bluuebunny/crossref_metadata_2025 huggingface dataset:
Low-cost all-polymer integrated circuits
Authors: Drury C. J. , Mutsaers C. M. J. , Hart C. M. , Matters M. , de Leeuw D. M.
Published: July 2002

A technology has been developed to make all polymer integrated circuits. It involves reproducible fabrication of field-effect transistors in which the semiconducting, conducting and insulating parts are all made of polymers. The fabrication on flexible substrates uses spin-coating of electrically active precursors and patternwise exposure of the deposited films. In the whole process stack integrity is maintained. Vertical interconnects are made mechanically. As a demonstrator functional 15-bit programmable code generators are fabricated. These circuits still operate when the foils are sharply bent. Due to the limited number of process steps the technology is potentially inexpensive.
Strain relaxation and strong impurity incorporation in epitaxial laterally overgrown GaN: Direct imaging of different growth domains by cathodoluminescence microscopy and micro-Raman spectroscopy
Authors: Bertram F. , Riemann T. , Christen J. , Kaschner A. , Hoffmann A. , Thomsen C. , Hiramatsu K. , Shibata T. , Sawaki N.
Published: July 2002

Epitaxial lateral overgrowth GaN structures oriented along the 〈112_0〉 direction were comprehensively characterized by cathodoluminescence (CL) microscopy and micro-Raman spectroscopy. CL microscopy directly visualizes the significant differences between the overgrown areas on top of the SiO2 mask and the coherently grown regions between the SiO2 stripes in quantitative correlation with micro-Raman spectroscopy mapping of the local strain and free carrier concentration. The overgrown GaN shows a partial strain relaxation and a high carrier concentration that strongly broadens the luminescence. A strong impurity incorporation is evidenced in the coalescence regions. In contrast, the local luminescence from the areas of coherent (0001) growth is dominated by narrow excitonic emission, demonstrating the superior crystalline quality.
Ultrahigh-density atomic force microscopy data storage with erase capability
Authors: Binnig G. , Despont M. , Drechsler U. , Häberle W. , Lutwyche M. , Vettiger P. , Mamin H. J. , Chui B. W. , Kenny T. W.
Published: July 2002

We report a simple atomic force microscopy-based concept for a hard disk-like data storage technology. Thermomechanical writing by heating a Si cantilever in contact with a spinning polycarbonate disk has already been reported. Here the medium has been replaced with a thin polymer layer on a Si substrate, resulting in significant improvements in storage density. With this new medium, we achieve bit sizes of 10–50 nm, leading to data densities of 500 Gbit/in.2. We also demonstrate a novel high-speed and high-resolution thermal readback method, which uses the same Si cantilevers that are used in the writing process, and the capability to erase and rewrite data features repeatedly.
Writing and reading of single magnetic domain per bit perpendicular patterned media
Authors: Todorovic Mladen , Schultz Sheldon , Wong Joyce , Scherer Axel
Published: July 2002

By fabricating patterned media with a large number of nanoscale single domain magnetic particles embedded in a nonmagnetic substrate, and by writing the magnetization for each of these particles in a desired direction, nonvolatile magnetic storage of information could reach densities much higher than what is currently thought possible for longitudinal continuous media. We have fabricated high aspect ratio perpendicular nickel columnar nanoparticles embedded in a hard Al2O3/GaAs substrate. We show that the magnetization states of the individual magnets can be controlled by demonstrating that prototype patterned “single magnetic domain per bit” data tracks can be written and read back using current magnetic information storage technology.
Nonlinear acoustoelectric interactions in GaAs/LiNbO3 structures
Authors: Rotter M. , Wixforth A. , Govorov A. O. , Ruile W. , Bernklau D. , Riechert H.
Published: July 2002

Surface acoustic waves accompanied by very large piezoelectric fields can be created in a semiconductor/piezoelectric hybrid system. Such intense waves interact with the mobile carries in semiconductor quantum well structures in a manner being strongly governed by nonlinear effects. At high sound intensities, a formerly homogeneous two-dimensional electron system breaks up into well confined stripes surfing the wave. As a result, we observe a strong reduction of electronic sound attenuation. On the other hand, large momentum transfer between the electron system and the wave results in nonlinear acoustoelectric effects and acoustoelectric amplification. We describe our experimental findings in terms of a generalized theory of the acoustoelectric effect and discuss the importance for possible device applications.
Self-enhancement in the electroluminescence of a near-infrared ionic dye
Authors: Suzuki Hiroyuki
Published: July 2002

This letter reports self-enhancement behavior observed in the near-infrared electroluminescence (EL) of an ionic dye, 2-[6-(4-dimethylaminophenyl)-2,4-neopentylene-1,3,5-hexatrienyl]-3-methylbenzothiazolium perchlorate doped in poly(N-vinylcarbazole). The EL intensity measured under a constant current, and therefore, the external EL quantum efficiency (φex), increases with time both when the EL is generated continuously in a constant current mode and kept in a no-bias field, whereas it decreases in a reverse-bias field. With an enhancement factor of about 80 under a constant current of 0.1 mA/cm2, φex reaches the 1% photons/electron level. I conclude that the behavior originates from the enhanced electron and hole injection caused by the alignment of the doped ionic dye molecules along the bias field.
Low-voltage, 30 nm channel length, organic transistors with a self-assembled monolayer as gate insulating films
Authors: Collet J. , Tharaud O. , Chapoton A. , Vuillaume D.
Published: July 2002

