bluuebunny/crossref_metadata_2025 huggingface dataset:
Secondary electron emission from vanadate-phosphate glasses
Authors: Flinn E. A. , Salehi M.
Published: February 2003

Secondary electron emission from V2O5-P2O5 glasses has been investigated for a range of primary energies between 90 eV and 5.5 keV. The sample compositions studied cover the useful range for these materials, from 50 to 95 mol % V2O5. The measurements were carried out on specimens freshly cleaved in ultrahigh vacuum. Accurate data for these materials have not previously been available.
Mass effects on angular distribution of sputtered atoms
Authors: Olson R. R. , King M. E. , Wehner G. K.
Published: February 2003

Sputtering metal targets at low ion energies (Hg or Ar at <300 eV) under normal ion incidence causes the lighter atoms (lighter isotopes or lighter elements of alloys) to be preferentially ejected in a direction normal to the target surface. Experimental results are shown for several elements and alloys at various bombardment energies. The amount of enrichment of the lighter species normal to the target surface decreases quite rapidly with increasing ion energy. The phenomenon is a result of reflective collisions because lighter atoms can be backscattered from heavier ones underneath but not vice versa. The effect provides an explanation why solar-wind-exposed lunar material is enriched in the heavier isotopes since sputtered lower-mass elements have a higher chance of achieving the lunar escape velocity.
Formation of iridium silicides from Ir thin films on Si substrates
Authors: Petersson S. , Baglin J. , Hammer W. , d’Heurle F. , Kuan T. S. , Ohdomari I. , de Sousa Pires J. , Tove P.
Published: February 2003

The formation of iridium silicides from the interaction of iridium films with single-crystal silicon substrates has been studied from 350 to 1000 °C. Three distinct phases, IrSi, IrSi1.75(?), and IrSi3, were identified. Different modes of formation were observed and investigated. IrSi and IrSi1.75 form in layers parallel to the substrate at temperatures from 350 to 900 °C. The growth of IrSi3 from nuclei that spread laterally occurs at about 1000 °C, where possible the kinetics were systematically studies.
Interface studies of AlxGa1−xAs-GaAs heterojunctions
Authors: Garne C. M. , Su F C. Y. , Shen Y. D. , Lee C. S. , Pearso G. L. , Spicer F W. E. , Edwall D. D. , Miller D. , Harris J. S.
Published: February 2003

Ion-depth profiling with Auger electron spectroscopy has been used to measure the interface width of MBE, VPE, and LPE AlxGa1−xAs-GaAs heterojunctions purposely fabricated to minimize interface width. By profiling the MBE structures with 250-eV Ar+ ions, it was possible to experimentally measure an interface width (10–90% Al p-p height) of ∼15 Å. The measured interface width of VPE and LPE AlxGa1−xAs-GaAs was found to be ∼65 and 100 Å, respectively. Since rectification has not in the past been observed in n-n AlxGa1−xAs-GaAs heterojunctions, n-n AlxGa1−xAs-GaAs heterojunctions were fabricated in this study to enhance the presence of the conduction-band discontinuity (enhancing any possible rectification) by growing these heterojunctions from lightly doped (1015–1016 cm−3) material; however, these heterojunctions did not exhibit rectification, in agreement with previous studies. The interface widths of these samples were then measured and found to be much smaller than present theories require to remove the barrier. Since compositional grading is not large enough to explain the absence of rectification, several alternative explanations to the absence of rectification are discussed.
Electrical properties of platinum in silicon
Authors: Brotherton S. D. , Bradley P. , Bicknell J.
Published: February 2003

The energy levels produced by platinum in silicon have been measured in p- and n-type material using deep-level transient spectroscopy and constant-capacitance thermal-emission-rate measurements. Within the sensitivity of the apparatus only two levels have been detected having thermal-emission activation energies of EC−ET=0.231 eV and ET−EV=0.321 eV. The majority-carrier capture cross sections of these levels have also been measured, giving σnA =7×10−15 cm2 and σpD=1.5×10−15 exp(−7.3 ×10−3/kT). Using these values together with thermal-emission data and assumed degeneracy factors of gA=0.5 and gD=2 in the equation of detailed balance, it was concluded that both levels were fixed to the conduction band edge.
The dc voltage dependence of semiconductor grain-boundary resistance
Authors: Pike G. E. , Seager C. H.
Published: February 2003

A model is developed to describe the potential barriers which often occur at grain boundaries in polycrystalline semiconductors. The resistance of such materials is determined by thermionic emission over these barriers. The dc grain-boundary current density as a function of applied voltage is calculated using several forms for the density of defect states within the boundary region. In all cases, the currents are Ohmic at low voltages; they can attain a quasisaturated level at intermediate voltages, and they display a sharp bias dependence at high voltages. The details of the intermediate and high-voltage characteristics are found to depend strongly on the grain-doping density and on the density and energy distribution of defect states at the grain boundary. Contrary to previous assertions, we find that the large current-voltage nonlinearities found in real materials are most likely associated with defect-state densities that decrease above the zero-bias Fermi level. The results of the model are compared with previous experimental data on Si and Ge bicrystals and on polycrystalline ZnO varistors. Finally, a detailed method for determining the energy density of grain-boundary defect states from current-voltage data is developed.
Recombination in heavily doped planar diodes
Authors: Possin G. E. , Kirkpatrick C. G.
Published: February 2003

