bluuebunny/crossref_metadata_2025 huggingface dataset:
Implementation of optically detected magnetic resonance spectroscopy in a commercial W-band cylindrical cavity
Authors: Janssen G. , Bouwen A. , Casteels P. , Goovaerts E.
Published: July 2002

By means of a custom-made fiber bundle for optical excitation and light collection we demonstrate the feasibility of W-band (95 GHz) optically detected magnetic resonance spectroscopy using a commercial high-frequency electron paramagnetic resonance spectrometer with a standard cylindrical cavity.
Rotational-temperature evolution of a N2+ ion beam in a storage ring probed by laser induced fluorescence spectroscopy
Authors: Rosén Stefan , Larsson Mats , Royen Peder , Rostohar Danijela , Lidberg Johan , Mannervik Sven , Shi Wei
Published: July 2002

Laser induced fluorescence spectroscopy has been applied for the first time on a stored fast molecular ion beam. The rotational temperature of the N2+ ion beam was studied as a function of storage time. For up to 1 s of storage time, a temperature of 1040 K can be used to describe the rotational energy distribution.
Low-frequency ac measurement of the Seebeck coefficient
Authors: Chen F. , Cooley J. C. , Hults W. L. , Smith J. L.
Published: July 2002

We have analyzed the sources of error in the measurement of the Seebeck coefficient and designed a low frequency ac method to reduce them. This method has high precision in a short time period compared to commonly used dc methods while it minimizes some major sources of error that other ac methods do not. Furthermore, the setup can be fit into a 3 mm diam × 7 mm Teflon pressure cell and has minimal side effects due to the heat conductance of the pressure medium. We have also proposed and tested several methods to calibrate the Seebeck coefficient of thermocouples under pressure.
Scanning superconducting quantum interference device microscope in a dilution refrigerator
Authors: Björnsson Per G. , Gardner Brian W. , Kirtley John R. , Moler Kathryn A.
Published: July 2002

We report on a scanning superconducting quantum interference device microscope operating at temperatures down to 20 mK in a dilution refrigerator. The instrument is designed for studying quantum mechanical coherence effects in mesoscopic systems and investigating magnetic effects on a mesoscopic length scale in novel materials. We have demonstrated the low-temperature operating capabilities of the instrument by studying superconducting tin disks and the superconducting transition of a thin-film tungsten sample and vortices in the same film. Looking forward, we discuss the applicability of the instrument to measurements of persistent currents in normal-metal rings.
Ultrashort pulse characterization using a scanning Fabry–Pérot étalon enabling rapid acquisition and retrieval of a sonogram at rates up to 1.52 Hz
Authors: Cormack I. G. , Sibbett W. , Ortega-Martinez R. , Reid D. T.
Published: July 2002

Rapid characterization of ultrashort pulses has been demonstrated by measuring a two-photon absorption sonogram trace. The use of a scanning Fabry–Pérot frequency filter has made it possible to acquire and retrieve a sonogram at rates as high as 1.52 Hz. We discuss details of the experimental setup, including the synchronization electronics and the acquisition/retrieval software. Excellent agreement is obtained between retrieved pulse data and independent experimental pulse measurements.
Reaction rates for proton transfer over small barriers and connection to transition state theory
Authors: Lill Markus A. , Helms Volkhard
Published: July 2002

Reaction rates of chemical reactions can be generally well described by classical transition state theory (TST) when considering zero-point energy and tunneling effects. TST is, however, not applicable for small energy barriers comparable in size to the zero-point energy or for cases where even no energy barrier is present. These situations are common for proton transfer in bulk water. Here, energy profiles for proton transfer between water and small organic molecules were computed quantum mechanically and were used as input for solving the time-dependent Schrödinger equation in one dimension. Proton transfer over small barriers occurs very fast and is completed after 10–40 fs. Transition probabilities can reach values as high as 100%. They can easily be fitted by an analytical expression. An interpolation for proton transfer rates is then derived for connecting the low-barrier-regime that should be treated by solving the time-dependent Schrödinger equation with the high-barrier-regime where TST applies.
Statistical thermodynamics of lattice models
Authors: Xing Jianhua
Published: July 2002

This work is a generalization of the work of Widom [J. Chem. Phys. 39, 2808 (1963)] and of Henderson [Mol. Phys. 95, 187 (1998)]. Based on geometric analysis and statistical thermodynamics arguments, a set of sum rules for two-component nearest-neighbor interaction models at thermodynamic equilibrium is derived. By choosing the density of one component ρ and the unlike-bond density ρ12 as two variables, it is shown that the energy is well-behaved; however, the entropy, s̃(ρ,ρ12), is independent of ρ within two-phase regions, but not outside. Temperature and chemical potentials determine the equilibrium ρ and ρ12. The exact entropy function for 1-D systems can be calculated, and an exact free energy density function is formulated. The result shows that s̃ is always dependent on ρ except at ρ12=0, which excludes the possibility of phase transitions at finite temperature.
Microfabrication and characterization of superconducting radio-frequency oscillators
Authors: Götz M. , Khanin V. V. , Zorin A. B. , Niemeyer J.
Published: July 2002

