bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature anomalies of Schottky-barrier diodes on n-type silicon
Authors: Jäger D. , Kassing R.
Published: February 2003

Experimental investigations of the temperature dependence of I-V and C-V characteristics of Schottky-barrier diodes lead to deviations from the thermionic-emission model. The barrier height and the ideality factor determined from forward I-V plots of Al, Au, and Pt Schottky contacts on n-Si strongly depend on temperature. Experimental results of forward I-V characteristics, Richardson plots, and reverse C-V data are given. An excess temperature is used as a parameter to describe the observed anomalies according to Levine’s analysis.
Propagation velocity of cathode-initiated surface flashover
Authors: Anderson R. A.
Published: February 2003

A polymethyl methacrylate insulator rod in vacuum is stressed by high-voltage pulses having 3-ns rise times, with the result that 40-mm-long incomplete discharges occur at the end of the rod. Time-resolved measurements of electron emission from different areas on the insulator surface indicate that a discharge propagates toward the anode at approximately 2×107 m/s during a pulse. A velocity of this order is expected if surface flashover results from an avalanche of electrons due to secondary emission at the insulator surface. Dependence of the velocity on the angle of the electric field relative to the insulator surface is predicted.
Emission of electrode vapor resonance radiation at the onset of dc breakdown in vacuum
Authors: Davies D. Kenneth , Biondi Manfred A.
Published: February 2003

Simultaneous time-resolved spectroscopic and current measurements have been made during the early stages of current growth leading to dc breakdown in vacuum between plane-parallel electrodes of dissimilar material. These measurements show that resonance radiation characteristic of anode material is emitted prior to that of cathode material from all regions of the interelectrode gap. Further, the radiation is emitted first from the cathode region of the gap. The results indicate that the initial current growth occurs in anode vapor followed at later times by the appearance of cathode vapor in the gap.
Reordering of amorphous layers of Si implanted with 31P, 75As, and 11B ions
Authors: Csepregi L. , Kennedy E. F. , Gallagher T. J. , Mayer J. W. , Sigmon T. W.
Published: February 2003

The effect of impurities on the epitaxial regrowth of Si from amorphous layers created by ion implantation into 〈100〉 and 〈111〉 Si was studied by channeling effect measurements with 2-MeV 4He ions. The Si wafers were first implanted at −180 °C with 28Si ions to form amorphous layers approximately 4000 Å thick and then were implanted with 31P, 75As, or 11B ions to concentration levels of about 0.2–0.5 at.%. For these layers with impurity species the growth rate is found to be significantly higher than for those without. The measured regrowth rate at 500 °C for 〈100〉 Si with an impurity concentration of ∼2×1020 cm−3 of 31P or 75As is a factor of 6 greater, and of 11B a factor of 20 greater, than the regrowth rate in amorphous layers without impurities. For the case of 31P implanted 〈100〉 Si the activation energy of regrowth is close to that (2.35 eV) found for impurity-free amorphous layers and for 11B implanted samples the energy is 1.9 eV. For 〈111〉 31P implanted Si specimens there is an increase in growth rate over that found in impurity-free samples and a high level of residual disorder.
Influence of 16O, 12C, 14N, and noble gases on the crystallization of amorphous Si layers
Authors: Kennedy E. F. , Csepregi L. , Mayer J. W. , Sigmon T. W.
Published: February 2003

Channeling effect measurements have been used to study the effect of impurities on the epitaxial regrowth of amorphous silicon layers on single-crystal silicon. Implantation was used to form the amorphous layers and also to introduce the impurities 12C, 14N, 16O, 20Ne, 40A, and 84Kr. For 16O implants, the growth rate at 550 °C depended on the 16O concentration and at the level of 0.5 at.% the rate was reduced from about 90 to about 10 Å/min. For similar atomic concentrations of 14N, the rate was comparable to the 16O case. For comparable concentrations of 12C, the regrowth rate was found to be three times higher than for that of the 16O case. Noble gas ions are also found to retard the growth rate of the amorphous layers. For 40Ar at about the 0.5-at.% level, the regrowth rate is appreciably slower than even that for the 16O case.
Dislocation damping and hydrogen pinning in austenitic stainless steels
Authors: Atrens A. , Fiore N. F. , Miura K.
Published: February 2003

The room-temperature damping of three Fe-18Cr-Ni alloys was determined as a function of vibrational strain amplitude at 80 kHz. The data are consistent with the Granato-Lücke theory of dislocation damping. Values of Lc (distance between minor pins) measured are consistent with those obtained from a thermodynamic analysis based on Suzuki locking. Hydrogen charging decreases both the damping and modulus defect, indicating that hydrogen pins dislocations in these alloys at room temperature. The pinning corresponds to four hydrogen atoms per 100 lattice atoms along the dislocation, and a hydrogen-dislocation (Hd) binding energy of 0.14 eV. The origin of the Hd interaction lies in the elastic misfit interaction, Suzuki interaction, or combination of both. These estimates of H concentration at dislocations and Hd interaction energy are consistent with the observed release rate of hydrogen from H-charged specimens undergoing plastic deformation.
Defect- and phonon-assisted tunneling in LPE In1−xGaxP1−zAsz DH laser diodes (λ∼1 μm)
Authors: Ludowise M. J. , Holonyak N. , Wright P. D. , Vojak B. A. , Rezek E. A. , Korb H. W.
Published: February 2003

