bluuebunny/crossref_metadata_2025 huggingface dataset:
Dynamic fracture phenomena in high-strength steels
Authors: Weimer Raymond J. , Rogers Harry C.
Published: February 2003

Brittle metals subjected to blast loads shatter into a large number of very small particles, the number and size of which are well characterized by the semiempirical cumulative distribution function of Mott. This function, however, contains no information regarding either the manner of breakup or the reason for a particular distribution. An earlier analytical study of the phenomenology of brittle fragmentation used statistical arguments to establish relationships between the energies associated with crack branching and the Mott parameters that characterize the particle distribution. That model predicts that the average mass of a particle from the shattered body is proportional to the fourth power of the crack-branching stress-intensity factor. In the present work on hypereutectoid steels, the ratio (KH/KIC)3.4 was experimentally determined to be linearly related to the average particle mass in reasonably good agreement with the model prediction, where KH is the dynamic stress intensity factor for incipient microbranching (hackle), and KIC is the plane-strain fracture toughness.
Superconducting T
c’s and phase relationships of sputter-deposited Nb3Ge
Authors: Buitrago R. H. , Toth L. E. , Goldman A. M.
Published: February 2003

Nb3Ge which is fully superconducting above 21 K has been prepared by sputter deposition in a very clean vacuum system at substrate temperatures in the range 500–550 °C, or 200 °C less than the temperatures needed in other sputtering systems. For a series of compound targets, superconducting Tc’s and metallurgical phases, as established from x-ray diffraction studies, were determined as a function of substrate temperature and argon pressure. Maximum Tc’s were found in films prepared over a narrow range of compositions and substrate temperatures. These conditions coincide with the region of phase stability for the A15. A small amount of oxygen (≳1.0%) as determined by Auger analysis, was found to be present in high-Tc films, while lower Tc films all had less oxygen.
The heteroepitaxy of InP on substrates of CdS using InI3 as the transport agent
Authors: Scranton R. A.
Published: February 2003

Indium phosphide is successfully transported down a temperature gradient by a reaction with indium tri-iodide. In contrast to transport with hydrogen, cadmium sulfide may be used as the substrate. Heteroepitaxial growth of InP on CdS is demonstrated. Preliminary in situ etching of the CdS is possible in this growth technique. The use of polycrystalline thin-film substrates and solar cell device possibilities are mentioned.
Electron mobility and free-carrier absorption in GaAs: Determination of the compensation ratio
Authors: Walukiewicz W. , Lagowski L. , Jastrzebski L. , Lichtensteiger M. , Gatos H. C.
Published: February 2003

Theoretical calculations of electron mobility and free-carrier absorption in n-type GaAs at room temperature were carried out taking into consideration all major scattering processes. It was found that satisfactory agreement between theoretical and experimental results on free-carrier absorption is obtained only when the effect of compensation is quantitatively taken into account. In conjunction with experimental studies it is shown that the electron mobility (for n≳1015 cm−3) and free-carrier absorption (for n≳1016 cm−3) are sufficiently sensitive to the ionized impurity concentration to provide a reliable means for determining the compensation ratio. Convenient procedures are presented for the determination of the compensation ratio from the free-carrier absorption coefficient and from the computed values of room-temperature electron mobility. Values of the compensation ratio obtained by these two procedures are in good agreement provided the carrier-concentration variations in the material are not appreciably greater than 10%.
Hole photogeneration in bisphenol-A-polycarbonate doped with N-isopropylcarbazole
Authors: Borsenberger P. M. , Contois L. E. , Ateya A. I.
Published: February 2003

The photoionization of holes in a polycarbonate polymer doped with N-isopropylcarbazole (NIPC) has been investigated as a function of electric field, temperature, wavelength, and NIPC concentration. The experimental results are compared to predictions of the Onsager theory, assuming the distribution of electron-hole separation distances are described by δ and simple exponential functions. The results show good agreement with analyses based on the assumption that the charge-pair configurations are described by a δ function. Depending on the NIPC concentration, the photogeneration efficiency can be described by a primary quantum yield between 0.03 and 0.20 and a thermalization distance between 18 and 20 Å. The photogeneration efficiency increases in steps with decreasing wavelength. Discontinuities are observed between the first and second and the second and third excited singlet states. The increase in efficiency with decreasing wavelength is explained by an increase in the thermalization distance, while the increase in efficiency with NIPC concentration is due to the concentration dependence of the primary quantum yield. The thermalization distance is independent of both temperature and NIPC concentration.
Direct determination of barrier voltage in ZnO varistors
Authors: van Kemenade J. T. C. , Eijnthoven R. K.
Published: February 2003

Single barriers in a ZnO varistor are measured separately. The step voltage at a grain boundary is 3.6 V at 1 μA. No great differences could be found between samples obtained from several suppliers. In a SEM the barriers could be detected by the voltage-contrast method. By using electron-beam-induced currents the spots where current is flowing may be located.
CO2 TEA laser discharge development—A high-speed-camera investigation
Authors: Sakai Y. , Takahashi M. , Sakamoto S. , Tagashira H.
Published: February 2003

