Measuring the temperature of nanoparticles

One of the holy grails of nanotechnology in medicine is to control individual structures and processes inside a cell. Nanoparticles are well suited for this purpose because of their small size; they can also be engineered for specific intracellular tasks. When nanoparticles are excited by radio-frequency (RF) electromagnetic fields, interesting effects may occur. For example, the cell nucleus could get damaged inducing cell death; DNA might melt; or protein aggregates might get dispersed.

Some of these effects may be due to the localized heating produced by each tiny nanoparticle. Yet, such local heating, which could mean a difference of a few degrees Celsius across a few molecules, cannot be explained easily by heat-transfer theories. However, the existence of local heating cannot be dismissed either, because it's difficult to measure thetemperaturenear these tinyheatsources.

Scientists at Rensselaer Polytechnic Institute have developed a new technique for probing the temperature rise in the vicinity of RF-actuated nanoparticles using fluorescentquantum dotsas temperature sensors. The results are published in theJournal of Applied Physics.

Amit Gupta and colleagues found that when the nanoparticles were excited by an RF field the measured temperature rise was the same regardless of whether the sensors were simply mixed with the nanoparticles or covalently bonded to them."This proximity measurement is important because it shows us the limitations of RF heating, at least for the frequencies investigated in this study,"says project leader Diana Borca-Tasciuc."The ability to measure the local temperature advances our understanding of these nanoparticle-mediated processes."

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Researchers create iridescent glass that can reflect UV or infrared light

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(PhysOrg.com) -- Using nanocrystals of cellulose, the main component of pulp and paper, chemistry researchers at the University of British Columbia have created glass films that have applications for energy conservation in building design because of their ability to reflect specific wavelengths of light, such as ultra violet, visible or infrared.

These nanoporous films, described in a paper published in today’s issue ofNature, may also be used in optical filters, sensors, or for molecule separation in the pharmaceutical industry.

“This is the first time that the unique, helical structure of cellulose has been replicated in a mineral,” says Mark MacLachlan, associate professor in the chemistry department at UBC and co-authour of the paper.“The films have many applications and we created them from an exciting new product derived from our wood processing industry right here in British Columbia.”

At the molecular level, the films have the helical structure of nanocrystalline cellulose, a building block of wood pulp, explains MacLachlan.

MacLachlan and PhD student Kevin Shopsowitz, post-doctoral fellow Hao Qi and Wadood Hamad of FPInnovations, stumbled upon this discovery while trying to create a hydrogen storage material.

The UBC researchers mixed the cellulose from the wood pulp with a silica, or glass, precursor and then burned away the cellulose. The resulting glass films are composed of pores, or holes, arranged in a helical structure that resembles a spiral staircase. Each hole is less than 1/10,000th of the diameter of a human hair.

“When Kevin showed me the films and they were red, blue, yellow and green, I knew we’d been able to maintain the helical structure found in thecellulose.”

“The helical organization we produced synthetically mimics the structure of the exoskeletons of some iridescent beetles,” says Shopsowitz.

The pores in the helix give the films a wide range of applications. When certain liquids are added to the film, the liquid gets trapped in the pores and changes the optical properties of the films.

“By functionalizing the pores to make them more selective to particular chemicals, we may be able to develop new sensors that are very sensitive for detecting substances in the environment,” says Shopsowitz.

To reduce the energy needed to cool buildings, windows could be treated with the transparent films that reflect infrared light– the light that heats up a building. Right now, metal particles are often used to do this but they tint the windows brown.

This research was done in partnership with FPInnovations, an organization dedicated to developing new products from the forest sector, and with funding from the Natural Sciences and Engineering Research Council of Canada.

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New high performance insulating plaster developed at Empa

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Empa scientists have developed a high performance plaster which boasts a thermal insulation value three-times better than convention plaster thanks to so-called aerogels. The new material offers an elegant method of renovating historic buildings to save energy without altering their appearances.

Those undertaking the renovation of historical buildings are frequently faced with the challenge of how to improve the thermalinsulationlevels of old structures effectively yet elegantly. To date there has been no method available which offers a technically satisfactory solution to this problem without noticeably changing the appearance of the historic building.

Now, however, researchers from Empa’s Building Technologies Laboratory, working in cooperation with a leading manufacturer of building materials, have developed an aerogel-based high performance insulatingplasterwhich will undergo field trials next year and is expected to be commercially available by 2013. Thanks to its mineral basis, the new plaster is both optically and in application very similar to the original historical building materials, and this makes it ideal for use on old buildings– on internal as well as external surfaces.

The"secret"behind the novel insulating plaster is a so-called aerogel. This substance possesses nanometer-sized pores and consists of 90 to 98 per cent air. These minute pores make aerogels an excellent material for use in the new insulating plaster, lending it a thermal conductivity value of less than 30 mW/m•K which is some two to three times better than that of conventional plaster.

A further advantage of the new plaster is its property of being simultaneously water repellent and permeable to water vapor. The new product is significantly more breathable than conventional plasters, and yet its surface does not become wet. Co-developer Thomas Stahl explains.”The porous structure of the aerogel makes the plaster permeable to water molecules, but for macroscopic water droplets the nano-pores are much to fine.”

The first buildings will be plastered with the new high performance material on a trial basis beginning in mid-2012. The additional cost of this innovative new plaster compared to conventional materials is expected to be between CHF 50 and 100 per square meter, depending on how thickly it is applied.

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UH professor taking next step with graphene research

The 2010 Nobel Prize in Physics went to the two scientists who first isolated graphene, one-atom-thick crystals of graphite. Now, a researcher with the University of Houston Cullen College of Engineering is trying to develop a method to mass-produce this revolutionary material.

Graphene has several properties that make it different from literally everything else on Earth: it is the first two-dimensional material ever developed; the world's thinnest and strongest material; the best conductor of heat ever found; a far better conductor of electricity than copper; it is virtually transparent; and is so dense that no gas can pass through it. These properties makegraphenea game changer for everything from energy storage devices to flat device displays.

Most importantly, perhaps, is graphene's potential as a replacement for silicon in computer chips. The properties of graphene would enable the historical growth in computing power to continue for decades to come.

To realize these benefits, though, a way to create plentiful, defect-free graphene must be developed. Qingkai Yu, an assistant research professor with the college's department of electrical and computer engineering and the university's Center for Advanced Materials, is developing methods to mass-produce such high-quality graphene.

Yu is using a technology known as chemical vapor deposition. During this process, he heats methane to around 1000 degrees Celsius, breaking the gas down into its building blocks of carbon andhydrogen atoms. Thecarbon atomsthen attach to a metallic surface to form graphene.

"This approach could produce cheap, high-quality graphene on a large scale,"Yu said.

Yu first demonstrated the viability of chemical vapor deposition for graphene creation two years ago in a paper in the journalApplied Physics Letters. He has since continued working to perfect this method.

Yu's initial research would often result in several layers of graphene stacked together on a nickel surface. He subsequently discovered the effectiveness of copper for graphene creation. Copper has since been adopted by graphene researchers worldwide.

Yu's work is not finished. The single layers of graphene he is now able to create are formed out of multiple graphene crystals that join together as they grow. The places where these crystals combine, known as the grain boundaries, are defects that limit the usefulness of graphene, particularly as a replacement for silicon-basedcomputer chips.

Yu is attempting to create large layers of graphene that form out of a single crystal.

"You can imagine how important this sort of graphene is,"said Yu."Semiconductors became a multibillion-dollar industry based on single-crystal silicon and graphene is called the post-silicon-era material. So single-crystal graphene is the Holy Grail for the next age of semiconductors."

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Revealing the secrets of chemical bath deposition

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X-ray absorption near-edge structure (XANES) spectroscopy is well known as a versatile and powerful technique for examining the microstructure of everything from crystalline solids to amorphous materials, even liquids. Its extreme sensitivity also makes it an ideal tool for probing the kinetics of various chemical reactions<i>in situ</i>.