We have prepared integrated oscillators consisting of niobium-made pancake coils and plate capacitors with sputter-deposited silicon dioxide as the dielectric. In combination with a GaAs-based preamplifier, samples with different layout parameters taken from the same wafer were operated in the liquid helium bath. Resonant frequencies in the range from 50 to 150 MHz were found.
The unimolecular dissociation of HCO. V. Mixings between resonance states
Authors: Brandt-Pollmann Ulrich , Weiß Jan , Schinke Reinhard
Published: July 2002

The unimolecular dissociation of HCO in its ground electronic state is considered. By performing calculations (filter diagonalization, absorbing potential) for nonzero angular momentum quantum numbers, it is demonstrated how mixings with near-by “background” states affect the linewidths of the narrower resonance states. This explains qualitatively the theoretically as well as experimentally observed behavior of the linewidth as a function of the vibrational quantum numbers.
New two-dimensional friction force apparatus design for measuring shear forces at the nanometer scale
Authors: Qian Linmao , Luengo Gustavo , Douillet Denis , Charlot Magali , Dollat Xavier , Perez Eric
Published: July 2002

A device to study the friction of two molecularly smooth surfaces separated by an ultrathin liquid film is presented along with its design, calibration, and performance. The apparatus can move one of the surfaces and measure the friction force on the other one bidimensionally for both processes. A high mechanical impedance system (104 N/m) measures continuous friction forces where only stick–slip was previously observed. The frequency and travel distance of the movement can be varied over a wide range (frequency from 10−4 to 7 Hz and distance from 1 to 800 μm) to provide variations of the shear rate over seven orders of magnitude. The actual movement provided by piezoelectric bimorph drive can be affected by the friction forces and is measured by strain gauges. The friction forces are measured with an accuracy of ±2μN with a capacitance sensor. The mechanical design prevents the surfaces from rolling under force. The apparatus is tested with hexadecane. The potential applications of this apparatus and its limitations are discussed.
Comment on “Collisionless shock and supernova remnant simulations on VULCAN” [Phys. Plasmas 8, 2439 (2001)]
Authors: Drake R. P.
Published: July 2002

This recent paper reports some real advances in experimental technique, but is misleading or incorrect in several places. First, the design assumes without discussion that the magnetic field will completely penetrate the plasma, but this is not likely. Second, when the magnetic field is present the surfaces of the converging plasmas will be Rayleigh–Taylor unstable. Third, any shocks produced in experiments like those reported may be collisionless but have no relevance to shocks in supernova remnants. Fourth, the experiment is not a meaningful hydrodynamic simulation of a supernova remnant. Finally, the hydrodynamic simulation results reported are also in error, leading to incorrect values for some scaling parameters.
Development of transferable interaction models for water. III. Reparametrization of an all-atom polarizable rigid model (TTM2–R) from first principles
Authors: Burnham Christian J. , Xantheas Sotiris S.
Published: July 2002

We present a reparametrization of an all-atom polarizable rigid model for water. The model is based on the earlier “Thole-type model” [J. Chem. Phys. 110, 4566 (1999)] and consists of a reparametrization of the two-body part of its potential energy surface from ab initio data. The new parametrization of the polarizable rigid model (TTM2–R) reproduces the structural pattern and absolute binding energies of the first few (n=2–6) water clusters to an impressive (<1%) accuracy with respect to the values obtained at the complete basis set (CBS) level of the second order perturbation theory. It also yields excellent agreement with the experimental second virial coefficient over the 423–773 K temperature range. The binding energies of the n=7–21 clusters are within 2–3% of the results with the newest version of the anisotropic site potential (ASP–W4). The new model produces a diffusion constant of 2.23×10−5 cm2 s−1 for the liquid at 300 K and average dipole moments of 2.65 and 2.86 Debye for liquid (300 K) and ice Ih (100 K), respectively. The corresponding average internal energies are −11.21 kcal/mol/molecule for the liquid (300 K) and −14.69 kcal/mol/molecule for ice (0 K). The computed liquid radial distribution functions are in excellent agreement with experiment and the lattice constants for ice Ih are within 0.02 Å (<0.2%) from the experimentally obtained ones. The computed densities are 1.046 g/cm3 for liquid water (300 K) and 0.942  g/cm3 for ice Ih (0 K). To this end, TTM2–R is an ab initio based model that accurately reproduces both the cluster energetics and structures in addition to several bulk properties for water and ice Ih.
Structure and bonding of propyne on Cu(111) from density functional periodic and cluster models
Authors: Valcarcel A. , Ricart J. M. , Clotet A. , Markovits A. , Minot C. , Illas F.
Published: July 2002

The interaction of propyne on Cu(111) has been studied by periodic and cluster model density functional based methods. The structure of adsorbed propyne predicted by the different models and methods is almost indistinguishable and in very good agreement with experiment. This is a highly distorted propyne with C1 and C2 in nearly sp2 hybridization. The adsorption site predicted by both surface models is also in agreement with experiment provided the cluster innermost region has the correct environment. The use of different functionals does not appear to have a noticeable effect on the adsorption geometry and position of the adsorbate relative to the surface. However, the adsorption energies computed by different exchange–correlation functionals may differ in roughly 0.35 eV. Periodic calculations carried out for different unit cells confirms the experimental long-range structure. Finally, a comparison of cluster and periodic adsorption energies permits to establish that the influence of the surface model on the predicted adsorption energies is much larger than the incertitude due to the choice of a particular exchange correlation functional.
Collision effects in the nonlinear Raman response of liquid carbon disulfide
Authors: Jansen Thomas l. C. , Swart Marcel , Jensen Lasse , van Duijnen Piet Th. , Snijders Jaap G. , Duppen Koos
Published: July 2002

