bluuebunny/crossref_metadata_2025 huggingface dataset:
Dipole, dipole–quadrupole, and dipole–octopole polarizability of adamantane, C10H16, from refractive index measurements, depolarized collision-induced light scattering, conventional ab initio and density functional theory calculations
Authors: Maroulis G. , Xenides D. , Hohm U. , Loose A.
Published: July 2002

Refractive index (RI) measurements, depolarized collision-induced light (CILS) scattering and ab initio quantum chemical calculations are used to determine the dipole (α), dipole–quadrupole (A), and dipole–octopole polarizability (E) of adamantane, C10H16. For this molecule of symmetry group Td the three polarizabilities can be represented by a single scalar quantity. From experiment we obtain for the static dipole polarizability at T≈400–500 K 107.5±1.1 e2a02Eh−1, and for the higher polarizabilities |A|=102.0±7.8 e2a03Eh−1, and |E|=720±80 e2a04Eh−1. We have performed conventional ab initio and density functional theory calculations with specifically designed basis sets. A very large [4s3p3d1f/3s2p1d] basis set consisting of 574 basis functions is thought to provide near-Hartree–Fock values for α,A and E: α=101.72 e2a02Eh−1, A=−6.5 e2a03Eh−1, and E=−71.0 e2a04Eh−1. Our final theoretical estimates for these properties are α=107.5±1.0 e2a02Eh−1, A=−8.0±1.5 e2a03Eh−1, and E=−76.5±5.5 e2a04Eh−1. Very strong electron correlation effects are found for both the first (β) and second (γ) hyperpolarizability. Our estimate for β≡βxyz and the mean γ̄ are 41.4±5.6 e3a03Eh−2 and (25±2)×103 e4a04Eh−3, respectively. For the octopole and hexadecapole moments we propose Ω=−4.4±0.2 ea03 and Φ=−100.8±5.5 ea04. The basis sets constructed in this work should provide reliable computational tools for the study of intermolecular interactions of adamantane.
Controllable π SQUID
Authors: Baselmans J. J. A. , van Wees B. J. , Klapwijk T. M.
Published: July 2002

We have fabricated and studied a promising kind of direct current superconducting quantum interference device (dc-SQUID) in which the magnitude and sign of the critical current of the individual Josephson junctions can be controlled by additional voltage probes connected to the junctions. We show that the amplitude of the voltage oscillations of the SQUID as a function of the applied magnetic field can be tuned and that the phase of the oscillations can be switched between 0 and π in the temperature range of 0.1–4.2 K using a suitable control voltage. This is equivalent to the external application of (n+1/2) flux quantum.
Low-threshold-current 1.32-μm GaInNAs/GaAs single-quantum-well lasers grown by molecular-beam epitaxy
Authors: Li Wei , Jouhti Tomi , Peng Chang Si , Konttinen Janne , Laukkanen Pekka , Pavelescu Emil-Mihai , Dumitrescu Mihail , Pessa Markus
Published: July 2002

Using solid-source molecular-beam epitaxy with a rf-plasma source, we have grown GaInNAs/GaAs single-quantum-well lasers operating at 1.32 μm. For a broad-area oxide stripe, uncoated Fabry–Perot laser with a cavity length of 1600 μm, the threshold current density is 546 A/cm2 at room temperature. The internal quantum efficiency for these lasers is 80%, while the materials losses are 7.0 cm−1. A characteristic temperature of 104 K was measured in the temperature range from 20 to 80 °C. Optical output up to 40 mW per facet under continuous-wave operation was achieved for these uncoated lasers at room temperature.
Finite-basis-set optimized effective potential exchange-only method
Authors: Ivanov Stanislav , Hirata So , Bartlett Rodney J.
Published: July 2002

