bluuebunny/crossref_metadata_2025 huggingface dataset:
Calibration of the power-recycled gravitational wave detector, GEO 600
Authors: Hewitson M. , Grote H. , Heinzel G. , Strain K. A. , Ward H. , Weiland U.
Published: August 2003

GEO 600 is an interferometric gravitational wave detector which, when completed, will employ a novel, dual-recycled optical scheme allowing its optical response to be tuned over a range of frequencies. The accurate calibration of the sensitivity of GEO to gravitational waves is a critical part of preparing GEO data for exchange with other detectors worldwide and for the extraction of scientific results. The final optical scheme that will be used in GEO will make it necessary to combine more than one output signal to optimally recover a calibrated strain channel. An on-line calibration scheme has been developed with a view to covering both the power-recycled and dual-recycled interferometer configurations of GEO. The recent worldwide coincident science run (S1) proved an excellent opportunity to test the calibration scheme of GEO in a power-recycled mode. The ability to track and study the stability of the calibration over long time scales was invaluable. A number of areas have been highlighted where improvement is necessary, but the scheme proved successful and produced a continuous real-time h(t) for the entire duration of the S1 science run. Consideration of the errors discussed throughout this article lead to a calibration accuracy for this science run of around 4% at high frequencies (>200 Hz) and about 6% for frequencies between about 50 and 200 Hz. This article presents the on-line calibration scheme that was developed for, and employed during, the recent S1 science run. The hardware signal injection is presented in detail followed by the on-line analysis method that allows real-time calibration of this interferometer configuration. The results of the calibration process are discussed and attention is drawn to the successes and to the points where improvement can be made.
Domain switching characteristics of the near stoichiometric LiNbO3 doped with MgO
Authors: Chen Yunlin , Lou Cibo , Xu Jingjun , Chen Shaolin , Kong Yongfa , Zhang Guangyin , Wen Jianping
Published: August 2003

MgO-doped stoichiometric LiNbO3 crystal has been produced using the Czochralski method and vapor transport equilibration technique. The domain reversal characteristics of the near stoichiometric single crystals with different Mg doping levels have been investigated. The switching field required for 180° ferroelectric domain reversal was compared with the near stoichiometric and congruent crystals. The near stoichiometric crystal doped with MgO shows lower switching field than the near stoichiometric and the congruent crystals. The switching field for the domain reversal in the near stoichiometric crystal doped with 2.0 mol % MgO was 1.8±0.2 KV/mm. This is about one third of the switching field for the near stoichiometric crystal, and one tenth of the switching field for the congruent crystal.
Correlation of microwave dielectric properties and normal vibration modes of xBa(Mg1/3Ta2/3)O3–(1−x)Ba(Mg1/3Nb2/3)O3 ceramics: II. Infrared spectroscopy
Authors: Chen Yi-Chun , Cheng Hsiu-Fung , Liu Hsiang-Lin , Chia Chih-Ta , Lin I-Nan
Published: August 2003

The relationship between the microwave dielectric properties and the IR active phonons of xBa(Mg1/3Ta2/3)O3–(1−x)Ba(Mg1/3Nb2/3)O3 ceramics was investigated. The IR modes were assigned, and the origin of dielectric response was determined. Among the 15 prominent IR modes, we found that the normal vibrations of the O layers and that of the Ta/Nb layers are strongly correlated to the measured dispersion parameters, such as the resonant strength (4πρ) and the damping coefficient (γ). The frequency shifts of the normal modes of the O layers and that of the Ta/Nb layers explain the linear decrease of microwave dielectric constant (K) as x increases, while the width of these modes correlate with the Q×f value.
Dielectric properties of nanoparticulate Ba2EuZrO5.5 perovskite at microwave frequencies
Authors: Konopka Janusz , Konopka Anna , Waldow Peter , Jose Rajan , Wołcyrz Marek
Published: August 2003

Dielectric properties of a complex perovskite material, Ba2EuZrO5.5, which was proposed as a suitable substrate for high TC superconducting films [R. Jose et al., J. Mater. Res., 15, 2125 (2000)], were measured in the frequency range from 0.47 to 26 GHz and in the temperature range from 77 to 350 K. In the present research, sintered bulk Ba2EuZrO5.5 material composed of nanocrystallites was used. The dielectric constant: ε′=32,25±0.3% was measured at 300 K, and the material was found to be rather lossy with tan δ close to 10−2. The temperature measurements show unusual behavior of the dielectric properties. In the range from 100 to 250 K, a considerable increase of the dielectric constant and losses were observed. This effect might be due to the tilting of B(B′)O6 octahedra commonly found in complex perovskite materials. Due to such behavior, the applications of Ba2EuZrO5.5 as a substrate for YBCO and BISCCO superconductors at high and microwave frequencies should be rather ruled out.
Intervalence-band and band-to-band transitions in CuGaTe2 single crystal
Authors: Rincón C. , Wasim S. M. , Marı́n G.
Published: August 2003