A process is described which produces a shallow pn-junction device with heavy surface doping and very high collection efficiency. Electron-beam techniques were used to measure collection efficiency as a function of depth and to modulate the surface recombination velocity through an MOS capacitor fabricated on the diode. The results of these studies indicate that surface recombination is the dominant effect on carrier loss.
Textures in diffusion-processed superconducting Nb3Sn and V3Ga layers
Authors: Togano K. , Tachikawa K.
Published: February 2003

The texture studies of the Nb3Sn and V3Ga superconducting tapes produced by the surface diffusion process (SDP) and by the composite diffusion process (CDP) were made by pole figure works using an x-ray diffractometer. The textures are described as (100)[011]+(112)[110] for the SDP-Nb3Sn and V3Ga layers and (100)[011] for the CDP-Nb3Sn and V3Ga layers, although exceptionally weak for the CDP-V3Ga layer. The results suggest that the A-15 grains grow into the bcc substrate phase with a parallel or nearly parallel orientation relationship. It is found that the weak texture of the CDP-V3Ga yields larger grain-boundary pinning force than the sharp texture of the SDP-V3Ga does.
Theory of ac losses in type-II superconductors with a field-dependent surface barrier
Authors: Clem John R.
Published: February 2003

The irreversible magnetic behavior of a type-II superconductor in a periodically varying longitudinal applied magnetic field is theoretically examined. Bulk pinning is characterized by a critical current density Jc, and surface-barrier effects are characterized by critical entry and exit fields Hen and Hex. Theoretical expressions for magnetic field and flux-density profiles, voltage waveforms, hysteretic-bulk and surface-energy losses, and the ac permeability are derived for the arbitrary flux-density (B) dependence of Jc, Hen, Hex, and the equilibrium magnetic field Heq. Numerical model calculations are performed to demonstrate the influence of the B dependence of the latter functions upon the measurable quantities.
Hysteretic losses of a type-II superconductor in parallel ac and dc magnetic fields of comparable magnitude
Authors: Thompson J. D. , Maley M. P. , Clem John R.
Published: February 2003

Measurements of 50-Hz hysteretic losses in Nb3Ge material have been performed in the presence of a dc-bias magnetic field. The measurements were made by an electrical technique with both the ac and dc magnetic fields parallel to the axis of long Nb3Ge-coated cylinders. With a fixed ac amplitude h0, the losses are observed to decrease as the dc field H0 is raised from zero, to pass through a minimum, and then to increase monotonically. The position of the minimum is observed to occur when H0=h0−Hs, where Hs is the field at which initial entry of flux into the sample is observed. Minimum depths which reach 30% of the zero-bias loss are found for samples in which Hs is large (?900 Oe). This ’’minimum’’ effect and other aspects of ac losses in the presence of a dc-bias field are explained qualitatively by a critical-state model that takes account of the magnetic field dependences of the critical current density Jc(B) and the surface barrier ΔH (B). The experimental results are also compared with the results of calculations based upon a recent theoretical treatment that allows the use of independently determined functional forms for Jc(B), ΔH (B), and H (B). Qualitative agreement is obtained between theory and experiment.
A tunnel-junction relaxation oscillator: Application to thermometry
Authors: Gerdt D. W. , Moody M. V. , Paterson J. L.
Published: February 2003

A superconducting tunnel junction will undergo relaxation oscillations when biased with an active voltage source along the negative conductance portion of its I-V characteristic. A simple calculation yields an implicit equation for this frequency f in terms of the circuit and junction parameters which is in qualitative agreement with experiment. Measurements on Al*-Pb : Bi junctions with transition temperature Tc(Al*) ∼1.8 K, over the temperature range 1.3 K<T<Tc, provide data on f versus T. The increase in f with decreasing temperature provides a technique for temperature measurement with a sensivity of ∼0.5 mK with a 1-sec counting time.
Convergence and disintegration of liquid jets induced by an electrostatic field
Authors: Mutoh Masayuki , Kaieda Shozo , Kamimura Kuniaki
Published: February 2003

Liquid jets are formed by application of an electrostatic field to insulating liquids, which are prepared to have specific conductivities of 10−12–10−7 Ω−1 cm−1 with the ionic additive and viscosity of 0.73–10.2 cP with the silicone intermediate. Convergence of the jets is studied in relation to the specific conductivity. Liquids with specific conductivities between 10−10 and 10−7 Ω−1 cm−1 form fine threads of liquid followed by successive disintegration to many fine droplets. Contribution of the charge term to the disintegration is estimated to be negligible in the axisymmetric mode of disturbance. The explanation is supported by the fact that the measured drop frequency is very well correlated with the theoretical result by Weber, who analyzed the distintegration process in terms of surface tension and viscosity. The coefficient of correlation is 0.98, and the gradient of regression line is 0.97.
Ion- and electron-assisted gas-surface chemistry—An important effect in plasma etching
Authors: Coburn J. W. , Winters Harold F.
Published: February 2003