We made nanometer-scale (gate length of 30 nm) organic thin-film transistors using a self-assembled monolayer (2 nm thick) as a gate insulator. The fabrication steps combine electron-beam lithography and lift-off techniques for the deposition of both metal electrodes and organic semiconductors with a chemical approach (self-assembly of organic molecules) to fabricate the gate insulator. Good performances of these transistors (with a record subthreshold slop of 350 mV/decade and a cutoff frequency of 20 kHz) and low-voltage operation (<2 V) are demonstrated down to a gate length of 200 nm. A gate voltage modulation of the source-to-drain tunnel current is demonstrated for the 30 nm gate length device.
Highly spin-polarized chromium dioxide thin films prepared by chemical vapor deposition from chromyl chloride
Authors: DeSisto W. J. , Broussard P. R. , Ambrose T. F. , Nadgorny B. E. , Osofsky M. S.
Published: July 2002

Highly spin-polarized chromium dioxide (CrO2) thin films were deposited on (100) TiO2 substrates by chemical vapor deposition using chromyl chloride as a precursor. The spin polarization, as measured by the point contact Andreev reflection technique, was 81±3%. X-ray diffraction θ/2θ scans indicated the films grew completely (100) oriented, in registry with the (100) oriented TiO2 substrate. X-ray diffraction φ scans on the CrO2 (110) reflection indicated the expected twofold symmetry, with no evidence of misaligned material. The resistivity at room temperature was 240 μΩ cm and decreased to 10 μΩ cm at 5 K, consistent with metallic behavior. The films were ferromagnetic with a Curie temperature of 395 K and a coercivity of ∼100 Oe at 298 K. The use of chromyl chloride as a precursor resulted in efficient and controlled CrO2 film growth.
Alternating current impedance and Raman spectroscopic study on electrochromic a-WO3 films
Authors: Lee Se-Hee , Cheong Hyeonsik M. , Tracy C. Edwin , Mascarenhas Angelo , Pitts J. Roland , Jorgensen Gary , Deb Satyen K.
Published: July 2002

The chemical diffusion of lithium ions in a-LixWO3 films is investigated using alternating current impedance spectroscopy and Raman scattering measurements. The diffusion coefficients increase with increasing x in a-LixWO3 up to x=0.072 and then decrease. Raman measurements show that the W6+=O/O–W6+–O ratio also increases at the early stage of lithium insertion and then decreases with further lithium insertion. We conclude that the diffusion kinetics of lithium ions in a-LixWO3 films is very closely related to the W6+=O/O–W6+–O ratio.
Efficient optical Kerr shutter for femtosecond time-resolved luminescence spectroscopy
Authors: Kinoshita S. , Ozawa H. , Kanematsu Y. , Tanaka I. , Sugimoto N. , Fujiwara S.
Published: July 2002

We have measured optical Kerr effect responses, transmission spectra, and emission properties due to two photon absorption for 17 kinds of optical glass materials and have evaluated their capabilities as an optical Kerr shutter (OKS) for time-resolved luminescence spectroscopy. There is a tendency that the larger the refractive index and dispersion are, the higher the electronic response of optical Kerr effect becomes. Transmission efficiency as high as several percents with the time resolution of 350 fs is obtained using a highly Bi2O3-doped glass plate under 200 kHz repetitive pulse excitation. The time-resolved luminescence spectrum of Zn-tetraphenylporphyrin dye solution is demonstrated using the combination of the OKS and a monochromator equipped with a charge coupled device detector.
Relation between the molecular orientations of a very thin liquid crystal layer and an underlying rubbed polyimide film
Authors: Ito Naoki , Sakamoto Kenji , Arafune Ryuichi , Ushioda Sukekatsu
Published: July 2002

By polarized infrared absorption spectroscopy, we have determined the relation between the molecular orientation of a rubbed polyimide film and that of a very thin liquid crystal (LC) layer (approximately a monolayer of 8CB molecules) in contact with the polyimide film. The molecular orientation of the rubbed polyimide film was determined by fitting theoretically the incident angle dependence of the infrared absorption for molecular vibrations polarized parallel to the length of the polymer. Approximately a monolayer of 8CB molecules was deposited on a rubbed polyimide film with previously measured molecular orientation. The molecular orientation of this LC layer was also determined by polarized infrared absorption. We found that the LC molecules and the polyimide chains are oriented, on average, along the rubbing direction and tilted up from the surface, and that the molecular order of the LC layer is higher than that of the underlying rubbed polyimide film.
Designing two-dimensional electron gases in GaAs/InGaAs/AlGaAs, δ-doped AlGaAs/GaAs, and AlGaAs/InGaAs/GaAs heterostructures for single electron transistor application
Authors: Fu Y. , Wang T. H. , Willander M.
Published: July 2002

We have theoretically studied two types of two-dimensional electron gases (2DEGs) in GaAs/InGaAs/AlGaAs and δ-doped-AlGaAs/GaAs heterostructures for single-electron transistor applications by self-consistently solving the Schrödinger and Poisson equations. Assuming the dominant effect of the ionized impurity scattering in determining the low-field carrier mobility, it has been shown that introducing an InGaAs layer to the conventional GaAs/AlGaAs heterostructure greatly increases the sheet density of the 2DEG and the corresponding carrier mobility. The δ-doped AlGaAs/GaAs and AlGaAs/InGaAs/GaAs heterostructures provide us with an even better control of the 2DEG with higher sheet density and carrier mobility.
Shifted metric procedure for flux tube treatments of toroidal geometry: Avoiding grid deformation
Authors: Scott B.
Published: July 2002

