bluuebunny/crossref_metadata_2025 huggingface dataset:
The first-order phase transformation in NaCN: A martensite transformation
Authors: Gash Philip W.
Published: February 2003

The first-order phase transformation in NaCN at 288 °K is identified as a martensite transformation accompanied by the formation of mechanical deformation twins of the first kind. Photomicroscopy measurements of the crystal surface morphology and nuclear magnetic resonance measurements of the domain orientation are in agreement with the predictions of the Weschsler, Lieberman, and Read theory of twin formation accompanying a martensite transformation. There are 24 domains; the group S2 leaves a domain invariant and the domain generating group of F operations is either O or Td. NaCN is identified as belonging to the ferroelastic species m3mF1̄.
Exchange striction of ferromagnetic solid solution of (Mn1−xTax)3B4
Authors: Ishii T. , Shimada M. , Koizumi M.
Published: February 2003

The thermal expansion of a ferromagnetic solid solution of (Mn1−xTax)3B4 was determined using a high temperature x-ray powder diffraction technique in the temperature range 300–973 K. From the thermal expansion curve, the values of the exchange striction along three axes were deduced. They were negative along both a and b axes, but the thermal expansion of the c axis was very small and exchange striction was not observed. It was considered that such an anisotropy in the thermal expansion of the present sample was due to the crystallographic structure of Ta3B4. The pressure dependence of the Curie temperature of (Mn0.8Ta0.2)3B4 was determined to be 0.77 deg/kbar from electrical resistivity measurements under high pressure. The observed value of dTc/dp is in good agreement with the value calculated using the molecular theory proposed by Bean and Rodbell.
Interdiffusion in copper–aluminum thin film bilayers. I. Structure and kinetics of sequential compound formation
Authors: Hentzell H. T. G. , Thompson R. D. , Tu K. N.
Published: February 2003

Interdiffusion in Cu–Al thin film bilayers at temperatures between 160 and 300 °C has been studied by a combination of glancing-incidence x-ray diffraction, Rutherford backscattering spectroscopy, and transmission electron diffraction and microscopy. A sequential intermetallic compound formation was observed in samples with an excess amount of Cu with θ-CuAl2 forming first, followed by η2-CuAl, and γ2-Cu9Al4. In samples with excess Al, the θ-CuAl2 is the first and the last phase formed. The thickening of these compounds was found to obey a parabolic relationship with time, and especially the thickening of θ-CuAl2 can be described by a prefactor of 7.4 cm2/s and an activation energy of 1.31 eV.
Interdiffusion in copper–aluminum thin film bilayers. II. Analysis of marker motion during sequential compound formation
Authors: Hentzell H. T. G. , Tu K. N.
Published: February 2003

Isolated W islands, 150 Å in diameter, have been deposited between Cu and Al thin film bilayers to serve as inert diffusion markers. Marker displacements have been measured consecutively by Rutherford backscattering spectroscopy during the sequential growth of CuAl2, CuAl, and Cu9Al4 intermetallic compounds upon annealing in the temperature range 160–250 °C. The intrinsic interdiffusion coefficients of Al and Cu in each of these compounds have been determined by applying an analysis of marker motion in a binary diffusion couple to the measured displacement data. Moreover, the prefactor and activation energy of the individual diffusivities have been calculated as shown below by measuring the marker motion as a function of temperature. For CuAl2, D0Al =0.4 cm2/s, QAl =1.25±0.05 eV, D0Cu =9.5 cm2/s, QCu =1.40±0.05 eV. For CuAl, D0Al =1.5×10−7 cm2/s, QAl =0.7±0.05 eV, D0Cu =1×10−2 cm2/s, QCu =1.1±0.05 eV. For Cu9Al4, D0Al =1.7×10−3 cm2/s, QAl =1.20±0.05 eV, D0Cu =2.4×10−2 cm2/s, QCu =1.30±0.05 eV. These values agree quite well to those chemical interdiffusion coefficients published in the literature for bulk samples. A discussion on sequential compound formation has been given on the basis of these measured values.
Hydrogen migration under avalanche injection of electrons in Si metal-oxide-semiconductor capacitors
Authors: Gale R. , Feigl F. J. , Magee C. W. , Young D. R.
Published: February 2003

Aluminum/silicon dioxide/silicon capacitors in which the oxide has been grown thermally under ultra-dry (≲1 ppm H2O) conditions and subsequently treated by low temperature water diffusion have been characterized electrically and chemically. Avalanche injection of electrons has been observed to produce the complex charging behavior previously observed in similar systems, which includes electron trapping and interface positive charge generation. Secondary ion mass spectrometry depth profiling of these structures has shown that electron injection also results in hydrogen transport. This is the first direct observation of hydrogen redistribution under the influence of an electron current. We demonstrate a linear relationship between injected charge fluence and areal density of hydrogen localized at the SiO2/Si interface. These results indicate that hydrogen release correlates with interface state generation, but not with bulk oxide trapping.
High temperature stability of PtSi formed by reaction of metal with silicon or by cosputtering
Authors: Murarka S. P. , Kinsbron E. , Fraser D. B. , Andrews J. M. , Lloyd E. J.
Published: February 2003

