bluuebunny/crossref_metadata_2025 huggingface dataset:
Chromium silicide formation by ion mixing
Authors: Shreter U. , So Frank C. T. , Nicolet M-A.
Published: February 2003

The formation of CrSi2 by ion mixing was studied as a function of temperature, silicide thickness and irradiated interface. Samples were prepared by annealing evaporated couples of Cr on Si and Si on Cr at 450 °C for short times to form Si/CrSi2/Cr sandwiches. Xenon beams with energies up to 300 keV and fluences up to 8×1015 cm−2 were used for mixing at temperatures between 20 and 300 °C. Penetrating only the Cr/CrSi2 interface at temperatures above 150 °C induces further growth of the silicide as a uniform stoichiometric layer. The growth rate does not depend on the thickness of the initially formed silicide at least up to a thickness of 150 nm. The amount of growth depends linearly on the density of energy deposited at the interface. The growth is temperature dependent with an apparent activation energy of 0.2 eV. Irradiating only through the Si/CrSi2 interface does not induce silicide growth. We conclude that the formation of CrSi2 by ion beam mixing is an interface-limited process and that the limiting reaction occurs at the Cr/CrSi2 interface.
Titanium diffusion into LiNbO3 as a function of stoichiometry
Authors: Holmes R. J. , Smyth D. M.
Published: February 2003

The diffusivity of Ti into LiNbO3 has been measured as a function of crystal orientation and Li/Nb ratio in the temperature range 980–1112 °C. The Li/Nb ratios of single crystal samples were adjusted by vapor phase equilibration with fixed Li2O activities. No anisotropy of diffusivity with crystal orientation could be detected. The diffusion constants for Ti in LiNbO3 decrease with increasing Li2O content. At 1050 °C, the values decrease from 2.60×10−12 cm2/s at the Li2O-deficient phase boundary (48.1 mol % Li2O) to 1.06×10−12 cm2/s at the congruently melting composition at (48.6 mol  % Li2O) to 0.4×10−12 cm2/s at the Li2O-rich phase boundary (50.0 mol % Li2O). It is suggested that enhanced lateral diffusion observed for stripe geometry Ti sources results from increased diffusivity in a surface layer formed by Li2O outdiffusion.
A15 Nb-Sn tunnel junction fabrication and properties
Authors: Rudman D. A. , Hellman F. , Hammond R. H. , Beasley M. R.
Published: February 2003

We have investigated the deposition conditions necessary to produce optimized films of A15 Nb-Sn (19–26 at. % Sn) by electron-beam codeposition. Reliable high-quality superconducting tunnel junctions can be made on this material by using an oxidized-amorphous silicon overlayer as the tunneling barrier and lead as the counter-electrode. These junctions have been used both as a tool for materials diagnosis and as a probe of the superconducting properties (critical temperature and gap) of the films. Careful control of the substrate temperature during the growth of the films has proved critical to obtain homogeneous samples. When the substrate temperature is properly stabilized, stoichiometric Nb3Sn is found to be relatively insensitive to the deposition temperature and conditions. In contrast, the properties of the off-stoichiometry (Sn-poor) material depend strongly on the deposition temperature. For this Sn-poor material the ratio 2Δ/kTc at a given composition increases with increasing deposition temperature. This change appears to be due to an increase in the gap at the surface of the material (as measured by tunneling) relative to the critical temperature of the bulk. All the tunnel junctions exhibit some persistent nonidealities in their current-voltage characteristics that are qualitatively insensitive to composition or deposition conditions. In particular, the junctions show excess conduction below the sum of the energy gaps (with onset at the counter-electrode gap) and a broadened current rise at the sum gap. The detailed origins of these problems are not yet understood.
Statistical comparisons of data on band-gap narrowing in heavily doped silicon: Electrical and optical measurements
Authors: Bennett Herbert S. , Wilson Charles L.
Published: February 2003

A system of subroutines for iteratively reweighted least squares (IRLS) computations has been applied to the published measured and theoretical data on band-gap narrowing in heavily doped silicon. The data include electrical and optical measurements at room temperature, photoluminescence and optical measurements for temperatures below 35 K, and theoretical calculations at 300 and 0 K. The IRLS procedure allows a clear graphical comparison of the various experimental and theoretical data in band-gap narrowing to be made. The results are (1) band-gap changes determined by the optical absorption are consistent at both 300 K and at temperatures below 35 K with recent theoretical calculations, (2) the electrical and optical measurements are not consistent with each other, and (3) the low temperature optical absorption data and the photoluminescence data are not consistent with each other.
The use of linear predictive modeling for the analysis of transients from experiments on semiconductor defects
Authors: Shapiro Finley R. , Senturia Stephen D. , Adler David
Published: February 2003

Many methods have been employed to analyze data from experiments which measure transient responses to excitations. One such experiment, deep level transient spectroscopy, is widely used in the study of semiconductor defects. The covariance method of linear predictive modeling, which is used in digital signal processing, can be applied to the problem of transient analysis. We describe the covariance method and its limitations, and present the results of its use to analyze the data from capacitance transient experiments.
Misfit dislocations in (111)A InP/In0.53Ga0.47As/InP double heterostructure wafers grown by liquid phase epitaxy
Authors: Yamazaki Susumu , Nakajima Kazuo , Komiya Satoshi , Kishi Yutaka , Akita Kenzo
Published: February 2003

