bluuebunny/crossref_metadata_2025 huggingface dataset:
Non-Contact Determination of Free Carrier Concentration in n-GaInAsSb
Authors: Maslar James E. , Hurst Wilbur S. , Wang Christine A. , Shiau Daniel A.
Published: April 2011

GaSb-based semiconductors are of interest for mid-infrared optoelectronic and high-speed electronic devices. Accurate determination of electrical properties is essential for optimizing the performance of these devices. However, electrical characterization of these semiconductors is not straightforward since semi-insulating (SI) GaSb substrates for Hall measurements are not available. In this work, the capability of Raman spectroscopy for determination of the majority carrier concentration in n-GaInAsSb epilayers was investigated. Raman spectroscopy offers the advantage of being non-contact and spatially resolved. Furthermore, the type of substrate used for the epilayer does not affect the measurement. However, for antimonide-based materials, traditionally employed Raman laser sources and detectors are not optimized for the analysis wavelength range dictated by the narrow band gap of these materials. Therefore, a near-infrared Raman spectroscopic system, optimized for antimonide-based materials, was developed.

Ga0.85In0.15As0.13Sb0.87 epilayers were grown by organometallic vapor phase epitaxy with doping levels in the range 2 to 80 × 1017 cm-3, as measured by secondary ion mass spectrometry. For a particular nominal doping level, epilayers were grown both lattice matched to n-GaSb substrates and lattice-mismatched to SI GaAs substrates under nominally identical conditions. Single magnetic field Hall measurements were performed on the epilayers grown on SI GaAs substrates, while Raman spectroscopy was used to measure the carrier concentration of epilayers grown on GaSb and the corresponding SI GaAs substrates. Contrary to Hall measurements, Raman spectra indicated that the GaInAsSb epilayers grown on GaSb substrates have higher free carrier concentrations than the corresponding epilayers grown on SI GaAs substrates under nominally identical conditions. This is contrary to the assumption that for nominally identical growth conditions, the resulting carrier concentration is independent of substrate, and possible mechanisms will be discussed.
Laser Power and Temperature Dependent Photoluminescence Characteristics of Annealed GaInNAs/GaAs Quantum Well
Authors: Khee Ng Tien , Fatt Yoon Soon , Weijun Fan
Published: April 2011

Photoluminescence (PL) of annealed GaInNAs quantum well (QW) with varying temperature and laser excitation intensity is measured to understand the low temperature PL properties of annealed 6 nm GaInNAs QW. The measurements show that localization effect still exist in the QW even after annealing. This effect is characterized by an activation energy of 11 meV below the e1 state, which is obtained from fitting the integrated PL intensity vs. temperature curve with a single-activation-energy (SAE) model. This center is suggested to be related to the main localization center below the e1 state that could be resulted by N or In compositional fluctuation even after annealing.
Crystal Growth and Electrical Characterization of InSbN Grown by Metalorganic Vapor Phase Epitaxy
Authors: Ishiguro T. , Kobori Y. , Nagawa Y. , Iwamura Y. , Yamaguchi S.
Published: April 2011

InSb1-xNx was grown on GaAs substrate by low-pressure metalorganic vapor phase epitaxy. Carrier gases were hydrogen or the mix of hydrogen and nitrogen. In both cases, X-ray analysis demonstrated that nitrogen was incorporated into InSb1-xNx up to 0.24.
Electrical Properties of β -FeSi2/Si Hetero-Diode Improved by Pulsed Laser Annealing
Authors: Tsuchiya Keiichi , Miura Noboru , Matsumoto Hironaga , Nakano Ryotaro , Uekusa Shin-ichiro
Published: April 2011

β-phase iron disilicide (β-FeSi2) was obtained on n-type silicon (111) substrate by using excimer laser annealing (ELA). β-phase crystal which have good electrical properties was grown within a narrow annealing condition such as energy density. All samples were annealed by excimer laser show n-type characteristic. Graded junction was formed in FeSi2/Si hetero diode.
Infrared Dielectric Properties of In1-xGaxAs Epilayers on InP (100)
Authors: Rowell N. L. , Yu G. , Lockwood D. J. , Poole P. J.
Published: April 2011

The concentration dependence of optical phonons in strained In1-xGaxAs epilayers grown on InP (100) by chemical beam epitaxy has been characterized with oblique angle polarized far-infrared reflectivity measurements. In this powerful method, the reflectance spectra contain sharp Berreman peaks exactly at the optical phonon frequencies. For radiation polarized in the plane of incidence (p-polarized), peaks for both the TO and LO phonons were observed. For s-polarization only the TO modes were observed. For heavily doped substrates the TO film phonons were observed as reflectance minima, whereas for lightly doped substrates they were seen as maxima. The measured spectra were curve resolved to separate the effects of the various modes which included GaAs-like longitudinal and transverse optic (LO and TO), a disorder induced, and InAs-like LO and TO phonons. The dielectric response function and phonon frequency dependences for all modes were obtained versus Ga fraction for x from 0.25 to 0.75 and the latter showed a quadratic dependence on x over this range. The effects of strain on the phonon frequencies could then be evaluated.
Electronic Structure of Native Point Defects in Zngep2
Authors: Jiang Xiaoshu , Miao M. S. , Lambrecht Walter R. L.
Published: April 2011

