bluuebunny/crossref_metadata_2025 huggingface dataset:
Field dependent change of the critical current density in neutron irradiated A15 superconductors with grain boundary pinning
Authors: Küpfer H. , Meier-Hirmer R. , Reichert T.
Published: February 2003

The dependence of the upper critical field (Hc2) and the critical current density ( jc) on fluence has been measured up to 1.2×1019 cm−2 (E≳1 MeV) for V3Si bulk material irradiated with neutrons at ambient reactor temperatures. Dislocation loops are identified by TEM as the part of the radiation induced defects responsible for jc. Using these results it is shown that the increase in jc of irradiated A15 superconductors with grain boundaries is not due to the raised Hc2 but corresponds to the radiation induced dislocation loops. The volume pinning force of these defects has the same temperature dependence but quite a different field dependence than the grain boundary pinning. By superposing the dislocation loop pinning on the grain boundary pinning we obtain an enhancement of jc which increases with increasing field in excellent agreement with the observed field dependent increase of jc in neutron irradiated A15 superconductors. Deviations from the experimental values for high-jc materials and consequences for the high field mechanism of Kramer’s model are discussed.
Measurements of acoustic velocity and attenuation shifts at the spin-reorientation phase transition of TmFeO3
Authors: Gorodetsky G. , Shtrikman S.
Published: February 2003

Measurements of sound velocity and attenuation changes at the spin-reorientation region are reported. The measurements were carried out with a magnetic field applied along the a axis of the orthorhombic crystal. A cw ultrasonic interferometer, which is described here in detail, was employed for these measurements. The observed velocity shifts are satisfactorily accounted for using a phenomenological model with a quadratic magnetoelastic term. The effect of magnetic domains on the attenuation peaks is also discussed.
Photoacoustic measurement of the ruby quantum efficiency
Authors: Quimby R. S. , Yen W. M.
Published: February 2003

We have measured the radiative quantum efficiency (QE) of the ruby fluorescence using a novel photoacoustic technique. The technique requires the measurement of the phase of the photoacoustic signal as a function of chopping frequency, and is applicable to systems with a simple decay scheme and a sufficiently long fluorescence lifetime. The measured value QE=0.900.05 is consistent with several previous optical measurements.
The effects of thermal stress on the temperature dependence of degradation in GaAs0.9P0.1 LED’s operating at high current densities
Authors: Shimano Noriyuki
Published: February 2003

Experiments on the temperature dependence of degradation in GaAs0.9P0.1 LED’s operating at high current densities have been carried out in order to establish the reliability of the LED’s for optical fiber communication systems. For the first time, direct experimental evidence is presented which shows that the values of activation energy for the degradation depend on the thermal stress caused by the different thermal expansion coefficients between the GaAs substrates and GaAs0.9P0.1 epitaxial layers. The activation energy for the degradation of the LED’s with GaAs substrates always has negative values (−0.3∼ − 0.1 eV), while LED’s without GaAs substrates always have positive values (0.25 ∼ 0.1 eV). Growth velocities of 〈100〉 DLD’s, which accompanied the degradation, also depend on the thermal stress and show an anomalous temperature dependence. Great care is required in using the conventional extrapolation techniques to predict lifetimes at room temperature.
Measurement of compression and shear waves in an impact experiment: Role of gauge leads in particle-velocity measurements
Authors: Gupta Y. M.
Published: February 2003

The role of gauge leads in measurement of shear waves by the IMPS method is examined in detail. The results presented here show the importance of gauge lead considerations in particle-velocity measurements. In particular, the use of side gauge leads is not desirable.
Temperature dependence of Hall mobility in indium–tin oxide thin films
Authors: Morris J. E. , Ridge M. I. , Bishop C. A. , Howson R. P.
Published: February 2003

Carrier concentrations and mobilities of vacuum-prepared indium–tin oxide films have been measured to determine the effects of annealing. The apparent variation of electron mobility with temperature in these films is interpreted in terms of a grain-boundary barrier model. No grain growth was observed in the films studied; all changes in electron density and mobility may be explained by oxygen diffusion in the grain boundaries and, from them, into the grains themselves.
Low-power nonlinear effects in the ferromagnetic resonance of spheres of Ba3Zn2Fe24O41
Authors: Goldberg I.B.
Published: February 2003

Foldover effects in the ferromagnetic resonance spectra of Ba3Zn2Fe24O41 (Zn2Z) were observed at 35 GHz. The critical microwave field for the effect was about two orders of magnitude smaller than that calculated for models of foldover due to magnetocrystalline anisotropy. Since these particles were spherical within optical microscope resolution, it is not anticipated that shape anisotropy contributes to this nonlinear effect. Because of the large anisotropy field (481 mT) it is likely that higher-order effects can also contribute to nonlinear behavior. This is the first reported example of foldover in a hexagonal ferrite.
Nickel and iron—Multivalence impurities in GaP
Authors: Ennen H. , Kaufmann U.
Published: February 2003

