bluuebunny/crossref_metadata_2025 huggingface dataset:
Specimen replication for electron microscopy using x rays and x-ray resist
Authors: Feder Ralph , Sayre David , Spiller Eberhard , Topalian John , Kirz Janos
Published: February 2003

We point out the advantages of the use of x-ray resist as the recording medium in contact x-ray micrography, with subsequent viewing under the scanning electron microscope. Untreated specimens may be replicated with a resolution better than 100 nm. Photographs of latex spheres obtained by this technique are presented.
Particle size and strain broadening in energy-dispersive x-ray powder patterns
Authors: Gerward L. , Mo/rup S. , Topso/e H.
Published: February 2003

An energy-dispersive x-ray method for a rapid analysis of the broadening of diffraction lines in powder patterns has been developed. Experimental results are given for magnetite powders with sizes in the range 50–200 Å and compared with the results of standard angle-dispersive diffractometry and electron microscopy. The greatest advantages of the energy-dispersive method compared with the angle-dispersive method are the absence of the Kα doublet, the simultaneous recording of a large part of the diffraction pattern, the fast data accumulation, and the adaptability of the technique to in situ studies. The method should be of special advantage for the study of solid-state reactions and processes such as sintering.
Bombardment-enhanced diffusion of arsenic in silicon
Authors: Maby E. W.
Published: February 2003

A theoretical model which describes a diffusion process enhanced by ion bombardment has been investigated for the case of arsenic in silicon. The model predicts a spatially variant diffusion coefficient of the form D*f (x,Ld), where Ld is an unknown constant characteristic of the diffusing medium and presumably independent of the diffusing species. An experimental value for Ld was determined which agrees well with the theory, but differs from the value obtained for boron in silicon.
Photoelectron microscopy of organic surfaces: The effect of substrate reflectivity
Authors: Dam Rudy J. , Griffith O. Hayes , Rempfer Gertrude F.
Published: February 2003

Photoelectron measurements of thin organic films deposited on a metal substrate may contain information from deep within the sample, derived from reflected ultraviolet light. This effect depends on the reflectivity of the substrate, the sample thickness and optical absorption coefficient, and the photoelectron escape depth. Calculations are given for phthalocyanine as a specific example. Contrast reversal and apparent see-through effects resulting from reflection are predicted in overlapping thin films. Photoelectron micrographs of thin films and grid patterns of phthalocyanine show that the reflection model is essentially correct. This effect can be substantially reduced by using a nitrocellulose-coated carbon substrate.
Theory of the inverted Lamb dip with a Gaussian beam
Authors: Maeda Hisatoshi , Shimoda Koichi
Published: February 2003

A theoretical calculation of one round trip of a Gaussian beam propagating in an absorbing gaseous medium is carried out. The inverted Lamb dip is found to be distorted in shape. Shifts of the center frequency are numerically obtained for several values of the beam parameters.
Capture cross section and trap concentration of holes in silicon dioxide
Authors: Ning T. H.
Published: February 2003

Hole trapping in thermally grown silicon-dioxide films has been studied using optically induced hot-hole injection in p-channel polysilicon-SiO2-silicon field-effect-transistor structures. Analysis of the data assuming a uniform trap distribution and no detrapping gives 3.1×10−13 cm2 and 1.4×1018 cm−3 for the capture cross section and the trap concentration, respectively. Initial hole-trapping efficiency is almost 99% for a 1000-Å SiO2 film.
Optical method for determining the grain resistivity in ZnO-based ceramic varistors
Authors: Philipp H. R. , Levinson Lionel M.
Published: February 2003

An optical technique for evaluating the grain resistivity in ZnO ceramic varistors is described. It is based on the existence of a rather sharp minimum in the infrared reflectance whose wavelength position depends on the free-electron density and hence on the ZnO grain resistivity. Values of resistivity obtained from optical measurements are in good agreement with those obtained using alternative evaluation techniques.
High magnetic field dependence of the Hall coefficient in n-type germanium and in other semiconductors with ellipsoidal surfaces of constant energy
Authors: Partain L. D. , Lakshminarayana M. R.
Published: February 2003

The linear dependence of the Hall coefficient on one over the magnetic field squared at high-field strength has been derived using Boltzmann transport theory results for high-symmetry-orientation semiconductor samples with ellipsoidal surfaces of constant energy such as n-type germanium and silicon. This treatment justifies the practice of linearly extrapolating such Hall coefficient data to infinite fields to obtain the net carrier concentration. Comparison to experimental data taken on n-type germanium at 77 °K shows that the theory accurately perdicts the slope of this straight-line variation. A criterion is developed in terms of the conductivity mobility and the anisotropy of effective mass and scattering which specifies how large the magnetic fields must be to allow this extrapolation to be performed accurately. It is shown that up to 90% errors are obtained when a single scattering mechanism correction factor is applied to low-field Hall coefficient data to estimate carrier concentration in the n-type germanium samples studied.
Asymmetric line shapes of localized optical excitations in condensed systems
Authors: Tyner C. E. , Drotning W. D. , Drickamer H. G.
Published: February 2003

