bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of ferromagnetic microstructures as electrodes for spin-polarized transport experiments
Authors: Meier G. , Halverscheid M. , Matsuyama T. , Merkt U.
Published: July 2002

Patterned ferromagnetic structures are intended as electrodes to drive a spin-polarized current through the quasi two-dimensional electron system of a semiconductor. To utilize such structures in transport experiments it is important to know their micromagnetic behavior. We have prepared Permalloy electrodes for the ballistic transport regime by electron-beam lithography on InAs single crystals. Using magnetic-force microscopy we measure the magnetization configurations at zero external magnetic fields. Micromagnetic simulations verify that the observed magnetization states are the energetically most favorable ones. In addition, the micromagnetic behavior in external magnetic fields is simulated.
On the concept of temperature for a small isolated system
Authors: Andersen J. U. , Bonderup E. , Hansen K.
Published: July 2002

The microcanonical temperature is shown to be a useful concept in calculations of the decay of a small isolated system with well defined energy. A simpler and more transparent description is obtained than in Klots’ formulation of finite-heat-bath theory, where the system is represented by a canonical ensemble. As a further illustration of the utility of the microcanonical temperature concept, we discuss a formula derived by Dunbar for the probabilities for excitation of a single oscillator in a collection of harmonic oscillators with well defined total energy. This formula expresses the excitation probabilities in terms of the temperature for a canonical ensemble with mean energy equal to the energy of the system. However, a much improved accuracy is obtained if the canonical temperature and heat capacity are replaced by their microcanonical values. We justify this replacement through a modified derivation, in which the microcanonical temperature appears as the canonical temperature of a fictitious system with level density ρ′(E), the derivative of the level density ρ(E) of the collection of oscillators.
Network model for deep bed filtration
Authors: Lee Jysoo , Koplik Joel
Published: July 2002

We study deep bed filtration, where particles suspended in a fluid are trapped while passing through a porous medium, using numerical simulations in various network models for flow in the bed. We first consider cellular automata models, where filtrate particles move in a fixed background flow field, with either no-mixing or complete-mixing rules for motion at a flow junction. The steady-state and time-dependent properties of the trapped particle density and filter efficiency are studied. The complete mixing version displays a phase transition from open to clogged states as a function of the mean particle size, while such a transition is absent in the (more relevant) no-mixing version. The concept of a trapping zone is found to be useful in understanding the time-dependent properties. We next consider a more realistic hydrodynamic network model, where the motion of the fluid and suspended particles is determined from approximate solutions of the time-dependent Stokes equation, so that the pressure field constantly changes with particle movement. We find that the steady-state and time-dependent behavior of the network model is similar to that of the corresponding cellular automata model, but the long computation times necessary for the simulations make a quantitative comparison difficult. Furthermore, the detailed behavior is extremely sensitive to the shape of the pore size distribution, making experimental comparisons subtle.
Comprehensive analysis of conditionally exactly solvable models
Authors: Roychoudhury Rajkumar , Roy Pinaki , Znojil Miloslav , Lévai Géza
Published: July 2002

We study a quantum mechanical potential introduced previously as a conditionally exactly solvable (CES) model. Besides an analysis following its original introduction in terms of the point canonical transformation, we also present an alternative supersymmetric construction of it. We demonstrate that from the three roots of the implicit cubic equation defining the bound-state energy eigenvalues, there is always only one that leads to a meaningful physical state. Finally we demonstrate that the present CES interaction is, in fact, an exactly solvable Natanzon-class potential.
Structural differences between deuterated and hydrogenated silicon nitride/oxynitride
Authors: Shih An , Yeh Shin-Hung , Lee Si-Chen , Yang T. R.
Published: July 2002

Hydrogenated and deuterated silicon nitride (a-SiNx:H and a-SiNx:D) and silicon oxynitride (a-SiOxNy:H and a-SiOxNy:D) films are prepared by plasma-enhanced chemical vapor deposition. Their transmission and photoluminescence spectra were measured. Both the photoluminescence and transmission spectra show that the deuterated films have higher energy gaps than those of the hydrogenated films in the same growth condition. The infrared absorption spectra of these samples are identified and compared in detail. From the infrared spectra, the interaction between N–D bond rocking vibration and Si–N bond stretching vibration is observed, which pushes N–D bond rocking vibration to a higher energy. It is also observed that the refractive index of deuterated film is lower than the hydrogenated film in the same growth condition due to its lower density.
Photocurrent and photoluminescence of a single self-assembled quantum dot in electric fields
Authors: Findeis F. , Baier M. , Beham E. , Zrenner A. , Abstreiter G.
Published: July 2002

We have fabricated single-quantum-dot photodiodes by embedding InGaAs quantum dots in the intrinsic region of an n-i-Schottky diode combined with near-field shadow masks. As a function of the bias voltage, we study one and the same quantum dot in the two complementary regimes of photocurrent and photoluminescence. The Stark shift of the exciton ground state continues monotonically in both regimes, confirming nicely the observation of the same quantum dot in photoluminescence and photocurrent. In the limit of high electric fields, we observe a broadening of the photocurrent linewidth from which we determine a strongly reduced exciton lifetime of below 1 ps.
First-order coil-to-flower transition of a polymer chain pinned near a stepwise external potential: Numerical, analytical, and scaling analysis
Authors: Skvortsov A. M. , Klushin L. I. , van Male J. , Leermakers F. A. M.
Published: July 2002

