bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of bulk carriers on PROM sensitivity
Authors: Sprague Robert A.
Published: February 2003

The PROM is an electro−optic image−recording device which uses bismuth silicon oxide as an active material. Because of the thickness of the crystal (150−1000 μm), carriers generated in the depth of the crystal and carriers trapped within the crystal must be considered in determining its operating parameters. This paper presents a simple model which relates crystal absorption and carrier diffusion to device sensitivity. The results show good correlation with experimental data and also give some explanation of why device resolution is better than would be expected with such a thick recording material.
Electrical characteristics of a double−discharge TEA CO2 laser
Authors: Dyer P. E. , James D. J.
Published: February 2003

The volume−discharge and arc−formation characteristics of a double−discharge self−sustaining TEA CO2 laser have been studied. The results indicate that the discharge is a form of high−pressure glow of limited stability. An experimental study of arc formation indicates that this may be a result of ionization and attachment instabilities which are predicted to grow in the transient discharge. A simple technique based on the experimental steady−state discharge characteristic has been used to maximize the stable energy density in a 7.5−cm gap system operating at atmospheric pressure.
Argon entrapment in metal films by dc triode sputtering
Authors: Lee William W. Y. , Oblas Daniel
Published: February 2003

Sputtered films of 12 elementary metals were analyzed for argon content by an rf spark−source mass−spectrographic method. All films were deposited using dc triode sputtering under similar conditions. Corrections in the data have been made to account for variations in target size and deposition rate. The experimental results are compared with sticking probabilities calculated using the Born−Mayer interatomic potentials; the agreement is fair except for elements having low atomic numbers, e.g., Cu and lower. The data confirm the role of reflected argon atoms in the entrapment mechanism at the substrate—as the atomic mass of the target material increases, the average energy of the reflected energetic argon atoms also increases, leading to the increased argon content in the film. The data also suggest that the entrapped argon content is dependent upon the atomic spacing of the film material.
Temperature dependence of spontaneous peak wavelength in GaAs and Ga1−xAlxAs electroluminescent layers
Authors: Dyment J. C. , Cheng Y. C. , SpringThorpe A. J.
Published: February 2003

We report the results of experiments which determine how the peak wavelength (λp) of the spontaneous emission spectrum shifts with junction temperature (T). The quantity ∂λp/∂T has been measured for homostructure, single−heterostructure, and double−heterostructure LED’s throughout the temperature range 293−413 °K. Particular emphasis was placed on how the presence of Al in a GaAs layer alters ∂λp/∂T. The principal results are as follows: (i) ∂λp/∂T ranges from 2.5 to 3.6 Å/°K for pure GaAs; (ii) ∂λp/∂T is decreased in direct proportion to the aluminum fraction x in Ga1−xAlxAs. An explanation of these results is presented which involves only the known magnitudes and temperature dependences of the direct energy band gaps of GaAs and AlAs; for example, at x=0.3, the calculated reduction is 35% which is in good agreement with the experimental data; (iii) the spectra for some LED’s have two peaks identified with band−to−band (BB) and band−to−acceptor (BA) recombination processes. For the BA peak ∂λp/∂T is 0.5 to 0.6 Å/°K higher and its amplitude decreases much more rapidly with increasing temperature than for the BB peak. This behavior has been explained by a model which takes into account the number of ionized acceptors as a function of temperature.
Extrinsic electroabsorption in high−resistivity GaAs
Authors: Jonath Arthur D. , Voronkov Edward , Bube Richard H.
Published: February 2003

We report here what we believe to be the first detailed investigation of extrinsic electroabsorption in a semiconductor for photon energies much less than the band gap. Apparatus capable of measuring a field−induced absorption constant change as small as 10−5 cm−1 was applied to a GaAs : O crystal with 300 °K Fermi level of 0.54 eV below the conduction band. Eleven pieces of major structure were detected at 300 and 80 °K between 0.52 and 1.39 eV, and variations of structure with light polarization, applied field, temperature, preillumination, and lock−in amplifier phase angle are reported. Both a first−harmonic and second−harmonic spectrum are obtained; the former is attributed to a Stark shifting of permanent dipole moments, and the latter to induced dipole character of the imperfections involved. Correlation between electroabsorption measurements and independent observations of photoconductivity, optical quenching, thermally stimulated conductivity, and space−charge injection is discussed.
Grain growth of evaporated Te films on a heated and cooled substrate
Authors: Okuyama Katsuro , Kumagai Yasuji
Published: February 2003

The effect of the substrate temperatures in a wide range between −150 and 270 °C on the grain size, crystal orientation, Hall mobility, and the carrier concentration of evaporated Te films has been investigated. The grain size and the corresponding Hall mobility were observed to increase remarkably with increasing substrate temperature above 50 °C and with decreasing temperature below 50 °C, contrary to the expectation. The carrier concentration decreased with increasing substrate temperature. The influence of Au nucleation centers on the crystallinity and electronic properties were also investigated. An x−ray diffractometer study indicated c−axis texture to occur with improving grain growth.
Correlation of the anisotropic etching of single−crystal silicon spheres and wafers
Authors: Weirauch Donald F.
Published: February 2003

