) that have an economic impact on companies.

    Indirectly, the paper also makes the case for a deliberate technology development policy and strategic guidance from the government in areas where market forces alone would not lead to timely solutions that are most beneficial for society overall.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    Posted: April 17, 2008

    + نوشته شده در  87/01/30ساعت 14:3  توسط مهندس محمدرضا فروغی  | 

    Companies fail to apprise investors of potential nanotechnology risks

    (Nanowerk Spotlight) Following just two days after we wrote about the food industry's deafening silence on their nanotechnology research and development (Food nanotechnology - how the industry is blowing it), the Investor Environmental Health Network today released a report that demonstrates that sectors affected by product toxicity risks are doing a poor job of informing shareholders of market risks they face due to toxic chemicals in their products. The report specifically addresses the situation for companies dealing with nanomaterials by noting that manufacturers are not disclosing the evidence of health risks of nanotechnology products, nor the lack of adequate product testing prior to their sales.

    An interesting observation is that some nanomaterial manufacturers are more open to communicating potential uncertainties than their customers. These customers of the nanomaterials are the manufacturers of an array of products from electronics to food and cosmetics - and they tend not to disclose the potential health and financial risks. IEHN's conclusion is that investors should be apprised of the state of the science by a company, instead of being misled to believe that the serious questions have been answered.

    The Investor Environmental Health Network (IEHN) is a collaboration of investment managers with more than $41 billion in assets. For their report, titled "Toxic Stock Syndrome: How Corporate Financial Reports Fail to Apprise Investors of the Risks of Product Recalls and Toxic Liabilities" (pdf download, 1.7 MB), they reviewed thousands of SEC filings and analyzed 25 individual company annual reports for 2006 and 2007. Not limited to nanotechnology, the report examines disclosures on supply chain weaknesses before and after the 2007 toy recalls due to lead paint, on scientific studies showing products causing asthma, and on the new European chemical regulatory program, REACH (Registration, Evaluation, Authorization and Restriction of Chemicals).

    In its section on nanotechnology and nanomaterials, the IEHN authors extensively quote from a widely circulated 2004 Swiss Re report "Nanotechnology - Small matter, many unknowns". One key quote addresses the fact that professional risk assessors already recognize the inherent danger in fast-emerging technologies such as nanotechnology, where risks and liabilities are not immediately apparent:

    "Risks arising out of the introduction of new products or innovative technologies need not reveal themselves immediately and may occur after an interval of years. Nanotechnology is set to spread to such a wide range of industries and in such a large number of applications and at such speed, that the individual claims conceivable on the basis of experience and resulting from defects can hardly expect to be long delayed. Things will become critical if systemic defects only emerge over time, or if a systematic change in behavior remains undetected for a long time. In that case, an unforeseeably large loss potential could accumulate, for example, in the field of health impairment."

    Confirming what we have written in the past here at Nanowerk regarding certain industry sectors' (food, cosmetics), shall we say – "reluctance" to share information about their products' nanomaterial ingredients, the authors write that "in general we observed that some of the specialists in the manufacture of nanotechnology products tended to engage in broader disclosure of potential health risks than those using nanotechnology as part of established consumer product lines."

    Some companies address potential nanotechnology risks

    The report specifically mentions nanomaterial and equipment manufacturers like Arrowhead Research Corporation, Luna Innovations, Nano-Proprietary Inc., and CVD Equipment Corp. as addressing potential health and safety concerns about their nanomaterials in their communication to the public.

    Arrowhead is quoted as disclosing that "nanotechnology-enabled products, such as those used in our chemical detection technologies, are new and may be viewed as being harmful to human health or the environment...Because of the size, shape or composition of the nanostructures or because they may contain harmful elements, nanotechnology-enabled products could pose a safety risk to human health or the environment. The regulation and limitation of the kinds of materials used in or to develop nanotechnology enabled products, or the regulation of the products themselves, could harm the commercialization of nanotechnology-enabled products and impair our ability to achieve revenue from the license of nanotechnology applications." The firm also discusses health risk concerns surrounding nanotechnology, and how these could affect market value.

    Luna Innovations acknowledges the limited safety record of nanomaterials, and foresees federal regulations surrounding nanotechnology. In an August 2007 quarterly report, the company states: "Our nanotechnology-enabled products are new and may be, or may be perceived as being, harmful to human health or the environment. While none of our current products are known by us to be hazardous or subject to environmental regulation, it is possible our current or future products, particularly carbon-based nanomaterials, may become subject to environmental regulation."

    Nano-Proprietary Inc., a company that focuses on carbon nanotube applications, makes a similar prediction of future regulations on nanotechnology in its 2007 10-K: "Products using our technology will be subject to extensive government regulation in the United States and in other countries...We do not believe that carbon nanotube field emission products will present any significant occupational risks to the operators of such equipment...Nevertheless, OSHA, the EPA, the CDRH and other governmental agencies, both in the United States and in foreign countries, may adopt additional rules and regulations that may affect us and products using our technology."

    IEHN quotes CVD Equipment Corp. as going the furthest of any company in acknowledging the concerns about its nanotubes products: "The health and environmental effects of nanotechnology are unknown, and this uncertainty could adversely affect the expansion of our business...There is no scientific agreement on the health effects of nanomaterials in general and carbon nanotubes, in particular, but some scientists believe that in some cases, nanomaterials may be hazardous to an individual’s health or to the environment...Since part of our growth strategy is based on sales of research equipment for the production of carbon nanotubes and the sale of such materials, the determination that these materials are harmful could adversely affect the expansion of our business."

    Some companies don't

    The IEHN authors point out that carbon nanotubes are an example of a nanotechnology that may have some of the most serious risks, and manufacturers are making some vague references to potential health concerns and regulatory risks. In contrast "our review of SEC filings showed that the users who add these substances to their products are making few if any disclosures of the uses, the potential health risks based on their structures, and the financial risks to user companies."

    NaturalNano Inc. is quoted as talking at length about its use of nanotubes technologies in health and beauty products and clothing, without flagging the health risk concerns relative to nanotubes.

    Another example listed is Procter & Gamble whose website includes a discussion of nanotechnology in its research and development section. "The summary on the website focuses on the documented safety of ultrafine metal oxides used in sunscreens, implying that nanoscale products should be equally safe, although ultrafine particles are generally much larger than nanoscale particles. P&G concludes, 'With a long history of safe use in FDA-regulated products and a demonstrated lack of dermal absorption, there is extensive confirmatory evidence that nanoscale zinc oxide and titanium dioxide may be safely used in cosmetics and OTC drug products'."

    IEHN writes that the cosmetics company Avon has made similar claims of product safety. In its spring 2008 statement in opposition to a shareholder resolution requesting a report on Avon’s policies on nanomaterials product safety, the company broadly asserts in the proxy that these materials are safe. "Avon’s evaluation included a specific assessment of the potential for nano-sized particles of these materials to be absorbed through the skin (several scientific studies have demonstrated that nano-sized titanium dioxide and zinc oxide do not penetrate the skin). In the opinion of Avon’s scientists (toxicologists and other safety professionals) each of these materials can be used safely in cosmetic products."

    IEHN says that neither Avon nor Procter & Gamble gives a balanced presentation of the scientific concerns about nanoparticles. "Some recent research on sunscreen ingredients in humans supports Avon’s and Procter & Gamble’s safety claim that the nanoparticles in sunscreen do not penetrate the skin, but others question whether testing is thorough enough to determine safety."

    The report goes on to list several uncertainties concerning safety of the nanoparticles used in sunscreens and the concludes: "Users of the sunscreen nanoparticles such as Avon and Procter & Gamble may be prematurely asserting safety, and neglecting to present a balanced picture of the limitations of testing conducted to date. Untested variables could influence the ability for nanoparticles to penetrate the skin or otherwise enter the body, including incidental consumption of the particles applied to the face, via the mouth."

    The report concludes with recommendations to companies, investors, and the SEC, including the following:

  • Companies should provide to shareholders additional information on chemical supply chain issues, including sources of materials, risk areas, and control systems.
  • Investors should press for better disclosure from companies, through direct correspondence and support of shareholder resolutions seeking such disclosure.
  • The SEC should issue new guidance to companies requiring them to more specifically report their product lines vulnerable to Europe's REACH regulation and should report more fully on credible adverse scientific findings that may impact the company.
  • By Michael Berger. Copyright 2008 Nanowerk LLC

    Posted: April 18, 2008 

    + نوشته شده در  87/01/30ساعت 13:58  توسط مهندس محمدرضا فروغی  | 

    Conductive and tunable transparent coatings made from monodisperse carbon nanotubes

    Posted: April 15, 2008

    (Nanowerk Spotlight) There are several touch sensor technologies available to power touch screens like the ones you can find on your bank ATM, airport check-in kiosk or other self-service terminals. What they all have in common is that they are sensitive to human touch because their screens are coated with a special transparent thin film that act as a sensor. This sensor generally has an electrical current or signal going through it and touching the screen causes a voltage or signal change. Apart from touch screens, transparent conductive thin films are used in numerous products such as flat-panel displays, solar cells or as thermal barriers in energy-saving windows. Future applications will include flexible displays for e-papers, smart cards, 'heads-up' displays integrated into cockpit and car windows, and windows that can be used as a light source at night.

    The technology to manufacture transparent, electrically conductive layers on transparent substrates is highly developed but suffers from reliance on the most widely used standard material - indium tin oxide (ITO). There are several problems with ITO that make it less than optimal for these applications: It is relatively brittle, which degrades its performance on flexible substrates; it has limited chemical stability leading to corrosion in device structures; its electrical properties greatly depend on the film preparation; and, most importantly, the Earth is running out of indium, making this material more and more expensive.

    All this has driven increased research activity in finding alternative novel transparent electrode materials with good stability, high transparency and excellent conductivity. Graphene is one good candidate (see: Ultrathin transparent graphene films as alternative to metal oxide electrodes) and films based on carbon nanotubes have attracted significant attention recently as well. Researchers now have demonstrated the use of metallic nanotubes to make thin films that are semitransparent, highly conductive, flexible and come in a variety of colors.

    conductive, flexible carbon nanotube colored thin film on flexible plastic substrates
    Photograph of conductive, flexible carbon nanotube 'stained glass' on flexible plastic substrates. The carbon nanotube films are arranged in order of increasing average diameter (clockwise starting from lower left): 0.9, 1.0, 1.05, 1.1, 1.4, and 1.6 nanometers. The ability to control nanotube diameter leads to the visible colors that are apparent in the photograph. (Image: Dr. Mark Hersam)

    "While there has been much progress in the development of single-walled carbon nanotube (SWCNT) transparent conductors in recent years, previous work has been limited by the unavoidable polydispersity of as-produced SWCNTs" Dr. Mark C. Hersam, a professor of Materials Science and Engineering at Northwestern University in Evanston, Illinois, explains to Nanowerk. "This polydispersity stems from the unique structure of SWCNTs. Although this structure imbues them with their remarkable characteristics, it also renders their properties highly sensitive to the nanotube diameter and helicity. Of all possible SWCNT chiralities, roughly one-third are metallic with the remainder being semiconductors whose bandgaps vary inversely with nanotube diameter."

    This polydispersity problem – where a given batch of SWCNTs contains material with a distribution of diameters and varying electronic character – also caused less than optimal results in previous work on transparent conductive nanotube networks because of the broad distribution of electrical and optical characteristics of the involved nanotube material.

    Utilizing a technique known as density gradient ultracentrifugation (DGU), Hersam's group has produced SWCNTs with uniform electrical and optical properties, enabling the production of transparent conductors consisting predominantly of metallic SWCNTs with small diameter distributions. Thin films formulated from these high purity carbon nanotubes possess 10-fold improvements in conductivity compared to pre-existing carbon nanotube materials.

    Hersam explains that in the DGU process SWCNTs undergo ultracentrifugation, after which colored bands of sorted SWCNTs can be recovered and incorporated directly into transparent conductive films.

    "Films generated from sorted metallic SWCNTs offer two major improvements over those produced from unsorted material" he says. "First, DGU eliminates poorly conducting, strongly absorbing carbonaceous impurities and semiconducting SWCNTs to enhance transparent conductor electrical performance and optical transmissivity. Second, since the optical absorption of metallic SWCNTs is strongly dependent on diameter, the angstrom-level control over nanotube diameter afforded by DGU results in films possessing a variety of different colors. These semitransparent conductive SWCNT coatings offer an unprecedented degree of control over the optical properties of the transparent conductor."

    SWCNTs sorted this way can be tuned with much higher fidelity than ITO, which can only be controlled in a much coarser way through film thickness and doping level. It is expected that metallic SWCNTs of monodisperse diameter will increasingly challenge ITO in transparent conductor applications, particularly those in which a high degree of optical tunability is required.

    "We expect conductive SWCNT coatings to enhance transparent conductor performance in multiple applications" says Hersam. "High transmittance regions of optimized films could be employed to increase the efficiency of devices such as flat panel displays, light emitting diodes, and solar cells. Conversely, the sharply peaked low transmittance regions of the coatings could be used to filter out unwanted portions of the optical spectrum that compromise device performance."

    He points out that high-purity carbon nanotube thin films not only have the potential to make inroads into current applications but also accelerate the development of emerging technologies such as organic light-emitting diodes and organic photovoltaic devices. "These energy-efficient and alternative energy technologies are expected to be of increasing importance in the foreseeable future."

    Hersam and first author Alexander Green, a graduate student in Hersam's group, have published their findings in the April 8, 2008 online edition of Nano Letters ("Colored Semitransparent Conductive Coatings Consisting of Monodisperse Metallic Single-Walled Carbon Nanotubes").

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/29ساعت 0:31  توسط مهندس محمدرضا فروغی  | 

    Food nanotechnology - how the industry is blowing it

    Posted: April 16, 2008

    (Nanowerk Spotlight) The food industry is excited about the potential of nanotechnology. Food companies are very much involved in exploring and implementing nanotechnology applications in food processing, packaging and even growing - but you don't hear about it anymore. At least not from the companies.

    Large industrial food companies, no stranger to big and expensive media campaigns, have buried the subject of nanotechnology in their public relations graveyard. Take Kraft Foods for example. While it took the industry’s nanotechnology lead when it established the Nanotek Consortium in 2000, it has since pulled back completely on the PR front. The Nanotek Consortium even was renamed the 'Interdisciplinary Network of Emerging Science and Technologies' (INEST), is now sponsored by Altria, and its single webpage makes no mention of food at all. Doing our regular check on the websites of large food companies (Altria (Kraft Foods), Associated British Foods, Cadbury Schweppes, General Mills, Group Danone, H.J. Heinz, Nestlé, Kellogg) we again found not a single reference to 'nanotechnology' or even 'nano'. The same is true for large food industry associations such as the Grocery Manufacturers/Food Products Association (GMA/FPA), which represents the world's leading food, beverage and consumer products companies.

