bluuebunny/crossref_metadata_2025_split huggingface dataset:
Challenges for High Temperature Silicon Carbide Electronics
Authors: Zetterling C.-M. , Koo S.-M. , Danielsson E. , Liu W. , Lee S.-K. , Domeij M. , Lee H.-S. , Ostling M. 
Published: June 2019

AbstractSilicon carbide has been proposed as an excellent material for high-frequency, high-power and high-temperature electronics. High power and high frequency applications have been pursued for quite some time in SiC with a great deal of success in terms of demonstrated devices. However, self-heating problems due to the much higher power densities that result when ten times higher electrical fields are used inside the devices needs to be addressed. High-temperature electronics has not yet experienced as much attention and success, possibly because there is no immediate market. This paper will review some of the advances that have been made in high-temperature electronics using silicon carbide, starting from process technology, continuing with device design, and finishing with circuit examples. For process technology, one of the biggest obstacles is long-term stable contacts. Several device structures have been electrically characterized at high temperature (BJTs and FETs) and will be compared to surface temperature measurements and physical device simulation. Finally some proposed circuit topologies as well as novel solutions will be presented.
Statistical Analysis of Micropipe Defect Distributions in Silicon Carbide Crystals
Authors: Elkington Troy , Emorhokpor Ejiro , Kerr Tom , Chen John , Essary Kevin , Golab Mike , Hopkins Richard H. 
Published: June 2019

AbstractThe density and distribution of micropipes (MPD's), a screw dislocation with a hollow core, are significant criteria for SiC wafer selection in device fabrication. For this reason the measurement of micropipes in SiC is an important problem. The micropipe distributions of 2’’ diameter 6H SiC wafers from three different PVT furnace designs in three different laboratories were statistically characterized. The micropipe distributions were measured in two ways: by KOH etching the wafer and then counting the hexagonal pits formed on the wafer surface using a microscope and imaging software; and by manually counting with an optical transmission microscope the micropipes on a un-etched wafer within a grid of 0.5mm squares superimposed over the wafer. None of the wafers had a random distribution of micropipes i.e. they did not follow a Poisson distribution. The micropipes were found to associate with each other i.e. there is a higher probability of there being other micropipes near a location where a micropipe has been found. In the eight samples characterized, 1.9% of the wafer area contained 32% of the total micropipes. We have analyzed the repeatability of the optical transmission microscopy method of micropipe characterization and found that it is dependent on the micropipe density; the standard deviation of the measurement increases with increasing MPD. The number of micropipes counted increases by about 10% with increasing magnification and 15% when the wafer is double side polished.
Characterization of High Quality Continuous GaN Films Grown on Si-Doped Cracked GaN Template
Authors: Soh C. B. , Zhang J. , Chi D.Z. , Chua S. J. 
Published: June 2019

AbstractIn this paper, deep level defects in high quality continuous GaN films grown over a cracked Si-doped GaN template has been studied using digital deep level transient spectroscopy (DLTS) and transmission electron microscopy (TEM). From TEM observation, it is found that the density of pure screw dislocations have been effectively suppressed while pure edge dislocations remained in substantial quantity. From DLTS measurement, trap levels at Ec -ET ∼ 0.11-0.12 eV, 0.24-0.27 eV, 0.60-0.63 eV were detected in the high quality GaN layer. DLTS measurement was also carried out on the underlying cracked Si-doped GaN template after the top high quality continuous GaN film was removed by plasma etching. An additional defect level at Ec-Et ∼ 0.37 eV was detected which we attributed to defect decoration at screw dislocation. Both the trap levels Ec-ET ∼ 0.24–0.27 eV, 0.60-0.63 eV are believed to originate from mixed screw/edge dislocation based on observation of the logarithmic capture behavior. Trap level at Ec -ET ∼ 0.24-0.27eV, however, experiences a more drastic increase in transient capacitance (i.e. in trap concentration) compared to that of Ec -ET ∼ 0.60-0.63 eV after plasma etching, illustrating that the latter is related to a higher proportion of edge dislocation. The 0.11-0.12 eV trap level, which exhibits an exponential capture kinetic, is believed to be related to nitrogen vacancies. This high quality continuous GaN layer can be used as a template to grow any device structure and the underneath cracked Si-doped GaN layer may help to release stress for the top continuous GaN layer. This can bring about a cracked free epilayer for subsequent device fabrication.
Modeling of Nitride Semiconductor Based Double Heterostructure Tunnel Diodes
Authors: Moret M. , Ruffenach S. , Briot O. , Aulombard R.L. 
Published: June 2019

