bluuebunny/crossref_metadata_2025_split huggingface dataset:
Rapid Selective Annealing of Cu thin films on Si Using Microwaves
Authors: Brain R. A. , Atwater H. A. , Barmatz M. 
Published: April 2011

ABSTRACTA key requirement for future integrated circuit fabrication is lower processing temperatures at all stages of fabrication. Typical rapid thermal annealing processes, utilizing infrared radiation, heat the film as well as the substrate and create the potential for device reliability problems. Microwave annealing may enable a novel solution to the problem of selective annealing of metallic or other conductive thin films, which is possible in the limit where the metal film thickness is less than the skin depth of the material at microwave frequencies. This technique is advantageous because the relatively low absorption of silicon deters substrate heating and the metallic thin film shields the rest of wafer.We have investigated the quality factor, Q, and temperature of silicon as a function of its doping concentration and power input into the microwave cavity. As a particular application of microwave selective annealing, we have microwave annealed sub-micron Cu thin films sputtered on patterned SiO2/Si substrates and demonstrated an improvement in trench filling for use in interconnect metallization applications.
Microwave Sintering of Continuous Zirconia Ceramic Fibers
Authors: Vogt Gerald. J. , Unruh Wesley. P. , Plovnick Ross. H. 
Published: April 2011

ABSTRACTContinuous yttria-stabilized zirconia ceramic fibers approximately 10–15 μm in diameter have been rapidly sintered by pulling them through a tuned, 2.45 GHz single-mode TE103 microwave cavity in ambient air. The resulting fibers were analyzed by X-ray diffraction, scanning electron microscopy, and single-filament tensile tests. They were found to be unsplit, to have a submicron grain structure and a tetragonal crystal structure, and to exhibit considerable strength and flexibility.
Continuous Microwave Sintering of Ceramics
Authors: Cheng Jiping , Fang Yi , Agrawal Dinesh K. , Wan Zhangguo , Chen Lei , Zhang Yunjin , Zhou Jian , Dong Xuebing , Qiu Jinyu 
Published: April 2011

ABSTRACTThe microwave sintering technology is still at the developmental stage due to the limitation of the volume (or size) and batch of the ceramic products that can be fabricated by microwave processing. The present paper introduces a new microwave processing technique, i.e. a continuous microwave sintering, which makes it possible to sinter ceramic products with an infinite length in a microwave field. By this technique, alumina-mullite ceramic rollers of 40 mm in diameter and 2400 mm in length have been successfully microwave sintered. The exploratory results show this new technique could offer some new opportunities to scale up microwave sintering for industrial applications.
Metalorganic and Microwave Processing of Eutectic Al2O3-ZrO2 Ceramics
Authors: Willert-Porada M. , Gerdes T. 
Published: April 2011

ABSTRACTThe spatial distribution and sintering activity of ZrO2 governs the microstructure evolution upon microwave sintering of alumina-zirconia ceramics. Using the same microwave sintering profile thermal runaway occurs, when ZrO2-powders with high specific surface area are employed, yielding ceramics with eutectic Al2O3-ZrO2 inclusions, whereas ZTA-type ceramics are obtained from low specific surface area powders. Microwave sintering yields ceramics with a higher density at a particular sintering temperature as compared to conventional sintering.
A Cascaded Microwave Plasma Source for Synthesis of Ceramic Nanocomposite Powders
Authors: Vollath Dieter 
Published: April 2011

ABSTRACTBased on the experience of the synthesis of nanophased ceramic powders with particle size in the range of a few nanometers, a new device for the synthesis of ceramic nanocomposite powders was designed. The new equipment is based on a 915 MHz microwave system built of IEC 153 R9 waveguide elements. The microwaves coming from the magnetron are split up in two branches using an E-plane power splitter. The reaction tube, made of quartz, passes consecutively both branches of the wave-guide system. Behind the applicators with the reaction tube, the waveguides are terminated with sliding shorts. These sliding shorts are adjusted in a way to ignite and operate a plasma in both branches of the waveguide system simultaneously. The system allows the production of homogeneous powders for nanocomposites. “Nanocoated particles” can be obtained in some special cases;for example ZrO2 particles synthesized with sizes in the range between 4 and 5 nm can be coated with a 1 to 2 nm layer of Al2O3 or vice versa. Metal chlorides are selected as precursors for the reactions. A mixture of, argon with 20 vol% oxygen is used as a plasma gas.
Microwave Curing of Silicon Carbide Ceramics from a Polycarbosilane Precursor
Authors: Shan Tzyy-Heng Alex , Cozzens Robert 
Published: April 2011

