bluuebunny/crossref_metadata_2025 huggingface dataset:
High current injection into SiO2 from Si rich SiO2 films and experimental applications
Authors: DiMaria D. J. , Dong D. W.
Published: February 2003

Chemically vapor deposited (CVD) Si rich SiO2 layers on thermal or CVD SiO2 layers incorporated into metal-insulator-semiconductor (MIS) capacitor structures are shown to give very large injected electron currents at low to moderate negative gate voltage biases. The dependence of this injection mechanism on the Si rich SiO2 composition and thickness, temperature, capacitor area, annealing conditions, gate metal (Al or Au), and underlying SiO2 thickness is described. Photocurrent measurements are discussed and are shown to give similar barrier energies as seen for ’’uniform’’ internal photoemission into SiO2. From the experimental electrical and photoelectrical measurements described here and transmission electron microscopy (TEM) and Auger studies of others, a possible model to explain this phenomenon based on electric field distortion caused by a two phase mixture of amorphous Si and SiO2 is presented. Two experimental applications of these structures are described. In one application, an electrically alterable read-only memory structure is fabricated, and it is shown to operate at lower voltage (?13 V) and power than popular commercially available devices. The other application involves a ’’multilayer’’ structure with alternating layers of polycrystalline Si islands (20 or 40 Å in diameter) and CVD SiO2 deposited on thermal SiO2 incorporated into an MIS capacitor which also gives large injected electron currents at moderate negative gate voltages similar to the currents observed with Si rich SiO2. This latter experimental application lends credibility to the proposed two phase model.
A method for determining temperatures and heat transfer coefficients with a superconductive sample
Authors: Gentile Dominique , Hassenzahl William , Polak Milan
Published: February 2003

The method that is described here uses the current-sharing characteristic of a copper-stabilized, superconductive NbTi wire to determine the temperature. The measurements were made for magnetic fields up to 6 T and the precision actually attained with this method is about 0.1 K. It is an improvement over one that has been used at 4.2 K to measure transient heat transfer in that all the parameters of the sample are well known and the current in the sample is measured directly. The response time of the probe is less than 5 μs and it has been used to measure temperatures during heat pulses as short as 20 μs. Temperature measurements between 1.6 and 8.5 K are described. An accurate formula based on the current and electric field along the sample has been developed for temperatures between 2.5 K and the critical temperature of the conductor, which, of course, depends on the applied field. Also described is a graphical method that must be used below 2.5 K, where the critical current is not a linear function of temperature.
Application of low-temperature scanning electron microscopy to superconductors
Authors: Clem John R. , Huebener R. P.
Published: February 2003

Scanning electron microscopy applied to specimens in close thermal contact with a liquid-helium bath can be used for a two-dimensional display of various sample responses arising from the localized excitation of the sample by the electron beam. As shown in recent experiments, the method becomes particularly interesting when applied to superconductors. A general response theory is outlined, and a detailed treatment is given for the special case of the thermal response associated with a strongly temperature-dependent electrical resistance of the sample.
Effect of magnetoresistance on electron paramagnetic resonance line shape in conducting media
Authors: Mullin D. P. , Furdyna J. K.
Published: February 2003

This paper discusses the problem of electron paramagnetic resonance (EPR) line shape of localized magnetic ions in conductors which exhibit a strong dependence of their electrical properties on the applied magnetic field. Semimetals and narrow-gap semiconductors with highly mobile charge carriers are specifically considered. When specimens (in the form of a plane-parallel slab) are much thinner than both the skin depth and the internal wavelength, the EPR line shape is Lorentzian, determined by the dissipative part of the dynamic magnetic susceptibility of the localized paramagnetic ions. When the specimens are thicker than the skin depth, a variety of line shapes is predicted, determined not by the value of the conductivity as such, but rather by the loss tangent (i.e., the ratio of the dissipative-to-dispersive components of the conductivity). This ratio, in turn, depends on the type of free carriers present (electrons or holes), carrier concentration, carrier mobility, as well as sample temperature and the value of the magnetic field at which EPR occurs. When the specimens are thicker than the internal wavelength, but thinner than the skin depth (a condition frequently satisfied in narrow-gap semiconductors and semimetals), Fabry-Perot–like geometrical resonances arise, which again profoundly affect the line shape. Specific ranges of the loss tangent, characteristic of narrow-gap semiconductors and semimetals, are discussed analytically and illustrated by numerical calculations. Where available, EPR data involving transmission experiments in Hg1−xMnxTe are presented.
Composition dependence of the Curie temperatures of amorphous alloys
Authors: Luborsky F. E.
Published: February 2003

The Curie temperatures of 25 amorphous alloy systems involving a binary metal together with metalloids have been fitted to phenomenological equations based on a localized band model involving only one adjustable parameter to describe the variation of Curie temperature with metal composition.
Compensation mechanisms in GaAs
Authors: Martin G. M. , Farges J. P. , Jacob G. , Hallais J. P. , Poiblaud G.
Published: February 2003