First-principles calculations are presented for various native point defects in ZnGeP2 us-ing a full-potential linearized muffin-tin orbital method in the local density approximation to density functional theory. Under Zn-poor conditions, the lowest Gibbs energy defects are found to be the Gezn antisite and Vzn. The Vae is found to have high energy of formation under any chemical potential conditions and is unstable towards formation of a Vzn and ZnGe pair. It is shown that the V−Zn cannot account for the ALI EPR spectrum commonly associated with this vacancy and an alternative model consisting of a Vzn – GeZn – Vzn is tentatively proposed.
Room-Temperature Defect Tolerance of Shape Engineered Quantum Dot Structures
Authors: Lamberti Matthew , Katsnelson Alex , Yakimov Michael , Agnello Gabriel , Tokranov Vadim , Oktyabrsky Serge
Published: April 2011

A quantum dot (QD) medium is expected to demonstrate superior performance in various devices when compared with quantum wells (QWs). One area of interest has been the improved defect tolerance of QD media, though it was demonstrated at low temperatures so far. In this study, the defect tolerance of shape-engineered QD structures is compared with that of a QW structure at temperatures up to 300 K. To create high defect densities both QD and QW structures were irradiated with high energy (1.5 MeV) protons (with doses up to 3×1014 cm-2). Then, the relative luminescence efficiency was measured by variable temperature photoluminescence. The shape-engineered QD structure withstood two orders of magnitude higher defect density than the QWs at room temperature. This improvement is correlated with the activation energy for thermal evaporation of 390 meV, acquired through a kinetic model.
Synthesis of Aligned ZnO Hexagonal Nanorods and Its Application to ZnS Based DC Electroluminescent Devices
Authors: Hirate Takashi , Tanaka Hironori , Sasaki Shinya , Ozawa Makoto , Li Weichi , Satoh Tomomasa
Published: April 2011

Highly oriented ZnO nanorods have been grown on p--Si(111) wafers using a low-pressure thermal CVD method. X-ray diffraction shows that the nanorods are grown with the c-axis normal to the substrate. An electroluminescent device with ITO/ZnS:Mn/nanorod-ZnO/p--Si structure where the ZnS:Mn and ITO layers are deposited by the electron beam deposition method on the ZnO nanorods layer operates stably in DC mode with high luminance.
Wide Bandgap Materials for Semiconductor Spintronics
Authors: Pearton S. J. , Abernathy C. R. , Thaler G. T. , Frazier R. , Norton D. P. , Kelly J. , Rairigh R. , Hebard A. F. , Park Y. D. , Zavada J. M.
Published: April 2011

Existing semiconductor electronic and photonic devices utilize the charge on electrons and holes in order to perform their specific functionality such as signal processing or light emission. The relatively new field of semiconductor spintronics seeks, in addition, to exploit the spin of charge carriers in new generations of transistors, lasers and integrated magnetic sensors. The ability to control of spin injection, transport and detection leads to the potential for new classes of ultra-low power, high speed memory, logic and photonic devices. The utility of such devices depends on the availability of materials with practical (>300K) magnetic ordering temperatures. In this paper, we summarize recent progress in dilute magnetic semiconductors such as (Ga,Mn)N, (Ga,Mn)P and (Zn,Mn)O exhibiting room temperature ferromagnetism, the origins of the magnetism and its potential applications in novel devices such as spin-polarized light emitters and spin field effect transistors.
The dispersion and polymer coating of ultrafine aluminum powders by the Ziegler Natta reaction
Authors: Roy Cédric , Dubois Charles , Lafleur Pierre , Brousseau Patrick
Published: April 2011

Ultrafine aluminum powders have been identified as very promising fuels as part of energetic materials formulations. However, the large specific surface area that gives these powders a high reactivity also makes them particularly difficult to maintain in an unoxidized state. They also agglomerate easily during compounding processes. The coating of the particles by a polymer could offer a solution to these problems. We carried out the in-situ synthesis of high density polyethylene on the surface of aluminum nanoparticles by the Ziegler-Natta process. The process was found to be flexible enough to control the amount of polyethylene grafted on the powders. Ultrasounds were applied during the polymerization process to enhance the dispersion of the particles in the solvent. The resulting characteristics of the coated powders are discussed by means of thermogravimetric characterizations and electronic microscopy.
Combustion Synthesis of Nanoscale Oxide Powders: Mechanism, Characterization and Properties
Authors: Varma Arvind , Mukasyan Alexander S. , Deshpande Kishori T. , Pranda Pavol , Erri Peter R.
Published: April 2011

Based on the analysis of extensive experimental data, we have formulated basic criteria necessary for the synthesis of a variety of oxides in the combustion mode, and defined optimum conditions for the production of high-surface area, well-crystalline nano-powders of desired phase composition and purity. Also, for the first time, detailed chemical mechanisms of interaction for various systems are identified, outlining specific roles of different fuels, oxidizers and thermal conditions
Nickel Aluminide Superalloys Created by SHS of Nano-Particle Reactants
Authors: Hunt Emily M. , Granier John J. , Plantier Keith B. , Pantoya Michelle L.
Published: April 2011

