[交流] 【原创】IMRC 2009----DAYS 1, 2

DAYS 1, 2 SUNDAY, MONDAY, August 16-17 The XVIII International Materials Research Congress 2009 (IMRC 2009) is being held from August 16 through the 20th, 2009, in Cancun, in the Yucatan peninsula of Mexico. The conference started on Sunday with an opening ceremony, including a plenary talk by Prof. Darrell Schlom of Cornell University, USA, in the evening followed by a toast (reception). The conference was off to a full start on Monday morning with a number of symposia conducting sessions as well as a poster session in the evening. The second plenary talk was presented by Prof. Subash Mahajan of Arizona State University, USA. Monday was also the first day of the exhibit. Pedro Hugo Hernández Tejeda (right) presenting a special award of appreciation to Alan Hurd (former president of MRS), with MRS-Mexico president Luis Enrique Sansores Cuevas in the foreground. CONTENTS Opening Session Plenary Lecture - Darrell Schlom Plenary Lecture - Subash Mahajan Technical Sessions Scenes from the Welcome Reception OPENING CEREMONY The first session of the XVIII International Materials Research Congress 2009 (IMRC 2009) in Cancun, Mexico, was the opening ceremony. Olivia Greave (Alfred Univ., USA) introduced the speakers. First, Luis Enrique Sansores Cuevas, President, MRS-Mexico, welcomed all attendees to the conference. The congress had made impressive strides in recent years. The present conference includes 1625 presentations slated from researchers from 44 countries. He also described the closer ties between MRS-Mexico and the Materials Research Society with 5 symposia co-organized at the current meeting and 12 planned for 2010. He thanked a number of people for making the conference a reality. Next, Alan Hurd, representing the Materials Research Society, also reiterated the close ties between the two Societies leading to this meeting and more in the future. This bodes well for materials research globally, and not just North America. He said that this conference is no longer a well-kept secret, with significant interest and participation from researchers. Next, Pedro Hugo Hernández Tejeda, one of the main forces behind these conferences recognized the efforts of Luis Enrique Sansores Cuevas and Alan Hurd in making this conference a reality, and presented them with plaques. Dr. Alan Hurd (representing the Materials Research Society), Dr. Jose Antonio de la Pena (Deputy Director for Science, National Council for Science and Technology (CONACyT), Mexico) and Dr. Luis Enrique Sansores Cuevas (President, MRS-Mexico) at the opening ceremony. Jose Antonio de la Pena (Deputy Director for Science, National Council for Science and Technology (CONACyT), Mexico) was the special guest of honor. He asked everyone to rise and declared the conference officially open. He then gave a presentation and overview of the current situation of Science and Technology in Mexico as well as the role that CONACyT plays in scientific research in the country. Mexico is the 11th largest economy in the world and is 53rd in competitiveness by one measure. However, in many respects, it still has a lot of catching up to do. In Latin America, it is second only to Brazil by most measures in scientific research. He described various special programs sponsored and encouraged by CONACyT including various thematic networks and the Mexicans Abroad Network. The latter encourages the integration of Mexican researchers working abroad with Mexican Universities. He also described new initiatives including the call for new topics for thematic networks, a new call for proposals for 10 new labs and the Collaboration in the Americas in Materials (CIAM). PLENARY LECTURE - DARRELL SCHLOM Gate Oxides beyond SiO2 and the High K Materials Revolution The first plenary talk of the congress was presented by Darrell Schlom (Cornell Univ., USA) on new gate oxide materials to replace SiO2 in current microprocessors that have been the backbone of the current information technology revolution. The very latest microprocessors use hafnium oxide as the gate oxide material. In order to continue along the Moore's law path with more and more transistors packed into a smaller space, it was recognized in the 1990s that while scaling, or reducing the thickness, of SiO2 worked to a point, quantum mechanical tunneling became a major issue at very small thicknesses leading to significant gate leakage current. Various high-K materials were suggested as alternatives in the 1990s. However, most of these still formed an SiO2 interface layer between Si and the oxide. Schlom and an undergraduate student performed a series of thermodynamic analyses and looked at various oxides, and they came up with a list of Si-compatible binary oxides, including HfO2. One of the materials in the list was LaLuO3. The rest of the talk focused on Schlom's and others work on this material. Recent studies have revealed that there is an abrupt and clean interface between LaLuO3 and Si. Amorphous LaLuO3 was also shown to have a higher dielectric