High temperature stability of platinum silicide, formed by reacting metal with silicon or by cosputtering metal and silicon in a desired ratio, has been studied. The properties of films, thus formed, were examined as a function of annealing temperature using a resistance measuring technique, Rutherford backscattering, Auger and x-ray analyses, transmission and scanning electron microscopic techniques, and by measuring forward current-voltge (I-V) characteristics of the silicide n-silicon Schottky diodes. It is shown that cosputtering silicon rich alloys prevents agglomeration of the silicide, but increases the resistivity and decreases the Schottky barrier height of the film. Platinum silicide dissolves increasing amounts of silicon on high temperature (700–1000 °C) treatments causing considerable degradation of properties. Although cosputtering silicon rich alloys reduces this behavior, electrical properties such as forward I-V characteristics still degrade due to high temperature anneals.
Doping and electrical properties of Mn in In1−x−yGaxAlyAs grown by molecular beam epitaxy
Authors: Silberg E. , Chang T. Y. , Ballman A. A. , Caridi E. A.
Published: February 2003

Epitaxial layers of p-type In1−x−yGaxAlyAs doped with Mn were grown by molecular beam epitaxy. The doping characteristics and electrical properties are studied using Hall measurements in the temperature range between 100 and 300 K. Secondary ion mass spectrometry (SIMS) was used to study Mn profiles and diffusion coefficients. The maximum hole concentration attainable at room temperature is relatively independent of the As flux and is found to decrease from 4×1018 for y=0 to 2×1016 cm−3 for y=0.48. The experimental results of the resistivity and Hall effect are used to determine the densities Na, Nd of acceptors and compensating donors and the activation energy. The acceptor activation energy Ea increases from 50 at y=0 to 200 meV at y=0.23. Ea is found to be independent of the hole concentration and the arsenic flux used during the molecular beam epitaxial growth. The hole mobility for hole concentration of ∼1017 cm−3 is about 140 cm2 V−1 s−1 and decreases with increasing y. SIMS measurements of the Mn profiles show that Mn diffusion is significant at temperatures 650 °C and above, but is insignificant under the growth condition at 493 °C. Abrupt junction and sharp Mn pulses (<0.15 μm wide) have been obtained. Mn surface segregation is negligible at growth temperatures above 500 °C.
Growth by molecular beam epitaxy and characterization of high purity GaAs and AlGaAs
Authors: Heiblum M. , Mendez E. E. , Osterling L.
Published: February 2003

We report on the growth by molecular beam epitaxy of high-quality GaAs and AlxGa1−xAs (x≲0.43), and discuss the effect of system parameters on material quality. The highest Hall mobility in GaAs at 77 °K was 144 000 cm2/V sec, and the photoluminescence spectra of undoped layers exhibited a strong free exciton line and a much reduced carbon peak with no carbon-related defects. A slow growth process at a substrate temperature of 600 °C produced excellent AlxGa1−xAs whose luminescence spectrum showed a distinct excition peak 4 meV wide. This AlxGa1−xAs is compared to layers grown at a faster rate at substrate temperatures of 700 °C.
Dielectric function for a quasi-two-dimensional semiconducting system
Authors: Lee Johnson , Spector Harold N.
Published: February 2003

We present a calculation of the dielectric function for a quasi-two-dimensional electron gas (Q2D) and compare our results with those obtained for two-dimensional (2D) and three-dimensional (3D) electron gases. We also compare our results to those obtained using the Thomas–Fermi approximation. We find that for a Q2D system with an active layer of thickness 100 Å, the use of the 2D and Thomas–Fermi approximations overestimate the dielectric function and the amount of screening except for small wave vector disturbances. We also compare our approach to that of Stern and Howard [Phys. Rev. 163, 816 (1967)] and find that the approaches agree if we make the Thomas–Fermi approximation. When we apply our results to the problem of the calculation of the momentum relaxation rate from a screened Coulomb potential due to scattering from ionized impurities, we find that our approach leads to a larger scattering rate than that using the Thomas–Fermi approximation because of the latter’s overestimate of the effect of screening.
Voltage and current expressions for a two-junction superconducting interferometer
Authors: Peterson Robert L. , McDonald Donald G.
Published: February 2003

The average voltage and circulating current of a superconducting interferometer containing two Josephson junctions (a dc SQUID) are calculated analytically, in various approximations, as functions of bias current and applied magnetic field or control current. The results are useful in calculations of the noise characteristics of the dc SQUID, as well as in other applications.
Cathodoluminescence assessment of electron beam recrystallized silicon
Authors: Myhajlenko S. , Ke W. , Hamilton B.
Published: February 2003

A preliminary report is given of dramatic changes observed in the cathodoluminescence (CL) properties of silicon melted under vacuum by electron beam excitation. The band edge luminescence is found to be modified and enhanced in the recrystallized material. These changes in the spectral character of the material correlate with changes in the minority carrier lifetime. In addition, deep level luminescence bands are also observed at 0.39, 0.52, and 0.58 eV. The behavior of CL transients as a function of beam excitation indicates that saturation of the bulk recombination path occurs, and this is believed to be related to the improved surface quality of the recrystallized material. Both n- and p-type silicon are found to exhibit these new properties. All the work has been performed on a purposely built scanning electron microscope optimized for CL work.
Space charge, elastic field, and dipole contributions to equilibrium solute segregation at interfaces
Authors: Yan M. F. , Cannon R. M. , Bowen H. K.
Published: February 2003