A study of the temperature dependence of the heavy-hole-band–split-off-band Ehs and of the heavy-hole-band–conduction-band EGA transitions in single crystal of p-type CuGaTe2 was made from the analysis of optical absorption spectra. Ehs and EGA were found to vary from 0.72 to 0.70 eV and 1.36 to 1.25 eV, respectively, between 10 and 300 K. It is found that the variation of EGA with T is mainly governed by the contribution of optical phonons with a characteristic energy εeff≈14 meV. From the analysis of Ehs(T) and EGA(T), the temperature dependence of the split-off-band–conduction-band transition energy EGC is also determined. It was found to vary from 2.08 to 1.95 eV in the temperature range from 10 to 300 K. A relatively low value of the characteristic phonon energy, εeff≈11 meV, obtained in this case, indicates that the major contribution to the shift of EGC versus T originates from acoustic phonons.
Dielectric properties of CdxZn1−xTe epilayers
Authors: Wang K. F. , Fu S. P. , Chen Y. F. , Shen J. L. , Chou W. C.
Published: August 2003

We report on the dielectric properties of CdxZn1−xTe (0.056⩽x⩽0.582) epilayers studied by capacitance and dissipation factor measurements at temperature 201 K<T<460 K and frequency 20 Hz<f<1 MHz. A Debye-like relaxation in the dielectric response has been observed, which is explained in terms of the presence of charge redistribution. The relaxation is found to be a thermally activated process, and the activation energies obtained from both dissipation factor and capacitance are in good agreement. It is also found that the activation energy decreases with increasing Cd content and this behavior is interpreted in terms of the four-center model, in which the number of Cd atoms appearing in the nearest-neighbor sites of a defect can have four possible configurations. In addition, we demonstrate that the transport mechanism of the carrier conduction in CdZnTe epilayers can be well described by the correlated barrier hopping model.
Influences of postimplantation annealing conditions on resistance lowering in high-phosphorus-implanted 4H–SiC
Authors: Senzaki Junji , Fukuda Kenji , Arai Kazuo
Published: August 2003

The dependences of sheet resistance (Rs), sheet carrier concentration, and carrier mobility on postimplantation annealing temperature and time have been investigated in high-phosphorus (P)-implanted 4H–SiC using Hall effect measurement. At an annealing temperature below 1200 °C, Rs decreases with an increase in annealing time due to the increases in sheet carrier concentration and carrier mobility, but the Rs available for SiC device applications is not obtained using even a long annealing time of 500 min. At an annealing temperature above 1600 °C, annealing for 30 min causes the Rs to increase due to an evaporation of the implanted layer. In addition, the precipitation of P donors occurs by long-time annealing regardless of annealing temperature, thereby reducing sheet carrier concentration in implanted layer. On the contrary, a Rs of less than 100 Ω/sq has been achieved at a short annealing time of 30 s because of the extremely high electrical activation of P donors exceeding its solubility limit. Based on these results, it is revealed that the decrease in Rs of the P-implanted 4H–SiC is necessary to satisfy the three requisites: (1) sufficient crystal recovery, (2) suppression of implanted layer evaporation, and (3) prevention of P precipitation, and is achieved by rapid thermal annealing at high temperature for a short time.
Langmuir probe diagnostics of a microfabricated inductively coupled plasma on a chip
Authors: Minayeva Olga B. , Hopwood Jeffrey
Published: August 2003

The experimental values for electron temperature and plasma density are measured in a microfabricated, inductively coupled plasma on a chip (ICP). The miniature ICP system consists of a planar plasma source that is microfabricated on a glass wafer and a miniature aluminum vacuum chamber (φ=6 mm). A reliable Langmuir probe diagnostic for microplasma reactors was developed because classic probe measurements would be hindered by the small plasma volume, the small surface area of grounded reactor walls, collisional ion sheathes, and the radio-frequency (rf) interference from the high-frequency power supply. Once the ion density and electron temperature are determined, the neutral gas temperature was estimated to be nearly equal to room temperature. At low pressures, one finds that the plasma sheath width limits the dimensional scaling of the reactor, since the sheath is, typically, ∼0.6 mm. The plasma operates from 0.1 to 10 Torr, and requires less than 3 W of transmitted power at a frequency of 493 MHz. Direct measurement of the power absorbed by the gas discharge, however, shows that between 2% and 18% of the power supplied to the microstructure is absorbed by the discharge. The transfer of power to the discharge is most inefficient at low pressures where the electron neutral collision frequency is less than that of the rf power supply.
Temperature-dependent photoluminescence of GaInP/AlGaInP multiple quantum well laser structure grown by metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine
Authors: Liu C. Y. , Yuan Shu , Dong J. R. , Chua S. J. , Chan M. C. Y. , Wang S. Z.
Published: August 2003

A GaInP/AlGaInP multiple quantum well laser structure was grown by low-pressure metalorganic chemical vapor deposition with tertiarybutylarsine and tertiarybutylphosphine. Laser diodes fabricated from this structure lased at room temperature. Photoluminescence (PL) measurements were performed from 10 to 230 K. The PL energy increased with temperature from 10 to 70 K and decreased above 70 K. The former was attributed to thermal activation of trapped carriers due to localization in the quantum wells, while the latter was attributed to temperature-induced band-gap shrinkage. The PL intensity as a function of temperature was fitted by employing two nonradiative recombination mechanisms with good agreement, resulting in two activation energies that correspond to losses of photogenerated carriers to nonradiative centers.
A simple polarizable model of water based on classical Drude oscillators
Authors: Lamoureux Guillaume , MacKerell Alexander D. , Roux Benoı̂t
Published: August 2003

