bluuebunny/crossref_metadata_2025 huggingface dataset:
Laser-Deposition Of High Luminance Thin Film Phosphors
Authors: Greer J. A. , Hook H. J. Van , Tabat M. D. , Nguyen H. Q. , Gammie G. , Koufopoulos P. F.
Published: April 2011

High luminance (brightness) thin-film phosphor materials have potential use in a variety of applications including heads-up, helmet-mounted, and electroluminescent displays, as well as in emerging flat-panel displays based on field emitter technology. Phosphor materials in thin film form offer several advantages over conventional powder phosphor screens. Since the film is nearly fully dense and in intimate contact with the underlying substrate, thin film phosphors transfer heat to the face plate much quicker than conventional, more porous, powder phosphor materials. This allows thin film phosphor screens to be driven at higher power levels, and therefore produce higher luminance, assuming the efficiency of the powder and film are the same. Fully dense phosphor films have smaller surface area, and will outgas less than conventional powder phosphor materials. Thin film phosphors have smaller grain sizes than conventional powder phosphor materials which will provide for smaller spot size, and thus, higher resolution. Furthermore, in applications such as field-emitter displays, powder phosphor particles can be physically dislodged from the screen due to the high electric fields produced by the large potential difference between the anode screen and gate electrode (or cathode), or dislodged by arcing which may occur if a powder particle protrudes significantly above the screen surface. Dislodged particles or damage produced by arcing could degrade display performance. Dense, thin-film phosphor materials which are well adhered to transparent substrates will provide much smoother surface morphologies, and should be able to withstand significantly higher electric field strength without arcing or screen degradation due to the dislocation of particles.
Nanocrystalline Silicon Films for Large Area Displays: Preparation and Properties
Authors: Vepřek S. , Tamura H. , Rückschloss N. , Wirscheui Th.
Published: April 2011

We discuss the possible preparation techniques of the light emitting nanocrystalline silicon for large area electroluminescence (EL) displays and the control and optimization of the EL properties of the material. Some open problems are addressed and their possible solutions briefly discussed.
Considerations for Large Area Fabrication Of Integrated a-Si and Poly-Si TFTs
Authors: Mei P. , Anderson G. B. , Boyce J. B. , Fork D. K. , Hack M. , Johnson R. I. , Lujan R. A. , Ready S. E.
Published: April 2011

The combination of a-Si low leakage pixel TFTs with poly-Si TFTs in peripheral circuits provides an excellent method for reducing the number of external connections to large-area imaging arrays and displays. To integrate the fabrication of the peripheral poly-Si TFTs with the a-Si pixel TFTs, we have developed a threestep laser process which enables selective crystallization of PECVD a-Si:H. X-ray diffraction and transmission electron microscopy show that the polycrystalline grains formed with this three-step process are similar to those crystallized by a conventional one step laser crystallization of unhydrogenated amorphous silicon. The grain size increases with increasing laser energy density up to a peak value of a few microns. The grain size decreases with further increases in laser energy density. The transistor field effect mobility is correlated with the grain size, increasing gradually with laser energy density until reaching its maximum value. Thereafter, the transistors suffer from leakage through the gate insulators. A dual dielectric gate insulator has been developed for these bottom-gate thin film transistors to provide the correct threshold voltages for both a-Si and poly-Si TFTs.
The Low Temperature Polysilicon TFT Technology for Manufacturing of Active Matrix Liquid Crystal Displays
Authors: Morita Tatsuo , Tsuchimoto Shuhei , Hashizume Nobuo
Published: April 2011

The amorphous silicon thin transistor (a-Si TIFT) has successfully industrialized the active matrix liquid crystal displays (AMLCDs), which would get a vast market on the basis of their wide potential use for displays. Whereas, the polysilicon TFT (p-Si TFT) also has been intensely investigated and intended to realize smarter AMLCDs, with monolithic peripheral circuits.

In this paper, we will discuss the applicable range of low temperature p-Si TFTs compared with high temperature p-Si TFTs. After reviewing the materials which comprise low temperature p-Si TFTs, we will introduce our self aligned aluminum gate process which could allow fast addressing even in enlarged AMLCDs in the future.
The Use of Injection Locked Magnetrons as a Source Microwave Processing Applications
Authors: Walker Chris M.
Published: April 2011

The Injection Locked Magnetron (ILM) has been used as a source of coherent power in a number of radar systems. It has a number of characteristics that make it particularly suitable to heating applications, above competing tube types used in radar applications.

