bluuebunny/crossref_metadata_2025 huggingface dataset:
Position Control of Nucleation in Solid-Phase Crystallization of a-Si/SiO2 by Ge Layer Insertion
Authors: Sadoh Taizoh , Nagatomo Kei , Tsunoda Isao , Kenjo Atsushi , Miyao Masanobu
Published: April 2011

The effects of Ge layer insertion on the solid-phase crystallization (SPC) of a-Si on SiO2 have been investigated. Three types of sample structures, i.e., (a) a-Si/a-Ge/a-Si/SiO2, (b) a-Si/a-Ge/SiO2, and (c) SiO2/a-Ge/a-Si/SiO2, were prepared and annealed at 600°C. For the structure (a) with a thin (∼ 5 nm) Ge layer, Ge atoms completely diffused into a-Si, and SPC was not enhanced. On the other hand, for the structure (a) with Ge layers thicker than 10 nm, Ge atoms were localized at the initial position. Such a localization of Ge atoms was remarkable for the structures (b) and (c) even for samples with thin Ge layers. For samples with Ge localization, significant enhancement of SPC of a-Si was observed. These results indicated that crystal nucleation was initiated in the inserted Ge layers, and then propagated into a-Si. The Ge layer insertion can be employed for positioning of crystal nucleation in SPC of a-Si.
High electron mobility in AlGaN/GaN HEMT grown on sapphire: strain modification by means of AlN interlayers.
Authors: Germain Marianne , Leys Maarten , Boeykens Steven , Degroote Stefan , Wang Wenfei , Schreurs Dominique , Ruythooren Wouter , Choi Kang-Hoon , Daele Benny Van , Tendeloo Gustaaf Van , Borghs Gustaaf
Published: April 2011

The performance of AlGaN/GaN High Electron Mobility (HEMT) transistors is directly related to the electrical characteristics of the two-dimensional electron gas formed at the interface thanks to the piezoelectric field. Modification of the Al content or thickness of the AlGaN layer can within a certain limit modify the carrier density and mobility in the 2DEG. However, further reduction of the sheet resistance requires strain engineering of the heterostructure. An effective way to reduce the sheet resistance, as well as to lower the threading dislocation (TD) density, is to perform strain engineering through the use of low temperature AlN interlayers inserted in the GaN buffer layer. From correlation of AFM, TEM and HRXRD mapping of the HEMT layers, the strain modification, as well as the mechanism reducing the TD density, can be explained by the highly defected nature of the AlN interlayer grown at low temperature, as well as its very small thickness. The LT AlN acts as a second nucleation layer for the GaN grown on top. Contrarily, when the AlN interlayer is grown at 1050°C, its high crystalline quality and the possibility to grow pseudomorphic and abrupt interfaces, allows its use at the AlGaN/GaN interface. Optimal combination of the AlGaN and AlN layer thickness leads to record values of the mobility at room temperature of 2050 cm2/Vs, for heterostructures grown on sapphire, which is approaching state-of-the-art for HEMT grown on SiC.
Delta-doped AlGaN/GaN Heterostructure Field-Effect Transistors with Incorporation of AlN Epilayers
Authors: Fan Z. Y. , Nakarmi M. L. , Lin J. Y. , Jiang H. X.
Published: April 2011

ABSTRATC

The simulation and experiment results of delta-doped AlGaN/GaN heterostructure field-effect transistors (HFETs) with the incorporation of highly-resistive AlN epilayer are reported. The high quality AlN epilayer is used as the dislocation filter for the HFET structure growth, and the high resistivity of AlN also removes the parasitic conduction related with the GaN bulk buffer. Delta doping can reduce gate leakage, further more, our simulation and growth results demonstrate that delta-doping in the barrier is more effective than uniform doping scheme to increase the sheet electron density. The influence of spacer layer thickness on the electron mobility and sheet electron density is also presented. The DC characterization of the fabricated devices shows our structure has a very high performance with a maximum current ∼ 1 A/mm.
A Study of Elemental Interdiffusion in GaN/Si Wafer Grown by Metalorganic Vapor Phase Epitaxy
Authors: Chen X. , Ishiko M. , Kuroiwa Y. , Sawaki N.
Published: April 2011

Secondary ion mass spectrometry (SIMS) study shows that a short-time interdiffusion process occurs at the interface of buffer/Si in the GaN/Si wafers grown by metalorganic vapor phase epitaxy (MOVPE). Increasing the growth temperature of the buffer layer from 1150°C to 1210°C reduces the dropping rate of Al concentration in the silicon substrate from ∼20nm/decade to ∼30nm/decade near the interface. The impact of the interdiffusion on the band structure is investigated by photocurrent spectroscopy measurement. The experimental results indicate that different build-in electric fields are formed in the GaN/n-Si(111) and GaN/p-Si(111) devices as the consequence of the MOVPE growth.
Real-time optical monitoring of gas phase dynamics for the growth of InN at elevated pressures
Authors: Dietz N. , Born H. , Strassburg M. , Woods V.
Published: April 2011

The request for increased performance in high-power / high-frequency optoelectronic devices requires new methods for the fabrication of high quality III nitride alloys that exhibit large thermal decomposition pressure such as InN and related materials. To extend the process and growth window towards elevated pressures, a high-pressure CVD system with integrated real time optical characterization techniques has been constructed. The built-in real-time monitoring techniques allow the characterization of gas flow dynamics, precursor decomposition kinetics, as well as the monitoring of the crucial steps of nucleation and film formation. The gas flow dynamics has been characterized and the process parameter are obtained under which the thin film growth process can be maintained under laminar flow condition. Laser light scattering (LLS) has been proven as the most robust optical tool to characterize the onset of turbulence.
Emission Mechanisms in UV Emitting GaN/AlN Multiple Quantum Well Structures
Authors: Furis Madalina , Cartwright Alexander N. , Wu Hong , Schaff William J.
Published: April 2011

