bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of Multipolar Resonant-Cavity and Magnetic Mirror Microwave ECR Sources for dry Etching of III-V Semiconductors
Authors: Pearton S. J. , Abernathy C. R. , Ren F. 
Published: April 2011

ABSTRACTTwo different microwave ECR sources have been examined for use in dry etching of GaAs, InP and related compounds. The first, a multipolar, tuned-cavity disk source (Wavemat) has been in operation for ∼4 years and provides stable, uniform discharges of BCl3/Ar, CH4/H2, SF6/Ar, HI/H2 and CCl2F2 for smooth, anisotropie pattern transfer into the III-V materials. Electron densities of -5 × 1011 cm-3 are achieved at 1 mtorr for microwave powers of >700W, as determined by microwave interferometry. Additional rf (13.56 MHz) biasing of the sample position is necessary for achieving practical etch rates. The second source is a Astex ECR high-profile geometry, with a drift-tube and secondary magnets near the sample position to improve the plasma confinement and etching uniformity. Similar electron densities are found as with the resonant cavity source, and optimization of the top and bottom magnet currents produces similar etch uniformities. Examples of the etching characteristics of III-V's as a function of microwave power, rf-induced dc bias and sample temperature are given.
Effect of Bandwidth on Uniformity of Energy Distribution in a Multi-Mode Cavity
Authors: Johnson Arvto C. , Lauf Robert J. , Surrett April D. 
Published: April 2011

ABSTRACTThis paper reports on the results of experimental studies of the effect of bandwidth on the uniformity of energy distribution in a multi-mode cavity as well as on the development of a theoretical model to, at least qualitatively, describe the effect of varying the processing frequency. Using a mapping method reported in earlier work, Microwave Laboratories and Oak Ridge National Laboratory personnel have graphically measured the effect of processing bandwidth on heating uniformity. These results can be compared to the effects of other attempts to improve uniformity e.g., “mode stirrers.” Additional insight into the effect of bandwidth on time-averaged energy distribution within the cavity can also be gained from the simple theoretical model, which is presented for comparison with the experimental results. Finally, this paper uses the presented results to comment on the scalability of the variable frequency microwave processing methodology for large-scale applications.
Comparison of Properties of Sintered and Sintered Reaction-Bonded Silicon Nitride Fabricated by Microwave and Conventional Heating
Authors: Tiegs Terry N. , Kiggans James O. , Lin H. T. , Willkens Craig A. 
Published: April 2011

ABSTRACTA comparison of microwave and conventional processing of silicon nitride-based ceramics was performed to identify any differences between the two, such as improved fabrication parameters or increased mechanical properties. Two areas of thermal processing were examined: (1) sintered silicon nitride (SSN) and (2) sintered reaction-bonded silicon nitride (SRBSN). The SSN powder compacts showed improved densification and enhanced grain growth. SRBSN materials were fabricated in the microwave with a one-step process using cost-effective raw materials. The SRBSN materials had properties appropriate for structural applications. Observed increases in fracture toughness for the microwave processed SRBSN materials were attributable to enhanced elongated grain growth.
Microwave Synthesis of Lead-Barium Titanate
Authors: Cheng Jiping , Fang Yi , Agrawal Dinesh K. , Roy Rustum 
Published: April 2011

ABSTRACTSince the volatilization of lead oxides is inevitable at high temperatures, the problems of maintaining stoichiometry and air pollution are of great concern in conventional synthesis of lead-barium titanate. We have demonstrated that the reaction between PbO, BaO and TiO2 could be greatly accelerated by using microwave energy. The synthesis of (PbxBa1-x)TiO3 can be completed in 10 minutes at about 750°C by microwave heating, while it takes at least 2 hours at 850°C in a conventional heating. The weight loss of PbO during microwave synthesis was much less than that in conventional synthesis. Thus the microwave synthesis technique may find wide applications for the preparation of various lead-containing materials in the production of electronic ceramics.
Experimental Study of the Non-Thermal Effect in Microwave Sintering of Piezoceramics
Authors: Bykov Y. , Eremeev A. , Holoptsev V. 
Published: April 2011

