bluuebunny/crossref_metadata_2025 huggingface dataset:
Evidence for a shallow level structure in the bulk of semi-insulating GaAs
Authors: Castagne M. , Bonnafe J. , Manifacier J. C. , Fillard J. P.
Published: February 2003

The technique of thermally stimulated conductivity is applied to the spectroscopy of shallow trap levels in semi-insulting GaAs. Twelve previously unknown conductivity peaks are reported and the activation energy for thermal release of carriers trapped in the corresponding levels are determined with the aid of Urbach’s law. The obtained values are in good agreement with results available from infrared emission and photoconductivity. It is argued that most of these levels are responsible for the unresolved Gaussian band proposed by Leach.
The plasma z-pinch effect on the I-V characteristic of fast discharge flash tubes
Authors: Lue Juh Tzeng , Song Dar Yuan , Yeh Ching-Kai
Published: February 2003

Our empirical results show that the I-V relationship of flash lamps operating in the preionized mode with peak current density higher than 2 kA/cm2 follows Marotta’s formula V=K0i0.85, and reduces to Gonz’s equation V=K0i0.5 for current density lower than 0.6 k A/cm2. At a high-current, short-pulse system, the inductance Lf and the equivalent negative resistance dLf/dt across the flash tube becomes more significant than the inductance of the external circuit. The plasma z-pinch equation can successfully solve these time-variation terms.
Elastic properties of piezoelectric PVF2
Authors: Toda Minoru
Published: February 2003

Vibration properties of PVF2 cantilevers were studied in vacuum to exclude air loading. Young’s modulus calculated from the resonant frequency at strain levels below 10−4 was 4–8×1010 dyn/cm2, a significantly higher value than hitherto reported with measurements at higher strain levels. As the vibration amplitude and strain was increased, resonance shifted to lower frequencies and hysteresis effects appeared. These effects are attributed to a decrease in Young’s modulus. The elastic loss factor η and Q value, measured from the resonance curve, yielded η=0.025–0.045 and Q=22–40 for the frequency range 8–200 Hz.
Quasiresonant laser-produced plasma: An efficient mechanism for localized breakdown
Authors: Tam A. C.
Published: February 2003

This paper deals semiquantitatively with the phenomenon of quasiresonant laser-produced plasma (QRLPP) generation, i.e., breakdown of an atomic vapor when a laser beam couples a resonant excited state with a high excited state. The origin of the breakdown, threshold conditions for the breakdown, and the the effect of inducible absorption are discussed. Furthermore, the QRLPP may exhibit an unusual asymmetrical behavior (observed for a Cs plasma) when the single mode cw dye laser is tuned near the quasiresonant absorption line: on the low-frequency wing, ’’noise-reduction’’ effect for the transmitted beam is observed, while on the high-frequency wing, ’’self-oscillation’’ of the plasma is observed. The self-oscillation seems to result from a periodic plasma diffusion from the laser focus. The QRLPP, produced by cw or pulsed lasers, is a very efficient plasma generation mechanism which appears to be useful for many atomic vapors, and the potential applications are discussed.
A combined Monte Carlo diode simulation code
Authors: Quintenz J. P. , Widner M. M.
Published: February 2003

A collisional Monte Carlo electron transport model has been combined with an existing relativistic electron beam diode simulation code to investigate the effect of electron material interactions on diode performance. The effects of electron scattering and deposition in various anode materials on the electron beam profile are detailed. Simulations of two enhanced electron deposition experiments are described.
Diagnostics in a fast high-density z-pinch
Authors: Hilko B. , Meyer J. , Albrecht G. , Houtman H.
Published: February 2003

A fast, high-density z-pinch discharge is suitable for the study of CO2 laser-plasma interactions. The plasma was investigated temporally and spatially using a variety of optical diagnostic techniques including streak and shadowgram photography, spectroscopy, and Thomson scattering off ion acoustic fluctuations. Peak electron densities of 4×1019 cm−3 and ion temperatures of 50 eV are observed. Shadowgrams show that at peak compression the plasma consists of an inner dense core ne ≳1019 cm−3 1 mm in diameter surrounded by a low-density region ne ∼1018 cm−3 that extends to a diameter of 4 mm.
Multiple equilibria in the oxygen positive column
Authors: Lee D. A. , Lewis Frank D.
Published: February 2003

The assumptions of straightforward moment models advanced to describe the equilibrium positive column in O2 discharges are examined in a derivation from first principles. A particular such model employed by others is shown to lead, with the addition of consistent models for ionization, recombination, and mobility, to a nonlinear two-point characteristic value problem. This problem is shown to have two distinct physically acceptable solutions at certain O2 pressures. In one of these solutions, ratios of the number densities of the charged species are constants across the column, while the ratios vary with radial position in the other.
Dependence of growth rate of quartz in fused silica on pressure and impurity content
Authors: Fratello V. J. , Hays J. F. , Turnbull D.
Published: February 2003