Studies of the anisotropic etching of silicon single−crystal wafers and spheres were conducted using 10−M potassium hydroxide as the etchant. The etch rates along the major slow−etch directions were measured. The sides of circular mesas etched into (111), (110), and (100) wafers were found to be inclined to the wafer surface. The angles of inclination varied with azimuthal position and could be correlated with the slow−etch directions measured from an etched sphere. A method was developed to predict these angles of inclination for surfaces of varied orientation using the rate of etching data and angular measurements from an etched sphere.
Elastic constants of polycrystalline α−uranium
Authors: Abey A. E. , Bonner B. P.
Published: February 2003

The elastic constants of polycrystalline α−uranium were determined as a function of pressure P. Measurements were made in the range from 100 kPa to 1.8 GPa. The initial Lamé constant λ is 53 GPa, the initial shear modulus μ is 86 GPa, and the bulk modulus is 110 GPa. The value for dμ/dP is 2.99. This is the largest dμ/dP reported thus far for any element.
Background gas pressure dependence and spatial variation of spontaneously generated magnetic fields in laser−produced plasmas
Authors: Case Roger S. , Schwirzke Fred
Published: February 2003

A spontaneous aximuthal magnetic field generated by electron currents which flow during the interval that a high−brightness 4−nsec full width at half−maximum intensity ruby laser was incident on a metallic target has been detected, its spatial characteristics evaluated, and its dependency upon background gas pressure investigated both experimentally and theoretically. The propagation velocity of the early component of this magnetic field is greater than 108 cm/sec, more than an order of magnitude larger than the plasma convective velocity, and indicates that the electron currents responsible for this fast field must flow through the background photoionized gas. The early component is first detected at a pressure of 5×10−6 Torr, and for a fixed spatial location, reaches a peak intensity at a pressure of 2×10−3 Torr. Its intensity is typically on the order of 1−10 G, a factor 10−100 times smaller than the spontaneously generated magnetic fields which are driven by pressure gradient effects in the expanding laser plasma. The pressure dependence of the pressure gradient magnetic field has also been evaluated and compared with previous experimental results, obtained at laser pulse lengths of greater than 20 nsec.
Evaporation of solids by laser pulses. II. Zirconium hydride
Authors: Olstad R. A. , Olander D. R.
Published: February 2003

The vaporization of hydrogen from the binary solid compound zirconium hydride induced by pulses from a Q−switch ruby laser was studied using a quadrupole mass spectrometer. The rate of vaporization of H and H2 during the rapid temperature transient was determined from the measured mass spectrometer signals. Application of an equilibrium model to the vaporization process predicts that predominantly H2 (rather than H atoms) should be emitted. The vaporized hydrogen should have a Maxwellian velocity distribution characteristic of the instantaneous surface temperature, and the rates of vaporization should be related to the equilibrium H2 and H pressures by the Langmuir equation. Since the equilibrium pressure is a function of both surface temperature and surface hydrogen concentration, it was necessary to solve simultaneously the time−dependent heat conduction and hydrogen diffusion equations in the heated zirconium hydride in order to predict the vaporization rates. It was found that H atoms and H2 molecules were emitted at thermal equilibrium with the surface. At low laser power density, the magnitude of the H2 signals agreed with the equilibrium model. At high laser power density, the magnitude of the H2 signals was less than predicted, possibly because of a diffusion barrier at the surface. The H atom signals were much larger than predicted, indicating that they were produced by a nonequilibrium surface process which favored direct vaporization of adsorbed hydrogen atoms rather than recombination followed by H2 desorption.
Temperature determination in high−pressure sodium discharges by detection of rf thermal noise
Authors: Anderson John M.
Published: February 2003

The electron temperature on the central axis of a discharge established in a mixture of sodium, mercury, and xenon gases at about 600 Torr pressure was measured by detection of radio−frequency thermal noise. The deduced value of 4200 °K compares favorably with determinations by spectroscopic methods and theoretical calculations.
Impedance characteristics of diodes operating in the self−pinch mode
Authors: Cooperstein G. , Condon J. J.
Published: February 2003

The impedance characteristics of large aspect ratio diodes employing hollow field emission cathodes operating in the self−pinch mode have been studied at electron kinetic energies between 400 and 800 keV and currents between 100 and 500 kA. The importance of correcting the anode−cathode gap spacing for closure due to plasma motion is recognized and taken into account in the definition of the diode aspect ratio in impedance calculations. With this correction, the impedance at peak diode voltage and current is found to be nearly independent of voltage and cathode surface area, and inversely proportional to the diode aspect ratio. Its amplitude is approximately 50% higher than that predicted by parapotential flow theory.
Diffraction by a composite cylinder
Authors: Hurd R. A. , Sachdeva B. K.
Published: February 2003

The diffraction of a plane electromagnetic wave by a composite circular cylinder is studied theoretically. The cylinder comprises two 180 ° sectors; one is a perfect conductor, the other a dielectric. The incident wave is polarized parallel to the axis of the cylinder. A quasistatic method of solution is employed; it presumes that (2π/λ) (radius of cylinder) <1.0 approximately. Some curves of backscattering and forward scattering are presented.
Investigations of glow discharge formation with volume preionization
Authors: Kline Laurence E. , Denes L. J.
Published: February 2003

