bluuebunny/crossref_metadata_2025 huggingface dataset:
Spectroscopic evidence of the formation of N–H and N–D complexes in plasma hydrogenated and deuterated ZnTe:N layers
Authors: Pelletier H. , Lusson A. , Theys B. , Chevallier J. , Magnéa N.
Published: July 2002

Homoepitaxially grown nitrogen-doped ZnTe layers have been exposed to a hydrogen (deuterium) plasma. After hydrogen (deuterium) diffusion, an infrared absorption band appears at 3346 cm−1 (2489 cm−1). It is assigned to the vibrational stretching mode of the N–H (N–D) bond. It is also shown that the absence of such detectable bands in heteroepitaxially grown ZnTe/CdZnTe layers can be explained by thermal strains originating from the difference between the ZnTe and the CdZnTe thermal expansion coefficients.
Depth-dependent spectroscopic defect characterization of the interface between plasma-deposited SiO2 and silicon
Authors: Schäfer J. , Young A. P. , Brillson L. J. , Niimi H. , Lucovsky G.
Published: July 2002

We demonstrate the use of low-energy cathodoluminescence spectroscopy (CLS) to study optical transitions at defect bonding arrangements at Si–SiO2 interfaces prepared by low-temperature plasma deposition. Variable-depth excitation achieved by different electron injection energies provides a clear distinction between luminescence derived from (i) the near-interface region of the oxide film, (ii) the Si–SiO2 interface, and (iii) the underlying crystalline Si substrate. Cathodoluminescence bands at ∼0.8 and 1 eV are assigned to interfacial Si atom dangling bonds with different numbers of back-bonded Si and O atoms. CLS also reveals higher photon energy features: two bands at ∼1.9 and 2.7 eV assigned to suboxide bonding defects in the as-grown oxide films, as well as a substrate-related feature at ∼3.4 eV. The effects of hydrogenation at 400 °C and rapid thermal annealing at 900 °C, and especially the combination of both process steps is shown to dramatically reduce the intensities of the CLS features assigned to interfacial and suboxide bonding defects.
Cobalt nanoclusters in silica glass: Nonlinear optical and magnetic properties
Authors: Cattaruzza E. , Gonella F. , Mattei G. , Mazzoldi P. , Gatteschi D. , Sangregorio C. , Falconieri M. , Salvetti G. , Battaglin G.
Published: July 2002

Fused silica plates were implanted with Co ions at room temperature at the energy of 50 keV and to the fluence of 4×1016 ions cm−2. The formation of metal nanoclusters was observed by transmission electron microscopy. The cluster size distribution is narrow with a mean-diameter value of about 3 nm. Atomic in-depth distribution was determined by Rutherford backscattering spectrometry, whereas the cobalt chemical state was characterized by electron spectroscopies. Nonlinear refractive index n2 is of the order of 0.2 cm2 G W−1, as determined by the Z-scan technique at a wavelength of 770 nm for 130 fs long pulses at a 76 MHz repetition rate. Zero-field-cooled and field-cooled magnetization curves at the liquid-helium temperature exhibit features of superparamagnetic behavior that are characteristic of assemblies of single-domain nanoparticles.
Electromechanical properties of electrostrictive poly(vinylidene fluoride–trifluoroethylene) copolymer
Authors: Zhao Xing-Zhong , Bharti Vivek , Zhang Q. M. , Romotowski T. , Tito F. , Ting R.
Published: July 2002

We report a large electrostrictive strain in electron irradiated poly(vinylidene fluoride–trifluoroethylene) copolymer at a composition with 65 mol % vinylidene fluoride, which also exhibits a large ratio of strain to applied field (∼275 pm/V). The strain response is nearly independent of the external driving condition (unipolar or bipolar field) and does not change with temperature in about 20 °C temperature range near room temperature. Moreover, near room temperature, the material can reach a relatively high quasistatic longitudinal electromechanical coupling factor k33∼0.33.
Superlattice AlAs/AlInAs-oxide current aperture for long wavelength InP-based vertical-cavity surface-emitting laser structure
Authors: Ohnoki N. , Koyama F. , Iga K.
Published: July 2002

A superlattice AlAs/AlInAs structure which can be formed on an InP substrate is proposed and demonstrated for use in oxide confinement long wavelength surface emitting lasers. The large strain of AlAs layers is relaxed by the use of a superlattice structure showing no defects and uniform oxidations. Also, an AlAs layer on an InP substrate provides us with a relatively large heterobarrier, and will be useful for improving temperature characteristics of long-wavelength vertical-cavity surface-emitting lasers. A current aperture of a few micrometers in diameter was formed by precisely controlling the oxidation time. We have demonstrated a current confinement by this oxide aperture. Low-threshold long-wavelength vertical-cavity surface-emitting lasers with this oxide confinement structure are expected.
Mechanism of generation of f–f radiation in semiconductor heterostructures
Authors: Zegrya G. G. , Masterov V. F.
Published: July 2002

A mechanism is proposed by which inverse distribution of Er3+ f electrons can be created in semiconductors with quantum wells. It is shown that, if the electrons are localized in quantum wells, the Coulomb excitation of Er3+ f electrons by electrons of the semiconductor has resonant nature. The resonant Coulomb excitation of f electrons I15/2→I11/2 produces electron population inversion for the I13/2 level. A possibility is demonstrated of developing a laser with wavelength λ=1.54 μm based on I13/2→I15/2 transitions.
Time resolved magneto-optical spectroscopy on InGaAs nanostructures grown on (311)A and (100)-oriented substrates
Authors: Lomascolo M. , Cingolani R. , Vaccaro P. O. , Fujita K.
Published: July 2002