constant than HfO2. The current generation of transistors uses the HfO2 gate, such as in Intel's Penryn processors. Manufacturers have also gone to a 45 nm thickness for the gate oxide along with the use of a metal gate. The future holds interesting possibilities. One is the use of III-V materials. Schlom has carried out a series of thermodynamic analyses for these materials in contact with various oxides as well. Varying the group III species was found to greatly affect the stability of the oxide on the semiconductor material. However, it was concluded that gate dielectrics that work for Si are also candidates for the III-V materials. Schlom concluded by thanking all the people working in the semiconductor industry for making the high-K revolution a reality. This is the primary reason for being able to continue Moore's law and provide low cost, low power, high speed computing to all. PLENARY LECTURE - SUBASH MAHAJAN Self-assembled nanostructures in mixed III – V and group III nitride layers and their influence on device behavior Semiconductor alloys, in contrast to solo semiconductor elements, allow for the tailoring of bandgaps and lattice constants to achieve a variety of optoelectronic applications. In the case of III-V ternary alloys, the alloy crystal structure is a mix of the two binary compounds. InGaAs, for example, is a mix of InAs and GaAs, where the ternary zinc-blende structure is composed of two zinc-blende sublattices-- one of the group III atoms (In and Ga) and the other of the group V atoms (As). Subash Mahajan (Arizona State Univ.) seeks to answer whether there is any pattern in the mixed-group sublattice, and what the implications of this are on device performance. He finds that phase separation occurs, to the detriment of some devices but also to the benefit of others, and that the microstructures resulting from the phase separation and ordering may be optimized for desired device performance. Atoms on the mixed sublattice will have different radii, resulting in varying bond lengths and thus residual stress in the material. Mahajan's group has observed that, in a variety of materials systems prepared by a variety of growth techniques, these residual stresses lead to phase separation in the bulk. For example, TEM micrographs of InGaAsP prepared by layer-phase epitaxy show spots of contrast on the order of 8 nm, as well as larger dark bands. They believe that these microstructures form as a result of phase separation due to lattice mismatch (the 8 nm-level contrast), which in turn causes layer buckling (the large bands contrast). Phase separation was further confirmed by the presence of satellite spots in the diffraction pattern of the sample. A thin InGaAsP layer, confined by InP, was grown by hydride-phase vapor epitaxy and similarly investigated by TEM. They observe satellite spots in the diffraction pattern due to ordering. To minimize the number of high-energy dangling bonds, the surface spontaneously reconstructs itself (2x4 reconstruction of the CuPt-type), resulting in local ordering on both the group III and the group V sublattices. Mahajan presented another example of this phenomenon in zinc-blende crystals with InGaAs, where "tremendous strain" produced by the bond length differences between Ga-As and In-As, again showing contrast in TEM images and implying phase separation. He noted that changing the growth conditions can change the scale of the separation, but that the basic mechanism of strain-induced separation remains. Mahajan's group finds that the wavelength of modulation is exponentially related to the activation energy for surface diffusion of As atoms on a Ga-In plane, which they calculate to be 0.25 eV. InGaAs, while having the same composition at different growth temperatures, was found to have variations in electron mobility over the same temperature range. He cited In-rich regions as the cause of this observed variation, as In-rich regions will have a lower bandgap than their Ga-rich counterparts, resulting in a higher concentration of carriers in the In-rich regions. Finally, three wurtzite structures were presented to further the hypothesis of phase separation in a different crystal symmetry. At 3% In, InGaN is not phase separated; but by 22% In, the central diffraction spot from a TEM sample is nonspherical, suggesting  phase separation. In this case, higher In concentrations produce a larger driving force for phase separation, resulting in shorter variation wavelengths. They observe regions of alternating contrast, concluding that this is due to the interaction between phase separated regions with different operating vectors. Stripe patterns in very thin specimens are thicker regions, containing overlapping modulations with multiple orientations. AlGaN grown by molecular beam epitaxy and analyzed with high-angle annular dark-field z-contrast TEM shows domain sizes limited by a defect structure, where the size difference again causes phase modulation. Lastly, the growth of AlGaN on AlN substrates was presented: while the AlN