A simple polarizable water model is developed and optimized for molecular dynamics simulations of the liquid phase under ambient conditions. The permanent charge distribution of the water molecule is represented by three point charges: two hydrogen sites and one additional M site positioned along the HOH bisector. Electronic induction is represented by introducing a classical charged Drude particle attached to the oxygen by a harmonic spring. The oxygen site carries an equal and opposite charge, and is the center of an intermolecular Lennard-Jones interaction. The HOH gas-phase experimental geometry is maintained rigidly and the dipole of the isolated molecule is 1.85 D, in accord with experiment. The model is simulated by considering the dynamics of an extended Lagrangian in which a small mass is attributed to the Drude particles. It is parametrized to reproduce the salient properties of liquid water under ambient conditions. The optimal model, refered to as SWM4-DP for “simple water model with four sites and Drude polarizability,” yields a vaporization enthalpy of 10.52 kcal/mol, a molecular volume of 29.93 Å3, a static dielectric constant of 79±5, a self-diffusion constant of (2.30±0.04)×10−5 cm2/s, and an air/water surface tension of 66.9±0.9 dyn/cm, all in excellent accord with experiments. The energy of the water dimer is −5.18 kcal/mol, in good accord with estimates from experiments and high level ab initio calculations. The polarizability of the optimal model is 1.04 Å3, which is smaller than the experimental value of 1.44 Å3 in the gas phase. It is likely that such a reduced molecular polarizability, which is essential to reproduce the properties of the liquid, arises from the energy cost of overlapping electronic clouds in the condensed phase due to Pauli’s exclusion principle opposing induction.
Studies of the laser filament instability in a semicollisional plasma
Authors: Michel P. , Labaune C. , Weber S. , Tikhonchuk V. T. , Bonnaud G. , Riazuelo G. , Walraet F.
Published: August 2003

The stability and nonlinear evolution of a laser filament in an underdense, semicollisional plasma are studied with a simulation code accounting for the ponderomotive and thermal effects together with the nonlocal electron transport. It is found that the filament is stable at low intensities, where the trapped laser power is below the self-focusing threshold. For larger powers, the filament is unstable with respect to bending. This instability, though predicted in theory (the m=1 mode), has not been seen so far in monospeckle modelling probably because of simulation symmetry. In our simulations an artificial noise source has been implemented in order to make nonsymmetric features appear. The instability leads to a complete breakup of the filament which reconstructs itself after some time and the process then repeats itself. Due to the filament instability the plasma sets in a regime of self-supported oscillations and results in temporal modulation and angular spreading of transmitted light. The numerical simulations are compared with theoretical predictions and experimental observations of speckle dynamics in the interaction of a randomized laser beam with preformed plasmas.
Electron acceleration and heating in collisionless magnetic reconnection
Authors: Ricci Paolo , Lapenta Giovanni , Brackbill J. U.
Published: August 2003

Electron acceleration and heating during collisionless magnetic reconnection is discussed by using the results of implicit kinetic simulations of Harris current sheets. Simulations up to the physical mass ratio are performed to study and compare electron dynamics in plasmas with different β values. The attention is focused on the typical trajectory of electrons passing through the reconnection region, on the electron velocity, in particular on the out-of-plane velocity, and on the electron heating along the in-plane and out-of-plane directions.
Raman spectroscopy and microwave properties of CaTiO3-based ceramics
Authors: Zheng H. , Bagshaw H. , Csete de Györgyfalva G. D. C. , Reaney I. M. , Ubic R. , Yarwood J.
Published: August 2003

x CaTiO 3 −(1−x) Sr ( Mg 1/3 Nb 2/3 ) O 3 (CTSMN) and yCaTiO3−(1−y)NdAlO3 (CTNA) microwave ceramics have been studied by x-ray diffraction (XRD), transmission electron microscopy (TEM), and Raman spectroscopy. TEM and XRD revealed that all compositions underwent octahedral tilt transitions on cooling, generally resulting in an a−a−c+ tilt system. The exception was the NdAlO3 end member, which had the R3̄c space group, consistent with an a−a−a− tilt configuration. Sr(Mg1/3Nb2/3)O3 (SMN), (x=0) also exhibited +/−1/3{hkl} reflections in x-ray and electron diffraction patterns associated with 1:2 long-range ordering of the B-site cations. For x⩾0.2, no 1:2 ordered reflections were observed. The long-range B-site ordering in SMN gave rise to sharp Raman bands at 391 and 825 cm−1. The 391 cm−1 band disappeared for x⩾0.2 and the width of the 825 cm−1 band became broader as x increased. It was concluded that for samples with x⩾0.2, only short-range ordering remained which decreased in correlation length as x increased. In CTNA solid solutions, a broad Raman band occurred at ∼800 cm−1 (absent for y=0 and 1 and strongest for y=0.5). The position of this band suggested that its origin was similar in nature to the ∼825 cm−1 band observed in CTSMN and therefore related to local short-range cation ordering. A relation between the presence of strong local order and poor Q in zero-temperature coefficient of the resonant frequency CTSMN (x≈0.2) is postulated.
One-dimensional heat conduction model for an electrical phase change random access memory device with an 8F2 memory cell (F=0.15 μm)
Authors: Kang Dae-Hwan , Ahn Dong-Ho , Kim Ki-Bum , Webb J. F. , Yi Kyung-Woo
Published: August 2003

