bluuebunny/crossref_metadata_2025_split huggingface dataset:
Persistence of Granular Structure during Die Compaction of Ceramic Powders
Authors: Walker William J. 
Published: June 2019

ABSTRACTGlass spheres were used as a model system to investigate granule failure during die compaction. Stresses within an assembly of spheres follow a network of pathways. When the spheres are of uniform composition, the magnitude of the stresses within a pair of contacting granules is a function of the locally transmitted stress and the diameter of the two spheres. Results obtained using glass spheres demonstrated the statistical nature of granule failure during compaction, with some granules failing at very low applied pressures while others (∼40% by volume) persist at even the highest applied loads. Within a distribution of granule sizes, those granules with smaller diameter were seen to have a higher probability of failure at low pressure than were larger granules. These results are consistent with those observed during die compaction of granulated alumina powder.
MBE Growth of GaN using NH3 and Plasma Sources
Authors: Sampath A.V. , Bhattacharyya A. , Sandeep I. , Ng H.M. , Iliopoulos E. , Moustakas T.D. 
Published: June 2019

ABSTRACTWe report on a comparative study of the growth of GaN in an arsenic free MBE system using either the method of plasma activation of molecular nitrogen or catalytic decomposition of ammonia on a heated substrate. We find that while growth with a plasma source leads to smooth films only under Ga- rich conditions, growth with ammonia leads to smooth films under ammonia-rich conditions. In both cases we find a 2×2 surface reconstruction when using an AlN buffer, which is evidence that material grown with this buffer layer has the Ga-polarity. In the case of plasma growth we also investigated the use of a GaNbuffer and found that at the growth temperature the surface is unreconstructed, however it undergoes 3×3 reconstruction upon cooling to 300 °C. This observation is evidence that material grown on a GaN buffer has the N-polarity.
Multiscale Simulations of Brittle Fracture and the Quantum-Mechanical Nature of Bonding in Silicon
Authors: Bernstein N. , Hess D. 
Published: June 2019

AbstractWe simulate the microscopic details of brittle fracture in silicon by dynamically coupling empirical-potential molecular dynamics of a strained sample to a quantum-mechanical description of interatomic bonding at the crack tip. Our simulations show brittle fracture at loads comparable to experiment, in contrast with empirical potential simulations that show only ductile crack propagation at much higher loading. While the ductility of the empirical potentials can be attributed to their short range, it is unclear whether the increased range of the tight-binding description is sufficient to explain its brittle behavior. Using the multiscale method we show that at a temperature of 1100 K, but not at 900 K, a dislocation is sometimes nucleated when the crack tip impinges on a vacancy. While this result is too limited in length and time scales to directly correspond to experimental observations, it is suggestive of the experimentally observed brittle to ductile transition.
Al Grain Boundary Embrittlement Promoted by Na Impurity: An ab initio Study
Authors: Lu Guang-Hong , Kohyama Masanori , Yamamoto Rayoichi 
Published: June 2019

AbstractWe calculate the electronic structure of AlΣ9 tilt grain boundary with substitutional Na impurity atoms by first principles pseudopotential method. Results show that by Na segregation Al grain boundary expands and the valence charge density decreases significantly along the boundary. There is no stronger bond than metallic bond in the boundary even with Na impurity. We therefore conclude that the mechanism of Na-promoted Al grain boundary embrittlement should be one kind of ‘decohesion model’.
Intrinsic and Extrinsic Size Effects in Plasticity by Dislocation Glide
Authors: Sevillano J. Gil 
Published: June 2019

AbstractA classification of size effects (SE) in plasticity is attempted. ”Intrinsic” SE are perceived when any internal length scale directly influencing some process or property interferes with the size of the material region where the process is going on or when two internal length scales directly affecting the same process or property interfere. ”Extrinsic” SE arise from the external imposition of spatial gradients in the plastic process or by the building up of internal gradients by the (externally induced) process itself. In dislocation-mediated plasticity plastic strain gradients are resolved by the storage of geometrically necessary dislocations (GND) leading to prominent size effects. Of course, mixed effects with intrinsic and extrinsic contributions can be found as well as superposed effects involving more than two characteristic lengths (i.e., size effects on size effects).The inclusion of both types of SE in continuum or crystallographic theories is commented.
Micromechanical Modeling of Two-Phase Steels
Authors: Nygårds Mikael , Chandrasekaran Dilip , Gudmundson Peter 
Published: June 2019

