bluuebunny/crossref_metadata_2025_split huggingface dataset:
Bond-Order Potentials with Analytic Environment-Dependent Tight-Binding Integrals: Application to BCC Molybdenum
Authors: Mrovec Matous , Nguyen-Manh Duc , Pettifor David G. , Vitek Vaclav 
Published: June 2019

AbstractWe present a new Screened Bond-Order Potential (SBOP) for molybdenum in which the environmental dependence of two-center tight-binding bond integrals has been implemented via a recently developed analytic expression. These bond integrals reproduce very well the numerical ab-intio values of screened LMTO bond integrals. In particular, they display the large discontinuity in ddπ between the first and second nearest neighbor of the bcc lattice whereas they do not show any discontinuity in ddσ. This dependence can be traced directly to the angular character of the analytic screening function and is shown to be critical for the behavior of the second nearest neighbor force constants. The new BOP eliminates the problem of the very soft T2 phonon mode at the N point that is found in most two-center tight-binding models. Preliminary study of the core structure of 1/2<111> screw dislocations performed using SBOP indicates that the core is narrower and less asymmetric than structures found in previous studies, in agreement with recent ab-initio calculations.
Efficient Treatment of Fixed and Induced Dipolar Interactions
Authors: Sagui Celeste , Darden Thoma 
Published: June 2019

AbstractFixed and induced point dipoles have been implemented in the Ewald and Particle-Mesh Ewald (PME) formalisms. During molecular dynamics (MD) the induced dipoles can be propagated along with the atomic positions either by interation to self-consistency at each time step, or by a Car-Parrinello (CP) technique using an extended Lagrangian formalism. The use of PME for electrostatics of fixed charges and induced dipoles together with a CP treatment of dipole propagation in MD simulations leads to a cost overhead of only 33% above that of MD simulations using standard PME with fixed charges, allowing the study of polarizability in largemacromolecular systems.
Multiple Donors in Zinc Oxide Substrates
Authors: Thonke K. , Kerwien N. , Wysmolek A. , Potemski M. , Waag A. , Sauer R. 
Published: June 2019

AbstractWe investigate by photoluminescence (PL) nominally undoped, commercially available Zinc Oxide substrates (from Eagle Picher) grown by seeded chemical vapor transport technique in order to identify residual donors and acceptors. In low temperature PL spectra the dominant emission comes from the decay of bound exciton lines at around 3.36 eV. Zeeman measurements allow the identification of the two strongest lines and some weaker lines in-between as donorrelated. From the associated two-electron satellite lines binding energies of the major donors of 48 meV and 55 meV, respectively, can be deduced.
Electrical Characterization of Laser-Irradiated 4H-SiC Wafer
Authors: Salama I. , Quick N. R , Kar A. , Chung Gilyong 
Published: June 2019

AbstractHighly conductive tracks are generated in low-doped epilayers on 4H-SiC wafers using a laserdirect write technique. The current-voltage characteristics are measured to study the effect of the applied voltage on the electric resistance and the surface contact of the irradiated tracks. The effect of multiple irradiations on the electronic properties of the fabricated tracks was investigated and compared with the effect of the conventional annealing process. A laser doping process was used to achieve n-type as well as p-type impurity doping in the substrate. The electronic properties of the doped tracks are measured and compared with those of the untreated wafers. Microstructural observation and surface analysis of the irradiated tracks are studied. Laser fabrication of rectifying contact on SiC substrates is demonstrated.
Correlation of Surface Morphologies with Mn Compositions of Ga1-xMnxAs Epilayers Grown by Liquid Phase Epitaxy
Authors: Kim Hwa-Mok , Leem Jae-Hyeon , Choi Sung Woo , Kim Deuk Young , Kang Tae-Won 
Published: June 2019

AbstractIn this letter, we investigated the correlation between as-grown surface morphologies and Mn compositions of Ga1-xMnxAs epilayers - a III-V diluted magnetic semiconductor - grown by liquid phase epitaxy (LPE). Ga1-xMnxAs epilayers were grown at 595 °C from 50 % Ga + 50 % Bi mixed solvent. The grown layers were characterized by energy dispersive x-ray analysis (EDS) and atomic forced microscopy (AFM). The Mn composition measured by EDS after growth process was varied from 1 to 7 %. As increasing Mn composition surface morphologies of as-grown Ga1-xMnxAs epilayers were varied. At higher Mn compositions, the morphology of the surface layers degrades strongly, preventing removal of the solution-melt from it. Key words: LPE, as-grown, surface morphology, Mn composition, Ga1-xMnxAs, energy-dispersive x-ray analysis (EDS), atomic forced microscopy (AFM).
Behavior of copper in CdGeAs2 crystals
Authors: Voevodin Valeriy G. , Voevodina Olga V. , Bereznaya Svetlana A. , Korotchenko Zoya V. , Ohmer Melvin C. , Goldstein Jonathan T. , Fernelius Nils C. 
Published: June 2019