The need for efficient UV emitting semiconductor sources has prompted the study of a number of heterostructures of III-N materials. In this work, the temperature dependence of the photoluminescence (PL) properties of UV-emitting GaN/AlN multiple quantum well (MQW) heterostructures were investigated in detail. In all samples studied, the structure consisted of 20 GaN quantum wells, with well widths varying between 7 and 15 Å, clad by 6nm AlN barriers, grown on top of a thick AlN buffer that was deposited on sapphire by molecular beam epitaxy. The observed energy corresponding to the peak of the emission spectrum is in agreement with a model that includes the strong confinement present in these structures and the existence of the large built-in piezoelectric field and spontaneous polarization present inside the wells. The observed emission varies from 3.5 eV (15 Å well) to 4.4 eV (7 Å well). Two activation energies associated with the photoluminescence quenching are extracted from the temperature dependence of the time-integrated PL intensity. These activation energies are consistent with donor and acceptor binding energies and the PL is dominated by recombination involving carriers localized on donor and/or acceptor states.

Moreover, the temperature dependence of the full width at half-maximum (FWHM) of the PL feature indicates that inhomogeneous broadening dominates the spectrum at all temperatures. For the 15 and 13 Å wells, we estimate that the electron-phonon interaction is responsible for less than 30% of the broadening at room temperature. This broadening is negligible in the 9 Å wells over the entire temperature range studied. Well width fluctuations are primarily responsible for the inhomogeneous broadening, estimated to be of the order of 250meV for one monolayer fluctuation in well width.
Surface Control of ZrB2 (0001) Substrate for Molecular-Beam Epitaxy of GaN
Authors: Suda Jun , Yamashita Hiroyasu , Armitage Robert , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: April 2011

Zirconium diboride (ZrB2) is a promising lattice-matched substrate for GaN-based materials. A key issue to realize high-quality heteroepitaxial growth is preparation of the substrate surface. The ZrB2 surface was studied by x-ray photoemission spectroscopy (XPS) and reflection high-energy electron diffraction (RHEED). XPS results indicated the presence of both ZrO2 and ZrB2 on the as-received substrate surface. Thermal cleaning at 1000°C in ultra-high vacuum, Ar+ ion sputtering, and wet chemical treatments were examined as surface preparation methods. After treatment with HF acid, the O peak intensity was much reduced. The combination of HF treatment and thermal cleaning resulted in sharp and intense RHEED from the ZrB2 surface. GaN grown on the surface by molecular-beam epitaxy exhibited intense photoluminescence, suggesting that this treatment is effective to obtain high-quality GaN on ZrB2 substrates.
The Influence of Substrate Polarity on the Blue Emission from As-doped GaN Layers Grown by Molecular Beam Epitaxy
Authors: Novikov S. V. , Zhao L. X. , Foxon C. T. , Harrison I. , Campion R. P. , Staddon C. R. , Kang S. W. , Kryliouk O. , Anderson T.
Published: April 2011

The influence of sample orientation and polarity on the blue emission from As-doped GaN layers grown by plasma-assisted molecular beam epitaxy (PA-MBE) was investigated. Arsenic doped GaN layers were grown under identical PA-MBE conditions on several types of substrates including c-plane (0001) sapphire and polar and non-polar GaN templates grown by metal-organic vapour phase epitaxy (MOVPE). Non-polar GaN MOVPE templates were grown on aplane (11–20) sapphire and LiAlO2 (100). The orientation and polarity have a strong influence on the morphology and the optical properties of As-doped GaN layers. Strong blue emission from As-doped GaN was observed only in the case of (000–1) oriented N-polarity layers.
Characterization of Photovoltaic Cells Using n-InN/p-Si Grown by RF-MBE
Authors: Morioka Chiharu , Yamaguchi Tomohiro , Naoi Hiroyuki , Araki Tsutomu , Suzuki Akira , Nanishi Yasushi
Published: April 2011

A newly reported narrow bandgap for indium nitride means that the indium gallium nitride system of alloys can be a candidate for new high efficiency solar cells covering most of the solar spectrum. In this paper, n-InN films were grown on p-Si (100) substrates. We characterize, for the first time, photovoltaic properties using n-InN/p-Si hetero-junction grown by RF-MBE.
Laser Diode Facet Degradation Study
Authors: Schwarz Ulrich T. , Schoedl Thomas , Kümmler V. , Lell A. , Härle V.
Published: April 2011

We study the degradation behaviour of GaN gain guided laser diodes (LDs) on SiC substrates with cleaved facets and reflective coatings on none, one, or both facets. This allows us to demonstrate that in addition to volume effects there is a contribution of the laser facets to laser degradation. We observe that for the uncoated LDs the threshold current density is increasing considerably faster compared to LDs with mirror coatings. Degradation is observed during operation but not during storage at ambient conditions and thus expected to be photon or current induced. Operation of the uncoated laser in a nitrogen atmosphere reduces the degradation rate with respect to operation in air.
Optical and Electrical Properties of Low to Highly-Degenerate InN Films
Authors: Haddad D. B. , Dai H. , Naik R. , Morgan C. , Naik V. M. , Thakur J. S. , Auner G. W. , Wenger L. E. , Lu H. , Schaff W. J.
Published: April 2011

