bluuebunny/crossref_metadata_2025_split huggingface dataset:
Statistical Mechanics of Stress Transmission in Static Arrays of Rigid Grains
Authors: Grinev Dmitri V. , Edwards Sam F. 
Published: June 2019

ABSTRACTWe develop the statistical-mechanical theory that delivers the fundamental equations of stress equilibrium for static arrays of rigid grains. The random geometry of static granular packing composed of rigid cohesionless particles can be visualised as a network of intergranular contacts. The contact network and external loading determine the network of intergranular forces. In general, the contact network can have an arbitrary coordination number varying within the system. It follows then that the network of intergranular forces is indeterminate i.e. the number of unknown forces is larger than the number of Newton's equations of mechanical equilibrium. Thus, in order for the network of intergranular forces to be determined, the number of equations must equal the number of unknowns. We argue that this determines the contact network with a certain fixed coordination number. The complete system of equations for the stress tensor is derived from the equations of intergranular force and torque balance, given the geometric specification of the packing. The granular material fabric gives rise to corrections to the Euler-Cauchy equation that become significant at mesoscopic lengthscales. The stress-geometry equation establishes the relation between various components of the stress tensor, and depends on the topology of the granular array.
Dislocation Multiplication in Germanium Single Crystals
Authors: Charbonnier Corinne , Kruml Tomas , Martin Jean-Luc 
Published: June 2019

AbstractThermal activation of <123> germanium single crystal deformation is studied by using stress-relaxation experiments. These exhibit a non logarithmic dependence of stress as a function of time. The athermal component of stress and the apparent activation volume are determined. The role of dislocation multiplication is discussed in terms of specific features of the monotonic and transient deformation behaviour.
Parallel Tight-Binding Simulations of Nanophase Ceramics: Atomic and Electronic Transport at Grain Boundaries
Authors: Tsuruta Kenji , Totsuji Hiroo , Totsuji Chieko 
Published: June 2019

AbstractWe report on tight-binding molecular dynamics (TBMD) of neck formation processes and atomistic and electronic diffusivity at grain boundaries of nanocrystalline silicon carbide. The TBMD simulations are based on an O(N) algorithm (the Fermi-operator expansion method) for calculating electronic contributions to energy and forces. The code has been fully parallelized on our PC-based parallel machines. The TBMD simulations of collision of SiC nanospheres show that the processes of neck formation depend strongly on contact angles between the two grains. Atomic diffusions are quite different in the necks formed with different angles. Also, the electronic transport property at grain boundary is investigated via a TB representation of an electronic diffusivity. A preliminary result on the diffusivity at a Σ=9 grain boundary of SiC indicates significant enhancement of electron mobility along the grain boundary.
Transition Regime Fracture Toughness-temperature Properties of two Advanced Ferriticmartensitic Steels
Authors: Spätig Philippe , Donahue Eric , Odette George R. , Lucas Glenn E. , Victoria Max 
Published: June 2019

AbstractAdvanced martensitic steels are leading candidate materials for fusion reactor structural components due to their resistance to void swelling, and good balance of physical and mechanical properties. However, irradiations at temperatures below about 400°C result in increases in the cleavage-to-microvoid coalescence transition temperature, as well as reductions in the upper-shelf tearing toughness. This paper reports on the transition regime fracture toughness properties of two unirradiated 7-9Cr martensitic alloys, F82H and T91. Effective fracture toughness-temperature curves, Ke(T), were measured in the transition regime using relatively small pre-cracked specimens. Three sets of data obtained on different specimen sizes and geometries for the two steels are analyzed. All the data can be placed on a single so-called master-curve, when shifts due to size/geometry and material are taken into account. The results from mechanical tests, finite element method (FEM) simulations of crack tip fields and confocal microscopy-fracture reconstruction observations are presented. The link between the different mechanisms taking place at various length scales, resulting in the complex process of cleavage fracture, is discussed.
Efficient silicon light emitting diodes made by dislocation engineering
Authors: Lourenço M. A. , Gwilliam R. M. , Shao G. , Homewood K.P. 
Published: June 2019