ABSTRACTSilicon carbide ceramic materials have been successfully formed from commercially available polycarbosilane using microwave radiation as the sole source of heat. Conventional thermal processing of the same polymeric precursor was also studied for comparison with microwave processing. Microwave heating enhances crystallinity at much lower curing temperature and within shorter times. Possible explanations for microwave enhanced processing are proposed.
Luminescence Parameters of PBX2 (X=F, CI, Br, I) Crystals
Authors: Voloshnovskii A. S. , Pidzyrailo M.S. , Mikhallik V.B. , Rodnyi P.A. 
Published: April 2011

ABSTRACTSpectral and kinetic parameters of PbX2 (X=F, Cl, Br, I) crystals emission are investigated under pulse photo- (∆t=l.0 ns) and X-ray (∆t=l.5 ns) excitation in the temperature region from 77 to 293 K. X-ray luminescence of the PbF2, PbC12 and PbBr2 crystals is considered as radiative decay of the self-trapped excitons at the defects, while subnanosecund and nanosecond emission components are regarded to the result of the thermal quenching. The nature of the fast X-ray luminescence for PbI2 crystals is discussed from the viewpoint of the possibility for observation of radiative core-valence transition.
Dye Mixtures for Ultrafast Wavelength Shifters
Authors: Cangopadhyay S. , Barashkov N. , Liu L. , Palsule C. , Borst W. , Wigmans R. 
Published: April 2011

ABSTRACTWe have produced fast wavelength shifters using mixtures of various Coumarin dyes with DCM in epoxy-polymers (DGEBA+HHPA) and measured the properties of these wavelength shifters. The particular mixtures were chosen because there is a substantial overlap between the emission spectrum of Coumarin and the absorption spectrum of DCM. The continuous wave and time-resolved fluorescence spectra have been studied as a function of component concentration to optimize the decay times, emission peaks and quantum yields. The mean decay times of these mixtures are in the range of 2.5-4.5 ns. The mean decay time increases with an increase in Coumarin concentration at a fixed DCM concentration or with a decrease in DCM concentration at a fixed Coumarin concentration. This indicates that the energy transfer is radiative at lower relative DCM concentrations and becomes non-radiative at higher DCM concentrations.
Heavy Fluoride Glasses as an Alternative to Crystals in High Energy Physics Calorimetry
Authors: Dafinei I. , Auffray E. , Lecoq P. , Schneegans M. 
Published: April 2011

ABSTRACTIn the quest for low cost scintillators to equip the very large electromagnetic calorimeters for future High Energy Physics experiments, scintillating glasses can offer an attractive alternative to crystals. The expected production price is indeed supposed to be reduced as compared to crystals, especially for very large volumes. An intense R&D effort has been made by the Crystal Clear collaboration to develop heavy scintillating fluoride glasses in close collaboration with the industry. Results will be shown on the fluorescence and scintillation properties as well as on the radiation resistance of different types of fluoride glasses. Ideas about possible improvement of present performances will also be given.
Nanosecond Uv-Scintillations in Cesium Iodide
Authors: Gavrilov Vladimir , Chernov Stanislav 
Published: April 2011

ABSTRACTFast UV-luminescence of CsI has been studied by time resolved luminescent spectroscopy. Experimental data support the conclusion that the high temperature (150–500 K) fast UV-luminescence arises from the trapping of free excitons in sites perturbed by lattice defects.
Fast Luminescence and Absorption in BGO and SiO2
Authors: Gavrilov Vladimir , Chernov Stanislav 
Published: April 2011

ABSTRACTThe spectra and kinetics of the fast luminescence and optical absorption of Bismuth Germanate (BGO) after excitation by single high-power nanosecond and subnanosecond electron pulses were studied. The short-lived optical absorption of the center responsible for BGO scintillations is assigned. The cause for the low scintillation yield in BGO is discussed in comparison with analogous measurements in crystalline and amorphous silicon dioxide. The ultrafast (decay time < 50 ps) luminescence is observed and it is concluded that it can be connected to intraband transitions.
The Kinetics of Excitonic Luminescence in Mixed Silver Halides
Authors: Kotomin E. , Millers D. , Grigorjeva L. , Eglitis R. 
Published: April 2011

