Tuesday, February 28, 2012

Green Nanotechnology Challenges and Opportunities

University of Oregon's Hutchison says nanotech approaches can reduce silver use, reap big benefits

BOSTON -- (Feb. 28, 2012) -- Using high-precision microscopy and X-ray scattering techniques, University of Oregon researchers have gained eye-opening insights into the process of applying green chemistry to nanotechnology that results in high yields, improves efficiency and dramatically reduces waste and potential negative exposure to human health or the environment.

University of Oregon chemist James E. Hutchison described his lab's recent efforts to monitor the dynamics of nanoparticles in an invited talk today at the American Physical Society's March Meeting (Feb. 27-March 2). It turns out, Hutchison said, that simply reducing the amount of gold -- the material used in his research -- in the initial stages of the process used to grow nanoparticles allows for better maintenance of the particle size.

That accomplishment, he said, has important implications. The use of lower concentrations of the precursor that forms the nanoparticles virtually eliminates the ability of nanoparticles to aggregate together and thus prevents variations of sizes of the desired end product.

"What we saw while observing the production process with small-angle X-ray scattering (SAXS) was amazing," Hutchison, said in an interview before his lecture. "We realized that it is possible to reduce the concentration of gold and allow the particles to still grow, but shutdown the coalescent, or aggregation, pathway."

Cadnium selenide nanoparticles

Cadnium selenide nanoparticles as seen with Scanning Transmission Electron Microscopy
He also summarized his lab's use of chemically modified grids (Smart Grids) in transmission electron microscopy to study how nanoparticles are shed from common objects such as silverware and copper jewelry -- findings that were detailed in the journal ACS Nano in October. They studied the transformation of silver nanoparticles coated on Smart Grids as well as the common objects and found that all forms produce smaller silver nanoparticles that could disperse into the environment, especially in humid air, water and light -- and likely have been doing that throughout time without any known health ramifications.

"There may be many beneficial applications to nanotechnology, but they are only beneficial if the net benefits outweigh the deleterious implications for human health and the environment," said Hutchison, who holds the Lokey-Harrington Chair in Chemistry at the University of Oregon.

These new monitoring and measuring techniques, he said, are vital to help understand what modifications are possible in the processes that grow nanoparticles for a desired product. Using green chemistry, he added, can help assure both efficiency and stability of a product, which, in turn, will lower the risk of unwanted environmental or harmful human-health consequences.

Hutchison is co-author of "Green Nanotechnology Challenges and Opportunities," a white paper published by the American Chemical Society's Green Chemistry Institute, and the National Research Council report, "A Research Strategy for Environmental, Health, and Safety Aspects of Engineered Nanomaterials." He also was the founding director of the Safer Nanomaterials and Nanomanufacturing Initiative (SSNI) of the Oregon Nanoscience and Microtechnologies Institute (ONAMI), a state signature research center.


About the University of Oregon

The University of Oregon is among the 108 institutions chosen from 4,633 U.S. universities for top-tier designation of "Very High Research Activity" in the 2010 Carnegie Classification of Institutions of Higher Education. The UO also is one of two Pacific Northwest members of the Association of American Universities.

Contact: Jim Barlow jebarlow@uoregon.edu 541-346-3481 University of Oregon

Saturday, February 25, 2012

Tunable color filter that uses optical nanoantennas to obtain precise control of color output

A new way to create and control color has implications for display screens and security tags.

Cambridge, Mass. - February 23, 2012 – Engineers at Harvard have demonstrated a new kind of tunable color filter that uses optical nanoantennas to obtain precise control of color output.

Whereas a conventional color filter can only produce one fixed color, a single active filter under exposure to different types of light can produce a range of colors.

The advance has the potential for application in televisions and biological imaging, and could even be used to create invisible security tags to mark currency. The findings appear in the February issue of Nano Letters.

Kenneth Crozier, Associate Professor of Electrical Engineering at the Harvard School of Engineering and Applied Sciences (SEAS), and colleagues have engineered the size and shape of metal nanoparticles so that the color they appear strongly depends on the polarization of the light illuminating them. The nanoparticles can be regarded as antennas—similar to antennas used for wireless communications—but much smaller in scale and operating at visible frequencies.

"With the advances in nanotechnology, we can precisely control the shape of the optical nanoantennas, so we can tune them to react differently with light of different colors and different polarizations," said co-author Tal Ellenbogen, a postdoctoral fellow at SEAS. "By doing so, we designed a new sort of controllable color filter."

Color of Nanoparticles

Caption: The color output of a new type of optical filter created at Harvard depends on the polarization of the incoming light.

Credit: Image courtesy of Tal Ellenbogen. Usage Restrictions: None.

Chromatic Plasmonic Polarizers

Caption: To demonstrate their work, researchers at Harvard created a plate of chromatic plasmonic polarizers that spells out the acronym "LSP." Under light of different polarizations, the letters and the background change color. The image at far right shows the antennas themselves, as viewed through a scanning electron microscope.

Credit: Photos courtesy of Tal Ellenbogen. Usage Restrictions: None.
Conventional RGB filters used to create color in today's televisions and monitors have one fixed output color (red, green, or blue) and create a broader palette of hues through blending. By contrast, each pixel of the nanoantenna-based filters is dynamic and able to produce different colors when the polarization is changed.

The researchers dubbed these filters "chromatic plasmonic polarizers" as they can create a pixel with a uniform color or complex patterns with colors varying as a function of position.

To demonstrate the technology's capabilities, the acronym LSP (short for localized surface plasmon) was created. With unpolarized light or with light which is polarized at 45 degrees, the letters are invisible (gray on gray). In polarized light at 90 degrees, the letters appear vibrant yellow with a blue background, and at 0 degrees the color scheme is reversed. By rotating the polarization of the incident light, the letters then change color, moving from yellow to blue.

"What is somewhat unusual about this work is that we have a color filter with a response that depends on polarization," says Crozier.

The researchers envision several kinds of applications: using the color functionality to present different colors in a display or camera, showing polarization effects in tissue for biomedical imaging, and integrating the technology into labels or paper to generate security tags that could mark money and other objects.

Seeing the color effects from current fabricated samples requires magnification, but large-scale nanoprinting techniques could be used to generate samples big enough to be seen with the naked eye. To build a television, for example, using the nanoantennas would require a great deal of advanced engineering, but Crozier and Ellenbogen say it is absolutely feasible.

Crozier credits the latest advance, in part, to taking a biological approach to the problem of color generation. Ellenbogen, who is, ironically, colorblind, had previously studied computational models of the visual cortex and brought such knowledge to the lab.

"The chromatic plasmonic polarizers combine two structures, each with a different spectral response, and the human eye can see the mixing of these two spectral responses as color," said Crozier.

"We would normally ask what is the response in terms of the spectrum, rather than what is the response in terms of the eye," added Ellenbogen.


The researchers have filed a provisional patent for their work.

Kwanyong Seo, a postdoctoral fellow in electrical engineering at SEAS, also contributed to the research. The work was supported by the Center for Excitonics, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, and Office of Basic Energy Sciences; and Zena Technologies. In addition, the research team acknowledges the Center for Nanoscale Systems at Harvard for fabrication work. +sookie tex

Contact: Caroline Perry cperry@seas.harvard.edu 617-496-1351 Harvard University

Friday, February 24, 2012

Creating glass-based, inorganic light-emitting diodes (LEDs) that produce light in the ultraviolet range

LOS ALAMOS, New Mexico, February 24, 2012—A multinational team of scientists has developed a process for creating glass-based, inorganic light-emitting diodes (LEDs) that produce light in the ultraviolet range. The work, reported this week in the online Nature Communications, is a step toward biomedical devices with active components made from nanostructured systems.