ABSTRACTComparative study of microwave sintering at frequencies 30 and 83 GHz, and the comparison between microwave and fast conventional sintering were undertaken with the aim to ascertain the possibility of specific non-thermal effects at microwave heating. It is shown that an enhancement of sintering can not be explained by the action of thermal stresses caused by peculiar distibution of the temperature field within the microwave-heated samples.
Feedback Control of Temperature Profiles During Microwave Joining of Ceramics
Authors: Li Mengli , Beale Guy O. , Black W. Murray 
Published: April 2011

ABSTRACTThe goal of this research is to develop an automatic feedback control system for ceramic samples being heated by microwave energy for the purpose of joining the samples. This paper describes two major topics connected with the research. First, the temperature control algorithm is described, and experimental results from testing that control algorithm with actual ceramic samples are presented. Secondly, the microwave cavity is modeled using a transmission line approach to relate iris and plunger positions to absorbed power. Equations are presented which give the proper positions for maximizing the absorbed power, and a control strategy for the iris and plunger is discussed. This research has been funded under NSF Grant No. DDM - 9115417.
The Role of Glassy Grain Boundary Phases in the Microwave Joining of Alumina
Authors: Davis Pamela , Binner Jon , Cross Tom , Fernie John 
Published: April 2011

ABSTRACTThe role of intergranular glassy phases in the microwave joining of alumina ceramic rods has been investigated. Alumina ceramics of different purities have been examined using a TE102 single mode rectangular resonant cavity operating at 2.45 GHz. Temperature and axial pressure were varied and the resultant join microstructures analyzed. The presence of a glassy grain boundary phase has been shown to improve the ability to microwave join alumina ceramics by increasing the dielectric loss of the ceramic and, when softened, by enabling the alumina grains to flow under the imposed load. Evidence has also been found for the sintering of individual grains where they have come into contact across the join line.
Seal Formation Rates of Microwave Heated Ethylene Carbon Monoxide Copolymers
Authors: Peterson Edward R. 
Published: April 2011

ABSTRACTEthylene carbon monoxide copolymer (ECO) has physical and thermal properties essentially identical to those of low density polyethylene, including a melt temperature near 100C and a low water vapor transmission rate. Unlike polyethylene, ECO absorbs and can be heated and melted with microwave and radio frequency energy. A conventional method of sealing flexible polymer containers is to apply the external heat to the walls with heated dies. The time of sealing is directly related to the thickness of the wall structure, its composition, and the temperature of the heated dies. The die temperature is often limited by the softening or melt temperature of the external polymer layer and/or degradation of surface inks or applied graphics. High frequency energy applied to a properly designed polymer structure deposits the energy into the internal absorbing layers, which transform that energy into heat. No heated dies are required. External layers of high frequency non-absorbing polymer act as thermal insulators, keeping the generated heat in at the seal location. Sealing rates can be several times faster than by conventional means.
Studies on the Scale-Up of the Microwave-Assisted Nitridation and Sintering of Reaction-Bonded Silicon Nitride
Authors: Kiggans J. O. , Tiegs T. N. , Kimrey H. D. , Maria Jon-Paul 
Published: April 2011

AbstractStudies using laboratory test samples have shown that microwave heating produces sintered reaction-bonded silicon nitride materials with improved properties [1,2]. The final challenge for processing this material by microwave heating is the development of a technology for processing larger batch-size quantities of these materials. Initial microwave scale-up experiments were performed using powder compacts of a bucket tappet geometry. In experiments using microwave-transparent boron nitride sample crucibles, temperature gradients within some crucibles led to larger variations in the sample densities than were obtained with the conventionally processed samples. The use of a microwave-suscepter type crucible made of silicon carbide and boron nitride resulted in an improved temperature uniformity and in density variations comparable to those obtained for the control groups.
Variable Frequency Microwave Processing of Thermoset Polymer Matrix Composites
Authors: Demeuse Mark T. , Johnson Arvid C. 
Published: April 2011

ABSTRACTThis paper reports on the use of variable frequency microwave processing to uniformly heat and post-cure large (>100 cm2) plates of thermoset polymer matrix composite (PMC) material consisting of isocyanate/epoxy mixtures. Prior work has indicated that microwave energy is capable of reducing the time or the temperature necessary to achieve full cure; however, single-frequency microwave heating results in non-uniformity of heating/curing in areas of over 12.5 cm2. By using a Variable Frequency Microwave Furnace and sweeping the microwave power over the 5 to 6 GHz frequency range at a power level of 150 Watts, uniform heating and curing of the PMC plates was achieved over an area of greater than 100 cm2-- and a volume of greater than 200 cm3. The overall temperature gradient across the surface of the plates was less than 10%. Finally, this paper also reports on observed, volume-related heating effects, which are postulated to be the result of heat loss from the sample surface.
Fluorescent Compounds for Plastic Scintillation Applications
Authors: Pla-Dalmau Anna , Bross Alan D. 
Published: April 2011

