bluuebunny/crossref_metadata_2025 huggingface dataset:
On the gas temperature in coaxial electric-discharge CO2 flow lasers
Authors: Shwartz Josef , Margalith Eliahu
Published: February 2004

An analytic and experimental investigation on the dependence of gas temperature on flow and discharge characteristics is presented. The entire range of slow- to fast-flowing coaxial CO2 electric lasers is considered. As is known, at low flow rates the gas temperature is proportional to the electric power input per unit length, while at high flow rates the gas end temperature is proportional to the ratio of total electric power and gas mass flow rate. In addition, gas pressure and entrance Mach number were found to have a noticeable effect on gas temperature; the temperature tends to increase with increasing pressure and to decrease with increasing Mach number. The agreement between theory and experiment is fairly good, so that estimates of gas temperature at given flow and discharge conditions can be obtained. Also presented is an experimental correlation between laser power output (or efficiency) and gas temperature. Finally, scaling laws for temperature-limited coaxial flow CO2 electric lasers are proposed.
Laser modulation spectroscopy of solids
Authors: Tang C. L. , Telle John M.
Published: February 2004

The usefulness of the electro-optically tuned wavelength-modulated cw dye laser for derivative spectroscopy of solids is demonstrated. The derivative spectrum corresponding to the 4I9/2→4G5/2 + 2G7/2 transitions of the trivalent neodymium ion in crystalline YAG at room temperature was studied and new features were observed.
Hole and electron transport in SiO2 films
Authors: Curtis O. L. , Srour J. R. , Chiu K. Y.
Published: February 2004

Carrier transport in SiO2 has been studied by exciting hole-electron pairs in an oxide film by a pulsed electron beam. The energy of the beam (4–8 kV) was chosen to minimize excitation in the Si substrate upon which the SiO2 was grown. Measurements of oxide current vs applied voltage were made with beam intensity and energy as parameters for SiO2 layers of three thicknesses. It is demonstrated that normalized current-vs-field curves are independent of beam intensity, beam energy, and film thickness over the range studied. These results indicate that the analysis used by various workers to determine the mobility-lifetime (μτ) product for SiO2 is invalid. Observed dependences of current on applied field can best be explained by geminate and/or columnar recombination. The present findings indicate that both holes and electrons traverse most of the SiO2 without appreciable permanent trapping. The amount of positive charge trapped at or near the SiO2–Si interface is a significant fraction of the ``collected'' charge, indicating that some of the holes that move to the interface do not penetrate it.
Resonant multiphoton ionization of neon by a ruby laser
Authors: Benattar R. , Sultan G.
Published: February 2004

We report resonant multiphoton ionization in neon. The study of the interaction volume shows that the size of the focused region depends on the laser power, order of interaction, and energy of photon. Thus we have chosen a resonant approach. The results show a discrepancy of 6 cm−1 between the experimental multiphoton resonance and the theoretically predicted one. We explain this discrepancy by the perturbative effect of the intense electromagnetic field of the laser on the resonant atomic level 11p [3/2]1,2 of neon.
Band structure enhancement and optimization of radiative recombination in GaAs1−x Px:N (and In1−x Gax P:N)
Authors: Campbell J. C. , Holonyak N. , Craford M. G. , Keune D. L.
Published: February 2004

The modulus of the wave function of an electron bound to a N isoelectronic trap in GaAs1−xPx:N or In1−xGaxP:N is enhanced near k = O because of the presence of the Γ conduction-band minimum. The band structure enhancement (BSE) and its effect on the quasidirect behavior of indirect GaAs1−xPx:N and In1−xGaxP:N has been investigated as a function of crystal composition x (x>xc). To evaluate the modulus of the wave function of the trapped electron, the Koster-Slater one-band one-site model has been employed. The effect of BSE on no-phonon recombination transitions involving the trapped electron is accentuated by orders of magnitude as the crystal composition is changed to bring the Γ conduction-band minimum, EΓ, near the N-trap level, EN. Absorption data taken on x = 1.0 and x = 0.53 GaAs1−xPx:N are consistent with the calculated increase in the probability density in the Γ region as EΓ decreases relative to EX. In order to assess the importance of the enhanced recombination probability on the performance of GaAs1−xPx LED's, the internal quantum efficiency has been calculated as a function of crystal composition. This calculation utilizes a model of the electron and hole recombination kinetics at isoelectronic impurities along with the standard band-to-band recombination kinetics. The calculated efficiency weighted by the photopic response of the eye agrees with LED brightness data and confirms that the optimum range of crystal compositions in which to fabricate GaAs1−xPx:N LED's is 0.6≤x≤0.8. This result is in good agreement with current GaAs1−xPx:N LED fabrication processes and the optimization procedure on Zn-diffused planar devices that has arisen empirically. That is, brightness data on state-of-the-art GaAs1−xPx:N and GaP:N Zn-diffused LED's support the analytical results developed here. The implications of BSE for In1−xGaxP:N LED's are discussed.
Optical absorption edge of LiNbO3
Authors: Redfield D. , Burke W. J.
Published: February 2004

