bluuebunny/crossref_metadata_2025 huggingface dataset:
Indium tin oxide thin films for organic light-emitting devices
Authors: Kim H. , Piqué A. , Horwitz J. S. , Mattoussi H. , Murata H. , Kafafi Z. H. , Chrisey D. B.
Published: July 2002

High-quality indium tin oxide (ITO) thin films (150–200 nm) were grown on glass substrates by pulsed laser deposition (PLD) without postdeposition annealing. The electrical, optical, and structural properties of these films were investigated as a function of substrate temperature, oxygen pressure, and film thickness. PLD provides very uniform ITO films with high transparency (⩾85% in 400–700 nm spectrum) and low electrical resistivity (2–4×10−4 Ω cm). The Hall mobility and carrier density for a 170-nm-thick film deposited at 300 °C are 29 cm2/V s and 1.45×1021 cm−3, respectively. Atomic force microscopy measurements of the ITO films indicated that their root-mean-square surface roughness (∼5 Å) is superior to that (∼40 Å) of commercially available ITO films deposited by sputtering. ITO films grown at room temperature by PLD were used to study the electroluminescence (EL) performance of organic light-emitting devices. The EL performance was comparable to that measured with commercial ITO anodes.
Elastic constants of tetrahedral amorphous carbon films by surface Brillouin scattering
Authors: Ferrari A. C. , Robertson J. , Beghi M. G. , Bottani C. E. , Ferulano R. , Pastorelli R.
Published: July 2002

The elastic constants of tetrahedral amorphous carbon (ta-C) and hydrogenated tetrahedral amorphous carbon (ta-C:H) thin films were determined nondestructively by surface Brillouin scattering. Besides the usual Rayleigh surface mode, we also observe a new pseudosurface acoustic mode of longitudinal polarization, which is a modified version of the longitudinal guided mode usually found in slow-on-fast supported films. The Young’s modulus E of a ta-C with 88% sp3 is 757 GPa, and the shear modulus G is 337 GPa. The moduli of ta-C:H with 70% sp3 and 30 at. % H are lower, E=300 GPa and G=115 GPa.
Z-contrast imaging and electron energy-loss spectroscopy analysis of chromium-doped diamond-like carbon films
Authors: Fan X. , Dickey E. C. , Pennycook S. J. , Sunkara M. K.
Published: July 2002

Metal-doped diamond-like carbon films were produced for the purpose of an electrochemical nanoelectrode. In this study we use Z-contrast scanning transmission electron microscopy to directly observe metal cluster formation and distributions within the chromium-doped carbon films. At low doping (∼6 at. % Cr), Cr is uniformly distributed within the C matrix; at high doping (∼12 at. % Cr), Cr-rich clusters are formed. Analyzing electron energy loss spectroscopy Cr L2,3 white line ratios, we find that the Cr tends to be metallic-like when it is uniformly distributed in the C matrix and carbide-like in the Cr-rich clusters. The carbon is more diamond-like at low doping and more graphite/carbide-like at high doping according to the sp2/sp3 electron percentage measurements.
Trapped magnetic fields larger than 14 T in bulk YBa2Cu3O7−x
Authors: Fuchs G. , Schätzle P. , Krabbes G. , Gruß S. , Verges P. , Müller K.-H. , Fink J. , Schultz L.
Published: July 2002

High trapped fields were found in zinc-doped, bulk melt-textured YBa2Cu3O7−x (YBCO) material showing a pronounced peak effect in the field dependence of the critical current density. Trapped fields up to 1.1 T were found at 77 K at the surface of a YBCO disk (diameter 26 mm, height 12 mm). Very high trapped fields up to 14.35 T were achieved at 22.5 K for a YBCO disk pair (diameter 26 mm, height 24 mm) by the addition of silver and using a bandage made of stainless steel. The pinning forces and trapped fields obtained in bulk YBCO material are compared with results reported for melt-processed NdBa2Cu3O7−x and SmBa2Cu3O7−x.
Long-term thermal stability of Ti/Al/Pt/Au Ohmic contacts to n-type GaN
Authors: Lee Ching-Ting , Kao Hsiao-Wei
Published: July 2002

We present a study of the long-term thermal stability and low specific contact resistance of Ti/Al/Pt/Au multilayer contacts to n-type GaN. The Ohmic performance can be maintained up to 60 and 540 min for thermal annealing at 950 and 850 °C, respectively, and even longer than 600 min for thermal annealing at 750 °C. By comparing the specific contact resistances for Ti/Al/Pt/Au and Ti/Al/Au Ohmic contacts to n-type GaN, the long-term thermal stability may be deduced as due to the contribution of the Pt barrier for preventing Au penetration.
Relationship between segregation-induced intergranular fracture and melting in the nickel–sulfur system
Authors: Heuer J. K. , Okamoto P. R. , Lam N. Q. , Stubbins J. F.
Published: July 2002