Discharge development processes, such as homogeneous glow formation, glow-to-filamentary arc transition, and arc formation, of moderate volume CO2 TEA laser medium with external ultraviolet (uv) volume preionization are studied by a high-speed-camera technique. The framing records in this paper supplement the earlier streak ones of CO2 TEA laser discharges of Sakai et al. The records show that instability appears as a bright spot at the cathode in the middle of the uniform glow stage, then propagates in the anode direction, keeping the shape of a bright spot or changing into a bright filament. This propagation continues even after termination of the volume-dominated glow. The discharge development is found, from an understanding of the current waveform, to be considerably sensitive to the CO2, N2, and He composition ratio, and the pulse-forming network and other characteristics are also studied. The glow-to-arc transition mechanism and the dominant contributor to suppress arc formation are discussed.
Contrast and imaging performance in the scanning acoustic microscope
Authors: Wickramasinghe H. K.
Published: February 2003

Several articles have been written on the subject of scanning acoustic microscopy. Nevertheless, apart from some specific papers dealing with reflection microscopy, little has been said about the various contrast mechanisms involved in the process of image formation, and the effects of parameters such as acoustic antireflection coatings on the lens surface and absorption in the water on the quality of the recorded image. This paper is devoted to an analysis of these problems. It is shown that in the amplitude mode of operation, the acoustic microscope acts as a phase contrast microscope and is sensitive to the local phase gradients in the object. Furthermore, it is shown that the effect of an acoustic antireflection coating on the lens surface is to substantially reduce the side lobe amplitude of the focal distribution at the expense of a slight increase in the width of the main lobe. Experimental observations agree with theory.
Variational formulations for heat conduction problems
Authors: Keramidas George A. , Ting Edward C.
Published: February 2003

By introducing suitable parameters, it is demonstrated that the heat conduction effect resembles an elastic deformation. The difference is that the mechanical stress variation induces an inertia effect, while the heat stress variation generates a diffusion effect. Guided by this resemblance, a compatible Lagrangian formulation and its complementary form are derived for the heat conduction problems. The results are similar to Biot’s variational principles. The advantages of using the complementary form for the approximate solutions are also discussed. Temperature distributions in a semi-infinite solid with prescribed wall temperatures and with described heat flux are considered as illustrative examples.
Interaction of a relativistic electron beam with surface waves
Authors: Shoucri Magdi M.
Published: February 2003

The electromagnetic surface modes at the interface between two plasma media are studied and the excitation of these surface waves in a plasma by a relativistic electron beam is discussed. Under the resonance condition ω?kzvb, it is shown that an electron beam crossing a plasma can excite a surface electromagnetic wave at the plasma frequency ω=ωp.
X-ray line spectra from exploded-wire arrays
Authors: Burkhalter P. , Davis J. , Rauch J. , Clark W. , Dahlbacka G. , Schneider R.
Published: February 2003

Temperatures and densities were determined from the plasma formed by implosion at the center of symmetrical exploded-wire arrays. Temperatures of 500–725 eV were found from line ratios in Al and Si spectra using various plasma models. The recombination temperatures for these elements were 500–550 eV. Higher implosion plasma temperatures of 1.5–2 keV were found in Ti and Fe data. The densities were ∼1×1020 electrons/cm3 for the spatially integrated implosion region. Intense emitting regions of ∼500 μm to ∼1.5 mm in size were observed in densitometer contours of Al-plasma pinhole camera x-ray images.
The triple-probe method applied to the direct display of plasma parameters in a supersonic flowing continuum plasma
Authors: Ogram G. L. , Chang Jen-Shih , Hobson R. M.
Published: February 2003

The calibration of electrostatic triple-probe voltage and current response in a supersonic continuum plasma has been carried out using a low-pressure shock tube. The electron temperature Te and charge number density Ne are compared to probe voltage and current response, respectively, for a useful range of plasma parameters (1≲Rp/λD≲10, 2≲M≲5, and 7<φ13<35, where Rp is the probe radius, λD is the Debye length, M is the shock Mach number, and φ13 is the nondimensional probe voltage). The dependence of probe response on Debye ratio Rp/λD and various flow parameters was investigated. The probe voltage response was found to depend significantly on the Debye ratio. Expressions for electron temperature determination by triple probe are presented.
Electron density measurements in vacuum arcs at anode spot formation threshold
Authors: Harris Jeffrey H.
Published: February 2003

CO2 laser interferometry was used to determine electron density profiles in copper vacuum arcs just before and after the transition from the low-voltage quiescent mode to the high-voltage mode associated with anode-spot formation. Just before transition, the electron-density profiles are peaked on axis, with maxima of 9×1014 cm−3 and 6×1014 cm−3 in the cathode and anode regions, respectively. At about 0.1 ms after transition, the electron-density profile in the cathode region remains unchanged, while the central electron density near the anode drops be a factor of about 2. No constriction in the density profile was observed at any axial position. Previously reported anode surface temperature measurements are used to attribute the sudden drop in electron density near the anode just after transition to a local increase in the electron-ion recombination rate caused by a sudden influx of relatively cold neutral atoms from the anode surface. The implications of these observations with regard to a mechanism for transition are discussed.
Fast crystallization and void precipitation in laser pulse annealing of thin germanium films
Authors: Andrew Rod , Lovato Mireille
Published: February 2003

