bluuebunny/crossref_metadata_2025_split huggingface dataset:
Binary Synaptic Connections Based on Memory Switching in a-Si:H for Artificial Neural Networks
Authors: Thakoor A. P. , Lamb J. L. , Moopenn A. , Khanna S. K. 
Published: March 2011

AbstractNonvolatile, associative electronic memory based on neural network models promises high (−109 bits/cm2 ) information storage density since the information is stored in a matrix of only two-terminal, passive interconnections (synapses). An electronic memory switch at each interconnect would be ideal as a programmable synapse. The massive parallelism in the architecture, however, requires that the ‘ON’ state of a synaptic connection must be unusually ‘weak’ (i.e., highly resistive). For example, a binary synapse should be 106Ω in its ‘ON’ state and >109Ω in the ‘OFF’ state for a 1024 × 1024 matrix (−256 K bits of programmable read only memory, PROM). The small deliverable switching energy dictated by the resistive ‘ON’ state requirement is a new constraint for switching in thin films. Memory switching in hydrogenated amorphous silicon (a-Si:H) along with ballast (current limiting) resistors patterned from resistivity-tailored, amorphous Ge-metal alloys are investigated for a binary PROM matrix. A lμm2 area of a-Si:H could be switched from a −1010Ω (OFF state) to −105Ω (ON state) by a voltage pulse of lpsec duration, with the switching energy of −1 nanojoule, delivered through a 106Ω ballast resistor. Programmable, read-only, 1600 synapse (40x40) test arrays of uniform connection strengths (variation ±2%) and a-Si:H switching elements have been fabricated. Suitability of the memory switching in a-Si:H for high-density neural networks is discussed.
Preparation of Boron-Rich Refractory Semiconductors
Authors: Aselage T. L. 
Published: March 2011

ABSTRACTBoron-rich refractory solids based on the rhombohedral structure of α-B exhibit electrical properties that range from a hopping-type semiconductor (boron carbide) to wide bandgap room temperature insulators (the boron pnictides B6P and B6As). As such, they are of interest for a variety of high temperature semiconductor applications. Preparation techniques for these unusual materials are reviewed, and new results on the crystal growth of boron carbides and B6As and on thin film deposition of B6P are presented.
On the Pressureless Sintering of Lanthanum Hexaboride Materials
Authors: Knoch Heinrich , Lipp Alfred 
Published: March 2011

ABSTRACTLaB6 powders of a particle size less than 2 μm can readily ge sintered to nearly pore free microstructures, when boron and carbon are used as additives. The microstructure consists of LaB6 B4C and C as seperate, finely divided phases. The preparatton of starting powders, the sintering process, and the resulting microstructures are discussed.
Silicon Carbide: Progress in Crystal Growth
Authors: Powell J. Anthony 
Published: March 2011

ABSTRACTSilicon carbide (SiC), with a favorable combination of semiconducting and refractory properties, has long been a candidate for high temperature semiconductor applications. Research on processes for producing the needed large-area high quality single crystals has proceeded sporadically for many years. Two characteristics of SiC have aggravated the problem of its crystal growth. First, it cannot be melted at any reasonable pressure, and second, it forms many different crystalline structures, called polytypes. Recent progress in the development of two crystal growth processes will be described. These processes are the modified Lely process for the growth of the alpha polytypes (e.g. 6H SiC), and a process for the epitaxial growth of the beta polytype (i.e. 3C or cubic SiC) on single crystal silicon substrates. A discussion of the semiconducting qualities of crystals grown by various techniques will also be included.
Highly Mismatched Hetero-Epitaxial Growth of Cubic Sic on Si
Authors: Matsunami Hiroyuki 
Published: March 2011

ABSTRACTSingle crystals of cubic SiC were hetero-epitaxially grown on Si by chemical vapor deposition (CVD) method. A carbonized buffer layer on Si is utilized to overcome the large lattice mismatch of 20 %. Optimum conditions to make the buffer layers and those structures are discussed. Crystal quality of the CVD grown cubic SiC is analyzed by using X-ray analyses and microscopic observations. Electrical properties controlled by impurity doping during epitaxial growth are described together with fundamental electronic devices.
Beta Silicon Carbide Growth with Device Applications
Authors: Harris G. L. , Spencer M. G. , Jackson K. , Jones A. , Osborne K. , Fekade K. , Wongchotigul K. 
Published: March 2011