We have measured the effects of pressure, temperature, and some variations in impurity content on the growth rate u of quartz into fused silica. Under all conditions the growth rate was interface controlled and increased exponentially with pressure with an activation volume averaging −21.2 cm3/mole. The activation enthalpy for all specimens extrapolated to a zero pressure value of 64 kcal/mole, within the experimental uncertainty. At a given stoichiometry the effect of hydroxyl content on growth rate is described entirely by a linear term COH in the prefactor of the equation for the growth rate. The effect of chlorine impurity can be described similarly. Also u is increased as the ideal stoichiometry is approached from the partially reduced state.
The dependence of frequency upon microwave power of wall-coated and buffer-gas-filled gas cell Rb87 frequency standards
Authors: Risley A. , Jarvis S. , Vanier J.
Published: February 2003

Previous studies of a commerical passive gas cell Rb87 frequency standard showed a strong dependence of the output frequency νRb upon the microwave power Pμλ. A major conclusion of that work was that the dependence of νRb upon Pμλ was due to a line inhomogeneity effect. The line inhomogeneity interpretation suggested that substituting a wall coating for the usual buffer gas would reduce the dependence upon Pμλ. As a part of the present work, a wall coating (a form of paraffin) was used and a reduction of this dependence by a factor of 100 was obtained. The present work has led to a more convincing theoretical demonstration of the line inhomogeneity effect. The paper discusses some of the details of the analytical procedure. There are certain major requirements that a wall coating would have to satisfy if it is to be superior to the usual buffer gas, and these are discussed in the text. The advantages demonstrated by the present work indicate that further studies are warranted to determine if an improved standard could be built based on a wall coating.
Effect of magnetometer response on magnetization behavior of β′-NiAl phase under constant applied field
Authors: Cho Seung-Am , Jaque Agustín
Published: February 2003

Magnetization and demagnetization behaviors of ordered β′-NiAl B2 phase are measured as a function of time under the constant applied fields by varying the electronic circuit time constant τc of magnetometer. It is clarified that the β′-NiAl does not have magnetic after effect at room temperature. The after effect of the phase observed previously at τc =30 sec was found to be the circuit response of the measurement system. This response showed the Voigt-Kelvin type anelastic behavior.
A measurement of the transverse range of (n,2n) recoils in Au
Authors: Roberto J. B. , Robinson M. T.
Published: February 2003

The lateral spread of ∼100 keV recoils in Au foils has been determined by a radioactive counting technique. A uniform distribution of recoils initially moving nearly parallel to the foil surfaces was generated by (n,2n) reactions with a high-energy neutron beam from a cyclotron. The fraction of (n,2n) activity which escapes the transverse surface is a measure of the transverse spreading of the recoils. Projected ranges were measured by orienting some of the foils perpendicular to the incident neutron beam. The experimental results are in excellent agreement with the predictions of the MARLOWE binary collision code, and indicate that the transverse range 〈‖ x‖〉 of ∼100 keV self-ions in Au is approximately one-sixth of the projected range.
A new polymer insulated gate field-effect transistor
Authors: Aktik M. , Segui Y. , Ai Bui
Published: February 2003

This paper describes the fabrication of a plasma-polymerized siloxane insulated-gate field-effect transistor which permits the study of the polymer-silicon interface. Preliminary results are reported on both fixed surface charge density (1.7×1012 cm−2) and hole mobility (500 cm2/V sec) in a P-channel metal-insulated semiconductor field-effect transistor.
Metastable atoms in gasdynamic and atomic beams: Velocity distribution and state density by laser diagnostics
Authors: Brinkmann U. , Kluge J. , Pippert K.
Published: February 2003

The velocity distributions and state densities of metastable Ca(4s4p 3P2) atoms emerging from discharge beam sources were measured by probing the Doppler shift in laser induced fluorescence. In order to cover the widely spread distribution of the longitudinal velocity component a single-mode dye laser was used in mode hopping technique. In this way up to 4 Å can be covered in steps of 182 MHz distance. The longitudinal and transverse components are sampled simultaneously. For the gasdynamic jet the transfer velocities were measured from some 10 m/s up to supersonic values. Using the transverse laser beam the absorption caused by Ca in the 3P2 state was tested. Absorptions up to 0.995 could be achieved in the free jet. A 3P density of 7×1011 cm−3 is calculated. Similarly for the atomic beam 2×1010 cm−3 is found, the flux being 4.7×1015 metastable atoms/s sr. Details of the atomic beam source for metastable atoms are given.
Barrier height reduction of the Schottky barrier diode using a thin highly doped surface layer
Authors: Wu Ching-Yuan
Published: February 2003

The interfacial layer theory considering the effects of the interface states and surface fixed charges is developed for the barrier height of the Schottky barrier diode with a thin uniformly doped surface layer. It is shown that the origins of the barrier height modification using the highly doped surface layer are mainly due to the increase of the electric field at the contact surface and the change of the interface properties. Design criterion for the maximum width of the highly doped surface layer is derived and calculated in detail for nickel barrier metal on n-type silicon with the specificed interfacial layer conditions. Comparisons between the the developed expression of the barrier height reduction with respect to the ion dose and the experimental data of Shannon et al. are made, which tend to support the proposed model.
The proximity effect in flux pinning
Authors: Kramer Edward J. , Freyhardt Herbert C.
Published: February 2003

