May 11, 2011 — Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have assembled nanoscale pairings of fullerenes and quantum dots, controlling particle size and arrangement precisely so as to better understand how these two-particle systems convert light to electricity.

This is a hybrid inorganic/organic, dimeric (two-particle) material that acts as an electron donor-bridge-acceptor system for converting light to electrical current, said Brookhaven physical chemist Mircea Cotlet, lead author of a paper describing the dimers and their assembly method in Angewandte Chemie (Access the article here: http://onlinelibrary.wiley.com/doi/10.1002/anie.201007270/abstract).

By varying the length of the linker molecules and the size of the quantum dots, the scientists can control the rate and the magnitude of fluctuations in light-induced electron transfer at the level of the individual dimer. The dimers could lead to power-generating units for molecular electronics or more efficient photovoltaic solar cells, said Cotlet, who conducted this research with materials scientist Zhihua Xu at Brookhaven’s Center for Functional Nanomaterials (CFN).

Figure. Left: Photoinduced electron transfer occurring in quantum dot-bridge-fullerene hererodimers and observed with single molecule microscopy. Right: Control of electron transfer (ET) rate by variation of interparticle distance (R, upper panel) and quantum dot size (D, lower panel).

Organic donor-bridge-acceptor systems have a range of charge transport mechanisms because their charge-transfer properties can be controlled by varying their chemistry. Recently, quantum dots have been combined with electron-accepting materials such as dyes, fullerenes, and titanium oxide to produce dye-sensitized and hybrid solar cells in the hope that the light-absorbing and size-dependent emission properties of quantum dots would boost the efficiency of such devices (so far, the power conversion rates of these systems have remained quite low). "Studying the charge separation and recombination processes in these simplified and well-controlled dimer structures helps us to understand the more complicated photon-to-electron conversion processes in large-area solar cells, and eventually improve their photovoltaic efficiency," Xu said.

Zhihua Xu (seated) and Mircea Cotlet (standing).

"Efforts to understand the processes involved so as to engineer improved systems have generally looked at averaged behavior in blended or layer-by-layer structures rather than the response of individual, well-controlled hybrid donor-acceptor architectures," said Xu.

The precision fabrication method developed by the Brookhaven scientists allows them to carefully control particle size and interparticle distance so they can explore conditions for light-induced electron transfer between individual quantum dots and electron-accepting fullerenes at the single molecule level.

The entire assembly process takes place on a surface and in a stepwise fashion to limit the interactions of the components (particles), which could combine in a number of ways if assembled by solution-based methods. This surface-based assembly also achieves controlled, one-to-one nanoparticle pairing.

To identify the optimal architectural arrangement for the particles, the scientists strategically varied the size of the quantum dots — which absorb and emit light at different frequencies according to their size — and the length of the bridge molecules connecting the nanoparticles.

For each arrangement, they measured the electron transfer rate using single molecule spectroscopy.

The scientists found that reducing quantum dot size and the length of the linker molecules led to enhancements in the electron transfer rate and suppression of electron transfer fluctuations.

"This suppression of electron transfer fluctuation in dimers with smaller quantum dot size leads to a stable charge generation rate, which can have a positive impact on the application of these dimers in molecular electronics, including potentially in miniature and large-area photovoltaics," Cotlet said.

A U.S. patent application is pending on the method and the materials resulting from using the technique, and the technology is available for licensing. Contact Kimberley Elcess at (631) 344-4151, [email protected], for more information.

This work was funded by the DOE Office of Science.

The Center for Functional Nanomaterials at Brookhaven National Laboratory is one of the five DOE Nanoscale Science Research Centers (NSRCs), premier national user facilities for interdisciplinary research at the nanoscale. Together the NSRCs comprise a suite of complementary facilities that provide researchers with state-of-the-art capabilities to fabricate, process, characterize and model nanoscale materials, and constitute the largest infrastructure investment of the National Nanotechnology Initiative. The NSRCs are located at DOE’s Argonne, Brookhaven, Lawrence Berkeley, Oak Ridge and Sandia and Los Alamos national laboratories. For more information about the DOE NSRCs, please visit http://nano.energy.gov.

One of ten national laboratories overseen and primarily funded by the Office of Science of the U.S. Department of Energy (DOE), Brookhaven National Laboratory conducts research in the physical, biomedical, and environmental sciences, as well as in energy technologies and national security. Learn more at http://www.bnl.gov

May 6, 2011 — Evident Technologies Corporation and Samsung Electronics Co. Ltd entered into a comprehensive patent licensing and purchasing agreement for Evident’s quantum dot LED technology. This agreement grants Samsung worldwide access to Evident’s patent portfolio for all products related to quantum dot LEDs from manufacture of the quantum dot nanomaterials to final LED production.