The discharge formation process has been studied experimentally for CO2 planar TEA laser discharges. Theoretical models are presented which predict the preionization electron and ion densities, the spatiotemporal development of the discharge plasma, discharge voltage, and current waveforms, and the quasisteady operating characteristics of the discharge. The preionization is provided in the experiments by a pulse of ultraviolet radiation. The discharge formation model accounts for cathode photoemission and anode collection of electrons, discharge−circuit interactions, and gaseous ionization processes. The model predicts that photoemission and anode collection can be neglected when strong preionization and moderate overvoltages are used. When photoemission and anode collection are neglected, the discharge formative time is independent of the discharge volume. Calculated and experimental voltage and current waveforms are in very good agreement. The results of the calculations show that the discharge formative time is determined primarily by the characteristics of the external circuit in the experiments. Formation calculations for a large−volume discharge show that a uniform glow discharge will develop even when the preionization is nonuniform along the electric field, and confirm that the formative time is approximately independent of the discharge volume.
Parametric performance predictions for high-power pulsed electric CO lasers
Authors: Center R. E. , Caledonia G. E.
Published: February 2003

A kinetic model of the pulsed electrical CO laser is used to survey the time-dependent laser performance on parameters such as gas mixture, initial translational temperature, and discharge pulse length for both multiline and selected-line operation. Predictions are presented for the total output efficiency, spectral distributions of the stimulated transitions, energy partitioning in the vibrational and translational modes, and the translational temperature history in CO-N2 mixtures. A brief description of the kinetic model is included. Simple scaling relationships are presented which can be used to scale the results to other densities in the pressure-broadened regime.
The mechanism of spark breakdown in air at atmospheric pressure between a positive point and plane. II. Theoretical: Computer simulation of the streamer track
Authors: Marode E.
Published: February 2003

Based on a model which was experimentally established, a numerical simulation is presented of the spatiotemporal evolution of electron density, current, and electrical field in the filamentary streamer track. The attachment process is taken into account in the continuity equation for electrons and the Poisson’s equation is simplified using a coefficient of capacity per unit length. Boundary conditions for the filament are deduced (i) from experimental measurements on the primary streamer and (ii) by assuming a constant cathode fall for the experimentally found cathode region. The results show good agreement between calculation and experiment for both currents and streak photograph.
Superconducting properties of getter-sputtered V3Al thin films as a function of sputtering gas, pressure, and substrate temperature
Authors: Schmidt P. H. , Bacon D. D. , Barz H. , Cooper A. S.
Published: February 2003

Superconducting transition temperatures of V3Al thin films prepared by getter sputtering have been found to vary significantly not only with variation of the deposition temperature, as previously reported, but also with variation of the deposition pressure and composition of the sputtering atmosphere. The film composition measured at Tc maxima obtained by varying the deposition temperature for nonoptimum pressures was found to depart significantly from the 3 : 1 stoichiometry. High-deposition pressures PD ≳175 mTorr are associated with films containing an excess of Al, while deposition pressures of less than 60 mTorr result in V-rich films. With near-optimum film deposition conditions for Ar, 155 mTorr pressure, and a deposition temperature of 800 °C, we have obtained a peak superconducting transition temperature of 11.8 °K.
Use of fluxoid quantization in the measurement of the inductance of single-junction SQUIDs
Authors: Pei S. S. , Lukens James E.
Published: February 2003

Calculations of the change in the flux linking a superconducting ring when a change in the fluxoid quantum state is induced are presented, taking into account the effect of thermodynamic fluctuation on the transition. A method is described by which this calculated flux value can be used to provide a calibration in a measurement of the inductance of the ring. The measurement procedure described is useful for rings with an inductance of 10−8 H and smaller, and will give results accurate to about 2%.
Coupling considerations for SQUID devices
Authors: Claassen J. H.
Published: February 2003

Most applications of superconducting quantum interference devices (SQUID’s) involve use of a coupling coil. There are two classes of such applications: magnetometry (magnetic field, field gradient) and voltage or current measurements. We have analyzed the factors which determine the ultimate sensitivity, and present a guide for optimization of signal/noise in each of the two cases. It is found that a single figure of merit, involving both the equivalent input noise of the SQUID and the effectiveness of the coupling to the coil, is applicable to either type of measurement. We propose that this figure of merit be used in evaluating the performance of new SQUID designs.
Amplification and laser action in a laser dye pumped by a copper-vapor laser
Authors: Decker C. David , Fahlen Theodore S. , Falk Joel
Published: February 2003

The 5106-Å output of a 250-mW copper-vapor laser has been used to obtain laser action in a Rhodamine 6G dye laser. The high gain of such a copper-vapor laser pumped dye solution has been demonstrated by amplifying the 5782-Å output of the same copper-vapor laser.
Electroluminescence in Al-Al2O3-Au diodes
Authors: Pong W. , Inouye C. , Matsunaga F. , Moriwaki M.
Published: February 2003