The elementary interaction force fp for a small normal conducting precipitate particle is usually estimated assuming that the entire condensation energy of the superconductor 1/2  μ0H2c is lost in the volume of the particle, i.e., that the particle is equivalent to a void. It is demonstrated that this assumption, which neglects the proximity effect, leads to a serious over estimate of fp, by as much as three orders of magnitude. The ratio of fp of a normal precipitate to fp of a void of the same volume is shown to be of the order (t/ξ0)2, where t is the smallest dimension of the particle and ξ0 is the BCS coherence length. In addition, the ratio is temperature dependent, becoming smaller (larger correction) as T approaches Tc. These predictions are compared with recent experimental measurements of pinning by voids and precipitates and are shown to rationalize some hitherto puzzling experimental discrepancies between pinning by the two types of defects. Application of these ideas to flux pinning by other defects, such as grain boundaries and dislocations, is also discussed.
An amplified and saturated readout echo in piezoelectric powder
Authors: Kimura Takashi , Yoshikawa Shokichiro
Published: February 2003

Even during the reading process, the repetitive application of an incident pulse gives rise to an increase and a saturation in the echo height in piezoelectric powder. This phenomenon was experimentally measured in detail as a function of the repetition period, the applied field strength, and the driving frequency. An attempt was made to explain the amplified and saturated readout echo theoretically by introducing an elementary model based on the particle rotational mechanism. In addition to the efficient enhancement of the deviation of the particle orientation, a fluctuation component was macroscopically investigated assuming that the increase and decrease is in unequilibrium during the repetitive application of the readout pulse sequence. The fluctuation was considered especially in the reading process to be caused by the deviation of the dipolar field associated with the statice deviation of the particle orientation caused by the two-pulse sequence. Calculated results derived from the fluctuation mechanism showed satisfactory agreement with experimental results.
Variations of strain and light scattering accompanying domain switching in lead lanthanum zirconate titanate ceramics
Authors: Chen Peter J. , Land C. E.
Published: February 2003

Experimental results relating mechanical strain and visible-light scattering to ferroelectric domain switching as the electric displacement of lead lanthanum zirconate titanate (PLZT) 7/65/35 is switched through the hysteresis loop are presented. Both strain and light scattering measurements were made before and after storing a photoinduced space-charge field ESC in first a radially constrained and then an unconstrained PLZT disc. The results of these measurements tend to clarify the role of ESC in photoferroelectric information storage. Specifically, ESC is nonvolatile and cannot be reoriented by an externally applied switching field alone. The thresholds for domain switching in the bulk of the PLZT are lowered in the direction of ESC, but they are increased to the extent of preventing some domain switching antiparallel to ESC.
Absolute efficiency of ZnCdS:Ag screens excited by an electron beam
Authors: Giakoumakis G. E. , Nomicos C. D. , Euthymiou P. C.
Published: February 2003

The absolute efficiency of ZnCdS:Ag screens under electron beam excitation is studied. This experimental study concerns the dependence of efficiency on the excitation voltage, on the screen’s thickness, and on the phosphor’s grain size. Measurements have shown that the appropriate excitation voltage for maximum efficiency of each screen is not the maximum possible, but depends on the grain size of the phosphor. All experimental results are discussed and explained, taking into account the arrangement of grains on the screen, the internal construction of each grain, and the penetration depth of electrons in the screen.
Edge emission of CuGaSe2
Authors: Massé G. , Lahlou N. , Yamamoto N.
Published: February 2003

The edge luminescence of CuGaSe2 is studied on single crystals, from liquid helium temperature to room temperature. Time resolved spectroscopy measurements permit us to describe one of the emission bands in terms of donor-acceptor pair transitions. Three other emission bands are observed. We attribute them to free-to-bound transitions. We determine three impurity levels: 110, 80, and 50 meV. Annealings in different atmospheres permit us to think that the 50-meV level is due to a cation vacancy acting as an acceptor, and the 80-meV level to a Se vacancy, which would act as a donor [Migliorato et al., J. Appl. Phys. 46, 1777 (1975)].
Thermally enhanced field emission from a laser-illuminated tungsten tip: temperature rise of tip
Authors: Lee M. J. G. , Reifenberger R. , Robins E. S. , Lindenmayr H. G.
Published: February 2003

Thermal field emission of electrons has been investigated from a tungsten field emitter illuminated by the focused beam of a laser operating at a range of wavelengths in the visible region of the spectrum. The temperature rise of the tip is determined as a function of the displacement of the focused spot of light along the shank, and of its polarization. The experimental data are compared with the results of a first-principle calculation of the temperature rise, based on an experimental investigation of the intensity distribution within the focused spot of light and of the geometry of the field emitter. The comparison shows that when the laser beam is focused close to the tip the temperature rise is anomalously large; evidence is presented which suggests that the temperature rise of the tip is substantially enhanced by diffraction effects.
Thermal oxidation of InP and properties of oxide film
Authors: Yamaguchi Masafumi , Ando Kohshi
Published: February 2003

Thermal oxidation of InP and properties of oxide films have been studied. Surface orientation dependence of the oxidation rate can be explained by orientation dependence of bond density available for reaction with oxygen molecules. The activation energy of the parabolic rate constant is 2.06 eV, which may be attributed to the value for oxygen diffusion through InP oxide. From the electron diffraction and infrared absorption measurements, it is found that the oxide film is composed of polycrystalline InPO4 (In2O3+P2O5) and that oxides thermally grown at high temperatures, above 620 °C become In rich and form lower oxides, such as In4O2 and In2O, owing to phosphorus evaporation. Resistivities of the thermally grown oxide films at room temperature range from 108 to 109 Ω cm and decrease with an increase in oxidation temperature and time, which may be mainly caused by lack of P2O5 in the oxide film.
Current gain of the bipolar transistor
Authors: Wu Ching-Yuan
Published: February 2003