The effect of S segregation to grain boundaries on the intergranular embrittlement of Ni has been studied at room temperature using Auger electron spectroscopy and slow strain rate tensile tests. The grain-boundary S concentration was varied by time-controlled annealing of dilute Ni–S alloy specimens at 625 °C. The ductile-to-brittle transition in Ni, as determined from percent integranular fracture and reduction-in-area measurements, occurred over a narrow range of S concentrations centered on 15.5±3.4 at. % S. This critical S concentration for 50% intergranular fracture of polycrystalline Ni is similar to the 14.2±3.3 at. % S required to induce 50% amorphization of single-crystal Ni by S+-ion implantation. This suggests that segregation-induced intergranular fracture, like implantation-induced amorphization, may be a disorder-induced polymorphous melting process. In agreement with experimental observations, the polymorphous melting curve for the Ni–S solid solution on the phase diagram drops rapidly to zero as the alloy composition approaches ∼18 at. % S. The critical grain-boundary concentration for intergranular fracture, while slightly less, is within experimental error of the concentration predicted for polymorphous melting as well as that measured for ion-implantation-induced amorphization.
Protected sample mount for vibrating sample magnetometer
Authors: Gretchnev Vasiliy T.
Published: July 2002

A modified sample mount is described that protects the sample during insertion in a vibrating sample magnetometer.
Supercapacitor electrodes from multiwalled carbon nanotubes
Authors: Frackowiak E. , Metenier K. , Bertagna V. , Beguin F.
Published: July 2002

Electrochemical characteristics of supercapacitors built from multiwalled carbon nanotubes electrodes have been investigated and correlated with microtexture and elemental composition of the materials. Capacitance has been estimated by cyclovoltammetry at different scan rates from 1 to 10 mV/s, galvanostatic discharge, and impedance spectroscopy in the frequency range from 100 kHz to 1 mHz. The presence of mesopores due to the central canal and/or entanglement is at the origin of an easy accessibility of the ions to the electrode/electrolyte interface for charging the electrical double layer. Pure electrostatic attraction of ions as well as quick pseudofaradaic reactions have been detected upon varying surface functionality. The values of specific capacitance varied from 4 to 135 F/g, depending on the type of nanotubes or/and their posttreatments. Even with moderate specific surface area (below 470 m2/g), due to their accessible mesopores, multiwalled carbon nanotubes represent attractive materials for supercapacitors as compared to the best activated carbons.
Effects of electron depletion on nonlinear dusty plasma oscillations
Authors: Tribeche M. , Hamdi R. , Zerguini T. H.
Published: July 2002

A kinetic analysis of the excitation of dust BGK (Bernstein–Greene–Kruskal) modes in a noncollisional dusty plasma is presented. It is found that in the case where all the electrons are attached to the dust particles, consequent modifications in the electrostatic potential structure can significantly influence the existence and properties of the nonlinear BGK modes. The derivation goes parallel to that done in standard kinetic analysis.
On the temperature, equipartition, degrees of freedom, and finite size effects: Application to aluminum clusters
Authors: Jellinek J. , Goldberg A.
Published: July 2002

The relationship between statistical ensembles (especially microcanonical ensemble) and dynamics, the equipartition theorem, and the notion of dynamical temperature are reexamined with an emphasis on finite size effects. A (dynamical) equipartition ansatz (postulate) is formulated and the notion of dynamical degrees of freedom is introduced. The utility of the dynamical degrees of freedom as an analysis tool is discussed and illustrated in applications to model aluminum clusters.
Development of the Los Alamos continuous high average-power microsecond pulser ion accelerator
Authors: Bitteker L. J. , Wood B. P. , Davis H. A. , Waganaar W. J. , Boyd I. D. , Lovberg R. H.
Published: July 2002

The continuous high average-power microsecond pulser (CHAMP) ion accelerator is being constructed at Los Alamos National Laboratory. Progress on the testing of the CHAMP diode is discussed. A direct simulation Monte Carlo computer code is used to investigate the puffed gas fill of the CHAMP anode. High plenum pressures and low plenum volumes are found to be desirable for effective gas puffs. The typical gas fill time is 150–180 μs from initiation of valve operation to end of fill. Results of anode plasma production at three stages of development are discussed. Plasma properties are monitored with electric and magnetic field probes. From this data, the near coil plasma density under nominal conditions is found to be on the order of 1×1016 cm−3. Large error is associated with this calculation due to inconsistencies between tests and the limitations of the instrumentation used. The diode insulating magnetic field is observed to result in lower density plasma with a more diffuse structure than for the cases when the insulating field is not applied. The importance of these differences in plasma quality on the beam production is yet to be determined.
Identification of Si and SiH in catalytic chemical vapor deposition of SiH4 by laser induced fluorescence spectroscopy
Authors: Nozaki Yoshitaka , Kongo Koichi , Miyazaki Toshihiko , Kitazoe Makiko , Horii Katsuhiko , Umemoto Hironobu , Masuda Atsushi , Matsumura Hideki
Published: July 2002

Radical species produced in catalytic chemical vapor deposition (CVD), often called hot-wire CVD, processes were identified by using a laser induced fluorescence technique. Ground state Si atoms could be detected at low pressures where collisional processes in the gas phase could be ignored. The electronic temperature of Si atoms just after the formation on the catalyzer (tungsten) surfaces was 1320±490 K, when the catalyzer temperature was 2300 K. By the addition of 0.5 Pa of Ar, the electronic temperature was lowered down to 450±30 K. The absolute density of Si atoms was 3±1×109 cm−3 at 10 cm below the catalyzer when the flow rate and the pressure of SiH4 were 0.5 sccm and 4 mPa, respectively. This density is just 0.3% of that of the parent SiH4 molecules. However, since the decay rate of Si atoms is fast, it can be concluded that atomic silicon is one of the major products on the heated catalyzer surfaces. SiH radicals could also be detected, but the production rate of this species is two orders of magnitude less than that of Si atoms. It was also discovered that volatile SiH4 molecules are produced by the atomic hydrogen attack on the amorphous silicon deposited on the chamber walls.
Compositional mapping of the argon–methane–hydrogen system for polycrystalline to nanocrystalline diamond film growth in a hot-filament chemical vapor deposition system
Authors: Lin T. , Yu G. Y. , Wee A. T. S. , Shen Z. X. , Loh Kian Ping
Published: July 2002