A one-dimensional heat conduction model is developed for a phase change random access memory device with an 8F2 memory cell structure (F=0.15 μm). The required current level for a reset operation, which corresponds to the phase switching from a crystalline (“1” state) to an amorphous phase (“0” state) of Ge2Sb2Te5, was investigated by calculating one-dimensional temperature profiles for the memory cell structure. It is revealed that a reset operation is not achieved at the current level (2 mA) reported for existing devices with a subquarter micron plug size when only TiN is used as a resistive heater. However, it is possible when an additional heating layer of 5 nm thickness is inserted between the TiN and Ge2Sb2Te5 layers, for which the electrical resistivity ρelec is higher than 105 μΩ cm, and the thermal conductivity κ and specific heat c are as low as those of Ge2Sb2Te5. In addition, it is shown that a reset operation at a low current level of 1 mA can be realized in this memory cell when amorphous carbon (κ=0.2 W/m K and ρelec=106 μΩ cm) is used as an additional heating layer. It is believed that this relatively simple one-dimensional heat conduction model is a useful tool for analyzing the device operation of phase change random access memory devices and for selecting the proper conditions for an additional heating layer allowing for low-current operation.
Strain relaxation in graded InGaN/GaN epilayers grown on sapphire
Authors: Song T. L. , Chua S. J. , Fitzgerald E. A. , Chen P. , Tripathy S.
Published: August 2003

Graded InGaN buffers were employed to relax the strain arising from the lattice and thermal mismatch in GaN/InGaN epilayers grown on sapphire. An enhanced strain relaxation was observed in GaN grown on a stack of five InGaN layers, each 200 nm thick with the In content increased in each layer, and with an intermediate thin GaN layer, 10 nm thick inserted between the InGaN layers, as compared to the conventional two-step growth of GaN epilayer on sapphire. The function of the intermediate layer is to progressively relax the strain that builds up in the InGaN layer. If the InGaN layers were graded too rapidly, more dislocations will be generated. This increases the probability of the dislocations getting entangled, thereby impeding the motion of the dislocations to relax the strain in the InGaN layer. The optimum growth conditions of the intermediate layer play a major role in promoting the suppression and filling of the V-pits in the GaN cap layer, and were empirically found to be a thin 10-nm GaN layer grown at 750 °C and annealed at 1000 °C.
Deposition and characterization of a self-propagating CuOx/Al thermite reaction in a multilayer foil geometry
Authors: Blobaum K. J. , Reiss M. E. , Plitzko J. M. , Weihs T. P.
Published: August 2003

Self-propagating formation reactions have been studied in multilayer foils and they are currently being investigated for applications in joining and ignition. Here, we introduce a reactive multilayer foil which contains a reduction-oxidation thermite reaction between CuOx and Al. Typically in reactive multilayer foils, elemental layers react and form a single intermetallic product. In this thermite reaction, however, aluminum and copper oxide are, respectively, oxidized and reduced and form aluminum oxide and copper. The fully dense multilayer foils provide a well-defined geometry for studying the thermodynamics, kinetics, and intermediate phase formation in the CuOx/Al thermite reaction. Here, sputter deposition of CuOx/Al multilayer foils is demonstrated, and x-ray diffraction and transmission electron microscopy, including high resolution transmission electron microscopy and electron spectroscopic imaging, are used to characterize the as-deposited foil and the final products. The heat released in the reaction is quantified using differential thermal analysis, and the velocity of the self-propagating reaction is reported.
Investigating the reaction path and growth kinetics in CuOx/Al multilayer foils
Authors: Blobaum K. J. , Wagner A. J. , Plitzko J. M. , Van Heerden D. , Fairbrother D. H. , Weihs T. P.
Published: August 2003

CuO x / Al exothermic reactions in multilayer foils were studied to identify reaction paths and reaction kinetics. Heating samples at a slow, controlled rate in a differential thermal analyzer showed that the reduction of CuOx and the oxidation of Al proceeded via two separate exotherms. To analyze this reaction pathway, samples were heated to various temperatures within these exotherms, quenched, and characterized with x-ray diffraction, Auger depth profiling, and transmission electron microscopy. Experimental evidence indicates that in the first reaction, CuOx is reduced to a mixture of CuO and Cu2O and an interfacial layer of Al2O3 grows to coalescence; the final products of the second exotherm are Cu, Al2O3, and Cu2O. The first exotherm was believed to be controlled by the two-dimensional, interface-limited growth of the Al2O3 layer, while the second exotherm was believed to be controlled by both the diffusion-limited one-dimensional growth of the Al2O3 and the interface-controlled growth of the Cu due to the reduction of Cu2O.
Resistance measurements of conducting C60 monolayers formed on Au and Cu films
Authors: Nouchi R. , Kanno I.
Published: August 2003

The resistances of conducting C60 monolayers formed on Au and Cu films were found to be 0.9±0.2 and 2.4±0.4 kΩ, respectively, by in situ resistance measurements. Although the amount of charge transferred to each C60 molecule from the Cu film was greater than that from the Au film, the conducting C60 monolayer formed on the Cu film had higher resistance than that formed on the Au film. This result is consistent with resistance data for alkali fullerides.
Conductivities of dilute suspensions of graded fibers
Authors: Gu Guoqing , Yu K. W.
Published: August 2003