The behavior of misfit dislocations in (111)A InP/In0.53Ga0.47As/InP double heterostructure (DH) wafers, grown by liquid phase epitaxy, has been investigated by x-ray and photoluminescence (PL) topography and compared with those in (100) and (111) B quaternary DH wafers. Misfit dislocations are generated at wafer edges and are located in close proximity to the heterointerface in the upper InP layers. These dislocations were determined to be the same as in the case of (100) DH wafers. The misfit dislocation free area, as determined by PL topography with Ar+ ion laser excitation, decreases rapidly when the upper InP layer thickness approaches about 1 μm. Nearly misfit dislocation free DH wafers were obtained by a two step growth of the upper InP layer. In (111)A ternary DH wafers, with a lattice mismatch of 0% to −0.03% at room temperature, misfit dislocations are mostly β-type 60° dislocations. These misfit dislocations are not observed by PL topography when ternary layers are excited by a Nd-doped Yttrium Aluminium Garnet (Nd:YAG) laser. Misfit dislocations of the α type, introduced in (111)B quaternary DH wafers with a lattice mismatch of the same sign and magnitude, are clearly observed as dark lines under Nd:YAG laser excitation.
Broad luminescent band in Zn-doped AlxGa1−xAs grown by metalorganic chemical vapor deposition
Authors: Sakamoto Masamichi , Okada Tsunekazu , Mori Yoshifumi , Kaneko Kunio
Published: February 2003

We have investigated by photoluminescence the low energy broad band in Zn-doped AlxGa1−xAs grown by metalorganic chemical vapor deposition. The emission peak energy of the band shifts monotonically with temperature. The temperature variation of the half-width does not fit the configuration coordinate model. The emission peak intensity increases nearly linearly with the V/III ratio in the vapor phase during growth. We suggest a ZnIIIVIII complex is responsible for the band, although the details of the recombination mechanism remain unknown.
Internal friction changes in NaCl at 77 K
Authors: Bielig G. A.
Published: February 2003

The behavior of B/B0, the fractional change in the dislocation damping coefficient, has been studied at 77 K for continuous and interrupted radiation experiments using λ rays. Preliminary results indicate that B shows similar increases as observed at room temperature, but there appears to be a decreasing component of B/B0 when the radiation is first switched on. Illumination with laser light (λ=633 nm) tends to ‘‘erase’’ previous B/B0 changes as well as unpinning dislocations.
Enhanced Raman scattering from cesium suboxides in photocathodes: Ag–O–Cs (S-1) and Bi–Ag–O–Cs (S-10)
Authors: von Raben K. U. , Lee K. C. , Chang R. K. , Benner R. E.
Published: February 2003

Raman spectra from photomultipliers having Ag–O–Cs photocathodes (S-1) are found to correspond to the vibrational spectrum of Cs11O3. The wavelength dependence of the Cs11O3 Raman intensity is compared with the radiant sensitivity of the S-1 photocathode, and the possible role of Ag islands in enhancing the Raman intensity and photocurrent is discussed. The composition near the edge of the Bi–Ag–O–Cs photocathode (S-10) was found to be Cs11O3.
Experiments on the reflection of lateral electromagnetic waves
Authors: Brown M. F. , King R. W. P. , Wu T. T.
Published: February 2003

The measured reflections of lateral waves at discontinuities and boundaries are shown for two frequencies. A cylindrical model lithosphere bounded at its perimeter in seven distinct ways is utilized. The resulting fields are compared with the theory of normally incident lateral waves.
Second-order coupling of two Love waves
Authors: Seshadri S. R.
Published: February 2003

The second-order contradirectional coupling of two Love waves in the presence of radiation of bulk elastic waves in the substrate is investigated. Particular attention is paid to the optimizations of the coupling between (a) the two Love waves, (b) the incident Love wave and the radiated bulk elastic wave, and (c) the incident bulk elastic wave and the excited Love waves. An analysis of reciprocity is also included.
Measurement of shock temperatures in metals by the thick foil technique
Authors: Rosenberg Z. , Partom Y.
Published: February 2003

We present a new technique for the measurement of temperatures in shock-loaded metals. The technique is based on measuring the resistance changes of a relatively thick gauge, made of the investigated metal, during planar shock loading. The metallic gauge is embedded between two discs of an insulating material of comparable acoustic impedance. With the aid of suitable calibration curves the resistance-time history yields the temperatures at the shocked state and the residual temperatures after stress release. We present results for aluminum and copper foil gauges which were embedded in glass and alumina targets, respectively. The measured temperatures of the shocked as well as of the released states were higher than those inferred by assuming adiabatic compression. The difference can be accounted for by considering the plastic work during the stress relaxation process which takes place in the foil gauges. The measured residual temperatures are also in good agreement with those measured by others using radiation detectors.
Optical phonons of aluminum nitride
Authors: Carlone C. , Lakin K. M. , Shanks H. R.
Published: February 2003

