bluuebunny/crossref_metadata_2025_split huggingface dataset:
GaSb-based Materials for Mid-infrared Photodiodes Operating in the 0.9–2.55 μm Spectral Range
Authors: Andreev I.A. , Kunitsyna E.V. , Mikhailova M.P. , Yakovlev Yu.P. , Ioffe A.F. 
Published: April 2011

ABSTRACTThe paper discusses some recent developments in the GaSb/GaInAsSb/GaAlAsSb heterostructure epitaxial growth and fabrication of GaInAsSb/GaAlAsSb photodiodes for the 0.9–2.55 μm spectral range.
Intersubband Transitions in InxGa1-xAs/AlGaAs Multiple Quantum Wells for Long Wavelength Infrared Detection
Authors: Workman Clayton L. , Wang Zhiming , Ma Wenquan , George Christi E. , Panneer Selvam R. , Salamo Gregory J. , Zhou Qiaoying , Omar Manasreh M. 
Published: April 2011

ABSTRACTWe report on intersubband transitions in InxGa1-xAs/AlGaAs multiple quantum wells (MQWs) grown by molecular beam epitaxy. The conduction band offset for this material system is larger than that of the well known GaAs/AlGaAs system, thus making it possible to design, grow, and fabricate quantum well infrared photodetectors operational beyond the 14 μm spectral region with minimized dark current. We have grown InxGa1-xAs/AlGaAs MQWs with indium compositions ranging from x = 0.08 to 0.20 verified by in situ RHEED oscillations, band offset measurements, and high-resolution X-ray diffraction. Band-to-band transitions were verified by photoluminescence measurements, and intersubband transitions were measured using Fourier transform infrared (FTIR) spectroscopy. Due to the high strain and introduction of dislocations associated with the high indium content, wells with indium compositions above ∼ 0.12 did not result in intersubband transitions at silicon doping levels of 2×1018 cm-3. A thick linear graded InxGa1-xAs buffer was grown below the MQW structures to reduce the strain and resulting dislocations. Intersubband transitions were measured in InxGa1-xAs wells with indium compositions of x = 0.20 and greater when grown on top of the linear graded buffer. In addition to these results, FTIR measurements on InGaAs/AlGaAs MQW multi-color, long-wavelength infrared detector structures are reported.
Single Crystal High Frequency Cavity-based EPR Spectroscopy of Single Molecule Magnets
Authors: Hill S. , Edwards R. S. , Jones S. I. , Maccagnano S. , North J. M. , Aliaga N. , Yang E-C. , Dalal N. S. , Christou G. , Hendrickson D. N. 
Published: April 2011

ABSTRACTWe report high frequency electron paramagnetic resonance (EPR) investigations of a series of high spin (total spin up to S = 10) manganese and nickel complexes which have been shown to exhibit single molecule magnetism, including low temperature (below ∼ 1K) hysteresis loops and resonant magnetic quantum tunneling. A cavity perturbation technique enables high sensitivity oriented single crystal EPR measurements spanning a very wide frequency range (16 to 200+ GHz). Fitting of the frequency and field orientation dependence of EPR spectra allows direct determination of the effective spin Hamiltonian parameters. Studies on a range of materials with varying (approximately axial) site symmetries facilitates an assessment of the role of transverse anisotropy (terms in the Hamiltonian that do not commute with ŝz) in the magnetic quantum tunneling phenomenon.
Microstructure and Magnetic Property of L1o CoPt–20 at.% C Magnetic Thin Film
Authors: Oh D. Y. , Park J. K. 
Published: April 2011

ABSTRACTThe CoPt-20at.%C thin films of 20nm thickness were sputter-deposited in the form of CoPt/Cn (n=1: carbon layer thickness=4nm; n=4: each carbon layer thickness=1nm) and were transformation-annealed at 650°C for various times. Carbon was found to dissolve into CoPt lattice and enlarge the c/a ratio of the ordered CoPt lattice. The amount of carbon dissolution increases with the decreasing carbon layer thickness at a given total carbon concentration.The carbon dissolution larger than a critical amount can lead to a shift of the phase equilibrium of ordering and produce a stable fine two-phase mixture of ordered and disordered phases at the equi-atomic composition of Co:Pt. This results in a fine and uniform stagnant grain structure of about 20nm on annealing at 650°C. The carbon dissolution by increasing the c/a ratio of the ordered CoPt lattice reduces both the saturation magnetization and the magnetocrystalline anisotropy constant of the film and leads to a reduction of coercivity of CoPt films.
Quantum Computing: From Bragg Reflections to Decoherence Estimates
Authors: Pfeifer Peter , Hou Chen 
Published: April 2011