    Faced with a complete nanotechnology communications blackout from the manufacturers, it is left to activist groups like Friends of the Earth to frame the discussion. These groups, together with a few public efforts in Europe (such as the European Food Safety Authority addressing nanotechnology food safety) are trying to figure out what the food industry is up to and if there might be any risks involved that we should know about (there also is an older report from PEN – Nanotechnology in Agriculture and Food – but this information probably is no longer up to date).

    These organizations argue that a lack of evidence of harm is not the same as reasonable certainty of safety, which is what food companies must demonstrate to food regulating bodies such as the FDA in the U.S. before introducing a new food additive. With regard to the FDA, though, it seems that government organizations are somewhat challenged with regard to assessing nanotechnologies (read: FDA Confronts Nanotechnology).

    While forward-looking companies are very open about what they are doing with nanotechnologies, even inviting public scrutiny (see: Nanotechnology risk framework by Environmental Defense and DuPont or Stakeholders applaud measure to develop nanotechnology EHS research roadmap), the entire industrial food sector is so scared of public scrutiny of their nanotechnology activities that they have stopped communicating about it at all. By leaving it to activist groups to spread the word about their nanotechnology activities, these companies run a huge risk of the public discussion about their nanotech products being framed by forces that usually are very critical, outspoken, and not necessarily balanced when it comes to perceived and potential risks.

    Rather than treating safety-conscious consumers as mature grown-ups who want to hear both sides of the story and then come to an informed opinion, the food companies' behavior is fueling the arguments of critics who think the industry is hiding something.

    The problem is that there is no transparency whatsoever about the use of nanotechnology in the food industry. It seems that the key players are worried that food nanotechnology will suffer the same fate as genetic engineering, which has come to be fiercely opposed, especially in Europe.

    What is even more puzzling about the food industry's behavior is that the 'nanotechnology' used in food products and processes today doesn't sound very scary. It's mostly nanoemulsions and nanoscale versions of commonly used ingredients and materials (although there has been some controversy recently about the use of nanoparticulate silver in antimicrobial applications).

    A recent report by Friends of the Earth titled "Out of the Laboratory and on to our Plates - Nanotechnology in Food & Agriculture" provides a good, current overview of nanotechnology's role in the food industry. While we leave it to you to judge the group's take on the industry, the perceived risks, and their recommendations, we think the report is a good source of nanotechnology examples of what is already happening in food production and what we can expect coming to our dinner tables soon.

    The report, which defines the term ‘nanofood’ as food which has been cultivated, produced, processed or packaged using nanotechnology techniques or tools, or to which manufactured nanomaterials have been added, lists some 100 cases of nanotechnology (mostly in the form of added nanoparticles) used in food processing, food packaging and in agriculture. Here are some examples:

    nanotechnology applications in food
    Examples of the current use of nanomaterials in agriculture, foods and food packaging (Image: Friends of the Earth)

    A lot of food products on supermarket shelves already undergo various degrees of (non-nanotechnology) processing that affect their biological and biochemical makeup and in many cases lead to what appears to be entirely artificial 'food' (read "Twinkie, Deconstructed" to get the idea). As nanotechnology developments in the fields of biology and biochemistry progress, expect more and more of it influencing the food industry and more complex nanotechnology applications to appear. For instance, active research is going on to create 'interactive foods' such as 'programmable' wine.

    There also is a potential for using more controversial materials: for example, carbon nanotubes are being explored as gelation and viscosifying agents and various kinds of fibers in packaging materials.

    The food industry's practically non-existing communication is a far cry from what is needed to create public confidence in their existing and coming range of nanotechnology enhanced food products and applications. Instead of seeking a public dialogue, food companies seem to have so little confidence in their own technology (or communication skills; or reputation) that they prefer to go into hiding.

    Why not come out guns blazing and educate the public about the exciting opportunties for nanotechnologies in the food sector? Why not demonstrate that the risk aspects of the technology are being thoroughly investigated? (Are they?) Why invite the cliché of 'bad corporate citizens' – companies that keep information from the public and hide the risky aspects of what they are doing; deny there is a risk at all; spend extraordinary amounts of money on lobbyists to escape stringent regulations; and only face a problem and deal with it after it happened and there is absolutely no other way of wiggling out (tobacco companies anyone?).

    If you are interested in some other background stories, we have several food related articles here on the Nanowerk site:

  • By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/29ساعت 0:26  توسط مهندس محمدرضا فروغی  | 

    Nanoparticles feel the heat


    Nanothermometers that monitor temperature changes in cells could improve an anticancer heat treatment, say scientists in Puerto Rico. 

    "Through the fluorescence change in the polymer, the temperature of the medium surrounding the nanoparticles can be monitored non-invasively, using a spectrofluorometer."

    Carlos Rinaldi and colleagues from the University of Puerto Rico have been working on improving magnetic fluid hyperthermia cancer treatment (MFH). MFH involves injecting a fluid containing magnetic iron oxide nanoparticles directly into tumours. The temperature of the surrounding cells is then increased from a normal 37 °C to about 42 °C by heat generated when an alternating magnetic field is applied. Whilst healthy cells can survive at 42 °C, tumour cells are destroyed. However, above 42 °C, damage to the healthy tissue can also occur. 

    To monitor the temperature of MFH-treated cells, Rinaldi coated the nanoparticles used with a temperature-responsive fluorescent polymer built from N-isopropylacrylamide (NIPAM) and a modified acrylamide. Through the fluorescence change in the polymer, the temperature of the medium surrounding the nanoparticles can be monitored non-invasively, using a spectrofluorometer. And, when the temperature gets too high, the heating can be stopped - the temperature then falls by heat transfer to the surrounding unaffected tissue. 'That is, the body's natural mechanisms bring the temperature down,' explained Rinaldi. 

    TEM image of magnetite nanoparticles
    TEM image of magnetite nanoparticles coated with poly(NIPAM-co-FMA)
    The work has potential applications in bioengineering, said Rinaldi. He foresees the clinical development of his nanoparticles in MFH treatments, and intends to test this application in vitro in the near future. 'However, there are many challenges to be overcome before these materials can be used in a clinical setting,' Rinaldi warned. 'A major challenge is controlling the transition temperature of the polymer so we can visualise temperature changes relevant to MFH.' 

    'Also, NIPAM typically agglomerates at temperatures above a lower critical solution temperature,' added Rinaldi, 'especially in media with high ionic strength. It is actually not clear yet if this will be a problem during treatment, but it would definitely be a problem if the particles are in the bloodstream. We are working on using copolymers and on functionalising the polymer to avoid this.'

    Dhirendra Bahadur, at the Indian Institute of Technology Bombay, Mumbai, India, said that the mechanism of cell death - a field of interest to his team - might be 'better understood and monitored through the approach.' He added that 'there are other possibilities, not only for monitoring but also for controlling the temperature in vivo by using tuned materials, which would have the additional advantage that over-heating may be avoided.'

    Elinor Richards


    + نوشته شده در  87/01/28ساعت 11:24  توسط مهندس محمدرضا فروغی  | 

    Oxford Instruments Acquire Leading Supplier of HVPE Technology and Processes

     Oxford Instruments plc has announced the acquisition of Technologies and Devices International Inc (TDI), a world leader in the development of Hydride Vapour Phase Epitaxy (HVPE) technology and processes. The acquisition is part of the strategy put in place by Chief Executive, Jonathan Flint, to acquire complementary technologies and double the size of the group over five years.

    TDI’s technology enables Oxford Instruments Plasma Technology to expand the range of products it already supplies to the High Brightness Light Emitting Diode (HBLED) market. HBLEDs are a very low energy light source and their widespread use will significantly reduce carbon emissions. Oxford Instruments is committed to supporting the conservation of energy resources and the preservation of the environment, and is delighted that this acquisition will strengthen and support this focus.

    Oxford Instruments Plasma Technology currently supplies its Plasmalab range of etch and deposition tools to leading HBLED customers. The addition of HVPE opens up the opportunity to deliver products to the epitaxy sector of the market. TDI’s leading edge technology gives HBLED manufacturers the benefits of lower manufacturing costs and improved output that HVPE delivers over conventional Metal Organic Chemical Vapour Deposition (MOCVD) techniques.

    TDI will remain at its present US facility in Silver Spring, Maryland to assure continuity of supply to existing customers of HVPE grown III-nitride materials. Tatiana Dmitriev, President, and Dr Alexander Usikov, Head of Research & Development will continue to lead the team.

    Andy Matthews, Managing Director of Oxford Instruments Plasma Technology, said: ”This acquisition is part of our on-going strategy to deliver added value to our current and future HBLED customers and gives us the opportunity to supply new markets. We are delighted that TDI will be joining us, and look forward to working with them on developing the HVPE process further for the benefit of our customers.”

    Tatiana Dmitriev, President of TDI said: ‘We are very happy to be part of the Oxford Instruments group of companies to further develop III-nitrides HVPE and carry on with the innovative work that my father, Vladimir, and his team have been conducting over the past 10 years.’

    Posted April 10th, 2008 

    + نوشته شده در  87/01/24ساعت 0:15  توسط مهندس محمدرضا فروغی  | 

    Understanding Liquid Wetting to Benefit Nanotechnology Developments

     The relationship between a thin liquid film or drop of liquid and the shape of the surface that it wets is explained with a new simplified mathematical formula published this week in Physical Review Letters.

    Understanding the precise interaction between liquids and surfaces is important for a number of areas, including the chemical industry and new nanotechnologies.

    A mathematical formula is used to explain how the relationship between the liquid and the surface changes as one wets the other. Previous formulas have all failed to explain what scientists found when they conducted experiments in this field, and have become increasingly complicated and technical.

    Professor Andrew Parry from Imperial College London’s Department of Mathematics, author of the new paper, has devised and tested a new way to explain this process. His formula takes into account fluctuations in the drop of liquid between the solid surface it sits on and the air above it, which have not been included in any previous formula.

    “Previous descriptions have all ignored or misrepresented these interactions and consequently were at odds with experimental results and computer simulations. The new formulation appears to explain all these outstanding problems in a very elegant manner," said Professor Parry.

    The study of wetting focuses on the process by which a liquid makes a surface completely wet, such as occurs if a glass of water is poured over a glass surface. However, liquids do not always make surfaces completely wet, and droplets can form on the surface, such as when water is poured on a waxy material.

    Scientists know that if the temperature increases these droplets can gradually flatten out, until the surface is completely wet, and is an example of a phase transition. Exactly how this transition to complete wetting takes place has been contested by physicists for 25 years.

    Wetting is of key importance in many applications ranging from oil recovery and the way pesticides are deposited on plant leaves, to inkjet printing.

    Professor Parry has been working on this problem for four years, and this paper is the final one in a series of three publications addressing this problem. Previously he devised the new mathematical model and now in this most recent publication he has proven that it works.

    Posted 8th April 2008

    + نوشته شده در  87/01/24ساعت 0:12  توسط مهندس محمدرضا فروغی  | 

    Nanotechnology Meets Tradition With Carbon Nanotubes Being Made into Flexible, High Tech Stained Gla

     Carbon nanotubes are promising materials for many high-technology applications due to their exceptional mechanical, thermal, chemical, optical and electrical properties. Now researchers at Northwestern University have used metallic nanotubes to make thin films that are semitransparent, highly conductive, flexible and come in a variety of colors, with an appearance similar to stained glass. These results, published online in the journal Nano Letters, could lead to improved high-tech products such as flat-panel displays and solar cells.

    The diverse and exemplary properties of carbon nanotubes have inspired a vast range of proposed applications including transistors, logic gates, interconnects, conductive films, field emission sources, infrared emitters, biosensors, scanning probes, nanomechanical devices, mechanical reinforcements, hydrogen storage elements and catalytic supports.

    Among these applications, transparent conductive films based on carbon nanotubes have attracted significant attention recently. Transparent conductors are materials that are optically transparent, yet electrically conductive. These materials are commonly utilized as electrodes in flat-panel displays, touch screens, solid-state lighting and solar cells. With pressure for energy-efficient devices and alternative energy sources increasing, the worldwide demand for transparent conductive films also is rapidly increasing.

    Indium tin oxide currently is the dominant material for transparent conductive applications. However, the relative scarcity of indium coupled with growing demand has led to substantial cost increases in the past five years. In addition to this economic issue, indium tin oxide suffers from limited optical tunability and poor mechanical flexibility, which compromises its use in applications such as organic light-emitting diodes and organic photovoltaic devices.

    The Northwestern team has taken an important step toward identifying an alternative transparent conductor. Utilizing a technique known as density gradient ultracentrifugation, the researchers have produced carbon nanotubes with uniform electrical and optical properties. Thin films formulated from these high purity carbon nanotubes possess 10-fold improvements in conductivity compared to pre-existing carbon nanotube materials.

    In addition, density gradient ultracentrifugation allows carbon nanotubes to be sorted by their optical properties, enabling the formation of semitransparent conductive films of a given color. The resulting films thus have the appearance of stained glass. However, unlike stained glass, these carbon nanotube thin films possess high electrical conductivity and mechanical flexibility. The latter property overcomes one of the major limitations of indium tin oxide in flexible electronic and photovoltaic applications.

    “Transparent conductors have become ubiquitous in modern society -- from computer monitors to cell phone displays to flat-panel televisions,” said Mark Hersam, professor of materials science and engineering in Northwestern’s McCormick School of Engineering and Applied Science and professor of chemistry in the Weinberg College of Arts and Sciences, who led the research team.

    “High purity carbon nanotube thin films not only have the potential to make inroads into current applications but also accelerate the development of emerging technologies such as organic light-emitting diodes and organic photovoltaic devices. These energy-efficient and alternative energy technologies are expected to be of increasing importance in the foreseeable future.”

    Posted 10th April 2008

    + نوشته شده در  87/01/24ساعت 0:8  توسط مهندس محمدرضا فروغی  | 

    Ivy's gripping nanotechnology secrete

    Posted: March 31, 2008

    (Nanowerk Spotlight) You probably have seen quite a number of research reports on the amazing climbing abilities of geckos. Here at Nanowerk, we ran several Spotlights on this topic, for instance on mimicking gecko toe structures to fabricate super-strong dry adhesives. One demonstration of so-called 'gecko tape' has already been used in building Stickybot, a quadruped robot capable of climbing smooth vertical surfaces, such as glass, acrylic and whiteboard.