Semi-insulating GaAs materials, undoped or doped with concentration of chromium varying from 6×1015 to 4×1017 cm−3, have been studied using both Hall effect measurements and optical absorption measurements. It is definitively concluded that compensation comes from the presence of the deep donor EL2 in undoped materials, and from both this deep donor and the deep acceptor related to chromium in Cr-doped materials. Sets of curves are given which allow the determination of ND-NA, the concentration of shallow donors and acceptors, knowing the Hall mobility and the Cr concentration in a given sample. Such curves can be a working tool for assessing any piece of semi-insulating GaAs in a routine way.
Quantum efficiency of InP field-assisted photocathodes
Authors: Maloney T. J. , Burt M. G. , Escher J. S. , Gregory P. E. , Hyder S. B. , Antypas G. A.
Published: February 2003

Reflection-mode quantum efficiencies have been calculated for the p-InP bias-assisted photoemitter (TE cathode) and have been found to be consistent with experimental data. The calculations, using Monte Carlo techniques, consider the transport of photogenerated electrons to the surface as well as the transmission of electrons at the surface into vacuum. Dependence of the predicted yield upon bias voltage and doping is discussed. Acceptor doping in the mid 1016/cm3 range is indicated as a good choice for a high quantum efficiency photocathode.
Specific contact resistance for alloyed Au-Zn contacts on p-type GaxIn1−xPyAs1−y
Authors: Casey H. C. , Logan R. A. , Foy P. W. , Augustyniak W. M. , Vandenberg J. M.
Published: February 2003

The specific contact resistance for a pulse plated and alloyed Au-Zn (16 at. % Zn) contact on p-type Ga0.28In0.72P0.39As0.61 was found to be 3.60.4×10−5 Ω cm2. Results of Rutherford backscattering measurements with 1.8-MeV 4He+ showed that the alloyed Au moved only ∼1500 Å into the quaternary layer, while In and GaAs were displaced to the surface.
Thin film electroluminescent cell with the low-threshold voltage of n-Ge-ZnSe:Mn2+-indium-tin oxide structure
Authors: Ohnishi H. , Hamakawa Y.
Published: February 2003

A dc-operated thin-film electroluminescent cell is fabricated by the use of a heterojunction contact of n-Ge to ZnSe as an efficient electron injector. The typical display performance of the cell having n-Ge-ZnSe:Mn2+-ITO structure is 100 fL in brightness and 16 mlm/W in luminous efficiency at 24.1 V×10mA.
Etching of SiO2 and Si in a He-F2 plasma
Authors: Vasile M. J.
Published: February 2003

The etching of SiO2 on Si in a plasma containing 80% helium/20% fluorine has been studied using direct ion sampling. Ionic species in the discharge show the transition from the SiO2 surface to the Si surface, and reflect changes in the gas composition in the region adjacent to the specimen very strongly. SiO2 etched at a rate of 90–100 Å/min when mounted on the ground electrode and at 350–450 Å/min when mounted on the rf electrode. Silicon etches at 2000 Å/min on the ground electrode and at 6000 Å/min on the rf electrode. The enhanced etch rates for the rf electrode are attributed to the increased kinetic energy of the ion bombardment. Reactive ion etching could account for the SiO2 removal rate, but not for the Si removal rate. A more dilute He-Fe2 mixture was used to etch polycrystalline Si with some degree of anisotropy, and with minimal attack on the photoresist mask.
The influence of crossed electric and magnetic fields upon the breakdown voltage and prebreakdown current in vacuum
Authors: Watson Alan
Published: February 2003

An experimental study is presented for the dependence of the breakdown voltage and the prebreakdown current on the crossed electrical and magnetic fields in vacuum. The magnetic field is varied in the range 0–250 G and the gap separation 0.5–3 cm. Bruce profiled copper electrodes which have been prebaked either in vacuum or hydrogen were employed. The breakdown voltage and the prebreakdown current are presented as functions of the magnetic flux density at fixed gap separation as well as at fixed flux density as functions of the gap separation. Comparison is made between these functions and curves calculated from the theory of the magnetic perturbation of the field emission from protrusions covered with semiconducting oxide layers and good agreement is obtained.
Electromagnetic macroparticle acceleration by a high pressure plasma
Authors: McNab I. R.
Published: February 2003

Simple equations are used to infer approximate values of the major parameters of an unusual plasma which was used by Rashleigh and Marshall to accelerate 3-g macroparticles to high velocities (5.9 km/s). Subject to the assumptions made here, these results indicate that for the applied current of 300 kA and generated pressure of 1.1×108 N/m2, the temperature of the ionized copper plasma was 4413 kK and the electron number density was (81)×1025 m−3. It is recommended that future experiments of this type should incorporate instrumentation techniques which can provide direct experimental evidence on these parameters.
Arsenic precipitation at dislocations in GaAs substrate material
Authors: Cullis A. G. , Augustus P. D. , Stirland D. J.
Published: February 2003

High-resolution diffraction utilizing an analytical electron microscope has been employed to identify small (∼500 Å-diam) precipitates attached to line dislocations in gallium arsenide. The results show that the precipitates consist of crystallites of elemental hexagonal arsenic embedded within the gallium arsenide matrix. Precipitates were observed in a range of semi-insulating, p-type, and n-type material and were not dependent on the presence of specific additional dopants for their occurrence. The way in which the particles may originate is discussed.
Electron spectroscopy study of silicon surfaces exposed to XeF2 and the chemisorption of SiF4 on silicon
Authors: Chuang T. J.
Published: February 2003