Electron paramagnetic resonance and optical absorption measurements have been used to monitor the relative Ni0, Ni–, and Ni– – concentrations in various GaP samples with widely differing Fermi-level positions. The data demonstrates that the two-electron trap state Ni– – dominates in n-type GaP, while Ni– and Ni0 are dominant in high-resistivity p-type material. Light-induced valency changes with below band-gap light were observed for all three charge states. The previously reported Fe– – level position is discussed in the light of the present Fe– – EPR data and the role of Ni and Fe as trapping centers in Zn-diffused GaP light-emitting diodes is emphasized.
Transit-time considerations in short-pulse photoconductivity
Authors: Mathur V. K. , Lee Chi H.
Published: February 2003

Little attention has been paid so far on the transit-time effects in the short-pulse photoconductivity. This paper discusses the effect of transit time on the time evolution of carriers in short-pulse photoconductivity. This is likely to effect the rise time of a fast-switching device. It is concluded that, due to the transit-time effects, a device using surface generation of carriers would have faster rise time than a device in which carriers are generated in the bulk, particularly when the specimen is thick.
Plasma poling of poly(vinylidene fluoride): Piezo- and pyroelectric response
Authors: McKinney J. E. , Davis G. T. , Broadhurst M. G.
Published: February 2003

A plasma poling technique and its use with polyvinylidene fluoride (PVDF) films is described. Specimens of biaxially drawn (blow extruded) PVDF containing both Form I ( β) and Form II (α) crystals were poled under various conditions in a plasma field while the charging current was monitored to determine the polarization. Subsequently, both piezoelectric and pyroelectric activity were measured in order to evaluate their magnitudes with respect to the remnant polarization (that is, the polarization remaining after returning the applied field to zero). The results are shown to be in reasonable quantitative agreement with the predictions of a model of PVDF consisting of a mixture of preferentially aligned crystals in randomized amorphous material.
Simple-heating-induced Josephson effects in quasiparticle-injected superconducting weak links
Authors: Kaplan S. B.
Published: February 2003

The characteristics of quasiparticle-injected superconducting weak links containing films with short electron mean-free paths have been studied. The behavior of these devices at T=4 K is shown to be consistent with a spatially localized nonequilibrium state in which the electrons and the crystal lattice are at an elevated temperature T*≳T.
Pyroelectric transient response of polyvinylidene fluoride
Authors: Das-Gupta D. K. , Doughty K.
Published: February 2003

The pyroelectric responses of conventionally poled films of polyvinylidene fluoride to a step input of radiation have been analyzed and shown to be well described by the superposition of two decaying exponentials governed by the thermal and the electrical time constants of the system respectively. The peak response of the pyroelectric current transient was observed to be proportional to both the pyroelectric coefficient d31 for PVF2 films of 25 μm thickness so that the peak current response curve may be used to evaluate p (T) and d31.
Quantitative photoacoustic spectroscopy applied to thermally thick samples
Authors: Poulet P. , Chambron J. , Unterreiner R.
Published: February 2003

Based upon the Rosencwaig and Gersho theory of the photoacoustic effect, a simplified model, which applies to thermally thick samples, is presented. The theoretical variations of the modulus and of the phase of the photoacoustic signal are compared to the experimental results for a wide range of very or moderately absorbing materials. The variations of the tangent of the phase with regard to the wavelength reproduce an absorption spectrum turning the photoacoustic spectroscopy into a quantitative technique.
Optical studies of anodic oxide films on GaAs using a rotating light-pipe reflectometer
Authors: Silberstein R. P. , Pollak Fred H.
Published: February 2003

We report the use of a rotating light-pipe reflectometer (RLPR) for the in situ optical study of anodic oxide films on GaAs during their growth and dissolution. Different stages in the oxidation process can be easily identified, including electro-etching, island formation, uniform film growth, and oxide dissolution. The dissolution curve is used to determine the dissolution rate as a function of oxide thickness. In addition, the RLPR is used to measure the spectral dependence of the reflectivity of anodized GaAs in situ. Using the reflectivity expression for a three-layer system (i.e., GaAs, oxide, electrolyte) we have been able to fit our data using the previously measured optical constants of the oxide.
Optical properties of ultrafine aluminum particles
Authors: Granqvist C. G. , Hunderi O.
Published: February 2003

Ultrafine Al particles with median diameters of 3–4 nm were produced by gas evaporation in He+O2. Optical transmittance measurements for wavelengths of 0.3–2.5 μm gave reproducible results. These can be reconciled with the Maxwell Garnett theory with one exception: the parallel band absorption, occurring at 0.85 μm in bulklike specimens, is much less visible than theoretically predicted. This is possibly caused by defect scattering inside the particles, which increases the featureless Drude absorption, although other mechanisms may also be operative. The study provides a basis for modeling ’’integrally’’ colored anodic Al2O3.
Scaling of (MHD) instabilities in imploding plasma liners
Authors: Hussey T. W. , Roderick N. F. , Kloc D. A.
Published: February 2003

