bluuebunny/crossref_metadata_2025 huggingface dataset:
IUPAC-NIST Solubility Data Series. 72. Nitromethane with Water or Organic Solvents: Ternary and Quaternary Systems
Authors: Sazonov Valerii P. , Marsh Kenneth N. , Shaw David G. , Sazonov Valerii P. , Chernysheva Mariya F. , Sazonov Nikolai V. , Akaiwa Hideo
Published: July 2002

The mutual solubilities and liquid–liquid equilibria of nitromethane ternary and quaternary systems with liquid solvents are reviewed. The solvents include water, inorganic compounds, and a variety of organic compounds such as hydrocarbons, halogenated hydrocarbons, alcohols, acids, esters, and nitrogen compounds. A total of 107 ternary and eight quaternary systems whose properties were described in the chemical literature through 1998 are compiled. For 22 systems, sufficient data were available to allow critical evaluation. All data are expressed as mass and mole fractions as well as the originally reported units. Similar reviews of gas, liquid, and solid solubilities for other systems have been published in the frame of Solubility Data Series. This is the 72 volume of this series.
Modeling of tunneling spectroscopy in high-TC superconductors
Authors: Shukrinov Yu. M. , Namiranian A. , Najafi A.
Published: July 2002

The tunneling density of states of high-Tc superconductors is calculated taking into account the tight-binding band structure, group velocity, and tunneling directionality for s-wave and d-wave gap symmetry. The characteristic density of states has asymmetry of the quasiparticle peaks, flat s-wave and cusplike d-wave subgap behavior, and an asymmetric background. It is assumed that the underlying asymmetry of the conductance peaks is primarily due to the features of the quasiparticle energy spectrum and that the d-wave symmetry enhances the degree of asymmetry of the peaks. Increasing the lifetime broadening factor changes the degree of asymmetry of the tunneling conductance peaks and leads to confluence of the quasiparticle and van Hove singularity peaks.
Noncontact method for measurement of the critical current densities and diagnostics of superconductors
Authors: Rostami Kh. R.
Published: July 2002

The role of the geometric factor of a superconducting sample in magnetic measurements of the critical current densities Jc is investigated. It is shown that a small difference of the shape of the sample from cylindrical does not have much effect on the value of Jc. It is found that the error in evaluating Jc for single crystals with the use of the standard expression for determining Jc of a ceramic is due to the low trapped magnetic flux density Btr in single crystals as compared to ceramics. A technique is proposed for determining Jc for single-crystal and ceramic samples from measurements of the spatial distribution of Btr produced by the Bean shielding supercurrents upon the transition of the whole volume of the sample to the critical state. A formula is obtained for determining Jc for single-crystal and ceramic superconducting samples in the form of polygonal and cylindrical slabs. To increase the accuracy of determining Jc the difference B0*−Bc1 was used instead of Btrmax(0) (B0* is the field that induces Btrmax(0) at the geometric axis of the sample, and Bc1 is the first critical magnetic field of the sample). The values of Jc and of the pinning force in YBCO and BSCCO single-crystal samples are estimated. It is established that the magnetic flux trapping mechanisms in these layered structures are different.
Equilibrium magnetic characteristics of high-Tc superconductors with allowance for the spatial distribution of the order parameter in the vortex cores. II. Vibrational contribution to the dynamic magnetic permeability
Authors: Mamsurova L. G. , Pigalskiy K. S. , Pogosov W. V.
Published: July 2002

The vibrational contribution μv(H) to the dynamic magnetic permeability μac′ is calculated with allowance for the spatial variation of the order parameter in the magnetic field region H≪Hc2, where the properties of type-II superconductors are usually described in the London approximation. The features of the behavior of the analytical relations μv(H) are analyzed for the case when the vortices execute small oscillations about their equilibrium positions corresponding to the thermodynamic-equilibrium vortex lattice. It is shown that taking into account the suppression of the order parameter in the vortex cores leads to substantial differences in the behavior of μv(H) in comparison with the analogous dependence obtained in the London approximation. It is found that the main factor responsible for these differences is a change in shape of the effective potential well in which the vibrational motion of the subsurface vortices takes place.
Structure of the superfluid component and spectrum of elementary excitations in the quantum Bose liquid He4
Authors: Pashitskiı̆ É. A. , Vil’chinskiı̆ S. I.
Published: July 2002

A self-consistent model is constructed for a superfluid Bose liquid in which the single-particle Bose–Einstein condensate (BEC) is suppressed on account of the strong interaction between bosons. The ratio of the density of the BEC to the total density of the Bose liquid is small, n0/n≪1, in contrast to the Bogolyubov theory for a nearly ideal Bose gas, in which the small parameter is the ratio of the number of overcondensate excitations to the number of particles in the intense BEC, (n−n0)/n0≪1. A closed system of nonlinear integral equations for the normal Σ̃11(p,ω) and anomalous Σ̃12(p,ω) self-energy parts is obtained in a renormalized perturbation theory constructed in the combined hydrodynamic (for p→0) and field (for p≠0) variables, the use of which ensures analyticity of the functions Σ̃ij(p,ε) for p→0 and ε→0 and a nonzero value of the superfluid order parameter Σ̃12(0,0)≠0 at T=0. It is shown that the structure of the quasiparticle spectrum E(p) and, in particular, the presence of a roton minimum are determined by the sign-varying and oscillatory behavior of the Fourier component of the pair interaction between bosons in the “hard spheres” model. An important role here is played by the renormalization (screening) of the pair interaction on account of many-particle (collective) effects, which are described by a polarization operator of the bosons on the “mass shell” and leads to enhancement of the effective attraction in certain regions of momentum space. It is shown that the superfluid component ρs at T→0 in this model is a superposition of the single-particle BEC and a pair coherent condensate, analogous to the condensate of Cooper pairs in superconductors. The structure of the superfluid state for T≠0 is also considered, with allowance for the appearance of a normal component ρn and a branch of second sound, the velocity of which goes to zero at the λ point. The applicability of the Landau superfluidity criterion is examined, and the question of the limiting permissible critical velocity of superfluid flow in the absence of quantum vortices is discussed.
Precessing states with “zero” magnetization in the superfluid A phase of liquid He3
Authors: Suramlishvili N. G.
Published: July 2002