A model of the polarizability of carbon disulfide dimers was constructed, using polarizabilities from accurate time-dependent density functional theory calculations as reference. This direct reaction field model takes dipole-induced dipole effects, induced multipole effects and effects due to the overlap of the electronic clouds into account in an approximate way. The importance of the induced multipole and the overlap effects is investigated. This polarizability model is subsequently used to calculate the third-order time-domain Raman response of liquid carbon disulfide. These results are compared to experimental data and earlier calculated response in which only dipole-induced dipole effects on the polarizability were included. The multipole effects are found to give a significant contribution to the subpico second part of the third-order Raman response.
Observation of latent reliability degradation in ultrathin oxides after heavy-ion irradiation
Authors: Suehle John S. , Vogel Eric M. , Roitman Peter , Conley John F. , Johnston Allan H. , Wang Bin , Bernstein Joseph B. , Weintraub C. E.
Published: July 2002

Constant voltage time-dependent-dielectric-breakdown distributions were obtained for both unirradiated and irradiated 3.0 and 3.2 nm thick SiO2 films subjected to Co60 gamma irradiation and heavy ions of 823 MeV Xe129 (linear energy transfer=59 MeV-cm2/mg). The gamma irradiation had no effect on oxide lifetime. The heavy ion irradiation substantially reduced oxide life even though the devices were biased at 0.0 V during irradiation. The reduction of oxide lifetime under constant-voltage stress conditions was a strong function of the heavy ion fluence.
Application of analytical k.p model with envelope function approximation to intersubband transitions in n-type III–V semiconductor Γ quantum wells
Authors: Cheah C. W. , Tan L. S. , Karunasiri G.
Published: July 2002

A 14-band k.p model combined with an envelope function approximation has been developed for the analysis of III–V semiconductor quantum wells by including the six Γ7, Γ8 conduction bands nonperturbatively. With appropriate approximations, the envelope functions associated with the Γ7, Γ8 bands can be expressed in terms of the two Γ6 conduction band envelope functions, which are the most important components in the electron wave function of an n-type direct-gap III–V compound semiconductor quantum well of zincblende structure. The Schrödinger-type equations for the Γ6 conduction band envelope functions are derived, together with the energy-dependent effective mass that includes the effect of band nonparabolicity, as well as the eigenenergy-dependent effective potential for the envelope wave functions. The Schrödinger-type equations and the boundary conditions for the conservation of probability flux in the 14-band k.p model are found to be different from those of the conventional effective mass model. The 14-band model is then applied to the study of intersubband transitions due to transverse magnetic (TM) and transverse electric (TE) mode infrared radiation in n-type Γ quantum wells, and the calculated absorption spectra are compared with those computed using an equivalent 8-band k.p model. It is found that the TM absorption spectra calculated using the two models are very similar, but the TE absorption spectra calculated using the 14-band model is up to 6 times higher than that calculated using the 8-band model. A design of the quantum well structure for enhancing TE absorption is also discussed.
Modeling of interfacial temperature effects due to an impulsive line heat source
Authors: Shendeleva M. L. , Molloy J. A. , Ljepojevic N. N.
Published: July 2002

Temperature fields generated by an instantaneous line heat source in the medium consisting of two half spaces of different thermal properties are modeled. The analytical calculations employ the Green functions for an impulsive line source derived previously using the Cagniard–de Hoop technique. The analytical model predicts the change of sign of the reflected temperature field along the interface for a certain range of parameters. It has also been found that for the heat source located in the less conductive medium the temperature peak arrival can occur before the peak from the source temperature field. The analytical results are found to be in excellent agreement with numerical modeling using the finite difference method.
Effects of space charge at the conjugated polymer/electrode interface
Authors: Mills C. A. , Taylor D. M. , Riul A. , Lee A. P.
Published: July 2002

Films of the polymer poly(4-dicyanomethylene-4H-cyclopenta[2,1-b:3,4-b′]dithiophene (PCDM) were electrodeposited onto indium tin oxide (ITO) coated glass substrates. The formation of a polymer was confirmed by the presence of an absorption band at ∼900 nm (∼1.4 eV) previously attributed to a π–π* transition. Diodes formed by evaporating aluminum counterelectrodes onto the films displayed nonlinear current–voltage characteristics that were independent of voltage polarity. Interestingly, at low applied voltages, the diodes exhibited two, stable, reversible conductance states differing by about an order of magnitude. The effect is similar to that reported recently in diodes formed from chromium-doped SrZrO3. ac admittance measurements carried out over a range of frequency coupled with the voltage dependence of the device capacitance at low frequency suggests that the two states arise from the presence of a field-dependent space charge at the ITO/PCDM interface.
Measurement of Ar metastables near a dielectric surface in barrier and plasma display panel discharges
Authors: Sakurai T. , Matsuzawa S. , Kamo Y.
Published: July 2002