We present a time-resolved magneto-photoluminescence study of In0.5Ga0.5As self-organized nanostructures grown on (100) and (311)A-oriented substrates by molecular beam epitaxy. The (311)A-oriented samples have a corrugated surface realizing a sort of quantum wire array, whereas the (100) samples exhibit Stranski–Krastanow islands. The different morphology of the nanostructures is reflected in the different electron/hole wave-function confinement along the three directions (perpendicular and parallel to the growth direction). We discuss the effects of the magnetic field (up to 8 T) on the recombination mechanism in these InGaAs nanostructures and on the transient dynamics of photoluminescence. We observe a clear decrease of the photoluminescence decay time with magnetic field flux indicating the exciton nature of the radiative low-temperature recombination processes.
Selective-area formation of Si microstructures using ultrathin SiO2 mask layers
Authors: Yasuda T. , Hwang D. S. , Park J. W. , Ikuta K. , Yamasaki S. , Tanaka K.
Published: July 2002

We have developed a technique to form Si microstructures at preassigned positions on Si substrates. The key element of this technique is resistless patterning of ultrathin SiO2 mask layers by direct electron-beam exposure. Selective-area growth of Si was accomplished by two different chemistries: flow-modulated plasma-enhanced chemical vapor deposition (CVD) at 473 K or ultra-high-vacuum CVD at 853 K. Epitaxial deposition was achieved by the latter growth method when a mask layer with minimum thickness for deposition selectivity (approximately 0.2 nm) was employed.
Adjustable emissions from silicon-rich oxide films prepared by plasma-enhanced chemical-vapor deposition
Authors: Tong J. F. , Hsiao H. L. , Hwang H. L.
Published: July 2002

Observation of sequentially adjustable, intense, and stable emissions at room temperature from amorphous silicon-rich oxide thin films without any thermal annealing is reported. Hydrogenated amorphous silicon-rich oxide (SiOx:N:H, 0<x<2) thin films were deposited by plasma-enhanced chemical-vapor deposition with a mixture of 5% silane in argon and nitrous oxide gases. The strong naked-eye-seeing photoluminescence (blue–white–orange) could be adjusted by changing the process gases flow rate ratio Γ (=[SiH4]/[N2O]). The degree of silicon richness was determined from secondary ion mass spectrometry. The microstructure-bonding configuration was examined by Fourier transform infrared spectroscopy. The implications of these studies for understanding the origins of silicon-based luminescence are discussed.
Strong isotope effects in the dissociation kinetics of Si–H and Si–D complexes in GaAs under ultraviolet illumination
Authors: Chevallier J. , Barbé M. , Constant E. , Loridant-Bernard D. , Constant M.
Published: July 2002

Under ultraviolet (UV) illumination of GaAs with photon energies above 3.5 eV, Si–H complexes are known to be efficiently dissociated at room temperature. Studying the dissociation kinetics of Si–H and Si–D complexes in GaAs, we have observed that, for a given incident UV photon density, the concentration of dissociated Si–D complexes is 10–20 times below the concentration of dissociated Si–H complexes. This strong isotope effect is discussed under the light of recent excitation models of Si–H(D) bonds at the surface of silicon and at the Si/SiO2 interface.
Structure observed in measured electron energy distribution functions in capacitively coupled radio frequency hydrogen plasmas
Authors: Mahony C. M. O. , McFarland J. , Steen P. G. , Graham W. G.
Published: July 2002

Electron energy probability functions measured with a passively compensated Langmuir probe in asymmetric capacitively coupled hydrogen and deuterium plasmas exhibit structure. The otherwise relatively continuous distribution appears to have an abrupt peak in electron density near 5 eV. This structure occurs at a higher energy in deuterium than hydrogen and there is a correlation between floating potential and the voltage at which the structure is observed in the second derivative of the I(V) characteristic. While the cause of the structure has yet to be clarified, spectroscopic observations and computer-based hydrogen models indicate that the high energy tail of the distribution is strongly modulated during the radio frequency cycle. The effect of this modulation on plasma properties and probe measurements has yet to be explored.
Degradation behavior in the remnant polarization of SrBi2Ta2O9 thin films by hydrogen annealing and its recovery by postannealing
Authors: Kwon Oh Seong , Hwang Cheol Seong , Hong Suk-Kyoung
Published: July 2002

The degradation behavior in the remnant polarization (Pr) of sol–gel-derived SrBi2Ta2O9 (SBT) thin films, with Pt top and bottom electrodes, by annealing under a 5% H2/95% N2 atmosphere is investigated. The hydrogen annealing is performed at temperatures ranging from 250 to 480 °C. By annealing, the Pr drops to almost zero for all temperatures. Postannealing at temperatures higher than 700 °C under an air atmosphere recovers the Pr. Interestingly, the recovery is most ineffective for the sample annealed at the Curie temperature of the SBT films. A phenomenological model that explains this anomalous recovery behavior is presented.
Single-electron transistor made of multiwalled carbon nanotube using scanning probe manipulation
Authors: Roschier Leif , Penttilä Jari , Martin Michel , Hakonen Pertti , Paalanen Mikko , Tapper Unto , Kauppinen Esko I. , Journet Catherine , Bernier Patrick
Published: July 2002