The extent to which gas-surface chemical reactions can be enhanced by energetic radiation (primarily ions and electrons) incident on the surface is described. Emphasis is placed on chemical systems which lead to volatile reaction products. In particular, the reactions of Si, SiO2, and Si3N4 with XeF2, F2, and Cl2 are examined experimentally. Possible mechanisms for the radiation-induced enhancement are discussed and some technological implications of this process in plasma etching technology and lithography are considered.
Spectral change mechanism in the pulsed high-pressure sodium arc
Authors: Johnson P. D. , Rautenberg T. H.
Published: February 2003

The enhancement of radiative output of the pulsed high-pressure sodium discharge in the blue region of the visible spectrum is due principally to radiation from the nd2D→3p2P transitions of the sodium atom where n=4–15. Excitation of these upper energy levels results from a transient non-steady-state increase in plasma temperature to about 5500 °K in the center of the arc. This temperature decays to a value near that encountered in steady-state excitation conditions in a time comparable to the empirically optimized pulse duration and to the previously determined time for plasma temperature relaxation.
A technique for determining gas temperature and atomic density such as in CuBr lasers
Authors: Taylor L. H. , Feldman R. B.
Published: February 2003

We have developed a general technique for simultaneously determining in situ both gas temperature and atomic number density of glow-discharge constituents. A theoretical absorption line profile is fitted, by minimizing the least squares, to the measured profile. The ground-state or excited-state density is accurately determined for a wide range of discharge operating conditions and the temperature can be determined within a more restricted range of discharge operating conditions. The technique is most accurate in the same region where absorption is most easily measured, i.e., 5–99% absorption. As an example of its usefulness we have applied this technique to the measured absorption of tunable dye laser radiation in CuBr laser discharges. The temporal variation of both the ground-state Cu density and the gas temperature were determined. In this case the temperature cannot be easily measured by other methods.
Departures from thermal equilibrium in a dense Z-pinch plasma
Authors: Neufeld C. R.
Published: February 2003

This paper presents on analysis of several features of the emission spectrum obtained from a dense hydrogen Z-pinch plasma. The spectrum is characterized by an extremely broad Hβ line and by the absence of an emission line at the Hα wavelength. Comparison with theory shows that the spectrum is inconsistent with the assumption of a thermal or collision-dominated plasma. The assumption of a substantial overpopulation of the atomic-hydrogen excited levels, ascribed to a rising degree of plasma ionization, provides a satisfactory description of the observed spectrum. This result illustrates the difficulty of establishing valid equilibrium criteria for transient plasmas, even in the case of plasma densities as high as 1019 cm−3.
Disclination-dislocation model of metallic glass structures
Authors: Morris Robert C.
Published: February 2003

A new model for the structures of metallic glasses is proposed which is based on a continuous three-dimensional network of mixed-character disclinations containing a subnetwork (discontinuous) of dislocation segments which terminate on disclination jogs. Given the known geometrical properties of disclinations and their function as sources, sinks, and termination sites for dislocations, the mechanism of formation of the proposed double network structure is discussed. The approximate strain energy density of the model is derived from the known linear elastic solutions for disclinations. Using the measured elastic constants of several typical metallic-alloy glasses, the calculated strain energy densities agree to within about 20% with the respective measured heats of crystallization, demonstrating the energetic feasibility of the model. The structural features of the model and its conceptual relationships to the microcrystalline and DRPS models are discussed and it is concluded that the disclination-dislocation model is not conceptually inconsistent with either and may in fact represent a useful refinement of the microcrystalline model and provide additional insight into processes involving cooperative atomic motions in DRPS models. Using the known relations between glide dislocations and disclinations combined with classical dislocation theory, an expression for the low-temperature yield stress of a disclination-dislocation glass is derived. The calculated yield stresses for several typical alloy glasses agree with the experimental values to within several percent and the experimentally observed linear dependence of yield stress on the shear modulus is correctly predicted. Some speculations as to glass formation and stability at low temperatures are discussed qualitatively from the perspective of the disclination-dislocation model. This discussion is based on the severely limited glide mobility of disclination cores which must move into coincidence and annihilate for crystallization to occur. Since the disclination cores can move conservatively via the generation or annihilation of glide disocations, it is proposed that glass formation from liquids and retention at low temperatures will be facilitated in systems in which the reference crystal has a high Peierls stress for dislocation glide.
Affect of annealing on uniform and nonuniform strains in a sputtered Mo film on Si
Authors: Adler T. , Houska C. R.
Published: February 2003

Sputtered films of 1.5 μm of Mo deposited on (111) -oriented Si failed either by blistering or localized eruptions after various thermal treatments. Investigations were carried out to determine the amount of strain in the film associated with this unstable mechanical behavior. Two types of measurements were employed. One employs macroscopic interferometer measurements to measure deflection and the other x-ray diffraction. A separation is made of intrinsic and thermally induced strains. The intrinsic strains are believed to be due mainly to Ar atoms embedded during sputtering which remain throughout annealing treatments. These atoms also introduce a broadening of the diffraction lines because of the special constraints associated within films. This effect is separated from the usual line broadening due to dislocations and small particle size. Annealing treatments reconfirm that dislocation mechanisms are not as effective in relieving nonuniform microstrain in films as they are in cold-work filings of the same material.
Scattering of long-wavelength elastic waves from localized defects in solids
Authors: Kohn W. , Rice J. R.
Published: February 2003