"We are excited that Samsung, the leader in consumer electronics, has licensed our quantum dot technology," said Dr. Clint Ballinger, CEO of Evident Technologies. "We already enjoy a terrific working relationship and look forward to the future of this technology."

Quantum dots are nanometer-sized semiconductor crystals that have great commercial promise in electronic applications from solar energy conversion to thermoelectrics to LEDs. Evident commercialized quantum dot LEDs with products launched in 2007.

Evident Technologies is a nanotechnology company specializing in the creation of semiconductor quantum dots. Learn more at http://www.evidenttech.com/.

May 5, 2011 — A coordination action on graphene has been funded by the European Commission (EC) to develop plans for a 10-year, EUR1 billion Future and Emerging Technology (FET) flagship. This is an

Image. Graphene, a single layer of carbon atoms, may be the most amazing and versatile substance available to mankind. Stronger than diamond, yet lightweight and flexible, graphene enables electrons to flow much faster than silicon. It is also a transparent conductor, combining electrical and optical functionalities in an exceptional way.

ambitious, large-scale visionary research initiative, aiming at a breakthrough for technological innovation and economic exploitation based on graphene and related two-dimensional materials.

 Graphene can trigger a smart and sustainable carbon revolution, with profound impact in information and communication technology (ICT) and everyday life. Its unique properties will spawn innovation on an unprecedented scale and scope for high speed, transparent and flexible consumer electronics; novel information processing devices; biosensors; supercapacitors as alternatives to batteries; mechanical components; lightweight composites for cars and planes.

Cambridge’s role, led by Dr Andrea Ferrari of the Department of Engineering, is to develop the science and technology roadmap for the future investment. These will be the structured plans for what new research on graphene and other two-dimensional materials is needed and the routes for the implementation of graphene in industrially viable technologies. The Cambridge team will determine what new facilities should be built in Europe for that.

"Graphene, a truly European technology, [2010 Nobel Prize for Physics winners Andre Geim and Konstantin Novoselov are both of the University of Manchester, UK and natives of Russia; Geim is a Dutch citizen], is at the crossroad between fundamental research and applications. Exploiting the full potential of graphene will have huge impacts on society at large. We are thrilled that the EU Commission shares our view and believes in our focused and open approach to moving forward, at a time when the international community, from United States to Korea, is moving significant resources to strengthen their know-how and facilitate the roadmap to applications," says Dr Andrea Ferrari.

The research effort of individual European research groups pioneered graphene science and technology, but a coordinated European level approach is needed to secure a major role for EU in this ongoing technological revolution.

Photo. Cambridge University’s Dr Andrea Ferrari, Department of Engineering.

The graphene flagship aims to bring together a large, focused, interdisciplinary European research community, acting as a sustainable incubator of new branches of ICT applications, ensuring that European industries will have a major role in this radical technology shift over the next 10 years. An effective transfer of knowledge and technology to industries will enable product development and production.

The graphene flagship includes over 130 research groups, representing 80 academic and industrial partners in 21 European countries. The coordination action is lead by a consortium of nine partners who pioneered graphene research, innovation, and networking activities. Coordinated by Chalmers University of Technology in Sweden, it includes the Universities of Cambridge, Manchester and Lancaster in the UK, the Catalan Institute of Nanotechnology in Spain, the Italian National Research Council, the European Science Foundation, AMO GmbH in Germany, and the Nokia corporation. The advisory council includes Nobel Laureates Andre Geim (University of Manchester), Konstantin Novoselov (University of Manchester), Albert Fert (THALES) and Klaus von Klitzing (Max-Planck Institute), the leading graphene theoretician Francisco Guinea (CSIC, Spain), as well as Luigi Colombo (Texas Instruments, USA) and Byung Hee Hong (SKK University, Korea), both pioneers of graphene mass production and graphene-based product development.

The pilot phase coordination action started May 1. Its main task is to pave the way for the full 10-year EUR1 billion flagship both in terms of the organizational framework and a scientific and technological roadmap for research and innovation. The action plan for the FET Flagship will be submitted in 2012 to the European Commission, aiming for GRAPHENE to be one of the two flagships launched in 2013.

More details on the graphene flagship pilot can be found at www.graphene-flagship.eu

More information on the EU Future Emerging Technology Flagship Initiative is at http://cordis.europa.eu/fp7/ict/programme/fet/flagship/home_en.html

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May 3, GLOBE NEWSWIRE — FEI Company (Nasdaq:FEIC), instrumentation company, is extending its ChemiSTEM Technology to enable atomic-level energy dispersive X-ray (EDX) spectroscopy across the periodic table.

The combination of increased current in an atomic-sized probe by Cs-correction and the increase in X-ray detection sensitivity and beam current of the ChemiSTEM Technology allows results to be obtained within minutes.