A polymer chain near a penetrable interface is studied in the Gaussian model, in the lattice random walk model and by a scaling analysis. The interface is modeled as an external potential u of a Heaviside step-function form. One end of the chain is fixed at a distance z0 away from this interface. When the end point is fixed in the high potential region, a first-order coil-to-flower transition takes place upon variation of the distance z0. Here, the flower has a strongly stretched stem from the grafting point towards the interface and, on top of it, a crown composed of the remaining segments in a (perturbed) coil conformation. The coil-to-flower transition is analyzed in terms of the Landau free energy. The order parameter is taken to be related to the fraction of segments residing in the energetically favorable region. Exact analytical expressions for the Landau function are obtained in the Gaussian model for any distances z0 and potential strength u. A phase diagram in the z0 versus u coordinates is constructed. It contains a line of the first-order phase transitions (binodal line) ending at a critical point z0=u=0, and two spinodal lines. Numerical results are obtained for several chain lengths in the lattice random walk model demonstrating the effects of finite extensibility on the position of the transition point. Excluded volume effects are analyzed within the scaling approach.
Low-temperature α peak of the internal friction in niobium and its relation to the relaxation of kinks in dislocations
Authors: Natsik V. D. , Pal’-Val’ P. P. , Pal’-Val’ L. N. , Semerenko Yu. A.
Published: July 2002

The influence of impurities on the parameters of the α peak of the internal friction in single-crystal and polycrystalline niobium is investigated; the internal friction is recorded in the temperature range 200–250 K at a vibrational frequency of ≈80 kHz. It is found that increasing the purity of the samples leads to an increase of the peak location temperature and to an increase of its width and amplitude. The structural sensitivity of this peak was observed previously in a study of the influence on this peak of a preliminary plastic deformation, thermocycling, and low-temperature recovery. A statistical description of the whole set of experimental data is proposed, which takes into account the dependence of the activation energy and attempt period on the impurity concentration and on the characteristic value and statistical scatter of the internal stresses. A new algorithm is developed for analyzing the experimental data to obtain empirical estimates for the values of the activation energy, its variance, the attempt period, and relaxation strength for the different structural states of the samples. It is shown that the α peak is a consequence of the resonant interaction of elastic vibrations with the thermally activated nucleation of kink pairs on dislocation segments lying in the valleys of the Peierls potential relief. Empirical estimates are obtained for the values of the main parameters characterizing this process. It is found that the properties of the α peak in niobium are in qualitative agreement with Engelke’s theory of the nucleation and relaxation of dislocation kinks.
Pulsed laser deposition system for producing oxide thin films at high temperature
Authors: Orita M. , Ohta H. , Hiramatsu H. , Hirano M. , Den S. , Sasaki M. , Katagiri T. , Mimura H. , Hosono H.
Published: July 2002

A pulsed laser deposition system capable of raising substrate temperatures up to 1500 °C in oxygen atmosphere has been developed to grow oxide thin films with excellent crystalline quality. The high temperature is achieved by condensation onto a substrate of infrared light emitted from a halogen lamp through a SiO2 rod serving as an optical guide. Deposition temperatures are regulated ranging from 1500 to 150 °C, under a partial oxygen pressure from 100 to 5×10−6 Pa. An appropriate thermal insulation between the substrate holder and the surrounding components suppresses the heat flow inbetween, leading to a smooth rotation of the substrate holder and preventing the mechanical components from being oxidized. A high-precision five-axis alignment mechanism equipped with a substrate manipulator allows for the development of an application in coaxial impact-collision ion scattering spectroscopy. As a demonstrative experiment, highly oriented Ga2O3 films, which are useful as deep ultraviolet transparent semiconductors, have been deposited on an Al2O3 (0001) single crystal substrate at 1000 °C under an oxygen pressure of 5×10−5 Pa.
Switchable broadband light reflection in polymer-stabilized cholesteric liquid crystals
Authors: Binet Corinne , Mitov Michel , Mauzac Monique
Published: July 2002

Due to the existence of a macroscopic helical structure, oriented cholesteric liquid crystals (CLCs) can selectively reflect light. The wavelength bandwidth for these Bragg reflections is limited: typically a few tens of nanometers due to limited birefringence values available in organic mesomorphic compounds. Here, we show that larger bandwidths may be reached by associating two layers of polymer-stabilized CLCs (PSCLCs). In the case of near-IR spectrum, it is shown that the optical properties of the bilayer system are not the sum of the individual properties. Time stability is investigated because the very existence of an interdiffusion between soft matter layers. Optical characteristics of the PSCLC can be tuned by an electric field and transitions between broadband reflecting, scattering, and transparent states are possible. For applications, switchable broadband reflections in liquid concentration media are relevant for white-or-black polarizer-free flat displays and “smart” windows in buildings.
Low-dose aluminum and boron implants in 4H and 6H silicon carbide
Authors: Saks N. S. , Agarwal A. K. , Ryu S-H. , Palmour J. W.
Published: July 2002