It is shown that long-wavelength elastic scattering data from an arbitrary localized defect in a uniform isotropic medium has a maximum information content of 22 parameters which are characteristic of the defect. These parameters are shown to consist of the mass excess δM and the 21 independent components of a fourth-rank tensor Dijkl, that depends on the elastic moduli variation δcijkl and static response properties of the defect region. This tensor and the contracted forms Dij (=Dijkk/3) and D (=Dkk/3) allow partial ’’inversion’’ of scattering data to determine properties of the defect. In particular, it is shown how to estimate the orientation and maximum stress intensity factor for defects in the form of planar cracks, to obtain lower bounds to maximum defect dimensions, and to represent defects in the form of inclusions or voids as approximately equivalent ellipsoids. The results are pertinent to the quantification of nondestructive examination of materials for defects in their interiors.
High-gradient magnetic separation in the region of high aerodynamic loading
Authors: Bullough W. A.
Published: February 2003

The engineering requirements are stated in respect to the testing of model filters and the extrapolation sizing of full-scale high-gradient magnetic separators for operation in the region of high aerodynamic loading, i.e., where large process capacities are involved and hence size and pressure loss are important considerations. Problems related to the characterization of the mesh are detailed, as are the scale effects associated with the model, i.e., with regard to entrance/exit ’’losses’’ and wall-drag/short-circuiting phenomena. Flexure and fluidization of the mesh and constructional problems associated with the roughness (or unevenness) of the fibers are demonstrated by reference to test results from an axial-filament cartridge. The case is made for flow-resistance tests to be carried out in advance of trajectory studies in order first to establish the flow regime. The effect of the flow condition on such considerations as interfiber, interparticle, and fiber/particle interference is discussed along with the limitations of flow resistance and trajectory analysis as design aids.
Molecular-iodine laser studies at low e-beam excitation rates
Authors: Eckstrom D. J. , Perry B. E. , Tang K. Y.
Published: February 2003

We have excited Ar/I2, Ar/HI, Ne/I2, and Ne/Ar/I2 mixtures using a 50-cm electron-beam machine with a current density of ∼6 A/cm2. Fluorescence yields ranged from 20 to 30% for all the mixtures. Only the Ar/I2 mixture lased, and it was the only mixture to show gain near 342 nm in diagnostic laser-probe measurements. Transient absorptions were found throughout the 300–380-nm region studied. The peak gain in the Ar/I2 system was less than expected based on the fluorescence yield and spectral bandwidth suggesting that the lower laser level is significantly populated. The maximum achievable laser efficiency under these conditions is calculated to be ?0.25%.
A Fourier transform technique for quantitative assessment of ion tracks in cellulose nitrate film
Authors: Joshi C. J. , Chapman G. D. , Sancton R. W.
Published: February 2003

An optical Fourier transform technique (OFT) is described whereby the density of ion tracks in cellulose nitrate (CN) film produced by fast ions from a laser-produced plasma may be quantitatively assessed. Such ions are analyzed by means of a Thomson parabola-type mass spectrometer employing CN film as a detector. The task of counting the 106–107 ion tracks in the CN film is onerous. If an electroetched mesh is placed over the film during exposure, the ion tracks representing the signal are confined to a rectangular two-dimensional array. This imposed periodicity provides a simple means to separate the signal from the inevitable etching noise present on the film by suitably masking the Fourier transform of the film. The subsequent enhanced image of the film has a markedly increased signal/noise ratio and may be processed for track density information by means of a scanning vidicon.
Lifetime measurements of 4-dimethylamino-4′-nitrostilbene fluorescence by picosecond optical amplification
Authors: Kobayashi T. , Degenkolb E. O. , Rentzepis P. M.
Published: February 2003

The fluorescence lifetime of 4-dimethylamino-4′-nitrostilbene (DMANS) in benzene and in the mixed solvents of cyclohexanol-methycyclohexane (2 : 5 volume ratio) and cyclohexanol benzene (2 : 5 volume ratio) was found to be ≳1 nsec, 160±40 psec, and 150±40 psec, respectively. The time dependence of the fluorescence intensity after excitation was monitored by the time-resolved gain of a picosecond light beam passing through the sample.
Facet oxide formation and degradation of GaAs lasers
Authors: Nash F. R. , Hartman R. L.
Published: February 2003

It has been suggested that the long-term degradation mode in (Al,Ga)As double-heterostructure lasers is caused by the growth of an optically thick reflectivity-lowering oxide formation on the emissive portion of the mirror facets. We find that the long-term degradation behavior of our superior lasers cannot be explained by this approach. While not ruling out all conceivable models for the oxide growth rate, our conclusions based upon two simple and physically plausible models corroborate our separate experimental study which found that facet oxide formation is not directly relevant to laser reliability in the regime characterized by cw operation in a 70 °C dry-nitrogen ambient and outputs of ∼5 mW/facet for stripe widths equal to 12 μ and lifetimes ?30 000 h. We have also examined a commonly used expression for the external differential quantum efficiency and find that it has historically been misinterpreted by many workers.
Acoustical image reconstruction in parallel-processing analog electronic systems
Authors: Delannoy B. , Torguet R. , Bruneel C. , Bridoux E. , Rouvaen J. M. , Lasota H.
Published: February 2003