phase wets the substrate, the GaN phase does not, again resulting again in periodic contrast in the TEM. Light-emitting devices, such as lasers and LEDs, can benefit from such phase separation: dislocations have been shown to act as nonradiative recombination centers, reducing device performance. However, a phase-separated microstructure will arrest dislocation glide and climb propagation that inevitably occurs as a result of energy from nonradiative recombination at the dislocations during carrier injection, resulting in a longer device lifetime. TALKS ENERGY FORUM David Ginley (NREL, USA) opened the Energy forum by stressing that the current energy crisis, especially from the perspective of alternative technologies, is a problem of scale; and will require "an integrated complex of different options" to solve. Energy solutions are enormously challenging, in that they directly affect security, economic productivity, and environmental impact for the entire world. Yet, within the crux of these three issues lies significant opportunity. US Energy Consumption of renewables is projected to grow only 3% from 2006 to 2030, and a similar trend for the world. Scaling of renewable energy has been labeled a "grand challenge" by the US government. Many examples illustrate that this is a massive paradigm shift-- governmental institutions are coordinating efforts, $150B have been invested in the US over the next 10 years, and the US government is being stacked with staff toting STEM PhDs. Key challenges include implementing renewables at gigawatt scales, displacing petroleum-based fuels, and reducing energy demands of building, vehicles, and industry. Ginley focused on particular sources of energy, highlighting current costs and projected (US) goals. Wind has grown substantially in investments from 2002 to 2008, as has photovoltaics and concentrated solar power (CSP). Wind is already close to grid parity. China is already a major player in PV, again highlighting that this is an international issue. We must scale with the world and produce across national boundaries. Biofuels will require significant transformitive technology to reach projected goals. While fuel cells look like they could be a long-term option, the energy cycle efficiency is US goals are ambitions -- for example, 20% of US electricity generation by wind by 2030-- underscoring that solutions must be global, requiring meetings that merge communities, such as this conference. Basic research, technology-driven, and industrial-driven development must be balanced to achieve the potential. Many higher-level questions remain: how can government, industry, and academe partner to enhance the growth? How can we store energy? How can we improve our current inefficiencies (e.g., incandescence vs. solid-state lighting)? How can we reach the goals set by the DOE within the deadline specified? Overall, energy solutions require a new approach-- multi-disciplinary, -institutional, and -national. As Ginley describes it, "a new way to do business for science." Recycling The Impact On The Energy Equation Recycling material refuse represents an opportunity to significantly reduce our materials consumption impact, said Randolph Kirchain (MIT, USA) in his presentation in the Energy Forum. Materials consumption is massive and growing rapidly-- the US EPA estimates that in 2006, Americans threw out 251M metric tons, or about 2 kg of trash per person per day. (Luckily, this number has been relatively constant since 1990, when curb-side recycling was introduced.) On the other end of the same equation, consumption of materials has skyrocketed in the past century in fuels, metals, construction, chemicals, and biomass -- each American takes in 80 kg per person per day (buildings, cars, etc.). Finally, materials production is energy-intensive-- the production of polymers from recycled materials represents 33% reduction in energy in comparison to raw materials; similarly, 50% for Al, Cu, Pb; and nearly 100% for precious metals and rare-earth metals (Au, Ag, Pt). Unfortunately, we still have a long way to go to improve recycling. Auto batteries are recycled at a rate of 99%, but aluminum cans are only at 45% and glass containers at an abysmal 25%. If the missing fractions could be recovered, then up to 1-2EJ/yr of energy could be saved. If industry were to recycle its waste, this could be an additional savings of 1.5-3 EJ/yr. Kirchain highlighted a few key opportunities to increase recycling rates: design products that can use recycled materials or easier to recycle at the end of life, collect manufacture waste, find ways to separate trash from recyclable materials, and combine recycled materials with product design. As an example of utilizing recycled materials into new product design, Kirchain's group described the uncertainty facing recyclers which may inhibit them from fully utilizing their recycle-ability with two different models. In this scenario, a recycler purchases recyclables from the market, and then blends them into an alloy of finished goods