The surface chemistry of silicon exposed to reactive XeF2 gas and the chemisorption of SiF4 on Si at −150 and 25 °C have been studied using XPS and AES. While SiF4 can be condensed at −150 °C, XeF2 is dissociatively chemisorbed and Xe does not stick on the surface. For both Si/SiF4 and Si/XeF2 at 25 °C, a layer of SiF2-like surface species is identified from the characteristic core level chemical shifts. The formation of this fluorinated surface layer hinders the adsorption of SiF4, but XeF2 reacts with this layer to form volatile SiF4. The behavior of fluorine chemisorption on silicon is illustrated for the first time and the role of surface fluorine in the silicon etching process is discussed in light of the new results.
Epitaxial regrowth of Ar implanted amorphous Si by laser annealing
Authors: Matteson S. , Révész P. , Farkas Gy. , Gyulai J. , Sheng T. T.
Published: February 2003

The epitaxial regrowth of argon-implanted self-implantation-produced amorphous silicon under Q-switched ruby laser pulses is reported. It is shown that pulse annealing succeeds in producing epitaxial regrowth in the present case where equilibrium thermal annealing fails. A highly porous layer filled with spherical voids is observed by transmission electron microscopy (TEM). Four-point probe measurements of the annealed layers exhibit a very high sheet resistance. The electrical properties are explained in terms of the unique microstructure of the pulse annealed layer.
Energy gap in Si and Ge: Impurity dependence
Authors: Mahan G. D.
Published: February 2003

The energy gap in silicon and germanium is calculated as a function of the concentration of donor impurities. The results are compared with the available data from optical experiments and devices. Previous theories are critically reviewed.
Quantum effect on transverse magnetoresistance of degenerate piezoelectric semiconductors in strong magnetic fields
Authors: Wu Chhi-Chong , Chen Anna
Published: February 2003

The quantum effect on the transverse magnetoresistance of degenerate piezoelectric semiconductors with the isotropic parabolic energy bands has been studied for the case where acoustic phonons are the dominant scattering mechanism. The calculation has been performed taking into account the inelasticity in the electron-phonon scattering due to the finite energy of phonons involved. It is shown that both deformation-potential and piezoelectric couplings play the same important role for the transverse magnetoresistance in strong magnetic fields B. These results are quite different from those of our previous work for nondegenerate semiconductors in which the acoustic-phonon scattering due to the piezoelectric coupling contributes very insignificantly to the transverse magnetoresistance. Numerical results also show that transverse magnetoresistances for both couplings oscillate with the magnetic field owing to the degeneracy of the electron gas. However, the number of oscillations will decrease when the magnetic field increases.
Electrographic development: An electrostatic calculation
Authors: Cheng Y. C. , Hartmann G. C.
Published: February 2003

The electrostatic field in the development region is mathematically analyzed for a spatially varying image. The effects of space charge due both to charge toner particles and the electrostatic image are included in the field calculation. The results are applied to simple models of xerography and photoactive pigment electrophotography.
Physics of the krypton fluoride laser
Authors: Johnson Thomas H. , Hunter Allen M.
Published: February 2003

The extremely complex kinetics of pumping, quenching, and absorption in krypton fluoride excimer lasers is now relatively well understood. A single comprehensive kinetic model, solved approximately by analytic means and more exactly by a computer code of moderate size, is capable of simulating with great accuracy the performance of KrF lasers pumped by e-beam sustained discharge, and self-sustained discharge. We present the results of applications of this model to interpret and predict the limiting behavior and scaling of KrF lasers. A measure of remaining uncertainties is discussed.
Semiconductor Raman laser
Authors: Nishizawa J. , Suto K.
Published: February 2003

The semiconductor Raman laser has been realized by using a GaP crystal. Pumping is made by a Q-switched YAG laser operating at 1.064 μm. The round-trip loss in the Fabry-Perot resonator is 2% or less. The Raman scattering from LO phonons stimulates in the 〈100〉 direction, while the forward and backward Raman scattering from TO phonons stimulate in the 〈110〉 direction. This semiconductor Raman laser is promising as a semiconductor far-infrared radiation source.
XeF laser characteristics studied at elevated temperatures
Authors: Ernst W. E. , Tittel F. K.
Published: February 2003

The electron-beam-pumped XeF laser operating on the B-X and C-A transitions shows a strong temperature dependence. Fluorescence, gain, and laser output measurements in Ar/Xe/NF3 and Ne/Xe/NF3 mixtures are reported for temperatures from 300 to 600 K. Elevated temperatures cause stronger mixing between the B and C states as well as among the vibrational levels within the B state. Together with the higher ground-state dissociation rate this leads to an improvement of the B-X lasing for 300k < T < 500 K, whereas the C-A laser emission ceases under these conditions.
A comparative study of the radio frequency discharge in gas mixtures of helium with flourine, oxygen, nitrogen, and argon
Authors: Vasile M. J.
Published: February 2003