Ultrafast cardiac-valve ultrasonic tomography requires parallel multichannel processing of received echoes. In parallel processing the level of secondary ’’ghost’’ images due to spatial undersampling is much higher than in slower series processors which use a selective field insonification. The paper describes a 20-channel moving-focus parallel-processing analog electronic system, which is realized in our laboratory. It is shown analytically that the secondary-image level is reduced and remains unchanged when the receiver angular aperture (aperture relative to distance) is limited and kept constant during the whole observation time.
Study of collective ion acceleration in vacuum
Authors: Destler W. W. , Uhm H. S. , Kim H. , Reiser M. P.
Published: February 2003

Theoretical and experimental studies of the collective acceleration of ions by a linear electron beam in an evacuated drift tube are presented. A one-dimensional theoretical model of the collective acceleration process that predicts accelerated proton energies of many times the electron-beam energy is presented. The formation of a virtual cathode downstream of the anode-cathode gap is discussed, and the subsequent movement of the virtual cathode downstream as the anode plasma expands allows for enhanced acceleration of ions trapped in the potential well of the virtual cathode. Experiments reported indicate that effective electron beam propagation and effective collective acceleration occurs when a plasma source initially well confined to the anode is present.
Producion of intense focused ion beams in a spherical magnetically insulated diode
Authors: Greenspan M.A. , Hammer D. A. , Sudan R. N.
Published: February 2003

A magnetically insulated ion diode has been constructed with a spherically focusing geometry. The diode has been operated at voltages of ∼250 and ∼500 kV, with impedances adjusted to 2–3 and 7–10 Ω, respectively. The pulse length was ∼85 ns. Total ion currents were ?30% of the diode current. In the high-voltage case, a focal current density of 2100 A/cm2 was obtained; this is ≳90 times the anode ion current density. Auxilliary magnetic fields were used to steer the beam, with the beam deflection as calculated for a single proton. The diode design and diagnostic techniques are described, as well as possibilities for improvements suggested by our data.
Giant electrostrictive effect in Ba : PZT
Authors: Leung K. M. , Liu S. T.
Published: February 2003

The electrostrictive effect of a Ba : PZT paraelectric ceramic was investigated using a sensitive capacitance dilatometer. This substance was found to exhibit a giant electrostrictive coefficient Q12 of −0.27 m4/C2, which is nearly five times as large as the value of Q12 for single-crystal BaTiO3.
Maximum stable zone length in float-zone growth of small-diameter sapphire and silicon crystals
Authors: Kim K. M. , Dreeben A. B. , Schujko A.
Published: February 2003

Maximum stable lengths of the floating-liquids zone (lmax) were measured in the small-diameter (d=0.25–1.5 mm) float-zone crystal growth of sapphire and silicon. A 100-W cw CO2 laser was used as power source. The measured ratios of lmax/d for sapphire and silicon are in good agreement with the theoretical analyses by Coriell, Hardy, and Cordes in the limiting case of small crystal diameters and by Rayleigh, assuming zero gravity.
Brillouin scattering from shear waves in amorphous polycarbonate
Authors: Durvasula L. N. , Gammon Robert W.
Published: February 2003

The high-frequency acoustic longitudinal- and shear-wave velocities in amorphous polycarbonate (Lexan) obtained from Brillouin scattering spectra are reported as a function of temperature from room temperature through the glass transition to the melting temperature (250°C). Comparison with low-frequency modulus-derived shear velocities is made: 20% dispersion is seen up to the glass transition and above this temperature completely different behavior is seen. The temperature dependence of the linewidths of the Brillouin components is also reported. A method for estimating the shear-wave Brillouin scattering intensity from tabulated photoelastic constants is given and applied to fused silica, PMMA, polystyrene, and polycarbonate to explain why shear waves have not been detectable in the Brillouin spectra of PMMA and polystyrene.
Soft x-ray emission and Auger electron spectroscopic study of FeS, Fe0.9S, Fe0.875S, and Fe0.5S
Authors: Marusak L. A. , Tongson L. L.
Published: February 2003

Soft x-ray emission spectra are obtained of sulfur in FeS, Fe0.9S, Fe0.875S, and Fe0.5S. The structure in the Kβ emission spectra is consistent with recent SCF-Xα calculations for ferrous iron in an octahedral crystal field. Broadening in the Kβ emission spectra with decrease in the Fe-S bond distance is in agreement with the trends predicted by the SCF-Xα calculations. The charge on the sulfur ions is calculated from the shifts of the Kα emission lines. Calculated charges on FeS and Fe0.5S are in good agreement with previous LCAO calculations and photoemission data. Shifts in the Kα line positions for Fe0.9S and Fe0.875S indicate that electroneutrality is satisfied by a reduction in charge on sulfur rather than the coexistence of ferrous and ferric iron. The Auger spectra of sulfur show sharp structure for FeS which gradually disappears as the sulfides become more cation deficient. The Auger data is discussed in terms of changes in the electronic density of states in the valence band as predicted by the SCF-Xα calculations.
Corrections to proximity effects in electron beam lithography. I. Theory
Authors: Parikh Mihir
Published: February 2003