The effective conductivity of a composite containing cylindrical fibers of graded materials has been theoretically investigated. Typical graded profiles were considered and the response to an applied electric field was studied in detail. The effective conductivity of the composites was calculated based on the analytic solution for an isolated graded fiber inclusion in the dilute limit. A composite containing fibers of graded shells was considered, which is a useful model to simulate the effect of a general graded conductivity profile.
The phase behavior of a binary mixture of rodlike and disclike mesogens: Monte Carlo simulation, theory, and experiment
Authors: Galindo A. , Haslam A. J. , Varga S. , Jackson G. , Vanakaras A. G. , Photinos D. J. , Dunmur D. A.
Published: August 2003

The phase behavior of a binary mixture of rodlike and disclike hard molecules is studied using Monte Carlo NVT (constant number of particles N, volume V, and temperature T) computer simulation. The rods are modeled as hard spherocylinders of aspect ratio LHSC/DHSC=5, and the discs as hard cut spheres of aspect ratio LCS/DCS=0.12. The diameter ratio DCS/DHSC=3.62 is chosen such that the molecular volumes of the two particles are equal. The starting configuration in the simulations is a mixed isotropic state. The phase diagram is mapped by changing the overall density of the system. At low densities stabilization of the isotropic phase relative to the ordered states is seen on mixing, and at high densities nematic–columnar and smectic A–columnar phase coexistence is observed. Biaxiality in the nematic phase is not seen. The phase diagram of the mixture is also calculated using the second virial theory of Onsager for nematic ordering, together with the scaling of Parsons and Lee to take into account the higher virial coefficients. The disc–disc and rod–disc excluded volumes are evaluated numerically using the exact overlap expressions, and the lower-order end-effects are incorporated. The exact rod–rod excluded volume is known analytically. In the case of the theoretical calculations, which are limited to translationally disordered phases, coexistence between two uniaxial nematic phases is predicted, as well as the stabilization of the disc-rich isotropic phases. As found in the simulation, biaxial nematic phases are not predicted to be stable. The phase equilibria of an experimental system is also reported which exhibits a behavior close to the system studied by computer simulation. As in the model mixtures, this system exhibits a marked destabilization of the ordered phases on mixing, while nematic–columnar demixing is observed at lower temperatures (the higher-density states).
Shielding of a slowly moving test charge in a dusty plasma with dynamical grain charging
Authors: Raadu Michael A. , Shafiq Muhammad
Published: August 2003

The dynamical charging of grains in a dusty plasma enhances the shielding of test charges. Time scales for charging are determined by the ambient plasma parameters and the grain dimensions. They can be very short, approaching the ion plasma period for grain sizes of the order of an electron Debye length. For a slowly moving test charge the response potential is found as a power series in the test charge velocity. Collisional effects are included. Analytical expressions for the response potential, valid for all radial distances, are found up to second order in the test charge velocity. The first-order dynamical charging term is shown to be the consequence of the delay in the shielding due to the dynamics of the charging process. The remaining first-order terms are given by analytical expressions that yield the well known asymptotic power law forms for large distances.
Extended multilinear variable separation approach and multivalued localized excitations for some (2+1)-dimensional integrable systems
Authors: Tang Xiao-Yan , Lou Sen-Yue
Published: August 2003

The multilinear variable separation approach and the related “universal” formula have been applied to many (2+1)-dimensional nonlinear systems. Starting from the universal formula, abundant (2+1)-dimensional localized excitations have been found. In this paper, the universal formula is extended in two different ways. One is obtained for the modified Nizhnik–Novikov–Veselov equation such that two universal terms can be combined linearly and this type of extension is also valid for the (2+1)-dimensional symmetric sine-Gordon system. The other is for the dispersive long wave equation, the Broer–Kaup–Kupershmidt system, the higher order Broer–Kaup–Kupershmidt system, and the Burgers system where arbitrary number of variable separated functions can be involved. Because of the existence of the arbitrary functions in both the original universal formula and its extended forms, the multivalued functions can be used to construct a new type of localized excitations, folded solitary waves (FSWs) and foldons. The FSWs and foldons may be “folded” in quite complicated ways and possess quite rich structures and multiplicate interaction properties.
Symmetry and pattern formation for a planar layer of nematic liquid crystal
Authors: Chillingworth David , Golubitsky Martin
Published: August 2003

Using equivariant bifurcation theory, and on the basis of symmetry considerations independent of the model, we classify square and hexagonally periodic patterns that typically arise when a homeotropic or planar isotropic nematic state becomes unstable, perhaps as a consequence of an applied magnetic or electric field. We relate this to a Landau–de Gennes model for the free energy, and derive dispersion relations in sufficient generality to illustrate the role of up/down symmetry in determining which patterns can arise as a stable bifurcation branch from either initial state.
Thermal properties of La0.5Sr0.5Co1−xNixO3−δ ceramics using photopyroelectric technique
Authors: Sebastian M. T. , Menon C. Preethy , Philip J. , Schwartz R. W.
Published: August 2003

La 0.5 Sr 0.5 Co 1−x Ni x O 3−δ  (0⩽ x ⩽0.6) ceramics were prepared using a conventional solid-state ceramic route. The thermal properties—thermal conductivity and heat capacity—of these ceramics were measured by the photopyroelectric technique. The thermal conductivity was found to increase with increasing Ni content. These materials were also found to exhibit a metallic-type variation of thermal conductivity with temperature, and no metal-insulator (M-I) transition was found to occur in any of the samples prepared by this route. However, a M-I transition was found to occur in La0.5Sr0.5CoO3−δ samples prepared by hot pressing. The difference is attributed to variations in oxygen content in the samples.
Effect of ion implantation parameters on Al dopant redistribution in SiC after annealing: Defect recovery and electrical properties of p-type layers
Authors: Lazar M. , Raynaud C. , Planson D. , Chante J.-P. , Locatelli M.-L. , Ottaviani L. , Godignon Ph.
Published: August 2003