The spectral dependence of the fundamental absorption edge of congruently grown undoped LiNbO3 has been measured from 10 to 667 K. Similar measurements on stoichiometric samples were made at 80 and 300 K. In all cases at all temperatures the edge is broad and featureless and showed very little dichroism (<0.01 eV). The spectral dependence of the absorption is exponential at high temperatures but not at low temperatures. Possible models to explain the observed shapes are discussed.
Determination of the anisotropy field of garnet bubble materials from domain observation
Authors: Shimada Y. , Kojima H. , Sakai K.
Published: February 2004

A simplified equation was derived by which the uniaxial anisotropy HK of the usual bubble materials can be determined from the field lying in the plane of the sample at which the domains disappear. It was found that a garnet film epitaxially grown on a (111) plane of Gd3Ga5O12 shows a sixfold symmetry of the domain erasing field which may be due to the cubic crystalline anisotropy of the sample. This implies that, if the cubic anisotropy cannot be neglected compared to the uniaxial anisotropy, the crystallographic axis in the plane of the film along which the domain erasing field is to be applied should be carefully determined. An estimation was made on the contribution of the cubic anisotropy to the domain erasing field when the field lies along a [110] axis.
The effect of cladding material on ac losses of commercial Nb3Sn tapes
Authors: Bussière J. F. , Garber M. , Suenaga M.
Published: February 2004

ac losses of commercial Nb3Sn tapes have been measured before and after removal of the normal metal cladding which is used to stabilize the superconductor. It is shown that materials which are frequently used to assist in bonding the normal metal to the Nb3Sn surface give rise to hysteretic losses which are much larger than those of the Nb3Sn itself in the low-field region of interest for power transmission, below 1000 Oe. Examples of such materials are superconductive Pb–Sn solders used in cladding tin-diffused tapes and ferromagnetic nickel flashes used in silver plating vapor-deposited tapes. These lossy materials are not essential and can be eliminated in tapes which are properly designed for power transmission. It is also shown that eddy current losses are acceptably small for normal metal cladding thickness of the order of 25 μm (ρ∼10−8 Ω cm).
Technique for fabrication of superconducting microbridges and small Josephson tunnel junctions
Authors: Yeh J. T. C.
Published: February 2004

A simple, versatile, and inexpensive technique for the fabrication of superconducting microbridges and small Josephson tunnel junctions is described. The technique is based on the use of fiber masks for the production of precisely controlled substrate channels and yields device dimensions of 1 μm or less.
Magnetic-field-induced recrystallization in MnBi
Authors: Chen Tu , Stutius W. E.
Published: February 2004

A magnetic annealing effect has been observed in a ferromagnetic MnBi single crystal. It was found that by heating an MnBi single crystal in a magnetic field perpendicular to the easy axis of magnetization of the crystal, the easy axis of the magnetization and the hexagonal c axis of the crystal would change into the direction parallel to the field through a recrystallization process induced by the magnetic annealing. This recrystallization phenomenon is similar to that observed by Boothby et al. on a polycrystalline sample. Based on the microstructure investigation and transformation kinetic analysis, it was found that the mechanism of the recrystallization in a single crystal is a thermally activated nucleation and interface controlled growth process. It was established that the magnetocrystalline anisotropy energy of the crystal is responsible for the recrystallization.
Higher-order models for static magnetization in thin films
Authors: Dodd R. E. , Wilson L. K.
Published: February 2004

The theoretical field positions of the standing spin-wave modes for selected Permalloy films and YIG films were obtained from a numerical solution of the spin-wave equation for the case of perpendicular resonance for different pinning conditions. The static magnetization M(z) was assumed to have an asymmetrical variation in which the magnetization has a minimum value at the substrate-film interface (z=0) and increases to a maximum value at the film-air interface (z=L). Comparisons of theoretical and experimental field positions show that a good fit of the experimental data occurs when the magnetization has a polynomial-type variation.
Sensitivity and detective quantum efficiency of electron microscope plates at high voltages
Authors: Ast D. G.
Published: February 2004

The voltage dependence of the electron sensitivity of photographic emulsions is analyzed in terms of experimentally established relations between (i) track density and energy loss rate (ii) incident energy and range. It is found that the latter strongly dominates the functional sensitivity at high energies. Calculated values are compared with experimental data by Dudley. The detective quantum efficiency of standard electron microscope plates is computed as a function of energy.
Specific heat of 2H NbSe2
Authors: Bevolo Albert J. , Shanks H. R.
Published: February 2004

The specific heats of four samples of 2H NbSe2 have been measured in the temperature range from 1 to 54 K. No anomalous behavior was found near 40 K where x-ray, NMR, and Hall-effect measurements have indicated the presence of a phase transition. An upper limit of 0.3 J/mole K has been placed on the magnitude of any anomaly in the heat capacity associated with this transition. Measurements of high-purity stoichiometric 2H NbSe2 sample gave a superconducting transition temperature of 7.23 K, a specific heat jump (ΔC) in zero field of 240 mJ/mole K, and a Debye temperature of 204 K. A deviation from the usual T3 behavior for the lattice contribution to the heat capacity was observed and assumed to be due to the two-dimensional layer structure of the compound. Our best estimate for the electronic coefficient of specific heat (γ) is about 10±5 mJ/mole K2. Based on the values for Tc and ΔC, the value for γ calculated from BCS theory is 23 mJ/mole K2 for 2H NbSe2 which is in disagreement with our estimated value for γ by a factor of 2.
Reply to ``Comments on `Luminescence from electron-irradiated silicon'''
Authors: Jones Colin E. , Streetman B. G. , Noonan J. R.
Published: February 2004