The density of Ar 1s5 metastable excited atoms in the vicinity of a surface in barrier and display panel discharges was measured by the laser-induced evanescent-mode fluorescence technique. The temporal and spatial distributions of excited atoms were also measured by conventional spontaneous emission and laser absorption methods. From these measurements at various pressures, the behavior of the metastable atoms is clarified and the flux of the metastable atoms on the barrier surface is estimated.
Ultraviolet light assisted oxygenation process for submicron YBa2Cu3O7−δ thin film devices
Authors: Herbstritt F. , Kemen T. , Marx A. , Gross R.
Published: July 2002

We have successfully fabricated superconducting nanobridges and grain-boundary junctions from epitaxial YBa2Cu3O7−δ thin films with thickness between 20 and 30 nm and width down to ∼100 nm. The patterning process turned out to severely deteriorate the transport properties resulting in structural damage, corrosion, and oxygen loss. The most crucial steps are the baking procedure used to cure the electron beam resist, the resist development, and the ion beam etching process. By optimizing these steps and applying a suitable post-treatment procedure a significant enhancement of the sample quality could be achieved. An ultraviolet light assisted oxygenation procedure after the patterning process enabled us to achieve superconducting transition temperatures between 80 and 87 K and critical current densities at 4.2 K up to 4×107 A cm−2 for the nanobridges and 5×103–2×105 A cm−2 for the grain boundary junctions. At 4.2 K junctions with width down to 100 nm corresponding to a junction area down to 2.3×10−3 μm2 showed superconductivity.
Blue cooperative luminescence in Yb3+-doped tellurite glasses excited at 1.064 μm
Authors: dos Santos P. V. , Vermelho M. V. D. , Gouveia E. A. , de Araújo M. T. , Gouveia-Neto A. S. , Cassanjes F. C. , Ribeiro S. J. L. , Messaddeq Y.
Published: July 2002

Blue luminescence emission around 480 nm through cooperative upconversion from pairs of Yb3+ ions implanted into 60TeO2–10GeO2–10K2O–10Li2O–10Nb2O5 tellurite glasses and excited by a cw laser at 1.064 μm is demonstrated. Cooperative luminescence emission enhancement owing to the temperature dependent multiphonon-assisted anti-Stokes excitation process of the ytterbium ions is also observed. The experimental results revealed a fourfold enhancement in the cooperative luminescence emission when the sample was heated in the temperature range of 20 °C–260 °C. The thermally induced enhancement is assigned to the effective absorption cross-section for the ytterbium ions which is an increasing function of the medium temperature.
Ferromagnetic resonance and microstructural studies of Ag/Fe–GaAs waveguide structures
Authors: Lee Chin C. , Wu W. , Tsai Chen S.
Published: July 2002

We report the growth and characterization of ferromagnetic iron/silver (Ag/Fe) multilayer structures on gallium arsenide (GaAs) (100) substrates by molecular beam epitaxy. The samples have been characterized by x-ray diffraction and ferromagnetic resonance (FMR) techniques. X-ray read-camera studies have demonstrated the epitaxial nature of crystalline Fe film grown on GaAs substrate, while x-ray rocking curve measurements reveal a narrow linewidth of only 0.3°. On the FMR technique, we focused specifically on the information contained in FMR linewidth ΔH(f ). Experimental results on ultrathin Fe/Ag films have been obtained with sufficient resolution to measure the linewidth broadening due to intrinsic damping. FMR linewidth is resolved to vary between 0.5 and 1.1 GHz in a frequency range of 20 GHz. Frequency-dependent FMR linewidth ΔHpp(ω) shows a typical linear dependence with a zero frequency offset ΔH(0) of almost zero value, indicating a near-perfect crystalline quality of the deposited magnetic film. The Gilbert damping parameter G is extracted to be 1.45×108 s−1 from the slope of the curve.
Unexpected simplicity in the S1–S dispersed fluorescence spectra of C213H2
Authors: Silva Michelle L. , Jacobson Matthew P. , Duan Zicheng , Field Robert W.
Published: July 2002

We have recorded dispersed fluorescence (DF) spectra (18 cm−1 resolution) from the JKaKc=110 rotational level of six vibrational levels in the S1 (Ã 1Au) state of C213H2. Improvements in our methods of recording and calibrating DF spectra, that have enhanced the quality of our data sets, are briefly discussed. More than 50 fractionated bright state patterns associated with approximately conserved polyad quantum numbers have been extracted from our DF data sets using a spectroscopic pattern recognition technique, extended cross correlation. These polyads extend to internal energies as high as 20 000 cm−1 above the zero-point vibrational level. The polyad fractionation patterns observed at high energy are surprisingly simple relative to the corresponding patterns of C212H2. Comparison between the DF spectra of C213H2 and C212H2 reveals slower intramolecular vibration redistribution in C213H2, particularly with nonzero quanta of CC stretch excitation. More than 15 patterns were extracted above the energy at which acetylene↔vinylidene isomerization is predicted to be energetically feasible (∼15 200 cm−1) and the dynamical information encoded in these patterns is addressed. In particular, we have analyzed a subset of the C213H2 polyads, the pure bending polyads, those with zero quanta of excitation in each of the stretch modes, (Ns=v1+v2+v3=0). The observed pure bending levels are reproduced to a root-mean-square error of <1.5 cm−1 by two different effective Hamiltonian models: an 11 parameter normal-mode and a 13 parameter local-mode model.
Conductance of a quantum point contact in the presence of spin–orbit interaction
Authors: Zhu Shi-Liang , Wang Z. D. , Hu Lian
Published: July 2002