AbstractWe present an investigation of the diffusion and melt doping of Cu in CdGeAs2. Cu was found to be an acceptor, its introduction in the melt allowed the controlled introduction of holes from ∼8·1016 cm-3 to ∼1·1018 cm -3. Introduction of Cu from the melt was also found to improve the homogeneity of the crystal. The saturation solubility of Cu introduced via diffusion doping was found to have an exponential dependence on the diffusion temperature, from 723 K to 873 K, obeying the equation N = N0 exp (- δH / kT) with the parameters N0 = 6.10+19 cm-3, δH = 0.3 eV, and k equal to Boltzman's constant. From 873 K to 923 K, the saturation solubility was found to decrease exponentially with temperature.
Electron-beam-induced reactivation of Si dopants in hydrogenated and deuterated 2D AlGaAs heterostructures. Application to the fabrication of nanostructures
Authors: Kurowski L. , Silvestre S. , Loridant-Bernard D. , Constant E. , Barbe M. , Chevallier J. , Constant M. 
Published: June 2019

AbstractHydrogen incorporation in n-type Si-doped GaAs epilayers is now a well-known process. This paper is devoted to the study of the stability of SiH (SiD) complexes when submitted to an electron beam in n-type Si-doped GaAs epilayer and also in 2D-AlGaAs heterostructures exposed to a hydrogen or deuterium plasma.The results obtained by Hall effect measurements on hydrogenated and deuterated GaAs epilayers with different thicknesses (0.2 and 0.35νm) and Si planar-doped AlGaAs/GaAs/InGaAs heterostructures exposed to an electron beam with different injection energies (10 to 50 keV) are presented. On one hand, the reactivation of Si dopants strongly decreases when deuterium is used. On the other hand, the study of this reactivation versus injection energies of electrons suggests an energetic electron excitation effect rather than a minority carrier generation effect. In addition, for the 0.2νm thick GaAs epilayer and the 2D heterostructures, the free carrier density does not vary significantly for low electron densities, and as a consequence, the reactivation of the Si dopants occurs above an electron dose threshold. This phenomenon might be attributed to the filling of surface states as the dopants are progressively reactivated.As a result, due to the electron dose threshold as well as their high electron mobility properties, Si planar-doped AlGaAs/GaAs/InGaAs heterostructures are particularly interesting to reactivate dopants, with a good spatial contrast, using an electron beam irradiation and the effects described in this paper could open the fabrication of high mobility 1D or 2D mesoscopic structures for electronic or optoelectronic applications.
Energy Storage Materials Based on Iron Phosphate
Authors: Prosini Pier Paolo , Carewska Maria , Lisi Marida , Passerini Stefano , Scaccia Silvera , Pasquali Mauro 
Published: June 2019

AbstractSeveral iron phosphates were synthesized by solution-based techniques and tested as cathodes in non aqueous lithium cells. The addition of phosphate ions to a solution of iron (II) produced crystalline Fe3(PO4)2. This material is easily oxidized by air to form an amorphous phase that is able to reversibly intercalate lithium. The amorphous compound was identified to be a mixture of FePO4 and Fe2O3. A new synthetic route was developed to prepare pure amorphous FePO4. Amorphous LiFePO4 was obtained by chemical lithiation of FePO4. The material was heated at 500°C under reducing atmosphere to obtain nano-crystalline LiFePO4. This latter material showed excellent electrochemical performance when used as cathode of lithium cells.
Metal-Organic Chemical Vapour Deposition of II-VI Semiconductor Thin Films Using Single-Source Approach
Authors: Afzaal Mohammad , Crouch David , O'Brien Paul , Park Jin-Ho 
Published: June 2019