The transition in diamond crystal morphology from well-faceted microcrystalline to nanocrystalline phases as a function of increasing argon (Ar) concentration has been studied in a hot-filament chemical vapor deposition (HFCVD) system. The range of Ar concentration in a Ar–methane–hydrogen mixture that permits well-faceted diamond growth is up to 90%. At a concentration of 95.5%, a marked transition into nanocrystalline diamond phase could be observed. Although no graphitic phases were observed by transmission electron microscope and x-ray diffraction up to 95.5% Ar concentration, Raman analyses revealed a proportionate increase in amorphous carbon content with an increase in Ar concentration. The addition of Ar appears to create an electron-rich gas environment because a plasma can be readily discharged by applying a bias to the sample. Analysis of the plasma by optical emission spectroscopy revealed a linear correlation between Ar addition and the occurrence of C2 dimers in the plasma. Our results identified the narrow Ar-methane-hydrogen composition window that is effective for the growth of thick and smooth nanocrystalline diamond in HFCVD.
Lorentz microscopy of circular ferromagnetic permalloy nanodisks
Authors: Schneider M. , Hoffmann H. , Zweck J.
Published: July 2002

Circular permalloy elements were fabricated by a combination of electron beam lithography, thermal evaporation and liftoff technique on electron transparent membrane substrates. The magnetic properties have been studied by Lorentz transmission electron microscopy. In situ magnetizing experiments have been carried out to obtain information about the nucleation and propagation of magnetic domains within the permalloy nanodisks and to determine the nucleation and saturation fields. The diameter of the patterned elements has been varied between 180 and 950 nm, the height was 15 nm. The experiments showed that the vortex configuration is the most favorable state in zero field conditions of all investigated permalloy nanodisks.
An ab initio study of the interaction in dimethylamine dimer and trimer
Authors: Cabaleiro-Lago Enrique M. , Rı́os Miguel A.
Published: July 2002

Clusters consisting of two and three dimethylamine molecules were studied by using the HF, DFT/B3LYP, and MP2 ab initio methods in conjunction with the 6-31+G* and aug-cc-pvdz/cc-pvdz basis sets. Three different minima were located for the dimer, two of which form a N–H⋯N hydrogen bond and present similar interaction energies. The most stable structure of the dimer possesses Cs symmetry and an interaction energy of −15.6 kJ/mol. The least stable minimum has an interaction energy of −7.9 kJ/mol and exhibits no N–H⋯N hydrogen bonds (the interaction is established via the methyl hydrogen atoms). In all the structures, electron correlation exhibits a significant contribution (more than 40% of the overall energy). Only cyclic structures were considered for the trimer, the most stable of which possesses an interaction energy of −43.9 kJ/mol. The dipole moments for the dimer differ by up to 30% from the vector addition of the molecular dipoles (in the trimer minima, this difference amounts to 40%); also, N–H distances are lengthened by effect of the interaction (by up to 0.004 Å in the dimer and 0.009 Å in the trimer), which suggests the presence of cooperative phenomena. Nonadditive terms contribute about 12% of the overall interaction energy, the contribution being primarily of the inductive type. Calculations predict significant red shifts in the vibrational frequency of the N–H group when it takes part in the formation of a hydrogen bond. Similarly, the N–H wagging frequency undergoes a blue shift with hydrogen bonding.
Full torus Landau fluid calculations of ion temperature gradient-driven turbulence in cylindrical geometry
Authors: Leboeuf J. N. , Lynch V. E. , Carreras B. A. , Alvarez J. D. , Garcia L.
Published: July 2002

Results of Landau fluid calculations of ion temperature gradient-driven turbulence in cylindrical geometry but which cover the whole plasma cross section are reported. A simple gyrofluid model is used which evolves in time equations for the ion density or vorticity, the parallel ion velocity, and the ion temperature where Landau damping is included through a linear closure relation. Adiabatic electrons and the electrostatic approximation are assumed to hold. Linear calculations indicate that the growth rates are significantly reduced in the presence of Landau damping. Nonlinear single helicity calculations serve to illustrate the spatial localization of the turbulence in the presence of Landau damping. Finally nonlinear multiple helicity calculations performed with three different values for the ratio of the central ion Larmor radius to the plasma minor radius denoted by ρ* exhibit a definite linear scaling of all the fluctuation characteristics, such as levels, scale sizes, quasilinear profile modifications, self-generated poloidal flows, and heat diffusivities, with ρ*.
An improved automated anodization apparatus for fabricating nanostructure devices and porous silicon
Authors: Garman C. , Sines P. , McGinnis S. P. , Das B.
Published: July 2002

This note describes an improved anodization apparatus that provides enhanced safety and efficiency, and is suitable for large-scale volume production. The improved anodization apparatus also provides increased electrolyte temperature control, and allows flexibility in the size and shape of the substrate. Overall, this equipment will find wide applications in the fabrication of template-based semiconductor nanostructures, porous silicon, and other devices that require electrochemical processing.
Manifestation of the band structure of the semimetal in the tunneling conductance of a metal–insulator–semimetal junction
Authors: Khachaturov A. I. , Hatta E. , Svistunov V. M.
Published: July 2002

