bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electrochemical Deposition of (Bi,Sb)2Te3 for Thermoelectric Microdevices
Authors: Fleurial Jean-Pierre , Herman Jennifer A. , Jeffrey Snyder G. , Ryan Margaret A. , Borshchevsky Alexander , Huang Chen-Kuo 
Published: June 2019

ABSTRACTNew experimental methods have been developed to electrochemically deposit p-type Sb-rich Bi2-xSbxTe3, Pb-doped and Bi-doped Bi2Te3, and PbTe thick films. Some of the deposited films were dense and had a smooth surface morphology. These films were deposited potentiostatically at room temperature in an acidic aqueous electrolyte. Experimental deposition of Bi2Te3 alloys into various thick nanoporous templates made out of anodized alumina has also been achieved. Miniaturized thermoelements for microdevices (25 μm tall, 60 μm diameter) were grown by plating through thick photoresist templates. The experimental techniques developed, as well as the transport properties of some of the films and filled templates, will be presented.
P-type SiGe/Si Superlattice Cooler
Authors: Fan Xiaofeng , Zeng Gehong , Croke Edward , Robinson Gerry , LaBounty Chris , Ahn Channing C. , Shakouri Ali , Bowers John E. 
Published: June 2019

ABSTRACTThe fabrication and characterization of single element p-type SiGe/Si superlattice coolers are described. Superlattice structures were used to enhance the device performance by reducing the thermal conductivity between the hot and the cold junctions, and by providing selective emission of hot carriers through thermionic emission. The structure of the samples consisted of a 3 μm thick symmetrically strained Si0.7Ge0.3/Si superlattice grown on a buffer layer designed so that the in-plane lattice constant is approximately that of relaxed Si0.9Ge0.1. Cooling up to 2.7 K at 25 °C and 7.2 K at 150 °C were measured. These p-type coolers can be combined with n-type devices that were demonstrated in our previous work. This is similar to conventional multi element thermoelectric devices, and it will enable us to achieve large cooling capacities with relatively small currents.
Thermoelectric Properties of Selenide Spinels
Authors: Jeffrey Snyder G. , Caillat T. , Fleurial J. -P. 
Published: June 2019

ABSTRACTMany compounds with the spinel structure type have been analyzed for their thermoelectric properties. Published data was used to augment experimental results presented here and to select promising thermoelectric spinels. Compounds studied here include Cu0.5Al0.5Cr2Se4, Cu0.5Co0.5Cr2Se4, Cu0.5In0.5Cr2Se4, and CuIr2Se4. Many exhibit low lattice thermal conductivity of about 20 mW/cmK, independent of temperature. Preliminary results are given for two series of compounds that were selected for further study: GaxCu1-xCr2Se4 and ZnxCu1-xCr2Se4.
Carrier Pocket Engineering for the Design of Low Dimensional Thermoelectrics with High Z3DT
Authors: Koga Takaaki , Cronin Stephen B. , Dresselhaus Mildred S. 
Published: June 2019

ABSTRACTThe concept of carrier pocket engineering applied to Si/Ge superlattices is tested experimentally. A set of strain-symmetrized Si(20Å)/Ge(20Å) superlattice samples were grown by MBE and the Seebeck coefficient S, electrical conductivity σ, and Hall coefficient were measured in the temperature range between 4K and 400K for these samples. The experimental results are in good agreement with the carrier pocket engineering model for temperatures below 300K. The thermoelectric figure of merit for the entire superlattice, Z3DT, is estimated from the measured S and σ, and using an estimated value for the thermal conductivity of the superlattice. Based on the measurements of these homogeneously doped samples and on model calculations, including the detailed scattering mechanisms of the samples, projections are made for δ-doped and modulation-doped samples [(001) oriented Si(20Å)/Ge(20Å) superlattices] to yield Z3DT ≈ 0.49 at 300K.
Where Should We Look For High Zt Materials: Suggestions From Theory.
Authors: Fornari M. , Singh D. J. , Mazin I. I. , Feldman J. L. 
Published: June 2019