LEDs based on solution-processed inorganic nanocrystals have promise for use in environmental and biomedical diagnostics, because they are cheap to produce, robust, and chemically stable. But development has been hampered by the difficulty of achieving ultraviolet emission. In their paper, Los Alamos National Laboratory's Sergio Brovelli in collaboration with the research team lead by Alberto Paleari at the University of Milano-Bicocca in Italy describe a fabrication process that overcomes this problem and opens the way for integration in a variety of applications.

The world needs light-emitting devices that can be applied in biomedical diagnostics and medicine, Brovelli said, either as active lab-on-chip diagnostic platforms or as light sources that can be implanted into the body to trigger some photochemical reactions. Such devices could, for example, selectively activate light-sensitive drugs for better medical treatment or probe for the presence of fluorescent markers in medical diagnostics. These materials would need to be fabricated cheaply, on a large scale, and integrated into existing technology.

The paper describes a new glass-based material, able to emit light in the ultraviolet spectrum, and be integrated onto silicon chips that are the principal components of current electronic technologies.

Nanocrystalline LEDs

Caption: Embedding nanocrystals in glass provides a way to create UV-producing LEDs for biomedical applications.

Credit: Los Alamos National Laboratory. Usage Restrictions: None.
The new devices are inorganic and combine the chemical inertness and mechanical stability of glass with the property of electric conductivity and electroluminescence (i.e. the ability of a material to emit light in response to the passage of an electric current).

As a result, they can be used in harsh environments, such as for immersion into physiologic solutions, or by implantation directly into the body. This was made possible by designing a new synthesis strategy that allows fabrication of all inorganic LEDs via a wet-chemistry approach, i.e. a series of simple chemical reactions in a beaker. Importantly, this approach is scalable to industrial quantities with a very low start-up cost. Finally, they emit in the ultraviolet region thanks to careful design of the nanocrystals embedded in the glass.

In traditional light-emitting diodes, light emission occurs at the sharp interface between two semiconductors. The oxide-in-oxide design used here is different, as it allows production of a material that behaves as an ensemble of semiconductor junctions distributed in the glass.

This new concept is based on a collection of the most advanced strategies in nanocrystal science, combining the advantages of nanometric materials consisting of more than one component. In this case the active part of the device consists of tin dioxide nanocrystals covered with a shell of tin monoxide embedded in standard glass: by tuning the shell thickness is it possible to control the electrical response of the whole material.


The paper was produced with the financial support of Cariplo Foundation, Italy, under Project 20060656, the Russian Federation under grant 11.G34.31.0027, the Silvio Tronchetti Provera Foundation, and Los Alamos National Laboratory's Directed Research and Development Program.

The paper is titled, "Fully inorganic oxide-in-oxide ultraviolet nanocrystal light emitting devices," and can be downloaded from the following online Nature Communications link: dx.doi.org/10.1038/ncomms1683

Its authors are Sergio Brovelli1, 2, Norberto Chiodini1, Roberto Lorenzi1, Alessandro Lauria1, Marco Romagnoli3,4& Alberto Paleari1
1. Department of Materials Science, University of Milano-Bicocca, Italy.
2. Chemistry Division, Los Alamos National Laboratory, Los Alamos, New Mexico.
3. Material Processing Center, Massachusetts Institute of Technology, Cambridge, Massachusetts..
4. On leave from Photonic Corp, Culver City, California. +sookie tex

Contact: Nancy Ambrosiano nwa@lanl.gov 505-667-0471 DOE/Los Alamos National Laboratory

Wednesday, February 22, 2012

How proteins in our bodies interact with nanomaterials

A new study led by nanotechnology and biotechnology experts at Rensselaer Polytechnic Institute is providing important details on how proteins in our bodies interact with nanomaterials. In their new study, published in the Feb. 2 online edition of the journal Nano Letters, the researchers developed a new tool to determine the orientation of proteins on different nanostructures. The discovery is a key step in the effort to control the orientation, structure, and function of proteins in the body using nanomaterials.

“To date, very little is known about how proteins interact with a surface at the nanoscale,” said Jonathan Dordick, director of the Center for Biotechnology and Interdisciplinary Studies at Rensselaer (CBIS), the Howard P. Isermann ’42 Professor of Chemical and Biological Engineering, and co-corresponding author of the study. “With a better understanding of how a protein interacts with a surface, we can develop custom nanoscale surfaces and design proteins that can do a variety of amazing tasks in the human body.”

Researchers seek to use nanotechnology in a variety of biological and medical applications, ranging from biosensors that can detect cancer in the body to scaffolds that help grow new tissues and organs, according to the researchers. Such technologies involve the interaction between biological cells and non-biological nanoscale materials. These interactions are controlled in part by proteins at the interface between the two materials. At such a minuscule level, the tiniest change in the structure of a material can vastly change the proteins involved and thus alter how the cells of the human body respond to the nanomaterial. In fact, proteins are among the most complex (and fickle) molecules in our bodies, rapidly changing their orientation or structure and thus their ability to interact with other molecules. Controlling their orientation and structure through their interactions with nanomaterials is essential to their reliable and safe use in new biotechnologies, according to Dordick.

Front and back face of Cytochrome C

Front and back face of Cytochrome C
“We have learned over the past decade to create nanomaterials with a wide variety of controlled structures, and we have discovered and begun to learn how these structures can positively impact cellular activity,” said Richard Siegel, the Robert W. Hunt Professor of Materials Science and Engineering at Rensselaer, director of the Rensselaer Nanotechnology Center, and co-corresponding author on the study.
“By learning more about the role of the nanostructure-protein interactions that cause this impact, we will be able in the future to harness this knowledge to benefit society through improved healthcare.

In addition to improved healthcare, this work will also help enable the manufacture of a wide range of new hierarchical composite materials—based upon synthetic polymers, biomolecules, and nanostructures—that will revolutionize our ability to solve many critical problems facing society worldwide.”

What the researchers found in this and their previous studies was that the size and curvature of the nanosurface greatly changed the way proteins oriented themselves on the surfaces and changed their structure, and this influenced protein stability. They found that nanostructures with smaller and more curved surfaces favored protein orientations that resulted in more stable proteins than structures with larger more flat surfaces.

To reach these conclusions, the researchers investigated several well-studied proteins, including cytochrome c, RNase A, and lysozyme and monitored their adsorption on different size silica nanoparticles. In this latest work, they chemically modified the adsorbed proteins to form chemical “tags” that provided the researchers with important information on how the proteins adsorbed on different silica surfaces. When the nanomaterials and proteins were studied using mass spectrometry, the tags provided valuable new information about the surface orientation of the proteins. Mass spectrometry analyzes the mass distribution of a material to determine its elemental composition and structural characteristics, and was very sensitive to the chemical tags added on the proteins.