Tunnel diode I-V, dI/dV, and d2I/dV2 characteristics are used to examine defect effects and phonon energies in In1−xGaxP1−zAsz double-heterojunction lasers (λ-1.1 μm) grown by liquid-phase epitaxy on InP substrates. Similar to the usual conductance minimum observed at zero bias, a conductance minimum in the dI/dV characteristics is observed at small forward bias (40⩽V⩽60 meV) and is identified as two-step tunneling (via defects) to Zn-acceptor states on the p-type side of the junction. An increase in the conductance is observed below the region of carrier injection and is attributed to tunneling from residual acceptor states on the n-type side of the junction. Fine structure in the dI/dV and d2I/dV2 characteristics permits the identification of optical phonon energies at two In1−xGaxP1−zAsz compositions (x=0.12, z=0.26; x=0.16, z=0.35) and in this region indicates two-mode behavior for the quaternary alloy.
A model for the current-voltage curve of photoexcited semiconductor electrodes
Authors: Wilson Ronald H.
Published: February 2003

A model to describe the behavior of photoexcited electrodes in an electrochemical cell is developed. In addition to the bulk semiconductor properties, the important parameters are a surface recombination parameter Sr and a surface electron transfer parameter St. It is the electron transfer process across the interface that leads to current in the external circuit. Using experimental curves for oxygen evolution at an n-type TiO2 electrode and Hall-Shockley-Read recombination to determine Sr, it is shown that the I-V curve in anodic bias is controlled by the competition between Sr and St. The physical basis for St is discussed and experimental approaches to investigate surface reactions are suggested.
Superparamagnetic and ferrimagnetic resonance of ultrafine Fe3O4 particles in ferrofluids
Authors: Sharma V. K. , Waldner F.
Published: February 2003

Coated ultrafine magnetite particles (average diameter around 100 Å) in five nonmagnetic liquids (commercial ’’ferrofluids’’) have been investigated by electron magnetic resonance at room temperature. A narrow signal can be attributed to the superparamagnetic fraction of the particles. A simple ’’superparamagnetic narrowing’’ model is consistent with the measurements. The ferromagnetic fraction gives a broad line. Both lines narrow upon dilution because the interparticle dipolar interaction is reduced. Variations of the viscosity have only minor effects on the signals. Dilution in trifluoroacetic acid seems to destroy the coating. The resulting agglomeration and sedimentation changes the magnetic resonance drastically. The reasons for the high value of the cubic anisotropy constant K1? (−5.8×105 erg/cm3) found for the ultrafine particles are discussed.
Location of charge centroid in electron-beam-charged polymer films
Authors: Gross B. , Sessler G. M. , West J. E.
Published: February 2003

The centroid of the charge distribution of electron-beam-charged polymer films electroded on both sides is determined by measurements of the charges on, or currents into, the two electrodes during or after electron-beam injection. Results obtained with 25-μm Teflon FEP films charged with a diffuse monoenergetic beam of 5–40-keV electrons show that the charge centroid is initially located between the average and maximum electron ranges regardless of whether the electrode of injection is floating or grounded (open or short circuit, respectively). During and after charging under open-circuit conditions the centroid moves further into the material beyond the maximum range.
Dielectric behavior of ferroelectric triglycine sulphate near the transition temperature
Authors: Mansingh Abhai , Eswar Prasad S. R. J.
Published: February 2003

The dielectric behavior of triglycine sulphate has been investigated near the phase-transition temperature for varying thicknesses of the crystal. Measurements have been carried out at a frequency of 1 kHz. The results indicate that the dielectric constant of triglycine sulphate does not go to infinity at the transition temperature. The deviation from the Curie-Weiss law near the transition temperature and the broadening of the peak with decreasing thickness of the crystal can be explained by assuming a surface layer of low dielectric constant, while internal bias can explain the shift in the transition temperature.
On the mechanism of operation of the type B impregnated cathode
Authors: Rittner E. S.
Published: February 2003

Hitherto unpublished data on life tests and evaporation rate of total barium from type B impregnated cathodes are presented. These data conflict with the recently deduced conclusion of Forman that the cathode surface is covered with less than a monlayer of adsorbed barium and that the barium coverage decreases with time. However, they are in agreement with the cathode mechanism proposed by Rittner and co-workers based upon extensive experimental studies. The Forman erroneous conclusion is traced to an inadequate oxygen content of the monolayer in synthesized cathode surfaces intended to simulate the real cathode.
The influence of oxygen on backscattering of excited H when H+1, H+2, and H+3 ions at 4–30 keV energy are incident on molybdenum
Authors: Rausch E. O. , Murray M. W. , Inouye H. , Thomas E. W.
Published: February 2003