Electron lithography at micrometer dimensions suffers from a seemingly fatal problem due to proximity effects. Three corrections techniques are discussed. The self-consistent technique computes the incident electron exposure such that identical average specific fragmentation occurs in each written shape of the pattern. A unique solution, that depends only on the form and on the magnitude of proximity function, is obtained. The unaddressed-region compensation technique attempts to compensate for proximity effects in regions between shapes; this, however, leads to computational complexities and impracticalities. The shape-dimension adjustment technique attempts to compute dimension of exposed shapes such that the shapes developed in the resist will have the designed dimension. A set of nonlinear (and impractical) equations are obtained in this case. The implementation of these techniques and the experimental results obtained therefrom are the subject of the two succeeding papers.
The penetration of thin metal plates by combined cw and pulsed-laser radiation
Authors: Towle L. C. , McKay J. A. , Schriempf J. T.
Published: February 2003

The accelerated penetration of thin metal plates by combined cw-plus-pulsed-laser radiation is shown to be due primarily to eliminating the necessity of furnishing the latent heat of melting which is a large fraction of the total energy budget in penetration with cw radiation alone. The effect is shown to be most dramatic in the case of painted plates, and largely independent of radial heat losses, in agreement with experiment.
Single-crystal elastic constants of vanadium and vanadium with oxygen additions
Authors: Greiner J. D. , Carlson O. N. , Smith J. F.
Published: February 2003

The single-crystal elastic constants of vanadium and of vanadium with 1.07, 1.85, and 3.46 at.% oxygen have been measured ultrasonically over the temperature range 4.2–300 K. These compositions cover virtually the complete composition range of the terminal solubility at the temperatures of the experiments. Monotonic but nonlinear increases with increasing oxygen content were observed for all three of the directly measured constants, and the compositional trends were found to be relatively insensitive to temperature so the same trends should persist at elevated temperatures. A Debye temperature of 401.2 K was evaluated for 0 K. The monotonic hardening of vanadium by oxygen addition contrasts with previously published results for niobium, where oxygen additions produced a slight initial softening followed by a hardening.
Thermal-explosion theory in an external field
Authors: Frankel Michael J.
Published: February 2003

The effects of a strong electric field on an explosive dielectric undergoing thermal decomposition were considered. The field effect was accounted for mathematically by the introduction of a Joule heating term in the thermal balance equation. It was found that Joule heating will have no effect on thermal-explosion parameters unless the condition φ<Ea, where φ is a conductivity activation energy and Ea is a chemical activation energy, is satisfied. It is suggested that thermal-explosion characteristics might be tuned by controlled doping of the explosive sample.
Photon-degradation effects in terrestrial silicon solar cells
Authors: Weizer V. G. , Brandhorst H. W. , Broder J. D. , Hart R. E. , Lamneck J. H.
Published: February 2003

An unexplained instability in terrestrial solar-cell output under various use conditions has been observed. The effect is similar to but not identical with previously observed photon-induced degradation phenomenon in radiation-damaged space solar cells. Reduction in cell output is observed in n+/p cells upon exposure to illumination or upon the application of a sufficiently high forward bias. Conversely, an enhancement in output is observed when p+/n cells are illuminated. Investigations performed on n+/p cells indicates that a recombination center located at Ec−0.37 eV in the forbidden band is responsible for the loss in output. The center is electrically inactive in its ground state but can be activated either by raising the minority-carrier quasi-Fermi level sufficiently close to the latent-center energy level in the band gap, or by direct excitation of electrons from the valence band to the latent-center level. The center has been identified as a complex of a lattice defect and a silver atom or cluster of atoms. The effect can be prevented either by preventing the introduction of silver or by eliminating lattice damage through sufficient surface material removal prior to diffusion while at the same time restricting diffusion temperatures to 875 °C or less. The effect in n-base cells is not fully understood at the present. It appears, however, that in either type of cell it is the p material that is responsible for the observed instabilities.
Comments on ’’Electrochemical doping of silicon with arsenic’’
Authors: Northrop D. C.
Published: February 2003

Antula has presented experimental data purporting to show that arsenic can be introduced into silicon by electrochemical means at room temperature. This is now shown to be incompatible with other experimental observations, and an alternative explanation of Antula’s results is offered.
Reply to ’’Comments on ’Electrochemical doping of silicon with arsenic’ ’’
Authors: Antula Jovan
Published: February 2003

The explanation proposed by Northorp cannot be correct.
Electron mobility in AlxGa1−xAs
Authors: Stringfellow G. B.
Published: February 2003

The electron mobility in AlxGa1−xAs grown by several techniques has been studied to determine whether VPE layers are more highly compensated than comparable LPE layers. The techniques used to grow layers included (1) organometallic VPE using Al(CH3)3, AsH3, and Ga(C2H5)3 or Ga(CH3)3, (2) ’’hybrid’’ organometallic technique using HCl to reduce C and O contamination, (3) standard AsH3+HCl VPE (GaAs only), and (4) LPE. The mobilities in VPE and LPE AlxGa1−xAs are found to be similar, and to depend strongly on solid composition, x. The temperature dependence of the electron mobility indicates that both compensation and space-charge scattering increase with x and contribute to the reduction of electron mobility.
Photoemission study of negative-electron-affinity GaP
Authors: Miyao Masahiro , Tanaka Akimasa , Sukegawa Tokuzo , Hagino Minoru
Published: February 2003