A recursive Green’s function technique is developed to calculate the spin-dependent conductance in mesoscopic structures. Using this technique, we study the spin-dependent electronic transport of quantum point contacts in the presence of the Rashba spin–orbit interaction. We observed that some oscillations in the “quantized” conductance are induced by the spin–orbit interaction, and suggest that the oscillations may stem from the spin–orbit coupling associated multiple reflections. It is also indicated that the 0.7 structure of the conductance observed in mesoscopic experiments would not arise from the spin–orbit interaction.
Effects of nitrogen on GaAsP light-emitting diodes
Authors: Sato Tadashige , Imai Megumi
Published: July 2002

The effects of nitrogen on GaAsP light-emitting diodes grown by hydride vapor phase epitaxy are described. Nitrogen acts as an isoelectronic trap and this localized state makes GaAsP a widely used material for from-yellow-to-red visible light-emitting diodes. The photoluminescence and electroluminescence spectra, brightness, and reliability were investigated systematically in line with the function of nitrogen concentration, from 0 (without nitrogen) to 2.3×1019 cm−3. When the nitrogen concentration reached 2.3×1019 cm−3, the total emission in the photoluminescence spectrum at 4.2 K showed a redshift. The study provides clarification of the effects of nitrogen on the diodes and demonstrates that the characteristics of the diodes strongly depend on the nitrogen concentration.
Boundary angle dependence of magnetoresistance induced by tilted nanocolumn boundaries in La0.7Sr0.3MnO3 grown on step-edged (100) GaAs substrates
Authors: Satoh Issei , Kobayashi Takeshi
Published: July 2002

The intergrain magnetoresistance (IMR) of La0.7Sr0.3MnO3 (LSMO) thin films at 77 K was examined. All LSMO films were grown on step-edged (100) GaAs substrates (step-edge angles ranged from 0 to 80°) by the Ar–F excimer laser ablation (pulsed laser deposition) method. Grains were formed by nanocolumns standing normal to the GaAs surface, resulting in the formation of mechanically contacting grain boundaries. Unlike the conventional bicrystal grain boundary, the present nanocolumn boundaries offered tunneling resistance with negligible influence of the boundary angles. The IMRs showed marked reduction with the application of magnetic field below 100 mT, followed by a gradual change with increasing field. They also clearly showed nanocolumn boundary angle dependence even in the large-angle region.
Analytical model for intrinsic residual stress effects and out-of-plane deflections in free-standing thick films
Authors: Jeong Jeung-hyun , Kwon Dongil , Baik Young-Joon
Published: July 2002

An analytical model for the influence of residual stress on the out-of-plane deflection in a free-standing thick diamond film (the bowing phenomenon) is presented. The variation in residual stress with film thickness is usually believed to cause the bowing. In this study, the stress variation is assumed to be produced by a gradual increase in substrate deformation resulting from layer-by-layer deposition of the film. The model uses the infinitesimal plate-bending theory to describe the layer-by-layer film growth more exactly, considering the two deformation modes of contraction or expansion and bending. To verify the suggested model, thick diamond films were fabricated on Si, Mo, and W substrates of varying thicknesses by microwave plasma assisted chemical vapor deposition. The model’s predictions on bowing, based on the intrinsic stress value measured by the curvature method, were in good agreement with the bowing curvature of the as-released films measured by a profilometer. This confirms that the bowing of thick films depends on the intrinsic stress variation of the film associated with a gradual increase in substrate deformation. A method of eliminating bowing by depositing different layers with different intrinsic stresses is discussed.
Stability of equilibrium in rotating magnetic field current drive for sustaining field-reversed configuration
Authors: Ohnishi Masami , Ishida Akio
Published: July 2002

The stability of the rotation of the ion and electron fluids is studied in regards to the balance of the forces exerted on the electrons by the resistive friction and the rotating magnetic field (RMF) applied for the sake of maintaining a field reversed configuration (FRC) in steady state. A simple analytical model with infinite-long plasma, rigidly rotating ions, and electrons and uniform plasma density is used. The linear stability analysis of the equilibrium rotation is carried out in the reduced zero-dimensional model, which includes the effects of ion rotation, radial plasma flow and separatrix radius change due to the flux conservation within the flux conserver. The analytical expression that gives the stability criterion is derived from the eigenvalues of the linearized equations. Based upon the stability criterion, an interpretation of the present experimental results and comments on future experiments are given for the penetration of the RMF into the FRC.
Formation of porous grain boundaries in polycrystalline silicon thin films
Authors: Kageyama Yasuyuki , Murase Yoshie , Tsuchiya Toshiyuki , Funabashi Hirofumi , Sakata Jiro
Published: July 2002