    In addition to the animal kingdom, scientists have started looking at plants to identify biological climbing mechanisms that could be exploited for engineering applications. One obvious candidate is ivy, a climbing woody plant. Researchers now have found that ivy secretes nanoparticles which allow the plant to affix to a surface and play an important role in the plant's climbing capability. This ivy secretion mechanism may inspire new, 'green' methods for synthesizing nanoparticles biologically or new approaches to adhesion mechanisms for mechanical devices.

    "Charles Darwin reported in 1876 that ivy rootlet secretes yellowish matter while climbing a surface" Dr. Mingjun Zhang tells Nanowerk. "But the questions are still open for what is contained in the secreted material and how the matter is related to the ivy climbing mechanism. We have first applied optical microscopy and AFM to study morphology of the secreted materials on a substrate surface and then treated these materials to solvent extraction and to use high-performance liquid chromatography/mass spectrometry (HPLC/MS) for analyzing the nanoparticle chemical composition."

    Zhang, an Associate Professor of Biomedical Engineering and Director, Nano Bio-systems, Bio-instrumentation and Automation Lab at the University of Tennessee, is first author of a recent paper in Nano Letters where he, together with collaborators from the university as well as Agilent Technologies, observed that ivy secretes large numbers of nanoparticles from tendrils of the adhering disk ("Nanoparticles Secreted from Ivy Rootlets for Surface Climbing").

    The most salient feature revealed through atomic force microscopy is the high degree of uniformity of the nanoparticles. The particles are about 70 nm in diameter and their average height is about 20–30 nm.

    Nanoparticles secreted from fingers of the adhering disks of an ivy rootlet
    Nanoparticles secreted from fingers of the adhering disks of an ivy rootlet. (Image: Dr. Zhang)

    Zhang and his team found that the nanoparticles are delivered from the ivy rootlets of the stem, to the adhering disk, and finally to its fingers. "Our observations support the hypothesis that the nanoparticles play a direct and important role for ivy surface climbing and are directly related to the ivy affixing capability" he says.

    In addition to a physical analysis, the scientists submitted the ivy nanoparticles to a chemical composition analysis through extract analysis by HPLC/MS. This analysis suggests empirical formulas for the 19 prevalent compounds of organic composition from the secreted nanoparticles.

    "These formulas indicate that most of these compounds contain oxygen, nitrogen, and sulfur" Zhang explains. "These compounds are widely known for their ability to generate polar materials and, most importantly, hydrogen bonding. Considering the surfaces that the nanoparticles normally or typically attach to are substrates like rocks, bricks, etc., which are inorganic or at least polar in nature, the composition suggests that the nanoparticles rely on hydrogen bonding to affix to different surfaces."

    By observing the evolution of the nanoparticles during the climbing process, the scientists noticed that a yellowish material was gradually secreted which, in the earliest stage, is in the gel state and later becomes dry. Once the secretion and drying are completed, the materials are attached firmly to the surface. It appears that water is evaporated during this process.

    Zhang notes that millions of adhering disks can generate remarkable adhesion for the ivy to affix to a surface. "The affixing mechanism formed by the nanoparticles and the adhering disk is unique" he says. "The ivy climbing mechanism by secreting nanoparticles has many advantages for surface climbing. First, joints are not needed and complex mechanics are avoided, yet the mechanism is flexible enough to adapt to various environments."

    Zhang's experiments with ivy may also inspire mechanisms for fabricating nanoparticles through plants. Considerable efforts have been made to generate nanoparticles biologically. In a previous Spotlight we showed some examples of how scientists are trying to use microorganisms and plants for the deliberate synthesis of nanomaterials (Truly green nanotechnology - growing nanomaterials in plants) – for instance the growth of gold nanoparticles in alfalfa sprouts or the biosynthesis of gold and silver nanoparticles from the Cinnamomum camphora leaf.

    Zhang is now looking to secure funding to develop his discovery into practical applications. Clearly, harnessing nanoparticles capable of adhesion through hydrogen-bonding mechanisms could be useful for designing new industrial and medical adhesives, similar to what researchers already have demonstrated by mimicking the gecko's climbing capabilities.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/23ساعت 12:15  توسط مهندس محمدرضا فروغی  | 

    Comparing apples with oranges - the problem of nanotubes risk assessment

    Posted: April 10, 2008

    (Nanowerk Spotlight) Despite their name, carbon nanotubes (CNTs) are not made of 100% carbon. Depending on which of the various synthesis techniques is used in their production, CNTs have variable chemistries and physical properties resulting from their different metal catalysts or amorphous carbon coatings. As a result, they may contain large percentages of metal and carbonaceous impurities which will have different environmental and toxicological impacts. In early toxicological studies, researchers obtained confounding results - in some studies nanotubes were toxic; in others, they were not. The apparent contradictions were actually a result of the materials that the researchers were using, not appreciating that 'carbon nanotubes' are really 'carbon nanotubes + metal + amorphous impurities'. Ignoring these impurities prohibits scientists from fully understanding the material's electronic character, environmental transport, transformation, and ecotoxicology.

    More recently, scientists have begun to acknowledge that the identity of these impurities and co-products is critical to CNTs' toxicology and chemical behavior. However, the chemical compositions of these fractions are not well defined and there have been no concerted efforts to identify and compile this information - without which accurate environmental risk assessments for specific CNT stocks is not possible.

    To address these needs, a group of researchers measured the elemental, molecular, and stable carbon isotope compositions of commercially available single-walled carbon nanotubes (SWCNTs) produced by ten companies in the United States, giving a true picture of their diversity and chemical complexity. This diversity and complexity is extremely important from both fate and toxicity perspectives.

    Other CNT analytical methods can only be used with relatively pure samples, and current environmental techniques rely on electron microscopy – which is very tedious and time consuming – to detect CNTs.

    "Our specific goals were to 1) identify metal catalysts and aromatic hydrocarbons that would be released with and affect the properties of SWCNTs, 2) seek compositional data suited to pursuing environmental exposure modeling of SWCNTs, and 3) find properties that would be helpful for detecting, and perhaps apportioning the sources of, SWCNTs in environmental matrices" Desirée Plata tells Nanowerk. "If we are going to predict the toxicities of nanomaterials, we need to know what they contain and understand how those components vary – e.g., are they always 15% nickel and 5% yttrium? Do they all have hydrocarbon contaminants that may desorb in the environment?"

    Plata, a joint program graduate student at MIT and the Woods Hole Oceanographic Institution (WHOI) and her mentors, chemists Phil Gschwend and Chris Reddy, found that the ten different carbon nanotubes had vastly different compositions. The scientists reported their results in the April 2, 2008 online edition of Nanotechnology (Industrially synthesized single-walled carbon nanotubes: compositional data for users, environmental risk assessments, and source apportionment).

    This study is the first time that anyone has explored the use of carbon isotopes or metal ratios to track carbon nanotubes in the environment. Both of these analytical methods can be used to detect nanotubes in bulk samples (e.g., in sediments or aerosols), allowing for high-throughput quantification of carbon nanotubes in complex matrices.

    Solutions obtained by dissolving different CNTs in concentrated acid
    Solutions obtained by dissolving different CNTs in concentrated acid. (Image: Desirée Plata)

    The results show that the metals associated with carbon nanotubes are available for reactions with the outside world. "Many people suspected that they would not present a true danger, since they would not be free to react with or travel to the environment" says Plata. "Since that is not the case, we need to adjust the way we account for nanotube toxicity, reactivity, and potential environmental effects."

    Plata and her collaborators think that the most concerning problem is the reactivity of the metal catalysts that travel with the CNTs. There are many approaches to try to minimize this effect, and probably the most effective approach, until we know more, will be to embed the materials inside of impermeable layers such as polymer matrices (which is used for instance in consumer products such as CNT-reinforced golf balls or tennis rackets).

    "If a manufacturer chooses to use CNTs in clothes, sunscreens, water-filtration devices, or permeable reactive barriers (to treat ground water), they may be assuming an unintended risk to the public and the environment" says Plata.

    This of course is the challenge that regulators are facing today: you can't regulate a toxin or tell if it is sitting in your backyard if you don't know how to find it in the first place or, even if you find it, don't know exactly what its effects are. Rather than modeling the risk of a generic, i.e., over-simplified, SWCNT, researchers need to develop nanomaterial risk assessment methods that take into account the actual diversity of these products and their interaction with the environment. This might lead to mathematical models relating certain CNT parameters to various degrees of toxicity.

    Plata says that the research community is moving towards being able to track these diverse chemicals which will help to develop sound analytical techniques. This will also enable manufacturers to weigh the material-specific risk assessments and design synthetic processes to achieve environmental objectives while simultaneously considering performance and manufacturing cost.

    An interesting side result from this research is that the unique metal ratios can be used to 'fingerprint' CNTs. The researchers note that, for example, in Houston there are several CNT manufacturers. If there were a release of CNTs to the environment, it would be possible to tell which manufacturer was responsible for the release based on the metal content of the nanotubes. The city of Houston could then identify a 'responsible party' and ask them to assist with the clean up.

    The good news from research like this one of course is that it is taking place before a real problem pops up. This represents a big paradigm shift from the way some sectors of industry and society used (and use) to operate, i.e., pollute first, then worry about it later when it becomes a problem. If the emerging nanotechnology-based companies act responsible (and smart), they will fully embrace being asked challenging product safety questions and they will proactively support finding all the required scientific answers so that they can become an integral part during the design of new industrial processes and materials.

    Plata says that, in a way, this is what environmental champions have been demanding since the 60s. "Rachel Carson wanted people to use DDT in a smart, indiscriminate way. She was against the ubiquitous distribution of poorly understood chemicals. Essentially, we're calling for the same type of action: use these chemicals, but use them in a smart way from start to finish. The old adage, 'it's easier to beg forgiveness than ask permission' doesn't apply to mother nature and it doesn't apply with public health. We need to be proactive about preventing future environmental catastrophes, and we have the means to do it."

    In previous work (Helping The Carbon Nanotube Industry Avoid Mega-Mistakes Of The Past), Plata and colleagues found that the process of nanotube manufacturing produced emissions of at least 15 aromatic hydrocarbons, including four different kinds of toxic polycyclic aromatic hydrocarbons (PAHs) similar to those found in cigarette smoke and automobile tailpipe emissions. They also found that the process was largely inefficient: much of the raw carbon went unconsumed and was vented into the atmosphere. The researchers are currently working with materials scientists and industry to mitigate these effects.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/23ساعت 11:58  توسط مهندس محمدرضا فروغی  | 

    Nanotechnology solutions for Alzheimer's disease

    Posted: April 11, 2008

    (Nanowerk Spotlight) Alzheimer’s disease (AD), a brain disorder named for German physician Alois Alzheimer who first described it in 1906, is a disease that destroys brain cells, causing problems with memory, thinking and behavior. Alzheimer’s gets worse over time, and it is fatal. It is also the most common form of dementia. The latest estimate is that 26.6 million people were suffering from Alzheimer’s disease worldwide in 2006, and this number will rise to 100 million by 2050 - 1 in 85 of the total population. The latest 2008 data for the US alone estimates that 5 million Americans have the disease, with an estimated increase to 11 to 16 million by 2050. Not only does Alzheimer's have no cure, even its cause is unknown (research has led to several theories that are still being investigated). The onset of AD is usually very slow and gradual and, since there is no test for it, there is no clear-cut line between normal age-related changes and warning signs. An absolute diagnosis of AD can only be determined during the examination of brain tissue, which is usually done during an autopsy (if you want to find out more - the Alzheimer's Association has a lot of information on its website). A recent report provides an overview of the promises that nanotechnology brings in research on diagnosis and therapy of AD.

    In the absence of a cure – since Alzheimer's is a progressive disease, and the brains natural regenerative capacity is thought to be minimal – an early diagnosis combined with some form of treatment that stops the pathogenic process is seen as the most promising way of battling the disease. However, as Dr. Amir Nazem and Dr. G. Ali Mansoori write in their paper (Nanotechnology Solutions for Alzheimer’s Disease: Advances in Research Tools, Diagnostic Methods and Therapeutic Agents), at the present there is not any single diagnostic tool for precise screening or early and accurate detection of the disease; and only a probable diagnosis with an 80% confidence, on average, is possible based on clinical criteria (including laboratory tests, neuroimaging and neuropsychological assessment).

    Nazem, a scientists at the Qaem Hospital, Mashhad University of Medical Sciences in Iran and Mansoori a professor in the Departments of Bioengineering and Chemical Engineering & Physics at the University of Illinois at Chicago describe possible approaches to early diagnoses and effective treatment of AD. They write that the development of nanotechnology approaches for early-stage diagnosis of AD is quite promising but acknowledge that scientists are still at the very beginning of the ambitious project of designing effective drugs and methods for the regeneration of the central nervous system.

    Summary of applications of nanotechnology in the treatment of Alzheimer's disease.
    Summary of applications of nanotechnology in the treatment of Alzheimer's disease. (Image: Journal of Alzheimer’s Disease 13 (2008) 199–223, IOS Press)

    Nanotechnology diagnostics approaches for Alzheimer's

    Since the neurodegenerative process due to AD begins well before the disease's symptoms become apparent, early detection diagnostic tools must be highly sensitive and certainly less invasive than, say, a brain biopsy. Nazem and Mansoori argue that nanotechnology can be the basis of new tools for very early detection of AD because of their potential of detecting ultra-low concentrations of AD biomarkers, and potentially being able to detect multiple biomarkers simultaneously. "In addition, by targeting the specific pathology related biomarkers, nanotechnology tools can diagnose underlying AD pathology early and independent from brain reserve (the reserve capacity of the brain that enables people to tolerate the pathological changes that occur in the brains of people with AD)."

    Bio-barcode assays and localized surface plasmon resonance (LSPR) nanosensors are mentioned as two methods for the cerebral spinal fluid (CSF) analysis for AD biomarkers. CSF has a higher degree of accuracy and can show brain tissue damages earlier than the known plasma biomarkers associated with AD. However, the in vitro CSF analysis requires the invasive procedure of lumbar puncture for obtaining a sample.

    The authors write that nanotechnology has the potential to provide us with ultra sensitive in vivo detection methods (for instance with quantum dots, although their toxicity could make this approach problematic) of the AD biomarkers in plasma. They believe that the ultimate goal for very early detection of an underlying AD pathology would be the development of a safe and implantable nanoscale biosensor for prolonged monitoring of AD biomarkers in the CSF.

    "Such a sensor must be able to transmit any biomarker detection event to an external device that records the transmitted signals and reports an estimated amount for the concentration of AD biomarkers in the CSF. Of course, in order to send such biosensor to a place exposing with CSF, it is necessary to design noninvasive approaches."