The interaction potentials between solute ions and grain boundaries in ionic solids are identified as (1) the electrostatic interaction between the charged solutes and grain boundaries, (2) the elastic energy due to the size misfit of solutes in the matrix, and (3) the dipole interactions between the solute-vacancy dipoles and the electric field in the grain-boundary region. We include these interaction potentials to evaluate the minimum free energy and the equilibrium solute and defect distributions in the grain-boundary region. Numerical calculations show that these interaction mechanisms, either acting individually or coupling with each other, lead to a nonuniform solute distribution near the grain boundary. Under certain conditions, both the elastic and dipole interactions can significantly modify the electrostatic potential near the boundary. Calculations also show that the grain-boundary segregation of an aliovalent solute can be induced or altered by another aliovalent solute of different size misfit with the matrix.
Influence of Au as an impurity in Ni-silicide growth
Authors: Hung L. S. , Zheng L. R. , Mayer J. W.
Published: February 2003

The growth of Ni silicides in Ni films on Si and in lateral diffusion couples with Ni films on Si patterns on Al2O3 is strongly influenced by the presence of 1–2 at. % Au in Ni. During silicide formation, Au accumulates at the silicide/ Ni and silicide/Si interface and retards phase formation at temperatures below the Au/Si eutectic. At temperatures of 400–500 °C (above the eutectic), the growth rate is enhanced by over two orders of magnitude. We believe the increase is due to the segregation of Au at the Ni-silicide grain boundaries and the transport of Si in the Au-Si liquid. The growth rate is independent of temperature from 600–800 °C and is limited by the diffusion of Si in the Au-Si liquid at a value of 10−5 cm2/sec.
Photoconductivity and photovoltaic effect in indium selenide
Authors: Segura A. , Guesdon J. P. , Besson J. M. , Chevy A.
Published: February 2003

Transport and phototransport properties of crystalline indium monoselenide (InSe) doped with a variety of elements are reported. Measured mobilities, lifetimes, and effective diffusion lengths of photoexcited carriers are used to interpret electrical and photovoltaic properties of several different structures. These include p-n junctions, bismuth/p-type InSe, platinum/n-type InSe, and indium tin oxyde (ITO)/p-type InSe. External solar efficiencies of the best devices are between 5% and 6%. The influence on the efficiency of the various parameters is evaluated, and ways of improvement are discussed.
Electrical conduction in biotite micas
Authors: Meunier M. , Currie J. F. , Wertheimer M. R. , Yelon A.
Published: February 2003

The direct current electrical conductivity tensor of biotitic phyllosilicates (mica) has been measured as a function of temperature, of electric field, and of chemical composition. It is found that conductivity depends exponentially upon iron impurity content, and upon electric field at high fields. The dependence upon temperature is more complicated. These results are best interpreted by a model in which mica is an isotropic Fermi glass in which electrical conduction takes places by nonadiabatic hopping of small polarons between iron sites in the crystal.
Use of neutron diffraction texture measurements to establish a model for calculation of ultrasonic velocities in highly oriented austenitic weld material
Authors: Allen A. J. , Hutchings M. T. , Sayers C. M. , Allen D. R. , Smith R. L.
Published: February 2003

Neutron diffraction has been used to measure the crystallite orientation distribution function for a cubic test sample of highly textured austenitic weld material. The longitudinal and transverse ultrasonic velocities in three orthogonal directions in the sample have been calculated from this function and compared with measured values for the sample. The Voigt approximation is found to give good agreement with experiment and appears to be the most useful approach for the calculation of ultrasonic velocities in highly textured materials.
Thermal effects in photothermal spectroscopy and photothermal imaging
Authors: Aamodt L. C. , Murphy J. C.
Published: February 2003

The effect of thermal parameters on photothermal spectroscopy and photothermal imaging for certain types of spatially heterogeneous samples has been studied. Results have been obtained for both photoacoustic and photothermal deflection modes of detection. Specific attention has been paid to optical saturation in samples whose properties exhibit gradual spatial changes and to the dependence of the photothermal signal on the individual thermal parameters. Most photothermal spectroscopy has been done using thermally homogeneous samples, and most photothermal imaging using optically saturated samples. In this paper, these limitations are relaxed, and the photothermal signal is assumed to depend simultaneously on gradual spatial variations in the optical absorption coefficient, thermal conductivity, and thermal capacity of the sample.
Model of the anode region in a uniform multi-cathode-spot vacuum arc
Authors: Boxman Raymond L. , Goldsmith S.
Published: February 2003

