bluuebunny/crossref_metadata_2025 huggingface dataset:
Non−Ohmic electron conduction in silicon surface inversion layers at low temperatures
Authors: Hess Karl , Neugroschel Arnost , Shiue C. C. , Sah C. T.
Published: February 2003

Deviations from Ohm’s law for electron conductivity in silicon surface inversion layers were observed from 4.2 to 20 K using MOS transistors with different amounts of oxide charges. The measurements were compared with a two−dimensional theory of hot electrons in inversion layers. It was found that above 6 K this theory can well account for the observed non−Ohmic behavior. From a comparison of the theory with experimental results the deformation potential constant ZA for scattering of electrons by acoustic phonons is found to be ZA=7.8±2.3 eV. The hot−electron theory is in apparent disagreement with the experimental results at temperatures below 6 K, which is discussed. At high drain voltages the samples with the largest amount of oxide charges showed a negative differential resistance.
Stoichiometry of the ternary semiconductor CuGaS2 : 57Fe as determined by Mössbauer spectroscopy
Authors: von Bardeleben H. J. , Goltzéné A. , Schwab C. , Friedt J. M. , Poinsot R.
Published: February 2003

Mössbauer experiments performed on iron−doped CuGaS2 showed the iron to be present in two valence states, Fe2+ and Fe3+. The ratio R of the Fe2+ to Fe3+ concentrations is stoichiometry dependent and could be controlled by adjusting the stoichiometry of the starting elements. Incorporation of iron during synthesis and growth from a stoichiometric mixture of the elements leads to R smaller than 0.01, i.e., almost only to Fe3+. With a gallium excess of 5%, R becomes as high as 1.2. Subsequent annealing of the latter samples in a sulphur atmosphere, oxidizes part of the divalent iron into Fe3+, resulting in R=0.3. Finally, the consequences of a transition−metal contamination upon the electrical properties of this semiconductor are pointed out.
Steady−state dark and photocurrents in a poly−n−vinylcarbazole−trinitrofluorenone photoconductor
Authors: Lakatos Andras I.
Published: February 2003

Dark and photocurrents were measured under steady−state conditions in a 1 : 0.6 molar poly−n−vinylcarbazole−trinitrofluorenone photoconductive polymer. Electric field and sample thickness measurements indicate that the dark currents are not space−charge limited but rather conform to a Poole−Frenkel or similar type field dependence at E?105 V/cm. The photocurrents generated by bulk absorbed light show linear behavior below 105 V/cm, above this field these currents increase approximately as E2. These currents are sublinear in light intensity. A model which includes the field−dependent photogeneration rate, a wide distribution of localized states in the energy gap, and field−independent free−carrier mobility is proposed to explain these results. The field dependence of surface generated hole currents shows a transition from space−charge to emission limitation with increasing applied field. Above 5×104 V/cm the field dependence of the photogeneration rate approaches an E1.5 dependence.
Two−dimensional domain walls in ferromagnetic films. III. Uniaxial anisotropy
Authors: Aharoni Amikam
Published: February 2003

The general two−dimensional model proposed for the structure of 180 ° domain walls is studied for the case of Permalloy films whose thickness is between 1000 and 10000 Å. The wall shape obtained by minimizing the energy with respect to the two Ritz parameters is highly asymmetric, which is in accordance with recent electron microscope observations. Such an asymmetry could be obtained before only by functions defined numerically during the energy minimization process. The wall energy for a 1000−Å−thick Permalloy film is 2.5 erg/cm2 which compares favorably with the value of 2.0 erg/cm2 computed by LaBonte to be the lowest possible wall energy in two dimensions. Very
Superconductivity in amorphous and microcrystalline transition−metal alloys
Authors: Johnson W. L. , Poon S. J.
Published: February 2003

Results of x−ray diffraction, electrical resistivity, critical magnetic field, and transport measurements for several bulk amorphous and microcrystalline transition−metal superconductors obtained by liquid quenching are presented and discussed. Simple Jc−Hc2−Tc relations are observed for this class of materials. A linear relation between electronic diffusivity and nearest−neighbors distance is derived from critical field measurements. The relationship between the formation of an amorphous phase by rapid cooling from the liquid state, lattice stability, and the characteristics of phase diagrams are discussed.
Relaxation oscillations in point−contact Josephson junctions
Authors: Taur Y. , Richards P. L.
Published: February 2003

Negative resistance regions have been observed on the static I−V curves of point−contact Josephson junctions when dc biased with a low−impedance source. An equivalent circuit model has been developed which successfully explains the experimental results in terms of relaxation oscillations. It is also found that such junctions can be operated either as a one−port amplifier for signals at 5 MHz or as a 36−GHz heterodyne mixer with large conversion gain.
Nonstoichiometry in A
BO3 compounds similar to PbTiO3
Authors: Shackelford James F. , Holman Robert L.
Published: February 2003

A statistical thermodynamic model of the nonstoichiometry in ABO3 compounds possessing volatile AO species is applied to mass−loss Knudsen effusion experimental (p,T,x) data. Good qualitative agreement is found between the model and the experiment. The nonstoichiometry is assumed to be accommodated by randomly occurring uncharged Schottky defects with an energy of formation about +0.5 eV/defect and an interaction energy of about −0.1 eV/defect pair. However, the theoretical model deviates from the experimental data describing the relationship between vapor pressure and the PbTiO3 defect concentration. This observation suggests that some refinements in the model (such as a consideration of the ordering and/or charging of lattice vacancies) will be necessary.
Thermal desorption spectra of inert−gas ions implanted into a nickel (100) crystal
Authors: Edwards D.
Published: February 2003