Power available is dependent upon the frequency of operation, ranging from several hundred watts at Ku-band to tens of kilowatts at L-band. Operation could be either cw or pulsed, but at higher power levels pulsed operation would be required. Designs for tubes at 1 GHz and 15 GHz will be presented.

ILMs could be made at any frequency from 800 MHz to 20 GHz, beyond which the magnetron becomes either too large to be practical or too small to fabricate. Locking bandwidths are typically 0.5%, sufficient to be able to guarantee the tube remains locked at the required operating frequency. A tuner would increase the tube life and compensate for frequency drift effects.

The tube life is dependent on the desired frequency of operation, ranging from several hundred hours at high frequency to an order of magnitude higher at low frequency. Adding a tuner will increase this several fold. ILMs are inherently rugged and may be run in any orientation, having been developed for airborne radar applications. Tubes are operated directly into a circulator and consequently can operate into high VSWR.

The magnetron is a low cost tube, hence its use in domestic microwave ovens. ELMs have a similar part count and complexity. Efficiency varies from approximately 45% in Ku-band to 80% at L-band. Operating voltages are lower for ILMs than other vacuum tubes, at 1 GHz a 100 kW system would require 20 kV and for a 15 GHz 200 watt system, a 2 kV power supply would be required. These would run in the region of 10% duty cycle, 1 kHz PRF. Tubes would have integral rare earth magnets and require cooling water. The required quantity of tubes would be the most significant cost driver.
Microwave Diagnosis of Carbon Black Rubber Compounds and Porosity Estimation in Composites
Authors: Zoughi Reza , Ganchev S. I. , Bhattacharyya J. , Gray S. , Radford D.
Published: April 2011

The results of an in depth study of the dielectric properties of various rubber compounds at different microwave frequencies are discussed. Subsequently, the influence of carbon black volume percentage on the dielectric properties of rubber is studied in a wide frequency range (5 -24 GHz). The results show that the real and imaginary parts of rubber dielectric constant increase as a function of increasing carbon black percentage. Frequencies around 5 GHz show more sensitivity to small changes in the carbon volume content. The presence of curatives in uncured rubber samples is detected, which is an indication of the sensitivity of microwaves to the chemical reaction triggered by these curatives. Similar approach is used to measure the air content in specially prepared model material (plastic microbaloon-filled epoxy) samples with varying degrees of uniformly distributed air inclusion. The results of these measurements for a wide range of frequencies is also reported. Measurement analysis resulted in detecting variation in the air volume fraction of around 1.5%. The results confirm the utility of microwave NDE techniques for local porosity detection and evaluation in dielectric composites.
Microwave Based Civil Structure Inspection Device
Authors: Sohns C. W. , Bible D. W.
Published: April 2011

A microwave based “wall probe” has been developed which is capable of nondestructive evaluation of architectural structures. By using microwaves in the 8 to 12 GHz range this probing instrument can detect subsurface characteristics through concrete, brick, wood or other building materials to depths in excess of 12 inches.

The instrument interrogates a structure from a single side by transmitting a microwave signal into the surface at some angle of incidence and receiving the reflected signal some distance away on the same side of the structure. The transmitted signal is partially reflected at each internal boundary of different dielectric constant, giving a composite reflection which contains information from each internal layer. The reflected composite signal is compared in phase and amplitude to the transmitted signal and that reading is considered the “signature” of the structure under test. Computer algorithms analyze the signature for recognizable features and nonstandard construction.
Density Dependence of High Temperature Dielectric Properties of Debased Alumina and the Effect of a High Loss Additive
Authors: Evans N. G. , Hamlyn M. G.
Published: April 2011

Research into microwave firing at Staffordshire University has been carried out since 1988 and dielectric property measurements have been used to help in developing process technology. The dielectric property measurement technique (cavity perturbation [1]) is that designed by Atomic Energy of Canada Ltd (A.E.C.L) [2]. The technique was chosen because of it's ability to analyse powder samples as well as solids. In order for dielectric property data to be of use in developing microwave processing, measurements have to be made on the starting materials of the process (i.e powders). When measurements are made on powders it is important to quote the bulk density at which the measurement was made since dielectric properties vary with density as well as frequency and temperature.
Decay Method for Measuring Complex Dielectric Constants During Microwave Processing
Authors: Iny O. , Barmatz M.
Published: April 2011