Experimenters utilizing the U.S. Department of Energy Office of Science’s Advanced Photon Source at Argonne recently demonstrated a new wrinkle for XANES that has opened a window on a poorly-understood technique for deposition of materials. These insights will encourage the development of better-controlled and more precise chemical synthesis techniques for semiconductor and other nanomaterial applications, and are valuable as a demonstration of the extension of XANES spectroscopy into other realms of experimentation.

While chemical bath deposition (CBD) is widely used in the laboratory and industry for the creation of thin films and nanostructures for semiconductors and photovoltaics, its actual molecular workings have remained something of a mystery. This has somewhat limited its utility, because precise tailoring of CBD products is not possible without a clear understanding and thus control of CBD mechanics. Scientists from Drexel University and the University of Notre Dame have obtained the first detailed look at how CBD operates at the molecular level, using XANES spectroscopy to witness in situ the formation of zinc oxide nanowires. The work was published in October 2010 inChemistry of Materials.

CBD begins with a water solution with chemical precursors containing the components from which the desired film structure will be formed. But because the precursor chemical species tend to be very dilute within the solution, identifying and isolating them to monitor their activity during the deposition process has been a daunting challenge.“It’s very difficult to find experimental techniques that will allow you to assess the different things that you need to measure,” said principal investigator Jason Baxter of Drexel University.“This has led to some criticism of CBD for being too recipe-based, where it can be difficult to take one set of conditions and say what might happen elsewhere.” XANES proved to be the ideal window into the CBD process.“It gives you very high sensitivity so you can measure species that are very dilute,” Baxter said.“So we were able to look at CBD with a degree of accuracy that people could not achieve before.”

The researchers subjected a solution of zinc nitrate and HMTA (hexamethylenetetramine) to different temperatures and pressures inside a custom-built microreactor device to induce ZnO nanowire growth, observing the reactions with XANES spectroscopy at the Materials Research Collaborative Access Team (MR-CAT) beamline 10-ID at the Advanced Photon Source. Baxter points out a particular advantage of XANES for the current work:“It also has good enough time resolution that we could actually watch the reaction proceeding in time. Every minute we could take a new set of data and look at thekineticsof the reaction.”

One open question the researchers sought to address was the specific role of HMTA in the ZnO CBD process. Previous work had suggested that HMTA might break down into intermediate forms that provided the raw materials for the ZnO film, perhaps even binding to zinc ions in the solution, or that it might act simply as a pH buffer to facilitate the reactions.

This firstin situview afforded by the XANES technique demonstrated that HMTA decomposes slowly under heating, releasing hydroxide ions that react with zinc ions in the formation of ZnO. This slow release of hydroxides also has the effect of minimizing ZnO saturation and thus controlling the solution pH.

“HMTA releases the hydroxide at the appropriate rate, just at the borderline where you’re primarily growing zinc oxide on the substrate with minimal precipitation,” says Baxter.

The team observed the growth of ZnO nanowires from zinc nitrate and HMTA precursors at 90° C after two hours, with typical hexagonal cross-sections and diameters of 300-500 nm.

They also employed principal component analysis (PCA) techniques to obtain quantitative data on the observed species during the CBD process. This showed that the ZnO nanowire growth occurred through direct crystallization from the precursor materials without any long-lived intermediates. The pH buffering provided by the HMTA helps to avoid overabundant precipitation of ZnO in the solution, allowing the controlled growth of the nanowire structures.

These new insights into the mechanisms of CBD will encourage the development of better-controlled and more precise chemical synthesis techniques for semiconductor and other nanomaterial applications.

The work is also valuable as a demonstration of the extension of XANES spectroscopy into other realms.

“I think the more widely useful part of this paper is actually in the application of XANESspectroscopyto a new type of system,” said Baxter.

He and his team plan to extend their work to study other CBD chemistries and processes.“You can actually see what’s happening as it is growing,” he said.“It gives one a lot of information about the process. I think that’s the exciting part.”

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Microreactor speeds nanotech particle production by 500 times

Engineers at Oregon State University have discovered a new method to speed the production rate of nanoparticles by 500 times, an advance that could play an important role in making nanotechnology products more commercially practical.

The approach uses an arrayed microchannel reactor and a"laminated architecture"in which many sheets, each with thousands of microchannels in them, are stacked in parallel to provide a high volume of production and excellent control of the processes involved.

Applications could be possible in improved sensors, medical imaging, electronics, and evensolar energyor biomedical uses when the same strategy is applied to abundant materials such as copper, zinc or tin.

A patent has been applied for, university officials say. The work, just published in the journalNanotechnology, was done in the research group of Brian Paul, a professor in the OSU School of Mechanical, Industrial and Manufacturing Engineering.

"A number of new and important types ofnanoparticleshave been developed with microtechnology approaches, which often use very small microfluidic devices,"said Chih-hung Chang, a professor in the OSU School of Chemical, Biological and Environmental Engineering, and principal investigator on the study.

"It had been thought that commercial production might be as simple as just grouping hundreds of these small devices together,"Chang said."But with all the supporting equipment you need, things like pumps and temperature controls, it really wasn't that easy. Scaling things up to commercial volumes can be quite challenging."

The new approach created by a research team of five engineers at OSU used amicroreactorwith the new architecture that produced"undecagold nanoclusters"hundreds of times faster than conventional"batch synthesis"processes that might have been used.

"In part because it's faster and more efficient, this process is also more environmentally sensitive, using fewer solvents and less energy,"Chang said."This could be very significant in helping to commercialize nanotech products, where you need high volumes, high quality and low costs."

This research, Chang said, created nanoparticles based on gold, but the same concept should be applicable to other materials as well. By lowering the cost of production, even the gold nanoclusters may find applications, he said, because the cost of the gold needed to make them is actually just a tiny fraction of the overall cost of the finished product.

Nanoparticles are extraordinarily tiny groups of atoms and compounds that, because of their extremely small size and large surface areas, can have unusual characteristics that make them valuable for many industrial, electronic, medical or energy applications.

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A wide range of nano-coatings in a few spray applications

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Easy-to-use nano-coating sprays with optical, electronic, biological properties, etc to cover surfaces. French teams from the Institut Charles Sadron and the Laboratoire de Biomateriaux et Ingenierie Tissulaire, have managed to improve and extend their technique of"layer by layer"deposition. This scientific synergy has led to the development of a very wide range of nano-coatings with new and varied applications that will doubtless be of great interest to industry. Their work was published online on 23 November 2010 on the site of the journal<i>Angewandte Chemie International Edition</i>.

Contact lenses, cars, non-stick saucepans or stickers: numerous objects in our daily lives have coatings with specific functions. Over fifteen years ago, Gero Decher invented a novel method of depositing nano-materials in the form ofthin films. The principle of this technique simply consists in“stacking”, with nanometric precision, layers whose structure and chemical functionalities are controlled by the sequence and nature of the constituents incorporated in the film (polymers, pigments, proteins, particles, etc.). This“layer-by-layer” method makes it possible to produce materials with extremely varied properties. Neither costly nor polluting, this process ranks among the ten most important results in chemistry over the last decade.

Recently, teams of chemists and physical chemistry specialists, headed by Gero Decher and Pierre Schaaf of the Institut Charles Sadron, have succeeded in making this deposition method even more powerful and easy to apply. Initially, the technique required successive dippings in different liquids and long deposition times. Now, using two bottles, the scientists can simultaneously spray two liquids on a surface to be coated. Time saving and logistical advantages are considerable.

Better still, this original method applies to a whole range of nano-coatings, including completely new classes of materials, such as purely inorganic films. The already wide range of applications of these thin films has therefore been further extended. The nano-coatings obtained by these various deposition methods have many applications in materials science: light emitting diodes, fuel cells, photovoltaic cells, anti-corrosion coatings, flexible screens, separation membranes, etc.

Furthermore, the introduction of biologically active molecules (peptides, enzymes, medicines, proteins, DNA, cells, etc.) within these films makes it possible to obtain nano-coatings that have numerous applications in life sciences: biocompatibility of implants, preparation of dressings, tissue engineering, gene transfection, pharmaceutical vectors, bio-sensors, etc. This host of applications is likely to meet industry's objectives to cut production costs, invest in sustainable product development and extend product ranges. In short, this innovative nano-assembly method makes it possible to envisage the elaboration of a large number of (bio)-materials or products that do not yet exist.