Advancements in nanotechnology for material processing have spurred the development of superalloys that provide improved protection against corrosion and wear. Nano-scale reactant particles offer unique thermal properties and increased homogeneity that may improve the microstructural features and macroscopic properties of the final product. In this study up to 10-wt% nano-scale molybdenum tri-oxide (MoO3) particles were added to micron scale nickel (Ni) and aluminum (Al). The goal was to produce a superalloy by generating excessively high heating rates and adding an oxidizer that would produce small quantities of Al2O3 (a strengthening agent) within the microstructure of the alloy. Experiments were performed on pellets pressed to 60% theoretical maximum density. Ignition and flame propagation were examined using a CO2 laser and imaging diagnostics that include a copper-vapor laser coupled with a high-speed camera. Product microstructure was examined using scanning electron microscopy. Abrasion testing was performed to evaluate the wear resistance properties of the superalloy. Results show that adding MoO3 increases the flame temperature and produces greater ignition sensitivity. Also, small quantities of MoO3 produce a more homogeneous microstructure and increase the overall wear resistance of the product.
Characterization of Nano-Sized Particles for Propulsion Applications
Authors: Risha Grant A. , Boyer Eric , Evans Brian , Kuo Kenneth K. , Malek Rafaat
Published: April 2011

Energetic nano-sized particles have been shown to have a great potential for use in the aerospace propulsion applications. Some of the unique combustion properties of nano-particles such as very rapid ignition and short combustion times make them particularly valuable for propulsion systems; they can be included in solid fuels, solid propellants, or even as energetic gellant in liquid systems. However, due to the novelty of the application and rapid development of production techniques, there is no comprehensive understanding of what characteristics of a nano-sized particle are important in contributing to desirable performance and ease of processing into a final usable form. Previous studies have shown that HTPB-based solid fuels containing various types of nano-sized particles showed differing performance results when tested in the same hybrid rocket motor under identical conditions. Many of these particles have data available only on the basic composition (aluminum, boron, boron carbide, etc.), average diameter, and/or BET surface area. In order to better understand and correlate observed combustion behavior with intrinsic material properties, the particles of interest need to be better characterized. A variety of standard particle characterization techniques were applied to the fifteen types of particles examined in this study and the results tabulated. Some of the parameters measured were average particle diameter, specific surface area, amount of active content, and oxide layer thickness. Trends in propulsion performance measured using a parameter of great interest to the hybrid rocket community (fuel mass burning rate) in general matched trends in particle characteristics (i.e. active content, surface area), but there were some noticeable exceptions. This study indicates that there is still much more to learn about the correlation between physical and chemical properties and measured combustion performance. Other parameters that should be examined in the future include particle size distribution, degree of agglomeration, reactivity and thermal effects (oxidation rate, onset temperature for oxidation exotherm, heat release associated with any excess stored energy), etc.
Formation of Nanostructured Energetic Materials via Modified Sol-Gel Synthesis
Authors: Walker Jeremy , Tannenbaum Rina
Published: April 2011

This study is concerned with the development of a modified sol-gel synthesis of Fe2O3 xerogels that would allow the design and control of the interfacial area between the oxidant iron oxide matrix and the metal reducing agent, thus optimizing the energetic yield of these highly energetic reactions. The modification consisted in the addition of a new class of di-functional template molecules, such as diamines or di-acids, as gelation agents. pH profile measurements indicated that the mechanism of reaction of propylene oxide and of succinic acid as the gelation agents was fundamentally different. Propylene oxide acts as a proton scavenger, reducing the hydrated iron species to Fe2O3, thus reducing the concentration of protons in the reaction mixture leading to an increase in pH. When succinic acid is used as the gelation agent, a decrease in pH versus time during the reaction indicates the formation of carboxylate ions, thus creating reactive molecules that are capable of stabilizing the Fe2O3 clusters during the growth process. Infrared spectra of the products in both reactions support presence of carboxylate groups in the Fe2O3 xerogels. X-ray diffraction analyses revealed low levels of crystallinity in both products, and the presence of different phases of Fe2O3.
First-Principles Equation of State for an Energetic Intermetallic Mixture
Authors: Lu X. , Hanagud S.
Published: April 2011

The thermodynamically complete equation of state P=P(ρ,T) for a intermetallic mixture of nickel and aluminum is obtained via first principle calculations for pressures up to 300GPa and temperatures up to 1000K. The calculations for the static-lattice EOS are carried out in the framework of the density functional theory (DFT), using generalized gradient approximations and ultrasoft psuedopotentials. The phonon modes are calculated by using the density functional perturbation theory (DFPT). First, the EOS for each species is obtained based on ab initio prediction of the electron ground state and thermal excitations. Then, the mixture theories are utilized to obtain the EOS for the mixture. Two mixture theories are proposed, which correspond to the two limiting cases. The nature of the real mixture is intermediate to those of the two idealized mixtures and hence can be modeled as a weighted combination of the two cases. The Comparisons of the EOS for nickel and aluminum obtained from existing shock Hugoniot data show good agreement with the theoretical results.
Nanoscale Energetics with Carbon Nanotubes
Authors: Wang Yubing , Malhotra Sanjay , Iqbal Zafar
Published: April 2011