to sell to industries that make new goods. Yet, many uncertainties arise that effect the way the recycler makes decisions: what will the consumer want in the future? What is the composition, price, availability, and quality variability from batch to batch of recyclables? Kirchain's group found that a linear risk model, which assumes that the consumer will use a mix of new and recycled material to produce a good, incorrectly accounts for the way that variation in the recycled materials accrues. An uncertainty-aware model, which uses probabilistic compositional constraints, describes reality more accurately. When applied to automotive scrap, an uncertainty-aware model reduces cost and increases recycled material incorporation when compared to the linear model. WATER FORUM Water Safety/Scarcity Panel Challenges and Opportunities for Sustainable Water – An Urban Perspective Rich Sustich, of the Clean Water America Alliance (CWA), opened the session with a look into how urban communities are uniquely affected by the availability of potable water.  He explained that even though urban areas contain the majority of the world’s population, infrastructure and management are outdated or ineffective, and the problems of water availability in these areas will likely escalate with population expansion and climate change.  He also noted that the current water systems are open to contamination, lack resistant retrofit materials, and need proactive contamination detections methods.  Sustich identified several key points in solving this dilemma that include:  technologies that focus on capture and reuse of water, the use of light weight, permeable building materials, and a real-time water sensing network.   The Control of Emerging Waterborne Viral Pathogens:  Inactivation Kinetics and Mechanisms Benito Marinas, of the University of Illinois, USA, gave an insightful presentation on the push to find alternative methods to disinfect drinking water.  He explained how the use of UV radiation combined with chlorine is effective on viral pathogens.  Several experimental studies showed adenovirus 2 and coxsackievirus B5 were inactivated by exposure to UV light and Cl2, and also how temperature and pH affect the activity of the disinfectants.   The results showed the adenovirus was more resistant to UV disinfection, and the coxsackievirus was more resistant to free chlorine.  The study presented also proposed a mechanism on how the adenovirus is inactivated.  The UV light and chlorine inactivation mechanism is believed to work by inhibiting E1A protein and DNA synthesis which stops the virus replication cycle.  He concluded that future materials research should include viral biosensors that will give early alert to infectious agents in the water supply.   Treatment and Water Quality Coordination Sofia E Garrido Hoyos, of the Instituto Mexicano de Tecnologia del Agua, presented a study detailing the issues regarding the water supply in Mexico, and the steps taken to address this concern.  Her talk indicated that significant problems in Mexican water resources are water quality and the inability to harvest a greater percentage of its precipitation and distribute it as drinking water.  Hoyos identified a need to improve water quality by increasing the water treatment standards.  New treatment plants constructed in Villa Nicolas Zapata and Ajuchitlan, Mexico, are under evaluation of adherence to the new standards.  The removal of arsenic from Mexican drinking water is a top concern.  Currently the maximum permissible limit of 0.025 mg L-1 is higher than the limit recommended by the World Health Organization (WHO), and the limit identified as a cancer risk by the Environmental Protection Agency (EPA). The technologies currently used to remove arsenic have the drawback of generating arsenic waste sludge.  Newer more promising treatments include capacitive deionization, sand filtration, and absorption of arsenic onto goethite. Symposium 1. Nanostructured Materials and Nanotechnology Template Synthesis of Mesoporous-Scandia Stabilized Zirconia Powders for Solid-Oxide Fuel Cell Applications Olivia Graeve's group at Alfred Univ., USA, comprehensively covers the preparation of ceramic powders for solid oxide fuel cells (SOFCs), including synthesis, sintering, and analysis of nanopowders prepared by precipitation with the help of steric stabilization. The final efficiency of a SOFC is dependent upon, among other variables, the morphology of the electrolyte-- this center section of the cell must be fully dense to allow oxygen diffusion through the bulk by vacancy diffusion. Additionally, oxygen diffusion may also occur along high surface-energy grain boundaries, increasing the cell efficiency dramatically. While the bulk diffusion is controlled mainly by doping, grain boundary diffusion can be controlled by managing the population of grain boundaries. The precipitation of nanopowders is a simple and controllable technique to produce the free-flowing, unagglomerated powders necessary for the bulk processing