Oriented polycrystalline films of AlN on Si(111) substrates and amorphous AlN films on sapphire substrates have been prepared by sputter deposition of aluminum in a nitrogen plasma. Phonons at 303, 426, 514, 614, 663, and 831 cm−1 (±3%) have been observed in the Raman spectra of the crystalline films. The 303-cm−1 phonon shifts to 288 cm−1 and the 663-cm−1 phonon to 650 cm−1 in the amorphous sample. By means of infrared absorption measurements with the electric field perpendicular to the c axis we have tentatively identified E1(LO) and E1(TO) modes near 800 and 610 cm−1, respectively. A tentative assignment of the other modes is made from partial data from orientation dependent scattering and results for other wurtzite structure compounds. A comparison of the AlN phonon frequencies with those of other known wurtzite structure compounds shows that Martin’s scaling equation is satisfied.
Pulsed laser irradiation of GaAs under oxygen and silane atmosphere: Incorporation, losses, influence of native oxide
Authors: Cohen C. , Siejka J. , Berti M. , Drigo A. V. , Bentini G. G. , Pribat D. , Jannitti E.
Published: February 2003

Gallium arsenide single crystals and thin GaAs amorphous deposits (in the 100-nm range) on Si have been irradiated by pulsed (15 ns) ruby laser under various pressures of 16O2. All the samples were anodically preoxidized in order to obtain a 10-nm-thick 18O enriched oxide, the aim being to study the influence of native oxide on oxygen incorporation during irradiation. Nuclear microanalysis and channeling experiments provide information on (i) 16O incorporation, (ii) 18O losses and concentration profile, (iii) Ga and As atoms out of crystallographic sites for single crystal irradiations, and (iv) Ga and As losses for thin films irradations. Our results demonstrate that a surface oxide is formed with a composition near the Ga2O3-As2O3 stoichiometry via oxygen penetration in the melted layer once the native oxide has been evaporated at irradiation energies above 1 J/cm2. Before complete evaporation,this latter oxide diffuses in GaAs and is responsible for defect creation at irradiation energies as low as 0.4 J/cm2. We also find that for irradiation in vacuum the surface composition varies continuously, from Ga to As rich, when the irradiation energy density goes from 0.4 to 1.5 J/cm2. Pulsed irradiations at 0.53 μm under silane atmosphere lead to strong Si doping. We show that the mechanism involved is pyrolisis of SiH4, surface deposition of the Si formed and finally diffusion of the deposited layer in GaAs during melting.
Vapor coating of electrostatically dispersed powders
Authors: Szirmai S. G. , Morton D. H. , Kelly P. L.
Published: February 2003

The deposition of vapors on electrostatically suspended dust has been studied through the construction of a laboratory-scale coating unit suitable for depositing coatings of high-melting point vapors (up to 1600 °C) on dispersed metal powders in a vacuum. Following a brief discussion of electrodispersion, the physical effect by which electrostatic suspensions may be generated, the construction and use of a laboratory coating unit is described. The equipment, which is housed in a vacuum enclosure at <10−5 Torr, consists partly of systems for maintaining the powder in a state of continuous suspension and flux and partly of others responsible for generating vapors. Our laboratory equipment, which relies on the indirect electron-beam heating of the evaporant, has a nominal capacity of 0.5-Kg coated metal powder per day and was successfully used for the production of powders treated with zinc, silver, tin, gold, and palladium. In discussing the potential for industrial scale use, it is shown that the process parameters of such a unit may be calculated with relative ease and it is concluded that a scale up to industrial size is feasible.
Amorphous silicon produced by ion implantation: Effects of ion mass and thermal annealing
Authors: Waddell C. N. , Spitzer W. G. , Fredrickson J. E. , Hubler G. K. , Kennedy T. A.
Published: February 2003

Characterization of the two optical states of amorphous Si produced by ion implantation is extended to include electron paramagnetic resonance, fundamental absorption edge, and density measurements in addition to infrared reflection. It is found that the properties of the two a-Si states are not dependent upon the mass of the incident ion (12C, 29Si, 31P, 120Sn) or upon the anneal temperature for 400 °≤TA≤600 °C. The dangling-bond density drops about a factor of 2 when the a-Si makes a transition between the two states. The absorption coefficient also drops by more than a factor of 5, but the density of the a-Si does not change when the transition occurs. The transition between states was not completed at TA=300 °C, so the annealing mechanism may be temperature dependent.
Mechanism and kinetics of tetrachlorosilane reactions in an argon-hydrogen microwave plasma
Authors: Mayo N. , Carmi U. , Rosenthal I. , Avni R. , Manory R. , Grill A.
Published: February 2003

The dissociation mechanism of silicontetrachloride to silicon by plasma with argon or in mixtures of argon and hydrogen was investigated by sampling the microwave induced plasma and its chemical components by (i) electrostatic double floating probe system (DFPS), (ii) quadrupole mass spectrometry (QMS), and (iii) electron spin resonance (ESR). Plasma diagnostics, i.e., determination of mean electron energy and positive ion density, were performed by DFPS. The reaction rate for chlorosilane fragmentation, polymerization, and silicon formation, in the plasma state were evaluated by QMS sampling of the plasma along the gas flow. ESR was used to investigate the amounts of free radicals adsorbed on solid alumina from different regions of the plasma. Comparing the two plasmas {SiCl4+Ar} to {SiCl4+Ar+H2} it was found that the dissociation of SiCl4 to Si in the argon plasma is mainly controlled by an ion-molecule mechanism while the dissociation in the presence of H2 is mainly controlled by the radical mechanism.
Modeling of thin-film solar cells: Nonuniform field
Authors: Crandall Richard S.
Published: February 2003

