bluuebunny/crossref_metadata_2025 huggingface dataset:
Particle densities in high current hollow cathode discharges
Authors: Koch H. , Eichler H. J.
Published: February 2003

Operating hollow cathode discharges at current densities in excess of 0.1 A/cm2 leads to an efficient production of metal vapor via the process of cathode sputtering. This method of metal vapor production has been exploited in numerous metal ion laser devices and in spectroscopic light sources. In this paper the main processes involved in high current hollow cathode discharges will be discussed for the special case of a Ne–Cu discharge that can be regarded as representative for other sputtering hollow cathode discharges. Starting from a set of balance equations, expressions for the current density dependence of the spatially averaged buffer gas ion-, metal ion-, and metal atom-density are derived. These expressions are verified experimentally by measurements of the spontaneous emission of a Cu II line and yield in a simple manner realistic data of these particle densities. Finally the obtained results are related to the characteristics of a Cu II laser.
Infrared rapid thermal annealing for GaAs device fabrication
Authors: Kohzu H. , Kuzuhara M. , Takayama Y.
Published: February 2003

A new post-implantation annealing technique, called infrared rapid thermal annealing (IRTA), is discussed for fabricating GaAs devices using ion implantation technology. The IRTA apparatus and capless annealing conditions are described. Also, electrical property and its uniformity of n or n+ type GaAs layers made by Si implantation to semi-insulating GaAs followed by IRTA are presented, and compared with those made by Si3N4 capped furnace annealing. A steeper carrier concentration profile with a higher peak carrier concentration in the n type active layer made by IRTA results in a higher transconductance without any anomalous characteristics on the GaAs metal–semiconductor field-effect transistor.
Thermal stability of electrically active dopants in laser annealed silicon films
Authors: Wilson S. R. , Paulson W. M. , Gregory R. B. , Tam G. , White C. W. , Appleton B. R. , Rai A. K. , Pronko P. P.
Published: February 2003

Single crystal Si wafers and polycrystalline Si films on Si3N4 have been implanted with large doses (1×1015/cm2–4×1016/cm2) of P or As and laser annealed with either a cw or pulsed laser. The samples were then subjected to thermal anneals between 450 and 900 °C to determine the thermally stable dopant concentration for each sample. Sheet resistance and Hall measurements have been used to measure the electrical properties in each case. SIMS, RBS, and TEM have been used to measure atomic profiles, As substitutionality and residual defects after laser and thermal annealing. In each case the maximum electrically active dopant concentration achieved by laser annealing decreased after a 700–800 °C thermal anneal.
Effects of nitrogen on dislocation behavior and mechanical strength in silicon crystals
Authors: Sumino Koji , Yonenaga Ichiro , Imai Masato , Abe Takao
Published: February 2003

The characteristics of dislocation behavior and mechanical strength in tensile tests are investigated on the silicon crystals that are doped with nitrogen at the time of crystal growth by the floating-zone technique. These are compared with those in the usual floating-zone-grown silicon crystals. Nitrogen atoms dispersed in a silicon crystal are shown to have no influence on the velocities of dislocations in motion in the temperature range above 600 °C. Dislocations in the nitrogen-doped crystal are, however, immobilized while the crystal is kept under a low or zero applied stress at elevated temperatures. Like Czochralski-grown silicon, nitrogen-doped silicon shows a much higher yield strength than usual floating-zone-grown silicon when crystals are dislocated. It is concluded that interstitial nitrogen atoms bring about the hardening of silicon crystals through locking of dislocations upon congregating on the latter.
6
0Co γ-ray and electron irradiation damage of GaAs single crystals and solar cells
Authors: Yamaguchi Masafumi , Amano Chikara
Published: February 2003

6 0Co γ-ray and high energy electrons (0.8–4 MeV) irradiation damage of GaAs solar cells were examined. Changes in minority carrier diffusion length in irradiated GaAs single crystals were also investigated by electron beam and 60Co γ-ray-induced current methods for solar cells. Damage constant of p-GaAs is smaller than that of n-GaAs. Equivalent damage rate in GaAs due to electron irradiation to 60Co γ-ray irradiation damage was clarified experimentally and theoretically. Experimental results for radiation damage of GaAs solar cell were also in satisfactory agreement with theoretical values, calculated from change in minority carrier diffusion length due to irradiation. Radiation damage in GaAs solar cells can be evaluated by using radiation damage data in GaAs single crystals. In-depth profiles for electron irradiation damage in GaAs and annealing behavior of radiation damage in GaAs were also examined.
Damage production in GaAs by H+ irradiation
Authors: Bhattacharya R. S.
Published: February 2003

Rutherford backscattering and proton induced x-ray emission in combination with channeling have been used to study damage production in GaAs by proton irradiation. The average cross section for displacement of Ga and As atoms has been determined and found to agree well with the cross section calculated from the elastic displacement theory of Kinchin and Pease. In addition, we have demonstrated that about 6% more Ga atoms are displaced than As atoms.
A model for laser induced diffusion
Authors: Fogarassy E. , Stuck R. , Toulemonde M. , Salles D. , Siffert P.
Published: February 2003

