bluuebunny/crossref_metadata_2025 huggingface dataset:
cw chemical lasers pumped by vibrational energy transfer: CO/CO2 and CO/N2O
Authors: Petersen Alan B. , Wittig Curt , Coleman Paul D.
Published: February 2003

A continuous-wave chemical laser has been constructed which produces simultaneous output from CO and either CO2 or N2O laser species. Excitation of the CO is chemical, via the O+CS→CO†+S reaction, and excitation of the triatomic is by vibrational energy transfer from CO†. Output powers of ≳3.0 W and ≳0.6 W have been obtained from CO and the triatomics, respectively.
dc analysis of parallel arrays of two and three Josephson junctions
Authors: Tsang Won-Tien , Van Duzer T.
Published: February 2003

Arrays of Josephson junctions are becoming of increasing interest, and the dependence of the maximum zero-voltage current on various factors is important in applications. When the array carries the maximum possible zero-voltage current it is said to be in the critical state. Sets of equations describing the critical-state behaviors of arrays of two and three junctions are derived. Account is taken of possible differences of the individual critical currents, self-induced flux, and asymmetric current feed. In a space having the phase differences across the junctions as coordinates, one can construct a locus relating the phase differences that are obtained when the array is in the critical state. It is shown that the periodic, symmetric, and other properties of the various relationships between variables can be inferred from the properties of the phase-difference locus.
Lithium neodymium tetraphosphate laser
Authors: Otsuka Kenju , Yamada Tomoaki , Nakano Jun’ichi , Kimura Tatsuya , Saruwatari Masatoshi
Published: February 2003

Laser action at λ=1.047 μm is reported in a lithium neodymium tetraphosphate crystal (LNP; LiNdP4O12) pumped longitudinally with a rhodamine 6G laser (λ=5965 Å) or a chopped Ar ion laser (λ=5145 Å). Comparing the measured threshold and round-trip loss of the resonator of the LNP laser with that of the Nd:YAG laser, the effective emission cross section for the ion in the 4F3/2 manifold of LNP is found to be 1.65 times that of Nd:YAG.
Interdiffusions in thin-film Au on Pt on GaAs (100) studied with Auger spectroscopy
Authors: Chang C. C. , Murarka S. P. , Kumar V. , Quintana G.
Published: February 2003

It has been proposed that interdiffusion of Pt, Au, and GaAs constitutes one major source of instability in GaAs microwave devices with Pt/Au metallization. In order to determine the extent of interdiffusion of these materials, preparations of Pt/GaAs and Au/Pt/GaAs were heat treated over the range 250–500 °C, and chemical depth profiles were obtained by measuring the surface composition with Auger electron spectroscopy while ion milling. Platinum films were 125–9000 Å thick. When Pt/GaAs was heated in vacuum, the Pt-GaAs interaction initiated with a rapid migration of Ga into Pt and simultaneous formation of an As-rich layer at the Pt/GaAs interface. Gallium eventually traveled the entire thickness of even the 9000-Å Pt film while arsenic stopped abruptly at a distance ∼2/3 of the way into the Pt. Little or no Au was detected (<1 at.%) in the Pt or GaAs after extensive Pt/GaAs reaction in Au/Pt/GaAs. The reacted Pt film displayed a multilayered structure with each layer containing different amounts of Ga, As, and O. Pt/GaAs heated in air behaved similarly with two added features: a surface layer containing mostly Ga and O formed over the Pt, and oxygen diffused through the (reacted) Pt to form an oxygen-rich layer at the Pt/GaAs interface. Interdiffusion (during air anneal) was found to be reduced when the GaAs was oxidized prior to Pt deposition.
Influence of the mercury vapor pressure on the isothermal growth of HgTe over CdTe
Authors: Svob L. , Marfaing Y. , Triboulet R. , Bailly F. , Cohen-Solal G.
Published: February 2003

The theory developed in the preceding article is applied to the epitaxial growth of HgTe on a CdTe substrate under isothermal EDRI conditions. In the absence of excess mercury, two different growth conditions can be distinguished. In the high-temperature case, pure HgTe is present at the surface of the epitaxial layer and the layer thickness is proportional to the square root of the Hg vacancy diffusion coefficient and of the vacancy concentration gradient. At low temperature (<450 °C), a CdHgTe solid solution exists at the surface of the epitaxial layers; its thickness depends linearly on the coefficient of interdiffusion and on the mercury concentration gradient at the surface. Mercury in excess influences the rate of interdiffusion, the evaporation of mercury from the substrate, and therefore the interdiffusion coefficient as well as the layer thickness and the surface composition. It was found that the interdiffusion coefficient D (varying between 0.5 μ2/h for cadmium-rich alloys and 100 μ2/h for mercury-rich compositions) decreases with increasing excess mercury pressure. This variation of the interdiffusion coefficient (only a high-temperature growth is considered here) leads to the final expression for the layer thickness as a function of the excess mercury pressure p0:e=e0√t exp(−kp0). From this formula it is seen that the time dependence of the layer thickness is not influenced by the presence of excess mercury. The surface composition depends only on p0 and not on time. Up to 4 atm, the cadmium content at the surface increases linearly with p0. For p0 ≳ 4 atm the growth of the layer is completely inhibited. These results are discussed on the basis of a mercury vacancy balance in the substrate and in the epitaxial layer. Vacancies created by the Kirkendall effect either diffuse towards the epitaxial layer surface or are annihilated by interaction with mercury diffused from the vapor phase. From the discussion of both mechanisms (taking into account that the layer thickness increases as √t) it follows that the average vacancy concentration and, consequently, the interdiffusion coefficient are independent of time, as is experimentally observed.
Estimation of frequency shift of an ion sound wave parametrically excited in Tonks-Dattner resonance
Authors: Ikezawa Shunjiro , Okuda Takayoshi
Published: February 2003