A model calculation for a thin film solar cell is presented to describe its photovoltaic behavior under the conditions that the photogenerated space charge causes significant distortion of the internal electric field. Expressions for the photocurrent, photocapacitance, and ambipolar-diffusion length are given.
Boron contamination in the intrinsic layers of amorphous silicon solar cells
Authors: Lee S. C.
Published: February 2003

The undoped hydrogenated amorphous silicon (a-Si:H) is well-known to be n− type. When this material is used to fabricate nip solar cells in a single chamber system, it tends to be contaminated by the residue dopants remaining from the deposition of the first boron-doped p layer unless adequate precautions are taken. The photoresponses of the indium tin oxide (ITO)/nip a-Si:H:F/stainless steel solar cells were measured by using band-passed blue (350 <λ<500 nm) and red (λ>580 nm) light. The blue light penetrates only about 1400 Å deep into the device whereas the red light is absorbed rather uniformly inside a typical 4000-Å-thick cell. These two responses as a function of applied biases can thus be used to find out the location of the carrier collection region which in turn tells us the degree of contamination in the i layer. Several examples will be discussed which illustrate the close relationships between the deposition parameters and the cell performances.
Intermetallic phases formed during tin implantation into iron and steels
Authors: Dionisio P. H. , de Barros B. A. S. , Baumvol I. J. R.
Published: February 2003

The surface layers of pure iron, high-carbon steel and stainless steel, ion implanted with 1×1017 Sn+ cm−2, have been characterized by means of 119Sn conversion electrons Mössbauer scattering. The intermetallic phases existent in the as-implanted samples are determined, and then the thermal decomposition of these phases are established. The phase transformations observed in the treated surfaces agree reasonably well with the phase diagrams reported in the literature for stoichiometric intermetallic phases formed in bulk.
Deposition parameters and film properties of hydrogenated amorphous silicon prepared by high rate dc planar magnetron reactive sputtering
Authors: Savvides N.
Published: February 2003

The sputtering characteristics for film deposition of hydrogenated amorphous silicon (a-Si:H) by dc planar magnetron reactive sputtering have been investigated for a range of H2/Ar pressures and applied power. These results indicate that the dc planar magnetron utilizing a silicon target is a high performance sputtering source offering a greater potential for the enlargement of solar cell area and a saving in device-processing time than other film deposition techniques currently in use. Film properties have been measured as a function of hydrogen partial pressure pH. Results are reported of the room temperature dark conductivity and photoconductivity of films versus pH for pH=0 –0.5 Pa. Films suitable for photovoltaic applications were prepared possessing dark conductivity ≲10−8 Ω−1 cm−1 and photoconductivity ∼10−4 Ω−1 cm−1. The optical absorption coefficient has been determined as a function of photon energy in the range 0.5–6.0 eV. The optical gap was found to increase with pH from 1.7 eV for unhydrogenated material to 2.0 eV for material prepared at pH=3 Pa.
Dynamics of capture from free-carrier tails in depletion regions and its consequences in junction experiments
Authors: Meijer E. , Grimmeiss H. G. , Ledebo L-Å.
Published: February 2003

Exponentially decaying tails of free carriers extend from the neutral material into the depletion region of p-n junctions or Schottky barriers. In nonequilibrium, deep level impurities in the depletion region may readily capture free carriers from these tails. The strongly nonexponential time dependence of the capture is calculated here and is compared with experimental data. This nonexponential time dependence is particularly important in deep level transient spectroscopy, and it also appears in many other junction measurements with deep level impurities.
Equilibrium distributions of electric field in a cell with adsorbed charge at the surfaces
Authors: Thurston R. N.
Published: February 2003

Ionic charge that is stuck at the solid-liquid surface attracts a diffuse layer of ions of the opposite sign in the liquid. The asymmetry in the electric field distribution that results when an applied field is combined with the intrinsic field in the diffuse charge layer has been cited as a possible cause of the dc switching effect observed in liquid crystal displays based on bistable boundary layer configurations [Robert B. Meyer and R. N. Thurston, Appl. Phys. Lett. 43, 342 (1983)]. Since the ratio of Debye screening length LD to cell depth d is an important parameter, it is useful to solve for the static equilibrium field distribution under constant voltage in a finite cell where LD/d is not small. This problem is solved here.
Mathematical model for a radioactive marker in silicide formation
Authors: Lien C.-D. , Nicolet M-A.
Published: February 2003

A mathematical model is constructed to interpret the profiles of radioactive 31Si tracers in a computer simulation proposed by R. Pretorius and A. P. Botha [Thin Solid Films 91, 99 (1982)]. This model assumes that only Si moves in the silicide, that the Si moves interstitially and convectively, and that the moving Si can exchange sites with the stationary Si in the silicide lattice. An analytical solution of this model is given and confirms the published computer simulation data. However, it is shown that the model is physically inadequate. Solutions of another model which assumes that metal, instead of Si, is the moving species for silicide formation (either interstitially, or substitutionally, or both), with self-diffusion of 31Si in the silicide during silicide formation. Almost all the experimental data can be fitted by solutions of both models. These examples demonstrate that radioactive tracer experiments alone are insufficient to determine the moving species when a solid binary compound film forms by reaction of adjacent elemental layers. Both inert marker and tracer data are needed to identify the moving species and the mechanisms.
Effects of surface states and of excitation on barrier heights in a simple model of a grain boundary or a surface
Authors: Landsberg P. T. , Abrahams M. S.
Published: February 2003