The configuration coordinate model is a useful approximation for describing localized excitations (absorption and emission) in condensed systems. It is frequently applied assuming Gaussian peaks. At ordinary temperatures there are two causes of asymmetric peaks. The problem of small relative displacement along the configuration coordinate has been discussed at length. It results in a high-energy tail on the absorption peak mirrored by a low-energy tail for emission. For a number of systems where the relative displacement qo along the configuration coordinate is large, asymmetries are observed which do not fit the above pattern. Jacobs and Thorsley have discussed this case in some detail. It is, however, difficult to use their equations directly to extract configuration coordinate parameters from experimentaly data. Experimentally observed absorption or emission peaks can be fit by a log-normal distribution function which establishes two parameters, b and E1/2. By an extensive series of numerical calculations based on their equations, we have developed a series of simple equations relating b and E1/2 and configuration coordinate parameters. We present these relationships and discuss briefly their application.
1/f noise as a nonstationary process: Experimental evidence and some analytical conditions
Authors: Tandon J. L. , Bilger H. R.
Published: February 2003

Evidence is presented to support the hypothesis that physical systems in thermodynamic nonequilibrium possess, among other fluctuation phenomena, nonstationary noise with a true 1/fα-power spectral density over all frequencies, and that such spectra are stable. Some consequences of this hypothesis are derived, and a class of time-dependent autocorrelation functions for such a process is proposed.
A note on the kinematical theory of x-ray diffraction from concentration profiles
Authors: Mittemeijer E. J. , Delhez R.
Published: February 2003

A note is presented on the kinematical theory of x-ray diffraction from a diffusion zone in a monocrystalline system as given by Houska. Assuming a linear variation of spacing in a coherently diffracting domain it is possible to simplify the treatment of diffraction from a diffusion zone by definition of one factor which characterizes the shape of the intensity function. This treatment may have special importance for certain types of powder samples in which the same concentration profile is present in each particle.
Normal-mode surface waves in the pseudobranch on the (001) plane of gallium arsenide
Authors: Stegeman G. I.
Published: February 2003

It is shown that two directions exist on the (001) plane of gallium arsenide for which the pseudobranch reduces to normal-mode surface waves; one corresponds to the usual saggital-plane surface waves along [110] and the second to a nonsaggital-plane SAW at 32.89 ° from the x axis.
Anisotropy of the transverse magnetoresistance in cubic magnetite at room temperature
Authors: Kostopoulos D. , Alexopoulos K.
Published: February 2003

The room-temperature transverse magnetoresistance of cubic synthetic magnetite was measured for various field strengths, with the field rotated within the (110) plane. The results can be interpreted as being due to a linear negative term and a positive term that saturates beyond 4 kG. The negative term is isotropic whereas the positive one is anisotropic, being largest for the [11̄0] and decreasing to about zero for the [001] direction.
Impurity and vacancy states in PbTe
Authors: Bauer G. , Burkhard H. , Heinrich H. , Lopez-Otero A.
Published: February 2003

We report measurements of the Hall effect and the transverse magnetoresistance of n- and p-type PbTe with carrier concentrations as low as 1.8×1016 cm−3 in magnetic fields up to 15 T. The data rule out the existence of deep impurity levels and are, however, not in contradiction with the presence of resonant levels due to Pb or Te vacancies within the bands according to the model by Parada and Pratt.
Dense-plasma production by a liquid-cathode arc
Authors: Thiell G. , Rosseler A. , Fabry M.
Published: February 2003

We describe an experimental apparatus allowing the study of a dense arc plasma generated between a solid anode and a liquid-potassium cathode.
Premelting in alkali halides due to the thermal formation of dislocations
Authors: Robinson W. H.
Published: February 2003

In a recent paper Allnatt and Sime described some high-temperature electrical-conductivity experiments on sodium chloride and potassium chloride in which the activation enthalpy for the conductivity was 110–210 eV and 440 eV, respectively. In this paper we suggest that the rapid rise in conductivity is due to the enhanced diffusion of charged defects along thermally formed dislocations. We present a formula for the conductivity along thermal dislocations and using it we calculate entropies of 1150k–2190k for NaCl and 4750k for KCl. Together with the high enthalpies these entropies are consistent with the Gibbs’s function for the formation of thermal dislocations approaching zero at the melting point, implying that on melting the crystal is highly dislocated.
Application of stochastic hopping transport to hole conduction in amorphous SiO2
Authors: McLean F. B. , Ausman G. A. , Boesch H. E. , McGarrity J. M.
Published: February 2003

Charge relaxation in MIS capacitors, employing a thin film of amorphous SiO2 as the gate insulator, was studied as a function of time and temperature following exposure to a pulsed 12-MeV electron beam. The results can be explained by rapid transport of the radiation-generated electrons to the electrodes followed by a much slower temperature-activated transport of the holes, which dominates the charge relaxation at observable times. It is shown that a stochastic transport model based on a continuous time random walk provides a good description of the data.
The nature of the pyroelectric effect of faulted ZnS crystals
Authors: Yacobi B. G. , Brada Y.
Published: February 2003

The pyroelectric effect (PE) in faulted ZnS crystals was studied experimentally in the temperature range from 100 to 300 °K. It has been found that the observed voltage pulses are due to a special pyroelectric effect which is not connected with the temperature dilation of the unit cell or any resulting change in the value of its dipole moment. The observed pyroelectric effect has been correlated with built-in electric fields in faulted ZnS crystals. Its temperature dependence is attributed to the different magnitude of the temperature dependence of the dielectric constants in the different ZnS crystal structures.
Defect structure induced during forward-bias degradation of GaP green-light-emitting diodes
Authors: Petroff P. M. , Lorimor O. G. , Ralston J. M.
Published: February 2003