We positioned semiconducting multiwalled carbon nanotube, using an atomic force microscope, between two gold electrodes at SiO2 surface. Transport measurements exhibit single-electron effects with a charging energy of 24 K. Using the Coulomb staircase model, the capacitances and resistances between the tube and the electrodes can be characterized in detail.
Enhancement of two-photon excited fluorescence using one-dimensional photonic crystals
Authors: Ye Jing Yong , Ishikawa Mitsuru , Yamane Yuji , Tsurumachi Noriaki , Nakatsuka Hiroki
Published: July 2002

We fabricated a one-dimensional photonic crystal structure with a defect layer of a poly(vinyl alcohol) thin film doped with 2-aminopurine (2AP). The defect induced a transmission peak in the photonic band gap at 610 nm, to which ultrashort laser pulses were tuned. We observed enhanced two-photon fluorescence emission from 2AP in the photonic crystal structure with a factor of 120. The enhancement was attributed to the high local field of light generated by a photonic state localized at the defect layer. Furthermore, under the enhanced light intensity, we carried out photobleaching experiments, which gave useful information on the photochemistry of 2AP.
Growth and physical properties of epitaxial metastable cubic TaN(001)
Authors: Shin C.-S. , Gall D. , Desjardins P. , Vailionis A. , Kim H. , Petrov I. , Greene J. E. , Odén M.
Published: July 2002

We report the growth of epitaxial metastable B1 NaCl structure TaN(001) layers. The films were grown on MgO(001) at 600 °C by ultrahigh vacuum reactive magnetron sputter deposition in mixed Ar/N2 discharges maintained at 20 mTorr (2.67 Pa). X-ray diffraction and transmission electron microscopy results establish the epitaxial relationship as cube-on-cube, (001)TaN∥(001)MgO with [100]TaN∥[100]MgO, while Rutherford backscattering spectroscopy shows that the layers are overstoichiometric with N/Ta=1.22±0.02. The room-temperature resistivity is 225 μΩ cm with a small negative temperature dependence between 20 and 400 K. The hardness and elastic modulus, as determined by nanoindentation measurements, are 30.8±0.9 and 457±16 GPa, respectively.
Microstructure and magnetic behavior of carbon-coated Co nanoparticles studied by nuclear magnetic resonance
Authors: Zhang Y. D. , Budnick J. I. , Hines W. A. , Majetich S. A. , Kirkpatrick E. M.
Published: July 2002

Spin-echo nuclear magnetic resonance (NMR) experiments have been carried out at 4.2 K and room temperature on carbon-coated nanoscale (average diameter ≈20 nm) face-centered-cubic (fcc) Co particles prepared by the Kratschmer carbon arc process for 0⩽H⩽9.0 kOe. Information concerning the magnetic structure and paramagnetic relaxation behavior of the nanoscale particle system has been obtained.
Ge–Si intermixing in Ge quantum dots on Si(001) and Si(111)
Authors: Boscherini F. , Capellini G. , Di Gaspare L. , Rosei F. , Motta N. , Mobilio S.
Published: July 2002

Exploiting Ge K-edge x-ray absorption spectroscopy we provide direct evidence of Si–Ge intermixing in self-organized strained and unstrained Ge quantum dots on Si, and provide a quantitative measurement of the average composition. For Ge/Si(001) dots with equivalent thickness in the range 5.8–38 nm and morphology ranging from that typical of coherently strained to that associated with relaxed dots we find that the average Si composition is approximately 30%. For Ge/Si(111), we find that the wetting layer has a Si composition near 50%. We discuss these results in terms of the energetics of dot formation and argue that strain-enhanced diffusion of Si into Ge should be considered as an important factor in minimizing the strain energy of the system.
Recording by microexplosion and two-photon reading of three-dimensional optical memory in polymethylmethacrylate films
Authors: Yamasaki K. , Juodkazis S. , Watanabe M. , Sun H.-B. , Matsuo S. , Misawa H.
Published: July 2002

We report the recording of a three-dimensional (3D) pattern in bulk polymethyl metacrylate (PMMA) films by microexplosion induced by a tightly focused (numerical aperture of oil-immersion objective was 1.3) single laser shot. Recording was done by picosecond (ps) single-pulse irradiation at 532 nm and by femtosecond at a 400 nm wavelength. The light-induced damage threshold of PMMA was found at ∼4 MW/cm2 for ps damaging. Readout of the 3D pattern was carried out by the recording of the transmission and the photoluminescence (PL) of bits. We demonstrate the possibility exciting PL of the optically damaged area inside the PMMA by one- and two-photon absorption.
Ferroelectric domain reversal in congruent LiTaO3 crystals at elevated temperatures
Authors: Battle Charles C. , Kim Sungwon , Gopalan Venkatraman , Barkocy Kendra , Gupta Mool C. , Jia Q. X. , Mitchell T. E.
Published: July 2002

We report a four-times decrease in the electric fields for 180° domain reversal in congruent LiTaO3 crystals with an increase in temperature from 22 to 250 °C. This is accompanied by a substantial broadening of the field range over which domain reversal takes place, by an order of magnitude. The large internal fields of ∼5.5 kV/mm at room temperature, as measured by the asymmetry in polarization hysteresis loop, disappears at higher temperatures. With increasing temperature, the domain switching changes from lateral growth dominated to nucleation dominated kinetics.
Glassy to inhomogeneous-ferroelectric crossover in (Pb, La)(Zr, Ti)O3 ceramics
Authors: Bobnar V. , Kutnjak Z. , Levstik A.
Published: July 2002