The optical and electrical properties of InN films with different levels of carrier concentrations have been investigated. Hall effect measurements at room temperature show that the InN films are n-type with carrier concentration, ne, ranging from ∼ 7 ×1017 cm-3 to ∼ 3 × 1020 cm-3 and corresponding mobility, //, of ∼ 1300 to 50 cm2V-1S-1. Optical absorption spectra of these films show a bandgap absorption edge ∼ 0.6 eV for the InN sample with the lowest ne, and 1.5 eV for the InN sample with the highest ne. However, after corrections for the degeneracy effects, all samples show an intrinsic Eg ∼ (0.60 ± 0.05) eV. Temperature dependent (5 – 600 K) electrical measurements show that ne is nearly independent of temperature below 300 K, perhaps due to the presence of donor energy levels resonating with the InN conduction band. However, all the samples show an exponential increase in ne above 300 K due to excitation of other shallow donor like sources. Mobility versus temperature graph shows a maximum ∼ 200 K for InN film with ne = 7 × 1017 cm-3 and moves towards lower temperature with increasing ne.
Pressure Dependence of Optical Transitions in In-rich Group III-Nitride Alloys
Authors: Li S. X. , Wu J. , Walukiewicz W. , Shan W. , Haller E. E. , Lu Hai , Schaff William J.
Published: April 2011

The hydrostatic pressure dependence of the optical transitions in InN, In-rich In1-xGaxN (0 < x < 0.5) and In1-xAlxN (x = 0.25) alloys is studied using diamond anvil cells. The absorption edges and the photoluminescence peaks shift to higher energy with pressure. The pressure coefficient of InN is determined to be 3.0±0.1 meV/kbar. Together with previous experimental results, our data suggest that the pressure coefficients of group-III nitride alloys have only a weak dependence on the alloy composition. Photoluminescence gives much smaller pressure coefficients, which is attributed to emission involving highly localized states. This indicates that photoluminescence might not be an accurate method to study the pressure dependence of the fundamental bandgaps of group III-nitrides.
Either step-flow or layer-by-layer growth for AlN on SiC (0001) substrates
Authors: Suda Jun , Onojima Norio , Kimoto Tsunenobu , Matsunami Hiroyuki
Published: April 2011

AlN was grown on 4H- or 6H-SiC (0001) on-axis substrates by plasma-assisted molecular beam epitaxy. By utilizing optimized SiC surface pretreatment, RHEED oscillations just after the growth of AlN were obtained with high reproducibility. This study focused on the growth kinetics of AlN and the correlation between kinetics and the crystalline quality of the grown layers. It was found that the growth mode changed from layer-by-layer to step-flow for high growth temperatures, while for lower temperatures the layer-by-layer growth mode persisted. The mechanism responsible for the change in growth mode is discussed. Symmetrical (0002) and asymmetrical (01–14) x-ray rocking curve measurements were carried out to evaluate the crystalline quality. For the (0002) peak, both high-temperature and low-temperature grown layers showed almost the same FWHM values. On the other hand, for the (01–14) peak, the FWHM of low-temperature grown AlN was much smaller (180 arcsec) than that of the high-temperature grown AlN (450 arcsec).
ZnO/AlGaN ultraviolet light emitting diodes.
Authors: Bagnall D. M. , Alivov Ya. I. , Kalinina E. V. , Look D. C. , Ataev B. M. , Chukichev M. V. , Cherenkov A. E. , Omaev A. K.
Published: April 2011

Ga doped n-type ZnO layers are grown using plasma assisted chemical vapor deposition on Mg doped p-type AlGaN epitaxial layers grown by hydride vapor phase epitaxy to form n-ZnO/p-AlGaN heterojunction light emitting diodes. I-V characteristics clearly show rectifying behavior with a threshold voltage of ∼3.2 V and intense ultraviolet electroluminescence with peak emission at 390 nm. The dominant emission mechanism is found to result from hole injection from the p-type AlGaN into the n-type ZnO. Significant emission up to 500 K is observed indicating possible applications in harsh environments.
Influence of AlN Overgrowth on GaN Nanostructures Grown by Molecular Beam Epitaxy
Authors: Gogneau N. , Monroy E. , Jalabert D. , Sarigiannidou E. , Rouvière J. L. , Daudin B.
Published: April 2011

The effects of AlN overgrowth on the structural properties of GaN nanostructures grown at 750°C by plasma-assisted molecular beam epitaxy have been investigated using Rutherford backscattering spectroscopy and transmission electron microscopy. The capping process induces a remarkable change in the dimension of the nanostructures. We demonstrate that the thickness/size reduction occurs at the first stage of AlN overgrowth and affects only the top GaN/AlN interface. This phenomenon is attributed to an exchange mechanism between Al atoms from the cap layer and Ga atoms in the nanostructures and depends on the strain state of the nanostructures.
III-Nitride Photonic Crystals for Blue and UV Emitters
Authors: Shakya J. , Kim K. H. , Li J. , Lin J. Y. , Jiang H. X. , Oder T. N.
Published: April 2011