A model is developed for the anode region of a uniform multi-cathode-spot vacuum arc. A first-order approach is used, in which the plasma up until the anode sheath is assumed to be produced solely by a multitude of cathode spots and is described by a zero-order plasma model previously developed, and the influence of the anodic emissions on this plasma is assumed initially to be negligible. Calculations of the electron mean-free-path and the Debye length indicate that the anode sheath may be modelled as collisionless. The anode potential is calculated by imposing the requirement of current continuity, and it is found that the overabundant supply of random electron current forces the anode to assume a negative potential with respect to the adjacent neutral plasma with a magnitude of approximately (1/3)(kTe/e)(vT/vd), where Te is the electron temperature, vd is the electron drift velocity, and the thermal velocity vT is defined by (kTe/2πme)1/2. The magnitude of the electric field at the anode surface is also calculated, and it is found that under certain circumstances, its value may approach the value of 107 V/m known to produce cathode spots. The possibility of ‘‘cathode spot’’ formation on the negatively charged anode is discussed. The energy flux incident on the anode surface is analyzed and is found to contain both a component originating from the electron flux, and a component originating from the ion flux. The two components are of the same order of magnitude, with the ion flux dominant at lower values of Te, and the electron flux dominant at higher values of Te. The overall energy flux is given by JφE, where J is the current density and φE is an effective anode drop whose value in a Cu arc ranges from 13 V for Te=1 eV to 33 V for Te=9 eV. Neutral atom emission from the anode surface by evaporation and by sputtering is analyzed. Evaporation will be significant after a sufficient heating time has elapsed, on the order of 64 ms for a 3 eV, 107 A/m2 Cu arc, for example. Sputtering, in the case of a Cu arc, may produce a local neutral density equal to 37% of the ambient ion density. All of the neutrals emitted from the anode surface are eventually ionized by electron impact. Extension of the model to cover arcs where macroparticle-produced plasma is significant, and where nonuniformities are produced by the electrode geometry or magnetic constriction, is discussed qualitatively.
D-3He proton yield as a diagnostic for D-T and D2 filled inertial confinement fusion experiments
Authors: Blue T. E. , Blue J. W. , Durham J. S. , Harris D. B. , Hnesh A. S. , Reyes J. J.
Published: February 2003

The ratio of D-3He to D-D reactions (RD3He/RDD) is proportional to fuel ρR for D2 and D-T filled targets. For D2 filled targets, the ratio varies as (RD3He/RDD)=0.14ρR, for ρR≲0.02 g/cm2. For present day D2 filled target experiments, it is necessary to detect 104 D-3He reactions against a background source of 108 D-D reactions. For D2 filled targets, detection of the 14.7-MeV proton of the D-3He reaction can be accomplished with sheets of the solid state nuclear track detector CR-39 and metal foils. Spatial coincidence can be used as a means of eliminating background due to imperfections in the track detector and background due to protons in the CR-39 which are elastically scattered by D-D neutrons.
Reducing the grain size of polycrystalline lead films by the use of barriers to grain growth
Authors: Ronay Maria , Serrano C. M.
Published: February 2003

The mechanical strength of lead-alloy films used in Josephson junctions is improved by reducing the grain size. One way to achieve this goal is to reduce the rate of grain growth. The activation energy for barrierless growth during vapor deposition was estimated to be about 540 cal/mole for lead films and is assigned to the ordering of atoms. Because of its small value, instead of reducing the rate of grain growths, it seemed best to stop growth by the application of a barrier layer. This is followed by the nucleation of new grains. Five requirements for a barrier-to-grain growth are given out of which the requirement of a high interfacial free energy between barrier and lead is stressed the most. In the experiments Nb, PdSn4, AuIn2, and PdIn3 were used as barriers between lead layers. The grain size of layered films was determined by transmission electron microscopy and was found to be about the same as if the total film thickness were equal to the thickness of one layer. Yet there are small differences between the different barrier layers; their effectiveness increases as their melting points increase. This is because all the requirements for a barrier-to-grain growth suggested in this paper are the better fulfilled the higher the melting point. Some of the layered films were tested for hillock formation due to thermal cycles between room temperature and 4.2 K; on some of them, the superconducting transition temperature was measured and nuclear backscattering spectra taken.
Possibility of self-epitaxial growth of laser irradiated AlSb films
Authors: Baufay L. , Pigeolet A. , Laude L. D.
Published: February 2003

Metallic films of alternating Al and Sb layers are laser pulse irradiated at room temperature in air in order to obtain the semiconducting compound AlSb. Using transmission electron microscopy and high resolution electron diffraction, the crystal growth is studied as a function of the spatial distribution of the laser beam. It is shown that by monitoring the beam inhomogeneities in an easy manner, it is possible to control the crystallite’s size, which may be 50 times the total thickness of the film. The possibility of a self-epitaxy without substrate is also demonstrated.
Determination of strain distributions in ion-implanted magnetic bubble garnets applying x-ray dynamical theory
Authors: Takeuchi T. , Ohta N. , Sugita Y. , Fukuhara A.
Published: February 2003

X-ray dynamical theory has been applied to determine strain distributions caused by ion implantation into magnetic bubble garnets. Experimental rocking curves obtained by a double-crystal x-ray diffractometer were compared with theoretical curves for assumed strain distributions, and after several trials, good fittings were obtained. It is shown that slight change in the assumed strain distribution leads to appreciable change in the theoretical rocking curve. Comparison between dynamical and kinematical treatments shows that dynamical treatment is more accurate. Applying the method, it was confirmed that strain by multiple ion implantation was basically the sum of those by single ion implantation.
Elastic modulus in composition-modulated copper-nickel foils
Authors: Tsakalakos T. , Hilliard J. E.
Published: February 2003