The temperature dependence of the dielectric nonlinearity a3=ε3/ε14 has been determined in 9/65/35 (Pb, La)(Zr, Ti)O3 ceramics. In zero electric field a deep in the temperature behavior of the static a3 has been observed indicating a crossover from paraelectric-like to glass-like behavior on cooling towards the freezing transition. By varying a bias electric field another glass-to-ferroelectric crossover has been observed in the temperature dependence of the static a3. The observed crossovers as well as the temperature dependence of the linear static dielectric constant agree with the predictions of the spherical random-bond–random-field model of relaxor ferroelectrics.
Temperature dependence and current transport mechanisms in AlxGa1−xN Schottky rectifiers
Authors: Zhang A. P. , Dang G. , Ren F. , Han J. , Polyakov A. Y. , Smirnov N. B. , Govorkov A. V. , Redwing J. M. , Cho H. , Pearton S. J.
Published: July 2002

GaN and Al0.25Ga0.75N lateral Schottky rectifiers were fabricated either with (GaN) or without (AlGaN) edge termination. The reverse breakdown voltage VB (3.1 kV for GaN; 4.3 kV for AlGaN) displayed a negative temperature coefficient of −6.0±0.4 V K−1 for both types of rectifiers. The reverse current originated from contact periphery leakage at moderate bias, while the forward turn-on voltage at a current density of 100 A cm−2 was ∼5 V for GaN and ∼7.5 V for AlGaN. The on-state resistances, RON, were 50 mΩ cm2 for GaN and 75 mΩ cm2 for AlGaN, producing figures-of-merit (VRB)2/RON of 192 and 246 MW cm−2, respectively. The activation energy of the reverse leakage was 0.13 eV at moderate bias.
Molecular-dynamics study of the mechanism and kinetics of void growth in ductile metallic thin films
Authors: Gungor M. Rauf , Maroudas Dimitrios , Zhou Shujia
Published: July 2002

A molecular-dynamics study is presented of the mechanism and kinetics of void growth and morphological evolution in ductile metallic thin films subject to biaxial tensile strains. The void becomes faceted, grows, and relieves strain by emission from its surface of pairs of screw dislocations with opposite Burgers vectors. Repeated dislocation generation and propagation leads to formation of a step pattern on the film’s surfaces. A simple phenomenological kinetic model of void growth is derived. Such kinetic equations can be used to formulate constitutive theories of plastic deformation for continuum-scale modeling of void evolution.
Dust transport phenomena in a capacitively coupled plasma reactor
Authors: Kim Heon Chang , Manousiouthakis Vasilios I.
Published: July 2002

The effect of particulate size on the spatial distribution of dust in a plasma environment is investigated through the simulation of a dust transport model coupled with plasma and neutral models. The dust transport model takes into account all important factors affecting dust behavior (gravitational, electrostatic, ion drag, neutral drag and Brownian forces). A Lagrangian approach is employed for the simulation of the dust transport model, tracking the individual trajectory of each particulate by taking a force balance on the particulate. Trap locations, for dust particles of sizes ranging from a few nm to a few μm, are identified in an electropositive plasma. The simulation results show that dust particles are trapped at locations where the forces acting on them balance. While fine particles tend to be trapped in the bulk, large particles accumulate near bottom sheath boundaries and around material interfaces, such as wafer and electrode edges where a sudden change in electric field occurs. Overall, small particles form a “dome” shape around the center of the plasma reactor and are also trapped in a “ring” near the radial sheath boundaries, while larger particles accumulate only in the “ring.” These simulation results are qualitatively in good agreement with experimental observation.
Generalized affine coherent states: A natural framework for the quantization of metric-like variables
Authors: Watson Glenn , Klauder John R.
Published: July 2002

Affine variables, which have the virtue of preserving the positive-definite character of matrix-like objects, have been suggested as replacements for the canonical variables of standard quantization schemes, especially in the context of quantum gravity. We develop the kinematics of such variables, discussing suitable coherent states, their associated resolution of unity, polarizations, and finally the realization of the coherent-state overlap function in terms of suitable path-integral formulations.
A frequency–domain inverse problem for a dispersive stratified chiral medium
Authors: Boutet de Monvel Anne , Shepelsky Dmitry
Published: July 2002

We study the inverse problem for a dispersive stratified chiral slab. The problem is treated as an analytic factorization problem in the complex plane of frequencies. Emphasis is made on the reconstruction of the spatial dependence of the medium parameters, whereas the frequency dependence is supposed to be a single-resonance Lorentz model. It is shown that, under the normal incidence of exciting plane waves, the scattering data as functions of alternating frequency allows reconstructing three independent combinations of four space-varying medium parameters. If one parameter is known, all other parameters are uniquely reconstructed.
Energy barrier effect on transient nucleation kinetics: Nucleation flux and lag-time calculation
Authors: Maksimov Igor L. , Sanada Masaaki , Nishioka Kazumi
Published: July 2002

Energy barrier effect on the transient nucleation kinetics is studied. For a high barrier case an advanced interpolation of the “boundary-layer” type is suggested that is valid for the entire time interval. The nucleation kinetics for the “nucleated cluster” size nc is described, the lag time estimate for n=nc is given. For a low barrier case a new “similarity” solution is reported. It is shown that analytical results provide an adequate description of the transient nucleation kinetics (in comparison with numerical solution of governing equation) for both high-barrier and low-barrier conditions.
Bosonic field propagators on algebraic curves
Authors: Ferrari Franco , Sobczyk Jan
Published: July 2002