ABSTRACTEpitaxial thin films of cubic-SiC (100) have been grown at temperatures ranging from 1340–1400°C by using a reduced pressure chemical vapor deposition system. In this work, we will report on the doping of SiC using trimethylalumium (TMA), phosphine, and nitrogen. The electrical measurements on the SiC layers have been performed (Hall, CV, DLTS, etc.) and will be discussed in reference to SiC MESFETs and other SiC device structures.
Investigation on the Gap Density of States in Amorphous Semiconducting Carbon Silicon and Carbon Tin Alloys
Authors: Mpawenayo P. , Nsabimana M. 
Published: March 2011

ABSTRACTThe density of states in a-Six C1-x:H and a-Cy Sn1-y:H (F) semiconducting materials has been investigated by phototheTmal deflection spectroscopy (PDS) and their photoconductive properties have been related to the gap states distribution parameters, the Urbach energy Eo and the localized states density gm. We found that an Eo of 200 meV is the highest value above which no photoconductivity can be detected. This threshold corresponds to a density of gap states of about 1019 eV−1 cm−3 for optical gaps ranging between 1.1 and 2.5eV. Fourier spectral analysis of the long photoresponse decay time observed in our fluorinated a-Cy, Sn1-y samples shows the existence of well defined trapping levels and randomly distributed defect states.
Electronic Transport Properties of Hot-Pressed B6Si
Authors: Wood C. , Emin D. , Feigelson R. S. , Mackinnon I. D. R. 
Published: March 2011

ABSTRACTMeasurements of the electrical conductivity, Seebeck coefficient and Hall mobility from -300 K to -1300 K have been carried out on multiphase hotpressed samples of the nominal composition B6Si. In all samples the conductivity and the p-type Seebeck coefficient both increase smoothly with increasing temperature. By themselves, these facts suggest small-polaronic hopping between inequivalent sites. The measured Hall mobilities are always low, but vary in sign. A possible explanation is offered for this anomalous behavior.
Thermoelectric Properties of SmSl−xAsx Alloys
Authors: Danielson L. R. , Alexander M. N. , Lockwood R. A. , Wood C. 
Published: March 2011

ABSTRACTThe electrical resistivities and the Seebeck coefficients of SmS1−xAsx alloys (0 ≤ x ≤ 1) have been measured between room temperature and 1273 K as part of a continuing search for high temperature materials having a high thermoelectric figure of merit and suitable for space power applications. SmS is an n-type semiconductor with an energy gap measured to be 0.16 eV. SmAs and SmS0.2As0.8 are itinerant electron conductors. Hysteresis between high and low resistivity states has been observed in our SmS0.9As0.1 and SmS0.8As0.2 samples. Alloys with x ≤ 0.05 appear to be the most promising high temperature thermoelectric materials.
Properties of Gallium Nitride
Authors: Pankove Jacques I. 
Published: March 2011

ABSTRACTGallium nitride has many useful properties that include a large direct gap, high electrical and thermal conductivities, and nearly the hardness of sapphire. GaN decomposes at -100°C, can sustain high electron velocities and exhibit acoustoelectric effects. But two challenges remain: to make it conducting p-type and to synthesize the cubic phase in a large single crystal instead of the usual hexagonal structure.
Origin of Paramagnetic Defect in Single Crystal and Ceramic B4C
Authors: Venturini E. L. , Emin D. , Aselage T. L. 
Published: March 2011

ABSTRACTWe compare electron spin resonance (ESR) spectra of B4C samples made by three methods. The samples are 1) two ceramics made by hot-pressing boron and carbon powders, 2) a polycrystal made by carbothermic reduction, and 3) a single crystal grown from a palladium metal melt. All samples show remarkably similar spectra between 2 and 100 K. In particular, all samples show a single Lorentzian absorption, a linewidth that decreases with increasing temperature, and an inverse temperature dependence of the integrated intensity. The integrated intensity of the paramagnetic spin signal corresponds to a density of 2×1019/cm2 localized spins. Having a single crystal sample enables us to meaningfully measure the angular dependence of the ESR linewidth. This angular dependence is consistent with the paramagetic centers being unpaired electrons centered on the central carbon atoms of positively charged C-C-C intericosahedral chains. These chains appear to replace 0.5 % of the positively charged C-B-C intericosahedral chains which occur in B4C.
A Theoretical Approach to the Thermal Conductivity of Boron Carbides
Authors: Kenkre V. M. , Fan X. 
Published: March 2011