Thin-film diodes composed of Al-Al2O3-Au films can be made to emit light under applied voltages. The spectral intensity of the electroluminescence was measured in the wavelength range 2000–6000 Å for different diode voltages. In this spectral range, the intensity was found to decrease nearly exponentially with increasing photon energy for a given voltage. The results also indicate that as the intensity of the short-wavelength emission is enhanced with increasing diode voltage above approximately 4 V, there is a corresponding decrease in intensity in the long-wavelength region. An attempt is made to explain the results in terms of a band model of the oxide.
Chemiluminescent reactions in a heat-pipe oven
Authors: Hessel M. M. , Drullinger R. E. , Broida H. P.
Published: February 2003

A heat-pipe oven has been used to contain and control the chemiluminescent reaction Ba+N2O→BaO*+N2. The heat-pipe oven permits Ba vapor to be maintained at any desired pressure. Reactions were easily controlled by varying the flow rate of N2O or pressure of Ba. A large volume (about 20 cm3) of chemiluminescence was produced and spectra were taken from 0.1 to 5 Torr. In addition to emission from BaO A1Σ-X1Σ, numerous atomic Ba lines also have been observed. This device is well suited to the study and control of chemical reactions between metal vapors and oxidizers.
High rate rf sputtered niobium: Effects of deposition rate on superconducting properties
Authors: Rock F. C. , Smith C. W.
Published: February 2003

The low-temperature electric properties of niobium films deposited using an rf sputtering system, in which the deposition rate (≳1000 Å/min) and self-bias potential (∼5 kV) are higher than normally encountered, are presented. Comparison is made to existing data on single-crystal Nb films as a function of thickness. It is found that high deposition rates can be the ’’special technique’’ needed to produce high-quality Nb films.
Laser heating and melting of thin films on low-conductivity substrates
Authors: Ghez R. A. , Laff R. A.
Published: February 2003

A laser beam, incident on a highly absorbent thin film supported by a poorly conductive substrate, causes that film to heat and melt. The time required to reach the melting point and that required to complete the melting process are calculated as a function of the incident laser flux. The calculations neglect heat losses arising from lateral diffusion, convection, and thermal radiation, but they account for a possible reflectivity change at the melting point. They yield a criterion for the minimal absorbed flux necessary to maintain stable monotonic melting.
High-contrast optical storage in VO2 films
Authors: Balberg I. , Trokman S.
Published: February 2003

When vanadium dioxide, VO2, undergoes its semiconductor-to-metal transition at 68 °C its reflectivity decreases by about a factor of 2 throughout the visible range. By using a thin VO2 film on a vanadium substrate we were able to achieve a much higher contrast between the reflectivities of the two VO2 phases. The VO2 film was grown as an antireflecting coating for one of the phases and thus the film thickness was used to determine the light wavelength at which the contrast will reach its maximum value. For example, with an 800-Å-thick film a contrast of 16 (rather than 2) was obtained at a light wavelength of 7000 Å. In utilizing the present system for optical storage the high contrast obtained yielded an order of magnitude higher read-out efficiency than the efficiency reported for VO2 films sputtered on glass. To demonstrate information recording in the present system, both a pulsed laser and a cw laser were used for spatially selective’’writing’’ in the film. It was found that the present system has high ’’write sensitivity’’ with a threshold, easy erasability, and high-resolution capability. Cyclic operation without fatique and the convenience of using the same cw laser for both writing and reading, are other advantages of the system described.
Arbitrarily shaped inhomogeneous optical fiber or integrated optical waveguides
Authors: Yeh C. , Dong S. B. , Oliver W.
Published: February 2003

Using the finite element technique, a numerical method is devloped so that one may obtain the propagation characteristics of optical waves along guiding structures whose cores may be of arbitrary cross-sectional shape and whose material media may be inhomogeneous in more than one transverse direction. Several specific examples are given and the results are compared with those obtained by other exact or approximate methods. Very close agreement was found. The method developed here can easily be applied to many important problems dealing with practical optical fiber or integrated optical waveguides whose cross-sectional index of refraction distribution may be quite arbitrary.
Theory of laser-materials damage by enhanced stimulated Raman scattering
Authors: Sparks M.
Published: February 2003

An analysis indicates that Raman-active crystals fail at intensities If which are greater than the enhanced stimulated Raman-scattering threshold intensity IR by an amount IT that is generally of the order of or less than IR. A typical value of IR at the ruby frequency is a few gigawatts per square centimeter, which is less than other intrinsic-mechanism thresholds. At intensities I≳IR, the excess intensity I−IR is converted into Stokes radiation and phonons in a distance l≪d, where d is the thermal diffusion distance for a 10-nsec pulse. The temperature rise from the rapidly thermalized phonons in the volume x<d is sufficient to cause material failure when I≳If.
Temperature dependence of minority-carrier lifetime in vapor-grown GaP
Authors: Wessels Bruce W.
Published: February 2003

Minority-carrier lifetimes in nitrogen-doped GaP grown by vapor phase epitaxy have been measured using the diode reverse-recovery technique. From the temperature dependence of the minority-carrier lifetime and utilizing the recombination model of Shockley, Read, and Hall, a recombination level at 0.15–0.19 eV was determined. The center, which is predominantly nonradiative, can be attributed to a donor-acceptor pair involving copper and an unknown donor.
Intensity variation of reflected energy from spherical glass shell laser fusion targets
Authors: Downward J. G.
Published: February 2003