In this paper we investigate the theory of massless scalar fields on nondegenerate algebraic curves. The propagator is written in terms of the parameters appearing in the polynomial defining the curve. This provides an alternative to the language of theta functions. The main result is the derivation of a third kind differential normalized in such a way that its periods around the homology cycles are purely imaginary. All the physical correlation functions of the scalar fields can be expressed in terms of this object. This paper contains a detailed analysis of the techniques necessary to study field theories on algebraic curves. A simple expression of the scalar field propagator is found in a particular case, in which the algebraic curves have Zn internal symmetry and one of the fields is located at a branch point.
Persistent oscillations of scalar and vector dispersion-managed solitons
Authors: Lakoba T. I. , Pelinovsky Dmitry E.
Published: July 2002

We show that both orthogonal and parallel internal modes exist on the background of a dispersion-managed (DM) soliton in randomly birefringent fibers. The orthogonal modes exist for arbitrarily small values of the dispersion map strength, while the parallel modes exist only when the map strength exceeds a certain threshold value. We demonstrate that initial perturbations of a DM soliton’s profile that consist of one or more internal modes, exhibit nearly stable oscillations over very long propagation distances, before decaying into radiation.
The uniqueness and approximation of a positive solution of the Bardeen–Cooper–Schrieffer gap equation
Authors: Bryce McLeod J. , Yang Yisong
Published: July 2002

In this paper we study the Bardeen–Cooper–Schrieffer energy gap equation at finite temperatures. When the kernel is positive representing a phonon-dominant phase in a superconductor, the existence and uniqueness of a gap solution is established in a class which contains solutions obtainable from bounded domain approximations. The critical temperatures that characterize superconducting–normal phase transitions realized by bounded domain approximations and full space solutions are also investigated. It is shown under some sufficient conditions that these temperatures are identical. In this case the uniqueness of a full space solution follows directly. We will also present some examples for the nonuniqueness of solutions. The case of a kernel function with varying signs is also considered. It is shown that, at low temperatures, there exist nonzero gap solutions indicating a superconducting phase, while at high temperatures, the only solution is the zero solution, representing the dominance of the normal phase, which establishes again the existence of a transition temperature.
Induced representations of the two parametric quantum deformation Upq[gl(2/2)]
Authors: Ky Nguyen Anh
Published: July 2002

The two-parametric quantum superalgebra Up,q[gl(2/2)] and its induced representations are considered. A method for constructing all finite-dimensional irreducible representations of this quantum superalgebra is also described in detail. It turns out that finite-dimensional representations of the two-parametric Up,q[gl(2/2)], even at generic deformation parameters, are not simply trivial deformations from those of the classical superalgebra gl(2/2), unlike the one-parametric cases.
Effect of couplings weakening and reversing in ferromagnetic Ising systems— Rigorous inequalities
Authors: Schwartz Moshe , Efrat Avishay , Monroe James L.
Published: July 2002

We consider Ising systems where all the many-spin couplings JA are positive. We show that the absolute value of all the many-spin correlations does not increase when the value of any of the couplings is reduced, taking any value in the interval [−JA,JA]. Results of this type are motivated by work in systems such as random field Ising models.
Structure and representations on the quantum supergroup OSPq(2|2n)
Authors: Zhang R. B.
Published: July 2002

The structure and representations of the quantum supergroup OSPq(2|2n) are studied systematically. The algebra of functions on the quantum supergroup, which specifies the quantum supergroup itself, is taken to be the superalgebra generated by the matrix elements of the vector representation of the quantized universal superalgebra Uq(osp(2|2n)). It is shown that the algebra of functions is dense in the full dual Uq(osp(2|2n))* of Uq(osp(2|2n)) and possesses a Hopf superalgebra structure. The left integral and right integral on the quantum supergroup are discussed. Induced representations are developed using the noncommutative geometry of quantum homogeneous supervector bundles, and a geometric realization of irreducible representations is obtained.
On Laplace–Darboux-type sequences of generalized Weingarten surfaces
Authors: Schief W. K.
Published: July 2002

Two novel classes of integrable surfaces (“generalized Weingarten surfaces of Class 1 and 2”) which may be defined in a coordinate-independent manner or, equivalently, via an extension of the classical Lelieuvre formulas are introduced. The classes 1 and 2 generalize Bianchi surfaces and surfaces of harmonic inverse mean curvature respectively and turn out to be governed by analogs of the Ernst–Weyl equation descriptive of gravitational and neutrino fields in general relativity. The latter connection is exploited to derive Laplace–Darboux-type transformations for Class 2 via the associated Loewner–Konopelchenko–Rogers representation. The Laplace–Darboux-type transformations are shown to have remarkable geometric properties in terms of sphere congruences. Connections with the Pohlmeyer–Lund–Regge vortex model and an inhomogeneous Heisenberg spin equation are recorded. A Bäcklund transformation for a particular Painlevé III equation is derived in a purely geometric manner and a geometric interpretation of an associated discrete Painlevé III equation is given.
Underdetermined systems of partial differential equations
Authors: Bender Carl M. , Dunne Gerald V. , Mead Lawrence R.
Published: July 2002

This paper examines underdetermined systems of partial differential equations in which the independent variables may be classical c-numbers or even quantum operators. One can view an underdetermined system as expressing the kinematic constraints on a set of dynamical variables that generate a Lie algebra. The arbitrariness in the general solution reflects the freedom to specify the dynamics of such a system.
Representations of quantum toroidal algebra Uq(sln+1,tor) (n⩾2)
Authors: Miki Kei
Published: July 2002

By the method of Chari and Pressley, representations of the quantum toroidal algebra Uq(sln+1,tor) (n⩾2) are studied.
Control of implicit chaotic maps using nonlinear approximations
Authors: Hill D. L.
Published: July 2002