AbstractThin films of CdS and CdSe have been deposited on glass substrates by low pressure metal-organic chemical vapour deposition (LP-MOCVD) using Cd[(EPiPr2)2N]2 (E = S, Se) as single-source precursors. These air-stable precursors are volatile, making them suitable for the deposition of thin films. As-deposited films were crystalline metal chalcogenides, as confirmed by X-ray powder diffraction (XRD), and their morphologies were studied by scanning electron microscopy (SEM).
Preparation of Doped Lanthanum Gallate Electrolyte for SOFC by Pulsed Laser Deposition
Authors: Kanazawa Seiji , Ito Takeshi , Yamada Kenji , Ohkubo Toshikazu , Nomoto Yukiharu , Ishihara Tatsumi , Takita Yusaku 
Published: June 2019

AbstractIn this study, doped lanthanum gallate (LSGM with the composition La0.9Sr0.1Ga0.8Mg0.2O3-δ, LSGMC with the composition La0.8Sr0.2Ga0.8Mg0.15Co0.05O3-δ) films for an electrolyte of the solid oxide fuel cell (SOFC) were prepared by pulsed laser deposition (PLD) technique. In the vacuum chamber, LSGM or LSGMC targets were set on the rotating target holder. A KrF excimer laser was introduced into the chamber at an incident angle of about 45 degree. The doped LaGaO3 film was deposited onto NiO substrates without heating in argon ambient gas. The NiO substrate can be used directly as an electrode in the fabrication of the SOFC. The deposited LSGM films were characterized by X-ray diffraction (XRD), secondary ion mass spectroscopy (SIMS) and scanning electron microscopy (SEM). As-deposited films were amorphous. After post annealing at 1273K for 6-10 hours, crystalline LaGaO3 was obtained. Films with thickness greater than several 10 μm showed an uniform and dense morphology. No gas leakage was found using thick films, which is an important characteristic for an electrolyte in fuel cells. The composition of the deposited films was slightly different to that of the target.
Synthesis and Thermoelectric Properties of Bi2 S3 Nanobeads
Authors: Fang Jiye , Chen Feng , Stokes Kevin L. , He Jibao , Tang Jinke , O'Connor Charles J. 
Published: June 2019

AbstractBismuth sulfide (Bi2S3), a direct band gap material with Eg ñ 1.3 eV, attracts high interest in thermoelectric investigations. In this work, nanometer-sized bismuth sulfide with unique morphology has been successfully prepared by a precipitation between bismuth 2-ethylhexanoate and thioacetamide in high-temperature organic solution with presence of proper capping/ stabilizing agents. By employing this technique, we are able to produce nanobeads of bismuth sulfide with an aspect ratio of ∼ 5, typically ~10 nm wide and ∼50 nm long according to the TEM observation. Characterization of XRD and TEM/HRTEM reveals that the as-prepared particles exist in single orthorhombic phase and possess high crystallinity. The composite ratio between Bi and S can be adjusted by varying the ratio between two precursors and was determined by using EDS (TEM) technique. Thermoelectric properties of these bismuth sulfide nanobeads were also investigated and will be discussed comparatively with those from commercial bulk materials.
MOCVD Growth of AlN/GaN DBR Structure Under Various Ambient Conditions
Authors: Yao H. H. , Lin C. F. , Wang S. C. 
Published: June 2019

AbstractHigh reflectivity AlN/GaN DBR structures were grown by MOCVD under three ambient gas conditions during the AlN layer growth. Highest peak reflectivity of about 94.5% with a stopband width of 18 nm at a center wavelength of 442nm was obtained under pure N2 gas ambient growth condition. The center wavelength of the DBR structures blue-shifted to 418 nm and 371 nm and the peak reflectivity also showed a reduction to 92 % and 79 % under the ambient gas conditions of a N2/H2 mixture and pure H2 respectively. Surface roughness showed slight increase from 8nm to 12nm, and the groove depth shows an increase from 25nm to 60nm with increasing the H2 ambient gas ratio. TEM results showed that AlN grown rate was reduction with the increasing H2 content in the ambient gas. The simulation result indicated that optical loss of AlN layers was increased from 450 cm-1 to 1850 cm-1 with the increasing H2 content in the ambient gas.
Low Ohmic Contact Resistance of GaN by Employing XeCl Excimer Laser
Authors: Lee Seung-Chul , Her Jin-Cherl , Han Sang-Myun , Seo Kwang-Seok , Han Min-Koo 
Published: June 2019