    Effective treatment

    An eventual cure for AD will require therapeutics that cease the disease progress and will reverse its resultant damages. As Nazem and Mansoori point out, the general focus of therapeutic approaches in nanomedicine have been on drug discovery and monitoring, controlled release of therapeutic agents, and targeted drug delivery. "The current and envisioned applications of nanotechnology in neurology consist of neuroprotection, neuroregeneration, and drug delivery beyond the brain blood barrier."

    While neuroregeneration treatments seem to be a considerable way out, and most likely will depend on effective stem cell technologies, neuroprotective applications could be available sooner and help in stopping or at least delaying the disease once diagnosed.

    Designing therapeutic agents that protect neurons against cellular neurotoxicity is a prevention approach to protect against neuro-degenerative diseases such as AD. "Oxidative stress and amyloid induced toxicity are the two basic toxicity processes in AD pathogenesis. Anti-oxidant and anti-amyloid therapeutics are the focus of current drug discoveries against these toxicity processes."

    In two previous Nanowerk Spotlights we addressed the applications of nanoparticles in reducing oxidative stress and in designing potent anti-oxidants.

    Even if a potent drug for AD was available, its effective delivery into the brain would be a significant challenge thanks to the blood brain barrier (BBB), the tight seal of endothelial cells that lines the blood vessels in the brain and acts as a barrier to protect its cells. BBB strictly limits transport into the brain through both physical (tight junctions) and metabolic (enzymes) barriers and keeps most substances such as chemicals and large biomolecules out of the brain. The use of nanotechnology offers tremendous hope in the treatment of brain disorders by offering a way for drugs across the BBB (Nanotechnology improves the prospect of better treatment for brain disorders). Since a large portion of the AD pathogenetic mechanism happens inside brain cells, the nanoparticulate drug carriers no only must overcome the BBB but also be delivered into the target cells in the brain.

    Without being able to give a time frame, of course, Nazem and Mansoori are confident that at some point in the future the increasing abilities offered by the combination of nanotechnology and some other novel approaches like stem cell technology could bring about a promising cure for Alzheimer's disease.

    By Michael Berger. Copyright 2008 Nanowerk LLC 

    + نوشته شده در  87/01/23ساعت 11:56  توسط مهندس محمدرضا فروغی  | 

    The art of peeling tomatoes and the science of tearing

    Posted: April 9, 2008

    (Nanowerk Spotlight) Have you ever tried to peel a fresh tomato? Then you probably know that frustrating feeling when you end up with lots of little, mostly triangular pieces of skin. Of course you will also have remembered your grandma's trick to pour hot water over a tomato before skinning it; surprisingly, the skin then comes off easily in just a few large pieces. There are lots of other examples from our daily lives with similarly aggravating experiences: Frustrated by scotch tape that won't peel off the roll in a straight line? Angry at wallpaper that refuses to tear neatly off the wall? Cursing at the price sticker that doesn't come off in one piece? Or you dutifully follow the 'tear along the dotted line' instruction on a re-sealable bag only to be confronted with a tear that is anywhere but on the dotted line.

    Physicists, mathematicians and materials engineers love these things because it gives them a chance to explain everyday phenomena with impressive looking formulas and diagrams. Wrinkling, folding and crumpling of thin films have been characterized by experiments, theory and numerical simulations. A new study now adds a new element: fracture. The results suggest that the coupling between elasticity, adhesion and fracture, imprinted in a tear shape, can be used to evaluate mechanical properties of thin films and could even be applied at the nanoscale.

    tearing scotch tape
    The problem: tway that adhesive tape tears in a triangular shape coming to a point. (Image: Donna Coveney)

    "We explained why pulling a flap from an adhesive film always leads to pointy tears" Dr. Enrique Cerda explains to Nanowerk. "Our work is not limited to adhesive films such as scotch tape. Pointy tears are obtained when trying to pull down wallpaper, skin a fruit or open a package. We also  expect similar geometries at the nanoscale when tearing films made of a few layers of atoms. The mechanism that produces tears is very simple: pulling a flap focuses elastic energy in the line connecting the flap with the film and this energy can be released by narrowing the tear. To do that, the two sides of the flap act as fracture cracks that propagate into the film, making the flap longer, and converge to a point."

    Cerda, a researcher in the Department of Physics at the University of Santiago de Chile, together with Michael LeBlanc from the University of Chicago and collaborators from the Centre National de la Recherche Scientifique (CNRS) in Paris and MIT in Cambridge, Massachusetts, has carried out a combined experimental and theoretical study to explore what is involved in determining the geometrical shapes observed when a film is ripped apart. In a paper published in the March 30, 2008 online edition of Nature Materials, they show how elasticity of thin sheets couples with adhesion and fracture to produce distinct shapes characterizing the tearing process ("Tearing as a test for mechanical characterization of thin adhesive films").

    "The mechanism we describe explains the observed variation for the tear length and then its shape – this triangular shape of the tear encodes the mechanical parameters related to forms of energy involved in the process." says Cerda. "A longer tear will have a more pointy shape than a shorter one. Elastic energy is used to break the atomic bonds of the film material, so surface energy increases. When there is adhesion the narrowing process also implies that the atomic bonds between adhesive and  film are broken, and the adhesive is exposed to the air. Thus, a shorter tear will be obtained when the adhesive is very strong. It will be easier to break film-film bonds than adhesive-film bonds. A longer tear will be obtained in the opposite case."

    The researchers provide a formula that predicts the tear shape based on three parameters that describe the three energies involved in the process – elasticity (stiffness), adhesive energy (how strongly the adhesive sticks to a surface) and fracture energy (how tough it is to rip). They propose a simple mechanism based on elasticity to understand the experimentally obtained, always triangular tear shapes:

    A pulling force deforms the surface and focuses elastic energy in a ridge or fold that joins the flap with the film (the area where the tape is peeling from the surface). This energy can be released in two ways: by decreasing its curvature (unpeeling in the pulling direction) or by simply reducing the width of the ridge (becoming narrower). The actual direction is a combination of both effects, but always leads to a narrowing of the tear.

    Tearing as a test for mechanical characterization of thin adhesive films tearing experiments with scotch tape
    Left: Schematic representation of the experimental set-up. The film is attached to a solid plane using an adhesive. Then a flap is cut and joined to a metal rod that acts as a winch drum. The rotation of the rod pulls the flap and starts the tearing. Right: Experiments using a film very similar to scotch tape with a thickness of 70 µm. The film was adhered to a substrate and then a 4-cm-wide flap was pulled. The experiment was repeated seven times at the pulling speed shown in the legend. The seven resulting scanned tears are shown overlapped in the image. (Images: Dr. Cerda)

    Armed with their new formula, the researchers can now measure the adhesion energy – which changes as a function of the substrate – very easily by studying the tear shape in each substrate (the adhesion energy of scotch tape, for instance, is different when applied to metal, plastic, or ceramics). This analysis can help to evaluate the mechanical properties of more complex systems that behave similarly to adhesive films.

    Cerda points out that the formalism he and his collaborators have developed can be used to investigate the mechanical properties of thin adhesive films. "As thickness is reduced owing to new technologies, traditional methods used to measure mechanical properties of a material in bulk form are not applicable" he says. "For instance, materials engineers could use this method to calculate one of the three key properties, if the other two are known. This could be particularly useful in microtechnologies, such as stretchable electronics, where the characterization of thin material properties is very difficult. Or nanofilms deposited on a substrate can be peeled off and the observed tear shapes can provide information of the film material properties."

    Cerda says that the researchers would like to know, for instance, the tear shapes in one layer of carbon atoms (graphene) to check how their analysis works at the atomic scale.

    Another potential application is in packaging. Many industrial food and other products are packaged in materials that behave elastically. The key conclusion from the study is that fracture propagates with its own physical rules. If materials engineers learn to understand and control these rules we could ultimately all benefit from better designed packaging materials.

    So, next time you scratch the edge of a scotch tape with your fingernail trying to tear off a piece, think of all the atomic bonds and surface energies you are about to mess with and try to appreciate the well-defined vertex angle of the resulting triangular, way too short piece. Or just start cursing.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/21ساعت 10:7  توسط مهندس محمدرضا فروغی  | 

    Producing isolated nanocrystalline diamond fibers at high growth rates

    Posted: April 8, 2008

    (Nanowerk Spotlight) Diamonds have been known in India for at least 3000 years and are thought to have been first recognized and mined there. The most familiar usage of diamonds today is as gemstones in jewelry but, apart from being a girl's best friend, it seems that diamonds, especially nanodiamonds, are quickly becoming a scientist's best friend as well. Diamonds are the hardest natural material - the word diamond comes from the Greek term adamas, which means 'invincible' - has the lowest coefficient of thermal conductivity, is electrically insulating, chemically inert, and optically transparent. In nanoparticulate form, diamonds possess an additional property that makes them so interesting for researchers: since they are carbon-based and non-toxic they are a suitable material for drug delivery, drug diagnostics and medical imaging applications.

    Recently, diamond-coated metallic and nonmetallic nanocomposite materials have gained a lot of attention in the scientific community. These nanocomposite structures have a better stiffness/weight ratio than any other existing material and thus have many potential applications in various strategic fields such as biosensors, energy applications, thermal management, and space technology.

    Diamond is also a very good candidate for solid-state electronic emitters because of its negative or very low electron affinity. Electron emitters can be used in vacuum microelectronics such as Spindt-type emitters. There are many reports concerning field emission from chemical vapor deposited diamond or diamond-like carbon thin films. Up to now, however, only a few examples on synthesis and field emission studies from tubular nanorods or nanowhiskers diamond-based systems have been published. These diamond-based nanoscale structures have been prepared by common – but very expensive – methods, either e-beam lithography or reactive ion etching.

    One of the challenges in fabricating nanodiamond coatings and composite materials is the difficulty of controlling the size, texture, and crystalline quality of the diamond particles. Now, researchers in Portugal have demonstrated for the first time the facile fabrication and the conformal coating of nanocrystalline diamond onto silica nanofibers by a two-step method: synthesis of templates on silicon wafer; and coating of the silica fibers with nanocrystalline diamond.

    "We prepared, for the first time, high-density nanocrystalline diamond (NCD) fibers with lengths of 50–100 µm and diameters of 1–5 µm using amorphous silicon dioxide (a-SiO2) nanofiber templates" Dr. Manoj Kumar Singh tells Nanowerk. "The templates were synthesized by a conventional Vapor-Liquid-Solid (VLS) growth process followed by conformal coating of as-synthesized templates with 15–20 nm-sized NCD grains using a high-power microwave plasma enhanced chemical vapor deposition technique (MPECVD). We confirmed not only the nanocrystalline nature of the diamond material but also the perfect crystallinity of the sample."

    Singh, a principal investigator in the TEMA-NRD (Nanotechnology Research Division) in the Department of Mechanical Engineering at the University of Aveiro in Portugal, explains that, unlike other reports on NCD fibers, this novel method can produce isolated nanocrystalline diamond fibers at high growth rates.

    The researchers expect this novel material to find applications in cold-cathode devices, heat sinks in microelectronics and structural materials in micro- and nanoelectromechanical systems.

    The scientists have reported their findings in the February 16, 2008 online edition of Chemistry of Materials ("Novel Two-Step Method for Synthesis of High-Density Nanocrystalline Diamond Fibers").

    Nanocrystalline diamond fibers

    The FE-SEM image shows the growth stages from nucleation to continuous fibrous structure formation of high-density diamond fibers. Insert shows high magnification image of a perfect NCD fiber. (Image: Dr. Singh, University of Aveiro)

    Using their simple and low-cost technique, the NRD team synthesized high-density nanocrystalline diamond fibers with lengths of more than 500 µm. After synthesizing the silica nanofiber templates, the researchers treated the substrates with nanodiamond powder (particle size 3–5 nm) using the dip method, thereby randomly attaching nanodiamond particles on the surface of a-SiO2 nanofibers by capillary forces. The nanodiamond particles act as seeds for the further growth of NCD on the nanofibers.

    Singh points out that the seeding process is a very critical phase for conformal coating as well as for controlling the diameter of NCD fibers.

    The scientists also observed that during the MPECVD process the nanodiamond (particle size ∼15 nm) does not nucleate directly on the a-SiO2 surface but instead an intermediate layer of amorphous carbon is formed and the nanodiamond nucleates directly onto this layer during CVD growth.

    Singh says that the team is now in the process of optimizing their technique. He adds: "We are also greatly interested in the development of NCD fiber reinforced polymer nanocomposites for biomedical applications and also as heat sinks in microelectronics."

    In separate work, published in the January 18, 2008 online edition of Applied Physics Letters, the scientists reported the fabrication of patterned nanocrystalline diamond submicrometer-tip arrays with length of ∼10 µm and diameters of 1–2 µm, using the same method ("Electron field emission from patterned nanocrystalline diamond coated a-SiO2 micrometer-tip arrays").

    By Michael Berger, Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/20ساعت 14:48  توسط مهندس محمدرضا فروغی  | 

    Using nanotechnology to improve Li-ion battery performance

    Posted: April 7, 2008

    (Nanowerk Spotlight) Lithium-ion batteries seem to be everywhere these days. They power most of the electronic devices we carry around with us - cell phones, laptops, MP3 players, digital cameras and so on. They get their name from the lithium ion that moves from the anode to the cathode during discharge and from the cathode to the anode during recharging. Due to their good energy-to-weight ratios, lithium batteries are some of the most energetic rechargeable batteries available today.

    In terms of weight and size, batteries have become one of the limiting factors in the continuous process of developing smaller and higher performance electronic devices. This not only applies to consumer electronics. As with so many other nanotechnology research, the military is a strong driver behind battery R&D. All of the electronic gizmos of a modern soldier - night vision goggles, flashlights, laptops, radios, GPS, etc. - are powered by batteries. The backup batteries soldiers are required to carry generally add several kilograms to their basic load, and the logistics necessary to supply the troops with sufficient numbers of replacement batteries is costly.

    To meet the demand for batteries having higher energy density and improved cycle characteristics, researchers have been making tremendous efforts to develop new electrode materials or design new structures of electrode materials. For instance, metallic tin has recently been widely researched as one of the promising anode materials for the next generation of high energy density lithium-ion batteries. This new anode material has a high theoretical specific capacity but its practical application is limited by its poor cycling performance. The problem with increasing the performance of lithium batteries is that none of the existing electrode materials alone can deliver all the required performance characteristics including high capacity, higher operating voltage, and long cycle life. Consequently, researchers are trying to optimize available electrode materials by designing new composite structures, often at the nanoscale.