It is shown that the frequency shift of the excited ion sound wave in Tonks-Dattner resonance is due to the nonlinear phenomenon represented by the frequency-mismatched factor of the nearly free resonance parametric theory derived by Nishikawa. It is also shown that the increase of the electron temperature is negligibly small so that the effect of the increase of the electron temperature on the shift can be neglected.
Experimental study of propagation of electrostatic ion waves in a magnetic field
Authors: Lee A. , Oleson N. L. , Jones W. D.
Published: February 2003

The results of an experimental investigation of electrostatic ion waves in an rf-generated argon plasma supported by a longitudinal magnetic field is presented. For off-axis wave propagation, observations agree quite well with the theoretical predictions of Joyce and Dory. Observations for parallel propagation, however, yield a dispersion curve exhibiting structure not predicted by linear theory.
p-n junction formation by Te+ ion implantation into solution-grown Pb1−xSnxTe
Authors: Kato Y. , Katayama Y. , Kobayashi K. L. I. , Komatsubara K. F.
Published: February 2003

The ion implantation of Te+ is used to convert layers of n-type Pb1−xSnxTe into p type. A Te+ ion concentration of greater than 1×1015 cm−2 and a suitable postanneal produce a p-type layer about 1 μm thick on the surface of n-type Pb1−xSnxTe.
Near-surface nucleation and crystallization of an ion-implanted lithia-alumina-silica glass
Authors: Arnold G. W.
Published: February 2003

Surface crystallization of a Au+-ion-implanted lithia-alumina-silica glass has been realized. Annealing of a glass sample implanted with 285-keV Au+ ions at 550 °C results in the growth of colloidal Au particles of 18–35-Å radius. The Au particles constitute sites for the precipitation of lithium metasilicate crystals at 550 °C. Further annealing at 750 °C allows the growth of quartz and β-spodumene crystals. The crystallized surface obtained after the high-temperature anneal was characterized by a Knoop microhardness number of 626, which is of the order of that obtained for commerical volume-crystallized glass-ceramics of similar composition.
Precursor decay in 1060 aluminum
Authors: Arvidsson Torkel E. , Gupta Y. M. , Duvall George E.
Published: February 2003

Pressure profile measurements for shock waves in 1060-0 aluminum show a decaying elastic precursor. Its amplitude diminishes from 1.06 kbar at a propagation distance of 1.38 mm to 0.53 kbar at 9.68 mm. Combining these precursor amplitudes with earlier measurements by others yields a curve of amplitude vs distance which runs from 1.38 to 25 mm. Decay rates obtained from this curve yield values of dislocation density 3–80 times greater than those inferred from etch-pit counts on polished surfaces. Rise times in the elastic precursor are greater at large distances than at small, suggesting effects of viscosity.
Low-temperature elastic constants of a superconducting coil composite
Authors: Weston W. F.
Published: February 2003

A resonant piezoelectric oscillator method for measuring elastic moduli was applied to composite materials. The complete set of elastic compliances of a superconducting coil composite was determined semicontinuously between 4 and 300 K. Also, two moduli of a layered fiber-glass–epoxy composite were determined; this composite is essentially the matrix material of the coil composite. The Young’s moduli, shear moduli, Poisson ratios, and elastic stiffness coefficients are also reported. Results agree closely with elastic data obtained by conventional testing methods.
Structure and properties of the system: poly(2,6-dimethyl-phenylene oxide) isotactic polystyrene. Wide-angle x-ray studies
Authors: Hammel R. , MacKnight W. J. , Karasz F. E.
Published: February 2003

PPO/iPS blends of various compositions have been crystallized isothermally and by solvent-induced treatment from the glassy state. The crystallinity as a function of composition has been determined from the integral scattering of the crystalline and amorphous regions. Applying Hosemann’s concept of the paracrystal, crystallite size and strain parameters have been calculated from peak broadening analysis. The results are compared to those obtained from DSC and small-angle x-ray measurements on the same samples.
Kinetic behavior of the thermal and mechanical properties of segmented urethanes
Authors: Wilkes Garth L. , Wildnauer Richard
Published: February 2003

Commerical and experimental urethane polymers were studied by thermal-mechanical methods including DSC and stress-strain analysis. The studies reveal that following thermal treatment these polymers show time-dependent mechanical properties. This time-dependent period may be many days while the degree of this dependence is influenced by annealing temperature. By DSC analysis it has been shown that the glass transition temperature of the soft segment, Tgs, is also greatly influenced by annealing treatment. Immediately following annealing temperatures above 130 °C, Tgs may be as much as 40 °C higher than its ’’long-time’’ value. With time, however, Tgs decreases to its original value. Higher-temperature endothermic behavior associated with hard-segment domains is also time dependent. Both the degree of Tgs shift and higher endothermic effects are correlated with annelaing temperature. The time-dependent behavior for a given annealing temperature has been related to to chemical structure (ester vs ether, and hydrogen bonding effects). The data are explained in terms of the thermal stability of domains.
Rate-determining factors for enthalpy relaxation of glassy polymers. Molecular weight
Authors: Marshall A. S. , Petrie S. E. B.
Published: February 2003

