bluuebunny/crossref_metadata_2025 huggingface dataset:
Space-charge effect on local electric breakdown of polyethylene at 77 K
Authors: Shimizu Noriyuki , Kosaki Masamitsu , Horii Kenji
Published: February 2003

The local breakdown of polyethylene adjacent to the tip of a needle electrode was studied at liquid-nitrogen temperature. It was found from the results of the local-breakdown voltage of various waveforms that the injected space charge from the needle electrode reduced the intense electric field at the needle tip. The injection depth of the space charge in polyethylene was assumed to be about 10 μm from the characteristic traces of the local breakdown and the light-emitting region at the needle tip when ac voltage was applied. The electric field distribution adjacent to the needle tip was calculated by incorporating an injected space-charge density of 3.87×10−3 C/cm3 (2.42×1016 electrons/cm3) which made the electric field strength at the needle tip equal to zero. The injected space charge modified the electric field such that the electric field strength at the edge of its distribution attained the maximum value. The results of the calculation give a reasonable explanation for the characteristic traces of the local breakdown.
Fluid mechanics of copper: Viscous energy dissipation in impact welding
Authors: Robinson J. L.
Published: February 2003

The aim of this paper is twofold; to explain the parametric bounds for successful impact welding, and thereby to confirm the existence of a new region V of inviscid fluid behavior of metals. The assumption of two regions of fluid behavior (viscid and inviscid) has previously permitted a description of wave formation in impact welding and has provided an estimate of about 107 s−1 for the critical strain rate dividing the two regimes. The model is extended here to a consideration of viscous energy dissipation. It is predicted that for sufficiently high impact velocities there will be some melting, and that for sufficiently low velocities the dissipation will prevent the formation of the reentrant jet needed to remove surface impurities and permit a bond to form. In this way upper and lower bounds to a bonding region are established. Fits to data of Cu-Cu bonding provide two estimates of the coefficient of viscosity, 102 and 2.2×102 N s m−2. These values of the critical strain rate and viscosity combine to give a critical strength of (1–2.2) ×109 N m−2. A theoretical value of 1.2×109 N m−2 lies in this range.
Pyroelectricity and piezoelectricity in nylon 11
Authors: Litt Morton H. , Hsu Che-hsiung , Basu P.
Published: February 2003

This paper describes preliminary pyroelectric and piezoelectric results obtained with commercial films of nylon 11. The results of dielectric-constant measurements in the temperature range 20–130 °C are also presented. Nylon 11 films show quite high pyroelectricity and the evidence indicates that there is probably dipole orientation in crystalline regions. Charge injection or volume polarization, as well as dipole orientation, was shown to contribute to the pyroelectricity unless the sample was thoroughly relaxed.
Monte Carlo calculation of electron back diffusion in a Townsend discharge
Authors: Burch D. S. , Whealton J. H.
Published: February 2003

The back diffusion of electrons in a Townsend discharge has been analyzed by a simple Monte Carlo calculation. The problem was formulated in terms of three parameters: the ratio of molecular mass to electronic mass, the average number of collisions of an electron, and v0/vd, the ratio of emission speed to drift speed. In all cases, the back diffusion is found to be small at low values of the third parameter. It rises to a maximum and then decreases at larger values of v0/vd. For an absorbing cathode, the back diffusion is found to be predicted by the Thompson-Loeb formula with surprising accuracy, considering the approximate nature of its theoretical basis. Results are presented in a form that permits reasonable estimation of the back diffusion to be expected in experimental situations for which the parameter E/N is sufficiently high that the thermal gas motion may be neglected and sufficiently low that ionization is unimportant.
Crystal growth: A comparison of Monte Carlo simulation nucleation and normal growth theories
Authors: van der Eerden J. P. , van Leeuwen C. , Bennema P. , van der Kruk W. L. , Veltman B. P. Th.
Published: February 2003

We simulated the growth of a (001) Kossel crystal surface on a special-purpose computer. Different nearest-neighbor bond energies in the two lateral directions of our solid-on-solid model were possible (anisotropy). The values which we obtained for the growth rate are much more accurate than previous results on a general-purpose computer. The supersaturation dependence of the growth rate was compared with predictions of mean field and nucleation theories and it was shown that the latter, if properly adjusted, apply even for relatively rough surfaces. The anisotropy dependence of the growth rate was used to determine the transition from step growth to continuous growth.
Surface study of ion-implanted silicon wafers using SAW convolver
Authors: Motamedi M. E. , Das P. , Bharat R.
Published: February 2003

Nonlinear space-charge-coupled interaction between a surface acoustic wave (SAW) propagating on a lithium niobate substrate and ion-implanted silicon samples placed in proximity to the SAW propagating surface has been studied. A pulsed dc electric field normal to the surface has been used to bend the surface potential for accumulation and depletion of charge carriers near the surface which in effect causes a change in attenuation of SAW. Experimental results are presented using three n-type silicon samples into two of whcih boron was implanted. Experimental results are found to substantiate theoretical predictions of attenuation, calculated on the basis of partial compensation of the silicon doping by the implanted ions. Similar studies have also been made using incident light of varying intensity on the semiconductor surface.
Complex defects introduced into Si by high-energy electron irradiation: Production rates of defects in n-Si
Authors: Wada Takao , Yasuda Kyoichiro , Ikuta Shiro , Takeda Michihiko , Masuda Haruho
Published: February 2003