Unique polycrystalline silicon (poly-Si) thin films, which were permeable to a concentrated hydrofluoric acid solution through their porous grain boundaries, were investigated to elucidate the formation mechanism of their microstructure. 0.1-μm-thick permeable poly-Si thin films were made through processes of amorphous silicon film formation by low pressure chemical vapor deposition, successive postannealing for crystallization, and excess phosphorus diffusion by a phosphorus oxichloride predeposition. At the grain boundaries, porous microstructures were formed after the films were cleaned in an SC1 solution (a 1:1:5 mixture of NH4OH:H2O2:H2O at 80 °C for 10 min), whereas segregated soluble precipitates observed by a field emission secondary electron microscope were present before the SC1 cleaning. Auger electron microscope revealed that the surface of the precipitates mainly consist of silicon (∼80 at. %) and oxygen (∼20 at. %). As a result of transmission electron microscope observation, it is concluded that enhancement of silicon atom mobility by the phosphorus doping process induced consequent segregation of the soluble precipitates at the grain boundaries.
Relaxation of cathodoluminescent characteristics of phosphors at low-energy electron excitation
Authors: Bukesov Sergei A. , Kim Jin Y. , Jeon Duk Y. , Strel’tsov Anton V.
Published: July 2002

The experimental data concerning the processes of brightness relaxation of phosphors either in vacuum fluorescent displays or in a testing system are presented and discussed. Both increase and decrease of cathodoluminescence (CL) brightness of phosphor screen were observed after the first few tens minutes of first period of CL device operation. It is understood that the relaxation behavior results from the change of electrical conductivity of the phosphor particle surface. The root cause of the electron-stimulated change in electrophysical characteristics of a luminescent phosphor particle is the contamination of phosphor surface by thin layer of carbon. A physical model of a CL device, which describes a change of both luminescent and electrophysical characteristics of the phosphor screen under low-energy electron excitation, is proposed. It describes well the relaxation processes of brightness in the wide period of a CL system operation. There is good agreement between the results of theoretical simulation of the model and experimental data.
Simulation of gravitational wave detectors
Authors: de Ronde J. F. , van Albada G. D. , Sloot P. M. A.
Published: July 2002

A simulation program that provides insight into the vibrational properties of resonant mass gravitational radiation antennas is developed from scratch. The requirements that are set necessitate the use of an explicit finite element kernel. Since the computational complexity of this kernel requires significant computing power, it is tailored for execution on parallel computer systems. After validating the physical correctness of the program as well as the performance on distributed memory architectures, we present a number of “sample” simulation experiments to illustrate the simulation capabilities of the program. The development path of the code, consisting of problem definition, mathematical modeling, choosing an appropriate solution method, parallelization, physical validation, and performance validation, is argued to be typical for the design process of large-scale complex simulation codes. © 1997 American Institute of Physics.
Two-photon spectroscopy of GaAs
Authors: Seiler D. G. , Littler C. L. , Heiman D.
Published: July 2002

Two-photon absorption spectra of GaAs were obtained using photoconductivity techniques. At zero magnetic field, the spectrum has a photon energy (ℏω) dependence of (2ℏω–Eg)3/2 just above the energy band gap (Eg), and can be described without considering exciton enhancement effects. Oscillatory behavior in the photoconductive response at zero field as a function of incident two-photon energy has been observed and shown to be due to the interaction of the photoexcited electrons and longitudinal optical phonons. At high magnetic fields, the spectra are quantitatively interpreted in terms of a modified Pidgeon–Brown energy band model.
Molecular-beam-epitaxy GaAs regrowth with clean interfaces by arsenic passivation
Authors: Miller D. L. , Chen R. T. , Elliott K. , Kowalczyk S. P.
Published: July 2002

Clean interfaces between GaAs layers grown by molecular-beam epitaxy (MBE) have been achieved by deposition of arsenic on the surface of the first layer grown, before removing it from the vacuum. Secondary ion mass spectroscopy, deep level transient spectroscopy, and capacitance-voltage carrier profiling show that this arsenic passivation procedure results in no measurable impurity incorporation, no deep levels, and no perturbation of carrier profiles in either n-type or p-type GaAs growth/regrowth interfaces after exposure to air. This is in contrast to growth over nonpassivated etched surfaces which showed large perturbations in free carrier profiles, deep level densities, and impurity incorporation at the interface. This demonstrates that nearly ideal growth/regrowth interfaces are achievable in MBE if impurity incorporation and nonstoichiometry are controlled.
Numerical evaluation of optical pump-probe experiments
Authors: Wintner E.
Published: July 2002

A new computer-based evaluation method is described which allows one to resolve rapid decay rates and to separate different decay mechanisms contributing to data from optical pump-probe experiments. This computer-fitting method is applied to the exemplary case of calculating the carrier lifetimes and quantifying different recombination processes in GaInAsP compounds observed experimentally by absorption bleaching. The carrier density is calculated by solving numerically the continuity equation in the general case of temporal, radial, and sample depth dependent generation and recombinations terms. Bleaching introduced by the pump beam is determined by using the appropriate theoretical relations and is then convolved in time and space with the probe beam to yield average bleaching values for comparison with the experimental ones. This evaluation method should also be applicable to many other pump-probe experiments.
Use of the peak shifts of the 3S-3P sodium resonance lines for the analysis of high-pressure sodium lamps
Authors: Reiser Paul A. , Wyner Elliot F.
Published: July 2002