We report the nanofabrication and characterization of triangular lattice array of photonic crystals (PCs) with diameter/periodicity as small as 100/180 nm on III-nitride Light Emitting Diodes (LEDs) using electron beam lithography and inductively-coupled-plasma dry etching. Under optical pumping, a maximum enhancement factor of 20 was obtained from the PCs for emission light intensity at the wavelength of 475 nm at room temperature. Under current injection, the total power at 20 mA of 300 × 300 μm2 unpackaged LED chips revealed an increase by 63% and 95% for 460 nm blue and 340 nm UV LEDs, respectively, as a result of the PC formation. Our results show that the fabrication of PCs enhances the power output significantly on the III-nitride LEDs, which currently have very low external quantum efficiency especially in the UV range.
Effects of Si-doping on the Microstructure of AlGaN/GaN Multiple-quantum-well
Authors: Liu R. , Ponce F. A. , Sahonta S-L. , Cherns D. , Amano H. , Akasaki I.
Published: April 2011

The effects of silicon-doping on the microstructure of Al0.07Ga0.93N/GaN multiple-quantum-well (MQW) have been studied by TEM. Significant changes of surface morphology and dislocation core structures have been observed due to Si-doping in the Al0.07Ga0.93N barriers. Threading dislocations create surface pits in the MQW as a result of Si doping. With an increasing doping level, the pits change the shape from small faceted pyramid to large cone. The formation mechanism of the surface pits has been discussed from both dynamics and kinetics points of view. We have also observed nanopipes constrict to form closed core screw dislocations in the MQW due to Si-doping.
Deep Defects in Fe-Doped GaN Layers Analysed by Electrical and Photoelectrical Spectroscopic Methods
Authors: Witte H. , Fluegge K. , Dadgar A. , Krtschil A. , Krost A. , Christen J.
Published: April 2011

The electrical activity of iron in Fe- doped, and in Si and Mg co-doped GaN layers grown on sapphire substrates by metal organic vapor phase epitaxy was studied as shown by temperature dependent Hall Effect (TDH) measurements. In all samples iron doping generates an acceptor defect, which compensates donors in n-type GaN. Furthermore, iron doping causes strong potential inhomogeneities, which decrease the Hall mobility in the layers. To verify, if iron creates only hole traps, defects in n-type Si:Fe and Fe doped samples were investigated. The well known dominant electron traps in n-type GaN at 520 – 550 meV and 480 meV were found by deep level transient spectroscopy and thermal admittance spectroscopy, respectively. A high Fe-doped GaN layer shows a low p-type conductivity dominated by the iron acceptor. An activation energy of EV+ 460 meV was determined by TDH indicating, that the iron acceptor correlates with this defect level.
Optical evaluation of pretreated InGaN quantum well structures
Authors: Böttcher T. , Bertram F. , Bergman P. , Ueta A. , Christen J. , Hommel D.
Published: April 2011

In order to optimize the quantum efficiency of InGaN quantum wells, different MOVPE growth sequences are compared using photo- and electroluminescence. In one study, the surface was pretreated with trimethylindium (TMIn) prior to the well deposition. In another study, growth interruptions were performed after the quantum well deposition to desorb segregated indium. In both cases, the room-temperature photoluminescence (PL) intensity is strongly enhanced. For the samples grown with TMIn preflow the wavelength distribution in low-temperature cathodoluminescence (CL) wavelength mappings is narrowed, which can be attributed to more homogeneous quantum wells. Furthermore, the decay times of the radiative recombination increase both at RT and 2K. A reason for this could be an improved indium profile along the growth direction or a more homogeneous In wetting layer due to the pre-wetted surface.
Modulation of Arsenic Incorporation in GaN Layers Grown by Molecular Beam Epitaxy
Authors: Novikov S. V. , Zhao L. X. , Foxon C. T. , Ja. Ber B. , Kovarsky A. P. , Harrison I. , Fay M. W. , Brown P. D.
Published: April 2011

GaN layers periodically-doped with arsenic were grown by plasma-assisted molecular beam epitaxy on sapphire substrates. Secondary ion mass spectroscopy studies using different secondary ions clearly confirmed the existence of As-modulation in the GaN/GaN:As periodically-doped structures, however, the degree of As-modulation is still under discussion. The use of modulation doping with As has a strong influence on the optical properties of GaN/GaN:As structures.
3C-SiC modulator for high-speed integrated photonics
Authors: Barrios Carlos Angulo , Thomas Christopher Ian , Spencer Michael , Lipson Michal
Published: April 2011

We propose a compact 3C-SiC electro-optic modulator for high-speed Si-based integrated optoelectronics operating at 1.55-μm-wavelength. The device is based on an optical microresonator using sub-micron size high-index-contrast SiC waveguides on a SiC-SiO2-Si [SiC-on-Insulator (SICOI)] platform. Three different electrode configurations are analyzed. Switching times on the order of tens of ps are predicted by using low bias voltages.
Effects of Very Small Particle Size on Processing and Safety Properties of Energetic Formulations
Authors: Wardle Robert , Lee Kenneth , Akester Jeff , Braithwaite Paul
Published: April 2011

Described in this paper are ongoing research efforts at ATK Thiokol on new formulations of gun propellants and explosives containing nano-sized materials. Funding for this work was provided both internally and by ARDEC. The nano-material properties as well as selected properties of intermediate compositions are reported.

The explosives section of this paper focuses on the theoretical evaluation of nano-aluminum in explosives. The theoretical cylinder expansion energy of two common aluminized explosives, PAX-3 and PAX-28, are examined. The comparison examines the effect of aluminum content in small aluminum particles on metal pushing performance at V/V0 = 6.5.