A flash-excited dye laser of moderate power has been used to irradiate thin amorphous Ge films prepared by vacuum evaporation. TEM examination shows that complete crystallization of thermally isolated films up to a few hundred angstroms thickness occurs for a single laser pulse of ∼80 mJ/cm2. The crystals formed are up to ∼1 μ across and include precipitated voids whose origin is discussed in terms of a high-temperature fast-crystallization process.
Current-voltage characteristics and surface currents in semi-insulating GaAs(Cr)
Authors: Jimenez-Lopez J. , Bonnafe J. , Fillard J. P.
Published: February 2003

Very recently Kitahara et al. published results of electrical I-V characteristics on GaAs-Cr samples. They found a steep rise in the current which is explained by a space-charge injection phenomenon; some discrepancies still remain unexplained. It will be shown in the present work that Kitahara’s experiments include a surface contribution that seems to be of critical importance.
The low-temperature specific heats of Y2(Co1−xAlx)17 alloys
Authors: Godwin L. M. , White H. W. , James W. J.
Published: February 2003

The specific heats of Y2(Co1−xAlx)17 alloys were measured in the temperature range 1.8–19.5 K for x=0, 0.08, and 0.12. The data below 11 K are well described by C=γT+βT3. Values of γ and β for the three samples were obtained. No evidence for a T3/2 term existed. This is not surprising due to the high Curie temperatures. The increase in the value of γ from alloying is significantly higher than that calculated by assuming a rigid-band model ignoring volume-change effects.
A solid rotor iron-free asynchronous machine
Authors: Rioux C. , Sultanem F.
Published: February 2003

Solid rotor iron-free asynchronous machines are important for the achievement of high-speed motors with high power-to-weight ratios. This paper presents a theoretical study of these machines, based on Maxwell’s relations, which is carried out using simplified two-dimensional models. Results are compared to experimental measurements.
Continuum modeling of electromagnetic waves in composite wave guides
Authors: Nayfeh Adnan H. , Jane Loh Jaine-I.
Published: February 2003

A continuum mixture theory with microstructure is developed for electromagnetic wave propagation in laminated waveguides. The theory leads to simple governing equations for the actual composite which retain the integrity of the propagation process in each constituent but allow them to coexist under derived interactions. The utility of the resulting equations is demonstrated by studying the response of the composite to harmonic excitations. In this case the dispersion relations are found to correlate well with some derived exact solutions.
Selective absorption of solar energy in ultrafine metal particles: Model calculations
Authors: Granqvist C. G. , Hunderi O.
Published: February 2003

We compute spectral reflectance from metal surfaces with coatings of ultrafine metal particles dispersed in an insulating medium. This model is appropriate to several kinds of selective absorbers for efficient photothermal conversion of solar energy. Our main interest lies in the parameters which govern λc—the wavelength below which the surfaces are good absorbers and above which they are good reflectors. We analyze the roles of coating thickness, substrate metal, particle shape and orientation, possible dielectric cores in the particles, and dielectric permeability (real and imaginary parts) of the embedding medium and of graded volume fractions of metal. A particularly interesting result is that an enhanced eccentricity of the particles is, under most conditions, highly effective for shifting λc towards longer wavelengths. A similar shift is also found for spherical metallic shells surrounding dielectric cores of increasing size.
Two-frequency 100-line addressing of a reflective twisted-nematic liquid-crystal matrix display
Authors: van Doorn C. Z. , de Klerk J. J. M. J.
Published: February 2003

Scanning of more than 100 lines of a reflective twisted-nematic liquid-crystal matrix display with full contrast can be achieved using a two-frequency addressing scheme and a liquid crystal showing a dielectric anisotropy that is positive for low frequencies and negative for high frequencies. It is shown that the electric field inhomogeneity, caused by the large dielectric constants, changes the optical response to low and high frequencies as well as the angular dependence of the optical transmission.
Infrared and electrical characterization of multilayered n-type GaAs wafers
Authors: Holm R. T. , Calviello J. A.
Published: February 2003

We have characterized GaAs epitaxial wafers (N active/N+ buffer/N+ substrate) intended for varactors and mixer diodes. I-V and C-V measurements demonstrated that the active layers were excellent. Transmission-loss measurements suggested that the buffer-layer carrier concentrations were too low and/or the wafers had an additional high-resistivity interface layer. The layer thicknesses were measured using a spherical drilling technique followed by chemical delineation. Analysis of infrared reflectance measurements provided the carrier concentrations of the layers as well as their thicknesses. Both the drilling-delineation measurements and the reflectance measurements confirmed the transmission-loss indications.
Photoluminescence in Mn-implanted GaAs—An explanation on the ∼1.40-eV emission
Authors: Yu Phil Won , Park Y. S.
Published: February 2003