A study has been made of the Hβ line intensity from excited H atoms scattered off Mo or Cu surfaces. Incident projectiles were 4–30-keV H+1, H+2, and H+3 ions. The integrated intensity of the atomic line emission increased as the ambient pressure of oxygen in the target chamber was raised from 10−11 to 10−6 Torr. The experimental data suggested that this change of intensity is caused by a reduction in the radiationless deexcitation of atoms by the Auger mechanism. A simplistic model was formulated which predicts the intensity as a function of ambient O2 pressure, projectile beam current density, and energy, but only in the case of H+ ions on Mo. An attempt to extend the model to H+2 ions was not successful. For Cu targets an increase in the intensity as a function of oxygen pressure was also observed. However, no attempt was made to test the model in this case. At an incident angle of 60° coefficients for sputtering of oxygen, Sox, adsorbed on Mo were determined to be 0.0025±0.0004, 0.011, and 0.017, respectively, for 20-keV H+1, H+2, and H+3 projectiles.
Drawing and annealing of fibrous material
Authors: Peterlin A.
Published: February 2003

The more-than-linear increase of elastic modulus with draw ratio, the gradual disappearance of meridional SAXS maximum, the drastic drop of elastic modulus after annealing and its recovery upon standing at room temperature if the sample was annealed with fixed ends so that it did not shrink, and the shape stability of such polyethylene samples and of superdrawn material (polyethylene, polypropylene, polyoxymethylene) during new annealing can be easily explained by the microfibrillar model of fibrous structure which was developed some years ago on the basis of electron microscopy and x-ray and ir investigation of plastically deformed linear polyethylene and isotatic polypropylene.
The monoclinic-to-trigonal transformation in selenium
Authors: Murphy K. E. , Altman M. B. , Wunderlich B.
Published: February 2003

The conversion of monoclinic selenium to trigonal selenium is studied by x-ray diffraction, optical microscopy, and thermal analysis between 343 and 487 K. Below the melting temperature of the monoclinic crystal the process is topochemical, but not topotactic. The melting of the monoclinic crystals to the pure Se8- ring melt occurs at 413 K (with a heat of fusion of 2.8 kJ/mole Se, and an entropy of fusion of 6.8 J/K/mole Se). The nucleation of the trigonal phase in the monoclinic single crystal is athermal and occurs in crystalline register with the monomer, either through the nature of the nucleating defect or through epitaxy. The time for the appearance of the fixed temperature-independent number of nuclei is governed by an activation energy of about 100 kJ/mole. The subsequent growth occurs by crystallization during polymerization in the direction of the macromolecular helix axis, independent of the host crystal. Above 360–380 K, the trigonal phase branches to spherulitic crystals with radial c-axis orientation. The linear crystal growth is described over the whole analyzed temperature range by the same exponential (−1/T) rate law with an activation energy of 113 kJ/mole, which indicates that ring opening is the rate-determining step.
Dynamic mechanical behavior of polyethylene during creep to failure in uniaxial extension
Authors: Crissman J. M. , Zapas L. J.
Published: February 2003

Dynamic mechanical measurements in torsion superposed on large uniaxial creep strains have been obtained on two types of polyethylene resins. At creep strains of about 10% it is observed that tanδ goes through a minimum and rises sharply thereafter.
cw optically pumped molecular iodine laser
Authors: Koffend J. Brooke , Field Robert W.
Published: February 2003

Laser oscillation on several I2 BO+u (v′=43, J′=12 and 16) →X1Σ+g(v″?9, J″=11, 13, 15, and 17) transitions is observed. The unique feature of this laser is that it is excited by a continuous-wave optical pump, single-longitudinal-mode 514.5-nm radiation from an Ar+ laser, and that it oscillates in a single (v′=43, v″) band for as long as 200 msec. Conversion efficiency of 0.14% with a maximum output power of 3 mW is achieved. Single-pass gain is observed to be 3±1% for the strongest transition. Thresholds of 100 mW and 1 W are observed for single-longitudinal-mode and multimode pumping, respectively. Some 30 laser transitions are observed, spanning nearly an octave of frequency from 570 to 1027 nm.
Effects of laser-modulated particulate incandescence on Raman scattering diagnostics
Authors: Eckbreth Alan C.
Published: February 2003

Laser-modulated particulate (soot) incandescence has been studied by measuring the laser-driven particle surface temperature in a propane diffusion flame as a function of laser focal flux. The experimental results display fair agreement with an analytical model of the process. Quite importantly, the absolute incandescence level displays a saturation behavior with increasing laser pulse energy. For laser Raman scattering diagnostics, this behavior means that the S/N ratio will increase with increasing laser flux level. Thus, for highest S/N ratio, it is preferable to operate at the highest possible flux short of gas breakdown and/or optical-component damage levels.
Spectroscopic measurements on a high-density Z-pinch plasma
Authors: Mercier J. , Neufeld C. R.
Published: February 2003

Using results of the quasistatic line-broadening theory applied to the blue wing of the Hβ line produced in a hydrogen Z-pinch discharge, a measured average electron density of at least 1.2×1019 cm−3 during the first compression has been obtained. The fitting remains good for wavelength displacements from the unperturbed line center somewhat smaller than the critical displacement for electron impacts given by the quasistatic theory, but clearly fails near the line center, where collisions dominate the profile. The measured density is consistent with relative continuum intensity measurements obtained from similar devices by other authors. The pinch plasma represents a target of critical electron density for CO2 laser radiation, and laser-plasma interaction experiments using this target are under way.
Eddy-current losses due to a surface crack in conducting material
Authors: Kahn A. H. , Spal R. , Feldman A.
Published: February 2003