ATK Thiokol and TACOM-ARDEC have teamed together to study the effect of nano-sized materials on advanced ETPE gun propellants. The gun propellant section of this paper focuses on the impact of nano-sized additives, specifically TiO2 and aluminum, on selected ETPE propellants. The safety properties of the nano-aluminum and nano-TiO2 analogs of two previously developed gun propellants, TGD-031 and TGD-035, are presented.
Combustion Synthesis of NiTi – TiC Composites with Controlled Porosity for Biomedical Applications
Authors: Burkes Douglas E. , Gottoli Guglielmo , Moore John J. , Yi Hu Chun , Ayers Reed A.
Published: April 2011

Combustion synthesis, or Self-propagating High- temperature Synthesis (SHS), is currently being used by the Center for Commercial Applications of Combustion in Space (CCACS) at the Colorado School of Mines to produce advanced porous materials for several important applications. These materials include ceramic, inter- metallic, and metal- matrix composites that can be used for orthopedic implants, heat exchanger and damping systems and micro-and macro-filter applications. Functionally graded materials, both in porosity and composition, can be produced using a range of combustion synthesis reactions systems. There are multiple factors that contribute to the final SHS product, e.g. reactant stoichiometry, initial relative density and pre-heat. The synthesis of nickel-titanium (NiTi) intermetallic compounds and composites is of considerable interest due to the ability to create a porous, shape memory and super-elastic alloy with high corrosion resistance. The synthesis effects of adding a carbon reactant so as to modify the reaction products and reaction exothermicity have been studied through the use of two different reaction stoichiometries involving elemental nickel, titanium and carbon. This paper outlines the synthesis of NiTi intermetallic composites based on the following SHS chemical reaction:

The effect of the carbon reactant and the initial sample green density on the apparent porosity, bulk density, pore size and pore distribution of the final materials has been studied and is presented within this paper. A NiTi- TiC intermetallic ceramic composite has been synthesized that is functionally graded in both composition and porosity: the latter grading being due to buoyancy and gas evolution effects. Proposed kinetic mechanisms that drive this synthesis process and control the graded structure are discussed in detail.
Modeling Laser Generated Shock Damage and Thermo-Mechanical Chaos in Nanoparticles
Authors: Gerstman Bernard S.
Published: April 2011

Continual advances in laser technology lead to shorter pulses and higher energies. As the duration of a laser pulse shortens, different physical mechanisms become important in determining the thermo-mechanical response of an absorbing particle. These thermo-mechanical responses fall into the general category of thermal heating (temperature rise), vaporization, and shock wave formation. Our theoretical work has produced a computational model that allows the quantitative calculation of all of these responses for a laser of any pulse duration or energy, absorbed by a particle of any size. We find that for relatively long pulses, particle damage occurs most easily, i.e. at the least pulse energy, due to thermal effects. As the pulse duration shortens, explosive vaporization can dominate as the primary damage mechanism. For short pulses, shock wave production becomes the dominant damage mechanism. We describe how the relative terms of “short” and “long” pulse duration can be determined from knowledge of the thermo-mechanical properties of the absorber. Conversely, when the thermo-mechanical properties are not known, we explain how our theoretical work leads suggests an experimental technique that allows measurement of these absorber properties. This technique is applicable to extremely small particles that present difficulties for thermo-mechanical measurements. Finally, we show computational evidence of chaotic behavioral response of the absorber. This results in some laser pulse durations and energies that cause anomalously small shock waves, whereas other durations and energies cause surprisingly large and damaging responses.
New Science and Technology the Basis of the Hydrogen Economy
Authors: Ovshinsky Stanford R.
Published: April 2011

Hydrogen is called the “ultimate fuel.” It is also the ultimate element. It was born in the Big Bang and almost all of known matter is composed of it. Its condensation into a star, our sun, through fusion, provides us the energy and the photons which power our earth and which we can utilize in the form of photovoltaics to break apart water and generate hydrogen as an energy source on earth.

The hydrogen economy is here. It has been initiated by the electric and hybrid vehicles which depend upon it for their operation through nickel metal hydride batteries and hydrogen as a fuel for the internal combustion engine and by outwitting the Carnot cycle for use as a fuel cell.

I will discuss the complete system needed for the hydrogen economy from generation to storage to infrastructure and use. Any one part of this loop is necessary but not sufficient.

Our global economy is based upon energy and the societal needs for a nonpolluting, non-climate change fuel which does not require strategic military defense as does oil. The transition from fossil fuels to hydrogen is of revolutionary import not only for its societal impact but also for the new materials science that it absolutely requires in all of its aspects. New science and new technologies build much needed new industries, which provide not only jobs but also feedback on our educational system.

Recall that the ages of civilization are known by their materials. Truly, the presentage will be known by the materials that make up the twin pillars of our global economy – energy and information. Therefore, I will address the new science, technology and atomic engineering of the materials so necessary to make positive, realistic and productive this revolutionary transition of energy from its fossil fuel beginnings to the present.
Recent Advances in Solid Hydrogen Storage Systems
Authors: Chao B.S. , Young R.C. , Myasnikov V. , Li Y. , Huang B. , Gingl F. , Ferro P.D. , Sobolev V. , Ovshinsky S.R.
Published: April 2011

Hydrogen energy offers great promise as an energy alternative. Hydrogen technologies can reduce and eliminate the release of carbon dioxide from fossil-fuel combustion, the main cause of global warming. One of the main challenges is hydrogen storage. Storing hydrogen in the solid-state hydride form holds a volumetric advantage over compressed and liquid hydrogen states. Solid hydrogen storage systems also have features of low-pressure operation, compactness, safety, tailorable delivery pressure, excellent absorption /desorption kinetics, modular design for easy scalability, and long cycle life.