Aluminum and boron p-type low-dose implants have been characterized in 4H- and 6H-SiC for anneals from 1300 °C to 1600 °C. In contrast to previous studies of heavily doped p-type layers, here we study more lightly doped layers for use as active regions in high-voltage power devices. Activation rates of the implanted ions, depth profiles from secondary mass ion spectroscopy, and surface roughness data using atomic force microscopy are presented as a function of anneal temperature. The temperature dependence of the free hole density and hole mobility are characterized with Hall effect measurements. For 1600 °C anneals, usable device quality p-type layers are obtained for both SiC polytypes and implant species. For anneals at or below ∼1500 °C, the implanted layers have much higher sheet resistivity due to the presence of unannealed compensating defects. These layers are not device quality. B-implanted layers have higher mobility, while activation of implanted Al is much higher and more uniform. Therefore, boron and aluminum have different advantages and disadvantages as p-type implants in SiC.
Alternate current characteristics of SiC powders
Authors: Mårtensson E. , Gäfvert U. , Önneby C.
Published: July 2002

Silicon carbide (SiC) powder is used in nonlinear field grading materials. The composite material, consisting of an insulating polymer matrix filled with the SiC grains, is usually a percolated system with established conducting paths. In order to explain the properties, the electrical characteristic of the SiC powder itself is of interest. The ac characteristics of SiC powders have been studied by dielectric response, capacitance–voltage, and ac-pulse measurements. The frequency, electric field, and pressure dependencies have been analyzed for green and black SiC, which have different doping. The ac characteristics of green and black SiC powders are governed by both the barrier regions at the SiC-grain contacts and the surrounding matrix. The nonlinear loss is determined by the conduction current at the contacts. Depending on the doping level of the SiC grains, the capacitance may be controlled by either the nonlinear capacitance of the barrier region or the linear capacitance of the surrounding matrix. Each contact zone may be modeled by a nonlinear resistance in parallel with both a nonlinear and a linear capacitance. The components are considered to be frequency independent. However, in order to explain the macroscopic frequency and field dependencies of the SiC powders, the use of a network of unique contact zones with dissimilar properties is suggested.
Exciton diffusion and optical interference in organic donor–acceptor photovoltaic cells
Authors: Stübinger Thomas , Brütting Wolfgang
Published: July 2002

The influence of the organic layer thickness on short-circuit photocurrent spectra and efficiency is investigated in heterojunction photovoltaic cells with the electron donor materials poly(p-phenylenevinylene) (PPV) and Cu-phthalocyanine (CuPc), respectively, together with C60 as electron acceptor material. The main process of photocurrent generation after light absorption, exciton generation, and exciton diffusion in the bulk of the absorbing material is given by the exciton dissociation at the donor–acceptor interface. We determined a strong dependence of the optimum layer thickness of the absorbing material on the exciton diffusion length by systematically varying the layer thickness of the electron donor material. Additionally, a significant photocurrent contribution occurred due to light absorption and exciton generation in the C60 layer with a subsequent hole transfer to PPV, respectively, CuPc at the dissociation interface. Using a simple rate equation for the exciton density we estimated the exciton diffusion lengths from the measured photocurrent spectra yielding (12±3) nm in PPV and (68±20) nm in CuPc. By systematically varying the layer thickness of the C60 layer we were able to investigate an optical interference effect due to a superposition of the incident with backreflected light from the Al electrode. Therefore both the layer thickness of the donor and of the acceptor layer significantly influence not only the photocurrent spectra but also the efficiencies of these heterolayer devices. With optimized donor and acceptor layer thicknesses power conversion efficiencies of about 0.5% under white light illumination were obtained.
Nanofabrication induced by near-field exposure from a nanosecond laser pulse
Authors: Watanabe Osamu , Ikawa Taiji , Hasegawa Makoto , Tsuchimori Masaaki , Kawata Yoshimasa
Published: July 2002

We demonstrate a photoinduced nanofabrication method, applicable to dimensions beyond the diffraction limit, by employing a nanosecond laser pulse with a high peak power. The second-harmonic wave of a Nd: yttrium–aluminum–garnet (YAG) laser with a 5 ns pulse width was irradiated onto the sample, which consisted of a hexagonal arrayed monolayer of nanoparticles on an azopolymer film. Topographical changes in the surface after irradiation were observed by atomic force microscopy. A transcription of the arrayed structure in the form of a dent structure was attained. In the case of 100 nm nanoparticles, the resolution of the transcription was beyond the diffraction limit. The dent depth and diameter were changed depending on the diameter of the nanoparticles and the irradiation power used. A depth analysis indicates a threshold for the ablation process.
Creeping flow through a pipe of varying radius
Authors: Sisavath Sourith , Jing Xudong , Zimmerman Robert W.
Published: July 2002

Creeping flow of a Newtonian fluid through tubes of varying radius is studied. Using an asymptotic series solution for low Reynolds number flow, velocity profiles and streamlines are obtained for constricted tubes, for various values of constriction wavelength and amplitude. A closed-form expression is derived to estimate the pressure drop through this type of tube. The results obtained with this new expression are compared to data from previous experimental and numerical studies for sinusoidally constricted tubes. Good agreement is found in the creeping flow regime for the pressure drop versus flow rate relationship. Our method offers an improvement over the integrated form of the Hagen–Poiseuille equation (i.e., lubrication approximation), which does not account for the wavelength of the constrictions.
Thermally stable dynamic piezoelectricity in sandwich films of porous and nonporous amorphous fluoropolymer
Authors: Mellinger Axel , Wegener Michael , Wirges Werner , Gerhard-Multhaupt Reimund
Published: July 2002