A generalized expression of current gain for nonuniformly doped bipolar transistor considering the effects of energy-gap narrowing, doping-dependent diffusivity, contact-surface and bulk recombinations, is derived by using generalized current flow equations and continuity equations. Based on the derived expression, the generalized expressions of current gain and transit times across the neutral base and emitter regions in the case of uniformly doped transistor structure are calculated in detail. Numerical results have shown that the recombination in heavily doped emitter may not be neglected and the conventional charge control expression of current gain does give erroneous predictions. Moreover, the current gain and transit time for a transparent emitter bipolar transistor have been studied, which are shown to be quite sensitive to the contact-surface recombination velocity, and are found to be useful in the study of microwave bipolar transistor.
A photoelectrophoretic image display system with a photoconductor electrode
Authors: Nakamura Kenichi , Matzuura Noriyuki , Tanaka Fujio
Published: February 2003

A novel image display system based upon the photoelectrophoretic phenomenon is studied. The display cell consists of a sandwich structure of an electrode-photoconductor layer-suspension (particles and suspending fluid)-counter electrode. A visual image is produced by three steps: (1) application of external voltage, (2) exposure to an optical image while the voltage is applied, and (3) a short circuiting of the cell. An important feature of this system is that during this operation a charge exchange between particles and electrodes is not required in exposed areas. In addition, this system permits the employment of less photosensitive particles. The effects of the photoconductor layer thickness, light intensity, external voltage, and fluid component on optical characteristics are studied. The forces acting on particles during this operation are also discussed.
Efficiency of quantum-utilizing solar energy converters in the presence of recombination losses
Authors: Ross Robert T. , Collins Jill M.
Published: February 2003

The presence of nonradiative losses limits the optimal absorbance of a solar energy converter. When nonradiative losses exceed radiative losses, the optimal absorbance at ν of a flat-plate device is approximately (hν−E0)/2.3 kT, where E0 is the threshold photon energy. For a given output potential, the optimal threshold E0 increases approximately as kT ln κ, where κ is the ratio of nonradiative to radiative decay rates within the absorbing material. The maximum efficiency of a terrestrial flat-plate device (AM 1.5, 28 °C) falls from 0.334 when κ=0, to 0.316 when κ=1, to 0.257 when κ=1000. Curves are displayed showing the dependence of efficiency on the potential of the process driven, the threshold photon energy, and the relative rate of nonradiative decay.
Experiments on the magnetic field of nerve action potentials
Authors: Barach J. P. , Freeman J. A. , Wikswo J. P.
Published: February 2003

Records of the magnetic field associated with the propagating action potential in a frog sciatic nerve have been obtained. Peak fields of about 60 picotesla are measured by a system utilizing a SQUID magnetometer, signal averaging, and a novel ferrite-core toroidal transformer. Design considerations for the latter are given and, for example, indicate that it need not have a large number of turns. A method is presented to obtain the net electric current threading the toroid by deconvolution of the magnetometer signal. This routine allows detailed magnetic or current profiles to be obtained of compound neural events.
Thin filament interferometric microphone
Authors: Miles R. B. , Gelfand Jack , Wilczek E.
Published: February 2003

A thin filament which follows the motion of a gas is used to measure small pressure fluctuations for photoacoustic spectroscopy. Optical heterodyne detection of laser radiation scattered from the filament provides a sensitive measurement of its displacement. This device may be particularly useful for low-pressure spectroscopy or under experimental conditions where the use of a standard microphone is inconvenient.
Thickness dependence of the photoconductivity of phosphorus-doped hydrogenated amorphous silicon
Authors: Solomon I. , Brodsky M. H.
Published: February 2003

The thickness and spectral dependences of the photoconductance of phosphorus-doped hydrogenated amorphous silicon show that the surface and interface layers are more photosensitive than the bulk, and further, that the interface layer is the more photoconductive of the two boundary layers. We interpret the results as further evidence for band bending at the film boundaries.
K
α satellite spectra as diagnostics for particle beam-target interaction
Authors: Nardi E. , Zinamon Z.
Published: February 2003

Spectrometry of Kα radiation emitted during the interaction of an intense particle beam with matter is proposed as a diagnostic. Temperature measurement is possible through the detailed analysis of the Kα satellite spectrum. The role of line self-absorption for this and other Kα measurements is discussed. The feasibility of such measurements is demonstrated in an electron beam-target interaction experiment.
The influence of a background plasma on the diocotron instability of a relativistic hollow electron beam
Authors: Bilow Henry J. , Uhm Han S.
Published: February 2003