The regimes of coherent precession of “zero” magnetization in a transverse rf field in the superfluid A phase of liquid He3 are investigated with dissipative processes taken into account.
Ballistic transport in a GaAs/AlxGa1−xAs one-dimensional channel fabricated using an atomic force microscope
Authors: Curson N. J. , Nemutudi R. , Appleyard N. J. , Pepper M. , Ritchie D. A. , Jones G. A. C.
Published: July 2002

We fabricate a one-dimensional constriction in a shallow, δ-doped GaAs/AlxGa1−xAs two-dimensional electron gas, by locally oxidizing the surface using an atomic force microscope. The channel exhibits ballistic conduction with up to seven conductance plateaus, quantized in units of 2e2/h. The dependence of the device conductance on dc bias voltage reveals the energy separation of the first two subbands to be ΔE1,2=5.5(±0.3) meV, which allows ballistic conduction to be observed up to a temperature of 20 K. A lateral electric field, combined with the hard-walled confinement due to the insulating lines, allows manipulation of the electron wave function in a way which is not possible with surface-gated devices.
Thermal conductivity of fullerite C60 crystals at low temperatures
Authors: Efimov V. B. , Mezhov-Deglin L. P. , Nikolaev R. K. , Sidorov N. S.
Published: July 2002

The thermal conductivity κ of extended crystals of fullerite C60 with transverse dimensions L of the order of a few millimeters is measured at low temperatures (down to 0.6 K). It is found that in the range from 7 to 0.6 K the temperature dependence of the thermal conductivity of the better of the samples is close to cubic, κ(T)∼T3, and the effective phonon mean free path estimated from the measured thermal conductivity and the published value of the specific heat of fullerite [J. R. Olson et al., Science 259, 1145 (1993)] has a value (lp≈0.6 μm) that is practically independent of temperature and much less than L, i.e., the phonon mean free path is limited by strong scattering on defects in the bulk of the sample.
Boundary layer instability induced by surface suction
Authors: Roberts P. J. D. , Floryan J. M. , Casalis G. , Arnal D.
Published: July 2002

It is shown that suction nonuniformities may induce a new instability of the Blasius boundary layer that results in the generation of streamwise vortices. Addition of a uniform suction is not effective in controlling this instability. It is shown that nonuniformities of surface blowing may induce a similar instability and that the characteristics of this instability are also little affected by the magnitude of the blowing. Finally, it is shown that suction nonuniformities appear to have a minimal effect on the traveling (Tollmien–Schlichting) wave instability.
Nonlinear oscillations of the magnetization in small cylindrical ferromagnetic particles
Authors: Ivanov B. A. , Yastremskiı̆ I. A.
Published: July 2002

The radially symmetric nonlinear oscillations of the magnetization in small cylindrical particles of a ferromagnet are considered in the cases of free and fixed boundary conditions at the lateral surface of the particles. It is found that even for nonlinear oscillations of small amplitude the dependence of the frequency on the amplitude of the oscillations is rather complicated and can include a series of bifurcations. The character of the oscillations depends substantially on the boundary conditions; for example, for free boundary conditions the solutions exhibit bifurcations that are not present in the case of fixed boundary conditions. We discuss the possibilities for generalizing the results to the case of oscillations in a cylinder with a more complicated angular dependence and to the case of radially symmetric oscillations in a spherical particle.
Families of particular solutions to multidimensional partial differential equations
Authors: Zenchuk A. I.
Published: July 2002

Dressing methods are known as productive tools for construction of the particular solutions to the big class of nonlinear partial differential equations (PDEs) which are integrable by the inverse scattering technique. Recently the modification of the dressing method based on the system of algebraic equations has been suggested which allows us to find the families of particular solutions to certain types of nonintegrable (in classical sense) nonlinear PDEs. This modification represents PDEs as closure reductions of an appropriate differential-difference system. In this article we study the dressing procedure in more detail. Particularly, we consider different families of particular solutions available through the dressing method based on the algebraic system. We give two examples of the differential-difference systems and related PDEs and point to other possible generalizations of the dressing method.
Soliton solutions of XXZ lattice Landau–Lifshitz equation
Authors: Tomoyuki SADAKANE
Published: July 2002

Multisoliton solutions of the partially isotropic (classical) lattice Landau–Lifshitz equation are constructed. A trigonometric version of the dressing method is proposed to this aim. The dressing matrix is a matrix valued periodic function of the spectral parameter, and takes almost the same form as the L-matrix except for the number of poles. Both the easy-axis (J1=J2<J3) and easy-plane (J1<J2=J3) cases can be treated in a parallel way.
The surface energy of finite clusters of soap bubbles
Authors: Fortes M. A.
Published: July 2002