The finite-basis-set optimized effective potential (OEP) method is presented from an integral equation point of view. It is shown that the projection method for solving the OEP integral equation provides a consistent and convenient approach for including orbital-dependent functionals and potentials in the finite-basis-set implementations of the Kohn–Sham theory. Different finite-basis-set realizations of the OEP method are introduced and tested within the exchange-only approximation. An exact condition involving the local multiplicative exchange potential and the nonlocal Hartree–Fock exchange potential built from Kohn–Sham orbitals is incorporated in our schemes. Numerical results are presented.
Cavity ring-down spectroscopy in the liquid phase
Authors: Xu Shucheng , Sha Guohe , Xie Jinchun
Published: July 2002

A new application for cavity ring-down spectroscopic (CRDS) technique using a pulsed polarized light source has been developed in the absorption measurement of liquids for “colorless” organic compounds using both a single sample cell and double sample cells inserted in an optical cavity at Brewster angle. At present an experimental capability of measuring absorption coefficients as small as 2–5×10−7 cm−1 has been demonstrated by measurement of the absorption baselines. The first spectra for CRDS in the liquid phase, the C–H stretching fifth vibrational overtones of benzene in the pure liquid and hexane solution are obtained. The optical absorption length for liquids in both a single sample cell and double sample cells of 1 cm length is up to 900 cm due to multipass of light within an optical cavity. Compared to the thermal lens and optoacoustic spectroscopic techniques, the sensitivity for CRDS mainly depends on the optical absorption path of the sample (single passing path of the sample times multipass times), is not determined by the laser power and the length of the sample cell. The absolute absorption coefficient and band intensity for the sample are determined directly by the spectroscopy.
Quantitative nuclear magnetic resonance characterization of long-range chain dynamics: Polybutadiene, polyethylene-oxide solution
Authors: Guillermo Armel , Cohen Addad Jean-Pierre
Published: July 2002

We report two sets of independent nuclear magnetic resonance (NMR) measurements of self-diffusion and proton transverse relaxation in molten cis1,4-polybutadiene (PB) performed in order to investigate chain dynamics properties. Self-diffusion coefficients were measured as a function of temperature and of molecular weight (M) over the range 104 to 6.7×104 g/mol. The crossover from the Rouse-type behavior (D≈M−1) to the reptation one was found to occur for MCross≈3×104 g/mol; for M>MCross the data were consistent with the scaling dependence: D≈M−2.4±0.05, in agreement with the data analysis recently reported in the literature. The thorough analysis of the transverse relaxation of protons attached to highly entangled PB chains (6.7×104⩽M⩽43×104 g/mol) gave evidence for the dynamics partition of one chain into two end-submolecules and one inner part clearly discriminated from one another. The number NEnd of monomeric units in one end-submolecule, independent of M, is shown to be closely related to the monomeric friction coefficient ζ0 measured from short chain diffusion over the temperature range 25 to 85 °C. The interpretation both of diffusion results and of proton relaxation of inner monomeric units lead to the definition of an effective friction coefficient ζ0Eff≈ζ0(M/NEnd)0.4 associated with the curvilinear diffusion of one chain in its tube. The friction coefficient ζLoc associated with local monomeric rotations is discriminated from ζ0 from its weaker temperature dependence. This approach was applied to polyethylene-oxide chains in solution (dimethyl formamide, 0.18⩽c⩽1, w/w) where the segmental size of end-submolecules was found to vary as 1/c. Experimental results are well matched by this specific NMR approach which accounts for the novel properties of the proton relaxation function.
Characterization of a diamond crystal x-ray phase retarder
Authors: Berman Lonny E. , Shen Qun , Finkelstein Ken D. , Doing Park , Yin Zhijian , Pan Guoqiang
Published: July 2002