The technique of using nonlinear approximations to design controllers for chaotic dynamical systems introduced by Yagasaki and Uozumi is extended in order to enable it to be used to design controllers for chaotic dynamical systems that are described by implicit maps and is then used to control the well-known bouncing ball system without recourse to the high-bounce approximation.
Effect of Pb(Yb1/2Nb1/2)O3 on structural and piezoelectric properties of Pb(Zr0.52Ti0.48)O3 ceramics
Authors: Yoon Ki Hyun , Lee Young Seok , Lee Hong Ryul
Published: July 2002

Solid solutions of xPb(Yb1/2Nb1/2)O3–(1−x)Pb(Zr0.52Ti0.48)O3, x=0–0.25, were investigated from the viewpoint of structural, dielectric, and piezoelectric properties. With increasing Pb(Yb1/2Nb1/2)O3 content (x), the structural change occurred from the tetragonal to the pseudocubic phase at room temperature. The morphotropic phase boundary (MPB) between the tetragonal and pseudocubic phases was shown in the region of x=0.05–0.10. Polarization and electric-field-induced strain exhibited a maximum at the composition near MPB. It may be concluded that both the ease of domain switching and the enhanced polarization play an important role in bringing about large electric-field-induced strain. At this composition, the remnant polarization and coercive field were 29.5 μC/cm2 and 4.5 kV/cm at 17 kV/cm, respectively, and a maximum electric-field-induced strain of 0.97×10−3 at 25 kV/cm was obtained. Also, the electromechanical coupling coefficient (Kp) and mechanical quality factor (Qm) were 0.47 and 65, respectively.
Density-functional studies of amphiphilic binary mixtures. II. Gas–liquid nucleation
Authors: Napari Ismo , Laaksonen Ari , Strey Reinhard
Published: July 2002

Density-functional theory is applied to study gas–liquid nucleation in binary mixtures consisting of Lennard-Jones atoms with hard-spherical cores (monomers) and bonded Lennard-Jones atoms of two (dimers) or three (trimers) hard spheres. Mixtures with and without amphiphiles are compared. In amphiphilic systems mutual enhancement of nucleation is observed regardless of reduced total interaction between the molecules. Monomer–dimer and monomer–trimer mixtures are compared. Increased chain length is shown to result in stronger enhancement of nucleation. Layered structures are shown to form in large critical clusters at certain vapor activities. The nucleation behavior of the amphiphilic systems resembles qualitatively the experimental observations of water–n-alcohol mixtures.
M
-body density functional theory and the generalized hypernetted-chain equation
Authors: Munakata Toyonori , Kim Kang
Published: July 2002

The HNC (hypernetted-chain) theory for two-body correlation in fluids is generalized so that up to M-body (M>2) correlation functions can be obtained self-consistently. Our approach is based on the M-body density functional theory and a generalized Percus idea where maximally M−1 particles are held fixed in space, leading to M−1 HNC equations for the correlation functions. These are supplemented with M−1 Ornstein–Zernike relations to give a closed set of equations. Due to the rather complicated structure of the coupled integral equations, we explicitly present the equations for the case M=3, which are compared with the HNC2 equations by Verlet. The M=3 theory is numerically solved for the case of a one-dimensional liquid.
Reflow of copper in oxygen anneal ambients
Authors: Lee Seung-Yun , Choi Sung-Ho , Kang Jin-Yeong , Park Chong-Ook
Published: July 2002

The effects of the grain growth and residual stress of Cu thin films on reflow were investigated. Agglomeration and grain growth of Cu films occurred during annealing in an oxygen ambient, while they were not observed in inert ambients. In the case of chemical vapor deposited Cu films, trench patterns of 0.5 μm with an aspect ratio of 2 were completely filled at annealing temperatures higher than 400 °C in oxygen ambient, due to the preferential agglomeration inside the patterns. Upon annealing at 400 °C in an oxygen ambient, the agglomeration terminated within 10 min, while the thickness of Cu oxide increased to 18.3 nm, and normal grain growth, resulting in increased capillary instability of Cu films, was observed. Because of a larger volume of Cu oxide than Cu, the formation of Cu oxide led to compressive stress in the films. By calculation, it was shown that compressive stress could decrease through grain growth. It is considered that the agglomeration and reflow in an oxygen ambient resulted from the relaxation of compressive stresses via grain growth.
Acceptor reactivation kinetics in heavily carbon-doped GaAs epitaxial layers
Authors: Mimila-Arroyo J. , Bland S. W.
Published: July 2002

The reactivation kinetics of the acceptor behavior of carbon in GaAs layers has been studied. The reactivation was achieved by ex situ rapid thermal annealing. To follow the carbon reactivation process, a multistage annealing experiment was performed, with changes in the sample carrier concentration monitored at each stage. An analysis of these data indicates that carbon reactivation follows a first-order kinetics process that can be explained by a model which includes the effects of dopant repassivation by hydrogen retrapping during hydrogen out-diffusion, and a dependence of the attempt frequency with the carbon concentration. The reactivation occurs with an activation energy of 1.41 eV.
Monte Carlo study of kinetic smoothing during dissolution and etching of the Kossel (100) and silicon (111) surfaces
Authors: van Veenendaal E. , van Beurden P. , van Enckevort W. J. P. , Vlieg E. , van Suchtelen J. , Elwenspoek M.
Published: July 2002