The biaxial elastic modulus Y[111] was measured by bulge testing on Cu-Ni thin foils containing short-wavelength composition modulations produced by vapor deposition. In the wavelength range of 1.3–3.0 nm, we observed a twofold increase in the modulus as compared with homogeneous foils. The increase was proportional to the square of the composition amplitude. The maximum modulus occurred at a wavelength of 1.7 nm and an average composition of 45 at. % Cu. The stress-strain curves of the modulated foils were reversible but non-Hookean, while homogeneous foils displayed a Hookean behavior with moduli in good agreement with those calculated from the single-crystal elastic constants of bulk Cu-Ni alloys.
Glow-curve analysis of thermally stimulated luminescence in CaF2:Mn
Authors: Cook D. Wayne , Gavathas Evangelos P. , Brown M. D.
Published: February 2003

Thermally stimulated luminescence (TSL) and emission spectra studies of CaF2:Mn have been conducted in the interval 80–300 K. X irradiation at 80 K and subsequent heating produces an intense TSL glow peak at 175 K with concomitant spectral emission consisting of a band whose maximum occurs at 495 nm with a full width at half-maximum of 0.290 eV. A detailed analysis of the 175-K TSL peak shows that the thermal process follows neither first- nor second-order kinetics but, in fact, obeys a 1.4-order kinetics expression. Pertinent parameters describing the glow peak are: frequency factor s=2.74×104 s−1, thermal activation energy E=0.234 eV, and heating rate β=0.079 K s−1. Previous work has shown that a TSL peak near 200 K, which produces 490-nm emission, is due to the de-excitation of substitutional Mn2+ ions. The glow peak was characterized by an activation energy of 0.5 eV with second-order kinetics. Although we agree with the physical model depicting TSL in CaF2:Mn, we believe that the process should be correctly described by 1.4-order kinetics.
The near ultraviolet quantum yield of silicon
Authors: Wilkinson F. J. , Farmer A. J. D. , Geist J.
Published: February 2003

New values for the quantum yield of silicon in the 3 to 5 eV spectral region are derived from reflectance and photoresponse measurements on oxide/p+/n/n+ photodiode structures. The new values fall between high and low estimates derived from a recent model of impact-ionization phenomena due to Alig, Bloom, and Struck. A prominent peak in the new spectrum near 4.5 eV is attributed to the way the photon energy in excess of the band-gap energy is distributed between the photogenerated electrons and holes at different photon energies due to the band structure.
Electron-beam uniformity of a large-area high-current accelerator diode
Authors: Patterson E. L. , Hamil R. A. , Samlin G. E.
Published: February 2003

Time-resolved photography of Cherenkov emission has been used to study large-area electron-beam uniformity and electron-beam propagation in air. For the 50-ns pulse widths used, we show that the time-dependent electron emission from large-area cathodes is typically very nonuniform. Pinching of the electron beam by its self-magnetic field can be prevented by the use of an applied axial magnetic field approximately equal to the self-magnetic field generated by the electron beam. When an applied field is used, beam nonuniformities introduced by the anode support structure persist through tens of centimeters of air outside the diode. These nonuniformities can reduce efficiency and beam quality of the laser. Beam rotation in the diode caused by the applied magnetic fields can result in significant loss of electron-beam energy to the anode chamber and foil-support structure. However, we have shown that emission can be reduced on areas of the cathode which map onto obstructions on the anode so the electron energy loss can be reduced.
Transient temperature profiles in solids heated with scanning laser
Authors: Chen Inan , Lee Sanboh
Published: February 2003

The temperature profiles of a semi-infinite slab heated with a scanning laser beam are calculated. The effects of the scanning velocity, the beam radius, and the beam shape on the temperature profiles are investigated. It is demonstrated that there exists a critical velocity below which the effects of the moving source become practically neglibible. The critical velocity is equal to the ratio of the diffusivity to the beam radius.
Critical sizes of cobalt fine particles with uniaxial magnetic anisotropy
Authors: Sato M. , Ishii Y.
Published: February 2003

Assuming that the wall energy of a fine ferromagnetic particle consists of the exchange, magnetocrystalline anisotropy, and stray field energies, the critical particle size lc of a single-domain structure is calculated for an elongated cobalt particle as a function of the axial ratio n. It is found that lc is 55 nm for a particle with an axial ratio of n=1, increases with an increase in n, and is 300 nm for a particle with n=10. The particle with a size larger than lc begins to contain two domains divided by a 180° wall. Using the wall energy of bulk material, which consists of exchange and magnetocrystalline anisotropy energies, the critical particle size lcb is also calculated, and lcb is found to be smaller than lc by about 10%.
Photolysis of Fe(CO)5 adsorbed on GaAs at 77 K
Authors: Bottka N. , Walsh P. J. , Dalbey R. Z.
Published: February 2003

It is shown experimentally that pentacarbonyl iron can be adsorbed and desorbed on a GaAs substrate at low temperatures and photolyzed with ultraviolet illumination to yield Fe film deposit. A simple double beam laser technique is used to monitor the sequence of events during adsorption, desorption, and UV illumination. This work is the first evidence for the direct formation of a thin metal film on a cold semiconductor surface by ultraviolet photolysis of a condensed organometal.
Degradation caused by substrate glass in WO3 electrochromic devices
Authors: Yamanaka Kazusuke
Published: February 2003