Recent experimental and analytical results indicate that the 0.97-eV luminescence from irradiated Si is characterized by monoclinic symmetry. The assignment of symmetry class for other luminescence peaks in this material is incomplete.
Amplification of acoustic waves due to an external temperature gradient in semiconductors
Authors: Sharma Satish , Singh S. P.
Published: February 2004

We propose that the application of an external temperature gradient to a semiconductor can lead to the amplification of the acoustic wave.
Possible explanation of the onset of switching in the amorphous semiconductor threshold switch
Authors: Fredericks G. E.
Published: February 2004

A criterion of the onset of switching in the amorphous semiconductor threshold switch is given. This criterion arises from the condition for the onset of one phonon-assisted hopping of small polarons.
Simultaneous diffusion of ion-predeposited arsenic and boron in silicon
Authors: Heinrich Helmut , Hastings L. , Rozenbergs J.
Published: February 2004

As and B were implanted into n-type Si at 40 keV. The shallow layer was used as a source for simultaneous diffusion and formation of a n-p-n structure. The diffusion coefficients obtained were the same as those for the diffusion of the individual dopants. It is suggested that this technique may be of interest for the formation of complex profiles which are too deep to be obtained by implantation alone.
Stress compensation in GaAs–Al0.24 Ga0.76 As1−y Py LPE binary layers
Authors: Brown R. L. , Sobers R. G.
Published: February 2004

To improve the performance and reliability of heterostructure GaAs lasers, it is important to reduce stress in the epitaxial layers caused by lattice mismatch between GaAs and AlxGa1−xAs. More precise measurements than previously available have been made on the lattice mismatch of binary layers of GaAs–Al0.24Ga0.76As1−yPy and GaAs–Al0.36Ga0.64As1−yPy from radius-of-curvature measurements. The heterostructures were grown by LPE, with various atom fractions of P, on (100) and (211) GaAs substrates. Liquidus values of P concentration at 780°C growth temperature to achieve room-temperature lattice matching have been determined to ±4%. The threshold value of the lattice mismatch and layer thickness product on (211) substrates necessary to avoid misfit dislocations is given.
Parallel-plate waveguide with sinusoidally perturbed boundaries
Authors: Nayfeh Ali H. , Asfar Omar R.
Published: February 2004

The method of multiple scales is used to obtain a uniformly valid asymptotic expansion for the propagation of TM modes on a parallel-plate waveguide with perfectly conducting boundary surfaces that are sinusoidally perturbed in the direction of propagation. The analysis shows that resonance occurs whenever the wave number of the wall distortion function is equal to the difference between the wave numbers of two propagating modes. It is further shown that the generated mode is the same order of magnitude as the excited mode due to resonance and that energy is continuously exchanged between the two modes as they propagate down the guide.
An approximate technique for analyzing the plasma of thermionic converters operating in the ignited mode
Authors: Ratafia Manuel , Keck James C.
Published: February 2004

An approximate analytic technique for solving the transport equations of thermionic energy converters is developed. Using an assumed parametric form for the ionization rate, the problem is reduced, essentially, to one of the solution of three simultaneous transcendental equations. A numerical iterative procedure for the solution of these equations is derived and implemented in a computer code and some illustrative solutions are obtained. A simple criterion for whether the converter is operating under equilibrium or nonequilibrium conditions and other simple relations describing the character of the solutions are derived. For nonequilibrium conditions, the assumed form for the ionization rate is found to agree well with the actual form, and the solutions obtained are in good agreement with previous results. The empirically observed minimum in the arc drop at the optimum value of the pressure-spacing product is predicted. The present theory is the only one known to the authors which shows this result. The solutions may be systematically improved by numerical integration and iteration and the range of applicability of the solutions can be extended to local thermodynamic equilibrium conditions by assuming a more general form for the electron production and to a greater variation in parameters by incorporating a recently derived improved set of boundary conditions into the analysis.
Parametrically excited instabilities near the hybrid resonant frequencies
Authors: Seshadri S. R.
Published: February 2004

The parametric excitation of the ordinary mode and the extraordinary mode propagating perpendicular to the magnetostatic field is investigated for the case of a cold uniform plasma. The pump wave is assumed to be another ordinary mode having its electric field oriented parallel to the magnetostatic field and its frequency exceeding the plasma frequency of the electrons. The extraordinary mode has three branches, namely, a high-frequency branch, an intermediate-frequency branch having a resonance at the upper hybrid resonant frequency, and a low-frequency branch which in the regime of hydromagnetic frequencies is the Alfvén wave and which also has a resonance at the lower hybrid resonant frequency. The ordinary mode does not parametrically couple with the high-frequency branch of the extraordinary mode but such a coupling takes place with the other two branches. This parametric coupling leads to instabilities of the extraordinary mode. Illustrative numerical results are presented for the parametric instabilities of the extraordinary mode near the upper hybrid resonant frequency, the lower hybrid resonant frequency, and the Alfvén wave frequency. Compared to the intermediate-frequency branch, the requirements for the parametric interaction are found to be met easily for the low-frequency branch. The dependence of the maximum growth rates of the parametric instabilities on the strength of the magnetostatic field is also examined.
Statistics of charged powder particles
Authors: Chen Inan
Published: February 2004