We have analyzed the asymmetry between growth and dissolution using Monte Carlo simulations of flat and vicinal (100) surfaces of a Kossel crystal. We find that at a high driving force dissolution is very anisotropic and nearly atomically flat surfaces are produced, if the nearest-neighbor bond strength is sufficiently large. This effect we call kinetic smoothing. For wet-chemical etching of the Si(111) surface, the chemical-etch reaction determines the annihilation rate constants. If the differences between the rate constants for removal of atoms from kink, step, and terrace sites are large enough, then we observe smooth surfaces and anisotropic etching, i.e., kinetic smoothing. If etching is anisotropic, knowledge of the annihilation rate constants suffices to find an analytical expression for the etch rate as a function of misorientation. This expression can be used to fit experimental etch rates for etching of vicinal Si(111) in potassium hydroxide.
Computer simulation of acetonitrile and methanol with ab initio-based pair potentials
Authors: Hloucha M. , Sum A. K. , Sandler S. I.
Published: July 2002

This study address the adequacy of ab initio pair interaction energy potentials for the prediction of macroscopic properties. Recently, Bukowski et al. [J. Phys. Chem. A 103, 7322 (1999)] performed a comprehensive study of the potential energy surfaces for several pairs of molecules using symmetry-adapted perturbation theory. These ab initio energies were then fit to an appropriate site–site potential form. In an attempt to bridge the gap between ab initio interaction energy information and macroscopic properties prediction, we performed Gibbs ensemble Monte Carlo (GEMC) simulations using their developed pair potentials for acetonitrile and methanol. The simulations results show that the phase behavior of acetonitrile is well described by just the pair interaction potential. For methanol, on the other hand, pair interactions are insufficient to properly predict its vapor-liquid phase behavior, and its saturated liquid density. We also explored simplified forms for representing the ab initio interaction energies by refitting a selected range of the data to a site–site Lennard-Jones and to a modified Buckingham (exponential-6) potentials plus Coulombic interactions. These were also used in GEMC simulations in order to evaluate the quality and computational efficiency of these different potential forms. It was found that the phase behavior prediction for acetonitrile and methanol are highly dependent on the details of the interaction potentials developed.
Strain status of self-assembled InAs quantum dots
Authors: Zhang K. , Heyn Ch. , Hansen W. , Schmidt Th. , Falta J.
Published: July 2002

Grazing incidence x-ray diffraction experiments employing the asymmetric (202) Bragg diffraction have been performed to characterize self-assembled InAs quantum dots grown by molecular-beam epitaxy. We find that the strain is elastically relaxed with different components. The volume distribution of partially strained InAs inside islands is peaked at intermediate strain values. The fraction of both almost fully strained and totally relaxed InAs is found to be small. In addition, a small volume fraction of relaxed InxGa1−xAs is found.
Growth of step-free surfaces on device-size (0001)SiC mesas
Authors: Powell J. Anthony , Neudeck Philip G. , Trunek Andrew J. , Beheim Glenn M. , Matus Lawrence G. , Hoffman Richard W. , Keys Luann J.
Published: July 2002

It is believed that atomic-scale surface steps cause defects in single-crystal films grown heteroepitaxially on SiC substrates. A method is described whereby surface steps can be grown out of existence on arrays of device-size mesas on commercial “on-axis” SiC wafers. Step-free mesas with dimensions up to 200 μm square have been produced on 4H-SiC wafers and up to 50 μm square on a 6H-SiC wafer. A limiting factor in scaling up the size and yield of the step-free mesas is the density of screw dislocations in the SiC wafers. The fundamental significance of this work is that it demonstrates that two-dimensional nucleation of SiC can be suppressed while carrying out step-flow growth on (0001)SiC. The application of this method should enable the realization of improved heteroepitaxially-grown SiC and GaN device structures.
Magnetotunneling in sputtered La0.7Ca0.3MnO3/Al2O3 multilayers
Authors: Luo Y. , Käufler A. , Samwer K.
Published: July 2002

Magnetic multilayers in the form of [La0.7Ca0.3MnO3/Al2O3]n+La0.7Ca0.3MnO3 were sputtered to study their magnetotunneling effect. Structural analyses were performed by standard x-ray scattering, showing a well-defined superlattice. Both current perpendicular to plane (CPP) and current in plane (CIP) methods were applied for the magnetoresistance measurements. The CPP value gives the tunneling effect through the thin insulating layers and shows a large low-field effect of about 60% for the trilayer junction and 50% for the superlattice structure at 5 K, respectively. The CIP effect is about 30% (5 K) for all samples and is dominated here by the contribution of the intergrain tunneling effect within the La0.7Ca0.3MnO3 layers.
Correlation between the roughness degree of a protein surface and the mobility of solvent molecules on the surface
Authors: Choi Jun-Ho , Lee Sangyoub
Published: July 2002

We investigate the effect of roughness degree of a protein surface on the solvent diffusion near the surface by carrying out the molecular dynamics simulations. As expected, the solvent molecules experience the larger frictional drag on a more corrugated protein surface. However, the roughness degree of a protein surface can be measured differently by different solvent molecules. It is shown that on the same protein surface the smaller solvent molecules experience the larger frictional drag than the larger ones. The observed trends in the mobility of solvent molecules on the protein surface correlates nicely with the correlation dimension of the protein surface, which we proposed recently as a new measure of the molecular surface roughness.
Local capacitance measurements on InAs dot-covered GaAs surfaces by scanning capacitance microscopy
Authors: Yamamoto H. , Takahashi T. , Kamiya I.
Published: July 2002