A model for laser induced diffusion is proposed, assuming the melting of Si surface under pulsed laser irradiation and the diffusion, in liquid phase, of a thin film deposited impurity. Depending on the thickness of the film, it results in a dopant distribution profile with a surface disordered layer induced either by segregation effects or precipitation of the dopant in excess of the solubility limit achieved by laser annealing. Experimental results obtained for a ruby laser irradiation of thin films of various dopants such as Sb, Ga, Bi, and In deposited on Si substrates are in good agreement with the model.
Separation of bulk and surface light absorption with an open photoacoustic cell
Authors: Helander Per , Lundström Ingemar
Published: February 2003

A spectroscopic method for the study of adsorption of molecules onto a solid is demonstrated. It is shown in particular how the spectra of molecules adsorbed onto a solid surface and molecules in a solution outside the surface can be recorded simultaneously. The method is based on the information present in the phase of a photoacoustic signal. The experiments made to demonstrate this method were performed with an open photoacoustic cell. In this cell the temperature oscillations in the sample are transferred to a window. The thermal expansions of the window are detected by a piezoelectric crystal. Light absorbing molecules on the surface of the window and in the bulk liquid give signals with different phases that can be separated by phase sensitive detection.
Kinetics of TiSi2 formation by thin Ti films on Si
Authors: Hung L. S. , Gyulai J. , Mayer J. W. , Lau S. S. , Nicolet M-A.
Published: February 2003

Silicide formation with Ti deposited on single crystal Si and Ti deposited on amorphous Si layers sequentially without breaking the vacuum was investigated using backscattering spectrometry and glancing-angle x-ray diffraction. For Ti deposited on amorphous Si, TiSi2 was formed with a rate proportional to (time)1/2 and an activation energy of 1.8±0.1 eV. For Ti deposited on single crystal Si, the reaction rate was slower and the silicide layer was nonuniform in thickness. We attribute the difference in behavior to the presences of interfacial impurities in the case where Ti was deposited on single crystal Si.
Metal-organic vapor deposition of CdTe and HgCdTe films
Authors: Hoke W. E. , Traczewski R.
Published: February 2003

Epitaxial films of CdTe and HgCdTe have been grown on 〈111〉A CdTe substrates using metal-organic reagents. Specular CdTe films were grown at the investigated substrate temperatures between 370 and 410 °C. Specular Hg1−x CdxTe films with X≥0.15 were obtained at substrate temperatures of 400–410 °C. The HgCdTe growth rate was nominally 6 μm/h for Hg0.8 Cd0.2Te. The HgCdTe films are n type and a liquid nitrogen mobility of 140 000 cm2/V sec was measured for Hg0.85Cd0.15Te. The interdiffusion width at the CdTe–HgCdTe heterojunction is nominally 1 μm.
Synchrotron radiation of wiggled electron beam in rectangular waveguide
Authors: Haus Hermann A. , Islam Mohammed N.
Published: February 2003

An analysis is presented of the spectrum radiated by an electron beam passing through a magnetic wiggler in a rectangular waveguide using a coupled-mode approach. The noise power radiated into each mode of the waveguide is calculated. In the limit of a highly overmoded waveguide and large relativistic parameter, the total emitted spectrum approaches that of a beam in free space. The radiation formulas are greatly simplified for a weak magnetic field.
Intense proton beam excitation of the high pressure Ar/N2 laser
Authors: Wiley L. G. , Hammer D. A.
Published: February 2003

In this paper, parametric studies are presented of a high pressure Ar/N2 gas laser excited by an intense proton beam from a magnetically insulated diode. Using power deposition of up to 140 MW/cm3, gas pressure up to 3040 Torr, variable N2 fraction (5%–90%), and several mirror reflectivities and gain lengths, laser power (up to 500 kW), efficiency (≲0.4%), gain, threshold conditions, and spectral characteristics have been studied. Laser action was achieved at three wavelengths in the second positive band of N2: 337.1, 357.1, and 380.5 nm. Comparison of the observations with predictions of a model showed that emission at all three wavelengths was expected, and initiation times and pulse durations of the three lines were accurately predicted. Observed similarities and differences between proton beam and electron beam excitation of the Ar/N2 laser are discussed.
Stimulated Raman emission of coherent phonons by impurities in a crystal
Authors: Fain Benjamin
Published: February 2003

The possibility of stimulated emission of coherent phonons by impurities (ions) embedded in a crystal is considered. It is shown that when the ions with homogeneously broadened levels are subjected to an electromagnetic field, the frequency Ω of which is larger than an eigenfrequency of the ion ω21, at the Raman frequency ωq=Ω−ω21, a coherent stimulated emission of phonons may emerge. The absorption rate of the pumping electromagnetic field has a singularity near the threshold of the phonon self-excitation.
Degenerate four wave mixing with long range surface plasmons in attenuated total reflection geometries
Authors: Stegeman G. I. , Karaguleff C.
Published: February 2003

We analyze the theory of degenerate four wave mixing by long range surface plasmons in an attenuated total reflection geometry. It is shown that large signal levels can be obtained with pulsed laser excitation for polydiacelyne materials.
Molecular dynamics simulation of crack tip processes in alpha-iron and copper
Authors: deCelis Benito , Argon Ali S. , Yip Sidney
Published: February 2003