AbstractEfficient room temperature silicon based light emitting diodes have been fabricated by conventional ULSI processes using a recently developed dislocation engineering approach. Strong silicon band edge luminescence was observed from devices fabricated by low energy boron implantation into silicon substrates followed by high temperature rapid thermal annealing. In this paper we review the luminescence properties of silicon light emitting diodes and give an example of how this approach can be employed to fabricate and optimise light emitting devices operating at different wavelengths.
Deep level study in epitaxial 4H-SiC grown on substrates inclined toward <1 100>
Authors: Kato Masashi , Ichimura Masaya , Arai Eisuke , Nishino Shigehiro 
Published: June 2019

AbstractEpitaxial layers of 4H-SiC are grown on (0001) substrates inclined toward <1120> and <1100> directions. Defects in these films are characterized by deep level transient spectroscopy (DLTS) in order to clarify the dependence of concentrations and activation energies on substrate inclination. DLTS results show no such dependence on substrate inclination but show thickness dependence of the concentration.
Influence of substrate surface morphology on defect generation during silicon carbide single crystal growth
Authors: Um Myung Yoon , Jeong Jae Kyeong , Kim Bum Seok , Na Hoon Joo , Song In Bok , Kim Hyeong Joon 
Published: June 2019

Abstract6H-SiC single crystals were grown on various substrates, treated mechanically and chemically in different conditions, by physical vapor transport. To investigate the defect evolution according to the different substrate treatment prior to the growth, the grown crystals were examined by optical micrograph, scanning electron microscopy, atomic force microscopy and molten KOH etching technique. The smoother substrate surface was, the lower defect density the grown SiC had. The highest quality SiC crystal was grown on substrate etched by hydrogen after polished by 0.25 νm diamond paste, having an edge/screw dislocation density of 7.3 ×102 / cm2 without micropipes. Defects, such as dislocations and micropipes, of the grown crystals are found to be strongly correlated with the substrate morphology.
Hydrogen Platelet Layer in Silicon Formed from Hydrogen Trapped onto Microbubbles of Gases
Authors: Usenko A.Y. , Carr W.N. , Chen Bo 
Published: June 2019

AbstractFeatures of a process of delamination of crystalline silicon layer from silicon wafer along hydrogen platelet layer formed by microwave plasma hydrogenation are described. The process involves first making a buried layer of nuclei for hydrogen platelets. Ion implantation of inert or low-soluble gases is used to form the layer. The nuclei are microbubbles that appear along Rp plane of implanted ions. Results for argon, xenon, and krypton implantation are compared. Wafers thus processed with a dose of 1015cm-2 are then hydrogenated with a microwave plasma. During hydrogenation, an atomic hydrogen diffuses into the silicon wafer and collects onto internal surfaces of the microbubbles. Then the hydrogen increases the internal surface of the microbubbles by growing a platelet type extensions to the microbubbles. The extensions grow preferably along the buried layer plane. A silicon layer above the layer of grown platelets were delaminated through pre-bonding/cut/post-bonding sequence as in the Smart-cut process. The plasma hydrogenation of the trap layer may be used as a step in a process of fabricating of SOI wafers with a very thin top crystalline silicon layer. Also, implant doses needed to form the microbubble trap layer are much lower than doses of direct implantation of hydrogen in the Smart-cut process. Temperature range of 200°C to 400°C during the hydrogenation process allows effectively grow extended hydrogen platelets from the nuclei. Mechanisms of nucleation of platelets as extentions of microbubbles are suggested. Control of hydrogen outdiffusion/platelet growth with thermal trajectory during plasma processing is discussed.
Direct-Write Printing of Silver Metallizations on Silicon Solar Cells
Authors: Curtis C. J. , Rivkin T. , Miedaner A. , Alleman J. , Perkins J. , Smith L. , Ginley D. S. 
Published: June 2019

AbstractDirect-write technologies offer the potential for low-cost materials-efficient deposition of contact metallizations for photovoltaics. We report on the inkjet printing of metal organic decomposition (MOD) inks with and without nanoparticle additions. Near-bulk conductivity of printed and sprayed metal films has been achieved for Ag and Ag nanocomposites. Good adhesion and ohmic contacts with a measured contact resistance of 400μΩ•cm2 have been observed between the sprayed silver films and a heavily doped n-type layer of Si. Silver deposited using the MOD ink burns through the Si3N4 antireflection coating when annealed at 850°C to form an ohmic contact to the n-Si underneath. An active solar cell device was fabricated using a top contact that was spray printed using the Ag MOD ink. Inkjet printed films show adhesion differences as a function of the process temperature and solvent. Silver lines with good adhesion and conductivity have been printed on glass with 100 μm resolution.
Study on the Dopedβ-FeSi 2 Obtained by Metal Vapor Vacuum Arc Ion Source Implantation and Post-Annealing
Authors: Wang Shuangbao , Liang Hong , Zhu Peiran 
Published: June 2019