ABSTRACTSeveral 2-(2'-hydroxyphenyl)benzothiazole, -benzoxazole, and -benzimidazole derivatives have been prepared. Transmittance, fluorescence, light yield, and decay time characteristics of these compounds have been studied in a polystyrene matrix and evaluated for use in plastic scintillation detectors. Radiation damage studies utilizing a 60Co source have also been performed.
Chromophore Doped Glasses as Scintillator Materials
Authors: Smith C. , Borrelli N. F. , Tick P. A. , Smith D. , Weber M. J. , Sangster T. C. , Lee H. W. , Hughes R. S. , Derenzo S. E. , Moses W. W. 
Published: April 2011

ABSTRACTA family of low melting temperature tin fluorophosphate glasses that can incorporate certain organic compounds has been under investigation. The glasses are comprised principally of SnF2, SnO, and P2O5; the addition of small amounts (< 5%) of Pb improves chemical durability. These materials are dense, reasonably water durable, and easily fabricated. Photoluminescence properties of glasses doped with pyrene, POPOP, stilbene 420 and several other organic molecules were studied. All of the doped glasses exhibited intense photoluminescence. Pyrene doped glass was found to have monomer-triplet and dimer-excimer pyrene species present, depending on the dopant concentration. Scintillation properties of the glasses were also investigated. Generally a very fast (~1 ns or less) but weak luminescence was observed. Results of these studies suggest that higher concentrations of the dyes must be incorporated into the glass and more efficient energy transfer from the glass host to the organic fluor must be attained for these materials to be useful as fast scintillators.
Time-Resolved Spectroscopy of Scintillation Materials using X-RAY Synchrotron Radiation
Authors: Belsky Andrey N. , Mikhaihin Vitaly V. , Rogalev Andrey L. , Zinin Eduard I. 
Published: April 2011

ABSTRACTThe time-resolved luminescence spectra and decay kinetics of BaF2, BGO, and CeF3, were measured with the dissector technique using X-ray synchrotron radiation (SR)of different spectral composition from wiggler mounted at VEPP-3 storage ring (Novosibirsk).Two effects of X-ray excitation energy on the luminescence parameters were observed: modifications of the emission spectrum and acceleration of decay kinetics. Under the excitation by soft X-ray SR the 220 nm emission band for BaF2 is broadened, whereas shorter wavelength part of CeF3 and BGO emission spectra increases. For luminescence decay of excitons and crossluminescence the degree of the deviation from the single exponential law depends on the photon energies and increases under soft X-ray excitation as well. These effects are supposed to be due to the interaction of electronic excitations created after the relaxation of deep core holes.Fast intrinsic luminescence was observed for Cdl2, and CsPbCl3 under X-ray SR excitation. 500 nm band of Cdl2 has characteristic time τ=4.6 ns, whereas 420 nm band of CsPbCl3 shows very fast decay with τ=0.2 ns.
Use of Plastic Optical Fibers for Charged Particle Tracking in High Energy Physics
Authors: Wayne Mitchell R. 
Published: April 2011

ABSTRACTA large tracking detector consisting of scintillating plastic optical fibers has been chosen by the D0 collaboration as a part of a planned upgrade at the Fermilab Tevatron. The tracker will utilize a state of the art photodetector known as the Visible Light Photon Counter. The benefits of fiber tracking in high energy physics will be presented along with recent progress in several key areas, including: optimization of scintillating dyes and light yields, fiber construction, fiber ribbon manufacture and placement, optical transmission and photodetection. The current status of the D0 development effort will be outlined, including results from the characterization of 5000 channels of VLPC. Finally, results from simulations of expected detector performance will be shown and discussed.
The Effect of Impurities On The Radiation Damage of Barium Fluoride Crystal
Authors: Ren Shaoxia , Chen Gang , Zhang Fengyin , Zheng Yanning 
Published: April 2011