ABSTRACTWe give an exposition of the principles of quantum computing (logic gates, exponential parallelism from polynomial hardware, fast quantum algorithms, quantum error correction, hardware requirements, and experimental milestones). A compact description of the quantum Fourier transform to find the period of a function—the key step in Shor's factoring algorithm—illustrates how parallel state evolution along many classical computational paths produces fast algorithms by constructive interference similar to Bragg reflections in x-ray crystallography. On the hardware side, we present a new method to estimate critical time scales for the operation of a quantum computer. We derive a universal upper bound on the probability of a computation to fail due to decoherence (entanglement of the computer with the environment), as a function of time. The bound is parameter-free, requiring only the interaction between the computer and the environment, and the time-evolving state in the absence of any interaction. For a simple model we find that the bound performs well and decoherence is small when the energy of the computer state is large compared to the interaction energy. This supports a recent estimate of minimum energy requirements for quantum computation.
Hrtem Investigation of Effect of Various Rare Earth Oxide Dopants on Epitaxial Zirconia High-k Gate Dielectrics
Authors: Kiguchi Takanori , Wakiya Naoki , Shinozaki Kazuo , Mzutani Nobuyasu 
Published: April 2011

ABSTRACTThe effects of several rare earth oxide on the capacitance-voltage (C-V) characteristics and the SiO2 interlayer growth of ZrO2 based gate dielectrics were examined. The width of the hysteresis window of La2O3 stabilized ZrO2 (LaSZ) gate dielectric was only 0.2V, on the other hands, that of Sc2O3 stabilized ZrO2 (ScSZ) gate dielectric was 1.4V HRTEM analysis indicated that the growth of SiO2 interlayer of RSZ (R=Sm,Nd,La) gate dielectric was about 1nm, which was less than half of the ScSZ one. These results indicate the advantage of the ZrO2 gate dielectric doped with rare earth oxide composed of larger ionic radius cation.
The Behavior of Cyclic Voltammetry Stripping (CVs) with Tin-Doped Indium Oxide in 0.3M Hydrochloric Acid
Authors: Li K. C. , Huang C. A. , Tu G. C. , Wang W. S. 
Published: April 2011

ABSTRACTThe cyclic voltammetry stripping (CVs) behavior of the tin-doped indium oxide (ITO) on SiO2 in 0.3M HCl is reported. The CVs result showed an obvious reduction-current peak that occurred during the first cathodic potential scanning. Smaller reduction current and more negative potential of the reduction-current peak were also observed for the ITO that was annealed at 500 °C. The result was attributed to the replenished oxygen-deficient site and the oxygen anion density is decreased in the ITO. The present study has proved that CVs is a useful method to differentiate the carrier concentration in ITO film controlled by different pretreatments. Many spherical In-Sn particles were formed on the ITO when the reduction current took place. During precipitation of these spherical particles, the grain boundaries of the ITO were dissolved and the ITO surface nearby the grain boundaries offered a preferred nucleation site for the formation of these spherical In-Sn particles. Based on the microstructure observed and the result derived from the short potential range scanning, the formation mechanism of the spherical particle is proposed.
Step bunching during Si(001) homoepitaxy caused by the surface diffusion anisotropy
Authors: Mysliveček J. , Schelling C. , Schäffler F. , Springholz G. , Šmilauer P. , Krug J. , Voigtländer B. 
Published: April 2011

ABSTRACTScanning tunneling microscopy experiments show that the unstable growth morphology observed during molecular beam homoepitaxy on slightly vicinal Si(001) surfaces consists of straight step bunches. The instability occurs under step-flow growth conditions and vanishes both during low-temperature island growth and at high temperatures. An instability with the same characteristics is observed in a 2D Kinetic Monte Carlo model of growth with incorporated Si(001)-like diffusion anisotropy. This provides strong evidence that the diffusion anisotropy destabilizes growth on Si(001) and similar surfaces towards step bunching. This new instability mechanism is operational without any additional step edge barriers.
Facet-Facet Barrier on Surfaces: Proposal and Experimental Validation
Authors: Huang Hanchen , Woo C. H. , Wei H. L. , Liu S. J. , Zhang X. X. , Altman M. , Wang E. G. 
Published: April 2011