In order to obtain information concerning the effect of molecular weight on the molecular mobility involved in the relaxation processes associated with the nonequilibrium thermodynamic state of glassy polymers, enthalpy-relaxation studies have been undertaken on glassy atactic polystyrenes of various molecular weights, ranging from 2.0×103 to 811×103. As was found in previous studies of enthalpy relaxation in organic glasses, the glass transition temperature Tg is the principal rate-determining factor. From a more detailed analysis of the data, however, it is evident that the relaxation processes at corresponding temperature intervals below Tg are a function of the molecular weight. The relaxation rate decreases somewhat with increasing molecular weight and approaches a limiting value at molecular weights in the vicinity of 50×103, the critical molecular-weight range in the molecular-weight dependence of glass transformation. For Aroclor 5460, a nonpolymeric material of lower molecular weight but having a Tg comparable to that of atactic polystyrene of molecular weight 2.0×103, a slightly faster relaxation rate was observed.
Electron-energy-loss study of the mercury chalcogenides
Authors: Katonak T. T. , Hengehold R. L.
Published: February 2003

Electron-energy-loss measurements have been made on crystals of HgSe, HgTe, and hexagonal HgS over the energy range 0–50 eV by reflection techniques. The measurements were made using electron-beam energies of 250 to 1000 eV from surfaces obtained by cleavage in ultrahigh vacuum. The resulting spectra showed structure dependent upon surface condition at 8.9, 9.1, and 8.1 eV in HgS, HgSe, and HgTe, respectively. This structure has been associated with surface plasmon excitation. Bulk plasma peaks were observed at 20.8, 17.2, and 14.7 eV and d-band transition peaks at 12.3 and 14.1 eV, 10.2 and 12.2 eV, and 10.2 and 11.8 eV, respectively, for HgS, HgSe, and HgTe. The large splitting of these latter peaks allows unambiguous identification as d-band transitions. The energies obtained from the energy-loss spectra are compared to those obtained from optical reflectivity and x-ray and uv photoemission.
Elastic and thermoelastic constants of nepheline
Authors: Bonczar L. J. , Barsch G. R.
Published: February 2003

The single-crystal elastic constants, their temperature coefficients, and the thermal expansion coefficients of natrual nepheline, (KAlSiO4)(NaAlSiO4)3, have been measured. The longitudinal modulus c11 and the shear modulus c66 have positive temperature coefficients. Since this implies the existence of a wide range of directions with a zero temperature coefficient of the ultrasonic travel time, nepheline may be a suitable substrate for ultrasonic surface-wave signal processing devices.
Work-function lowering by dielectric metal vapor (Hg, W, etc.)
Authors: Leycuras André
Published: February 2003

We show experimentally the role of electron thermal injection on the measurements of the electrical conductivity of dense mercury vapor. We propose an explanation of this increase of the thermal emission and apply it to high current emission observed in situations where a hot dense vapor is involved such as exploding wires, cathode spots, and metal surfaces irradiated by intense laser pulses.
Secondary electron emission induced by 5–30-keV monatomic ions striking thin oxide films
Authors: Dietz L. A. , Sheffield J. C.
Published: February 2003

We have made an experimental investigation of how ion velocity and angle of incidence affect the magnitude and uniformity of secondary electron yield from thin amorphous oxide films. Flat target surfaces of Al2O3 and BeO in a high vacuum of 10−8–10−9 Torr are bombarded with singly-charged positive ions of Li, Na, K, Rb, Cs, and Ni isotopes. Each of these elements has a different yield versus velocity response. Our data are consistent with Parilis and Kishinevskii’s prediction of a common velocity threshold. Our estimate of the threshold velocity is 5.5×106 cm/sec. For a given element we find, within our experimental error, that isotopes of different masses but with the same impact velocity produce identical average secondary electron yields. Furthermore, the statistical variances of their secondary electron frequency distributions also are identical. These results demonstrate the absence of an isotope effect on secondary electron emission. In general, secondary electron yield is not linear with ion velocity. Additional results are obtained for MgO and Ta2O5 surfaces. We find that secondary electron yield depends strongly on the electronic shell structure of a projectile ion, that is, on its atomic number Z. Our data can be interpreted qualitatively using the Fano-Lichten-Barat electron promotion model for ion-atom collisions when the Z’s are unequal. We describe a statistical model of secondary electron emission in which each ion-atom collision below a surface may result in the release of one or more electrons. In this model the random sequence or order in which target atoms are struck, the unequal amount of electronic excitation generated during collisions of a projecticle ion with different kinds of target atoms, and the electronic properties of an oxide surface are all factors which shape the frequency distribution of observed secondary electrons. Each ion impact produces a pulse of secondary electrons. A pulse is just the sum of many localized showers of electrons released along the path of a projectile ion, reduced by electron absorption in the target during diffusion of the internal secondary electrons to the surface and escape. The statistics of ion-induced secondary electron emission are described remarkably well by the Polya (negative binomial) distribution.
Near-field measurements of subnanosecond-created laser plasmas
Authors: Olsen J. N. , Mendel C. W.
Published: February 2003

