bluuebunny/crossref_metadata_2025_split huggingface dataset:
In Situ SEM Observations and Electrical Measurements During the Annealing of Si/Ni Contacts to SiC
Authors: Ervin Matthew H. , Jones Kenneth A. , Derenge Michael A. , Zheleva Tsvetanka S. , Wood Mark C. 
Published: June 2019

AbstractNickel (Ni) contacts to n-type silicon carbide (n-SiC) are annealed to ∼950°C in order to achieve their good ohmic properties through the reaction of the Ni with Si from the SiC to form nickel silicides. Unfortunately, the physical contact, and therefore the reliability, is poor. A possible cause is that the silicidation reaction liberates C from the SiC, which then diffuses throughout the contact. The reaction also produces a poor morphology and voids form at the metal-SiC interface. To try to understand the processes that produce the good electrical properties and at the same time improve the physical properties, we studied the reactions of Si/Ni contacts with 1:1 and 1:2 stoichiometric ratios as well as Ni-only contacts on n- and p-type SiC, both visually and electrically in situ using a hot stage and microprobe-equipped scanning electron microscope (SEM). The visual observations of the Ni-only film show that it does not react with the SiC until the temperature reaches 500–550°C. For the n-type SiC, the electrical measurements show a decrease in contact resistivity as the anneal temperature is increased from 500°C to 650°C. Increasing the anneal temperature further increases the resistivity until it begins to drop precipitously as the temperature approaches 950°C and higher. The visual observations of the Si/Ni contacts show that the Si and Ni are reacting at ∼600°C, with phases nucleating and then growing laterally. The electrical measurements for the n-type samples show that the contact resistance initially drops at 100–300°C indicating that there may be reactions, unseen by the SEM, at lower temperatures. The resistance continues to rise and fall over the intervening temperatures but begins to consistently and significantly fall at temperatures above 850°C, and then reaches ohmic values at 900–950°C. Because the silicidation reactions are seen to occur at temperatures far below those required to achieve ohmic properties, it is clear that silicide formation, while it may be necessary, is not sufficient for the formation of Ni-ohmic contacts to n-SiC. In this work, it has been observed that reaction of the Ni with the SiC appears to be necessary for achieving ohmic properties. While this may form a more intimate contact, it is proposed that damaging the SiC surface with this reaction is an important part of ohmic contact formation, possibly through increased current tunneling through interface defect states.
The Effects of Sapphire Surface Treatments and Nitridation on GaN Nucleation Grown using Hydride Vapor Phase Epitaxy
Authors: Dwikusuma F. , Kuech T. F. 
Published: June 2019

AbstractWe have studied the effects of sapphire surface treatments and nitridation on GaN nucleation grown using the hydride vapor phase epitaxy technique. The surface treatments used were airannealing at 1400°C, etching in pure H2SO4 at 250°C, and etching in a 3:1 mixture of H2SO4:H3PO4 solution at 250°C. A nitridation step was carried out using 20% NH3 in N2 gas mixture at 1100°C. GaN nucleation and the early stage s of growth was investigated by short time growth and quench experiments. Atomic force microscopy and double crystal x-ray diffraction were used to examine the sapphire surface morphology, GaN island density, and GaN island structure. A lower density of GaN islands was grown on the air-annealed sapphire compared to the H2SO4-etched and 3:1 H2SO4:H3PO4-etched sapphire. GaN islands grown on the 3:1 H2SO4:H3PO4-etched sapphire had a broad mosaic spread due to preferential growth on surface pits. Sapphire nitridation resulted in a higher GaN island density with a smaller mosaic spread. A high density and uniform nucleation of GaN islands is critical in producing high quality thick GaN films. The H2SO4-etched sapphire and nitridation resulted in a high density of uniform GaN islands.
Effect of Si Layer in The ZnO Thin Films by Pulsed Laser Deposition
Authors: Kang Hong Seong , Kang Jeong Seok , Kim Jae Won , Lee Sang Yeol 
Published: June 2019

AbstractZnO thin films and ZnO-Si-ZnO multi-layer thin films have been deposited by pulsed laser deposition (PLD). And then, the films have been annealed at 300°C in oxygen ambient pressure. The optical and structural properties changed by Si layer in ZnO thin film. UV and visible peak position was shifted by Si layer. Electrical properties of the films were improved slightly than ZnO thin film without Si layer. The optical and structural properties of ZnO thin films and ZnOSi-ZnO multi-layer thin films were characterized by PL (Photoluminescence) and XRD(X-ray diffraction method), respectively. Electrical properties were measured by van der Pauw Hall measurements.
Fabrication and Characterizations of ZnO and ZnO:Mn Nanocrystalline Thin Films
Authors: Liu Yichun , Zhao Dongxu , Zhang X.T. , Shen Dezhen , Henderson D.O. , Mu R. 
Published: June 2019