Calculations are reported for the spatial distribution of magnetic fields in the neighborhood of a long surface crack in a conductor, where a uniform ac magnetic field is applied parallel to the length of the crack. The problem is resolved into tractable parts consisting of the cases of eddy currents near a semi-infinite crack with a sharp tip and eddy currents near a square corner. The semi-infinite crack problem is solved exactly by a modification of Sommerfeld’s diffraction theory and the corner problem is treated by a Green’s function obtained by the method of images. The composite solution is valid for a crack of depth equal to four times the electromagnetic skin depth or greater. From the solution, the Poynting vector is calculated and its integral over the surface computed. The change in power dissipation relative to the ’’uncracked’’ surface is given in a simple form.
A phase transition in NiF2 at elevated pressures
Authors: Jamieson J. C. , Wu A. Y.
Published: February 2003

A pressure-induced phase transition occurs in NiF2 at room temperature from a tetragonal to an orthorhombic structure. To the limits of our x-ray dispersion (CuKα radiation, 114.6-mm camera), it may be second or first order and becomes resolvable at about 40 kbar. We suggest that it may be magnetic in origin but the Bloch 10/3 rule virtually precludes its identification with the low-temperature weakly ferromagnetic orthorhombic form. Another possibility is that it is strain induced via a soft mode and not magnetic in origin.
Surface energy of spinel
Authors: Mishra Raja K. , Thomas G.
Published: February 2003

The contributions of the Coulomb electrostatic interaction and the Born-Mayer repulsive interaction to the surface energy MgAl2O4 are calculated. These results are compared with the surface-energy values calculated from elastic constants. The results show that surfaces parallel to {111} planes are of lowest energy for MgAl2O4 spinel as well as some spinel ferrites. Except for qualitative evidence, most of these predictions await experimental verification, including the predictions of the composition of freshly cleaved spinel surfaces.
Delayed secondary-electron emission in thin MgO layers
Authors: Dresner J.
Published: February 2003

We have observed and characterized a delayed secondary-electron emission in dense layers of MgO, 50–650 Å thick, which persists for as long as 10−2 s after interruption of the primary electron beam. The total delayed charge as well as the initial value of the delayed current are proportional to the secondary current under bombardment. The delayed current is proportional to the sample thickness for nonpenetrating primary electrons (100 eV), but decreases as the primary energy increases. During electron bombardment, these layers acquire a field of about 5×106 V/cm across them. The field permits the extraction into vacuum of electrons thermally released from bulk traps. This is the origin of the delayed emission. Part of the electron current injected at the metal contact is also extracted, yielding a field-enhanced component of secondary emission. The current through the MgO is mostly carried by electrons; the holes are relatively immobile. Impact ionization is not involved in these phenomena when the film thickness lies in the above range.
Decomposition of garnet epitaxial layers caused by annealing
Authors: Stacy W. T. , Huyberts M. A. H. , Metselaar R. , Voermans A. B.
Published: February 2003

The changes in chemical composition which accompany the process of stress relief in garnet epitaxial layers during annealing have been studied. It is shown that the process involves the evaporation of PbO and formation of Fe2O3 crystals on the layer surface. The associated volume reduction of the garnet layer results in the observed decrease in the lattice-misfit stress. Weight-loss measurements with a thermobalance have been employed to monitor the evaporation of PbO, and a quantitative comparison with the amount of Fe2O3 observed by optical microscopy has been made. These results are interpreted in terms of a specific decomposition reaction and are found to be in numerical agreement with x-ray diffraction measurements of the lattice changes.
The influence of recombination center data on the I-V characteristics of silicon p+-i-n+ diodes
Authors: Dudeck I. , Kassing R.
Published: February 2003

Calculations have been made of dc I-V characteristics of long p+-i-n+ diodes with deep levels showing a negative differential resistance region. The influence of the recombination center data, especially of the capture coefficients of both electrons and holes, cn and c−p, is discussed. The calculations show that cn only influences the high injection regime and the minimum voltage, whereas c−p only influences the prebreakdown region and the breakdown voltage; thus a new method arises to determine cn and c−p in the same sample. These results are confirmed in silicon p+-i-n+ diodes with the gold acceptor acting as recombination center. Theory and experimental results are in complete agreement for cn=3.2×10−8 cm3 s−1 and c−p=1×10−7 cm3 s−1. Finally, these values are compared with those given in the literature.
The physics of excess electron velocity in submicron-channel FET’s
Authors: Huang R. S. , Ladbrooke P. H.
Published: February 2003

A transport-equation model is used to examine the processes by which the velocity of an electron injected from a source contact into an n channel can overshoot the saturated drift velocity by a factor of 3 or more (depending upon the material). The results agree semiquantitatively with earlier Monte Carlo calculations and show that the excess electron velocity can persist for distances on the order of 1 μm, with obvious benefit to the transit time of the carrier (and hence the fT) in submicron-channel FET’s. Data for Ge, Si, and GaAs are given.
Toroidal SQUID with ferromagnetic core superconducting transformer
Authors: Cerdonio M. , Ricci F. F. , Romani G. L.
Published: February 2003

Ferromagnetic cores have been used for the secondary of a superconducting flux transformer in connection with a toroidal SQUID. Circuit analysis predicts an easier matching of the transformer for large inductances of the primary. Experimental data show a general agreement with the circuit analysis and a comparatively small increase in noise due to the metallic core.
Saturated electron drift velocity in 6H silicon carbide
Authors: v. Muench W. , Pettenpaul E.
Published: February 2003