The thermal desorption spectra of inert−gas ions (neon, argon, krypton, and xenon) implanted at various energies (20 eV−7 keV) into a nickel (100) crystal are reported. Particular features of the spectra are found to be relatively insensitive to the species of bombarding ion. An inert−gas diffusion process is observed at the higher incident energies and an estimate of 2.1 eV is obtained for the activation energy for substitutional neon diffusion in nickel.
Study of conductive gold film lifetime under high current densities
Authors: Etzion M. , Blech I. A. , Komem Y.
Published: February 2003

The lifetimes of gold films were measured at electrical current densities of (0.8−1.15) ×106 A/cm2 and temperatures of 220−500 °C. The effective activation energy was found to be 0.42 eV. Electromigration caused the formation of voids, hillocks, and whiskers. All films failed near the cathode, suggesting that gold atoms migrate in the direction of electron flow. The film lifetime is governed both by the temperature gradients and local structural changes. An approximate equation which takes into account these effects was derived to evaluate the film lifetimes.
Thin−film breakdown counter of fission fragments
Authors: Tommasino L. , Klein N. , Solomon P.
Published: February 2003

A new kind of detector of heavy fission fragments is described. The detector is a thin−film capacitor in which electrical breakdowns are nonshorting. The detection is based on the counting of breakdowns which arise when heavy fission fragments hit the capacitor. These breakdowns occur at fields distinctly lower than those due to the application of the field only. The lowering of the breakdown field is discussed considering the thermal or electronic effects for silicon dioxide detectors. The detectors offer immediate information on the magnitude of particle fluxes and may possibly serve to identify the particles.
Electric energy generation by shock compression of ferroelectric ceramics: Normal−mode response of PZT 95/5
Authors: Lysne P. C. , Percival C. M.
Published: February 2003

Reproducible and predictable electrical pulses with peak powers of a few hundred kilowatts lasting for a few microseconds can be obtained from shock−wave compressed ferroelectrics. In this work, impact−loading techniques are used to investigate the electromechanical response of poled specimens of a ferroelectric ceramic, PZT 95/5, to long−duration shock pulses. The experiments are conducted in the normal mode in which the shock propagation vector is perpendicular to the remanent polarization. Current histories are obtained as a function of load resistance for a fixed shock amplitude of 1.4 GPa, and few additional experiments investigate the stress dependence of the electrical response. A simple, though specific, model is developed that gives good agreement with observed results. The extension of this model to other materials and shock−loading conditions is discussed.
Elastic constants of tungsten−rhenium alloys from 77 to 298 °K
Authors: Ayres R. A. , Shannette G. W. , Stein D. F.
Published: February 2003

The adiabatic single−crystalline elastic constant of W−3 at.% Re and W−10 at.% Re were measured in the temperature range 77−298 °K. The elastic anisotropy ratio, C44/C′, was found to follow the behavior predicted by Fisher for transition−metal alloys. Re additions to W decrease the elastic constant C′ which indicates decreasing stability of the bcc structure. This behavior is believed to be related to the d−band structure. The Debye temperature for alloys was calculated and found not to vary appreciably from the value for pure W.
Radiation pattern, reactive power, and resistive aperture antennas
Authors: Borgiotti Giorgio V.
Published: February 2003

Novel expressions are established for the active and reactive powers of a radiating aperture as integrals, extended to the visible and invisible space of the wave−number plane, of quadratic forms involving the components (in a chosen vector basis) of the Fourier Transform (FT) of the transverse electric field. The physical counterpart of a certain choice of the basis is a particular decomposition of the radiation patterns into two partial patterns differently polarized. As an application of this formalism it is shown that the components of the radiation pattern polarized in the plane of incidence (for each direction of propagation) or orthogonal to it are related to the capacitive and inductive terms in the reactive power. It is also established that a circularly polarized pattern is necessarily associated with zero reactive power. More general conditions are then established and it is shown that zero reactive power is obtained when the Plane Wave Spectrum (PWS) representing the aperture field has certain properties of rotational symmetry on the wave−number plane. An eigenvalue equation (defining those conditions) is established and the structures of the solution discussed. The physical antenna structures whose field can be represented by a PWS of the type studied are then identified with self−complementary apertures having rotational symmetry. Their inherent broad−band properties are briefly discussed from the viewpoint of PWS theory.
High-frequency pyromagnetic effect in CoS2−xSex compounds
Authors: Malwah M. L. , Bené R. W. , Walser R. M.
Published: February 2003