AbstractThis paper provides a brief summary of the structural and optical study of ZnO and ZnO:Mn materials fabricated from simple process: oxidation of ZnS and ZnS:Mn thin films grown by LPMOCVD. Both structural analysis and optical characterization have confirmed the good quality ZnO material formation. XRD results suggest that the fabricated ZnO film is composed of ∼30 nm ZnO nanocrystals with a hexagonal wurtzite structure. Raman spectra show a strong resonant multiphonon effect. In all cases, a UV emission is observed at ∼ 380 nm. A green emission is also observed in the ZnO nanocrystalline film. On the other hand, it is demonstrated that the Mn doping in ZnS film can dramatically affect the luminescence properties of end products: nanocrystalline ZnO thin films. The photoluminescence spectra of the films with an optimized Mn doping concentration only showed the ultraviolet emission, while the green emission was fully quenched. It is argued that the presence of the Mn can effectively passivate the electron and hole trapping sites at the surface and interface of the ZnO nanocrystals.
Electrical Characterization of Defects Introduced in 4H-SiC During High Energy Proton Irradiation and Their Annealing Behavior
Authors: Ahoujja M. , Crocket H. C. , Scott M. B. , Yeo Y.K. , Hengehold R. L. 
Published: June 2019

AbstractWe report on the electrical properties of defects introduced in epitaxial 4H-SiC by 2 MeV protons using deep level transient spectroscopy (DLTS). After proton irradiation with a dose of about 1.5×1014 cm-2, the DLTS measurements were made, and the rate window shows a single broad peak between 280 and 310 K. The intensity of this peak remains unchanged after a thermal anneal at 900°C for 20 min. However, after annealing at or above 1100°C, the peak intensity gradually decreases with anneal temperature up to 1500°C, indicating a decrease in the defect concentration. Because a complete damage recovery of the SiC is not observed even after annealing at 1500°C, we believe a higher temperature annealing is necessary for a complete recovery. Using a curve fit analysis, a set of deep levels of defect centers were found with energy ranging between 567 and 732 meV. These traps do not exhibit a significant change in the trap energy or capture cross-section parameters as a function of anneal temperature, but the decrease in the trap density with increasing anneal temperature demonstrates a damage recovery.
Er doped GaN by Gas Source Molecular Beam Epitaxy on GaN Templates
Authors: Rousseau N. , Briot O. , Ribes V. , Aulombard R.L. 
Published: June 2019

AbstractSince the work of Favennec et al.[1] it is well known that the quenching of luminescence from rare earth ions decreases with the host band gap. This has led to a large activity with silicon implanted or doped with RE, and then GaAs was used, in hope to realize simple, cheap light emitters. With a band gap of 3.4 eV at room temperature, GaN is even better suited to such applications. As a matter of fact, Steckl et al.[2] have demonstrated a green light emitting device based on Er doped GaN. This resulted in a renewed effort in this direction, but the crystal quality still have to be mastered and the physical phenomenon involved to be understood. In this work, GaN and Er-doped GaN with various Er concentrations were grown by gas source molecular beam epitaxy on high quality GaN templates grown by metalorganic chemical vapour deposition. In order to understand the influence of the Er incorporation on the crystal quality of GaN, Er-doped GaN were grown with a concentration between 0.1% and 5%. High quality undoped GaN were also grown, as a reference material, to show how the smallest amount of Er may affect drastically the structural and optical properties. All the samples were characterized by scanning electron microscopy, atomic force microscopy and X-ray diffraction. With these measurements, we demonstrate a strong correlation between the Er concentration and the surface roughness and the crystalline quality. This study shows that the activation of the Erbium luminescence is not improved with improving crystal quality. This assumption supports the idea that Er luminescence should be related to defect center in GaN.
Time of Flight of Drifting Electrons and Holes in Stabilized a-Se Film
Authors: Lee Dong-Gil , Park Ji-Koon , Choi Jang-Yong , Kim Jae-Hyung , Nam Sang-Hee 
Published: June 2019