The n-type silicon crystals of about 0.15, 0.9, and 10 Ω cm (pulled material) and 120 Ω cm (float-zone material) are exposed to 2–9-MeV electron beams at total integrated fluxes up to about 1018 electrons/cm2. The production rates of each complex defect in irradiated silicon are investigated. They are obtained from the condition of charge neutrality by using the experimental values of the resistivity as a function of bombardment dose. The electron energy dependence and the impurity density dependence of the production rate are determined for each complex defect. The results suggest that a configuration of the defect states at Ec−0.3 eV may be associated with a phosphorus atom, and in the intrinsic region the two occupied and vacant states should be symmetrically located above and below the middle of the energy gap, respectively.
Secondary electron emission from solid hydrogen and deuterium resulting from incidence of keV electrons and hydrogen ions
Authors: So/rensen H.
Published: February 2003

The secondary electron emission (SEE) coefficient δ was measured for solid hydrogen and deuterium resulting from the normal incidence of 0.5–3-keV electrons and 4–10-keV H+, H2+, H3+, and D3+ ions. The SEE coefficients for solid hydrogen are 60–70% of those for solid deuterium, and the coefficients are small, in contrast to what is expected for insulating materials. One explanation is that the secondary electrons lose energy inside the target material by exciting vibrational and rotational states of the molecules, so that the number of electrons that may escape as secondary electrons is rather small. The losses to molecular states will be largest for hydrogen, so that the SEE coefficients are smallest for solid hydrogen, as was observed. For the incidence of ions, the values of δ for the different molecular ions agree when the number of secondary electrons per incident atom is plotted versus the velocity or the stopping power of the incident particles. Measurements were also made for oblique incidence of H+ ions on solid deuterium for angles of incidence up to 75°. A correction could be made for the emission of secondary ions by also measuring the current calorimetrically. At largest energies, the angular dependence corresponds to δ (ϑ) =δ (ϑ)(cosϑ)−1.
Particle heating in a radio-frequency plasma torch
Authors: Yoshida Toyonobu , Akashi Kazuo
Published: February 2003

A numerical model was developed to predict the behavior of a particle in a radio-frequency (rf ) plasma. The analysis obtained the heat, mass, and momentum transfer of a single particle injected into an rf plasma. The governing equations for vaporization of a liquid particle were taken from the model which was used to simulate the vaporization process of liquid droplets in a rocket combuster. All the thermodynamical and transport properties were calculated as functions of temperature in order to simulate the actual behavior more precisely. The boundary conditions are a finite temperature at the particle center and a heat balance at the particle surface. Thermodynamical equilibrium at the particle surface was always assumed. ’’Moving-boundary problems’’ in the case of melting or vaporizing processes were solved by the use of a ’’moving grid system’’. Four sizes of iron particles injected into the rf argon plasma have been computed: r0=20, 40, 60, and 80 μ. The iron particles with radii less than 70 μ could be melted under the assumed plasma conditions. It was found that the potentiality as concerns powder processing of an rf plasma was overestimated by previous models.
Anode scattering effects on electron pinch radius in low-impedance REB diodes
Authors: Johnson David J. , Goldstein Shyke A.
Published: February 2003

The effect of different anode material on the size of very intense pinches is studied from the radial structure of the bremsstrahlung from a tightly pinched relativistic electron beam. Time-dependent data are obtained which point out the influence of scattering by the anode which electrons experience near the pinch axis. The scattering broadens the bremsstrahlung FWHM for pinches with high-Z (80) anodes to 6 mm, compared to 4 mm for low-Z (13) anodes. When anodes composed of low- and high-Z elements in different annular regions are used, translation of backscattered electrons enhances the current density upon the low-Z regions and decreases it upon the high-Z regions.
Characteristics of TE modes in a plane-parallel waveguide filled with warm moving plasma magnetized along a transverse direction
Authors: Mukherjee Pradeep K.
Published: February 2003

The characteristics of TE modes in a transversely magnetized plane-parallel waveguide containing a relativistically moving warm plasma have been studied. The effects of the finite electron temperature of the plasma have been incorporated in terms of an anisotropic pressure. Using the first three moment equations in conjunction with Maxwell-Minkowski equations, we have derived the dispersion relation and the cutoff frequencies for the TE mode. It is found that the TE mode is modified due to the thermal motion of electrons to depend upon the velocity of the moving medium and the applied magnetic field. Numerical results for the cutoff frequencies are presented for several values of the parameters characterizing the electron-plasma temperature, the velocity of the moving medium, and the strength of the applied magnetic field.
Relative rates of nickel diffusion and copper diffusion through gold
Authors: Tompkins H. G. , Pinnel M. R.
Published: February 2003