The dynamics of imploding foil plasmas is considered using first-order theory to model the implosion and to investigate the effects of magnetohydrodynamic instabilities on the structure of the plasma sheath. The effects of the acceleration-produced magnetohydrodynamic (MHD) Rayleigh-Taylor instability and a wall-associated instability are studied for a variety of plasma implosion times for several pulsed power drivers. The basic physics of these instabilities is identified and models are developed to explain both linear and nonlinear behavior. These models are compared with the results of detailed two-dimensional magnetohydrodynamic simulations. Expressions for linear Rayleigh-Taylor growth are developed showing its dependence on driving current, plasma conductivity, and density gradient scale length. A nonlinear saturation model, based on magnetic field diffusion, is developed. The model for a wall instability involves the interaction of the plasma sheath with the electrode wall and the material ablated from the electrode. The growth of this instability is shown to be limited by field diffusion. Comparison with two-dimensional simulations has been excellent.
X-ray photoelectron spectroscopy and paramagnetic resonance evidence for shock-induced intramolecular bond breaking in some energetic solids
Authors: Owens F. J. , Sharma J.
Published: February 2003

Solid samples of 1,3,5, trinitro 1,3,5, triazacyclohexane (RDX), trinitrotoluene (TNT), and ammonium nitrate were subjected to shock pulses of strength and duration less than the threshold to cause detonation. The recovered shocked samples were studied by x-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The results of these measurements indicate that the shock pulse either broke or altered the internal bonds of the molecules of the solid. The results of the shock decomposition are compared with measurements of the uv and slow thermal decomposition of these materials using the same experimental techniques.
Dielectric spectroscopy of a-Se and some a-Se : As alloys
Authors: Abkowitz M. , Pochan D. F. , Pochan J. M.
Published: February 2003

Dielectric activity is observed in a-Se and in some a-Se : As alloy films in the neighborhood of their respective glass transition temperatures. When measurements are made at fixed frequency in the temperature scan mode, enthalpy relaxation and volume hysteresis effects are readily identified. Relaxation behavior conforms to the phenomenological WLF equations and for a:Se C1=10.4 and C2=20.5 K. The free volume fraction is 0.042. Arsenic addition to a-Se significantly broadens the relaxation distribution function and increases the relaxation oscillator strength. The effective incremental dipolar contribution per As atom is 0.6 D despite the very small Pauling ionicity of the Se : As bond. The latter is consistent with the formation of a polar pyramidal complex at each incorporated As site. Sub-Tg relaxation processes are not observed in a-Se. Dielectric activity in homopolar a-Se could reflect contributions from polar chemical impurities, deformation induced dipoles, or dipoles associated with native charged defect pairs. It is the latter two which are the most likely candidates. In both cases estimates of the unit dipole strength and density will vary depending on calculational models.
Raman measurements of temperature during cw laser heating of silicon
Authors: Lo H. W. , Compaan A.
Published: February 2003

We present the first Raman data from laser-heated silicon obtained in situ during the laser irradiation. Analysis of the Stokes to anti-Stokes ratios yields temperatures at the center of the laser spot which range from room temperature to the melting point as laser power is increased. The data agree well with the nonlinear heat diffusion calculations of Lax for Gaussian beam profiles when the temperature dependence of the silicon absorption coefficient is included. In addition, we show that analysis of the spectral profile of the Raman line can yield information on strain effects produced in the laser-heated spot.
Anomalous high-field electron injection and photoconduction in thin-film alkali halides
Authors: Pisanias Michael N. , Hamill William H.
Published: February 2003

Transient ion currents in thin-film alkali halides at ca. <2 V, which may exceed 10−4 A cm−2 at 1 ms, decay rapidly according to I∝t−m with 0<m<1 and activation energies of ca.1 eV. At slightly higher applied voltages, e.g., 2.3 V for KI, there are well-defined thresholds for electronic conduction. The current rises slowly and may approach 0.1 A cm−2 within 1 s, depending on voltage and temperature. For oscilloscopic presentation the initial applied voltage is 3.5–6.0 V for KI and with appropriate external resistance the increasing electronic current sweeps the potential difference across the film downward. This procedure discloses other discrete conduction regimes at 3.8 and 2.4 V. The noise amplitude attains 20% of the mean value with a random frequency estimated at ∼1 MHz. This current is attributed to field injection associated with a compact space charge at the cathode resulting from precursor defect ion drift in the disordered film. These thresholds have been confirmed by photoconductivity measurements of I versus hν in the 2–4-eV range by injection from the Al cathode. For KCl, KBr, KI, and RbI the thresholds for I versus V were verified and three injection modes were found altogether for each system.
Emission of particles from a charged sphere into a magnetic field
Authors: Sherman Christopher
Published: February 2003

Trajectories of particles emitted normally from a charged sphere into a constant magnetic field are examined. Calculations are made which separate such trajectories into two classes, those which return to the sphere and those which do not.
Models of high-power discharges for metal-Xe excimer lasers
Authors: Shuker R. , Gallagher A. , Phelps A. V.
Published: February 2003