This paper reports evidence of a degradation-induced defect structure in green GaP light-emitting diodes (LED’s). The defect structure in undegraded diode material has been characterized by transmission electron microscopy (TEM). The main defects consist of pairs of dislocations and single dislocations in the n and p epitaxial layers. The origin of these dislocation pairs is traced to dislocation loops in the substrate or at the n-layer–substrate interface. The TEM observations in slowly degraded LED’s indicate that bulk electroluminescence degradation phenomena may be accounted for by the formation of new dislocations in the vicinity of the p-n junction. These new dislocations appear during forward biasing of the device by climb of the original dislocations in the epitaxial layers. This defect structure, which is composed of helical dipoles and dislocation loops, resembles that reported in rapidly degraded GaAlAs-GaAs (DH) lasers suggesting that the degradation mechanisms for both the green GaP LED’s and laser devices may be similar.
Epitaxial growth of GaAs from thin Ga solution
Authors: Doi A. , Asano T. , Migitaka M.
Published: February 2003

Thin GaAs layers are grown by liquid-phase epitaxy from thin Ga solutions (0.25–10 mm) using a horizontal sliding boat. The thickness of the GaAs layers is compared with theoretical values which were calculated assuming that the growth process is diffusion controlled. Numerical calculations are done on the growth rate, layer thickness, and As concentration in the Ga solution assuming a critical supercooling of 6 °C obtained by an experiment. The experimental values agreed well with the calculated values. It was found that the thickness of the GaAs epitaxial layer could be controlled by the following five growth parameters: initial temperature, initial supercooling, cooling rate, solution thickness, and growth duration.
Logic design of Josephson network
Authors: Nakajima K. , Onodera Y. , Ogawa Y.
Published: February 2003

New logic circuits are designed which employ as information bits the flux-quantum vortices occurring in Josephson junctions of extended dimensions. It is shown that Josephson lines can be interconnected in certain direct ways so that complete logic capability can be achieved with networks of Josephson lines alone.
Comparison of long- and short-range magnetic-order development in Ni3Mn
Authors: Patton Carl E. , Baker Glenn L. , Vardeman Michael
Published: February 2003

The magnetic-order development in polycrystalline Ni-Mn alloys near the Ni3Mn composition has been studied as a function of atomic ordering during anneal at both 500 °C (short range) and 400 °C (long range) after an initial quench from 1000 °C. The data were analyzed using a simple Langevin superparamagnetism model to obtain a qualitative description of the magnetic-cluster-growth kinetics in each case. For annealing at 500 °C, the clusters seem to ’’pop in’’ during the initial 5-min anneal, remain at constant concentration up to 3–5 h, and then decrease in concentration. The cluster moment increases smoothly, with a roughly exponential time dependence and a time constant of about 20 h. For annealing at 400 °C, the behavior is reversed. The moment remains constant for annealing times up to 200 h. The concentration increases continuously and evidences no saturation at the 200-h time limit of the present data.
Temperature-induced magnetization reversal in an amorphous ferrimagnet
Authors: Venturini E. L. , Richards Peter M.
Published: February 2003

Both temperature- and magnetic-field-induced magnetization reversals have been studied near the compensation temperature Tcomp in rf-sputtered amorphous Gd-Co thin films using a vibrating sample magnetometer. The net magnetization in these films goes smoothly through zero at T=Tcomp and can be switched through 180° from a metastable state opposite to the applied magnetic field direction to a stable state parallel to the field by varying either the temperature or the field strength. If the reversal occurs through a uniform rotation of the magnetization, a simple two-magnetic-sublattice model allows an effective anisotropy energy Keff to be determined from the switching data. Keff exhibits the same anomalous decrease near Tcomp as previously reported using magnetic resonance and static magnetization data.
Effects of focused collisions on shock-wave propagation in crystalline solids
Authors: Brinkman J. A.
Published: February 2003

Focusing phenomena of the type encountered in radiation damage processes are shown to exist when shock waves of sufficient energy are produced in monatomic single crystals. The energy range in which such focusing becomes important is that in which the compressive shock-wave stresses are large relative to the inherent mechanical strength of the solid material, typically 1–25 eV per atom. Thus it is shown that the crystalline structure and orientation can be important in the high-energy regime in which material has generally been considered to behave as an inviscid compressible fluid, deforming by hydrodynamic flow. The dynamic propagation of edge dislocations at supersonic velocities is also predicted as a consequence of the operation of focused collision processes.
Approximate theory of power extraction from a multiline cw gas-dynamic laser cavity
Authors: Brunné M. , Milewski J. , Stánco J. , Zieliński A.
Published: February 2003

Based upon the rate equation formalism the problem of the existence of different longitudinal modes within the active cavity of a cw gas-dynamic laser is considered. The flat parallel mirror cavity supplied with a fast transverse flow of the optically active medium is analyzed. The analytical formulas for the total output power and laser efficiency are given as well as for the single-line output and single-line load coefficients (efficiencies). The CO2 and/or CO2/N2/H2O(He) molecular mixture is kept in mind as a practical analogue for the optically activated medium under consideration. A numerical example concerning a cw gas-dynamic laser driven by benzene combustion in air is presented.
Electron velocity distributions, fractional energy transfer, and collision rates for potential Na, NaHe, and NaXe electrically excited laser discharges
Authors: Schlie LaVerne A.
Published: February 2003