Abstractβ-FeSi2 was firstly formed by implanting Si wafers with Fe ions at 50 kV to a dose of 5×1017/cm2in a strong current Metal Vapor Vacuum Arc (MEVVA) implanter. Secondly, Ti implantation was performed on these Fe as-implanted samples. The Fe + Ti implanted samples were furnace annealed in vacuum at temperatures ranging from 650 to 975°C. The XRD patterns of the annealed samples correspond to β-FeSi2 structure (namely β-Fe(Ti)Si2). When annealing was done above 1050°C, the β-Fe(Ti)Si2 transformed into α-Fe(Ti)Si2. This implies that introducing Ti stabilizes the β-FeSi2 phase. Resistance measurements were also performed.
TEM Studies and Contact Resistance of Au/Ni/Ti/Ta/n-GaN Ohmic Contacts
Authors: Zakharov D.N. , Liliental-Weber Z. , Motayed A. , Mohammad S.N. 
Published: June 2019

AbstractOhmic Ta/Ti/Ni/Au contacts to n-GaN have been studied using high resolution electron microscopy (HREM), energy dispersive X-ray spectrometry (EDX) and electron energy loss spectrometry (EELS). Two different samples were used: A - annealed at 7500C withcontact resistance 5×10-6 Ω cm2 and B-annealed at 7750C with contact resistance 6×10-5 Ω cm2. Both samples revealed extensive in- and out-diffusion between deposited layers with some consumption ofGaNlayerand formation of TixTa1-xN50 (0<x<25) at the GaN interface. Almost an order of magnitude difference in contact resistances can be attributed to structure and chemical bonding of Ti-O layers formed on the contact surfaces.
Optical and Structural Investigation of AlN Grown on Sapphire with Reactive MBE Using RF Nitrogen or Ammonia
Authors: Yun F. , He L. , Xiu F. , Morkoç H. , Bai S. , Shishkin Y. , Devaty R. P. , Choyke W. J. 
Published: June 2019

AbstractAlN epitaxial layers in a thickness range of 0.065 to 0.6 microns have been grown on double-side polished c-plane sapphire by molecular beam epitaxy (MBE) using either RF nitrogen or ammonia as the nitrogen source. The samples were characterized by XRD, room temperature (RT) and low temperature (2K) optical absorption (transmission) measurements. The XRD (0002) peak FWHM diminishes from 380 arcsec to 84 arcsec when the thickness of the AlN films is increased from 65 nm towards 0.6 μm. All the samples grown with ammonia (NH3), representing N-rich conditions, exhibited optical bandgap exceeding 6 eV at RT. For samples grown with RF nitrogen source, we find that higher nitrogen flow (partial pressure of 8.3-9.4 × 10-5 Torr) results in optical bandgap values larger than 6.0 eV, regardless of the XRD results. The bandgap is found to be smaller than 6.0 eV for the samples grown with lower nitrogen partial pressure (1.0-3.5 x 10-5 Torr), regardless of sample thickness and the XRD data.
Transient Capacitance Characterization of Deep Levels in Undoped and Si-Doped GaN
Authors: Nakamura S. , Liu P. , Suhara M. , Okumura T. 
Published: June 2019

AbstractThe deep levels in both undoped and Si-doped GaN layer grown by metalorganic chemical vapor deposition have been characterized by photocapacitance and transient capacitance spectroscopy. The increase in the photocapacitance was observed in both GaN samples in the range of 1.8 to 2.2 eV. This is due to the photoionization of carriers from the deep levels associated with the yellow luminescence (YL). In addition, the transient capacitance measurements after the photoionization were also performed in the range of 1.8 to 3.4 eV. The notable transient of capacitance was observed at the photon energies of about 2.1 and 3.4 eV, the former could be associated with the change in the charge state of the YL center and latter might stem from some other defects capturing photogenerated carriers. By using the isothermal capacitance transient spectroscopy (ICTS) analysis, the ICTS peaks due to the deep levels associated with YL were detected at about t = 150 s in both GaN samples. In addition, another ICTS peak was detected only in the Si-doped GaN samples. It is considered that this peak is associated with the deep levels deeper than YL levels and the deeper levels originate from defects induced by Si doping.
Modeling of Thermal Conductivity of Polycrystalline GaN Films
Authors: Kotchetkov D. , Balandin A. A. 
Published: June 2019