Single wall carbon nanotubes (SWNTs) with diameters below 1 nm prepared by chemical vapor deposition (CVD), and with diameters of 1.3 nm and higher prepared by laser ablation and carbon-arc techniques, were electrochemically functionalized with hydrogen and nitro groups, and chemically derivatized with 4-nitroaniline. Hydrogen adsorption on SWNTs was carried out in the presence or absence of electrodeposited catalytic nanoparticles of magnesium. SWNTs deposited on Teflon-coated membranes by vacuum filtration and lifted off as free-standing nanopaper, were used as the electrodes for electrochemical functionalization reactions. Hydrogen uptake on the nanotubes was characterized by micro-Raman spectroscopy, thermogravimetry and thermopower measurements. Electrochemically-induced functionalization with −NO2 groups on metallic, laser-synthesized SWNTs was clearly detected by Raman spectroscopy. Chemical functionalization was achieved on CVD-produced SWNTs by acidification to form −COOH groups followed by reaction with thionyl chloride and then with 4-nitroaniline. Photoacoustic effects that are likely to be precursors of photo-induced initiation of energetic reactions, were observed to occur at varying laser intensities for these materials in experiments using a pulsed Nd-YAG laser emitting at 532 nm.
Synthesis and characterization of Manganese doped ferroxane nanoparticles
Authors: Cortalezzi Maria M. , Rose Jerome , Tsui Eliza , Barron Andrew R. , Bottero Jean-Yves , Wiesner Mark
Published: April 2011

Ferroxane nanoparticles are precursors to iron oxide ceramic porous membranes. The ferroxane-derived ceramics have an average pore size of 24 nm and a surface area of 80 m2/g. Previous work has shown that these membranes have a molecular weight cut off of 180,000 dalton and their permeability is comparable to commercially available membranes. The ferroxane nanoparticles were reacted with manganese acetyl acetonate and then applied to the fabrication of mixed metal oxides. The nanoparticles were dried to form a ceramic chip. Upon sintering, asymmetric mixed metal oxide ceramic membranes were obtained. The materials were characterized by EXAFS, EDAX imaging and IDX mapping. EXAFS showed that the atomic environment of the iron and dopant material was different from those in the initial compounds, thus confirming that the reaction took place. The concentration of dopant metal was between 7% and 10%, with uniform concentration throughout the material.
The Hydrogen Programs in China
Authors: Wang Qidong , Lei Changpin Chen Yongquan , Chen Lixing , Wang Xinghua
Published: April 2011

According to the stages of development, the hydrogen program in China can be divided into four periods since 1978. The chief activities and accomplishments in each period on hydrogen production, hydrogen processing and use of hydrogen in the form of energy are introduced. The work of consciously transforming the present energy system based upon coal-firing power plants and petroleum powered internal combustion engine vehicles into a hydrogen economy system with primary energy mainly based on renewable energies and recycling of biomass and the use of both electricity and hydrogen as energy vectors is just on its start.
Hydrogen Storage Properties of Magnesium Based Nanostructured/Amorphous Composite Materials
Authors: Au Ming
Published: April 2011

In this work, nanostructured composite materials Mg-Ni, Mg-Ni-La, Mg-Ni-Ce and Mg-LaNi5 have been synthesized using the mechanical alloying process. The new materials produced have been investigated by X-ray diffraction (XRD), TEM, SEM and EDS for their phase compositions, crystal structure, grain size, particle morphology and the distribution of the catalyst elements. Hydrogen storage capacities and the hydriding-dehydriding kinetics of the new materials have been measured at different temperatures using a Sieverts apparatus. The results show that amorphous/nanostructured composite material Mg50%-Ni50% absorbs 5.89wt% within five minutes and desorbs 4.46% hydrogen within 50 minutes at 250°C respectively. Adding 5% La into Mg-Ni composite materials reduces the starting temperature of hydrogen absorption and desorption from 200°C to 25°C which suggests the formation of unstable hydrides. The composite material Mg80%-LaNi5 20% absorbs 1.96% hydrogen and releases 1.75 wt% hydrogen at 25°C. It is observed that mechanical alloying accelerates the hydrogenation kinetics of the magnesium based materials at low temperature, but a high temperature must be provided to release the absorbed hydrogen from the hydrided magnesium based materials. It is believed the dehydriding temperature is largely controlled by the thermodynamic configuration of magnesium hydride. Doping Mg-Ni nano/amorphous composite materials with lanthanum reduces the hydriding and dehydriding temperature. Although the stability of MgH2 can not be easily reduced by ball milling alone, the results suggest the thermodynamic properties of Mg-Ni nano/amorphous composite materials can be alternated by additives such as La or other effective elements. Further investigation toward understanding the mechanism of additives will be rewarded.
Effect of Heat Treatment on Properties of Ti-Mn Based Laves Phase Hydrogen Storage Alloys
Authors: Lijun Jang , Hailing Tu , Yi Chen , zhuo Huang , Feng Zhan
Published: April 2011

Effect of heat treatment on the properties and microstructure of non-stoichiometric Ti-Mn based hydrogen storage alloys were investigated. The results were presented that the hydrogen storage capacity was increased and the width of P-C-T Plateau extended, but the slope of plateau increased after heat treatment. Through SEM, EDS and XRD analysis, it was found that the crystal parameters and cell volume was increased, meanwhile the composition homogeneity effectively enhanced and the content of C15 phase decreased after heat treatment. The accretion of slope of plateau would be related to the ratio of valence electron/atom of the alloys.
Investigation of Ti-doped NaAlH4 by solid-state NMR
Authors: Herberg Julie L. , Maxwell Robert S. , Majzoub Eric H.
Published: April 2011