The Boltzmann transport equation including elastic, inelastic, ionization, electron-electron, and electron-ion interactions has been numerically solved to determine the electron velocity distribution, the fractional electron energy transfer, and the collision rates for potential Na, NaHe, and NaXe electrically excited laser discharges. Previously reported theoretical and experimental cross-section data from the literature were used in the calculations. Na, like all of the alkali atoms, has a very large cross section (∼4×10−15 cm2) for electronic excitation of the first level (an allowed optical resonant ns→np transition). This value greatly exceeds all other low-energy inelastic cross sections for both the Na and the He and/or Xe buffer gases. Such a combination of cross sections enables the input electron energy to be very efficiently transferred to the potential upper laser level, Na(3 P). The computed distribution functions are shown to be strongly non-Maxwellian and exhibit an energy variation indicative of this large resonant cross section in Na. Using the electron energy conservation equation reveals that indeed the electronic excitation of the Na first level dominates the electron energy exchange processes for the Na and the Na He/Xe mixtures. For example, in pure Na 100% of the electron energy is transferred to the Na(3 P) state in the E/N range 5×10−16 to 5×10−15 V cm2. In both the NaHe (1:99) and the NaXe (1:7600) mixtures, over 90% of the electron energy is transferred to this same Na(3 P) level in the E/N range of 5×1017 to 4×10−16 and (1.2–7) ×10−17 V cm2, respectively. At the second Na electronic level, 4P, electron energy transfer is down from that of the Na(3 P) by nearly three orders of magnitude for all of the mixtures. For the optimum values of E/N as cited above the mean electron energy for the Na, NaHe, and NaXe mixture lies in the range 0.6–1.4, 0.92–2.4, and 1.2–2.7 eV, respectively. Also, the normalized collision rates, ν/N (cm3 sec−1), for the Na(3 P) level are shown to have a value approximately 10–100 times that calculated for the normalized vibrational excitation rates of CO and CO2 laser discharges. These high pumping rates are a direct result of the large resonant transition cross section and give these systems excellent potential for high-power high-efficiency cw laser operation. Other discharge transport properties, like drift velocities and characteristics energies, are presented. Electron-electron interactions have negligible effects on the ’’tail’’ of distribution for partial ionization ratios, ne/N, values up to 10−3 due to the large Na(3 P) inelastic cross. The results and their generalizations to all the alkali systems along with recommended cross-section data needed are discussed.
Mechanical response and thermal coupling of metallic targets to high-intensity 1.06-μ laser radiation
Authors: Hettche L. R. , Tucker T. R. , Schriempf J. T. , Stegman R. L. , Metz S. A.
Published: February 2003

Mechanical response and thermal coupling measurements are reported for aluminum and titanium targets exposed to high-intensity 1.06-μ laser radiation. Measurements are made in air and vacuum for pulse lengths from 1 to 100 μsec, providing incident fluences of between 106 and 108 W/cm2. Total momentum delivered to the target and time-resolved pressure developed over the target surface were measured at irradiances spanning the threshold for laser-supported detonation (LSD) wave ignition. The slope of the impulse/energy ratio shows a marked discontinuity at LSD threshold intensity. Peak target surface pressure is found to increase as the 2/3 power of the beam intensity in agreement with the hydrodynamic model of LSD wave propagation. Thermal coupling coefficients α for Al and Ti drop continuously from ∼0.3 to 0.07 over the intensity range examined. This behavior is consistent with the presence of an optically absorbing plasma at the target surface. The decrease in α is attributed to an increase in the plasma propagation velocity with intensity.
Loss measurements in GaAs and AlxGa1−xAs dielectric waveguides between 1.1 eV and the energy gap
Authors: Merz J. L. , Logan R. A. , Sergent A. M.
Published: February 2003

Loss measurements in thick dielectric slab waveguides of GaAs cladded by AlGaAs liquid-phase-epitaxy layers have been made utilizing spontaneous Raman scattering. In these experiments, incident radiation at 1.06 μm is focused onto a cleaved edge of the waveguide layer and Raman-scattered photons are detected at 90°. The attenuation of the resulting signal is measured as a function of the propagation distance along the guide. Spatial resolution of 0.2–0.5 mm has been achieved for samples 3–5 mm long. Results are reported for a variety of GaAs waveguide layers, including lightly doped p-type layers, n-type layers varying between 1016 and 1018 cm−3, and AlxGa1−xAs waveguide layers with x?0.1. For waveguides with impurity concentrations above the mid-1017 cm−3 range, the loss is dominated by free-carrier absorption, but for relatively pure layers of GaAs and AlGaAs a residual loss well below 1 cm−1 is observed. Transmission measurements as a function of photon energy between 1.1 eV and the energy gap of the material show that the losses are approximately constant in this energy range.
Flux pinning in bronze-processed Nb3Sn
Authors: Luhman Thomas , Pande C. S. , Dew-Hughes David
Published: February 2003