Recent treatments of flute-mode-type turbulence in closed magnetic flux surface geometry align the coordinates to the magnetic field, leaving the field with one nonvanishing contravariant component. Magnetic shear leads to strong deformation of coordinate cells in the plane perpendicular to the field, impacting the results. To remedy this one can apply shifts in the drift angle coordinate, the one which remains purely periodic. All operations involving polarization and nonlinear advection are then performed locally on an orthogonal grid, allowing arbitrarily sheared and shaped magnetic geometries in computations.
Steady-state fully noninductive operation with electron cyclotron current drive and current profile control in the tokamak à configuration variable (TCV)
Authors: Sauter O. , Angioni C. , Coda S. , Gomez P. , Goodman T. P. , Henderson M. A. , Hofmann F. , Hogge J.-P. , Moret J.-M. , Nikkola P. , Pietrzyk Z. A. , Weisen H. , Alberti S. , Appert K. , Bakos J. , Behn R. , Blanchard P. , Bosshard P. , Chavan R. , Condrea I. , Degeling A. , Duval B. P. , Fasel D. , Favez J.-Y. , Favre A. , Furno I. , Kayruthdinov R. R. , Lavanchy P. , Lister J. B. , Llobet X. , Lukash V. E. , Gorgerat P. , Isoz P.-F. , Joye B. , Magnin J.-C. , Manini A. , Marlétaz B. , Marmillod P. , Martin Y. R. , Martynov An. , Mayor J.-M. , Minardi E. , Mlynar J. , Paris P. J. , Perez A. , Peysson Y. , Piffl V. , Pitts R. A. , Pochelon A. , Reimerdes H. , Rommers J. H. , Scavino E. , Sushkov A. , Tonetti G. , Tran M. Q. , Zabolotsky A.
Published: July 2002

Fully noninductive, steady-state electron cyclotron current drive (ECCD) has been demonstrated for the first time in experiments carried out in the tokamak à configuration variable (TCV) [O. Sauter et al., Phys. Rev. Lett. 84, 3322 (2000)]. By appropriately distributing six 0.45 MW ECCD sources over the discharge cross section, fully noninductive, stable, and stationary plasmas with Ip up to 210 kA were obtained for the full discharge duration of 1.9 s, corresponding to more than 900 energy confinement times and more than 10 current redistribution times at an average current drive efficiency η20CD=0.01[1020 A W−1 m−2]. These experiments have also demonstrated for the first time the steady recharging of the ohmic transformer using ECCD only. The effect of localized off-axis electron cyclotron heating (ECH) and EC current drive (ECCD) (co- and counter-) is investigated showing that locally driven currents amounting to only 1% of Ip significantly alter sawtooth periods and crash amplitudes. An improved quasi-stationary core confinement regime, with little or no sawtooth activity, has been obtained by a combination of off-axis ECH and on-axis CNTR–ECCD.
The structure of liquid tetrachlorides CCl4, SiCl4, GeCl4, TiCl4, VCl4, and SnCl4
Authors: Jóvári Pál , Mészáros György , Pusztai László , Sváb Erzsébet
Published: July 2002

Neutron diffraction measurements have been carried out for determining the total structure factor of liquid CCl4, SiCl4, GeCl4, TiCl4, VCl4, and SnCl4. The data were interpreted using the reverse Monte Carlo method, where the procedure started from results of molecular dynamics calculations. It is demonstrated that simple repulsive interatomic potential models are suitable for describing the most important structural features qualitatively. Based on detailed analyses of particle configurations, it is shown that “corner-to-face” type near-neighbor arrangements, that have been promoted for the interpretation of these structures over the last 20 years, are actually very rare, their occurrence being around 5% only. Instead, the dominance of “corner-to-corner” type orientational correlations is found.
Extending the vibrational self-consistent method: Using a partially separable wave function for calculating anharmonic vibrational states of polyatomic molecules
Authors: Wright Nicholas J. , Gerber R. Benny
Published: July 2002

A new method for the treatment of correlation effects between modes in vibrational self-consistent-field (VSCF) calculations is introduced. It is based upon using a partially separable form for the wave function. As a result, some of the modes are treated as mutually fully correlated, while the rest are separable. The modes which are explicitly coupled together in the calculation are chosen on physical grounds. Trial calculations are performed upon H2O, H3O+, and CH3NH2 and indicate that the method performs well. The agreement with experiment for the explicitly coupled modes is improved when compared to both the vibrational self-consistent-field method and its correlation-corrected extension. When interfaced with an electronic structure code this method opens the way for the accurate first-principles prediction of vibrational frequencies of strongly coupled modes. If only a few modes are mutually strongly coupled, the method has a very favorable scaling with system size, as does VSCF itself.
A theoretical study of H–Ar–Cl
Authors: McDowell Sean A. C.
Published: July 2002

Ab initio calculations at the B3LYP and MP4(SDQ) levels of theory were performed on the noble gas-containing compound H–Ar–Cl. The calculations indicate that the molecule should be metastable with an activation barrier of 73.0 kJ mol−1 for the lowest-energy fragmentation to HCl and Ar. Similar calculations on H–He–Cl and H–Ne–Cl failed to locate stable species. This result suggests that it should be possible to generate and observe H–Ar–Cl at sufficiently low temperatures.
Temperature dependence of exchange field in exchange-spring magnets
Authors: Yin J. H. , Sun Z. G. , Zhang Z. R. , Zhang H. W. , Shen B. G.
Published: July 2002