The intrinsic crack tip processes of either propagation by cleavage or blunting by the nucleation of dislocations from the nonlinearly stressed region at the crack tip have been simulated by a molecular dynamics approach in alpha-iron and in copper, utilizing the Johnson and Morse potentials, respectively, and a new fixed stress boundary condition at the border between the inner discrete region and the outer anisotropic linear continuum. The simulations showed that alpha-iron is inherently brittle, and fails by cleavage along a cube plane when the stress intensity factor reaches the critical Griffith value. No dislocations are nucleated in iron and even the development of restricted crack tip twinning in special orientations does not alter this intrinsic brittleness. In copper crack tip blunting at a level somewhat less than the Griffith stress intensity factor always prevented brittle crack growth by cleavage. Thus, copper is inherently ductile. Because it permitted the unhindered development of substantial nonlinear crack tip displacements, and did not prevent dislocations from penetrating through the border between the inner nonlinear material and the outer linear continuum, the new stress boundary condition was found to be far superior to the fixed or flexible boundary conditions used at this border by previous investigators. This is reflected in the observed critical stress intensity factors for brittle cleavage that were found to be nearly equal to the expected Griffith value for the stress boundary condition while the displacement boundary conditions gave results nearly three times higher.
Calculation of electron swarm parameters in fluorine
Authors: Hayashi M. , Nimura T.
Published: February 2003

Swarm parameters of electrons have been calculated for fluorine by a Monte Carlo simulation and the Boltzmann equation method for the first time. Values of these parameters have been obtained for ratios of the electric field to the gas number density E/N from 100 to 3000 Td (E/p0 =35∼1000 V/cm Torr). Available experimental and theoretical cross sections were used for the calculations.
The collision half-width for the R(0) line of the ν3 band of methane
Authors: Walker H. C. , Phillips W. J.
Published: February 2003

The collision half-width for the R(0) absorption line of the ν3 band of methane has been determined as a function of temperature with nitrogen and carbon dioxide as the broadening gases. The measurements were made in the temperature range from 300 to 1000 K with broadening gas pressures in the range from 5 to 15 psi (absolute). Methane partial pressures sufficient to produce approximately 60% absorption at line center for each condition were used. The line spectrum was produced with a Laser Analytic LS-3 tunable diode laser spectrometer. A best-fit Voigt profile to the experimental line shape was used to determine the broadening which is characterized by the collisional or Lorentz half-width.
Kerr electro-optic field mapping measurements in water using parallel cylindrical electrodes
Authors: Zahn Markus , Takada Tatsuo , Voldman Steven
Published: February 2003

An extensive set of Kerr electro-optic field mapping measurements are reported for highly purified water over the temperature range of 8.8–29.5 °C. The Kerr constant is independent of temperature over this range and equals B≂3.4×10−14 m/V2. Pulsed high voltages up to 140 kV across parallel cylindrical electrodes with a 1-cm gap are applied on millisecond time scales. For early times, the measured results agree with the space-charge-free electric field distribution while for times greater than 500 μsec, there is significant space-charge distortion due to positive charge injection.
Thermal diffusivity of i
n s
i
t
u composites
Authors: Ostenson J. E. , Finnemore D. K. , Verhoeven J. D. , Gibson E. D. , Shanks H. R.
Published: February 2003

The thermal and electrical transport properties for Cu-Nb metal-metal composites have been measured in order to determine the suitability of these materials for high strength structural members where high thermal conductivities are needed. In the temperature range between zero and 400 °C the thermal diffusivity of the cold drawn alloy is about 10% less than annealed Cu. The rule of mixtures, in fact, describes the data well.
Effect of surfactants on strength of gallium arsenide single crystals
Authors: Roshchina A. V. , Matveenko V. N. , Lisovskaya T. D. , Gorbylev V. A.
Published: February 2003

Optical resonators of heterojunction lasers essentially involve (110) cleavage surfaces. Cleaving single crystals, however, is a difficult procedure, whereas its quality largely determines the life of the resonators. Surfactants showing no chemisorption on the surface of single crystals may decrease the number of defects brought about by cleaving (Rehbinder effect). Again, it is not easy to find an appropriate surfactant for this procedure, since this is done semiempirically. The present paper deals with strength measurements of GaAs single crystals in the presence of surfactants and the selection of an optimum medium for cleaving.
Temperature distribution in the diamond anvil pressure cell at high temperature
Authors: Munro R. G. , Block S. , Piermarini G. J. , Mauer F. A.
Published: February 2003

The temperature distribution in a diamond anvil pressure cell is investigated theoretically for a model cell having a cylindrical external heater. For a heater surface at 1000 absolute degrees above the ambient temperature, it is found, at steady state, that the region of the sample chamber is, for all practical purposes, isothermal at a temperature of about 11 degrees below the temperature of the heater. When the heater temperature is subsequently incremented instantaneously by 10 degrees, a new steady state is reached in about 30 sec.
Fabrication of double heterostructure diode laser material by compositional interdiffusion
Authors: Bryant F. J. , Qadeer A.
Published: February 2003