Mass spectrometric sampling of the positive ions from the rf discharge in an 80 mole % helium-20 mole % flourine mixture showed the principal ions to be F+2 and F+. Impurity ions observed in the specially constructed discharge vessel were O+2 and CF+3 accounting for 10 –15% of the total ions. Very high ion flux was obtained from the discharge in the helium-flourine mixture, relative to discharge in pure gases. This effect was also found for mixtures of helium with oxygen, nitrogen, and argon. Floating double probe measurements showed that the average electron energy is higher in the helium mixtures than in the pure gases for comparable pressure and power input. Probe measurements also showed that the degree of ionization was higher in the helium mixtures, but the variations were not as large as the mass spectrometric measurements indicated. Some evidence was found to indicate that F− modifies the sheath, but retardation measurements clearly show the charged particle loss from helium-flourine plasma to be controlled by positive ion-electron ambipolar diffusion.
The general critical state model in two dimensions and zero applied field: A uniqueness theorem and some consequences
Authors: Migliori A.
Published: February 2003

A general critical state model describes the field and current distributions in a hard Type II superconductor with a local relation between the field and current density. We show here that such models cannot provide a magnetically shielded region in superconducting wires in zero applied field.
Field effect and thermoelectric power on boron doped amorphous silicon
Authors: Jan Zimmer S. , Bube Richard H. , Knights John C.
Published: February 2003

Field effect and thermoelectric power measurements have been made as a function of temperature on a series of B doped amorphous silicon samples prepared by glow discharge decomposition of silane. The investigation complements an earlier one on As doped amorphous silicon prepared by the same method. Incorporation of boron leads to an increase in the density of localized states lying 0.42 eV above the valance edge. The density of surface states is less than or equal to 1.5×1011 cm−2 eV.−1 Electrical transport is interpreted in a two channel model, involving transport both in extended valence states and in a band of localized states associated with the B acceptors. The effect of hydrogen evolution due to thermal annealing on the localized state densities and transport processes is also investigated.
Exchange energy near singular points or lines
Authors: Aharoni Amikam
Published: February 2003

The conventional expression for the exchange energy in a continuous material is valid for slowly varying functions only. It breaks down at singularities and introduces unphysical infinities. In order to correct this, it is suggested here to postulate another expression which is always finite, and can be used conveniently with functions which vary slowly over most of the material, and rapidly in some parts of it.
Photoelastic studies of three-dimensional stress field caused by a cylindrical punch
Authors: Chu S. N. G. , Li J. C. M.
Published: February 2003

A stress-freezing technique is used to observe the stress distribution inside a cylindrical body produced by a coaxially loaded cylindrical punch. The flat end of the punch is pressed against the top surface of a vertical cylinder. After the stress is frozen in, a thin vertical diametric slice is prepared for photoelastic observation. The stress distribution is compared with theoretical results calculated for a semi-infinite body using the following two boundary conditions: uniform displacement of the punch and uniform pressure under the punch. The agreement is good at long distances (three times the punch radius) with either boundary condition. At short distances, the observed stress distribution is in between but close to the uniform displacement boundary condition. These results support the use of mixed stress distributions under the punch in a previous finite-element calculation of impressing creep velocities.
Piezoelectric photoacoustic detection: Theory and experiment
Authors: Jackson Warren , Amer Nabil M.
Published: February 2003

The theory of piezoelectric photoacoustic spectroscopy is developed for condensed-matter samples. Treating the sample as an elastic layer and neglecting the transducer’s effect on the sample, the three-dimensional uncoupled quasistatic thermoelastic equations are solved using a Green’s function for the stress. An expression for the dependence of the signal on absorption, modulation frequency, thermal properties, and mechanical properties of the sample is derived. The theoretical predictions are experimentally verified, the sources of noise are analyzed, and the noise equivalent power is estimated. Finally, considerations for detector optimization are discussed.
A method for increasing the etch-rate ratio of oxides to nonoxides in inert-gas ion milling processes
Authors: Gerlach-Meyer U. , Coburn J. W. , Kay E.
Published: February 2003

The etch-rate ratio of oxides to nonoxides in inert gas ion milling systems can be increased by injecting a flux of halocarbon gas molecules onto the surface along with the inert-gas ion beam. In order for the halocarbon to be effective, it must adsorb on the surfaces of interest and the halogon must form a volatile reaction product with the surfaces. The system Ar+/CCl4/Si and SiO2 is used to illustrate this method.
X-ray photoelectron spectroscopy and Auger electron spectroscopy studies of glow discharge Si1−xCx:H films
Authors: Lee Wen-Yaung
Published: February 2003

X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) were used to characterize the air-exposed and sputter-cleaned surfaces of glow-discharge-produced Si1−xCx:H (x=0.05 to 0.90) films. On the air-exposed surfaces, silicon was preferentially oxidized with the enriched carbon existing as graphite or hydrocarbon. Signal intensities obtained from the surfaces sputter cleaned with 1 keV Ar+ ion beams indicated no significant preferential sputtering of C to Si for these films. The values of the carbon 1s and silicon 2p and 2s binding energies as well as the valence band spectra suggested a significant change in the local atomic configurations at x∼0.6–0.7. Based on these XPS and AES results and the reported IR absorption data, a slightly cross-linked, carbon and hydrogen substituted polysilicon and an almost fully cross-linked, silicon and hydrogen substituted polycarbon were proposed to describe the structure of films below and above x∼0.6–0.7, respectively.
The Bloch-wave characteristic impedance of a rectangular waveguide with discrete periodic loading
Authors: Mallick Amiya Kumar , Sanyal Gitindra Saran
Published: February 2003

