bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intersubband Transitions in InAs/AlSb Quantum Wells
Authors: Li J. , Kolokolov K. , Ning C. Z. , Larraber D. C. , Khodaparast G. A. , Kono J. , Ueda K. , Nakajima Y. , Sasa S. , Inoue M. 
Published: April 2011

ABSTRACTWe have studied intersubband transitions in InAs/AlSb quantum wells experimentally and theoretically. Experimentally, we performed polarization-resolved infrared absorption spectroscopy to measure intersubband absorption peak frequencies and linewidths as functions of temperature (from 4 K to room temperature) and quantum well width (from a few nm to 10 nm). To understand experimental results, we performed a self-consistent 8-band k·p band-structure calculation including spatial charge separation. Based on the calculated band structure, we developed a set of density matrix equations to compute TE and TM optical transitions self-consistently, including both interband and intersubband channels. This density matrix formalism is also ideal for the inclusion of various many-body effects, which are known to be important for intersubband transitions. Detailed comparison between experimental data and theoretical simulations is presented.
Recent Developments in Magnetic Recording Heads
Authors: Tanaka Atsushi , Oshiki Mitsumasa 
Published: April 2011

ABSTRACTRecently developed and future magnetic head technologies are reviewed. Scaling of dimensions brought about significant increases in recording densities in the last decade. On the recording head aspect, as the read head is narrowed, large improvements in sensitivity are required. Therefore, spin-valve read heads have been improved by introducing synthetic ferromagnetic pinned layers, a spin filter back layer and a specular scattering layer. The current perpendicular to plane (CPP) structure is now being adopted instead of the current in plane (CIP) structure which is the present magnetic head structure. Under heads with a CPP structure, tunneling magnetoresistance (TMR) devices and multilayer GMR are candidates. In CPP mode, we can make better use of “spintronics” or spin-dependent conduction phenomena because device character depends more directly on the spin-dependent electronic states of the materials. Future technologies of read head are also discussed.
Materials selection for SrTiO3-based epitaxial oxide field-effect devices
Authors: Shibuya K. , Ohnishi T. , Kawasaki M. , Koinuma H. , Lippmaa M. 
Published: April 2011

ABSTRACTWe have studied the growth of four wide gap insulator materials, CaHfO3, CaZrO3, NdGaO3, and LaGaO3 on SrTiO3. CaHfO3 was selected as the best material for forming the insulator layer of an all-oxide field-effect device because the films had the best crystallinity on SrTiO3 (100) and the highest breakdown field. (La,Sr)TiO3 was selected as a metallic oxide for fabricating the source and drain electrodes. Metallic layers were obtained by depositing ultrathin amorphous LaTiO3 films at room temperature on SrTiO3 and postannealing at high temperature to promote Sr diffusion from the substrate into the film.
Surface Dynamics of GaAs Thin Film Formation by Pulsed Laser Deposition Investigated Using RHEED
Authors: Pun A. , Durbin S.M. , Kennedy J. , Markwitz A. , Reeves R. , Zheng J.P. 
Published: April 2011

ABSTRACTPost-growth surface dynamics of epitaxial GaAs (100) thin films grown by pulsed laser deposition (PLD) have been studied using dynamic reflection high-energy electron diffraction (RHEED) in an effort to better understand the growth mechanisms present in pulsed laser deposition. Results have indicated, as expected, that processes occurring at reduced substrate temperatures manifest themselves more slowly than at elevated temperatures. This has been shown through the analysis of static RHEED images and dynamic specular beam intensity as well as profile scans.
Time Resolved Studies of Focused Ion Beam Induced Tungsten Deposition
Authors: Langfischer H. , Harasek S. , Wanzenboeck H. D. , Basnar B. , Bertagnolli E. 
Published: April 2011