Dordick and Siegel were joined in the research by Siddhartha Shrivastava and Joseph Nuffer of Rensselaer. The research was funded by the National Science Foundation. The paper is titled “Position-specific chemical modification and quantitative proteomics disclose protein orientation absorbed on silica nanoparticles. +sookie tex

Contact: Gabrielle DeMarco demarg@rpi.edu 518-276-6542 Rensselaer Polytechnic Institute

Monday, February 20, 2012

Working transistor consisting of a single atom placed precisely in a silicon crystal VIDEO

In a remarkable feat of micro-engineering, UNSW physicists have created a working transistor consisting of a single atom placed precisely in a silicon crystal.

The tiny electronic device, described today in a paper published in the journal Nature Nanotechnology, uses as its active component an individual phosphorus atom patterned between atomic-scale electrodes and electrostatic control gates.

This unprecedented atomic accuracy may yield the elementary building block for a future quantum computer with unparalleled computational efficiency.

Until now, single-atom transistors have been realised only by chance, where researchers either have had to search through many devices or tune multi-atom devices to isolate one that works.

"But this device is perfect", says Professor Michelle Simmons, group leader and director of the ARC Centre for Quantum Computation and Communication at UNSW. "This is the first time anyone has shown control of a single atom in a substrate with this level of precise accuracy."

The microscopic device even has tiny visible markers etched onto its surface so researchers can connect metal contacts and apply a voltage, says research fellow and lead author Dr Martin Fuechsle from UNSW.

"Our group has proved that it is really possible to position one phosphorus atom in a silicon environment - exactly as we need it - with near-atomic precision, and at the same time register gates," he says.

Caption: In a remarkable feat of micro-engineering, UNSW physicists have created a working transistor consisting of a single atom placed precisely in a silicon crystal.

Credit: UNSWTV. Usage Restrictions: None.

Caption: Dies ist der weltweit erste Einzelatom-Transistor der mit atomarer genauigkeit hergestellt wurde. Martin Fueschle, University of New South Wales in Australien.

Credit: UNSWTV. Usage Restrictions: None. +sookie tex
The device is also remarkable, says Dr Fuechsle, because its electronic characteristics exactly match theoretical predictions undertaken with Professor Gerhard Klimeck's group at Purdue University in the US and Professor Hollenberg's group at the University of Melbourne, the joint authors on the paper.

The UNSW team used a scanning tunnelling microscope (STM) to see and manipulate atoms at the surface of the crystal inside an ultra-high vacuum chamber. Using a lithographic process, they patterned phosphorus atoms into functional devices on the crystal then covered them with a non-reactive layer of hydrogen.

Hydrogen atoms were removed selectively in precisely defined regions with the super-fine metal tip of the STM. A controlled chemical reaction then incorporated phosphorus atoms into the silicon surface.

Finally, the structure was encapsulated with a silicon layer and the device contacted electrically using an intricate system of alignment markers on the silicon chip to align metallic connects. The electronic properties of the device were in excellent agreement with theoretical predictions for a single phosphorus atom transistor.

It is predicted that transistors will reach the single-atom level by about 2020 to keep pace with Moore's Law, which describes an ongoing trend in computer hardware that sees the number of chip components double every 18 months.

This major advance has developed the technology to make this possible well ahead of schedule and gives valuable insights to manufacturers into how devices will behave once they reach the atomic limit, says Professor Simmons.

Contact: Bob Beale bbeale@unsw.edu.au 61-041-170-5435 University of New South Wales

Saturday, February 18, 2012

Griffith University PhD candidate awarded for innovative image of the shadow of a single atom

A Griffith University PhD candidate will be awarded tonight for his innovative image of the shadow of a single atom.

Ben Norton, from the Kielpinski group in the Centre for Quantum Dynamics, takes out the runner up prize in the CiSRA Extreme Imaging Competition following extensive work on high resolution imaging.

Run by Canon Australia and CiSRA, Canon Inc.'s Australian research centre, the Extreme Imaging competition aims to promote and celebrate local research at the intersection of imaging and technology.

"Atoms are the building blocks of matter. A human hair is a billion atoms wide," said Professor David Kielpinski, from Griffith's Centre for Quantum Dynamics. "So just manipulating and isolating a single atom is extremely difficult, let alone imaging it.

"Ben has had to use some very special tricks to do both.

"First of all he cools them down, to within a degree of ‘absolute zero’, the coldest temperature possible (about−273.15 °C), to keep them still. Then he traps them inside an ultra-high vacuum, holding them steady using electric fields. These techniques are very hard, but they have been done before. What is new is how Ben images them.

"To do this he uses a special flat lens made using concentric rings, which was originally developed for lighthouses. These lenses can be made so small and light that they can be put inside the vacuum chamber with the atoms, allowing Ben to collect as much light as possible. This last trick has allowed Ben to take some of the highest resolution images of atoms ever made, including the first ever image of the shadow of a single atom, by measuring how much light is absorbed when the atom is there."

image of the shadow of a single atomProfessor Kielpinski said imaging single atoms is important for understanding not just physics, but also in the new field of quantum computing. “The techniques developed in this project may have other applications too, such as ultra-high resolution imaging of biological cells.

"I really appreciate that this work has been considered worthy of the Canon prize – it's been an amazing opportunity. I am also very grateful for the strong support I have received from my supervisors at Griffith throughout my research there." +sookie tex

Contact: Dean Gould d.gould@griffith.edu.au 61-411-657-381 Griffith University

Friday, February 17, 2012

Researchers test nanoscale carbon clusters for chemotherapy

Rice University, MD Anderson researchers test nanoscale carbon clusters for chemotherapy

A mixture of current drugs and carbon nanoparticles shows potential to enhance treatment for head-and-neck cancers, especially when combined with radiation therapy, according to new research by Rice University and the University of Texas MD Anderson Cancer Center.

The work blazes a path for further research into therapy customized to the needs of individual patients. The therapy uses carbon nanoparticles to encapsulate chemotherapeutic drugs and sequester them until they are delivered to the cancer cells they are meant to kill.

A paper on the research was published this month in the American Chemical Society journal ACS Nano.

The new strategy by Rice chemist James Tour and Jeffrey Myers, a professor of head-and-neck surgery at MD Anderson, combines paclitaxel (PTX) and Cetuximab (Cet) with hydrophilic carbon clusters functionalized with polyethylene glycol, known as PEG-HCC.

Cetuximab, the targeting agent, is a humanized monoclonal antibody that binds exclusively to the epidermal growth factor receptor (EGFR), a cell-surface receptor overexpressed by 90 percent of head-and-neck squamous cell cancers. Paclitaxel, an active agent in chemotherapy, is used to treat lung, ovarian, breast and head-and-neck cancers. In combination, they have the ability to target and attack cancerous cells.

Nanoparticles may enhance cancer therapy

Nanoparticles may enhance cancer therapy
Because paclitaxel is hydrophobic – it won't mix with water – the substances are generally combined with Cremophor EL, a castor oil-based carrier that allows the compound marketed as Taxol to be delivered intravenously to patients.

Tour, Myers and their associates have found a simple way to mix PTX and Cetuximab with carbon clusters that adsorb the active ingredients. The new compound is water-soluble and is more effective at targeting tumors than Taxol while avoiding the toxic effects of paclitaxel and Cremophor on adjacent healthy cells, they wrote.

"It's very common to administer cortical steroids to limit the allergic response to Cremophor EL," said Tour, Rice's T.T. and W.F. Chao Chair in Chemistry as well as a professor of mechanical engineering and materials science and of computer science.

Tour said the Cet/PTX/PEG-HCC elements combine easily. "We show in the paper that when we take paclitaxel up in our hydrophilic carbon clusters, we can deliver these just as well as commercial Taxol.