Epilayers of 6H and 4H–SiC were Al implanted with various doses to form p-type layers after a postimplantation annealing performed at 1700 °C/30 min. Rutherford backscattering spectrometry in the channeling mode analyses carried out before and after annealing show virgin nonimplanted equivalent spectra if the implanted layers are not amorphized. The amorphous layers are recrystallized after annealing with a residual damage level of the lattice relative to the quantity of the dopant implanted. Secondary ion mass spectrometry measurements performed on the implanted samples before and after annealing illustrate a good superposition of the profiles obtained before and after the annealing on nonamorphized samples. Dopant redistribution occurs after annealing, only on amorphized layers, with an intensity that increases with the implanted dose. Deduced from sheet resistance measurements, the dopant activation increases with the implanted dose. Activation of 80%–90% is obtained from capacitance–voltage measurements on samples implanted with a 1013 cm−2 total dose.
Copper grain boundary diffusion in electroless deposited cobalt based films and its influence on diffusion barrier integrity for copper metallization
Authors: Kohn A. , Eizenberg M. , Shacham-Diamand Y.
Published: August 2003

Electroless deposited Co-based alloys have been proposed as diffusion barriers for ultralarge-scale integrated microelectronic devices. In this study, Cu grain boundary diffusion in electroless deposited Co0.9W0.02P0.08 and Co0.9P0.1 in the temperature range between 300 and 450 °C was quantitatively studied and compared to physical vapor deposited (PVD) pure Co films. The transport of Cu atoms through these films is predominately via the grain boundaries, namely type-C diffusion kinetics. The diffusivity values were extracted from Cu depth profiles measured by secondary ion mass spectrometry. Copper diffusion through the various Co films obeys an Arrhenius relationship. Copper diffusivity in the electroless films is 2–3 orders of magnitude smaller than in PVD Co films. The diffusivity of Cu through electroless deposited Co0.9W0.02P0.08 is 5–10 times smaller than in electroless deposited Co0.9P0.1. The reduced diffusivity in the electroless films is a result of the significantly lower value of the pre-exponential factor. A qualitative explanation for the reduction of this factor is suggested based on a former study, which demonstrated that the Cu concentration in grain boundaries of electroless deposited Co-based films is considerably smaller than in pure Co. The obtained diffusivity values are compared with a functional electrical evaluation of barrier integrity in metal–oxide–semiconductor capacitors. We show that Cu diffusivity values combined with a failure criterion are in agreement with the electrical evaluation results and are of practical relevance in predicting barrier integrity.
Influence of roughness on the detachment force of elastic films from self-affine rough surfaces
Authors: Palasantzas G. , De Hosson J. Th. M.
Published: August 2003

This article concentrates on the influence of roughness on the detachment force of elastic films on self-affine rough surfaces. It is shown that the self-affine roughness at the junction of an elastic film and a hard solid substrate influences its detachment force in a way that the detachment force can be smaller than that of a flat surface for relatively high elastic modulus E depending also on the specific roughness details. For rougher surfaces the effect of elastic energy becomes more dominant with increasing ratio between the roughness amplitude and the roughness correlation length along the interface (w/ξ). The detachment force shows a maximum after which it decreases and becomes even lower than that of a flat surface. Similar is the case of partial contact where the detachment force also increases as the contact length increases up to a maximum (for contact lengths larger than the roughness correlation length ξ), and further decreases followed by saturation.
Extended edge states in finite Hall systems
Authors: Ferrari Christian , Macris Nicolas
Published: August 2003

We study edge states of a random Schrödinger operator for an electron submitted to a magnetic field in a finite macroscopic two dimensional system of linear dimensions equal to L. The y direction is L-periodic and in the x direction the electron is confined by two smoothly increasing parallel boundary potentials. We prove that, with large probability, for an energy range in the first spectral gap of the bulk Hamiltonian, the spectrum of the full Hamiltonian consists only on two sets of eigenenergies whose eigenfuntions have average velocities which are strictly positive/negative, uniformly with respect to the size of the system. Our result gives a well defined meaning to the notion of edge states for a finite cylinder with two boundaries, and extends previous studies on systems with only one boundary.
Optical studies of transparent ferroelectric strontium–barium niobate/silica nanocomposite
Authors: Lu S. G. , Mak C. L. , Wong K. H.
Published: August 2003

Transparent ferroelectric strontium–barium niobate (SBN) doped silica nanocomposites were prepared via a modified sol–gel process. Their structural properties were characterized by x-ray diffraction and Raman spectroscopy. It was found that by annealing the nanocomposites at temperatures between 600 and 800 °C, pure tetragonal tungsten bronze phase SBN crystallites with sizes ranging from 8 to 23 nm were obtained. Differential scanning calorimetry measurement has indicated that nanometer size ferroelectric SBN has a reduced phase transition temperature compared with that of bulk SBN. Photoluminescence and optical transmission studies of these composites have revealed noticeable blueshifts in the emission band peak and the absorption edge, respectively. The refractive index of the nanocomposite annealed at 700 °C was measured by ellipsometry. The value obtained is larger than that of pure sol–gel derived silica but smaller than that of SBN crystal, and can be described by the Bruggeman effective medium approximation.
Electronic interactions in codeposited films of naphthalene tetracarboxylic derivatives and metals
Authors: Nakayama Ken-ichi , Niguma Yasuro , Matsui Yoshitaka , Yokoyama Masaaki
Published: August 2003