to produce SOFCs. These precipitates are typically amorphous gels of metal hydroxides that must be crystallized by heat treatment, but this heating step can lead to the formation of undesireable agglomerates, introducing interparticle porosity and plaguing future bulk processing techniques. Through the delicate balance of steric stabiliation by surface functional groups, cleaning steps, and heat treatment, Graeve's group has acheived particle sizes down to 10 nm. They found that washing stabilized particles in water produces hydrogen bonds between the surface groups, leading to a strong bond between particles and leaving porosity in the final sintered product. Alternatively, washing stabilized particles in ethanol produces well-dispersed particles. Finally, leaving some residual surfactant on the particle surface keeps the particles from coming into physical contact (and thus necking during heat treatment), which burn off at the end of the heat treatment, leaving completely unagglomerated powders. A major challenge of particle analysis is appropriately characterizing both the size of the crystallite, typically achieved by TEM and x-ray line broadening, as well as that of any agglomerates, which may be composed of multiple particles, interparticle vacancies, and larger voids. Graeve utilizes dynamic light scattering as a simple yet comprehensive technique to describe the distribution of particle sizes in a solution that is sensitive to sizes from 0.8 nm to 6.5 microns. With this technique, she was able to conclude that her powders have a final particle size centered around 10-15 nm. Symposium 2. Theory and Computer Simulation of Materials Nonmagnetic and Magnetic Superatoms: Towards Design of Nanoscale Materials with Precise Control Over Properties Shiv N. Khanna (Virginia Commonwealth Univ., USA), in his talk in symposium 2, described the use of nanoclusters as a path towards designing materials with very precise control over properties. The motivation of this work was to design new nanoscale materials with tunable optical, electronics, magnetic and catalytic properties using assemblies of designer clusters. One class of such clusters are superatoms, with the ultimate aim of using these to form crystals. The quantum states in metal clusters are grouped into electronic shells, similar to atoms. Filling of the electronic shells with paired electrons results in local minima in energy; leading to stable species called magic clusters. These findings led to the realization that selected clusters can mimic chemical properties of elemental atoms on the periodic table and can be classified as superatoms. Thus far, the work on superatoms has focused on non-magnetic species. Khanna then described how magnetic superatoms could be formed. For instance, in alkali-doped clusters, the alkali hosts can stabilize and enhance spin moments on transition metal sites. Systems having both localized and delocalized electron states yield magnetic superatoms, where localized electrons stabilize magnetic moments while filled nearly free electron shells lead to stable species.Such magnetic superatoms assemblies could be ideal for molecular electronic devices, as the coupling could be altered by charging or weak fields. He described various building blocks that have been proposed to form designer clusters and macroscopic nano-assemblies. He concluded by discussing the idea of a tunable band gap using such various cluster assemblies. A three step protocol for cluster assembled materials was proposed including gas phase synthesis for identifying potential motifs for assembly, theoretical energy landscapes to confirm characteristics of potential motifs and finally synthesis of the material. Quantum Modelling Of Nanocrystals, Nanowires, And Nanofilms In his talk in symposium 2, James Chelikowsky (University of Texas, Austin, USA) presented advances in hardware and algorithims to examine systems from 1 to 10,000 atoms, in order to gain insights into the properties of matter across the entire nanoscale. Chelikowsky's group employed two key computational methods: pseudopotential theory, to focus on chemically-active electronic states (i.e., the valence states), and density function theory, to convert a many-electron problem into a one-electron problem via the Kohn-Sham (KS) equation. The KS equation is solved self-consistently to give the spatial and energetic distribution of the electron states, from which the total energy may be extracted. To reduce the computation time when modeling large systems (1000-10,000 atoms) at the nanoscale, the Hamiltonian could be simplified, the code could be optimized to the available hardware, and/or the algorithm could be improved. Chelikowsky noted that "hardware is transitory, but algorithms are forever," and so focused on improvement of the algorithm. The KS equation was solved in reach space by finite differencing, with the system of interest defined as a nanocrystal. Chelikowsky's group assumed that the wavefunction vanished beyond the domains, that there were no