The model of a grain boundary (or of a surface) used here employs parallel quasi-Fermi levels but does not require the depletion approximation. Shockley–Read–Hall recombination via the surface states (including Auger effects) is utilized and the resulting surface trap occupation is displayed as a generalization of the well-known Fermi–Dirac distribution function. This enables one to cover equilibrium and steady-state conditions in one treatment. The barrier height has been given as a function of bulk doping, surface energy level density, and also as a function of excitation intensity. The latter is determined by the separation between the quasi-Fermi levels and can be due to incident light or carrier injection. A number of experimental curves have been fitted satisfactorily on the basis of the theory. Among the conclusions, we note that there is a maximum (with respect to doping) in the barrier height, and that illumination reduces the barrier height. The effect of the energetic position of the surface states is also traced here.
Interfacial effects due to tunneling to insulator gap states in amorphous carbon on silicon metal-insulator-semiconductor structures
Authors: Khan A. Azim , Woollam John A. , Chung Y.
Published: February 2003

ac conductance and capacitance measurements over the range 10 Hz to 10 MHz for amorphous carbon on silicon metal-insulator-semiconductor structures are reported. Data can be interpreted as being due to tunneling of electrons into gap states located in the dielectric. Interface state densities as low as 1.3×1010 eV cm2 are found.
Temperature dependence of the current in SiO2 in the high field tunneling regime
Authors: Ricco B. , Fischetti M. V.
Published: February 2003

In this work, we study the effect of temperature on the tunneling current in thin SiO2 films (≊200 Å) and show that a reversal of behavior is produced by increasing fields. While in the lower range (≤9 MV/cm) the current is well represented by the Fowler–Nordheim model and increases with temperature, it substantially disagrees with the theory at fields close to breakdown (>10 MV/cm) where it is larger than expected and decreases with increasing temperature. This cannot be explained with the formation of (quasi) stable positive charge which is known to be created by high field stress but, under our experimental conditions, is found to be negligibly small. Therefore, we deal with a new kind of effect for which few different possibilities are suggested as mechanisms at the microscopic level.
Crystal site determination of dilute alloying elements in polycrystalline Nb3Sn superconductors using a transmission electron microscope
Authors: Tafto J. , Suenaga M. , Welch D. O.
Published: February 2003

It is demonstrated that quantitative site occupancy of dilute constituents, 2 at. %, in polycrystalline materials of typical grain size 0.3 μm can be obtained by using the channeling effect in electron induced x-ray emission. The important alloying elements Ti and Ta which improve the superconducting properties of Nb3Sn made by the bronze process were both found to occupy the Nb sites.
Structural and morphological investigation of the development of electrical conductivity in ion-irradiated thin films of an organic material
Authors: Lovinger A. J. , Forrest S. R. , Kaplan M. L. , Schmidt P. H. , Venkatesan T.
Published: February 2003

Thin films of 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) develop low electrical resistivity (<10−3 Ω cm) after irradiation with 2-MeV Ar+ ions. Electron microscopy and diffraction show that vacuum-deposited films of this material consist, prior to ion-irradiation, of discrete crystalline grains (∼20–50 nm diameter) in which the molecules are disposed closely parallel to the substrate (average inclination ∼10°–15°). Upon irradiation with up to ∼1014 Ar+/cm2, the grains become progressively more defect-ridden and eventually amorphous. At that stage, the resistivity begins to decrease by ∼12 orders of magnitude at doses between ∼1014 and ∼5×1016 Ar+/cm2, while the intergranular boundaries become diffuse and the grains begin to merge. The temperature dependence of resistivity in this regime is as exp(const/T1/2), which is consistent with our morphological and structural results as it implies carrier hopping between conducting islands embedded in a nonconducting matrix. At the highest ion doses (>5×1016 Ar+/cm2) the grains become connected into a rather uniform and featureless network akin to amorphous carbon, and the resistivity reaches its lowest value and becomes independent of temperature. The amorphous-carbon-like character of the highly irradiated material is evidenced not only by its diffraction pattern but also by its crystallization with a graphitic-type structure during annealing to 1200 °C.
Magnetization configurations in plate-shaped fine particles of hcp cobalt
Authors: Sato M. , Ishii Y.
Published: February 2003

In order to find out the magnetization configurations in the plate-shaped fine particles of hcp colbalt, the energy densities of the particle with various magnetization configurations are calculated as a function of the particle radius r0 for the axial ratio n from 1 to 1/8. It is found that the particle has a single domain structure if r0 is smaller than the critical radius rc, and that rc is 17 nm for n=1/2, 12 nm for n=1/4, and 11 nm for n=1/8. It is also found that the particle with r0 larger than rc has a form of the curling configuration: the spins stand up in the center of the particle, but become the circular configuration in the off-center region, and that the particle has this curling configuration to r0 of 33 nm for n=1/2 and 200 nm for n=1/4.
Magnetostriction and thermal expansion of single crystal and polycrystalline alloys of iron and aluminum in the vicinity of Fe3Al
Authors: Cook Jason M. , Pavlovic A. S.
Published: February 2003