ABSTRACTSurface processing is generally kinetics limited. Migration barriers, both on flat surfaces and near steps, therefore are of crucial importance. In this paper, we describe a kinetic barrier that separates two neighboring facets on surfaces. The contrast of this concept relative to the conventional Ehrlich-Schwoebel barrier is shown through molecular dynamics/statics calculations on copper and aluminum. The effects of this new kinetic barrier are demonstrated through lattice Monte Carlo simulations. The predicted effects are in direct correspondence with validation experiments on copper and silver thin films.
Ab-Initio Theory of Grain-Boundary Segregation in α-Alumina: Energetics, Atomistic and Electronic Structures
Authors: Fabris Stefano , Elsässer Christian 
Published: April 2011

ABSTRACTThe modifications in atomistic structure, chemical bonding, and energetics induced by sub-stitutional cation impurities isolated in bulk and segregated at grain boundaries of α-Al2O3 were investigated by first-principles electronic-structure calculations. The dependency of these modifications on the boundary type, species and concentration of defects, was studied by selecting the following variety of systems: two different twin boundaries (the prismatic Σ3 (1010) and the pyramidal Σ13 (1014) twins), five cation impurities X (X=Ti, Sc, Y, Ca, and La), and two concentration regimes for the segregant (≈ 3 and ≈ 6 atoms/nm2). A partial covalent character is found to be a distinctive feature of the X-O bond in both bulk and interfacial atomic environments, and to drive the structural distortions of the octahedral XO6 clusters. The energetics of segregation reveals a linear relationship between segregation energy and impurity size.
Orientation Dependence of Photochemical Reduction Reactions on SrTiO3 Surfaces
Authors: Giocondi Jennifer L. , Rohrer Gregory S. 
Published: April 2011

ABSTRACTPolished and annealed surfaces of randomly oriented crystallites were used to study the orientation dependence of the photochemical activity of SrTiO3 surfaces. Silver cations reduced from an aqueous solution produce solid silver metal at the reaction site. The amounts of silver produced by a fixed exposure were used as a relative measure of each grain's activity. The surface structure of the grains was observed using atomic force microscopy and the surface orientation of each grain was determined by electron backscattered diffraction. Surfaces annealed in air for 6h at 1200° C were bound by some combination of the following three planes: {110}, {111}, and a complex facet inclined approximately 24° from {100}. By correlating the orientations of individual grains to the amount of deposited silver, we conclude that surfaces with the complex {100} facet are the most active.
Surface Chemistry of Mesoporous Materials: Effect of Nanopore Confinement
Authors: Wang Yifeng , Bryan Charles , Xu Huifang , Gao Huizhen 
Published: April 2011

AbstractAcid-base titration and metal sorption experiments were performed on both mesoporous alumina and alumina particles under various ionic strengths. It has been demonstrated that surface chemistry and ion sorption within nanopores can be significantly modified by a nano-scale space confinement. As the pore size is reduced to a few nanometers, the difference between surface acidity constants (ΔpK = pK2 – pK1) decreases, giving rise to a higher surface charge density on a nanopore surface than that on an unconfined solid-solution interface. The change in surface acidity constants results in a shift of ion sorption edges and enhances ion sorption on that nanopore surfaces.
Effect of Si and P on the Formation and Crystallization of Ti25Hf50Ni25 Metallic Glasses
Authors: Huett V. T. , Kelton K. F. 
Published: April 2011

ABSTRACTTi255Hf50Ni25 metallic glasses, prepared by rapid quenching, are strongly metastable with a 65°C separation between the glass transition temperature, Tg = 335°C, and the onset temperature for primary crystallization. The deep metastability of the glass is likely due to sluggish nucleation and growth kinetics, limited by the Hf diffusion. The glass crystallizes to a nano-scale microstructure consisting of an icosahedrally symmetric ordered phase. This phase is metastable and transforms to a stable Ti2Ni-type phase with annealing at higher temperatures. The primary crystallization to a metastable icosahedrally-ordered phase suggests that the local structure of the glass contains a high degree of icosahedral short-range order. Here, glass formation and crystallization were studied in alloys containing 2 at.% of Si and P.
Microstructure and mechanical properties of slowly cooled Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 with ductile bcc phase
Authors: Kühn Uta , Eckert Jürgen , Mattern Norbert , Radtke Nicolle , Schultz Ludwig 
Published: April 2011