The distribution of the electrical charge and the charge-to-mass ratios of powder particles are related to the distribution of the particle radii. The latter distribution is assumed to be log-normal and the particle charge is assumed to be quadratic in its radius. It is found that neither the microscopic average values nor the macroscopic average values are always good representations of the electrical properties of the powder sample. The variations of the average and the median values of the distributions as functions of the standard deviation of particle size are studied.
Shock wave study of the α ⇄ ε phase transition in iron
Authors: Barker L. M. , Hollenbach R. E.
Published: February 2004

Plate impact experiments producing plane waves of up to 40 GPa (400 kbar) peak stress were performed using Armco iron specimens and impactors. Highly accurate time-resolved measurements of the resulting free-surface velocities of the specimens were obtained with the VISAR laser interferometer instrumentation system. The free-surface velocity profiles provide new information concerning the rate effects associated with the α → ε polymorphic phase transition at 13 GPa, the material strength and release wave speeds at 10 and 40 GPa, and the stress level at which the iron reverts back to the α phase on unloading. A strong magnetic field was found to produce no measurable change in the phase-transition stress. The accuracy of the ``factor-of-2'' assumption relating free-surface velocity to particle velocity in iron was also evaluated experimentally.
Surface reactions on MOS structures
Authors: Alessandrini E. I. , Campbell D. R. , Tu K. N.
Published: February 2004

The morphology of surface reactions for Au/SiO2/Si structures has been studied as a function of environment. It was found that the reaction between thin gold film dots and thermally oxidized Si was strongly influenced by the partial pressure of oxygen. When samples are held at elevated temperatures (above 500 °C) in the dynamic vacuum, an apparent decomposition of the oxide film with subsequent migration of Au along the exposed silicon surface was observed. The migration was found to follow the crystallographic directions of the silicon. Reduction of the oxide was dependent on the presence of the Au layer as regions free of Au remained intact. The reaction as a function of time, temperature, SiO2 thickness, and ambient conditions has been studied using optical microscopy as well as electron microprobe, microscopy, and diffraction techniques.
Effects of ionizing radiation on thin-oxide (20–1500 Å) MOS capacitors
Authors: Share S. , Epstein A. S. , Kumar V. , Dahlke W. E. , Haller W.
Published: February 2004

Metal-oxide-semiconductor capacitors with SiO2 oxides ranging from 20 to 1500 Å thick were exposed to a 60Co γ radiation dose of 106 rad(Si). Both p- and n-type substrates and Al- and Au-metal electrodes were used. For devices with oxides less than 100 Å thick, little or no parallel shift, no increased distortion, and no increased dispersion as a result of irradiation were observed in the C-V characteristic, indicating negligible buildup of oxide charge and negligible change in the interface density upon irradiation. For oxides thicker than 100 Å, the oxide-charge buildup increased greatly with thickness in the p-type devices, whereas in the n-type devices the oxide-charge buildup was comparable to the thin-oxide value. Interpretation of the p-type Al-metal electrode devices for oxides thicker than 100 Å are consistent with 1018 cm−3 hole traps residing in the oxide. However, for oxides thinner than 100 Å, a larger value of oxide-charge buildup is predicted in these p-type Al-metal electrode devices than observed. Differences in oxide-charge buildup between p- and n-type Al-metal electrode thick-oxide devices can be understood qualitatively by metal-semiconductor work-function differences.
Optical absorption in epitaxial PbTe films on BaF2
Authors: McCarthy S. L. , Weber W. H. , Mikkor M.
Published: February 2004

Results are presented for below-band-gap (λ∼5−12 μm) optical-absorption measurements at 300 and 77 K on epitaxial p-type PbTe films grown on BaF2. These results indicate a significant reduction in the absorption previously reported on PbTe epitaxial films on NaCl substrates. A few samples show an additional absorption suggestive of impurity effects. He4 ion-backscatter spectra of these films show a surface contamination of chlorine. The results of room-temperature optical-absorption measurements on less contaminated samples agree reasonably well with bulk sample behavior. In low-carrier-concentration films (p < 1017 cm−3) impurity effects appear to eliminate any temperature dependence of the absorption. The presence of the surface contamination does not affect the dc transport or refractive-index properties.
Kinetics of recombination in nitrogen-doped GaP
Authors: Dapkus P. D. , Hackett W. H. , Lorimor O. G. , Bachrach R. Z.
Published: February 2004

