bluuebunny/crossref_metadata_2025 huggingface dataset:
The permeability of polycrystalline materials
Authors: Grimes Craig A. , Grimes Dale M.
Published: July 2002

This work addresses the relationship between grain properties, grain packing density, and the permeability and permittivity spectra of composite, polycrystalline material. The scattered multipolar fields about a single sphere are related to the polarizability of an ordered congregation of such spheres. Using the Clausius–Mossotti relation the effective permeability and permittivity spectra of a congregate polycrystalline material, formed by a cubic array of identical spheres, is determined for arbitrary packing density, permittivity, and permeability of the individual spheres. Although the spectra are considered over a range where the product of the external wave vector and sphere radius is kept small, typically less than one-tenth, the product of the internal wave vector and sphere radius is unrestricted. Changes in the packing density and internal wavelength have a dramatic effect on the calculated permeability and permittivity spectra.
Measurement method and experimental research on characteristics of a magnetic microstrip substrate
Authors: Zhu Sheng-chuan , Zhang Yao-xi , Zhang Dao-zhi
Published: July 2002

The characteristic measurements of single and coupled strips on a magnetic microstrip substrate have been done by using the new methods. By using a reflex ring resonator (in the single-strip case) and a quarter-wavelength coupled meander line (in multistrip case), the microstrip wavelength, the phase shift, and attenuation parameters can be determined conveniently and precisely.
On the theory of nonlinear spin wave dynamics in ferromagnetic films (abstract)
Authors: Slavin A. N.
Published: July 2002

The aim of this work is to develop a theory of nonlinear spin waves (SW) in ferromagnetic films (FF) appropriate for description of rich nonlinear SW dynamics observed in Refs. 1 and 2. We use classical Hamiltonian formalism developed in Ref. 3 for unbounded ferromagnets in combination with the theory of dipole-exchange SW spectrum for FF.4 The main distinctions in theoretical description of nonlinear SW phenomena between the case of unbounded ferromagnet3 and the case of FF can be formulated as follows: (1) Local character of SW excitation in FF leads to the increase of threshold values for SW parametric decay processes because the parametrically excited travelling SW carry out energy from the region of pumping localization; (2) additional selection rules should be taken into account in the analysis of SW parametric processes in FF. These selection rules are determined by conservation law for the transverse component of the SW wave number. In particular, in three-wave decay of surface SW with the increase of its amplitude after degenerate decay into SW pairs having equal numbers (n, n) the nondegenerate decay into SW modes having numbers (n, n+1) takes place. This effect has been recently observed in Ref. 2; (3) three-wave and four-wave coefficients of the SW Hamiltonian function in FF turn out to be analytical functions of their arguments even in the longwave spectral region kL≪1 where the long-range dipole–dipole interaction is dominant. The analytical properties of these coefficients enable us to derive nonlinear Schrodinger equation which is used for theoretical description of SW envelope solitons formation, SW modulational instability, and formation of SW strange attractor observed in Ref. 1.
Magnetic-field dependence of the phosphorus nuclear spin-relaxation rate in the quasi-two-dimensional XY antiferromagnet BaNi2(PO4)2
Authors: Gaveau P. , Boucher J. P. , Regnault L. P. , Henry Y.
Published: July 2002

The phosphorus nuclear spin-lattice relaxation rate 1/T1 has been measured in the quasi-two-dimensional XY antiferromagnet BaNi2(PO4)2. The divergence observed just above the ordering temperature TN ≂ 23.6 K is analyzed within the context of the Kosterlitz–Thouless transition. For a magnetic field H perpendicular to the XY plane, the data presented here agree well with a recent model of freely moving vortices. The field dependence observed for H parallel suggests a drastic slowing down of the vortex velocity in that case.
Multiple spin echo formation (abstract)
Authors: Golub V. O. , Kotov V. V. , Pogorely A. N.
Published: July 2002

Multiple spin echo formation for quadrupole nuclei (I≳1/2) in magnetics having inhomogeneous hyperfine and quadrupole interactions was investigated using two and three pulses technique. It was shown that the ‘‘forbidden’’ echo appearance is possible for the time intervals comparable with the characteristic times of the quardupole and hyperfine broadening. The amplitude drop when the time interval between exciting pulses increases is determined not by relaxation time (as usual) but by inhomogeneity having the larger characteristic time (HFI or quadrupole). Multiple spin echo signal for the two pulses technique is due to the transitions with quantum numbers m2≳m1.1 However, when three pulses technique with ‘‘unusual’’ exciting pulses sequence (τ12≳τ23) is used transitions with m1<m2 take part in generation of some additional echo signals. This is confirmed by amplitude and time dependences for the echo signals.
Temperature dependence of the magnetic excitations in the modified triangular induced moment antiferromagnet RbFeBr3 at the soft mode point (abstract)
Authors: Visser D. , Dorner B. , Harrison A.
Published: July 2002

The singlet ground state antiferromagnet RbFeBr3 shows an induced moment behavior at low temperatures and orders antiferromagnetically at TN=5.5 K. A second magnetic phase transition takes place at 2.0 K. The magnetic phase between 2 K <T<5.5 K may be partially ordered while at T<2.0 K a modified triangular magnetic structure will be adopted. The temperature dependence of the magnetic excitations at the soft mode point Q(1/3,1/3,1) show a switching of intensity at 2 K. Above 4 K the magnetic excitations start to broaden. Above TN the magentic excitations show a renormalization behavior. The temperature dependence of renormalization is well described by the theoretical predictions of the DCEFA model.
Characterization of thermodynamically non-equilibrium high-temperature oxygen plasma downstream region
Authors: Wickramanayaka Sunil , Meikle S. , Sekiguchi A. , Hosokawa M. , Hatanaka Y.
Published: July 2002