Magnetostriction and thermal expansion measurements of single crystals of ordered Fe3Al (25.24 at. % Al) are presented for temperatures between 77 and 296 K. Two magnetostriction constants are shown to be sufficient to describe the magnetostriction in the range of measured temperatures. Neither the magnetostriction constants nor the thermal expansion measurements showed any indication of the anomaly centered around 220 K which had been observed [J. M. Cook and A. S. Pavlovic, J. Appl. Phys. 50, 7710 (1979)] in single crystals having a concentration of 24.88 at. % aluminum. In addition, magnetization measurements did not show any trace of the anomaly. Thermal expansion measurements performed on polycrystalline samples of 23.92, 24.59, and 25.20 at. % Al showed the presence of the anomaly in the 24.59 at. % Al sample but not in the other two polycrystalline samples. This leads to the conclusion that the anomalous behavior is concentration dependent.
Effective phase and group indices for In1−xGaxP1−yAsy/InP waveguide structures
Authors: Burkhard H.
Published: February 2003

Effective phase and effective group indices for the complete wavelength range of the In1−xGaxP1−yAsy/InP system have been theoretically determined for symmetrical waveguide structures. A comparison between our theory and experimental data gained on a large number of our own lasers as well as on data from literature shows a very good agreement. This result confirms our calculation and rules out the dispersion behavior near the band-gap energy of the models of Afromowitz [Solid-State Commun. 15, 59 (1974)] and Adachi [J. Appl. Phys. 53, 5863 (1982)]. The results of our calculation allow us to determine the active layer thickness of DH lasers from the knowledge of the mode spacing and the laser length.
Solid solution, lattice parameter values, and effects of electronegativity in the (Cu1−xAgx)(Ga1−yIny)(Se1−z Tez)2 alloys
Authors: Avon Julie E. , Yoodee Kajornyod , Woolley John C.
Published: February 2003

Equilibrium conditions for the alloy system (Cu1−xAgx)(Ga1−yIny) (Se1−zTez)2 were determined throughout the complete range of composition. Polycrystalline samples of 125 different compositions, i.e., with x, y, and z=0, 0.25, 0.5, 0.75, and 1.0, were prepared by a melt and anneal technique. Different annealing temperatures in the range 600–800 °C were used depending upon the alloy composition and annealing times of up to 5 months used to attain equilibrium conditions. Debye-Scherrer x-ray powder photographs were used to investigate the equilibrium conditions. It was found that single phase chalcopyrite structure was obtained for all compositions of the copper (x=0), indium ( y=1), and tellurium (z=1) sections but that miscibility gaps occurred in the silver (x=1), gallium ( y=0), and selenium (z=0) sections, and that these miscibility gaps extended through the general alloy system. Values of lattice parameters a and c were determined for all samples showing single phase condition and for each of the above sections the variations of a and c with composition were fitted to power series in the appropriate composition coordinates. Hence contours of constant a and constant c were determined. From the parameters for each section, general series expressions in x, y, and z were developed and the values from these compared with the experimental data for the general alloys. It is shown that a modified Weaire and Noolandi relation of the form [2−(c/a)] =K(XI−XIII+qXVI)2 fits all of the experimental data. Averaged values of K and q were obtained by fitting separately to different sections of the alloy system and also to all alloys of the complete system.
Denuded zone formation in p 〈100〉 silicon
Authors: Murray E. M.
Published: February 2003

The effects of gas-ambient and heat-treatment order on denuded zone formation in p 〈100〉 silicon wafers have been investigated. A model of silicon self-interestitial interaction with oxygen out-diffusion and precipitate growth is presented to explain the observed variations.
Doping effects on conductivity and electron spin resonance in post-hydrogenated polycrystalline silicon
Authors: Hasegawa S. , Kishi K. , Kurata Y.
Published: February 2003

The effects of plasma hydrogenation on the electrical properties and electron spin resonance (ESR) are investigated for phosphorus and boron doped polycrystalline silicon films produced by annealing from chemical vapor deposited amorphous silicon. In lightly doped films, the dark conductivity and photoconductivity increase with hydrogenation. The photoconductivity also increases with increasing doping ratio. These increases of the dark conductivity and photoconductivity correspond well to a decrease of ESR spin density due to dangling bonds. In hydrogenated films doped with phosphorus or boron, it is found that the dark conductivity first decreases with increasing doping ratio, and then rapidly increases. These results for the electrical properties and ESR are discussed in terms of the two-phase model in which crystallites with surface bandbending and a damaged layer between the crystallites are included. As a consequence the electrical properties are indicated to have a close relation to the density of dangling bonds in the damaged layer, and the dark conductivity and photoconductivity are controlled by surface conduction of crystallites and a short lifetime of photogenerated carriers in the damaged layer, respectively, depending on the density of dangling bonds. The temperature dependence of the photoconductivity is also discussed based on this model.
Small-signal charge transport in Schottky-barrier punch-through devices
Authors: El-Gabaly M.
Published: February 2003

Small-signal charge-transport properties of Schottky-barrier punch-through injection and transit-time structures are theoretically investigated. A numerical model of the structure which considers carrier diffusion, realistic dependence of carrier velocity upon electric field and doping density, and nonequilibrium carrier injection over the forward-biased metal-semiconductor contact is formulated. This model predicts accurately the experimental small-signal behavior of the device and determines quantitatively the validity of various simplifying assumptions used in existing theories. Based on the present study, an improved analytical model for the device is suggested and its validity and limitations are identified. Also, the difference in the small-signal performance between Schottky-barrier and p-n junction devices is explained.
Analytical integration of the Thomas–Fermi scattering cross section
Authors: Ashworth D. G. , Moulavi-Kakhki M.
Published: February 2003