The Bloch-wave characteristic impedance as well as the Bloch-wave propagation constant of a rectangular waveguide periodically loaded with a series of thin, circular, centrally located, metal posts along the direction of propagation has been investigated both theoretically and experimentally. The theoretical analysis has been made to explore the frequency dependence of the real and imaginary parts of the Bloch-wave characteristic impedance. As a part of the analysis, the study of the ω-β diagram has also been exercised. The experimentally obtained data show agreement with the theoretical results.
Single-crystal solar cell heterojunctions involving N-cadmium sulfide
Authors: Arienzo M. , Loferski J. J.
Published: February 2003

A chemical vapor deposition method capable of depositing high-quality epitaxial layers of CdS on single-crystal substrates has been employed for the fabrication of heterojunction photovoltaic devices of the type n-CdS/p-InP, n-CdS/p-CdTe, n-CdS/p-GaAs, and n-CdS/p-Ge. Analysis of the photovoltaic responses shows that all the devices generally have good collection efficiency, i.e., that at zero bias, photogenerated carriers crossing the junction do not suffer appreciable recombination at interface states. The solar energy conversion efficiency is, however, strongly influenced by the interface states through the open circuit voltage and the fill factor. Analysis of the dark current-voltage characteristics shows the existence of a low-temperature low-bias voltage tunneling current in all of the devices. In at least two devices, n-CdS/p-InP and n-CdS/p-CdTe, there exists, at temperatures equal to or higher than 300 °K, a tunneling recombination current which flows through states near or at the interface with a thermal activation energy of about 0.6 eV.
New activation methods for long-life and highly stable GaP-GaAlP heterojunction cold cathodes
Authors: Kan Hirofumi , Katsuno Hironobu , Nakamura Tsutomu , Hagino Minoru , Sukegawa Tokuzo
Published: February 2003

By new activation methods, namely, activation by Cs, Sb, and O2 (our former new method), or Cs, Ag, and O2 (our present new method), stabilized negative electron affinity (NEA) cold cathodes can be obtained, and continuous operation over 6000 h has been achieved with GaP-GaAlP cold cathodes at emission current density of about 10−1 A/cm2. It is found that a major source of rapid degradation of the cold cathode is the loss of the activation material from NEA surface because of nonthermal equilibrium for the activation material. By the new activation methods, the efficiency of the cold cathode showed an increase of 20 ∼60% over that of the conventional method.
Optical emission spectroscopy of reactive plasmas: A method for correlating emission intensities to reactive particle density
Authors: Coburn J. W. , Chen M.
Published: February 2003

The addition of a small concentration of suitably chosen noble gas to a reactive plasma is shown to permit the determination of the functional dependence of reactive particle density on plasma parameters. Examples illustrating the simplicity of this method are presented using F atomic emission from plasma-etching discharges and a comparison is made to available data in the literature.
Extended x-ray absorption fine structure of NaBr and Ge at high pressure
Authors: Ingalls R. , Crozier E. D. , Whitmore J. E. , Seary A. J. , Tranquada J. M.
Published: February 2003

The x-ray absorption spectra of Ge and of Br in NaBr have been measured to pressures of 52 and 21 kbars, respectively, in a boron carbide and diamond anvil cell in which pressure was measured via the ruby-fluorescence technique. Although Bragg peaks from the diamond anvil reduced the accuracy, atomic spacings in both materials could be determined by extended x-ray absorption fine-structure (EXAFS) analysis. Changes in the nearest-neighbor separations in NaBr, and Ge to at least 40 kbars, agreed with literature values, indicating that the EXAFS phase shifts are quite insensitive to such pressures. In addition the near-edge peak positions in the NaBr spectra appeared to readily shift with pressure, which suggests that NaBr may be quite suitable as a pressure standard in future work of this type.
Redistribution of implanted oxygen and carbon in silicon
Authors: Koyama H.
Published: February 2003

This paper reports new experimental results on the measurements of oxygen and carbon in silicon. 18O and 13C in-depth distribution has been measured in silicon as a function of postimplant furnace and laser annealing using secondary ion mass spectroscopy. Analysis shows that a complicated structure appears in the 18O atomic profile following 900–1100 °C furnace annealing. The 18O redistribution is substantially caused by implantation-induced damage gettering of 18O in silicon. Because of a fast annihilation of displacement damages by laser annealing, any complicated redistribution was not observed in the laser-annealed 18O atomic profile. No such structure was observed in the furnace- and laser-annealed 13C atomic profiles, implying some differences in the atomic behavior of carbon and oxygen in silicon.
Temperature dependence of the phonon dispersion in Tl3PSe4
Authors: Fincher C. R. , Shapiro S. M.
Published: February 2003

Previous ultrasonic measurements have shown a softening of one of the acoustic-phonon branches in thallium phosphorus selenide (Tl3PSe4) when subject to hydrostatic pressure. These measurements also show a 60% softening between room temperature and 90 K. In order to further characterize this material and to investigate the possibility of a phase transition at temperatures less than 90 K, we have used inelastic neutron scattering to measure the phonon dispersion along symmetry directions. The measurements agree well with the ultrasonic measurements previously reported for all branches except the soft ab shear described by the strain component e6. The ab shear is found to be 60% stiffer than the ultrasonic value with very little temperature dependence.
Oxidation of tantalum disilicide on polycrystalline silicon
Authors: Murarka S. P. , Fraser D. B. , Lindenberger W. S. , Sinha A. K.
Published: February 2003