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All sprayed at once: Ultrathin coatings made through simultaneous spraying of interacting substances

(PhysOrg.com) -- Coatings functionalize surfaces or protect them from processes such as corrosion, abrasion, and weathering, and may provide an aesthetic appearance—automotive coatings and non-stick frying pans are good examples. Contact lenses, implants, LEDs, or photovoltaic cells require extremely thin coatings.

In the journalAngewandte Chemie, the teams led by Gero Decher at the Institut Charles Sadron in Strasbourg (France) have now introduced a new process for the production of ultrathin coatings that is especially simple, versatile, and suitable for large-scale processes.

A simple yet powerful method for the assembly of nanoscale films is the already well-known layer-by-layer technique. Two mutually interacting species, for example positively and negatively charged polymers, are consecutively adsorbed from solution, forming hybrid thin films through a self-organization process. One major improvement to this method was introduced with the technique of spray-assisted deposition, in which atomized mists of solutions containing each of the two substances are sprayed on asurfacein an alternating fashion. This accelerates the process and facilitates scaling up to industrial levels.

The French–German researchers led by Decher and Pierre Schaaf at the Centre National de la Recherche Scientifique and Jean-Claude Voegel at the Institut National de la Santé et de la Recherche Médicale have now been able to make another substantial improvement to this technique: In“simultaneous spraycoatingof interacting species” (SSCIS), the two complementary components are not applied consecutively, but are simultaneously sprayed against a receiving surface. Depending on the process conditions, the partner substances rapidly form a continuous layer. The thickness of the film is controlled by changing the spraying time and can range from a few nanometers to a few micrometers. This results in highly homogenous coatings that can even possess optical quality.

The one-step process is cheap, robust, user-friendly, and unbelievably versatile. In principle, all pairs of substances that interact with each other, such as inorganic ions of opposite charge, are suitable for use with the simultaneous spray process. It is thus possible to produce films of calcium fluoride (for optical components) or deposits of calcium phosphate (for use in biomaterials).

Interestingly, the new technique also works with pairs that do not produce intact layers when the conventional layer-by-layer process is used. Thus the presented results open up a wealth of new possibilities to produce surfaces with tailored specific functionalities, for example for catalysis, to make implants more biocompatible or for tissue engineering.

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Risk review suggests that carbon nanotubes be treated, for now, 'as if' hazardous

(PhysOrg.com) -- In a new paper published by the Society for Risk Analysis, a UC Berkeley researcher argues for caution when dealing with carbon nanotubes. Because environmental and health information on carbon nanotubes is incomplete and sometimes conflicting, an"anticipatory governance"approach to the technology is needed, says post-doc researcher Mark Philbrick.

While offering great promise in a host of new applications, carbon nanotubes (CNTs) could be harmful to humans and a new risk review suggests that product designers and others should provisionally treat CNTs"as if"they are hazardous.

Carbon nanotubes are extremely small, with a diameter measured in nanometers. A nanometer is one-billionth of a meter, or about one eighty-thousandth the thickness of a human hair. CNTs are very versatile and come in several forms, conferring great strength while also being very light.

Because environmental andhealth informationon CNTs is incomplete and sometimes conflicting, an“anticipatory governance” approach to the technology is needed, according to Mark Philbrick, post-doctoral researcher at the Center of Integrated Nanomechanical Systems at the University of California, Berkeley. Anticipatory governance is an approach designed to support decision makers where there is uncertainty about safety, a common situation when managing emerging technologies.

The research was funded by the National Science Foundation and the conclusions are detailed in Philbrick's article“An Anticipatory Governance Approach to Carbon Nanotubes,” in the November issue of the journalRisk Analysispublished by the Society for Risk Analysis. The entire November issue is devoted to risk analysis articles related to nanotechnology.

An anticipatory approach is particularly important until the toxicity and behavior of CNTs in the environment are better understood, especially as they can remain airborne for extended periods, and share some characteristics with asbestos. While a few rodent studies have found similarities between the health effects of inhaling both substances, there is not enough data to draw firm conclusions.

The article notes the promise held out by CNTs is immense: some types conduct electricity and heat better than copper, others are stronger than steel while weighing less than aluminum, and yet others could be used in targeted drug delivery. These properties could find uses in aircraft frames, sensors, and electrical transmission. Nevertheless, treating them“as if” they are hazardous is a prudent course of action given uncertainty about their potential health consequences, the author said.

Given the“conflicted character of the data,” how“relevant actors” should respond is the central question Philbrick asks in developing strategies for utilizing CNTs. He asserts that treating carbon nanotubes“as if” they are hazardous implies limiting exposure throughout product life-cycles. This means implementing strong engineering controls for CNT research and manufacturing, avoiding applications where the CNTs would be routinely released to the environment, and planning for recycling at the end of a product’s useful life. The article also argues that“the anticipatory governance approach is particularly important as innovation rates in nanotechnologies exceed our capacity to assess human and environmental consequences of these innovations, especially when deployed at commercial scales… it helps identify uncertainties in our knowledge and focuses future research to address those gaps."

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Scientists imitate nature to engineer nanofilms

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In nature, water striders can walk on water, butterflies can shed water from their wings, and plants can trap insects and pollen. Scientists at the Naval Research Laboratory are part of a research team working to engineer surfaces that imitate some of these water repellency features found in nature.

This technology offers the possibility of significant advances for producing new generations of coatings that will be of great value for military, medical, and energy applications. The research is published in the December 2010 issue ofNature Materials.

Dr. Walter Dressick from NRL, working with Professor Melik Demirel of Penn State and Dr. Matthew Hancock of MIT, have collaborated to create an engineered water-repellant thin film. What sets this development apart from earlier technologies is that this newest film has the ability to control the directionality of liquid transport.

In this system, parylene nanorods are deposited on the surface by a simple, straightforwardvapor depositionmethod. The single step usually takes less than 60 minutes, compared with the more complex, multi-step lithography processes often used in previous systems. This is the first time this kind of surface has been engineered at the nanoscale.

In the newly created surface, the nanorods that form the film are smooth on a micron scale. This size and smoothness in the posts means that when droplets are placed on the surface, they move without being distorted in any way. Also, they can be moved without pumps or optical waves. Previous systems caused thewater dropletsto be distorted, which could rupture, spill, or destroy the cargo in the droplet when used in medical or microassembly applications. As they continue the research, the team will focus on optimizing the droplet transport mechanism and tuning the preparation method.

Looking to the future, researchers are hopeful that this film could be used as a coating on the hull of ships where it would reduce the drag and slow the fouling. In industry applications, the film might have uses in directional syringes and fluid diodes, pump-free digital fluidic devices, increased efficiency of thermal cooling for microchips, and tire coatings.

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Doctoral candidate publishes on graphene's potential

Since graphene was first isolated in 2004 with the help of Scotch tape, researchers have excitedly turned to the material to discover its potential applications. A single layer of carbon atoms whose applications range from ultrafast electronics to biosensors to flexible displays, graphene is strong, light, transparent, and a conductor of heat and electricity. But what can we do with this new material? As researchers across the globe peel away layer after layer of potential application, Milan Begliarbekov, a doctoral candidate at Stevens Institute of Technology, has found some unique applications for this distinctive material.

Graphene is charged with possibilities for Milan. With the help of a world-class Stevens faculty, support from the National Science Foundation (NSF) Graduate Teaching Fellows in K-12 Education (GK-12) program through the New Jersey Alliance for Engineering Education (NJAEE), and an award from the Air Force Office of Scientific Research (AFOSR), Milan is conducting groundbreaking research of the material. He has already published two papers ongrapheneinApplied Physics Lettersin pursuit of his Ph.D. and has a third paper in the pipeline. Both published articles have also been selected for theVirtual Journal of Nanoscale Science and Technology.

His first published article,"Determination of edge purity in bilayer graphene usingµ-Raman spectroscopy,"confirms a technique for differentiating between monolayer and bilayer graphene, and introduces a new method to quantify the composition of graphenes chiral edges throughµ-Raman spectroscopy.