AbstractA two-dimensional micromechanical model based on the finite element method is presented to model two-phase ferritic/pearlitic steels, by aid of generalised plane strain elements. A periodic representative cell containing 100 ferrite grains, and the desired fraction pearlite is used. By applying periodic boundary conditions, loading by an average stress or strain state is possible.Uniaxial tensile tests were performed on specimens containing the ferrite and pearlite microstructures, and on two-phase materials containing 25% and 58% pearlite respectively. The stress-strain data of the pearlite material is used to fit a laminar dependent Taylor relation to represent the pearlite workhardening. Thereafter, laminar spacings in the two-phase materials are measured, and the total stress-strain response of the materials is modelled. Comparisons between generated data and experiments show good agreement up to a strain of 2%.
Defect Accumulation and Recovery in Ion-Implanted 6H-SiC
Authors: Jiang W. , Weber W. J. , Wangxya C. M. 
Published: June 2019

AbstractSingle crystal wafers of <0001>-oriented 6H-SiC were irradiated at different temperatures using a variety of ion species. The disorder on both the Si and C sublattices has been studied in situ using a combination of ion beam analyses in multiaxial channeling geometry. The fraction of the irradiation-induced defects surviving simultaneous recovery processes decreases with decreasing ion mass and with increasing irradiation temperature. Some of the Si and C defects are well aligned with the <0001> axis and the rate of C disordering is higher than that of Si disordering. Three recovery stages in Au2+-irradiated 6H-SiC have been identified.
Possible shallowing of nitrogen donors in diamond
Authors: Miyazaki Takehide , Uda Tsuyoshi 
Published: June 2019

AbstractAmong many doping issues of diamond semiconductors, establishment of a shallow n-type impurity is a very important and yet challenging subject. Although both nitrogen (N) and hydrogen (H) are omnipresent impurities in diamond, they create only deep half-filled states in the energy gap. In this study, we present a theoretical proposal of a mechanism that makes N donors in diamond as shallow as possible. A complex of two adjacent substitutional N atoms with H sitting between the N atoms, an N-H-N defect, has a donor level approximately 1 eV shallower than of an isolated substitutional N defect.
Defect Engineering in CCD Image Sensors
Authors: McColgin William C. , Shantharama Lingadahalli G. , Lavine James P. 
Published: June 2019

AbstractDefect engineering principles are integral to the design and manufacture of high-quality CCD image sensors. As examples, we describe the use of epitaxial silicon for defect control, hydrogen passivation of interface defects, and several forms of impurity gettering. The high sensitivity of image sensors to contaminants reveals that boron segregation gettering of iron dominates gettering by oxygen precipitates for both fast and slow cooling cycles. We estimate that the gettering efficiency for iron is 99.95%.
Radiation hardness of AlGaN/GaN based HEMTs
Authors: Vitusevich S.A. , Klein N. , Belyaev A.E. , Danylyuk S.V. , Petrychuk M.V. , Konakova R.V. , Kurakin A.M. , Rengevich A.E. , Avksentyev A.Yu. , Danilchenko B.A. , Tilak V. , Smart J. , Vertiatchikh A. , Eastman L.F. 
Published: June 2019

AbstractIn this work we present steady-state characteristics and low-frequency noise spectra of AlGaN/GaN based high electron mobility transistors (HEMTs) exposed to gamma ray radiation. The devices with a variety of gate length (150-350 nm) and width (100-400 νm) were irradiated by 60Co gamma rays with doses in the range of 104-109 Rad and flux of 102 Rad/s. Dose dependencies of basic operating parameters of the transistors, such as saturation current (Isat), transconductance (gm), channel conductance (gc), and threshold voltage (VT) are analysed. Our study show that visible changes of above mentioned parameters are observed under relatively small doses (105 Rad) and strongly depend on the HEMT's topology. The transconductance decreases and threshold voltage becomes more negative for all devices while deviation of these parameters from its initial values does not exceed 20% at highest irradiation dose. At the same time variation of the channel conductance as well as saturation current depends to a high extent on the gate voltage (Vg). At |Vg| < |Vcr|, both Isat and gc show a reversal proportional to the cumulative dosage of radiation. However, at |Vg| > |Vcr|, drain saturation current and channel conductance increase with the cumulative dosage of radiation. The effect is more pronounced in short-length-gate devices.
Nitrogen-Stabilized H2* Defects in GaP:N
Authors: Janotti A. , Zhang S. B. , Wei Su-Huai 
Published: June 2019