Oxidation characteristics of the tantalum disilicide films have been investigated in the temperature range of 900°–1050 °C in dry oxygen and steam ambients. The silicide does not oxidize in dry oxygen and oxidizes in steam at a rate lower than that of doped polycrystalline silicon films as long as there is a polycrystalline silicon layer between the silicide and the gate oxide. Under these circumstances, the silicide retains its electrical and mechanical characteristics. The oxide on the silicide has an etch rate (in buffered hydrofluoric acid) similar to that of thermal SiO2 on silicon. Electrical characteristics of the oxide appear to be similar to those of the wet oxide on polycrystalline silicon. In the absence of polycrystalline silicon, between the silicide and the gate oxide, oxidation leads to a loss in the conductivity of the silicide and eventually to a mechanical instability of the film. An oxidation mechanism, which assumes silicon diffusion by substitution through the silicide, has been proposed.
Electron mobility in compensated GaAs and AlxGa1−xAs
Authors: Stringfellow G. B. , Künzel H.
Published: February 2003

The dependence of electron mobility μ on temperature T in GaAs and AlxGa1−xAs indicates that for compensated material a term having μ∝T−1/2 causes a significant reduction in the mobility measured at high temperatures. The magnitude of the T−1/2 term in mobility, denoted μCA, is found to be linearly proportional to the compensating acceptor concentration over a range of more than two orders of magnitude in samples with no intentional doping where carbon is the major compensating acceptor. Intentional compensation using Ge and Zn is found to have no effect on μCA. Illumination (hν≳EG) has no effect on μCA. Such illumination is demonstrated to significantly reduce the size of space-charge layers at the n-i interface. Thus, the T−1/2 mobility is not due to scattering by space-charge regions as has been previously assumed. The acceptor C, or an associate involving C, is concluded to be the scattering center responsible for μCA. The effect may be due to the short-range central-cell potential resulting from the large electronegativity difference between C and the As for which it substitutes in the lattice.
Optically induced conductivity changes in discharge-produced hydrogenated amorphous silicon
Authors: Staebler D. L. , Wronski C. R.
Published: February 2003

Long exposure to light decreases the photoconductivity and dark conductivity of some samples of hydrogenated amorphous silicon (a-Si : H). Annealing above ∼150 °C reverses the process. The effect occurs in the bulk of the films, and is associated with changes in density or occupation of deep gap states. High concentrations of P, B, or As quench the effect. Possible models involving hydrogen bond reorientation at a localized defect or electron-charge transfer between defects are discussed. An example is shown where these conductivity changes do not affect the efficiency of an a-Si : H solar cell.
Thermally stimulated current and thermoluminescence due to electron detrapping by local molecular motions in polyethylene-terephthalate
Authors: Ito D. , Nakakita T.
Published: February 2003

Simultaneous measurements of the dielectric loss tangent (tanδ) and thermoluminescence (TL) or of thermally stimulated current (TSC) and thermoluminescence have been carried out in order to study electron trapping phenomena in polyethylene-terephthalate (PET). Close correlations between the various measurements have been observed. In tanδ measurements made at 1 kHz and at temperatures ranging from −190° to 150 °C four peaks are observed, viz., at −140° ( β3), −110° ( β2), −40° ( β1), and 150 °C (α). Correlations between the simultaneous measurements of TL and tanδ and that of TL and TSC indicate that the electrons are mainly liberated from their traps by the β1 relaxation. Comparison with available dielectric loss data of oligoethylene-terephthalate suggests that the β1 relaxation of PET should be attributed to the motions of the carboxyl groups in the main chains. Photoelectroluminescence (PEL) for PET has been observed and degradation of the sample has been noted at the luminous region of the PEL. The coincidence of the PEL spectrum with that of TL suggests that the luminescence center should be attributed to that part of the polymeric chains which are liable to chain scission.
A model for the dissociation pulse, afterglow, and laser pulse in the Cu/CuCl double pulse laser
Authors: Kushner M. J. , Culick F. E. C.
Published: February 2003

A model which completely describes the Cu/CuCl double pulse laser is presented. The dissociation discharge pulse and afterglow are simulated and the results are used as initial conditions for an analysis of the pumping discharge pulse and laser pulse. Experimental behavior including the minimum, optimum, and maximum delays between pulses, and the dependence of laser pulse energy on dissociation energy are satisfactorily reproduced. An optimum tube temperature is calculated, and the dependence of laser pulse energy on tube temperature (i.e., CuCl vapor pressure) is explained for the first time.
Mode locking of strip buried heterostructure (AlGa)As lasers using an external cavity
Authors: van der Ziel J. P. , Mikulyak R. M.
Published: February 2003