Pr 8 Fe 88 B 4 ribbons prepared by melt spinning have been investigated by x-ray diffraction, differential thermal analysis, thermomagnetic analysis, atom force microscopy, and superconducting quantum interface device magnetometer. The results show that the annealed ribbons consist of the Pr2Fe14B and α-Fe phases. The magnetization of soft α-Fe phase remains parallel to the magnetization of the hard Pr2Fe14B phase for fields less than the exchange field (Hex). The exchange field in exchange-spring magnets, determined from the demagnetization curves measured at various temperatures, increases with decreasing grain size and measure temperature. The temperature dependence of exchange field was analyzed qualitatively by the expression Hex=(AK)1/2/(Mst).
193 nm photolysis of vinyl bromide: Nascent product distribution of the C2H3Br→C2H2 (vinylidene)+HBr channel
Authors: Liu Dean-Kuo , Letendre Laura T. , Dai Hai-Lung
Published: July 2002

The internal energy content of the photofragments HBr and C2H2 from the minor channel of the photolysis of C2H3Br with 193 nm radiation has been measured using time-resolved infrared Fourier transform IR emission spectroscopy with 0.5 μs resolution. Vibrational level population and the rotational population of the HBr fragment are determined from 1.0 μs following the photolysis until complete HBr relaxation. The nascent distribution of HBr is extrapolated, from a collision quenching model with a Boltzmann distribution, to be at 8690 and 7000 K for the vibration and rotation respectively. The product vibrational energy distribution supports a reaction mechanism based on the 3-centered HBr elimination process yielding vinylidene and HBr. The nascent internal energy of vinylidene is deduced to be 24 kcal/mol. Vinylidene isomerizes to acetylene and the acetylene emission bands, ν3, ν4+ν5 and ν5, are detected.
The stability of polar oxide surfaces: The interaction of H2O with ZnO(0001) and ZnO(0001̄)
Authors: Wander A. , Harrison N. M.
Published: July 2002

Recently, a new mechanism for the stabilization of the polar surfaces of ZnO has been proposed. This mechanism involves the transfer of electrons between the (0001) and (0001̄) surface. In the current study an alternative mechanism involving the adsorption of water onto the polar surfaces has been investigated using ab initio all electron, hybrid density-functional theory. On the basis of the current study, such a stabilization mechanism can be ruled out at low-temperatures and low-partial pressure of water. In addition, we present evidence that the ZnO(0001̄)–O surface may be a gas sensor for hydrogen.
Electrical properties and modeling of ultrathin impurity-doped silicon dioxides
Authors: Chang Wai-Jyh , Houng Mau-Phon , Wang Yeong-Her
Published: July 2002

The electrical properties of silicon dioxides doped with impurities (fluorine and/or nitrogen) are investigated in this article. Pure silicon dioxide (SiO2), fluorine-doped silicon oxide (SiOF), nitrogen-doped silicon oxide (SiON), and nitrogen-doped SiOF (SiOFN) are our choices for investigation in this study. The oxide films are prepared from liquid-phase-deposited fluorinated silicon oxides under O2 or N2O annealing. The leakage current as a function of applied voltage for impurity-doped oxides was simulated using a generalized trap-assisted tunneling (GTAT) model at moderate fields of 5–8 MV/cm. Two important parameters, trap energy level Φt and trap concentration Nt, are directly derived by this model from simple current–voltage characteristics. The relationships of Φt and Nt on various experimental conditions (annealing temperature, time, gases, and initial oxide thickness) are comprehensively studied based on GTAT modelings.
Influence of the temperature and excitation power on the optical properties of InGaAs/GaAs quantum wells grown on vicinal GaAs(001) surfaces
Authors: Martini S. , Quivy A. A. , Tabata A. , Leite J. R.
Published: July 2002

Photoluminescence experiments were performed as a function of temperature and excitation intensity in order to investigate the optical properties of In0.1Ga0.9As/GaAs quantum wells grown on vicinal GaAs(001) substrates with different miscut angles. The misorientation of the surface played an important role and influenced the intensity, efficiency, energy, and full width at half maximum of the optical emission, as well as the segregation of indium atoms. It is shown that at high temperature the optical properties of InGaAs quantum wells grown on vicinal substrates are slightly inferior to ones of the same structure grown a nominal surface because of the faster escape of the carriers.
Adsorption and thermal dehydrogenation of ammonia on Ru(112̄1)
Authors: Jacobi K. , Wang Y. , Fan C. Y. , Dietrich H.
Published: July 2002

Adsorption and thermal dehydrogenation of NH3, adsorbed at 80 K on the open Ru(112̄1) surface, was studied using high-resolution electron energy-loss spectroscopy (HREELS) and thermal desorption spectroscopy (TDS). For the NH3 monolayer, a strong dipole-active mode is found at 15 meV which is newly assigned to Tz, the frustrated-translation mode perpendicular to the surface of NH3 bonding with the nitrogen atom to the Ru surface. Increasing the temperature, 70% of NH3 desorbs before a channel for dehydrogenation opens at about 280 K. The remaining 30% decomposes completely during further warming to 470 K. The dehydrogenation of NH3 gives rise to four peaks in the H2 TDS which are assigned to desorption of coadsorbed hydrogen at 220 K and three dehydrogenation reaction steps at 320, 360, and 420 K in accordance with HREELS. The reaction intermediates NH2 and NH are identified through HREELS. In a new interpretation NH2 is characterized by intense modes at 163 meV (rocking) and at 189 meV (scissoring). Using a maximum entropy algorithm six frequencies for ν(Ru–N) were resolved at 46, 50, 58, 61, 69, and 75 meV.
Thermal diffusivity measurements in the photoacoustic open-cell configuration using simple signal normalization techniques
Authors: Balderas-López J. A. , Mandelis A.
Published: July 2002