The higher reactivity and density of thermodynamically non-equilibrium high-temperature plasmas than that of glow-discharge plasmas are confirmed by the observation of atomic oxygen concentration and the population densities of the O(3P), O(1D), and O(1S) energy states. At 60 cm from the plasma exit, the downstream flow mainly consisted of the O(1D) state. This flow is about 95% O(1D) at 1000 W and the fraction of O(1D) state slightly decreases with increasing power due to the production of O+ ions. The flow is about 55% 0(1D) for 200-W glow-discharge plasmas, which also give a low atomic oxygen concentration.
Zeeman electron mass anomaly in InP as determined from orbital and spin splitting of donor 2P levels using high-resolution photoluminescence spectroscopy
Authors: Reynolds D. C. , Bajaj K. K. , Collins T. C.
Published: July 2002

The effective mass of an electron in InP determined from Zeeman splittings of the donor 2P level shows a strong magnetic field dependence. This Zeeman effective mass is approximately 45% smaller than the cyclotron mass at low magnetic fields. This was deduced from both the orbital and spin splittings of the 2P donor levels. The magnetic field splittings were determined from radiative transitions resulting from collapse of donor bound excitons leaving the terminal state in an excited state. The magnitude of the effect is much larger than that previously observed in GaAs. This anomaly is qualitatively explained on the basis of level mixing resulting from random static electric fields present throughout the crystal due to ionized impurity centers. The mass obtained from the orbital splitting is in good agreement with that obtained from the spin splitting.
The anomalous photovoltaic effect in polycrystalline zinc telluride films
Authors: Pal U. , Saha S. , Chaudhuri A. K. , Banerjee H. D.
Published: July 2002

The anomalous photovoltaic effect has been studied in polycrystalline ZnTe films. Increase of photovoltage on Te doping and a decrease on Zn doping is observed. The effect of phase transition, grain-boundary potential barrier, and surface space charge on the photovoltaic effect are reviewed and studied. Analysis of different experimental results reveals that the generation of emf in angularly deposited films on an insulating surface is mainly due to formation of p-n or p-p+ junctions at the grain boundaries and the surface band bending.
Thermally stable Pd/Ge ohmic contacts to n-type GaAs
Authors: Tsuchimoto Jun’ichi , Shikata Shin’ichi , Hayashi Hideki
Published: July 2002

The thermally stable Pd/Ge ohmic contacts to n-type GaAs are obtained by a rapid thermal annealing method. Compared to the conventional AuGe based ohmic metals, the surface morphology is smooth with high uniformity of constituent. A small deterioration from 1.01.0× 10−5 Ω cm2 to 1.2 × 10−5 Ω cm2 is observed at 300 °C for 103 h. The activation energy was 1.9 eV and the lifetime of this contact, defined as the time of 10% deterioration, is expected to be over 109 years at 70 °C. The mechanism of the deterioration for Pd/Ge ohmic contacts is also discussed, utilizing Auger electron spectroscopy and x-ray photoemission spectroscopy analysis.
Critical current density of screen printed YBa2Cu3O7−x sintered thick film
Authors: Senda Masakatsu , Ishii Osamu
Published: July 2002

This paper investigates the critical current density (Jc) of sintered YBa2Cu3O7−x thick film prepared by the screen printing method. Two thick films with different crystal morphologies, which exhibit a Jc of 70 and 700 A/cm2 at 77 K, are compared in terms of crystal orientation, the pinning force in the grains, and the pinning force at the grain boundaries. Both these thick films exhibit random crystal orientations, and have many weak links. An M-H examination suggests that these two thick films have similar pinning forces in the grains, and no anisotropy of the pinning force. The larger Jc-H hysteresis exhibited in the film with the larger Jc implies an improvement in the pinning force at the grain boundaries. This improvement may cause the larger Jc.
Simulation of tunneling current from gate edges of metal-oxide-silicon structures
Authors: Ramaswami R. , Lin H. C. , Kuchimanchi R.
Published: July 2002

A numerical model has been developed to calculate the electron tunneling current component from gate edges of metal-oxide-silicon capacitor/transistor structures, which had been neglected in previous studies. Tunneling probability from the gate edge is obtained by direct solution of the time-independent Schrödinger equation, using Schwarz–Christoffel transformation to map the nonplanar gate edge region to a rectangular domain, and solving the transformed Schrödinger equation by finite element methods.
Latencies in action potential stimulation in a two-dimensional bidomain: A numerical simulation
Authors: Barach John Paul
Published: July 2002

A numerical simulation is performed in which a uniform planar slab of idealized cardiac tissue is stimulated at the center. The cardiac slab is modeled as an anisotropic bidomain; within each domain current flow is determined by a forced diffusion equation in which the transmembrane current connecting the domains provides the forcing term. An action potential (AP) propagates outward after a time latency dependent upon the stimulus size and the physiological variables. Its isochrones are elliptical with an asymmetry that is a small fraction of the imposed asymmetry in resistivity. External voltages resemble the first derivative of those in the internal domain and tests with continuing stimuli exhibit a relaxation time of about 3 ms and space constants that agree with other work. The AP latency increases very strongly near threshold stimulus and decreases as the log (stimulus) for large stimuli in the ‘‘virtual cathode’’ range. Latencies in the longitudinal, transverse, and diagonal directions are found to be the same over a wide range of stimulus size and type.
Field variation of the rf penetration depth and its effect on kinetic inductance in Bi2Sr2CaCu2Ox microstrip transmission lines
Authors: Byrne D. P. , Kwor R. Y. , Kalkur T. S.
Published: July 2002