High-power (∼108 W/l) discharges in metal-doped Xe are modeled for typical metal atom densities of 1015–1017 cm−3 and Xe densities of ∼1020 cm−3, and electron densities of 1014–1017 cm−3 as appropriate for proposed excimer lasers. Na is used as a prototype species, while its properties are varied to indicate some of the changes that could result from the use of different metals. The model includes sixteen excited levels of Na, three ionic species, the excimer levels of NaXe, and Na2. The degree of ionization is determined by collisional multistep excitation and ionization of excited atoms versus dissociative recombination of electrons with Na+2. Steady-state conditions in the positive column are calculated for typical gas temperatures of ∼0.06 eV and electron temperatures Te of 0.3–0.5 eV. The Na population distribution is largely Boltzmann at the electron temperature and the electron density is close to the Saha equilibrium value except at low electron temperatures and very high extracted laser powers. Useful gain and extracted powers of ∼10 MW/cm3 are predicted for the higher Te and Na densities, with the pulse width limited to ∼10−7 sec by gas heating. The model indicates that a metal which produces a deeply bound product state via dissociative recombination could yield a very efficient high-power laser or gain cell.
Characteristics of a TEA CO2 laser preionized by ultraviolet light
Authors: Yamabe Chobei , Matsushita Toshio , Sato Saburo , Horii Kenji
Published: February 2003

The discharge characteristics of the main electrode both in low-voltage and in high-voltage regimes at 1 atm pressure are described. The number of initial electrons effective in the main gap discharge depend on the polarity of the main electrode. The photoemission of the electrons from the cathode situated near the uv source is very large and accounts for about 70 –80% of the total electrons. Also described is the influence of additive gas on both the electrical discharge and laser output power.
Development of highly repetitive phosphate glass lasers
Authors: Kuroda Hiroto , Masuko Harutake , Maekawa Shigeru , Izumitani Tetsuo
Published: February 2003

High repetition rate operation of glass lasers up to 30 Hz has been successfully achieved for the first time by developing and using new kinds of phosphate glass. The key point of the success is to make the variation of optical path measured at any distance from the center of the glass rod nearly equal to zero by canceling out the effect of the temperature change of the index of refraction with that of the thermal expansion. This provides a new criterion on the glass design. The glass laser will not suffer any more from the disadvantage of the low thermal conductivity of the material, and its quality may become comparable with that of the YAG laser. The application of these kinds of glass into high-power lasers has enabled us to construct a high repetition rate high-power laser system (1 GW, 10 Hz), which will provide new applications to basic science and engineering.
Phase matching temperature variation of second-harmonic generation in Li out-diffused LiNbO3 layers
Authors: Noda Juichi , Fukuma Masaharu , Ito Yoshio
Published: February 2003

Li out-diffusion occurs in LiNbO3 during Ti in-diffusion for waveguide fabrication. Phase matching temperature measurements of 1.06-μm second-harmonic generation are used to observe waveguide parameters. Undesired Li out-diffusion effects can be minimized by using a high (over 49%) melt mole fraction of Li2O or by using a high Ti-diffusion temperature.
On the use of the photoacoustic effect for investigating phase-transitions in solids
Authors: Siqueira M. A. A. , Ghizoni C. C. , Vargas J. I. , Menezes E. A. , Vargas H. , Miranda L. C. M.
Published: February 2003

By exploring the dependence of the photoacoustic signal on the thermal properties of the sample, we demonstrate experimentally the usefulness of the photoacoustic effect for investigating phase transitions in solids. Special application is made for the case of Al-doped VO2. We also describe the photoacoustic cell utilized and the complete characterization of the cell is done by using a piece of germanium in single-crystal form which has well known thermal properties.
Variational description of the positive column with two-step ionization
Authors: Crawford F. W.
Published: February 2003

The ionization balance in diffusion-dominated discharges may depend on both one- and two-step ionization processes. The Spenke diffusion equation (D∇2n+νn+kn2=0) describing such conditions is solved in this paper by the Rayleigh-Ritz variational method. Simple analytic approximations to the density profile, and the similarity relation between ν, k, D, and the discharge dimensions, are derived for planar and cylindrical geometry and compared with exact computations for certain limiting cases.
Interferometric measurement of asymmetric electron density profiles of laser-created plasmas from composite plane targets
Authors: Illingworth R. , Thareja R. K. , Raven A. , Rumsby P. T. , Stamper J. A. , Willi O.
Published: February 2003

Interferograms of composite plane-target coronal plasmas have been analyzed by separate Abel inversion on each side of the interface between plasmas of different atomic number. The density difference measured across the interface changes sign near the central region of the interface. The absence of Faraday rotation of a visible probe beam in previous experiments is explained.
Determination of the total emittance of n-type GaAs with application to Czochralski growth
Authors: Jordan A. S.
Published: February 2003

We have calculated the total emittance εt of n-type GaAs as a function of doping level and thickness in the temperature range between 300 and 1500 °K. εt is related to the spectral emittance ελ, which in turn depends on the index of refraction, thickness, and absorption coefficient α. To obtain a theoretical representation of α, a model is constructed which includes contributions by the fundamental edge, interconduction band, and free carriers (acoustic and optical phonons and ionized impurities). Since this two-parameter model offers a good description of assorted α measurements with respect to wavelength, impurity level, and temperature, the evaluation of ελ is relatively straightforward. At each temperature, εt is computed by the numerical integration of ελ over a wide wavelength range followed by normalization to σT4. The calculations show that εt increases with temperature and doping level. At 1300 °K, for a 1-cm-thick sample, as the carrier concentration rises from 1016 to 1017 cm−3, εt increases from 0.28 to 0.68, respectively. These results are compared with those for Ge and general comments are made on the εt of p-type and semi-insulating GaAs. Finally, employing εt as one of the parameters in the quasi-steady state heat transfer/thermal stress model for dislocation generation in the Czochralski growth of GaAs, we explain the inherent difficulty encountered in pulling sizable defect-free crystals in terms of the severe thermal strss generation in excess of the critical resolved shear stress. One realistic set of conditions that would lead to a dislocation-free GaAs is small diameter (∼1 cm), light doping concentration (∼1016 cm−3), and shallow ambient temperature gradient (<100 °K).
Z dependence of thick-target β-ray backscattering
Authors: Sharma K. K. , Singh M.
Published: February 2003