A generalized model for the open photoacoustic cell configuration (OPC) technique, involving one-dimensional heat diffusion across two layers, is presented. The analytical results are particularly suitable for applications with dielectric solids, such as polymers and resins. Two effective normalization procedures for simple and reliable measurement of the thermal diffusivity of this kind of materials using an OPC are also presented. The thermal diffusivity of three different materials (a dental resin, an epoxy resin, and a polymer foil) was measured and excellent agreement was obtained with some values reported in the literature. © 2001 American Institute of Physics.
Lead oxide nanobelts and phase transformation induced by electron beam irradiation
Authors: Pan Z. W. , Dai Z. R. , Wang Z. L.
Published: July 2002

β- PbO 2 nanobelts, with a rectangular cross section, a typical length of 10–200 μm, a width of 50–300 nm, and a width-to-thickness ratio of 5–10, have been successfully synthesized by simple elevated evaporation of commercial PbO powders at high temperature. The PbO2 nanobelts are enclosed by top surfaces ±(201) and side surfaces ±(101̄) and their growth direction is [010]. Each PbO2 nanobelt is found to have a large polyhedral Pb tip at one of its ends, suggesting the growth is dominated by a vapor–liquid–solid mechanism. Electron beam irradiation of the PbO2 nanobelts results in the phase transformation from PbO2 to PbO and finally to Pb.
Nonexistent electron affinity of OCS and the stabilization of carbonyl sulfide anions by gas phase hydration
Authors: Surber Eric , Ananthavel S. P. , Sanov Andrei
Published: July 2002

We report the formation of heterogeneous OCS–water cluster anions [(OCS)n(H2O)k]− (n⩾1,n+k⩾2), of which OCS−⋅H2O is the most interesting species in view of the near absence of unhydrated OCS− in the same ion source. The presence of OCS−⋅H2O indicates that the intra-cluster formation of OCS− does occur as part of the [(OCS)n(H2O)k]− formation mechanism. In this light, the near absence of unhydrated OCS− anions points towards their metastable nature, while the abundance of the hydrated anions is attributed to the stabilizing effect of hydration. These conclusions are supported by the results of an extensive theoretical investigation of the adiabatic electron affinity (EA) of OCS. We conclude that the EA of OCS is either negative or essentially zero. The best estimate based on the Gaussian-3 theory calculation puts the EA at −0.059±0.061 eV. A study of the structure and energetics of OCS−⋅H2O predicts the existence of four structural isomers. Using the coupled-cluster theory, we find that the most stable structure is stabilized by 0.543 eV relative to the separated OCS−+H2O limit.
Evaluation of nematic liquid-crystal director-orientation using shear horizontal wave propagation
Authors: Inoue M. , Yoshino K. , Moritake H. , Toda K.
Published: July 2002

The nematic liquid-crystal director-orientation in the vicinity of the interface between a liquid-crystal layer and a glass substrate is evaluated in various orientations under an applied electric field, using shear horizontal (SH) wave propagation. The measured acoustic phase delay is related to numerical analysis of the propagation characteristics of the SH wave in a trilayer structure containing a nematic liquid-crystal layer (4-cyano-4′-pentylbiphenyl: 5CB) between two glass plates. This technique using SH wave propagation in a liquid-crystal cell is promising for evaluating the nematic liquid-crystal director angle in the vicinity of the interface.
Fiber bundles in quantum physics
Authors: Sen R. N. , Sewell G. L.
Published: July 2002

The theory of fiber bundles provides a natural setting for the description of macroscopic quantum systems, wherein their classical and quantum features are represented by actions on the base manifolds and the fibers, respectively, of the relevant bundles. We provide realizations of this picture in the description of (a) quasiparticle excitations of many-body systems, especially those in superfluid helium, (b) the interplay between the microscopic and macroscopic dynamics in certain irreversible processes, such as that of a laser, and (c) local thermodynamic equilibrium. In particular, (b) involves the treatment of a dynamical system which is defined on a vector bundle.
Effects of super-Gaussian electron velocity distributions on the ion feature of Thomson scattering off two-ion plasmas
Authors: Liu Z. J. , Zheng Jian , Yu C. X.
Published: July 2002

The influence of super-Gaussian velocity distributions on the ion feature of Thomson scattering off two-ion plasmas is studied. The analytical solution to the dispersion equation shows that although both the frequencies of the two (fast and slow) ion-acoustic waves increase with the index of the super-Gaussian, the slow wave is more weakly dependent on the index due to the screening of the light ions. In the case that plasma can sustain two lightly damped ion-acoustic waves, the inferred plasma parameters such as electron temperature and plasma temperature ratio may suffer some errors without consideration of super-Gaussian electron velocity distributions. Since the relative intensity between the resonant peaks of the fast and slow waves is sensitive to the super-Gaussian index, the super-Gaussian velocity distributions may be measurable with Thomson scattering off laser-heated two species ion plasmas.
Generalized lower-hybrid drift instabilities in current-sheet equilibrium
Authors: Yoon Peter H. , Lui Anthony T. Y. , Sitnov Mikhail I.
Published: July 2002