The emission properties of Mn-implanted layers in GaAs are investigated with respect to changes in excitation intensity, temperature, substrate, and encapsulation. The substrates used were n-type conducting and Cr-doped semi-insulating crystals. The depth-dependent measurements of the Mn emission show an increase of the diffusion coefficient with dose for Si3N4 encapsulated samples, whereas a suppression of Mn diffusion is observed for SiO2 encapsulated samples. A large energy shift from ∼1.36 to 1.41 eV is observed for Mn emission at 4.2 °K at various excitation intensities. The energy shift increases with the concentration of compensating donors in the n-type substrate material. The excitation-dependent emissions are due to the donor-acceptor pair type transitions in the normal and the random-impurity-potential-disturbed energy states of the bands. Another emission becomes dominant at T≳∼30 °K following the quenching of the donor-acceptor pair type transitions with an increase of the temperature. An activation energy 95±15 meV is obtained from the temperature quenching of the emission intensity and the energy shift is observed to follow the band-gap variation. The possible radiative mechanisms are discussed.
Secondary electron emission measurements on materials used for superconducting microwave cavities
Authors: Padamsee H. , Joshi A.
Published: February 2003

The secondary electron emission coefficients for Nb, Nb2O5, Nb3Sn, NbN, Ti, and TiN, materials applied in microwave superconducting cavities, have been measured as a function of primary electron energy from 200 to 2000 eV. Data for ’’clean’’, ’’oxidized’’, and ’’as-prepared’’ surfaces are presented. Companion Auger spectra show the constituents of the surface under test. The results should be helpful in improving techniques for preparation of surfaces of high-power rf cavities that suffer in performance from multipactoring.
Coercivity and microstructure of Sm(Co0.87Cu0.13)7.8
Authors: Nagel H.
Published: February 2003

The magnetic hardness of Sm(Co0.87Cu0.13)7.3 in bulk form is caused by pinning of the domain walls at precipitates which are of the Sm(Co,Cu)5 type. The hard magnetic properties of both the 2 : 17 matrix and the 1 : 5 precipitate phase have been investigated in the temperature range between 77 and 800 K. The domain-wall energies have been determined from the surface domain patterns observed by means of the magneto-optical Kerr effect. It is shown that the coercivity mechanism in Sm(Co0.87Cu0.13)7.8 cannot be explained by the difference of the magnetic crystal anisotropy constants K1 of matrix and precipitate phase only. However, the coercivity may be described by the decrease in the domain-wall energy γ at the precipitates. γ of the 2 : 17 matrix was found to be five times that of the 1 : 5 precipitate phase (38 and 7.5 erg cm−2, respectively) resulting in an attractive interaction between the precipitates and the domain wall. The magnetic field necessary to overcome this attractive interaction has been estimated to be approximately 5 kOe, i.e., comparable to the experimentally obtained value of 4 kOe.
Surface-treatment effect on photoluminescence of InP
Authors: Nagai Haruo , Noguchi Yoshio
Published: February 2003

Three types of characteristic behavior of photoluminescence (PL) intensity response were found for InP crystal surfaces according to various surface preparations and measuring ambients. Gradual increase of photoluminescence intensity with time occurs on the surface etched by methanol-Br2 etching solution and in all the examined ambients: N2, H2, Ar, O2, air, and vacuum (6×10−3 Torr). A gradual decrease appears on the surface treated by HNO3, HF, HCl, and H3PO4 and in the O2-containing ambients. These tendencies can be repeated reversibly by treating the surface using each method. Influence of the crystal orientation and conduction type on these phenomena was investigated. PL intensity from the surface treated by AgNO3 and CuSO4 solution is fixed at a low level irreversibly.
Comment on the mechanism of operation of the impregnated tungsten cathode
Authors: Forman R.
Published: February 2003

Recent life-test measurements, over 20 000–30 000 h, on impregnated tungsten cathodes in tubes employing an open-type electron-gun structure, show emission current degradation with time. This is in contrast to those recently published by Rittner on B-type cathodes, run in close-spaced diodes, taken some years ago. These more recent life-test results are consistent with the model suggested by Forman and disputed by Rittner that the barium coverage on an impregnated cathode is less than a monolayer for most of its life and decreases with time.
The independent fourth-order elastic coefficients for the trigonal and hexagonal symmetry classes
Authors: Markenscoff Xanthippi
Published: February 2003

The eighth-order tensors invariant under the transformations corresponding to the trigonal and hexagonal crystal classes are obtained on the basis of a group theoretic approach and the list of the independent fourth-order elastic constants is presented.
Measurement of grain-boundary diffusion at low temperature by the surface-accumulation method. II. Results for gold-silver system
Authors: Hwang J. C. M. , Pan J. D. , Balluffi R. W.
Published: February 2003

Grain-boundary diffusion rates in the gold-silver system were measured at relatively low temperatures by the surface-accumulation method which was analyzed in Paper I. The specimen was a polycrystalline gold film possessing columnar grains on which a silver layer was initially deposited epitaxially on one surface. During subsequent low-temperature annealing lattice diffusion was frozen out, and diffusion then occurred along the grain boundary and free-surface short circuits. The silver, therefore, diffused into the film from the silver layer along the boundaries, eventually reaching the opposite surface where it accumulated and was measured by Auger spectroscopy. The silver layer acted as an effective constant silver source, and grain-boundary diffusivities were calculated from the accumulation data. However, the exact location of the effective constant source in the silver layer could not be determined and this led to an uncertainty in the values of the grain-boundary diffusivities of a factor of 10. Lower- and upper-bound values were therefore described by Db(lower bound) =7.8×10−6 exp(−0.62eV/kT) and Db(upper bound) =7.8×10−5 exp(−0.62eV/kT) cm2/s in the temperature range 30–269 °C. An examination of available grain-boundary diffusion data (including the present) suggests a tendency for the observed activation energy to decrease with decreasing temperature, and this was ascribed to a spectrum of activated jumps in the grain boundary and/or a spectrum of grain-boundary types in the specimen employed. The constant source behavior was tentatively ascribed, at least in part, to a grain-boundary ’’Kirkendall effect’’ resulting from the faster diffusion of silver than gold. The work indicates a need for increased understanding of the details of grain-boundary diffusion in alloys.
Temperature-compensated surface-acoustic-wave devices with SiO2 film overlays
Authors: Parker T. E. , Wichansky H.
Published: February 2003