artificial supercells, and there were no plane waves. These assumptions allowed for flexible boundary conditions, allowing for solutions in a variety of dimensionalities. The novelty of the algorithm lies in the utilization of a damped Chebyshev subspace iteration, rather than a standard diagonalization technique, to allow for "filtering" to enhance the components of the wavefunction in the filtered region of interest. This is a method is not restricted to particular classes of materials, and is faster than linear scaling methods. The density of states for Si quantum dots were calculated, and replicated well that of bulk Si, including expected van Hove singularities. Chelikowsky showed preliminary results of the location of a single P dopant within a Si nanocrystal, and compared his results to published hyperfine splitting results. At the nanoscale, the group found that it can be energetically favorable for an impurity to diffuse to the surface of the system, resulting in "self-purification;" and that this effect is enhanced as the size of the system is reduced, suggesting that there is a critical size below which P will be energetically expelled to the surface. He found similar results in both nanocrystal and nanowire systems. Finally, Chelikowsky showed variations in this tendency with the nature of the dopant in Si: Li behaves similarly to P, but B is more likely to be found near the surface of the system, likely due to stress from a larger size mismatch. Symposia 5. Advanced Structural Materials The Evolution of Al-Li Alloys for Aerospace Applications Roberto Rioja, of Alcoa, Inc, USA, described the growth of aluminum and aluminum-lithium alloys in the aerospace industry and the role Alcoa played in the development of the latest alloy technologies.  Alcoa is a leading innovator in aluminum products.  One of their first alloys, the 2017-T4, was used in the construction of airplane fuselages and wings.  The drive to design lighter, stronger, fatigue resistant, lower cost, air-craft led to the addition of varying amounts of lithium being added.  Quantities as low as 0.5% lithium produced substantial changes in mechanical properties.  Other early alloys such as the 2020, containing a 1% lithium concentration, were used in American aircraft such as the RA-5C in the 1950s.  Over a period of forty years, aluminum-lithium alloys, such as the 2195 plate and the 2009 sheet were developed as components for the A380 Super Jumbo Jet, and the space shuttle, specifically its external fuel tank.  Rioja explained how anisotropy of mechanical properties can be reduced in the alloy at the microstructure level by hot working the material “cold” then “hot”.  He concluded that Al-Li alloys offer improved performance compared to conventional materials and that the use of Al-Li alloys will only increase as the cost of fuel increases. Symposia 6. New Trends in Polymer Chemistry 6FDA-Based Copolyimide Membranes for Desulfurization of Kerosene Claudia Straut, of the University of Duesseldorf, Germany, described her investigation into the removal of sulfur-aromatic compounds from kerosene by novel membrane materials.  The research was motivated by the need to reduce aircraft emissions, and by the possibility of instituting hybrid fuel cell technology in airplanes.  Hybrid fuel cells on planes will provide increased efficiency and electrical power without the use of operational engines.  Currently hybrid cells are not an option because the levels of sulfur found in jet fuel is damaging to the cell and conventional desulfurization methods cannot be used on board an airplane.  The copolyimide membranes have the advantage of being compact units that require little maintenance, and consume low amounts of energy.  Straut’s research showed any number of diamine monomers can be used to synthesize the membranes, but the effects on the physical properties of the membrane include changes in packing density, free volume, separation characteristics, and chemical and thermal stability.  The new membranes capabilities are evaluated based on an enrichment factor, which is defined as how efficient the separation ability is, and its flux.  The study was able to demonstrate that 6FDA-copolyimide membranes reduced sulfur-aromatic compounds found in kerosene and that the material exhibited stability at high temperature, and resistance to degradation by chemicals present in kerosene mixtures.  