Milan's second article,"Aperiodic conductivity oscillations in quasiballistic graphene heterojunctions,"establishes a new signature of Klein tunneling in graphene heterojunctions. The research has applications in nanolectronics such as graphene field effect transistors (GFET), which have been shown to be capable of ultra-high frequency (300 GHz) operation.

Milan's next article, yet to be published, is"Quantum Inductance and High Frequency Oscillators in Graphene Nanoribbons."The paper proposes a novel technique for measuring the speed of ultra-high frequency transistors. Currently it is very difficult to measure ultra-high-frequency signals above 40 GHz by purely electronic means. However, Milan's research indicates that graphene nanoribbons can serve as all-electronic ultra-high frequency oscillators and filters, which would extend the possibilities of high-frequency electronics into new realms.

Since graphene planes were first isolated, much research has focused on the material's applications in nanoelectronics, due to its high electrical conductivity. But researchers at Stevens have taken a different approach, pioneering applications of this unique material in optics. Milan's research represents a fine example of this innovative thinking.

As he works with a material whose greatest applications may still be unrealized, Milan says he enjoys the level of creativity he is afforded in exploring graphene's possibilities."I like working with Professor Strauf, because of the freedom he gives me to choose my own research projects,"Milan says."He allows me to explore things I find interesting, rather than asking me to work on a pre-defined research objective."

"Given that the our team just started two years ago to work with graphene in a collaboration with Professor Yang's group from the Mechanical Engineering Department, Milan's research success is quite remarkable,"says Dr. Stefan Strauf, Assistant Professor of Physics and Engineering Physics (PEP) and Director of the Nanophotonics lab."Milan is one of these unique graduate students you would like to clone into a dozen in your lab in order to implement all of his ideas."

The exploration of ideas has also led to the creation of a system that utilizes graphene's unique reaction to light. Working with Stevens faculty Dr. Stefan Strauf and Dr. Chris Search, who is also an Assistant Professor of PEP, Milan is determined to convert new ideas into patentable technology."We are pleased to announce that with the help of the Office of Academic Entrepreneurship, Milan is in the process of applying for a patent with a novel application of graphene that exploits its near-perfect efficiency as aconductor,"says Dr. Christos Christodoulatos, Professor and Associate Provost of Academic Entrepreneurship.

In addition to the AFOSR grant, Milan was also supported by the NSF GK-12 program through NJAEE. As an NJAEE fellow from 2008 to 2010, Milan worked alongside teacher mentors in local high school classrooms to expose younger students to cutting edge science and engineering research. The GK-12 program was established to support the NSF's goal of enhancing science, technology, engineering, and mathematics (STEM) curriculums for K-12 teachers and students."The NJAEE program provides a unique opportunity for graduate students to enhance their teaching and communication skills, instills in them the spirit of innovation and entrepreneurship, and at the same time provides them a forum to share their passion and enthusiasm for science and engineering with younger students,"says Dr. Frank Fisher, Associate Professor of Mechanical Engineering and co-Director of the Stevens Nanotechnology Graduate Program who is a co-PI on the NJAEE project."Milan was just fantastic as a NJAEE Fellow, and has recently been able to apply these skills as an instructor in the Physics department here at Stevens as well as Queensborough Community College of CUNY."

The patent and papers are the most recent examples of Milan's success at Stevens. As an undergraduate at Stevens, Begliarbekov took advantage of both the Charles V. Schaeffer, Jr. School of Engineering and Sciences and what would become the College of Arts and Letters to graduate with two degrees, a B.S. in Physics and a B.A. in Literature. Having taken graduate-level courses in nanotechnology as an undergraduate,"I was already ahead of the curve,"he says, when it came to searching for a graduate program.

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What changes will nanoelectronics bring to our lives?

We are surrounded by nanoelectronics through products such as computers, mobile phones, sensors and electric cars. Nanoelectronics may also grow much stronger in the energy efficiency area in the near future. However, the sustainable growth faces several challenges.

Innanoelectronics, miniaturisedelectronic circuitsare integrated on semiconductor chips where the basic element is the transistor. The size of the transistors produced is under 100 nm. Andreas Wild is Executive Director of the ENIAC JU. The task of this public-private partnership is to coordinate European research in nanoelectronics. He sees many interesting changes coming with the evolution of nanoelectronics.

“We have little electronics in the buildings, but the buildings are huge energy consumers. There will be an influx of nanoelectronics that will completely change the ways we are living in and using buildings, making them energy self-consistent, extremely comfortable and adaptable to the needs of the people. The buildings will be able to read how many people are inside, what are they doing, then adjust everything and also give the people a human interface to express their wishes. Rather than pilot projects this will be the norm. Europe has already issued regulations. I believe in the next five to ten years nobody will construct a building that haven’t got these features.”

Laurent Malier, CEO of the research center CEA-Leti in France, highlights another area where nanoelectronics may be prominent.“What we are going to explore more are nanoelectronic devices for biology and healthcare. It could be easy and low cost diagnostics. This is an area of growth in a large perspective,” he said.

The sustainable growth of nanoelectronics faces several challenges.“You see technological challenges, materials, processes and so forth. You see design challenges, how to put together billions of components quickly, reliably and predictably. Then there are systemic challenges, what are the functions that all these billions oftransistorsare supposed to achieve on every chip and how do they relate to the everyday life of the people using the devices,” Wild said.

Malier sees additional challenges.“One is the compromise between low electrical power consumption and very fast processing capability. The other one is lithography, the capability to reduce the size of features. The third one is to increase complexity with either 3D integration, stacking chips on each other, or integration of new functions.”
We are dependent on nanoelectronic devices and soon we might see a drastic reduction in our energy consumption thanks to the advances in this area.

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Secrets of nanohair adhesion un-peeled by UA polymer scientists

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Not long after Dr. Ali Dhinojwala, chairman of The University of Akron Department of Polymer Science, unpeeled the secret (fine, clingy hairs) behind the remarkable adhesion of gecko feet, he and fellow researchers came up with a synthetic replica: carbon nanotubes. Now, five years after that initial discovery, the basis of the success of these nanotubes is published in the Oct. 12, 2010, issue of the American Chemical Society’s<i><a href="http://pubs.acs.org/doi/pdf/10.1021/nl102398w">Nano Letters</a></i>.

While the story of nanotubes is one of success, not all carbon nanotubes are equal, nor is the individual adhesion performance of each strand, according to Dhinojwala. Although Dhinojwala and UApolymerscience graduate student Liehui Ge determined that these 8-nanometer-diameter carbon hairs— each 2,000 times smaller than the diameter of a human hair— adhere powerfully to glass and similar substrates, they furthered their research to learn why some strands have a firmer grip than others.

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Getting a grip on adhesion

Findings by the UA scientists, in collaboration with Lijie Ci and Anubha Goyal, researchers with the Department of Mechanical Engineering and Materials Science at Rice University; Rachel Shi, UA Research Experience for Undergraduates (REU) intern; and L. Mahadevan, professor of applied mathematics and professor of organismic and evolutionary biology at Harvard University, reveal that the softer the nanotube, the greater its adhesion.

Using a combination of mechanics, electrical resistance and scanning electron microscopy (SEM) to study the contact between hairs of a large number of vertically aligned carbon nanotubes with glass or silicon substrates, the researchers found that soft nanotubes clasp and curve when pressure is applied, contributing to their adhesive strength.

“We found out that the diameter of the tubes is an important parameter for adhesion because we have to balance the adhesion and bending rigidity of the tubes,” Ge says.“Also, if you apply a high pressure, the tubes bend and buckle and make a larger contact area with the surface, which is the reason for higheradhesion.”

The dry adhesive, unlike liquid glue counterparts, promises successful use in extreme atmospheric and temperature conditions and in other applications that present challenges.

“The carbon nanotube-based gecko adhesives are going to open up opportunities to using these materials on robots, to climb vertical walls, and could actually be used in outer space (vacuum condition) because these materials stick without any liquid glue,” Dhinojwala says.