The fraction of the energy reflected by spherical glass shell targets irradiated with 1.06-μm laser pulses is measured for average intensities up to 4×1015 W/cm2. The on-target energies ranged up to 230 J with laser pulse half-widths of from 0.03 to 1.0 nsec. The glass shells ranged in diameter from 57 to 553 μm. Using the KMS Fusion two-channel disk laser system, the shells were illuminated at 1.06 μm from opposite sides at near-normal incidence. Two illumination systems were investigated. In the first, the target was illuminated with a pair of f/0.6 lenses providing approximately 80° per side (full cone angle) of near-normal incidence. In the second, the f/0.6 lenses were used in conjunction with an ellipsoidal mirror system which provides 144° per side (full cone angle) of normal illumination to with 18°. The fraction of the energy reflected from the targets was found to vary as a power of the average intensity on target over the range 4×1013 to 4×1015 W/cm2. Within this range no sudden onset of enhanced energy absorption or reflection by the targets was observed. Measurements were also made of the 1.06-μm radiation scattered from the target at 45° and 90° to the laser axis. The scattering was roughly isotropic. The light reflected from the targets was found to be approximately 20% depolarized.
Spectral distribution of photoionization cross sections by photoconductivity measurements
Authors: Grimmeiss H. G. , Ledebo L-Å.
Published: February 2003

A new technique for measuring the spectral distribution of photoionization cross sections in photoconductors is presented. The method makes use of the fact that the occupancy of an impurity level is not changed during illumination with photons of different energy if the photocurrent is kept constant. A constant photocurrent is achieved by adjusting the light intensity. The spectral distribution of the photoionization cross section is then given by the inverse of the photon flux as a function of the photon energy. To demonstrate the applicability of this measuring technique, measurements were performed on oxygen-doped GaAs samples. Three deep energy levels (two 0.46 and 0.79 eV below the conduction band and one 0.48 eV above the valence band) were investigated and the spectral distribution of five photoionization cross sections were measured. All of them are in good agreement with calculated values, and thus an accurate determination of the threshold energies is achieved. For comparison, similar investigations were performed with p+n junctions giving results which are in good agreement with the photoconductivity measurements.
Theory of the carrier-density fluctuations in an IGFET near threshold
Authors: Brews J. R.
Published: February 2003

A three-dimensional perturbation-theory treatment of the carrier-density fluctuations in the insulated-gate field-effect transistor (IGFET) above threshold and their effect upon the source-drain current is presented. The fluctuations are considered to be generated by interface charge nonuniformities. It is shown that such fluctuations reduce the source-drain current over that for a uniform device with the same average carrier density. It is found that the fluctuations increase with decreasing carrier density, that they are larger in a shallow channel than in a deep channel, and that the increase in fluctuations with decreasing carrier density is quite abrupt. The critical carrier density below which carrier-density fluctuations are important is found to be ?1011 carriers/cm2 at 300 °K and ?1012 carriers/cm2 at 0 °K for ordinary-device charge densities. The difference in the threshold for the onset of fluctuations at the two temperatures is attributable to the smaller amplitude of fluctuations at high temperatures. For interface charge densities in the neighborhood of 1010/cm2 or lower no effect of fluctuations upon the IGFET current at 300 °K is expected, but there will still be an effect at low temperatures. These results are expected to be important in interpreting dc IGFET mobility measurements.
Admittance spectroscopy of impurity levels in Schottky barriers
Authors: Losee D. L.
Published: February 2003

Measurements of the complex admittance of Schottky-barrier diodes as a function of temperature provide a spectroscopy of deep trapping levels. The measurement conditions are usually close to thermal equilibrium, thus assuring the validity of equilibrium occupation probabilities. An exact (i.e., to arbitrary accuracy) solution for the junction admittance is given. The problem is reduced to solution of a simple initial-value problem, the final integration being carried out by computer. It is shown that the dispersion in capacitance due to slow trapping levels can lead to serious errors in estimates of junction doping concentrations and barrier height determinations. Examples are given for p-type ZnTe where Shockley-Read-Hall (SRH) centers are dominant and for n-type CdTe and Cd1−xZnTe where double-acceptor centers are dominant. For junctions formed on CdTe : Ga it is shown that one of the steps in capacitance observed in a thermally stimulated capacitance survey is actually a high-frequency response step and is not due to slow emission from a trapping center.
Measurement of dipolar relaxation times and dielectric constants using thermally stimulated current
Authors: Hino Taro
Published: February 2003

A method for measuring the distribution of dipolar relaxation times and the dielectric constants by thermally stimulated current (TSC) is described. A technique of ’’thermal sampling’’ is used to isolate the TSC due to dipoles with a single relaxation time from the TSC due to dipoles with distributed relaxation times. A theory is developed to calculate distributions of the relaxation times from the TSC measured by the thermal sampling. Dielectric loss factors in polyethylene terephthalate are calculated from the TSC data and they are compared with the experimental values of the dielectric loss factors obtained from the absorption current measurement.
Plasma diagnosis by laser beam scanning
Authors: Cheng T. K. , Casperson Lee W.
Published: February 2003