The low-temperature diffusion of nickel through gold has been evaluated using Auger electron spectroscopy. Samples used were printed-wiring-board fingers having a nickel ’’diffusion barrier’’ plated between the copper substrate and the cobalt-hardened gold contact surface. A coefficient was determined for diffusion via the gold defect structure at 150°C using both first-arrival and surface-accumulation approaches. Both methods yield comparable results with a coefficient D′ of (2–7) ×10−15 cm2/sec. This is between one and two orders of magnitude smaller than that determined for copper under nearly identical conditions. Results of other investigations are compared and contrasted to the present findings. The surface reaction of nickel with air and chlorine-containing environments is sufficiently rapid that diffusion is the rate-limiting step in the accumulation of nickel at the gold surface.
High-speed high-current field switching of NbO2
Authors: Shin S. H. , Halpern T. , Raccah P. M.
Published: February 2003

The field-switching properties of NbO2/NbO or NbO2/(reduced NbO2) devices have been investigated. Under an applied electric field they switch from a high (≳10 kΩ) to a low (∼10 Ω) resistance in times shorter than 0.7 ns. For pulse durations of several ns, the current carrying capability is higher than 80 A. The switching mechanism appears to proceed in two stages: the field-assisted Poole-Frenkel mechanism for low applied field and thermal runaway. However, the unique switching properties of NbO2 could also be understood by a small poloron-conduction mechanism.
N-type switching erroneously attributed to field-enhanced trapping
Authors: Domingo George , Greiling Paul , Holm-Kennedy James W.
Published: February 2003

N- or S-type switching in the I-V characteristics of semiconductor resistive bars immersed in liquid nitrogen occur if the I2R power per surface area generated in the semiconductor exceeds a certain threshold value. Such switching has been consistently misinterpreted and attributed to field-enhanced trapping. This communication briefly explains the thermal switching, identifies numerous errors in the literature, and describes an experiment to distinguish bertween thermal and electronic switching.
Low-frequency current oscillation and negative photoconductivity in n-type epitaxial GaAs film
Authors: Ito M. , Mimura T. , Ishikawa H.
Published: February 2003

Low-frequency current oscillation (20–100 Hz) and photoelectric properties have been investigated with an n-type GaAs epitaxial layer partially compensated by zinc. A high electric field region is found at the anode side and the threshold electric field of the oscillation is about 2.5 kV/cm. Negative photoconductivity is due to a deep level of Ev+0.87 eV and a zinc level of Ev+0.03 eV at the interface between the epitaxial layer and a semi-insulating substrate. For the oscillation mechanism, a model of redistribution of the electrons in deep traps between the epitaxial layer and the interface is discussed.
II-VI solid-solution films by spray pyrolysis
Authors: Feigelson Robert S. , N’Diaye Abdourahim , Yin Shaiw-Yih , Bube Richard H.
Published: February 2003

A complete range of solid-solution films has been prepared by spray pyrolysis for the CdSxSe1−x and ZnxCd1−xS systems. The composition of the sprayed film is compared with the composition of the spraying solution and correspondence plots are given. The large variation in resistivity with x in the ZnxCd1−xS system appears to be only incidentally dependent on the method of preparation.
Effect of thermal stress on the easy axis of amorphous Fe40Ni40P14B6
Authors: van Diepen A. M. , den Broeder F. J. A.
Published: February 2003

By use of the 57Fe Mössbauer effect the axis of easy magnetization in amorphous Fe40Ni40P14B6 (Metglas 2826) between 78 °K and 300 °K is found to lie predominantly in the plane of the ribbon in the zero external field. However, because of the positive magnetostriction of this alloy, it is possible to force the magnetization direction out of the plane by cooling the ribbon to low temperatures after it is sandwiched at room temperature between a material with a higher thermal expansion coefficient.
Correlation in simultaneous TSC and TSL measurements
Authors: Gasiot J. , Fillard J. P.
Published: February 2003

It appears from the literature that efforts to correlate thermally stimulated currents (JTSC) and thermoluminescence (JTSL) have been unsuccessful; it should be pointed out that the mathematical formulation of the correlation starts from the unjustified identification of JTSL with the filling rate of the recombination centers − dm/dt. In the present paper a method is proposed to check this critical point; as a result, it appears from records of −(d/dt)(JTSC/JTSL) that JTSL departs from −dm/dt in every experimental situation we have explored up to now.
Excitation spectra of shallow donors in GaP
Authors: Scott Walter
Published: February 2003

The excitation spectra of S, Se, Te, and Si donors in GaP is presented. The spectra are qualitatively similar to each other, but there is a large species dependence of the excited-state binding energies. Phonon-assisted transitions to excited states are observed in the continuum-absorption region which involve LO, LA, and TA phonons.
Dependence of LED light distribution on electrical drive parameters
Authors: Szczepanek Paul S. , Gault Charles S. , Mandelberg Hirsch I.
Published: February 2003

Two types of sources that have been used for fiber optic communication systems are solid-state lasers and light-emitting diodes (LED’s). Since the lifetimes of the LED’s are considerably longer than those of the solid-state lasers, LED’s are preferred presently for system applications. We have shown that the intensity distribution, and hence, the amount of optical power coupled from an LED into a fiber, is dependent on the average power level as well as the voltage bias on th LED. Under pulsed operation the LED intensity distribution is therefore dependent both upon the average power level as well as the duty cycle. The dependence has been measured in both the edge as well as dome emitters.
Absorption, refractive index, and birefringence of AlAs-GaAs monolayers
Authors: van der Ziel J. P. , Gossard A. C.
Published: February 2003