Porous amorphous fluoropolymer films of very low stiffness were produced by a solvent evaporation technique. Corona-charged sandwich films consisting of a porous and a nonporous layer exhibit piezoelectric thickness-extension resonances in their dielectric spectrum, through which the temperature dependence of their dynamic stiffness, coupling factor, and piezoelectric coefficient could be determined. Their strong piezoelectricity with coefficients of up to 600 pC/N at temperatures of at least 120 °C could make these polymer electret films interesting candidates for sensor and actuator applications in elevated temperature environments.
Metal drift behavior in low dielectric constant organosiloxane polymer
Authors: Mallikarjunan A. , Murarka S. P. , Lu T.-M.
Published: July 2002

Metal drift into a low dielectric constant (low κ) hybrid organosiloxane (OS) polymer has been investigated using metal/OS/SiO2/Si capacitors. Compared to Cu, Al gate metal capacitors showed larger flatband voltage shifts in the capacitance–voltage (C–V) curves upon bias temperature stressing (BTS). To elucidate the mechanism and source of this bias instability, further BTS experiments were performed with gate metals tantalum and platinum. It is suggested that all these metals, except Pt, drift into the dielectric and the extent of drift appears to be directly related to the metal’s tendency to oxidize. The calculations, assuming singly ionized metal species, show that the charges/cm2 entering the dielectric fall in the order Pt<Cu<Ta<Al. A mechanism is proposed linking the presence of oxygen in OS to the ionization of the metals, and consequent drift through the dielectric under applied electric fields.
The vibrational and rotational dynamics of acetylene solvated in superfluid helium nanodroplets
Authors: Nauta K. , Miller R. E.
Published: July 2002

Infrared spectra are reported for C212H2, C213H2, C12C13H2, and C212HD solvated in superfluid helium nanodroplets, corresponding to excitation of the C–H stretches. For the lowest rotational states (J=0 and J=1), molecular rotation is only weakly hindered by the liquid and the associated transitions are sharp, having small frequency shifts relative to the gas phase. In contrast, the R(1) transitions of C212H2 and C213H2, which access the corresponding J=2 rotational states, are much broader and more strongly shifted from the gas phase. The linewidths of the R(0) transitions show a strong isotopic dependence, which we take as evidence that vibrational resonances present in some of the isotopomers enhance the vibrational relaxation rate.
High-pressure rotational deformation apparatus to 15 GPa
Authors: Yamazaki D. , Karato Shun-ichiro
Published: July 2002

A new apparatus has been developed that allows large-strain plastic deformation experiments under high pressure with a controlled strain rate in simple shear deformation geometry. A modification is made to a Drickamer-type opposed anvil apparatus to allow torsion tests by attaching a rotation actuator composed of a dc servomotor and a gear box. A thin disk of a sample (less than ∼0.8 mm thick and to ∼4 mm diameter) can be sheared between two anvils under pressure by a rotation actuator. Specimens of Fe were sheared to strains exceeding γ∼6 at pressures up to ∼15 GPa. Nearly simple shear deformation was achieved when the initial sample thickness is less than ∼0.4 mm. This apparatus allows studies of plastic flow and deformation microstructures under high pressures.
Near-resonant absorption in the time-dependent self-consistent field and multiconfigurational self-consistent field approximations
Authors: Norman Patrick , Bishop David M. , Jo/rgen Aa. Jensen Hans , Oddershede Jens
Published: July 2002

The linear response function has been derived and implemented in the time-dependent self-consistent field and multiconfigurational self-consistent field approximations with consideration made for the finite lifetimes of the electronically excited states. Inclusion of damping terms makes the response function convergent at all frequencies including near-resonances and resonances. Applications are the calculations of the electric dipole polarizabilities of hydrogen fluoride, methane, trans-butadiene, and three push–pull systems. The polarizability is complex with a real part related to the refractive index and an imaginary part describing linear absorption. The relevance of linear absorption in nonlinear optics is effectively expressed in terms of figures-of-merit. Such figures-of-merit have been calculated showing that the nonresonant linear absorption must be considered when the nonlinear optical quality of a material is to be assessed.
The thermal diffusivity of water at high pressures and temperatures
Authors: Abramson Evan H. , Brown J. Michael , Slutsky Leon J.
Published: July 2002

Thermal diffusivities of fluid water have been measured to a pressure of 3.5 GPa, a density of 1.4 g cm−3 and a temperature of 400 °C. Above 100 °C, both the diffusivities and the related conductivities are found, unexpectedly, to scale as the square-root of absolute temperature; in contrast, the excess conductivities are highly dependent on temperature. Measurements at 25 °C, extending into a metastable regime with respect to ice VI, do not scale in this manner and this anomalous behavior is not suppressed by pressures up to 1.3 GPa.
Nanopatterning effects on magnetic anisotropy of epitaxial Fe(001) micrometric squares
Authors: Jaque D. , Martı́n J. I. , Armelles G. , Costa-Krämer J. L. , Briones F. , Vicent J. L.
Published: July 2002