A simple derivation is presented of a general integral equation relating the surface energy of a free cluster of bubbles to the pressure excesses in the bubbles and a new differential equation for the change in energy in reversible transformations of a cluster is derived. It is shown that the integral equation has a simple geometrical interpretation. A general form of the equation is written which can be applied to wet clusters with finite Plateau borders. Other consequences of the energy equation are drawn.
Resonant conditions for Love wave guiding layer thickness
Authors: McHale G. , Newton M. I. , Martin F. , Gizeli E. , Melzak K. A.
Published: July 2002

In this work, we report an investigation of polymer overlayer thickness in a Love wave device working at a fundamental frequency of 110 MHz and at the 330 MHz harmonic. At both frequencies, we observe the initial reduction in insertion loss associated with a Love wave device. Significantly, we also observe a series of resonant conditions as the layer thickness is further increased. The separation of these resonances is attributed to an increase in thickness of half of the acoustic wavelength in the polymer.
Current status of the Synchrotron Radiation Center
Authors: Moore C. J. , Altmann K. N. , Bisognano J. J. , Bosch R. A. , Eisert D. , Fisher M. , Green M. A. , Hansen R. W. C. , Himpsel F. J. , Höchst H. , Julian R. L. , Kleman K. , Kubala T. , Pedley B. , Rogers G. C. , Severson M. , Stott J. P. , Taylor, J. W. , Trzeciak W. S. , Wallace D. J. , Wehlitz R. , Bissen M.
Published: July 2002

The Synchrotron Radiation Center operates the Aladdin electron storage ring at energies of 800 meV or 1 GeV in support of a broad range of national and international research programs with a major focus on the study of valence electrons, spectromicroscopy, and nanolithography. Upgrades to the storage ring have improved the stability of the source, and experiments with low emittance lattice configurations show the feasibility of increased brightness for new or enhanced research. Three recently installed undulators, two pure permanent magnet devices and an electromagnetic device, and the associated instrumentation offer experimentalists high flux combined with high resolution. The status of the existing instrumentation, recent scientific results, and an overview of plans for new undulator-based instruments to cover the photon energy range from 7.8 to 400+ eV will be presented.
Internal wave excitation by a vertically oscillating elliptical cylinder
Authors: Sutherland B. R. , Linden P. F.
Published: July 2002

Laboratory experiments are performed to measure the amplitude of internal waves generated by an elliptical cylinder oscillating vertically with different frequencies and amplitudes in a uniformly stratified fluid. The experimental results are compared with the theoretical predictions of Hurley and Keady (1997). Though in qualitatively good agreement with experiments, the theory underestimates the amplitude of low-frequency waves and overestimates the amplitude of high-frequency waves. The measured beam width is underestimated by theory, which neglects the dynamics of viscous boundary layers surrounding the cylinder. When the cylinder oscillates at a frequency less than half the buoyancy frequency, experiments reveal that two sets of waves beams are generated. The secondary set of waves have double the frequency of the primary waves and are excited due to nonlinear processes.
Manifestation of toroidal excitations in the polariton spectrum of an insulator at its boundary with a metal in an electric field
Authors: Chupis I. E.
Published: July 2002

A study is made of the influence of toroidal excitations on the spectrum of surface polaritons of an insulator at its boundary with an ideal metal in a static electric field perpendicular to the contact surface. It is shown that the toroidal polariton mode can be radiative and have normal or anomalous dispersion. A distinguishing feature of the toroidal polariton mode in comparison with an electric-dipole mode is that it crosses the light line, i.e., it can be resonantly excited by an electromagnetic wave propagating along the contact surface. This feature means that it is possible to identify a toroidal polariton mode in the spectrum by varying the angle of incidence of the electromagnetic wave.
Zero-dimensional excitons in CdTe/ZnTe nanostructures
Authors: Marsal L. , Besombes L. , Tinjod F. , Kheng K. , Wasiela A. , Gilles B. , Rouvière J.-L. , Mariette H.
Published: July 2002

Thin CdTe layers embedded in ZnTe matrix grown by atomic layer epitaxy have been studied by time resolved spectroscopy and spatially resolved spectroscopy. The presence of Cd-rich dotlike islands in these CdTe nanostructures is shown by both atomic force microscopy and high resolution transmission electron microscopy. Zero-dimensional nature of excitons is shown both by the temperature dependence of the decay time and observation of sharp exciton lines in microphotoluminescence spectra. Zero-dimensional excitons probed by microphotoluminescence present a doublet structure linearly polarized along two orthogonal directions. This doublet structure is attributed to bright heavy-hole exciton states split by the local asymmetry of the localization potential. Reversible spectral shifts in the emission of some single quantum dots are observed on a time scale of hundreds of milliseconds. These small shifts can be attributed to the Stark effect caused by fluctuating electric fields and can significantly affect time-integrated transition linewidths.
Mean flow precession and temperature probability density functions in turbulent rotating convection
Authors: Hart J. E. , Kittelman S. , Ohlsen D. R.
Published: July 2002