A class of drift instabilities in one-dimensional current-sheet configuration, i.e., classical Harris equilibrium, with frequency ranging from low ion–cyclotron to intermediate lower-hybrid frequencies, are investigated with an emphasis placed on perturbations propagating along the direction of cross-field current flow. Nonlocal two-fluid stability analysis is carried out, and a class of unstable modes with multiple eigenstates, similar to that of the familiar quantum mechanical potential-well problem, are found by numerical means. It is found that the most unstable modes correspond to quasi-electrostatic, short-wavelength perturbations in the lower-hybrid frequency range, with wave functions localized at the edge of the current sheet where the density gradient is maximum. It is also found that there exist quasi-electromagnetic modes located near the center of the current sheet where the current density is maximum, with both kink- and sausage-type polarizations. These modes are low-frequency, long-wavelength perturbations. It turns out that the current-driven modes are low-order eigensolutions while the lower-hybrid-type modes are higher-order states, and there are intermediate solutions between the two extreme cases. Attempts are made to interpret the available simulation results in light of the present eigenmode analysis.
ZrNbCuNiAl bulk metallic glass matrix composites containing dendritic bcc phase precipitates
Authors: Kühn U. , Eckert J. , Mattern N. , Schultz L.
Published: July 2002

We report on phase formation of a multicomponent Zr66.4Nb6.4Cu10.5Ni8.7Al8 glass-forming alloy upon copper mold casting. A bcc phase embedded in a glassy matrix forms for moldcast bulk samples yielding an in-situ bulk metallic glass matrix composite upon slow cooling from the melt. Upon annealing, the first exothermic transformation of the material is related to precipitation of an icosahedral phase from the glassy matrix. The formation of the bcc phase-containing metallic glass composite is strongly governed by the alloy composition and the actual cooling rate during solidification. Room-temperature compression tests reveal significant yielding and plastic deformation before failure.
Determination of temperature dependent structure evolution by fast-Fourier transform at late stage spinodal decomposition in bicontinuous biopolymer mixtures
Authors: Lorén Niklas , Langton Maud , Hermansson Anne-Marie
Published: July 2002

The evolutions of the bicontinuous microstructures of aqueous phase separating gelatin/maltodextrin mixtures quenched to different end temperatures were determined by confocal laser scanning microscopy (CLSM). The growth of the bicontinuous microstructures was quantified by Fourier image analysis. Weighted least squares were applied in order to be able to use all the spectral information. The results of Fourier image analysis and weighted least squares were related to existing theories on coarsening. The mixtures were quenched from 60 °C to different end temperatures ranging between 10 °C and 37 °C and the concentration was held constant at 4.2 w/w % gelatin and 7.9 w/w % maltodextrin. The results showed that the mixture phase separated through spinodal decomposition at all temperatures. A crossover was found from structure growth governed by diffusion to structure growth governed by hydrodynamic flow. The results showed that the structure evolution at the beginning of the phase separation was temperature independent with a growth proportional to the time raised to one-third. After the crossover, the growth of the characteristic distance between the maltodextrin domains was temperature dependent with a growth proportional to the time raised to an exponent that varied from 0.75 to 1.58. It was found that the growth exponent increases with decreasing end temperature, i.e., increasing quench depth. The maximum intensity of the circularly averaged two-dimensional fast-Fourier transform of the CLSM micrographs was found to grow exponentially with time. The increases in the maximum intensity were proportional to the time raised to an exponent that varied from 1.98 to 4.97. It was found that this exponent increases with decreasing end temperature. Before the crossover, the relation between the growth exponent of the microstructure and the growth exponent of the maximum intensity, as compared with existing theories on coarsening, showed that the phase separation was in the intermediate or transitional stages of spinodal decomposition. Similarly, after the crossover, it was found that phase separation was in the late stages of spinodal decomposition. Furukawa master plots showed that the structure growth obeyed dynamical scaling and that the dimensionality of the growth was three, given off-critical conditions.
Energy distribution for undergate-type triode carbon nanotube field emitters
Authors: Yu SeGi , Yi Whikun , Lee Jeonghee , Jeong Taewon , Jin Sunghwan , Heo Jungna , Kang J. H. , Choi Y. S. , Lee Chang Soo , Yoo Ji-Beom , Kim J. M.
Published: July 2002

Field emission energy distribution (FEED) has been measured for undergate-type triode carbon nanotube (CNT) field emitters where the gate electrodes are located underneath the cathode electrodes. The diode-type emission for these CNT emitters was found to follow the Fowler–Nordheim relation, whereas the triode-type emission exhibited the deviation from this relation. The FEED peaks for the undergate CNT emitters under the triode-type emission shifted to lower energy as the gate voltage increased, indicating nonmetallic behavior for the CNT emitters. There exist two different characteristic FEED peaks, where their peak energy shifts as a function of the gate voltage belong to two different slopes. From the difference in the position and intensity of the peaks, it was found that one was field emission directly from CNTs and the other might be emitted from CNTs through glass powders which were added during the CNT field emitter fabrication process.
Beating polymer gels coupled with a nonlinear chemical reaction
Authors: Yoshida Ryo , Kokufuta Etsuo , Yamaguchi Tomohiko
Published: July 2002

We report on a beating polymer gel that exhibits periodical volume changes (swelling and deswelling) in a closed solution without external stimuli, like autonomous heartbeat. The mechanical oscillation is driven by the chemical energy of the oscillatory Belousov–Zhabotinsky (BZ) reaction. The gel is a copolymer gel of N-isopropylacrylamide (NIPAAm) in which ruthenium tris(2,2′-bipyridine) [Ru(bpy)3], known as a catalyst of the BZ reaction, is covalently bonded to the polymer chain. The poly[NIPAAm-co-Ru(bpy)3] gel provides an open system where the BZ reaction proceeds, when immersed in an aqueous solution containing the reactants of the BZ reaction (with the exception of a catalyst). The chemical oscillation in the BZ reaction generates the periodical changes of the charge of Ru(bpy)3 in the gel network between reduced [Ru(II)] and oxidized [Ru(III)] states. The gel swells at the oxidized state because the hydrophilicity of the polymer chains increases, while at the reduced state the gel deswells. Thus, the chemical energy is transduced into the mechanical energy to drive the polymer gel oscillation with a period of about 5 min, depending on the composition of the surrounding solution. The oscillation mode of the gel depends on its size scaled by the wavelength of the BZ pattern. Sufficiently small bead-like gels demonstrate isotropic beating. A large rectangular gel shows mechanical oscillation with a peristaltic motion coupled with the propagating chemical waves. The dynamic behavior of the chemical and mechanical oscillations have been analyzed with a model simulation.
Damage center formation in SiO2 thin films by fast electron irradiation
Authors: Pfeffer R. L.
Published: July 2002