A procedure is developed for determining the radial electron density and temperature profiles of a rotationally symmetric plasma. This high-resolution technique involves measuring the deflection of laser beams incident transverse to the plasma. Diagnosis of a stable atmospheric pressure argon arc with CO2 and He-Ne laser beams yields results in good agreement with spectroscopic methods.
Traveling-wave electron-beam–semiconductor system for picosecond rise-time pulse generation
Authors: Norris C. B.
Published: February 2003

This paper describes a powerful pulse generation technique based on the use of a swept electron beam to excite traveling waves on a stripline semiconductor target. A simplified wave analysis of the swept stripline target shows that the pulse rise time is not restricted by the effects of carrier transit time or target capacitance which typically limit the rise time of other beam-semiconductor devices. The swept stripline is thus capable of rise times approaching the very short time required for equilibration of the carrier pair creation process in the electron-bombarded semiconductor. The output capability of the swept stripline is discussed, and a near-optimum design method is presented for long uniform striplines. It is estimated that output levels of 100 V with output/rise time values of 10 V/psec and 10 A/psec are feasible. An experimental result from a short nonoptimum silicon stripline target shows a 5-V 2-A pulse with a rise time estimated to be ∼10 psec.
The effect of lattice parameter mismatch in NEA GaAs photocathodes grown on GaP/InxGa1−xP substrates
Authors: Enstrom R. E. , Fisher D. G.
Published: February 2003

Transmission-mode negative electron affinity (NEA) GaAs photocathodes were investigated. In order to assess quantitatively the effect of lattice-parameter mismatch between the cathode and substrate, several 1-μm-thick GaAs photocathode layers were vapor deposited onto GaP/InxGa1−xP composite substrates with x ranging from O to about 0.5; the corresponding lattice mismatch varied from 0.2 Å to approximately zero. Photoluminescence and ir free-carrier absorption measurements of the Zn doping concentration in the 1-μm-thick GaAs layers revealed that the doping concentration was about 3–6 times greater than that obtained on 15-μm-thick GaAs layers grown under identical Zn partial pressure conditions. Photoemission measurements showed that the transmission-mode quantum efficiency at a wavelength of 0.7 μm increased from about 0.045 electron/photon for GaAs on GaP to 0.13 electron/photon for GaAs on In0.50Ga0.50P as the lattice-parameter mismatch decreased to approximately zero. Correspondingly, transmission-mode white-light sensitivity values increased from 195 to 390 μA/lm. The photoemission spectral response curves were analyzed to determine values for back interface recombination velocity s and electron diffusion length L. In general, several combinations of these parameters gave a good fit to the data. However, for samples near the lattice match point, s was restricted to relatively low values and, for a given value of s, the corresponding value of L was significantly higher than that for any sample with an appreciable amount of lattice mismatch.
Depolarization of microwaves in electromagnetic polarimetry: Influence, detection, and measurement
Authors: Sardos René
Published: February 2003

Precise polarimetric measurement with microwaves is taking on a growing interest (in plasmas and ferroelectricity, as well as Faraday, Cotton-Mouton-Voigt, Kerr, and other effects) and it is for this reason that the present author draws attention to the fact that in order to make meaningful measurements of rotation and ellipticity, account must be taken of the possible depolarization of waves. It is demonstrated that the measurement of wave depolarization can be made with the aid of a two-wave interference depolarimeter and polarimeter-ellipsometer used in conjunction with a single detector. Thus, point-by-point measurements are conducted which give simultaneously depolarization, rotation, ellipticity, and the sign of the ellipticity. It is shown that a depolarimeter and polarimeter-ellipsometer using a three-wave interferential analyzer can also be used to obtain all these values, and in addition can record their variations, which is indispensable for the study of unstable phenomena, or for a too rapid evolution where point-by-point measurements cannot be made.
A new approach to ion acceleration with electron beams
Authors: Young F. C. , Friedman M.
Published: February 2003

The propagation of an unneutralized relativistic electron beam with ν/γ≳1 around a grounded wire creates a highly localized high-density plasma. Multi-MeV ions were observed to be accelerated collectively from this plasma by the electron beam. If a deuterated polyethylene wire is used up to 1014 deuterons with a mean energy of about 3 MeV are generated and directed along the axis of the wire. It was demonstrated that the acceleration mechanism is applicable to higher-atomic-number ions. If an aluminum wire is used 12–30-MeV aluminum ions are produced.
Effect of oxygen on dislocation movement in silicon
Authors: Hu S. M. , Patrick W. J.
Published: February 2003