ABSTRACTIn this study we investigate the nucleation and growth mechanisms of tungsten films processed by focused ion beam (FIB) induced chemical vapor deposition. For our investigation we use a 50 keV Ga+ ion beam focused on the substrate target and tungsten hexacarbonyl (W(CO)6) as precursor gas. Mediated by the substrate the energy of the impinging ions leads to the decomposition of the tungsten hexacarbonyl molecules adsorbed on the substrate into volatile parts and nonvolatile residues forming a metal deposit. Time resolved FIB secondary electron microscope imaging in combination with atomic force microscopy reveal first the formation of isolated nuclei and further their coalescence finally resulting in the formation of a contiguous metal layer. Despite the local impacts of the ion beam within the irradiated area of the substrate the localization of the nucleation spots is neither correlated to the spot centers nor to the scan path of the ion beam. After formation, the nanoscale tungsten nuclei preserve their positions and typical shapes during further deposition. Only after merging the nuclei to a contiguous tungsten layer, a further regime of growth sets on which is characterized by deposition of tungsten on a tungsten surface. In this regime the deposition process is determined by the total ion dose and the average current density the samples are subjected to. In this regime, deposition yields up to 3.5 atoms per incident gallium ion are achieved. The contiguous layer quality is determined by Auger electron analysis. The measured growth data were interpreted by adopting the analytic Ruedenauer Steiger approach mainly incorporating ion current density, precursor gas transformation rate, and ion induced sputtering. As a result, the critical ion current density, where ion sputtering exceeds deposition, was identified by the model. Because the model shows excellent agreement with the measurement it should be suitable for further survey concerning focused ion beam process development.
Morphological Instability of Solid-on-Liquid Thin Film Structures
Authors: Huang Rui , Suo Z. 
Published: April 2011

ABSTRACTSubject to a compressive membrane force, a solid film on a liquid layer may form wrinkles. When the solid film is very thin, surface stresses contribute to the membrane force. When the liquid layer is very thin, the two interfaces bounding the liquid interact with each other through forces of various physical origins. We formulate the free energy of the solid-on-liquid structure, and carry out a linear perturbation analysis. A dimensionless parameter is identified to quantify the relative importance of flexural rigidity, membrane force, and interfacial force. Depending on the nature of the interfacial force, several intriguing behaviors are possible; for example, the solid film may remain flat under a compressive membrane force, or form wrinkles under a tensile membrane force.
Buckling of Thin Films on Substrates: From Straight-Sided Wrinkles to Both Worm-Like and Varicose Structures
Authors: George M. , Cleymand F. , Coupeau C. , Colin J. , Grilhé J.W. 
Published: April 2011

ABSTRACTThe evolution from straight-sided wrinkles to both worm-like and varicose structures has been investigated mainly by atomic force microscopy. The elastic energy variation related to the formation of these two buckling structures has been computed and discussed. It is shown that both transitions are energetically favourable above a longitudinal (along the initial wrinkle axis) critical stress of few GPa in compression, that is of the order of the internal compressive stresses present in the thin films.
Correlation between microstructure, DC resistivity and magnetoresistance of SrRuO3 films.
Authors: Khamchane K. , Gunnarsson R. , Ivanov Z.G. , Vorobiev A. , Rundqvist′ P. , Gevorgian S. 
Published: April 2011

ABSTRACTWe have investigated the correlation between microstructure, DC resistivity and magnetoresistance of SrRuO3 thin films. The films were epitaxially grown by pulsed laser deposition on (001) SrTiO3 substrates in a temperature range of 690–810°C. According to x-ray measurements, the structure of all films is a mixture of highly oriented domains of strained orthorhombic phases (ortho-I and ortho-II) with different lattice parameters. Films deposited at 780°C show a minimum resistivity (270 μΩcm at 300 K) and a maximum magnetoresistance (8% at 5 K). These films consist mainly of ortho-I phase (a=0.393 nm). Films deposited at 690°C (predominantly ortho-II) have the highest resistivity (up to 1700 μΩcm at 300 K) and lowest magnetoresistance (3% at 5K).
Influence of Structure and Chemistry on Piezoelectric Properties of Pzt in a Mems Power Generation Application
Authors: Eakins L.M.R. , Eakins D.E. , Richards C.D. , Norton M.G. , Richards R.F. , Bahr D.F. 
Published: April 2011