ABSTRACTTwo kinds of luminescence (excitonic luminescence and excitonic molecule luminescence) were investigated for solid solutions AgBr1-xClx after pulsed electron beam and N2 laser irradiation. Careful theoretical treatment of a set of experimental excitonic luminescence kinetics is presented. It is shown that the effective activation energy of Agoi migration is a linear function of the composition x. The narrow peak of the excitonic molecule luminescence shifts from 2.66ev in pure AgBr towards higher energies as x increases.
A Modified Fast Analog Technique for Determining Luminescence Decay Times of Scintillators
Authors: Liu L. , Borst W. , Palsule C. , Gangopadhyay S. 
Published: April 2011

ABSTRACTWe have modified our previous fast analog technique to determine the luminescence decay times of scintillators following an excitation with a Sr90β3-source. In the original technique [1], the sample was excited with a nitrogen-pumped dye laser, and the fluorescence pulses (consisting of typically 50 to 1000 photons) were detected by a multi-channel plate photomultiplier tube (MCP-PMT). The output from the MCP-PMT was directed to a fast waveform digitizer triggered externally by the exciting laser. In the modified technique, the digitizer acquires the fluorescence decay in the internal trigger mode, as no corresponding external trigger pulse is available from the Sr90source. For efficient light collection from scintillators, an ellipsoidal mirror assembly has been tested. The fluorescence decays are acquired as multi-photon pulses and are subsequently corrected for the temporal instrument response by using a deconvolution technique. The overall time resolution of the technique is about 100 ps. The fluorescence decay time obtained using this technique for a commercial scintillator (SCSN-81) agrees well with literature. We also discuss our results on new epoxy-polymer based scintillators prepared in our laboratory. The primary motivation for this work was development of new scintillators with shorter fluorescence decay times for high collision rate experiments.
Electronic Structure and Associated Optical Properties of LAPO4:Ce
Authors: Mishra K. C. , Johnson K. H. 
Published: April 2011

ABSTRACTLanthanum phosphate activated by cerium and terbium is a well known lamp phosphor which is used for its green emission. In this paper, we have investigated the electronic structure and associated optical properties of lanthanum phosphate doped with cerium using the self consistent field scattered wave molecular orbital cluster approach. Relativistic corrections are included for the lanthanum and cerium centered clusters. In spite of the small magnitude of crystal field splitting, a significant admixture of the f-like orbitals with the ligand orbitals is observed for cerium. The optical transitions are calculated using the transition state formalism. The absorption peaks due to electronic transition from the f-like states to d-like states of cerium are found to be 271 rim, 259 nm, 245 nm, 208 nm and 194 nm which are in good agreement with the experiment. The nature of the band gap transition in lanthanum phosphate is also discussed.
Methods For A Systematic, Comprehensive Search for Fast, Heavy Scintillator Materials
Authors: Derenzo S. E. , Moses W. W. , Weber M. J. , West A. C. 
Published: April 2011

ABSTRACTOver the years a number of scintillator materials have been developed for a wide variety of nuclear detection applications in industry, high energy physics, and medical instrumentation. To expand the list of useful scintillators, we are pursuing the following systematic, comprehensive search: (1) select materials with good gamma-ray interaction properties from the 200,000 data set NIST crystal diffraction file, (2) synthesize samples (doped and undoped) in powdered or single crystal form, (3) test the samples using sub-nanosecond pulsed x-rays to measure important scintillation properties such as rise times, decay times, emission wavelengths, and light output, (4) prepare large, high quality crystals of the most promising candidates, and (5) test the crystals as gamma-ray detectors in representative configurations. An important parallel effort is the computation of electronic energy levels of activators and the band structure of intrinsic and host crystals to aid in the materials selection process.
Scintillation Mechanism and Radiation Damage in CexLa1-xF3 Crystals
Authors: Wojtowicz A. J. , Lempicki A. , Wisniewski D. , Brecher C. , Bartram R. H. , Woody C. , Levy P. , Stoll S. , Kierstead J. , Pedrini C. , Bouttet D. , Koepke CZ. 
Published: April 2011