The effect of oxygen on dislocation movement in silicon was studied by the method of indentation dislocation rosettes. The size of the rosettes was correlated with the concentration and the state of oxygen in the samples, as determined by means of infrared spectroscopy. In the range of oxygen concentration investigated, up to 1.5×1018 oxygen atoms per cm3, neither interstitially dissolved oxygen nor SiO2 precipitates were found to have any appreciable dislocation-pinning effect. The formation of small oxygen clusters was found to lead to considerable hardening, but at the same time to induce a profusion of dislocation clusters. The oxygen clusters formed in the temperature range from 700 to 900 °C at oxygen concentration levels of ?1×1018 atoms/cm3. The appearance of such clusters was taken to be the reason for the observed broadening of the 1107-cm−1 infrared absorption band and the simultaneous shrinking of its peak height, maintaining an approximately constant integrated peak area.
LPE growth and properties of GaP- (AlGa)As-GaAs heterostructures as a function of the GaP substrate roughness
Authors: van Oirschot T. G. J. , Acket G. A. , Bartels W. J.
Published: February 2003

The growth by liquid phase epitaxy (LPE) of GaP- (AlGa)As-GaAs heterostructures and the properties of the GaAs top layer in these structures have been studied as a function of the GaP substrate surface roughness. A correlation was found between the substrate roughness value and the size of the subgrains invariably present in the epilayers. Uniformly distributed subgrains of minimum size (∼10 μm in diameter) were observed for lapped substrates with roughness values near 0.3 μm, deviations from this value both upwards and downwards producing subgrains of increasing size and eventually also an increasing number of growth defects. The measured average values of the lifetimes of minority carriers for p-type (Ge, Zn) and n-type (Sn) doped GaAs top layers were found to be almost independent of the substrate treatment and of the doping level of these layers. Furthermore, the diffusion lengths estimated from the lifetime values were about 2 μm for layers of both doping types. The average external photoluminescence quantum efficiency (about 0.3% for 5×1018 cm−3 p-doped layers) is fairly independent of the substrate treatment and appears to be consistent with the lifetime measurements. Its spatial distribution, however, closely follows the subgrain distribution and is more homogeneous for layers grown on lapped than on polished substrates.
Heavy-ion sputtering yield of silicon
Authors: Andersen H. H. , Bay H. L.
Published: February 2003

The sputtering yield for 45-keV Ar+ irradiation of amorphous silicon is found to be in very good agreement with theory. In connection with earlier reported yields measured relative to those of argon, we here report absolute yields for 16 different ions (7⩽Z1⩽83). In no case does the difference between theory and experiment amount to more than 15%. The energy dependence of lead sputtering yield on silicon (25 keV⩽E⩽500 keV) is also reported and found to agree with theory.
Resistivity, grain size, and structure of vacuum-deposited Co films
Authors: van Gurp G. J.
Published: February 2003

Co films were deposited by electron-beam evaporation onto oxidized Si wafers. The resistivity was measured after annealing at temperatures up to 500 °C. The resistivity after deposition is about 8 μΩ cm and decreases to the bulk value on annealing. This occurs in two stages: 230–380 °C (stage A) and 410–430 °C (stage B). Stage A is attributed to a decreasing grain boundary scattering owing to grain growth and secondary recrystallization and can be described as a second-order reaction. The grain size d increases in this temperature interval from about 0.07 to 4 μm. The rate constant of the resistivity recovery is temperature dependent with an activation energy of 1.58 eV which is suggested to be the grain boundary migration energy. A deviation from Matthiessen’s rule is explained as being due to the preferred hcp (001) orientation which is strongly enhanced by annealing. Stage B is attributed to a reduction of the number of dislocations, stacking faults, and twin boundaries. A grain boundary resistivity of 1.0×10−11 Ω cm2/d is found and the reflection coefficient for grain boundary scattering is calculated to be 0.2.
Temperature coefficient of resistance in ultrathin metal films
Authors: Kazmerski L. L. , Racine Diane M. , Ayyagari M. S.
Published: February 2003

The temperature coefficient of resistance (TCR) of ultrathin (40–120 Å) metal films is investigated. The effects of temperature, island size, interisland separation, and thickness are incorporated into an analytic expression for the TCR based upon an activated tunneling model. Experimental data are presented to verify the relationships. Anomalous effects, including experimental data, are discussed. An analytic treatment of this situation results in the inclusion of an additional negative term in the TCR expression when compared to the activated tunneling case. The possibilities of positive and negative TCR are indicated.
High-temperature electron and hole mobilities in pure and doped CdS
Authors: Vydyanath H. R. , Kröger F. A.
Published: February 2003

Electron and hole mobilities determined in pure and doped CdS at high temperatures are explained on the basis of conventional scattering theories. Scattering at ionized impurities is found to be a major factor in limiting the mobilities in doped samples up to the highest temperatures.
Bleustein wave reflection and bulk wave generation by an electrode of finite dimensions
Authors: Curtis R. G. , Redwood M.
Published: February 2003

A theoretical analysis of the reflection, transmission, and bulk wave scattering of Bleustein-Gulyaev waves by an electrode of finite thickness and finite length is conducted. The surface region outside the electrode is assumed to be coated with an infinitely thin perfectly conducting metal layer, since without this layer the surface wave would be so deeply penetrating that it would be of little interest. The theory uses Green’s function and Fourier transform techniques and does not involve any physical approximations; the near-field part of the Green’s function being evaluated numerically after simplification by contour integration. The method could be extended to deal with a general surface wave. Numerical results are presented for aluminum and gold layers on PZT-4 ceramic. A series of such reflectors cascaded together is also considered.
Decrease in the void growth rate by interstitial trapping
Authors: Koehler J. S.
Published: February 2003