The doping dependence of the bulk efficiency for both n- and p-type GaP:N has been investigated experimentally and theoretically. Experimental data are presented for p-type Zn,N-doped, n-type Te,N-doped, and n-type S,N-doped GaP over a majority-carrier range 5×1016−2×1018 cm−3. The efficiency data and photoluminescent decay time data on the same samples are compared to a simple equilibrium model for the recombination kinetics in nitrogen-doped GaP. The model predicts that the efficiency should scale linearly with the minority-carrier lifetime, majority-carrier concentration, and the nitrogen concentration in the doping range considered. The comparison of the theoretical results with the experimental data shows that the bulk efficiency of p-type material agrees quantitatively with the analytical prediction. For Te- and S-doped material, which have widely different and varying minority-carrier lifetimes, the bulk efficiency of n-type material is shown to depend linearly upon the minority-carrier lifetime over the entire doping range considered. However, the normalized efficiency η/τmc is shown to depend upon the net donor concentration as η/τmc∝(ND-NA)0.5−0.6 above ND−NA≈3×1016 cm−3, independent of the donor, rather than linearly as predicted by theory. This deviation from theory remains unexplained. The data and analysis suggest that screening is of little importance over the doping rane considered. The lower limit on the nonradiative Auger lifetime of the bound excitons in p-type material is determined to be τxA≥(100−200)(1017cm−3/p) nsec. The strong variation of the minority-carrier lifetime with doping for n-type material is attributed to nonradiative centers extrinsic to the nitrogen center because of the different dependences observed for S- and Te-doped material and no firm conclusion can be drawn about the strength of nonradiative Auger recombination.
Transient photoconductivity current-time profiles in low carrier mobility solids
Authors: Fleming R. J.
Published: February 2004

A recent explanation by Silver et al. of the shape of transient photoconductivity current-time traces observed in thin films of such markedly different materials as anthracene, selenium, arsenic triselenide, and poly(n-vinyl-carbazole) is questioned. It is suggested that a carrier-trap distribution proposed by Spear and Le Comber to account for the time variation of transient currents flowing in thin amorphous silicon films exposed to electron-beam pulses is unlikely to be found in many other materials. Calculations are performed which show that there is no particular widely occurring trapped space-charge distribution which would yield the experimentally observed photocurrent traces. An explanation of the shape of such traces involving radiative recombination of mobile positive holes and trapped electrons within a limited volume close to the cathode, followed by photogeneration of additional carriers through the sample bulk, is also rejected. Finally a charge-transport mechanism involving phonon-assisted tunnelling of carriers between localized states in the mobility gap is proposed, the carriers tunnelling not to the nearest state but to one further away which is energetically more favorable.
Spectroscopic measurement of the space-charge distribution in insulators, semiconductors, and photoconductors
Authors: Sheng S. J. , Hanson D. M.
Published: February 2004

The use of Stark spectroscopy to measure the space-charge distribution in insulators, semiconductors, and photoconductors is described and illustrated with experimental results for an organic photoconductor. The observed charge distribution is understood in terms of the variation of charge carrier generation and trapping through the crystal.
Infrared-stimulated luminescence in ZnS grown by chemical vapor deposition
Authors: Zucca R. , Cory E. S. , Espinosa G. P. , Hengstenberg D. H. , Lim T. C.
Published: February 2004

When ZnS crystals that have been doped with nearly equal amounts of Cu activator and a coactivator are held at liquid-He temperature, they exhibit an enhancement of the normal uv-excited luminescent emission when illuminated with infrared radiation near 10 μm. A study of this effect in epitaxial films grown and doped with Cu and Cl by chemical vapor deposition (CVD) is presented. Measurements of the spectral dependence, the temperature dependence, and the time dependence of this effect are reported. The measurements indicate no fundamental difference between the effect in CVD-grown epitaxial films and bulk ZnS. At the same time, the spectral- and time-dependence measurements extend beyond previous results. The spectral-dependence measurements support the current model in terms of release of electron into the conduction band by the ir photons before the electrons decay. The time dependence results and an analysis of temperature effects deepen inconsistencies between the ir stimulation and the related ir absorption. A modification of the model in terms of two traps is proposed. With this modification, the model accounts qualitatively for all the observed effects.
Static and dynamic coercivities of hard magnetic bubbles
Authors: Patterson R. W.
Published: February 2004

Investigations into the translational properties of hard magnetic bubbles have revealed that both static and dynamic coercivities increase with increasing Bloch-line density. The increase of coercivity is felt to be related to a corresponding increase of wall energy density. Comparisons of experiment with theory indicate that the equations of motion require the addition of a phenomenological coercive term which is independent of Bloch-line density and which acts parallel to the applied drive field. The magnitude of this coercive term is the difference between the static and dynamic coercivities.
Measured frequency dependence of the surface resistance of superconducting niobium
Authors: Bauer W. , Giordano S. , Hahn H.
Published: February 2004

The surface resistance of a superconducting niobium cavity oscillating in the TE11n modes has been measured over a frequency range from 1.7 to 7.8 GHz, and a frequency dependence proportional to f2 ± 0.1 has been found. The result differs from the f1.7 dependence predicted by the approximate microscopic theory. A possible explanation for the observed anomaly is given by smearing of the density-of-states maximum due to inhomogeneities in the superconductor.
A position-sensitive detector using a RC network with quasidistributed constants
Authors: D'Amico A. , Proca G. A. , Renaud J. F.
Published: February 2004