    Demonstrating the benefits of directed nanostructure-design of electrode materials, Chinese scientists have prepared tin nanoparticles encapsulated in elastic hollow carbon spheres. This tin-based nanocomposite exhibits a very high specific capacity, excellent cycling performance, and therefore shows great potential as anode materials in lithium-ion batteries.

    "Metallic tin is considered to be a very promising anode material for lithium batteries mainly for three reasons" Prof. Li-Jun Wan explains to Nanowerk. "Firstly, its theoretical specific capacity is much higher than that of conventional graphite. Secondly, the tin anode has higher operating voltage than graphite, so it is less reactive and the safety of batteries during rapid charge/discharge cycle could be improved. And thirdly, a significant advantage of metallic tin over graphite is that it does not encounter solvent intercalation – which causes irreversible charge losses – at all. Unfortunately, the biggest challenge for employing metallic tin as applicable active anode materials is that it is suffering from huge volume variation during the lithium insertion/extraction cycle, which leads to pulverization of the electrode and very rapid capacity decay."

    Wan, Director of the Institute of Chemistry at the Chinese Academy of Sciences (CAS) in Beijing, PR China, together with members of the Beijing National Laboratory for Molecular Sciences, has published a paper in the February 27, 2008 online edition of Advanced Materials that describes this novel carbon nanocomposite as a promising anode material for high-performance lithium-ion batteries ("Tin-Nanoparticles Encapsulated in Elastic Hollow Carbon Spheres for High-Performance Anode Material in Lithium-Ion Batteries").

    synthetic scheme of tin nanoparticles encapsulated with elastic hollow carbon spheres
    A schematic illustration of the structure and the lithiation process of the tin nanoparticles encapsulated with elastic hollow carbon spheres. (Image: Dr. Wan)

    "Not only is this a further example of the directed nanostructure-design of electrode materials for lithium-ion batteries, but also the strategy could be extended to other anode and cathode materials by using elastic hollow carbon spheres as buffer and container" says Wan.

    The CAS scientists successfully have realized a novel structure design of tin-based anode material to solve the problem of capacity decay. The key to their composite material are nano-sized tin particles that are put into hollow carbon containers, resulting in tin nanoparticles encapsulated with elastic hollow carbon spheres (TNHCs).

    The TNHCs were prepared by in-situ reducing tin oxide hollow spheres with carbon coating. As described in their paper, the tin oxide spheres were firstly synthesized according the Stöber method and used as templates to prepare hollow spheres. Next, polycrystalline tin oxide was deposited on silicon dioxide spheres to form uniform shells. Then their cores were etched to get hollow spheres. After that, the carbon precursor layers were coated on the outer surface of the spheres. Finally the product was dried and heat-treated to carbonize the carbon precursor shell, and meanwhile the inner tin oxide shells were reduced to metallic tin by the carbon shells themselves to get the final TNHCs.

    tin nanoparticles encapsulated with elastic hollow carbon spheres
    a) SEM image of tin oxide coated silicon dioxide spheres; b) TEM image of the hollow tin oxide spheres; c) and d) SEM and TEM image of TNHCs, respectively. The inset in (c) is a close view of a single broken carbon spherical shell studded with tin particles. (Reprinted with permission from Wiley)

    These TNHCs with uniform size of ca. 500 nm diameter encapsulate multiple tin nanoparticles with a diameter of less than 100 nm in one thin hollow carbon sphere with a thickness of only about 20 nm. This nanocomposite material is characterized by a tin content of up to 74% by weight (which results in a high theoretical specific capacity of 831 milli-ampere hours per gram) and a void volume in the carbon shell as high as about 70–80% by volume.

    Wan explains that the approx. 1:3 tin nanoparticles to void volume ratio and the elasticity of the thin carbon spherical shell efficiently accommodate the volume change of tin nanoparticles due to the lithium-tin alloying-dealloying reactions, and thus prevent the pulverization of the electrode. "As a result, this type of tin-based nanocomposite has very high specific capacity of >800 milli-ampere hours per gram in the initial 10 cycles, and >550 milli-ampere hours per gram after the 100th cycle, as well as excellent cycling performance, exhibiting a great potential as anode materials in lithium-ion batteries."

    The researchers point out that their results successfully demonstrate the power of the strategy of using elastic hollow carbon spheres as buffer and container and could be extended to other anode and cathode materials.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/19ساعت 22:0  توسط مهندس محمدرضا فروغی  | 

    Nanotechnology's role in next generation biofuel production

    (Nanowerk Spotlight) Years of engineering research and design, together with uncounted billions of dollars from government and industry, went into the development of the modern petroleum industry. It would be unreasonable to expect that we can replace this industry with greener alternatives without a similarly expansive and sustained effort. Point in case is a recently published roadmap to 'Next Generation Hydrocarbon Biorefineries' that outlines a number of novel process pathways for biofuels production based on scientific and engineering proofs of concept demonstrated in laboratories around the world. The key conclusion from this (U.S.-centric) report is that "while the U.S. has made a significant investment in technologies focusing on breaking the biological barriers to biofuels, principally ethanol, there has not been a commensurate investment in the research needed to break the chemical and engineering barriers to hydrocarbon fuels such as gasoline, diesel, and jet fuel."

    This statement of course holds true not only for biofuels but for any kind of green energy technology. The production of ethanol from corn (about 95% of ethanol in the U.S. is produced from field corn whereas Brazil, the world leader in ethanol production, uses sugar cane) has come under intense scrutiny and discussion for its potential environmental and economic side effects (see fore example Panel Sees Problems in Ethanol Production or read the UN report on sustainable bioenergy - pdf download, 1 MB). Advances in agriculture and biotechnology have made it possible to inexpensively produce lignocellulosic biomass (plant biomass that is composed of cellulose and lignin) at costs that are significantly lower (about $15 per barrel of oil energy equivalent) than crude oil.

    The key bottleneck for lignocellulosic-derived biofuels is the lack of technology for the efficient conversion of biomass into liquid fuels. Advances in nanotechnology have given us an unprecedented ability to understand and control chemistry at the molecular scale, which promises to accelerate the development of biomass-to-fuels production technologies.

    If you manage to ignore the sound of thundering herds of hypsters stampeding into their green (green as a dollar bill, that is) future you will find plenty of examples that science and technology, especially nanotechnology, is providing us with the capabilities to improve the design of materials, processes and applications that minimize hazard and waste. There are many examples of very specific opportunities here on the Nanowerk website; for instance, just a few days ago we ran a news story about how nanosieves save energy in biofuel production.

    Also, if you are interested, we have posted Nanowerk Spotlights on 'green' topics ranging from nanotechnology and water treatment, to clean hydrogen production or a more general overview on nanotechnology's potential to reduce greenhouse gases.

    The production of hydrocarbon fuels from biomass (biofuels) has become a big issue recently because they appear to offer a relatively short-term solution to replacing part of the petroleum-based fuels in our energy production with 'green' hydrocarbon fuels. These 'green' hydrocarbon fuels are essentially the same as those currently derived from petroleum, except that they are made from biomass. A word of caution: 'green' in this context does not necessarily mean that these fuels are better for the environment, although they often are, but rather than from 'black' fossil-based sources they come from renewable 'green' plant material.

    the three primary needs for the biofuel economy
    (Source: Breaking the Chemical and Engineering Barriers to Lignocellulosic Biofuels: Next Generation Hydrocarbon Biorefineries)

    A new report (in draft format) on biofuel production, titled Breaking the Chemical and Engineering Barriers to Lignocellulosic Biofuels: Next Generation Hydrocarbon Biorefineries (pdf download, 8.9 MB) is based on the results from a June 2007 workshop and was issued by the University of Massachusetts Amherst.

    The purpose of the workshop was to articulate the essential role of chemistry, chemical catalysis, thermal processing, and engineering in the conversion of lignocellulosic biomass into green gasoline, green diesel and green jet fuel.

    Sponsored by the National Science Foundation and the Department of Energy, the workshop identified the basic research needs and opportunities in catalytic chemistry and materials science that underpin biomass conversion and fuel utilization, with a focus on new, emerging and scientifically challenging areas that have the potential for significant impact. The report illuminates the principal technological barriers and the underlying scientific limitations associated with efficient processing of biomass resources into finished fuels: "The limiting factor to biofuels production is simply that low-cost processing technologies to efficiently convert a large fraction of the lignocellulosic biomass energy into liquid fuels do not yet exist."

    The report is structured into six main chapters:

  • Selective thermal processing of cellulosic biomass and lignin
  • Utilization of petroleum refining technologies for biofuel production
  • Liquid-phase catalytic processing of biomass-derived compounds
  • Catalytic conversion of syngas
  • Process engineering & design
  • Crosscutting scientific issues
  • Chapter six in particular deals with the design of recyclable, highly active and selective heterogeneous catalysts for biofuel production using advanced nanotechnology, synthesis methods and quantum chemical calculations.

    One sidebar in the report addresses the nanoscience of catalyst synthesis: "Calls are often heard to 'transform the art of catalyst preparation into a science.' One arena in which this is occurring is in fundamental studies of catalyst impregnation, the process by which a solution containing dissolved metal precursors is contacted with the high-surface-area catalyst support. In this vein of work, the chemical fundamentals of impregnation are being understood and exploited for simple, rational methods to make metal nanoparticles. Most industrial catalysts are of this sort and employ aluminum oxide or carbon as the support." It the shows an example of platinum/silica catalyst synthesis by strong electrostatic adsorption (SEA).

    Fundamental understanding of catalytic chemistry is obtained when the detailed, atomic scale structure of a catalyst and its chemical composition is known and can be correlated to its catalytic activity and selectivity. So far, the tools for in situ real-time monitoring of catalyst structure at the nanoscale are not very effective and the report urges for spectroscopic, scattering and imaging tools to be developed. For instance, next-generation electron microscopes that allow for imaging of nanometer sized features in thin liquid layers are needed to explore the structural changes of catalysts in aqueous environments.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/18ساعت 0:6  توسط مهندس محمدرضا فروغی  | 

    Nanotechnology grinders

    (Nanowerk Spotlight) 'Field evaporation' is the phenomenon by which surface atoms are ionized (evaporated) under an applied, extremely high electric field of the order of several volts per nanometer. Electric fields of this magnitude can only be achieved by applying a high field to an extremely sharp needle such as the specimen tip in a Field Ion Microscope. Field evaporation was first reported over 50 years ago and has since developed into the powerful Atom Probe Field Ion Microscopy which is able to reproduce the atomic structure of a piece of material in three dimensions.

    Today, field evaporation is mainly used for material characterization, and the behavior of nanomaterials at extremely strong electric fields is of great scientific and technological interest. In principle, the field evaporation phenomenon can be utilized not only for materials characterization, but also for materials processing and morphology control with extremely high precision because of its unique atom-by-atom removal capability. However, detailed structural evolution of nanomaterials during field evaporation has never been directly observed and this limitation has greatly restricted the potential applications of field evaporation as a materials-processing tool.

    Now, researchers in Beijing have reported the first direct observation of field evaporation phenomena using a transmission electron microscopy (TEM) technique. By conducting in situ TEM field evaporation experiments on individual carbon nanotubes (CNTs), the researchers were able to reveal details about the structural evolution of the nanomaterials via direct observation. Using this technique, they have been able to perform controlled engineering of the CNTs with atomic precision, for example, grinding and shortening of CNTs, shaping of the open ends of CNTs, and opening of CNT caps.

    "In traditional Field Ion Microscopy and atom probe investigation, the field evaporation phenomenon is mainly utilized for material characterization, and only the structural information on the tip surface or the evaporated segments of the specimen can be obtained, instead of “seeing” the structural evolution of the sample directly" Dr. Lian-Mao Peng explains to Nanowerk. "Our work provides the first direct observation of the detailed structural evolution of nanomaterials during field evaporation. We also show that field evaporation can be utilized not only for material characterization, but also for material processing and morphology control with extremely high precision."

    Peng is director of the Key Laboratory for the Physics and Chemistry of Nanodevices and professor of Nanoscale Science and Technology at Peking University. In a new paper published in the January 29, 2008 online edition of Advanced Materials, Peng and his group demonstrate that positive field evaporation in combination with in situ TEM may actually provide a very simple and effective means for controlling the morphology of nanomaterials with atomic precision ("Grinding a Nanotube").

    Peng notes that – analogous to laser-stimulated field evaporation – an electron beam has a similar effect for promoting the field emission process. However, the size of the laser beam is typically several micrometers and covers the entire area of the probed nanomaterial. In contrast, the spot size of the electron beam in a TEM can be made as small as few or even sub-nanometer. "The desired sample area may therefore be selected by the electron beam conveniently and precisely, and site-selective evaporation may be promoted" he says.

    Evolution of the end structure of a CNT during field evaporation
    Evolution of the end structure of a CNT during field evaporation. The series of TEM images record the end smoothening and shortening process. The arrows in (e) indicate the final CNT termination site in (f). (Reprinted with permission from Wiley-VCH Verlag)

    He also points out that many other approaches have been developed to control the length or end structure of individual CNTs, for example, the cutting of CNTs by various methods such as the use of an AFM tip, a focused e-beam, a CNT 'nanoknife' (also developed be Peng's group), and electron ablation have been reported.

    "Compared to these methods, which have a precision of only several to several tens of nanometers, the most notable advantage of our in situ field evaporation method is the extremely high precision in controlling the CNT length" explains Peng. "On average, over a period of several seconds (or even longer), only one layer of carbon atoms is evaporated from the end of a CNT. Furthermore, positive field evaporation is a self-regulating process wherein the emitter surface can be processed to become very regular in shape and smooth at the atomic scale. Owing to these two advantages of our method, we believe that we have achieved atomic precision, which is hardly achievable by other approaches."

    Field evaporation depends critically on the local electric field, which means that the atoms subjected to the highest local electric field are the first to be evaporated. Consequently, in most cases, once the initial end structure is obtained, the subsequent evolution of this end structure towards the final end structure is basically predetermined. "Usually all we can do is to change the speed of evolution or to stop the evaporation at some intermediate but not entirely stable morphology before a steady state is established" says Peng. "In our experiments, we show that in situ TEM field evaporation has the unique capability of changing the evaporation sequence. Therefore, this process enables more precise control of the end structure of nanomaterials."

    The Chinese scientists emphasize that their findings show that, in principle, the field evaporation phenomenon can be utilized not only for materials characterization, but also for materials processing and morphology control with extremely high precision.

    This unique atom-by-atom removal capability, which may have the potential to replace other existing morphology-control method, could provide highly controlled engineering of nanomaterials.