Magneto-optic (MO) studies are performed on regular arrays of Fe(100) micrometric squares, where the elements are patterned with different sizes (2.5–10 μm) and separations (0.2–0.6 μm). When a laser beam is focused inside the patterned structure a Bragg diffraction pattern is produced allowing MO studies on both reflected and diffracted spots. The magnetic anisotropy has been analyzed by in-plane MO hysteresis loops finding that, for square sizes below 2.5 μm, it is not consistent with the Fe crystalline cubic anisotropy, presenting a uniaxial-like behavior. The magnitude of the corresponding anisotropy constants has been determined by analyzing the array response (on reflected and diffracted spots) to a rotational magnetic field in a magneto-optical torque setup. For square sizes of 10 μm the anisotropy induced by patterning is negligible whereas for the small squares (2.5 μm) the uniaxial magnetic constant has been found to be roughly 0.2 times the Fe cubic anisotropy constant.
Impedance and specific heat of RM4Al8 and RAg6In6 compounds
Authors: Gurevich A. M. , Dmitriev V. M. , Eropkin V. N. , Kotur B. Yu. , Prentslau N. N. , Suski V. , Terekhov A. V. , Shlyk L. V.
Published: July 2002

The results of experimental investigations of the temperature dependences of the surface resistance and specific heat of ternary rare-earth compounds are presented: LuFe4Al8, ScFe4Al8, CeFe4Al8, CeCr4Al8, YFe4Al8, YCr4Al8, YMn4Al8, UCu4Al8, LaAg6In6, and PrAg6In6, which have ThMn12 structure. It is shown that at a certain temperature, characteristic for each compound with Fe, Cr, and Mn, below the Néel temperature a jump is observed in the total impedance and specific heat. At lower temperatures a negative magnetoresistance is observed in these compounds in weak magnetic fields. Superconducting phases are found in the compounds ScFe4Al8 (Tc=6 K), YCr4Al8 (Tc=4.5 K), YFe4Al8 (Tc=6 K), and PrAg6In6 (Tc=8.3 K).
Solutions of mixed quantum-classical dynamics in multiple dimensions using classical trajectories
Authors: Wan Chun-Cheng , Schofield Jeremy
Published: July 2002

The multithreads algorithm for solving the mixed quantum-classical Liouville equation is extended to systems in which multiple classical degrees of freedom couple explicitly to a quantum subsystem. The method involves evolving a discrete set of matrices representing operators positioned at classical phase space coordinates according to precise dynamical rules dictated by evolution equations. The propagation scheme is based on the Trotter expansion of the time evolution operator and involves trajectory (thread) branching and pruning operations at each time step. The method is tested against exact numerical solution of the quantum dynamics for two models in which the nonadiabatic evolution of two heavy coordinates (nuclei) induces changes in population in two electronic states. It is demonstrated that the multithreads algorithm provides a good quantitative as well as qualitative description of the dynamics for branching ratios and populations as a function of time. Critical performance issues such as the computational demand of the method, energy conservation, and how the scheme scales with the number of classical degrees of freedom coupled to the quantum subsystem are discussed.
Vapor–liquid–solid tri-phase pulsed-laser epitaxy of RBa2Cu3O7−y single-crystal films
Authors: Yun K. S. , Choi B. D. , Matsumoto Y. , Song J. H. , Kanda N. , Itoh T. , Kawasaki M. , Chikyow T. , Ahmet P. , Koinuma H.
Published: July 2002

We report on the fabrication of single-crystalline thin films of RBa2Cu3O7−y (R: rare-earth element, R123) using an approach of vapor–liquid–solid tri-phase epitaxy. This method is based on application of pulsed-laser deposition under appropriate compositions and conditions predetermined from the relevant thermodynamic phase diagram. The laser-ablated gases of R, Ba, and Cu, and their oxides dissolve into a liquid Ba3Cu5Ox (3BaCuO2+2CuO) layer placed on the film/substrate surface, penetrate to reach the liquid–solid interface with a seed R123, and are condensed into the solid R123 phase under a quasiequilibrium state. The uniform single-crystalline nature of the film was verified by x-ray diffraction, atomic-force microscopy, and transmission electron microscopy by the observation of giant grain size and atomic-scale surface smoothness.
Holographic recording of fast phenomena
Authors: Liu Zhiwen , Steckman Gregory J. , Psaltis Demetri
Published: July 2002

We report on a holographic method for recording fast events whose speed is limited by the laser pulse duration if the recording material has sufficient sensitivity to reliably record a frame of the fast event with a single pulse. The method we describe uses the angular selectivity of thick holograms to resolve frames that are recorded with adjacent pulses. Two specially designed cavities are used to generate the signal and reference pulse trains. We experimentally demonstrate the system by recording laser induced shock waves with a temporal resolution of 5.9 ns, limited by the pulse width of the Q-switched Nd:yttrium–aluminum–garnet laser used in the experiments.
Exploiting past visits or minimum-barrier knowledge to gain further boost in the temperature-accelerated dynamics method
Authors: Montalenti F. , Voter A. F.
Published: July 2002

We present a more efficient version of the temperature accelerated dynamics (TAD) method. Without introducing any new approximation, we show how it is possible to make the TAD method faster when a system visits a state more than one time. We demonstrate the method for the diffusion of silver tetramers on Ag(100), obtaining an additional boost (relative to standard TAD) of ∼4 at T=400 K and ∼11 at T=200 K. Larger boosts can be obtained at lower temperatures and/or for different systems. This new formalism also offers a way to gain this additional boost in the dynamics on the first visit to a state, provided information is available about the lowest barrier for escape from the state.
Diffusion and dynamics of macro-particles in a complex plasma
Authors: Vaulina O. S. , Vladimirov S. V.
Published: July 2002