Laboratory results for high Rayleigh number convection in a rotating cylinder heated from below are presented. Time series of temperature fluctuations reveal: (a) There is a large-scale overturning meridional cell that precesses in the retrograde direction (opposite to the direction of the basic rotation) when viewed from the coordinates attached to the container. This precessing cell is prevalent at low to medium basic rotation rates, but is suppressed when the thermal Rossby number becomes less than about one half. (b) The temperature fluctuations at the centerpoint of the apparatus display a transition from nearly exponential, to Gaussian, then back to toward an exponential probability density function as the Taylor number is raised. The Rayleigh number required for Gaussian statistics is of order 1010. As the Rayleigh number increases, the Taylor number interval over which nearly Gaussian statistics are found becomes wider. These findings agree with previous turbulent rotating convection experiments at lower Rayleigh number in which Gaussian statistics were not observed.
Superconductivity of Ca(Al0.5,Si0.5)2, a ternary silicide with the AlB2-type structure
Authors: Imai Motoharu , Nishida Kenji , Kimura Takashi , Abe Hideki
Published: July 2002

A ternary silicide Ca(Al0.5,Si0.5)2 was prepared by Ar arc melting. Powder x-ray diffraction measurement indicates that it has the AlB2-type structure with lattice constants of a=4.1905(5) and c=4.3992(8) Å, where Si and Al atoms are arranged in the disordered honeycomb lattice and Ca atoms are intercalated between them. The silicide is isostructural with a superconductor MgB2. Electrical resistivity and dc magnetization measurements revealed that it is a superconductor with a TC of 7.7 K.
Effect of light illumination on antiferromagnet-metamagnet phase transitions in the garnet Ca3Mn2Ge3O12
Authors: Bedarev V. A. , Gapon V. I. , Gnatchenko S. L. , Baran M. , Szymczak R. , Desvignes J. M. , Le Gall H.
Published: July 2002

The effect of linearly polarized light illumination on the metamagnetic phase transition in the antiferromagnetic garnet Ca3Mn2Ga3O12 is studied. The crystal is exposed to light propagating both along the tetragonal axis [001] and along the [100] direction. In both cases, a change of the field Ht of the metamagnetic phase transition is observed under illumination, and this change depends on the orientation of plane or polarization of the light with respect to the crystal axes. In the first case, k‖H‖[001], the value of Ht decreases on exposure to light with the polarization E‖[110] and increases on exposure to light with the polarization E‖[11̄0]. In the second case, k‖H‖[100], the value of Ht decreases irrespective of the orientation of the plane of polarization of the light with respect to the crystal axes. However, the magnitudes of the change of Ht are different for light with the polarization E‖[011] and with the polarization E‖[01̄1]. The change of the field of the metamagnetic phase transition in the second case is much larger than in the first case. A phenomenological theory of the photomagnetic effects observed in the antiferromagnetic garnet Ca3Mn2Ge3O12 is developed. It is shown that the effect of light illumination on the metamagnetic phase transition is related to the photoinduced magnetic moment in this antiferromagnet. The magnetic moment induced by linearly polarized light in the garnet Ca3Mn2Ge3O12 is detected experimentally by means of a SQUID magnetometer.
Interaction of Pr3+ optical centers in the Y2SiO5 crystal
Authors: Malyukin Yu. V. , Zhmurin P. N. , Lebedenko A. N. , Sholkina M. A. , Grinev B. V. , Znamenskiı̆ N. V. , Manykin É. A. , Orlov Yu. V. , Petrenko E. A. , Yukina T. G.
Published: July 2002

It is shown on the basis of studies of the optical spectra and luminescence decay of nonequivalent Pr3+ optical centers in the Y2SiO5 crystal that the occupation of the nonequivalent cation sites of the crystal lattice by the activator ions is irregular. For excitation in the region of the optical transitions H43→1D2in the temperature interval 6–80 K there is no transfer of electronic excitation energy between Pr3+ ions localized in different cation sites. The luminescence decay law of the Pr3+ optical centers is determined by the concentration of activator ions and has a complicated non-single-exponential character; the quenching of the luminescence of the Pr3+ ions is due to the formation of dimers of these ions. © 2002 American Institute of Physics.
Stability of convection in the mush under rocking motion
Authors: Chen Falin , Chung C. A. , Lai M. H.
Published: July 2002

We implement a linear stability analysis for the mush under rocking motion. Owing to the rocking motion, the shifted gravity induces a parallel flow. Without rocking, all the instability modes propagating in different directions are of equal stability criteria. With rocking, except for the longitudinal mode propagating in the direction perpendicular to the induced flow, all modes are to various extents inhibited by the induced flow. More precisely, all these modes are inhibited by the periodical buoyancy reduction in the direction of density gradient, which essentially stabilizes the system without preferred direction.
Dependence of semiconductor energy bands on the isotopic composition. A universal relation for monoatomic crystals
Authors: Zhenov A. P.
Published: July 2002

The influence of the isotopic composition of the components of semiconductor compounds on the structure of the energy bands Ef,n is discussed. The respective roles of changes in the volume of the unit cell of the crystal and of renormalization of the electron–phonon interaction upon changes in the isotopic composition are considered. For the case of monoatomic systems in the virtual crystal approximation a universal relation is obtained for the dependence of the bands on the composition and temperature.
Photoinduced magnetic linear dichroism in a YIG:Co film
Authors: Miloslavska O. V. , Kharchenko Yu. N. , Kharchenko N. F. , Yurko V. G. , Stupakiewicz A. , Maziewski A.
Published: July 2002

The spectra of linear dichroism induced by a magnetic field are observed in a cobalt-doped yttrium iron garnet (YIG:Co) film grown in the (001) plane. The linear dichroism spectra are highly sensitive to the orientation of the magnetic field. The spectrum measured with the magnetic field directed along the crystallographic axis [100] turned out to have a form identical to the spectrum of the “rigid” photoinduced linear dichroism, known from earlier experiments. The similarity of these spectra may be regarded as evidence of the magnetic origin of the major part of the optical anisotropy induced by light with polarization E∥[100] in the nonmagnetized YIG:Co film.
Anisotropy of the critical current and the guided motion of vortices in a stochastic model of bianisotropic pinning. II. Observed effects
Authors: Shklovskij V. A. , Soroka A. A.
Published: July 2002