The concentrations of E′ centers (ESR-active oxygen vacancies) produced by 30–160 keV electron irradiation have been measured in thermal SiO2 films at doses far exceeding any previously reported. The dependences of these concentrations on electron energy and fluence were measured in both steam-grown and dry oxides. Results indicated that ionization rather than atomic displacement is the predominant formation mechanism. Significant differences in dose dependence were found between oxide types, reflecting the role of hydrogen in damage annealing.
Heteroepitaxial growth of SrO films on Si substrates
Authors: Kado Yuichi , Arita Yoshinobu
Published: July 2002

Epitaxial growth of SrO thin films onto Si(111) and (100) substrates by means of molecular-beam epitaxy has been demonstrated. The orientation relationships between epitaxial SrO and Si were found to be (111)SrO//(111)Si and [112̄]SrO//[112̄]Si, (100)SrO//(100)Si and [011]SrO//[001]Si. The composition of the grown films was Sr:O=1:1. In addition, it has been shown that it was possible to grow layers with no Si surface oxidation and no noticeable interdiffusion at the interfaces. These SrO films possess a low dielectric constant (3.0) and a high breakdown field (5×106 V/cm).
A method to estimate the yield of an underground nuclear explosion
Authors: Moss William C.
Published: July 2002

We have modeled the motion of a spherically diverging shock front, due to a point source explosion, using the Rankine–Hugoniot equations and an assumption about the partitioning of energy in the shocked sphere. Our analysis shows that the yield can be determined from measurements of the time dependence of the position and the particle velocity at the shock front, and the initial bulk density of the geologic medium. We compare and contrast our analysis with another theoretical model and experimental data, and show that our model has the potential to determine the yield accurately over an extended range of time, distance, and geologic media.
Exchange forces between domain wall and electric current in permalloy films of variable thickness
Authors: Hung C.-Y. , Berger L.
Published: July 2002

Wall displacements are induced by large current pulses crossing a wall, in Ni81Fe19 films. In films of thickness w<35 nm containing Néel walls, the sense of wall motion is found to be independent of the magnetization sense in the two domains adjacent to the wall, and is identical to the sense of motion of the electronlike charge carriers. This shows that the wall motion is not caused by stray magnetic fields, but rather by s-d exchange forces generated by conduction electrons. The value ≂5×107 A cm−2 of the needed current density agrees with predictions of a theory based on s-d exchange. In the case of cross-tie walls in films with 35 nm <w<86 nm, the sense of wall motion does depend on the sense of the domain magnetizations. The force of the circumferential magnetic field of the current is probably important, here.
The thermal conductivity of Li2O⋅Al2O3⋅nSiO2 glasses between 5 and 100 K
Authors: Hanna B. , Bohn R. G.
Published: July 2002

The thermal conductivity of the Li2O⋅Al2O3⋅nSiO2 family of glasses for n=4,6,8,10, and 12 was measured between 5 and 100 K. For all the glasses in this study, including a vitreous silica sample, the thermal conductivity exhibits the traditional plateau between 10 and 20 K followed by a monotonic increase at higher temperature. The compositional dependence is discussed in terms of the elastic properties and comparisons are made to previous work.
Theoretical model for self-interstitial generation at the Si/SiO2 interface during thermal oxidation of silicon
Authors: Taniguchi Kenji , Shibata Yoshiaki , Hamaguchi Chihiro
Published: July 2002

Using a grating pattern of parallel nitride and oxide stripes on the silicon surface, self-interstitial concentration at the Si/SiO2 interface is accurately determined by means of oxidation-induced stacking fault growth observation. The results show that the interstitial concentration at the interface is found to be determined by the oxidation of interstitials in the oxide rather than self-interstitial diffusion in bulk silicon. A newly proposed physical model incorporates the balance among the generation rate of interstitials at the oxidizing interface, the annihilation rate of interstitials due to surface regrowth, and the rate at which they diffuse into the oxide and react with incoming oxidants. For higher oxidation rates, the model predicts that the interstitial concentration follows a 0.5 power dependence on oxidation rate. For slower oxidation rates, the concentration at the interface becomes lower than the equilibrium interstitial concentration, leading to the oxidation-retarded diffusion of dopants with a high fractional interstitialcy diffusion component.
Electron paramagnetic resonance of an intrinsic defect in RuS2 single crystals
Authors: Yu Jiang-Tsu , Lin Shoei-Sheng , Huang Ying-Sheng
Published: July 2002

A paramagnetic species of spin 1/2, with the four 〈111〉 axes of the cubic lattice as the symmetry axes, has been observed by electron paramagnetic resonance in undoped, as-grown RuS2 single crystals. The g values at 10.8 K are g∥ =2.022±0.001 and g⊥ =2.088±0.001. The most probable origin of this paramagnetic species is an S− ion adjacent to an S vacancy.
Phase relationships in the Tb-Dy-Fe ternary system
Authors: Westwood P. , Abell J. S. , Pitman K. C.
Published: July 2002