The dynamics of charged macro-particles in a complex “dusty” plasma is investigated for the conditions relevant for laboratory experiments on weakly ionized gas-discharge plasma and modeled by the Brownian dynamics method. The parameters responsible for order and scaling of the particle dynamics in the dissipative system of strongly interacting macro-particles are determined. The expression for the diffusion rate of macro-particles in strongly correlated liquid-type structures is derived and analyzed. The condensation of macro-particles (the growth of clusters) is numerically observed in the transition of the liquid-type Yukawa system to the qualitatively new dynamic state.
Vacuum ultraviolet pulsed field ionization-photoelectron study of OCS in the energy range of 15–19 eV
Authors: Chen Wenwu , Hochlaf M. , Rosmus P. , He G. Z. , Ng C. Y.
Published: July 2002

Vacuum ultraviolet pulsed field ionization-photoelectron (PFI-PE) spectra for OCS have been obtained in the energy range 15.0–19.0 eV, covering the vibronic bands of OCS+ (A 2Π, B 2Σ+, and C 2Σ+). The ionization energies for the formation of the ground vibrational levels of OCS+ (A 2Π3/2, A 2Π1/2, B 2Σ+, and C 2Σ+) from the ground OCS(X 1Σ+) state have been determined as 15.0759±0.0005 eV, 15.0901±0.0005 eV, 16.0403±0.0005 eV, and 17.9552±0.0005 eV, respectively. We have also generated the theoretical adiabatic three dimensional potential energy functions (PEFs) for OCS+(A 2Π) by employing the complete active space self-consistent field and internally contracted multireference configuration interaction methods. Using these PEFs, the spectroscopic constants and low-lying rovibronic energy levels for OCS+(A 2Π) are calculated variationally. These calculations have made possible the identification of many PFI-PE vibronic bands for OCS+(A 2Π), which are originated from vibronic and Fermi resonance interactions. Owing to the different equilibrium geometries between the OCS+(A 2Π) and OCS(X 1Σ+) states, the PFI-PE spectrum for OCS+(A 2Π) exhibits a long vibronic progression extending well above the OCS+(B 2Σ+) state. On the contrary, the PFI-PE spectra for OCS+ (B 2Σ+ and C 2Σ+) are overwhelmingly dominated by the ground (0,0,0) bands, exhibiting only weak vibrational progressions.
Magnetic resistivity and electron–magnon scattering in 3d ferromagnets
Authors: Raquet B. , Viret M. , Broto J. M. , Sondergard E. , Cespedes O. , Mamy R.
Published: July 2002

We determine the collective spin excitations and their contribution to the intrinsic resistivity in 3d ferromagnets by high field magnetotransport experiments. Well above the technical saturation of the magnetization, in the single domain magnetic state, the longitudinal magnetoresistance has a nonsaturating negative slope of about 0.02–0.05 μΩ cm T−1 at 300 K for Fe, Co, and Ni. We demonstrate its magnetic origin and assign the effect to a decrease of the electron–magnon scattering due to the damping of spin waves in high field. A convincing agreement is found between the high field measurements and our theoretical calculation of the spin flip electron–magnon scattering. This provides a unique estimate of the pure magnetic resistivity in 3d ferromagnets.
Accurate relativistic Gaussian basis sets determined by the third-order Douglas–Kroll approximation with a finite-nucleus model
Authors: Nakajima Takahito , Hirao Kimihiko
Published: July 2002

Highly accurate relativistic Gaussian basis sets with a finite-nucleus model are developed for the 103 elements from H (Z=1) to Lr (Z=103). The present GTO sets augment the relativistic basis sets with a point-charge model proposed in the first paper of this series. The relativistic third-order Douglas–Kroll approach is adopted in optimizing the orbital exponents of a basis set by minimizing the atomic self-consistent field (SCF) energy. The basis sets are designed to have equal quality and to be appropriate for the incorporation of relativistic effects. The performance of the present basis sets is tested by calculations on a prototypical molecule, gold dimer using SCF and the singles and doubles coupled-cluster model with perturbative triples [CCSD(T)]. Several spectroscopic constants are calculated for the ground state of Au2. At the basis set superposition error (BSSE) corrected CCSD(T) level, the deviation from experiment is ΔRe=0.018 Å, Δωe=−3 cm−1, and ΔDe=−0.17 eV. The finite-size nucleus effect makes Re, ωe, and De smaller by 0.004 Å, 1 cm−1, and 0.05 eV, respectively. The application shows that the present relativistic Gaussian-type orbitals (GTO) basis sets with a finite-nucleus model are accurate and reliable.
Rotational tunneling of NH4 and NH3D and dipolar interaction in (NH3.6D0.4)2PtCl6
Authors: Prager M. , Schiebel P. , Grimm H.
Published: July 2002

At 10% deuteration ammonium hexachloroplatinate still exhibits the cubic phase Fm3m of the protonated material at all temperatures. Rotational tunneling of the ammonium isomers NH4+ and NH3D+ was measured by neutron spectroscopy. At temperatures T⩾18 K the energies and intensities of the observed tunneling transitions agree with a statistical occurrence of ammonium isomers and a cubic environment. Below T=18 K there is no change of the NH4 spectrum while the NH3D transition adopts an unresolved broad intensity distribution before it transforms into a new structured low temperature spectrum. The intermediate spectrum is interpreted as fingerprint of a potential distribution of statistically distributed disordered NH3D ions interacting by long-range dipolar coupling. The low-temperature spectrum finds an explanation as frozen minimum energy configurations of coupled NH3D dipoles. A dipole moment of NH3D of 0.05 D can be derived from the difference of tunnel splittings.
Visualizing nonlinear resonance in classical and quantum mechanics
Authors: Burns Marshall
Published: July 2002