AbstractThe presence of N in III-V compounds such as GaAs and GaP drastically changes the behavior of H. We studied atomic structures of N-related hydrogen complexes in GaP:N using first-principles method. We show that the formation of the strong N-H bond is responsible for the stabilization of H2* complex that is otherwise unstable against the formation of H2 molecule. This provides the first theoretical proof that H2* can be stable in III-V semiconductor. The previously proposed H-N-H dihydride model is found to be unstable against spontaneously transforming into H2*, which involves only monohydrides, H-N and H-Ga. The calculated local vibration frequencies and isotope shifts are in good agreement with experiment.
Application of X-ray synchrotron techniques to the characterization of the chemical nature and recombination activity of grown-in and process-induced defects and impurities in solar cells
Authors: Buonassisi T. , Vyvenko O.F. , Istratov A.A. , Weber E.R. , Schindler R. 
Published: June 2019

AbstractResults of the application of a combination of synchrotron radiation based analytical techniques, X-ray Beam Induced Current (XBIC) and microprobe X-ray Fluorescence (ν-XRF) to the analysis of shunts and lifetime limiting defects in solar cells are reported. XBIC, a new lifetime measurement technique similar to the Laser Beam Induced Current (LBIC) technique, uses a focused X-ray beam to generate minority charge carriers, which are then collected by the p-n junction of the solar cell. The X-ray beam is focused down to a spot size varying from approximately 1×1 νm to 5×5 νm, depending on the settings of focusing mirrors and slits. The sample stage is moved by computer-controlled step motors with sub-micron accuracy. Since the X-ray Beam Induced Current, which characterizes the minority carrier diffusion length in the spot where the X-ray beam hits the sample, and the X-ray Fluorescence signal, which characterizes the chemical nature of the precipitates under the beam, are measured at the same time, the chemical nature of the defects and impurities and their recombination activity can be studied simultaneously, in situ, and with a micron-scale resolution.We present the results of the applications of these techniques to low lifetime regions in fully processed solar cells. The solar cells were pre-characterized by LBIC and thermography, and regions of interest (containing shunts) were selected. An ν-XRF scan in this area of low lifetime revealed the presence of silver and titanium far from the contact strip, suggesting a process-induced defect.
Raman and optical absorption studies of silicon carbide structure damage by ion implantation
Authors: Muntele Claudiu I. , Muntele Iulia C. , Ila D. , Poker David B. , Hensley Dale K. 
Published: June 2019

AbstractThe work reported here deals with studying the defects induced by heavy ion implantation as well as the degree of crystalline lattice recovery after annealing in a high purity argon environment between 600 and 1600 °C. We implanted 6H, n-type silicon carbide with Pd and Au ions at 1015 ions/cm2, and used Micro-Raman (MR) and optical absorption (OA) spectroscopy techniques for investigating the lattice properties and damage evolution at various stages during the fabrication process.
The Effect of Defects and Dopants on Thermal Conduction in GaN Films
Authors: Zou J. , Kotchetkov D. , Balandin A.A. , Florescu D.I. , Pollak F.H. 
Published: June 2019

AbstractWe present a theoretical investigation of the effects of dislocations, impurities and dopants on the thermal conductivity of GaN layers. It is shown that the experimentally observed decrease of the room-temperature thermal conductivity with increasing doping density is a result of enhanced phonon relaxation on silicon dopant atoms. Scattering of acoustic phonons on free carriers plays a relatively minor role in GaN. The functional dependence of the thermal conductivity on doping density is in good agreement with experiment. A developed model can be used for thermal budget calculation in high-power density GaN devices.
Comparative Investigation of Photoluminescence of In- and Si- doped GaN/AlGaN Multi-Quantum Wells
Authors: Sun W. H. , Wang L. S. , Chua S. J. 
Published: June 2019