ABSTRACTPZT films between 1 and 3 μm thick were grown using solution deposition techniques to study the effects of crystal structure, orientation, chemistry and PZT/PZT crystallization interfaces on the piezoelectric output of these films. By varying the chemistry of the film from Zr-rich to Ti-rich the film orientation increased towards {h00}. PZT with 60 wt% Ti exhibited tetragonality and produced greater electrical output at a given strain than the rhombohedral films with concentrations less than 50 wt% Ti. Multiple steps of solution deposition left identifiable PZT/PZT interfaces within the film. TEM, FESEM, and Auger spectroscopy were used to characterize these interfaces, which form upon crystallization of the amorphous PZT film. Internal PZT interfaces are associated with both structural defects (voids) as well as chemical variations such as Pb deficiencies.
Phase and Morphology in Mixed CuO-WO3 Films for Chemical Sensing
Authors: El Madi A. , Meulendyk B. , Pilling R. S. , Bernhardt G. , Lad R. J. , Frederick B. G. 
Published: April 2011

ABSTRACTSemiconducting metal oxide (SMO) chemiresistive sensors are highly sensitive toward a broad range of hydrocarbons. To develop a gas phase sensor with selectivity toward organophosphorus compounds, such as chemical warfare agents and pesticides, we have developed dosimeters based upon a poisoning mechanism. Here, we report the growth and characterization of WO3 thin films, modified with Cu2O. XPS data show that exposure to phosphonate compounds leads to accumulation of phosphate on the surface, together with dramatic changes in the surface segregation of copper. We present XRD and XPS results to characterize the phase changes following growth, annealing, and exposure to phosphonate compounds. The correlation between sensor response and phosphorous accumulation shows that the highest activity occurs at intermediate coverages of Cu2O, in the15–25 Å range, on 500 Å WO3 films.
Effects of Superimposed Pressure on Flow and Fracture of Two Bulk Amorphous Metals
Authors: Wesseling Paul , Lowhahphandu Peravudh , Lewandowski John J. 
Published: April 2011

ABSTRACTTension and compression tests have been performed with high alignment fixtures on two different zirconium-based bulk metallic glass specimens at atmospheric pressure as well as with levels of superimposed hydrostatic pressure up to 700 MPa. The results show essentially no difference in applied flow stress or fracture stress between compression and tension specimens over the range of pressures tested. However, a difference in fracture plane angle between compression and tension specimens was observed, suggesting a normal stress effect, as in granular solids, on the flow and fracture behavior of the bulk metallic glass specimens. The data are compared to various flow and fracture theories over a very wide range of normal stresses. Over the range tested, a Mohr-Coulomb flow theory appears to best describe the data.
Crystallization of Glassy Powder from Aluminum-Rare Earth- Transition Metal Alloys
Authors: Vasiliev A.L. , Aindow M. , Blackburn M.J. , Watson T.J. 
Published: April 2011

ABSTRACTThe microstructures exhibited by gas atomized powders of two alloys, Al-6Gd-6Ni-1Fe and Al-5Y-10Ni (at. %), have been analyzed using electron microscopy. It was found that the microstructure depends critically on the particle size obtained during atomization. Small particles (<1μm) tend to be completely amorphous. Larger particles (1–10μm) can also be amorphous, but often contain a mixture of amorphous material and crystalline Al. Three distinct morphologies are observed: nanocrystalline particles, fractal and dendritic growths embedded in an amorphous matrix. The yet larger particles (>30μm) are often fully crystalline, consisting of fine interspersed Al and intermetallic grains.
Single Particle Jumps in a Binary Lennard-Jones Glass
Authors: Vollmayr-Lee K. 
Published: April 2011

ABSTRACTWe study a binary Lennard-Jones mixture below the glass transition with molecular dynamics (MD) simulations. To investigate the dynamics of the system we define single particle jumps via their single particle trajectories. We find two kinds of jumps: metastable jumps, where a particle jumps back and forth between two or more states, and real jumps, where a particle does not return to any of its former states. For both the real and metastable jumps we present as a function of temperature the number of jumps, jump size, time between jumps, and energy.
Electron screening in bulk amorphous Pd-Ni-P and Pd-Ni-Fe-P alloys
Authors: Li Q. , Greig D. , Matthew J. A. D. , Shen T. H. , Seddon E. A. , Beamson G. 
Published: April 2011