ABSTRACTRecent spectroscopic and radiation damage experiments on a series of CexLa1-xF3 crystals suggest that the scintillation light output is limited by an unusual quenching mechanism, which also plays a major role in minimizing radiation-induced damage. The intensity of the radiation-induced absorptions is a strong function ofthe Ce content x, reaching a maximum for x = 0.03 and a minimum for x = 1. This peculiar dependence appears to be due to the influence of deep-lying Ce levels onboth scintillation mechanism and radiation damage. We suggest that various charge transfer processes can explain many aspects of the performance of CexLa1-xF3 scintillators.
Light Output and Radiation Damage in A YAIO3:Ce 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 2.1 × 2.1 × 2.1 cm3 crystal of YA103:Ce. The light yield produces approximately 2867 photoelectrons per MeV on a photomultiplier tube with abialkali photocathode. The scintillation and light transmission properties of the crystalwere characterized before and after exposure to 1 Mrad of 60 Co gamma rays. Significant radiation induced optical absorption was observed near the optical band edge ofthe crystal, along with an extremely intense phosphorescence after irradiation. Partial spontaneous recovery from the damage occurred at room temperature, and it was possible to induce additional recovery by optical bleaching.
Electronic Trap Defects in Y2O3:Eu and (Y,Gd)2O3:Eu X-Ray Scintillators
Authors: Duclos Steven J. , Greskovich Charles D. , O'clair Chester R. 
Published: April 2011

ABSTRACTDetailed properties of the defects and energy transfers responsible for afterglow in transparent sintered ceramic Y2O3:Eu and (Y,Gd)2O3:Eu based scintillators have been determined by transient thermoluminescence ('TL) and spectral measurements of afterglow emission. X-ray excited TTL spectra between 150 K and 350 K reveal 4 defect transitions for 3 mole percent Eu. Adequate modeling of this data requires for each defect transition a trap depth energy, an attempt-to-escape frequency, a broadened density of trap state energies, and a trap filling frequency. These defect parameters have been determined and can be used to predict afterglow dependence on time after excitation shut-off, exposure time, and temperature. The afterglow emission spectra at all temperatures are characteristic of Eu under S6 site-selective UV excitation of these rare-earth C-type structure scintillators. This indicates that states associated with the Eu activator on the S6 site are the terminal states upon thermal release of trapped charge carriers.
A Review of the Status and Developmental Issues for Continuously-Reinforced Ti-Aluminide Composites for Structural Applications
Authors: Miracle D. B. , Smith P. R. , Graves J. A. 
Published: April 2011

AbstractA significant materials-based activity to develop Ti-aluminide metal matrix composites for high temperature aerospace structural applications is now underway. A review of the approaches, progress, and status of the development of continuously-reinforced Ti-aluminide metal matrix composites with matrices which contain a significant volume fraction of the ordered orthorhombic Ti2AlNb phase will be presented. The principal application considered is a gas turbine compressor rotor ring, and this influences the development approaches and properties goals. Specific development activity that will be presented includes modification and control of the matrix composition and microstructure, fiber coating treatments to control interdiffusion between the fiber and the matrix, and to improve the ability of the interface to support a mechanical load, and efforts to improve the properties of SiC monofilaments used as reinforcements. Critical issues that define the requirements for additional studies will be presented.
Fracture and Fatigue Resistance of Ag/Ta-coated SCS-6/Ti3Al Composites
Authors: Chiu Hsing-Pang , Yang J.-M. 
Published: April 2011

AbstractThe effect of a Ag/Ta coating on the fracture resistance of a notched SCS-6 fiber-reinforced Ti3Al matrix composite under both static and fatigue loading was investigated. The crack propagation patterns and damage mechanisms under various loading conditions were characterized and compared with the uncoated composite counterparts. The results show that the Ag/Ta-coated composites exhibit typical mode-I failure patterns under both static and fatigue loading, while mixed mode-I & H failure patterns were observed in the uncoated SCS-6/Ti-25-10 composite. Localized interfacial debonding, matrix cracking and fiber fracture in the crack wake were the responsible damage mechanisms for the Ag/Ta-coated SCS-6/Ti-25-10 composite. Extensive interfacial debonding, crack splitting and branching, however, were found to be the dominant mechanisms in the uncoated SCS-6/Ti-25-10 composite.
Composites Based on Molybdenum Disilicide: Progress and Prospects
Authors: Hardwick D. A. 
Published: April 2011