In this paper we present the results of the pyromagnetic measurements on CoS2−xSex in the frequency range 100 Hz–10 MHz. The effect of the eddy current losses on the frequency response behavior is calculated and seems to explain the experimental data fairly well. The high-frequency response measurements also reveal in these compounds the presence of a surface magnetic state with a Curie temperature higher than that of the bulk material. The surface Curie temperature as well as the thickness of the surface region depend on the level of selenium doping. The depth of the surface region increases with higher level of selenium doping and varies from about 0.5 to 25 μ. The cause for the existence of the surface magnetic state is believed to be the selenium deficiency near the surface. A possible selenium doping profile near the surface consistent with our experimental data is also suggested.
An experimental investigation of the surface magnetization of iron using the magneto-optical Kerr effect
Authors: de Waard H. , Uggerho/j E. , Miller G. L.
Published: February 2003

Using the magneto-optical Kerr effect, it is shown that the surface magnetization and the bulk magnetization of both polycrystalline and single-crystal iron plates behave quite differently. In particular, a distinctive ’’lag’’ is observed in the surface magnetization, except when the single crystal is magnetized along the easy 〈100〉 direction. The surface magnetization of the single crystal is highly anisotropic. Implantation of a dose of 1015 Fe+ ions/cm2 into a polycrystalline plate causes a change in the shape of the magnetization curve.
Statics and dynamics of domain walls in bubble materials
Authors: Hubert Alex
Published: February 2003

The wall structure of planar domain walls in magnetic thin films of perpendicular anisotropy is calculated starting from a differential equation somewhat generalized from the one first introduced by Slonczewski. Solving this differential equation both for static and for stationary moving walls by a finite-difference method yields as results the wall profiles, the effective masses, the energies, and the critical velocities for ordinary walls as well as for Bloch line carrying, so-called heavy, walls. The critical velocities which were obtained are generally smaller than previously assumed. One conclusion drawn from the character of the instabilities at the critical velocities is that there will be no dynamically induced stacking of horizontal Bloch lines for films in the thickness range preferred for bubble applications.
Impulsive loading of targets by HF laser pulses
Authors: Marcus S. , Lowder J. E.
Published: February 2003

Measurements of impulse coupling coefficients for 180-nsec HF (2.7 μm) laser pulses on aluminum targets are reported. The targets were irradiated both at atmospheric and reduced pressure. Coupling coefficients of up to 13 dyn sec/J were observed. These short-pulse 2.7-μm measurements are compared with 1.06-μm short-pulse measurements reported in the literature.
X-ray examination of epitaxial PbSnTe and PbTe
Authors: Lambert V. L.
Published: February 2003

Laue back-reflection photographs are used in a simple method of x-ray examination of epitaxial PbSnTe and PbTe. When BaF2 is utilized as the growth substrate and a copper target x-ray tube is used, this method permits x-ray reflections from the substrate and from the epitaxial layer to be identified separately.
Etch pits and dislocations in {100} GaAs wafers
Authors: Angilello J. , Potemski R. M. , Woolhouse G. R.
Published: February 2003

The reliability of molten KOH for revealing dislocations intersecting {100} faces of GaAs has been tested using transmission x-ray topography. It is found to be a ’’faithful’’ etch.
Obliquity-factor correction to solid-state radiation patterns
Authors: Lewin L.
Published: February 2003

The Huygens obliquity factor, in a special form appropriate to the dielectric-air interface of the laser, provides an additional factor to the existing radiation pattern formula, and leads to a beam sharpening which gives good agreement with experimental measurements. A simple approximate formula relates the half-power angles as calculated with and without the correction, though it is inadequate to take into account finer structure-dependent features.
Enhanced superconductivity and lattice instability in Nb-Rh alloys
Authors: Johnson W. L. , Poon S. J.
Published: February 2003

Superconductivity with transition temperature above 10 °K has been observed in a new Nb-Rh intermediate phase. The new metastable phase is obtained by liquid quenching the binary alloy or by the addition of a small percentage of carbon to form a stable ternary alloy.
Laser-light-induced relaxation in amorphous Sb2S3 films
Authors: Matsuda A. , Yoshimoto N.
Published: February 2003

Laser-light-induced motion of the amorphous-mica substrate system has been disucssed. From the results of wavelength and temperature dependence and time constant of the effect, a thermal model has been proposed.
Velocity distribution and angular distribution of molecular beams from multichannel arrays
Authors: Beijerinck H. C. W. , Verster N. F.
Published: February 2003

Three stainless-steel multichannel arrays with channels of 16, 50, and 140 μm diameter have been investigated experimentally. The whole flow pattern is measured, including the angular dependence of the velocity distribution. All measurements concern the opaque mode, with λ⩽L and λ⩾α, where λ is the mean free path in the source and α and L are the radius and length of the channel, respectively. The results are compared with the predictions for free molecular flow in the same channel, as a function of the reduced source density n*=L/λ. The peaking factor is 30% lower than predicted by the Giordmaine-Wang model. At angles ϑ larger than the half-width–half-maximum ϑ1/2 the angular distribution is not perturbed by the opaque conditions; for ϑ<ϑ1/2 it levels off to a lower peaking factor due to operation in the opaque mode. The center-line beam shows an increasing loss of slow molecules for increasing n*. At n*=10 the gain in mean translational energy is 15%, much larger than predicted by the model of Olander. The deformation of the velocity distribution decreases with increasing angle, and for ϑ≳ϑ1/2 the molecules again have an unperturbed Maxwell-Boltzmann distribution.
Forced mode locking of a single-line high-pressure CO laser
Authors: Nurmikko Arto V.
Published: February 2003