ABSTRACTTernary and quaternary bulk amorphous Pd-Ni-P and Pd-Ni-Fe-P alloys were prepared by fast quenching in water. X-ray photoemission spectra of Pd-Ni-P have previously been measured by Alamgir et al. (Phil. Mag. B 79, 239 (1999)). These results have been extended by (a) measuring the Auger spectra and the Auger parameters of key elements, (b) cross correlating the data with PdNi binaries, and (c) investigating the effects of adding Fe. It is shown that the Auger parameters change systematically across the composition range and the results are discussed in terms of possible charge transfer, changes in d-band character, and covalent bonding.
Fatigue Behaviour of Some Fe-Based Metallic Glass Wires
Authors: Verduzco J. A. , Hand R. J. , Davies H. A. 
Published: April 2011

ABSTRACTThe fatigue behaviour of melt-spun Fe78-xCrxSi10B12 and Fe77.5-xCrxSi7.5B15 (0≤×≤8) amorphous alloy wires is compared with those of HT steel wires. The wires were tested in a novel bend fatigue testing machine that imparts compressive to tensile stresses. Tensile strength and microhardness were also measured; these and the fatigue performance improved with the substitution of Fe by Cr. The fatigue performance of the glassy alloy wires was generally similar to that of HT steel wires when expressed on the basis of bend strain but inferior when expressed on the basis of bend stress. Fractography studies revealed differences in the fracture surface features for the amorphous wires, depending on the stress range amplitude. It was also observed that corrosion pits nucleated on the surfaces of glassy wires with zero or low Cr content and resulted in crack initiation at these points.
Long-Term Stabilization of Uranium By U(VI) Phosphate Mineralization in Weathered Bedrock and Soils Developed Over a Granite-Hosted Uranium Deposit
Authors: Jerden James L. , Sinha A. K. 
Published: April 2011

ABSTRACTThe unmined Coles Hill U deposit in the Virginia Piedmont represents a unique natural laboratory for studying the long-term containment of U by phosphate minerals. The primary ore assemblage consists of coffinite and apatite and is hosted in foliated granite. Geochemical and mineralogical studies of the weathered bedrock and soils developed over the primary ore body indicate that U transport is inhibited by the precipitation of meta-autunite group minerals. The lower part of the profile, which consists of ground water saturated saprolite, contains 1400 mg/kg U (in the solid). This concentration is 1.5 times greater than the mean ore grade of the deposit, indicating that the saprolites are enriched in U relative to the underlying primary ore. Uranium within the saprolite is dominantly associated with 10 to 500 μm long, tabular crystals of (Ba, Ca, Sr) meta-autunite. Ground waters from this zone contain less than 14 μg/L dissolved U suggesting that the U(VI) phosphate minerals present are capable of controlling dissolved U concentrations at values lower than the US-EPA maximum contaminant level (30 μg/L). Mineralogical characterization of the unsaturated soil horizons indicate that geochemical conditions in these zones are not conducive to U stabilization by meta-autunite mineralization. In the vadose zone U is primarily associated with Al phosphate (crandallite) and with P adsorbed or coprecipitated with iron oxide mineral coatings. Geochemical gradients suggest that significant amounts of U have been leached from the vadose zone by infiltrating fluids and reprecipitated below the water table, where the activity ratio of dissolved phosphate to carbonate increases. Based on regional weathering rates, the processes responsible for stabilization of U within the Coles Hill system are estimated to have been active for hundreds of thousands of years.
Reactions Controlling Äspö Groundwater Chemistry
Authors: Emrén Allan T. 
Published: April 2011

ABSTRACTSamples of groundwater are often found to be close to saturation with respect to some minerals. A common approach to modelling of groundwater chemistry is to assume that such minerals control some chemical property of the groundwater. As an example, calcite is often supposed to control the pH value (in addition to concentrations of calcium and carbonate). Here, three models have been used to investigate the control of chemical properties of a groundwater from the Äspö site at the Swedish East Coast.In the first model, a set of minerals has been selected, in which all minerals are close to saturation with respect to the groundwater. Then an attempt has been made to model formation of the groundwater from rain by letting PHREEQE equilibrate the rain with the minerals.The second model is similar, but the mineral set used is similar to the one observed at Äspö, and includes also minerals that are far from saturation. To handle the complex situation with numerous minerals and spatial variability, the CRACKER program was used to simulate formation of groundwater from rain.In the third model, the CRACKER program has been used with the observed groundwater. In the simulation, the water has been disturbed locally, and the relaxation of water chemistry has been studied.Results from all three kinds of models show that no conclusions on regulation of chemical properties in groundwater can be drawn from saturation properties of minerals. Rather, most properties are controlled by complicated interactions, including spatial variability, irreversible reactions and mixing.
Sodium Zirconium Phosphate [NZP] as a Host Matrix for High Level Radioactive Wastes
Authors: Seida Yoshimi , Yuki Mami , Suzuki Kazunori , Sawa Toshio 
Published: April 2011