Active and passive mode locking of strip buried heterostructure lasers is observed using an external cavity consisting of a lens and a mirror. Using the second-harmonic-generation method to obtain the second-order autocorrelation function we obtain Gaussian pulses as short as 35.7 psec (FWHM) at a 1.9-GHz repetition rate. The optical spectrum of the mode locked laser consists of longitudinal modes of the composite cavity spaced by ∼0.05 Å, whose amplitudes are modulated by the 2.09-Å-mode spacing of the laser itself, and contained under a Gaussian envelope of 9.5-Å FWHM. Additional very sharp structure (∼1.6-psec FWHM) in the autocorrelation is shown to result from the presence of several laser mode groups.
Laser action in photopumped GaAs ribbon whiskers
Authors: Stone J. , Burrus C. A. , Campbell J. C.
Published: February 2003

We have observed laser action in single-crystal ribbon whiskers of GaAs. The whiskers were grown with various dopants by a vapor transport process and were used, as grown, in an ultrashort cavity composed of high reflectivity dielectric mirrors. The structure was longitudinally photopumped, and it operated in a single mode at room temperature.
Electrically pumped relativistic free-electron wave generators
Authors: Bekefi G.
Published: February 2003

Stimulated scattering induced by the longitudinal electric field of a pump wave is studied theoretically for the case of dense relativistic electron beams traveling in cylindrical metal waveguides. Two processes are examined. In one, the pump wave decays parametrically into a slow and a fast space-charge wave. In the other, it decays into a slow space-charge wave and a TM wave of the guide. The frequency characteristics and stimulated growth rates are given for each process, as a function of beam diameter, velocity, and density.
Thin-film waveguide evanescent dye laser and its gain measurement
Authors: Sasaki K. , Fukao T. , Saito T. , Hamano O.
Published: February 2003

Superradiant waveguide evanescent-type dye lasers are realized by polyurethane top layers containing Rhodamine 6G and Rhodamine B respectively on single-mode glass waveguides with N2 uv laser pumping. A new determination method of gain factor (negative absorption coefficient) by active guide length dependence of a triangle shape top layer is proposed.
On the shifts of self-reversed maxima of the sodium resonance radiation
Authors: Yu-Min Chien
Published: February 2003

Relationships between partial pressures and shifts of blue wing and red wing maxima of the self-reversed D lines in a high-pressure sodium-mercury discharge have been calculated. A van der Waals model is used in the calculation of the interaction between sodium and mercury atoms. A useful and convenient formula has been derived for estimating mercury pressure in a sodium-mercury discharge from easily measured parameters (the shift of red wing maximum and the shift of blue wing maximum).
Vacuum ultraviolet absorption cross sections for halogen containing molecules
Authors: Roxlo C. , Mandl A.
Published: February 2003

Vacuum ultraviolet absorption cross sections for the compounds Cl2, Br2, I2, HCl, HBr, HI, CCl4, CCl3Br, CF3Br, CF3I, HgCl2, HgBr2, and HgI2 have been measured between 170 and 230 nm. Studies of the Xe*2 discharge lamp used are reported. The absorption bands of various mercuric halides are identified.
Development and investigation of relativistic electron beams with finite energy spread and improved emittance
Authors: Fink J. , Schilling H. B. , Schumacher U.
Published: February 2003

This paper presents experimental results in the development of low-emittance relativistic electron beams with finite energy spread, which—among other applications—is suitable for suppressing collective instabilities in an electron-ring accelerator. The measurements were performed with a divided cathode in an electron-beam gun, one half of which is connected via a resistor with the high-voltage terminal. The energy difference can be varied up to 100 keV in proportion to the resistance, with equal subcurrents. The beam parts are well separated, and their radial distance is about equal to the radial difference of the corresponding electron closed orbits, such that electron-ring formation with minimum radial betatron oscillations should be possible. The beam emittance is as small as about 100 mrad cm and the current is 800 A.
Temperature dependence of the minimum in AC power losses of (Nb0.99Zr0.01)3Sn in parallel AC and DC magnetic fields
Authors: Kovachev V. T.
Published: February 2003

ac losses PL of bronze-processed (Nb0.99Zr0.01)3Sn strips have been measured between 4.2 and 16.5 K in the presence of a dc magnetic field H0. The measurements were performed using an electronic wattmeter with both ac and dc fields parallel to the long flat surfaces of the sample. A minimum in the function PL(H0) was observed for fixed ac amplitudes h0. This minimum was found to occur in the entire temperature range between 4.2 and 16.5 K. A similar minimum was recently reported in Nb3Ge [Thompson et al., J. Appl. Phys. 50, 3514 (1979)] at 4.2 K. The position of the minimum is explained here by the same physical model as in Thompson et al. [J. Appl. Phys. 50, 3514 (1979)]; and Clem (ibid. 3518), but extending the model to include the temperature dependence of the entry surface shielding fields ΔHen(B,T) for flux density in the sample B=0. It is also shown here that loss minimum measurements can be used for the determination of ΔHen(0,T) in the temperature range 4.2–16.5 K.
The effects of ion implantation on La, Ga:YIG films as observed by spin wave resonance
Authors: Algra H. A. , Robertson J. M.
Published: February 2003

A ferromagnetic resonance (FMR) study of the effects of ion implantation into La, Ga:YIG (yttrium iron garnet) films is presented. H+, Ne+, and Ar+ are used with doses ranging from 1014 to 1016 ions/cm2 and implantation energies up to 200 keV. It is observed that the field for uniform resonance changes, and also that the magnetic film thickness decreases, depending on the ion and dose used. The experimental spin-wave spectra are compared with theoretical spectra, yielding a profile for the anisotropy through the film thickness. It is argued that the observed changes in the magnetic film thickness are due to the existence of paramagnetism in the implanted top layer of the film.
Light scattering effects in photoacoustic spectroscopy
Authors: Helander Per , Lundström Ingemar , McQueen Douglas
Published: February 2003