A simple and clear relationship between the anisotropy of the current density jc and the guided motion of vortices along the basal planes of a bianisotropic potential is established on the basis of a physical analysis of experimentally observed effects. This relationship is expressed in the form a diagram of the possible dynamical states of the vortex ensemble on the (jx, jy) plane. A theoretical analysis of the nonlinear resistive responses in the “rotating current” scheme, which has been used to investigate the anisotropy of the pinning in a number of experimental studies, is given for the first time. The most typical behaviors of the various resistive responses are presented graphically.
Magnetic properties of a lead-doped BKBO single crystal
Authors: Barilo S. N. , Gatal’skaya V. I. , Shiryaev S. V. , Smirnova T. V. , Szymczak H. , Szymczak R. , Baran M.
Published: July 2002

A single crystal of Ba0.65K0.35Pb0.2Bi0.8O3 (BKPBO) grown by the method of electrochemical deposition is investigated. The crystal is single-phase with the cubic perovskite structure. The isotherms of the field dependence of the magnetization for 0.1Tc⩽T⩽0.72Tc are well described by the collective pinning theory. The temperature dependence of the collective pinning length Lc(T) agrees with the mechanism of δl pinning, which is due to spatial fluctuations of the mean free path of the charge carriers. The magnetic properties of BKPBO are compared with those for crystals of the BKBO system.
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u spectroscopic ellipsometry study of the growth of microcrystalline silicon
Authors: Kumar Satyendra , Drevillon B. , Godet C.
Published: July 2002

High sensitivity, high-energy resolution, and the capability to obtain data in situ make ellipsometry a useful tool for addressing a number of problems in thin-film deposition processes. Dielectric functions ε̃=ε1−i ε2 of glow-discharge-produced microcrystalline silicon films (μc-Si) are determined by using spectroscopic ellipsometry (SE). ε2 spectra present a shoulder near 4.2 eV which corresponds to the E2 optical transition observed in crystalline silicon. This peak is not observed in amorphous silicon spectra. c-Si is described as a mixture of amorphous phase, microcrystallites, and voids. The choice of the microcrystalline reference phase is discussed in particular by comparing the microcrystallite volume fraction determined from SE and x-ray measurements. Strong variations in the nature of the material are observed during growth: the density deficiency and the surface roughness both increase as functions of film thickness up to 0.4–0.5 μm.
Electrical transport properties of transition-metal disilicide films
Authors: Nava F. , Tu K. N. , Mazzega E. , Michelini M. , Queirolo G.
Published: July 2002

Electrical resistivity in the temperature range of 2–1100 K and Hall-effect measurements from 10 to 300 K of CoSi2, MoSi2, TaSi2, TiSi2, and WSi2 polycrystalline thin films were studied. Structure, composition, and impurities in these films were investigated by a combination of techniques of Rutherford backscattering spectroscopy, x-ray diffraction, transmission electron microscopy, and Auger electron spectroscopy. These silicides are metallic, yet there is a remarkable difference in their residual resistivity values and in their temperature dependence of the intrinsic resistivities. For CoSi2, MoSi2, and TiSi2, the phonon contribution to the resistivity was found to be linear in temperature above 300 K. At high temperatures, while a negative deviation from the linearity followed by a quasisaturation was observed for TaSi2, the resistivity data of WSi2 showed a positive deviation from linearity. It is unique that the residual resistivity, ρ(2 K), of the WSi2 films is quite high, yet the temperature dependent part, i.e., ρ(293 K) − ρ(2 K), is the smallest among the five silicides investigated. This suggests that the room-temperature resistivity of WSi2 can be greatly reduced by improving the quality of the film, and we have achieved this by using rapid thermal annealing.
Refractive index, n, and dispersion, −d
n/dλ, of GaAs at 2 K determined from Fabry–Perot cavity oscillations
Authors: Reynolds D. C. , Bajaj K. K. , Litton C. W. , Peters G. , Yu P. W. , Parsons J. D.
Published: July 2002

Fabry–Perot cavities were used to obtain experimental values for the quantity (n−λ dn/dλ) near the absorption edge in GaAs at 2 K. Here n is the refractive index and λ is the wavelength of light. Using an adjusted Sellmeier-type equation, n and −dn/dλ were calculated as a function of wavelength at 2 K. These are the only available values of n and −dn/dλ for GaAs at 2 K of which we are aware.
High-reflectivity GaAs-AlGaAs mirrors: Sensitivity analysis with respect to epitaxial growth parameters
Authors: Baets R. , Demeester P. , Lagasse P. E.
Published: July 2002

High-reflectivity multilayer structures, consisting of a periodic stack of quarter-wavelength GaAs and AlGaAs layers, have been investigated concerning their optical behavior with respect to various deficiencies in the epitaxial growth process. Theoretical curves are compared with experimental ones from structures grown by metalorganic chemical vapor deposition. These layer structures are also shown to be useful in the characterization of thickness uniformity of an epitaxial growth process.
Vacancy supersaturation in Si under SiO2 caused by SiO formation during annealing in Ar
Authors: Ahn S. T. , Kennel H. W. , Tiller W. A. , Plummer J. D.
Published: July 2002