Variation of β-ray backscattering with the atomic number of target material has been studied using thick targets of polythene, aluminum, iron, copper, zinc, tin, silver, tungsten, and lead for five β emitters, viz., 35S, 147Pm, 204Tl, 32P, and 90Sr-90Y. Effects of geometry and β-ray end-point energy have been investigated using a reflection geometry in which the geometry factors were varied by more than 40 and β-ray energy varied over a range 0.167–2.27 MeV. It is found that the mean value of the index of Z dependence of β-ray backscattering is 1.840.05 over these regions of geometry and energy. Deviations for soft β emitters have been confirmed as due to air absorption. The importance of these results in studies of two-component systems is emphasized.
Extreme ultraviolet induced forward photoemission from thin carbon foils
Authors: Hsieh K. C. , Keppler E. , Schmidtke G.
Published: February 2003

Thin carbon foils have become integral parts of low-energy particle detectors in forthcoming space experiments. In these devices, the foil acts as electron source for signal generation. Since 10–20-eV photons can also generate electrons from these foils and since intense HLα and He i resonance lines prevail in space environment, forward photoemission yield in carbon foils must be investigated. Crabon foils of 2.0, 7.0, and 14.0 μg cm−2 thickness (density 1.35 g cm−3) are subjected to 121.6-nm or 10.2-eV photons and 58.4-nm or 21.2-eV photons and the corresonding forward photoemission yield and transmittance are obtained. Energy distributions of photoemitted electrons are also measured.
Photoluminescence analysis of annealed silicon crystals
Authors: Tajima Michio , Kishino Seigô , Kanamori Masaru , Iizuka Takashi
Published: February 2003

The photoluminescence (PL) technique has been used in the analysis of heat-treated silicon crystals to investigate the origin and the behavior of thermally induced defects. The PL measurements were made at liquid helium and liquid nitrogen temperatures on various groups of commercial wafers which were subjected to an isochronal annealing at a temperature between 450 and 1250 °C for 64 h. The PL results were compared with the results obtained by other characterization techniques, in particular, the infrared (IR) spectroscopy. After heat treatment at 450 °C, a new PL pattern appeared at 4.2 K, if the crystal contained a high concentration of oxygen. The new pattern is proved to be associated with the thermally induced donors. The PL and IR results classified Czochralski-grown wafers into two categories. Various heat treatments made a great change in the PL spectra for some wafer groups (category I), but a little change for the other wafer groups (category II). Correspondingly, the decrease in the interstitial oxygen concentration due to annealing was large for category I and small for category II. The PL intensity reduction at lower temperatures (600<T<900 °C) was closely correlated with the formation of silicon-oxygen complexes. It can be concluded that the Si-O complexes is produced with greater ease in category I than in category II. The variation in the configuration and/or the density of the Si-O complexes may induce the PL spectral change. Possible factors which separate the two categories are residual carbon and the thermal history of the crystal.
Liquid phase epitaxial growth of CdTe/Hg1−xCdxTe multilayers (0.3<x<0.5)
Authors: Chu M. , Wang C. C.
Published: February 2003

CdTe/Hg1−xCdxTe multilayers (0.3<x<0.5) were obtained for the first time by a liquid phase epitaixal (LPE) technique. The layers were grown on (111)A oriented CdTe substrates. The surface morphology of these multilayers is similar to those of HgCdTe single layers reported before. The cross diffusion at the CdTe/Hg1−xCdxTe interface has been as small as 0.3 μm for the thin CdTe epilayer. The first CdTe/HgCdTe heterojunction sensitive to ∼2.8 μm at 77 K has been demonstrated.
Current suppression induced by conduction-band discontinuity in Al0.35Ga0.65As-GaAs N-p heterojunction diodes
Authors: Wu C. M. , Yang E. S.
Published: February 2003

Curent suppression in Al0.35Ga0.65As-GaAs N-p heterojunctions is observed experimentally. The data are explained by examining the carrier transport modified by electron accumulation in the interface potential notch resulting from the conduction-band discontinuity. In addition, it is found that the temperature dependent I-V measurements can be used to deduce the magnitude of ΔEC at the junction interface.
Photoionization measurements in the CO2 laser gas mixture seeded with tripropylamine
Authors: Rozkwitalski Z. , Grodel M.
Published: February 2003

The influence of the tripropylamine content in the CO2 laser gas mixture on the spatial distribution of electrons produced by photoionization has been studied. The data, obtained for a standard CO2 TEA laser uv source, indicate that two processes are involved in the mechanism of tripropylamine photoionization. Photoabsorption parameters for both processes have been found.
A new loss mechanism in ultralow loss optical fiber materials
Authors: Mori Hidefumi , Izawa Tatsuo
Published: February 2003