AbstractAs the temperature demands increase in advanced aerospace systems, engineering materials that can withstand 1200° to 1600°C exposure in air must be developed. MoSi2 is an intermetallic compound that has many, though not all, of the necessary physical and mechanical properties for use in this temperature regime. At ambient and moderate temperatures MoSi2 is brittle, but once the ductile-to-brittle transition temperature (DBTT) is exceeded, it rapidly loses strength. Recent progress in, and current status of, the research efforts in MoSi2 matrix composites will be reviewed, with an emphasis on the critical issues that currently impede progress to application.
The Influence of Mobile Dislocation Density on the Fracture Toughness of B2-Based Ni-Fe-Al Alloys
Authors: Misra A. , Noebe R. D. , Gibala R. 
Published: April 2011

AbstractThe deformation and fracture behaviors of two directionally solidified multi-phase Ni-Fe-Al ordered alloys were investigated. One alloy consisted of continuous β+γ lamellae with fine γ precipitates within the γ phase. The NiAl-based β phase of this alloy exhibited <100> slip even when deformed parallel to the [001] growth direction. This material exhibited an initiation fracture toughness of ∼ 30 MPa √m and tensile ductility of 10%. The second alloy consisted of aligned but discontinuous γ lamellae within a continuous β phase. Again, the γ phase contained γ precipitates, but unlike the previous alloy, the β phase also contained a fine dispersion of bcc precipitates due to spinodal decomposition. The β phase of this alloy deformed by <111> slip. This four-phase alloy exhibited a fracture toughness of ∼ 21 MPa √m and tensile ductility of 2%. Observations of the plastic zone in both alloys indicated significant plasticity in the β phase due to easy slip transfer from the ductile second phase. The enhanced fracture resistance of these multiphase materials compared to single phase β alloys is attributed in large part to intrinsic toughening of the β phase by an increased mobile dislocation density due to efficient dislocation generation from the β/γ interfaces.
Fracture Toughness of Two Cr2Hf+Cr Intermetallic Composites as a Function Temperature
Authors: Ravichandran K. S. , Miracle D. B. , Mendiratta M. G. 
Published: April 2011

AbstractFracture toughness as a function of temperature was evaluated for two Cr2Hf+Cr intermetallic composites, each in two different microstructural conditions. The proeutectic microstructures based on Cr-6.5Hf (at%) showed a significant increase in fracture toughness with an increase from room temperature to 600°C. The coarse microstructure obtained by heat treatment at 1500°C showed evidence of ductile behavior of Cr at a lower test temperature (200°C) relative to that of one heat treated at 1250°C (400'C). In the eutectic microstructures based on Cr-13Hf, only a small increase in fracture toughness at 600°C was seen. The results are analyzed in the light of fracture micromechanisms.
Microstruciture and Properties of Intermetallic Matrix Composites Produced by Reaction Synthesis
Authors: Alman D. E. , Hawk J. A. , Dogan C. P. , Ziomek-Moroz M. , Petty A. V. 
Published: April 2011

AbstractIn this US Bureau of Mines study, a variety of TiAl based composites were produced in situ by reaction synthesis. Mixtures of elemental Ti, Al and B and Ti, Al, and Si powders were reactive hot-pressed to form TiAl reinforced with 10, 20, 25 or 60 vol. pct. TiB2 or Ti5Si3. Microstructural evaluation of the resultant composites confirmed that the reaction products were primarily TiAl and TiB2 or Ti5S3, with a small amount of Ti3Al. The hot-press temperature and pressure had a significant effect on the density of the composites. In general, higher temperatures and initiating the reaction under pressure promoted dense composites. Room temperature biaxial flexure strength tests indicated that the addition of the reinforcing phases can improve the strength of TiAl. Potentiodynamic experiments revealed that TiAl, TiAl+TiB2 and TiAl+Ti5Si3 composites display active-passive corrosion behavior in both acidic and alkaline solutions.
Processing and Mechanical Properties of Laminar Al2O3-Ni3Al Composites
Authors: Schneibel J. H. , Alexander K. B. 
Published: April 2011

AbstractSeveral compositions of the intermetallic alloy Ni3Al were examined with respect to (a) their wetting of Al2O3 and (b) their energy absorption capability in Al2O3/Ni3Al laminates. Wetting is enhanced by small additions of carbon (e.g., 0.1 at. %), and bonding by additions of zirconium (e.g., 1 at. %). Chevron-notched laminate specimens were tested in three-point bending to assess the energy absorption due to the presence of a thin layer of Ni3Al. A nickel aluminide with the composition Ni-22Al-lZr-0.1C-0.1B was found to have a reasonable combination of wetting, adhesion and energy absorption. Interfacial bonding was found to be weak in all laminates.