    For example, Peng's group demonstrated that the length of a nanomaterial can be controlled with atomic precision, and its end can be 'ground' to become an atomically smooth structure. The control of length and end structure is very important for improving the performance of single nanomaterials as e.g. field emitter or scanning probe. For instance, the researchers propose that if a vertically aligned CNT film is processed by positive field evaporation, the field emission sites can be made more uniform, resulting in a higher current density and better emission stability, which is highly required for field emission display application.

    Another example is opening the caps of CNTs, which is of great importance for nanotechnology: the hollow cores of CNTs can be filled with fullerenes and metal nanowires, thereby forming nanocomposites exhibiting novel electrical and magnetic properties. A crucial step involved in these filling procedures is the opening of the CNT caps by chemical or physical methods. CNTs also have been demonstrated to make nanopipes or nanopipettes in nanofluidic devices, where an open end is required for jetting and imbibing liquids.

    "As we have demonstrated, our method not only enables CNTs to be opened, but also provides precise control over the size of the hole in the cap, which may affect the jetting or imbibing rate" says Peng.

    In previous work, the team already has demonstrated the controlled removal of carbon atoms at the tip of a CNT and the fabrication of various tip structures (Engineering the cap structure of individual carbon nanotubes and corresponding electron field emission characteristics). This, however, was achieved via electron field emission induced evaporation, instead of field evaporation. Electron field emission is much harder to control than the new technique, resulting in a much less perfect structure.

    Peng and his team are now working on getting more higher resolution structural information of the very end tips of nanomaterials, and to observe how a single atom, or cluster of atoms, moves along and away from the surface at the application of an extremely strong field.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/17ساعت 23:57  توسط مهندس محمدرضا فروغی  | 

    Nanometrics Achieves Milestone Shipment of 1,000th Integrated Metrology System

    Posted: February 19, 2008

    (Nanowerk News) Nanometrics Incorporated (Nasdaq: NANO), a leading supplier of advanced metrology equipment to the semiconductor industry, today announced the 1,000th shipment of its Integrated Metrology® (IM) system, highlighting the company’s leadership position in the IM market for semiconductor manufacturing. The milestone system was a Nanometrics 9010 SCRIBE unit integrated into an advanced plasma etch system used to control critical gate etch applications in advanced logic devices.

    Nanometrics introduced its first IM system in 1998, an ultra-compact, real-time metrology system used in chemical mechanical polishing (CMP) thickness control applications. “Due to rapid customer acceptance and advancing process control requirements, Nanometrics’ integrated metrology products evolved into a leading-edge tool set specializing in CMP, CVD, etch, and photolithography process control applications,” said Steve Bradley, Nanometrics’ director of Integrated Metrology Business. “Our customers see substantial improvements in process control capability and end of line product yield as a benefit of integrated metrology adoption. Reaching this milestone in such a short time reflects the industry’s ongoing acceptance of integrated metrology and Nanometrics’ commitment to innovative process control solutions.”

    Nanometrics 9000 Series IM systems provide 300 mm thin film and optical critical dimension (OCD) metrology solutions for all critical semiconductor processing applications. The 9000 Series incorporate state-of-the-art motion-control, optics, and modeling software, enabling comprehensive control over critical processes, including measurement of complex film stacks as well as 2D and 3D modeling of advanced structures.

    About Nanometrics

    Nanometrics is a leader in the design, manufacture and marketing of high-performance process control metrology systems used in semiconductor manufacturing. Nanometrics standalone and integrated metrology systems measure various thin film properties, critical dimensions, overlay control and optical, electrical and material properties, including the structural composition of silicon and compound semiconductor devices, during various steps of the manufacturing process. These systems enable semiconductor manufacturers to improve yields, increase productivity and lower their manufacturing costs. The company maintains its headquarters in Milpitas, California, with sales and service offices worldwide. Nanometrics is traded on the NASDAQ Global Market under the symbol NANO. Nanometrics’ website is http://www.nanometrics.com.

    Source: Nanometrics

    + نوشته شده در  87/01/16ساعت 23:8  توسط مهندس محمدرضا فروغی  | 

    Nano-antennas light up molecules

    Posted: March 27, 2008

    (Nanowerk Spotlight) A key challenge in nano-optics is to bring light to and collect light from nano-scale systems. In conventional electronics, the interconnect between locally stored and radiated signals, for example radio broadcasts, is formed by antennas. For an antenna to work at the wavelength of light it needs to be greatly scaled down, to the nanoscale.

    Antennas play a key role in our modern wireless society. The electromagnetic waves sent and received by antennas are the messages that enable communication between electronics. Antennas with a wide variety of sizes make it possible for us receive radio broadcasts, watch television and talk to others on a mobile phone. For an effective communication, the antenna needs to direct signals towards their intended target and, vice versa, collect signals from a desired source.

    Now, researchers have shown that the concept of an antenna is equally well applied to direct the visible light sent out by a single molecule. For an antenna to work with visible light, it needs to be millions of times smaller than a conventional antenna. In this case, it is only 80 nanometer long. By placing the antenna near an individual molecule the light from that molecule is re-directed; the molecular message can be steered to a desired target, making efficient communication possible.

    These novel nano-antennas have important implications. In (bio)sensing, light can be sent to a molecule and, in turn, its response aimed to a detector. Furthermore, the antennas can be part of efficient nano-sized light sources. Finally, it is interesting to see that the antenna designs that revolutionized communication keep finding new applications, this time at the nanometer scale.

    a molecule lighting up close to a nano-antenna
    Artist's impression of a molecule lighting up close to a nano-antenna (Image: T. H. Taminiau)

    "We have shown that a metal nano-particle functions as an optical antenna for a single molecule" Dr. Niek van Hulst tells Nanowerk. "We demonstrated that the light emitted by a molecule is directed by an optical monopole antenna, just as radio waves are directed by a radio antenna. The direction in which the light is emitted depends on the antenna design, not on the molecule."

    Van Hulst, a professor at the Institute of Photonic Sciences (ICFO) in Barcelona, Spain, explains that there are two ways in which this advances the field of nano-optics: by increasing the understanding of optical antennas and by experimentally demonstrating them.

    "First, by studying the most elementary system, an individual molecule coupled to a simple monopole antenna, we reveal how an optical antenna works. The resulting direction of emission was not anticipated and will change the interpretation of previous and future experiments.

    "Second, the experimental demonstration serves as a proof of principle and gives a clear guideline how to proceed and implement the large available library of (radio) antennas for applications in nano-optics."

    Tim Taminiau, a PhD student in van Hulst's group, and first author of a recent paper in Nature Photonics describing these optical nano-antennas ("Optical antennas direct single-molecule emission") remarks that the concept of an antenna and directing emission has of course been known for over a century.

    "But our demonstration on the nano-scale with visible light coming from molecules is a first" he says. "It is the first experiment where a single molecule is brought near a well-defined optical antenna and the effects on the direction of molecular emission are studied. There are several differences between working with visible light compared to radio frequencies. For example, metals behave different at optical frequencies and this has to be taken into account into the antenna design. The experimental demonstration presented here shows that despite the differences the same ideas can be applied in nano-optics as in antenna theory."

    calculated emission of a molecule coupled to a dipole antenna
    The calculated emission of a molecule coupled to a dipole antenna (Image: T. H. Taminiau)

    Taminiau explains that the original motivation of the research team might seem unrelated at first: " We set out to build a better microscope" he says. "By building an optical antenna for a single molecule, one can communicate efficiently with that molecule. The antenna can be moved around; we can select the molecule we communicate with. Since the antenna is so small, we can do this with very high precision. The antenna thus acts like a high resolution microscope (resolution of around 20 nm, the antenna radius). However to use the antenna in this way, it first is crucial to understand how it works!"

    In a previous paper in Nano Letters the researchers already discussed some other details of the antenna and its functioning as a microscope ("λ/4 Resonance of an Optical Monopole Antenna Probed by Single Molecule Fluorescence").

    Optical antennas can be used to efficiently send light to and receive light from nano-sized systems. Van Hulst points out that in a sensor, one can use optical antennas to bring light to a small active area and direct the response obtained towards detector. "Antennas could be used to create efficient and directed nano-optical light sources" he says. "When the antenna position can be varied they can be used in high resolution (sub-diffraction limited) optical microscopes."

    This work now opens several avenues of exploration. Since antennas can interact with single molecules, it will be interesting to see the connections and applications of optical antennas in quantum optics and quantum information. Taminiau points out that especially the ability of an antenna to enhance the interaction of a molecule – or atom, ion or quantum dot – with light is an interesting prospect for quantum optics.

    "Having demonstrated an elementary antenna, it will be interesting to now move on to incorporate more complicated and specific antennas into nano-optics" says van Hulst. "One can think of narrowband cavity antennas or highly directive Yagi-Uda antennas (TV-antenna) on the nano-scale. For now, it is interesting to see how old concepts lead to novel tools on the nano-scale."

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/16ساعت 12:42  توسط مهندس محمدرضا فروغی  | 

    Nanotechnology manufacturing key to industrialized countries' future competitiveness

    Posted: March 28, 2008

    (Nanowerk Spotlight) An Interagency Working Group (IWG) on Manufacturing Research and Development established by the National Science and Technology Council (NSTC) has identified three technology areas as key research and development priorities for future manufacturing: Manufacturing R&D for Hydrogen Technologies; Nanomanufacturing; and Intelligent and Integrated Manufacturing. The Working Group summarized their findings in a new report titled "Manufacturing the Future" (pdf download, 3.3 MB). Although this report is specific to the U.S., most of its general conclusions and recommendations apply to most other industrialized nations and their industrial nanotechnology efforts as well.

    Nanotechnology is viewed throughout the world as a critical driver of future economic growth and as a means to addressing some of humanity’s most vexing challenges (e.g. energy, environment, health). Because of its broad range of prospective uses, nanotechnology has the potential to impact virtually every industry, from aerospace and energy to healthcare and agriculture.

    Nanomanufacturing R&D integrates science and engineering knowledge and develops new processes and systems to assure quality nanomaterials, to control the assembly of molecular-scale elements, and to predictably incorporate nanoscale elements into nano-, micro-, and macroscale products utilizing new design methods and tools. Efforts in this area are directed toward enabling the mass production of reliable and affordable nanoscale materials, structures, devices, and systems. Nanomanufacturing includes the integration of ultra-miniaturized top-down processes and evolving bottom-up or self-assembly processes.

    The IWG cites the three manufacturing areas it covers in its report as being important to U.S. economic and national security. It identifies these areas as potentially leveraging scientific and technological advances to transform knowledge and materials into valuable products. Much of this research falls under the American Competitiveness Initiative, a government-funded mandate to increase investments in R&D, education and entrepreneurship. These manufacturing areas also correspond to existing priorities established by the federal government through the Hydrogen Fuel Initiative, the National Nanotechnology Initiative (NNI) and the Networking and Information Technology Research and Development Program.

    "Our objective was to focus on issues of national importance, and to identify manufacturing areas that have the potential to deliver major benefits to the economy," said David Stieren, executive secretary of the group that produced the report and technology deployment manager of the Commerce Department's National Institute of Standards and Technology (NIST) Hollings Manufacturing Extension Partnership. "These benefits include creating new jobs, enhancing manufacturing competitiveness and making progress toward accomplishing major national goals,” he said.

    The IWG states that its efforts in nanomanufacturing complement the continuing nanomanufacturing efforts organized under the NNI. The IWG looks to align nanomanufacturing activities with other federal manufacturing programs and to serve as a forum for joint program planning in nanomanufacturing. The IWG also draws upon enterprise-level manufacturing research and other advanced development expertise common to a broad array of manufacturing enterprises. This expertise ranges from supply chains to methods and tools to design integrated products, to the infrastructure to assure the producibility and predictability of nanoscale products, and the productivity of nanomanufacturing processes and enterprises.

    The IWG report defines nanomanufacturing as all manufacturing activities that collectively support practical approaches to designing, producing, controlling, modifying, manipulating, and assembling nanoscale elements or features for the purpose of realizing products or systems that exploit properties seen at the nanoscale. In order for nanomaterials to be mass produced reliably and affordably, scientists and engineers have to overcome hurdles relative to developing top-down processes (miniaturizing devices and structures to their smallest possible sizes) and bottom-up approaches (building nanostructures and nanodevices from the ground up by using tiny building blocks).

    Reflecting the very early stage of nanomanufacturing efforts, there is a need for the development of a metrology infrastructure for nanotechnology, especially with respect to establishing standards and to supporting successful commercialization of R&D. The report points out that instrumentation and metrology are vital aspects of manufacturing, and it will be important that the nanomanufacturing R&D community will work closely with the instrumentation and metrology community.

    In the U.S., the NNI has recognized the need to establish user facilities that make often costly, state-of-the-art instrumentation available to all researchers. In addition, to supporting large-scale, multidisciplinary research, including for nanomanufacturing, the NNI has funded a number of research centers. The resulting infrastructure is geographically distributed and, in the case of user facilities, available to the broad research community. Several nanomanufacturing-related research center and user facilities are highlighted in the report:

  • NSF National Nanomanufacturing Network (NNN) (list of Nanomanufacturing Centers)
  • NSF Nanoscale Science and Engineering Centers (NSECs)
  • Systematic control and manufacture at the nanoscale are envisioned to evolve in four overlapping generations of new nanotechnology product types that start with nanoscale building blocks and evolve through complex heterogeneous systems. Each anticipated generation of products will provide a nanotechnology base for further innovation, leading to succeeding generations of products of increasing complexity and functionality:

    First Generation (beginning ∼2000): passive nanostructures, illustrated by nanostructured coatings, nanoparticles, dispersion of nanoparticles, nanocomposites, and bulk nanostructured materials — nanostructures made of metals, polymers, ceramics; bio-building blocks.

    Second Generation (beginning ∼2005): active nanostructures, illustrated by transistors, amplifiers, targeted drugs and chemicals, biological and non-biological sensors, actuators, and adaptive structures.

    Third Generation (beginning ∼2010): three-dimensional nanosystems and systems of nanosystems using various synthesis and assembly techniques such as bio-assembly, networking at the nanoscale, and multiscale architectures.

    Fourth Generation (beginning ∼2015): materials by design and heterogeneous molecular nanosystems, where each molecule in the nanosystem has a specific structure and plays a different role. Molecules will be used as devices, and from their engineered structures and architectures will emerge fundamentally new functions. Since the path from fundamental discovery to nanotechnology applications takes about 10–12 years in recent nanotechnology developments, now is the time to begin exploratory research in 3D integrated, heterogeneous devices, structures, and systems that involve materials by design and molecular nanosystems.