The experimental results presented here demonstrate for the first time the feasibility of compositional interdiffusion (CID) as a fabrication technique for double heterostructure diode lasers of graded band-gap energy. The emission wavelengths of double heterostructure PbS1−xSex diode lasers, fabricated by a two-stage CID anneal, were found to depend on annealing parameters such as the temperatures and times of the two anneals and on the source materials used. The emission wavelength of the lasers was adjusted to be between 5.9 (x=0.55) and 4.8 μm (x=0.20) by changing the temperature of the second anneal, a process which also produced the p-n junction at different depths. The interdiffusion coefficient in PbS0.8Se0.2 was estimated to lie in the range (0.4–1.1)×10−11 cm2 s−1.
Calculations of optimum phase match parameters for the biaxial crystal KTiOPO4
Authors: Yao J. Q. , Fahlen Theodore S.
Published: February 2003

The expression for the optimum phase matching angle for the biaxial crystal KTiOPO4 (KTP) is presented and numerically calculated. The theoretical effective nonlinear coefficient, walk-off angle, and conversion efficiency are determined. The results provide some theoretical and practical guidance for optimum operation of biaxial crystals, with specific numerical calculations for KTP.
A new focusing method for nondestructive evaluation by surface acoustic wave
Authors: Nongaillard B. , Ourak M. , Rouvaen J. M. , Houze M. , Bridoux E.
Published: February 2003

The focalization of surface acoustic wave on piezoelectric substrates has been largely studied. It is of great interest, in the nondestructive testing area, to use focused surface acoustic waves to monitor defects like cracks which are hardly detected by acoustic bulk waves. In this paper, a new method for nondestructive testing is reported, which uses cylindrically focused surface acoustic beams. This allows for an increase in sensitivity in the detection mode and in spatial resolution in the imaging mode. Using a very simple geometrical model, the resolution and conversion efficiency of the system are estimated.
Nonplanar surface characterization by acoustic microscopy
Authors: Poirier M. , Castonguay M. , Neron C. , Cheeke J. D. N.
Published: February 2003

We report the measurement of the acoustic material signature (AMS), amplitude and phase, on planar and nonplanar surfaces. The one-dimensional AMS is then used simultaneously with the scanning mode of the acoustic microscope to obtain the acoustic images of nonplanar surfaces. This technique is shown to be useful to test the quality of small spherical cavities used in the acoustic lenses fabrication, and also to characterize subsurface defects. This technique is based on the interpretation of fringe patterns appearing in the acoustic images.
Effects of high-pressure SF6 gas dissolved in an insulating oil on dc conduction currents and ac partial discharges
Authors: Hirano Takehiko
Published: February 2003

The pressure dependence of the effects of the dissolved high-pressure (1–12 atm) SF6 gas on the electrical conduction and prebreakdown phenomena of an insulating oil has been studied. The pulsed conduction currents in the oil dissolved SF6 gas under a high dc electric field of more than 100 kV/cm depend on both high equilibrium pressure (solubility) and high applied hydrostatic pressure, i.e., the pulsed currents are suppressed by both pressures. The ac partial discharge-inception voltage in the oil containing dissolved SF6 gas of an equilibrium pressure of 10 atm (466 vol %) under an applied hydrostatic pressure of 12 atm has a value of 1.4 times larger than that for a degassed oil at 5×10−5 Torr. The results obtained suggest that electron affinity of SF6 gas enhances the dielectric strength of the oil saturated with SF6 gas. The degree of enhancement is apparently related to the amount of SF6 gas absorbed by the oil, which in turn is a function of the applied hydrostatic pressure.
Energy deposition and microstructural modification in dynamically consolidated metal powders
Authors: Gourdin W. H.
Published: February 2003

A model is presented for the deposition of energy at powder particle surfaces during dynamic consolidation. The average energy flux incident on the surface of a powder particle is estimated to be E/τA where E is the specific energy deposited by the shock, τ is the shock rise time, and A the measured powder specific surface area. This flux is assumed to be constant over the rise time of the shock, falling abruptly to zero for times longer than τ. Solution of the thermal transport equation subject to this boundary condition yields the thermal history within a powder particle having the area-equivalent diameter 𝒟=6/ρ0A, where ρ0 is the solid density. The magnitude of the temperatures and the heating and cooling rates indicate likely material transformations. The penetration of a given isotherm provides an estimate of the volume fraction of material transformed. Good agreement is found between model calculations and measurements of the extent of local martensite formation in consolidated 4330V steel powder and of local melting in consolidated aluminum-6% silicon and copper powders. The general implications of the model are discussed.
Atomic correlations of stepped surfaces and interfaces
Authors: Pimbley J. M. , Lu T.-M.
Published: February 2003

We have developed a scheme to evaluate the atomic pair correlation function exactly for stepped surfaces and interfaces. This pair correlation function is particularly useful in calculating the diffracted beam width and shape from an arbitrary distribution of steps using low-energy electron diffraction, reflection high-energy electron diffraction, and grazing x-ray diffraction. We have made model calculations for several realistic terrace width distributions. By comparing the calculated and measured diffracted beam widths and shapes, one can extract valuable, quantitative structural information on surfaces, interfaces, and epitaxially grown films.
Preparation and structure of carbon film deposited by a mass-separated C+ ion beam
Authors: Miyazawa Takeo , Misawa Shunji , Yoshida Sadafumi , Gonda Shun-ichi
Published: February 2003