A simple rugged position-sensitive detector for electronic readout of charged particles analyzer is described. It consists of a terminated electrical line with almost distributed RC constants. The prototype detector consists of 560 RC groups of total length 28 mm. Techniques pertinent to printed circuits have been used. A mathematical treatment of a realistic theoretical model is presented together with preliminary experimental results.
Unusual secondary defect distributions in quenched gold
Authors: Westmacott K. H.
Published: February 2004

Unusual secondary defect structures consisting of high concentrations of stacking-fault tetrahedra precipitated in shells around large voids were found in oxygen-annealed and quenched high-purity gold. The observations are explained in terms of impurity segregation during growth of the void followed by heterogeneous nucleation of tetrahedra on the impurities. A strong impurity/vacancy binding energy is suggested by the magnitude of the impurity enrichment around the voids, and the apparent effectiveness of the impurities in nucleating tetrahedra.
Migration of gold atoms through thin silicon oxide films
Authors: Madams C. J. , Morgan D. V. , Howes M. J.
Published: February 2004

Rapid migration of the gold electrode on C–SiOx–Au devices has been found for temperatures above the Au/Si eutectic point. Approximate concentration profiles have been determined by means of Rutherford scattering. Electrical measurements have been performed on both virgin and diffused devices. Comment is made on the relevance of electrode migration to the forming process and bistable memory switching in metal-insulator-metal devices.
Optical memory effect in As–Se chalcogenide glass films
Authors: Tokuda W. , Katoh T. , Yasumori A. , Nakamura K.
Published: February 2004

In connection with optical memory effect, the change in the transmission by exposure to light is studied for amorphous As–Se glass films. The change is found to be dependent upon the As content. In addition, photodecomposition is observed for the As60Se40 film, but not for the As40Se60 film.
Composition determination of AlxGa1−xP alloys using diffracted x-ray intensities
Authors: Sonomura H. , Nanmori T. , Saito S. , Miyauchi T.
Published: February 2004

It is fundamental and important to determine the composition of an alloy as the alloy is prepared. This study deals with a method of composition determination for the AlxGa1−xP ternary compound. The relative integrated intensity of a diffracted x ray as a function of composition is calculated for the AlxGa1−xP system. The intensities of reflections having indices whose sum is an odd multiple of 2 depend strongly on composition. This is ascribed to the fact that atomic scattering factors of Al and P are nearly equal and considerably smaller than that of Ga. The diffracted x-ray intensities for the AlxGa1−xP crystals are measured. The ratio I200/I111 decreases drastically with Al content and agrees closely with the calculated curve. It is concluded that the composition of the AlxGa1−xP alloy can be deduced simply from the diffracted x-ray intensity ratio.
Frequency characteristics of an interdigital transducer for Lamb wave excitation
Authors: Toda Kohji
Published: February 2004

The frequency characteristics of the surface displacements of the Lamb waves excited by interdigital transducers on unpolarized piezoelectric ceramic plates have been analyzed by using the same method as Tseng's analysis of Rayleigh wave excitation. This analysis has lead to the conclusion that the transducer operates most effectively when the wavelength of the Lamb wave is equal to the half-period of the electrode. The dispersive characteristics of the zeroth modes in a comparatively thick specimen are also shown. Our discussion dwells on the frequency dependence of the surface displacement on the total number of the electrode fingers in a transducer and the electrode configurations.
Platinum silicide formation: Electron spectroscopy of the platinum-platinum silicide interface
Authors: Danyluk S. , McGuire G. E.
Published: February 2004

Platinum silicide formation has been studied by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) in conjunction with argon ion depth profiling. These techniques were used to probe the chemistry of the interface between the Pt metal and PtSi formed from two standard platinum deposition processes: dc sputtering and filament evaporation. The results indicate that after sintering in nitrogen, the PtSi is separated from the platinum metal by a ``protective'' layer which has tentatively been identified as PtSiO4. This ``protective'' layer has a significantly slower etch rate in standard etchants than the platinum metal and platinum silicide and may be formed during sintering by an interaction between the platinum metal and the native silicon dioxide. The platinum silicate identification is based on the XPS ``chemical shifts'' found for both the platinum and silicon core levels. The silicate layer formation appears to be independent of the technique for platinum deposition.
Uranium self-diffusion in stoichiometric uranium monocarbide
Authors: Matzke Hj. , Routbort J. L. , Tasman H. A.
Published: February 2004

Self-diffusion measurements, with 233U as the tracer, have been obtained for stoichiometric arc-cast UC at temperatures between 1480°C and the melting point and for zone-refined UC single crystals at temperatures between 1500 and 2125°C. α spectroscopy was used to measure the α-energy degradation from which the diffusion profiles were determined. Conventional sectioning techniques were employed to determine the profiles at high temperatures. The results obtained from arc-cast UC yielded a curved Arrhenius plot. Computer programs were developed to fit the sum of two exponentials to the experimental data. This was accomplished by changing one or two of the parameters, D0,1, D0,2, ΔH1, and ΔH2, in steps and adjusting the remaining parameters to obtain the minimum standard deviation σ. The resultant equation was DUCU=6.9 exp(−141 000/RT)+3.6×10−5exp(−84 500/RT) cm2sec−1. The data obtained from the single crystals showed a linear Arrhenius plot described by DUCU=11.7 exp(−141 900/RT) cm2sec−1. The influence of impurities at low temperatures (< lim ∼2100°C) is the most probable cause of the curvature in the Arrhenius plot for the arc-cast UC.
Introduction rates and annealing of defects in ion-implanted SiO2 layers on Si
Authors: EerNisse E. P. , Norris C. B.
Published: February 2004