ABSTRACTThe key challenges in discovering new high ZT thermoelectrics are understanding how the nearly contradictory requirements of high electrical conductivity, high thermopower and low thermal conductivity can be achieved in a single material and based on this identifying suitable compounds. First principles calculations provide a material specific microscopic window into the relevant properties and their origins. We illustrate the utility of the approach by presenting specific examples of compounds belonging to the class of skutterudites that are or are not good thermoelectrics along with the microscopic reasons. Based on our computational exploration we make a suggestion for achieving higher values of ZT at room temperature in bulk materials, namely n-type La(Ru,Rh)4Sb12 with high La-filling.
Granular Flows in the Elastic Limit
Authors: Campbell Charles S. 
Published: June 2019

ABSTRACTThis paper describes recent computer simulation studies into the rheological behavior of granular materials in the regime that lies between the quasistatic and rapid-flow regime. This investigation was prompted by studies of landslides, hopper flows and the “phase change” (i.e. the change between solidlike and fluid-like behavior) all of which indicated that the shear-to-normal stress ratio (the effective friction coefficient for the material) increased with shear rate. The results presented herein do demonstrate that the stress ratio varies with a dimensionless parameter created by scaling the shear rate with the stiffness of the interparticle contacts. In dense regimes, the stresses themselves scale with the stiffness indicating that they are generated by the elastic response of particle networks. Such speculation is supported by studies that show that the normal stresses are strongly dependent on the interparticle friction coefficient which affects the ability of internal elastic particle structures to support load and by the time variation of stress, which shows a spiky behavior as the structures form and break. However, analyses also indicate that these observations cannot explain the hopper, landslide and phase-change as these systems operate in regimes different from those in which the effect was observed. Finally, the effects of non-linear contacts are investigated and an appropriate scaling that takes the non-linearity into account is proposed.
A Nonequilibrium Approach for Self-Diffusion in Unbounded Rapid Granular Flows
Authors: Jalali Payman , Zamankhan Piroz , Polashenski William 
Published: June 2019

ABSTRACTA nonequilibrium simulation scheme is introduced to investigate the transverse diffusive motion in unbounded shear flows of smooth, monodisperse, inelastic spherical particles. A certain labeling algorithm is used in this scheme to extract a one-way particle mass flux which results a concentration gradient for the labeled particles. The self-diffusion coefficient can then be obtained from Fick's law. Using this scheme, one may find that the self-diffusion phenomenon across any layer inside the granular shear flow is analogous to the classic diffusion problem across a membrane. Under steady conditions, the current simulation results revealed that the particle diffusivity can be described by a linear law. This finding justifies the assumption of a linear law relationship in the kinetic theory type derivation of an expression for self-diffusivity. Moreover, it is shown that the results of self-diffusion coefficient obtained from the computer simulations are in agreement with the predictions of kinetic theory formulations in the range of solid volume fractions less than 0.5.
An Experimental Study of the Fluctuations in Granular Drag
Authors: Albert István , Tegzes Pál , Albert Réka , Sample John , Barabási Albert-László , Vicsek Tamás , Kahng B. , Schiffer Peter 
Published: June 2019

ABSTRACTWe study fluctuations in the drag force resisting the motion of an object being pulled through a dense spherical granular medium. These fluctuations are stick-slip in nature due to the jamming and reorganization of the grains. The fluctuations in the force are periodic at small depths, but they become “stepped” at large depths. We interpret this transition as a consequence of the long-range nature of the force chains.
Multiscale Modeling of Dislocation Processes in Bcc Tantalum: Bridging Atomistic and Mesoscale Simulations
Authors: Yang L. H. , Tang Meijie , Moriarty John A. 
Published: June 2019

AbstractPlastic deformation in bcc metals at low temperatures and high-strain rates is controlled by the motion of a/2<111> screw dislocations, and understanding the fundamental atomistic processes of this motion is essential to develop predictive multiscale models of crystal plasticity. The multiscale modeling approach presented here for bcc Ta is based on information passing, where results of simulations at the atomic scale are used in simulations of plastic deformation at mesoscopic length scales via dislocation dynamics (DD). The relevant core properties of a/2<111> screw dislocations in Ta have been obtained using quantum-based interatomic potentials derived from model generalized pseudopotential theory and an ab-initio data base together with an accurate Green's-function simulation method that implements flexible boundary conditions. In particular, the stress-dependent activation enthalpy for the lowest-energy kink-pair mechanism has been calculated and fitted to a revealing analytic form. This is the critical quantity determining dislocation mobility in the DD simulations, and the present activation enthalpy is found to be in good agreement with the previous empirical form used to explain the temperature dependence of the yield stress.
Stresses in Thin Coatings from Curvature Measurements on Non-Planar Substrates
Authors: Wikström A. , Gudmundson P. 
Published: June 2019