"But you can never break into a market with something that's just as good as what's already out there. You have to be substantially better. The beauty of what we're doing is that we can potentially use a much smaller amount of the drug for chemotherapy. Just eliminating the Cremophor is a real advantage," he said.

Tour noted a recently approved chemotherapy drug that combines paclitaxel with albumin nanoparticles, Abraxane, also shows promise. "That works well, but it still only has about 10 percent of the market after six or seven years of use," he said.

Myers, the Hubert L. and Olive Stringer Distinguished Professor in Cancer Research at MD Anderson, said combining Cet/PTX/PEG-HCC and radiation therapy in tests on mice showed a significant boost in killing tumors. "Our hypothesis is that PTX, the chemotherapy drug, sensitizes the cancer cells to the effects of radiation and the Cetuximab/PEG-HCC increases the delivery of PTX to the cancer cells," he said.

Unlike Cremophor, Tour said, the enhanced carbon clusters are nontoxic. Biodistribution and toxicity studies showed the "large majority" of PEG-HCCs are excreted through the kidneys, while trace amounts in the livers and spleens of mice tested showed no damage to the organs.

The strategy sprang from conversations between Tour and Rice chemist and Nobel laureate Richard Smalley, who died of leukemia in 2005. "I was sitting with Rick at MD Anderson while he was being treated, and we got to talking about using carbon particles for delivery as carbon-based carriers.

"But we had nothing specific," Tour said. "I started to work on this without funding, and shortly after Rick's passing in October 2005, I met with Jeff Myers."

"I wanted to establish a multidisciplinary program to study nanoparticle-based therapeutics for cancer in general, and more specifically, head-and-neck cancer," Myers said. "At the time, Dr. Garth Powis (professor and chair of the Department of Experimental Therapeutics at MD Anderson) directed me to Dr. Mauro Ferrari (now president of The Methodist Hospital Research Institute and an adjunct professor of bioengineering at Rice), who ultimately put me in touch with Dr. Tour.

"His enthusiasm for science and willingness to further explore the potential of carbon nanoparticles to treat cancer patients was apparent right away, and we launched a collaborative effort that has been quite productive," he said.

Myers is pleased with what the team has accomplished so far. "This collaborative work has 'proved the principle' that carbon nanoparticles can be used to non-covalently link a chemotherapeutic drug with a targeting antibody that can deliver the drug specifically to a cancer cell," he said. "This principle could be used to deliver other drugs to other types of cells through specific targeting of cell surface receptors as a method of increasing the therapeutic ratio.

"Though I am not an expert in these other areas, this could potentially have applications in infectious diseases, neurologic disorders and cardiovascular illnesses," he said.

Tour sees potential for clinical uses of PEG-HCCs for brain cancer and traumatic brain injuries as well as chemotherapy, but acknowledged the introduction of such drugs for human use is a long way off. "To get a drug through all the different phases, including trials, typically takes 12 to 14 years and about $1.25 billion," he said. "That can sometimes be expedited through experimental trials with patients who have no other options, but it's still a long and expensive haul."

Still, he said the new work is a strong step in the right direction. "This paper is the highlight of six years of research," he said. "It all came together. This is the crescendo, right here."

The paper's lead authors are Daisuke Sano, a former postdoctoral fellow at MD Anderson, now at Yokohama City University Graduate School of Medicine in Japan, and Jacob Berlin, a researcher in Tour's Rice lab and now a professor at City of Hope Hospital, Duarte, Calif. Co-authors are Rice alumnus Tam Pham and graduate student Daniela Marcano; and Ge Zhou, an assistant professor in the Department of Head and Neck Surgery, David Valdecanas, laboratory coordinator in experimental radiation oncology, and Luka Milas, professor and chair of the Department of Experimental Radiation Oncology, all at MD Anderson.

The research was supported by The Alliance for NanoHealth through a Department of Defense subcontract from the University of Texas Health Science Center at Houston; the Mission Connect Mild Traumatic Brain Injury Consortium, also funded by the Department of Defense; the Nanoscale Science and Engineering Initiative of the National Science Foundation; the MD Anderson Cancer Center PANTHEON Program; a National Institutes of Health Cancer Center Support Grant; and an MD Anderson Cancer Center Support Grant.

Contact: David Ruth david@rice.edu 713-348-6327 Rice University

Scott Merville University of Texas M. D. Anderson Cancer Center 713-792-0661 SMerville@mdanderson.org Mike Williams 713-348-6728 mikewilliams@rice.edu

Wednesday, February 15, 2012

Nanoscale materials in superlattice structures helps to enhance the sensitivity of infrared detectors

Arizona State University researchers are finding ways to improve infrared photodetector technology that is critical to national defense and security systems, as well as used increasingly in medical diagnostics, commercial applications and consumer products.

A significant advance is reported in a recent article in the journal Applied Physics Letters. It details discovery of how infrared photodetection can be done more effectively by using certain materials arranged in specific patterns in atomic-scale structures.

It’s being accomplished by using multiple ultrathin layers of the materials that are only several nanometers thick. Crystals are formed in each layer. These layered structures are then combined to form what are termed “superlattices.”

Photodetectors made of different crystals absorb different wavelengths of light and convert them into an electrical signal. The conversion efficiency achieved by these crystals determines a photodectector’s sensitivity and the quality of detection it provides, explains electrical engineer Yong-Hang Zhang.

The unique property of the superlattices is that their detection wavelengths can be broadly tuned by changing the design and composition of the layered structures. The precise arrangements of the nanoscale materials in superlattice structures helps to enhance the sensitivity of infrared detectors, Zhang says.

Zhang is a professor in the School of Electrical, Computer and Energy Engineering, one of ASU’s Ira A. Fulton Schools of Engineering. He is leading the work on infrared technology research in ASU’s Center for Photonics Innovation. More information can be found at the center’s Optoelectronics Group website.

ASU engineers are working on technological advances that promise to help enhance infrared photodetection used in sophisticated weapons and surveillance system, industrial and home security systems, medical diagnostics and night vision equipment for law enforcement and driving safety. Photo by: Orkun Cellek/ASU
Additional research in this area is being supported by a grant from the Air Force Office of Scientific Research and a new Multidisciplinary University Research Initiative (MURI) program established by the U.S. Army Research Office. ASU is a partner in the program led by the University of Illinois at Urbana-Champaign.

The MURI program is enabling Zhang’s group to accelerate its work by teaming with David Smith, a professor in the Department of Physics in ASU’s College of Liberal Arts and Sciences, and Shane Johnson, a senior research scientist in the ASU’s engineering schools.

The team is using a combination of indium arsenide and indium arsenide antimonide to build the superlattice structures. The combination allows devices to generate photo electrons necessary to provide infrared signal detection and imaging, says Elizabeth Steenbergen, an electrical engineering doctoral student who performed experiments on the supperlattice materials with collaborators at the Army Research Lab.

“In a photodetector, light creates electrons. Electrons emerge from the photodetector as electrical current. We read the magnitude of this current to measure infrared light intensity,” she says.

“In this chain, we want all of the electrons to be collected from the detector as efficiently as possible. But sometimes these electrons get lost inside the device and are never collected,” says team member Orkun Cellek, an electrical engineering postdoctoral research associate.