Temperature-stable surface-acoustic-wave (SAW) devices have been fabricated with an rf-sputtered SiO3. film overlay on YZ LiTaO2. The material properties of this composite structure relevant to surface-acoustic-wave propagation have been thoroughly studied. For an SiO2 film thickness of approximately one-half of an acoustic wavelength, a piezoelectric coupling coefficient of 0.014 is present and the temperature stability of phase delay is similar in magnitude to that of bulk acoustic waves in AT-cut quartz. A variation in delay of less than one part in 105 is observed over the temperature range −40 to 80 °C. The film-overlay structure is dispersive and the nature of this dispersion has been fully characterized. The dependence of the phase and group delay on temperature and frequency has been measured. For most characteristics, theoretical as well as experimental values have been determined. In addition to YZ LiTaO3, five other cuts of LiTaO3 have been analyzed theoretically. To demonstrate potential applications for this structure, several practical devices have been fabricated and tested. Narrow-band delay lines have been fabricated for use in SAW-controlled oscillators. These oscillators showed a temperature stability nearly ten times better than similar devices fabricated on ST-cut quartz. Also, to demonstrate a wide-bandwidth application, a 13-bit Barker code, matched-filter pair has been fabricated. These devices also performed well.
A study of the deep electron traps in semiconducting CdS
Authors: Grill C. , Bastide G. , Sagnes G. , Rouzeyre M.
Published: February 2003

Deep-level transient spectroscopy by means of capacitance transients has been applied to study the characteristics of deep electron traps in low-resistivity CdS. Thermal activation of the capacitance transients for Schottky barriers formed on three different single crystals indicates the presence of nine electron traps located between 210 and 730 meV from the conduction band. Measured trap concentrations range from low 1011 to high 1014 cm−3. Among the nine detected electron traps there is one with an activation energy of 210 meV which is found in the three crystals, while the traps located at 420, 470, and 730 meV from the conduction band are found in two crystals only, although not the same two crystals in all cases. Direct capture-cross-section measurements are performed for the level situated at 210 meV by studying the time-dependent peak amplitude associated with trap refilling. It is shown that a time exponential variation of the trap filling process is only obtained under suitable biasing conditions. No significant variation of the capture cross section S∼3×10−13 cm2 is obtained in the explored temperature range 100–120 °K.
Quantum efficiencies of thin-film IV-VI semiconductor photodiodes
Authors: Holloway H.
Published: February 2003

An analysis is given of the reflection-loss-limited quantum efficiency of thin-film IV-VI semiconductor photodiodes. The results are applied to deduction of the optimum structures for ir detector applications and are illustrated by calculations for PbTe and Pb0.8Sn0.2Te.
Spectral response measurements of minority-carrier diffusion length in Zn3P2
Authors: Wyeth N. Convers , Catalano A.
Published: February 2003

Spectral response measurements have been made on metal-semiconductor junction diodes of single-crystal p-type zinc phosphide (Zn3P2) and Al, Mg, and Be. Two different experimental configurations were used and the minority-carrier diffusion lengths calculated using a simple theoretical treatment of the data. In one experimental mode, the light is incident on the surface of the semiconductor opposite the metal junction. The spectral response is peaked and a lower limit on the diffusion length can be calculated from the peak height and sample thickness without detailed knowledge of the optical properties of the semiconductor. In the other mode, light is incident through the metal layer and the diffusion length is calculated by analyzing the spectral response function using known values of the optical absorption coefficient. On samples for which both modes were used, the results are in good agreement. The diffusion lengths measured are in the range of 5–10 μm.
Electrically controllable polarization conversion in thin-film acoustic surface waveguides and its application
Authors: Sugimoto M. , Makimoto T.
Published: February 2003

A method is presented by which not only interference can be induced between two modes whose polarization directions are mutually orthogonal, i.e., between the so-called Rayleigh- and Love-type modes, but also the strength of the interference can be controlled electrically. It is shown that by applying this method electrically tunable polarization conversion can be obtained along some properly prepared acoustic surface waveguides of thin-film type. As such waveguides, two examples are considered, each of which is composed of a properly oriented thin α-quartz film either on a fused-quartz or on a fused-rutile substrate, and the basic properties of the polarization conversion are calculated. The applicability of this phenomenon to some practical devices is also discussed.
Optically broadened lattice vibrational spectra in amorphous arsenic chalcogenides
Authors: Utsugi Yasushi , Mizushima Yoshihiko
Published: February 2003