Superconducting critical currents have been measured at 4.2 K and applied magnetic fields up to Hc2 for a series of solid-state processed-Nb3Sn conductors. Variations were made in the alloy content of the matrix and core as well as heat-treatment times at 700 °C to produce a wide range of superconducting critical currents. The pinning-force density, Fp (=Jc×B), plotted as a function of reduced field, h (=H/Hc2), exhibits a peak, Fpmax, at a reduced field hp. Fpmax varies from 81×108 dyn/cm3 at hp=0.2 to 18×108 dyn/cm3 at hp=0.32. The high values of Fpmax for these samples are related to Nb3Sn grain sizes which are 1000 Å or less. At 2 kG the flux-line lattice spacing is approximately 1000 Å or nearly one flux line per grain. Kramer has proposed a model to account for flux pinning in such hard type-II superconductors, and while the pinning-site density in the present samples is near the upper limit to which Kramer’s model was meant to apply, it is possible to interpret the present data using his model. The dynamic pinning force fs (h) calculated by Kramer for flux-lattice shear around pinning sites too strong to be broken by the Lorentz force has the magnetic field dependence h1/2 (1−h)2. In the high pinning-density limit where √ρ=1/2a0, ρ being the pinning density and a0 the flux-line lattice spacing, the magnetic field dependence of fs (h) must be changed to h3/2 (1−h)2/(h1/2−n)2, where n equals (φ0ρ/Hc2)1/2, by incorporating the field dependence of a0. Using this new field dependence enables a prediction of Fpmax, and associated hp values, which fit the present data for bronze-processed Nb3Sn. It is concluded that near the upper limit of pinning density to which the theory applies a sharp increase in Fpmax may occur without significant shifts in hp to lower values. This result is added to the model’s prediction for lower pinning-density materials, i.e., when lower values of Fpmax increase there is a shift in hp to smaller values.
Long-term frequency and intensity stabilization of a cw dye laser
Authors: Abate J. A.
Published: February 2003

A method to stabilize the output frequency and intensity of a cw dye laser for periods of several hours is described. The dye laser frequency is controlled by a servo system which locks it to a Lamb-dip stabilized He : Ne laser to an accuracy better than 1 MHz with the help of a scanning Fabry-Perot interferometer. The dye laser intensity is controlled to better than 1% by direct control of the pumping source.
Coupled-mode theory of Raman amplification in lossless optical fibers
Authors: Capasso F. , Di Porto P.
Published: February 2003

Raman amplification in weakly guiding optical fibers is investigated for the two cases of weak and strong mode coupling. Use is made of the statistical ensemble of similar fibers introduced by Marcuse for studying mode coupling in optical waveguides. In the weak-coupling case, the Stokes powers of different modes increase independently, and the gain of each mode depends on the initial poewrs of all laser modes. In the strong-coupling case, power equipartition between Stokes modes takes place throughout the fibers, and the common gain is the average of the individual mode gains.
Electronic-circuit analogue of a two-level homogeneous medium
Authors: Carruthers J. A. , Hoschette J. , Tsang P.
Published: February 2003

Simple electronic circuits have been developed to give both the transient and steady-state response of a homogeneous resonant medium for various input waveforms. The circuits represent an analogue approach to obtaining solutions to the polarization equations for the saturable medium, and there are obvious equivalences between parameters of the medium and various voltages, currents, etc., of the circuit. The circuit analogue has obvious value for instructional purposes in spectroscopy, lasers, etc., but also offers promise of providing solutions for such difficult problems as pulse propagation in an inhomogeneous laser gain medium.
Spectroscopic properties and laser performance of Nd3+ in lanthanum beryllate
Authors: Jenssen H. P. , Begley R. F. , Webb R. , Morris R. C.
Published: February 2003

The neodymium-doped lanthanum beryllate (La2Be2O5 : Nd3+ or BEL : Nd) laser crystal is monoclinic, space group C2h6-C2/c. The fundamental vibration directions of light and the corresponding refractive indices have been determined as a function of wavelength. At 1 μm the indices are nX=1.9641, nY=1.9974, and nZ=2.0348. The energy levels of Nd3+ for the five lowest manifolds are presented. The low concentration limit for the Nd3+ 4F3/2 fluorescent lifetime in this crystal is 150 μsec and the two observed laser transitions have stimulated emission cross sections of 2.1×10−19 cm2 for E∥X and 1.5×10−19 cm2 for E∥Y. The laser wavelengths are 1.070 and 1.079 μm, respectively. In laser testing a higher slope efficiency was obtained in La2Be2O5 : Nd than in Y3Al5O12 : Nd (YAG : Nd). A Q-switched output of 450 mJ from a 6.4-mm-diam by 76-mm-long X-axis rod of BEL : Nd has been achieved for the 1.079-μm transition, while a YAG : Nd rod of the same size in the same system yielded 160 mJ. The higher Q-switched output in BEL : Nd is consistent with the lower stimulated emission cross sections as compared to that of YAG : Nd.
Optically pumped superfluorescent Na2 molecular laser
Authors: Henesian M. A. , Herbst R. L. , Byer R. L.
Published: February 2003

We have optically pumped an Na2 molecule at 0.473 and 0.659 μm and obtained superfluorescent laser emission on a series of green and yellow molecular B-X–band transitions and laser oscillation in the near infrared on A-X–band transitions. Pump saturation, laser gain, and laser saturation intensity are reported.
Liquid-crystal orientation induced by polymeric surfaces
Authors: Dubois J. C. , Gazard M. , Zann A.
Published: February 2003