At high temperatures and low oxygen partial pressures, decomposition of SiO2 can occur to form volatile SiO by the reaction Si+SiO2→2SiO. Since the Si atoms are supplied from the substrate, vacancies are generated at the SiO2/Si interface. This has been confirmed by observations of enhanced diffusion of Sb, retarded diffusion of P, and an accelerated shrinkage of extrinsic stacking faults in Si under thin SiO2 annealed in Ar at 1100 °C. As the oxide thickness increases, the vacancy supersaturation rapidly decreases, which is probably a result of a reduced SiO generation flux with increasing oxide thickness as the out-diffusion of SiO tends to control the rate of the overall decomposition process. When a polysilicon layer is on top of SiO2/Si, the SiO formation process occurs nonuniformly and circular features appear where the poly-Si layers have been completely removed. Vacancies were injected only through these circular features while the vacancy concentration in the rest of the region was not perturbed.
A variational principle for the equations of piezoelectromagnetism in elastic dielectric crystals
Authors: Lee P. C. Y.
Published: July 2002

In piezoelectric or ferroelectric crystals, which are often employed in ultrasonics applications, the acoustic field of small amplitude is governed by the equations of elasticity of infinitesimal displacement gradients and the electromagnetic (EM) field is governed by Maxwell’s equations. The interactions between the mechanical and electromagnetic fields are mainly due to the couplings in the constitutive equations. The governing equations consisting of field equations and constitutive equations are called the equations of piezoelectromagnetism. In a dielectric crystal of volume V bounded by a surface S which separates V from an outer vacuum V′, the kinetic-energy density and electric enthalpy density are defined. By introducing these density functions in a variational principle and by requiring the independent variations of the mechanical displacement, the scalar and vector potentials of the EM field, it is shown that the equations of piezoelectromagnetism and the appropriate jump conditions are obtained. The present variational principle reduces to those for Maxwell’s equations, the equations of elasticity, and the equations of piezoelectricity, respectively.
Optical constants of ε-GaSe
Authors: Adachi Sadao , Shindo Yōichi
Published: July 2002

The optical response of ε-GaSe for light polarization perpendicular to the c-axis in the 2.0–5.0-eV photon-energy range has been studied at room temperature by spectroscopic ellipsometry. The measured dielectric-function spectra reveal distinct structures at energies of the E1 (∼3.6 eV) and E3 (∼4.9 eV) critical points (CPs). The experimental data are analyzed on the basis of a simplified model of the interband transitions. The E1 structure is characterized by a two-dimensional (2D) M0 CP plus 2D discrete exciton, and the E3 structure is assumed to act as a damped harmonic oscillator. Results are in satisfactory agreement with the experiment over the entire range of photon energies.
Initial stages of the formation of the Au/GaAs(001) interface: A low-energy ion scattering study
Authors: Charatan Robert M. , Williams R. Stanley
Published: July 2002

Submonolayer coverages of Au on GaAs(001) substrates prepared by various ex situ chemical cleaning procedures using low-energy ion scattering techniques are investigated. This research is compared with previous results for 1 ML of Au deposited on Si(111). A comparison of the energy spectra showed substantial broadening in the Li+ backscattering ion peak from Au deposited on GaAs, as compared to the Au on Si. Li+ impact collision ion scattering spectroscopy (ICISS) results showed that the gold formed an ordered overlayer above the Si surface, which was thermally stable to 500 °C. Even for depositions on room-temperature GaAs(001), shadowing of Au by substrate atoms at low scattering angles showed that Au penetrated below the GaAs surface. The estimate of the average penetration depth into the room-temperature substrate is two to three atomic planes of the GaAs crystal. An ICISS experiment showed that the Au atoms sampled by the ion beam were not ordered on lattice sites, but appeared to occupy multiple and/or random positions within the substrate. Upon annealing to 300 °C, the gold atoms were more ordered, but did not penetrate significantly further into the GaAs. At higher annealing temperatures, the Au either diffused further into the substrate or became incorporated in islands, and occupied favored subsurface sites.
Ion channeling study of Scx(Yb,Er)1−xAs films on GaAs (001)
Authors: Guivarc’h A. , Ballini Y. , Minier M. , Guenais B. , Dupas G. , Ropars G. , Regreny A.
Published: July 2002

1.8 MeV He+ ion backscattering and channeling was used to study various lattice matched and mismatched ScxYb1−xAs and ScyEr1−yAs films grown on GaAs (001). The lattice matching leads to excellent epitaxy with χmin as low as 1.5% along the [001] direction. It is demonstrated unambiguously that the interface peaks result from the first atoms of the Ga rows of the substrate, indicating that the As sublattice is continuous across the rare-earth monoarsenide/GaAs interface. These lattice matched heterostructures are proposed as ideal tools for studying ion channeling phenomena. Concerning the mismatched heterostructures, it is shown that the mosaic resulting from the strain relaxation, and the lattice tilt occurring for thick films can be evaluated directly from aligned spectra.
Thin-film selective emitter
Authors: Chubb Donald L. , Lowe Roland A.
Published: July 2002