The saturated electron drift velocity has been measured in epitaxial 6H silicon carbide layers. The saturation occurs at an electric field of approximately 2×105 V/cm. The saturated drift velocity is 2×107 cm/s at room temperature, i.e., a factor of 2 higher than in silicon.
Breakdown field in vapor-grown silicon carbide p-n junctions
Authors: v. Muench W. , Pfaffeneder I.
Published: February 2003

The electrical breakdown of one-sided abrupt p-n junctions in 6H silicon carbide has been investigated. The diodes are produced by vapor growth and mesa etching. Breakdown fields in the range (2–3.7) ×106 V/cm have been observed for p layers with 1017<NA<2×1018 cm−3. These figures tend to support the results of van Opdorp and Vrakking.
Evidence for surface asperity mechanism of conductivity in oxide grown on polycrystalline silicon
Authors: Anderson R. M. , Kerr D. R.
Published: February 2003

High conductivity observed in oxides grown on polycrystalline silicon has been previously speculated as being due to asperities on the silicon surface, which enhance the oxide field. Direct evidence of these asperities is shown here in SEM micrographs. The presence of the asperities is strongly correlated with the oxide conductivity (as controlled by the oxidation temperature).
Magnetostriction as a function of glass formers in amorphous alloys of Fe-P-B-Al
Authors: Brooks H. A. , Chen H. S.
Published: February 2003

Magnetostriction of amorphous-metal alloys has been found to exhibit an unexpected dependence on the glass formers P and B in Fe-P-B-Al. This observation has led to the determination of lower values for magnetostriction in the series Fex(P1−yBy)1−x−0.3Al0.03 and for the cobalt-substituted series (FexCo1−x)0.77P0.14B0.06Al0.03.
Electrostatic observations of laser-induced optical damage in LiNbO3
Authors: Schein L. B. , Cressman P. J. , Tesche Frederick M.
Published: February 2003

A new technique for observing optical damage is reported. It is based on detecting electrostatic potentials which result from the laser-induced macroscopic charge separation responsible for optical damage. This new technique has been used to determine, for the first time, the charge distribution of the displaced charges. For uniform circular illumination of diameter D, the charges appear to reside in a thin cylindrical shell also of diameter D, with the negative charge on the positive ferroelectric axis. For a Gaussian illumination, we observe the charge distribution to change with increasing exposure time, approaching a cylindrical-shell charge distribution, a result which may provide an explanation for ’’optical clean-up’’. This new technique for probing optical damage is as sensitive as standard optical techniques and is unaffected by temperature variations and mechanical vibrations.
Charge transport through a polymer foil
Authors: Chudleigh P. W.
Published: February 2003

The charge-transport mechanism in FEP (A) polymer foils charged with an ethyl alcohol contact has been studied by measuring the decay of voltage across the foils. Each foil was metallized on one surface and stored at 100 °C in an open-circuit configuration. Voltage decay is shown to occur by charge transport through the foil and to be in good agreement with the predictions of a model in which charge is transported by hopping of injected carriers between localized trapping centers. The model is characterized by three parameters: the free-carrier mobility, the mean free time of a carrier between traps, and the mean capture time in a trap. Evaluation of these parameters enables the effective carrier mobility at long decay times to be estimated—e.g., with a charging voltage of −500 V, the effective mobility of negative charge carriers in FEP (A) approaches 2.2×10−16 cm2/V sec at 100 °C.
TEA CO2 laser radiation induced EMF’s in tellurium
Authors: Ribakovs G. , Gundjian A. A.
Published: February 2003

A comprehensive set of measurements is presented with the purpose of obtaining and interpreting all tensor components necessary to describe the fast emf’s induced in intrinsic and extrinsic single-crystal tellurium samples exposed to TEA CO2 laser radiation in the range between 115 and 300 K. Three distinct mechanisms for the generation of the fast signals have been identified, namely, the fourth-rank tensorial photon drag effect, a third-rank tensorial optical rectification effect dependent on the carrier type and concentration, and a spurious signal predominant only at low temperatures in structurally imperfect crystals. The experimental results show that, for the photon drag effect, the important tensorial coefficients relating the induced electric field to the incident laser power density are T*1133=T*2233 with room-temperature values in undoped and extrinsic crystals respectively equal to 0.85×10−7 and 1.1 ×10−7 cm/A. The values of the finite third-rank tensor components χ*122=χ*212=χ*111 are correspondingly obtained to be 0.25×10−7 and 0.7×10−7 cm/A. Finally, the magnitude of the low-temperature spurious signal is found to vary from sample to sample with maximum values attained at lowest temperatures ranging from essentially zero to in excess of 3 V/MW cm−2, depending on the sample used. The results concerning the photon drag effect are found to be consistent with the theory, and the third-rank tensorial signal is ascribed to a nonlinear conductive behavior in the material.
Theory of the photon drag effect in tellurium
Authors: Ribakovs G. , Gundjian A. A.
Published: February 2003