Using various spectroscopic techniques, we have investigated the electronic interactions between organic molecules and metals in codeposited films to clarify the properties of the organic/metal interface, and to elucidate the potential of promising organic materials in electronics. Naphthalene tetracarboxylic anhydride codeposited with indium showed marked changes in its electronic absorption and electron spin resonance peaks under atmospheric conditions. X-ray diffraction and infrared absorption measurements revealed that these electronic interactions prevent any aggregation of organic molecules that results in the formation of microscopically mixed and amorphous-like films. From measurements on various combinations of organic molecules and metals, we have concluded that these electronic interactions can be attributed to partial charge transfer from the metal to carbonyl oxygen of the organic molecules.
Design of specularly reflective layers in spin valves
Authors: Hong Jongill , Kanai Hitoshi
Published: August 2003

We confirmed that the location of a specularly reflective oxide layer is critical to enhance the giant magnetoresistance effect in a spin valve. In particular, embedding an oxide layer in the pinned layer is more effective than placing oxide on top of the free layer to increase the giant magnetoresistance values when the free layer is thick, and this makes the spin valve robust for high density magnetic recording. This behavior can be explained by the mirror effect that arises as a result of the structure of the spin valve.
Rapid density-measurement system with vibrating-tube densimeter
Authors: Kayukawa Yohei , Hasumoto Masaya , Watanabe Koichi
Published: August 2003

Concerning an increasing demand for environmentally friendly refrigerants including hydrocarbons, thermodynamic properties of such new refrigerants, especially densities, are essential information for refrigeration engineering. A rapid density-measurement system with vibrating-tube densimeter was developed in the present study with an aim to supply large numbers of high-quality PVT property data in a short period. The present system needs only a few minutes to obtain a single datum, and requires less than 20 cm3 sample fluid. PVT properties in the entire fluid-phase, vapor-pressures, saturated-liquid densities for pure fluid are available. Liquid densities, bubble-point pressures and saturated-liquid densities for mixture can be obtained. The measurement range is from 240 to 380 K for temperature and up to 7 MPa for pressure. By employing a new calibration function, density can be precisely obtained even at lower densities. The densimeter is calibrated with pure water and iso-octane which is one of the density-standard fluids, and then measurement uncertainty was evaluated to be 0.1 kg m−3 or 0.024% whichever greater in density, 0.26 kPa or 0.022% whichever greater in pressure and 3 mK for temperature, respectively. The performance of the present measurement system was examined by measuring thermodynamic properties for refrigerant R134a. The experimental results were compared with available equation of state and confirmed to agree with it within ±0.05% for liquid densities while ±0.5% in pressure for the gas phase.
Calculation and measurement of the time-of-flight spread in a hemispherical electron energy analyzer
Authors: Kugeler O. , Marburger S. , Hergenhahn U.
Published: August 2003

We have determined the transit time distribution of electrons passing a high resolution hemispherical energy analyzer. Comparison of our measured results with analytical expressions reveals that differing transit times between electrons of equal kinetic energy mainly build up on the Kepler-type orbits on which the electrons travel through the hemispheres. To facilitate the measurements, we have installed a position sensitive electron detector capable of single event detection into our spectrometer. This device is based on a delay-line anode. We briefly report on the energy resolution achieved in comparison with a slower readout system via a fluorescent screen. The transit time distribution is important in coincidence experiments, where electrons detected in the hemispherical analyzer are to be related to events in other detectors. We discuss the feasibility of electron–electron coincidence experiments using a hemispherical detector plus a time-of-flight drift tube for energy discrimination of an electron pair.
Radiation measurements by a cryogenic pn junction InSb detector with operating temperatures up to 115 K
Authors: Kanno Ikuo , Yoshihara Fumiki , Nouchi Ryo , Sugiura Osamu , Murase Yasuhiro , Nakamura Tatsuya , Katagiri Masaki
Published: August 2003

Pn junction-type radiation detectors were fabricated with an InSb substrate. The detectors had 1000 times higher resistances than those of previously reported Schottky-type detectors. The output pulses of the preamplifier were analyzed from the point of view of the contribution of electrons and holes. The energy spectra of Am241 alpha particles were measured at operating temperatures of up to 115 K. The inherent voltage of the detector was estimated.
In situ characterization of ultrafast laser pulses for sum frequency surface studies
Authors: Arnolds Heike , Symonds Jonathan P. R. , Zhang Vanessa L. , King David A.
Published: August 2003

Femtosecond laser pulses used for studies of metal surfaces in ultrahigh vacuum can be characterized by sum frequency generation. Deposition of an ultrathin alkali metal film enhances the surface nonlinear response by two orders of magnitude and allows the measurement of all necessary laser pulse parameters in 30 min at a repetition rate of 10 Hz.
Trapped-particle diocotron modes
Authors: Hilsabeck T. J. , O’Neil T. M.
Published: August 2003