Zhang says the team’s use of the new materials is reducing this loss of optically excited electrons, which increases the electrons’ carrier lifetime by more than 10 times what has been achieved by other combinations of materials traditionally used in the technology. Carrier lifetime is a key parameter that has limited detector efficiency in the past.

Another advantage is that infrared photodetectors made from these superlattice materials don’t need as much cooling. Such devices are cooled as a way of reducing the amount of unwanted current inside the devices that can “bury” electrical signals, Zhang says.

The need for less cooling reduces the amount of power needed to operate the photodetectors, which will make the devices more reliable and the systems more cost effective.

Researchers say improvements can still be made in the layering designs of the intricate superlattice structures and in developing device designs that will allow the new combinations of materials to work most effectively.

The advances promise to improve everything from guided weaponry and sophisticated surveillance systems to industrial and home security systems, the use of infrared detection for medical imaging and as a road-safety tool for driving at night or during sand storms or heavy fog.

“You would be able to see things ahead of you on the road much better than with any headlights,” Cellek says.

The research team’s paper is reported on in the article “One giant leap for IR technology” on the LAB & FAB TALK website of Compound Semiconductor magazine.

Joe Kullman, Joseph.Kullman@asu.edu (480) 965-8122 Ira A. Fulton Schools of Engineering.

Monday, February 13, 2012

Molecule that structurally and chemically replicates the active part of the widely used industrial catalyst molybdenite

A technique for creating a new molecule that structurally and chemically replicates the active part of the widely used industrial catalyst molybdenite has been developed by researchers with the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab). This technique holds promise for the creation of catalytic materials that can serve as effective low-cost alternatives to platinum for generating hydrogen gas from water that is acidic.

Christopher Chang and Jeffrey Long, chemists who hold joint appointments with Berkeley Lab and the University of California (UC) Berkeley, led a research team that synthesized a molecule to mimic the triangle-shaped molybdenum disulfide units along the edges of molybdenite crystals, which is where almost all of the catalytic activity takes place. Since the bulk of molybdenite crystalline material is relatively inert from a catalytic standpoint, molecular analogs of the catalytically active edge sites could be used to make new materials that are much more efficient and cost-effective catalysts.

“Using molecular chemistry, we’ve been able to capture the functional essence of molybdenite and synthesize the smallest possible unit of its proposed catalytic active site,” says Chang, who is also an investigator with the Howard Hughes Medical Institute (HHMI). “It should now be possible to design new catalysts that have a high density of active sites so we get the same catalytic activity with much less material.”

Says Long, “Inorganic solids, such as molybdenite, are an important class of catalysts that often derive their activity from sparse active edge sites, which are structurally distinct from the inactive bulk of the molecular solid. We’ve demonstrated that it is possible to create catalytically active molecular analogs of these sites that are tailored for a specific purpose. This represents a conceptual path forward to improving future catalytic materials.”

molybdenite complex and the PY5Me2 ligand

Using a molybdenite complex and the PY5Me2 ligand, Berkeley Lab researchers synthesized a molecule that mimics catalytically active triangular molybdenum disulfide edge-sites. The result is an entire layer of catalytically active material. Molybdenum atoms are shown as green, sulfur as yellow.
Chang and Long are the corresponding authors of a paper in the journal Science describing this research titled “A Molecular MoS2 Edge Site Mimic for Catalytic Hydrogen Generation.” Other authors are Hemamala Karunadasa, Elizabeth Montalvo, Yujie Sun and Marcin Majda.

Molybdenite is the crystalline sulfide of molybdenum and the principal mineral from which molybdenum metal is extracted. Although commonly thought of as a lubricant, molybdenite is the standard catalyst used to remove sulfur from petroleum and natural gas for the reduction of sulfur dioxide emissions when those fuels are burned. Recent studies have shown that in its nanoparticle form, molybdenite also holds promise for catalyzing the electrochemical and photochemical generation of hydrogen from water. Hydrogen could play a key role in future renewable energy technologies if a relatively cheap, efficient and carbon-neutral means of producing it can be developed.

Currently, the best available technique for producing hydrogen is to split water molecules into molecules of hydrogen and oxygen using platinum as the catalyst. However, with platinum going for more than $2,000 an ounce, the market is wide open for a low cost alternative catalyst. Molybdenite is far more plentiful and about 1/70th the cost of platinum, but poses other problems.

“Molybdenite has a layered structure with multiple microdomains, most of which are chemically inert,” Chang says. “High-resolution scanning tunneling microscopy studies and theoretical calculations have identified the triangular molybdenum disulfide edges as the active sites for catalysis; however, preparing molybdenite with a high density of functional edge sites in a predictable manner is extremely challenging.”

Chang, Long and their research team met this challenge using a pentapyridyl ligand known as PY5Me2 to create a molybdenum disulfide molecule that, while not found in nature, is stable and structurally identical to the proposed triangular edge sites of molybdenite. It was shown that these synthesized molecules can form a layer of material that is analogous to constructing a sulfide edge of molybdenite.

“The electronic structure of our molecular analog can be adjusted through ligand modifications,” Long says. “This suggests we should be able to tailor the material’s activity, stability and required over-potential for proton reduction to improve its performance.”

In 2010, Chang and Long and Hemamala Karunadasa, who is the lead author on this new Science paper, used the PY5Me2 ligand to create a molybdenum-oxo complex that can effectively and efficiently catalyze the generation of hydrogen from neutral buffered water or even sea water. Molybdenite complexes synthesized from this new molecular analog can just as effectively and efficiently catalyze hydrogen gas from acidic water.

“We’re now looking to develop molecular analogs of active sites in other catalytic materials that will work over a range of pH conditions, as well as extend this work to photocatalytic systems” Chang says.

Adds Long, “Our molecular analog for the molybdenite active site might not be a replacement for any existing catalytic materials but it does provide a way to increase the density of active sites in inorganic solid catalytic materials and thereby allow us to do more with less.”

This research was supported by the DOE Office of Science, in part through the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub.

# # #

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit www.lbl.gov.

DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

Additional Information: For more about the research of Christopher Chang, visit the Website at www.cchem.berkeley.edu/cjcgrp/, For more about the research of Jeffrey Long, visit the Website at alchemy.cchem.berkeley.edu/ For more information about the Joint Center for Artificial Photosynthesis visit the Website at https://solarfuelshub.org/

Saturday, February 11, 2012

Development of molecule-based electronics

Researchers at the Nano-Science Center at the University of Copenhagen have developed a new nano-technology platform for the development of molecule-based electronic components using the wonder material graphene. At the same time, they have solved a problem that has challenged researchers from around world for ten years.

Since its discovery in 2004, graphene has been called a wonder material, in part because it is 200 times stronger than steel, a good electrical conductor and is just a single atom layer thick. With these properties, there are sky-high expectations for what graphene can be used for. That is why researchers around the world are working on developing methods to make and modify graphene. In a recently published article in the journal Advanced Materials, researchers in nano-chemistry at the Department of Chemistry describe how they are among the first in the world to be able to chemically produce large flakes of graphene.

- Using chemical and physical processes, that we have been working to develop in recent years, we are now able to produce such large flakes of graphene that we can use the flakes as components in an entirely new technology platform within molecule-based electronics, says nano-chemist Kasper Nørgaard, who along with his Danish and Chinese colleagues in the Danish-Chinese Center for Molecular Nano-Electronics at the Nano-Science Center, is behind the new platform as well as the solution to ten year old problem.