Carbon films were deposited using mass-separated C+ ions of 300 and 600 eV. The films have diamond-like characteristics such as transparency in the visible spectral region with wavelengths longer than about 650 nm and in the infrared, and high electrical resistivity. Transmission electron diffraction analysis shows that the film is amorphous and does not contain graphitically bonded carbon atoms. Kα x-ray emission spectrum of the carbon in the film agrees well with that of diamond. In the x-ray photoemission spectrum of the film, no characteristic energy loss due to π plasmon was observed. The atomic density of the film calculated from the energy loss due to the plasma oscillation of valence electrons is 1.7×1023 atoms/cm3, which is in good agreement with that of diamond. These results indicate that the film deposited using C+ ion beam consists of tetrahedraly bonded carbon atoms.
Measurement of the thickness of thin layers by ultrasonic interferometry
Authors: Houze M. , Nongaillard B. , Gazalet M. , Rouvaen J. M. , Bruneel C.
Published: February 2003

An ultrasonic interferometer working in a pulsed mode is described in this paper. It allows for the measurement of coating thicknesses as thin as 5 μm with a 5% precision over different substrates at a very high rate (up to 1000 times per second). The optimal conditions for this interferometric measurement are defined theoretically and the probe characteristics have been optimized technologically. This, together with the design of a very large frequency bandwidth (from 90 to 510 MHz) electronic setup, leads to interesting performances. The advantages of the system for achieving thickness measurements are discussed and comparisons are made with other systems.
First-order statistics of Jacobi elliptic functions having random phase with an application to holography
Authors: Barakat Richard
Published: February 2003

The first-order statistics (probability density function, characteristic function, probability of exceeding a specified value, first two moments) of the Jacobi elliptic functions cn(θ,k) and sn(θ,k) are evaluated when θ is a random variable uniformly distributed over the period T=4K(k). The resultant expressions reduced to those of the corresponding trignometric functions cos θ and sin θ as k→0. An application of the formal results is made to the holography of vibrating surfaces.
Investigation of hole formation on Cr/Al, Si/Al, and C/Al bilayer films by laser beam irradiation
Authors: Yoshii Kumayasu , Umeno Masataka , Murata Seiji , Kawabe Hideaki , Yamada Koichi , Watanabe Isao , Kubo Takahiro
Published: February 2003

Transmission, replica, and scanning electron microscopy studies of the holes formed by laser irradiations on Cr/Al, Si/Al, and C/Al bilayer films were carried out. For Cr/Al and C/Al films, well-shaped circular holes were formed independently of the thickness ratio. In the case of Si/Al film, circular holes were formed only when the thickness ratio of Si was small. The peripheral regions of holes had several types of swell. In Cr/Al film there existed the steep swell at the hole edge and successively the gentle swell. The swells of C/Al film were rough in shape with thickness irregularities. Many thinned portions appeared in the swell of Si/Al having large thickness ratio of Si. The threshold power to form a hole was much lowered by coating the Al film with Cr, Si, or C, and the threshold value of 0.4 W for 60-nm-thick Al was reduced to about 0.04 W for 10 nm Cr/50 nm Al and 0.08 W for 20 nm Si/40 nm Al. The numerical analysis for temperature rise of the bilayer films was made using the finite difference method considering the phase transitions of the materials. The mechanisms of hole and swell formations in the bilayer films are also discussed.
Modification of the optical and structural properties of dielectric ZrO2 films by ion-assisted deposition
Authors: Martin P. J. , Netterfield R. P. , Sainty W. G.
Published: February 2003

Low-energy bombardment by argon and oxygen ions has been used in the deposition of thin dielectric films of ZrO2. The film packing density has been improved from 0.83 to unity with a corresponding increase in the refractive index from 1.84 to 2.19. The highest stable refractive index measured was 2.23 for oxygen ion-assisted deposition of ZrO2 on a substrate heated to 300 °C. Ion bombardment during condensation of evaporated ZrO2 on a room temperature substrate results in crystallization into the cubic phase which is consistent with previous studies of ion impact crystallization by thermal-spike processes. At elevated substrate temperatures the monoclinic phase is also present.
Anisotropic etching of SiO2 in low-frequency CF4/O2 and NF3/Ar plasmas
Authors: Donnelly V. M. , Flamm D. L. , Dautremont-Smith W. C. , Werder D. J.
Published: February 2003

Anisotropic etching of SiO2 films is reported in low frequency (∼100 kHz), moderate-pressure (0.35 Torr) CF4/O2 and NF3/Ar plasmas. Rates up to 2000 Å/min were achieved with high selectivity over GaAs and InP substrates. The etching mechanism was studied with optical spectroscopy and downstream chemical titrations. Anisotropy is attributed to ion-enhanced reactivity of fluorine atoms with SiO2 at rates up to two hundred times larger than purely chemical etching by fluorine atoms. Damage and product sputter desorption models of this process were evaluated. These two models are nearly mathematically equivalent at steady state, and show that the effectiveness of ions in etching by enhanced reaction is roughly 15 times that in physical sputtering under these conditions.
Optimization of shaped charges
Authors: Haugstad B. S. , Dullum O. S.
Published: February 2003