The optical absorption coefficient and photoemissive quantum yield were measured for liquid-phase-epitaxial GaP layers containing 2% of indium. The transport properties of photogenerated electrons in NEA GaP was analyzed by the two-valley diffusion model of Xc1 and Lc1 conduction bands and compared with experimental results. From the results of the analysis, diffusion lengths and escape probabilities were determined for NEA GaP with net acceptor concentrations of 2.03×1016 to 3.5×1019/cm3.
Hologram writing in lithium niobate: Beam coupling and the transport length in the bulk photovoltaic effect
Authors: Young L. , Moharam M. G. , El Guibaly F. , Lun E.
Published: February 2003

Holograms were written in a short-circuited antireflection-coated crystal of iron-doped lithium niobate, using essentially uniform illumination of the whole crystal to minimize light-envelope space-charge field effects. The results were compared with the predictions of a computer model which allows for space-charge feedback and for the modification of the writing light pattern by interaction with the hologram being written, but which assumes short transport lengths of electrons (on the scale of the hologram grating spacing) for diffusion, drift, and the bulk photovoltaic effect. The measured ’’virtual’’ field Ev to which the bulk photovoltaic effect is equivalent (for these assumptions) was about 45 kV/cm so that the bulk photovoltaic effect, rather than diffusion, dominated the writing process under the above conditions. The development of the diffraction efficiency was consistent with the computed data but the beam coupling (transfer of energy between the writing beams) was much greater than predicted. The observed beam coupling could occur with the drift-equivalent process of the bulk photovoltaic effect if the transport distance in this effect was on the order of 24 nm, which is larger than has been generally considered probable. In repeated write-erase experiments the beam coupling was variable, more so than the diffraction efficiency. The variability is, we believe, due to parasitic holograms such as are involved in the scattering process observed with these crystals and also to residual space-charge fields from repeated write-erase cycles. If the transport length is indeed long, the term καI used to describe the bulk photovoltaic effect (where κ is a parameter specific to a dopant, α is the absorption coefficient, and I is the intensity) is inapplicable to hologram writing conditions since it implies short transport length. A new representation for this bulk photovoltaic effect allowing for an arbitrary transport length is proposed. This representation is shown to introduce a significant phase shift in the refractive-index pattern relative to the light pattern and can thus account for the beam coupling observed.
Temperature effects in photoelectrochemical cells
Authors: Kamat P. V. , Karkhanavala M. D. , Moorthy P. N.
Published: February 2003

The performance of photoelectrochemical cells made of an n-type TiO2 photoanode and the O2/OH− redox electrolyte system have been studied at different temperatures. It has been found that when only the photoanode compartment is heated, the open-circuit voltage decreases (∼2.0 mV K−1) and the short-circuit current increases (∼0.8 mA m−2 K−1); however, the power output shows a small increase and a fall thereafter. The behavior is similar to that of Schottky-barrier solar cells. When both of the electrode compartments are heated, the power output increases with increasing temperature (∼0.4 mW m−2 K−1) and this can be attributed to the enhancement of the rate of the electrochemical reaction at the counterelectrode.
Analog-to-digital conversion with a SQUID: Conditions for a countable pulse train
Authors: Peterson Robert L.
Published: February 2003

A superconducting loop containing a Josephson junction develops voltage pulses when it admits and expels magnetic flux quanta, and thus may be used as an A/D converter. We here develop and discuss several conditions which must be satisfied for the generation by the SQUID of an unambiguously countable pulse train, from which the analog signal can be faithfully reconstructed. These conditions can be satisfied over a broad range of realizable values of inductance and resistance. The capacitance, however, must be carefully controlled. The results of simulations are also presented, illustrating the various ways in which the pulse trains are affected.
A study of amorphous superconducting transition metal-metalloid alloys produced by coevaporation
Authors: Johnson W. L. , Tsuei C. C. , Raider S. I. , Laibowitz R. B.
Published: February 2003

The structure and superconductivity of several niobium and molybdenum-base superconducting alloys obtained by coevaporation were studied. The formation of an amorphous phase is shown to depend on both alloy composition and substrate temperature in a systematic way. The variation of the superconducting transition temperature with alloy composition is compared for amorphous and crystalline forms of the same alloy composition, and the factors which govern superconductivity are discussed. Results of superconductive tunneling experiments involving amorphous molybdenum-base alloys show a ratio of energy gap to transition temperature of about 3.5. These results are presented as evidence that these amorphous alloys are weak-coupling superconductors.
Critical curves for determining magnetization directions in implanted garnet films
Authors: Shir C. C. , Lin Y. S.
Published: February 2003

Critical curves have been calculated for the graphical determination of the magnetization direction as function of applied magnetic field in ion-implanted garnet films having cubic anisotropy. Up to three stable magnetization directions may exist when the applied field is inside the critical curves. This leads to the formation of charged walls. The hard magnetization directions are found to be favorable directions for charged walls and the easy magnetization directions are unfavorable. The complex domain-wall patterns revealed by Ferrofluid techniques in 1-μm magnetic bubble devices are explained by using the calculated critical curve. Futhermore, critical curves for several different symmetries have also calculated to correspond to different crystallographic orientations and garnet material parameters.
Neutron-diffraction study of the magnetic structure of MnPt alloys
Authors: Severin C. S. , Chen C. W. , Stassis C.
Published: February 2003