In this paper, solid hydrogen storage systems (such as portable power canisters, lightweight fiber wrapped vessels, and aluminum tubular vessels, developed by Texaco Ovonic Hydrogen Systems LLC) will be discussed. A system of four canisters each storing approximately 80 grams of reversible hydrogen is shown to run a 1 kW PEM fuel cell for more than 247 minutes at full power. Canisters show no plastic deformation after more than 500 charge/discharge cycles. The measured strain on canister surfaces indicates that DOT stress limits are not exceeded. The canisters are in the early commercialization stage for uninterrupted power supply (UPS) and auxiliary power unit (APU) applications.

A lightweight fiber-wrapped vessel engineered with metal hydride and internal heat exchanger is being developed for onboard applications. At the system level, the vessel has a volumetric energy density of 50 grams of hydrogen per liter and a gravimetric density of 1.6 wt.%. The vessel is capable of storing 3 kg of hydrogen with a fast refueling capability. Ninety percent of the storable hydrogen can be refueled in 10 minutes at 1500 psig. The vessel can easily release the hydrogen at a rate of 350 slpm at 70°C.

Aluminum tubular vessels are being designed and tested for bulk storage and infrastructure applications including stationary power, hydrogen shipment and hydrogen service stations. The tubular vessel dimensions may be designed for specific applications. For example, a tubular vessel 6 inches in diameter and 62 inches in length can store up to 1 kg of hydrogen.
Properties of the Magnetic Hydride YFe2H4 from First Principles Calculations
Authors: Singh D.J. , Gupta M.
Published: April 2011

YFe2H4 is a ferromagnetic metal with magnetization higher than the Laves phase parent compound, YFe2. Here, the electronic and magnetic properties of YFe2H4 are studied using density functional calculations, in order to elucidate the reasons for this. The electronic structure of YFe2H4 differs from that of YFe2 both because of the lattice expansion upon hydriding and because of chemical interactions involving H. However, the main reason for the increased magnetization is found to be the lattice expansion.
Hydrogen absorption of C14 Laves NiTiZr-NiVNb pseudo-binary alloys
Authors: Ishikawa Kazuhiro , Noda Shintaro , Suzuki Kiyonori , Aoki Kiyoshi
Published: April 2011

Hydrogen absorption and desorption properties of C14 Laves NiTiZr-NiVNb and NiTiZr-NiVZr pseudo-binary alloys were investigated by using the Sieverts' apparatus, XRD and the hydrogen analyzer. The hydrogen capacity and the 50% hydrogen desorption temperature, Td, of the C14 Laves NiTiZr alloy is 1.5 (H/M) and 850 K, respectively. On the other hand, the hydrogen capacity of the C14 NiVNb alloy is 0.2 H/M. In the Ni(TiZr)1−x(VNb)x pseudo-binary system, the hydrogen capacity of the alloys is decreased with increasing x, but the 50% hydrogen desorption temperature is almost constant. The substitution of VNb reduces the hydrogen absorption capacity of the C14 Laves NiTiZr alloy. The hydrogen desorption temperature of Ni(Ti1−xVx)Zr alloy is reduced to 580 K without serious decrease of the hydrogen capacity with increasing x.
Changing Np Redox Speciation in the Synchrotron Beam
Authors: Skanthakumar S. , Gorman-Lewis D. , Locock A. , Chiang M.-H. , Jensen M. P. , Burns P. C. , Fein J. , Jonah C. D. , Attenkofer K. , Soderholm L.
Published: April 2011

X-ray absorption data, obtained from Np(V) in two environmentally-related samples, show evidence of significant metal-ion reduction in the synchrotron beam. The data are presented and possible sources of reduction are discussed.
In SituActinide X-ray Absorption Spectroelectrochemistry
Authors: Antonio Mark R. , Chiang Ming-Hsi , Williams Clayton W. , Soderholm L.
Published: April 2011

By using electrochemical techniques in simultaneous combination with EXAFS, we can stabilize a targeted charge state of a solution complex and probe the coordination of selected actinide (An) ions. In addition, we can acquire sufficient XANES over a range of controlled electrochemical potentials, in the vicinity of a redox couple, to perform a Nernst analysis. The prospect of this technique to provide here-to-fore unattainable information is demonstrated through examples of Np, Pu, and Bk speciation in solution.
Role of Spin-Orbital Splitting of 5f-Orbitals of Uranium Atom in the Formation of Its Chemical State
Authors: Batrakov Yuri F. , Krivitsky Andrey G. , Puchkova Elena V.
Published: April 2011

Chemical shifts (ChSh) of nine emission lines of the uranium L-series in uranium oxides UO2+x (x=0−1) with respect to UO2 were studied by using a precise crystal-diffraction X-ray spectrometer and the changes in energy of spin-orbital splitting (SOS) − Δδnl± of inner nl-orbitals of the uranium atom were calculated from the data of ChSh of spin-doublet lines. For UO2+x oxides, a linear decrease in Δδnl± values with increasing degree of uranium oxidation was found.