Orientation induced on liquid crystals by plane polymeric surfaces has been investigated. Thin polymerized films were prepared from hexamethyl disiloxane, methyl methacrylate, and isobutylene by a glow-discharge process; from γ glycidoxy-propyl-trimethoxy silane by dip coating; from polytetrafluoroethylene by sputtering. Critical surface tension γC of each film and surface tension γLV of various pure nematic compounds were measured, and orientation induced by the former on the latter was tested. When γC is very low, in front of γLV, very good homeotropic structure is observed. Conversely, high-energy surfaces seem to induce homogeneous structure.
Interaction of metal layers with polycrystalline Si
Authors: Nakamura K. , Olowolafe J. O. , Lau S. S. , Nicolet M-A. , Mayer J. W. , Shima R.
Published: February 2003

Solid-phase reactions of metal films deposited on 0.5-μm-thick polycrystalline layers of Si grown by chemical vapor deposition at 640 °C were investigated by MeV 4He backscattering spectrometry, glancing angle x-ray diffraction, and SEM observations. For the metals Al, Ag, and Au, which form simple eutectics, heat treatment at temperatures below the eutectic results in erosion of the poly-Si layer and growth of Si crystallites in the metal film. Crystallite formation is observed at T≳550 °C for Ag, T ≳400 °C for Al, and T ≳200 °C for Au films. For the metals Pd, Ni, and Cr, heat treatment results in silicide formation. The same initial silicides (Pd2Si, Ni2Si, and CrSi2), are formed at similar temperatures on single-crystal substrates.
Backscattering analysis of the composition of silicon-nitride films deposited by rf reactive sputtering
Authors: Mogab C. J. , Lugujjo E.
Published: February 2003

Amorphous silicon-nitride films prepared by rf sputtering of an 8-in.-diam silicon target in a nitrogen discharge have been analyzed using 1.8-MeV-4He-ion backscattering to determine the dependence of film composition on the discharge pressure and rf power. Films with thicknesses between 1000 and 2200 Å were deposited on (111) silicon substrates at pressures ranging from 2 to 20 mTorr and rf power densities between ∼1 and 5 W/cm2 of target area. The target-to-substrate spacing was held constant at 5 cm. Film composition, measured as the silicon-to-nitrogen ratio (NSi/NN), was found to be uniform through the film thickness (with a depth resolution of ∼350 Å) and across the substrate surface. However, films deposited in separate runs under closely controlled and nominally identical conditions exhibited variations in NSi/NN of up to 8%. The silicon-to-nitrogen ratio (NSi/NN) in the deposited films varied from approximately 0.60 to 0.80 over the range of power and pressure investigated. The observed dependence of composition on the nitrogen discharge pressure exhibited similar features at all power densities. At the lowest pressures employed (2–4 mTorr) the films were always nitrogen rich as compared to the stoichiometric compound Si3N4. As the nitrogen pressure was increased up to ∼8–10 mTorr the films became progressively less nitrogen rich. Beyond this point the composition tended to a value (NSi/NN) nearly independent of pressure, but dependent on the rf power density. The pressure dependence of composition is consistent with reaction occurring at the substrate. The tendency for films to become less nitrogen rich with increasing nitrogen pressure is attributed to a reduction in the flux of chemisorbable nitrogen species at the substrate as pressure is increased.
Space-resolved spectra of laser-produced plasmas in the XUV
Authors: Feldman U. , Doschek G. A. , Prinz D. K. , Nagel D. J.
Published: February 2003

Monochromatic images of laser-produced plasmas have been obtained in the 200–550-Å region using a slitless normal-incidence spectrograph. The plasmas were produced by subnanosecond 1016 W cm−2 irradiation of thick and thin targets containing a wide variety of elements. The XUV emission is observed to extend several millimeters from the target surface. Secondary regions of emission were frequently observed 2–3 mm from the target. The regions of plasma emission usually lie along the direction of the incident laser pulse. The ions present in the spectra are formed at electron temperatures that range from ∼7×105 to ∼7×106 K. Density-sensitive spectral line ratios are used to show that the plasma electron density decreases by no more than an order of magnitude over a few millimeters. Similar spectra were observed on both sides of 7-μm Fe foil irradiated with a 100-psec pulse, implying a penetration velocity on the order of 107 cm sec−1. It was deduced from spectra of thin foils that the penetration of the laser pulse used is about 10 μm of iron. A technique is proposed for obtaining time- and space-resolved spectra over time intervals of a few tens of picoseconds. The imaging properties of the slitless spectrograph and a method of improving the spatial resolution of the instrument are discussed in the Appendix.
Viscoelastic relaxation of hexanediol in prefreezing region
Authors: Kono R. , Yoshizaki H.
Published: February 2003