More than 10 years ago when it was being proclaimed that nanotechology could revolutionise computer technology, it was in part because they imagined that the development of molecular electronics was just around the corner.

Development of molecule-based electronicMolecular electronics involves replacing traditional electrical components with molecules, creating tiny electronic circuits for use in, for example, computers and data storage. This has proven to be more challenging than anticipated, in part because the components short-circuited when the molecules were contacted with electrodes and were therefore unable to create a workable circuit. Graphene is the solution to the problem.

- We can now place one of our graphene flakes on top of the molecules, protecting the system from short circuits. That is how we developed a new technology platform for use in the development of new electronics based on molecules, says Kasper Nørgaard, who explains that in the Danish-Chinese collaboration, they are trying to use molecules with different properties in the platform, for example, molecules that can alternate between being conductive and non-conductive. This paves the way for the electronics of the future in areas such as memory technology, ultra-thin displays and solar cells. +sookie tex

More information, contact: Kasper Nørgaard: kn@nano.ku.dk. Mobil: +45 29176481

Nano-Science Center || WEB: University of Copenhagen Universitetsparken 5 2100 København Ø Contact: Rikke Bøyesen rb@nano.ku.dk || . +sookie tex

Thursday, February 09, 2012

Microscopic channels of gold nanoparticles have the ability to transmit electromagnetic energy that starts as light and propagates via "dark plasmons

'Dark plasmons' transmit energy, Rice University researchers show how far nanoparticle chains can carry a signal.

Microscopic channels of gold nanoparticles have the ability to transmit electromagnetic energy that starts as light and propagates via "dark plasmons," according to researchers at Rice University.

A new paper in the American Chemical Society journal Nano Letters shows how even disordered collections of nanoparticles in arrays as thin as 150 nanometers can be turned into waveguides and transmit signals an order of magnitude better than previous experiments were able to achieve. Efficient energy transfer on the micrometer scale may greatly improve optoelectronic devices.

The Rice lab of Stephan Link, an assistant professor of chemistry and electrical and computer engineering, has developed a way to "print" fine lines of gold nanoparticles on glass. These lines of nanoparticles can transmit a signal from one nanoparticle to the next over many microns, much farther than previous attempts and roughly equivalent to results seen using gold nanowires.

Complex waveguide geometries are far easier to manufacture with nanoparticle chains, Link said. He and his team used an electron beam to cut tiny channels into a polymer on a glass substrate to give the nanoparticle lines their shape. The gold nanoparticles were deposited into the channels via capillary forces. When the rest of the polymer and stray nanoparticles were washed away, the lines remained, with the particles only a few nanometers apart.

50-nanometer spherical gold nanoparticles

A scanning electron microscope image, left, shows a 15-micron line of 50-nanometer spherical gold nanoparticles. At right is a fluorescence image of the same chain, coated with a thin film of Cardiogreen dye using 785 nm laser excitation. (Credit Link Lab / Rice University)
Plasmons are waves of electrons that move across the surface of a metal like water in a pond when disturbed. The disturbance can be caused by an outside electromagnetic source, such as light. Adjacent nanoparticles couple with each other where their electromagnetic fields interact and allow a signal to pass from one to the next.

Link said dark plasmons may be defined as those that have no net dipole moment, which makes them unable to couple to light. "But these modes are not totally dark, especially in the presence of disorder," he said. "Even for the subradiant modes, there is a small dipole oscillation.

"Our argument is that if you can couple to these subradiant modes, the scattering loss is smaller and plasmon propagation is sustained over longer distances," Link said. "Therefore, we enhance energy transport over much longer distances than what has been done before with metal-particle chains."

To see how far, Link and his team coated the 15-micron-long lines with a fluorescent dye and used a photobleaching method developed in his lab to measure how far the plasmons, excited by a laser at one end, propagate. "The damping of the plasmon propagation is exponential," he said. "At four microns, you have a third of the initial intensity value.

"While this propagation distance is short compared to traditional optical waveguides, in miniaturized circuits one only needs to cover small length scales. It might be possible to eventually apply an amplifier to the system that would lengthen the propagation distance," Link said. "In terms of what people thought was possible with nanoparticle chains, what we've done is already a significant improvement."

Link said silver nanowires have been shown to carry a plasmon wave better than gold, as far as 15 microns, about a sixth the width of a human hair. "We know that if we try silver nanoparticles, we may propagate a lot longer and hopefully do that in more complex structures," he said. "We may be able to use these nanoparticle waveguides to link to other components such as nanowires in configurations that would not be possible otherwise."

Graduate student David Solis Jr. is the lead author of the paper. Co-authors are graduate students Britain Willingham, Liane Slaughter, Jana Olson and Pattanawit Swanglap, junior Scott Nauert and postdoctoral research associates Aniruddha Paul and Wei-Shun Chang, all of Rice.

The research was supported by the Robert A. Welch Foundation, the Office of Naval Research, the National Science Foundation, the American Chemical Society Petroleum Research Fund and a 3M Nontenured Faculty Grant.


Contact: David Ruth david@rice.edu 713-348-6327 Rice University

Tuesday, February 07, 2012

Vibrating microcantilevers to detect chemical and biological agents for applications from national security to food processing

WEST LAFAYETTE, Ind. - Researchers have learned how to improve the performance of sensors that use tiny vibrating microcantilevers to detect chemical and biological agents for applications from national security to food processing.

The microcantilevers - slivers of silicon shaped like small diving boards - vibrate at their natural, or "resonant," frequency. Analyzing the frequency change when a particle lands on the microcantilever reveals the particle's presence and potentially its mass and composition.

The sensors are now used to research fundamental scientific questions. However, recent advances may allow for reliable sensing with portable devices, opening up a range of potential applications, said Jeffrey Rhoads, an assistant professor of mechanical engineering at Purdue University.

Creating smaller sensors has been complicated by the fact that measuring the change in frequency does not work as well when the sensors are reduced in size. The researchers showed how to sidestep this obstacle by measuring amplitude, or how far the diving board moves, instead of frequency.

"When you try to shrink these systems, the old way of measuring does not work as well," Rhoads said. "We've made the signal processing part easier, enabling small-scale, lower-power sensors, which are more reliable and have the potential for higher sensitivities."

Researchers have learned how to improve the performance of sensors that use tiny vibrating "microcantilevers," like the one pictured here, to detect chemical and biological agents for applications from national security to food processing. (Vijay Kumar, Birck Nanotechnology Center, Purdue University)
Findings are detailed in a paper appearing online this week in the Journal of Microelectromechanical Systems, which is available at http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=6145730. The paper was written by graduate research assistants Vijay Kumar and J. William Boley, undergraduate student Yushi Yang, mechanical engineering professor George Chiu and Rhoads. An earlier paper was published in April in the weekly journal Applied Physics Letters.

The work is based at the Dynamic Analysis of Micro- and Nanosystems Laboratory at Purdue's Birck Nanotechnology Center.

The aim is to apply the new approach to build sensors capable of reliably measuring particles that have a mass of less than one picogram - or trillionth of a gram - at room temperature and atmospheric pressure.

The microcantilever sensors have promise in detecting and measuring constituents such as certain proteins or DNA for biological testing in liquids, gases and the air. The devices might find applications in breath analyzers, industrial and food processing, national security and defense, and food and water quality monitoring.

"One question about these sensors is whether they will continue to work in the field," Rhoads said. "We've been doing a lot of blind, false-positive and false-negative tests to see how they perform in a realistic environment. We've had only a few false positives and negatives in months of testing."