The influence of a background plasma on the diocotron instability of a relativistic hollow electron beam is investigated within the framework of a cold fluid model. The background plasma is taken to have a uniform density except at the mean radius of the electron beam where the density is assumed to be discontinuous. Of the charged species comprising the plasma, only the electrons influence the dynamics of the beam-plasma system; the effect of the ions is negligible because of their small plasma frequency. A dispersion relation for the eigenfrequencies of the system is derived and employed to examine instabilities. It is found that the fundamental (l = 1) mode, which is unconditionally stable for a hollow electron beam in a vacuum, is now unstable for certain parameter regimes. The appearance or growth of instabilities with increases in the plasma density discontinuity is observed, while increases in the relativistic factor γb are seen to exert a stabilizing influence. It is also found that thin beams are generally more unstable than thick ones.
Small energy loss rate of an electron and deexcitation of metastable molecules by superelastic collisions in high-pressure oxygen glow discharge
Authors: Nobata Kanehiro , Yamamoto Soji
Published: February 2003

Very small values of an electric field divided by pressure (E/P) were experimentally obtained in the positive column of the oxygen glow discharge at higher pressure where the positive column contracts. E/P was also measured in the nitrogen positive column for comparison. From both measured values of the electron temperature and E/P we find that the average fraction of the energy of an electron lost at each collision with an oxygen molecule becomes extremely small at higher pressures. The reason for this is investigated. The average fraction of electron energy lost by the inelastic collision for excitation to low lying metastable states is calculated. In this calculation the superelastic collision of an electron with a metastable molecule and the diffusion of the metastable molecules are both taken into account.
Lightning leader laboratory simulation by means of rectilinear surface discharges
Authors: Larigaldie S. , Labaune G. , Moreau J. P.
Published: February 2003

Gliding discharges over dielectric slabs can be made quasirectilinear by using a correctly shaped guiding electrode located behind the slab. Such guided discharges are characterized by the accessibility of their parameters to various diagnostic techniques, such as velocity, current, and voltage measurements, spectroscopy, and fast photography. In this paper the behavior of negative gliding-surface discharges is studied with a view of understanding the behavior of the lightning leader. Theoretical predictions obtained by computation from a simplified model are compared with experimental data, and the result of this comparison is discussed.
Mixed slow-wave operation of a wide-band dielectric gyrotron
Authors: Choe Joon Y. , Uhm Han S. , Ahn Saeyoung
Published: February 2003

The bandwidth broadening effect of mixing two slow-wave modes in a dielectric loaded gyrotron is investigated for a small axial momentum spread. The usual intermediate wavelength mode (IWM) integrates with the short wavelength mode (SWM) by reducing the electron beam radius, and creates a mixed slow wave. The resulting bandwidth for the mixed mode gyrotron becomes at least twice broader than that for the pure IWM at the small velocity spread (≲1%) with a substantial contribution of the SWM. Moreover, the presence of the SWM reduces considerably the troublesome heat dissipation in the dielectric layer. Therefore, the mixed mode operation can allow up to several times more power than the usual IWM mode operation.
The on-state of single-crystal and polycrystalline NbO2
Authors: Vezzoli Gary C. , Doremus L. W. , Levy Steve , Gaulé G. K. , Lalevic B. , Shoga M.
Published: February 2003

Single-crystal and polycrystalline NbO2 switching devices were studied by double pulse and pulse interruption techniques. Results for single-crystal devices indicated a recovery time of 0.8–1.2 ms that is independent of the polarity relationship of the first and second switching pulses. Voltage interruptions, obtained by pulses of variable duration in opposition to the on-voltage, provided excursions into the on-state and revealed plateau regions in device voltage versus time. Hence the opposition or ’’diagnostic’’ pulse provides a region of rapidly decreasing on-state voltage followed by a region of zero on-voltage, from which current-voltage (I-V) data can be measured. An I-V curve of the on-state, thus obtained, showed a transitional region from an Ohmic state to a lower conductance subregime (of on-state). Below the holding voltage the time required to develop this lower-conductance subregime is about 50 ns for a single-crystal device, agreeing favorably with results from cw studies. The related time interval for polycrystalline devices is 250–350 ns. The interval between the holding voltage and the beginning of the transitional regime (10–20 ns) is interpreted to be the trapped carrier lifetime or emission time.
Calculation of the Auger lifetime in p-type Hg1-xCdxTe
Authors: Casselman T. N.
Published: February 2003

The Auger lifetime in nondegenerate p-type Hg1−xCdxTe is calculated as a function of composition, temperature, and hole density in the limit of small modulation. Two Auger recombination mechanisms are considered: the classic two-band mechanism involving electron-electron collisions and a three-band mechanism with hole-hole collisions. The calculation is based on an unambiguous set of overlap integral coefficients which appear in the intrinsic lifetime expressions. The results show that the intrinsic lifetimes for the two mechanisms are the same order of magnitude over a wide range of composition and temperature. Predicted Auger and radiative lifetimes are compared, and for 8–14-mm photodetectors based on ideal (defect-free), nondegenerate Hg1-xCdxTe, Auger recombination is the lifetime-limiting mechanism for operating temperatures below 200 K and carrier concentrations greater than 1016 cm−3.
Effect of ribbon thickness on resistivity of amorphous Fe-B-Si
Authors: Mogro-Campero A. , Luborsky F. E.
Published: February 2003