ABSTRACTDifferent impurities influence the radiation damage of barium fluoride (BaF2 )crystal in different ways. Stable metal elements, such as alkali elements and alkali earth elements, have no effect on the radiation resistance. Most transtion metal elements areharmful to the radiation resistance. There are three kinds of effects of rare earth elements. Stable trivalence elements, such as Y, La and Lu, have no effect on the radiation resistance, while the elements which changes its valence from +3 to +4 under irradiation, such as Ce and Pr, are harmful. The elements which changes its valence from +3 to +2 underirradiation, such as Sm,Eu,Dy and Yb, are useful in eliminating color centers in visible range. Oxygen and hydroxyl ions which were introduced into the crystal from the raw material of BaF2 or a low vacuum during crystal growing are very harmful to the radiation resistance. The formation of “Complex Color Centers” is considered as the cause of the radiation damage of BaF2 crystal in this paper.
Light Output and Radiation Damage in A Lead Tungstate Crystal
Authors: Kierstead J.A. , Stoll S.P. , Woody C.L. 
Published: April 2011

ABSTRACTThe optical absorption, light output and effects of radiation damage have been studied ina 2.2 × 2.2 × 12.8 cm3 crystal of lead tungstate. The crystal exhibits a longitudinal attenuation length which varies from roughly 13 cm to 1.5 m over the region where the scintillation emission occurs (400-800 nm). The light yield produces approximately 10 photoelectrons per MeV on a photomultiplier tube with a bialkali photocathode. The scintillation and light transmission properties of the crystal were characterized before and after exposure to 1 Mrad of 60Co gamma rays. Significant radiation induced optical absorption was observed in this crystal, along with a considerable amount of phosphorescence after irradiation. Partial spontaneous recovery from the damage occurred at room temperature, and it was possible to induce additional recovery by optical bleaching.
Wear Behavior of MoSi2 and MoSi2 Matrix Composites
Authors: Alman D. E. , Hawk J. A. , Petty A. V. 
Published: April 2011

AbstractThe U.S. Bureau of Mines is examining the wear behavior of a variety of advanced materials, including the intermetallic compound MoSi2. The high stiffness and hardness of MoSi2 make it attractive for use in applications requiring wear resistance. This research reports on the results of pin abrasion wear tests for a variety of powder processed MoSi2 and MoSi2 matrix composites. The effect of the addition of ductile (Nb) and brittle (SiC) reinforcements, as well as the influence of reinforcement type and orientation geometry, on abrasive wear is discussed. Comparisons of the wear behavior of MoSi2 and MoSi2-based composites with other materials, such as refractory metals, aluminides, and ceramics, are made.
Status and Development of Nickel Aluminide (NiAl) Composites
Authors: Amato R. A. , Yang J.-M. 
Published: April 2011

AbstractNiAl-based composites are a new class of engineering materials being developed for high temperature structural applications in oxidizing and aggressive environments. This paper discusses some of the recent advances in developing continuous fiber-reinforced polycrystalline NiAl-based composites. Several key issues including matrix alloy development, fiber development, fabrication development and mechanical behavior will be addressed.
The Athermal Strengthening of Discontinuous Reinforced NiAl Composites
Authors: Wang L. , Xu K. , Arsenault R. J. 
Published: April 2011

AbstractAn increase in the athermal component of the yield stress at low temperatures is the caused of the high temperature strengthening of discontinuously reinforced NiAl matrix composites. The reinforcements stabilize the microstructure. The strengthening in the temperature range of 300–1273K, is believed to be related to the grain size refinement and effective pinning of grain boundaries. This conclusion was obtained from analysis of data from AlN, TiB2 and Al2O3/NiAl particulate composites.
Creep Behavior and Microstructures of Nb-26Ti-48Al Alloy and Composite
Authors: Feng C. R. , Michel D. J. 
Published: April 2011

AbstractThe creep behavior of Nb-26Ti-48Al alloy and its composite were investigated. After creep testing, precipitates were observed in the composite and mobile dislocations were found to be pinned by these precipitates. The combined effects of the reinforcements and the pinned dislocations were responsible for a reduced creep rate of the composite. The possible creep mechanisms were discussed based on the stress exponent and the activation energy of creep.
Ambient Temperature Synthesis of Bulk Intermetallics
Authors: Ratzker M. , Lashmore D. S. , Dariel M. P. 
Published: April 2011