ABSTRACTThe thermal conductivity of boron carbides at high temperatures presents a fundamental challenge to theory. One of the striking features is that, while in B4C it displays “normal” behaviour in that it decreases with increasing temperature, in B9C it is nearly temperature-independent. We address this feature through a model calculation which assumes the heat current to be due to carrier phonons whose frequency is modulated by lower-frequency phonons which “dress” the carrier phonons through strong interaction. Preliminary calculations show satisfactory but partial agreement with experiment for reasonable parameters and delineate areas for further investigation of the vibrational properties of boron carbides.
A Spectroscopic Study of the Conditions Required for Plasma Etching of Aluminium in BCl3 and Cl2 Plasmas
Authors: Cairns J. A. , Smailes R. , Blaikley D. C. W. , Banks P. M. , Hancock G. , Hussla I. , Katzschner W. 
Published: March 2011

ABSTRACTOptical Emission Spectroscopy (OES) with argon actinometry has been used to study the influence of machine parameters on the composition of a BCl3 RF plasma discharge in the absence and presence of aluminium. Two steady state models are proposed to account for the appearance of the various species seen, and to explain their relative abundances in response to changes in power and pressure. The validity of the actinometric technique for measuring relative changes in ground state concentrations is discussed also.
The Potential of Infrared Video Thermography for Control of Arc-Plasma Spray Fabrications
Authors: Harris D. , Kelly M. 
Published: March 2011

ABSTRACTInfrared video thermography was used to evaluate the plasma plume and particle streams created by dc plasma jets operating in air and spraying several types of materials. The temperatures of the plasma plume were measured with the aid of a graphite ‘witness.’ By using the thermography system in an 8khz line scan mode, we were able to obtain data relative to the average velocity of particle groups injected into the plasma. The effects of process parameters could be observed in real time using these methods, showing the potential for real time process control.
Pulsed Inductive Plasma Processing for Amorphous Thin Film Formation
Authors: Ebihara Kenji , Maeda Sadao 
Published: March 2011

ABSTRACTA pulsed electromagnetic inductive discharge is used to prepare amorphous thin films. The pulsed plasma is generated by supplying pulsed current (maximum peak 70 kA, period 13 μs ) to a one-turn coil wound round a Pyrex glass tube. Amorphous silicon(a-Si) and amorphous carbon (a-C) films were deposited in mixture gas (20% SiH4, 80% Ar) and pure methane, respectively. The films formed on the subltrates set normal to the tube axis at a pressure of 10–200mTorr and a gas flow rate of 10–20 sccm. Deposition rate was about 1 nm per a single discharge shot. The deposited films of a few hundred nanometer thickness adhered well to room-temperature substrates. The a-Si films had optical gap of ˜ 1.7 eV. The a-C films were transparent in the IR range and had optical gap of 1.0 ˜ 2.0 eV. Relative spectral intensity measurement of the Balmer emission from hydrogen atoms showed that the electron temperature at the high electromagnetic compression phase is 1˜ 2 eV in silane discharges and 2˜5 eV in methane discharges.
Photoresist Stripping Using a Remote Plasma: Chemical and Transport Effects
Authors: Loewenstein Lee M. , Huffman Craig H. , Davis Cecil J. 
Published: March 2011

ABSTRACTPhotoresist removal from silicon substrates has been achieved by a dry processing method using a plasma remote from the substrate to produce active species. Although the principal gas used is oxygen, the addition of small amounts of other gases (N2O, HCI, HBr, H2, Cl2, CF4, and CHF3) has been shown to significantly enhance resist removal. The measured temperature dependences indicate that the effect of these additives may be a combination of oxygen atom production enhancement by neutral and ionic mechanisms as well as independent reaction with the resist.
A Kinetic Model for Low-Pressure RF Discharge Etching of Silicon Using SF6
Authors: Paranjpe Arit P. , Kychakoff George , Self Sidney A. 
Published: March 2011