A detailed microscopic theory of the photon drag effect due to CO2 laser induced direct electronic intervalence band transitions in tellurium is presented based on the solution of Boltzmann’s transport and the resulting current equations. The numerical evaluation of the theoretically derived expression is shown to agree favorably with the reported experimental results.
On oxygen enrichments in Nb surface layers and their apparent conductivity as observed by the superconducting penetration depth Δλ (T,f,Bac)
Authors: Schwarz Wolfgang , Halbritter Jürgen
Published: February 2003

Various measurements on superconducting Nb surfaces show strong deviations from BCS theory of homogeneous materials. To study causes for these deviations, penetration-depth Δλ (t,f,Bac) and resistance ΔR (T,f,Bac) measurements were carried out. The observations prove that weak superconducting regions exist at Nb surfaces, with transition temperature T*c below 7.2 K showing up in several aspects: (1) The transitions to the normal state sum up to Δλ0(f,Bac). (2) The proximity above T*c between normal and superconducting regions enhances λ to λeff causing a step Δλ0(Bac) and a slope λ0=dλeff/dy enhanced over the BCS values. (3) The apparent resistance of shielding currents passing such normal regions embeded in a superconductor is low and decreasing further with Bac, even for Bac≳10−4 T, indicating overheating of quasiparticles. These normal regions with T*c’s below 7.2 K embeded in Nb with Tc?9.3 K give the first clear evidence for causes of, for example, lowered Bc3/Bc2 above T*c, differences in mean free paths l obtained from λ0 and Bc3, respectively, or the low rf breakdown fields Bcrit(f) and its dependence on frequency. The reason for the weak superconducting spots in Nb, which has been anodized or handled in air after UHV firing, is oxygen enrichment in a surface layer. The amount of the statistically distributed weak spots increases with cold working or electron impact. Possible mechanisms causing such O-enrichment or suboxide precipitation are discussed.
Theoretical study of irreversible Bloch-wall jumps and static losses
Authors: Allia P. , Vinai F.
Published: February 2003

A preliminary theory is developed for the static losses in ferromagnetic materials due to independent Barkhausen jumps. A linear relation between the area swept by the wall and the corresponding duration of the jump is obtained both on the basis of considerations of the pressure acting on the wall and by direct calculation of the energy loss. The latter method can be applied to the case of correlations between jumps. The energy spectrum of the single jump and the field on the wall are obtained by making use of an exact general formula for eddy-current density.
Measurements of the velocity spectrum of sputtered Na from a NaI target by a Doppler-shift laser spectrometer
Authors: Husinsky W. , Bruckmüller R. , Blum P. , Viehböck F. , Hammer D. , Benes E.
Published: February 2003

By means of a Doppler-shift laser spectrometer (DSLS) we have measured the energy spectrum of Na emerging from a NaI surface bombarded with He+, Ne+, Ar+, Kr+, and Xe+ ion beams of about 30 μA/cm2 and within an energy range 10–30 keV. The measured spectra consist of a thermal and a high-energy contribution, the relative intensities of which strongly depend on the mass of the bombarding ions. The sputter mechanism can be explained by formation of so-called excitons in the bulk and by the random collision cascade theory. Furthermore, selective sputtering of I in the case of Kr+ and Xe+ bombardment must be taken into account. The use of the DSLS yields a good signal-to-noise ratio even for particle densities less than 100 particles/cm3 within a velocity interval Δv=50 m/sec. The velocity resolution achieved was 50 m/sec in the energy region up to 1 eV and 1% in the high-energy region.
What is the mechanism of hydrogen absorption in rare-earth intermetallics?
Authors: Buschow K. H. J. , Cohen R. L. , West K. W.
Published: February 2003

We have studied the intermetallic compounds EuPd and EuRh2, and the corresponding saturated hydrides, via Eu Mössbauer spectroscopy, magnetic measurements, and x-ray diffraction. In both intermetallics, the Mössbauer parameters, indicative of the environment about the Eu ion, change substantially in the hydriding process and approach those of EuH2. We interpret those changes as evidence that the hydrogen absorption occurs via the formation of EuH2 ’’complexes’’. For the EuRh2, a simple thermodynamic argument supports this approach. The EuRh2 maintains the same crystal structure under H2 absorption, but the Eu3+ becomes Eu2+, and the lattice volume increases by 40%. EuPd changes structure under H2 absorption, but the Eu remains divalent. Results of magnetic and crystallographic measurements are presented. With partial hydriding, only the pure intermetallic and saturated hydride phases are observed to occur.
Preliminary study for the construction of a low-energy electron-diffraction apparatus using a high-tension source
Authors: Berger Colette , Dupuy Jean Claude , Laydevant Louis , Bernard René
Published: February 2003

This paper is a study towards the construction of a low-energy electron-diffraction apparatus using a Johansson objective for its optical system. A theoretical study in Gaussian approximation shows that the diffraction pattern is formed in the focus plane of the objective; its dimensions do not depend on the electron energy. By computing courses of electron trajectories, a more accurate investigation is carried out. A variation of 100 eV in electron energy induces broadening less than 7% in the diffraction pattern. The size of each spot in the pattern is lower than 0.6 mm, while the aperture of the primary beam is lower than 1.6 mm. The objective is shown to carry out by itself the filtering of the secondary electrons, the better this filtering the smaller the aperture radius. This study points out important advantages in using this device for the diffraction of low-energy electrons—advantages which were first perceived in preliminary experiments.
Bit packing density of the BEAMOS target
Authors: Possin G. E.
Published: February 2003