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DNA can act like Velcro for nanoparticles

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DNA can do more than direct how bodies our made -- it can also direct the composition of many kinds of materials, according to a new study from the U.S. Department of Energy’s Argonne National Laboratory.

Argonne researcher Byeongdu Lee and his colleagues at Northwestern University discovered that strands of DNA can act as a kind of nanoscopic"Velcro"that binds differentnanoparticlestogether."It’s generally difficult to precisely control the assembly of these types of nanostructures,"Lee said."By using DNA, we’re borrowing nature's power."

The"Velcro"effect of the DNA is caused by the molecule’s"sticky ends,"which are regions of unpaired nucleotides— the building blocks of DNA— that are apt to bond chemically to their base-pair partners, just like in our genes. When sufficiently similar regions contact each other, chemical bonds form a rigid lattice. Scientists and engineers believe these complex nanostructures have the potential to form the basis of new plastics, electronics and fuels.

In 2008, Lee and his colleagues attached DNA to spherical nanoparticles made of gold, hoping to control the way the particles arrange themselves into compact, ordered crystals. This process is called nanoparticle"packing,"and Lee believed that by affixing DNA to the nanoparticles, he could control how they packed together."Materials that are packed differently— even if they are made from the same substance— have been shown to exhibit dramatically different physical and chemical properties,"Lee said.

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While the 2008 experiment showed that DNA appeared to control that instance of nanosphere packing, it was not known whether the effect would occur with different nanoparticle geometries. The more recent experiment looked at different shapes of nanoparticles to determine whether their contours affected how they packed.

According to Lee, the spherical nanoparticles in the earlier experiment tended to arrange themselves into one of two separate types of cubic crystals: a face-centered cube (a simple cube with nanospheres at each vertex and additional ones located in the middle of each face) or a body-centered cube (a simple cube with an additional nanosphere located in the middle of the cube itself). The type of lattice that the nanoparticles formed was determined by how the"sticky ends"attached to the nanoparticles paired together.

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In the more recent experiment, the particles' shape did change the material's final structure, but only insofar as it altered how the DNA"sticky ends"attached to each other. In fact, the study showed that dodecahedral (12-sided) nanoparticles arranged into a face-centered cubic configuration while octahedral (8-sided) nanoparticles formed body-centered cubes— even when the nanoparticles were attached to identical strands of DNA."We may be able to make all different types of nanoparticle packing structures, but the structure that will result will always be the one that maximizes the amount of binding,"he said.

"The face-centered cubic structure is the most compact way for the nanoparticles to arrange themselves, while the body-centered cubic is slightly less compact. TheDNAbinding is really the true force controlling the construction of the lattice,"he added.

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A new twist for nanopillar light collectors

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Sunlight represents the cleanest, greenest and far and away most abundant of all energy sources, and yet its potential remains woefully under-utilized. High costs have been a major deterrant to the large-scale applications of silicon-based solar cells. Nanopillars– densely packed nanoscale arrays of optically active semiconductors– have shown potential for providing a next generation of relatively cheap and scalable solar cells, but have been hampered by efficiency issues. The nanopillar story, however, has taken a new twist and the future for these materials now looks brighter than ever.

“By tuning the shape and geometry of highly ordered  nanopillar arrays of germanium or cadmium sulfide, we have been able to drastically enhance the optical absorption properties of our nanopillars,” says Ali Javey, a chemist who holds joint appointments with the Lawrence Berkeley National Laboratory (Berkeley Lab) and the University of California (UC) at Berkeley.

Javey, a faculty scientist with Berkeley Lab’s Materials Sciences Division and a UC Berkeley professor of electrical engineering and computer science, has been at the forefront of nanopillar research. He and his group were the first to demonstrate a technique by which cadmium sulfide nanopillars can be mass-produced in large-scale flexible modules. In this latest work, they were able to produce nanopillars that absorb light as well or even better than commercial thin-film solar cells, using far less semiconductor material and without the need for anti-reflective coating.

“To enhance the broad-band optical absorption efficiency of our nanopillars we used a novel dual-diameter structure that features a small (60 nanometers) diameter tip with minimal reflectance to allow more light in, and a large (130 nanometers) diameter base for maximal absorbtion to enable more light to be converted into electricity,” Javey says.“This dual-diameter structure absorbed 99-percent of incident visible light, compared to the 85 percent absorbtion by our earlier nanopillars, which had the same diameter along their entire length.”

Theoretical and experimental works have shown that 3-D arrays of semiconductor nanopillars– with well-defined diameter, length and pitch– excel at trapping light while using less than half the semiconductor material required for thin-film solar cells made of compound semiconductors, such as cadmium telluride, and about one-percent of the material used in solar cells made from bulk silicon. But until the work of Javey and his research group, fabricating such nanopillars was a complex and cumbersome procedure.

Javey and his colleagues fashioned their dual diameter nanopillars from molds they made in 2.5 millimeter-thick alumina foil. A two-step anodization process was used to create an array of one micrometer deep pores in the mold with dual diameters– narrow at the top and broad at the bottom. Gold particles were then deposited into the pores to catalyze the growth of the semiconductor nanopillars.

“This process enables fine control over geometry and shape of the single-crystalline nanopillar arrays, without the use of complex epitaxial and/or lithographic processes,” Javey says.“At a height of only two microns, our nanopillar arrays were able to absorb 99-percent of all photons ranging in wavelengths between 300 to 900 nanometers, without having to rely on any anti-reflective coatings.”

The germanium nanopillars can be tuned to absorb infrared photons for highly sensitive detectors, and the cadmium sulfide/telluride nanopillars are ideal forsolar cells. The fabrication technique is so highly generic, Javey says, it could be used with numerous other semiconductor materials as well for specific applications. Recently, he and his group demonstrated that the cross-sectional portion of the nanopillar arrays can also be tuned to assume specific shapes– square, rectangle or circle– simply by changing the shape of the template.

“This presents yet another degree of control in the optical absorption properties of nanopillars,” Javey says.

Javey’s dual-diameter nanopillar research was partially funded through the National Science Foundation’s Center of Integrated Nanomechanical Systems (COINS) and through Berkeley Lab LDRD funds.

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New possibilities for solar energy with molecular 'stencils'

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Scientists at the U.S. Department of Energy’s Argonne National Laboratory have begun to use molecular"stencils"to pave the way to new materials that could potentially find their way into future generations of solar cells, catalysts and photonic crystals.

Researchers at Argonne’s Center for Nanoscale Materials and Energy Systems Division have developed a technique known as sequential infiltration synthesis (SIS), which relies on the creation of self-assembled nanoscale chemical domains into which other materials can be grown. In this technique, a film composed of large molecules called block copolymers acts as a template for the creation of a highly-tunable patterned material.

This new method represents an extension of atomic layer deposition (ALD), a popular technique for materials synthesis that is routinely used by Argonne scientists. Instead of just layering two-dimensional films of differentnanomaterialson top of one another, however, SIS allows scientists to construct materials that have much more complex geometries.

“This new technique allows us to create materials that just weren’t possible with ALD or block copolymers alone,” said Seth Darling, an Argonne nanoscientist who helped to develop SIS in collaboration with Argonne chemist Jeff Elam.“Having the ability to control the geometry of the material we’re making as well as its chemical composition opens the door to a whole universe of new materials.”

According to Darling, the success of the technique relies on the unique chemistry of block copolymers. Every block copolymer is composed of two chemically distinct subunits; for instance, one subunit might have an affinity for water while the other might repel water. In such a case, like would seek out like, creating a heterogeneous matrix of interspersed homogenous regions.

“You can think of a block copolymer as like a pair of molecular Siamese twins where one likes to talk and one likes to read quietly,” Darling said.“If you put a bunch of these twins together in a room, the talkative ones are going to try to be near the talkative ones and the readers are going to try to be near the readers, but they can’t simply all separate themselves to either side of the room, and it’s this action that gives us the geometries we’re looking for.”