We have developed a fast in-situ method for measuring the quality factor, Q, and resonant frequency, fr, for an isolated microwave resonant mode. The mode resonant frequency was continuously monitored using a phase modulation frequency tracking technique. The quality factor was determined by periodically switching off the microwave power and fitting the decay curve to an exponential. The cavity perturbation method was used with small spherical samples (ka « 1). Combining the Q and fr data with a non-contact measurement of the sample temperature permits the calculation of the temperature dependence of the real (ε′) and imaginary (ε″) dielectric constants. Because of the speed of this technique (≈1 μSce), it can be used during processing to continuously measure the dielectric constants of the material without perturbing the sample temperature. Measurements were performed using isolated TM010 and TEI11 cylindrical cavity modes. Care was taken to minimize the perturbing effects of the sample support. The accuracy of the frequency tracker was verified at room temperature from measurements on several alumina spherical samples. The decay technique was also verified from measurements on several small spherical nylon samples.
Microwave Processing - An Emerging Industrial Technology?
Authors: Stein Dale F. , Edgar Richard H. , Iskander Magdy F. , Johnson D. Lynn , Johnson Sylvia M. , Lob Chester G. , Shaw Jane M. , Sutton Willard H. , Tien Ping K. , Munns Thomas E.
Published: April 2011

The Department of Defense (DoD) and the National Aeronautics and Space Administration (NASA) requested that the National Research Council's National Materials Advisory Board conduct a study to assess the current status of microwave processing technology, identify applications of microwave technology where resulting properties are unique or enhanced relative to conventional processing or where significant cost, energy or space savings can be realized, and to recommend future activities in microwave processing. A committee was established to perform the study and report on their findings. This paper is a summary developed from the committee's report, Microwave Processing of Materials (NMAB Report Number 473, Copyright 1994 by the National Academy of Sciences, National Academy Press, Washington, DC).
Mathematical Model of Thermal Spikes in Microwave Heating of Oxide Ceramic Fibers
Authors: Thomas J. R. , Unruh Wesley P. , Vogt Gerald J.
Published: April 2011

Experiments on microwave sintering of ceramic fibers in a single-mode cavity have revealed the presence of thermal spikes and “hot spots” which sometimes travel along the fiber and eventually disappear. They are triggered by relatively small increases in microwave power, and thus have obvious implications for the development of practical microwave-based fiber processing systems. These hot spots are conjectured to originate at slight irregularities in the tow morphology, and propagate as the result of solid phase transitions which take place at elevated temperatures and reduce the dielectric loss coefficient є”.

An elementary mathematical model of the heat transfer process was developed which reproduces the essential features of the observed phenomena, thus lending support to our conjecture. This model is based on the assumption of one-dimensional heat conduction along the axis of the fiber tow, and radiation losses at the surface.
Microwave-Enhanced Regeneration of Adsorbents
Authors: Weissenberger Arne P. , Schmidt Philip S.
Published: April 2011

An experimental investigation was carried out to determine the regeneration characteristics of adsorbent beds using microwave heating. Tests were performed with water on F-200 activated alumina and on types 4A and 13X zeolite molecular sieves and with methanol on 4A and 13X zeolites. For these systems, microwave heating produced very high rates of regeneration with either gas purge or vacuum purge. Dielectric properties of both the adsorbent and the adsorbate affect the heating response. Temperature profiles in the adsorbent bed show that microwave heating eliminates the mass transfer front characteristic of conventional regeneration. This may have potential implications for improved bed life. The ultimate goal of the program is the recovery of volatile organic compounds (VOCs) by regenerating adsorbents with little or no dilution in a stripping medium.
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

Two 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

This 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

A 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

Since 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

Comparative 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

The 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

The 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

Ethylene 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

Studies 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

This 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

Several 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

A 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

The 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

A 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

Different 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

The 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.
Choice of Compounds with Fast Core-Valence Transitions
Authors: Rodnyi Piotr A.
Published: April 2011

It is now well established that in a number of wide gap ionic crystals a specific intrinsic luminescence can be observed due to radiative hole transitions between the upper core band and valence band. The progress in knowledge about core-valence (CV) transitions is considered in papers [1-3].
Wear Behavior of MoSi2 and MoSi2 Matrix Composites
Authors: Alman D. E. , Hawk J. A. , Petty A. V.
Published: April 2011

The 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

NiAl-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

An 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

The 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

Room-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

A 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

The 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

This 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

The 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.
Nano-Size Silicon Whiskers Produced by Chemical Vapor Deposition
Authors: Shen Lu , Xiao Youming , Ma Ying , Galasso Francis S. , Suib Steven L. , Freihaut James D.
Published: April 2011