AbstractThe GaN/AlGaN multi-quantum-wells (MQWs) have been grown via metalorganic chemical vapor deposition (MOCVD). Micro-Photoluminescence (PL) measurement has been performed on non-, In- and Si- doped GaN/AlGaN multi-quantum-well samples in the temperature ranges of 90-300 K. In the non-doped GaN/AlGaN multi-quantum-wells we observed the free exciton peak at 3.4587 eV at 90 K. Other exciton related peaks are located at 3.4346, 3.4177, 3.394, 3.3129eV, which are probably associated with the strongly localized excitons involving the defects. In In-doped GaN/AlGaN MQWs, the free exciton peaks have a slight red-shift from 3.4712 to 3.4629 eV, but the PL intensities become stronger with increasing trimethylindium (TMIn) flow from 10.6 to 42.6-νmol/min. With Si-doping in the well layers, photoluminescence exhibits an envelope of exciton bands ranged from 3.4796eV (free exciton) to 3.43915eV. The excitonic peaks in the bands vary in intensity and position with sample temperature. In addition, we have also observed the LO phonon replica of AlGaN interacted by the laser line due to the resonance effect.
The Strain relaxation and dislocation density of SiGe films in micron size window with different mask material grown by MBE
Authors: Zhang Xiang-jiu , Xiong Hui , Hu Jihuang , Jiang Zuiming , Fan Yongliang , Lin Jun , Chen Yuerui 
Published: June 2019

AbstractThe strain relaxation and the misfit dislocation density in micron size windows with different mask materials were studied. Experiments showed that the misfit dislocation density and the strain in the SiGe films would be affected not only by the size of the windows but the mask material. Experiments also showed that after annealing the SiGe films grown in the micron size windows would be much more stable than films grown in the large area on the same wafer.
Thermal Evolution of Deuterium in 4H-Sic
Authors: Delamare R. , Ntsoenzok E. , Sauvage T. , Shiryaev A. , Veen A. van , Dubois Ch. 
Published: June 2019

Abstract4H-SiC samples were implanted at room temperature with 30 keV D+ ions at a dose of 5×1016 D+/cm2. Nuclear reaction analysis (NRA) and secondary ion mass spectroscopy (SIMS) measurements were performed to study the deuterium profiles after subsequent annealing at 1000-1250°C for 10min.Also, analytical techniques: RBS/C and thermal desorption spectroscopy (TDS) were carried out to characterize the evolution of implantation induced defects upon annealing. According to the NRA measurements, no deuterium release was found in the sample annealed at 1000°C. However, increasing the temperature to 1150°C led to a 40% decrease of deuterium content. Similar results about the evolution of D profiles upon annealing have also been obtained by SIMS measurements. In addition, SIMS measurements show that the maximum of the deuterium concentration shifts to the surface. Deuterium desorption at annealing temperatures higher than 1000°C was further confirmed by TDS experiments. Results from RBS/C indicated that during the desorption of deuterium, the implantation induced damage was annealed. These results are discussed.
Preparation and Characterization of Tin/Carbon Composites for Lithium-Ion Cells
Authors: Guidotti Ronald A. , Irvin David J. , Even William R. , Gross Karl 
Published: June 2019

AbstractA number of Sn/C composites were prepared for evaluation as anode materials for Li-ion cells. In one case, samples were prepared by incorporation of Sn species into organic precursors that were then pyrolyzed under an Ar/H2 cover gas to prepare the Sn/C composites. They were also prepared by decoration of various types of carbon with nanoparticles of Sn by electroless deposition using hydrazine. The carbons examined included a disordered carbon prepared in house from poly(methacrylonitrile), a mesocarbon microbead (MCMB) carbon, and a platelet graphite. The Sn/C composites were examined by x-ray diffraction (XRD) and scanning electron microscopy (SEM) and were also analyzed for Sn content. They were then tested as anodes in three-electrode cells against Li metal using 1M LiPF6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) solution. The best overall electrochemical performance was obtained with a Sn/C composite made by electroless deposition of 10% Sn onto platelet graphite.
Synthesis and Processing of High Capacity, High Cycle life and High Discharge Rate Defective Manganospinel films for Rechargeable batteries
Authors: Singh Deepika , Hofmann Heinrich , Kim Won-Seok , Craciun Valentin , Singh Rajiv K. 
Published: June 2019