ABSTRACTThe variation of etch rate with power, pressure and flow is studied using a coupled electron and chemical kinetics model. The electron kinetics model involves a solution of the electron continuity and current continuity equations in conjunction with the Boltzmann equation. The temporal variation of the electric field, electron energy distribution function (EEDF) and electron number density in the bulk of an RF discharge, is calculated using measured current waveforms, and calculated species concentrations. Electron generation through electron-impact ionization, is balanced by attachment and diffusion losses. A time-dependent solution of the Boltzmann equation is employed to investigate the problem of non-equilibrium, between the EEDF and the instantaneous field. Rates for electron impact processes are calculated using the EEDF.Rate equations for the different species are solved to obtain steady state species concentrations. Radicals and ions produced by electron-impact processes are lost through neutral recombination, ion-ion neutralization, diffusion to reactor surfaces and flow losses. The calculated ion number densities far exceed the electron number density. A transport model that considers the diffusion of etchant species to the wafer and subsequent reaction, is used to compute the etch rate.
Gate Oxide Damage in Dry Photoresist Stripping Environments
Authors: Sibbett Karen H. , Ulacia J. Ignacio , McVittie James P. , Reichelderfer Richard F. 
Published: March 2011

ABSTRACTThe effect of oxygen plasma stripping environments on the electrical properties of thin oxides has been studied. A barrel, parallel plate and downstream stripper are compared. Damage, measured by shifts in flatband voltage (Δ Vfb), increases in the density of interface traps (Dit), and degradation in minority carrier lifetimes, was observed in all plasma processed samples. Plasma treated wafers had 10–100 fold increases in Dit but recovered to nearly control levels after a 450 °C anneal. ΔVfb and lifetimes did not recover in all cases. Mobile ion contamination dominated in the high temperature (≥ 250 °C) downstream stripping tool. The mobile ion concentration was halved by decreasing the process temperature in the downstream etcher. Ion bombardment-induced damage appears to be most important in the parallel plate configuration. Lifetime results were poor for wafers etched in an unshielded barrel reactor and did not recover after anneal. Use of an etch tunnel improved results to control levels. Degradation of minority carrier lifetimes measured using the photoconductivity technique correlated well with changes in Vfb and Dit. This measurement provides a simple method for evaluating plasma-induced damage.
Plasma Process Routes to Synthesis of Carbide, Boride and Nitride Ceramic Powders
Authors: Becker Aaron J. , Meyer Thomas N. , Smith Frances N. , Edd Jon F. 
Published: March 2011

ABSTRACTAn iterative technique to develop plasma processing, consisting of identifying materials with unique properties, calculating conversion efficiencies, product purity and power from thermodynamic data for the chemical reactions selected to produce it and modeling the process mathematically and physically to determine capital and labor costs is illustrated with production of silicon carbide and titanium diboride in Alcoa's DC plasma facility. The work shows that submicron silicon carbide and titanium diboride containing less than 0.2% oxygen can be produced with plasmas at costs competitive with traditional processes. It has also been reported that aluminum nitride, a material which has the high thermal conductivity needed for high power electronic substrates, can be satisfactorily produced by reacting aluminum powder with nitrogen in an RF plasma system. Future application of plasmas for production of ceramics will depend on discovery of unique properties and cost effective process optimization.
Stability Studies of Plasma Sprayed Zirconia
Authors: Eaton Harry E. , Novak Richard C. 
Published: March 2011

ABSTRACTSprayed partially stabilized zirconia (PSZ) has a non equilibrium microstructure due to the splat quench nature of the spray process and it will undergo phase transformation with time at temperature. This study examines the phases present in sprayed PSZ versus powder history, exposure to temperature, and silica impurity level. Finally, thermal quench behavior is examined versus phase content.
Beta-SiC Synthesis in a Thermal Argon Plasma Jet Reactor
Authors: Kong Peter C. , Pfender E. 
Published: March 2011

ABSTRACTUltrafine beta-SiC powders are synthesized in a thermal argon plasma jet reactor by a reaction between methane and silicon monoxide. High temperatures (>10000 K) and rapid quench rates (>106 K/s) lead to a high degree of super-saturation of the chemical vapor, resulting in homogeneous nucleation of ultrafine SiC particles. The maximum conversion of SiO to SiC determined by thermogravimetric analysis is 97%. Particle size analyses show a bimodal distribution with the majority of the particles falling in a size range from 2 to 40 nm. Larger particles with sizes larger than 80 nm are also observed. Characteristically-shaped SiC single-crystal platelets are observed throughout this work.
A Mathematical Representation of the ion Nitriding Process
Authors: Marchand J -L. , Ablitzer D. , Szekely J. , Michel H. , Gantois M. 
Published: March 2011