Sponge type deposits composed of nanometer sized Si whiskers were formed on Davisil (porous SiO2) gel substrates by chemical vapor deposition (CVD) using methyltrichlorosilane (MTS) as a precursor and H2 as carrier gas. The diameters of the fine whiskers are estimated to be 100 nm or smaller from SEM observations. XRD analyses revealed that the coatings formed at 800 and 900°C contained microcrystalline Si and the Auger analysis indicated the existence of free carbon. The surface area of the coated Davisil was approximately 189 ± 5 m2/g, as obtained from BET measurements. The coatings were also applied on several other substrates, such as AIN and low surface area (< 224 m2/g) silica gel, with the same coating conditions. On these substrates, highly porous Si has also been observed on AIN substrates, and nonporous, half sphere shaped coatings were observed on low surface area silica gel substrates.
Barium Titanium Alkoxides for Barium Titanates: Synthesis, Characterization, and Applications
Authors: Day Victor W. , Eberspacher Todd A. , Klemperer Walter G. , Liang Shurong
Published: April 2011

Several new crystalline bimetallic alkoxide precursors for barium titanates processing have been prepared: {[Ba(Solv)2]2[Ti(OAr)6]2} (1) (Solv = coordinated solvent molecule, Ar = aryl group), [Ba(CH2OHCH2OH)4(H20)][Ti(OCH2CH2O)3] (2), Ba[Ti2(OR)9]2 (3) (R = methyl, ethyl, and n-propyl), and [Ba(BzOH)Ti2O(OBz)8]2 (4) (Bz = benzyl). These precursors have been characterized by elemental analysis, IR, NMR, and single-crystal X-ray diffraction techniques. Compound 1 is well-suited for sol-gel processing of BaTiO3 powders and thin films under a variety of conditions. The facile preparation of 2 using relatively inexpensive starting materials makes it a viable alternative for the synthesis of BaTiO3 fine powders. Both compounds 3 and 4 are fairly moisture-sensitive; hydrolysis of these precursors under acidic conditions affords the formation of gels instead of precipitates. The reactivity of 3 toward hydrolysis can be tailored by varying the alkyl group.
Characterization of the Interaction of Hydrogen with Iridium Clusters in Zeolites by Inelastic Neutron Scattering Spectroscopy
Authors: Nicol J.M. , Udovic T.J. , Cavanagh R.R. , Xu Z. , Kawi S. , Mure T. , Gates B.C.
Published: April 2011

Incoherent inelastic neutron scattering (IINS) measurements of hydrogen bound to Ir6 clusters in the nanoscale pores of zeolite NaY and similar clusters in KL zeolite are reported. On the basis of hydrogen uptake measurements and the observation of peaks in the IINS spectra, we infer that hydrogen is bound to the metal nanoclusters in the zeolite pores. The HINS data for both zeolites are similar and consistent with the presence of IrH2 species.
Sonochemical Synthesis and Catalytic Properties of Nanostructured Molybdenum Carbide
Authors: Suslick Kenneth S. , Hyeon Taeghwan , Fang Mingming , Cichowlas Andrzej A.
Published: April 2011

Molybdenum hexacarbonyl in hexadecane was irradiated with high intensity ultrasound under argon at 90°C to yield face centered cubic molybdenum carbide, Mo2C. After thermal treatment, oxygen and excess carbon were removed to give stoichiometric Mo2C. SEM micrographs showed that the surface was extremely porous. TEM micrographs showed that the solid was an aggregate of particles with diameters of ≈ 2 nm. This material has a very high surface area, 188 m2/g as determined by BET gas adsorption. Catalytic studies have been conducted on the dehydrogenation of cyclohexane and the hydrogenolysis of ethane. The sonochemically prepared Mo2C shows good catalytic activity for the dehydrogenation of cyclohexane with 100% selectivity for formation of benzene without hydrogenolysis to methane. The material revealed poor catalytic activity for the hydrogenolysis of ethane.
Application of Fractals and Kinetic Equation in Modelling Cluster and Ultrafine Particle Size Distributions
Authors: Chaiken J. , Goodisman Jerry
Published: April 2011