The findings focus on detecting gases and show that the new sensors should be capable of more reliably measuring smaller quantities of gas than is possible with current sensors.

Measuring amplitude is far easier than measuring frequency because the amplitude changes dramatically when a particle lands on the microcantilever, whereas the change in frequency is minute.

"We haven't beaten the sensitivity of all other sensors yet," Rhoads said. "But the difference is that we are trying to do it with a compact device that is truly implementable at the microscale, while many others use fairly large laboratory equipment."

The researchers tested the cantilevers in a chamber filled with precisely controlled quantities of methanol to study their reliability. A patent is pending on the invention.

The research has been partially funded by the National Science Foundation. Student support was provided by Purdue and the Purdue Research Foundation.

Writer: Emil Venere, 765-494-4709, venere@purdue.edu Sources: Jeffrey Rhoads, 765-494-5630, frhoads@purdue.edu George Chiu, 765 494-2688, gchiu@purdue.edu

Note to Journalists: Electronic copies of the research papers are available from the journal or by contacting Emil Venere, Purdue News Service, at 765-494-4709, venere@purdue.edu

Sunday, February 05, 2012

Transistor that may prove the missing link for graphene to become the next silicon

In a paper published this week in Science, a Manchester team lead by Nobel laureates Professor Andre Geim and Professor Konstantin Novoselov has literally opened a third dimension in graphene research. Their research shows a transistor that may prove the missing link for graphene to become the next silicon.

Graphene – one atomic plane of carbon – is a remarkable material with endless unique properties, from electronic to chemical and from optical to mechanical.

One of many potential applications of graphene is its use as the basic material for computer chips instead of silicon. This potential has alerted the attention of major chip manufactures, including IBM, Samsung, Texas Instruments and Intel. Individual transistors with very high frequencies (up to 300 GHz) have already been demonstrated by several groups worldwide.

Unfortunately, those transistors cannot be packed densely in a computer chip because they leak too much current, even in the most insulating state of graphene. This electric current would cause chips to melt within a fraction of a second.

This problem has been around since 2004 when the Manchester researchers reported their Nobel-winning graphene findings and, despite a huge worldwide effort to solve it since then, no real solution has so far been offered.

The University of Manchester scientists now suggest using graphene not laterally (in plane) – as all the previous studies did – but in the vertical direction. They used graphene as an electrode from which electrons tunnelled through a dielectric into another metal. This is called a tunnelling diode.

Graphene electronics

Graphene electronics are becoming ever closer to reality.
Then they exploited a truly unique feature of graphene – that an external voltage can strongly change the energy of tunnelling electrons. As a result they got a new type of a device – vertical field-effect tunnelling transistor in which graphene is a critical ingredient.

Dr Leonid Ponomarenko, who spearheaded the experimental effort, said: "We have proved a conceptually new approach to graphene electronics. Our transistors already work pretty well. I believe they can be improved much further, scaled down to nanometre sizes and work at sub-THz frequencies."

"It is a new vista for graphene research and chances for graphene-based electronics never looked better than they are now", adds Professor Novoselov.

Graphene alone would not be enough to make the breakthrough. Fortunately, there are many other materials, which are only one atom or one molecule thick, and they were used for help.

The Manchester team made the transistors by combining graphene together with atomic planes of boron nitride and molybdenum disulfide. The transistors were assembled layer by layer in a desired sequence, like a layer cake but on an atomic scale.

Such layer-cake superstructures do not exist in nature. It is an entirely new concept introduced in the report by the Manchester researchers. The atomic-scale assembly offers many new degrees of functionality, without some of which the tunnelling transistor would be impossible.

"The demonstrated transistor is important but the concept of atomic layer assembly is probably even more important," explains Professor Geim. Professor Novoselov added: "Tunnelling transistor is just one example of the inexhaustible collection of layered structures and novel devices which can now be created by such assembly.

"It really offers endless opportunities both for fundamental physics and for applications. Other possible examples include light emission diodes, photovoltaic devices, and so on."


Contact: Daniel Cochlin daniel.cochlin@manchester.ac.uk 0044-161-275-8387 University of Manchester

Friday, February 03, 2012

Biosolar breakthrough promises cheap, easy green electricity that taps into photosynthetic processes to produce efficient and inexpensive energy

UT biosolar breakthrough promises cheap, easy green electricity, Barry D. Bruce, professor of biochemistry, cellular and molecular biology, at the University of Tennessee, Knoxville, is turning the term 'power plant' on its head

Barry D. Bruce, professor of biochemistry, cellular and molecular biology, at the University of Tennessee, Knoxville, is turning the term "power plant" on its head. The biochemist and a team of researchers have developed a system that taps into photosynthetic processes to produce efficient and inexpensive energy.

Bruce collaborated with researchers from the Massachusetts Institute of Technology and Ecole Polytechnique Federale in Switzerland to develop a process that improves the efficiency of generating electric power using molecular structures extracted from plants. The biosolar breakthrough has the potential to make "green" electricity dramatically cheaper and easier.

"This system is a preferred method of sustainable energy because it is clean and it is potentially very efficient," said Bruce, who was named one of "Ten Revolutionaries that May Change the World" by Forbes magazine in 2007 for his early work, which first demonstated biosolar electricity generation. "As opposed to conventional photovoltaic solar power systems, we are using renewable biological materials rather than toxic chemicals to generate energy. Likewise, our system will require less time, land, water and input of fossil fuels to produce energy than most biofuels."

Their findings are in the current issue of Nature: Scientific Reports.

Barry Bruce

Barry Bruce

Algae could be the next power source

Algae could be the next power source.
To produce the energy, the scientists harnessed the power of a key component of photosynthesis known as photosystem-I (PSI) from blue-green algae. This complex was then bioengineered to specifically interact with a semi-conductor so that, when illuminated, the process of photosynthesis produced electricity. Because of the engineered properties, the system self-assembles and is much easier to re-create than his earlier work. In fact, the approach is simple enough that it can be replicated in most labs—allowing others around the world to work toward further optimization.

"Because the system is so cheap and simple, my hope is that this system will develop with additional improvements to lead to a green, sustainable energy source," said Bruce, noting that today's fossil fuels were once, millions of years ago, energy-rich plant matter whose growth also was supported by the sun via the process of photosynthesis.

This green solar cell is a marriage of non-biological and biological materials. It consists of small tubes made of zinc oxide—this is the non-biological material. These tiny tubes are bioengineered to attract PSI particles and quickly become coated with them—that's the biological part. Done correctly, the two materials intimately intermingle on the metal oxide interface, which when illuminated by sunlight, excites PSI to produce an electron which "jumps" into the zinc oxide semiconductor, producing an electric current.

The mechanism is orders of magnitude more efficient than Bruce's earlier work for producing bio-electricity thanks to the interfacing of PS-I with the large surface provided by the nanostructured conductive zinc oxide; however it still needs to improve manifold to become useful. Still, the researchers are optimistic and expect rapid progress.

Bruce's ability to extract the photosynthetic complexes from algae was key to the new biosolar process. His lab at UT isolated and bioengineered usable quantities of the PSI for the research.

Andreas Mershin, the lead author of the paper and a research scientist at MIT, conceptualized and created the nanoscale wires and platform. He credits his design to observing the way needles on pine trees are placed to maximize exposure to sunlight.