Results are shown of methods for representing the behavior of one-dimensional hydrogen perturbed by an electromagnetic wave. Different methods are used in classical and quantum mechanics. The quantum mechanical results appear to demonstrate the existence and overlap of resonance subspaces in Hilbert space, analogous to resonance zones in the classical phase space.
Magnetic materials for recording: An overview with special emphasis on particles (invited)
Authors: Sharrock M. P. , Bodnar R. E.
Published: July 2002

Modern recording media—tapes and disks—are made using a broad variety of magnetic materials, each presenting a unique combination of strengths and weaknesses. Although recording surfaces can be made by the deposition of thin magnetic films on a support material, most commercially available media are made by coating the support material with a dispersion of magnetic particles in an organic binder. This approach has been used for decades and is capable of being extended to future applications. The particles that are dispersed in such coatings can be of many compositions. The general requirements placed on magnetic recording materials are outlined, and the relative merits of the most significant candidates are described. Of the important particulate materials, the cobalt-modified iron oxides are treated most fully, because of their economic as well as technical interest.
Electrochromic characteristics of liquid-crystal materials
Authors: Nakamura Kenichi , Nakada Kazuhiro , Ito Yasuo , Koishi Eizo
Published: July 2002

The time dependence of optical density during a coloration and bleaching sequence has been investigated in the isotropic phase for several liquid-crystalline materials doped with a small amount of tetra-n-alkyl-ammonium iodide. As a result, a rate equation fitting experimental results obtained for low current densities has been derived: dOD/dt=αJ−κ(OD+OD0), where OD is the change in optical density of colored cells after the application of dc current, J is the applied current density, α is a coefficient related to the coloration rate, κ is a coefficient governing the bleaching rate, and OD0 is a constant for a given cell. Furthermore, the dependence of these coefficients upon electrolyte concentration, cell thickness, and cell temperature has been studied. The value of α is almost independent of device parameters, while κ is dependent upon the latter two parameters.
Thin film interactions of Al and Al(Cu) on TiW
Authors: Palmstro/m C. J. , Mayer J. W. , Cunningham B. , Campbell D. R. , Totta P. A.
Published: July 2002

Thin-film reactions of Al/Ti22W78 (∼10 wt. % Ti) with and without ∼2 at. % Cu in the Al were investigated by transmission electron microscopy for vacuum annealing in the temperature range 300–600 °C. The reactions are nonuniform and the presence of Cu has little effect on the reaction kinetics. Reactions are grain boundary dominated and start at 400 °C with the formation of WAl12.
Minority-carrier properties of thin epitaxial silicon films fabricated by limited reaction processing
Authors: Sturm J. C. , Gronet C. M. , Gibbons J. F.
Published: July 2002

Generation lifetimes and diode properties have been measured in epitaxial silicon films grown by limited reaction processing. Generation lifetimes from 1.4 to 94  μs were measured by observing the recovery of MOS capacitors from deep depletion. Planar diodes fabricated in both n- and p-type epitaxial films show excellent behavior in both forward and reverse bias. p-n junctions formed by growing p-type epitaxial silicon directly on an n-type substrate show no evidence of excessive interface defects or traps.
Experimental study of SF6/N2 and SF6/CCl2F2 mixtures by the steady-state Townsend method
Authors: Fréchette M. F.
Published: July 2002

Prebreakdown ionization currents have been measured in SF6/N2 and SF6/CCl2F2 mixtures and respective gases by the steady-state Townsend method over the range of reduced fields 70≤E/p20≤200 V cm−1 Torr−1. Relevant collisional processes to be included in the formulation of the current-growth equation are briefly reviewed; electron detachment was accordingly neglected in the present current-growth analysis. A numerical simulation has been carried out to quantify the errors expected when numerically retrieving the transport coefficients. A two-parameter model, for which the initial current I0 is considered known, is found to give the best performance. Nonlinear regression analysis using Marquardt’s procedure is performed for evaluation of the ionization (α), attachment (η), and effective ionization (ᾱ) coefficients. The limit fields are obtained from the condition ᾱ(E/p*)=0. The coefficients for the respective gases compare well with available data in the literature with the exception of the attachment coefficient in SF6 which shows a more pronounced decrease than the general trend as E/p increases. In the case of SF6/N2 mixtures, good agreement is found for the effective ionization coefficients. The attachment coefficients do not saturate but rather increase with the SF6 partial density. In SF6/CCl2F2 mixtures, the variation of ᾱ is found to be nonlinear with the percentage mixture ratio. The resulting limit field exhibits small positive and negative synergistic effects, 6% and 3%, respectively; at 25% SF6 content, the limit field is approximately 5% greater than that of pure CCl2F2. For SF6/N2 mixtures, however, the limit field never exceeds that of SF6.
Angular discrimination of light transmission through polymer-dispersed liquid-crystal films
Authors: Wu Bao-Gang , West John L. , Doane J. William
Published: July 2002