AbstractMechanical elastic and inelastic properties of thin coatings are often studied by means of the curvature measurement technique in combination with the Stoney formula. It is then implicitly assumed that the elastic substrate is initially flat which implies that the curvatures theoretically remain constant over the substrate. If the substrate has a slight initial curvature, a different situation arises. In this case, the curvatures will vary over the substrate. It has recently been shown that in spite of this, the stresses that appear in the thin coating will remain constant over the surface of the substrate. Therefore, measured curvatures can generally not be used to extract layer stresses without a proper compensation for the initial curvature. A general method for the extraction of mechanical properties from curvature measurements on non-planar substrates is outlined. The method is valid for linear as well as non-linear shell theories. The compensation needed to evaluate a coating on a circular substrate with spherical initial curvature is studied for all relevant parameters. The results are particularly discussed in relation to curvature measurements on silicon wafers.
Hybrid Electronic-density-functional/molecular-dynamics Simulation on Parallel Computers: Oxidation of Si Surface
Authors: Ogata Shuji , Shimojo Fuyuki , Nakano Aiichiro , Vashishta Priya , Kalia Rajiv K. 
Published: June 2019

AbstractA hybrid quantum mechanical/molecular dynamics simulation scheme is developed by embedding a quantum mechanical system described by the real-space density-functional theory in a classical system of atoms interacting via an empirical interatomic potential. A novel scaled position method for handshake atoms coupling the quantum and the classical systems is introduced. Hybrid simulation run for oxidation of Si (100) surface is performed to demonstrate seamless coupling of the quantum and the classical systems.
Features of Vacancy Interaction with Interstitial Clusters in BCC Metals
Authors: Pelfort Marta , Osetsky Yuri N. , Serra Anna 
Published: June 2019

AbstractRecent theoretical calculations and atomistic computer simulations have shown that one-dimensional (1D) glissile clusters of self-interstitial atoms (SIAs) play an important role in the evolution of the microstructure in metals and alloys under cascade damage conditions. Theoretical treatments based on the production bias model (PBM)and cascade-induced source hardening clarify many features of materials behaviour under irradiation by considering 1D glissile SIA clusters. However, further progress in understanding irradiation phenomena demands a detailed knowledge of different reactions where glissile SIA clusters take part. The latest version of the PBM has demonstrated that there is a significant lack of knowledge on mechanisms such as the interaction between mobile clusters and other microstructure components, changes on glide directions or the reduction of cluster mobility. Some aspects of interactions have been recently studied and the formation of immobile complexes of glissile clusters in the bulk and near dislocations has been shown. However, in addition to the cluster - clusters and cluster – dislocation interactions, the interactions of clusters with point defects should be considered. Here we present the first results on interaction between a SIA cluster and vacancy in bcc-iron. The interactions were studied by both atomistic simulations and elasticity theory. Some qualitative differences between the results obtained by these two methods were found, thereby demonstrating the need for the atomistic approach. It is shown that the interaction with vacancies can reduce and, in some cases, suppress the mobility of SIA clusters. The results are discussed in the light of both experimental data and theoretical predictions.
Fabrication of p-Type Zns with Blue-Ag Emission by Triple-Codoping Method
Authors: Kishimoto S. , Yamamoto T. , Iida S. 
Published: June 2019

AbstractWe have succeeded in the fabrication of low-resistivity p-type ZnS with blue -Ag emission by triple-codoping using Ag, a Zn-substituting species, In, a Zn-substituting species, and N, a S-substituting species. For the realization of blue-Ag emission at 436 nm, we use In species as co-activators with Ag activators. For the control of conduction type to obtain p-type ZnS thin films, we introduce N species as acceptors into ZnS codoped with the Ag and In. On the basis of the analysis of the experimental data and calculated results, we proposed a model for ZnS:(Ag, In, and N), in which some of the In species act as coactivators with Ag activators and other In species act as reactive codopants with N acceptors.
Optical Methods for Defect Characterization in Light-Ion Implanted Silicon Carbide
Authors: Muntele Claudiu I. , Muntele Iulia C. , Ila Daryush , Poker David B. , Hensley Dale K. 
Published: June 2019