AbstractSignificant effort to develop a robust rechargeable battery has been put in the past two decades. The efforts were mainly focused on developing rechargeable battery systems which exhibit high capacity, long cycle life and high discharge rate capabilities. LiMn2O4 based cathodes have been researched extensively as they are not only economical but also environmentally desirable. Research includes composition and doping variation, formation of novel phases and microstructural tailoring, but none of the material modifications have successfully satisfied all the above mentioned performance criteria. In this paper we show a correlation between processing parameters, microstructure and electrochemical performance of Li-Mn-O cathode films. In addition we discuss the formation of metastable oxygen-rich lithium manganospinels, using a unique ultraviolet assisted deposition process. These defective films exhibit high capacity (> 230 mAh/gm), long cycle life (less than 0.05 % capacity loss per cycle for the first 700 cycles), and high discharge rates (> 25 C for 25 % capacity loss). The long cycle life and high capacity was attributed to the ability to cycle the Mn+ valence to less than 3.5 without onset of Jahn-Teller structural transformation, while the high discharge rate was attributed to the extremely high diffusivity of Li+ in the defective Li1-δMn2-2δO4 phase.
Texture Evolution in Zr Grain-refined by Equal Channel Angular Pressing
Authors: Yu S.H. , Ryoo H.S. , Shin D.H. , Hwang S.K. 
Published: June 2019

AbstractTo explore a possibility of obtaining an ultra fine grain size in hcp materials, equal channel angular pressing (ECAP) was applied to commercially pure Zr with the initial grain size of 20 μm. To ensure the crack-free specimen during the severe deformation it was necessary to adopt different die designs at the two processing temperatures, room temperature and 350°C. Submicrometer scale grains, in the order of 200 nm, were obtained by employing the die design of 90°/20° and the deformation temperature of 350°C. With the proper choice of the processing parameters, the refined grains were surrounded by the high angle boundaries. During the severe plastic deformation, the crystal texture underwent a significant change, from a fiber texture to that of a strong (0002) component mixed with a medium {1010} components, suggesting a dual <a> slip mode of deformation on the plane of the maximum shear stress.
Carbon Nanotube-Perovskite-Composites as New Electrode Material
Authors: Weidenkaff Anke , Ebbinghaus Stefan G. , Lippert Thomas , Montenegro Macarena J. , Reller Armin 
Published: June 2019

AbstractIn this paper we describe the synthesis and characterisation of La1-xAxCoO3 (A=Ca, Sr) (0 < x < 0,5) of different morphologies using pulsed laser deposition, ceramic methods and alternative soft-chemistry techniques. Furthermore the potential use of a La1-xCaxCoO3/carbon nanotube composite material for oxygen electrodes is discussed.
HVPE-GROWN AlGaN/GaN HEMTs
Authors: Luo B. , Ren F. , Mastro M. A. , Tsvetkov D. , Pechnikov A. , Soukhoveev V. , Dmitriev V. , Baik K. H. , Pearton S. J. 
Published: June 2019

AbstractHigh quality undoped AlGaN/GaN high electron mobility transistors(HEMTs) structures have been gorwn by Hydride Vapor Phase Epitaxy (HVPE). The morphology of the films grown on Al2O3 substrates is excellent with root-mean-square roughness of ∼0.2nm over 10×10μm2 measurement area. Capacitance-voltage measurements show formation of dense sheet of charge at the AlGaN/GaN interface. HEMTs with 1μm gate length fabricated on these structures show transconductances in excess of 110 mS/mm and drain-source current above 0.6A/mm. Gate lag measurements show similar current collapse characteristics to HEMTs fabricated in MBE- or MOCVD grown material.
Mocvd Zinc Oxide Films for Wide Bandgap Applications
Authors: Rice C.E. , Tompa G.S. , Provost L.G. , Sbrockey N. , Cuchiaro J. 
Published: June 2019

AbstractZnO is a wide bandgap (3.2 eV) semiconductor with potential application in LEDs, lasers, and transparent transistors, among other uses. These applications require uniform thickness, high quality materials (amorphous, poly- or single crystal), pinhole- and defect-free-single-and multilayer-conformal coatings. These attributes are generally best achievable by MOCVD. We have mounted a significant effort to develop automated MOCVD systems and process technologies for single and multicomponent oxides. The reactors use high speed rotation and are of a vertical orientation built to all metal UHV standards. We have demonstrated reactor scaled performance from 3” to 12” diameter depositions planes with modeling scales through 24” diameter. Metalorganics are used for zinc and dopant sources as well as dopant gases to optimize performance at low pressures. In this paper we will discuss our most recent results with epitaxial ZnO films, achievements in p-type doping, multilayer structures, and polycrystalline doped ZnO films.