Straut further indicated that the market for newer membrane materials is not limited to aircraft engines; it also includes gas separation, vapor recovery, dialysis, and bioethanol treatment. Symposium 12. Technological Innovation and its Influence on Materials Processing Developing a Mechanofusion Reactor to Elaborate Composite Powders in Semi-Continuous Mode Composite particles, formed by combining different materials in particle form, allow for new particle functionalities and/or improvement of inherent characteristics of the individual materials. A "host" particle is coated by "guest" particles to form a coated particle by a mechanofusion reactor. A mixture of the materials, already in powder form, is introduced into a rotating chamber, where a compression hammer first compresses the powder mixture and then a blade scrapes the powder from the chamber wall for removal from the chamber. However, because the chamber rotates around a vertical axis of rotation, operating inconveniences exist, most notably a nonuniform loading area, creating irregular wear of the hammer and scraper pieces within the chamber. Cuenca-Alvarez (CIITEC - Instituto Politécnico Nacional, Santa Catarina Azcapotzalco, Mexico City) has altered the configuration from a vertical axis of rotation to a horizontal axis, and developed an electronics system to allow for direct communication between the operator and the rotating chamber for seamless control of the reactor parameters during operation. The new horizontal design enables regular wearing of the hammer and scraper pieces. He was able to reduce the rotation speed by half in comparison to the vertical orientation, while maintaining high levels of performance. The composite particles produced will be used in sprays for thermal protective coatings. Symposium 13. Advances in Semiconducting Materials Termination of Open-Core Dislocations in GaN Films Grown on (111) Silicon O.E. Contreras's group at Universidad Nacional Autónoma de México, Ensenada, B.C., México, focused on GaN grown on Si(111). III-Nitrides have a wide range of applications, most notably solid-state lighting. Growth of single-crystal GaN films on Si by metalorganic chemical vapor deposition (MOCVD) is important for devices for integration with current semiconducting processes, which is biased strongly towards Si substrates. First, an Al layer was deposited at 720 deg C, then an AlN buffer layer, and finally GaN at 1050 deg C. TEM cross-sectional images show a combination of screw- and edge-type dislocations, created by the high lattice mismatch between GaN and Si substrate. AFM shows hexagonally-shaped holes. Using TEM images, Contreras was able to determine that these "nanopipe" dislocations behave like screw dislocations-- essentially, a screw dislocation with a hollow core, similar to previously published work. However, LEDs will require thicker films, so additional GaN layers were grown, separated by low-temperature AlN layers, achieving films as thick as 5 microns. TEM cross-sections show polycrystalline AlN separating layers and nanopipes that penetrate only the GaN layers, but do not go through the AlN layers. Contereras suggests that the nanopipe is capped by the low-temperature AlN layer. To determine if the nanopipe is filled (with AlN, for example) or empty, Contreras performed HAADF-STEM and EDS linescans to prove that the nanopipes are indeed hollow tubes. At the AlN layer, epitaxial lateral overgrowth occurs and caps the nanopipe. Symposium 17. Perovskites: Properties and Potential Applications Electric-Field Control of Single Magnetic Domains in a Magnetoelectric Thin Film The magnetoelectric effect was first described by Debye in 1926. Subsequently, there has been continuing work in this field, including the development of thin film structures and single domain structures more recently. In his talk, G.P. Carman (Univ. California, Los Angeles, USA) described a layered Ni-nanobar/PZT-film magnetoelectric device. An electric field was used to control the metastable magnetic single-domain structure within the Ni-nanobar due to the magnetoelectric effect, which is the coupling of the piezoelectric, mechanical, and magnetostrictive effects. Magnetic force microscopy MFM showed that the magnetic single-domain structure in the Ni nanobar evolves from an initial single-domain state to a transitional S-domain state when an electric field was applied. The magnitude of the electric field was varied from 0.1 to 2 MV/m showing the evolution of these metastable magnetic domain states. The spin-structure of the single-domain was seen to change with the application of an electric field due to magnetostriction. Upon removal of the electric field, the single-domain reverts to its original single-domain configuration implying the spin-structure reverted to its original configuration. The magnetization produced by these metastable magnetic domain states were also compared to remnant magnetization states when a magnetic field was applied to compare magnetic field induced changes to electric field induced changes. These results confirm the multiferroic/magnetoelectric effect, showing promise for controlling nano-scale magnetic fields for use in a wide range of applications including nano-scale magnetic motors and ferroelectric/ferromagnetic based memory devices. Symposium 18. Solar-Hydrogen and Biofuels Technical and Economic Feasibility of Using Hydrogen Energy Storage System in Wind Farms Energy produced by harvesting wind power is growing in use.  It’s a renewable, clean, abundant resource.  Mexico’s Isthmus of Tehuantepecon has tremendous wind resource potential but it is still insufficient to support development of wind energy infrastructure.  