AbstractDouble heterostructure diodes were widely studied in the 80's, based on the use of “classical” III-V materials, i.e. based on (Ga, Al, In, As, P). Negative differential conductivities were predicted in these systems, making them highly interesting for hyperfrequency applications, but experimental results were always far from theoretical predictions, which resulted in a loss of interest for these systems. Recently, there has been a lot of efforts devoted to Nitride semiconductors, based on (Al,Ga,In)N alloys. These materials have been regarded as potential candidates for high frequency, high power applications, since they both exhibit high electron saturation velocities and high thermal and chemical stability. Moreover, although they usually contain a lot of growth defects, device properties were surprisingly good with regards to defect densities. In this work, we have modeled double heterostructure tunnel diodes based on AlGaN/GaN system. The extremely high conduction band offset in these materials, along with the quite low dielectric constants, and built-in electric fields (originating from both the spontaneous and piezoelectric polarization), are extremely favorable parameters, which may renew the interest for such devices in this material system. It will be shown that the built-in electric field leads to a symmetric potential profile under a given external applied bias, which optimizes the transmission coefficient in the structure. We have calculated extremely high peak/valley ratios, which suggests that even mid quality samples could still exhibit interesting device properties.
ZnO Thin Films Grown at Various Substrate Angles by Pulsed Laser Deposition
Authors: Kang Jeong Seok , Kang Hong Seong , Kim Jae Won , Lee Sang Yeol 
Published: June 2019

AbstractZnO thin films were grown with different plume-substrate angles and growth times by pulsed laser deposition. The angles between plume propagation direction and substrate plane were changed from 0°, 45° to 90°. The growth time was changed in order to adjust film thickness. From the XRD pattern exhibiting dominant (002) XRD peak of ZnO, all films were found to be c-axis oriented. Optical property of ZnO thin films were investigated by PL(Photoluminescence). The ratio of UV/green luminescent intensity of ZnO thin film increased, as the angle between plume and substrate plane decrease from 90° to 0°.
Atomic and Electronic Structure of Boron-Doped Diamond Grain Boundaries Studied by Arhvtem and ab-Initio Calculation
Authors: Togawa Hiroyuki , Ichinose Hideki 
Published: June 2019

AbstractAtomic resolution high-voltage transmission electron microscopy and electron energy loss spectroscopy were performed on grain boundaries of boron-doped diamond, cooperated with the ab-initio calculation. Segregated boron in the {112}∑3 boundary was caught by the EELS spectra. The change in atomic structure of the segregated boundary was successfully observed from the image by ARHVTEM. Based on the ARHVTEM image, a segregted structure model was proposed.
The Shallow Implantation of Bismuth During the Growth of Bismuth Nanocrystals in Al2O3 by Pulsed Laser Deposition
Authors: Suárez-García A. , Barnes J-P. , Serna R. , Petford-Long A. K. , Afonso C. N. , Hole D. 
Published: June 2019

AbstractThe effect of the laser energy density used to deposit Bi onto amorphous aluminum oxide (a-Al2O3) on the growth of Bi nanocrystals has been investigated using transmission electron microscopy of cross section samples. The laser energy density on the Bi target was varied by one order of magnitude (0.4 to 5 J cm-2). Across the range of energy densities, in addition to the Bi nanocrystals nucleated on the a-Al2O3 surface, a dark and apparently continuous layer appears below the nanocrystals. Energy dispersive X-ray analysis on the layer have shown it is Bi rich. The separation from the Bi layer to the bottom of the nanocrystals on top is consistent with the implantation range of Bi species in a-Al2O3. As the laser energy density increases, the implantation range has been measured to increase. The early stages of the Bi growth have been analyzed in order to determine how the Bi implanted layer develops.
Unique Functional Micro/nano-structures Created by Femtosecond Laser Irradiation
Authors: Hong M.H. , Huang S.M. , Wang W.J. , Tiaw K.S. , Teoh S.H. , Luk'yanchuk B. , Chong T.C. 
Published: June 2019