Peak powers in excess of 1 kW and pulsewidths in the nanosecond regime have been measured by forcibly mode locking a high-pressure CO laser operating on single vibrational-rotational transitions. Successful short-pulse operation has been achieved on some 30 lines in the 5.1–5.3-μ wavelength region.
Self-focusing of near-infrared laser beams in GaAs
Authors: Miller Robert C. , Nordland W. A.
Published: February 2003

Self-focusing of Q-switched Nd-YAG laser radiation in single-crystal GaAs has been studied. Near- and far-field intensity distributions measured after the light has passed through 1 cm of GaAs are given for various incident pulse energies. The self-focusing correlates qualitatively with linear absorption but is found to be most pronounced in p-type material. This self-focusing is believed to be of thermal origin, resulting from absorption coupled with a refractive index that increases with temperature.
Carrier-density fluctuations and the IGFET mobility near threshold
Authors: Brews J. R.
Published: February 2003

The behavior of the inversion-layer mobility observed in the IGFET at biases close to threshold is explained in terms of small fluctuations in the density of minority carriers. These fluctuations are in response to localized charges at the oxide-semiconductor interface. The theory predicts the abrupt drop of mobility with decreasing carrier density near threshold which is observed in the dc conductance mobility, field-effect mobility, and Hall mobility. The analysis also indicates that the dc mobility drop occurs at higher carrier densities at 4.2 °K than at 300 °K due to the larger fluctuations of the minority carriers at low temperatures (when they are all in a single quantum subband) than at high temperatures (when they are distributed over a large number of subbands). The anomalous threshold shift of the IGFET with temperature for temperatures below 77 °K is attributed to carrier population changes with temperature, i.e., with the  freezeout  with decreasing temperature of carriers from higher subbands, where fluctuations are small, into the lowest fluctuation-dominated quantum subband. The Chen-Muller mobility step with increasing carrier density is well described. A large number of other experimental facts are qualitatively accounted for by the analysis, which can be made more quantitative with more accurate evaluation of various integrals, etc. In particular, orientation dependence, doping level dependence, and field dependence are all contained in the theory. A striking feature of the calculation is the marked dependence of the dc mobility dropoff upon interface quality as measured, e.g., by the interface charge density. This suggests that the low-field mobility provides a good monitor for process control in device fabrication and that greater control may lead to sharper turn on, lower leakage, or closer threshold tolerances especially for low-voltage complementary metal-oxide-semiconductor (CMOS) applications.
Fabrication of flexible superconducting Nb3Al tape
Authors: Harasyn D. E. , Toth L. E.
Published: February 2003

Flexible tapes of Nb3Al were prepared by cold welding sheets of niobium and aluminum in a rolling mill followed by a brief high-temperature heat treatment. They were also prepared by a vapor deposition process followed by heat treatment under a high aluminum vapor pressure. Superconducting layers were typically 1 mil thick and had Tc’s in the range 16–18 K. Jc(H) measurements indicate that properly prepared Nb3Al tapes can carry large current densities (8×104 A/cm2 at 70 kOe). Present research shows that considerable metallurgical difficulties, associated with the high reaction temperatures and brittleness of the Nb3Al phase, need to be overcome before these processes can become commercial.
Determination of suprathermal electron distributions in laser-produced plasmas
Authors: Slivinsky V. W. , Kornblum H. N. , Shay H. D.
Published: February 2003

A K-edge filter technique was used to measure absolutely the x-ray emission from laser-heated CD2 plasmas from 1 keV to above 100 keV. A Nd : glass laser system supplied a focused pulse of about 25 J in 4 nsec. The measurements clearly differentiate the suprathermal from the thermal portion of the x-ray spectrum. Thus, for the first time, we can determine the relative intensity of the high-energy x rays. The results are compared with two-dimensional energy-transport hydrodynamic code calculations.
Effect of negative ions on current growth and ionizing wave propagation in air
Authors: Kline Laurence E.
Published: February 2003

The spatiotemporal development of electron and ion densities, electric fields, and luminosity are calculated for electron pulse experiments in overvolted parallel-plane gaps by numerically solving continuity equations together with Poisson’s equation. Experimental coefficients for primary ionization, cathode photoemission, photoionization, and luminosity are used. Unambiguous determination of the coefficients for attachment, detachment, and charge transfer is not possible from available experimental results. Therefore, the calculations are repeated for three sets of coefficients for these processes, corresponding to the following assumptions: unstable negative ions, stable negative ions, and no negative ions. The results of the calculations show, in each case, that the electron pulse initiates an avalanche which grows exponentially until the onset of space-charge effects. The calculated growth rate is strongly affected by the assumed attachment, detachment, and charge-transfer coefficients. When the total number of electrons in the avalanche reaches ∼108, anode- and cathode-directed ionizing waves, or streamers, develop from the avalanche and produce a weakly ionized filamentary plasma. The calculated ionizing wave velocities are strongly increasing functions of the space-charge–enhanced electric field within the waves and are insensitive to the assumed attachment, detachment, and charge-transfer coefficients. The numerically calculated ionizing wave velocities are in approximate agreement with a simple analytical theory.
The mechanism of spark breakdown in air at atmospheric pressure between a positive point and a plane. I. Experimental: Nature of the streamer track
Authors: Marode E.
Published: February 2003