Neutron-diffraction patterns have been obtained for quenched and annealed samples of MnPt. The magnetic structure was found to be antiferromagnetic with the spins on the Mn atoms aligned normal to the [001] direction. The moments on the Mn and Pt atoms were determined to be (4.0±0.4) μB and (0.4±0.4) μB, respectively. These values for the moments are in good agreement with those obtained in earlier investigations. However, we do not find the previously claimed change in spin direction as a function of alloy composition.
Origin of the magnetostriction effects from Mn3+, Co2+, and Fe2+ ions in ferrimagnetic spinels and garnets
Authors: Dionne Gerald F.
Published: February 2003

A new model is proposed to explain the magnetostriction effects in ferrimagnetic spinels and garnets with Mn3+, Co2+, and Fe2+ ions substituted into octahedral sites. Considerable experimental evidence has revealed that small amounts of each of these ions will alter substantially the magnitude of either the λ100 or λ111 magnetostriction constant, depending on the particular ion. The theory is based on the concept that Jahn-Teller effects produce local site distortions of tetragonal (favoring 〈100〉 axes) or trigonal (favoring 〈111〉 axes) symmetry which are able to switch among the different axes of the particular family in order to select the axis closest to the direction of the magnetic field. For Mn3+ ions, the local site distortions are expected to be tetragonal (c/a≳1), in accordance with observations in a variety of magnetic oxides where static cooperative effects are present and will produce large positive changes in the λ100 constant. With Co2+ ions the distortion is also tetragonal, but of the opposite sign (c/a<1) (consistent with cooperative effects in CoO) and will produce large negative changes in λ100. In the case of Fe2+ ions, the distortion is trigonal (α<60°), as evidenced by its behavior in FeO, and will produce large positive changes in the λ111 constant. In each case reviewed, the theoretical results are in complete agreement with the available room-temperature magnetostriction-constant data on a qualitative basis. An estimate of the magnitude of the elastic energy of the local site distortion suggests that crystal-field energy-level splittings required to create the observed magnetostrictive effects are only on the order of 10−2 cm−1.
Mössbauer effect in an aged metallic glass
Authors: Tseng P. K. , Chuang S. Y. , Chen H. S.
Published: February 2003

Mössbauer spectra of Fe75P16B6Al3 glass were investigated as a function of the annealing temperature from 300 to 700 K. It is found that the magnetization axes of Fe nuclei lie in the ribbon plane of the as-quenched sample. Annealing at temperatures below 450 K causes negligible changes in the spectra. With further annealing above 550 K, it is found that the magnetization is strongly polarized toward the direction perpendicular to the ribbon plane. Possible formation of magnetic domains at high annealing temperature is proposed to account for the strong polarization which cannot be explained merely by the simple stress-releasing process.
Pyroelectricity in thiourea formaldehyde polymer
Authors: Vasudevan P. , Nalwa H.S. , Taneja K.L. , Tewari U.S.
Published: February 2003

The dielectric behavior of thiourea formaldehyde is reported as a function of temperature and frequency. Dielectric anomalies are found at 140–150 °C. Also, on heating the samples, spontaneous current evolution was observed around 140–180 °C.
Donor-acceptor pair radiative recombination from ion-implanted donors and acceptors in GaAs
Authors: Klein P. B. , Comas J. , Bishop S. G.
Published: February 2003

Photoluminescence spectra from VPE GaAs implanted with overlapping distributions of Be acceptors and Se donors have been studied as a function of excitation intensity and temperature. Donor-acceptor pair radiative recombination involving implanted acceptors and implanted donors has been observed for the first time and provides the first direct evidence for the optical activation of implanted donors in GaAs.
Time-domain photoacoustic spectroscopy of solids
Authors: Mandelis A. , Royce B. S. H.
Published: February 2003

Most conventional photoacoustic spectroscopy of solids has employed a periodically modulated light source. The availability of high-intensity pulsed light sources of short pulse duration makes possible the study of the time response of a photoacoustic system in which the solid is excited by a single optical pulse. A one-dimensional theoretical model is presented in which the time dependence of the photoacoustic response is evaluated for systems of variable optical absorption coefficient and sample thickness. The analysis is restricted to the case for which nonradiative relaxation processes occur instantaneously on the time scale of the measurement. Typical response curves for optically excited systems are presented and interpreted in terms of physical processes occurring in the cell.
Extraction of aberrationless high-perveance ion beams from a quiescent equilibrium plasma
Authors: Whealton J. H. , Whitson J. C.
Published: February 2003

A singular solution of the Poisson-Vlasov equation is approached for ions extracted through a cylindrical bore aperture from an equilibrium quiescent plasma. This solution has emittance-dominated ion-beam optics with no significant contribution to beam divergence due to aberrations. The singular point occurs in the limit as the plasma electrode potential approaches the source plasma potential. Other properties of this condition are that (1) the optimum perveance is significantly higher than for an electrically isolated plasma electrode, and (2) the sensitivity to plasma density fluctuations is higher than for an isolated plasma electrode. An additional finding is that an electrically isolated plasma electrode produced the highest beam divergence for optimum plasma density but minimum sensitivity to plasma density fluctuations.