A method is presented whereby the Thomas–Fermi scattering cross section may be written in a form which is directly integrable, thus enabling the nuclear energy loss of energetically implanted ions to be expressed in analytical form as a function of the impact parameter.
The effect of heavy dose implantations of B and C on the crystal structure and superconducting transition temperature of A-15 Nb3Al
Authors: Clapp Mireille Treuil
Published: February 2003

The effect of ion implantation on metastable phase formation and superconducting transition temperature (Tc) has been investigated. The particular alloys studied were Nb3Al1−xBx and Nb3Al1−xCx. A-15 Nb3Al was used as the substrate material. Large doses of B and C (up to 23 at.%) were implanted into Al depleted surfaces. A series of implantation energies and doses was chosen to maintain the (Al+B) and (Al+C) concentrations equal to 25 at. %. This is necessary for achieving high Tc materials. Auger analysis indicated that there was very good agreement between experimental and theoretical dopant profiles immediately after implantation. After annealing up to 900 °C the B atoms showed very little redistribution; however the C atoms tended to migrate towards the surface. Structural analysis using a READ camera and a diffractometer indicated that the large doses of B and C had been implanted into the A-15 structure without affecting its stability; this A-15 phase remained stable up to 950 °C. Implantation caused the lattice parameter of the A-15 phase to increase by 1%–2%. There was no increase in the superconducting transition temperature above that of the substrate (18 K). This work is consistent with other studies; implantation has successfully produced metastable phases; however implantation into A-15’s has not increased their Tc’s.
Comparison of channeling radiation from diamonds with and without platelets
Authors: Park H. , Pantell R. H. , Swent R. L. , Kephart J. O. , Berman B. L. , Datz S. , Fearick R. W.
Published: February 2003

Channeling-radiation spectra produced by planar-channeled relativistic positrons and electrons in Type-Ia and Type-IIa diamonds have been measured. Because of the presence of platelets in the Type-Ia diamond, some of the spectra measured for this crystal differ markedly from their counterparts for the Type-IIa diamond. These striking differences illustrate the potential applications of channeling radiation as a diagnostic tool for studies of impurities or defects in crystals.
Residual strains in amorphous silicon films measured by x-ray double crystal topography
Authors: Kuo C. L. , Vanier P. E. , Bilello J. C.
Published: February 2003

A new application of double crystal topography using selected diffraction from portions of bent crystals was used to determine the curvature of single crystal Si wafers coated with hydrogenated amorphous Si (a-Si:H) films. This direct imaging method allowed measurements of the radii of curvature R of bent crystals over a range ≂0.2–1000 m. Using this procedure two different series of a-Si:H films were measured to compare the internal strains and monitor these as a function of film thickness. The curvature of the sample crystals was shown to be inversely proportional to the thickness of the film. The internal stress was found to be independent of film thickness, but only depended on the processing conditions.
Lattice match: An application to heteroepitaxy
Authors: Zur A. , McGill T. C.
Published: February 2003

We define the concept of lattice match for any pair of crystal lattices in any given crystal direction, allowing for a periodic reconstruction of the interface. An algorithm for a systematic search for all possible matches is developed, and some examples of nonstandard lattice matches are given for CdTe on GaAs and sapphire to illustrate the method. For the case of CdTe on GaAs, our results agree with published results, both with respect to growth plane and orientation for CdTe(111) on GaAs(100). For CdTe on sapphire, our results agree with published results with respect to growth plane.
Yield-stress and stress relaxation measurements in cobalt
Authors: Raza S. M.
Published: February 2003

Yield stress of polycrystalline cobalt (5N) was studied in the temperature range 15–300 K and interpreted by a theoretical model which provided an agreement with experimental results. Logarithmic stress relaxation was also studied in polycrystalline cobalt at natural strains of up to 8% at 15, 25, 40, and 55 K. Activation energies, i.e., 1.27±0.35 eV, deduced from a single barrier model of logarithmic stress relaxation, i.e., u0=k(T0+AT2)×[m+2.3 (dσ/ds)c] where T0 and A are constants), which allows for ‘‘quantum’’ effects below T≤70 K, favors vacancy formation and dynamic recovery as the rate determining process. The occurrence of structural effects such as ‘‘strain enhancement’’ (semiempirical fact) at low temperatures, suggests that a single barrier model is not sufficient to explain the ‘‘anomalies’’ appertaining to the temperature dependence of the yield stress and of the accompanying modes of plastic deformation. However, both quantum and structural effects seem to play an important role in the determination of low temperature deformation peculiarities.
Thermionic-field emission from interface states at grain boundaries in silicon
Authors: De Groot A. W. , McGonigal G. C. , Thomson D. J. , Card H. C.
Published: February 2003

An extension of Shockley–Read–Hall kinetics is presented for interface states at grain boundaries in silicon. The emission of majority carriers by these states is generalized to include thermionic field emission (TFE), which is shown to be important in many practical cases. Comparison is made with experimental results obtained on studies of isolated grain boundaries in silicon. One of the principal results is that energy distributions of interface states deduced from electrical characteristics of grain boundaries must be interpreted using a model which includes TFE. The importance of TFE increases with the doping concentration of the silicon N and the voltage applied across the grain boundary V and decreases with temperature. It is legitimate to neglect TFE from the interface states and consider pure thermal emission only for NV≲1016 cm−3 V at a temperature of 300 K, or NV≲1015 cm−3 V for 130 K.
Photochromic properties of silver complex oxides
Authors: Hirono Takushi , Yamada Tomoaki
Published: February 2003