The introduction rates and isochronal annealing behavior of structural defects created by atomic collision or ionization in SiO2 layers thermally grown on Si in O2 and steam are investigated by measuring the induced volume compaction for ion and electron bombardments. The use of compaction measurements permits study of the introduction and annealing of defects with little confusion from changes in the charge state of the defects. The structural damage created by ion energy deposited into atomic collisions is found to be complex, possibly consistent with a thermal process involving reordering of the noncrystalline network of Si–O tetrahedra, and to anneal in a slow featureless manner beginning around 300°C and returning to the original density near the original growth temperature. The structural damage created by ion or electron energy deposited into ionization is identified with broken Si-O bonds and found to anneal completely in a single well-defined stage centered at 650°C. The ionization-induced structural defect is the same for ion and electron ionization if no appreciable atomic collision energy deposition occurs simultaneously. Additional structural damage arising from an interaction between atomic collisions and ionization is demonstrated. The results demonstrate that other workers' observation of annealing in damaged oxides at 300°C corresponds to emptying of charged defects rather than annealing of the structural defects.
Comparison of Langmuir probe and Thomson scattering measurements of electron temperature and density
Authors: Jones Larry A.
Published: February 2004

Measurements of electron temperature and density made with Langmuir probes are compared to those made by Thomson scattering. The comparison is made over a range of electron density [(0.3−1.6)×1015 cm−3] and temperature (1–2 eV). The two diagnostic techniques agree to within 20% in the case of the electron temperature and to within 10% in the case of the electron density.
Quasistatic calculation of radial plasma velocity in laser-heated solenoid
Authors: Halverson W.
Published: February 2004

The one-dimensional quasistatic model of a laser-heated magnetically confined plasma is used to compute the radial plasma flow velocity.
Evolution of parametrically excited ion-acoustic waves
Authors: Klein L. A. , Cheo B. Ru-Shao , Stern R. A.
Published: February 2004

A technique for experimentally determining growth and decay characteristics of parametrically excited plasma waves is described. The method is based on switching the pump power between two levels and observing the evolution of the excited waves in time. By using a nonlinear phenomenological model, the linear damping frequency and decay rates of the excited waves are found as is a coupling coefficient between the pump and excited waves. Experiments were conducted in the positive column of an argon discharge in a Tonks-Dattner structure using a microwave pump. Observed damping of the excited ion-acoustic wave at pressures between 10 and 44 mTorr is shown to be consistent with ionization collisions, while the decay rate is shown to be a linear function of pump power.
Effect of electron-electron and electron-ion collisions in Hg, CO2/N2/He, and CO/N2 discharges
Authors: Rockwood Stephen D.
Published: February 2004

Through numerical solution of the Boltzmann transport equation, including the effects of electron-electron and electron-ion collisions, the dependence of transport coefficients and excitation rates on E/N and the fractional ionization have been obtained for electrical discharges in Hg, He/N2/CO2, and N2/CO mixtures. The results for Hg show a sensitive dependence on fractional ionization when E/N < 10−16 V cm2. However, for the molecular gases with values of E/N typical of laser discharges, the dependence on fractional ionization is generally weak. The one exception noted is the 1/0.25/3 CO2/N2/He mixture.
Cathode spot erosion and ionization phenomena in the transition from vacuum to atmospheric pressure arcs
Authors: Kimblin C. W.
Published: February 2004

Cathode properties of arcs are investigated for ambient gas pressures of 10−3−725 Torr. Copper, silver, and carbon electrodes are used in controlled ambients of either nitrogen, argon, or helium. Experimental techniques include pressure-dependent observations of the ionized cathode vapor detected at cylindrical collectors surrounding the electrodes, arc photography, and measurements of the cathode erosion rate for copper at 100 A using the weight loss method. At pressures approaching atmospheric, it is shown that the measured erosion rate is reduced from that in vacuum by about an order of magnitude. Increasing the ambient pressure also decreases the distance from the cathode spots at which the 8% ion current can be detected. Data extrapolation shows that cathode spots at atmospheric pressure, particularly in the lighter gases, are still associated with the fundamental ion current. Comparison between the measured reductions in both the erosion rates and the ion currents indicates that vapor and ion redeposition on the cathode contribute to the decreased erosion. It is concluded that the cathode spots of low current arcs at pressures approaching atmospheric are basically similar to vacuum arc cathode spots. The final section of the paper compares current-dependent erosion data for copper arcs in vacuum and air, and shows the importance of collective cathode spot heating.
Auger electron spectroscopy study of cathode surfaces during activation and poisoning. I. The barium-on-oxygen-on-tungsten dispenser cathode
Authors: Springer R. W. , Haas T. W.
Published: February 2004