The near field of expansion for plasmas created by a 40-psec 1.0–1.5-J laser has been probed to measure the electron density and local electric and magnetic fields. Holographic interferometry was used to measure the electron density in the range 1017 to 6×1018 cm−3 at delays of 2.5–22 nsec. Space-charge electric fields of up to 1900 V/cm were detected by deflection of a fast He+ ion beam probe as late as 26 nsec after irradiation. Spontaneous magnetic fields of up to 50 G, rising in 10 nsec, were seen 4 mm from the target, decaying rapidly and often reversing at 8 mm. The temperature in the blowoff estimated from the combination of local electric field and electron-density scale length is high compared to predictions based on a peak Te=160 eV inferred from a multichannel soft x-ray spectral analysis. An anisotropic fast ion group appears in the interferometric density profiles and ejection of ∼109 fast electrons is observed in the electric field measurements. These effects are compared to the early time ion collector signal and nonthermal x-ray spectrum, respectively.
Microstructure and flux pinning in commercial Nb-25% Zr superconducting wires
Authors: Santhanam A. T. , Moon D. M. , Mathur M. P. , Ashkin M. , Deis D. W.
Published: February 2003

A detailed structural examination was carried out on commerical Nb-25% Zr conductors which had been heavily cold worked and annealed in the temperature range 600–700 °C for times ranging from 1/4 to 10 h. The magnetization of some of these wires had previously been measured (Mathur et al.) as a function of applied magnetic field at temperatures ranging from 4.2 °K to the transition temperature and the results were interpreted in terms of a flux-pinning model proposed by Kramer. Additional magnetization measurments on larger-diameter wires were made to aid in the interpretation of the flux-pinning mechanisms. Transmission electron microscopy, x-ray analysis, and hardness measurements revealed that the predominant structural change in the annealed wires was recovery of dislocation structure. No βZr or αZr precipitates were detected. It is concluded that the optimum flux-pinning properties in Nb-25% Zr conductors for the processing schedules studied are associated with a highly recovered and small dislocation cell structure.
Spontaneous annihilations in magnetic bubble propagation
Authors: Callen Herbert , Doyle William D. , Seitchik Jerold
Published: February 2003

The mechanism of bubble annihilations during bubble propagation on T-bar circuits is analyzed. Particular emphasis is given to the observation that successive bubbles disappear with a logarithmic time dependence. A model is suggested in which the bubbles interact indirectly through the medium of remanent effects in the T-bar overlays, and it is shown that this model leads to the observed time sequence of annihilations. Several alternate models are discussed and are shown to be unacceptable. Experimental data in support of the remanent-interaction model are presented.
Instantaneous radial wall velocities in magnetic garnet bubble domains
Authors: Zimmer G. J. , Gál L. , Vural K. , Humphrey F. B.
Published: February 2003

Using an optical sampling microscope with a sample time of 10 nsec, single-exposure photographs of the transient bubble-domain configuration resulting from a uniform pulse field applied parallel to the bias field has been recorded at known times with respect to the applied pulse field. In this way the actual dynamic domain configuration of the bubble was observed. Mixed LPE garnet samples with a nominal composition of Y1.57Eu0.78Tm0.65Ga1.05Fe3.95O12 and material parameters, for nonimplanted (implanted), 4πM=184 (205) G, thickness is 6.8 (6.9) μm, Q=16.7 (16.6), α=0.026 (0.029), γ=1.1×107 rad/sec Oe, and A=2×10−7 erg/cm, were investigated. The radius of the bubble plotted as a function of the time delay between the leading edge of the expanding field pulse and the exposure, for delays less than 1 μsec, gave straight lines for all but the low pulse fields (<40 Oe). For these field pulses, a clear velocity saturation of 5.30±0.05 m/sec over the range 40<Hp<112 Oe was observed for the implanted sample. A less-pronounced velocity saturation of 5.8±1 m/sec over the range 40<H0<80 was observed for the nonimplanted sample. For higher field pulses, an increase in velocity with increased drive was observed with a mobility of 1.9 cm/sec Oe (0.87 cm/sec Oe) for the nonimplanted (implanted) from a threshold at about 80 Oe (112 Oe) with a zero field intercept at 4 m/sec. Low-drive data fit calculated curves that accounted for the changing effective drive field as the bubble expanded and assumed a simple mobility and saturation velocity. Bubble-collapse radial velocity measurements also indicated velocity saturation of 6.5 m/sec (5.5 m/sec) comparing favorably with the radial expansion measurements. This observed radial saturation velocity has the same value as the theoretical peak velocity of Slonczewski; the high-field mobility agrees with the Walker high-field limit.
Stripline coupling to Josephson oscillators
Authors: Ganz Tomas , Mercereau J. E.
Published: February 2003

The observation and analysis of self-induced steps in the current-voltage characteristics of superconducting quantum interference bridges, strongly coupled to superconducting microstrip cavities, are reported. A two-fluid model is used to analyze the results and estimate the amplitude of the oscillating supercurrent in the GHz range as a function of critical current.
Dynamic stability and quenching currents of superconducting multifilamentary composites under usual cooling conditions
Authors: Duchateau J. J. , Turck B.
Published: February 2003