The causes of degradation resulting from alkaline elemental diffusion from various glass substrates into WO3 films is clarified. Cells with a soda-glass substrate covered with a transparent conductive layer that was heat treated (250 °C, 1 h, in vacuum) before WO3 evaporation show poor initial coloring-erasing properties. The life of such cells is found to be short. Secondary ion mass spectroscopy analysis shows that the poor cell properties are due to Na diffusion from the soda-glass substrate into the WO3 films through the transparent conductive layer. On the other hand, cells with a 7059 glass or a spin-on-glass-coated soda-glass substrate showed good initial coloring-erasing properties, even if these substrates had been heat treated before WO3 evaporation. These cells demonstrate a high reliability. The results open the way for expanded use of WO3 film in realizing more advanced electrochromic devices.
An enhanced sensitivity null ellipsometry technique for studying films on substrates: Application to silicon nitride on gallium arsenide
Authors: Alterovitz Samuel A. , Bu-Abbud George H. , Woollam John A. , Liu David C.
Published: February 2003

General considerations are applied to optimize the sensitivity of ellipsometric measurements for thin films on a substrate. s- or p-wave suppression conditions are found to give maximum sensitivity. Approximate values of the optical parameters of the films and substrate are used to calculate discrete film thicknesses for the s- or p-wave suppression to occur. For null fixed-wavelength ellipsometry, these calculations are limited to experimentally available wavelengths, e.g., at strong emission lines from a Hg lamp. Films with thicknesses near the calculated ones are then deposited on the substrate. The ellipsometric parameters ψ and Δ are obtained at multiple angles of incidence and wavelengths, and a least-squares procedure is used for the analysis. The method has been applied to silicon nitride films on GaAs. The problem of correlation between the calculated optical parameters of the system is addressed. It is shown that the multiple-wavelength analysis decreases significantly the correlations as compared to single-wavelength analysis.
Calculation of intrinsic carrier concentration in Hg1−xCdxTe
Authors: Hansen G. L. , Schmit J. L.
Published: February 2003

Intrinsic carrier concentration in Hg1−xCdxTe is calculated as a function of temperature and composition using the Kane nonparabolic approximation for band structure and recent measurements of the heavy hole mass mh and energy gap Eg. An expression fitted to these calculations is: ni[5.585−3.820x+1.753(10−3)T −1.364(10−3)xT] ×(1014)E3/4gT3/2 exp(−Eg/2kbT). The fit of this approximation is within 1% of the calculated ni for the range Eg>0, 50<T<300 K and x<0.7. It is also within 15% of experimental ni obtained from Hall measurements.
Measurement of the lifetime of silver atoms on silver bromide grain surfaces in photographic emulsion by the multiflash method
Authors: Hada Hiroshi , Kawasaki Mitsuo
Published: February 2003

The multiflash exposure method, which is a new useful and powerful tool for studying the nature of the photolytic silver atom on silver halide grain surface, is reported. The lifetime of the photolytic silver atom and the corresponding activation energy are easily and quantitatively determined by this method. The lifetime at 20 °C and the apparent activation energy were 1.1 s and 0.7 eV, respectively, on (100) surface of a chemically unsensitized silver bromide grain in a wet air environment. In a vacuum environment the lifetime was prolonged to 300 s and the activation energy was decreased to 0.40 eV.
Effect of ionized donors on the electron and hole densities of states in silicon
Authors: Lowney Jeremiah R. , Bennett Herbert S.
Published: February 2003

A self-consistent second Born aproxiamtion has been used to calculate the change in the electron and hole densities of states due to ionized donors in silicon. The results are compared with a previous partial-wave technique and found to be in good agreement for a case of common applicability, i.e., a donor density of 1020 cm−3 at room temperature.
Sphere assemblage model for polycrystals and symmetric materials
Authors: Schulgasser Kalman
Published: February 2003

The problem of the prediction of the effective conductivity of a polycrystal given the conductivity of the single crystal is considered in the light of what can be learned from a constructible polycrystal model for which the effective conductivity can be exactly calculated. It is shown that if the only information known about the internal geometry of the polycrystal is that the aggregate is statistically homogeneous and isotropic it is not possible to narrow appreciably the well-known ‘‘average conductivity-average resistivity’’ bounds on the effective conductivity. The model also casts some light on the analogous problem for two phase symmetric materials.
Influence of radiative recombination on the minority-carrier transport in direct band-gap semiconductors
Authors: von Roos Oldwig
Published: February 2003

When radiative (band to band) lifetimes and nonradiative (multiphonon via flaws) lifetimes become comparable, as is the case for GaAs, the customary diffusion equation for minority carriers under low level injection conditions must be augmented by terms originating from photon transport. Using the generalized van Roosbroeck–Shockley relation between absorption and emission as well as radiative transfer theory, the relevant equations for free carrier transport are derived. Subsequently, it is shown that the influence of the reabsorbed recombination radiation on carrier transport while unimportant at low doping levels becomes important for n-type GaAs at high doping levels. We also determine the external luminescence flux taking due account of multiple emission and absorption events inside the sample.
High-field drift velocity of electrons at the Si–SiO2 interface as determined by a time-of-flight technique
Authors: Cooper J. A. , Nelson D. F.
Published: February 2003