Effects of photoirradiation on amorphous As2Se3 and As4Se5Ge1 thin films are measured in far-infrared (ir) experiments. Optically enhanced broadenings of the dominant ir absorption bands, similar to that in amorphous Se-Ge, are described. The broadening degree seems to correspond to an increased randomness in the bond angle of the pyramidal structure. In amorphous As4Se5Ge1, a localized molecular vibration model, consisting of As-Se and Se-Ge bonds, is justified.
Secondary-electron emission by energetic ions incident on metal surfaces
Authors: Decoste R. , Ripin B. H.
Published: February 2003

An experimental technique, especially well adapted to measure secondary-electron coefficients for energetic ions incident on any charge-collector surface, is described. The technique uses a laser-produced plasma as an ion source, a high-energy ion analyzer as an ion energy and species filter, and a tubular electrode arrangement to suppress or attract the secondary electrons at the charge collectors. The secondary-electron coefficients for several ionization states of carbon and hydrogen ions incident on copper surfaces are given as a function of incident ion energy between 15 and 150 keV/Z.
Variation of beta-ray backscattering with target thickness
Authors: Sharma K. K. , Singh M.
Published: February 2003

Backscattering of beta rays from 204Tl and 90Sr-90Y beta emitters has been studied as a function of target thickness for elemental targets of aluminum, copper, tin, and lead. Values of target thickness corresponding to saturation backscattering intensity are found to be independent of the nature of target material and geometry but depend strongly on beta end-point energy. From thin-target approximation, values of self-absorption coefficients and Z dependence have been obtained and are found to agree with semiempirical results.
Nuclear-pumped 3He-Ar laser modeling
Authors: Wilson J. W. , DeYoung R. J. , Harries W. L.
Published: February 2003

Theoretical models of nuclear-pumped lasers are of interest for the purpose of system optimization and identification of new and more efficient nuclear-pumped laser systems. A first-order model of the 3He-Ar 1.79-μm laser is developed, compared to experimental results, and used to explain the qualitative features of this system. The results indicate that direct excitation of the argon upper level is at best very inefficient for population inversion. For argon concentrations which give the most efficient laser operation, the 3He(n,p)3H energy is used to produce atomic helium ions that quickly convert into helium molecular ions. These molecular ions subsequently form argon atomic ions through charge transfer. The dominant pumping mechanism is collisional-radiative recombination of the argon atomic ion and subsequent radiative cascading into the upper laser level. The formation of argon molecular ions is in competition with argon atomic ion recombination; this combined with the dissociative recombination of argon molecular ions into the lower laser level terminates laser action for argon concentrations above 20%.
Anomalous absorption and dispersion of sound waves in diethylamine melanin
Authors: Kono Ryusuke , Yamaoka Toshihiko , Yoshizaki Haruyo , McGinness John
Published: February 2003

Longitudinal and shear mechanical relaxation data are reported for a hydration of 20% of synthetic diethylamine melanin. The longitudinal attenuations per wavelength αλ at frequencies between 1 and 5 MHz show an enormously large amount of absorption above room temperature. The amount αλ/2π=0.55–0.95 at a temperature of 60 °C in the frequency of 1 MHz has never been found in usual polymeric substances where αλ/2π∼0.1. The longitudinal data are interpreted in terms of a combined relaxation and resonance process. Measurements of the shear impedance in the temperature range from −10 to +60 °C, with frequencies ranging from 5.2 to 362 MHz, indicate a distribution of relaxation times, represented by the Davidson-Cole spectrum. Temperature dependency of limiting shear modulus is found to obey the Hirai-Eyring equation.
Pre-breakdown discharges in mercury–rare-gas mixtures
Authors: Partlow W. D. , Kline L. E.
Published: February 2003

We have examined the properties of mercury–rare-gas discharges operated at low fields where volume ionization is negligible. The discharge current is due to thermionically produced electrons and is limited by the electron mobility. The mixtures consisted of mercury and either Ar, Kr, or Xe at 30–760 Torr. Temperatures were varied from 50 to 250 °C. uv and visible radiation production, as well as electrical properties, were measured and compared to theoretical calculations. The measured positive volt-ampere characteristics agree well with theory. The calculated efficiency for excitation of Hg 3P1 in these discharges is greater than 50% over a wide range of conditions. The low measured radiation production efficiency (less than 5%) is consistent with model calculations which include quenching of the 3P1 by Hg and the rare gas to the 3P0 state and its subsequent decay by the formation of mercury excimers.
Resonant excitation of the upper hybrid wave by two em beams
Authors: Sodha M. S. , Maheshwari K. P. , Sharma R. P. , Kaushik S. C.
Published: February 2003

Resonant excitation of an upper hybrid wave by the mixing of two coaxial Gaussian em beams in a collisionless hot magnetoplasma has been investigated; the electric vectors of beams are polarized along a uniform static magnetic field and the beams propagate perpendicular to the magnetic field. The resonant excitation of the upper hybrid wave occurs when the difference frequency of the two em waves and difference of their propagation vectors satisfy the dispersion relation corresponding to the upper hybrid wave. Furthermore, because of the Gaussian intensity distribution of the two beams the electrons are redistributed by the ponderomotive force, cross focusing of the two em beams occurs, and the power of the excited upper hybrid beam (which depends on the background electron concentration, the intensities of the two em beams, and the magnetic field) are correspondingly modified. The present analysis is also applicable to an inhomogeneous magnetoplasma in the WKB approximation.
Light-induced phenomena in dye-polymer systems
Authors: Novotny V. , Alexandru L.
Published: February 2003