The band structure of artificial periodic crystals grown by molecular-beam epitaxy and consisting of sequential AlAs and GaAs monolayers differs slightly from AlxGa1−xAs random alloys having a comparable average Al content. The measured direct band gaps are up to 110 meV higher than the alloys, and the indirect gaps up to 70 meV higher. The measured dispersion of the refractive index agrees best with the theoretical dispersion curve of an alloy composition having a higher Al content than in the monolayer. This is consistent with the higher band gap of the monolayer. The alloy and monolayer exhibit a birefringence resulting from strain-induced anisotropy of the lower and upper cutoffs of the complex part of the dielectric constant. The strain results from the differential thermal contraction of the layers and the GaAs substrate on cooling from the growth temperature to room temperature. The birefringence of the monolayer sample contains an additional contribution resulting from the periodic structure.
Effects of high-intensity electron bombardment on the secondary-emission characteristics of a MgO/Au-cermet film
Authors: Dionne Gerald F. , Fitzgerald James F.
Published: February 2003

An experiment to determine the durability of a 75 MgO/25 Au-cermet film secondary-emission cathode has been carried out over a period of 4000 h. A 2-keV electron beam of 2 A/cm2 current density was applied to a single spot and the secondary-electron-yield curve was monitored at regular intervals. To determine changes in chemical composition, Auger analysis was carried out with the same electron beam. Results of these tests indicated a decrease in maximum yield from 8.4 to 3.7 and a corresponding increase in the first crossover energy of 16 to 25 eV. Inspection of the relative intensities of the Auger spectral lines revealed that both Au and Mg increased relative to 0, with the Au line showing a steady increase during the first 500 h and then leveling off after 1500 h for the remainder of the testing period. The discovery of an apparent Au deficiency in the outer layers of the film is in accord with the initially high yield and the expected differential sputtering effects during argon sputter etching prior to the experiment. A surface profilometer measurement indicated that a crater of approximately 500 Å in depth was etched during the bombardment.
Laser-induced microwave damage to dielectric materials
Authors: Rao K. V. N.
Published: February 2003

Dielectric samples of (1) pyroceram, (2) slip-cast fused silica (SCFS), (3) impregnated slip-cast fused silica (ISCFS), and (4) silicon nitride (Si3N4) were subjected to 10.6-μm CO2-laser radiation of irradiances up to 800 W/cm2. The increase in loss tangent at 6 GHz was measured both during and after laser irradiation using the microwave cavity perturbation technique. Surface temperatures of the samples were measured by an infrared thermometer. Theoretical and experimental evidence indicated that the complex permittivity changes were confined only to the surface layers (∼0.2 to ∼0.5 mm thick) of the samples.
Material removal produced by a high-power-density electron beam
Authors: Miyazaki T.
Published: February 2003

Material removal produced by the interaction of high-power-density electron beam with metal was studied theoretically and experimentally. A mechanism of molten metal removal due to the generation of bubbles inside the target metal is proposed, based on the observed phenomenon and the calculation, which takes into account heat-conduction theory and the penetration of the electron beam into the target metal. Further, as an extension of this mechanism, a drilling mechanism is proposed. These proposed mechanisms could successfully explain the results obtained experimentally.
An investigation of active surfaces of microchannel plates using Auger electron and ESCA spectroscopic techniques
Authors: Siddiqui Saeed H.
Published: February 2003

The nature of secondary electron emission surfaces of microchannel plates (MCP’s) has been investigated using Auger electron and ESCA spectroscopies. The chemical compositions of a few monolayers of interchannel and intrachannel surfaces have been determined. By making use of ion-milling techniques along with Auger electron spectroscopy, the composition versus depth profiles of interchannel surfaces have been obtained. It has been found that the compositions of thin layers (∼ 100 Å) of surfaces of MCP’s with self-emission and higher than normal electrical conductivities are different from those of MCP’s without such defects. The presence of an alikali-rich surface is found to be more effective in influencing the electrical conductivities of channels than their secondary emission characteristics. Other characteristics of microchannel plates which can be gainfully studied with these techniques have been outlined.
Improvement of the photovoltaic efficiency of a metal-insulator-semiconductor structure: Influence of interface states
Authors: Viktorovitch P. , Kamarinos G.
Published: February 2003

We study the working of a photovoltaic MIS structure. We point out the important influence of the insulating layer and of the interface states on the improvement of the photovoltaic yield; both their kinetic and electrostatic actions are examined. Our study shows that there exists an optimum thickness δopt of the insulating layer which provides a maximum electrical power at the output of the device. We give general basic equations for the calculation of δopt and present some results concerning silicon.
A systematic experimental and theoretical investigation of the grain-boundary resistivities of n-doped BaTiO3 ceramics
Authors: Ihrig H. , Puschert W.
Published: February 2003