AbstractLarge area, flat panel detectors are being investigated for digital radiogrpahy and fluoroscopy. Theses detectors employ an x-ray conversion layer of photoconductor to detect x-rays. The amorphous selenium layer that is currently being studied for its use as an x-ray photoconductor is not pure a-Se but rather a-Se doped with 0.2-0.5% As and 10-30 ppm Cl, also known as stabilized a-Se. The suitability of the stabilized a-Se is largely determined by its charge on generating, transporting and trapping properties.In this paper, a conventional time-of-flight measurement was carried out to analyze the transport properties of charge carriers. A laser beam with pulse duration of 5 ns and wavelength of 350 nm was illuminated on the surface of the stabilized a-Se with thickness of 400 μm. The photo response signals of the hole and electron were measured at the applied electric field of 10 V/μm as a function of time. The measured transit times of the hole and electron were about 229.17μs and about 8.73μs at 10 V/μm, respectively. The measured mobility indicated a slight dependence with respect to the applied electric field with a range of 4-10 V/μm. The experimental results showed that the measured mobility of the hole and electron was 0.04584 cm2V-1s-1 and 0.00174 cm2V-1s-1 at the electric field of 10 V/μm.
Effects of Pre-Process Temperature Stressing on AlGaN/GaN HEMT Structures
Authors: Yannuzzi Mark J. , Moser Neil A. , Fitch Robert C. , Jessen Gregg H. , Gillespie James K. , Via Glen D. , Crespo Antonio , Jenkins Thomas J. , Look David C. , Reynolds Donald C. 
Published: June 2019

AbstractIn an effort to investigate the stability of the surface and hetero-interface of AlGaN/GaN HEMTs during high temperature device processing steps, AlGaN/GaN HEMT samples were subjected to temperatures from 650°C to 1150°C for a period of 30 seconds prior to processing. Hall and photoluminescence measurements were performed on samples before and after temperature stressing. The samples annealed at 700°C and 1150°C were then processed, and electrical parametric data were collected during and after processing. Large increases in HEMT Schottky gate diode reverse leakage current are observed at higher pre-process annealing temperatures, while the low-field mobility decreases.
Surface Acoustic Waves And Guided Optical Waves In AlGaN Films
Authors: Bu Gang , Ciplys Daumantas , Shur Michael , Gaska Remis , Fareed Qhalid , Rimeika Romualdas , Yang Jinwei , Khan Asif 
Published: June 2019

AbstractAlxGa1-xN layers grown by MOCVD on sapphire substrates have been tested using the surface acoustic wave and guided optical wave techniques. Samples with molar fraction of Al up to 0.36 have been investigated. The parameters S11 of single surface acoustic wave transducers and S12 of two-port devices have been measured with the network analyzer. The values of the surface acoustic wave velocity and electromechanical coupling coefficient for the layer-substrate structure have been extracted and calculated using material parameters available from literature. The attenuation of guided optical waves along the propagation track in AlxGa1-xN layers has been measured using the CCD imaging technique. The attenuation dependence on the mode order and layer thickness has been studied. Our results show that the properties of AlxGa1-xN that determine surface acoustic wave and guided optical wave propagation are similar to the properties of GaN films within a relatively wide range of x up to x =0.36.
Cathodoluminescence Study of Gadolinium–Doped Yttrium Oxide Thin Films Deposited By Radio–Frequency Magnetron Sputtering
Authors: Fowlkes J. D. , Rack P. D. , Bansal R. , Fitz–Gerald J.M. 
Published: June 2019

AbstractA multi–layer gadolinium–doped yttrium oxide thin film was deposited in a combinatorial fashion on a Si (001) substrate using radio–frequency magnetron sputtering. Alternating layers of Y2O3 and Gd were deposited for a total of 9 layers. The film was homogenized in composition by an 850°C 12 hour thermal treatment producing a range of composition from Y1.96Gd0.04O3-Y1.54Gd0.46O3 in a single film. Ultraviolet emission with a peak wavelength at 314-315nm was observed from the gadolinium 8S7/2 - 6P7/2 transition via cathodoluminescence (CL) excitation. The CL–induced intensity was found to be maximum at 9 at% Gd (Y1.82Gd0.18O3) and an optimized electron probe of Vacc = 13 keV was determined for the 1 μm thick thin film. Gadolinium activator saturation was observed for sample current density greater than 0.03 μA/cm2. Non- radiative decay via thermal pathways is suspected for the observed activator saturation.
Large Area 6H- and 4H-SiC Photoconductive Switches
Authors: Doğan S. , Yun F. , Roberts C.B. , Parish J. , Huang D. , Myers R. E. , Smith M. , Saddow S. E , Ganguly B. , Morkoç H. 
Published: June 2019