Ultrasonic shear relaxation data are reported for the associated liquid hexanediol-1,6 at frequencies between 8.6 and 750 MHz in the temperature range 43–70 °C. The data in the vicinity of the freezing point indicates a single relaxation time. This is the only liquid measured in the associated liquids which exhibits a single relaxation time. Above 45 °C, the results obtained are interpreted in terms of additive contributions to ρVs′2, comprising (1) a relaxation process at relatively high frequencies which follows the single relaxation; (2) a limited summation of relaxation processes at lower frequencies originating from the Rouse mode motion in concentrated polymer solution. Agreement is found between experimental results and the calculated behavior based upon the sum of the above two separate relaxation processes. The strong temperature dependence of the limiting shear modulus at high frequencies is thought to be due to the transformation from a two-dimensional to a linear polymer structure.
An approximate analytical model for the late-stage sintering of an array of rods by viscous flow
Authors: Cosgrove G. J. , Strozier J. A. , Seigle L. L.
Published: February 2003

The late stages of sintering of a linear array of rods by viscous flow have been studied theoretically. An approximate model in which the actual interface profile is assumed to be locally planar has been developed. Within the framework of the model, analytic solutions to the steady-state Navier-Stokes equations have been derived and the course of sintering followed by advancing the profile through a sequence of short-duration time intervals. After each step the profile is mathematically redefined and new values for the velocities and pressure calculated. In the later stages a logarithmic plot of the reduced neck radius versus time displays a distinctly nonlinear character. Thus the kinetics cannot be described by a simple exponential function as can the early stages when Kuczynski’s geometric simplifications remain valid. A comparison between the two models reveals the rate of neck growth in the later stages to be significantly less for the locally planar interface model. It is suggested that this reduction is due to a lower stress gradient for the flow or material into the neck as a result of the dependence of stress in the neck region upon the changing curvature everywhere.
Electron mobility in epitaxial silicon near a sapphire substrate
Authors: Lehovec Kurt , Lin Shi-Tron
Published: February 2003

A test structure comprising an interdigital silicon network is used to obtain the silicon sheet resistance and the space-charge capacitance adjacent to a sapphire substrate by applying distributed network analysis. The bulk carrier mobility and impurity concentration are determined from these data by a new method which is independent of interface states. An electron mobility of 1200 cm2/V sec in the silicon beyond 0.2 μ from the sapphire interface is found with a marked decrease as the interface is approached.
Contact currents in silicon nitride
Authors: Arnett P. C. , DiMaria D. J.
Published: February 2003

Simultaneous dark-current and flat-band–voltage measurements on metal-Si3N4-Si capacitors were used to deduce Si-Si3N4 contact-current–contact-field characteristics under positive and negative voltage bias. Whereas total-current–average-field characteristics are functions of counterelectrode material and nitride thickness, these contact-current–contact-field characteristics were dependent solely on the local properties of the Si-Si3N4 interface. Fowler-Nordheim analysis of the contact characteristics assuming 2-eV barrier heights as determined by internal photoemission indicated low effective masses of 0.05–0.13m0 for electrons and 0.005m0 for holes. Alternatively, use of an effective mass of 0.4m0 (as observed in SiO2) led to effective barrier heights of 0.8–1.2 eV for electrons and 0.44 eV for holes. Several mechanisms, including trap-assisted tunneling, are discussed which could account for different dark-current and photoemission barrier heights. In addition, simultaneous photocurrent and flat-band–voltage measurements as a function of voltage bias were performed to assist in determining the dominant photocurrent carrier type (electrons or holes) and the limiting photocurrent mechanism (contact or bulk).
Strain-enhanced superconductivity in crystalline Te-Ge-As alloys
Authors: Gerber J. A. , Sample H. H. , Neuringer L. J.
Published: February 2003

The superconducting properties of crystalline Te-Ge-As alloys were studied using electrical, magnetic, and specific-heat measurements. The experiments were carried out in the range 0.05–4.2 K and in magnetic fields up to 15 kG, sufficient to quench the superconductivity in our samples. In addition, the structural properties of the alloys were studied by x-ray diffraction and scanning electron microscopy. The crystalline Te-Ge-As alloys formed with excess (greater then 50 at.%) Te were comprised of Te plus a Te-GeTe laminar structure. The superconducting transition temperatures of Te-rich alloys of this system are greater than those of bulk GeTe. We attribute the enhanced transition temperatures observed for these alloys to the existence of strains induced in the GeTe regions by the laminar structure of the specimens. For the alloy (Te0.81Ge0.15As0.04) with the highest transition temperature (Tc=0.8 to 0.9 K), we have calculated the values of the following superconducting parameters: Hc(0), ξ (0), κ (0), and Hc1(0).
A concept of lubrication in finger joints
Authors: Pagowski S. , Munro M. , Piekarski K.
Published: February 2003

From a previous study it was found that both sliding and rolling are present during finger joint articulation. The rolling tends to pump synovial fluid through the joint gap. A typical finger joint is modeled and expressions are obtained for this fluid flow. A range of values for the coefficient of friction which are quite close to measured values is obtained. An estimate of joint spacing is also determined.
Electrical properties of iron oxide-polyethylene glycol humidity-sensitive elements
Authors: Nicholas M. E. , Pitkanen D. E. , Lavine C. F. , Zook J. D. , Hagen G. P.
Published: February 2003