AbstractFemtosecond (fs) laser application in three-dimensional (3D) optical recording is introduced. The laser irradiation on transparent glass and polymer matrix doped with fluorescent material is carried out, which changes the physical or chemical properties of the recording media and records information bits. With the change of the focusing positions inside the transparent substrates, 3D optical recording can be available for ultrahigh capacity data storage. Feasibility on fs laser drilling of poly-caprolactone (PCL) thin films for tissue engineering is investigated. It is found that precisely defined micro-hole arrays can be formed on the sample surfaces. Hydrophilic property of the processed samples is much improved, which provides good conditions for tissue cells to anchor on the man-made skin. Fs laser applications to form nanostructures on substrate surfaces are studied. Fs laser combination with near-field scanning optical microscopy (NSOM) to induce surface property modification in the sub 50-nm under NSOM tip and nanoparticles is also discussed.
Nonlinear Optical Spectroscopy of Cadmium Chalcogenide Nanocrystals
Authors: Seo J.T. , Yang Q. , Creekmore S. , Mangana J. , Anderson J. , Pompey C. , Temple D. , Peng X. , Qu J. L. , Yu W. , Wang A. , Jung S. , Ruh H. , Mott A. , Namkung M. 
Published: June 2019

AbstractWe report on the nonlinear optical properties of cadmium telluride (CdTe) semiconductor colloidal quantum dots. Transmission electron microscopy measurements revealed that the size of CdTe nanocrystal quantum dots, dependent on the growth reaction time, was ∼2-10 nm or near the exciton Bohr radius. The strong blue-shifts of the CdTe, CdSe and CdS nanocrystal absorption spectra and the atomic-like discrete energy states of exciton indicate an exciton quantum confinement. These are completely different optical properties from the bulk crystals. The energy transition for exciton absorption was assigned as h1→e+, h2→e+, h1+→e-, and h2+→e- for the 1st, 2nd, 3rd and 4th exciton absorption peaks. Z-scan and I-scan nonlinear spectroscopy revealed that the CdTe nanocrystal quantum dot in toluene (∼8 × 10-5 mol/L) has the negative nonlinearity (self-defocusing) with ∼ -1 × 10-13 m2/W and a high nonlinear figure of merit of ∼200. For the optical power self-limiting experiment, the CdTe nanocrystal was almost opaque above ∼0.8 MW/cm2 at the position of z∼6.9 cm.
Oblique-incidence Reflectivity Difference (OI-RD) and Leed Studies of Adsorption and Growth of Xe on Nb(110)
Authors: Thomas P. , Nabighian E. , Bartelt M.C. , Fong C.Y. , Zhu X.D. 
Published: June 2019

AbstractWe studied adsorption, growth and desorption of Xe on Nb(110) using an in-situ obliqueincidence reflectivity difference (OI-RD) technique and low energy electron diffraction (LEED) from 32 K to 100 K. The results show that Xe grows a (111)-oriented film after a transition layer is formed on Nb(110). The transition layer consists of three layers. The first two layers are disordered with Xe-Xe separation significantly larger than the bulk value. The third monolayer forms a close packed (111) structure on top of the tensile-strained double layer and serves as a template for subsequent homoepitaxy. The adsorption of the first and the second layers are zeroth order with sticking coefficient close to one. Growth of the Xe(111) film on the transition layer proceeds in a step flow mode from 54K to 40K. At 40K, an incomplete layer-by-layer growth is observed while below 35K the growth proceeds in a multilayer mode.
Ultrafast Pulsed Laser Deposition of Chalcogenide Glass Films for Low-loss Optical Waveguides
Authors: Luther-Davies B. , Kolev V. Z. , Lederer M. J. , Yinlan R. , Samoc M. , Jarvis R. A. , Rode A. V. , Giesekus J. , Du K.-M. , Duering M. 
Published: June 2019