The behavior of a point to plane discharge has been analyzed electrically and optically for centimetric gaps in air at atmospheric pressure. This shows that for both steady and pulsed applied potentials the evolution always consists of the sequence: primary streamer, secondary streamer, dark space (more or less pronounced), transient arc. Experiments are presented that are directed towards obtaining an indication of the physical meaning of these different phases. A time-resolved spectroscopic analysis leads to an evaluation of the electron energy within the secondary streamer of ∼1.4 eV. This indicates that the secondary streamer does not correspond to a very strong ionizing region. Three significant observations have been obtained using a device that is able to distinguish between conduction and displacement currents: (i) the secondary streamer occurs within a conducting filament built up by the primary streamer, (ii) when the primary streamer arrives at the plane, a cathode region appears giving continuity between the collected current at the plane and that flowing in the conducting filament, and (iii) there is a strong injection of negative charge into the gap from this cathode region. Finally, by varying the oxygen partial pressure, it is shown that the current within the discharge is mainly due to electrons. These results lead to a model of the discharge evolution in which the filament track of the primary streamer can be considered as a transient positive column of a glow discharge, whose cathode region is formed when the primary streamer arrives at the cathode. The secondary streamer thus appears to be the luminosity of a positive column.
Time and space resolution of bulk acoustic waves generated concomitantly with Rayleigh surface waves by an interdigital transducer
Authors: Nall B. H.
Published: February 2003

Surface acoustic waves (SAW) and unwanted bulk acoustic waves (BAW) are radiated simultaneously from an interdigital transducer in commonly used SAW crystal substrates. This is a report of tracking BAW groups in their initial passages through a crystal. Directly radiated BAW phase fronts are time resolved via tone burst drive and photomultiplier scan of diffraction patterns produced by a 6328-Å laser probe interacting with the BAW. Laser tracking of the paths of the energy radiation shows sharply defined BAW beams in 9.5×9.5×26-mm specimens. Identity of modes, radiation angles, measured counterclockwise from the backward SAW path, and the approximate amplitudes, measured relative to the SAW or to the main BAW lobe are as follows: (a) In Y-cut Z-propagating (PPG) LiNbO3 there are (i) equal longitudinal lobes (LL) at 37 ° and at 81 ° with relative amplitudes (RA) <0.04; (ii) Y-Z shear lobes (SL) at 28 °, 54 °, 114 °, and 162 ° with RA’s of 0.12, 0.12, 0.15, and 0.35. (b) In X-cut Z-PPG LiNbO3 there are (i) a LL at 40 ° with RA <0.04; (ii) X-Z SL at 24 °, 28 °, and 71 ° with RA’s of 0.35, 0.10, and 0.10; and (iii) a tangential SL at 32 ° with RA of 0.08. (c) In X-cut Y-PPG quartz there are LL at 54 ° and at 90 °; RA’s are 0.15 and 0.3. (d) In ST-cut quartz there are (i) a LL at 26 ° with RA=0.10; (ii) Y′-X SL at 10 °, 21 °, and 27 °, with RA’s of 0.15, 0.40, and 0.15. (e) In [111]-cut [11̄0]-PPG BGO there LL at 53 ° and 90 °; RA’s are 1.0 and 0.9. (f) In [1̄1̄2]-cut [111]-PPG BGO there are LL at 87 °, 108 °, and 143 ° with RA’s of 0.6, 1.0, and 0.4. In (b) – (e) there is mirror image radiation in the fourth quadrant. The most surprising result here is the presence of broadside radiation. An adequate theoretical explanation is not yet available.
Grain-boundary electrotransport of liquid zones in thin metal films
Authors: Howard J. K.
Published: February 2003

The electrotransport of liquid alloy zones in polycrystalline metal films has been investigated. The experimental results suggest that the liquid forms. preferentially, at grain-boundary triple points and then is electrotransported along the boundaries. It is proposed that the direction of zone motion can be predicted from the slope of the liquidus and the electron-scattering cross sections for the constituents of the alloy. Experimental results for the Al-Sn system support this proposal. In particular, the velocity of the liquid zone was measured and the result was used to compute the quantity 〈D〉Z*=−5.6×10−6 cm2/sec at 240 °C. Here 〈D〉 represents the apparent diffusion coefficient for the liquid alloy, and Z* represents the effective charge of the solute, which is proportional to the electromigration driving force.
Ultrasonic modulation of light with a liquid crystal in the smectic-A and nematic phases
Authors: Bartolino R. , Bertolotti M. , Scudieri F. , Sette D. , Sliwinski A.
Published: February 2003

An acoustic light modulator, using a liquid crystal (CBOOA) in nematic or smectic phase, is presented. It is shown that with good acoustical matching it is possible, in the nematic phase, to have a modulation of light from very low frequencies up to about 1 MHz, at the least. To the authors’ knowledge this is the first time that modulation has been observed at such high frequencies in the acoustic domain. This behavior is explained as a consequence of the elastic properties of the nematic. Some interesting results are also obtained which follow the behavior of the modulation vs temperature. In the smectic phase it is shown that it is possible to have a modulation only at very high frequencies, as one would expect from the elastic properties of this phase.
Field electron cathode stability studies: Zirconium/tungsten thermal-field cathode
Authors: Swanson L. W. , Martin N. A.
Published: February 2003