AbstractWe present preliminary results of a theoretical investigation of the thermal conductivity of polycrystalline GaN films. It is assumed that grain boundaries play a major role in limiting the thermal conductivity, which is calculated using the phonon-hopping transport approach. The effect of the grain size, size dispersion, and inter-grain interface structure on the thermal conductivity values is analyzed. The obtained results are compared with available experimental data for polycrystalline films and model predictions for crystalline GaN films.
Thermal Boundary Resistance and Heat Diffusion in AlGaN/GaN HFETs
Authors: Filippov Konstantin A. , Balandin Alexander A. 
Published: June 2019

AbstractWe theoretically investigate the thermal boundary resistance and heat diffusion in AlGaN/GaN heterostructure field-effect transistors. Our calculations based on the diffuse mismatch model show that the thermal boundary resistance at the interface between GaN and SiC can strongly influence the temperature rise in the device channel.
GaP-based MIS Capacitors Using a SiN Gate Dielectric
Authors: Chen A. , Woodall J. , Wang X.W. , Ma T.P. 
Published: June 2019

AbstractGallium Phosphide (GaP) Metal-Insulator-Semiconductor (MIS) capacitors were fabricated with synthesized SiN as the gate dielectric. The interface property and the SiN bulk quality were studied with capacitance-voltage (C-V) measurements and current-voltage (I-V) measurements. The total interface state density of 3×1012 cm-2 and the fixed charge density in SiN of 7×1012cm-2 were estimated from the C-V measurements. The leakage current density was as low as 15nA/cm2 at an effective electric field of 3MV/cm. The effective electric field in SiN at breakdown was as high as 10MV/cm. Constant current stress measurements showed bulk trap density of 2×1011 cm-2 in SiN, which is much lower than that for CVD SiN or SiO2.
First AlGaN Free-Standing Wafers
Authors: Melnik Yu.V. , Soukhoveev V.A. , Tsvetkov K.V. , Dmitriev V.A. 
Published: June 2019

AbstractSingle crystal AlGaN bulk materials have been fabricated, for the first time. AlGaN thick (up to 0.6 mm) layers were grown by hydride vapor phase epitaxy on SiC substrates. The substrates were removed resulting in free-standing AlGaN wafers up to 0.5 inch in diameter. Fabricated AlGaN wafers were investigated by x-ray diffraction, transmission electron microscopy (TEM), and cathodoluminescence. X-ray diffraction and TEM studies confirmed single crystal structure of grown material. Based on x-ray diffraction results, AlN concentration in grown material was estimated of about 35 mol.%. Cathodoluminescence measurements demonstrated a number of peaks in UV spectral region with the most intense luminescence at a wavelength of about 325 nm (100 K). The wafers demonstrated n-type conductivity with electron concentration in the 1017 cm-3 range at room temperature. Development of AlGaN substrates with controlled alloy composition may lead to stress-free device epitaxial structures for AlGaN-based transistors and UV emitters and sensors.
Temperature Dependent Cathodoluminescence Characterization of Ultraviolet Emitting Films Grown by Pulsed Laser Deposition
Authors: Fitz-Gerald J.M. , Hoekstra J.G. , Bansal R.K. , Fowlkes J.D. , Rack P.D. 
Published: June 2019

AbstractStrontium sulfide (SrS) is known to have an indirect bandgap of ∼ 4.32 eV. When doped with tellurium (Te), ultraviolet emission occurs at 360 nm (for Tes singlet) and 400nm (for Tes- Tes dimers) due to radiative recombination from bound exciton states. In this paper we discuss the ultraviolet emission of pulsed laser deposited thin films of SrS:Te grown as SrS-Te and SrSTe- SrS multi-layer structures on Si substrates. The Te doping was incorporated by conventional diffusion into the SrS films. Temperature dependent ultraviolet emission measurements were taken and will be discussed along with results from microstructural and chemical characterization techniques.
Laser Pointing Stability Measured by an Oblique-incidence Optical Transmittance Difference Technique
Authors: Gray J. , Thomas P. , Zhu X.D. 
Published: June 2019