AbstractWe have investigated a new method by which selective high doping concentration of GaN can be obtained using XeCl excimer laser and presented low ohmic contact resistance fabricated by the proposed method. We have irradiated silicon film deposited by sputtering on GaN using XeCl excimer laser and formed ohmic contact on the region irradiated by laser. Ohmic contact resistance by laser doping process was effectively reduced to 0.27 ohm-mm while 0.66 ohm-mm was measured in ohmic contact by conventional method. We have verified that silicon is diffused into GaN by high laser energy during laser irradiation through SIMS analysis and ohmic contact resistance is reduced due to increase of doping concentration under ohmic contact region.
Experimental Evaluation of a-Se Flat-Panel X-ray Detector for Digital Radiography
Authors: Choi Jang-Yong , Park Ji-Koon , Lee Dong-Gil , Kang Sang-Sik , Nam Sang-Hee 
Published: June 2019

AbstractNowadays, large area, flat panel solid state detectors are being investigated for digital radiography. In this paper, development and evaluation of a selenium-based flat-panel digital xray detector are described. The prototype detector has a pixel pitch of 139μm and a total active imaging area of 7″×8.5″, giving a total of 1.9 million pixel. This detector include a x-ray imaging layer of amorphous selenium as a photoconductor which is evaporated in vacuum state on a TFT flat panel, to make signals in proportion to incident x-ray. The film thickness was about 500μm. To evaluate the imaging performance of the digital radiography (DR) system developed in our group, sensitivity, linearity of the response of exposure, the modulation transfer function(MTF) and detective quantum efficiency(DQE) of detector was measured. The measured sensitivity was 4.16×106 ehp/pixel mR at the bias field of 10 V/μm: The beam condition was 41.9 KeV. Measured MTF at 2.5 lp/mm was 52%, and the DQE at 1.5 lp/mm was 75%.
Analysis of Leakage Currents in AlGaN/GaN Current Aperture Vertical Electron Transistors (CAVETs)
Authors: Ben-Yaacov Ilan , Seck Yee-Kwang , DenBaars Steven P. , Hu Evelyn L. , Mishra Umesh K. 
Published: June 2019

AbstractA complete analysis of leakage currents in AlGaN/GaN Current Aperture Vertical Electron Transistors (CAVETs) with regrown aperture and source regions was carried out. The total observed leakage current was found to be a combination of both gate leakage and source leakage. Two paths for source leakage have been identified; electrons passing directly through the insulating layer to the drain region as well as electrons traveling through the aperture but underneath the 2DEG at the AlGaN/GaN interface. Source leakage through the insulating layer resulted from pits formed at the onset of regrowth, as the sample was heated to growth temperature, and was successfully eliminated by optimizing regrowth conditions. Source leakage underneath the 2DEG occurred when the unintentionally doped (UID) GaN layer above the insulating layer was not fully depleted and could be eliminated by reducing the thickness of the UID GaN layer. Gate leakage has been attributed to the enhanced incorporation of n-type impurities inside as well as above the aperture region during regrowth, resulting in a narrowing ofthegateSchottkybarrier.
Modulation of Energy Band Gap of ZnO Thin Films Grown by Pulsed Laser Deposition
Authors: Lee Sang Yeol , Li Yuan , Lee Jang-Sik , Lee J. K. , Nastasi M. , Crooker S.A. , Jia Q.X. , Kang Hong-Seong , Kang Joeng-Seok 
Published: June 2019

AbstractZnCdO thin films were deposited on (001) sapphire substrates by pulsed laser deposition. Modulation of the energy band gap of ZnCdO was induced by changing the processing parameters. The optical energy band gap of ZnCdO thin films, measured by photoluminescence and transmittance, changed from 3.289 eV to 3.311 eV due to the variation of annealing temperatures. The change of the optical properties was attributed to the change of the stoichiometry of ZnxCd1-xO as illustrated by Rutherford backscattering spectroscopy.
Femtosecond Pulses as a New Photonic Source for Growing Thin Films by Pulsed-laser Deposition
Authors: Millon Eric , Perrière Jacques , Albert Olivier , Etchepare Jean , Boulmer-Leborgne Chantal 
Published: June 2019