The contribution of the electron band of the semimetal to the differential conductance of a metal–insulator–semimetal tunnel junction is found. It is established that the tunneling conductance depends substantially on the barrier parameters. The conductance curve exhibits a convexity with a maximum that in general does not correspond to the edges of the band or to a saddle point of the band, as has been proposed previously. It is shown that the band structure is well resolved in the second derivative of the current with respect to the voltage, d2I/dV2.
Analog of the Grüneisen parameter for orientational excitations in the low-temperature phase of fullerite C60
Authors: Natsik V. D. , Podol’skiı̆ A. V.
Published: July 2002

A theoretical analysis of the heat capacity and thermal expansion of the low-temperature sc phase of fullerite C60 is made, based on the concepts of double-well orientational states of the molecules — the pentagonal and hexagonal configurations. To describe the coupling of the orientational states of the molecules with macroscopic deformations of the crystal lattice, it is assumed that the deformations contribute corrections to the energy parameters of the double-well states, and a parameter g(or) is introduced which is equivalent to the Grüneisen parameter in the theory of the thermal expansion of harmonic crystals. It is shown that this model can be used to obtain a qualitative description of the anomalies observed in the thermal properties of fullerite C60 near the orientational glass temperature Tg≃90 K, and the possibilities for obtaining empirical estimates of the parameter g(or) are discussed.
On the theory of carrier-induced ferromagnetism in diluted magnetic semiconductors
Authors: Semenov Yu. G. , Ryabchenko S. M.
Published: July 2002

Two different approaches (presented in the literature as alternative approximations) to the problem of carrier-induced ferromagnetism in the system of disordered magnetic ions of a diluted magnetic semiconductor are analyzed. They are based on a self-consistent procedure for the mean exchange fields and the RKKY interaction. Calculations in the framework of an exactly solvable model are carried out, and it is shown that these approaches stem from two different contributions to the magnetic susceptibility. One stems from the diagonal part of the carrier-ion exchange interaction and corresponds to the mean field approximation. The other one stems from the off-diagonal part of the same interaction and describes the indirect interaction between localized spins via free carriers. These two contributions can give rise to different magnetic properties. Thus the aforementioned contributions are complementary and not alternative to each other. A general approach is proposed and compared with different approximations to the problem under consideration.
Low-temperature strain aging in In–Pb alloys under conditions of stress relaxation
Authors: Fomenko L. S.
Published: July 2002

In the stress-relaxation regime the dynamic strain aging (DSA) in single crystals of the substitutional solid solutions of substitution In–Pb with 6 and 8 at. % Pb is investigated at temperatures of 77–205 K. It is determined how the DSA-related post-relaxation hardening depends on the duration of the stress relaxation, the rate of change of the stress at the end of the relaxation, the temperature, the concentration of the alloy, the flow stress, and the degree of deformation. It is shown that the DSA kinetics is described by an equation of the Harper type with an exponent of 1/3 and a low value of the activation energy for the process (0.3–0.34 eV), which makes for a low temperature for the onset of DSA (∼0.17 Tm, where Tm is the melting temperature) and is indicative of a pipe character of the diffusion. It is assumed that the obstacles to the motion of dislocations in these crystals are impurity complexes, the strength of which increases during DSA as a result of the pipe diffusion of impurity atoms along dislocations.
Current-driven dust ion-acoustic instability in a collisional dusty plasma with charge fluctuations
Authors: Tribeche M. , Zerguini T. H.
Published: July 2002

The extended fluid analysis of the excitation of dust ion-acoustic waves (DIAWs) in a collisional dusty plasma [Merlino, IEEE Trans. Plasma Sci. 25, 60 (1997)] is reconsidered to include self-consistently the fluctuations in the charges of the dust grains, which liberate or capture electrons and protons. The numerical results show that the dust charge fluctuations can have a significant influence on the excitation of the DIAW and may deeply modify its nonlinear features.
Optical strain sensor using median density grating foil: Rivaling the electric strain gauge
Authors: Zhao Bing , Xie Huimin , Asundi Anand
Published: July 2002

In this article, a novel compact optical diffraction strain sensor using medium density grating foil is presented. The grating, generally with a frequency of 300–500 lines/mm attached on the surface of a specimen, is illuminated by a focused laser beam. The centroids of diffracted beam spots from the grating are automatically determined with two position-sensitive detector sensors connected to a personal computer. The shift of second-order diffracted beam spots due to the specimen deformation is then detected. The influences of noise sources and system geometry on system performances, such as sensitivity, spatial resolution, strain range, and measurement linearity are discussed. Strain sensitivity of 1.3 microstrain can be achieved. The spatial resolution for strain measurement of 0.4 mm is attainable. The system can be used for continuous measurement and for both static and dynamic tests.
Structure, surface composition, and electronic properties of β-In2S3 and β-In2−xAlxS3
Authors: Kamoun N. , Belgacem S. , Amlouk M. , Bennaceur R. , Bonnet J. , Touhari F. , Nouaoura M. , Lassabatere L.
Published: July 2002