We describe a new technique for the study of high-field transport at semiconductor–insulator interfaces. In this technique, we observe the time-of-flight of discrete charge packets introduced by a pulsed laser. The packets drift in a region of uniform applied tangential field at the interface. We present data on the room temperature drift velocity of electrons at the interface between (100) silicon and thermally grown silicon dioxide as a function of both tangential and normal electric fields. We observe velocities near saturation of 8.9×106 cm/s at a tangential field of 4 V/μm and a normal field of 9 V/μm, and extrapolate to a saturation velocity of 9.2×106 cm/s independent of normal field. This value is more than 40% higher than reported by early workers, and is close to the saturation velocity observed in bulk silicon.
High-temperature optical fiber thermometer
Authors: Dils R. R.
Published: February 2003

A high-temperature optical fiber thermometer made from single crystal sapphire has been developed for use from 600 to approximately 2000 °C. The device consists of a small blackbody cavity which is sputtered on the end of a thin (0.25–1.25-mm diameter, 0.05–0.30-m length) sapphire fiber, a connecting low-temperature glass fiber, and a conventional optical detector. The radiance from the cavity is used to measure its temperature. The present instrument is calibrated at a single temperature and uses the fundamental radiation laws to extrapolate to other temperatures. It is accurate and has a high sensitivity and rapid temporal response. There appear to be a number of applications of the device both in science and industry.
Fusion reactivities for several beam and target ion distributions
Authors: Slaughter Dennis
Published: February 2003

Fusion reactivities 〈σv〉 in the mean ion energy range 0.1–200 keV have been calculated for the reactions: D(d,n), T(d,n), D(d, p), 3He(d, p) and T(t,2n); and for several different ion energy and angular distributions considered plausible in hot, magnetically confined plasmas. Calculations were carried out to a numerical accuracy of about 5% and the resulting variation of reactivity with mean ion energy is found to be well represented by a simple polynomial function. The polynomial functions are plotted as a function of mean ion energy and their coefficients given. Results of the calculations show that fusion reactivity is very sensitive to the functional form of the speed distribution at mean energies below a few keV, but reactivity is roughly independent of the form of the speed distribution (within a factor of 2) above 10 keV for most of the reactions investigated. Similarly, the importance of the ion angular distribution is large at energies below a few keV but small at high ion energies.
On the measurement of surface free energy and surface tension of solid metals
Authors: Kumikov V. K. , Khokonov Kh. B.
Published: February 2003

Measurements of surface free energy and surface tension of solid metals reported in the literature are collected and compared and preferred values are suggested. The basic criteria which determine the value of obtained results are shown.
Properties of Pd/Au thin film layered structures
Authors: Carcia P. F. , Suna A.
Published: February 2003

We have synthesized, by rf sputtering, Pd/Au layered structures with periodicities (Pd+Au layers) that vary from 15–95 Å. The films have been characterized by x-ray diffraction. The individual metal layers have (111) orientation perpendicular to the plane of the film. We accurately model the positions and intensities of x-ray lines by a one-dimensional diffraction grating of Pd and Au layers and relate the observed x-ray line widths to loss of long-range layer coherence induced by dislocations at Pd–Au interfaces. We also find that the in-plane electrical resistivity of the films varies inversely, and the temperature coefficient of resistance directly with the layer period. We account for both of these trends by considering scattering of electrons from the metal interfaces, using a modified Fuchs theory.
Numerical analysis of steady-state thermal breakdown
Authors: Hikita M. , Ieda M. , Sawa G.
Published: February 2003

A procedure for numerically solving the fundamental equations of steady- state thermal breakdown has been presented. Assuming an ionic conduction and using the published experimental conduction data for poly (ethylene–terephtalate) film, the current–voltage characteristics, the temperature dependence of the critical electric field, and the profiles of temperature and field in the bulk at a constant ambient medium temperature are given. The calculations indicated that moderation of field distortion occurs if a nonlinear field dependence of conduction current is used in place of Ohm’s law. The degree of the moderation of field distortion depends on the functional form of the temperature and field dependence of conduction current and the magnitudes of parameters involved therein. Unless these are established and a quantitative evaluation of the thermal breakdown process based on them are made, thermal breakdown cannot be excluded as a possible mechanism for thick samples of polymers.
Dispersion of the refractive index of InP and ZnTe
Authors: Jensen B. , Torabi A.
Published: February 2003

An analytical expression for the real part of the refractive index n near the fundamental absorption edge is given in terms of experimentally known quantities for a given semiconductor. It is derived from a quantum mechanical calculation of the complex dielectric constant which assumes the band structure of the Kane theory. The expression obtained is a function of the band-gap energy, the effective electron and heavy hole masses at the band edge, the spin orbit splitting energy, the carrier concentration for n- or p-type materials, the temperature, and the frequency of the incident radiation. Also involved is the value of n at the fundamental absorption edge, which is not accessible to measurement. However, an equation for n at the absorption edge can be found in terms of experimentally obtainable values of n near the absorption edge and solved to give the desired quantity. The refractive index can then be predicted to a high degree of accuracy over the entire frequency spectrum up to the band edge. In particular, the dispersion near the fundamental absorption edge which has been observed experimentally for a number of III-V and II-VI compounds is predicted and its precise calculation enabled. Within limits of the above statement regarding n at the absorption edge, there are no adjustable parameters involved. This constitutes a significant improvement over previous theories of the refractive index of a semiconductor, which typically involve several adjustable parameters. Theory is compared with available experimental results for InP and ZnTe. A method of determining the heavy hole effective mass from measurement of n in compounds where it is unknown is discussed.
Optically recording interferometer for velocity measurements with subnanosecond resolution
Authors: Bloomquist D. D. , Sheffield S. A.
Published: February 2003