In recent years, the development of Ti-doped NaAlH4 as a hydrogen storage material has gained attention because of its large weight percentage of hydrogen (∼5 %) compared to traditional interstitial hydrides. The addition of transition-metal dopants, in the form of Ti-halides, such as TiCl3, dramatically improves the kinetics of the absorption and desorption of hydrogen from NaAlH4. However, the role that Ti plays in enhancing the absorption and desorption of H2 is still unknown. In the present study, 27Al, 23Na, and 1H MAS (Magic Angle Spinning) NMR (Nuclear Magnetic Resonance) has been performed to understand the titanium speciation in Ti-doped NaAlH4. All experiments were performed on a sample of crushed single crystals exposed to Ti during growth, a sample of solvent-mixed 4TiCl3 + 112NaAlH4, a reacted sample of solvent-mixed TiCl3 + 3NaAlH4 with THF, and a reacted sample of ball-milled TiCl3 + 3NaAlH4. The 27Al MAS NMR has shown differences in compound formation between solvent-mixed TiCl3 + 3NaAlH4 with THF and the ball-milled TiCl3 + 3NaAlH4. 27Al MAS NMR of the ball-milled mixture of fully-reacted TiCl3 + 3NaAlH4 showed spectral signatures of TiAl3 while, the solvent-mixed 4TiCl3 + 112NaAlH4, which is totally reacted, does not show the presence of TiAl3, but suggests the existence of Al2O3.
Ion Irradiation Effects in Solid Oxide Fuel Cell Electrolytes
Authors: Cheng Jeremy , Pornprasertsuk Rojana , Saito Yuji , Prinz Fritz B.
Published: April 2011

Single crystal Ytrria-stabilized Zirconia was irradiated with Xe2+ and Xe3+ ions at 320 and 450 keV over a range of doses from 1013 to 1016 ions/cm2. Damage appears as a 150 nm surface layer with a dense dislocation network. The X-ray diffraction pattern shows an increasing lattice expansion with increasing dose that reaches a saturation point. Ion irradiation increases the surface conductance of the material; this effect is removed with certain post-treatments. Preliminary isotope depth profiling indicates enhanced ion diffusion in the damaged layer.
Synchrotron Diffraction Study of the Isothermal Oxidation of Uranium Dioxide at 250°C
Authors: Rousseau Gurvan , Desgranges Lionel , Nièpce Jean-Claude , Bérar Jean-François , Baldinozzi Gianguido
Published: April 2011

The structural evolution of UO2 during its oxidation to U3O8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases that are likely to appear during the long-term storage of spent nuclear fuel. Our results are in disagreement with the literature in which the existence of an intermediate cubic phase is not reported. Instead, an α-U3O7 tetragonal phase (c/a < 1) was mentioned but not definitively observed. These previous interpretations may have been the result of poor instrumental resolution.
“Burst-like” Characteristics of the δ/α′ Phase Transformation in Pu-Ga Alloys
Authors: Blobaum Kerri J.M. , Krenn Christopher R. , Haslam Jeffery J. , Wall Mark A. , Schwartz Adam J.
Published: April 2011

The δ to α′ phase transformation in Pu-Ga alloys is intriguing for both scientific and technological reasons. On cooling, the ductile fcc δ-phase transforms martensitically to the brittle monoclinic α′-phase at approximately −120°C (depending on composition). This exothermic transformation involves a 20% volume contraction and a significant increase in resistivity. The reversion of α′ to δ involves a large temperature hysteresis and begins just above room temperature. In an attempt to better understand the underlying thermodynamics and kinetics responsible for these unusual features, we are examining the δ/α' transformations in a Pu-0.6 wt% Ga alloy using differential scanning calorimetry (DSC) and resistometry. Both techniques indicate that the martensite start temperature is −120°C and the austenite start temperature is 35°C. The heat of transformation is approximately 3 kJ/mole. During the α ′ → δ reversion, “spikes” and “steps” are observed in DSC and resistometry scans, respectively. These spikes and steps are periodic, and their periodicity with respect to temperature does not vary with heating rate. With an appropriate annealing cycle, including a “rest” at room temperature, these spikes and steps can be reproduced through many thermal cycles of a single sample.
Experimental verification of the need for either jj or intermediate coupling in the 5f states of plutonium
Authors: Moore K. T. , Wall M. A. , Schwartz A. J. , Chung B. W. , Tobin J. G. , Shuh D. K. , Schulze R. K.
Published: April 2011

Here, we demonstrate the power of electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM) to investigate the electronic structure plutonium. Using EELS, TEM, and synchrotron-radiation-based X-ray absorption spectroscopy (XAS), we provide the first experimental evidence that Russell-Saunders (LS) coupling fails for the 5f states of Pu. These results support the assumption that only the use of jj or intermediate coupling is appropriate for the 5f states of Pu. EELS experiments were performed in a TEM and are coupled with image and diffraction data, therefore, the measurements are completely phase specific. It is shown that EELS in a TEM may be used to circumvent the difficulty of producing single-phase or single-crystal samples due to its high spatial resolution.
Soft X-ray Synchrotron Radiation Investigations of Actinide Materials Systems Utilizing X-ray Emission Spectroscopy and Resonant Inelastic X-ray Scattering
Authors: Shuh D. K. , Butorin S. M. , Guo J.-H. , Nordgren J.
Published: April 2011

Synchrotron radiation (SR) methods have been utilized with increasing frequency over the past several years to study topics in actinide science, ranging from those of a fundamental nature to those that address a specifically-targeted technical need. In particular, the emergence of microspectroscopic and fluorescence-based techniques have permitted investigations of actinide materials at sources of soft x-ray SR. Spectroscopic techniques with fluorescence-based detection are useful for actinide investigations since they are sensitive to small amounts of material and the information sampling depth may be varied. These characteristics also serve to simplify both sample preparation and safety considerations. Examples of investigations using these fluorescence techniques will be described along with their results, as well as the prospects for future investigations utilizing these methodologies.
Actinide Materials Research Supported by the Office of Basic Energy Sciences, U.S. Department of Energy
Authors: Morss Lester R.
Published: April 2011