Kinetic inductance effects in thin-film superconductors can be utilized in a number of interesting electronic applications. High-Tc films are particularly promising in this regard, as their penetration depths can be made quite large. In this communication we report on observations of strong kinetic inductance effects in a multilayer resonator structure deposited on a single substrate. The influence of temperature and of rf and dc magnetic fields on these effects are presented. We find that the penetration depth in Bi-Sr-Ca-Cu-O films can be externally influenced, and treated potentially as a design parameter for applications, since one may ultimately be able to exercise some degree of control over the material properties that most strongly affect it, namely crystal granularity, surface roughness, and film epitaxy.
Integrated-mirror étalons for 1.3-μm operation grown by molecular-beam epitaxy
Authors: Khitrova G. , Iwabuchi T. , Chuang C. L. , Yoon T.
Published: July 2002

The design and growth of a Fabry-Pérot étalon for operation at 1.3 μm is described. The étalon consists of two integrated mirrors, each with 12 pairs of GaAlInAs/AlInAs quarter-wave layers, and a spacer of GaInAs/AlInAs multiple quantum wells between them. The étalon is grown lattice matched to InP. At 1.35 μm the peak transmission is 50% and the full width/half maximum linewidth is 16 nm.
Comment on: ‘‘The effect of charge state on the local vibrational mode absorption of the carbon acceptor in semi-insulating GaAs’’
Authors: Moore W. J. , Shanabrook B. V.
Published: July 2002

A recent study of the effect of photoquenching of EL2 on the compensation of carbon acceptors in GaAs and the resulting effect on the carbon local vibrational mode, LVM, concluded that there was no broadening of the LVM associated with bound holes on neutral carbon acceptors. The failure to observe broadening of the LVM in this study was a result of the failure to neutralize a significant fraction of the carbon atoms by photoquenching EL2. We show that, in the experiment reported, at most only about 3%–4% of the carbon acceptors were neutralized. Such very small modifications of the ionized carbon concentration are unobservable in the LVM spectra unless the spectral stability and signal-to-noise ratio are exceptional.
Response to: ‘‘Comment on ‘The effect of charge state on the local vibrational mode absorption of the carbon acceptor in semi-insulating GaAs’ ’’
Authors: Fischer D. W. , Manasreh M. O.
Published: July 2002

In a previous report we showed the effect of photoquenching the EL2 donor in GaAs on the carbon acceptor electronic absorption and local vibrational mode (LVM) absorption spectra. We agree that for the sample used to illustrate these effects, only a small portion (9% or less) of the total carbon was neutralized by the photoquench. Other samples have been studied, however, in which a much larger fraction (30% or more) of the carbon has been neutralized with no effect on the carbon LVM. We therefore maintain that our previous conclusion, i.e., a change in the charge state of carbon has no significant effect on the LVM structure, is still valid.
Magnetotransport in spatially periodic space-charged semiconductors
Authors: Zitter R. N.
Published: July 2002

A ballistic transport model which predicts the generation of spatially periodic space charge in a semiconductor by a steady-state current is extended to include the effect of a transverse magnetic field. Analytic solutions are obtained showing how the magnetic field affects the periodicities of both longitudinal and transverse potentials.
Polarization effects in the optical reorientation of freely suspended smectic-C liquid-crystal films
Authors: Abbate G. , Maddalena P. , Marrucci L. , Santamato E.
Published: July 2002

A linearly polarized laser beam propagating in a freely suspended smectic-C liquid-crystal film can induce reorientation of the molecular director. A theoretical model is presented which, unlike previous works, takes into account the effects of the polarization changes of the light into the sample. Despite the nonlinearity of the problem, an analytical solution is found. The stability analysis of the trivial solutions has also been carried out. A physical interpretation of the results, some of which are unexpected on the basis of the old models, is given in terms of angular momentum conservation.
Damage due to electron, ion, and x-ray lithography
Authors: Miller P. A. , Fleetwood D. M. , Schubert W. K.
Published: July 2002

Electron, ion, and x-ray lithography are all being advocated as replacements for optical lithography at some time in the future for high-volume production of integrated circuits. Of some concern is the potential for radiation damage to underlying circuit layers caused by these lithographies. In this paper we report results of an experiment designed specifically to compare damage to radiation-hardened circuits arising from the three nonoptical lithographic technologies. We employ flood exposures of metal-oxide-semiconductor (MOS) capacitors by electrons, ions, and x rays to simulate lithographic exposures. We report results of characterizations by capacitance-voltage analysis, radiation-hardness testing, and bias-stress testing. Degradation in radiation hardness is used as measure of residual damage caused by the simulated lithographic irradiations that is not annealed out at low temperatures. We find minimal damage to the oxide resulting from lithographic doses of ions. We measure voltage shifts due to oxide- and interface-trap charge introduced by x rays and electrons and find that they can be removed by standard post-metallization anneals. We find that the radiation tolerance of MOS capacitors so irradiated and annealed is nearly identical to that of devices that did not see irradiation and annealing. Moreover, in all cases, no bias-temperature instabilities resulted from the exposure-anneal sequences. We find that all three types of lithographic techniques are promising candidates for use in advanced, radiation-hardened integrated circuit technologies.
Exotic magnetic states in Heisenberg antiferromagnetism (invited) (abstract)
Authors: Haldane F. D. M.
Published: July 2002