Depending on the initial substrate, the block copolymers, and the processing that materials scientists use, regions can form that have many different shapes, from spherical to cylindrical to planar. While there are many types of block copolymers, in general they cannot serve as wide an array of purposes as inorganic materials. The challenge, according to Darling, is to bring the self-assembly of block copolymers together with the functionality of inorganic materials.

The physical and chemical properties of a material generated using SIS depend on how block copolymer chemistry and morphology interact with the chemistry of ALD techniques.“We can tailor our materials synthesis efforts in a much more precise way than we ever could before,” Darling said.

Darling and Elam have spent most of their careers at Argonne focused on the development of new types of materials, including the development of solar cells that combine organic and inorganic components. They believe that the types of materials that SIS can generate will drive fundamental solar energy technologies to greater efficiencies and lower cost.

“Oursolar energyfuture does not have a one-size-fits-all solution,” Elam said.“We need to investigate the problem from many different angles with many differentmaterials, and SIS will give researchers like us many new routes of attack.”

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Ultrafast imaging of electron waves in graphene (w/ Video)

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The fastest"movies"ever made of electron motion have been captured by researchers using the U.S. Department of Energy’s Advanced Photon Source (APS) at Argonne and the Frederick Seitz Materials Research Laboratory at the University of Illinois at Urbana-Champaign (UIUC). The movies, which were created by scattering x-rays off of graphene, show that the interaction among graphene’s electrons is surprisingly weak.

Using inelastic x-ray scattering experiments at the X-ray Science Division 9-ID x-ray beamline at the APS, physicists from UIUC imaged the motion of electrons ingraphenewith resolutions of 0.533Å and 10.3 attoseconds. Their results were published in the November 5 issue ofScience.

Exactly how small and how fast are these measurements? An angstrom is 1/10,000,000,000 of a meter, about the width of a hydrogen atom. And an attosecond is to a second as a second is to the age of the Universe.

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Animation of n(x,y,t) at two different vertical scales.

The 2010 Nobel Prize for Physics was awarded to Andre Geim and Konstantin Novoselov for their work on graphene, a single-atom-thick sheet of carbon atoms arrayed in a honeycomb pattern that exhibits many intriguing properties, including great strength, flexibility, excellent electrical conductivity, and heat resistance. As a result, graphene is a candidate material for a wide range of applications, including a new generation of low-cost, flexible electronics. A major outstanding question about this material is whether the electrons in graphene move independently, or if their motion is correlated by Coulomb repulsion.

The researchers in this study found that graphene screens Coulomb interactions surprisingly effectively, causing it to act like a simple, independent-electron semimetal. Their work explains several mysteries, including why freestanding graphene fails to become an insulator as predicted. The study also demonstrates a new approach to studying ultrafast dynamics, creating a new window on the most fundamental properties of materials.

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A greener way to grow carbon nanotubes

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Given their size, strength and electrical properties, carbon nanotubes— tiny, hollow cylinders made of carbon atoms— hold promise for a range of applications in electronics, medicine and other fields. Despite industrial development of nanotubes in recent years, however, very little is known about how they form or the environmental impacts of their manufacture.

It turns out that one process commonly used to produce carbon nanotubes, or CNTs, may release several hundred tons of chemicals, including greenhouse gases and hazardous air pollutants, into the air each year. In a paper published last week on theACS Nanowebsite, the researchers report that in experiments, removing one step in that process— a step that involves heating carbon-based gases and adding key reactive“ingredients”— reduced emissions of harmful by-products at least tenfold and, in some cases, by a factor of 100. It also cut the amount of energy used in the process by half.

“We were able to do all of this and still have good CNT growth,” says Desiree Plata, who led the research between 2007 and 2009 as a doctoral student in MIT’s joint program with the Woods Hole Oceanographic Institution. Now a visiting assistant professor in MIT’s Departments of Aeronautics and Astronautics and Civil and Environmental Engineering (CEE), Plata collaborated on the paper with several MIT and University of Michigan researchers, including Philip Gschwend, Ford Professor of Engineering in CEE, and John Hart, a mechanical engineering professor at the University of Michigan. The study is part of a long-term effort to change the approach to material development so that environmental chemists work with the young CNT industry to develop methods to prevent or limit undesirable environmental consequences.

In their study, Plata and her colleagues analyzed a common CNT manufacturing process known as catalytic chemical vapor deposition. In this method, manufacturers combine hydrogen with a“feedstock gas,” such as methane, carbon monoxide or ethylene. They then heat the combination in a reactor that contains ametal catalystlike nickel or iron, which then forms CNTs. The problem is that once the CNTs form, unreacted compounds (up to 97 percent of the initial feedstock) are often released into the air.

Turning off the heat

In a custom-made laboratory-scale reactor, the researchers heated hydrogen and ethylene, which is commonly used in high-volume CNT manufacturing, and then delivered it to a metal catalyst. They found that more than 40 compounds formed, including greenhouse gases like methane and toxic air pollutants like benzene.

The researchers suspected that not all of those compounds were essential for growing CNTs, and they knew that heating the feedstock gas plays a critical role in creating the dangerous compounds. So they combined unheated ethylene and hydrogen with several of the 40 compounds, one by one, to see which combination of compounds led to the best growth. They observed that certain alkynes, or molecules that have at least two carbon atoms stuck together with three distinct bonds, produced the best growth, while other compounds that are undesirable by-products, such as methane and benzene, did not.

Plata and her colleagues accomplished their dramatic reduction in both harmful emissions and energy consumption by impinging room-temperature alkynes, with ethylene and hydrogen, directly onto the metal catalyst, without heat. They also learned that they could reduce the amount of ethylene and hydrogen used by about 20 and 40 percent, respectively, and still achieve the same rate and quality of CNT growth. Plata says that while the results of lab experiments are hard to generalize, in a market that is expected to reach several billion dollars within several years, these changes could translate into“significant cost savings” for manufacturers.

Industry reaction

Although it’s too soon for manufacturers to adopt the method presented in the paper, David Lashmore, vice president and chief technology officer of Concord, N.H.-based Nanocomp Technologies, says the method is something his company is willing to try as it looks for ways to minimize the environmental effects of its production process.“This is of high interest to us and could have a broad impact on our process economics,” he says.

Plata points out that the MIT study analyzed only one of several feedstock gases used to make CNTs, and that the same analysis needs to be done for the others. But for her own part, she is now focusing on how CNTs form, trying to determine the precise interaction of the metal catalyst and the hydrocarbons in this process. Knowing the catalyst’s role could help researchers manipulate CNTs’ formation atom by atom— much more precisely than they can now, she says.

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This story is republished courtesy of MIT News (http://web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

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Nobel Prize for Physics is 'wine from vines that took a decade to plant,' says Geim

As joint-winner of this year’s Nobel Prize for Physics - awarded for the creation of the 'wonder material' graphene - Andre Geim has become a 'poster boy' for the success of UK physics.

In an exclusive interview for November’s Physics World, Geim, who moved to the UK in 2001, outlines his remarkably positive views on UK research funding, singling out former science minister Lord Sainsbury as a key architect in securing support for a strong UK science base.

Geim and his Manchester University colleague Konstantin Novoselov are the first UK-based physicists to win the Nobel Prize for Physics since Nevill Mott in 1977, thanks to their isolation ofgraphene- a sheet of crystalline carbon just one atom thick whose remarkable electronic properties make it ripe for commercial exploitation.

Samsung, the electronics giant, is already considering the material for use as a transparent conductive material in their touch screen technology, while researchers around the world are jumping on the bandwagon to explore other applications for which the material’s lightweight strength and conductivity could make it ideal.

Geim enthuses about the huge amount of research his discovery triggered:“It’s like a line of people going through a mountain pass to a new place to dig for gold. Every one of them has a rucksack full of wooden stakes to put in the ground to claim their patch.”

Geim also provides some insight into why he believes the UK is well-poised for more scientific success.

As he says:“I’m scared for the moment when I next have to apply for a grant and a referee will decide that he can teach a lesson to a Nobel laureate. In the UK, your previous achievements are no guarantee of future funding and I accept, and actually salute, this system because it forces people to keep running.”