The fundamental research topic in actinide chemistry and materials sciences is the role that the 5f electrons play in bond formation, which provides the central focus for DOE BES-supported actinide science. Structural systematics of the actinide metals, oxides, and other compounds as a function of atomic number are well established. Magnetic measurements have shown that the light actinide metals have delocalized 5f orbitals (i.e., the 5f electrons form bands), whereas the f electrons become localized at americium. Thus, the magnetic behavior of the first part of the actinide series resembles that of the d transition metals whereas the heavier actinides exhibit behavior similar to the rare earth metals. Spectroscopic results have established electronic energy levels, crystal field splitting, and near-neighbor coordination. The 5f orbitals participate in the band structure of materials that contain the light actinide metals and some of their intermetallic compounds, and perhaps in molecular compounds. Molecular-level information on the geometry and bonding in solids, at surfaces, and in clusters can now be obtained at BES-supported facilities.
Am Doping in Copper-Oxide Superconducting Systems
Authors: Skanthakumar S. , Soderholm L.
Published: April 2011

The effect of Am doping on the physical properties of three superconducting systems (RBa2Cu3O7, Pb2Sr2R1−xCaxCu3O8 and R2−xMxCuO4) have been studied using x-ray diffraction, x-ray absorption spectroscopy (XAS) and magnetic susceptibility experiments. Am is incorporated into all three systems as the tetravalent ion and superconductivity is not observed in any of the resultant compounds. The absence of superconductivity in Pb2Sr2Am0.5Ca0.5Cu3O8 is attributed to the transfer of charge from Am to the Cu-O planes. Systems that cannot incorporate a tetravalent ion, notably AmBa2Cu3O7 and Am2CuO4, do not form. Although Pr1.85Am0.15CuO4 forms with similar structure to Pr1.85Ce0.15CuO4, and Am like Ce is tetravalent, it is not superconducting. We argue that the absence of superconductivity in the Am doped Pr compound it is due to the hybridization of radially-extended f orbitals on the magnetic Am4+ ion with the Cu-O band states.
Photoelectron and X-ray Absorption Spectroscopy of Pu
Authors: Tobin J. G. , Chung B. , Schulze R. K. , Farr J. D. , Shuh D. K.
Published: April 2011

We have performed Photoelectron Spectroscopy and X-Ray Absorption Spectroscopy upon highly radioactive samples of Plutonium at the Advanced Light Source in Berkeley, CA, USA. First results from alpha and delta Plutonium are reported as well as plans for future studies of actinide studies.
Electronic Structure of δ-Pu and PuCoGa5 from Photoemission and the Mixed Level Model
Authors: Joyce John J. , Wills John M. , Durakiewicz Tomasz , Guziewicz Elzbieta , Butterfield Martin T. , Arko Aloysius J. , Moore David P. , Sarrao John L. , Morales Luis A. , Eriksson Olle
Published: April 2011

The electronic structure of δ-phase Pu metal and the Pu-based superconductor PuCoGa5 is explored using photoelectron spectroscopy and a novel theoretical scheme. Excellent agreement between calculation and experiment defines a path forward for understanding electronic structure aspects of Pu-based materials. The photoemission results show two separate regions of 5f electron spectral intensity, one at the Fermi energy and another centered 1.2 eV below the Fermi level. A comparison is made between the photoemission data and five computational schemes for δ-Pu. The results for δ-Pu and PuCoGa5 indicate 5f electron behavior on the threshold between localized and itinerant and a broader framework for understanding the fundamental electronic properties of the Pu 5f levels in general within two configurations, one localized and one itinerant.
Fermi liquid instabilities and superconductivity near quantum critical points in f-electron materials
Authors: Maple M. B. , Frederick N. A. , Jeffries J. R. , Ho P.-C. , Zapf V. S.
Published: April 2011

Recent experiments on single crystals of the compounds CeRh1−xCoxIn5 and PrOs4Sb12 are briefly reviewed. The temperature-composition (T-x) phase diagram of the heavy fermion pseudoternary system CeRh1−xCoxIn5, delineating the regions in which superconductivity, antiferromagnetism, and the coexistence of these two phenomena occur, has been established. Entropy vs x isotherms and residual resistivity vs x plots exhibit peaks near the critical concentration xcr ≈ 0.8 at which the Néel temperature appears to vanish (quantum critical point). The filled skutterudite compound PrOs4Sb12 exhibits unconventional superconductivity below Tc = 1.85 K that involves heavy fermion quasiparticles with an effective mass m* ≈ 50 me, where me is the mass of the free electron. The unconventional superconducting state appears to consist of several distinct superconducting phases and to break time reversal symmetry. A high field ordered phase occurs below ∼ 1 K and between ∼ 4.5 T and ∼ 15 T that appears to be associated with quadrupolar order. The heavy fermion state and superconductivity in PrOs4Sb12 may originate from the interaction between Pr3+ electric quadrupole moments and the charges of the conduction electrons. When Ru is substituted for Os in PrOs4Sb12, a minimum in Tc occurs at Pr(Os0.4Ru0.6)4Sb12, suggesting a competition between two types of superconductivity.
To Data Management and Beyond… for Photovoltaic Applications
Authors: Nelson Brent , Friedman Dan , Geisz John , Albin David , Benner John , Wang Qi
Published: April 2011