The emission angular distribution, total energy distribution, noise spectrum, and emitter life have been measured for the W/Zr thermal-field cathode. The results give an emitter life in excess of 1000 h at T=1350 to 1450 K, P?2×10−8 Torr, and a total current of ∼100 μA. A low-noise highly confined beam long the (100) direction can be obtained. A source brightness of 1010 A/cm2 sr at 3 kV and an energy spread of less than 0.9 eV were measured under operational conditions.
Gas-phase electrochemistry. I. Electrocapillary effects at the mercury-gas interface
Authors: Oref I. , Nemirovsky Y.
Published: February 2003

The first phase of a systematic study of the electrochemical phenomena at the metal-gas interface is presented. An experimental and theoretical analysis of the phenomenon of electrocapillarity at the metal-gas interface is described. Experimental curves of the relative reduction of surface tension vs applied potential were obtained at the interface between a mercury electrode and vacuum or He, HBr, and ethanol at various bulk pressures. The electrocapillary curves resemble the theoretical electrocapillary curves obtained from first principles. The potential of the maximum surface tension is at zero voltage. At 4 kV the surface tension decreases significantly. The variation in the surface tension at this voltage is about 100 erg cm−2. The electrocapillary curve at the mercury-He interface approaches the ’’vacuum’’ curve. The effect of ethanol involves an absolute depression of the surface tension, but the general shape remains the same as that of He. The HBr curve differs from all others due to surface reactions.
A correlation method for semiconductor transient signal measurements
Authors: Miller G. L. , Ramirez J. V. , Robinson D. A. H.
Published: February 2003

A wide variety of experiments in semiconductor physics involve the observation of a particular class of time-dependent transient signals; namely, decaying exponentials. Such signals are characteristic of systems relaxing back to equilibrium following an abrupt change in the populations of carriers occupying the available states. The magnitudes of such signals indicate the density of states involved, while the decay time constants (as a function of temperature) provide information on the energy level of the states in question. As such, both the amplitudes and the time constants of such signals are of physical interest. The problem of processing such signals has been examined using the theory of linear filtering and as a result a special purpose signal processor has been developed. This processor performs a continuous real-time cross correlation between the experimental signals and an appropriately synchronized locally generated exponential waveform. The resulting system has been used to process signals from transient space-charge measurements on reverse-biased gold-doped silicon junction diodes, providing both correlation spectra that yield energy levels and also trap profiles that expose the spatial distribution of the gold inside the junctions.
Study on the anomalously high photovoltaic effect in germanium thin films
Authors: Ma William , Anderson R. M. , Hruska S. J.
Published: February 2003

The physical and electrical properties of obliquely vacuum-deposited germanium films are studied. The deposition angle, defined as the angle between the source flux and the substrate plane, ranged from 15 ° to 75 °. The magnitude of the photovoltage and the film resistivity decreases as the deposition angle increases. Various amounts of high-purity oxygen and nitrogen are introduced during the film deposition and the effects upon the film characteristics are observed. The photovoltage produced by these films upon illumination are examined. The photovoltages are typically reproducible within a factor of 4 or less. The maximum variation in photovoltage among supposedly identical films is less than a factor of 8. Both the magnitude and the polarity of the photovoltage can be controlled. The amount of nitrogen during deposition, from PN2≈1×10−6 to 1×10−4 Torr, has little effect upon either the photovoltage or the film resistivity. The amount of oxygen during deposition, from PO2≈1×10−6 to 1×10−4 Torr, alters the photovoltage and the resistivity drastically. The magnitude of the photovoltage and the film resistivity increases as the amount of oxygen during deposition increases. For 15 ° samples the average measured photovoltage magnitudes are 76.0, 27.6, and 12.3 V/cm for samples deposited in PO2≈1×10−4, 1×10−5, and 1×10−6 Torr, respectively; for 60 ° samples the average measured photovoltage magnitudes are 1.02, 0.58, and 0.125 V/cm. The average resistivity of the 15 ° samples is 2.10×108 and 9.18×106 Ω cm for samples deposited in oxygen partial pressure of 1×10−4 and 1×10−6 Torr, respectively. The corresponding average resistivities for 60 ° samples are 3.86×107 and 3.26×105 Ω cm. In addition, the polarity of the photovoltage reverses as the partial pressure of oxygen during deposition is increased from 1×10−5 to 1×10−4 Torr. The magnitude of the photovoltage is directly related to the resistivity of the films. The photovoltage increases as the thickness of the film increases. No relationship between the photovoltage and the film thickness gradient is observed. X-ray diffraction measurements indicate that the films are amorphous. ESCA investigation of the films indicates that the freshly deposited films consist of germanium and its associated oxides. ESCA study of aged films indicates that the films deposited in nitrogen atmosphere consist primarily of Ge and two oxides or hydroxides, while the films deposited in oxygen atmosphere consist primarily of Ge and one oxide or hydroxide. All films contain oxygen; however, no nitrogen is present in the films (even films deposited in high nitrogen partial pressures). A qualitative film structural model, based on nucleation and growth phenomena, is proposed to explain the observed effect.
Nondestructive inspection of transparent microtargets for laser fusion
Authors: Stone R. R. , Gregg D. W. , Souers P. C.
Published: February 2003