An x-ray phase retarder plate based on a diamond single crystal diffracting in the asymmetric Laue geometry has been characterized at the X25 wiggler beamline at the National Synchrotron Light Source. The forward diffracted (transmitted) beam, using the (111) Bragg planes in a 0.5 mm thick wafer with a (001) surface normal, was employed. A polarization analyzer based on a GaAs(111) crystal oriented to diffract the (222) and a different reflection simultaneously was used to determine the Stokes–Poincaré polarization parameters of the beam transmitted by the diamond phase plate, at several settings of the diamond about its (111) rocking curve. At 7.1 keV, the phase plate performed as expected and it was proven possible to produce, with the plate, an almost completely left- or right-handed circularly polarized x-ray beam from a linearly polarized incident beam.
Pulsed-laser assisted nanopatterning of metallic layers combined with atomic force microscopy
Authors: Huang S. M. , Hong M. H. , Lu Y. F. , Lukỳanchuk B. S. , Song W. D. , Chong T. C.
Published: July 2002

Pulsed-laser assisted nanopatterning of metallic layers on silicon substrates under an atomic force microscope (AFM) tip has been investigated. A 532 nm Nd:YAG pulsed laser with a pulse duration of 7 ns was used. Boron doped silicon tips were used in contact mode. This technique enables processing of structures with a lateral resolution down to 10 nm on the copper layers. Nanopatterns such as pit array and multilines with lateral dimensions between 10 and 60 nm and depths between 1.5 and 7.0 nm have been created. The experimental results and mechanism of the nanostructure formation are discussed. The created features were characterized by AFM, scanning electron microscope and Auger electron spectroscopy. The apparent depth of the created pit has been studied as a function of laser intensity or laser pulse numbers. Dependence of nanoprocessing on the geometry parameters of the tip and on the optical and thermal properties of the processed sample has also been investigated. Thermal expansion of the tip, the field enhancement factor underneath the tip, and the sample surface heating were estimated. It is proposed that field-enhancement mechanism is the dominant reason for this nanoprocessing.
Low-temperature unsteady creep of parahydrogen single crystals
Authors: Alekseeva L. A. , Pustovalova A. V. , Khatuntsev V. I. , Butenko Yu. V.
Published: July 2002

The low-temperature plasticity of single crystals of solid parahydrogen (orthohydrogen concentration ∼0.2%, nonhydrogen impurities ∼1.5×10−4%, and isotopic impurities of hydrogen — deuterium — [D]/[H]∼(5–6)×10−3%) in the is investigated in the temperature range 1.8–4.2 K under conditions of sample creep under the influence of a static mechanical stress σ. A complicated dependence of the constant of the logarithmic creep of p-H2 on the stress and temperature is observed, along with the anomalous features of the creep that indicate either the possible involvement of vacancies in the kinetics of the unsteady creep of parahydrogen single crystals at small σ or the coherent motion of kinks on dislocations.
Anomalous isotope effect in the permeation, retention, and reemission at interaction of energetic hydrogen with niobium
Authors: Livshits A. I. , Notkin M. E. , Bacal M.
Published: July 2002

A niobium membrane sample was placed in H or D plasma and electrically biased. Isotope effects for H vs. D in factors of 20, 40, and 40, respectively, were observed in plasma driven permeation, retention, and in the reemission, within a narrow range of bias voltages (40–80 V) at the lowest metal temperature investigated (910 K). The phenomenon occurred at the “superpermeation” of suprathermal hydrogen arising from an oxygen monolayer at the metal surface. The phenomenon is supposed to be caused by dynamics of the oxygen monolayer under the action of ion sputtering and surface segregation of dissolved O. Such and even much stronger isotope effects are also expected on other metals with a similar “real” surface. This isotope effect may be important for D/T-mixture recycling, retention and permeation at its interactions with plasma facing components of fusion reactors as well as for the applications of superpermeable membranes for pumping of hydrogen isotopes and their separation from He.
Heat conduction nanocalorimeter for pl-scale single cell measurements
Authors: Johannessen E. A. , Weaver J. M. R. , Cobbold P. H. , Cooper J. M.
Published: July 2002