Material science tends to focus around a specific class of materials and devices. After an idea is created, an experiment is postulated, and then materials are grown and devices are fabricated. These materials and devices are characterized using a variety of techniques. Data from these laboratory steps are analyzed, conclusions are formulated, and knowledge is passed on through publications, presentations, and patents. Typically, data are tracked in the area of what is grown and what is measured, but corporate knowledge is often lost as to what motivated certain experiments or what was learned from those experiments. This can be due to many factors including corporate culture, lack of reporting of negative results, and lack of reporting of full data sets. Proper application of informatics must realize that data does not equal knowledge, but is the foundation for creating knowledge, which is far more useful than mere information. Combinatorial approaches for material growth, device fabrication, and subsequent characterization accelerate experimental throughput. Integrating these systems and their data at all levels ultimately will lead to key knowledge to discover new materials and invent new device structures. Well-designed informatics systems must fully relate all types of data and information, make full use of automation, enable data mining, and have an easy-to-use, fast, user interface.
Combinatorial Materials Development using Gradient Arrays. Sphere Covering Lattice Designs: Designs for Efficient use of Experimental Resources.
Authors: Cawse James N.
Published: April 2011

Gradient arrays are now common tools in combinatorial chemistry for discovery of new leads to commercial materials. Although the cost per sample has dropped markedly with new high throughput methods, efficient use of experimental resources is still important. Examination of gradient arrays from an informational standpoint suggests that designs which use the concepts of sphere packing and covering will be more efficient than simple gradients. This is especially true in higher dimensional systems.
The Magnetic Structure of the Rare-Earth Intermetallic Compound La3Co29Si4B10
Authors: Zhang Heng , Hofmann M. , Kennedy S. J. , Campbell S. J.
Published: April 2011

A quaternary rare-earth intermetallic compound La3Co29Si4B10 has been synthesized and the crystal and magnetic structures investigated by neutron diffraction over the temperature range 7–300 K. Rietveld refinements of the neutron diffraction patterns demonstrate that La3Co29Si4B10 is tetragonal and isostructural with Nd3Ni29Si4B10. The magnetic scattering indicates that the moments of the Co sublattice are collinear and lie in the basal plane. The mean magnetic moment for the Co atoms is μ ∼ 0.5 μB, or 13.6μB/F.U., in agreement with magnetization measurements.
Using Non-linear Regression to Predict Bioresponse in a Combinatorial Library of Biodegradable Polymers
Authors: Smith Jack R. , Knight Doyle , Kohn Joachim , Rasheed Khaled , Weber Norbert , Abramson Sascha
Published: April 2011

We have developed an empirical method to model bioresponse to the surfaces of biodegradable polymers in a combinatorial library using Artificial Neural Networks (ANN) in conjunction with molecular modeling and machine learning methodology. We validated the procedure by modeling human fibrinogen adsorption to 22 structurally distinct polymers. Subsequently, the method was used to model the more complicated phenomena of rat lung fibroblast and normal human fetal foreskin fibroblast proliferation in the presence of 24 and 44 different polymers, respectively. In each case, the root mean square (rms) percent error of the prediction was substantially less than the experimental variation, showing that the models can distinguish high and low performing polymers based on structure/property information. Using this method to screen candidate materials in terms of specific bioresponse prior to extensive experimental testing will greatly facilitate materials development for biomedical applications.
Heterogeneous Design. Structural diagrams of ternary systems
Authors: Lutsyk Vasily I. , Vorob'eva Vera P.
Published: April 2011

It is proposed to supplement a phase diagram by a structural diagram, which represents the mass portions of phases, conglomerates or their elements upon the system concentration at fixed temperature. Methods of structural diagrams and concentration maps construction are considered. Concentration map is a projection of structural diagram. It marks a concentration triangle by the lines of constant mass portions of a phase or its elements.
High Throughput Measurements of Polymer Fluids for Formulations*
Authors: Beers Kathryn L. , Cabral João T. , Walls Howard J. , Amis Eric J.
Published: April 2011

Rapid prototyping of microfluidic handling devices has gained popularity due to the ability to quickly test and modify new design features several times in one day. At the NIST Combinatorial Methods Center (NCMC), we have modified common microfluidic fabrication techniques to extend their use to organic fluids. Ultraviolet (UV) curable adhesives were used to create molded resins with increased solvent resistance. This has allowed the preparation of new types of combinatorial libraries and development of new measurement methods to complement the small sample sizes of these libraries. Most importantly, it can be used to tie together multiple stages of the formulation process, from the synthesis of polymers to the measurement of complex-fluid properties, in small and inexpensive platforms. Our first demonstrations of this technology are in the areas of emulsions and polymer blends. Measurement techniques include light and x-ray scattering and rheology. Milli-fluidic handling and measurements will increase the dimensions of parameter space that are available to accurate and systematic study of polymer solutions. These capabilities will also enable the generation of new information in the field of polymer formulations, which is presently dominated by empirical knowledge.
COMBINATORIAL SYNTHESIS AND REACTIVITY SCREENING OF ELECTRO-OXIDATION CATALYST GRADIENTS
Authors: Jayaraman Shrisudersan , Hillier Andrew C.
Published: April 2011