The resistivity of amorphous alloys is sentitive to their atomic structure. It has been reported recently that there are significant differences in room-temperature resistivities as a function of wheel speed (which determines ribbon thickness in the technique of rapid quenching from the melt). These results were interpreted as evidence for a variety of amorphous structures. We have found no differences in resistivities of samples of a similar composition as a function of wheel speed. The reasons for this disagreement are unknown.
Photoluminescence of proton-bombarded and annealed GaAs
Authors: Snyman H. C. , Neethling J. H.
Published: February 2003

Room-temperature photoluminescence measurements were made on 300-keV proton-bombarded GaAs as a function of dose, post-bombardment time, and temperature of anneal and were compared with measurements on unbombarded surfaces annealed under identical conditions. For heavy-dose (1017 protons cm−2) samples the photoluminescence signal recovers exponentially with temperature of anneal, with an apparent activation energy of 1.15 eV. For lower-dose samples deterioration or saturation of the recovery process occurs at an anneal temperature of approximately 800 °C. This is explained in terms of the formation of As vacancies near the surface during annealing.
Oscillations in a SnO2-based gas sensing device exposed to H2 gas
Authors: Kanefusa Shinji , Nitta Masayoshi , Haradome Miyoshi
Published: February 2003

An oscillation has been found in the resistivity of gas sensing devices of sintered SnO2 mixed with Pd, Rh, and MgO exposed to H2 gas in air. This phenomenon depends on the H2 gas concentration, the working device temperature, and the voltage applied to the device. Its waveforms consist of two structures and are conspicuously noticeable at 92 °C device temperature and 40 V voltage applied across the device.
Self-magnetically insulated ion diode
Authors: VanDevender J.P. , Quintenz J.P. , Leeper R.J. , Johnson D.J. , Crow J.T.
Published: February 2003

Light ion diodes for producing 1–100 TW ion beams are required for inertial confinement fusion. The theory, numerical simulations, and experiments on a self-magnetically insulated ion diode are presented. The treatment is from the point of view of a self-magnetically insulated transmission line with an ion loss current and differs from the usual treatment of the pinched electron beam diode. The simulations show that the ratio V/IZ0=0.25 in such a structure with voltage V, local total current I, and local vacuum wave impedance Z0. The ion current density is enhanced by a factor of approximately 2 over the simple space-charge limited value. The simulation results are verified in an experiment. An analytical theory is then presented for scaling the results to produce a focused beam of protons with a power of up to 1013 W.
Effect of thermal contact resistance on the photoacoustic signal
Authors: Quimby R. S. , Yen W. M.
Published: February 2003

We show both theoretically and experimentally that under essentially all conditions of experimental interest, the thermal contact resistance between sample and gas plays a negligible role in photoacoustic spectroscopy of solids.
Isothermal equations of state of potassium
Authors: Kim Kwang Yul , Ruoff Arthur L.
Published: February 2003

Volume versus pressure data of 1-m-long polycrystalline potassium has been obtained as a function of hydrostatic pressure up to 7 kbars at 28.58 °C. The length change has been measured to an accuracy of less than 500 Å using a Fabry-Perot type He-Ne laser interferometer in a temperature-controlled environment with temperature variations ±0.001 °C. The isothermal bulk modulus B0 and its pressure derivative B′0 at atmospheric pressure and 28.58 °C are B0=31.01±0.02 kbars and B′0 =3.91±0.01, when the first-order Murnaghan equation is used; and B0=30.84±0.02 kbars and B′0 =4.16±0.02, when the Keane equation is used. The Keane equation yields B0″ =−0.145 kbar−1 in the applied pressure range. Various two- and three-parameter equations of state have been used to fit the measured pressure-volume data. The Keane and Birch equations represent the data most closely when these equations are extrapolated into a higher-pressure region.
Analysis and application of stationary reference grating method for optical detection of surface acoustic waves
Authors: Komotskii V. A. , Black T. D.
Published: February 2003

The opitcal detection of surface acoustic waves (SAW) using stationary reference gratings (SRG) on a substrate is considered. The theory based on Fourier analysis of light diffracted from a grating interacting with a SAW is developed. As shown theoretically and confirmed experimentally the interaction of light with SAW and SRG produces an amplitude modulation of light in the 0 and ±1 orders of diffraction with a depth of modulation proportional to the SAW amplitude. The detection of SAW amplitudes on the order of 10−3 Å was predicted by theoretical analysis and confirmed by experimental measurements with a bandwidth of detection of 1 kHz. It was demonstrated that second harmonics of comparable amplitudes could also be detected. Measurements of the amplitude of SAW reflected from the free edge of the substrate, as well as SAW reflected from an interdigital transducer, were also demonstrated. It was shown that the SRG method of optical detection can be used for signal processing, for smoothly varying delay, for spectrum analysis, and for filtering.
Pressure dependence of electrical properties of metal-oxide semiconductor transitors
Authors: Moret B. , Destruel P. , Ai Bui
Published: February 2003

This paper gives some results on the effects of hydrostatic pressure on electrical characteristics of metal-oxide semiconductor transistor devices . An enhancement of about 4%–5% in the drain-source current has been obtained for pressures of the order of 4000 bars. A study of this effect shows that the current increase in essentially due to a change of the mobility of carriers at the interface, rather than to a modification of the oxide layer or interface.
Reply to ’’Comment on ’A unified explanation for secondary ion yields’ and ’Mechanism of the SIMS matrix effect’’’
Authors: Williams P. , Deline V. R. , Evans C. A. , Katz W.
Published: February 2003