A direct optical marking process based on dye diffusion in a dye-polymer system is described. Relevant thermal and spectral properties of dye and substrate were investigated. Typical marking performance is outlined for magenta dye films on Mylar. Marked bits were submicron in size and energy-density requirements below 100 mJ/cm2 were observed. A mechanism of the process is proposed and good quantitative agreements are obtained between experimental and predicted power thresholds and sensitivities.
Lateral spread of P+ ions implanted in silicon through the SiO2 mask window
Authors: Sakurai T. , Kawata H. , Sato T. , Hisatsugu T. , Hashimoto H. , Furuya T.
Published: February 2003

The lateral spread of implanted P+ ions and the shape of the mask window have been observed simultaneously using the technique of staining the cleaved surface and scanning electron microscopy for the Si samples with the SiO2 mask window with a tapered edge. The mask edge with a gradient of 45° or 78° to the Si surface and the implanted n-type region with a carrier concentration higher than 2×1017/cm3 are observed in the same photograph. The observed maximum lateral spread when the gradient of the mask edge is 45° is about 1.6 times larger than that when the gradient is 78°. The calculated results of the lateral spread agree relatively well with the experimental data although the precise analysis based on the definite basis is necessary.
Alkali motion in alkali silicate glass
Authors: Doi Akira
Published: February 2003

Alkali motion in alkali silicate glass was studied by the method of ionic thermocurrent which was developed as a highly sensitive technique for studying relaxation of polarized impurity-vacancy dipoles in ionic crystals. Two current peaks were observed in the temperature range −196–100 °C, and were ascribed to orientational depolarization of pseudodipoles composed of localized alkali–nonbridging oxygen and to thermal relaxation of space charges near the cathode. Heterogeneous distribution of alkalis in alkali silicate glass was verified by large differences in ionic thermocurrent and in the evaluated density of localized alkalis from sample to sample taken from even the same glass film, as well as by the distribution in activation energies for dipolar orientation and space-charge relaxation. It was also concluded that the neutralization process of alkalis in glass was due to tunneling of electrons through the potential barrier in the space-charge–electrode double layer.
The effects of electron bombardment on the surface composition of WO3, oxidized W and Ta foils
Authors: Lin T. T. , Lichtman David
Published: February 2003

By using both Auger electron spectroscopy and electron-stimulated desorption measurement techniques, electron-beam-irradiation-induced oxide reduction has been observed on WO3 and Ta2O5. In both cases, the light element (oxygen) is preferentially removed which in turn leaves the specimens’ surface enriched with the metal element. In addition, visible darkening in the beam-illuminated area provides evidence of beam-irradiation-induced oxide reduction and irradiation-enhanced diffusion effects. Measurements of Auger electron intensities from the composition altered overlayer indicate that the beam-irradiated overlayer consists of nearly equal parts of metal and oxygen atoms upon extended electron bombardment. The observed changes in the surface composition of contaminated specimens also show additional beam effects like induced out-diffusion and beam-induced desorption. A brief comparison with the published results concerning ion irradiation on the corresponding specimens is also included.
A critical evaluation of equations of state by piezo-optic measurements
Authors: Vedam K. , Limsuwan Pichet
Published: February 2003

Precision optical interferometric measurements on a number of liquids at high pressure reveal pronounced nonlinear piezo-optical (Δn versus P) behavior, but linear elasto-optic (Δn versus ε where ε is the Eulerian strain) relationship. This paper reexamines this linear Δn-ε relationship rather critically by a least-squares analysis and it is shown that it can be used to discriminate between the various equations of state prevalent in the literature. It is found that the second-order Murnaghan (ME2), second-order Birch (BE2), and the Keane equations of state yield the best fits to the experimentally observed piezo-optic data. Further, purely from thermodynamic and physical reasoning we can rule out ME2 and BE2, thus leaving the Keane equation as the only equation of state among those considered that can satisfactorily describe the elastic and elasto-optic behavior of liquids in its entire stability field. Since the various equations of state considered in this paper are also used for the study of isotropic solids as well, it is believed that the above conclusions should be valid in general for all isotropic solids and liquids.
Metal electrode diffusion into polymer films
Authors: Segui Y. , Ai Bui , Bagnol C. , Pistre J. , Danto Y. , Barriere A. S.
Published: February 2003

Evidence is given for the diffusion of gold from the electrodes into polymer layers. The analysis of backscattering of particles is used to find the profile and the concentration of these impurities.
Stress effect on the magnitude of acoustic emission during magnetization of ferromagnetic materials
Authors: Kusanagi H. , Kimura H. , Sasaki S.
Published: February 2003

The effect of stress on the magnitude of acoustic emission during magnetization of mild steel and nickel has been investigated. It has become clear that the magnitude of acoustic emission during magnetization shows a strong dependence on stress. This effect should have nondestructive testing applications suited for field inspection.
Near-resonance nonlinear propagation of monochromatic radiation in a gas medium
Authors: Vasconcellos J. I. Cotrim
Published: February 2003