An arc model for a high-pressure sodium lamp is developed which relates the position of the peaks of the self-absorbed 3S-3P sodium resonance D line to the operating densities and pressures of sodium and mercury. Vapor pressure equations for a Na-Hg amalgam are derived and used to relate the pressures to the temperature and molar ratio of the amalgam reservoir. Allowing for change in amalgam composition due to preferential evaporation of Hg, the amalgam and vapor pressure data are then related to the total amounts of Na and Hg in the arc tube. In order to obtain agreement with experimental data for D-line widths between 25 and 200 Å, it is found necessary to maintain the distinction between the two doublets of the Na D line. In addition, it is shown that the effect of the temperature profile is practically negligible in relating the peak shifts to the average Na and Hg densities.
Calculated temperature dependence of the band gap of HgTe-CdTe superlattices
Authors: Guldner Y. , Bastard G. , Voos M.
Published: July 2002

We present calculations of the band gap and of the corresponding cutoff wavelength of HgTe-CdTe superlattices. These calculations are done for different temperatures as a function of the thickness of the layers, showing in particular that interesting cutoff wavelengths for infrared detectors (∼10 μm) can be obtained with reasonable thickness between 4 and 300 K.
Lattice parameter variation and magnetization studies on titanium-, zirconium-, and tin-substituted nickel-zinc ferrites
Authors: Das A. R. , Ananthan V. S. , Khan D. C.
Published: July 2002

The variation of lattice parameter, saturation magnetization, and Curie temperature on the addition of Ti4+, Zr4+, and Sn4+ to some Ni-Zn ferrite compositions are reported and the results are explained on the basis of the movement of the substituting ions first to the tetrahedral and finally to the octahedral sites of the spinel lattice.
Discharge and ion extraction properties of a beam-plasma ion source
Authors: Rosing M. G. , Conrad J. R.
Published: July 2002

The discharge and ion extraction properties of a beam-plasma ion source have been studied experimentally. The extractable ion current is maximized when the discharge column length is chosen to be an optimum length. The peak extracted ion current can exceed the Child–Langmuir current as much as an order of magnitude.
An inert marker study for palladium silicide formation: Si moves in polycrystalline Pd2Si
Authors: Ho K. T. , Lien C.-D. , Shreter U. , Nicolet M-A.
Published: July 2002

A novel use of Ti marker is introduced to investigate the moving species during Pd2Si formation on 〈111〉 and 〈100〉 Si substrates. Silicide formed from amorphous Si is also studied using a W marker. Although these markers are observed to alter the silicide formation in the initial stage, the moving species can be identified once a normal growth rate is resumed. It is found that Si is the dominant moving species for all three types of Si crystallinity. However, Pd will participate in mass transport when Si motion becomes obstructed. off
Effects of a transition layer on CoCr films
Authors: Byun C. , Sivertsen J. M. , Judy J. H.
Published: July 2002

The effects of a transition layer separating the substrate and the columnar structure of rf sputtered CoCr films on their magnetic and structural properties have been investigated. The films were removed from glass substrates and the transition layer was etched directly by rf sputtering. It is shown that the abrupt change or anomalous jump observed in the in-plane magnetization hysteresis loop of some CoCr films is caused by a fine-grained transition layer which is about 1000 Å thick and has a coercivity of 200 Oe. The measured in-plane coercivity increased to 1000 Oe when the transition layer was completely removed while no change was observed in the perpendicular coercivity or saturation magnetization. Only films having a transition layer showed a large decrease in the effective anisotropy field as determined from the in-plane loop when sputter etched to a depth of 2000 Å from the top surface. The dispersion of the hcp (002) axes was found to be 3° for films without and 16° for films with a transition layer. These dispersions were found to be independent of the sputter-etched depth indicating that the intrinsic dispersion of the orientation of CoCr films is established by the transition layer.
Recovery of magnetostriction values from torsional rigidity variations
Authors: Garshelis I. J. , Fiegel W. S.
Published: July 2002

The effects of longitudinal fields on torsional rigidity are examined. A simple model is found to predict salient features not heretofore recognized. Torsional rigidity is found to be diminished in the region where the magnetoelastic and magnetostatic energy densities are comparable to the anisotropy. In higher fields there is a consistent stiffening due to the reduction of the magnetoelastic component of the total shear strain. This stiffening is diminished with increasing torsion. The experimental visibility of each of these features in any real material depends on its elastic strength, Ms, and effective values of its anisotropy and magnetostriction. Recovery of an average absolute value of the magnetostriction requires an assessment of the manner in which the torsional rigidity varies with applied fields and torsion.
Suppression of thermal donor formation in heavily doped n-type silicon
Authors: Wada Kazumi , Inoue Naohisa
Published: July 2002

It is found by deep level transient spectroscopy (DLTS) that the oxygen thermal donor formation is suppressed in Czochralski silicon doped with donor impurities more than 1×1016 cm−3. The result is explained by a new model considering electron-hole equilibrium. The dopant concentration dependence of the thermal donor formation is analyzed, based on the model, and it is concluded that the thermal donor is a doubly charged donor.
A Pb-alloy film preparation technique for Josephson junctions
Authors: Waho Takao , Hasumi Yuji , Arai Kunihiro
Published: July 2002