Direct conversion of thermal energy into electrical energy using a photovoltaic cell is called thermophotovoltaic energy conversion. One way to make this an efficient process is to have the thermal energy source be an efficient selective emitter of radiation. The emission must be near the band-gap energy of the photovoltaic cell. One possible method to achieve an efficient selective emitter is the use of a thin film of rare-earth oxides. The determination of the efficiency of such an emitter requires analysis of the spectral emittance of the thin film including scattering and reflectance at the vacuum-film and film-substrate interfaces. Emitter efficiencies (power emitted in emission band/total emitted power) in the range 0.35–0.7 are predicted. There is an optimum optical depth to obtain maximum efficiency. High emitter efficiencies are attained only for low (≤0.05) substrate emittance values, both with and without scattering. The low substrate emittance required for high efficiency limits the choice of substrate materials to highly reflective metals or high-transmission materials such as sapphire.
Mechanism for the formation of 90° dislocations in high-mismatch (100) semiconductor strained-layer systems
Authors: Gosling T. J.
Published: July 2002

A rigorous calculation, within the framework of linear continuum elasticity, is performed to evaluate the energy of a rectangular 1/2[101](1̄11) 60° dislocation glide loop nucleated at the site of a pre-existing 1/2[1̄10](111) 60° dislocation at the (100) interface between a strained epitaxial layer and its substrate. This nucleation event gives rise to an interfacial segment of 1/2[011](100) 90° dislocation, which extends as the glide loop expands. The presence of the pre-existing 60° dislocation is found to reduce dramatically the energy of the loop relative to the energy of a comparable isolated loop. Results obtained for the elastic energy barrier to formation of such a loop for varying mismatch strain are incorporated into kinetic rate equations available in the literature. It is thus demonstrated that the mechanism of 90° dislocation formation described is expected to become experimentally significant at mismatch strains of around 2%. This result is in excellent agreement with the experimentally determined mismatch strain threshold at which significant 90° dislocation formation is observed to commence in GexSi1−x/Si(100) and InxGa1−xAs/GaAs(100) strained-layer heterosystems.
Effect of strain on confined optic phonons of highly strained InAs/InP superlattices
Authors: Tran C. A. , Jouanne M. , Brebner J. L. , Masut R. A.
Published: July 2002

We have measured Raman scattering and high-resolution x-ray diffraction from highly strained [(InAs)4(InP)4]N short-period superlattices grown on InP substrates by atomic layer epitaxy at 355 °C. The InAs and InP confined phonons are observed in these highly strained short-period superlattices. The energy of the InAs confined longitudinal-optical phonon (LO) modes of a fully strained superlattice (with N=8) is blue shifted by about 10 cm−1 compared to the LO phonon of bulk InAs. This effect is explained by the large biaxial strain existing in the InAs layers. The observed frequency shift agrees with the lattice-mismatch strain given by elasticity theory and independently measured by high-resolution x-ray diffraction. No evidence of a frequency shift of the InP confined LO modes in the N=8 fully strained superlattice is observed, indicating that the strain is confined to the InAs layers. We show that in a partially relaxed superlattice (with N=20), the InAs layers are in compression, while the InP layers are in tension. In this case the InP confined LO1 phonons are red shifted by about 3 cm−1 compared to the InP LO1 phonons of the N=8 fully strained superlattice, and the shift of the InAs confined LO phonons with respect to the LO phonons of bulk InAs is also reduced.
Orientation of the electric-field gradient arising from a vacancy in Hg0.79Cd0.21Te
Authors: Hughes Wm. C. , Austin J. C. , Swanson M. L.
Published: July 2002

We have used the perturbed angular correlation technique to measure the orientation of the electric-field gradients (EFGs) due to vacancy trapping by substitutional indium donors in the II-VI semiconductor Hg0.79Cd0.2Te. Previously, two hyperfine interaction frequencies were measured and were attributed to the trapping of a metal vacancy at a next nearest-neighbor site to the indium atom in bulk solid-state recrystallized materials. In the present experiments, measurements are done on thin-film samples to find the principal axes of the EFGs. Both EFGs are found to have principal axes parallel to a 〈111〉 crystal axis, despite the fact that a simple point charge model supports a 〈110〉 EFG for this 〈110〉-oriented In-VHg complex. A similar situation exists for indium-vacancy pairing in other II-VI semiconductors. We propose that the 〈111〉 EFG orientation arises from the electric dipole moments of the highly polarized Te ions in the region of the vacancy.
Concentration-dependent optical-absorption coefficient in n-type GaAs
Authors: Lush G. B. , Melloch M. R. , Lundstrom M. S. , MacMillan H. F. , Asher S.
Published: July 2002

The doping-dependent, near-band-edge optical-absorption coefficient α(hν) was deduced from optical transmission measurements in n-type GaAs thin films. The selenium-doped films were grown by metalorganic chemical-vapor deposition and doped to produce room-temperature electron concentrations from 1.3×1017 to 3.8×1018 cm−3. The transmission measurements covered photon energies between 1.35 and 1.7 eV and were performed on double heterostructures with the substrate removed by selective etching. The results show good qualitative agreement with previous studies and good quantitative agreement, except for the heavily doped samples. For n0=3.8×1018 cm−3, α(1.42 eV) is approximately four times that reported by previous workers. Secondary-ion-mass spectrometry measurements on films grown under differing conditions demonstrate that α(hν) is sensitive to electrically inactive dopants and supports the hypothesis that precipitates or compensation influenced previous measurements. These comprehensive results on high-quality, uncompensated material should prove useful for fundamental studies of optical transitions in n-type GaAs as well as for modeling optoelectronic devices.
Semi-insulating properties and photoluminescence quenching in Cu-diffused InP
Authors: Xie K. , Wie C. R.
Published: July 2002