AbstractThe work reported here deals with studying the defects induced by light ion (Al, N) implantation in 4H and 6H silicon carbide, both p-type (Al-doped) and n-type (N-doped). Confocal Micro-Raman (MR) was used for monitoring the (480 – 540) cm-1 spectral region of amorphous silicon. A broad peak forms in this region because of silicon atoms relocated as interstitials, translating into a locally stressed crystalline lattice. The locally relaxed lattice at these atoms' locations of origin also gives a broadening of the characteristic Raman peaks of each type of material. UV/Vis Optical Absorption (OA) Spectroscopy has also been employed as a good tool for dopant and carrier trapping levels embedded in the band gap of the silicon carbide material. MR and OA data collected from virgin samples, as implanted, and after annealing at two different temperatures (1100 and 1600 °C) are discussed in this paper.
Raman Scattering Spectra in Be-Implanted GaN Epilayers
Authors: Wang L. S. , Sun W. H. , Chua S. J. 
Published: June 2019

AbstractIon-implantation has been an interesting topic on impurity-doping in GaN. Raman measurement is a strong tool for the characterization of semiconductors. We have investigated the Raman scattering spectra in Be-implanted GaN epilayers. In as-implanted GaN, new Raman bands at ∼310, ∼360, 669 cm-1 appeared. From phonon-dispersion curves for hexagonal GaN, the ∼300 cm-1 and 669 cm-1 bands were assigned to the highest acoustic-phonon branch and the optical-phonon branch at the Brillouin zone boundaries, respectively. Two sharp bands at 168 and 199 cm-1 were observed in the Raman spectra of Be-implanted GaN after post-implantation annealing treatments. We tentatively assign these two bands to Be-related local vibrational modes.
Native Defect Formation and Ionization Energies in Cadmium Telluride
Authors: Jaffe John E. , Bliss Mary 
Published: June 2019

AbstractDeep intrinsic energy levels near the middle of the band gap in CdTe have been reported in a number of experiments. Based on earlier defect-supercell electronic structure calculations, at least some of these features have been attributed to the second ionization level of the Cd vacancy, while the TeCd antisite, possibly complexed with a Cd vacancy, has also been suggested to account for some midgap levels. Using high-accuracy LDA calculations with full lattice relaxation out to third neighbors, we find that (i) both acceptor states of the Cd vacancy are shallow, (ii) the donor states of an isolated TeCd are both more than 1 eV above the valence band maximum, (iii) the TeCd-VCd complex does indeed have acceptor states near midgap in CdTe and probably accounts for the native defect states in that energy range.
Study of Er-related Defects in a-Si:H(Er) Films Used in Light Emitting Heterostructures
Authors: Nazarov A. , Vovk Ja. , Lysenko V. , Kon'kov O. , Terukov E. , Ashok S. 
Published: June 2019

AbstractDefects relating to Er-doping of hydrogenated amorphous silicon films in amorphous/ crystalline (a-Si:H(Er) / n-Si) heterostructures used as light emitters were studied. Electrical parameters of the defects were evaluated by thermally activated current (TAC) and capacitance (TACap) spectroscopy, and high-frequency (1 MHz) capacitance-voltage (C-V) characteristics measured at 77 K. For charging of the traps, visible light illumination at low temperatures and thermal-bias stress at various temperatures were used. The amplitude of TAC was found to increase monotonically with increase of Er concentration in the a-Si:H film. The traps, with activation energies in the range 0.10 - 0.35 eV and 0.5 - 0.6 eV, were charged under both light and thermal-bias stress, and may be associated with the deep levels in the band-gap of a-Si:H. High-temperature current peaks with activation energies of 0.8-0.9 eV emerged only under thermal-bias stress and were strongly dependent on the charging temperature. It is suggested that these high-temperature thermally activated processes are related to polarization of the Er-O bonds in the amorphous matrix of a-Si:H. C-V measurements show that charging of the structure by negative substrate bias leads to net electron trapping in the a-Si:H(Er) film, whereas charging by positive bias result in net hole trapping. The model of Er-related electroluminescence in a-Si:H(Er) / n-Si heterostructures involving electron-hole recombination via deep levels located in the vicinity of [Er-O] inclusions is discussed.
Low-Temperature Properties of Compensated Ge Films Used for Cryogenic Thermometers
Authors: Mitin V. F. , Kholevchuk V. V. , Dugaev V. K. , Vieira M. 
Published: June 2019