AbstractUltra-fast pulsed laser deposition using high-repetition-rate short-pulse lasers has been shown to provide high optical quality, super smooth thin films free of scattering centres. The optimized process conditions require short ps or sub-ps pulses with repetition rate in the range 1-100 MHz, depending on the target material. Ultra-fast pulsed laser deposition was used to successfully deposit atomically-smooth, 5micron thick As2S3 films. The as-deposited films were photosensitive at wavelengths close to the band edge (≈520 nm) and waveguides could be directly patterned into them by photo-darkening using an Argon ion or frequency doubled Nd:YAG laser. The linear and nonlinear optical properties of the films were measured as well as the photosensitivity of the material. The optical losses in photo-darkened waveguides were <0.2 dB/cm at wavelengths beyond 1200nm and <0.1 dB/cm in as-deposited films. The third order nonlinearity, n2,As2S3, was measured using both four-wave mixing and the z-scan technique and varied with wavelength from 100 to 200 times fused silica (n2,Silica ≈3×10-16 cm2/W) between 1500nm and 1100nm with low nonlinear absorption.Encouraged by the Ultrafast laser deposition results, we have built a new specialized modelocked picosecond laser system for deposition of optical films and for laser formation of nanoclusters. The newly developed “state of the art” powerful Nd:YVO laser can operate over a wide range of wavelengths, intensities, and repetition rates in MHz range. A brief description of the 50W laser installation is presented.
Pulsed Laser Processing of Metals and Semiconductors in Reactive Atmospheres: Laser Nitriding and Carburizing
Authors: Carpene Ettore , Schaaf Peter 
Published: June 2019

AbstractHard surface coatings and thin layers can be synthesized by irradiating pure substrates with short laser pulses in reactive atmospheres. Various lasers with different pulse durations τ and wavelengths λ can be used for this purpose: XeCl excimer laser, Nd-YAG laser, free electron laser and Ti:sapphire laser. The irradiation of materials such as aluminum, iron and silicon in controlled nitrogen and methane atmospheres leads to surface modifications (e.g. hardness improvement) and to the formation of homogeneous coatings. The evolution of the surface properties (phase formation, hardness) as well as the mass transport mechanisms during the laser irradiation have been studied in detail as a function of the experimental parameters (laser fluence, ambient gas pressure, number of laser shots) for the Excimer Laser treatments. The formation of homogeneous AlN layers after irradiation of aluminum substrates in N2 atmosphere, the synthesis of homogeneous cementite coatings after irradiation of iron substrates in CH4 atmosphere and the successful incorporation of carbon after irradiation of (100) and (111) silicon single crystals in methane gas will be reported.
Self-Limited Photo-Assisted Synthesis of Silicon Nanocrystals
Authors: Chen C. Y. , Kimura S. , Sen S. , Nozaki S. , Ono H. , Uchida K. , Morisaki H. 
Published: June 2019

ABSTRACTAnomalous growth of silicon (Si) nanocrystals (NCs) was observed during Raman scattering measurements of nanosilica SiOx (x=0.9) powder with an average diameter of 40 nm. It was found that Si NCs were formed by exposure to the laser beam. This photo-assisted synthesis is similar to the thermal synthesis of Si NCs, which forms Si NCs by thermally decomposing SiOx into Si and SiO2. However, the photo-assisted synthesis is more effective in forming Si NCs than the thermal synthesis. Even one second after irradiation of the nanosilica SiOx powder with laser, Si NCs with an average size of 5 nm were formed. The Si NC size increases with increasing the laser power and exposure time. It is interesting to observe a self-limited size for higher laser power and prolonged exposure. The photo-assisted synthesis of Si NCs is proved to be a promising technique with a wide range of applications in nanotechnology.
Radiation Induced Dissolution of UO2
Authors: Christensen Hilbert , Bjergbakke Erling 
Published: June 2019

AbstractA model for the radiation induced dissolution of U02has been developed and tested using experiments described in the literature. The model makes use of computer calculations based on a reaction mechanism in which the dissolution is initiated by reactions of H202, OH and H02 radicals with the U02surface. The model gave a fair agreement between calculated and experimental results: For a dose rate of 400 rad/s the calculated yields of oxidation were 2.6 and 2.1 % - h−1· m−2after 1 and 2 h, respectively. The corresponding experimental yields were 1.9 and 1.5 % ·h−1· m−2, when corrected for dissolution without irradiation. The effect of various initial concentrations of H202has been tested, and a reasonable rate constant for the reaction of U02and H202has been found. The requirement for the rate constant is that H202begins to be effective above concentrations of 10−3 mol · dm−3in accordance with experiments by L. Johnson.
The Determination of the Solubility of Amorphous UO2 (Sn and the Mononuclear Hydrolysis Constants of Uranium(IV) at 25° C.
Authors: Bruno Jordi , Casas Ignasi , Lagerman Bo , Munoz Maria 
Published: June 2019