Mohammad Khaja Nazeeruddin in the lab of Michael Graetzel, a professor at the Ecole Polytechnique Federale in Lausanne, Switzerland, did the complex testing needed to determine that the new mechanism actually performed as expected. Graetzel is a pioneer in energy and electron transfer reactions and their application in solar energy conversion.

Michael Vaughn, once an undergraduate in Bruce's lab and now a National Science Foundation (NSF) predoctoral fellow at Arizona State University, also collaborated on the paper.

"This is a real scientific breakthrough that could become a significant part of our renewable energy strategy in the future," said Lee Riedinger, interim vice chancellor for research. "This success shows that the major energy challenges facing us require clever interdisciplinary solutions, which is what we are trying to achieve in our energy science and engineering PhD program at the Bredesen Center for Interdisciplinary Research and Graduate Education of which Dr. Bruce is one of the leading faculty."

The Bredesen Center is a joint UT/Oak Ridge National Laboratory academic unit. Bruce is also a co-principal investigator and scientific thrust leader in TN: SCORE, the Tennessee Solar Conversion and Storage Using Outreach, Research and Education. The $20 million project is funded by the NSF and focuses on promoting research and education on solar energy problems across Tennessee. Additionally, he co-founded and is associate director of UT's Sustainable Energy Education.

Bruce's work is funded by the Emerging Frontiers Program at the National Science Foundation.

Contact: Whitney Heins wheins@utk.edu 865-974-5460 University of Tennessee at Knoxville

Wednesday, February 01, 2012

Varying morphology of block copolymers & chemical nature of nanorods provide controlled self-assembly in nanorods and nanorod-based nanocomposites

A relatively fast, easy and inexpensive technique for inducing nanorods - rod-shaped semiconductor nanocrystals - to self-assemble into one-, two- and even three-dimensional macroscopic structures has been developed by a team of researchers with the U.S. Department of Energy (DOE)'s Lawrence Berkeley National Laboratory (Berkeley Lab). This technique should enable more effective use of nanorods in solar cells, magnetic storage devices and sensors. It should also help boost the electrical and mechanical properties of nanorod-polymer composites.

Leading this project was Ting Xu, a polymer scientist who holds joint appointments with Berkeley Lab's Materials Sciences Division and the University of California (UC) Berkeley's Departments of Materials Sciences and Engineering, and Chemistry. Xu and her research group used block copolymers - long sequences or "blocks" of one type of monomer bound to blocks of another type of monomer - as a platform to guide the self-assembly of nanorods into complex structures and hierarchical patterns. Block copolymers have an innate ability to self-assemble into well-defined arrays of nano-sized structures over macroscopic distances.

"Ours is a simple and versatile technique for controlling the orientation of nanorods within block copolymers," Xu says. "By varying the morphology of the block copolymers and the chemical nature of the nanorods, we can provide the controlled self-assembly in nanorods and nanorod-based nanocomposites that is critical for their use in the fabrication of optical and electronic devices."

Xu is the corresponding author of a paper describing this research that has been published in the journal Nano Letters under the title "Direct Nanorod Assembly Using Block Copolymer-Based Supramolecules." Co-authoring the paper were Kari Thorkelsson, Alexander Mastroianni and Peter Ercius.

CdS Nanorods and Block Copolymers

Caption: This transmission electron micrograph (a) shows cadmium sulfide nanorods forming arrays that are aligned and oriented parallel to the cylindrical microdomains of block copolymers. The schematic drawing (b) illustrates copolymers with nanorods.

Credit: Image courtesy of Berkeley Lab. Usage Restrictions: None.

CdS Nanorods Self-Assembled

Caption: This TEM tomography reconstruction of cadmium sulfide nanorods that self-assembled within block copolymers shows their ordered macroscopic alignment.

Credit: Courtesy of Berkeley Lab National Center for Electron Microscopy. Usage Restrictions: None.
Nanorods – particles of matter a thousand times smaller than the stuff of today's microtechnologies – display highly coveted optical, electronic and other properties not found in macroscopic materials. To fully realize their vast technological promise, however, nanorods must be able to assemble themselves into complex structures and hierarchical patterns, similar to what nature routinely accomplishes with proteins.

Xu and her research group first enlisted block copolymers as allies in this self-assembly effort in 2009, working with the spherical nanoparticles commonly known as quantum dots. In that study, they lashed quantum dots to block copolymers via a "mediator" of small adhesive molecules. In this latest development, Xu and her group again made use of adhesive molecules, but this time to mediate between the nanorods and supramolecules of block copolymers. A supramolecule is a group of molecules that act as a single molecule able to perform a specific set of functions.

"Block copolymer supramolecules self-assemble and form a wide range of morphologies that feature microdomains typically a few to tens of nanometers in size," Xu says. "As their size is comparable to that of nanoparticles, the microdomains of block copolymer supramolecules provide an ideal structural framework for the co-assembly of nanorods."

Xu and her group incorporate nanorods into solutions of block copolymer supramolecules that form spherical, cylindrical and lamellar microdomains. During the drying process energy is contributed to the system from the interactions between nanorod ligands and polymers, the entropy associated with polymer chain deformation upon nanorod incorporation, and the interactions between individual nanorods. Xu and her group observed that these energetic contributions determine the placement and distribution of the nanorods, as well as the overall morphology of the nanorod-block copolymer composites. These energetic contributions can be easily tuned by varying the supramolecular morphology, which is accomplished simply by attaching different types of small molecules to the side chains of the block copolymers.

"We can readily access a wide library of nanorod assemblies including arrays of nanorods aligned parallel to block copolymer cylindrical microdomains, continuous nanorod networks, and nanorod clusters," Xu says. "Since the macroscopic alignment of block copolymer microdomains can be obtained in bulk and in thin films by the application of external fields, our technique should open up a viable route to manipulate the macroscopic alignments of nanorods."

This new technique can produce ordered arrays of nanorods that are macroscopically aligned with tunable distances between individual rods - a morphology that lends itself to the production of plasmonics, which are materials that hold great promise for superfast computers, ultra-powerful optical microscopes, and even the creation of invisibility carpets. It is also a straightforward nanoparticle self-assembly technique that can produce a continuous network of nanorods with nanoscopic separation distances. Such networks can enhance the macroscopic properties of nanocomposites, including electrical conductivity and material strength.

Xu credits much of the success of this research to the exceptional capabilities and staff at the National Center for Electron Microscopy (NCEM), a DOE national user facility at Berkeley Lab, which is home to the world's most powerful electron microscopes.

"For the study of three-dimensional nanorod assemblies, we needed to implement high-resolution tomography and this posed a challenge not only for collecting the imaging data but also for processing it," Xu says. "The expertise and skill of NCEM's Peter Ercius was invaluable."

Xu and her group are now investigating the self-assembly of semiconductor nanocrystals that take the shapes of cubes or tetrapods, both of which have important potential applications for photovoltaic and other technologies.

"We'd also like to investigate the self-assembly of nanoparticles into combinations of different shapes," Xu says.


This research was supported by the DOE Office of Science.

Lawrence Berkeley National Laboratory addresses the world's most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab's scientific expertise has been recognized with 13 Nobel prizes. The University of California manages Berkeley Lab for the U.S. Department of Energy's Office of Science. For more, visit www.lbl.gov.

Contact: Lynn Yarris lcyarris@lbl.gov 510-486-5375 DOE/Lawrence Berkeley National Laboratory