The influence of light scattering on photoacoustic signals is treated. Theoretical and experimental results are compared. The theoretical results are based on a model in which the photons diffuse through the sample. An equation governing the diffusion process is solved with appropriate boundary conditions. This gives the distribution of photons in the sample. The photoacoustic signal is then calculated and the result is compared with the result for nonscattering samples, giving the influence of the light scattering. The experimental results are obtained by measuring the photoacoustic signal for both scattering and nonscattering samples. The experimental and theoretical results are in good agreement. The differences are mainly due to the incompleteness of the original diffusion theory. An improved theory incorporating internal reflection at the sample surface is also analyzed. The paper illustrates the effects of light scattering on photoacoustic signals. It also shows how to estimate theoretically the photoacoustic signal from a light-scattering sample.
The temperature dependence of optical and mechanical properties of Tl3AsSe3
Authors: Ewbank M. D. , Newman P. R. , Mota N. L. , Lee S. M. , Wolfe W. L. , DeBell A. G. , Harrison W. A.
Published: February 2003

The refractive indices of Tl3AsSe3 as a function of wavelength and temperature are reported. Also included are the variations with temperature of the coefficients of thermal expansion. Within the context of a simplified LCAO theory the apparent anomalous temperature dependences of the refractive indices are explained.
Radiation spectra and angular distribution of emitted quanta for planar channelled particles: radiation of single particle
Authors: Kheifets S. , Knight T.
Published: February 2003

A method of calculating the radiation characteristics for the motion in an arbitrary one-dimensional potential is developed. Expressions for channelling radiation frequencies, polarization angles, and the number of emitted photons as functions of quanta angles, particle energy, amplitude of oscillations, and divergence in a plane parallel to the trapping crystal planes for any given harmonic number are found. The problem is treated in the classical approximation. Numerical examples of the application of the derived formulae for channelling in the (1,1,0) direction of a silicon crystal are given. The results are presented both for electrons and positrons. Comparison of the calculation results for two choices of continuum potential for positrons is also given.
Photoelectrochemical and solid-state properties of LuRhO3
Authors: Jarrett H. S. , Sleight A. W. , Kung H. H. , Gillson J. L.
Published: February 2003

Rare-earth rhodates of the distorted perovskite structure are semiconductors with a band gap of 2.2 eV. They may be doped either n or p type. The oxides are stable against photodecomposition at the potential for hydrogen evolution. With ceramic p-type LuRhO3 as the cathode and n-type TiO2 as the anode of an electrolytic cell sufficient photopotential is developed both to photoelectrolyze water in sunlight with no externally applied potential and to generate power simultaneously. As synthesized, LuRhO3 is p type as determined by thermoelectric power measurements, but may be doped n type by the introduction of Th+4 during synthesis. Electrical resistivity data show that this oxide passes through compensation as the doping level increases, the activation energy at compensation being one-half the optical band gap. The concentration of donor and acceptor impurities was determined by magnetic susceptibility to be in the vicinity of 1% for all samples. From these data, an estimate of 2.5 cm2/V sec can be made for the mobility of holes and 1 cm2/V sec for the mobility of electrons. Unlike most n-type oxides reported, LuRhO3 possesses deep lying impurity levels and surface capacitance is far from Mott-Schottky behavior. We have developed a theory of surface capacitance for deep levels, and the data agree well with theory. It is interesting to note that the Fermi level of LuRhO3 is pinned to the electrolyte at the same potential independent of whether the oxide is p or n type.
Electron backstream to the source plasma region in an ion source
Authors: Ohara Yoshihiro , Akiba Masato , Arakawa Yoshihiro , Okumura Yoshikazu , Sakuraba Junji
Published: February 2003

The flux of backstream electrons to the source plasma region increases significantly with the acceleration voltage of an ion beam, so that the back plate in the arc chamber should be broken for quasi-dc operation. The flux of backstream electrons is estimated at the acceleration voltage of 50–100 kV for a proton beam with the aid of ion beam simulation code. The power flux of backstream electrons is up to about 7% of the total beam output at the acceleration voltage of 75 kV. It is pointed out that the conventional ion sources such as the duoPIGatron or the bucket source which use a magnetic field for source plasma production are not suitable for quasi-dc and high-energy ion sources, because the surface heat flux of the back plate is increased by the focusing of backstream electrons and the removal of it is quite difficult. A new ion sourc which has an electron beam dump in the arc chamber is proposed.
Fast and efficient plasma heating through superelastic laser energy conversion
Authors: Measures R. M. , Wizinowich P. L. , Cardinal P. G.
Published: February 2003

Superelastic laser energy conversion has been shown to be capable of extremely rapid rates of plasma heating with relatively modest values of laser irradiance. In the case of a boron III plasma, dTe /dt≳1013 °K sec−1 has been predicted for a initial boron III ion density of 1017 cm−3. The laser irradiance needed to achieve this rate of change of the free-electron temperature is about 5×108 W cm−2 per cm of path length.