Combinatorial methods represent an appealing experimental method for the discovery of heterogeneous catalysts. One can efficiently identify candidate materials or sample vast regions of composition space using a combination of dense catalyst libraries and high-throughput reactivity screening techniques. This is particularly appealing for the discovery of novel catalysts for low temperature fuel cells where multi-component systems have shown improved performance. For example, the poison tolerance of typical anode catalysts can be improved by the addition of oxophilic components such as ruthenium, molybdenum, tin or osmium. Consequently, a vast composition space must be sampled in order to identify catalyst compositions or regions of composition space with greater activity. Combinatorial methods represent a practical means to speed-up the catalyst discovery process. In this manuscript, we demonstrate a novel method for combinatorial catalyst discovery based upon the synthesis and reactivity mapping of catalyst composition gradients. Samples consisting of uniform variations in surface composition of metals catalysts (Pt-M1 and Pt-M1−M2, where M1, M2 = Ru, Mo, Sn or Os) are fabricated using a gel-transfer technique. A concentration gradient of source metal ions is produced in a swollen polymer gel and then transferred onto a surface by electrodeposition to create a continuous composition gradient. An in situ reactivity-mapping tool based on the scanning electrochemical microscope is used to interrogate these catalyst gradients for the hydrogen oxidation reaction in the presence of adsorbed carbon monoxide.
Synthesis and Screening of Materials Libraries of Buried Compound Semiconductors by Ion Beam Implantation
Authors: Großhans I. , Karl H. , Stritzker B.
Published: April 2011

A combinatorial approach was employed to ion beam synthesis and optical analysis of buried II-VI compound CdSe semiconductor nanocrystals. Typically standard ion implantation setups are designed in a way to create a laterally homogenous dose distribution of the implanted ion species. In order to achieve intentional lateral variations of the implanted doses a special implanter endstation was constructed. Computer controlled apertures in front of the wafer cover up in succession parts of a 4 in. wafer, so that a lateral pattern of distinct dose combinations of the implanted elements Cd and Se was generated. The obtained materials library consists of 1:1 stoichiometric, but also off-stoichiometric dose ratios. After implantation the wafers passed through a rapid thermal heat treatment, where the implanted material forms buried semiconductor nanocrystals. Photoluminescence spectra of the elements of the materials library were screened in rapid succession in an optical cryostat into which the whole wafer was mounted and cooled down. The obtained spectra were compared and key-parameters determined which control the photoluminescence properties. In this contribution will be shown, that slight variations of the dose ratio significantly alter the optical properties and that new efficient photoluminescent materials and processing parameters can be found. In this way, also other complex interdependencies of physical and chemical parameters in the field of multiple element ion beam implantation might be efficiently investigated.
Combinatorial material library synthesis from insoluble oxide suspension using a drop-on-demand inkjet delivery system
Authors: Chen Lei , Huang Sungxiang , Bao Jun , Liu Chihui , Liu Wenhan , Gao Chen
Published: April 2011

A combinatorial synthesis method was developed by ejecting insoluble oxide suspensions using a drop-on-demand inkjet delivery system. The insoluble oxide suspensions with ultrafine/nano particles were prepared by grinding the oxide power in water using a high-energy ball mill. Using luminescent materials as model systems, it was established that the technique is very well suited to combinatorial synthesis of insoluble oxides.
Design, Use and Results from Combinatorial Steady-State Reactors for the Optimization of Highly Selective Heterogeneous Catalysts in Liquid Systems
Authors: Spivack James L , Webb Jimmy , Flanagan William P , Sabourin Cheryl , May Ralph , Hassib Lamyaa
Published: April 2011

A reactor was designed, built and successfully operated that allowed the simultaneous running of 96 independent reactions at steady-state. Since the problem involved the attainment of 98% in selectivity from a starting point of 93%, very precise reproducibility in selectivity was required. Because selectivity varies with time in a batch reactor, and since commercial reactors for this process are continuous, continuous reactors operated at steady-state were required. Longterm standard deviation in selectivity of <0.2% was attained. Information feedback from so many reactors allowed study of variation in catalyst composition, liquid retention times, space velocity, temperature and other variables to be accomplished in relatively short time. Comparison between heterogeneous and homogeneous catalysis in the same reactors gave insight into the underlying mechanisms determining activity and selectivity. Results from 200 uL reactors scaled very well to laboratory and pilot plant sizes.
Combinatorial Catalysis Survey concerning Proton Exchange Membrane Fuel Cell Technology – As a Part of “MATERIOMICS” –
Authors: Yamada Yusuke , Ueda Atsushi , Shioyama Hiroshi , Mathew Thomas , Ioroi Tsutomu , Yasuda Kazuaki , Akita Tomoki , Ichikawa Satoshi , Tanaka Koji , Kohyama Masanori , Kobayashi Tetsuhiko
Published: April 2011

Our efforts to combine the combinatorial technology and microstructure analysis to develop catalysts for proton exchange membrane fuel cell (PEMFC) technology have been described. This offers the realization of “materiomics” in comprehensive material research. Catalyst technologies are indispensable for wide use of PEMFC, which are regarded as the low emission and highly efficient energy conversion device for the next generation. We have applied the combinatorial method for the hydrogen production and/or purification of catalysts, and anode catalyst investigations. The catalyst library consisting of precious metals loaded on various metal oxides was tested for water gas shift reaction and steam reforming of methanol and/or DME. Various metal oxides added to platinum loaded on carbon were screened for anode catalysts. The microstructure of each catalyst was analyzed by employing scanning electron and/or transmission electron microscopy. This paper mainly describes the catalysis screening results of above reactions that form a part of “materiomics”.