The electrical resistivities, current-voltage characteristics, and thermopowers of a series of n-doped BaTiO3 ceramics having systematically varying resistivity anomalies (posistor or PTC effect) are analyzed in light of the theoretical description of the grain-boundary resistivity by a Schottky-type potential barrier model (Heywang’s barrier). The observed current-voltage dependences agree well with this model over a wide voltage range. However, the agreement between the theoretical and experimental temperature curves of the low-voltage resistivities is weak if the surface acceptor states, which result as recently suggested from an excess of barium vacancies in the immediate vicinity of the grain surface, are assumed to be at the same energy. Satisfactory agreement is obtained when the acceptor states are distributed over a certain energy interval. An estimate of the surface charge then reveals that the resistivity below the Curie point is governed by a residual potential barrier originating from an excess of surface charge which cannot be compensated even by an optimum alignment of the spontaneous polarization.
Fluorine-cycle incandescent lamps
Authors: Hill John C. , Dolenga Arthur
Published: February 2003

Tungsten-halogen incandescent lamps containing either bromine or iodine as the halogen are commercially available and exhibit a life or light output superior to that of nonhalogen lamps. To further increase the life of this kind of lamp, fluorine was tried as the halogen. By adding bromotrifluoromethane (CBrF3) to the fill gas, lamp life more than twice that of lamps containing bromine alone was achieved. To avoid deleterious side effects of the fluorine cycle, a small amount of oxygen is required in the lamp. This oxygen can be supplied simply by omitting some of the processing steps normally used to remove residual oxygen.
Theoretical calculations of the electrodynamic properties of ferromagnetic levitation systems
Authors: Bohn G. , Langerholc J.
Published: February 2003

A model is given which allows an analytical treatment of the electrodynamic properties of a suspension electromagnet, and the corresponding equations are solved in zeroth and first order. The zeroth-order results are employed to derive an effective magnetization curve; the value and slope of the permeability curve so obtained are then inserted into the first-order formulas to obtain the frequency-dependent linearized system parameters, which are subsequently compared with existing results.
Laser heating effect on second harmonic generation in CDA and CDA
Authors: Sato Takuzo
Published: February 2003

Time variations of the output of second harmonic generation (SHG) at 532 nm in KDP, CDA, and CD*A were measured by using a Q-switched YAG laser as a fundamental source with pulse peak power of 25 MW, pulse duration of 8 nsec, and pulse repetition rates of 15 and 30 pps. Theoretical time variations of SHG in CDA and CD*A were also discussed and compared with the experimental results.
Evaluation of flashlamp reflectors for the atomic iodine photodissociation laser
Authors: Palmer R. E. , Padrick T. D. , Pettit R. B.
Published: February 2003

A number of possible materials for use as flashlamp reflectors in an atomic iodine photodissociation laser have been tested both for high reflectance in the laser pumpband and for durability. Of the reflectors tested, the optimum metallic reflector is MgF2-overcoated aluminum, and the optimum nonmetallic reflector is BaSO4 powder.
Comment on ’’Permeation of helium and hydrogen from glass-microsphere laser targets’’
Authors: Brysk Henry
Published: February 2003

In a recent paper, Tsugawa et al. presented experimental observations on the rate of outgassing of glass microspheres. They compared the data with predictions from Fick’s law and found a clear qualitative disagreement. It is shown here that their results appear to be consistent with a permeability which, instead of being constant at fixed temperature, is a linear function of the pressure difference across the glass.
Thermal attenuation of ultrasonic waves in yttrium iron garnet at ultrahigh frequencies (500–1000 MHz)
Authors: Roy B. , Mazumder N.
Published: February 2003

Using second- and third-order elastic constant data, the average Grüneisen number 〈γ〉, the average square Grüneisen constant 〈γ2〉, and the nonlinearity constant D have been calculated for yttrium iron garnet (YIG). Attenuation of ultrahigh-frequency (500 and 1000 MHz) acoustic waves (both longitudinal and shear) propagating along 〈100〉 and 〈110〉 directions, caused by Akhieser loss and thermoelastic phenomena, have been evaluated for YIG at 300 °K. Of these, the Akhieser loss is found to be greater. For shear waves propagating in the 〈100〉 direction, the Akhieser loss accounts for about 12% of the measured loss reported in the literature at 500 MHz and about 25% at 1000 MHz.
Shock compression of molybdenum to 2.0 TPa by means of a nuclear explosion
Authors: Ragan III C. E. , Silbert M. G. , Diven B. C.
Published: February 2003

The principal Hugoniot of molybdenum has been determined at a pressure of 2.0 TPa by measuring directly both the shock velocity and the particle velocity behind the shock. Neutrons from an underground nuclear explosion were used to generate a high-pressure shock in a slab of molybdenum by rapidly fission heating an adjacent slab of enriched uranium. A shock velocity of 18.2 mm/μs (±5%) was obtained by determining the transit time of the planar shock between two points in the molybdenum separated by 9.87 mm. A particle velocity of 10.7 mm/μs (±5%) was obtained by observing the Doppler shifts of six neutron resonances in the energy region from 200 to 800 eV in the moving shocked molybdenum. The pressure and density derived from this pair of measurements are 2.0 TPa (20 Mbar) and 24.8 g cm−3, respectively. This experiment represents the first direct determination of a point on the Hugoniot of any material in this pressure region, and the resulting data point is in good agreement with theoretical estimates. This measurement was a successful demonstration that the Doppler-shift technique can be used to obtain particle velocities in this pressure region. It appears that errors in both the shock velocity and the particle velocity can be reduced to approximately ±2% in an improved measurement, resulting in a well-defined Hugoniot for molybdenum, which can be used as a standard in future impedance-matching experiments.
Characteristics of metal-diffused LiNbO3 for acoustic devices
Authors: Boyd G. D. , Schmidt R. V. , Storz F. G.
Published: February 2003