When quantum effects are small, Heisenberg antiferromagnets have a Néel ordered ground state, but strong zero-point fluctuations can lead to new ‘‘exotic’’ spin-liquid ground states without long-range Néel order. These effects are strongest in low dimensions and frustrated systems, and always occur in one dimension. The nature of the new ground state can depend on whether the microscopic spins have integer or half-integer S. As an example of such systems the rich phase diagram of the one-dimensional S=1 Heisenberg antiferromagnet with additional biquadratic exchange and uniaxial on-site anisotropy will be discussed in detail.
Triple-layered NdCo amorphous-alloy films for magneto-optical media
Authors: Iiyori Hideo , Takayama Shinji
Published: July 2002

Magneto-optical recording materials with high remanent Kerr rotation at a short wavelength were successfully obtained in a trilayer form. NdCo amorphous films with an in-plane magnetization were sandwiched between TbFeCo amorphous films with strong perpendicular anisotropy and high coercivity. The thickness of the top layer of the TbFeCo film facing an incident laser beam is less than the light-penetration depth. Triple-layered films [Tb18Fe49Co33 (5 nm thickness)/Nd18Co82(10 nm)/Tb18Fe49Co33(200 nm)] thus obtained show a remanent Kerr rotation angle θKr = 0.37°–0.46° at wavelength λ=400–850 nm, coercivity Hc = 2 kOe, and good square loop (Mr/Ms = 1). The figure of merit √R̄θK, where R is reflectivity, is 0.24–0.31 at λ=400–850 nm, which is higher than that of conventional TbFeCo amorphous films (√R̄θK = 0.12–0.27 at λ=400–850 nm).
Magnetoresistance in amorphous NdFeB/FeB compositionally modulated multilayers
Authors: Peral G. , Briones F. , Vicent J. L.
Published: July 2002

Resistance measurements have been done in amorphous Nd12Fe80B8 sputtered films and in amorphous sputtered Nd26Fe68B6/Fe92B8 multilayers between 6 and 150 K with applied magnetic field parallel (LMR) and perpendicular (TMR) up to 7 T. The samples were grown by dc triode sputtering, with nominal unequal (2:1) layer thicknesses. The layered character of the samples have been tested by x-ray diffraction. Longitudinal magnetoresistance (LMR) is positive and transverse magnetoresistance (TMR) is negative. The magnetoresistance values are higher than in amorphous ferromagnets, and multilayering of these alloys produces much larger magnetoresistance values than either alloy alone and there is a strong dependence on the multilayer wavelength. The MR shows a weak temperature dependence in the temperature interval that was investigated.
Optical waveguides in KTa1−xNbxO3 produced by He ion implantation
Authors: Fluck D. , Gutmann R. , Günter P. , Irmscher R.
Published: July 2002

MeV He ion implantation is used to produce optical waveguides in KTa1−xNbxO3 (x=0.37). The detailed refractive index profiles of the implanted planar waveguides are reconstructed from the measured mode spectra at the wavelength of 632.8 nm. The absorption and the tunneling losses of the lowest mode of the waveguides are determined. Ionic collision is proposed to be the mechanism which causes the observed variation of the refractive index.
Depth profiling of nonuniform optical absorption in thin films: Application to hydrogenated amorphous silicon
Authors: Asano A. , Stutzmann M.
Published: July 2002

The amplitude of interference fringes in optical absorption spectra for thin films has been analyzed in the range of low absorption coefficients and was found to be related to a depth profile of absorbers, e.g., defects. This method has been applied to the subband-gap optical absorption spectra measured by photothermal deflection spectroscopy for hydrogenated amorphous silicon thin films. It is shown that the analysis of interference fringes provides unique information about surface and interface defects in this material.
Effects of surface energy on the microstructures of thin Sb films
Authors: Chou L. H.
Published: July 2002

Thin Sb films have been prepared on glass substrates by rapid thermal evaporation. Films with thicknesses varying from 260 to 1300 Å were used for the study. X-ray-diffraction data showed that for films deposited at room substrate temperature, an almost random grain orientation was observed for films 1300 Å thick and a tendency for preferred grain orientation was observed as films got thinner. For films 260 Å thick, only two x-ray-diffraction peaks−(003) and (006)−were observed. After thermal annealing, secondary grains grew to show preferred orientation in all the films. This phenomenon was explained by surface-energy-driven secondary grain growth. This paper reports the effects of deposition rate, film thickness, and annealing time on the secondary grain growth and the evolution of thin Sb film microstructures. Transmission electron microscopy and x-ray diffraction were used to characterize the films.
Evolution of stress and strain during the consolidation of a fluid-saturated porous elastic sphere
Authors: Mason D. P. , Solomon A. , Nicolaysen L. O.
Published: July 2002