The properties of high-resistivity InP with resistivity up to 107 Ω cm, obtained by thermal diffusion of Cu at 800 °C for over 20 h into undoped and p-type InP samples, are investigated. Hall-effect measurements showed that the compensation mechanism in the slowly cooled sample is different from that in the quickly cooled samples. Photoluminescence was quenched in the quickly cooled samples when annealed at 350 °C and the anneal temperature at which the sample resistivity and carrier mobility reached the maximum. It is shown that the electrical compensation in the slowly cooled sample could be understood by a simple deep-level compensation model. However, the semi-insulating behavior of the quickly cooled samples appears to be consistent with an internal Schottky depletion model associated with the Cu precipitates. The photoluminescence quenching is due to the Cu precipitates acting as effective nonradiative recombination centers.
Superconducting TlSr2(Ca,Cr)Cu2O7 thin films with critical current density up to 106 A/cm2
Authors: Tang Y. Q. , Chen K. Y. , Chan I. N. , Chen Z. Y. , Shi Y. J. , Salamo G. J. , Chan F. T. , Sheng Z. Z.
Published: July 2002

Superconducting TlSr2(Ca,Cr)Cu2O7 thin films with zero resistance temperature Tc up to 102 K and critical current density Jc as high as 106 A/cm2 at 77.7 K have been successfully prepared via laser ablation and thallium diffusion. Prolonged low temperature annealing in air was used for film processing. X-ray diffraction patterns indicated that the films were highly oriented 1212 phase with c axes normal to the LaAlO3(100) or MgO(100) substrates.
Magnetic and magnetoresistance properties in Ni80Fe20/Cu multilayers with in-plane uniaxial magnetic anisotropy
Authors: Inomata K. , Hashimoto S.
Published: July 2002

Magnetic properties and magnetoresistance were investigated for Ni80Fe20/Cu multilayers with different Ni80Fe20 and Cu thicknesses that were prepared on an MgO (110) substrate using ion beam sputtering with different Ar ion acceleration voltage (VB). The structure of Ni80Fe20 is epitaxial distorted face centered tetragonal with (110) orientation, as was determined by x-ray and electron diffraction measurements. Thus, the induced in-plane uniaxial magnetic anisotropy depends on the VB and the Ni80Fe20 layer thickness. A giant magnetoresistance at room temperature was obtained up to 20% for (15 Å Ni80Fe20/10 Å Cu)60 multilayers, and oscillated for Cu layer thickness with 12 Å period. The saturation field Hs for the giant magnetoresistance (GMR) is in good agreement with 2J/dMs, where J, d, and Ms are layer exchange coupling, magnetic layer thickness, and saturation magnetization, respectively. The small field changes ΔH of 20 and 8 Oe needed for GMR were attained for n=16 (MR=12%) and 2 (MR=6.5%), respectively, in (70 Å Ni80Fe20/10 Å Cu)n with in-plane uniaxial anisotropy.
Millimeter-wave detection by YBaCuO step-edge microbridge Josephson junction
Authors: Fukumoto Yoshito , Ogawa Rikuo , Kawate Yoshio
Published: July 2002

Millimeter-wave detection was investigated using a step-edge microbridge Josephson junction fabricated by a YBaCuO thin film for both the video detection and harmonic mixing detection. Current–voltage (I–V) characteristics, which could be described by the resistively shunted junction (RSJ) model, were obtained up to 70 K with the IcR product of 150 μV at 70 K. The responsivity and noise equivalent input power were calculated as 2400 W/V and 4.4×10−14 W/√Hz, respectively, in the video detection assuming the RSJ model approximation. Clear dependence of the intermediate frequency output on the applied dc bias voltage was observed in the harmonic mixing detection with the harmonic numbers of 5–16, reflecting the change of dynamic resistance at the constant voltage steps induced by the local oscillation signal on the I–V curve. A minimum detection power of −59.4 dB m and a conversion efficiency (η) of −49.6 dB were obtained for the harmonic number (N) of 5 at 60 K. The relationship between the η and N was expressed as η∝N−2.2.
Hot-stage transmission electron microscopy studies of phase transformations in tin-modified lead zirconate titanate
Authors: Xu Z. , Viehland D. , Yang P. , Payne D. A.
Published: July 2002

The temperature dependence of phase stability for tin-modified lead zirconate titanate solid solution ceramics Pb(0.98)Nb0.02[(Zr1−x, Snx)1−yTiy]1−zO3 (PZST) was investigated by hot-stage transmission electron microscopy. Compositions studied included, a material that was antiferroelectric (AFE) at room temperature with x=0.42 and y=0.04, and a material that was ferroelectric (FE) at room temperature with x=0.43 and y=0.08 (abbreviated as PZST 42/4/2 and 43/8/2, respectively). PZST 42/4/2 was found to exhibit a sequence of phase transformations on heating of AFE–multicell cubic (MCC)–simple cubic (SC), whereas PZST 43/8/2 had a sequence of FE-AFE-MCC-SC. Previously referred to F spots (i.e., 1/2[111] superlattice spots) were observed in all four phases. The diffraction intensities for the F spots decreased with increasing temperature, and eventually disappeared above 300 °C. Electron diffraction confirmed the presence of the MCC phase which was characterized by the existence of weak 1/2[110] superlattice spots in the temperature region between the AFE and SC phases. In each composition the AFE phase was characterized by arrays of one-dimensional antiphase domain boundaries and (1/x)[110] superlattice spots. The modulation wavelength for the superlattice spots was found to be a strong function of temperature and was incommensurate with the lattice. The thermal stability of phases in the crystalline solution PZST system is discussed in terms of the observed microstructural features.