ABSTRACTWe report about the preparation and properties of a Be-free Zr66.4Nb6.4Cu10.5Ni8.7Al8.0 alloy with a glassy or a nanocrystalline matrix and ductile bcc precipitates, which were developed with the aim to improve the mechanical properties. The samples were prepared in form of rods by injection casting into a copper mold. The phase formation as well as the resulting microstructure and the mechanical properties of the different samples have been investigated upon cooling from the melt at different quenching rates. The formation of the bcc phase embedded in a glassy matrix is strongly governed by the alloy composition and the actual cooling rate during solidification, because the glass forming ability is much lower compared to Zr-based alloys containing Be. Already small reductions in cooling rate lead to precipitation of additional crystalline phases. Compression tests reveal that the in-situ glassmatrix composite undergoes work hardening and plastic deformation prior to failure. Surprisingly, also a nanocrystalline matrix leads to high elastic strain values. These features significantly improve the mechanical behavior of the composites compared to the monolithic glass.
Fragility of Metallic Glass Forming Liquids
Authors: Fan G. J. , Wunderlich R. K. , Fecht H.-J. 
Published: April 2011

ABSTRACTBased on the available kinetic and thermodynamic data, we compare the kinetic fragility and thermodynamic fragility of different metallic glass forming liquids. The results indicate a correlation between the kinetic and thermodynamic fragility in metallic glass forming liquids, consistent with the energy landscape model which predicts a connection between the kinetic and thermodynamic properties of supercooled liquids. The metal - metalloid glass forming alloys such as PdNiCuP are found to exhibit a distinctively different correlation as compared to early – late transition metal – type metallic glass forming alloys such as ZrTiCuNiBe. For the same thermodynamic fragility the former exhibit a much larger kinetic fragility indicating that the two classes of alloys have a different liquid structure. In addition, the relationship between the kinetic fragility and the Gibbs free energy difference between the undercooled liquid and the crystalline phases has been discussed in both metal metalloid glass forming alloys and early - late transition metal – type metallic glass forming alloys.
Strain Localization in a Molecular-Dynamics Model of a Metallic Glass
Authors: Falk Michael L. , Shi Yunfeng 
Published: April 2011

ABSTRACTMolecular dynamics simulations of a two-dimensional amorphous solid exhibit strain localization when loaded in uniaxial tension with free boundaries. The degree of localization depends sensitively on the rate of loading and on the existence of surface defects. Regions of both dilation and contraction arise during the shear band slip process. These dilation and contraction events correspond to dynamic free-volume generation and annihilation during shear. Correlations of the dilation and contraction of the material reveal a length scale of 1–4 atomic diameters associated with this physical process. Dilation is observed to result in nanometer scale cavitation.
Calculations of the Structure and Properties of Rapidly Quenched Ni/Zr Alloys
Authors: Cherne F. J. , Baskes M. I. , Schwarz R. B. , Srinivasan S. G. 
Published: April 2011

ABSTRACTUsing molecular dynamics and a modified embedded atom potential developed by our group we studied the diffusivity and viscosity of molten Ni1-xZrx alloys as a function of composition, temperature, and cooling rate. Previous results indicate that these potentials represent the Ni-Zr system quite well. Liquid alloys were quenched at rates of 5 × 1011 and 1012 K/s. For x > 0.04 the solidified alloys were crystalline. For higher x values, the solidified alloys were amorphous. For the amorphous alloys, the composition dependence of the calculated glass transition temperature Tg follows the general trend of experimental Tg values. The calculated viscosity and diffusivity show systematic variation with composition. For the undercooled Ni-6 at.% Zr melt the calculated viscosity shows the Vogel-Fulcher-Tammann (VFT) behavior characteristic of a “fragile” glass.
Effect of temperature on formation of murataite and murataite-pyrochlore ceramics
Authors: Kirjanova O. I. , Stefanovsky S. V. , Yudintsev S. V. 
Published: April 2011

ABSTRACTProcesses of phases formation in the ceramic mixtures with basic compositions (wt.%) 10 CaO, 10 MnO, 5 Al2O3, 5 Fe2O3, 55 TiO2, 5 ZrO2, 10 UO2 (M1) and 8 CaO, 8 MnO, 4 Al2O3, 4 Fe2O3, 20 Gd2O3, 44 TiO2, 4 ZrO2, 8 UO2 (M4) were studied using X-ray diffraction, scanning and transmission electron microscopy. The batches were milled, compacted in pellets at 200 MPa, and heat-treated in a resistive furnace at 1100 °C, 1300 °C, 1400 °C, and 1500 °C as well as melted in a cold crucible at ∼1600 °C. Reactions in the mixtures heat-treated at 1100 °C were not completed and samples contained significant amount of unreacted and intermediate (altered rutile, cubic oxide solid solution, perovskite) phases. Within the temperature range 1100–1300 °C reactions are mainly completed and ceramics sintered at 1300 °C are composed of major murataite and minor rutile (M1) or major murataite and pyrochlore and minor zirconolite and perovskite (M4). However full homogenization at 1300 °C has not been reached yet and to obtain the ceramics with uniform compositions of the phases sintering at 1400 °C or melting at 1500–1600 °C were required.In the ceramic sample M1 two murataite varieties with five- (murataite-5C) and eight-fold (mu-rataite-8C) fluorite-type unit cells were found. The sample M4 is composed of pyrochlore, murataite-8C and zirconolite-3O. In the sample M1 murataite-5C is enriched with U and Ca and depleted with iron group elements as compared to murataite-8C. Fraction of murataite-5C concentrates about 80% of total U and about 70% of Mn+Fe (corrosion products). Waste elements partitioning among the phases in the M4 sample depends significantly on temperature of heat-treatment.
The effect of pH on chlorite dissolution rates at 25°C
Authors: Gustafsson Åsa B. , Puigdomenech Ignasi 
Published: April 2011