AbstractPhotoconductive Semiconductor Switches (PCSS) were fabricated in planar structures on high resistivity 4H-SiC and conductive 6H-SiC and tested at DC Bias voltages up to 1000 V. The gap spacing between the electrodes is 1 mm. The average on-state resistance and the ratio of on-state to off-state currents were about 20 Ω and 3×1011 for 4H-SiC, and 60 Ω and 6.6×103 for 6H-SiC, respectively. The typical maximum switch current at 1000 V is about 49 A for 4H-SiC. Photoconductivity pulse widths for all applied voltages were 8-10 ns. The observed performance is due in part to the removal of the surface damage by high temperature H2 etching and surface preparation. Atomic Force Microscopy (AFM) images revealed that very good surface morphology, atomic layer flatness and large step widths were achieved with this surface treatment and these atomically smooth surfaces likely contributed to the excellent switching performance of these devices.
Molecular Dynamics Simulations of Nucleation and Crystallization Processes During Excimer-Laser Annealing of Amorphous Silicon on Glass
Authors: Motooka T. , Munetoh S. , Min Lee Byoung , Nisihira K. 
Published: June 2019

AbstractWe have investigated atomistic processes of nucleation and crystallization in excimer-laser annealed thin Si films on glass based on molecular-dynamics (MD) simulations using the Tersoff potential. MD cells composed of up to approximately 50000 Si atoms were heated to produce melted Si, and then melted Si was quenched under various supercooled conditions with or without a temperature gradient and the corresponding nucleation processes were visualized. Lateral growth of thin Si crystalline films was also simulated by embedding a crystalline nano-particle with various crystal surfaces in melted Si. It has been found that the crystal surfaces become predominantly {111} during the lateral growth processes.
Production of III-V Nanocrystals by Picosecond Pulsed Laser Ablation
Authors: Wu M. H. , Mu R. , Ueda A. , Henderson D. O. 
Published: June 2019

AbstractIn As nanoparticles have been produced by picosecond pulsed laser ablation of bulk targets in the presence of an inert backing gas. Atomic force microscopy measurements show particles ranging in size from one to ten nm. Stoichiometry of the targets, determined by Rutherford backscattering measurements, are typically preserved within ten percent. Optical absorption and raman scattering data help confirm the crystalline, quantum confined nature of the nanoparticles.
Synthesis of Photosensitive Organic-Inorganic Hybrid Polymers via Anhydrous Sol-Gel Process for Integrated Optics
Authors: Luo Xinshi , Zha Congji , Luther-Davies Barry 
Published: June 2019

AbstractPhotosensitive organic-inorganic hybrid polymers were synthesised for integrated optical and optoelectronic devices by a non-hydrous sol-gel process of hydrolysis/condensation of 3-methacryloxypropyltrimethoxysilane (MPS), diphenyldimethoxysilane (DPhDMS), and zirconium isopropoxide (TPZ) with boric acid under anhydrous conditions. The methacryl groups of MPS are UVpolymerizable, which are suitable for low cost fabrication of waveguides with a “UV write/develop” process. The incorporation of DPhDMS and TPZ was found useful in reducing the optical loss and in enhancing the thermostability of the polymer. The refractive index of the hybrid polymer is tuneable from 1.4950 to 1.5360 by variation of the ratio among MPS, DPhDMS and TPZ. Optical characterisation showed that the material has low optical losses at the telecommunications windows (0.16 dB/cm at 1310 nm and 0.4 dB/cm at 1550nm). The hybrid polymer also showed a low birefringence (1.2×10-4), a large thermo-optic (TO) coefficient (-2.77 ×10-4), and an outstanding linearity of dn/dT in a wide range of temperature (from 25 °C to 200 °C). Waveguides forming ability for the hybrid polymer with UV imprinting was also demonstrated.
Factors Influencing the Lithium Extraction Rate in Layered Oxide Cathodes of Lithium Ion Cells
Authors: Manthiram A. , Choi J. 
Published: June 2019