AbstractWe describe an oblique incidence optical transmittance difference technique for determining the pointing stability of a laser. In this technique, we follow the angular drift a monochromatic laser beam by measuring the relative changes in transmittance through a parallel fused quartz window for s- and p- polarized components of the beam in response to the drift. This method is shown in the present experiment to have the sensitivity to detect angular changes in the range of 1.7 νradians. To demonstrate the technique we measured the angular drifts of two commercially available lasers.
Mechanical Properties and Morphology of Pulsed – Laser Deposited BaTiO3 Thin Films
Authors: Xu Jie , Durisin Daniel P. , Auner Gregory W. 
Published: June 2019

AbstractBaTiO3 thin films have been grown on Si(100) substrate by KrF pulsed – laser deposition (PLD). The process parameters such as background gas pressure, substrate temperature, and laser fluence were varied in order to investigate their influence on the crystal structure, surface morphology and mechanical properties. The films were characterized by X-ray diffraction (XRD), UV/VIS/NIR spectrometer, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). The hardness, Young's modules and scratch testing of BaTiO3 films were measured using nano-indenter. The stoichiometric BaTiO3 films having uniform grains were grown. The defects and particulates were generated at higher laser fluence. The size and density of particulates were increased with tighter laser focus. The results from dynamic scratch test indicated that the films with good adhesion were grown at moderate laser fluence.
Inorganic-organic Hybrid Materials for Real 3-D Sub-νm Lithography
Authors: Houbertz R. , Schulz J. , Fröhlich L. , Domann G. , Popall M. , Serbin J. , Chichkov B. 
Published: June 2019

AbstractReal 3-D sub-νm lithography was performed with two-photon polymerization (2PP) using inorganic-organic hybrid polymer (ORMOCER®) resins. The hybrid polymers were synthesized by hydrolysis/polycondensation reactions (modified sol-gel synthesis) which allows one to tailor their material properties towards the respective applications, i.e., dielectrics, optics or passivation. Due to their photosensitive organic functionalities, ORMOCER®s can be patterned by conventional photo-lithography as well as by femtosecond laser pulses at 780 nm. This results in polymerized (solid) structures where the non-polymerized parts can be removed by conventional developers.ORMOCER® structures as small as 200 nm or even below were generated by 2PP of the resins using femtosecond laser pulses. It is demonstrated that ORMOCER®s have the potential to be used in components or devices built up by nm-scale structures such as, e.g., photonic crystals. Aspects of the materials in conjunction to the applied technology are discussed.
Biocompatibility Studies of the Nitinol Thin Films
Authors: Dinu C.Z. , Tanasa R. , Dinca V.C. , Barbalat A. , Grigoriu C. , Bucur E.O. , Dauscher A. , DeStefano V. Ferrari , Dinescu M. 
Published: June 2019

AbstractPulsed Laser Deposition method (PLD) was used to grow nitinol (NiTi) thin films with goal of investigating their biocompatibility. High purity Ni and Ti targets were alternatively ablated in vacuum with a laser beam (λ=355 nm, 10 Hz) and the material was collected on room temperature Ti substrates. X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy and atomic force microscopy analyses have been performed to investigate the chemical composition, crystalline structure and surface morphology of the NiTi films. The nitinol layers biocompatibility has been tested using as a metric the extent to whichthe cells adhereduring the culture period on the surface of NiTi layers deposited on Ti substrates. Vero and fibroblast cell lines dispersed into MEM (Eagle) solution containing 8% fetal bovine serum, at 37° C, were used for tests. Preliminary studies indicate that the interaction at the interface is specifically controlled by the surface morphology, (especially by surface roughness), and by the chemical state of the surface. Cell behavior after contact with NiTi/Ti structure for different intervals (18, 22 and 25 days for the Vero cells, and after 10 and 25 days for fibroblasts) supports the conclusion that NiTi is a very good candidate as a biocompatible material.