The refractive index of the polymer np is adjusted relative to the ordinary refractive index of dispersed droplets of nematic liquid crystal no to regulate the angle of maximum transmission through a film in the presence of an applied field. Maximum transmission occurs at normal incidence when np≤no with the breadth of the angle of view being largest at np=no. When np>no, maximum transmission is peaked at an angle away from normal incidence, the value of the angle depending upon the ratio np/no. Angular discriminating filters are therefore possible with these films. The optical response of these materials as a function of applied field is also shown to be dependent on the ratio np/no as is the contrast exhibited by information displays. Methods for measuring the scattering cross section of a nematic droplet are also described.
Electron-spin resonance and photographic effect of positive holes trapped by cyanine dyes adsorbed on silver bromide microcrystals
Authors: Tani Tadaaki
Published: July 2002

Electron-spin resonance (ESR) of positive holes trapped by cyanine dyes adsorbed on silver bromide microcrystals has been analyzed and correlated with their photographic effects. The ESR signal and desensitization (i.e., inefficiency in latent image formation caused by dyes) appeared in the presence of the dyes whose highest occupied levels were higher than the surface level of AgBr, which was situated 0.26 eV above the top of its valence band. Both the ESR signal and latent images formed in the presence of a cyanine dye decayed for several minutes by a second-order reaction. The activation energy of the decay was 0.4 eV, and nearly the same as the energy difference between the surface level and the highest occupied level of the dye. It is considered from the above-stated result that the desensitization was caused by the reaction between latent images and positive holes which were once trapped by the dye, and then thermally released to the surface level.
Secondary ion mass spectrometry sensitivity factors versus ionization potential and electron affinity for many elements in HgCdTe and CdTe using oxygen and cesium ion beams
Authors: Wilson R. G.
Published: July 2002

We implanted ions of 45 elements into HgCdTe, and into CdTe in some cases, at a variety of energies and fluences, and successfully measured the resulting depth distributions for 43 of them using oxygen and cesium primary ion beams and positive and negative secondary ion mass spectrometry (SIMS), respectively. Relative sensitivity factors for SIMS were determined for these elements in HgCdTe and CdTe using the known implantation fluences. The SIMS relative sensitivity factor is proportional to the inverse of the relative ion yield. We have plotted the results from oxygen SIMS and positive ions versus ionization potential (I), and from cesium SIMS and negative ions versus electron affinity (A) of the implanted elements. These data can be used to test models and theories about the dependence of positive and negative ion yield on I and A. Many of the data from oxygen SIMS for elements with ionization potential between 5 and 10 eV are consistent with the model of positive ion yield dependence on exp(−I), but some elements differ reproducibly and consistently from that model. Elements with ionization potential less than 5 eV and greater than 10 eV follow different dependencies. The data from Cs SIMS tend to fit the model of negative ion yield proportional to exp(+A), but no consistent single curve can be drawn through the data. The data for CdTe agree with those for HgCdTe within experimental error.
Electrical and optical properties of indium tin oxide thin films prepared on low-temperature substrates by rf magnetron sputtering under an applied external magnetic field
Authors: Nanto H. , Minami T. , Orito S. , Takata S.
Published: July 2002

Indium tin oxide (ITO) films were prepared with relatively high deposition rate by rf magnetron sputtering under an applied external dc magnetic field. The films with resistivity as low as 2×10−4 Ω cm and average transmittance above 85% at wavelengths between 400 and 800 nm were able to form on the substrates at temperatures below 140 °C by using a target composition of 95 wt. % In2O3–5 wt. % SnO2. The characteristic features of the ITO films deposited on low-temperature substrates were their high carrier concentration and relatively low mobility. It was found that the use of a 95 wt. % In2O3–5 wt. % SnO2 target is better than that of a 90 wt. % In2O3–10 wt. % SnO2 target for deposition on low-temperature substrates, while the use of a 90 wt. % In2O3–10 wt. % SnO2 is desirable for deposition on substrates of high temperatures, about 350 °C. It was also found that the resistivity of the ITO films deposited on low-temperature substrates can be lowered by heat treatment at 400 °C in either a vacuum or nitrogen gas. After heat treatment at 400 °C in air, the magnitude of the resistivity of the ITO films increased several times. The resistivity after heat treatment in air was easily regained to the as-deposited state by sequential heat treatment at 300–400 °C in hydrogen gas.
Electrical and thermoelectrical properties of Zn3P2 films grown by the hot wall epitaxy technique
Authors: Babu V. Suresh , Vaya P. R. , Sobhanadri J.
Published: July 2002

Zinc phosphide thin films were prepared by the hot wall epitaxy technique. The transport properties of films grown at different substrate temperatures from 200 to 350 °C were studied from room temperature up to 600 °C. Films were also grown in pure oxygen and nitrogen atmospheres at a pressure of 10−6 Torr, and the conductivity of the films was measured in situ. Thermoelectric measurements on films grown on mica were also done at various temperatures ranging from 300 to 800 K. Arrhenius plots of electrical conductivity yielded an electronic band gap of 1.32 eV and acceptor levels of 0.21 and 0.49 eV corresponding to interstitial phosphorus and absorbed oxygen levels, respectively. Variation of growth temperature, pressure, and nature of the gas present inside the chamber during growth are shown to result in a range of electrical resistivities and to be responsible for changes in carrier concentration. The sign of Seebeck coefficient was found to change from positive to negative at a temperature of 240 °C for a film grown on mica at a substrate temperature of 350 °C.