Absorption characteristics for LiF, BaF2, CsI, KCl, KRS-6, and SiO2 have been measured by laser calorimetry in order to estimate the transparency limit. Weak absorption tails, which differ from the Urbach tail, were observed to follow an exponential law. It is found that the weak absorption tail indicates the transparency limits for these materials.
Barrier heights of evaporated metal contacts on Zn3P2
Authors: Wyeth N. Convers , Catalano A.
Published: February 2003

Contact barrier heights are reported for twelve metals on zinc phosphide (Zn3P2). The results do not show a simple dependence on metal work function, but correlate with a chemical heat of reaction indicating the importance of chemical bonding at the metal/semiconductor interface.
Donor-acceptor-type complex in GaAs—Further comment
Authors: Dean P. J. , Herbert D. C.
Published: February 2003

A sharp luminescence line at 1.51165 eV with the unusual properties of very large Zeeman splittings and very small splittings under uniaxial stress compared with typical shallow bound excitons was recently reported by Reynolds, Almassy, Litton, Nam, and McCoy [J. Appl. Phys. 49, 5336 (1978)]. We show that the description favored by these authors, electron-hole recombination at either a neutral double donor–single acceptor or a double acceptor–single donor complex, is inadequate to account for the properties they report. In particular, the effects of the local axial field of the complex on the zero field and magnetic character of the electron-hole states have been disregarded. We discuss possible interpretations and conclude that recombination within a biexciton bound to a neutral axial complex containing a biacceptor and two single donors can give a satisfactory explanation of all the unusual properties reported for the 1.51165-eV line.
The temperature dependence of the elastic constants of a machinable glass-ceramic
Authors: Harrington S. N. , Brewer J. A. , Pederson D. O.
Published: February 2003

The velocities of longitudinal and transverse ultrasound at a frequency of 10 MHz have been measured in a machinable glass ceramic (Corning Macor 9658) over the temperature range from 4.2 to 300 K using a pulse-echo overlap technique. The glass ceramic is a glassy matrix containing randomly oriented mica crystallites which are approximately 2 μ thick and 5–20 μ square, and which comprise approximately 50% of the volume. The room-temperature elastic constants calculated from the sound velocities are in good agreement with values calculated from the technical specifications given for Macor by Corning Glass Works. The longitudinal elastic constant at 4.2 K is 8.145×1010 N/m2 and the shear elastic constant at 4.2 K is 2.729×1010 N/m2. The general temperature dependence of the elastic constants is characteristic of a glassy material. The Debye heat capacity is shown to be less than the measured heat capacity at low temperatures as is typical of glassy materials.
Effects of solitary waves upon the shock profile in a three-dimensional lattice
Authors: Powell John D. , Batteh Jad H.
Published: February 2003

Shock propagation in a three-dimensional monatomic fcc lattice is studied using a computer-molecular-dynamic technique. It is demonstrated that compression of the lattice gives rise to a spectrum of well-defined longitudinal pulses (solitary waves) which propagate in the vicinity of the shock front amid the thermal background of the lattice. The properties of these pulses are examined in some detail and it is demonstrated that they are not completely stable. Rather, they tend to decay as they propagate into the lattice, producing both random thermal motion and, in some cases, transverse solitary-wave motion. The effects of the solitary waves upon the temperature, density, and stress profiles and upon the approach to thermal equilibrium behind the shock front are investigated. Our results are compared with those of others and some indication of desirable future work is given.
Grain-boundary self-diffusion in Pb
Authors: Gupta D. , Kim K. K.
Published: February 2003

We have carried out self-diffusion studies along grain boundaries in polycrystalline Pb specimen in the temperature range of 70–200 °C. Pb203 radioactive isotope (half life of 52.1 h) was used as a tracer, and precision microtome serial sectioning and high-efficiency gamma counting techniques were employed. The combined diffusion parameter δDb in Pb grain boundaries is expressed by the Arrhenius relation δDb=(6.1±0.9)×=10−9 exp(−0.46±0.01 eV/kT)(cm3/sec) .
Determination of the high-temperature bulk modulus from self-diffusion experiments demonstrated for tungsten
Authors: Falter C. , Zierau W.
Published: February 2003

An expression relating the temperature dependence of the Gibbs free energy of a defect process (such as formation, migration, or activation) to the thermoelastic properties of a crystal which has recently been shown to follow from a purely general thermodynamical basis has been applied to analyze self-diffusion measurements in tungsten. It is shown that the high-temperature bulk modulus can be predicted up to the melting point from the measured diffusion. Additionally, as an example for the accordance of diffusion and elastic data, the slight curvature in the Arrhenius plot of the diffusion coefficient of potassium as well as its activation volume are shown to follow from thermoelastic experiments.
Improved molecular-beam epitaxial GaAs power FET’s
Authors: Wood C. E. C. , DeSimone D. , Judaprawira S.
Published: February 2003