ABSTRACTA mathematical formulation and computed results are presented to describe the velocity fields, temperature fields and concentration of the activated species in an ion nitriding process, operated at 1–5 torr pres-sure. The theoretical predictions, which are based on the two-dimensional trasnport equations and on a model for computing the electron number density, gave results in broad agreement with experimental findings reported by others for similar systems.
Effect of Particle Loading on DC Plasma Jet Profile During Low Pressure Plasma Deposition
Authors: Wei Daniel Y.C. , Apelian Diran , Farouk Bakhtier 
Published: March 2011

ABSTRACTIn modelization of plasma jet profiles and calculating individual particle trajectories and the local temperature profile of the injected particles it has generally been assumed that the particles injected into the plasma plume constitute a dilute system. The latter allows one to decouple the jet profile calculations from the particle trajectory and temperature calculations. However, in practice, low pressure plasma deposition is carried out under high loading conditions to minimize thermal energy losses. In addition, the plasma experiences local cooling and deceleration due to the high loading of the injected particles. The effect of powder injection rates (10 kg/hr -30 kg/hr) on the plasma and the particles was studied and numerically modeled. An axisymmertrical parabolic supersonic flow model with compressibility corrected k-… turbulence formulation was developed and used in this study to describe the jet flow. The exchange of energy and momentum between the injected particles and the plasma flow was treated by considering the source term of the governing equations. The effect of particle loading on the resulting jet profiles, particle trajectories and temperature profiles are presented and discussed.
Does Host Size and Feeding Status Influence the Egg Load of Microplitis rufiventris (Hymenoptera: Braconidae)?
Authors: Khafagi Wedad E , Hegazi Esmat M , Andersson Peter , Schlyter Fredrik 
Published: March 2011

Abstract
Laboratory experiments were conducted to determine the effect of host instar and feeding status on the egg load of early life stage in Microplitis rufiventris Kokujev (Hymenoptera: Braconidae), a solitary koinobiont endoparasitoid of some noctuid pests. The wasps that developed from fourth or fifth instars of Spodoptera littoralis (Boisduval) larvae were heavier in weight than those from earlier stages. Different numbers of mature eggs were found in the two ovaries of the female wasp. Egg loads, corresponding to fitness, were significantly influenced by female weight and feeding status. However, the interactions between the two treatment factors were not significant. The average number of mature eggs carried by females at eclosion time ranged from 52 eggs in smaller wasps to 62 eggs in larger wasps. Females that were fed had higher egg loads and egg maturation rate than unfed females. However, female wasps were capable of maturing considerable number of eggs without feeding; suggesting that they produce a certain portion of eggs from nutritional reserves that had been stored during larval stage. Female wasps are weakly synovigenic, with an egg maturation at a rate of ≈1.8 eggs per h. Further investigation is required to verify the rate of egg maturation and eventually egg resorption in different stages of adult female M. rufiventris.
Analysis of Surstylus and Aculeus Shape and Size using Geometric Morphometrics to DiscriminateRhagoletis pomonellaandRhagoletis zephyria(Diptera: Tephritidae)
Authors: Yee Wee L , Sheets H David , Chapman Peter S 
Published: March 2011

AbstractRhagoletis pomonella (Walsh) and Rhagoletis zephyria Snow (Diptera: Tephritidae) both occur in the U.S. Pacific Northwest and are frequently confused with one another due to their morphological similarity. The apple maggot, R. pomonella, is a threat to commercial apples [Malus domestica (Borkh.) Borkh.] in the Pacific Northwest, whereas R. zephyria attacks snowberry (Symphoricarpos Dill. ex Juss) and is not considered a threat. Configuration of the surstyli in males is used to discriminate between species, but this character shows overlap. In this study, we reexamined surstyli configurations in the two species. We then used geometric morphometrics to test the hypotheses that shapes of surstyli and of aculei between the two species differ and that combining aculeus shape and size measures improves discrimination. We found that all R. pomonella had an inwardly curved surstyli configuration (based on a ratio of width across bases of prensisetae to width between the outer edges of the surstyli near their ends), whereas R. zephyria included specimens having either a parallel or divergent configuration. Using canonical variates analysis, multivariate analysis of variance, and an assignments test, we found that surstylus shape classified 99.8% of males correctly to species. Aculeus shape accurately classified 85.3% of females to species. Combining aculeus shape and length increased classification accuracy to 94.5%. Within species, surstylus and aculeus shape did not discriminate among fly populations from different host fruit, collection areas, or both. Use of surstylus shape would benefit regulatory agencies that depend on accurate identifications of R. pomonella for quarantine and management measures.