However, Orlando Danguillecourt, of Instituto de Estudios de la Energia, Mexico, described in this study in a poster presentation, how wind energy can be used to store energy in the form of hydrogen. Wind potential was mapped at micro-localized areas in the Isthmus of Tehuantepecon and the data was fed into a computer model processed by HOMER software.  The simulation showed that electrolytic production of hydrogen can be obtained from the excess wind farm energy, based on the current electrical systems and wind conditions in the Isthmus of Tehuantepecon.  But improvements in technology are needed to reduce the costs of wind turbines, electrolyzers, and hydrogen storage systems and make hydrogen production more affordable. Symposium 19. Photovoltaics, Solar Energy Materials and Thin-Films Organic PVs: Status and Promise "This is the time for photovoltaics, a very interesting time," Bernard Kippelen (Georgia Institute of Technology, USA) began, summarizing the excitement and promise of his field. The photovoltaic (PV) field is currently dominated by silicon, CdTe, and other inorganic materials. Yet, organic materials represent significant advantages, especially due to economies of scale-- to reduce the cost of PVs for the realization of this technology to its full capacity, solar cells must be able to be manufactured efficiency, and this is precisely where organic materials are strongest. "Organics are the newcomers on the block, even though they've been studied for quite some time..." We have long known that organic materials can be processed at room temperature, so they are compatible with most substrates and can be printed quickly by ink-jet printers. High power conversion efficiency is an important metric of any PV. Organic power conversion efficiencies currently stand around 6-7%, and while this lags their inorganic counterparts, "the efficiencies keep going up." One way to improve the power conversion efficiency is to optimize the device length scales with the diffusion length scales of the carriers: organic PVs operate by dissociation of excitons, which are generated at the interfaces between donor and acceptor materials. These materials must be thin, as the excitonic diffusion length is limited; but they must also be sufficiently thick for efficient light absorption. Donor-acceptor heterojunctions have been achieved in multilayer thin-film and interpenetrating bulk geometries. Kippelen's group focused on pentacene/C60 solar cells. Pentacene is a common hole-transport material and C60 an electron-transport materials, both with high charge mobilities. Large external quantum efficiencies of up to 70% are explained by a large exciton diffusion length in pentacene (70 nm), which was calculated by electron transport equations with the assumption that exciton dissociation occurs at the donor-acceptor interface. Power conversion efficiency can also be improved by understanding the origin of the open circuit voltage through an equivalent circuits model. While lower bandgap materials may be capable of harvesting more photons, the open circuit voltage also evolves -- this relationship must be understood to maximize cell efficiency. By studying the temperature-dependence of the reverse saturation current, Kippelen determined that this current is temperature-activated by promoting carriers at the donor-acceptor interface between the HUMO of the donor material and the LUMO of the acceptor material, forming a ground state transfer complex. Finally, efficiency can be improved through device packaging. Organics-- in particular, pentacene and C60-- are sensitive to oxygen and moisture, so much so that functional devices can fail to operate within a few hours of exposure to air. Kippelen's group experimented with protecting their devices with 200 nm of Al2O3 deposited by atomic layer deposition (ALD), increasing shelf-lifetimes to more than 10,000 hrs with stable efficiencies over the entire lifetime. Alternatively, ALD can be combined with plasma-enhanced chemical vapor deposition to achieve improved lifetimes. SCENES FROM THE WELCOME RECEPTION                 ABOUT THE MEETING SCENE The Meeting Scene e-mails are compiled and edited by Dr. Gopal Rao, Web Science Editor, Materials Research Society. Contributors include Megan Brewster (Massachusetts Institute of Technology) and Tara Washington (University of Florida). Megan Brewster and Tara Washington, under the Apprentice Science Reporter program, are supported by the IMI Program of the National Science Foundation under Award No. DMR04-09848, managed by the International Center for Materials Research, University of California, Santa Barbara, USA. You have received this as a subscriber to the Meeting Scene or as a member of MRS-Mexico. To Unsubscribe, please e-mail braughler@mrs.org. Archived Meeting Scene Issues are available online. View all free MRS e-newsletters and alertsand subscribe. [ Last edited by hslining on 2009-8-21 at 08:45 ]

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