When asked who should take the credit for getting things right in UK science, Geim singles out Lord Sainsbury, who he says was"exceptionally helpful"to UK science during his spell as science minister from 1998 to 2006.

"Thanks to him, it is no longer the case that when you have visitors to your university, you are ashamed to show them your facilities or even the bathroom. Sainsbury's efforts on funding have paid off with thisNobel prize-- it is the first glass of a Nobel wine from vines that took a decade to plant.”

Geim, who calls for research to be restricted to just the UK's top 50 universities while leaving the others to focus on teaching, is cautiously optimistic about the future."There is more to come,"he says."But there is a danger that with a sharp axe a decade of work can be destroyed in hours. Science is very delicate: easy to destroy but very hard to repair."

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Sugar and slice make graphene real nice

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Future computers may run a little sweeter, thanks to a refinement in the manufacture of graphene at Rice University.

Rice researchers have learned to make pristine sheets ofgraphene, the one-atom-thick form of carbon, from plain tablesugarand other carbon-based substances. They do so in a one-step process at temperatures low enough to make graphene easy to manufacture.

The lab of Rice chemist James Tour reported in the online version of the journalNaturethis week that large-area, high-quality graphene can be grown from a number of carbon sources at temperatures as low as 800 degrees Celsius (1,472 F). As hot as that may seem, the difference between running a furnace at 800 and 1,000 degrees Celsius is significant, Tour said.

"At 800 degrees, the underlying silicon remains active for electronics, whereas at 1,000 degrees, it loses its critical dopants,"said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering andmaterials scienceand of computer science.

Zhengzong Sun, a fourth-year graduate student in Tour's lab and primary author of the paper, found that depositing carbon-rich sources on copper and nickel substrates produced graphene in any form he desired: single-, bi- or multilayer sheets that could be highly useful in a number of applications.

Sun and his colleagues also found the process adapts easily to producing doped graphene; this allows the manipulation of the material's electronic andoptical properties, which is important for making switching and logic devices.

For pristine graphene, Sun started with a thin film of poly (methyl methacrylate) (PMMA) -- perhaps best known in its commercial guise as Plexiglas -- spun onto a copper substrate that acted as a catalyst. Under heat and low pressure, flowing hydrogen and argon gas over the PMMA for 10 minutes reduced it to pure carbon and turned the film into a single layer of graphene. Changing the gas-flow rate allowed him to control the thickness of the PMMA-derived graphene.

Then it got more interesting, Sun said. He turned to other carbon sources, including a fine powder of sucrose -- aka table sugar."We thought it would be interesting to try this stuff,"Sun said."While other labs were changing the metal catalysts, we tried changing the carbon sources."

Sun put 10 milligrams of sugar (and later fluorene) on a square-centimeter sheet of copper foil and subjected it to the same reactor conditions as the PMMA. It was quickly transformed into single-layer graphene. Sun had expected defects in the final product, given the chemical properties of both substances (a high concentration of oxygen in sucrose, five-atom rings in fluorene); but he found potential topological defects would self-heal as the graphene formed.

"As we looked deeper and deeper into the process, we found it was not only interesting, but useful,"Sun said.

He tried and failed to grow graphene on silicon and silicon oxide, which raised the possibility of growing patterned graphene from a thin film of shaped copper or nickel deposited onto silicon wafers.

Doped graphene opens more possibilities for electronics use, Tour said, and Sun found it fairly simple to make. Starting with PMMA mixed with a doping reagent, melamine, he discovered that flowing the gas under atmospheric pressure produced nitrogen-doped graphene. Pristine graphene has no bandgap, but doped graphene allows control of the electrical structure, which the team proved by building field-effect transistors.

"Each day, the growth of graphene on silicon is approaching industrial-level readiness, and this work takes it an important step further,"Tour said.

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Graphene's strength lies in its defects

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The website of the Nobel Prize shows a cat resting in a graphene hammock. Although fictitious, the image captures the excitement around graphene, which, at one atom thick, is the among the thinnest and strongest materials ever produced.

A significant obstacle to realizing graphene's potential lies in creating a surface large enough to support a theoretical sleeping cat. For now, material scientists stitch individual graphene sheets together to create sheets that are large enough to investigate possible applications. Just as sewing patches of fabric together may create weaknesses where individual patches meet, defects can weaken the"grain boundaries"where graphene sheets are stitched together— at least that is what engineers had thought.

Now, engineers at Brown University and the University of Texas–Austin have discovered that the grain boundaries do not compromise the material's strength. The grain boundaries are so strong, in fact, that the sheets are nearly as strong as pure graphene. The trick, they write in a paper published inScience, lies in the angles at which the individual sheets are stitched together.

"When you have more defects, you expect the strength to be compromised,"said Vivek Shenoy, professor of engineering and the paper's corresponding author,"but here it is just the opposite."

The finding may propel development of larger graphene sheets for use in electronics, optics and other industries.

Graphene is a two-dimensional surface composed of strongly bonded carbonatomsin a nearly error-free order. The basic unit of this lattice pattern consists of six carbon atoms joined together chemically. When a graphene sheet is joined with another graphene sheet, some of those six-carbon hexagons become seven-carbon bonds— heptagons. The spots where heptagons occur are called"critical bonds."

The critical bonds, located along the grain boundaries, had been considered the weak links in the material. But when Shenoy and Rassin Grantab, a fifth-year graduate student, analyzed how much strength is lost at the grain boundaries, they learned something different.

"It turns out that these grain boundaries can, in some cases, be as strong as pure graphene,"Shenoy said.

The engineers then set out to learn why. Using atomistic calculations, they discovered that tilting the angle at which the sheets meet— the grain boundaries— influenced the material's overall strength. The optimal orientation producing the strongest sheets, they report, is 28.7 degrees for sheets with an armchair pattern and 21.7 degrees for sheets with a zigzag layout. These are called large-angle grain boundaries.

Large-angle grain boundaries are stronger because the bonds in the heptagons are closer in length to the bonds naturally found in graphene. That means in large-anglegrain boundaries, the bonds in the heptagons are less strained, which helps explain why the material is nearly as strong as puregraphenedespite the defects, Shenoy said.

"It's the way the defects are arranged,"Shenoy said."The grain boundary can accommodate the heptagons better. They're more relaxed."

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Swiss researchers clarify reaction pathway to fabricate graphene-like materials

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Graphene is a promising material for tomorrow’s nanoelectronics devices. Precise and upscaleable methods to fabricate graphene and derived materials with desired electronic properties are however still searched after. To overcome the current limitations, Empa researchers have fabricated graphene-like materials using a surface chemical route and clarified in detail the corresponding reaction pathway. The work has just been published in the scientific journal“Nature Chemistry“. The scientists combined empirical observations using scanning tunnelling microscopy with computer simulations.

Electronic components are getting smaller and smaller, with microelectronic components gradually being replaced by nanoelectronic ones. On nanoscale dimensions, silicon, which is at the present stage the most commonly used material in semiconductor technology, reaches however a limit, preventing further miniaturization and technological progress. New electronic materials are therefore in great demand. Due to its outstanding electronic properties,graphene, a two-dimensional carbon network, is considered as a possible replacement. However, several obstacles must be overcome before graphene can be used in semiconductor technology. For instance, currently there is no easily applicable method for large-scale processing of graphene-like materials.

Empa researchers of the nanotech@surfaces Laboratory reported on a surface chemical route to fabricate small fragments of graphene, so-called nanographenes. Using a prototypical polyphenylene precursor, the researchers clarified, together with scientists at the Max Planck Institute for Polymer Research in Mainz (Germany) and the University of Zurich, how the reaction pathway runs in detail on a copper surface und how the building blocks can be transformed into planar nanographenes directly on the surface. The work has been published last Sunday in the scientific journalNature Chemistryas an advanced online publication.

Successful partners: experiment and simulation

For their investigations the researchers combined empirical observations, in particular from scanning tunnelling microscopy with computer simulations. The simulations are used to determine whether a theoretically possible reaction step is energetically possible or not. The result: the reaction pathway consists of six steps with five intermediate products. Two of them are stabilised by the surface so that they can be stably imaged with the scanning tunnelling microscope. The reaction barriers connecting the different intermediates are lowered through a catalytic effect of the substrate.