ABSTRACTThe Swedish nuclear industry is planing to dispose spent nuclear fuel encapsulated in copper canisters in granitic bedrock at a depth of approx. 500 m. The reducing capacity of the geo-sphere is important for canister corrosion and radionuclide migration. The main inorganic reduc-tants are Fe(II)-containing minerals: biotite in the bedrock, and pyrite and chlorite in the fracture filling minerals as well as in the buffer and backfill. As a consequence, the dissolution of chlorite is an important parameter when considering the reducing capacity available to groundwaters around the repository.The weathering rates of a chlorite sample from Taberg in central Sweden has been studied in 0.01 M NaCl media at (25±1)°C in the pH region 2–12. The chlorite was characterized before and after grinding and sieving, and was found to have a relatively low Fe-content, with the formula (Mg9.44 FeII0.72Al1.68)(Si6.47Al1.4FeIII0.13)O20(OH)16. Kinetic experiments were performed using a thin-film continuous flow-through technique with flow rates of 5 mL/h or 2.7 mL/h. This technique prevents the precipitation of secondary phases such as iron(III) hydroxides. Solution samples were taken after a reaction time of 0–30 days. The contents of released Al, Fe, Mg and Si were analyzed using an Inductively Coupled Plasma emission spectroscopy (ICP-AES) technique and then normalized to the Brunauer-Emmet-Teller (BET) surface area and flow-rate in order to obtain rates of dissolution. The dissolution rate of the chlorite studied was pH-dependent, and a minimum was observed in the neutral pH region. The dissolution rate (based on Si data) decreased from 7×10-11 mol/(m2 s) at pH=2 to 4×10-13 mol/(m2 s) at pH≈7 and then in-creased to 3×10-12 mol(m2 s) at pH=12.
Ab-initio Studies of Plutonium with Relevance to Nuclear Waste Management
Authors: Setty Arun K. , Cooper B. R. , Price D. L. 
Published: April 2011

ABSTRACTPlutonium, well known for its unusual nuclear and material properties, has remained an unsolved problem for over a half century. Due to the continuing issue of safe, longterm nuclear waste storage, gaining an understanding of plutonium and its compounds cannot be overstated. Self-irradiation in plutonium leads to vacancy formation [1], and our computations indicate that the electronic structure we predict for pure delta plutonium is preserved in the presence of vacancies, and that vacancies do stabilize the delta phase. A preliminary study of self-diffusive properties of plutonium, and of diffusion at the interface of plutonium and iron indicates that plutonium atoms readily diffuse across the interface with steel. This has relevance in nuclear waste storage in steel containers for assessing the depth of penetration to be dealt with in surface treatment for decontamination. The effect of thermomigration (Soret effect) in the plutonium-steel system appears to facilitate the movement of plutonium atoms into the bulk steel.
Accounting for EBR-II Metallic Waste Form Degradation in TSPA
Authors: Ebert W. L. , Lewis M. A. , Barber T. L. , Johnson S. G. 
Published: April 2011

ABSTRACTA metallic waste form (MWF) will be used to immobilize cladding hulls from spent sodium-bonded nuclear fuel rods. Laboratory tests were conducted to determine if the HLW glass degradation rate model used in Total System Performance Assessment (TSPA) calculations can be used as an upper bound for the degradation rate of the MWF. Static tests were conducted with monolithic MWF samples in pH buffer solutions to measure the degradation rates at 50, 70, and 90°C. The measured degradation rates of the MWF were compared to the rates calculated with the HLW glass degradation model. The degradation rates were calculated as the product of the specific dissolution rates and the anticipated exposed surface areas of glass and MWF in a breeched canister. This comparison showed that the rate calculated using the HLW glass degradation model bounds the rates measured for the MWF at all pH values and temperatures. These results support the potential use of HLW glass as a surrogate for MWF degradation for the purpose of performance assessment.