Films of α-Fe2O3 particles in a polyethylene glycol matrix exhibit electrical properties which are strong functions of relative humidity. Electrical impedance measurements over the frequency range 10−3–105 Hz were used to establish equivalent circuits for the samples including the electrodes. The variation of the equivalent-circuit elements with electrode geometry can be used to give a simple physical interpretation to the equivalent-circuit elements. We conclude that the humidity response is associated with the bulk resistance of the glycol. This resistance is dependent upon ion mobility which in turn depends on the viscosity. Viscosity is, of course, a function of water content. The resistance is in series with the electrode capacitance due to dipole double layers. By a suitable choice of electrode geometry, the impedance of the series capacitance will be negligible at a convenient operating frequency.
Electromagnetic generation of electronically steered ultrasonic bulk waves
Authors: Moran T. J. , Panos R. M.
Published: February 2003

The frequency dependence of the propagation direction of ultrasonic shear and longitudinal waves generated by a meander-line electromagnetic transducer (EMAT) at MHz frequencies has been determined. The results are found to agree well with theory and demonstrate that electronic beam steering is possible using EMAT’s. The relative efficiency of generation in aluminum was also studied and, for a specific meander-line geometry with a permanent magnet providing the necessary static magnetic field, it was found to be relatively flat versus frequency. Efficiency for shear-wave generation (frequency range, 5–9 MHz) was about 4 dB per conversion less than the Rayleigh-wave generation efficiency at 4.6 MHz, and for longitudinal waves (frequency range, 10–24 MHz) about 10 dB less.
Effect of the magnetic linewidth of YIG on the propagation characteristics of magnetoelastic Rayleigh waves
Authors: Parekh J. P.
Published: February 2003

The effect of magnetic loss in YIG on the propagation characteristics of magnetoelastic Rayleigh waves is determined for the case of propagation on a (100) YIG surface in the direction of a [001]-oriented tangential bias field. The maximum absorption rate of the surface waves decreases with increase in the magnetic linewidth, but because of the nonresonant nature of the surface waves the leakiness of these waves is a stronger determining factor of the absorption rate.
Resistance variation and field effects in thin gold films after growth in an electric field
Authors: Andersson Thorwald
Published: February 2003

The film resistance has been monitored during the deposition of gold onto glass at room temperature in UHV. The film structure during the growth could be related to the depositing resistance and to the resistance during aging after halts in the deposition. In the discontinuous stage the tunneling length of electrons increases exponentially with aging times larger than 2 h. The electric-field-dependent resistance was measured 20 h after deposition. An Ohmic region at low fields was followed by a region proportional to the square root of the applied field.
Pressure shear waves in fused silica
Authors: Abou-Sayed A. S. , Clifton R. J.
Published: February 2003

Simple wave solutions are presented for the case of pressure shear waves in a hyperelastic material which models fused silica. The adiabatic strain energy function of this material is written as an expansion to third-order terms in the strains. The analysis includes interaction of the simple waves with a free surface. Comparison of computed particle velocity-time profiles for the free surface with profiles observed in experiments shows good agreement. The solutions also indicate that the shear wave propagating in a shear-strain-free region of fused silica is essentially nondispersive.
Phase transition in NaNO3
Authors: Johnson E. R. , Frances A. , Wu C. Cm.
Published: February 2003

A new phase transition occurring in NaNO3 at about 260 °K in both cooling and heating cycles is reported. The transition is associated with an expansion of the lattice resulting in approximately a 3.6% decrease in the density.
Photoelectronic properties of high-resistivity GaAs : O
Authors: Lin Alice L. , Omelianovski Eric , Bube Richard H.
Published: February 2003

The photoelectronic properties of high-resistivity n-type GaAs : O have been investigated through measurements of dark conductivity and Hall effect, optical absorption, photoconductivity, and photo-Hall effect as a function of photon energy, light intensity and temperature, optical quenching of photoconductivity, and thermally stimulated conductivity. The results of all measurements can be described consistently by a four-level model (0.5, 0.7, 1.0, and 1.25 eV below the conduction band edge) plus eight electron trapping states (with depth between 0.15 and 0.54 eV) common to many different types of high-resistivity GaAs. At 82 °K, illumination with photons of energy between 1.0 and 1.25 eV produces a major shift in the photoconductivity toward p type and a persistent quenching of n-type photoconductivity that recovers abruptly only upon warming above 105 °K. Low-frequency photocurrent oscillations are associated with the 1.25-eV level. The capture cross section of five of the electron trapping states is small [(5–8) ×10−19 cm2)] and decreases with electric field.
Effects of inhomogeneities on the parametric excitation of the upper-hybrid resonance
Authors: Chan V. S. , Seshadri S. R.
Published: February 2003

The effects of the inhomogeneities of the number density and the magnitude of the magnetostatic field on the characteristics of the parametrically excited instability of the extraordinary mode near the upper-hybrid resonant frequency are investigated for the case in which the pump wave and the backscattered idler wave are both ordinary modes. The three interacting waves propagate parallel to a given direction perpendicular to the magnetostatic field whose direction remains unchanged throughout the warm plasma of infinite extent. The parametrically excited instability of the upper-hybrid wave is of the convective or the absolute type according to whether the effective wave number has a linear or a quadratic profile. For both types of instabilities, there are two threshold values for the amplitude of the pump field and they correspond to the requirements for overcoming the damping losses and the convective losses. Numerical results for the various threshold amplitudes are presented as functions of the strength of the magnetostatic field. The inhomogeneities generally increase the various threshold amplitudes as compared to the case of a homogeneous plasma.