Although the filaments in a composite are individually stable against the flux jump, the self-field of the conductor as a whole gives rise to stability problems. The way in which flux penetrates into the composite is determined by the apparent thermal and magnetic diffusivities. If the ratio of these two diffusivities is not small, the flux jumps can be slowed down. Therefore, it is too pessimistic to consider only adiabatic conditions in composites as usual. The differential thermal and electrical equations have been solved in the case of a cylindrical composite, taking into account the particular conditions of cooling. Stability of the composite is only achieved if a criterion more optimistic and realistic than the well-known adiabatic criterion is satisfied. Stability curves may be used to predict the degraded quenching currents of a composite in the presence of the flux jump if the thermal diffusivity and the enthalpy of the medium in contact with the conductor are included.
Domain wall kinetics in soft ferromagnetic metallic glasses
Authors: O’Handley Robert C.
Published: February 2003

Domain wall kinetics are studied in glassy iron-base wire and iron-nickel–base ribbon. These materials exhibit high wall mobilities. The wire is examined in a single-wall regime below the nucleation field. Here reversal takes place by propagation of a domain wall of 2.5-cm axial length along the wire. The mobility normal to the wall is 270 cm/sec Oe. In the case of glassy iron-nickel–base ribbon the number of walls taking part in reversal is measured to be two. Using this number, the wall mobility is 1700 cm/sec Oe. The viscosity limiting the wall mobility is partitioned into a (calculated) eddy-current contribution and a spin-relaxation contribution. The latter constitutes about 40% of the total viscosity in the wire and about 50% in the ribbon samples. Gilbert damping constants for these samples, 0.44 (wire) and 0.19 (ribbon), are small compared with similarly obtained values for comparable polycrystalline alloys.
Dielectrically induced surface waves and the magnetodynamic modes of a YIG plate
Authors: Parekh J. P.
Published: February 2003

The magnetodynamic surface and volume modes of a YIG plate metallized at one surface are described for the case of propagation at right angles to a tangentially applied bias field. The connection of the dielectrically induced surface wave on a YIG half-space to the magnetodynamic volume modes of a YIG plate is indicated.
Time variation of electron density in a pulsed He-Kr+ ion laser
Authors: Kato Isamu , Satake Toshiaki , Nakaya Masao , Shimizu Tukasa
Published: February 2003

The time variation of the electron density has been measured in the early afterglow of microwave-pulse excited He, Kr, and He-Kr gas discharges. It is observed that the decay of the electron density is mainly caused by volume recombination of electrons and ions, and that an ionization by He metastable atoms occurs in the afterglow plasma, and that about 2 μsec after, the decay of electron density decreases.
Electron transport properties of copper films. II. Thermoelectric power
Authors: Thakoor A. P. , Suri Ritu , Suri S. K. , Chopra K. L.
Published: February 2003

Thermoelectric power (TEP) of as-deposited and annealed polycrystalline and epitaxially grown copper films of thickness 100–5000 Å has been measured. The TEP increases with the film thickness to reach a saturation value at about 3000 Å. The thickness dependence decreases markedly with increasing annealing temperature and also with increasing temperature of deposition. The saturation value of the TEP of as-deposited films is about 1.5 times the bulk value of copper and decreases rapidly with annealing to approach the single-crystal bulk value. In sharp contrast to the behavior of the TEP, the resistivity and its temperature coefficient and the carrier concentration of the same copper films exhibit little size effects and insignificant changes due to annealing for thicknesses larger than 1000 Å. The observed thickness dependence of the TEP of unannealed and annealed films shows no agreement with the Fuchs-Sondheimer (F-S) theory. Further, there is no correlation between the thickness dependence of the TEP and the temperature coefficient of resistivity as expected on the basis of the F-S theory. Since the thickness variation of the TEP changes markedly with annealing, the observed dependence is not a genuine mean free path effect. The observed linear dependence of the TEP on the inverse of the film thickness (as expected from the F-S theory) is totally accidental and, therefore, physically meaningless values of U= (∂ lnl/∂ lnE)EF are obtained from the slopes of the lines. Arguments have been advanced to suggest that the observed thickness dependence of the TEP can be understood only in terms of the effect of a large thickness-dependent concentration of structural defects frozen in the metal films. The defect-induced changes in the TEP would be caused by the distortions in the Fermi surface and, hence, changes in the energy dependence of the mean free path or relaxation time at the Fermi surface.
Trap-perturbed emission-limited current in amorphous selenium films
Authors: Berg J. I. , Miller N. C.
Published: February 2003

The photoinduced discharge characteristics for positively charged amorphous selenium films were studied under constant light intensities chosen to give discharge times comparable to release times of holes from deep traps (approximately 7 sec). Hole mobilities, lifetimes, and field-dependent quantum efficiencies were measured by means of a pulsed-light technique. A modified light-discharge technique was used to measure trap release times. The discharge rate as a function of surface potential is expalined semiquantitatively in terms of a uniform space-charge model which includes the effects of decreased electron-hole generation rate because of trapped space charge, reduced carrier range because of capture of holes by traps, and the release and transport of holes captured at earlier times in the discharge period.
Microwave magnetoconductivity of polar semiconductors
Authors: Nag B. R.
Published: February 2003