Efficient design of shaped charges requires a full calculation of all three basic processes involved: liner collapse, jet fragmentation, and subsequent penetration in the target. Claims have been made [S. S. Grigoryan and N. S. Sanasaryan, Mekh. Zhidkosti Gaza 6, 9 (1974); N. S. Sanasaryan, ibid. 6, 151 (1975)] that for given standoff distance, a certain initial jet velocity profile exists that corresponds to maximum penetration at this distance. We demonstrate that no such profile exists. In fact, the velocity profile yielding maximum penetration depth corresponds to infinite strain and is therefore of no practical interest. We abandon the ‘‘moving tank’’ representation of the jet formation adopted by previous authors, and treat the initial axial profiles of jet velocity and strain rate as independent quantities that are intrinsically related only through the shaped charge design. A general relationship is derived between initial axial profiles of jet velocity, strain rate, and total strain for a jet fragmenting exactly in the bottom of the crater it produces. The result is applied to two different fragmentation models of the jet, and the resulting constraints imposed on quantities associated with the initial jet is derived. We indicate how analytical relationships of this sort may help to improve liner geometries by identifying those parts of the liner where the ‘‘optimum’’ requirement of fragmentation in the crater bottom is least satisfied. Crude arguments indicate that the use of variable angle—variable thickness liners can improve penetration depths by typically a few tens of percent relative to conventional, straight conical liners.
Spectroscopic determination of mass ablation rate in laser produced plasmas
Authors: Gupta P. D. , Kumbhare S. R.
Published: February 2003

The measurements of mass ablation rate and ablation thickness in laser produced plasmas from layered targets using a luminosity time of flight spectrometer are reported. The results show a steady state ablation in the laser intensity range of 1011–5×1012 W/cm2 of a Nd:glass laser. A mass ablation rate of 2×104 g/cm2/sec is observed for aluminum plasma at the laser intensity of 5×1011 W/cm2 which is consistent with the estimate obtained using a self-regulating model for plasma heating. This technique offers a simple and direct method for measuring the ablation parameters.
Toward a fundamental model for steady point-plane corona discharges
Authors: Henson Bob L.
Published: February 2003

A mathematical model expressed in prolate spheroidal coordinates is developed from fundamental equations for steady state corona discharges from needle-to-plane electrodes. The bases of the theory are the Poisson and current continuity equations coupled with a mobility model for the transport of the charge carriers. The potential and field are constrained to be consistent with boundary conditions at the plane electrode, the surface boundary of the glow discharge, and the surface delineating the finite bound of the distribution of space charge. In the fully developed corona glow the steady state current is assumed to be limited by space-charge fields at the glow boundary surface and a potential V0 across the glow region is required to sustain the discharge. An additional requirement is that the space-charge region must satisfy a power-balance equation. Utilizing current vector potential methods results in a current density exactly yielding Warburg’s law at the plane electrode. A current-potential characteristic equation varying as the square of the potential drop across the space-charge region is predicted, but because the space-charge swarm is finite the current is collected from a finite area of the plane electrode only. The calculated potentials and fields are given in terms of quadratures. All of the solutions are exact in that no approximations are used in the calculations, and the solutions predict the assumed boundary values. An appendix discusses possible empirical tests of the theory.
Negative ion production in hydrogen plasmas confined by a multicusp magnetic field
Authors: Bacal M. , Bruneteau A. M. , Nachman M.
Published: February 2003

The density of negative hydrogen ions and the plasma characteristics are investigated as a function of the discharge current and the neutral gas pressure for several configurations of the magnetic multipole, and in the absence of magnetic containment fields. It is shown that the hybrid magnetic multipole configurations, characterized by a relatively low lifetime for wall losses of primary electrons (10−7 s) contain high relative densities (10%–50%) of negative ions. The transition from the low density to the high density regime has been observed.
Interaction between boron and intrinsic defects in GaAs
Authors: Elliott K. R.
Published: February 2003

A model has been developed to describe the interaction between boron and antisite defects in bulk grown undoped liquid uncapsulated Czochralski GaAs. This model helps explain the observed experimental behavior. The model indicates that the residual double acceptor can most likely be associated with either GaAs or BAs.
Lateral GaAs growth over tungsten gratings on (001) GaAs substrates by metalorganic chemical vapor deposition and applications to vertical field-effect transistors
Authors: Asai H. , Adachi S. , Ando S. , Oe K.
Published: February 2003

Lateral epitaxial growth of GaAs over tungsten gratings of 5-μm wide lines and spaces on (001) GaAs substrates has been performed using metalorganic chemical vapor deposition (MOCVD). The lateral overgrowth is strongly dependent on the grating direction on the (001) plane, as well as on the growth temperature. A vertical field effect transistor with a grating gate of 1.25-μm wide lines and spaces is demonstrated as one application of this MOCVD overgrowth technique. The drain I-V characteristics of the device are similar to those for a triode tube.
Composition and electronic properties of electrochemically deposited CdTe films
Authors: Takahashi Makoto , Uosaki Kohei , Kita Hideaki
Published: February 2003

The composition, type of semiconductivity, and resistivity of CdTe films deposited electrochemically from an aqueous solution of pH=1.4 containing 1 M CdSO4 and 1 mM TeO2 were investigated. X-ray diffraction peaks confirmed the formation of CdTe in the films deposited at potentials between −0.20 and −0.65 V (vs Ag/AgCl). The films deposited at potentials more positive than −0.35 V contained free Te in addition to CdTe. X-ray measurements showed that the more positive the deposition potential, the higher the concentration of free Te in the film. Auger electron spectroscopy measurements also confirmed that the Te/Cd ratio was higher in the films deposited at more positive potentials. The films deposited at potentials more positive than −0.35 V were p type and those deposited at more negative potentials were n type. The relation between the deposition potential and sheet resistance was ‘‘volcano’’ like and it seemed that the films deposited around −0.35 V where the semiconductivity of the films changed showed maximum resistivity.
Free carrier lifetime in semi-insulating GaAs from time-resolved band-to-band photoluminescence
Authors: Weiner J. S. , Yu P. Y.
Published: February 2003