Figures. Atomic-level EDX spectroscopy of the material Strontium Titanate; the individual atomic positions of the crystal structure can be easily distinguished by their chemical signal (red is Strontium, green is Titanium). These images are based on raw data, with no signal post-processing, and the individual atomic column positions in the structure are visible and clearly distinguished from their neighbors with very high contrast and signal-to-noise quality. The sampling of these atomic-level chemical maps is 0.075 Angstroms per pixel, the highest sampling density obtained so far by any atomic spectroscopy technique using scanning/transmission electron microscopy (S/TEM). These chemical maps were acquired in just minutes on a Titan G2 60-300 S/TEM with ChemiSTEM Technology.

"One of the most important applications for the new technology will be element-specific imaging at atomic resolution," said Professor Ferdinand Hofer of Graz University of Technology, Austria. The technology will be applied to study interfaces in semiconductors, solar cell materials, LEDs and ceramic materials with previously unknown detection sensitivity and accuracy.

George Scholes, FEI’s vice president for product management, adds, "The ChemiSTEM Technology will enable breakthough results in many key application areas for our customers, such as catalysis, metallurgy, microelectronics, and green energy materials, to name a few. For example, in a recent experiment with ChemiSTEM Technology, our customer was able to clearly resolve the core-shell structure of 5nm catalyst nanoparticles in about three minutes and with three times greater pixel resolution than a previous experiment with conventional technology. And the conventional technology failed after three hours of data collection to clearly resolve the same structure."

ChemiSTEM Technology achieves a factor of 50 or more enhancement in speed of EDX elemental mapping on scanning/transmission electron microscopes (S/TEMs) compared to conventional technology employing standard EDX Silicon-drift detectors (SDDs) and standard Schottky-FEG electron sources. It combines FEI’s proprietary X-FEG high brightness electron source, providing up to five times more beam current at a given spatial resolution; the patent-pending Super-X detection system, providing up to ten times or more detection sensitivity in EDX; and fast scanning electronics, capable of achieving EDX spectral rates of up to 100,000 spectra per second. Additionally, the windowless detector design employed for each of ChemiSTEM Technology’s four integrated SDD detectors has proven to optimize the detection of both light and heavy elements.

This combination of high detection sensitivity and high spectral rates of up to 100,000 spectra per second are enabling better EDX mapping of materials that are highly sensitive to electron beam damage, such as composition analysis in nanometer-scale Indium Gallium Nitride quantum wells used in light emitting diode (LED) devices, and semiconductor devices with potentially mobile dopant materials, as well as many others devices used in emerging nanotechnologies.

FEI (Nasdaq:FEIC) provides electron- and ion-beam microscopes and tools for nanoscale applications across many industries: industrial and academic materials research, life sciences, semiconductors, data storage, natural resources and more. More information can be found at www.fei.com.

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May 2, 2011 — Asylum Research’s Cypher atomic force microscope (AFM) is routinely achieving resolution of atomic-scale point defects in liquid.  While scanning tunneling microscopes have demonstrated point defect resolution since their invention, it has been more elusive in AFM.  Many commercial AFMs can routinely image atomic lattices in ambient and liquid conditions, but the lack of point defects has led most researchers to conclude that the contact areas are typically several atoms across. 

Figure. Successive AC mode topography images of the cleavage plane of a calcite crystal in water. The repeated point defects demonstrate the true atomic resolution capabilities of the Cypher AFM.  Arrows indicate scan direction.  Scan size 20nm; Z scale 3.2Å; Cantilever Amplitude 4Å; Cantilever Frequency 454 kHz.

More recently, instrumental improvements have brought true atomic resolution to ultra-high vacuum (UHV) AFM.  Achieving true-atomic resolution under ambient conditions at the liquid-solid interface brings this resolution to an environment highly relevant for much practical research.  The Cypher AFM’s signal-to-noise and support for ultra-small probes have enabled this breakthrough in atomic scale imaging.

Asylum Research took the most popular imaging mode, AC-mode (also known as tapping, intermittent-contact, or dynamic AFM) and improved the resolution, Jason Cleveland, Asylum Research CEO, said. It was achieved with improved signal-to-noise ratio from the use of ultra-small cantilevers with megahertz resonant frequencies in liquid; the optical lever detection noise floor was pushed to 25 fm/rtHz, allowing the measurements to remain thermally limited even with very stiff cantilevers and amplitudes as small as 1 Angstrom. Cypher’s low open-loop noise of 5pm in X, Y, and Z allows the stability to image at this scale, even on a scanner with a 30µm lateral range.

Asylum Research provides atomic force and scanning probe microscopy (AFM/SPM) for materials and bioscience applications. Asylum’s Cypher AFM is a small sample AFM/SPM providing low-drift closed loop atomic resolution. Learn more at www.AsylumResearch.com.

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