An iteration method is presented for the accurate calculation of the microwave magnetoconductivity of polar semiconductors. The method is an extension of Rode’s iteration method for the evaluation of dc conductivity. The real and imaginary parts of the two perturbation components of the distribution function are obtained at each step of iteration by solving the four simultaneous equations relating the components. The iteration procedure is found to converge within 5–10 steps. The method has been applied to obtain the magnetoconductivity tensor of n-InSb at 10, 35, 85, and 135 GHz for magnetic induction up to 0.1 Wb/m2. All the relevant scattering mechanisms and the effects of band nonparabolicity have been taken into account. The calculated values of conductivity differ significantly from those obtained by applying the Drude theory and do not agree with those deduced from a cavity perturbation experiment.
Ion-implantation effect on time-dependent breakdown in SiO2
Authors: Li Seung P.
Published: February 2003

Field emission of positive ions from the meta/SiO2 interface in MOS structures, a failure mechanism in time-dependent dielectric breakdown, is shown to be controllable by a retarding field through ion implantation near the metal inteface.
Charge multiplication in Au-SiC (6H) Schottky junctions
Authors: Glover G. H.
Published: February 2003

The avalanche multiplication rate for carriers in 6H polytype SiC has been determined from photocurrent data with the assumption of equal hole and electron rates. The optical-phonon mean free path was determined by fitting to the Baraff theory to be λ=58 Å at 300 K. Avalanche breakdown voltages were in accord with Sze’s empirical prediction.
Electromigration of Ni in Al thin-film conductors
Authors: d’Heurle F. M. , Gangulee A. , Aliotta C. F. , Ranieri V. A.
Published: February 2003

An analysis of mass transport during electromigration in Al+Ni thin-film conductors indicates an anomalously large grain-boundary diffusivity of Ni in Al+Ni. This large value may be explained if the grain-boundary adsorption coefficient for solute atoms is assumed to be inversely proportional to the solubility limit.
New dithiene complexes for Q-switching and mode-locking infrared lasers
Authors: Reynolds G. A. , Drexhage K. H.
Published: February 2003

Computer results show high efficiencies can be obtained for solar energy conversion with thin back-surface field (BSF) cells. A large effect of the back-surface reflectivity is also predicted for such thin cells. The quality of the back-surface diffused layer is found to be an important parameter.
Stimulated Raman scattering from a multigigawatt liquid laser amplifier
Authors: Green M. , Andreou D. , Little V. I. , Selden A. C.
Published: February 2003

Stimulated Raman scattering has been observed for the first time during the amplification of giant pulses in a travelling-wave laser amplifier using Nd+3 : POCl3 : ZrCl4 as the active medium. Spectral and time characteristics of the input and output pulses are reported as well as measurements of the energy conversion to Raman wavelengths. The generation of forward-travelling narrow intense light pulses due to stimulated Raman scattering is also reported.
Population difference of two-level atomic system due to a running pulsed field
Authors: Nayfeh Munir H. , Nayfeh Ali H.
Published: February 2003

The method of multiple scales is used to derive an expression for the population difference in an absorbing atomic system due to a running pulsed field. The main contribution to this expression comes from a quasi-steady-state part which has the same functional form as the hole produced by a continuous running field, except that the saturation parameter contains the time dependence of the field. The expression includes also an oscillatory term and a quasisteady term, which decay with a rate that is equal to the inverse of the lifetime of the levels.
Xenon-dimer-laser net-gain measurements
Authors: Johnson A. Wayne , Gerardo J. B.
Published: February 2003

The gain of the vacuum-ultraviolet xenon-dimer laser was evaluated by employing a double-pass technique with spectral filtering of the probe radiation. At the wavelength center of the continuum-emission spectrum (λ0 ?1720 Å), the net-gain coefficient at pressures less than 1.1×104 Torr was found to be g0= (1.05±0.2) ×10−25Ps cm−1, where Ps is the spontaneous-emisssion intensity of the continuum-emission band in units of photons/sec cm3. By comparison of laser-output waveforms with temporally resolved net-gain measurements, it is shown that the laser intensity is limited by an unidentified time-dependent loss mechanism that is either foreign to the excited medium or that is driven by the laser radiation. While we do not know the source of this mechanism, our observations show that this time-dependent loss mechanism is not associated with the lasing states of the xenon dimer. At very high pressures (≳1.3×104 Torr) the effects of photoscattering by the background xenon were found to reduce the value of g0.
Pseudo-Kikuchi maps of Nb-diffused LiTaO3 thin-film optical waveguides
Authors: Standley R. D. , Ramaswamy V.
Published: February 2003

Electron diffraction phenomena which naturally occur in scanning electron microscopy are applied to the study of the crystal structure of LiTaO3 surface layers following Nb diffusion. Kikuchi maps, which relate to the reciprocal lattice of the crystal, are given for LiTaO3 oriented along the (01.0) and (00.1) crystal axis. Details on sample preparation and microscopy parameters are given along with a brief discussion as to how Kikuchi maps are predicted for this crystal. The techniques used allow observation of only the surface layer; the results are not masked by diffraction effects due to the substrate.
Laser-induced desorption of gas from metallic surfaces
Authors: Schwirzke F. , Brinkschulte H. , Hashmi M.
Published: February 2003

The processes associated with the interaction of focused laser radiation and stainless-steel targets suspended in a UHV chamber have been investigated. Plasma formation in the vicinity of the target surface was observed with increasing laser energy. Simultaneously, the laser-induced desorption of gas increases by three orders of magnitude. The experimental results show that most of the gas is not released from the small laser-illuminated area of the target but from the considerably larger surrounding surfaces of the vaccum chamber by impact of the rapidly expanding plasma cloud.
Radiative decay in the afterglow of strongly depleted Na-Ne-Ar low-pressure discharges
Authors: van Gemert M. J. C.
Published: February 2003