ABSTRACTThe lithium extraction rate and the rate capability of layered LiNi0.5–0.5yMn0.5–0.5yCoyO2 with 0 ≤ y ≤ 1 have been investigated, respectively, by chemically extracting lithium with the oxidizer NO2BF4 in acetonitrile medium and electrochemically discharging at various C-rates. Both the chemical lithium extraction rate and the electrochemical rate capability are found to increase with increasing Co content y in LiNi0.5–0.5yMn0.5–0.5yCoyO2. While no clear relationship is seen between electrical conductivity and the rate capability, increasing cation disorder between the lithium and transition metal planes with decreasing Co content is found to decrease the chemical lithium extraction rate and rate capability. The lithium extraction rate also influences the structure (P3 vs O1 vs O3) of the end members Ni0.5–0.5yMn0.5–0.5yCoyO2-δ obtained by extracting all the lithium with 100 % excess NO2BF4 in an acetonitrile medium.
Transient and Steady-State Radionuclide Transport Through Penetrations in Nuclear Waste Containers
Authors: Chambre P. L. , Lee W. W.-L. , Kim C. L. , Pigford T. H. 
Published: June 2019

AbstractIn this paper we analyze the transport of radionuclides through penetrations in nuclear waste containers. Penetrations may result from corrosion or cracks and may occur in the original container material, in degraded or corroded material, or in deposits of corrosion products. We do not consider how these penetrations occur or the characteristics of expected penetrations in waste containers. We are concerned only with the analytical formulation and solutions of equations to predict rates of mass transfer through penetrations of specified size and geometry. Expressions for the diffusive mass transfer rates through apertures are presented. We present numerical illustrations for steady-state mass-transfer rates through a circular hole, including concentration isopleths. The results are extended to multiple holes, including a criterion for hole spacing wherein superposition of single-hole solutions can be used. Results illustrated for holes in thin-walled containers show that significant mass transfer can occur even if a small fraction of the container area is perforated. We also illustrate the case of holes facing a water gap, instead of being in intimate contact with porous rock. In this case the radionuclide flux from many small holes approaches that from a bare waste cylinder.
Evaluation of the Susceptibility of Astm A216 Grade Wca Mild Steel to Stress Corrosion Cracking in Simulated Salt Repositopy Environments
Authors: Pitman S. G. 
Published: June 2019

AbstractIn current conceptual designs, a mild steel (ASTM A?16 Grade WCA) is the relerence container material for use in high level nuclear waste packages intended for emplacement in a salt repository. The resistance of the steel to stress corrosion crackinq (SCC) is being investigated as part of the effort underway to verify the suitability of the material for waste package applications. Static tests (U-bend and bolt-loaded fracture toughness specimens) and dynamic tests (slow strain rate and corrosion fatigue) were conducted on both as-cast and weldment specimens of the material, in both low-Mg and high-Mg halite-saturated brines, in the temperature range of 90 to 200°C. The investigations indicate that the steel is not susceptible to SCC under the test conditions employed.
Materials Interactions Relating to Long-Term Geologic Disposal of Nuclear Waste Glass
Authors: Bibler Ned E. , Jantzen Carol M. 
Published: June 2019

AbstractIn the geologic disposal of nuclear waste glass, the glass will eventually interact with groundwater in the repository system. Interactions can also occur between the glass and other waste package materials that are present. These include the steel canister that holds the glass, the metal overpack over the canister, backfill materials that may be used, and the repository host rock. This review paper systematizes the additional interactions that materials in the waste package will impose on the borosilicate glass waste form-groundwater interactions. The repository geologies reviewed are tuff, salt, basalt, and granite. The interactions emphasized are those appropriate to conditions expected after repository closure, e.g. oxic vs. anoxic conditions. Whenever possible, the effect of radiation from the waste form on the interactions is examined. The interactions are evaluated based on their effect on the release and speciation of various elements including radionuclides from the glass. It is noted when further tests of repository interactions are needed before long-term predictions can be made.
Transport and Reaction Kinetics at the Glass:Solution Interface Region: Results of Repository-Oriented Leaching Experiments
Authors: Abrajano Teofilo A. , Bates John K. 
Published: June 2019

AbstractRepository-oriented leaching experiments involving Savannah River Laboratory (SRL) 165 type glass under a γ-radiation field (1= 0.2 × 104 R/h) have been performed by the Nevada Nuclear Waste Storage Investigations (NNWSI) project. In this communication, we discuss glass surface analyses obtained by SEM, nuclear resonance profiling, and SIMS together with leachate solution data in relation to a mechanism that couples diffusion, hydrolysis (etching and gelation), and precipitation to qualitatively describe the release of different glass components to the leachant solutions. The release of mobile (e.g., Li) and partly mobile (e.g., B) species is controlled primarily by interdiffusion with water species across the interdiffusion zone. Glass components that are immobile in the interdiffusion zone are released to the solution by etching. For prediction of long-term steady-state concentrations of glass components with low solubility, the relative rates of release from the glass and secondary mineral precipitation must be taken into account.