On the basis of the comparison of experimental Δδnl± values with Dirac-Hartree-Fock atomic calculations, it was concluded that the observed variations in Δδnl± values are due to the redistribution of electron and spin density between the 5f7/2- and 5f5/2-levels of the fine structure of the uranium atom without changes in atomic charge state.
Electronic structure calculations of δ-Pu based alloys
Authors: Landa Alex , Söderlind Per , Ruban Andrei
Published: April 2011

First-principles methods are employed to study the ground-state properties of δ-Pu-based alloys. The calculations show that an alloy component larger than δ-Pu has a stabilizing effect. Detailed calculations have been performed for the δ-Pu1−cAmc system. Calculated density of Pu-Am alloys agrees well with the experimental data. The paramagnetic → antiferromagnetic transition temperature (Tc) of δ-Pu100−cAmc alloys is calculated by the Monte-Carlo technique. By introducing Am into the system, one could lower Tc from 548 K (pure Pu) to 372 K (Pu70Am30). We also found that, contrary to pure Pu where this transition destabilizes δ-phase, Pu3Am compound remains stable in the antiferromagnetic phase that correlates with the recent discovery of the Curie-Weiss behavior of δ-Pu100−cAmc alloys at c ≥ 24 at. %.
Imaging polymer supported organic molecules by mass spectrometry Application in combinatorial chemistry
Authors: Enjalbal C. , Maux D. , Combarieu R. , Martinez J. , Aubagnac J-L.
Published: April 2011

In combinatorial chemistry, most libraries are prepared according to solid-phase synthesis strategies using resins or pins. Although synthesis and purification steps are facilitated, reaction monitoring presents difficulties. Since the polymeric support is not soluble, an analytical method able to cope with a solid sample is thus required to perform direct identification of the anchored molecules without any chemical treatment. Static-Secondary Ion Mass Spectrometry (S-SIMS) was investigated in that purpose. Positive and negative ion mass spectra were acquired to identify single beads whereas mixtures (Mix and Split libraries or pooled beads issued from different batches) were profiled through imaging experiments.
High-Throughput Adhesion Evaluation and Scale-up of Combinatorial Leads of Organic Protective Coatings
Authors: Ezbiansky Karin , Medford George , Reitz Hariklia , Potyrailo Radislav A. , Chisholm Bret J. , Morris William G. , Cawse James N. , Flanagan William P. , Hassib Lamyaa , Molaison Chris A.
Published: April 2011

Coupling of combinatorial chemistry methods with high-throughput (HT) performance testing and measurements of resulting properties has provided a powerful set of tools for the 10-fold accelerated discovery of new high-performance coating materials for automotive applications. This approach replaces labor-intensive steps with automated systems for evaluation of adhesion of 8 × 6 arrays of coating elements that are discretely deposited on a single 9 × 12 cm plastic substrate. Performance of coatings is evaluated with respect to their resistance to adhesion loss. This parameter is one primary consideration in end-use automotive applications. Coating leads identified from the HT screening have been validated on the traditional scale. Details of these validation studies are discussed.
Management of Combinatorially Acquired Multi-dimensional Data through Object-Oriented Virtual Sample Library
Authors: Todoroki Shin-ichi , Inoue Satoru
Published: April 2011

Combinatorial methods bring about plentiful data not only in size but also in dimension. To handle multi-dimensional data easily, a virtual container of combinatorially acquired data is developed which is called “virtual sample libraries” (VSL). VSL stores the data hierarchically in the order of (1) coordinates in the sample library, (2) names of the measurements performed, and (3) data obtained from each measurement. Thus, the loads for analysis and visualization of multi-dimensional data are reduced because the stored data can be accessed intuitively, that is, just by tracing the hierarchy structure. This framework is easily constructed by the aid of object-oriented script language which is good at describing complicated data structure. Visualization of combinatorially acquired 7-dimensional data is demonstrated.
Sensors for High-Throughput Materials Characterization: 24-channel Array of Quartz Crystal Microbalances
Authors: Morris William G. , Potyrailo Radislav A.
Published: April 2011

We have developed a multichannel materials characterization system based on thickness-shear mode (TSM) sensors, also known as quartz crystal microbalances (QCMs). The sensors are arranged as a 6 × 4 array that is compatible with available 24-well plates that can be manipulated with standard robotic equipment. Our sensor system can measure frequencies from 5 MHz to 20 MHz with a noise level of less than 0.1 Hz for a 1 sec acquisition interval. The sensors can be placed in a gas-flow-though cell for studies of vapor-sorption properties, or they can be immersed into a 24-well plate array for studies of materials solubility. The sensor array is connected to the measurement electronics through a multi-conductor cable, enabling the sensors to be operated in a temperature, pressure, or chemical environment, which would otherwise adversely affect the electronic stability. The 24-channel array has been applied to the screening of sensor materials for determination of chlorinated organic solvents at part per billion levels in groundwater wells. The primary screen is the discovery screen where materials are exposed to a single analyte concentration. The secondary screen is the focused evaluation where the best subset of these materials is exposed to analytes and interferences. The tertiary screen involves evaluation of material performance under conditions mimicking the long-term application. Six families of potential sensor materials were examined with rapid downselection by using this approach.
Automatic Reaction Modeling in Chemical Vapor Depositions Using Multiple Process Simulators
Authors: Takahashi Takahiro , Funatsu Kimito , Ema Yoshinori
Published: April 2011

The identification of appropriate reaction models is very helpful for developing chemical vapor deposition (CVD) processes. In this paper we propose a novel system to analyze experimental data of various CVD reactors and identify reaction models automatically using Genetic Algorithms (GA) with multiple process simulators and modeled functions. We demonstrate that this system is able to adequately model reaction systems, and that complex analysis of various experimental data increased the reliability of the reaction modeling results.
Microstructure design in the ternary systems with the only solubility gap
Authors: Lutsyk Vasily I. , Zyryanov Alexandr M.
Published: April 2011

New algorithms to design the microstructures in a ternary system with the solubility gap in one binary system have elaborated. They permit to visualize, to sect and to project a sophisticated surface with a trough.
Combinatorial Materials Design through Database Science
Authors: Suh Changwon , Rajagopalan Arun , Li Xiang , Rajan Krishna
Published: April 2011