ABSTRACTVarious elements (Cs, Sr, Ba, Zr, Ru, Pd, Ce, Nd, Gd, Fe, Cr, Ni, Mo and Te) in the simulated high-level radioactive wastes generated from commercial PUREX reprocessing were immobilized by a ceramic solidification using sodium zirconium phosphate, NaZr2(PO4)3 as a host matrix. The convertibility of the elements to the specific M, A and X sites in NZP crystal structure was determined with consideration of stoichiometry, charge balance and ion size of each element. Small disk samples of NZP waste form containing the elements were prepared by the sol-gel synthesis followed by calcination and compression sinteration at high temperature. The physicochemical structures such as produced phase in the waste forms and dispersion of the embedded elements in the NZP waste forms were investigated by means of XRD and SEM/EDX. Chemical behavior of the embedded elements and the limit of substitution of the NZP structure for the elements were investigated by the series of analysis. Moreover, in order to increase the limit of substitution of NZP, the effectiveness of pretreatment with heating the sol-gel products at 473–773K was experimentally investigated. The capability of embedding of NZP for the elements in HLW has been discussed.
Neptunium Substitution into the Structure of Alpha-U3O8
Authors: Finch Robert J. , Jeremy Kropf A. 
Published: April 2011

ABSTRACTWe synthesized powder samples of NpxU3-xO8 with x between 0 and 0.33. Analyses of solids by x-ray absorption spectroscopy indicate that Np occupies U sites and is predominantly tetravalent. Lattice parameters vary smoothly as a function of Np concentration. The a and b parameters (parallel to structural sheets in U3O8) depend strongly on Np concentration below x = 0.3; however, extrapolation of a least-squares fit up to x = 1 (the maximum value of x if Np is tetravalent) suggests little expected change in a or b for values of x greater than approximately 0.5. The c cell parameter (perpendicular to the plane of the sheets) shows relatively small dependence on Np concentration for all values of x. The a and b cell parameters vary in a complementary fashion, such that the a-b plane and unit-cell volumes remain nearly constant for small x (below ∼0.2). The projected volume increase at higher x may be accommodated by expansion along c; the maximum volume expansion for NpxU3-xO8 is projected to be less than 0.2% up to x = 1. Our results demonstrate that NpxU3-xO8 forms a homogeneous solid solution up to (at least) x = 0.33, and that a complete solid solution may exist between α-U3O8 and NpU2O8; however, the structure of NpU2O8 may resemble that of β-U3O8.
Electron Microscopy Study of Reaction Sintered HLW Glass
Authors: Gong Weiliang , Lutze Werner 
Published: April 2011

ABSTRACTReaction sintering under pressure can be used to vitrify radioactive waste. We used defense waste simulate with high concentrations of refractory oxide ZrO2 (∼36 wt%). Silicate glasses with 30 to 50 wt% of waste loading were prepared by hot isostatic pressing (800 °C, 28 MPa). Amorphous silica (50 to 70 wt%) was added to calcined waste simulants. The reaction sintered final products were characterized by scanning and analytical electron microscopy. Our results showed that a continuous glass phase formed. Waste components such as Na2O, CaO, MnO2, Fe2O3, and Al2O3 dissolved in the glass phase. ZrO2 dissolved as well but reached its solubility limit. Nanometer size crystals of baddeleyite (ZrO2) suggest that their presence is a result of super-saturation of the glass phase rather than incomplete dissolution. The sodium concentration increases in the early stages of reaction sintering and decreases towards the end and so does solubility of ZrO2 and other oxides. The microstructure of reaction sintered glasses is determined by a) the concentrations of refractory oxides, b) the concentration of reaction sintering agents, c) the particle size of glass formers, and d) sintering conditions, e.g., temperature and time. Evidence is provided by respective analytical data and micrographs.