Using the exact solution for a sine-driven two-level atom we have calculated the nonexponential attenuation experienced by a monochromatic electromagnetic beam nearly resonant with a gas of two-level atoms. The atoms are assumed to undergo collision, spontaneous decay plus inhomogeneous (Doppler, etc.) broadening. Resulting intensity-vs-distance plots for a plane wave are given for various degrees of relative homogeneous and inhomogeneous linewidths, for several saturation conditions and for several detuning frequencies. A comparison is also made with collision-broadened and linear attenuation regimes.
Electrostatic effects of interface states on carrier transport in semiconductor heterojunctions
Authors: Card H. C.
Published: February 2003

A theory of the electronic transport properties of contacts between two dissimilar semiconductors is presented, which includes the effects of bias-dependent interface state charge on the electrostatic potential distribution in the contact. The quasi-Fermi level for the interface states is determined by the competition between the capture of electrons and holes at the interface for a given bias voltage. The conditions for diffusion-limited or thermionic-emission-limited current flow are defined in terms of heterojunction parameters and material properties. Ignoring the direct recombination currents through interface states, the interface states have no effect on diffusion-limited current, but when the transport is limited by the thermionic emission of carriers there are pronounced electrostatic effects on this current from interface states. A limiting density of interface states ∼1011–1012 cm−2 eV−1 has been established above which the current-voltage (J-V) relations are independent of the parameters characterizing these states, and for this condition the n* value of the exponential J-V characteristics is ?2 over an appreciable range of bias voltage.
The operation of the semiconductor-insulator-semiconductor solar cell: Experiment
Authors: Shewchun J. , Dubow J. , Wilmsen C. W. , Singh R. , Burk D. , Wager J. F.
Published: February 2003

We have reported on the theory of semiconductor-insulator-semiconductor (SIS) solar cells in a previous publication. In this paper, the fabrication and properties of indium tin oxide/p-Si single-crystal solar cells will be described. The ITO is deposited by the ion-beam sputtering method. Best photovoltaic devices are obtained when the composition of indium tin oxide (ITO) is 91 mole% and 9 mole% SnO2. The device properties as a function of the ITO composition will be described. The thickness and the composition of the oxide-silicon interface is critical for device performance. The existence of a thin interfacial layer is demonstrated by Auger spectroscopy. The effect of temperature on device performance and the spectral response are compared with the theory. The SIS model accurately matches the major trends observed in experimental nITO/p-Si solar cells.
Microstructure and magnetism in amorphous rare-earth–transition-metal thin films. II. Magnetic anisotropy
Authors: Leamy H. J. , Dirks A. G.
Published: February 2003

Amorphous thin films of GdxCo1−x, HoxCo1−x, GdxFe1−x, and YxFe1−x (0.1<x<0.7) possess an anisotropic microstructure when prepared by vapor or sputter deposition onto room-temperature substrates. The structure consists of mutually parallel columnar regions of high density that are surrounded by a network of low-density material of 10–30 Å thickness. This structure is produced by geometrical shadowing of the incident vapor atoms by the growing film. If separate vapor sources are used to deposit each alloy constituent, compositional inhomogeneities are also formed by shadowing effects. These produce an in-plane magnetic anisotropy that may be eliminated by deposition onto rotating substrates. Annealing at temperatures between 250 and 400 °C, deposition in oxygen-contaminated environments, or bias-sputter deposition produces compositional inhomogeneities at the surface of the columns. Development of this inhomogeneity is accompanied by production of an easy axis of magnetization perpendicular to the film surface in Gd-Co alloys, and development of a diffuse diffraction maximum at 0.38 Å−1. Upon annealing at 500 °C, this diffuse ring is transformed into a set of closely spaced Bragg maxima that correspond to Gd2O3 crystallites. All of the films exhibit large biaxial tensile stresses in the as-deposited state. These are reduced by deposition in oxygen and by bias-sputter deposition. Tensile stress and perpendicular magnetic anisotropy are linearly correlated in Gd-Co alloys, but the magnetostrictive contribution to perpendicular anisotropy is only 0.01 of the observed value.
The magnetic properties of amorphous Y3Fe5O12
Authors: Gyorgy E. M. , Nassau K. , Nassau K. , Eibschutz M. , Waszczak J. V. , Wang C. A. , Shelton J. C.
Published: February 2003

Amorphous (vitreous) Y3Fe5O12 has been prepared using the twin-roller quenching technique. The material is antiferromagnetic with a Néel temperature of approximately 40 K. The Mössbauer spectra indicate that the iron environment in the amorphous material is different from that in crystalline Y3Fe5O12 (YIG).
A study of the mechanism of cw laser annealing of arsenic-implanted silicon
Authors: Gat A. , Lietoila A. , Gibbons J. F.
Published: February 2003

In this paper we report on experiments designed to study the mechanism by which a continuous scanning laser anneals implantation-amorphized silicon. A stationary Ar laser beam was used to irradiate an As-implanted Si sample at constant power for different anneal times. The size of the annealed spot was found to increase with exposure time. The annealing spot size was also calculated for each exposure time by assuming the laser annealing mechanism to be a simple solid-phase epitaxial regrowth. Comparison of experiment and theory suggests that, at least for amorphous layers, the cw laser simply heats the substrate to a temperature where solid-phase epitaxial regrowth can occur quickly.