β- In 2 S 3 and β-In2−xAlxS3 thin films have been deposited on different substrates using the spray pyrolysis technique at 320 °C. X-ray diffraction, atomic force microscopy, and scanning electron microscopy were used to characterize the structure of the films; the surface compositions of the films were studied by Auger electrons spectroscopy and energy dispersive spectrometry (EDS), the work function and the photovoltage by the Kelvin method. Using these techniques, we have specified the effect of the nature of the substrate, of its surface morphology, of the introduction of small amounts of Al in the layer, on the properties of the films. The best crystallized of β-In2S3 were obtained for deposits on pyrex. This was improved by the introduction of Al atoms. The work function differences (φmaterial–φprobe) for β-In2S3 and β-In2−xAlxS3 deposited on steel were equal to −150 meV and to −180 meV, respectively. Putting Al atoms in the film increases φm (by about 30 meV) and induces the formation of a negative surface barrier. The concentration of In, S, and O elements increased when the samples were annealed under a vacuum, whereas the concentration of carbon decreased. The best composition was obtained for In2S3 deposited on SnO2 and annealed. The introduction of Al increases O and C concentrations and reduce In, Cl, and S concentrations. Analysis of the film compositions by EDS gives the following concentrations [In]=37%, [S]=52%, and [Cl]=11%.
The method of ion current measurement on capacitive-coupled plasma
Authors: Iseki Yasushi , Hayashi Kazuo , Noda Etsuo
Published: July 2002

A small device, the conduction current probe, has been developed for the multi-point observation of ion currents. The probes are mounted on an electrode of a capacitive-coupled rf plasma source. The probe obtains the conduction current entering the electrode as a function of time by shielding the rf displacement current. The conduction current consists of the ion current as well as the electron one. The ion current is nearly constant although the electron one synchronizes with the rf electric field and flows in the short time of a rf cycle. Therefore, the ion current is obtained from the constant region of the conduction current. The experiments on a rf magnetron have revealed that the probe is a useful device for studying the parametric properties of the plasma source.
Magnetodynamic nonlinearity of the electrical properties of uncompensated metals
Authors: Sobol V. R. , Mazurenko O. N.
Published: July 2002

The magnetodynamic nonlinearity of the electrical properties of uncompensated metals, wherein the drift of charge carriers at a high density in crossed electric and magnetic fields leads to generation of a self-field of the current, is investigated experimentally and analytically. The experiment is done on cylindrical conductors made from high-purity polycrystalline aluminum, in an arrangement in which the radial current is acted on by an external magnetic field coaxial to the sample. The electric potential and the nonlinear correction to it are determined over a wide range of values of the energy dissipation, all the way up to levels corresponding to the boiling crisis of liquid helium. In the approximation that the contributions to the resistive effect of the external field and self-field are additive, the results of a calculation based on the macroscopic field equations are found to be in good agreement with experiment. Questions pertaining to the concentration of magnetic field energy of the current for a cylindrical geometry of the conductor are discussed in the approximations of long and short solenoids.
Relaxation dynamics in the high-frequency crystal-field spectroscopy of PrNi5 point contacts
Authors: Balkashin O. P. , Brill T. M. , Jansen A. G. M. , Wyder P. , Sukhodub G. L. , Yanson I. K.
Published: July 2002

High-frequency point-contact (PC) spectroscopy is used to investigate the kinetics of relaxation processes in the intermetallic rare-earth compound PrNi5. A difference is observed in the spectral response between the conventional low-frequency PC data and the response signal to microwave and far-infrared radiation of PrNi5–Cu point contacts. This difference is connected with the f-shell electronic levels (CEF levels) and phonon temporal dynamics. The phonon reabsorption contribution to the spectra above the Debye energy decreases for microwave and far-infrared frequencies. However, the crystal-field contribution to the spectra at 4.2 meV is enhanced for high frequencies, reflecting the relaxation processes specific for these Fermi-statistics electronic excitations. The characteristic frequency for CEF-level relaxation is evaluated as ∼200 GHz.
Electrophysical properties of crystals containing small superconducting inclusions
Authors: Sugakov V. I. , Shevtsova O. N.
Published: July 2002

The influence of superconducting inclusions on the electrophysical properties of a semiconductor or insulator crystal is investigated. The critical magnetic field of an isolated spherical inclusion is calculated under the assumption that the radius of the inclusion is smaller than or of the order of the coherence length. The conductivity of a crystal containing a set of inclusions is calculated as a function of temperature and magnetic field. It is assumed in the conductivity calculations that the concentration of inclusions is insufficient for the appearance of superconductivity in the whole sample (i.e., it is below the percolation threshold). It is shown that the presence of superconducting inclusions leads to a sharp increase in the conductivity of the sample at low temperatures and to a strong dependence of the conductivity on magnetic field (magnetoresistance). The magnetoresistance is due to suppression of the superconductivity in the inclusions as the magnetic field is increased. The influence of a variance in the dimensions of the inclusions on the temperature and magnetic-field dependence of the conductivity is investigated.
Raman scattering in the vicinity of the ferroelastic phase transition to the monoclinic phase in KSc(MoO4)2
Authors: Nesterenko N. M. , Peschanskiı̆ A. V. , Fomin V. I.
Published: July 2002