The diffusion of Co, Ni, Cu, and Zn in LiNbO3 has been studied. The diffusion coefficients and activation energies are given. The effect of the diffused dopants on the acoustic velocity has been measured.
Infrared and high-energy electron diffraction analyses of electron-beam-evaporated MgO films
Authors: Aboelfotoh M. O. , Park K. C. , Pliskin W. A.
Published: February 2003

Infrared spectroscopy and reflection high-energy electron diffraction have been used to analyze MgO films deposited at various deposition rates on ’’infrared’’ silicon wafers and hard glass substrates at various temperatures. Infrared spectra obtained for MgO films deposited at rates of 1350–1500 Å/min on substrates at room temperature and at 200 °C showed that the amount of hydroxyl groups present was significantly less in the 200 °C deposited films. The spectra also showed that the amount of hydroxyl groups present in films deposited at a very fast rate (∼7800 Å/min) was much less than that in films deposited at a very slow rate (∼160 Å/min) on substrates at 200 °C. Some of the hydroxyl groups initially present in films deposited at ∼160 Å/min and most of the hydroxyl groups in films deposited at ∼1350 Å/min were removed by annealing the films in dry nitrogen at 500 °C. The electron diffraction patterns obtained for MgO films (100–3000 Å) deposited at rates of 1350–1500 Å/min on substrates at a temperature in the range from room temperature to 200 °C showed that the films initially nucleated in random orientation and as the film thickness was increased to and above 500 Å, a 〈111〉 preferred orientation developed at the surface independent of substrate temperature. These results suggest that adsorption of residual water on MgO does not influence the mode of film growth. The 〈111〉 preferred orientation developed in films deposited on substrates at 200 °C dissolved, and some degree of the 〈100〉 preferred orientation developed upon annealing in dry nitrogen at 500 °C. The preferred orientation remained, however, unchanged when these films were annealed in dry air. The orientation also remained unchanged when films deposited on substrates at room temperature were annealed in dry nitrogen at 500 °C. These results suggest that the presence of hydroxyl ions and oxygen adsorption inhibit surface diffusion and, hence, the dissolution of the orientation during annealing.
Acoustoelectric absorption in degenerate nonparabolic semiconductors
Authors: Sharma S. S. , Sharma S. K.
Published: February 2003

We solve the Boltzmann equation for electrons in nonparabolic semiconductors in the presence of an acoustic wave to obtain the distribution function which varies as the acoustic wave. This is used to calculate the current density associated with the acoustic wave and, hence, its absorption coefficient as a function of the energy gap and the degeneracy parameter. The scattering of electrons with ionized impurities is taken to be the dominant scattering mechanism.
Hall effect in amorphous thin-film magnetic alloys
Authors: McGuire T. R. , Gambino R. J. , Taylor R. C.
Published: February 2003

Amorphous magnetic alloys have unusually large extraordinary Hall coefficients (Rs) defined by the ratio of the Hall resistivity to the net magnetic moment of the alloy. We have studied the Hall effect in amorphous films in the ternary ferrimagnetic systems Co-Gd-Mo and Co-Gd-Au, alloys which exhibit compensation temperatures (Tcomp). Above Tcomp the Hall coefficient Rs is positive and below Tcomp the sign of Rs changes to negative in a discontinuous manner, probably limited by the homogeneity of the sample. We have also prepared amorphous Gd-Au and Y-Co films and measured Rs which we use to qualitatively separate the effects of the Co and Gd sublattices in the ternary alloys. We attribute the sign of Rs to a combined effect of a negative Gd and a positive Co Hall coefficient. Above Tcomp the Co is dominant and points in the direction of the applied field H while Gd is antiparallel to H. Thus, both sublattices contribute in a positive sense to Rs. Below Tcomp the Gd moment is dominant and the sign of Rs is reversed for both sublattices. Values of Rs up to 25×10−9 Ω cm/G are measured near Tcomp and when Mo is present Rs is reduced to 5×10−9 Ω cm/G. Molybdenum is known to cause a strong decrease in the moment of the cobalt sublattice and this probably is the reason Rs decreases. Our interpretation of the Hall effect in these ferrimagnetic systems differs from other recently proposed models.
Magnetic domain behavior during the hcp-to-fcc phase transition in cobalt using Lorentz electron microscopy
Authors: Lewis W. F.
Published: February 2003

We have investigated the magnetic domain behavior during the hcp-to-fcc phase transition in cobalt using electron microscopy. From single-crystal and polycrystalline samples it has been observed that defects, such as stacking faults and grain boundaries, will aid the transformation of the domain structure between the two phases. From the domain pattern we have also made estimates of the domain wall energy γ and exchange constant A in both the hcp and fcc phases. These values are compared with the results from other experiments.
Hysteresis curves and magnetization processes in a model for an amorphous magnet with random uniaxial anisotropy
Authors: Chi Mely Chen , Alben Richard
Published: February 2003