AbstractRoom-temperature intermetallic compound formation occurs when one of the component metals has a very low melting point or when two metals in close contact interdiffuse very rapidly. Compound formation at room temperature at the interface of superposed thin films has been observed in several instances, often in systems relating to electronic materials. The overall amount of compound produced in such configurations, however, is limited, due to the intrinsic limitations involved in the thin layer geometry. Bulk quantities of intermetallic can be produced at ambient temperature in solids by increasing the interface area between the components that interdiffuse rapidly. This condition can be achieved by having small size powder particles of one component coated with a layer of the second component. The very large interface area leads to rapid formation of bulk quantities of compounds even at ambient temperature. By appropriate control of the initial constituents and the coating parameters, it is possible to custom-prepare various intennetallic compounds present in binary systems such as silver-tin, gold-tin and silver-indium in which fast interdiffusion takes place.
Wear Behavior of SHS Intermetallic Matrix Composites
Authors: Hawk J. A. , Alman D. E. 
Published: April 2011

AbstractA number of discontinuously reinforced, intermetallic matrix composites (i.e., TiAl/TiC, TiAl/TiB2, TiAl/Ti5Si3) were formed in situ through self-propagating, high-temperature synthesis (SHS) between elemental powders. This Bureau of Mines study characterizes the abrasive wear behavior of these composites. Wear behavior is discussed with respect to process history, and type and volume fraction of reinforcement. Generally, higher process temperatures lead to dense composites, resulting in better wear resistance. The wear behavior of the SHS intermetallic composites is compared to other intermetallics, produced by conventional techniques.
Fracture Characteristics of Metal-Intermetallic Laminates Produced by SHS Reactions
Authors: Alman D. E. , Rawers J. C. 
Published: April 2011

AbstractThe tensile behavior of metal-intermetallic layered composites produced by reacting dissimilar elemental foils was studied by U.S. Bureau of Mines researchers. The layered composites were produced by initiating an SHS reaction between Ni and Al foils or Ti and Al foils. The reaction consumed the aluminum foil, resulting in well bonded metal (Ni or Ti) metalaluminide layered composites. Tensile tests revealed that the tensile behavior of the composites was dependent upon the thickness of the intermetallic layer (which in the present case corresponds directly to volume fraction). Composites, in which the intermetallic layers had cracked extensively, behaved in a ductile or tough manner. Not surprisingly, these composites consisted of a relatively thick metal layer compared to the intermetallic layer. It was found that the cracking of the intermetallic layers occurred prior to the deformation of the metal layer. Those composites that had relatively thick intermetallic layers, compared to the metal layer, behaved in a brittle manner. These composites had few cracks in the intermetallic region.
Rare Earth/ Organic Dye Nanocomiposites by the Sol-Gel Method
Authors: Bescher Eric P. , Mackenzie John D. , Ohtsuki Tomoko , Peyghambarian Nasser 
Published: April 2011

ABSTRACTThis paper describes the processing of rare-earth/organic dye composites fabricated via three different sol-gel routes. In the first approach, low hydroxyl ormosil matrices were fabricated via reaction of a methyl-modified silicon halide with tertiary alcohol and subsequently doped with erbium iodide and a near-infrared dye. In the second approach, gels were made from tetramethoxysilane and doped with erbium complexes and dyes. In the third approach, a hybrid siloxane method was used. No Er3+ luminescence at 1.55 mm was observed in any of the three cases, mainly due to the strong absorption of the matrices centered around 1.4 mm. Fluorescence of Er3+ in the visible was observed in the first matrice, but no dye luminescence was detected. Dye luminescence was observed in the second type matrix, along with some reabsorption of the dye luminescence by Er3+. In the third approach, neodymium exhibited optical activity in the near infrared, as well as the dye.
Nanosized Metal Particles by Control of the Metal Dispersion During Sol-Gel Processing
Authors: Schubert Ulric , Görsmann Claus , Tewinkel Stefan , Kaiser Andreas , Heinrich Thomas 
Published: April 2011

ABSTRACTThe previously developed method to prepare highly dispersed metals in SiO2 by sol-gel processing of metal complexes containing alkoxysilyl-substituted ligands was extended to the preparation (i) of bimetallic particles in SiO2 and (ii) of highly dispersed metals in TiO2.