Void growth during neutron or charged-particle irradiation at temperatures in the range 0.4Tm⩽T⩽0.6Tm is described in pure metals and in metals containing impurities which trap interstitials. It is shown that the equations for the steady state can be integrated analytically. For cases in which strong trapping occurs the recombination rate is enhanced and the rate of void growth is reduced. A discussion of how strong trapping can be achieved is given.
Photostimulated exoelectron emission from ultrahigh vacuum quenched platinum wires
Authors: Berger A. S.
Published: February 2003

High-purity platinum wires were radiation quenched from high temperature at pressures below 5×10−10 Torr. The electron emission induced by uv illumination was measured during subsequent isochronal annealing cycles. When compared with the electron emission of well-annealed Pt wires it is found that increased emission occurs in the quenched samples after annealing in the temperature regime 350–550 °C. A model based upon monovacancy diffusion kinetics and vacancy-enhanced solute diffusion agrees with the experimentally determined annealing kinetics.
Estimation of the critical resolved shear stress for dislocation glide through a random mixture of distinct obstacles
Authors: Hanson Kenton , Morris J. W.
Published: February 2003

Using techniques drawn from the statistical theory of branching processes, we approximate the critical resolved shear stress for the athermal planar glide of a dislocation, idealized as a flexible line of constant tension, through a random mixture of immobile point obstacles of distinct types. The approach simultaneously permits an estimate of the geometric properties of the particular obstacle configuration which determines the critical resolved shear stress. The estimates are shown to be in good agreement with empirical results obtained through direct computer simulation of glide through a random mixture of ’’strong’’ and ’’weak’’ points. A simple extension permits an estimate of the velocity of thermally activated glide through an array of mixed obstacle types at low temperature.
Source self-mixing in the detection of extended incoherent sources
Authors: Cohen Steven C.
Published: February 2003

We consider the self-beating of incoherent light from an extended source at a wide-band photomixer. The intermediate frequency mean squared current is found to be proportional to the product of the direct detected source power and the power within the i.f. bandpass about the optical frequency and within the heterodyne field of view. Thus the ratio of the heterodyne signal to self-beating power is proportional to the ratio of local oscillator power to direct detected power. This ratio is usually large for systems employing efficient local oscillators that generate shot-noise-limited operation. In less efficient systems, such as those employing tunable diode lasers, the effects of self-mixing may be significant.
Effect of elastic uniaxial strain on the electrical resistance of In2Bi single-crystal whiskers
Authors: Key William S. , Davis Jack Hayne
Published: February 2003

Eight single-crystal whiskers of In2Bi with 〈001〉 orientations, grown by the squeeze technique, were elastically strained up to 0.7% of their lengths while measuring the voltage across the current-carrying whisker. The strain-resistance (ε-R) coefficient was found to be characterized by the relation ΔR/Rε=a+bε, where a=8.94±0.26 and b=175±20.
Mach waves and reflected rarefactions in aluminum
Authors: Neal T.
Published: February 2003

A rarefaction wave in aluminum shocked to 27.7 GPa (277 kbar) is examined with radiographic techniques, and the bulk sound speed is determined. A Mach reflection in aluminum is also examined radiographically and the results are compared with the simple three-shock theory of Mach waves. Then a modified three-shock model is developed which is consistent with the experimental results. The modified model leaves some quantities undetermined but closely bounded.
Energy dissipation in a thin polymer film by electron beam scattering: Experiment
Authors: Hawryluk R. J. , Smith Henry I. , Soares A. , Hawryluk Andrew M.
Published: February 2003

A series of experiments of scanning electron beam exposure of PMMA films on silicon, copper, and gold substrates is described, and compared with the calculations of Monte Carlo and analytic models of energy dissipation per unit volume. Film thickness was varied from 1000 to 10 000 Å, accelerating voltage from 10 to 20 kV, and linear charge density from 1×10−9 to 1×10−5 C/cm. Good agreement was obtained in the comparison with the predictions of Monte Carlo calculations, whereas some discrepancies were observed in the comparison with the analytic models. The assumption inherent in the theoretical approaches that PMMA acts like a linear recording medium, in the sense that exposure is additive, is experimentally evaluated by means of an Abel inversion. The assumption that developed profiles represent surfaces of equal energy dissipation was examined by means of a computer simulation of the development process.
α-phase Hugoniot of iron
Authors: Barker L. M.
Published: February 2003

The published data on the α-phase Hugoniot of iron have appeared to indicate a ’’softening’’, relative to expected behavior, of the Hugoniot as the phase-transition stress of 13 GPa (130 kbar) is approached. This has been interpreted as evidence of a partial early transition to the high-pressure ε phase in shock experiments. A careful reexamination of the available data and data reduction procedures reveals that the α-phase Hugoniot of iron appears to be quite normal to 13 GPa, and therfore the Hugoniot data give no indication of an early partial phase transition. The Hugoniot data are fit by the linear shock-velocity–particle-velocity relation U=C0+1.33u, where C0=4.63 mm/μsec.