A Pb-alloy film preparation technique is proposed and applied to high-reliability Josephson junctions with small threshold current spreads. Fine-grained films with the average grain sizes as small as 30 nm are obtained. This is accomplished by condensing Pb, In, and Au molecular beams onto liquid-nitrogen-cooled substrates. Fine grains result from AuIn2 particles being dispersed finely and uniformly in alloy films. Josephson junctions are fabricated using these fine-grained films as base electrodes. The threshold current standard deviation is reduced to 2.4%. This is due to the fine grain size and surface passivation treatment for the base electrodes. The cumulative failure is found to be less than 0.13% after 8400 thermal cycles between 4.2 K and room temperature. This is the best value reported thus far. This technique achieves fine-grained metal alloy films providing new properties. These properties promise to aid development of high-performance Josephson IC’s.
Interactions between cleaved (Hg,Cd)Te surfaces and deposited overlayers of Al and In
Authors: Davis G. D. , Byer N. E. , Riedel R. A. , Margaritondo G.
Published: July 2002

The interactions between the clean, cleaved Hg0.72Cd0.28Te surfaces and thin evaporated layers of Al and In have been investigated with ultraviolet photoelectron spectroscopy using synchrotron radiation. Deposition of ultrathin layers of either metal was found to deplete the surface of much of its Hg by breaking the Hg-Te bonds to form a very thin interlayer of Al2Te3 or one of the several indium tellurides. In contrast, no interaction between the metals and the CdTe component was observed. Upon deposition of additional Al, a metallic Al overlayer was grown, with some Te diffusing to the surface. Some of the Hg freed by the initial reaction diffused into the semiconductor and formed a degenerate n+ layer capable of ohmically coupling n-type material to the metallic overlayer.
Substrate-dependent electrical properties of low-dose Si implants in GaAs
Authors: Yeo Y. K. , Hengehold R. L. , Kim Yong Yun , Ezis A. , Park Y. S. , Ehret J. E.
Published: July 2002

A comprehensive electrical study of low-dose (1012−1013 cm−2) Si implants in both liquid-encapsulated Czochralski (LEC) grown undoped and horizontal Bridgman grown Cr-doped semi-insulating GaAs has been made using Hall measurements. The optimum annealing temperature is 850 °C, and an apparent electrical activation efficiency of 90% has been achieved with room-temperature implantation for both substrates. The carrier depth profiles are much broader and the peak concentrations are much lower than those expected according to the Lindhard–Scharff–Schiott (LSS) theory. Although the carrier profiles for both substrates agree with each other relatively well, the mobilities for the undoped substrates are significantly higher than those for the Cr-doped substrates at all low doses.
Electrical activation of implanted Be, Mg, Zn, and Cd in GaAs by rapid thermal annealing
Authors: Pearton S. J. , Cummings K. D. , Vella-Coleiro G. P.
Published: July 2002

The formation of p channel (p∼3×1017 cm−3) and p+ regions (p>5×1018 cm−3) in GaAs by rapid annealing of Be, Mg, Zn, or Cd implants at 900–950 °C is reported. The electrical characteristics of each species were investigated by capacitance-voltage profiling, Hall-effect and microwave photoconductance measurements, and particular emphasis was placed on determining the uniformity of activation over 2-in.-diam wafers. The results demonstrate that rapid thermal annealing is well suited to GaAs integrated circuit applications.
Ga-As liquidus at temperatures below 650 °C
Authors: DeWinter J. C. , Pollack M. A.
Published: July 2002

Measurements of Ga-As liquidus composition versus temperature in the range 350–650 °C are reported. The data are described by a constant interaction parameter α≊−3600±1200 cal/mole in this range, rather than the temperature dependent value of α required to fit available higher-temperature data.
Depth profiles of manganese implants in InP after annealing
Authors: Chaplain R. , Gauneau M. , L’Haridon H. , Rupert A.
Published: July 2002

This paper reports on depth profiles of Mn implants, after annealing, obtained by secondary ion mass spectrometry. Two types of samples implanted with manganese were studied: unintentionally doped n-type (5–10×1015 e cm−3), and n-type S-doped (n=5×1018 e cm−3) substrates. In unintentionally doped substrates it is found that Mn exhibits a well-defined two-species diffusion front as other acceptors: Be, Zn, or Cd. On the contrary in S-doped substrates it does not move. The study of the correlations between the movement of the residual impurities and the implanted Mn atoms, or Zn in a comparative sample, has led us to propose a model based on an interstitial-substitutional reaction involving the impurity sites and taking place in the bulk of the semiconductor.
Photoluminescence properties of nitrogen-doped ZnSe grown by molecular beam epitaxy
Authors: Park R. M. , Mar H. A. , Salansky N. M.
Published: July 2002

Nitrogen-doped ZnSe layers (∼0.5 μm thick) have been grown by molecular beam epitaxy (MBE) onto (100)-oriented GaAs substates using both N2 and NH3 gas sources as alternative sources of nitrogen. The low-temperature photoluminescence spectra obtained from N-doped ZnSe layers were dominated by strong donor-acceptor (D-A) pair recombination emission. A no-phonon emission peak (QN0 ) at 2.699 eV together with four distinct longitudinal optical (LO) phonon replicas of QN0 were readily resolved. The amplitudes of this series of D-A pair recombination peaks were found to increase in a monotonic fashion with increasing overpressure of N2 and NH3 in the MBE growth chamber. In addition an acceptor-bound exciton peak (IN1 ) was detected at 2.7917 eV from layers grown using large N2 or NH3 overpressures (∼10−4 mbar.).