Capacitance images responsible for surface depletion were observed on an InAs dot-covered GaAs surface by scanning capacitance microscopy. We performed local capacitance versus bias voltage measurements on quantum dots (QDs) and a wetting layer (WL) as well as conductance versus bias voltage (G–V) measurements. Both results indicate that the surface depletion is more suppressed beneath the QDs than under the WL. In addition, the conventional thermionic equation theory fitted to the measured G–V curves shows that the interface barrier height between the GaAs and the InAs QD increases as the QD size is reduced. We ascribe this result to the influence of the surrounding WL, whose surface Fermi level is strongly pinned at the midgap of the n-GaAs.
Electromigration in YBa2Cu3O7−δ using a metal clad near-field scanning optical microscope probe
Authors: Huerth S. H. , Taylor M. P. , Hallen H. D. , Moeckly B. H.
Published: July 2002

Electromigration or electron-induced-migration (EIM) of oxygen in the hightemperature superconductor YBa2Cu3O7−δ alters the superconducting properties through variations in the oxygen concentration. We study this process with unprecedented spatial resolution and find that the transport of oxygen through a grain boundary into a neighboring grain is unlikely, and that hot electron effects dominate the mechanism for EIM in this system. The extent of the EIM effects implies that grain boundary scattering is strong for these electrons. EIM is induced with the tunnel current from the metal cladding on a near-field optical microscope (NSOM). Variations in the oxygen concentration due to fabrication, aging, and electromigration are imaged optically and corroborated to the grain structure.
Theoretical study of electronic states of platinum pentamer (Pt5)
Authors: Majumdar D. , Dai Dingguo , Balasubramanian K.
Published: July 2002

Geometries and energy separations of the various low-lying electronic states of Pt5 with different structural arrangements have been investigated. The complete active space multiconfiguration self-consistent-field (CASMCSCF) method followed by large-scale multiconfiguration singles plus doubles configuration interaction (MRSDCI) that included up to 1.64 million configuration spin functions have been used to compute several electronic states. A 1B2 (C2v) electronic state of a distorted tetragonal pyramid equilibrium structure was found to be the minimum energy geometry. We also compared our MRSDCI results with density functional as well as Mo/ller-Plesset second-order perturbation calculations. The dissociation and atomization energies have been computed and the results, together with our previous findings for the smaller Ptn (n=2–4) clusters, were compared with other group 10 member clusters viz., Nin (n=2–5) and Pdn (n=2–5) and the experimental findings.
Molecular beam epitaxy growth of GaN on C-terminated 6H–SiC (0001¯) surface
Authors: Guan Z. P. , Cai A. L. , Cabalu J. S. , Porter H. L. , Huang S.
Published: July 2002

We report the results of successful growth of GaN on the C-terminated surface of SiC. A combination of direct heating and hydrogen plasma treatment was employed for surface preparation. High-quality epitaxy was achieved in epilayers as thin as 2000 Å, as evidenced by the x-ray diffraction full width at half maximum of 90 arc sec and 4.2 K donor-bound exciton peak width of 1.4 meV. The epilayers exhibit clear signatures of compressive strain, suggesting a more favorable growth mode than can be achieved on the Si-terminated surface.
Matroid theory and Chern–Simons
Authors: Nieto J. A. , Marı́n M. C.
Published: July 2002

It is shown that matroid theory may provide a natural mathematical framework for a duality symmetries not only for quantum Yang–Mills physics, but also for M-theory. Our discussion is focused in an action consisting purely of the Chern–Simons term, but in principle the main ideas can be applied beyond such an action. In our treatment the theorem due to Thistlethwaite, which gives a relationship between the Tutte polynomial for graphs and Jones polynomial for alternating knots and links, plays a central role. Before addressing this question we briefly mention some important aspects of matroid theory and we point out a connection between the Fano matroid and D=11 supergravity. Our approach also seems to be related to loop solutions of quantum gravity based in an Ashtekar formalism.
The mixed P, T derivative of isothermal bulk modulus for solids
Authors: Jeon Hunmoo , Cho Bongkee
Published: July 2002

Using the generalized Gilvarry [J. Appl. Phys. 28, 1253 (1957)] equation of state, we show that for the case where the Murnaghan equation of state holds, ∂2B/∂T∂P=0 where B is the isothermal bulk modulus. This leads to the following results: (1) The product αBδ is independent of volume and pressure at constant temperature, where α=(∂ ln V/∂T)P and δ is the Anderson–Gruneisen parameter. (2) The isothermal bulk modulus can be separated into two functions, B(T,P)=B(T)+B(P), where B(T) is a function of temperature only and B(P) is a function of pressure only. (3) (∂ ln(αB)/∂ ln η)T=−(∂ ln δ/∂ ln η)T, where η=V/V0. (4) (∂ ln(αB)/∂P)T=−(∂ ln δ/∂P)T. (5) If φ=δ, where φ=(∂B/∂P)T, then δ is independent of pressure and volume.
Poisson algebras associated with constrained dispersionless modified Kadomtsev–Petviashvili hierarchies
Authors: Chang Jen-Hsu , Tu Ming-Hsien
Published: July 2002

We investigate the bi-Hamiltonian structures associated with constrained dispersionless modified Kadomtsev–Petviashvili (KP) hierarchies which are constructed from truncations of the Lax operator of the dmKP hierarchy. After transforming their second Hamiltonian structures to those of the Gelfand–Dickey-type, we obtain the Poisson algebras of the coefficient functions of the truncated Lax operators. Then we study the conformal property and free-field realizations of these Poisson algebras. Some examples are worked out explicitly to illustrate the obtained results.