The low-energy lattice modes are investigated above and below the temperature of the phase transition from the trigonal to the monoclinic phase in KSc(MoO4)2 by the Raman scattering method. The Raman spectra exhibit anomalies at temperatures above the phase transition to the monoclinic phase (T∼260 K) in the region of external oscillations of the tetrahedral anion. Anomalous behavior of the damping Ag of the soft mode is observed in the temperature region 240–260 K. A model of the phase transition is discussed.
Optical constants of indium bromide
Authors: Kolin’ko M. I. , Bovgyra O. V. , Piasecki M.
Published: July 2002

The optical functions of layered indium bromide single crystals are determined by the Kramers–Kronig technique using the polarized reflection spectra measured in the 2–30 eV region at liquid helium temperature. The spectra and the corresponding optical functions are found to exhibit strong anisotropy due to features of the group-theoretic selection rules and the crystal structure of indium bromide. The results are interpreted in comparison with the known optical properties and energy-band parameters of isoelectronic and isostructural (in relation to InBr) semiconductors. The origin of the principal structures of the spectra which are important for determining the quantitative parameters of the energy-band structure of InBr is identified.
On the appearance of an orthogonal component of the spontaneous polarization in linear pyroelectrics in the low-temperature region
Authors: Novik V. K. , Gavrilova N. D.
Published: July 2002

The appearance of an orthogonal component of the spontaneous polarization in the absence of signs of ferroelectricity does not violate the Curie–Neumann principle. These components are formed during the growth of a linear pyroelectric and are inherent to it always, but their values are several orders of magnitude smaller than the spontaneous polarization along the preferred polar axis. The low-temperature appearance of the components is due solely to a feature of the mechanism of their pyroelectricity — disordering of the charged structural units in asymmetric potential wells.
Radiative recombination via intrinsic defects in CuxGaySe2
Authors: Bauknecht A. , Siebentritt S. , Albert J. , Lux-Steiner M. Ch.
Published: July 2002

A detailed analysis of the radiative recombination processes in CuxGaySe2 epitaxial layers is presented aiming at an investigation of the intrinsic defect levels as a function of chemical composition. CuxGaySe2 is grown by metalorganic vapor phase epitaxy to allow a precise control of composition. Temperature and excitation intensity dependent photoluminescence is used to identify different recombination mechanisms and to determine the ionization energies of the defect levels involved. Defect-correlated optical transitions in Cu-rich epilayers are described in a recombination model consisting of two acceptor and one donor levels showing ionization energies of (60±10) meV, (100±10) meV, and (12±5) meV, respectively. The identification of a shallow compensating donor in CuxGaySe2 and the assignment of the 100 meV state to an acceptor are the most important new aspects in this model. Photoluminescence properties of layers showing Ga-rich compositions are discussed in a model of highly doped and highly compensated semiconductors—the model of fluctuating potentials.
Evolution of perturbation in charge-varying dusty plasmas
Authors: Popel S. I. , Golub’ A. P. , Losseva T. V. , Bingham R. , Benkadda S.
Published: July 2002

The nonstationary problem of the evolution of perturbation and its transformation into nonlinear wave structure in dusty plasmas is considered. For this purpose two one-dimensional models based on a set of fluid equations, Poisson’s equation, and a charging equation for dust are developed. The first (simplified) model corresponds to the case [Popel et al., Phys. Plasmas 3, 4313 (1996)] when exact steady-state shock wave solutions can exist. This simplified model includes variable-charged dust grains, Boltzmann electrons, and inertial ions. The second (ionization source) model takes into account the variation of the ion density and the ion momentum dissipation due to dust particle charging as well as the source of plasma particles due to ionization process. The computational method for solving the set of equations which describe the evolution in time of a nonlinear structure in a charge-varying dusty plasma is developed. The case of the evolution of an intensive initial nonmoving region with a constant enhanced ion density is investigated on the basis of these two models. The consideration within the ionization source model is performed for the data of the laboratory experiment [Luo et al., Phys. Plasmas 6, 3455 (1999)]. It is shown that the ionization source model allows one to obtain shock structures as a result of evolution of an initial perturbation and to explain the experimental value of the width of the shock wave front. Comparison of the numerical data obtained on the basis of the ionization source model and the simplified model shows that the main characteristic features of the shock structure are the same for both models. Nevertheless, the ionization source model is much more sensitive to the form of the initial perturbation than the simplified model. The solution of the problem of the evolution of perturbation and its transformation into shock wave in charge-varying dusty plasmas opens up possibilities for description of the real phenomena like supernova explosions as well as of the laboratory and active space and geophysical experiments.
Polymer melt droplets adsorbed on a solid wall: A Monte Carlo simulation
Authors: Milchev Andrey , Binder Kurt
Published: July 2002

Using a coarse-grained bead-spring model of flexible polymers, we study the contact angle of polymer melt droplets sitting at a flat structureless wall, when the strength ε of the adsorption potential Vwall(z)=ε/z3 is varied. For this purpose, droplets containing 2048 or 4096 monomers for chain lengths N=16 and N=32 were carefully equilibrated at temperatures in the range from 74% to 82% of the Theta temperature, and the density profile of these droplets both in the z direction perpendicular to the substrate surface and in the radial direction was obtained. Beyond a critical value of ε we find that the contact angle vanishes, i.e., the droplets spread out and form a flat film. Such flat polymer films are also studied with considerably more polymers (up to 24 576 monomers contained in the simulation box). It is shown that the density profile ρ(z) is affected by the hard wall (exhibiting the characteristic layering oscillations) up to about z=5 (measuring lengths in units of the length of an effective bond), while at larger z the profile is flat and has the melt density at that temperature, with an interface to the “gas” at about z=20. Analyzing the capillary wave spectrum of the interfacial fluctuations, the surface tension of the polymer melt is extracted. Via the anisotropy of the local pressure near the wall, the wall excess free energy of the polymer melt is found as well, and the Young equation is tested. Thus methods have been developed that allow a systematic study of polymer–wall interactions and wetting vs dewetting behavior.
Suppression of superconductivity by crystallographic defects in epitaxial Sr2RuO4 films
Authors: Zurbuchen Mark A. , Jia Yunfa , Knapp Stacy , Carim Altaf H. , Schlom Darrell G. , Zou Ling-Nian , Liu Ying
Published: July 2002