The method is described for the nondestructive inspection of small (<100-μm outside diameter) hollow thin (<2-μm wall thickness) transparent shells used as laser-fusion targets. Utilizing the interference properties of light, this method enables measurements of sphericity and absolute wall thickness to accuracies better than ±10%. The equipment and calibration procedure are discussed.
Glow discharge optical spectroscopy for microvolume elemental analysis
Authors: Greene J. E. , Sequeda-Osorio F. , Natarajan B. R.
Published: February 2003

Glow discharge optical spectroscopy (GDOS) is an analytical technique whereby neutral sample atoms are sputtered into a glow discharge, excited by inelastic electron collisions, and decay emitting a characteristic luminescence which is monitored. We have shown that GDOS is capable of quantitative elemental analysis of microvolume solid samples and exhibits no evidence of ’’matrix effects’’. The sensitivity of GDOS for several different metallic and semiconducting elements has been determined and the variation in sensitivity for the elements studied is in the range of one order of magnitude. The present minimum detectable concentrations range from approximately 0.1 to 50 ppm for sputtering rates of 2 μg/sec and the possibility of reducing these detection limits seems quite good. Precipitated alloy samples studied by GDOS were found to exhibit radical changes in surface topography after short periods of sputtering. The precipitates sputtered slower than the bulk and formed protrusions above the sample surface. Surface topographical changes during sputtering appear to be the ultimate limit to GDOS depth resolution.
Photocurrents and photoconductive yield in MOS structures during x irradiation
Authors: Farmer J. W. , Lee R. S.
Published: February 2003

Photocurrents and photoconductive yield have been studied in the SiO2 layer of MOS structures during x irradiation. Electrode effects were also studied. The study shows that electron injection into the oxide is not important at low doses and dose rates, but electron injection from electrodes becomes significant when sufficient space charge accumulates in the oxide to reduce the barrier at the Si-SiO2 interface. The data reported here are consistent with a model where the holes are mobile in SiO2 but are preferentially trapped at the Si-SiO2 interface. Photoconductive yield measurements exhibit a field dependence which is inconsistent with a model based on the Onsager theory of geminate recombination. Charge generation due to the dissociation of excitons is suggested as a possible mechanism to account for the observed field dependence of the yield.
Heavy-ion sputtering yields of gold: Further evidence of nonlinear effects
Authors: Andersen H. H. , Bay H. L.
Published: February 2003

The sputtering yield of vacuum-deposited gold targets has been measured with 18 different 45-keV ions throughout the periodic system. The results are compared with previously reported results obtained with copper, silicon, and silver targets and with the predictions of the Sigmund theory. The variation in the yield with projectile atomic number is found to be consistent with theory although rather large deviations are found for both heavy and light projectiles. The large experimental yields for heavy projectiles as well as the maximum in the energy dependence of the yield, which is more pronounced than predicted by theory, are explained by nonlinear effects in very dense collision cascades. This interpretation is supported by data obtained from irradiation with atomic and molecular ions of the same elements. The deviations for light projectiles are considered mainly to be due to the lack of a surface correction term in the theory.
Evidence of absence of electrode-limited conduction in thin (≳140 Å) Ta2O5 films
Authors: Young Peter L.
Published: February 2003

We report room-temperature high-field (E≳106 V/cm) electrical conduction measurements in ’’flaw-free’’ thin Ta2O5 films (140–2400 Å), with gold and aluminum counterelectrodes. The experimental results rule out electrode-limited conduction even though dlogi/dV1/2 corresponds to the Schottky process.
A spontaneous current from the metal(1) -polymer-metal(2) system
Authors: Ieda Masayuki , Sawa Goro , Nakamura Shyuhei , Nishio Yoji
Published: February 2003

The spontaneous current Is is found from the metal-polyethylene terephthalate-metal (M1-PET-M2) system in the high-temperature region, 80–150 °C. The open-circuit voltage difference is also observed, both the sign and the magnitude of which are determined solely by the combination of M1 and M2. It is suggested that the spontaneous current is due to an electromotive force, possibly associated with an oxidation-reduction reaction at the electrode metals.
Control of the uniaxial magnetic anisotropy in LPE-grown iron garnet films by small ruthenium substitutions
Authors: Krumme J. P. , Hansen P. , Bartels G. , Mateika D.
Published: February 2003

The stress-dependent part Kλu of the uniaxial magnetic anisotropy constant Ku in epitaxial ferrimagnetic garnet films can be tailored in a wide range to the desired magnitude by slight substitution of ruthenium ions, which affect Ku via the magnetostriction constant λ111. For Gd2.7Yb0.3Fe4.8−xRuxAl0.2012 this quantity Kλu is varied in the range 0⩽Kλu≲2300 erg cm−3 where 0⩽x≲0.02. Thereby, other technical constraints determining the chemical composition of such films can be kept practically unchanged.
Reflectance of a powered sample immersed in a liquid
Authors: Simmons E. L.
Published: February 2003

Reflectance theories have sometimes been tested in the past using powdered samples immersed in various liquids as a means of varying the relative index of refraction. It is shown here that the measured reflectance of such samples is not equal to the true diffuse reflectance of the powder because of reflection of light back onto the
Reduction of cw laser melt-through times in solid materials by transverse gas flow
Authors: Robin James E. , Nordin Paul
Published: February 2003