AbstractWe have measured the solubility 8f amorphous UO2in a wide pH range (2 to 10.5), in 0.5 M NaClO, at T=25 C. The species responsible for the solubility are U(OH) + and U'0H)h, with the stability constants lo:1,3=-1.1± 0.1 and log, 4 =- 5.4_.O. 2, respectively. No evidence for U(OH) is f6und up to pH=10.5. The same model explains satisfactorily the solubility data obtained by Parks and Pohl(5) at T=1000 C., in the pH range 1 to 10. The measured solubility of amorphous UO2 (s) in the pH_ýange 6 to 10.5, under reducing conditions, is rather high,. U(IV) =5 10 mols/l. This is in good agreement with previous data of Gayer and Leider(6) and Galkin and Stepanov(9).
Carbon-14 in Waste Packages for Spent Fuel in a Tuff Repository
Authors: Konynenburg R. A. Van , Smith C. F. , Culham H. W. , Smith H. D. 
Published: June 2019

AbstractCarbon-14 is produced naturally by cosmic ray neutrons in the upper atmosphere. It is also produced in nuclear reactors, in amounts much smaller than the global inventory. About one-third of this is released directly to the atmosphere, and the other two-thirds remains in the spent fuel. Both the Environmental Protection Agency and the Nuclear Regulatory Commission have established limits on release of the 14C in spent fuel. This is of particular concern for the proposed repository in tuff, because of the unsaturated conditions and the consequent possibility of gaseous tansport of 14C as CO2Existing measurements and calculations of the 14C inventory in spent fuel are reviewed. The physical distribution and Wemical forms of the 14C are discussed. Available data on the release of 14C from spent fuel in aqueous solutions and in gaseous environments of air, nitrogen, and helium are reviewed. Projected N behavior in a tuff repository is described. It is concluded that 14C release measurements from spent fuel into moist air at temperatures both above and below the in situ boiling point of water as well as detailed transport calculations for the tuff geological environment will be needed to determine whether the IOCFR60 and 40CFR191 requirements can be met.
Statistical issues in Pitting Corrosion of Carbon Steel
Authors: Mcneil M. B. 
Published: June 2019

AbstractA review is given of the state of understanding of the statistical distributions of pit depths and pit populations in carbon steel, with special reference to underground carbon steel structures, which appear to bear significant similarities to the alloys and conditions expected in basalt and salt high level waste repositories.The data base on pit depth distributions is reviewed and the various phenomenological equations which have been used to rationalize laboratory and field observations are discussed and classified in terms of the statis- tical models underlying them. The present state of understanding of the physical phenomena underlying these distributions is reviewed, and sugges- tions for appropriate future research are presented.
Metal-Matrix Corrosion Studies in Canadian Shield Granitic Groundwaters
Authors: Mathew P. Mani , Krueger Paul A. 
Published: June 2019

AbstractThe Canadian Nuclear Fuel Waste Management program is evaluating two basic supported-shell container concepts for used-fuel immobilization.One concept uses a compacted particulate material within the container to sunport a thin, corroston-resistant shell. The other concept, called “the metal-matrix concept”, uses a cast-in-place metal matrix for shell support.This paper describes corrosion studies on the candidate matrix materials, lead, zinc and aluminum-7 wt.7 Si (A1-7 wt.7 Si), in the temperature range 293 to 423 K and the dissolved oxygen content range 8 to 410 mg/L. Test specimens were analyzed for general and localized corrosion and the corrosion products were identified.The results showed that, unlike lead, zinc and Al-7 wt.% Si are susceptible to localized corrosion. Lead showed only low general corrosion rates of 2 to 83 pm/a compared with zinc (36 to 15800 μm/a) and Al-7 wt.% Si (6 to 209 μm/a) in the above temperature and oxygen content ranges. Maximum pit depths of about 0.9 mm on Al-7 wt.% Si and 0.6 mm on zinc were observed. These results indicate that, of the candidate matrix metals studied, lead has the greatest potential to retard radionuclide release from used-fuel disposal containers.