    Delivering the many anticipated nanotechnology products of the future will require entirely new manufacturing processes. These include cost-effective methods for synthesizing and processing nanotubes, particles, fibers, and quantum dots; nanotube dispersion in nanocomposites; atomic-layer deposition for nanoelectronics; positioning, imaging, and measurement at nanoscale resolution; and modeling of material-energy interactions and manufacturing processes from nanoscale to macroscale. Several of these manufacturing processes are currently being realized, and they will need to be refined continuously to fully realize the promise of future nanotechnology products. The report addresses the four key challenges in material and manufacturing processes:

  • Scale-up and modular nanomaterial building blocks
  • Integrating bottom-up and top-down nanoscale assembly processes
  • Combining multiple assembly processes
  • Moving beyond optical-resolution probing and metrology
  • The IWG points out that the three research sectors covered in its report are also interdependent. For example, the design and cost-effective production of nanomaterials to store hydrogen may be critical to our country’s transition away from an oil-dependent transportation system. Also, intelligent, flexible manufacturing may reduce the time and cost of incorporating nanoscale components into real world applications, according to the report. Finally, the three research sectors offer an opportunity to contribute to sustainable manufacturing by incorporating materials, processes, and systems that use energy and materials effectively and use environmentally preferable materials.

    While most of the report's section on nanomanufacturing is of a technical nature, it also raises a number of important societal issues arising from the widespread implications that will result from moving the industrial base towards nanomanufacturing:

  • What will new nanomanufacturing enterprises look like, and what steps are needed to create them? What new industries will result?
  • What impact will these new processes, systems, and industries have on our current industrial base?
  • What will be the skill sets required for a technically literate workforce and the corresponding infrastructure for education?
  • What will be the size of a typical nanomanufacturing enterprise, and how will such enterprises be distributed?
  • Will products be high-volume, low-value; or low-volume, high-value; or a mix; and will the new industries be transformative?
  • What are the potential environmental implications of nanotechnology and nanomanufacturing, and how might those implications affect investment?
  • With the potential creation of new industries, what economic, health, safety, national security, and sustainability issues should be anticipated — and what proactive measures should be taken to address those issues?
  • And, ultimately, what will be the benefits of creating the new industries and how can those anticipated benefits be optimized?
  • By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/16ساعت 12:39  توسط مهندس محمدرضا فروغی  | 

    Newly formed Nanotechnology Protection Agency (NPA) to regulate molecular assemblers

    Posted: April 1, 2008

    (Nanowerk Spotlight) The newly created U.S. Nanotechnology Protection Agency (NPA) announced today, April 1, 2008, that, effective immediately, all laboratories and production facilities for molecular assemblers (commonly called nanobots) need a special license and have to follow strict guidelines in all research and production facilities that deal with nanoassemblers. At the same time, the NPA declared gray goo a hazardous substance.

    The new agency also announced the finalists of its Nanobot Hazard Symbol contest. Hundreds of people from all over the globe participated in the NPA's competition to design a Nanobot-Hazard Symbol that cautions people to be vigilant in the presence of molecular assemblers. The winning design will be submitted to international standard-setting bodies responsible for hazard characterization and could be used as a label on workroom walls and individual nanobots. Here is the leading entry from the United States:

    nanobot warning sign

    While the NPA regulations will have an immediate economic impact on many nanotechnology companies, most have been preparing for this dreaded day. However, public and media reactions seem to indicate that the public and many organizations were taken completely by surprise.

    The Project for Exposing Nanotechnologies (PEN) issued a statement in which it said that this new regulation has been overdue. Coincidentally, PEN already has scheduled a press conference and webinar to introduce the release of its new report "Do nanobots dream? – The philosophical and ethical issues surrounding molecular assemblers." Sandwich lunch will be served.

    A spokesperson for Friends of the Earth Australia criticized the NPA’s decision as "too little, too late." She said that FoE has talked about nanobots in sunscreens for ages and only now does the world wake up to this problem. "Every summer beachgoers in Australia go bonkers over the little holes that sunscreen nanobots drill into their skin. While the holes are only nanometers-deep and generally more a nuisance than a health risk, some people, especially those with thin skin, need to be hospitalized and have the nanobots surgically removed by specially trained nano-dermatologists."

    Taking a more positive spin on this issue, Invest Australia, the Australian inward investment agency, points out that Nanobot-Dermatology is now taught at 80% of Australian universities and that the first start-ups have begun commercializing this new field. Australia is now the world leader in procedures and instruments, the agency said.

    "Where is the warning sign for green goo?" asked the ETC. Nanofood applications messing up our spinach are as dangerous as the gray stuff. "There are many canaries emerging in the nanotechnology coal mine," the organization’s executive director said in a statement. "Nanobots are perhaps among those making the most noise and it is absolutely essential that everyone sits up and takes notice."

    Elsewhere, CRN has announced a joint event with Kurzweil to discuss the role of nanobots in the coming singularity and to debate what shade of gray the color of nanogoo most likely will be.

    While the rest of the world is only slowly waking up to the news, and academic circles take a measured and scientific approach, the public and media reactions in the U.S. have been swift and strong on both sides of the debate.

    A spokesperson for the National Association of Molecular Assembler Systems (MOLEASS) said that the new regulation would increase the production cost for nanobots. "This is the straw that breaks the camel’s back" she said. "It is absolutely imperative that the U.S. immediately increases the import duties for all molecularly assembled products from China in order for our American companies to stay competitive and to save tens of thousands of American jobs." She accused nanoassembly firms in Asia to unfairly undercut American manufacturers by skirting safety regulations. "Having smaller fingers, they already have an unfair advantage in the assembly process" she points out.

    "We are all for a safe handling environment for these exciting products" she emphasizes, "but American manufacturers can’t be singled out to have the strictest regulations on the planet imposed on them. What we need is an international approach that is fair to everyone. We need to thoroughly study the issues before we jump to conclusions." As a demonstration how serious they take their responsibilities, MOLEASS introduced a 10-year grant program for researchers to explore the environmental impact of molecular assembly technology. "We need to wait for all cards to be on the table before we can say anything definitive. Panicky reactions like the one we saw from NPA today are not helpful at all. With our grant program, we'll know more by 2018."

    America Rules, the conservative Washington-based think tank, agrees: "This is just another example of bureaucrats in Washington creating unnecessary red tape that makes American-made nanoproducts uncompetitive on the world market. This has short-sighted liberal anti free market policy written all over it. Our inventors and creative minds are now forced to compete with one hand tied behind their back."

    A senior senator in Washington even went so far as to call the debate about nanobots "the biggest hoax ever perpetrated on the American people." Much of the debate over gray goo is predicated on fear, rather than science, he said. "Environmental extremists and their elitist organizations have succeeded in turning one of the biggest industrial achievements of our great country into a perversion of science."

    In a meeting with religious groups at the White House, the President said that Gray Goo is just a theory and should be studied alongside competing theories. The President said that he has learned a lot about nanotechnology from his discussions with Michael Crichton, author of Prey. "What concerns me most" he said, "is that some scientists claim that nanobots are a form of life. We should take these claims seriously. Make no mistake, this administration will do whatever it takes to protect live, no matter how small or gray it is." He then signed an executive order that imposes a moratorium on nanobot research in the United States. Effective immediately, federal research grants will only be available for research on the existing 14 families of nanobots, but not the creation of new ones.

    At the same meeting, religious leaders criticized the NPA's effort to regulate nanobot replication rates. They were especially critical of a plastic thin film – so-called nanocondoms – that seals molecular assembly platforms to prevent nanobots from escaping the staging area but also protects them from becoming infected with a virus. The televangelists, who think that nanotechnology is morally unacceptable anyway, made it clear that a responsible society should pledge abstinence to any assembler activity and not engage in frivolous molecular assembly. Some forward-looking Intelligent Design experts have begun to explore scientific similarities between armageddon and a gray goo scenario and insist that their theory be included in high school curricula across the country.

    In a move that surprised observers with its swiftness, the Department of Homeland Security (DHS) announced today that it has begun upgrading its colored threat warning system to include the color gray. "If these nanobots fall into the hands of islamic fundamentalists and other evildoers, the risks to our homeland are enormous" said a DHS press officer. "As soon as we see any signs of gray goo, we’ll go to Threat Level Gray and a set of carefully designed emergency procedures will take effect."

    Elsewhere in Washington, a bipartisan group of Members of Congress introduced a new bill that seeks $180 million in emergency funding to patch holes in the fence along the Mexican border in order to prevent illegally built nanobots from getting through. "The risks to our country are unacceptable" says Congressman S. Gonzales from New Mexico in an appearance on TV morning talkshows. "If these undocumented nanobots succeed coming into our country the damage to our economy would be incalculable." Already, the Minuteman, a vigilante group, have issued their members handheld scanners that allows them to detect small concentrations of gray goo alongside the border. "As soon as we see the first signs of foreign looking nanobots, or if we find their programming language is not English, we’ll squash them like, well, little bugs" said the group's argus-eyed Chief Vigilant Officer.

    CNN is planning a "Anderson Cooper 360" special where Anderson will host a 24-hour ‘Nanothon’ from the factory floor of one of the affected nanobot companies to show the impact on workers’ families after the NPA regulation takes effect. Designed as a joint event with YouTube, viewers are invited to send in clips with their personal experiences, good or bad, with nanobots and any actual footage of gray goo.

    Representatives for two market research firms, Lachs Research and Terrifica, also appeared well-prepared to further exploit their deep understanding of nanotechnology. The NPA announcement coincided with both firms releasing their latest market research reports (both priced at a reasonable $4999.95) forecasting the market for nanobots. "Our latest report is the definitive guide to the use of molecular assemblers for, well, everything" says one senior consultant. "We examined over 2000 different companies, analyzing where they are in their product pipeline, the available market, size and weight of the individual nanobots, all available operating systems, and the mind-boggling value that these tiny little buggers will add to the world economy. We conservatively estimate the market for nanobot-enabled technologies to be $4.5 trillion by 2014 but this value could increase significantly in a very short time if the self-replication rate of molecular assemblers becomes exponential."

    William R. Inge, the British vicar known as the Gloomy Dean, once said that "anxiety is interest paid on trouble before it is due." A half-century after his death, Britain still leads the way in anticipating bad news.

    Leading the charge, the Prince of Wales, upon being briefed on the issue, immediately condemned the "irresponsible attitude of molecular scientists...who ...play dice with God’s creation." He called on corporate leaders and scientists worldwide to take a step back and think about the consequences of their actions. His Royal Highness, on route to a fox hunt, was very surprised to learn from a reporter that the reason his new riding coat was water repellant and blood stain resistant was due to novel textile fibers coated with nanoparticles.

    In Europe, the EU Commission is preparing regulation similar to the NPA’s. One insider told Nanowerk that the new law, which needs to be translated into all 20 official EU languages, is being held up because the French don’t have a word for gray goo. "We always associated this term with British food" said the French delegate. "Mon dieu, if this is what nanofood tastes like we don’t want to have anything to do with it."

    This all of course is great news for a group of nanotechnology start-up companies that stand to reap fortunes from nanobot detection and gray goo clean-up technologies. Venture capitalists and all the big names in the investment newsletter industry are exited as never before about the potential. "This really is the breakthrough for the gray-green nanotechnology industry" said Charles 'Tiny' Goldmuenz, one of the leading nanotechnology investment experts and editor of the popular Goldmuenz report. "I am especially exited about the upcoming IPO of Botzap, Inc., a developer of disposable handheld gray goo detection scanners to be soon sold under the trade name Goo-Scan™ at all major department stores for only $9.95. The company holds 65 patents, has an incredibly strong management team and has already gone through $42 million venture capital funding. The company clearly is poised to be the frontrunner in this field and we hope that some day it even will be profitable."

    Brandnew update: A recent research report from UC San Francisco sensationally claims the discovery of pink goo. This exciting new substance achieves its zero-friction properties through large numbers of slip-sliding nanobots embedded in petroleum jelly. This nanocomposite material glows a lovely pink under bathroom lights, hence its nickname.

    "It’s far too early to say if there are any risks for the environment from this substance" one of the UCSF researchers explains to Nanowerk. "We are still performing field tests but it appears that the nanobots get really slippery inside the jelly." First results also show that pink goo bots tend to feed on gray goo bots, so the end of the world might actually look quite pretty when seen from outer space, especially just before sunset.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/16ساعت 12:33  توسط مهندس محمدرضا فروغی  | 

    Extremely sensitive protein detection with quantum dot self-assemblies

    Posted: April 3, 2008

    (Nanowerk Spotlight) In proteomics research, the study of the structure and function of proteins, chemical as well as physical methods are used to detect proteins. Physical methods are mostly applied after chromatography. They are either based on spectroscopy like light absorption at certain wavelengths or mass determination of peptides and their fragments with mass spectrometry. Chemical methods are used after two-dimensional electrophoresis and employ staining with organic dyes, metal chelates, fluorescent dyes, complexing with silver, or pre-labeling with fluorophores. What these various methods have in common is that they are not very fast, can be expensive, sometimes don't offer the sensitivity required, and are not always easy to handle. Since protein detection can be a powerful tool for diagnosing, prognosing, and monitoring cancers and other medical conditions, researchers are working towards developing detection platforms that can multiple specific molecules from the complex mixture present in serum, and is rapid, sensitive, and simple to administer.

    When a malignant cancer develops in the human body, the cancer cells produce certain types of proteins. Identifying these proteins enables early detection of cancer. One of the goals of nanobiotechnology is to develop protein chips that are sensitively responsive to a very tiny amount of specific proteins in order to enable early stage diagnosis. For example, a protein that is known to bind to a protein produced by a cancer cell could be attached to a biochip. If this particular cancer cell protein were present in a sample passed over the chip, it would bind to the protein on the chip, causing a detectable change in the electrical signal passing through the chip.

    Researchers now have demonstrated a simple and rapid way of detecting proteins of interest using nanoparticles. This single step reaction starts with nanoparticle-antibody conjugates that form large aggregates if the intended protein molecules are present in the solution. The large aggregates can be characterized individually by laser scattering and fluorescence.

    "Compared to traditional proteomic detection techniques, antigen mediated quantum dot agglomeration combined with flow-based detection on a microfluidic device has the potential to offer better sensitivity, ease of use, speed, and cost of testing" Dr. Todd D. Giorgio tells Nanowerk. "We have developed a novel antigen detection technique based on fundamental nanoscale phenomena. This technique has several advantages over conventional antigen detection strategies due to the use of solution-phase biofunctionalized quantum dots and a microfluidics-based detection strategy. We carried out sensitive detection completely in the fluid phase, in a single step, and with minimal incubation."