Time-resolved band-to-band photoluminescence offers a quick and contactless technique for determining the photoexcited free carrier lifetime in GaAs samples with deep traps.
Comparison of models of the built-in electric field in silicon at high donor densities
Authors: Lowney Jeremiah R. , Geist Jon C.
Published: February 2003

The built-in electric field for holes due to donor-density gradients in n-type silicon is calculated at 300 K for donor densities between 1×1018 and 1×1020 cm−3. The calculation is based upon a recent model of band-gap narrowing that includes the effects of ionized impurities, many-body interactions, and an estimate of spatial fluctuations of the band-gap edge caused by the random distribution of donor atoms in the silicon crystal. This model of band-gap narrowing differs significantly from a number of other band-gap narrowing models currently in use in that it agrees with the band-gap narrowing measured optically at 35 and 300 K rather than that inferred from electrical measurements. The built-in electric field based on this model, which also differs significantly from the results of most previous models, decreases significantly above a donor density of 1×1019 cm−3 with a reversal of the field above 7×1019 cm−3. The implications of this work for photodiodes are discussed.
Nonlinear generation of sum and difference frequency waves by two helicon waves in a semiconductor
Authors: Salimullah Md. , Ferdous Tahmina
Published: February 2003

This paper presents a theoretical investigation of the nonlinear generation of electrostatic waves at the sum and the difference frequency when two high amplitude elliptically polarized helicon waves propagate along the direction of the externally applied static magnetic field in an n-type semiconductor. The nonlinearity arises through the ponderomotive force on electrons. It is noticed that the power conversion efficiency of the difference frequency generation is much larger than that of the sum frequency generation. The power conversion efficiency may be easily increased by increasing the density of electrons in the semiconductor.
Photocurrent deep level transient spectroscopy in silicon
Authors: Brotherton S. D.
Published: February 2003

Photocurrent deep level transient spectroscopy (PCDLTS) is investigated as a technique for the detection of centers in the minority half of the band gap. The photocurrent and resulting peak shapes are analyzed and compared with experimental results obtained from gold-doped silicon diodes illuminated with different wavelength sources. It is shown that by suitable selection of the photon wavelength, reliable detection of levels in the minority half of the band gap is possible in long lifetime material. However, for centers with a large ratio of majority carrier capture cross section to minority carrier capture cross section, their detection in short lifetime material is likely to be more difficult, unless the material is thinned down and used with an appropriately matched photon source.
Conductance along iron-doped silicon grain boundaries
Authors: Miremadi Bijan K. , Morrison S. Roy
Published: February 2003

Sheet conductance along grain boundaries in silicon is found for polycrystalline material with iron quenched into the grain boundaries. With quenched p-type samples at low temperature, current across grain boundaries is blocked, current through the grains is blocked, but if there are any grain boundaries parallel to the current flow a high conductivity is observed. This conductivity is interpreted as sheet conductivity of 10−1–10−4 mho/sq, decreasing with decreasing iron concentration. The observation will enable future studies of the effect of conducting grain boundaries on devices such as solar cells.
An i
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u x-ray study of gold/barrier-metal interactions with InGaAsP/InP layers
Authors: Vandenberg J. M. , Temkin H.
Published: February 2003

The effectiveness of barrier metal such as Cr, Ni, Pd, Pt, and Ti in gold metallization contacts on InGaAsP/InP was studied. Using a temperature-dependent in situ x-ray technique the alloy formation in the contacts was investigated in the temperature range 130–500 °C and compared with previous studies on contacts without the presence of a barrier. These results were further compared with x-ray analysis of gold/barrier contacts subjected to a standard metallization alloying procedure. The results of the slow temperature ramps (0.4 °C/min) used for the in situ x-ray analysis provided insight into the long-term stability of the contacts. From the temperatures at which alloy formation occurs with and without the presence of a barrier, a measure of the effectiveness of the incorporated barrier could be obtained. While Ni and Pd were found to be ineffective barriers, Pt and Ti are resonably effective in slowing down Au-semiconductor interactions. Cr and bimetallic Ti/Pt were found to exhibit long-term stability in both Au/InP and Au/InGaAs contacts.
Field-effect studies on p-type CuInTe2 metal-insulator-semiconductor structures
Authors: Dawar A. L. , Kumar Anil , Kumar Partap , Mathur P. C.
Published: February 2003

Field effect studies on metal-insulator-semiconductor structures of p-CuInTe2 thin films grown on mica are made in the temperature range 77–295 K. An increase in carrier density and a decrease in the mobility is observed on the application of a negative gate field. The effect of a positive gate field is the opposite. The Hall coefficient is found to remain practically constant at a lower temperature range (77–180 K) and then decreases with a further rise of temperature. The study of the effective field effect mobility μFE reveals that the surface states charge scattering mechanism dominates the scattering process.
Nonlinearity effects in the current-voltage characteristic of p-type yttrium iron garnet epitaxial films
Authors: Paoletti A. , Scarinci F. , Tucciarone A. , Brandle C. D.
Published: February 2003