An investigation of the metallurgy of a pseudobinary section of the ternary-phase diagram has been performed by means of differential thermal analysis, x-ray diffraction, and metallography. Microstructural observations and lattice parameter variations have been interpreted in terms of the existence of a solid solubility range for the Laves phase. Thermal analysis has established the details of the phase relationships in the region of the Laves phase and on the basis of the results a modified phase diagram is proposed.
Phase coherent length measurements in single-crystal NiSi2 films
Authors: Matsui Makoto , Ohshima Takashi , Komori Fumio , Kobayashi Shun-ichi
Published: July 2002

The phase coherent length lφ of conduction electrons in single-crystal NiSi2 films has been measured using weak localization phenomena. Logarithmic temperature dependence and logarithmic magnetic-field dependence of the conductivity observed in epitaxially grown NiSi2 single-crystal films with thicknesses from 6 to 40 nm are interpreted in terms of the two-dimensional weak localization with strong spin-orbit interaction. Considerably long-phase coherent lengths are obtained by fitting analyses using magnetoconductance data; lφ=0.8 μm at 4.2 K and 1.5 μm at 2 K. This is due to a very low concentration of magnetic scatterers in NiSi2. Because of its long-phase coherent length, the single-crystal NiSi2 film can be applied to novel quantum interference devices.
Doping and crystallographic effects in Cl-atom etching of silicon
Authors: Ogryzlo Elmer A. , Ibbotson Dale E. , Flamm Daniel L. , Mucha John A.
Published: July 2002

Absolute rates for the intrinsic reaction between Cl atoms and surfaces of P-doped polycrystalline silicon, P-doped Si(100) and As, Sb-doped Si(111) substrates were measured for the first time as a function of dopant concentration (Ne) and substrate temperature in a downstream reaction system. This study clearly shows that when there is no ion bombardment, increasing Ne increases the Si-Cl reaction rate even when silicon is lightly doped (∼1015 cm−3), in contrast to in-discharge studies. Moreover, results showed that crystal orientation influences the Cl-Si reaction more than Ne, for Ne<1020 cm−3. The data are fitted to a modified Arrhenius expression, R=νNγenClT1/2e−E/kT, with R the etch rate and nCl the gas phase Cl concentration. The calculated values of the activation energy E are 4.1–4.7 kcal/mole for all doping levels and crystallographic orientations. Therefore, the doping effect is manifested solely in the preexponential (νNγe) of the Arrhenius expression, and the data qualitatively agree with a charge-transfer mechanism which facilitates chemisorption of chlorine.
Strain relaxation of CdTe(100) layers grown by hot-wall epitaxy on GaAs(100) substrates
Authors: Tatsuoka H. , Kuwabara H. , Nakanishi Y. , Fujiyasu H.
Published: July 2002

The strain relaxation of CdTe(100) layers grown on GaAs(100) substrates by hot-wall epitaxy was investigated by measurement of optical properties, x-ray analysis, and transmission electron microscopy. It is considered from transmission electron microscopy observation that relaxation of most of the strain due to lattice mismatch occurred at the interface. However, a small amount of strain, of the order of 10−3, remained in layers thicker than 0.7 μm, and it was relaxed as the layer thickness increased. The residual strain of 4×10−4, which exists in layers thicker than 10 μm, was due to the difference between the thermal expansion coefficients of the layer and the substrate. Moreover, for layers thicker than 17 μm, split ground (n=1) and first excited (n=2) free-exciton states due to internal strain have for the first time been observed by photoluminescence and reflectance spectroscopy. The results show that CdTe layers with excellent crystallinity and homogeneity in strain are obtained.
The effects of CdCl2 on the electronic properties of molecular-beam epitaxially grown CdTe/CdS heterojunction solar cells
Authors: Ringel S. A. , Smith A. W. , MacDougal M. H. , Rohatgi A.
Published: July 2002

Significant improvements in CdTe/CdS solar cell efficiency are commonly observed as a result of a postdeposition CdCl2 dip followed by a 400 °C heat treatment during cell processing which increases CdTe grain size. In this paper, we investigate the electronic mechanisms responsible for CdCl2-induced improvement in cell performance along with possible performance-limiting defects resulting from this process in molecular-beam epitaxy-grown polycrystalline CdTe/CdS solar cells. Current density-voltage-temperature (J-V-T) analysis revealed that the CdCl2 treatment changes the dominant current transport mechanism from interface recombination/tunneling to depletion region recombination, suggesting a decrease in the density and dominance of interface states due to the CdCl2 treatment. It is shown that the change in transport mechanism is associated with (a) an increase in heterojunction barrier height from 0.56 to 0.85 eV, (b) a decrease in dark leakage current from 4.7×10−7 A/cm2 to 2.6×10−9 A/cm2 and, (c) an increase in cell Voc from 385 to 720 mV. The CdCl2 also improved the optical response of the cell. Substantial increases in the surface photovoltage and quantum efficiency accompanied by a decrease in the bias dependence of the spectral response in the CdCl2-treated structures indicate that the CdCl2 treatment improves carrier collection from the bulk as well as across the heterointerface. However, deep level transient spectroscopy measurements detected a hole trap within the CdTe depletion region of the CdCl2-treated devices at Ev + 0.64 eV which is attributed to the formation of VCd-related defects during the annealing process after the CdCl2 dip. J-V-T analysis demonstrated that this trap is the probable source of dominant recombination in the CdCl2-treated cells. An inverse correlation was found between the density of the Ev + 0.64 eV trap and cell Voc, suggesting that the heat treatment with CdCl2 may eventually limit the CdTe/CdS cell performance unless the formation of this defect complex is controlled or eliminated.