    Giorgio, a Professor of Biomedical Engineering and Professor of Chemical Engineering at Vanderbilt University in Nashville, Tennessee, and Chinmay P. Soman, a student in his group, have published a paper in Langmuir that describes their novel approach to to sensitive and rapid antigen detection ("Quantum Dot Self-Assembly for Protein Detection with Sub-Picomolar Sensitivity").

    "Our paper demonstrates a novel and efficient method for detecting low concentration proteins, which could be used for early diagnosis and frequent monitoring of diseases such as cancer using just small volume blood sample" says Soman, the paper's first author.

    Quantum Dot Self-Assembly for Protein Detection
    The graphic depicts a possible implementation of this technology for improved ease of use, consisting of a microfluidic chip and a dedicated hand held or benchtop device. (Image: Daniel Dorset)

    While conventional protein detection methods are time consuming and labor intensive, the method developed by the Vanderbilt researchers could be automated to reduce time and cost. Giorgio says that, compared to other nanoparticle-based protein detection methods, their approach offers a better potential to detect multiple proteins simultaneously and quantitatively.

    Another advantage is that the technique requires only very small volumes of samples – it may be possible to detect proteins from a small blood sample. The antigens in this study were detected to sub-picomolar concentration, comparable to the detection of the same molecules by conventional techniques such as ELISA or Western blot.

    "Our agglomeration-based detection strategy is already comparable to conventional immunorecognition techniques in terms of sensitivity" says Giorgio. "The flow-based detection approach also enables characterization of multiple properties of individual self-assembled structures, thus providing a tool for investigating self-assembly in a novel and powerful manner, which may lead to insights into this important nanoscale phenomenon."

    Soman explains that for their technique, quantum dots are conjugated with polyclonal antibodies using a streptavidin-biotin interaction. In the presence of the appropriate antigen molecules, these quantum dot/antibody conjugates rapidly self-assemble into colloidal structures with sizes that are 1-2 orders of magnitude larger than the constituents. "The size, structure, and fluorescence characteristics of these self-assembled structures are a function of the relative concentration of the conjugates and the antigen molecules, among other factors" he says. "These attributes of the colloidal structures can be characterized by several techniques, including flow cytometry, dynamic light scattering, and electrical sensing zone or Coulter counter method.

    Non-specific aggregation of nanoparticles can be a problem when a lot of proteins are present in the sample, such as in serum. This is a well known problem when nanoparticles and biological materials interact, and it is especially important for applications such as this one that depend on predictable size of the nanoparticles over time. Giorgio and Soman show that this problem can be solved by effective surface engineering of the nanoparticles to minimize non-specific interactions.

    The scientists say that they managed to separately detect two different proteins with high sensitivity and specificity. Currently, they are investigating simultaneous detection of multiple proteins from a complex mixture such as a serum.

    "Our technique requires minimal sample volume, is amenable to multiplexing, automation, and implementation in a microfluidic chip, and is completely modular," says Giorgio. "This makes it an ideal candidate as a platform technology for frequent and low cost proteomic testing and monitoring of cancers, as well as an advanced point-of-care diagnostic based on a diverse array of intermolecular recognition-based biomarker sensing.".

    The implementation of this and other protein detection techniques on microfluidic and/or semiconductor chips (lab-on-a-chip) is expected to make diagnostics simpler, faster and cheaper, leading to better therapy effectiveness and survival rates for serious diseases. However, the maturation of proteomics into a clinically proven technology will be required before these compact diagnostic devices can be commercialized.

    By Michael Berger, Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/16ساعت 12:24  توسط مهندس محمدرضا فروغی  | 

    A role for nanotechnology in capturing and storing greenhouse gases

    Posted: April 4, 2008

    Nanowerk Spotlight) The greenhouse effect is primarily a function of the concentration of water vapor, carbon dioxide, and other trace gases in the Earth's atmosphere that absorb the terrestrial radiation leaving the surface of the Earth. Changes in the atmospheric concentrations of these greenhouse gases can alter the balance of energy transfers between the atmosphere, space, land, and the oceans. The capture and storage of greenhouse gases could play a significant role in reducing the release of greenhouse gases into the atmosphere (read more about capture and storage of carbon dioxide here). Carbon dioxide (CO2) is the most important greenhouse gas and captures the limelight in most reports on global warming. While other greenhouse gases make up less of the atmosphere, they account for about 40 percent of the greenhouse gas radiation sent back to Earth. They can also be much more efficient at absorbing and re-emitting radiation than carbon dioxide, so they are small but important elements in the equation. In fact, molecule-for-molecule some gases containing lots of fluorine are 10,000 times stronger at absorbing radiation than carbon dioxide. A new systematic computational study shows an interesting approach of how nanotechnology, in this case the use of carbon nanotubes and other nanomaterials, could lead to effective filters for the capture and storage of greenhouse gases.

    Tetrafluoromethane (CF4), an extremely stable molecule whose lifetime in the atmosphere is 50 000 years (compared to an average CO2 lifetime of 50-200 years), is such a particularly powerful greenhouse gas – also called super greenhouse gas – that, when present in the troposphere, has a particular ability to absorb the outgoing infrared radiation, thus causing a temperature increase of the atmosphere.

    The global warming potential (GWP) index is intended as a quantified measure of the globally averaged relative radiative forcing impacts of a particular greenhouse gas. It is defined as the cumulative radiative forcing – both direct and indirect effects – integrated over a period of time from the emission of a unit mass of gas relative to CO2 as a reference gas. The GWP for carbon dioxide is 1 per hundred years while that for tetrafluoromethane is 6500 per hundred years (read more about GWP from the EPA's U.S. Greenhouse Gas Inventory Program: Greenhouse Gases and Global Warming Potential Values;; pdf download, 76 KB).

    Total worldwide emissions of CF4, a perfluorocarbon (PFC) gas, are small in comparison to carbon dioxide but it is a much more efficient absorber of infrared radiation than CO2 and therefore its global warming potential is vastly higher. PFCs have been extensively used in the microelectronic and semiconductor industry in plasma cleaning of chemical vapor deposition chambers. Although the semiconductor industry is moving away from the use of PFCs toward other less problematic gases, other sources of PFCs are still significant: as an unintended byproduct during aluminum production; as drop-in replacement of chlorofluorocarbon refrigerants; as potential solvents and cosolvents for supercritical fluid extraction processes; and in the petrochemical industry. New uses for PFCs are being explored, e.g. for therapeutic purposes (e.g., NMR imaging), eye surgery, and modifiers for inhaled anesthetics. As a consequence, it is estimated that global emissions of PFCs will rise 150% in the next 50 years. That means that super greenhouse gases even with small emissions have the potential to influence climate far into the future and could become a serious environmental problem.

    "We have conducted simulations that show that single-walled carbon nanotubes (SWCNTs) can serve as efficient nanoscale vessels for encapsulation of tetrafluoromethane at room temperature" Dr. Robert Holyst tells Nanowerk. "A good filter should keep the CF4 molecules inside and stay cheap. Carbon seems promising, but in order to efficiently store CF4 we need well defined pores inside the carbon material. Carbon nanotubes are a carbon material that offers well defined pore sizes for storage applications and they are also most efficient in terms of storage capacity."

    adsorbing greenhouse gases in ncarbon nanotubes
    This movie shows a Monte Carlo simulations of CF4 adsorption in carbon nanotubes with pore sizes of 1.01 nm)

    Holyst, a professor in the Institute of Physical Chemistry at the Polish Academy of Sciences, together with Dr. Piotr Kowalczyk, a Postdoctoral Research Fellow in the Department of Applied Physics at RMIT University in Australia, has published his findings in the March 7, 2008 online edition of Environmental Science & Technology (Efficient Adsorption of Super Greenhouse Gas (Tetrafluoromethane) in Carbon Nanotubes). The two scientists have found that the amount of the encapsulated CF4 under the ambient external conditions (1 bar, 300 K) is maximized for well defined pore sizes of SWCNTs. These pore sizes change as we change the external pressure. They also demonstrate that the high enthalpy of adsorption cannot be used as an only measure of storage efficiency.

    "We found that the optimal balance between the binding energy (i.e., enthalpy of adsorption) and space available for the accommodation of molecules (i.e., presence of inaccessible pore volume) is a key for encapsulation of van der Waals molecules (a stable cluster consisting of two or more molecules held together by van der Waals forces or by hydrogen bonds)" says Holyst.

    He explains that carbon nanotubes can have a very narrow distribution of pore sizes, which is particularly important in view of the results predicting a maximum adsorption at some pore sizes. "In carbon nanotubes we can highly compress the gas reaching the density of a solid phase. We also point out that optimal structure of carbon nanotubes for volumetric storage capacity is different from the structure for the optimal mass storage capacity, thus it is important whether we consider optimal adsorbent for mass or for volumetric storage."

    In their models the two researchers show that in the search for optimal adsorbents one has to take into account two elements: heat of adsorption and pore sizes, since it is not true as is commonly believed that high adsorption enthalpy is the sole condition for high adsorption capacity.

    "The key for optimizing the amount of CF4 trapped in the nanotubes upon assumed operating external conditions is the size of the internal cylindrical pores and interstitials channels of an idealized bundle of SWCNTs" explains Kowalczyk. "Due to a large molecular size of CF4, the internal pores play predominant role in the process of encapsulation of CF4 via the physical adsorption mechanism."

    This work shows that an optimized structure of SWCNTs bundles seem to be very promising for the encapsulation of CF4 and superior in comparison to the currently used activated carbons and zeolites. The efficiency of encapsulation in nanotubes can be explained by their intermediate properties in comparison to these other materials.

    Holyst raises the point that, in practice, CF4 exists as a gas mixture (for example, a mixture with nitrogen that can mimic the air mixture). "So the question arises about the transferability of our simulation results to the selective adsorption of CF4 from a gas mixture" he says. "Previous studies suggest that our current simulation results of CF4 adsorption in carbon nanotubes are transferable for the problem of CF4-N2 mixture adsorption. Our results as well as those previous results show that optimal adsorption is achieved only when the distribution of pore sizes is sharp."

    Based on these model simulations, what is now needed are experimental investigations of the capture and storage of CF4 in a real bundle of SWCNTs in order to develop this concept as a practical solution that works on an industrial scale.

    By Michael Berger. Copyright 2008 Nanowerk LLC

    + نوشته شده در  87/01/16ساعت 12:5  توسط مهندس محمدرضا فروغی  | 


    The science of developing materials at the atomic and molecular level in order to imbue them with special electrical and chemical properties. Nanotechnology, which deals with devices typically less than 100 nanometers in size, is expected to make a significant contribution to the fields of computer storage, semiconductors, biotechnology, manufacturing and energy.

    Envisioned are all kinds of amazing products, including extraordinarily tiny computers that are very powerful, building materials that withstand earthquakes, advanced systems for drug delivery and custom-tailored pharmaceuticals as well as the elimination of invasive surgery, because repairs can be made from within the body.

    Larry Bock, CEO of Nanosys, who helped launch more than a dozen successful biotech companies in his career, believes that nanotech will impact even more industries than biotech. In an excerpted article from the March 2003 Nanotech Report, he compared nanotechnology with the microelectronics industry. Bock said that "a single chemistry graduate student can create novel devices and device architectures not even imaginable or manufacturable by today's biggest microprocessor companies. That is because these devices are fabricated chemically, or from the bottom up. Existing microelectronics technology is fabricated by etching wafers, or from the top down." See AFM, STM, Buckyball, nanotube and MEMS.

    Fixing One Cell at a Time
    By 2020, scientists at Rutgers University believe that nanorobots will be injected into the bloodstream and administer a drug directly to an infected cell. This nanorobot has a carbon nanotube body, a biomolecular motor that propels it and peptide limbs to orient itself. Because it is composed of biological elements such as DNA and proteins, it will be easily removed from the body. For more information, see http://bionano.rutgers.edu/Mavroidis_Final_Report.pdf. (Image courtesy of the Bio-Nano Robotics team at Rutgers University: Constantinos Mavroidis, Martin L. Yarmush, Atul Dubey, Angela Thornton, Kevin Nikitczuk, Silvina Tomassone, Fotios Papadimitrakopoulos and Bernie Yurke.)
    + نوشته شده در  86/12/09ساعت 10:29  توسط مهندس محمدرضا فروغی  | 

    Nanotechnology-based Flexible Hydrogen Sensors

    With hydrogen vehicles already embracing carbon-reduction footprints, global warming seems to be moving a step further with its nobility its sensors. The now available hydrogen sensors may soon be replaced by a newly developed flexible sensor, which is not only comparatively cheaper but also explores the world of nano-technology! Thanks the researchers at the U.S. Argonne National Laboratory.What could help make the sensors cheaper is the use of only palladium  nanoparticles instead of pure palladium. But, of course this will not compromise on its pure-palladium-like efficiency. To add to, it can be used in many applications ranging from aircraft to portable electronics. To detect a hydrogen leakage caused by even tiny pinholes in the space shuttle pipe, the new technology can be of great use. This is how the new flexible hydrogen sensor is fabricated: The new sensing devices is fabricated by using a two-step process separated by hig] h and low temperatures. First, at around 900 degrees C, researchers grow SWNTs [single-walled carbon nanotubeson a silicon substrate using chemical vapor deposition. Then, researchers transfer the SWNTs onto a plastic substrate at temperatures lower than 150 degrees C using a technique called dry transfer printing. And the result:-The new sensors are highly sensitive, thus fast responding and quick recovering. The plastic sheets it uses help reduce the overall weight, increasing the mechanical flexibility as well as shock resistance. Thus, its wide range - as well as sensitive and affordable - applications seem to be making the hydrogen (or eco-friendly) vehicles gradually affordable to more and more people who are environmentally conscious, but could not serve it because of the hard-to-meet costs.

    + نوشته شده در  86/12/02ساعت 9:7  توسط مهندس محمدرضا فروغی  | 

    East meets west

    Curcumin is a major component of the spice turmeric, which has been used in Eastern medicine for thousands of years.  Curcumin and beta-carotene, another bioactive compound, both have limited use in Western medicine due to poor bioavailability, but all that could change thanks to mesoporous silica particles

    ادامه مطلب
    + نوشته شده در  86/11/20ساعت 17:44  توسط مهندس محمدرضا فروغی  | 

    DNA nanowires

    Fastening azide-functionalised gold nanoparticles onto modified DNA holds great promise for nanoscale electrical circuits, say German researchers.

    The trend for miniaturisation in electronics, and size and cost limitations of conventional lithographic techniques, has led researchers to develop alternative routes to nanoelectronic components


    ادامه مطلب
    + نوشته شده در  86/11/20ساعت 16:28  توسط مهندس محمدرضا فروغی  | 

    مطالب جدیدتر