We briefly describe a model which seems to be applicable to a variety of coalescence growth systems. Spanning cluster growth, particle growth and hillock formation in thin metal films, this model is based on the Smoluchowski kinetic equations and fractals. We describe how this model has been able to suggest the effect of translational to internal energy conversion in coalescing systems in determining the shape of particle size distributions. We also suggest how this model can be employed to account for the behavior of hillocks in supersaturated alloy films under thermal annealing conditions.
Grain-Size Stability and Microhardness of Copper-Fullerene Nanocomposites
Authors: Holtz R.L. , Barrera E.V. , Milliken J. , Provenzano V.
Published: April 2011

Nanocomposites of copper with low concentrations of dispersed fullerenes were synthesized by simultaneous sputtering of copper and sublimation of fullerenes. Postdeposition heat treatments at 400 and 800 °C were performed to assess the thermal stability of the microstructure and the effect on the Vicker's microhardness. The as-deposited copperfullerene composite has submicron-scale granularity, in contrast to pure copper which has conventional columnar growth. Grain growth in the heat-treated fullerene-containing specimens is suppressed and the microhardness enhanced relative to pure copper.
Structural Characterization of Ordered Phases in Hydrocarbon Dendrimers
Authors: Buchko Christopher J. , Sioshansi Atisa , Xu Zhifu , Moore Jeffrey S. , Martin David C.
Published: April 2011

Structural characterization of phenylacetylene dendrimers (PADs) makes it possible to explore the relationship between molecular architecture and condensed phase organization. The size and geometry of the PAD series is precisely controlled, with phenylacetylene units emanating from a central phenylene in the manner of a tridendron. The branched molecule rapidly increases in size with each synthetic generation. The “shape-persistent” nature of the phenylacetylene molecule makes it ideal for use in the construction of self-assembling supramolecular systems.

Transmission electron microscopy (TEM) has been used to identify the crystal structure of lower generation PADs, and wide-angle X-ray studies confirm the decrease in crystallinity with size. Hot stage optical microscopy studies of thermal transitions reveal melting points for lower generation PADs, and an apparent glass transition for the amorphous higher generations. This type of structural information is essential to the rational design of self-assembling materials.
Nanostructured Fe-Co Catalysts Generated by Ultrasound
Authors: Suslick Kenneth S. , Fang Mingming , Hyeon Taeghwan , Cichowlas Andrzej A.
Published: April 2011

Bimetallic catalysts have been studied intensively because of their unique activity and selectivity. Unsupported alloy catalysts, however, are usually of limited value due to their very small surface areas. We have now developed a sonochemical synthesis of bimetallic alloys that provides both high surface areas and high catalytic activity. We have produced Fe-Co alloys by ultrasonic irradiation of mixed solutions of Fe(CO)5 and Co(CO)3(NO) in hydrocarbon solvents. The alloy composition can be controlled simply by changing the ratio of precursor concentrations. After treatment at 673K under H2 flow for 2 hours, we obtain nearly pure alloys. BET results show that the surface areas of these alloys are large (10-30 m2/g). TEM and SEM show that the alloy particles are porous agglomerates of particles with diameters of 10-20 nm. Sonochemically prepared Fe, Co, and Fe-Co powders have very high catalytic activity for dehydrogenation and hydrogenolysis of cyclohexane. Furthermore, sonochemically prepared Fe-Co alloys show high catalytic selectivity for dehydrogenation of cyclohexane to benzene; the 1:1 ratio alloy has much higher selectivity for dehydrogenation over hydrogenolysis than either pure metal.
Development and Characterization of Artificial Microstructures in Long Lengths of Superconducting Wire
Authors: Jablonski P. D. , Lee P. J. , Larbalestier D. C.
Published: April 2011

Conventional Nb-Ti superconductors are optimized by thermal and mechanical treatments which ultimately produce a nanostructure consisting of 1-2nm thick ribbons of α-Ti dispersed in a matrix of β-Nb-Ti. Several groups are now investigating artificial dispersions of second phase in Nb-Ti which may develop stronger flux pinning nanostructures. However, these new methods generally require true strains of 30 or more. We avoid these large strains (and their associated problems) by forming our composites from a mixture ∼ -50¼m size Nb and Nb-Ti powders, thus permitting the desired nanostructure to be produced with strains of order 12. Nb pinning particles were found to develop an irregular shape, tending to nanometer thick ribbons at large strains. The final size nanostructure resembles conventional Nb-Ti, except that the “second” phase is Nb rather than α-Ti. The critical current density (Jc) was found to increase by over two orders of magnitude to peak values of 5490 and 1980A/mm2 at 2 and 5T as the particle thickness was reduced.