Comments made in the preceding paper are critically discussed. It is argued that conclusions reached in our earlier papers were conservative and justified within our experimental accuracy. Negative-ion yields under cesium bombardment scale with surface cesium concentration and electron affinity in a manner analogous to the scaling of positive-ion yields with surface oxygen concentration and ionization potential. Fluorine is shown to be an exception, due probably to saturation effects.
Charge exchange and energy loss of carbon ions in air-plasma channels
Authors: Wright Thomas P. , Green Thomas A. , Mehlhorn Thomas A.
Published: February 2003

A model is developed to study two loss mechanisms duing the propagation of high-power beams of carbon ions in current-carrying air-plasma channels. Such channels can provide the necessary standoff between the diodes and the target in light-ion-driven inertial confinement fusion. Particle losses due to radial charge exchange diffusion across the channel magnetic field as well as collisional energy losses are studied. Semiempirical charge exchange cross sections are derived from literature sources and used in a Monte Carlo transport code with the energy loss modeled in the continuous slowing down approximation. We conclude that charge exchange losses are probably not of major concern for light ion beam inertial confinement fusion reactor configurations using channel transport, whereas collisional energy loss can be detrimental if the plasma channel density is too large.
The interaction between plasma and macroparticles in a multi-cathode-spot vacuum arc
Authors: Boxman Raymond L. , Goldsmith S.
Published: February 2003

The interaction between the interelectrode plasma and macroparticles (droplets) produced by a multitude of cathode spots in a vacuum arc between Cu electrodes is analyzed, using previous experimental measurements of the macroparticle size distribution and erosion rate and a flowing plasma model. The effect of the plasma on the macroparticles is considered by treating the macroparticles as floating probes and calculating the particle, momentum, and energy fluxes to them. It is found that slow macroparticles are significantly deflected form their original trajectories owing to ion bombardment, and that steady-state macroparticle temperatures of 2000–2600 K are obtained from the balance of the energy influx (primarily from ion bombardment) with the evaporative outflux. The effect of the macroparticles on the plasma is considered by calculating the production rate of neutral atoms and ions originating from macroparticle evaporation, by examining the possibility of occlusion of the discharge path by macroparticles, and of cathode-spot formation on detached particles. The calculated neutral density is proportional to J and is in the range 0.02–0.5% of the electron density, depending upon electron temperature and macroparticle velocity. In the 107 A m−2 Cu arc, the calculated neutral density is in the range 1×1017–2.5×1018 m−3. The neutral atoms are eventually ionized and the rate of ion production from the macroparticles can become significant in comparison with that of cathode-spot-produced ions under certain conditions. Occlusion of the discharge path is negligible, and the occurrence of sustained cathode-spot activity on the macroparticles is improbable.
Plasma etching of Si and SiO2 in SF6–O2 mixtures
Authors: d’Agostino Riccardo , Flamm Daniel L.
Published: February 2003

The products of reaction and etch rates of Si and SiO2 in SF6-O2 plasmas have been studied as a function of feed composition in an alumina tube reactor at 27 mHz, 45 W, and 1 Torr. There is a broad chemical analogy with CF4-02 plasmas. As in CF4-02 mixtures, the rate of Si etching and 703.7-nm emission from electronically excited F atoms each exhibit distinct maxima as a function of feed gas composition; these data support a model in which fluorine atoms, the etching species, compete with oxygen atoms for chemisorption on the Si surface. Without oxygen in the feed or Si in the reactor, no stable products could be detected. With an SF6-O2 mixture in the absence of silicon, the final reaction products are F2, SOF4, and SO2F2. The product distribution was unaffected by small SiO2 substrates. When Si is etched, SiF4 is the only stable silicon-containing etch product and SOF2 is formed in oxygen-poor mixtures. Rapid etch rates (≳104 Å/min for Si) can be obtained with a high selectivity in favor of silicon (Si:SiO2≳40:1); thus SF6-O2 mixtures may represent an attractive alternative to CF4-O2 for the plasma etching of silicon and SiO2.
Anode plasma behavior in a magnetically insulated ion diode
Authors: Johnson D. J. , Burns E. J. T. , Quintenz J. P. , Bieg K. W. , Farnsworth A. V. , Mix L. P. , Palmer M. A.
Published: February 2003

The nature and time evolution of the ’’surface flashover’’ anode plasma in a magnetically insulated ion diode is studied. Holographic interferometric and spectrographic measurements indicate a plasma with an electron density of 5×1016 cm−3 and a temperature of approximately 5 eV which is created by electric breakdown along a surface parallel to the imposed pulsed electric field. The divergence of the ion beam accelerated from this plasma is governed by the spatial nonuniformities of the plasma. The beam is composed primarily of protons for the experiments studied. Contrary to previous expectations, a substantial C+4 beam component was not observed.
Production of field-reversed plasma with a magnetized coaxial plasma gun
Authors: Turner W. C. , Granneman E. H. A. , Hartman C. W. , Prono D. S. , Taska J. , Smith A. C.
Published: February 2003