I-V characteristics are measured in p-type YIG:Ca epitaxial films. In, Au, and Pt contact pads are utilized. In all cases nonlinear I-V characteristics are found which are interpreted in terms of space-charge-imited currents through a two-layer structure. We measure the same activation energy (U=0.227±0.002 eV) in the bulk and thin layers, which form at the contact pads. We conclude that the layers solely differ in Fe4+ concentration. In spite of the I-V nonlinearity, contacts are ohmic in all cases and full linearity of the characteristics are obtained by high temperature annealing in an O2 atmosphere.
Stationary motion of a domain wall in the presence of an in-plane magnetic field in a bubble garnet film
Authors: Kosiński R. A. , Engemann J.
Published: February 2003

The stationary motion of a domain wall in bubble garnet film in the presence of an in-plane magnetic field Hy, perpendicular to the wall surface, is examined. Conditions for the occurrence of Walker and Bloch line-type wall structures are discussed.
A composite numerical model for the coercivity of soft magnetic materials
Authors: Sukiennicki A. , Della Torre E.
Published: February 2003

The merging of two numerical coercivity models, the first valid for low-magnetization materials and the second valid for high-magnetization materials, permits us to obtain a qualitative composite model which encompasses a wide range of material parameters for soft magnetic materials. It is possible to sort out with this model the range of validity of each submodel. Furthermore, experiments are suggested which would differentiate between the submodels and help to determine the arbitrary parameters inherent in them.
Electron paramagnetic resonance linewidth of superparamagnetic particles
Authors: Morais P. C. , Tronconi A. L. , Skeff Neto K.
Published: February 2003

Superparamagnetic particles have been investigated by electron magnetic resonance. We have shown that the temperature dependence of the linewidth (above the freezing temperature) is sensitive to the pattern of particle size distribution. The behavior of the linewidth as a function of temperature is explained if we assume an anisotropic Dzyaloshinskii–Moriya type of interaction where the relaxation process occurs by a longitudinal component.
Dielectric relaxation in distributed dielectric layers
Authors: Kita Yasuo
Published: February 2003

The Maxwell–Wagner theory of interfacial polarization was extended to the layer system in which the layer properties are distributed continuously. The equation was derived to transform the distribution of relaxation times into that of layer properties. Each layer was characterized by the thickness and by the time constant which is defined as the ratio of permittivity to conductivity for the layer. The distribution of layer properties which yields the relaxation of the Cole–Cole type was calculated to show the applicability of the transformation thus derived. The calculation in the Cole–Cole type clarified that the system consists of two types of layers, i.e., the one of narrow distribution with a longer time constant than the characteristic relaxation time of the Cole–Cole type and the other of broad distribution with a shorter time constant. It was proved that the system considered here did not yield the Davidson–Cole type dielectric relaxation. Model experiments were carried out and proved the theory appropriate.
Optical properties of electrochemically deposited CdTe films
Authors: Ou S. S. , Stafsudd O. M. , Basol B. M.
Published: February 2003

The optical properties of electrochemically deposited CdTe films were investigated. The index of refraction and the absorption coefficients in the 450–850-nm range were measured for as-deposited n-type films and converted p-type films. It was found that the converted p-type films had higher optical absorption coefficients near the band edge than that of the n type. This change can be attributed to defect absorption. The absorption data yielded information concerning the band structure of the electrodeposited CdTe.
Hole traps and trivalent silicon centers in metal/oxide/silicon devices
Authors: Lenahan P. M. , Dressendorfer P. V.
Published: February 2003

We report electron spin resonance (ESR) measurements of E′-center (a ‘‘trivalent silicon’’ center in SiO2) density as well as capacitance versus voltage (C-V) measurements on γ-irradiated metal/oxide/silicon (MOS) structures. We also report a considerable refinement of earlier ESR measurements of the dependence of radiation-induced Pb -center (a ‘‘trivalent silicon’’ center at the Si/SiO2 interface) occupation as a function of the Fermi level at the Si/SiO2 interface. These measurements indicate that the Pb centers are neutral when the Fermi level is at mid-gap. Since the Pb centers are largely responsible for the radiation-induced interface states, one may take ΔVmg Cox/e (where ΔVmg is the ‘‘mid-gap’’ C-V shift, Cox is the oxide capacitance, and e is the electronic charge) as the density of holes trapped in the oxide. We find that radiation-induced E′ density equals ΔVmg Cox/e in oxides grown in both stream and dry oxygen. Etch-back experiments demonstrate that the E′ centers are concentrated very near the Si/SiO2 interface (as are the trapped holes). Furthermore, we have subjected irradiated oxide structures to a sequence of isochronal anneals and find that the E′ density and ΔVmg annealing characteristics are virtually identical. We conclude that the E′ centers are largely responsible for the deep hole traps in thermal SiO2 on silicon. This observation coupled with observations regarding the Pb center indicates that two intrinsic centers, both involving silicon atoms lacking one bond to an oxygen atom, are largely responsible for the two electrically significant aspects of radiation damage in MOS devices: charge buildup in the oxide and interface-state creation at the Si/SiO2 interface.