An optically recording velocity interferometer system, called ORVIS, has been developed to measure particle velocity histories in shock wave experiments on condensed matter. The interferometer fringe motion is recorded with a high speed electronic streak camera, rather than with photomultiplier tubes and oscilloscopes as in previous interferometry systems. With this approach, the particle velocity of a witness foil in a detonation wave experiment was measured with 300-ps time resolution. We believe that 20-ps time resolution can be achieved with this technique which would represent an improvement of two orders of magnitude over previous measurement techniques.
Electron drift velocities in gas mixtures of He, N2, and CO2
Authors: Cornell Michael C. , Littlewood Ian M. , Brooks Howard L. , Nygaard Kaare J.
Published: February 2003

An electron swarm experiment has been used to obtain electron drift velocities in the He:CO2:N2 mixtures 0:1:1, 3:1:2, and 3:1:1. The E/N range of 3 to 57 Td was studied with total gas pressure varied from 50 to 200 Torr. These particular mixtures have not been previously studied experimentally. Good agreement is observed between theoretical calculations and experimental data.
Behavior of Cs+-UF−6 ion-pair plasmas in radiofrequency quadrupole-dipole fields. II. Theory
Authors: Wagner Albert F.
Published: February 2003

The behavior of a flowing Cs+-UF−6 ion-pair plasma in the radiofrequency (rf) quadrupole-dipole fields of a mass filter has been studied theoretically. The theoretical calculations were designed to simulate the experimental observations of the preceding paper. For low-density plasmas, the calculations involved trajectory studies of isolated ions in quadrupole-dipole fields with or without fringe fields. For high-density plasmas, two-dimensional particle-in-cell trajectory studies were used to self-consistently incorporate space-charge effects into the simulated plasma behavior in perfect quadrupole-dipole fields uncomplicated by fringe fields. Three aspects of the interaction of the plasma with the radiofrequency fields were investigated: (1) the effects of fringe fields, especially on the injection of the plasma into the quadrupole-dipole field, (2) confinement by and transmission of the flowing plasma through a quadrupole field, and (3) mass-sensitive ejection of ions from the plasma by superimposed quadrupole and dipole fields. For each of these three topics, the theoretical results were compared to the experimental observations, especially in regards to the effect of increasing plasma density. In general, the agreement between theory and experiment is good. The theoretical calculations suggest a limiting current of several hundred microamperes that can be transmitted by the mass filter. The limit is reached when the plasma density increases to the level where the plasma frequency is comparable to the applied rf quadrupole frequency. At higher densities, successive layers of the plasma peel off and are driven out by the applied field until the limiting density is reached. This effect interferes with mass-sensitive ion ejection by the applied dipole field and also induces additional plasma loss in fringe fields. Furthermore, since the dipole frequency is much lower than the quadrupole frequency, it is consequently much reduced from the plasma frequency near the limiting currents. As a result, the applied dipole field has difficulty penetrating the plasma, which leads to significant degradation of mass resolution.
Growth of titanium silicide on ion-implanted silicon
Authors: Révész P. , Gyimesi J. , Zsoldos É.
Published: February 2003

Silicon samples implanted with high doses of 121Sb, 75As, 31P, 16O, and 40Ar prior to Ti evaporation were studied to measure the growth of Ti-silicide layers. The annealing behavior of these samples was investigated by four-point probe measurement, Rutherford backscattering, and by x-ray diffraction. The samples implanted with Sb, As, and P atoms enabled the growth of TiSi2 to be observed, though its final thickness was less than half when compared to that of the nonimplanted samples. Simultaneously with the diffusing-out atoms of Sb, during annealing, segregation of Sb atoms takes place at the TiSi2/Ti interface and at the Ti surface. Using a simple model for the out-diffusion of Sb atoms, the activation energy of the diffusion coefficient of Sb in the Ti silicide was determined, giving a value of Ea=1.9 eV. During out-diffusion, As atoms tend to be distributed homogeneously in the silicide layer. With Ar- and O-implanted samples, precipitation of Ti atoms can be observed at the implantation depth, and at higher annealing temperatures, the metal layer flakes off the sample. A simple model is given to explain this behavior. X-ray diffraction measurements of these samples showed the presence of the unstable TiSi phase, but no trace of the TiSi2 phase was found after annealing at 700 °C.
Effect of arsenic dimer/tetramer ratio on stability of III–V compound surfaces grown by molecular beam epitaxy
Authors: Wood C. E. C. , Stanley C. R. , Wicks G. W. , Esi M. B.
Published: February 2003

Using a post-effusion thermal cracking furnace, the ‘‘arsenic stabilization’’ efficacy of As2 versus As4 on the surfaces of (100) GaAs, Al0.48In0.52As, Ga0.47In0.53As and (AlGa)0.47In0.53As has been studied. Dimers were found to be no more efficient than tetramers either slightly below, at, or above the upper congruent sublimation temperature.