The evolution of stress and strain during the consolidation of a fluid-saturated porous elastic sphere subjected to a uniform normal surface traction is investigated. The solution of Cryer [Q. J. Mech. Appl. Math. 16, 401 (1963)] for the pore fluid pressure is extended by deriving and fully analyzing new analytical solutions for the strain tensor of the elastic skeleton, the total stress tensor, the trace-free stress deviator tensor, and the effective stress tensor. Asymptotic expansions for small values of time of the stress and strain components, which determine the behavior of these components during the initial stages of the consolidation, are derived. Computer-generated graphs of the exact analytical solutions are presented, which provide insights regarding the redistribution of stress and strain throughout the consolidation. As fluid is expelled from the outermost layers of the sphere, fluid discharge builds up quickly to a peak rate and then subsides slowly as successively deeper layers are drained. During this initial consolidation, the stresses, strains, deviator stresses, and effective stresses within the outermost layers all change very rapidly. The nature of the Mandel–Cryer effect (pore fluid pressure increase within the sphere during initial fluid expulsion) is illuminated. Two other quantities, the transverse component of the total stress tensor and the total mean normal pressure, also show changes of opposite sign in the near surface and deeper regions, respectively: diminution in the outermost layers and simultaneous increase in the deeper portions. All of these effects are derived from Biot’s theory of poroelasticity, in which the dilatation satisfies the diffusion equation.
Transit time for resonant tunneling in semiconductor heterostructures
Authors: García-Calderón Gastón , Rubio Alberto
Published: July 2002

We consider a resonance formalism to obtain an expression for the transit time in double-barrier resonant structures in terms of the partial decay widths Γ0n and ΓLn as τtr = (ℏ/Γ0n + ℏ/ΓLn)/4. We demonstrate that the time scale associated to the tunneling current density integrated across a sharp resonance is inversely proportional to τtr. We also show that the dwell time, the transmission phase time, and the Larmor traversal time are not appropriate notions for the transit time except when the partial decay widths are equal as is the case for a symmetric potential profile.
Study of the broad luminescence bands in Ge-implanted GaAs centered at 1.44–1.46 eV
Authors: Keefer K. J. , Yeo Y. K. , Hengehold R. L.
Published: July 2002

Above- and below-band-gap excitation photoluminescence studies were performed on GaAs samples implanted with Ge, Ga, As, {Ge+Ga}, and {Ge+As} to assess the nature of a broad luminescence band, the so-called Q band, centered in the 1.44–1.46-eV range. Below-band-gap excitation enabled resolution of the broad band into two separate overlapping bands. These measurements, in conjunction with sample temperature-dependent studies, indicate that the main contribution to the broad band observed in Ge-implanted GaAs is due to the Ga antisite double-acceptor defect.
Theoretical and experimental studies of CO2 laser evaporation of clouds
Authors: Caramana E. J. , Webster R. B. , Quigley G. P. , Morse R. L.
Published: July 2002

A study of the effects of laser radiation on cloud drops and of the possibility of producing a clear optical channel in a cloud is presented. In order to produce a model that is appropriate to a realistic cloud with a distribution of drop sizes it is first necessary to study what happens to a single water drop subjected to laser radiation of different intensities. Various heating regimes are mapped out as a function of laser flux and fluence at the 10.6 μm wavelength. It is found that typical cloud drops can superheat until they become unstable and explode from the center. For a long laser pulse the boundary for this to occur is found to be 50(5/r)2 kW/cm2, where r is the drop radius in microns. Using these results a model that is spatially one-dimensional through the cloud is constructed for a distribution of drop sizes. Laser beam intensity as the light penetrates a cloud is calculated from Mie scattering and absorption cross sections for a beam diameter that is small in the sense that light scattered once is assumed lost. The internal temperature distribution of the drops is calculated and a phenomenological drop explosion model is given for drops that reach the unstable 305 °C spinodal temperature at their center. Energy and water mass content are conserved as the cloud background is modified in an average sense by drop evaporation or recondensation. Recondensation is treated in the diffusion regime according to the Kohler model, with vapor pressure over a drop modified by surface tension and dissolved nonwater content. Comparison with experimental data for a laboratory produced cloud is given and good agreement, particularly with respect to the predicted onset of drop explosion, is found. Results are also presented for hypothetical cloud conditions and laser intensities. The possibility of clearing a thin cloud with low fluence to the 3.8 μm is considered, as well as the passive evaporation of melted ice crystal clouds.
A study of the effect of misfit-induced strain on the kinetics of solid phase epitaxy in the Si1−xGex on 〈001〉 Si system
Authors: Paine David C. , Evans Neal D. , Stoffel Ned G.
Published: July 2002

In this paper we present the results of an experimental determination of the rate of solid phase epitaxical regrowth of amorphous Si1−xGex on 〈001〉 Si as a function of temperature and Ge concentration. Layers of chemical vapor deposited Si1−xGex roughly 200-nm thick containing 5.4, 11.6, and 17.0 at. % Ge were amorphized with a two-step process of 100 keV, followed by 200 keV, 29Si ion implantation. This procedure left the near surface region of the substrate, including the entire Si1−xGex film, amorphous to a depth of 380 nm. The epitaxical recrystallization of the alloy portion (5.4, 11.6, or 17 at. % Ge) of the amorphous layer results in the development of large lattice mismatch stresses (0.5–2 GPa). The rate of epitaxical regrowth of the amorphous material was studied with isothermal heating and in situ transmission electron microscopy observations. Isothermal annealing at temperatures between 476 and 602 °C show that, compared to pure unstrained Si, the rate of regrowth is decreased in strained alloys of Si1−xGex. Furthermore, we report that the activation energy for strained-layer regrowth of Si1−xGex is not a strong function of composition and, for all three compositions, was in the range 3.2±0.2 eV. This is significantly larger than the activation energy for the homoepitaxical regrowth of unstrained pure Si. Stress related origins of these observations are discussed.
Initial sequence and kinetics of silicide formation in cobalt/amorphous-silicon multilayer thin films
Authors: Miura H. , Ma E. , Thompson C. V.
Published: July 2002