Predeposition of tin has been used as the sole dopant source to produce exponentially decreasing free-donor profiles in molecular-beam epitaxial GaAs films. The incorporation was found to be first order with respect to surface tin concentration and have an effective activation energy of −1.35±0.1 eV, which does not agree with a Schottky barrier model of incorporation. Films with such profiles were used to fabricate power FET structures which demonstrated good linearity. Source-to-drain series resistances have also been reduced by supplemental doping under the contact regions and by degenerate Ge doping of the surface regions, followed by uninterrupted growth of thin epitaxial Ge overlayers for nonalloyed tunnel-contact metallizations.
LEED-investigations and work-function measurements of the first stages of epitaxy of tungsten on tungsten (110)
Authors: Hahn P. , Clabes J. , Henzler M.
Published: February 2003

The arrangement of tungsten atoms (0.2–4 monolayers) evaporated onto W(110) has been studied with LEED and work-function measurements in ultrahigh vacuum. For temperatures of T=300–430 K island growth has been derived from rings, which are visible at characteristic energies, around each spot of the LEED pattern. By increasing substrate temperature the islands coalesce in the [001] direction. For T=520–800 K the surface shows microfacets with step edges in the [11̄0] direction. Step-free epitaxial growth has been observed at T=950 K. The decrease of work function during evaporation confirms the formation of islands and facets. The average dipole moment per edge atom has been determined by combination of LEED and work-function data. Quantitative evaluation of the LEED pattern yields the distance between islands, size of islands, and number of rows of atoms per terrace. The results show that the LEED pattern provides information on epitaxial growth which is not available with any other technique.
Relation of drift velocity to low-field mobility and high-field saturation velocity
Authors: Thornber K. K.
Published: February 2003

From an investigation of the behavior of the momentum distribution function of electrons or holes under scattering rate and momentum scaling transformations, a number of interesting results are derived concerning the parameterization of drift-velocity–vs–electric-field relations in terms of mobility and saturation velocity. Indeed it is determined that saturation velocity is invariant under scaling of the magnitude of the scattering rates, which alters mobility, while mobility is invariant under scaling of the magnitude of the momentum, which alters saturation velocity. This independence between mobility and saturation velocity is utilized to generalize to interfaces velocity-field relations valid the the bulk. Using the transformation of drift velocity under both rate and momentum scaling, partial experimental data can be used to predict high-field saturation velocities. These velocities need not be reduced due to higher scattering rates as much as their low-field counterparts. Nonzero magnetic fields and nonuniform scaling are also considered.
Si and GaAs photocapacitive MIS infrared detectors
Authors: Sher A. , Tsuo Y. H. , Moriarty John A. , Miller W. E. , Crouch R. K.
Published: February 2003

Improvement of the previously reported photocapacitive MIS infrared detectors has led to the development of exceptional room-temperature devices. Unoptimized peak detectivities on the order of 1013 W−1 cm Hz1/2, a value which exceeds the best obtainable from existing solid-state detectors, have now been consistently obtained in Si and GaAs devices using high-capacitance LaF3 or composite LaF3/native-oxide insulating layers. The measured spectral response of representative samples is presented and discussed in detail together with a simple theory which accounts for the observed behavior. The response of an ideal MIS photocapacitor is also contrasted with that of both a conventional photoconductor and a p-i-n photodiode, and reasons for the superior performance of our detectors are given. Finally, fundamental studies on the electrical, optical, and noise characteristics of our MIS structures are analyzed and discussed in the context of infrared-detector applications.
Influence of hydrogen on optical properties of a-Si : H
Authors: Bruyère J. C. , Deneuville A. , Mini A. , Fontenille J. , Danielou R.
Published: February 2003

We report on the optical properties of a-Si : H prepared by cathodic sputtering of a Si target in an 80% argon/20% hydrogen reactive gas at ∼9×10−3 Torr. The deposition rate φ (by means of the rf voltage) and the substrate temperature were varied. The total hydrogen content [H] and the concentration of hydrogen involved in SiH bonds [H1] or in SiH2 bonds [H2] were measured. We find [H]≳[H1]+[H2], two times higher in some preparation ranges (ν?15 Å/min or ν=100 Å/min), which implies the occurrence of hydrogen atoms H′ not bonded in the usual SiH or SiH2 forms. The optical absorption coefficient, the optical energy gap E0, and the refractive index ns were measured. E0 decreases as v increases, is independent of Ts for φ≳30 Å/min, and decreases as Ts increases for v≳30 Å/min. ns increases toward the crystalline value as φ increases and Ts decreases. The similarity of the properties of the layers obtained by sputtering and glow discharge is emphasized. We suggest equilibrium between hydrogen bonds as SiH and SiH2 and the other form(s) and that the optical gap is controlled by the deformation of the silicon matrix by the various hydrogen species.
Measurement of electron energy distribution in a magnetic multipole ion source
Authors: Goede A. P. H. , Green T. S. , Singh B.
Published: February 2003

The electron energy distribution in a magnetic multipole ion source has been measured utilizing a retarding potential energy analyzer. The observed distribution of the primary electrons is spread out from the thermal population to energies 30% above the discharge energy. Implications on the theory of ionization efficiency are discussed.
Triggerable semiconductor lasers and light-coupled logic
Authors: Copeland John A.
Published: February 2003