Recent experiments have characterized trapped-particle modes on a non-neutral plasma column [A. A. Kabantsev, C. F. Driscoll, T. J. Hilsabeck, T. M. O’Neil, and J. H. Yu, Phys. Rev. Lett. 87, 225002 (2001)], and in this paper we present a theoretical model of the modes. Theoretical predictions for the mode frequency, damping rate, and eigenmode structure are compared to experimental observation. The modes are excited on a non-neutral plasma column in which classes of trapped and passing particles have been created by the application of a potential barrier. The column resides in a Malmberg–Penning trap, and the barrier is created by applying a voltage to an azimuthally symmetric section of the wall near the axial mid-point of the column. Low energy particles near the edge of the column (where the barrier is strong) are trapped in one end or the other, while high energy particles near the center of the column transit the entire length. The modes have azimuthal variation l=1,2,…, and odd z-symmetry. The trapped particles on either side of the barrier execute E×B drift oscillations producing density perturbations that are 180° out of phase with each other, while passing particles run back and forth along the field lines attempting to Debye shield the perturbed charge density. The mode is damped by collisional scattering across the separatrix between trapped and passing particles. The damping rate is calculated using a boundary layer analysis of the Fokker–Planck equation. It is also shown that the damping is associated with the radial transport of plasma particles.
Electroluminescent devices based on cross-linked polymer blends
Authors: Bozano Luisa D. , Carter Kenneth R. , Lee Victor Y. , Miller Robert D. , DiPietro Richard , Scott J. Campbell
Published: August 2003

We report the electrical and optical properties of two-component blends of electron and hole transporting materials in single and bilayer structures for organic light emitting diode (OLED) applications. The materials considered were a blue-emitting bipolar transporting polyfluorene, poly(9,9-di-n-hexylfluorene) (DHF), and a hole-transporting material, poly-[4-nhexyltriphenylamine] (HTPA). We compare the steady state OLED performance, transport, and optical properties of devices and describe morphology studies of the polymer films based on cross-linkable (x) blends with the analogous non-cross-linkable blends. The cross-linkable blends exhibit highest efficiency at low concentrations of the hole transporting material. At these concentrations the single layer OLEDs reach efficiencies greater than 0.1%, and are higher than for single layer x-DHF or the binary non-cross-linkable blend by more than an order of magnitude. Bilayer structures with homogeneous x-HTPA as hole transport layer show efficiencies between 0.08% and 0.96%, depending on the blend concentration in the emitting layer and on the top contact. We interpret these results in terms of the relative degree of phase segregation in the cross-linked networks versus the non-cross-linkable blends.
Permissible symmetries of multi-domain configurations in perovskite ferroelectric crystals
Authors: Erhart Jiřı́ , Cao Wenwu
Published: August 2003

Permissible symmetries of multi-domain structures are analyzed in the m3̄m→3m, m3̄m→4mm and m3̄m→mm2 ferroelectric species. Domain structures produced by the application of external electric and/or mechanical fields that allow for the formation of two-dimensional domain superlattice are described in terms of effective group symmetry. Based on our analysis, the most perspective directions for properties enhancement through domain engineering are specified for perovskite ferroelectric crystals having tetragonal, rhombohedral, and orthorhombic symmetries.
Surface plasmon waveguides with gradually doped or NiAl intermetallic compound buried contact for terahertz quantum cascade lasers
Authors: Indjin D. , Ikonić Z. , Harrison P. , Kelsall R. W.
Published: August 2003

Improved designs of surface plasmon waveguides for use in GaAs/AlGaAs terahertz quantum cascade lasers are presented. Modal losses and confinement factors are calculated for TM modes in metal-variably doped multilayer semiconductor and metal-intermetallic compound layer clad structures and compared with those obtained in recently realized metal-highly doped semiconductor clad layer structures. Considerable improvements of the mode confinement factors are predicted, and guidelines for choosing the confinement layer parameters are given.
Porosity in plasma enhanced chemical vapor deposited SiCOH dielectrics: A comparative study
Authors: Grill A. , Patel V. , Rodbell K. P. , Huang E. , Baklanov M. R. , Mogilnikov K. P. , Toney M. , Kim H.-C.
Published: August 2003

The low dielectric constant (k) of plasma enhanced chemical vapor deposited SiCOH films has been attributed to porosity in the films. We have shown previously that the dielectric constant of such materials can be extended from the typical k values of 2.7–2.9 to ultralow-k values of k=2.0. The reduction in the dielectric constants has been achieved by enhancing the porosity in the films through the addition of an organic material to the SiCOH precursor and annealing the films to remove the thermally less-stable organic fractions. In order to confirm the relation between dielectric constant and film porosity the latter has been evaluated for SiCOH films with k values from 2.8 to 2.05 using positron annihilation spectroscopy, positron annihilation lifetime spectroscopy, small angle x-ray scattering, specular x-ray reflectivity, and ellipsometric porosimetry measurements. It has been found that the SiCOH films with k=2.8 had no detectable porosity, however the porosity increased with decreasing dielectric constant reaching values of 28%–39% for k values of 2.05. The degree of porosity and the pore size determined by the dissimilar techniques agreed within reasonable limits, especially when one takes into account the small pore size in these films and the different assumptions used by the different techniques. The pore size increases with decreasing k, however the diameter remains below 5 nm for k=2.05, most of the pores being smaller than 2.5 nm.