The sequence of cobalt silicide phase formation in cobalt/amorphous-silicon multilayer thin films has been investigated using differential scanning calorimetry, cross-sectional transmission electron microscopy, thin film x-ray diffraction, and energy dispersive x-ray analysis in a scanning transmission electron microscope. Multilayer thin films with various overall atomic concentration ratios (2Co:1Si, 1Co:1Si, 1Co:2Si) and various bilayer thicknesses were used in this study. It was found that an amorphous intermixed layer about 10 nm thick preexisted at the as-deposited cobalt/amorphous-silicon interface. Crystalline CoSi was always the first phase to nucleate in the interdiffused layer. The CoSi nucleates and coalesces into a continuous layer at temperatures as low as about 260 °C, but does not thicken until the next phase forms. Which phase forms second is determined by whether Co and Si remain after formation of the CoSi layer. The activation energy for the initial nucleation and growth of the CoSi layer was found to be 1.6±0.1 eV. When excess cobalt is present, Co2Si is the next phase to form at about 350 °C. Co2Si grows with the coexisting CoSi layer remaining approximately a constant thickness of about 5 nm. The activation energy for growth of the Co2Si was 2.0±0.1 eV. After the cobalt is fully consumed, Co2Si reacts with excess silicon (if there is any) to form more CoSi at about 400 °C. This process has an activation energy of 1.9±0.1 eV. If excess silicon still exists after all of the Co2Si has transformed to CoSi, CoSi2 formation follows at about 500 °C with an activation energy of 2.5±0.1 eV. The activation energies of the above phase transformations were determined by analyzing calorimetric data.
Electrical resistivity of inhomogeneous alloys
Authors: Klemens P. G.
Published: July 2002

The resistivity of an inhomogeneous medium is expanded in Fourier components and the effective resistivity is defined in terms of the rate of entropy production per unit current density. The effective resistivity lies below the volume average by an amount proportional to the mean square fluctuation in resistivity and containing an angular factor, as previously obtained by Herring. The angular factor is obtained in the absence of a preferred direction, and for the case of ellipsoidal symmetry. The effect of the neglect of higher order terms is discussed. The theory is applied to two-phase systems of low contrast and to cases of nonuniform solute concentration. Homogenization increases the resistivity. The time dependence of this increase is discussed in general and for solute clusters.
Shubnikov–de Haas oscillations on molecular-beam-epitaxy-grown Hg1−xCdxTe alloy doped with indium
Authors: Rafol S. B. , Sou I. K. , Faurie J. P.
Published: July 2002

Shubnikov–de Haas oscillations on the transverse resistivity ρxx and longitudinal resistivity ρzz of as-grown indium-doped alloys of Hg1−xCdxTe (0.24<x<0.34) grown by molecular-beam epitaxy on (111)B and (100) growth directions are observed in the temperature range from 1.2 to 25 K and in fields up to 12 T. The n-type density from the periodicity, the effective mass m* from the temperature dependence of the amplitude, and the Dingle temperature TD are determined from ρxx and ρzz oscillations. The oscillations establish the high Hall density which is found at low fields. The TD in ρxx is found to be higher in comparison to TD in ρzz. However, this difference decreases as the Hall density increases. The TD discrepancy is probably due to greater inhomogeneity in the plane of the layer. The TD is higher than the temperature calculated from the weak-field Hall mobility. The density and effective mass are used to calculate the energy band gap, Fermi energy, and the band-edge effective mass. The calculated energy band gaps are in good agreement with the reported results.
Oxide films grown on GaAs(110) at 20 K: Stability during Cr overlayer formation
Authors: Seo J. M. , Chen Y. , Weaver J. H.
Published: July 2002

GaAs oxide films were formed by x-ray illumination of condensed O2 on GaAs(110) at 20 K, and their stability was investigated during subsequent Cr overlayer formation with atoms at 20 and 300 K and with preformed clusters. High resolution synchrotron radiation photoemission results for overlayer formation at 300 K show that Cr atoms reduce the GaAs oxides to form Cr oxides, Cr—As, and Cr—Ga bonding configurations. These reactions first involve the As2O5-like species and then progress to the As2O3-like and Ga2O3-like oxides, reflecting the relative stability of the oxides and their spatial distributions. For overlayer formation at 20 K, the Cr atoms initially reduced the As-oxide surface layers but had little effect on the Ga oxides, and a nonuniform metallic overlayer was formed after 1.5 Å Cr deposition. These low-temperature results demonstrate that kinetic constraints imposed at 20-K limit Cr diffusion and, hence, oxide reduction. In contrast, the deposition of Cr clusters onto oxidized GaAs produced a metallic layer with minimal oxide disruption. This different final state can be understood by noting that the bonding of Cr atoms in metallic Cr clusters establishes an activation barrier for reaction that is not present for atom deposition.
Laser-induced damage threshold measurements of optical dielectric coatings at λ=1.06 μm
Authors: Milev I. Y. , Dimov S. S. , Terziev D. V. , Iordanova J. I. , Todorova L. B. , Gelkova A. B.
Published: July 2002