We consider the magnetic field behavior of a simple model for an amorphous ferromagnet with random single-ion anisotropy. The spins are taken as classical unit vectors located at sites of a dense random packing model and coupled via nearest-neighbor exchange interactions. An easy-axis direction is chosen at random for each site. For large anisotropy, the coercivity is very large and the hysteresis curves resemble those found for amorphous TbFe2 at low temperature. As the anisotropy is reduced, there is a fairly abrupt change in the behavior of the model indicating that sufficiently weak random anisotropy is effectively averaged away. We have examined the energy of metastable states. The results indicate that the canted aligned state is always more stable than low-moment spin-glass-like states. We also consider the magnetization process in the presence of imposed domain walls and find that wall motion is preceeded by magnetization rotation in the high-coercivity regime.
Resonant modes of magnetostatic waves in a normally magnetized disk
Authors: Ikuzawa Yoshiaki , Abe Kenji
Published: February 2003

It is assumed that the resonance absorption of magnetostatic waves is caused by those standing waves set up in a normally magnetized disk. The resonance conditions are derived for magnetostatic waves pinned at the small edge of the disk, and the excitation of different sets of modes of magnetostatic waves by rf magnetic fields of different configurations is described. The resonance conditions are combined with the inhomogeneous internal magnetic field of a disk to analyze the absorption spectrum of the disk. Experimental observations of the modes are performed using a disk of single-crystal yttrium iron garnet, at C- and X-band frequencies, and at ordinary temperatures. Some experimental results are compared with the theory and it is shown that the analysis gives a satisfactory description of the observed absorption spectra.
High-pressure pulsed electrical CO laser
Authors: Boness M. J. W. , Center R. E.
Published: February 2003

The design and performance of a 16-l high-pressure pulsed electric discharge CO laser is reported. The gas was excited using the electron-beam sustained discharge technique. Cryogenically cooled gas flowed subsonically through a room-temperature cavity. Thermal isolation was provided by the formation of free convection boundary layers on the warm flow walls which preserved the cryogenic gas temperature and maintained good medium uniformity. Beam-quality measurements indicated better than 1.5 times diffraction-limited peformance with single pulse energies of 1600 J and an electrical efficiency of approximately 40%. Comparisons are made between the actual laser performance and predictions based on the CO laser kinetics code.
Laser power and gain measurements on the sequence bands of CO2
Authors: Reid J. , Siemsen K.
Published: February 2003

An experimental technique is reported which converts a conventional cw CO2 laser into one which lases on a series of new laser bands. These bands are identified as the (0002–[1001,0201]I,II) and the (0003–[1002,0202]I,II) sequence bands of CO2, and lie in the 10-μm wavelength region. The technique involves placing a cell containing hot CO2 in the laser cavity to suppress the regular 0001 bands. We report the first detailed power and gain measurements on the new laser bands. More than 80 laser lines have been observed in the 0002 bands, with cw output powers as high as 10 W. Gain measurements are reported for a variety of discharge conditions, and gain coefficients greater than 0.3%/cm have been obtained. We have also observed several laser lines in the 0003 sequence band of CO2. Possible applications of the new laser lines are discussed, particularly their use in determining vibrational temperatures in CO2 discharges.
A free-floating superconducting bolometer—A sensitive heat-pulse detector
Authors: Chin M. A.
Published: February 2003

A free-floating (no substrate) granular aluminum superconducting bolometer has been made and tested. Sensitivity and time-constant measurements were compared with those of similar bolometers fabricated on glass and Al2O3 substrates. The responses were first studied with the bolometer isolated in a vacuum chamber which was immersed in a superfluid liquid-helium bath and cooled by conduction through the contact leads, and again after incremental increases of helium gas were introduced into the sample chamber. The measurements show that for low gas pressures (≲10−4 cm Hg) the floating bolometer was between one and two orders of magnitude more sensitive than identical bolometers on substrates. With increasing gas pressure, the formation of a superfluid helium film of an approximate thickness of three atomic layers caused a reduction of the floating bolometer sensitivity by nearly two orders of magnitude. The effect of bolometers on substrates was, on the other hand, only 30%. The results provide strong evidence that the Kapitza conductance into helium occurs in the first two or three atomic layers.
Spall studies in uranium
Authors: Cochran S. , Banner D.
Published: February 2003

We have studied spall by observing the effect of spallation on the free-surface velocity of a plate-impact target. We believe that the spall signal is a sensitive measure of the damage done to the target. We have formulated a simple theoretical model and incorporated it in a hydrodynamic computer code, to simulate the first few stress reverberations in the target as it spalls. The simple model successfully describes the principal features of our measurements in uranium and in a few other metals.
Evolution of a CO2-laser-produced cadmium plasma
Authors: Green J. M. , Silfvast W. T. , Wood II O. R.
Published: February 2003

The evolution of a CO2-laser-produced cadmium plasma formed in the presence of a background gas at low pressure is described. The processes which give rise to plasma formation, spectral emission, expansion, and internal structure are discussed. The suitability of such a plasma as a potential laser medium is considered and some of the most likely and least likely regions and conditions for achieving gain are identified.
Growth and propagation mechanism of 〈110〉-oriented dark-line defects in GaAs-Ga1−xAlxAs double heterostructure crystals
Authors: Nakashima Hisao , Kishino Seigô , Chinone Naoki , Ito Ryoichi
Published: February 2003