Photosensitivity and heat bleaching property were quantitatively investigated for 23 silver complex oxides which contain B, Al, Si, P, Ga, Ge, In, Sn, Sb, Te, Hg, and Pb as constituent elements. Almost all the synthesized compounds are photosensitive to visible light. Light energy necessary to darken the oxides is distributed in a wide range, from 10 mJ/cm2 to more than 1 kJ/cm2. It was found that nine oxides show good photochromic properties and four oxides among them have sensitivity to near-infrared light. The photosensitive spectral range is discussed on the basis of electronegativity of atomic groups around silver ions.
Reply to ‘‘Comment on ‘A study of cathode edge emission’ ’’
Authors: Zhao Yong-xiang
Published: February 2003

Hasker has questioned the hypothesis of edge emission in an electron gun, and explained the phenomenon of the perveance increase with decreasing accelerating potential in a different way. It is shown in this reply that an electron gun employed in a klystron is quite different from that in a cathode-ray tube and so are the current characteristics. It is demonstrated that the influence of initial velocities on the ‘‘bulk current’’ of a klystron is not large, although it is essential for both Hasker’s theory and the ‘‘edge emission’’ theory explanation of perveance changes.
Optical and electrical properties of heavily phosphorus-doped epitaxial silicon layers
Authors: Lubberts G. , Burkey B. C.
Published: February 2003

The index of refraction and the absorption coefficient of epitaxial Si films were measured as a function of wavelength (0.4–0.75 μm) and with phosphorus doping as parameter. These optical constants, obtained from reflectance and transmittance measurements of epitaxial Si films on sapphire substrates, were compared with literature values and with recent measurements of heavily P-doped poly-Si films. In heavily P-doped films (near the solid solubility) of poly and epi Si the absorption coefficients are about the same. Also, the Hall mobilities were measured as a function of carrier concentration in the range 6×1019–4×1020/cm3 and compared with the mobilities derived from infrared reflectance measurements on both poly and epi Si.
Laser oscillations in the bound-excitonic region of CdS
Authors: Song J. J. , Wang W. C.
Published: February 2003

By employing a simple hemispherical resonator configuration, laser oscillations were observed from vapor-grown undoped CdS platelets pumped by 4-nsec dye laser pulses. The lasing shifted toward longer wavelengths from 4885 to 5180 Å by varying the temperature of the samples from 5 to 250 °K. The laser emission observed at low temperatures is attributed to the acoustic-phonon-coupled I1 bound-exciton transitions. The resonant behavior of this laser process is also reported.
Colliding pulse mode locking for an antiresonant cavity of a Nd:glass laser
Authors: Buchert J. M. , Basa D. K. , Tzu C. , Alfano R. R.
Published: February 2003

Mode-locking a Nd:silicate glass laser system by counterrunning pulses in a thin Kodak 9860 saturable absorber dye has produced considerably shorter pulses than that generated in a conventional standing-wave cavity configuration. The pulse duration of the pulse train was measured to be about 3.5 psec.
Reflection of acoustic waves from water/composite interfaces
Authors: Nayfeh Adnan H. , Crane Robert L. , Hoppe Wally C.
Published: February 2003

Theoretical and experimental results are presented for the reflection of acoustic waves from liquid-fibrous composite interfaces. For this purpose the composite is oriented such that the fibers are parallel to the propagation directions. Because of the complex microstructure of composites, continuity conditions exist on both the macro (water/composite interface) and micro (fiber/matrix interface) scales. Due to the number and nature of these conditions exact solutions are exceedingly difficult, if not impossible to obtain. As an alternative we formulate an approximate analysis in which the composite medium is replaced by a homogeneous, yet dispersive medium. In the process of replacing the composite with such a material model, the micro continuity conditions are utilized. The validity of the analytical model is verified by comparisons with experimental results obtained from graphite/epoxy and boron/epoxy composites specimens. Results are found to correlate very well with the analytical model, especially at low frequency ranges.
Optical constants of a hydrogenated amorphous carbon film
Authors: Smith F. W.
Published: February 2003

The real and imaginary parts, n and k, of the complex index of refraction of a hydrogenated amorphous carbon (a-C:H) film have been determined for photon energies between 1.45 and 4.9 eV from measurements of reflectance R and transmittance T. Both n and k, and consequently ε1 and ε2 (the real and imaginary parts of the dielectric constant), show a considerable variation with subsequent annealing of the a-C:H film up to Ta=750 °C, with the most rapid changes occurring for Ta=450 °C and above. The optical gap Eopt is observed to decrease from 2.2 eV to 0 as the film is annealed, signaling the development of graphitic short range order in the film. Using an effective medium approximation to model the optical properties of the film, we find that the as-deposited film contains amorphous diamond-like, graphitic, and polymeric components. With annealing, the amorphous diamond-like and polymeric components decrease, the amorphous graphitic component grows, and a void component appears. We discuss the local order present in the as-deposited and annealed film.