AbstractLow temperature microsensors are designed for cryogenic applications. As a material for the sensors we use heavily doped compensated Ge films deposited on the semi-insulating GaAs substrates. We present the results of experimental and theoretical study of the low temperature resistance as a function of temperature and magnetic field for some models of temperature sensors. The computer simulations show a good agreement with experimental data.
Fabrication of Copper-Indium-Disulfide Films onto Mo/Glass Substrates Using Pulsed Laser Deposition
Authors: Mu R. , Wu M.H. , Liu Y. C. , Ueda A. , Henderson D.O. , Hmelo A.B. , Feldman L.C. , Hepp A. 
Published: June 2019

AbstractPico-second pulsed laser deposition (PLD) was employed to fabricate copper indium disulfide (CIS) thin films onto pure silica and Mo coated glass substrates. By properly preparing the target materials and controlling the elemental ratio of the Cu, In and S in the deposited film followed by post-thermal annealing, good quality copper-indium-disulfide(CIS) films can be obtained. A series of characterizations were conducted including XRD, RBS, IR, UV-Vis, AFM and STM analyses.
Absorber Films of Ag2S and AgBiS2 prepared by Chemical Bath Deposition
Authors: Rodriguez A. Nuñez , Nair M.T.S. , Nair P.K. 
Published: June 2019

AbstractAg2S thin films of 90 nm to 300 nm in thickness were deposited at 70°C on glass substrates immersed in a bath mixture containing silver nitrate, sodium thiosulfate and dimethylthiourea. When the films are heated in nitrogen at temperatures 200°C to 400°C, crystallinity is improved and XRD pattern similar to that of acanthite is observed. These films possess electrical conductivity of 10-3 (ohm cm)-1, are photoconductive and exhibit an optical band gap of 1.36 eV. When Ag2S thin film is deposited over a thin film of Bi2S3, also obtained by chemical bath deposition from bismuth nitrate, triethanolamine and thioacetamide, and heated at 300°C to 400°C in nitrogen, a ternary compound, AgBiS2 is formed. This material has an electrical conductivity of 5x10-5 (ohm cm)-1, is photoconductive and possesses optical band gap 0.95 eV.
A Promising New Photo-Catalyst InVO4for Water Molecule Decomposition in the Visible Wavelength Region
Authors: Oshikiri M. , Seitsonen A. P. , Parrinello M. , Boero M. , Ye J. , Zou Z. 
Published: June 2019

AbstractA promising vanadium-based photo-catalyst (InVO4) has been proposed recently by our group. This catalyst has been shown to be active in the visible light range, up to a wavelength of about 600 nm, and is able to promote the decomposition of water. In this paper, we focus on its electronic structure, computed via first principles calculations, in order to figure out analogies and differences with similar systems (InNbO4, InTaO4and BiVO4) that have already been reported to act as photo-catalysts. An attempt is made to address the problem of the wavelength dependency of the photo catalytic activity of the InMO4(M = V, Nb, Ta) family and how this is related to the crystal structure. Finally, by using anab initiomolecular dynamics approach, we inspect the relaxation/reconstruction phenomena occurring at the exposed surface of the InVO4catalyst induced by the absorption of a water molecule, that represents a crucial step in the catalysis reaction.
Anomaly of Thermal Properties in Thin Films of La1-x SrxCoO3 Series Fabricated as Thermoelectric Materials
Authors: Takata Yoshiaki , Haneda Hajime , Adachi Yutaka , Wada Yoshiki , Mitsuhashi Takefumi , Ohtani Makoto , Fukumura Tomoteru , Kawasaki Masashi , Koinuma Hideomi 
Published: June 2019

AbstractComposition spreads of La1-xSrxCoO3 (LSCO) were synthesized as thermo-electric transducer material by means of combinatorial material synthesis, and information on their thermal diffusivity throughout the specimens was obtained. Meanwhile, it is anticipated that the composition spreads of LSCO have a variety of characteristic properties of light absorption corresponding to their composition, namely their compositional variable, x. Hence, we used transient optical pump-and-probe techniques in a reflection geometry to measure thermal diffusion times on LSCO. The results of signal analysis indicate that LSCO is a peculiar synthesized substance whose apparent thermal diffusivity, 1/ι, changes abruptly at the critical point, where the compositional variable x is equal to 0.3.