Epitaxial Sr2RuO4 thin films grown by pulsed-laser deposition from high-purity (99.98%) Sr2RuO4 targets on (001) LaAlO3 were found to be not superconducting down to 0.4 K. Structural disorder is believed to be responsible. A correlation was observed between higher resistivity ratios in electrical transport measurements and narrower x-ray diffraction rocking curve widths of the Sr2RuO4 films. High-resolution transmission electron microscopy revealed that the dominant structural defects, i.e., the defects leading to the observed variation in rocking curve widths in the films, are {011} planar defects, with a spacing comparable to the in-plane superconducting coherence length of Sr2RuO4. These results imply that minimizing structural disorder is the key remaining challenge to achieving superconducting Sr2RuO4 films.
Giant volume magnetostriction in CMR manganites R1−xSrxMnO3(R=Sm, Nd)
Authors: Abramovich A. I. , Michurin A. V.
Published: July 2002

Magnetization, ac initial magnetic susceptibility, resistance, magnetoresistance, thermal expansion and magnetostriction measurements are made on R1−xSrxMnO3 (R=Sm, x=0.33, 0.40, 0.45; R=Nd, x=0.33, 0.45) compounds. For all compounds in the TC region we observe a large volume contraction ΔV/V≈0.1% and unusual behavior of the volume magnetostriction ω, namely, a peak of anomalous magnitude of negative volume magnetostriction on the ω(T) curve. We obtain a giant negative volume magnetostriction of ∼5×10−4 at a relatively low magnetic field B=0.9 T and ∼10−3 at a high magnetic field B=13 T for Sm samples. The magnetostriction of Nd compounds is one order of magnitude less. For all compounds the giant magnetostriction is accompanied by colossal negative magnetoresistance equal to 78, 72, and 44% at B=0.9 T for Sm compounds with x=0.33, 0.40, and 0.45, respectively. All of the observed properties are explained in the framework of an electronic phase separation model.
Electronic structure and magnetostrictive sensitivity of Fe–B metallic glasses
Authors: Beznosov A. B. , Fertman E. L. , Eremenko V. V. , Desnenko V. A.
Published: July 2002

The effect of mechanical tensile stresses 0⩽σ⩽62 MPa on the low-field (0⩽H⩽45 Oe) magnetization curves of the metallic glasses Fe100−xBx (x=14,16,17,20) is studied at temperatures of 77 and 300 K. The correlation between the electronic structure of the glasses and their magnetostrictive sensitivity κs is revealed: the eutectic metallic glass Fe83B17, which possesses a special electronic structure with a 30% lower conduction (sp) electron density, has a value of κs differing substantially from that of the other metallic glasses studied. Under low stresses (0⩽σ⩽22 MPa) the eutectic alloy possesses a magnetostrictive sensitivity κs(σ1) which is higher than that of the rest of the alloys studied, while under high stresses (22 MPa⩽σ⩽62 MPa) its magnetostrictive sensitivity κs(σ2) is close to zero.
Effect of a negative biquadratic interaction on the phase states and spectra of coupled magnetoelastic waves of an easy-plane ferromagnet
Authors: Fridman Yu. A. , Kozhemyako O. V. , Eingorn B. L.
Published: July 2002

The spectra of the coupled magnetoelastic waves of an easy-plane ferromagnet with a negative biquadratic interaction are investigated. It is shown that in this case the existence region of the quadrupolar phase is narrowed substantially in comparison with the case of a positive biquadratic interaction. The phase diagram of the system is constructed.
On the nonmonotonic dependence of the critical temperature of the superconducting transition on the carrier density in fullerite C60
Authors: Loktev V. M.
Published: July 2002

A simple qualitative explanation for the bell-shaped form of the functions Tc(nf) in solid C60 is proposed (Tc is the critical temperature of the superconducting transition, and nf is the number of carriers (fermions)—electrons or holes—per molecule). This explanation is based on the many-fold degeneracy of the initial fullerene molecular states from which the conduction and valence bands are formed and the interaction of the carriers with Jahn–Teller intramolecular vibrations.
Effect of phase transformation on remanence enhancement in bulk Fe–Pt magnets
Authors: Xiao Q. I. , Thang P. D. , Brück E. , de Boer F. R. , Buschow K. H. J.
Published: July 2002