BEAMOS, beam addressed metal oxide semiconductor, is an electron-beam-addressed semiconductor digital mass-memory device. Its operation is based on electron-beam writing of stored charge in an unstructured MOS layer and electron-beam reading of this stored charge through its effect on the surface-recombination velocity of the oxide silicon interface. The surface-recombination velocity controls the diffusion of electron-beam-generated carriers in the n layer of the np diode underlying the oxide layer. This control of carrier diffusion by surface-recombination-velocity patterns is the unique feature of the BEAMOS target concept. The data storage capacity of BEAMOS-type devices is limited by the electron-beam spot size and target construction. A model of the target resolution (bit packing density) is described which includes the effects of incident beam spot size, electron scattering in the target layers, and injected minority-carrier diffusion in the n layer of the target. Measurements of electron-beam scattering are summarized and applied to the writing and reading mechanisms of the target. The minority-carrier diffusion equation is solved by a relaxation method similar to the method of sources. This leads to a model for the target bit packing density, which includes both electron scattering and minority-carrier diffusion. For present BEAMOS targets, the dominant limitation is shown to be minority-carrier diffusion, which can be controlled by the n-layer thickness. Predictions of the model are compared with measurements on actual targets. The ultimate packing density of the concept is also discussed. Packing densities of more than 2×107 bits/cm2 have been demonstrated, and densities as high as 109 bits/cm2 may be possible.
Oxygen precipitation and stacking-fault formation in dislocation-free silicon
Authors: Patel J. R. , Jackson K. A. , Reiss H.
Published: February 2003

The kinetics of the growth of Frank interstitial stacking-fault loops formed as a result of oxygen precipitation at high temperatures in bulk dislocation-free silicon have been measured over a temperature range 1000–1200 °C. From TEM observations at early and later stages of stacking-fault formation, it is concluded that the fault can be nucleated at a precipitate particle (assumed to be SiO2) by either interstitial collapse or by a dislocation reaction involving a perfect dislocation dissociating to form a Shockley and Frank partial. Once nucleated, the fault grows by (1) oxygen diffusing to the central precipitate and (2) interstitials, formed to accommodate the large volume change accompanying precipitation, migrating to the stacking fault causing it to grow. A detailed model of the growth of a precipitate and its related fault involving several steps in series has been worked out in the Appendix. The assumptions underlying this derivation have been treated in the Appendix and the preceding paper. The theory predicts a t3/4 growth law for stacking faults which is observed experimentally over the temperature range investigated. The theory also predicts that the temperature dependence of the growth of stacking faults has an activation energy which is three-fourths of that for self-diffusion, ∼3.8 eV for the most recent measurements.
Influence of particle size ratio on the continuity of aggregates
Authors: Kusy R. P.
Published: February 2003

A model is developed which considers the volume fraction of dispersed phase necessary to form an infinitely long network as a function of the particle size ratio. Recognizing that neither a monolayer nor a double layer of dispersed particles around the primary phase is a necessary condition for continuity, the surface fraction of primary phase covered by the dispersed phase and the ratio of dispersed phase particles which are occluded from, versus contiguous to, the primary phase are estimated either empirically or by reference to probability theory. The theoretical results are compared with earlier experimental work on electrical properties of compacted mixtures of polymer and metal powders.
Photodetection properties of Cu2Se-AgInSe2 heterojunctions
Authors: Tell B. , Wiegand J. J.
Published: February 2003

Heterojunctions were formed by vacuum evaporation of p-type Cu2Se on n-type AgInSe2 substrates. The photodetection characteristics of these diodes are vastly improved over those previously reported. At λ=1.05 μm, the room-temperature quantum efficiency approaches the reflection-limited value (∼0.7) as compared to ∼0.2 previously reported. In addition, the efficiency of the present diodes becomes greater than unity at low reverse biases. At 77 °K, even more dramatic gains can be achieved at low reverse biases. The structure appears to operate as an optically activated switch and is interpreted as a combination of photovoltaic and photoconductive mechanisms.
Uniaxial stress component in diamond anvil high-pressure x-ray cameras
Authors: Singh A. K. , Balasingh C.
Published: February 2003

The effect of the uniaxial stress component on the lattice strains measured with a diamond anvil x-ray apparatus has been discussed. The results are compared with those published earlier for the tungsten carbide anvil apparatus.
Low-temperature diffusion of Al into polycrystalline Si
Authors: Nakamura Kunio , Kamoshida Mototaka
Published: February 2003

Diffusion of Al into a polycrystalline Si layer chemically deposited at 640 °C was studied by capacitance-voltage characteristics, sheet resistance, and electron microprobe measurements in the 180–550 °C temperature range. It has been found that diffusion of Al into polycrystalline Si takes place at temperatures as low as 300 °C, and that the polycrystalline Si becomes electrically conductive. The sheet resistance of polycrystalline Si decreases with increasing annealing temperature. Annealing at a higher temperature, however, induces migration and recrystallization of Si in Al, and the original polycrystalline-Si layer loses its integrity.
Superconducting lead variable-thickness microbridges
Authors: Yeh J. T. C. , Buhrman R. A.
Published: February 2003