The decay of the intensity of Na resonance lines has been measured in the afterglow of Na-Ne-Ar low-pressure discharges. A relation has been derived to analyze the time behavior of the decay in terms of a position-independent radiative decay time of excited atoms, τ. It is found that τ is close to the measured decay time of the emitted radiation, τL. A new experimental criterion is suggested to define the critical current in alkali metal vapor–noble gas discharges.
Heat sealing of Teflon electrets by annealing
Authors: Gross B. , Sessler G. M. , West J. E.
Published: February 2003

The delayed radiation-induced conductivity (DRIC) generated in the irradiated volume of Teflon FEP electrets charged by electron-beam injection can be eliminated by annealing at temperatures between 100 and 180 °C for periods of the order of 10–106 sec. The decay and eventual disappearance of the DRIC may be studied by themally stimulated current (TSC) measurements. While the irradiated region of the material shows a short-circuit TSC peak at temperatures between 40 and 100 °C, depending on time after charging, the peak temperature of the annealed Teflon is at 180–190 °C corresponding approximately to the characteristics of the nonirradiated material. The electrets are thus ’’heat sealed’’ in the sense that conduction in the irradiated region is reduced to the values observed for nonirradiated Teflon. Teflon films charged by other methods exhibit more severe electrical changes which cannot be completely eliminated with the present method.
Interaction of Al layers with polycrystalline Si
Authors: Nakamura K. , Nicolet M-A. , Mayer J. W. , Blattner R. J. , Evans C. A.
Published: February 2003

Auger electron spectroscopy, MeV 4He+ backscattering spectrometry and scanning electron microscopy have been used to investigate interactions between Al films and polycrystalline layers of CVD Si deposited on SiO2. Depth profiling techniques showed that intermixing of the Al and Si occurred in the 400–560 °C temperature range (i.e., below the eutectic). Dissolution of the poly Si into the Al film occurs followed by nucleation and growth of Si crystallites in the Al film. The morphology of the final structure depends on the relative thicknesses of the as-deposited Al and Si layers. In the case of the original Al thickness being greater than that of the Si, the Si forms large precipitates in the Al matrix. For Al layers thinner than those of the Si, a nearly continuous Si film is formed on the outer surface. The thickness of this final Si film is approximately that of the original Al layer. The remaining Si and the Al form a two-phase layer between the outer Si film and the SiO2 substrate.
Nucleation and growth of silicon on tungsten and molybdenum in a field emission microscope
Authors: Sinha M. K. , Venkatachalam G. , Bhatia Charanjit S.
Published: February 2003

Nucleation and growth of silicon on tungsten and molybdenum substrates at temperatures at and above room temperature have been investigated by field emission microscopy. In the Si-W system, formation of a single nucleus is not observed although growth of silicon crystallites around {100} and {110} planes does occur. These crystallites are stable up to 1250 and 960 °K, respectively. On molybdenum tips, individual nuclei of silicon form on {211} regions and three-dimensional crystallites stable up to 1450 °K grow on the ledges of {110} and {211} planes. The crystallites form also on those areas of the tip which do not receive silicon vapor directly from the evaporator. The temperature of the tungsten tip at the time of silicon deposition does not affect the growth of silicon. However, the range 750–800 °K for a molybdenum tip is most suitable for nucleation and crystallite growth.
Second-order treatment of combined effects of space-charge and external fields on plane-symmetric zero-emittance beams of charged particles
Authors: Bosi G.
Published: February 2003

An earlier first-order treatment of the space-charge spread of zero-emittance charged particle beams under the influence of plane-symmetric external fields is revised and extended to include second-order effects. Elliptic and rectangular cross-section beams are investiged and conditions for parallel beam transport are carried out.
Yield stress of cemented tungsten carbide
Authors: Ruoff Arthur L. , Wanagel John
Published: February 2003

Cemented tungsten carbide yields plastically at room temperature in the presence of a large hydrostatic pressure component. By approximate analysis of the state of stress in supported opposed anvils and by measurement of the pressure at which the anvil tips exhibit a permanent deviation from planarity, we have obtained the yield stress of such materials. Our value for the yield stress of a 3% cobalt cemented tungsten carbide is 86 kbar.
Torsional-mode losses at contacts between homogeneous fiber waveguides and supporting structures
Authors: Rosenberg R. L. , Boyd G. D.
Published: February 2003

A fundamental torsional mode, transmitted through a homogeneous fused silica fiber of circular cross section, is used to probe the acoustic contact losses at the fiber supports. Losses introduced by clamping-bar supports are measured over one to two decades of clamping force for clamping materials spanning a wide range of elastic properties. The data are found to agree approximately with an analysis proceeding from one basic assumption, that the power loss caused by an element of contact area is proportional to the area. Development of this concept leads to a loss exponent proportional to F2/3 and s2/3, where F is applied force and s is a mean compliance parameter for the fiber and support bars. Measurements also show that the frequency dependence of the loss exponent is either weak or nonexistent. The F2/3 law plus a calculated dependence of loss on the fiber and support-bar diameters are used to extrapolate the data to smaller loads and thinner supports to estimate losses for several types of supporting structures.
Pressure dependence of the yield stress of potassium at low homologous temperature
Authors: Chua Jaime O. , Ruoff Arthur L.
Published: February 2003