The laser-induced damage thresholds for λ=1.06 μm of commercially available (produced at Institute of Optics) dielectric optical coatings, both antireflective and high reflectance, have been determined. The dependence of the optical coatings stability on design and selection of materials has been investigated. An improvement of the coatings durability by using nonquarterwave layers in addition to the basic design of the mirrors has been obtained. The choice of the coating materials is also discussed.
Comments on ‘‘Effects of using the more accurate intrinsic concentration on bipolar transistor modeling’’ [J. Appl. Phys. 6
8, 5911 (1990)]
Authors: Rode D. L. , Rosenbaum F. J.
Published: July 2002

Four points are raised concerning accuracy of results, correctness of approach, and significance of findings in the cited publication.
Reply to ‘‘Comments on ‘Effects of using the more accurate intrinsic concentration on bipolar transistor modeling’ ’’ [J. Appl. Phys. 6
8, 5911 (1990)]
Authors: Liou J. J.
Published: July 2002

This reply addresses the issues raised by Rode and Rosenbaum regarding the bipolar junction transistor model developed in the subject paper [J. Appl. Phys. 68, 5911(1990)]. The error associated with Eq. (4) in the subject paper is discussed and corrected, the value of the space-charge-region recombination time used is specified, and the results are recalculated. It is shown that the error in Eq. (4) does not alter notably the trends of the current gain calculated using the two different intrinsic concentrations.
Recombination properties of photogenerated minority carriers in polycrystalline silicon
Authors: Murti M. R. , Reddy K. V.
Published: July 2002

An experimental investigation of the influence of grain boundaries on the recombination of photogenerated minority carriers in polysilicon is reported here. Spatial dependence of photoconductance across an isolated grain boundary was utilized to evaluate the diffusion length of electrons in the grain and the interfacial recombination velocity. Intensity dependence of these parameters provided some insight into the modulation of the grain boundary potential barrier under illumination. Photoconductance was found to vary with photon flux as Gr, where r=1.0 in regions of the grain far away from the boundary and r=0.4 at the grain boundary plane. The barrier height and electron capture cross section in the grain boundary traps were obtained to be 0.12 eV and 1.16 × 10−16 cm2, respectively.
Hole transport in liquid crystalline media. II. Hole drift mobilities of copolymers of acrylates with side-chain mesogens and dimeric carbazoles
Authors: Ikeda Tomiki , Mochizuki Hiroyuki , Hayashi Yuko , Sisido Masahiko , Sasakawa Tomoyoshi
Published: July 2002

Hole drift mobilities of films of copolymers of acrylates with side-chain mesogens and dimeric carbazoles were measured by the time-of-flight method. The copolymers were composed of acrylates with side-chain phenylbenzoate or cyanobiphenyl and acrylates with side-chain 1,2-trans-bis(9H-carbazol-9-yl)cyclobutane (DCZB). Incorporation of the DCZB moiety into the copolymers resulted in homogeneous dispersion of the carrier molecules, but destabilization to a great extent of the liquid-crystalline phase of the resulting copolymers. The hole drift mobility was found to be enhanced in copolymer films with more ordered structure of the DCZB moieties, indicating that orientation of the active molecules is favorable for the hole transport.
Effect of vanadium on the RE and Fe sublattice anisotropies in some REFe12−xVx(RE=Y,Er,Tb) tetragonal compounds
Authors: Pareti L. , Solzi M. , Marusi G. , Ibarra M. R. , Algarabel P. A.
Published: July 2002

The compounds REFe12−xVx(RE=Y,Er,Tb) having the tetragonal crystal structure of ThMn12 exist in the composition range 1.5≤x≤4. The dependence of the magnetic properties on the vanadium content were investigated in order to evidence and study any influence of vanadium on the magnetic anisotropy of both iron and RE sublattices and, as a consequence, on the magnetic phase diagram of these systems. The influence of vanadium was found to be remarkable on Tc, Ms, and Fe anisotropy, which decrease in all the compounds with increasing V content. However the largest effect was observed on the RE anisotropy and particularly in TbFeV, where the anisotropy of the Tb sublattice is turned from planar to axial by increasing the vanadium concentration, thus giving rise to strong effects on the macroscopic magnetic behavior and on the magnetic phase diagram of these systems. The large variation of the spin reorientation transition temperature Tsr, observed by varying V content on both ErFeV and TbFeV, can justify the spread in the literature data which could be attributed to small not considered stoichiometry differences with respect to the nominal composition.
A study of adsorption of a cyanine dye to cubic AgBr microcrystals suspended in a dried gelatin layer
Authors: Tani Tadaaki , Suzumoto Takeshi
Published: July 2002

The amount of a cyanine dye [3,3′-bis(4-sulfobutyl)-9-methylthiacarbocyanine] adsorbed to cubic AgBr microcrystals m suspended in dried gelatin (i.e., dried emulsion) was measured by preparing dried emulsion layers, which were smooth and thick enough for treatment by the Kubelka–Munk equation and gave useful information on the adsorption of the dye and materials of photographic interests to the microcrystals. The saturated amount of the adsorbed dye M in a dried emulsion layer was smaller than that in a liquid emulsion, since functional groups of gelatin and a stabilizer (4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene) in the solution phase of the liquid emulsion were forced to be adsorbed to the microcrystals on drying. The dye adsorption increased the concentration of interstitial silver ions in the microcrystals by repelling silver ions at kink sites on the surface of the microcrystals into interstitial positions, especially when m approached M. The number of silver ions repelled into interstitial positions was less than 0.001 of that of the dye molecules adsorbed to the microcrystals.
Coloration of chromium-doped yttrium aluminum garnet single-crystal fibers using a divalent codopant
Authors: Tissue Brian M. , Jia Weiyi , Lu Lizhu , Yen William M.
Published: July 2002