Large scale materials databases have been traditionally used for search and retrieval of experimental and theoretical data. In this paper, three different cases are used to illustrate applications of statistical techniques in databases that extend beyond searching. A complete large scale database of molten salts is visualized for pattern seeking. In the second case, a large virtual combinatorial library of chalcopyrite semiconductors is developed from a small experimental and theoretical dataset. This involves selecting statistically appropriate parameters based on the physics of the materials. In the third case, ‘secondary’ descriptors are developed for a zeolites database to better understand the topology of mesoporous structures and as a materials design tool. These examples serve to demonstrate how databases can be used to identify important combinations of parameters relevant to combinatorial experimentation.
The Evolution of Short-Range Order in Ti-Hf-Ni Alloys with Hydrogenation
Authors: Sadoc Anne , Huett Van T. , Kelton K. F.
Published: April 2011

The evolution of the short-range order in a Ti-Hf-Ni 3/2 approximant phase, has been studied as a function of hydrogenation by means of extended X-ray absorption fine structure (EXAFS). The local structure of the non-hydrogenated alloy has been derived from that of 1/1 Ti-Zr-Ni. After hydrogenation, drastic changes are observed in the local structure of Ti-Hf-Ni. Preliminary results of the EXAFS analysis are also presented for an amorphous Ti-Hf-Ni alloy.
Atomic structure, Electronic States, and Stability of Icosahedral Quasicrystals
Authors: Zijlstra Eeuwe S. , Bose Shyamal K.
Published: April 2011

Several existing models of icosahedral quasicrystals (QCs) are improved upon and studied by ab initio electronic structure methods. The following approach is used to optimize the models: 1) interchange of atoms in the existing (skeletal) models based on available knowledge of the local atomic environments, and 2) subsequent relaxation of the atomic positions using forces determined via first principles density functional methods. After minimizing the total energy, we investigate the ground state, and compare calculated results with available photo-emission spectroscopy (PES) and Mössbauer spectroscopy data. Significant improvement with respect to the starting (skeletal) model is achieved in several cases. We also examine the validity of the concept of negative valences of the transition metal atoms in QCs as advanced by Friedel.
Aging of the surface of an Al-Cr-Fe approximant phase in ambient conditions: chemical composition and physical properties
Authors: Veys D. , Weisbecker P. , Fournée V. , Domenichini B. , Weber S. , Rapin C. , Dubois J. M.
Published: April 2011

We have investigated the surface properties of quasicrystalline and approximant phases in the Al-(Cu)-Cr-Fe system upon aging in ambient conditions. We found that some of these properties (like the electrochemical behavior, wetting or friction) slowly evolves with the length of exposure to normal atmospheric conditions, reaching a stable state only after several days. This report essentially focuses on one of these alloys, an Al65Cr27Fe8 approximant phase with g-brass structure. In a first part, we describe the effect of aging on the electrochemical behavior of this alloy and we propose an interpretation based on a simple electrical model of the oxidized surface. In a second part, we present a model describing the surface as a stacking of several layers (oxides, oxy-hydroxides, contamination) whose thickness evolves with time. The model is supported by X-ray reflectivity, angle-resolved photoemission spectroscopy and secondary neutral mass spectroscopy measurements.
Early stages of Al-nanocrystal formation in Al92Sm8
Authors: Wilde G. , Rösner H. , Boucharat N. , Hamann J. , Tong W. S. , Perepezko J. H.
Published: April 2011

Several proposals involving solute effects, phase separation or quenched-in nuclei and heterogeneous nucleation have been advanced to account for the high nanocrystal density that evolves during primary crystallization in marginal glass-forming alloys, but recent crystallization measurements and kinetics analyses provide new evidence for the role of the as-quenched structure on nanocrystal synthesis. Here, isothermal microcalorimetry investigations and quantitative electron microscopy measurements including high-resolution imaging and electron spectroscopy analyses were performed on a model system at different temperatures well below the glass transition to monitor the nanocrystallization isothermally as a function of time. From the combined measurements, the size distribution and the transformed fraction can be determined with a high accuracy for extended ranges of temperatures and times. In addition, calorimetric measurements in the glassy, liquid and crystalline states of the model alloy serves to analyze, for the first time, the fragility characteristics of a marginal glass-former that presents an important parameter in the context of the kinetic stability of the material against premature crystallization.
Formation of High-Strength Zr-Nb-Cu-Ni-Al Alloys by Warm Extrusion of Gas Atomized Powders
Authors: Rozhkova E. A. , Yang X. Y. , Wheelock P. B. , Eckert J. , Kühn U. , Sordelet D. J.
Published: April 2011

Recently developed Zr-based metallic glass composites containing a ductile phase demonstrate improved mechanical properties such as high strength combined with good ductility compared to the glass monoliths. Zr-Nb-Cu-Ni-Al amorphous powders with bcc phase precipitates were obtained by high pressure gas atomization. Formation of the bcc phase in the amorphous matrix strongly depends on the material composition and cooling rates during solidification. Melt spinning using various wheel speeds selected to simulate the cooling rates during gas atomization was used to define a specific composition for gas atomization. Gas atomized powders were consolidated by warm extrusion. Various processing conditions including starting powder particle size, extrusion temperature and extrusion ratio were examined to obtain materials having various microstructural features. Structure and thermal stability of consolidated bulk metallic glass composites as well as selected mechanical properties will be discussed.