We have studied the atomic disorder–order transformation occurring around the equiatomic composition in Fe–Pt ingots by isothermal annealing at temperatures well below the face-centered-cubic–face-centered-tetragonal (fcc–fct) transformation temperature. We have determined the relative amount of the low-temperature hard-magnetic fct phase precipitated in the high-temperature magnetically soft fcc phase by means of x-ray diffraction. As a function of annealing time, the particle size and the relative amount of the fct phase increase at the expense of the fcc phase. We have followed these changes by means of magnetic measurements. The coercivity was found to increase continuously with annealing time, eventually reaching a maximum. The occurrence of remanence enhancement and the continuously changing degree of exchange coupling between the magnetically soft and the hard phase are explained in terms of the Kneller–Hawig model [E. F. Kneller and R. Hawig, IEEE Trans. Magn. MAG-27, 3588 (1991)].
Air flow actuation of micromechanical oscillators
Authors: Neuzil P. , Sridhar U. , Ilic B.
Published: July 2002

Conventional techniques for the actuation and detection of micro- and nanoelectromechanical structure resonant frequency involve rather inconvenient structure actuation or an extremely sensitive detection system. In an alternate approach, we demonstrate a method to actuate micromachined low-stress silicon-oxide cantilevers by air flow. The output signal related to the amplitude of oscillation was enhanced by more than three orders of magnitude in contrast to the amplitude gain due to the thermal noise response of the system. The quality factor dependence with varying flow rate was also observed.
Magnetic and conversion electron Mössbauer spectral study of amorphous thin films of DyxFe100−x and Dy20Fe80−yCoy
Authors: Fleury-Frenette K. , Delwiche J. , Grandjean F. , Vandormael D. , Long Gary J.
Published: July 2002

Amorphous thin films of DyxFe100−x and Dy20Fe80−yCoy, with various x and y values and of ∼40 nm thickness, have been prepared by sputtering on polyimide films. Their magnetization curves and the Mössbauer spectra indicate that at 295 K the iron moments are preferentially oriented parallel to the film in Dy2Fe98 and that Dy6Fe94 is paramagnetic. The DyxFe100−x thin films, where x is 17, 20, 24, 29, 32, 35, and 37, show perpendicular magnetic anisotropies and moderate coercive fields of at most 150 kA/m, whereas the Dy20Fe80−yCoy thin films, where y is 8, 13, 16, and 20, thin films show stronger perpendicular anisotropies and larger coercive fields of ∼400 kA/m. The introduction of cobalt into the amorphous thin films increases their coercive field and the perpendicular magnetic anisotropy. The Mössbauer spectra of the DyxFe100−x and Dy20Fe80−yCoy amorphous thin films consist of broadened sextets which have been analyzed with a distribution of hyperfine fields by assuming that the iron moments are oriented perpendicular to the plane of the film. Detailed fits of the Mössbauer spectrum of Dy20Fe80 indicate that the cone angle of the iron magnetic moments cannot be determined with accuracy. The average hyperfine fields in the DyxFe100−x amorphous thin films are smaller than those in the crystalline dysprosium–iron intermetallic compounds. The average hyperfine field increases from ∼140 kOe in the DyxFe100−x films to ∼220 kOe in the Dy20Fe80−yCoy films, an increase which is in agreement with the increase in the saturation magnetization. The x dependence of the isomer shift indicates that there is strong dysprosium–iron bonding, whereas the y dependence of the isomer shift reveals an enhancement of the d-electron localization. From earlier x-ray magnetic circular dichroism results and the Mössbauer spectral results presented herein, iron magnetic moments of 0.87 or 0.67 μB, corresponding to 2.9 or 2.8 holes in the iron 3d band, have been obtained for the DyxFe100−x amorphous thin films with x greater or smaller than 27, respectively.
Mulliken population analysis based evaluation of condensed Fukui function indices using fractional molecular charge
Authors: Kinkar Roy Ram , Hirao Kimihiko , Krishnamurty Sailaja , Pal Sourav
Published: July 2002

A thorough study on the nature of Mulliken population analysis (MPA) based condensed Fukui function (FF) indices has been performed. It is claimed analytically that nothing can be predicted about the sign of condensed FF indices, even when evaluated by using very small fractional molecular charge (i.e., approximately following the analytical definition of FF indices). The corresponding numerical demonstrations on different chemical systems confirm our claim.
Shear Alfvén waves in a magnetic beach and the roles of electron and ion damping
Authors: Vincena S. , Gekelman W. , Maggs J.
Published: July 2002

Experiments are performed in the Large Plasma Device (LaPD) [Gekelman et al., Rev. Sci. Instrum. 62, 2875 (1991)] at the University of California, Los Angeles to study the propagation of the shear Alfvén wave in a parallel gradient of the background magnetic field. The waves are excited by modulating a field-aligned electron current drawn to a disk antenna with a radius on the order of the electron skin-depth, δ=c/ωpe. The resulting shear waves have a nonzero parallel electric field and propagate both parallel and perpendicular to the background magnetic field. In this experiment, the wave is launched in a region where its frequency, ω equals one-half the local ion-cyclotron frequency, ωci and the local Alfvén speed, vA, is approximately equal to the electron thermal speed, v̄e. The wave propagates along a slowly decreasing background field to where ω=ωci and vA≈v̄e/2. The wave thus propagates from a region where Landau damping is significant to where ion-cyclotron damping dominates. Detailed two dimensional measurements of the wave magnetic field morphology are presented. The measured wavelength decreases in accord with WKB solutions of a modified wave equation. Wave damping is also observed and dissipation by both ions and electrons is required in the WKB model to fit the data. Suppression of the damping via electrons in the model results in a predicted wave magnetic field amplitude twenty times larger at the ion-cyclotron resonance point than observed.