We report the first investigation of superconducting lead variable-thickness microbridges. The bridges were fabricated by a two-step deposition process without breaking the vacuum using oblique evaporation. The characteristics are presented and compared with theoretical predictions.
Structrue simulation of transition-metal-metalloid glasses. III
Authors: Boudreaux D. S. , Gregor J. M.
Published: February 2003

Improvements to the scheme for simulating atomic structures of metallaic glasses by dense random packings of various sized spheres have been implemented. Improved control of alloy composition and an energetic relaxation scheme are discussed in this paper. In addition, the methods described are applied to the study of a Pd80Si20 glass and the results compared to high-resolution neutron-diffraction studies on this alloy.
Estimation of surface layer structure from Rayleigh wave dispersion. II. Sparse-data case—analytical theory
Authors: Richardson J. M. , Tittmann B. R.
Published: February 2003

The ill-posed nature of the estimation of subsurface properties from dispersion data necessitates the application of special approaches in which a priori information supplements the experimental data. Here we consider a particular approach involving the use of estimation theory combined with a nonparametric mathematical model of the measurement process. In a previous paper we considered the somewhat artificial case of continuous dispersion data (or, in practice, data that is sufficiently dense and extensive that interpolation and extrapolation can be carried out with impunity using standard techniques). Here we treat the sparse-data case using an estimator that is optimized for an input composed of a discrete data set. The treatment starts with a mathematical model giving a probabilistic description of the possible results of measurement including measurement errors. As usual, the estimator (a function providing the estimated profile of subsurface properties in terms of measured data) is optimized in a least-mean-square sense for its performance on the model. The theory also yields auxiliary measures pertaining to bias, data versus model dominance, resolution, and a posteriori variance.
Low-frequency 1/f noise in MOSFET’s at low current levels
Authors: Aoki Masaaki , Katto Hisao , Yamada Eizaburo
Published: February 2003

Low-frequency 1/f noise in Si n-channel MOSFET’s is measured at 300 and 77 K. It is found that the equivalent input-noise resistance Rng increases at low current levels from 100 to 10−2 μA in both the saturation and linear regions. A theory is developed to account for this characteristic, assuming the activated conduction at low electron concentrations due to the surface potential roughness as proposed by Chen and Muller. Theoretical calculations are made for the linear region of operation. Excellent agreement is obtained between the theory and the experiment at both temperatures.
Superconducting and mechanical properties of i
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u formed multifilamentary Cu-Nb3Sn composites
Authors: Harbison James P. , Bevk J.
Published: February 2003

A systematic experimental study of the variations of superconducting transition temperature and critical-current density is reported for in situ formed multifilamentary Cu-Nb3Sn composites containing 10 at.% Nb and 2–3 at.% Sn annealed at either 650 or 700 °C. A particular emphasis was placed on the evaluation of uniformity, thermal stability, and mechanical strength. Critical-current density was measured as a function of transverse magnetic field and was found to increase in samples measured in a bent position. The overall critical-current performance is comparable to that of reinforced stabilized conventional composites. Large residual resistivity ratios are indicative of a clean high-conductivity matrix surrounding each individual filament, an important requirement for thermal stability. High resistance to plastic flow in these composites is attributed to strong filament-to-matrix bonding and small interfilament spacing. The ultimate tensile strength at 77 °K reached a value of ∼100 ksi (690 MPa). The measured uniformity of both critical currents and mechanical properties is found to be consistent with microstructural observations. Finally, an overall comparison is made with conventional continuous-filament superconducting composites.
Numerical evaluation of the response of a Josephson tunnel junction in an arbitrary circuit
Authors: Harris Richard E.
Published: February 2003

A numerical technique is presented for calculating the response of a Josephson tunnel junction when connected to an arbitrary circuit. The approach includes all of the details of the microscopic theory including sine and cosine terms as well as the quasiparticle current together with its reactive art. An example is given, and techniques for reducing computation time are discussed.
Manipulation of 1-μm bubbles with coarse (≳4 μm) overlay patterns
Authors: Lin Y. S. , Almasi G. S. , Keefe G. E.
Published: February 2003

This paper reports on the propagation and transfer of 1-μm bubbles in ion-implanted contiguous-disk devices, made by conventional photolithographic techniques. Bubble-propagation circuits are made of undulating patterns masked from implantation on a low-Q garnet film, which is grown on top of and exchange coupled with a medium-Q garnet film which supports the small bubbles. A double-garnet composite combines the good features of a medium-anisotropy storage layer to stabilize bubbles and, more importantly, of a small-anisotropy driving layer to ensure the creation of a planar magnetization layer by ion implantation. A fundamentally different propagation mechanism employing the charged walls around the implanted pattern edges is explained. The value of the charged walls is that they lend themselves to coarse-featured devices. Furthermore, they can be substantially lengthened to bridge a large gap between two propagation circuits to assist bubble transfer across that gap. We describe a switching gate employing such a bridging charged wall to transfer 1-μm bubbles across a 4-μm gap. Also included is an implantability analysis of several garnet compositions, pointing out why the ability to create a planar magnetization by implanting a single bubble layer diminishes as the bubble size approaches the 1–2-μm range. An implication is that a double-garnet composite, such as used in our contiguous-disk devices, may also be essential to other bubble devices (Permalloy bar and bubble lattice) for bubbles under 1–2 μm in diameter.