AbstractThe femtosecond (fs) lasers display noticeable specificities compared with the nanosecond (ns) ones operating in the UV domain, and classically used for the pulsed-laser deposition (PLD) technique. The ultra-short laser pulses offer the feature of minimal thermal damage induced in the target material, and the very high intensities (1012-14 W/cm2) available with fs lasers are likely to allow the ablation of any kind of materials, even the wide band gap insulators.The morphology, structure, composition and properties of the films obtained by fs PLD are studied according to the experimental growth conditions, the nature of the target material, and the dynamic expansion of plasma plume. In the case of ZnO, smooth, dense and nanocrystalline films (10 to 30 nm crystallites) can be epitaxially grown on adequate substrates (i.e. sapphire). On the contrary, BaTiO3 films are formed by the random stacking of aggregates (10 to 200 nm) leading to a non negligible surface roughness,. In addition, the chemical composition of fs PLD thin films of multicomponent compound (i.e. BaTiO3) is not homogeneous, an enrichment in the lighter element being observed in the central part of the film. These properties are related to the phenomena taking place during the various steps of the process (laser-matter interaction, plasma formation, expansion) through time resolved emission spectroscopy and plume optical imaging measurements.
Oxidation of Candutm Fuel by the Products of the Alpha Radiolysis of Groundwater
Authors: Sunder S. , Shoesmith D.W. , Johnson L.H. , Wallace G.J. , Bailey M.G. , Snaglewski A.P. 
Published: June 2019

AbstractThe oxidation of CANDUTM fuel by the products of alpha radiolysis of water is being investigated using X-ray Photoelectron Spectroscopy and electrochemical techniques. Possible mechanisms of oxidation of U02by 02 and H202, two of the oxidants formed during radiolysis of water, are discussed. Oxidation by H202depends upon its concentration and the pH of the solution. The oxidation of U02by the products of alpha radiolysis of water, formed by an alpha flux comparable with that expected at the used- fuel surface at the estimated time of waste container failure, caused very little dissolution of UO2fuel. The presence of reductants in groundwater reaching the fuel surface will diminish the fuel oxidation by the radiolysis products.
Experimental study of the Dissolution of spent fuel at 85°C in Natural Ground Water
Authors: Wilson Charles N. , Shaw Henry F. 
Published: June 2019

AbstractSemi-static dissolution tests using pressurized water reactor spent fuel rod segments and NNWSI reference J-13 well water in sealed stainless steel vessels at 85°C are being conducted in support of the Waste Package Task of the NNWSI Project. Test specimens include: bare fuel plus the empty cladding hulls, fuel rod segments with artificially induced cladding defects and water-tight end caps, and undefected fuel rod segments with water-tight end caps. The test conditions approximate those expected in the proposed NNWSI Project repository when the waste package has cooled sufficiently to allow water to enter a breached container and contact the fuel rods, some of which may exhibit various degrees of cladding failure. Periodic solution samples (unfiltered and filtered) were analyzed for most radionuclides for which cumulative release limits are listed by the U.S. Environmental Protection Agency. Results from the first six-month cycle of the 85° C tests are presented and are compared with results from the first cycle of a previous test series run at 25° in fused silica test vessels.
A Corrosion Model for Nuclear Waste Containers
Authors: Walton John C. , Sagar B. 
Published: June 2019

AbstractTheory of a mechanistic model for estimating the maximum rate of uniform corrosion for a steel or copper container in a saturated repository environment is described. Four oxidants that are considered are oxygen, sulfate, radiolysis products, and water. Rates of corrosion from oxygen and sulfate reduction are assumed limited by the rate of inward diffusion of the oxidant through the rock, packing, and corrosion product layers surrounding the container. Reduction of water is limited by kinetic processes as influenced by mass transfer of products and reactants, temperature, and pH. Substantial changes in the system resulting from the corrosion process are predicted to occur over time.
Performance Analysis of a Repository for Low and Intermediate Level Reactor Waste
Authors: Vieno Timo , Nordman Henrik , Vuori Seppo , Peltonen Esko 
Published: June 2019

AbstractIn Finland, utilities producing nuclear energy are responsible for the management of the radioactive waste, including final disposal. As regards low and intermediate level waste, the approach has been adopted to employ the power plant sites for locations of repositories. The repositories will be excavated at the depth of about 50 to 125 m in the bedrock of the two Finnish nuclear power plant sites, Loviisa and Olkiluoto.The performance analysis presented in this paper has been carried out for the Preliminary Safety Analysis Report (PSAR) of the Olkiluoto reposi- tory. A flexible model has been developed to estimate the release of radio- nuclides from waste packages and their subsequent transport through the engi- neered barriers in the repository. Gradual degradation of the engineered barriers is accounted for by altering parameters at fixed time points. Safety margins of the disposal concept have been evaluated by including disturbed evolution scenarios in the analysis.