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Computer-generated image shows details of one of the two intermediate products that the Empa researchers identified with the scanning tunnelling microscope.

To be capable of being integrated in electronic circuits, the graphene-like material must however be manufactured on semiconductor surfaces instead of metal ones. The researchers have simulated whether their approach could also work on these surfaces and the results are very promising, showing that surface-supported synthesis is a possible way to fabricate tailored nanographenes on a range of different substrates.

The three pillars of today’s science: theory, experiment, and simulation

Progress in today’s scientific research relies at the same time on theory, experiments, and to an increasing extent oncomputer simulations. These simulations are complementary to often complex lab experiments and make it possible to get further information that cannot be obtained with experimental methods alone. The combination of experiments and simulations as well as the deduced theories therefore allow for a more and more accurate explanation and precise prediction of natural phenomena.

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An engineered directional nanofilm mimics nature's curious feats

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(PhysOrg.com) -- In nature, textured surfaces provide some plants the ability to trap insects and pollen, certain insects the ability to walk on water, and the gecko the ability to climb walls. Being able to mimic these features at a larger scale would spur new advances in renewable energy and medicine. In a paper published in the October 10 issue of<i>Nature Materials</i>, a team of researchers from Penn State, the Naval Research Laboratory, and Harvard Medical School report on the development of an engineered thin film that mimics the natural abilities of water striding insects to walk on the surface of water, and for butterflies to shed water from their wings.

Although superhydrophobic self-cleaning surfaces are an active area of research, this development marks an engineering breakthrough in the ability to control the directionality of liquid transport. Using an array of poly(p-xylylene) nanorods synthesized by a bottom-up vapor-phase technique, the researchers were able to pin water droplets in one direction with enormous adhesive forces proportional to the number of nanorods and thesurface tension, while releasing droplets in the opposite direction.

The differential between the pin and release force is 80 micronewtons, over ten times the values reported in other engineered surfaces with ratchet-like features, and the first such surface to be engineered at the nanoscale. Recently, the authors also demonstrated directional adhesion and friction of these surfaces, similar to the way a gecko can climb a wall (J. Applied Physics, 2010). Gecko’s feet contain approximately 4 million hairs per square millimeter, whereas polymer nanorods can be deposited at 40 million rods per square millimeter.

The nanofilm produced by this technique, called oblique angle deposition, provides a microscale smooth surface for the transport of smallwater dropletswithout pumps or optical waves and with minimal deformation for self-powered microfluidic devices for medicine and for microassembly.

In work sponsored by the U.S. Navy, the nanofilm is envisioned for use as a coating that would reduce drag on the hull of vessels and retard fouling. Potential industrial and energy related uses are as directional syringes and fluid diodes, pump-free digital fluidic devices, increased efficiency of thermal cooling for microchips, coatings for tires, and even in energy production from rain drops.

The lead on the Penn State team, Melik Demirel, associate professor of engineering science and mechanics and corresponding author on the report, believes that the current laboratory basedvapor phasetechnique, which although relatively simple still requires a vacuum, can be replaced by a liquid phase technique, which would allow for scaling the production of their material to industry size.“The major impact of our method is that for the first time we can create a controlled directional surface at thenanoscale,” Demirel concludes.

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Graphene: Singles and the few

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(PhysOrg.com) -- A timely review analyzing the correlation of synthesis methods and physical properties of single-layer and few-layered graphene flakes.

A review of methods used for synthesizing both single and few-layer graphene and the resulting properties is presented by C.N.R. Rao and colleagues at the Jawaharlal Nehru Centre for Advanced Scientific Research and Indian Institute of Science, Bangalore. The article was published recently inScience and Technology ofAdvanced Materials.

The group not only compares the electrical, magnetic and surface properties of the resulting graphene {2} but based on their own research, the authors describe the physical properties of graphene-polymer composites and field-effect transistors fabricated using graphene.

Since the first report on the mechanical isolation of graphene fromgraphite, the interest in the physical properties and potential applications—such as transparent electrodes for solar cells, nano-electronics and robust mechanical structures—has led to an unprecedented increase in the number of publications on the synthesis, properties and applications of this unique 2D-material.

But the field is still in its infancy, with challenges and issues to be resolved, in particular the effects of the synthesis method on the properties of the resulting graphene.

The Nobel Prize in Physics 2010 was awarded to Andre Geim and Konstantin Novoselov of University of Manchester"for groundbreaking experiments regarding the two-dimensional material graphene"—a unique structure of carbon just one atom thick that has caught the imagination of materials scientists world-wide.

The Manchester researchers reported on the extraction and properties of graphene in 2004 {1}. The simplicity of the‘synthesis’ surprised many scientists, for who would have imagined being able to isolate an atomic layer of carbon from a block of graphite with a piece of adhesive tape?

Single-layer graphene (SLG) is produced by mechanically‘peeling off’ a layer of carbon from highly ordered pyrolytic graphite, which is then transferred onto a silicon substrate. Chemically, SLG is prepared by the reduction of a dispersion of single-layer graphene oxide with hydrazine. This resulting reduced graphene oxide (RGO) is a black suspension that contains residual oxygen, and this distinguishes it from SLG obtained by other methods.

Non-chemical methods of producing SLG layers include heating Si-terminated (0001) single-crystal 6H-SiC in vacuum between 1250 and 1450ºC for a few minutes and decomposition of hydrocarbons— methane, ethylene, acetylene and benzene— on sheets of catalytic transition metals such as Ni. The authors’ own research on chemical vapor deposition on nickel and cobalt films showed the number of layers to depend on the choice of hydrocarbons and experimental conductions, and importantly, that the graphene layers were difficult to remove from the metal surface after cooling.

Well-known methods for producing few-layer graphene are thermal exfoliation of graphite oxide at 1050ºC, the chemical reaction of an aqueous solution of SGO with hydrazine hydrate at the refluxing temperature or by microwave heating, heating 4–6 nm nanodiamond particles in an inert or reducing atmosphere above 1500ºC, and arc evaporation of graphite in a hydrogen atmosphere. The team found the latter method yields graphene with only 2–3 layers of 100–200 nm sized flakes although they note that controlling the number of layers of graphene is still a challenge.

The surface area of graphene is an important parameter for applications such as gas sensing and storage of gases such as hydrogen. In comparison to single-layer graphene, which theory predicts to have a large surface area of 2600 m²/g, measurements by the Bangalore group on few-layer graphene showed the surface area to be 270–1550 m²/g.

The electronic structure of graphene is determined by the‘edge states’ of graphene flakes, with bilayer graphene predicted to be ferromagnetic. Rao and co-workers showed the Curie-Weiss temperatures obtained from the high-temperature inverse susceptibility data to be negative in all samples measured by them, indicating antiferromagnetism. The authors note the possibility of the coexistence of different types of magnetic states within a single flake of graphene. In addition, all graphene samples showed magnetic hysteresis at room temperature, with electron paramagnetic resonance measurements suggesting that this behavior did not originate from transition-metal impurities.

Electrical measurements showed semiconducting behavior in few-layer graphenes with conductivity increasing between 35 and 300 K, which is different from the metallic nature exhibited by the single-layer graphene, and the electrical conductivity of graphene samples decreased with increasing number of layers. Furthermore, few-layer graphene samples were n-type and suitable for the fabrication of field-effect transistors, and the best transistors were realized with few-layer graphene produced by arc discharge of graphite in hydrogen. In measurements on composites of a polymer and few-layer graphene (PMMA-RGO, PMMA-HG and PVA-EG), the electrical conductivity of the composites increased with increasing graphene content. Thermoelectric measurements revealed a relatively small thermopower in few-layer graphenes compared with single-layergraphene. Interestingly, few-layer graphenes with the largest surface area showed the strongest interaction with electron-donor and acceptor molecules via molecular charge transfer.

This review contains 68 references and 21 figures and provides an invaluable source of up-to-date information for newcomers and experts in this exciting area of research.

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