Tensile stress-strain curves for polycrystalline potassium were obtained at liquid-nitrogen temperature (T=0.23Tm) and up to a pressure of 5.15 kbar. Pressure shifts the stress-strain curve upward. The yield stress versus pressure was measured. Theoretical dislocation models for the effect of pressure on the yield stress are reviewed herein. It is shown that the effect of pressure on the yield stress owes its origin to the effect of pressure on the effective elastic constant only. The present experimental results for the yield stress σ0 as a function of pressure P are in excellent agreement with the equation σ0=σ00[1+(Ce′0/C0) P], where σ00 is the yield stress at zero pressure, Ce0 is the value of the elastic constant Ce=G/(1−ν) at zero pressure, and Ce′0 is the value of the pressure derivative of the elastic constant Ce at zero pressure. Here G is the bulk shear modulus and ν is Poisson’s ratio. If Ce′0/C0 is replaced by E′0/E0 (where E is Young’s modulus) or G′0/G0 the agreement is also within experimental error. In this study, the yield stress was found to increase by 42% at 5.15 kbar.
Nonequilibrium stationary coupling of solitons
Authors: Nakajima K. , Sawada Y. , Onodera Y.
Published: February 2003

By computer simulation, interaction of two solitons with the same screw sense of the sine-Gordon equation, which retain their shapes and velocities upon collision with other solitons even in the presence of bias and loss terms, are examined. It is confirmed that they can couple when the bias is greater than a critical value. The conditions and mechanism of coupling are examined in detail. They are explained in terms of the energy of interaction between the ripple structures trailed by energy dissipative moving solitons. The distance D between coupled solitons can be expressed as D= (n−1/2−δ) λ (n is an integer), where λ is a wavelength of the ripple structure and δ≪1.
Surface micromorphology of vapor-phase-grown CdS platelet crystals
Authors: Chang S. C. , Mark P.
Published: February 2003

LEED, replica TEM, and SEM studies reveal that the large-area (112̄0) faces of vapor-phase-grown CdS platelet crystals actually consist of closely abutting uniaxial (101̄0) microfacets oriented along the polar axis. It is suggested that this surface micromorphology might be related to the cleavage properties of CdS.
Crystal growth and x-ray microanalysis of mixed crystals of Cd1−xMnxS
Authors: Komura Hiroo , Kondo Yoshio , Mitsuhashi Hiroji
Published: February 2003

Mixed crystals of Cd1−xMnxS with the wide range of Mn concentration (0⩽x⩽0.3, 0.7⩽x⩽1) were grown with the Bridgman-Stockbarger technique in high-pressure Ar atmosphere. X-ray microprobe analysis indicates that the Mn concentration in grown crystals differs to a great extent from that of the mixed powder charge in the carbon crucible. The Mn concentration is fairly homogeneous in a wide area of the grown crystals.
Inherent time delay for dielectric breakdown in shock-loaded x-cut quartz
Authors: Graham R. A. , Yang L. C.
Published: February 2003

Dielectric breakdown in shock-loaded x-cut quartz is examined under conditions of both impact loading and Q-switched laser-irradiation loading. It is observed that breakdown is characterized by an inherent time delay which depends on the magnitude of the electric field. For pulse duration less than about 30 ns, dielectric breakdown is not observed.
White-light interferometric measurement of the wall thickness of hollow glass microspheres
Authors: Weinstein Berthold W.
Published: February 2003

A simple interferometric technique using both a white-light and a monochromatic-light source can be used to measure the wall thickness of hollow glass microspheres to better than 0.05 μm. The entire procedure requires only a few minutes per sphere and can easily be made to take into account the effects of any gas with which the ball is filled.
Dislocation structures in fatigued copper-aluminum alloys
Authors: Chu T. K.
Published: February 2003

Low-temperature (1.5–30 K) thermal conductivity measurments are used for a nondestructive determination of dislocation structures generated by cyclic deformation in two copper-aluminum alloys (1 and 15 at.% Al in Cu). A torsional strain mode is adopted with an amplitude of a few percent. Fatigue life is estimated to be approximately 1000 cycles. In both alloys the change in lattice thermal resistivity due to deformation follows a T−2 dependence above 10 K, and a T−1 dependence below 2 K. At intermediate temperatures it is found to be composed of a T−2 and a T−3 term. This temperature variation is interpreted as due to phonon scattering by dislocations and by dislocation structures. Electron microscope observations by others indicate that these structures form cell walls in the lower-concentration alloy, and dislocation bands in the higher-concentration alloy. A dipole wall model of these substructures is proposed, and the corresponding lattice thermal resistivity calculated using a simple extension of Klemens’s theory of phonon scattering by the various lattice defects. These calculations give reasonable agreement with the experimental results. Dislocation densities are estimated to be of the order of 1012 cm−2 in the substructures, and of the order of 1010 cm−2 in the crystal matrix. It is found that dislocation substructures are formed during the first quarter -cycle of straining. Subsequent strain reversal tends to ’’condense’’ dislocations into cell walls and dislocation bands. As a result, there is a vary rapid saturation of dislocations in the substructures, which is almost complete after two cycles of deformation.