We have grown single-crystal fibers of Cr:YAG and Cr,Ca:YAG under oxidizing and reducing conditions by the laser-heated-pedestal-growth method. The Cr:YAG crystals were light green due to Cr3+ in octahedral sites, while the Cr,Ca:YAG crystals were brown. The presence of the divalent codopant was the dominant factor determining the coloration in these single-crystal fibers, while the oxidizing power of the growth atmosphere had little effect on the coloration. The Cr,Ca:YAG had a broad absorption band centered at 1.03 μm and fluoresced from 1.1 to 1.7 μm, with a room-temperature lifetime of 3.5 μs. The presence of both chromium and a divalent codopant were necessary to create the optically-active center which produces the near-infrared emission. Doping with only Ca2+ created a different coloration with absorption in the blue and ultraviolet. The coloration in the Cr,Ca:YAG is attributed to Cr4+ and is produced in as-grown crystals without irradiation or annealing, as has been necessary in previous work.
An intense lithium ion beam source using vacuum baking and discharge cleaning techniques
Authors: Moschella J. J. , Kusse B. R. , Longfellow J. P. , Olson J. C.
Published: July 2002

We have developed a high-purity, intense, lithium ion beam source which operates at 500 kV and 120 A/cm2 with pulse widths of 125 ns full width half maximum. The beams were generated using a lithium chloride anode in planar magnetically insulated geometry. We have found that the combination of vacuum baking of the anode at 250 °C followed by the application of 100 W of pure argon, steady-state, glow discharge cleaning reduced the impurity concentration in the beam to approximately 10% (components other than chlorine or lithium were considered impurities). Although the impurities were low, the concentration of chlorine in the 1+ and 2+ charge states was significant (∼25%). The remaining 65% of the beam consisted of Li+ ions. Without the special cleaning process, over half the beam particles were impurities. It was determined that these impurities entered the beam at the anode surface but came originally from material in the vacuum chamber. After the cleaning process, recontamination was observed to occur in approximately 6 min. This long recontamination time, which was much greater than the expected monolayer formation time, was attributed to the elevated temperature of the anode. We also compared the electrical characteristics of the beams produced by LiCl anodes to those generated by a standard polyethylene proton source. In contrast to the polyethylene anode, the LiCl source exhibited a higher impedance, produced beams of lower ion current efficiency and had longer turn on times.
Numerical modeling of dynamic powder compaction using the Kawakita equation of state
Authors: Mann A. P. , Pullin D. I. , Macrossan M. N. , Page N. W.
Published: July 2002

Dynamic powder compaction is analyzed using the assumption that the powder behaves, while it is being compacted, like a hydrodynamic fluid in which deviatoric stress and heat conduction effects can be ignored throughout the process. This enables techniques of computational fluid dynamics such the equilibrium flux method to be used as a modeling tool. The equation of state of the powder under compression is assumed to be a modified version of the Kawakita loading curve. Computer simulations using this model are performed for conditions matching as closely as possible with those from experiments by Page and Killen [Powder Metall. 30, 233 (1987)]. The numerical and experimental results are compared and a surprising degree of qualitative agreement is observed.
Crystallographic characterization of GexSi1−x/Si superlattices grown by remote plasma-enhanced chemical vapor deposition
Authors: Qian R. , Anthony B. , Hsu T. , Irby J. , Kinosky D. , Banerjee S. , Tasch A. , Rabenberg L. , Magee C.
Published: July 2002

Single-crystal GexSi1−x/Si superlattices have been successfully fabricated using remote plasma-enhanced chemical vapor deposition, a novel low-temperature thin-film growth technique. Reflection high-energy electron diffraction, cross-sectional transmission electron microscopy (XTEM), plan view TEM, x-ray-diffraction, and secondary-ion mass spectroscopy techniques have been applied to study the crystallographic properties of the superlattice structures. Arrays of dislocation lines, which are either parallel or perpendicular to each other, have been observed in the superlattices for those cases in which the total layer thickness exceeds the critical layer thickness. The location, orientation, and Burgers vectors of the misfit dislocation lines have been analyzed. Possible mechanisms of the generation of the misfit dislocations are also discussed.
Electro-optic mode-displacement silicon light modulator
Authors: Pirnat Thomas , Friedman Lionel , Soref Richard A.
Published: July 2002

A new type of guided-wave electro-optical intensity modulator is proposed and analyzed. The waveguide consists of an N-type Si core layer on a P-type Si substrate. Foward bias on the N+-N-P-P+ diode decreases the refractive index of the core and displaces the fundamental guided mode downward into the substrate. However, the mode is not extinguished because the substrate is bounded by a P+ contact. A spatial filter at the output converts the mode displacement into optical intensity modulation. A Poisson and continuity equation solver and multilayer waveguide simulation were used to obtain numerical estimates of mode displacement in a realistic structure.
Optical waveguiding in Si/Si1−xGex/Si heterostructures
Authors: Namavar F. , Soref R. A.
Published: July 2002

Waveguiding at 1.3 μm has been observed in a submicrometer strained layer of Si1−xGex sandwiched between a Si capping layer and a Si substrate. This structure is a precursor of the waveguided Si/Si1−xGex/Si heterojunction bipolar transistor. The buried alloy layer, grown by chemical vapor deposition, had a Ge content of either 8% or 18%. The SiGe layer was ∼1500 Å thick beneath a 2-μm Si cap. The observed TE0 mode profile agreed with theory.