Experimental data are presented on the production of field-reversed deuterium plasma by a modified coaxial plasma gun. The coaxial gun is constructed with solenoid coils along the inner and outer electrodes that, together with an external guide field solenoid, form a magnetic cusp at the gun muzzle. The net flux inside the inner electrode is arranged to be opposite the external guide field and is the source of field-reversed flux trapped by the plasma. The electrode length is 145 cm, the diameter of the inner (outer) electrode is 15 cm (32 cm). The gun discharge is driven with a 232-μF 40-kV capacitor bank. Acceleration of plasma through the magnetic cusp at the gun muzzle results in entrainment of field-reversed flux that is detected by magnetic probes 75 cm from the gun muzzle. Field-reversed plasma has been produced for a variety of experimental conditions. In one typical case, the guide magnetic field was B0=4.8 kG and the change in axial magnetic field ΔBz normalized to B0 was ΔBz /B0=−3.1. Total field-reversed flux (poloidal flux) obtained by integrating ΔBz profiles is in the range 2×103 kG cm2. Measurement of the orthogonal field component indicates a sizable toroidal field peaked off axis at r≃10 cm with a magnitude of roughly one-half the poloidal field component that is measured on magnetic axis. Reconnection of the poloidal field lines has not been established for the data reported in the paper and will be addressed in future experiments which attempt to trap and confine the field-reversed plasma in a magnetic mirror.
Numerical simulation of field-reversed ϑ-pinches
Authors: Pietrzyk Z. A.
Published: February 2003

Field-line reconnection and the behavior of closed field-line plasma have been studied using a two-dimensional Lagrangian code. The effects of field-line divergence of the pinch end, active and passive mirrors, and laser heating are considered. A physical interpretation of plasma behavior for different experimental techniques is given. These calculations aid in understanding some of the experimental results of Los Alamos and the Kurchatov Institute.
Adiabatic compression of a microwave field by a plasma discharge
Authors: Birx D. L. , Scalapino D. J.
Published: February 2003

If electromagnetic radiation in a microwave cavity is spatially compressed in an adiabatic manner the frequency of the radiation is increased. Here we report on a theoretical and experimental study of this effect using a plasma discharge to spatially compress the radiation.
Failure of Paschen’s scaling law for Ne-0.1% Ar mixtures at high pressures
Authors: Sahni O. , Lanza C.
Published: February 2003

The criterion for voltage breakdown in Ne-0.1% Ar mixtures is generalized to include the pressure-dependent conversion of atomic to molecular neon ions. A strong dependence of the Paschen curve on gas pressure results by incorporating a significant difference in the secondary electron coefficients for the atomic and molecular neon ions. The effective secondary emission coefficient γ of the gas mixture now becomes pressure dependent. The deviation from Paschen’s law observed recently in ac plasma display panels is accounted for by the present theory to the extent that it shows qualitatively all the important characteristics of the experimental results.
Convection in horizontal high-pressure mercury, mercury plus iodine, and metal halide additive arcs
Authors: McLain D. K. , Zollweg R. J.
Published: February 2003

A two-dimensional (r, ϑ) numerical model has been developed to describe free convection in horizontal high-pressure arcs consisting primarily of mercury vapor confined in quartz arc tubes. The calculated vertical location of the hot core of the arc was found to agree with experiments within 1–2 mm, both with and without an applied transverse magnetic field to force the arc downward. An energy balance calculation of the quartz wall has been used to determine the quartz wall temperature distribution. For somewhat constricted mercury plus iodine arcs, two stable arc configurations were found to exist over a range of applied transverse magnetic fields.
Excitation of helium by electron impact
Authors: Ganas P. S.
Published: February 2003

A simple analytic central potential with two adjustable parameters is proposed for the helium atom. The potential parameters are obtained by appealing to the precise values of optical oscillator strengths calculated by Schiff et al. Using the Born approximation we calculate 1 1S–n 1P electron-impact excitation cross sections up to 5 keV. Good agreement with experiment is obtained.
The effect of background gas on the propagation of a high-intensity Nd: glass laser beam to a target
Authors: Palmer R. E. , Anthes J. P. , Palmer M. A.
Published: February 2003

The x-ray emission from a Ni target irradiated with an 8-ns Nd: glass laser pulse focused to ∼5×1013 W/cm2 did not change when up to 2-torr Xe was added to the target chamber. This suggests that the incident laser beam was not affected appreciably as it propagated through the background gas to the target.
Segregation in Czochralski grown calcium gallium germanium garnet single crystals
Authors: Roth T. F. , Mishra R. K. , Thomas G.
Published: February 2003

Morphology and crystallography of the formation of small segregates in Czochralski grown calcium gallium germanium garnet are studied using TEM and STEM. Based on the observations, the following model has been developed for the formation of these defects. Evaporative loss of Ge from the melt during the crystal growth and the resulting local deviations from stoichiometry lead to random nucleation of small plate-like precipitates, rich in Ga. As these precipitates grow, strain field interaction leads first to the formation of three-dimensional segregates, and later to their alignment along the elastically soft 〈100〉 directions. Isolated segregates are also observed. Some of the segregates contain a central void filled with oxygen gas, while some others with or without a void have one or more dislocation loops around them. These segregates have the same garnet structure but a different chemical composition; they are rich in Ga and depleted in Ge. The model suggests that segregate-free crystals can be grown by suppressing the evaporative loss of Ge from the melt during crystal growth.