A computer model of a semiconductor laser has shown that deep-level electron traps with realistic physical parameters can cause a device to emit light in very short (20 ps) pulses, with high peak power (0.5 W) and a few nanoseconds repetition rate. The pulses appear suddenly as threshold current is reached causing the average output power to suddenly jump to a few milliwatts. A single optical pulse can be triggered by a longer current pulse containing fewer electrons than the number of photons omitted. These triggerable semiconductor lasers can shorten and amplify a detected light pulse making possible a number of lightwave-logic applications.
Acoustic emission induced by hydride formation in tantalum
Authors: Cannelli G. , Cantelli R.
Published: February 2003

Acoustic emission activity during hydride formation in tantalum at CH=7.2 at.% was detected as a function of temperature by measuring the ringdown count rate, the total number of events, and their amplitude distributions. Elastic modulus and internal friction measurements were also conducted in the same specimen to provide evidence of H precipitation. There are indications that, as in niobium, the acoustic emission phenomenon is caused by cracking at the precipitate particles.
Characterization of ion-implanted GaAs by ellipsometry
Authors: Kim Quiesup , Park Y. S.
Published: February 2003

Ion-implanted GaAs has been studied by ellipsometry. The profiles of the implantation damage at a dose of 1012–1015 ions/cm2 as revealed by the extinction coefficient were compared with the damage theory and the LSS projectile theory. The damage which remains after thermal or laser annealing was also examined by ellipsometry. Recovery of the crystallinity of the implanted GaAs is similar to that observed in Rutherford backscattering (RBS), Hall measurements, and other studies. As opposed to the case of thermal annealing, electrical activation of the implanted after annealing by a Q-switched ruby laser is more subject to the influence of the damage profile created by implantation. The damage profiles indicate that the high degree of damage in the narrow region (probably an amorphous state) is necessary for liquid-state epitaxial growth after laser annealing.
On-state decay in NbO2: Relationship to recombination and to nonlinear I-V
Authors: Vezzoli Gary C.
Published: February 2003

When addressed with a 1-MHz sinusoidal or triangular wave signal, the on-state of NbO2 shows two regimes of conductance. The lower-conductance regime occurs over the voltage range less than the holding voltage and shows, for the most part, superlinear I-V characteristics. Decay studies indicate that the time interval in this low-conductance or lower-current subregime is an inverse linear function of the on-state mobile charge density. This study also indicates that the subsequent positive peak current is also an inverse linear function of the time interval in the lower-conductance subregime of the previous cycle. The nonlinear lower-current subregime of the on-state I-V characteristics is thus directly related to the decay of the charge density of the true on-state, the decay being induced by a critical time duration of subholding voltage conditions. It is hence believed that the lower-current regime is a consequence of a relaxation-induced trapping phenomenon, and that the recovery of the high-conductance true on-state metal-like regime is due to the field-induced liberation of electrons from trapping centers. These data reinforce our earlier contention that both a critical charge concentration and a critical electric field intensity are inseparably necessary to maintain the on-state in NbO2.
Sputtered oxide/indium phosphide junctions and indium phosphide surfaces
Authors: Tsai Ming-Jong , Fahrenbruch Alan L. , Bube Richard H.
Published: February 2003

The reason that sputtered indium-tin oxide (ITO)/InP solar cells junctions with large lattice mismatch have the same efficiency as CdS/InP junctions with good lattice match is shown to be that sputtered ITO/InP junctions actually consist of n+-ITO/n-InP/p-InP buried homojunctions. To demonstrate this and to show that the homojunction formation is caused by thermal damage to the InP surface during sputtering deposition rather than from impurity diffusion from the oxide, a series of five different metal oxide/InP junctions have been formed by sputtering of the oxide, all with high solar efficiency. Junctions have been prepared both from single-crystal InP : Cd and from epitaxial crystal films of InP : Zn. The effects of sputter deposition of the oxide have been simulated by sputter etching of the InP surface, and the effects analyzed through measurements of the properties of Au/InP junctions, and of the Hall effect and photoluminescence of InP surfaces. Some heat treatment of the sputtered cells is required to achieve maximum efficiency, but excessive heat treatment causes degradation and often transformation from homojunctionlike to heterojunctionlike solar cell behavior. An actual In2O3/InP heterojunction solar cell has been prepared by thermal oxidation of the InP.
Influence of a high-temperature hydrogen anneal on the memory characteristics of p-channel MNOS transistors
Authors: Maes Herman E. , Heyns Guido L.
Published: February 2003

The effects of a postnitridation high-temperature hydrogen anneal on p-channel metal-nitride-oxide-semiconductor (MNOS) memory transistors have been studied. It is shown that, although the density of surface states at the Si-SiO2 interface decreases with increasing temperatures, anneal temperatures exceeding the nitride deposition temperature should not be used, since they result in a nitride degradation. Short anneals at 800 °C result in a 30% reduction in the threshold voltage decay rates by elimination of backtunneling of stored charges towards the interface states. At the same time the hydrogen anneal technique guarantees a more reliable operation of transistors in the memory array and strongly increases the channel mobilities. In hydrogen-annealed MNOS transistors the degradation process is retarded resulting in better endurance figures.