The effects of a subsonic transverse gas flow over a solid target surface irradiated by a high-energy cw laser are investigated. The coupling of gas-flow energy into the melt layer amplifies Kelvin-Helmholtz–type capillary instabilities. The subsequent breakoff and entrainment of the top of these unstable waves provides the mechanism which reduces the melt-through time tb for finite-thickness slabs. The analysis shows that for low to moderate laser power densities, the enhancement mechanism arises from melt removal thus increasing the heat conduction to the melt-solid interface, while for higher power densities the primary enhancement originates from suppression of front surface vaporization. The predicted behavior of tb with gas-flow Mach number agrees qualitatively with experimental results and shows that the observed increase in tb above Mach 0.5 is a natural consequence of the gas compressibility. The laser-induced melt is assumed to be incompressible and viscid, and the gas is assumed to be inviscid and to obey the equations of linearized compressible flow theory. The effect of surface tension at the gas-melt interface is also included.
Electron transport properties of thin copper films. I.
Authors: Suri Ritu , Thakoor A. P. , Chopra K. L.
Published: February 2003

The thickness dependence at 300 and 80 K of the electrical resistivity and its temperature coefficient, Hall coefficient, mobility, and thermoelectric power of as-deposited and annealed thin (< 1000 Å) evaporated polycrystalline copper films and films deposited at elevated temperatures have been studied. All transport parameters in carefully prepared and well-characterized films exhibit monotonically increasing size effects with decreasing film thickness. Both annealing and deposition at elevated temperatures cause considerable reduction of the ’’apparent’’ size effects in all the transport parameters of the room-temperature deposited films. A critical analysis of the observed size effects shows that the data in all cases depart markedly from the predictions of the Fuchs-Sondheimer theory (and also that of the Mayadas-Shatzkes theory which takes into account the grain boundary surface scattering). The departure from theory is different for each transport parameter. The annealing studies show that the enhanced size effects are due to the presence of a large concentration of structural defects in the films. The observed behavior may be understood by assuming the large concentration of point and/or line defects to decrease with film thickness and with annealing as well as deposition of films at elevated temperatures. The thermopower data suggest strongly that the large concentration of defects causes distortion of the Fermi surface and thereby a strong energy dependence of the mfp or relaxation time at the Fermi surface.
Monolithic Ga1−xInxAs mesa lasers with grown optical facets
Authors: Blum F. A. , Lawley K. L. , Holton W. C.
Published: February 2003

Optically pumped laser oscillation at 77 K has been observed in vapor-grown epitaxial Ga1−xInxAs (0⩽x⩽0.1) mesa structures which have vertical as-grown crystalline facets furnishing the optical feedback. Several hundred mesas were grown on a single slice using photolithography and selective vapor-phase epitaxy. The best mesas are flat to within a few hundred angstroms and the edges are very sharp and well defined. Details concerning the growth, morphology, and emission characteristics of the mesa lasers are given.
New interpretation of the far-infrared SO2 laser spectrum
Authors: Steenbeckliers Guy , Bellet Jean
Published: February 2003

The 32S16O2 laser spectrum is definitively identified. The ten transitions observed involve the Fermi resonance which mixes the vibrotational levels 3ν2,J15,J−15 and ν1+ν2,J13,J−13 of the ground electronic state, with J=29, 30, and 31. By using the value of 14.73 cm−1 for the anharmonic constant k122, the difference of the band centers (ν1+ν2)−(3ν2) is obtained with great accuracy; it is equal to 114.59±0.01 cm−1.
Dependence of gain on tube radius in CO2 waveguide lasers
Authors: Shirahata Hiromichi , Fujioka Tomoo
Published: February 2003

The wall depletion rate of the excited (0001) level of CO2 molecules was taken into consideration for the optical gain of a CO2 waveguide laser. The numerical calculation revealed that the change of the unsaturated gain has a maximum value with respect to the radius of the discharge tube, and the maximum point moves to a higher gain and a smaller radius with an increase in gas pressure.
Highly efficient frequency doubling of visible dye laser radiation in RDP
Authors: Kato K.
Published: February 2003

The highly efficient frequency doubling of the high-power visible dye laser radiation in rubidium dihydrogen phosphate (RDP) is reported. An over-all power conversion efficiency of 52% was obtained at a fundamental pump power of 7 MW at 6370 Å. In addition, the temperature variation of the birefringence of RDP has been measured to be d (ne2−n01)/dT= (1.1±0.1) ×10−5 °C−1.
The upper critical field of rf-sputtered WNx and MoNx films
Authors: Reichelt K. , Bergmann G.
Published: February 2003

The upper critical field and other electronic properties, such as resistivity, temperature coefficient of resistance, and the Hall constant of rf-sputtered WNx and MoNx films were measured. It was observed that the upper critical field is independent of the nitrogen partial pressure, whereas the resistivity is strongly affected. The structure and diffraction patterns of these films were also investigated by transmission electron microscopy (TEM). Our measured results are interpreted in terms of the influence of microscopic regions, which affect differently the normal and superconducting properties, as is found for NbNx films.