Auger electron spectroscopic analyses of the chemical changes taking place on a commonly used dispenser cathode have been carried out during activation and poisoning by several reactive gases (O2, CO, CO2, H2, N2, Ar). The chemical composition and work-function changes on the cathode were correlated at various stages of activation and poisoning, both at room temperature and at operating temperature. During activation, a process of considerable cleaning up of unwanted contaminants (chiefly carbon) occurs. Poisoning by reactive gases causes changes in the Ba–O ratio. A good agreement with the theoretical predictions for barium and oxygen concentrations of ∼1014 atoms/cm2 made by Zalm and our results was found. Over all, our results show that the excess barium adsorption model correctly explains electron emission from the dispenser cathode.
Optical guided waves in CdSxSe1−x diffused layers
Authors: Brillson L. J. , Conwell E. M.
Published: February 2004

We have observed the modes of a CdSxSe1−x diffused waveguide using prisms to couple 6328-Å radiation in and out of the guiding layer. The mode lines could be separated and their angular dispersion in air was measured. The diffusion profile of the CdSxSe1−x surface was determined by Auger electron spectroscopy and ion milling techniques. The refractive-index profile obtained from this procedure was well fitted by three linear segments. The number of modes and the mode spectrum were calculated for this profile using the WKB approximation. Good agreement was obtained between experiment and theory.
Investigations of microwave Faraday rotation in single crystals of n-type germanium at liquid-N2 temperature
Authors: Sethi B. R. , Srivastava G. P.
Published: February 2004

Free-carrier Faraday rotation measurements have been performed at liquid-N2 temperature in single crystals of n-type germanium using 24.0-GHz radiation in order to investigate experimentally the nature of its variation with B over a wider range of μB than possible from the room-temperature study. The investigations have been extended with B along all the three principal orientations, viz., [001], [111], and [110] of n-Ge crystals, in order to examine experimentally the validity of the predictions of the Donovan-Webster theory regarding anisotropy in the Faraday rotation with respect to magnetic field orientations at the liquid-N2 temperature. The measured rotation at this low temperature has been found, in general, to be less than that predicted by the above theory. The discrepancy between the experiment and theory disappears on the inclusion of the contribution of ionized impurity scattering in the Donovan-Webster theory, which takes into account lattice scattering only. The measurements have been further carried out in samples of different resistivities in order to study the effect of increase of conductivity of the sample on the nature of variations of θ with B at liquid-N2 temperature. The values of the lattice and the impurity mobilities in different samples have been determined. The variation of observed Verdet constant with conductivity for n-Ge at liquid-N2 temperature has also been reported.
Electrical properties of AgInSe2
Authors: Tell B. , Kasper H. M.
Published: February 2004

The temperature dependence of the electrical properties of a series of widely varying conductivity crystals of AgInSe2 is presented. The room-temperature electron concentration can be varied from greater than 1018 cm−3 to less than 1012 cm−3. The room-temperature carrier concentration can be reduced below ∼1017 cm−3 by annealing in Se, which however produces undesirable effects on the electron mobility. The conductivity is dominated by shallow donors (binding energy less than 20 meV) which are probably extrinsic impurities.
Comparison of optical to injection excitation in GaAs heterostructure lasers
Authors: Rossi J. A. , Chinn S. R. , Hsieh J. J. , Finn M. C.
Published: February 2004

By using the same GaAs–Ga1−xAlxAs heterostructure material to make both optically excited and junction lasers we have compared the performance of the two classes of lasers under pulsed room-temperature operation. We find that junction lasers have higher differential quantum efficiencies for reasons which are probably inherent in the excitation technique. However, the power efficiencies are higher for the optically pumped samples; by optical excitation of a single heterostructure, we have obtained 20% power conversion efficiency, a factor of 2 better than previous results.
Numerical method for evaluating three-dimensional magnetic fields in the region of a current-carrying conductor
Authors: DeMichele D. W. , Darby J. B.
Published: February 2004

A numerical method is developed for calculating the magnetic field within a rectangular conductor of finite cross section. The analysis begins with the equation of the law of Biot and Savart, which is a triple-integral expression. Two of the integrations in this expression can be evaluated analytically, which will yield a single integration that must be evaluated numerically. The present method provides a numerically stable argument for the remaining integration that can be evaluated for arbitrary coil shapes and is computationally efficient. An accuracy of at least three significant figures is obtained by comparing the present method with the limited number of analytic solutions for three-dimensional fields, resulting from a current-carrying conductor at points external to and within the conductor.
Radio-frequency echoes from nickel powder
Authors: Kupca S. , Searle C. W.
Published: February 2004

Echoes, following a two-pulse rf excitation, were observed in Ni powder. The frequency and temperature ranges were 20–100 MHz and 4.2–300°K, respectively. The echoes are due to mechanical oscillations of the particles excited by magnetostrictive coupling. The relaxation time of the echoes depends strongly on the external magnetic field and history of the sample; it arises from losses due to microeddy currents inside the individual particles.