Application of external stress on a double heterostructure (DH) crystal is used to induce 〈110〉-oriented dark-line defects (DLD). The stress is applied by using a four-point mechanical bending apparatus. Resulting DLD formation is found to depend on stress direction and DH crystal orientation. This asymmetric DLD introduction can be explained by the difference in glide motion between α and β dislocations. It is shown that a threshold stress exists for the DLD formation. This threshold stress and the growth velocity of the DLD’s strongly depend on optical pump intensity. Extension of the DLD’s into the ternary passive layers is observed by x-ray topography and phase-contrast microscopy. This observation suggests that stresses caused by local heating at the site of a defect play an important role in inducing 〈110〉 DLD’s. These experimental results lead to the conclusion that dislocation glide processes are responsible for 〈110〉-DLD propagation.
Effect of ion bombardment on the surface composition of Cu-Ga alloys studied by differential reflectometry and AES
Authors: Dove D. B. , Pantano C. G. , Andrews J. B.
Published: February 2003

Measurements have been made on the effects of ion-beam milling on the surface of Cu-Ga alloys using a technique in which the optical reflectivity of an ion-bombarded surface is compared with a nonbombarded region. The differential-reflectometry method has a sensitivity to less than a 1% change in composition in the surface layer and probes the surface to a depth order of 50–100 Å corresponding to the optical skin depth. The results have been correlated to changes in the peak heights of Cu and Ga measured by Auger electron spectroscopy. In this way it has been found that negligible selective sputtering of the Cu and Ga occurs when the alloys are ion bombarded with 2-keV argon ions. The ratio of the AES peak heights due to Ga and Cu from the oxide differed from that of the alloys by about a factor of 2.
Electrical measurement of the lateral spread of the proton isolation layer in GaAs
Authors: Matsumura Hideki , Stephens Kenneth G.
Published: February 2003

Information on the lateral spread of ions and/or damage is contained in the depth distribution normal to a target surface if ions are implanted into a tilted target. Following this principle the lateral spread of the carrier removal distribution formed by 300-, 400-, and 500-keV proton implants in GaAs is evaluated from the several depth distributions of carrier removal which are formed by implants with different tilting angles and measured by the Copeland method. It is found that the lateral spread of carrier removal is largest at a depth near the projected range of protons. For instance the removal rate drops to 10% of its maximum value at about 0.7 μ laterally from a mask edge for 400-keV protons for which the projected range is about 3.3 μ. It is also found that the lateral spread increases as the incident energy increases but that the ratio of the lateral to the longitudinal spreads decreases.
Analysis and some applications of a condenser microphone used as an ionization chamber for intense α fluxes
Authors: Pointu A. M. , Allaf A. K. S. , Fitaire M.
Published: February 2003

It is shown that intense α fluxes, when incident on a condenser microphone, produce noise, and that this noise is due to α ionization in the capacitor interelectrode space which acts as a tiny ionization chamber. Statistical analysis of random events is presented which leads to relations between this noise, incident α fluxes, and α ionization efficiency. Applications of these results to α-activity measurement and absolute Bragg-curve determination are discussed. α activities from 100 μCi/cm2 to several Ci/cm2 can be measured and good spatial resolution can be achieved using small microphones.
Energy analysis of H− ions from a hollow-discharge duoplasmatron
Authors: Wiesemann K. , Prelec K. , Sluyters Th.
Published: February 2003

Energy spectra of H− ions from a HDD source operating in mixtures of helium, hydrogen, and cesium reveal that negative ions are generated by a volume process and by a surface process. A marked difference was observed in the pressure dependence of the low- and high-energy groups, corresponding to the volume and the surface processes, respectively. The active surfaces could be identified. Some evidence that, besides collisional attachment processes, ion-molecular reactions have an influence on the yield of H− ions in volume reactions could be found.
Efficient laser ionization of sodium vapor—A possible explanation based on superelastic collisions and reduced ionization potential
Authors: Measures Raymond M.
Published: February 2003

The recently observed efficient ionization of sodium vapor by a laser tuned to the sodium resonance line can be explained in terms of the large population of resonance-state atoms created by laser-induced radiative equilibrium. This large population of excited atoms represents (a) a reservoir of energy that can rapidly be transferred to the free electrons via superelastic collisions and (b) a source of pseudo-ground- state atoms possessing a much reduced ionization energy. Three-photon ionization is proposed as the mechanism for creation of the primary pool of free electrons.
A short-period helical wiggler as an improved source of synchrotron radiation
Authors: Kincaid Brian M.
Published: February 2003

A new kind of wiggler is proposed as an improved source of synchrotron radiation from high-energy electron storage rings. The electrons are made to travel in a short-period helix by a transverse helical magnetic field. The radiation spectrum produced is calculated and it is shown that the helical wiggler design could produce a total intensity (photons sec−1 per unit bandwidth) improvement of several hundred and a brightness (photons sec−1 per solid angle per unit bandwidth) improvement of 4×104 over the present state of the art in synchrotron radiation sources.