An ultrasensitive nanocalorimeter for use with pl-scale biological samples using silicon microfabrication technology has been developed in which a 720 pl reaction vessel, a calibration heater, and a thermoelectric transducer of 125 μK sensitivity were integrated into a single multilayer thin-film configuration. The resolution of the system ranged from 10 to 25 nW depending on the heat capacity, conductance and power density of the samples studied. The device has been used in heat conduction measurements of the energy released from the enzyme catalyzed hydrolysis of hydrogen peroxide using purified catalase, and for the determination of the catalase activity within a single mouse hepatocyte. The nanocalorimeter has the potential for integration in a high-density array format, where the change in temperature from ultralow volume cellular assays could be used as a generic analytical tool for high throughput screening of bioactive compounds.
Agglomeration of submicrometer particles in weak periodic shock waves
Authors: Shuster K. , Fichman M. , Goldshtein A. , Gutfinger C.
Published: July 2002

Agglomeration of submicrometer particles in the presence of acoustic fields was treated experimentally. Fast agglomeration of aerosol particles in weak periodic shock waves was observed. The rate of particle agglomeration in shock waves was found to be much faster than in continuous sound waves.
Rapid thermal annealing in GaNxAs1−x/GaAs structures: Effect of nitrogen reorganization on optical properties
Authors: Grenouillet L. , Bru-Chevallier C. , Guillot G. , Gilet P. , Ballet P. , Duvaut P. , Rolland G. , Million A.
Published: July 2002

We report on the effect of rapid thermal annealing (RTA) on the photoluminescence (PL) properties of GaNxAs1−x/GaAs structures. In particular, a blueshift of the PL peak energy is observed when annealing the samples. The results are examined as a consequence of a RTA-induced nitrogen diffusion inside the GaNxAs1−x material rather than diffusion out of the alloy, which homogenizes initial nitrogen composition fluctuations. We propose a simple model that describes the RTA-induced blueshift of the low temperature PL peak energy. This model is in good agreement with experimental results and is consistent with recent studies in which lateral composition fluctuations in the GaNAs alloy were reported.
A novel tape target for use with repetitively pulsed lasers
Authors: Fill E. , Bayerl J. , Tommasini R.
Published: July 2002

A compact tape drive applicable in experiments with repetitively pulsed lasers is described. By exposing fresh material to the laser pulse at each shot, it is possible to obtain up to 104 shots in a single run. A particular tape can be used many times. The tape target provides stable output, is easy to adjust, and is low cost in operation. The possibility of illuminating samples with the rear-side emission is a further advantage for many applications. Experiments are described in which a copper tape, 10 m long, 12 mm wide, and 25 μm thick, is used to generate Cu Kα radiation. Applying 2 TW titanium–sapphire laser pulses, yields 2.7×109 Kα photons/Sr per shot. Bragg and powder spectra generated with this radiation are shown.
Gas phase trapped ion studies of collisionally formed MgC60+ complexes
Authors: Thompson R. I. , Welling M. , Schuessler H. A. , Walther H.
Published: July 2002

A series of experiments were performed to study the formation of MgC60+ complexes via Mg++C60 collisions, and to study the structure and stability of the resulting complexes via optical spectroscopy and mass spectrometry. Collision experiments were carried out in a linear ion trap apparatus under conditions of controlled collision energies, reactant densities, and buffer gas pressure. Ion trap mass spectrometry was used to measure the relative reaction rates for complex formation, charge transfer, and fragmentation reactions in Mg++C60 collisions. Laser-induced photodissociation was then used to study the MgC60+ complexes in order to measure their stability and identify their molecular structure. Absolute photodissociation cross sections were determined for complexes generated at low collision energies and reactant densities over the wavelength range of 1300–280 nm and were in the range from 2×10−20 cm2 to 5×10−17 cm2 in magnitude. The shape of the generated cross-section curve indicates that at low collision energies most of these complexes are exohedrals. More refined measurements of samples generated at optimum buffer gas pressures and higher collision energies demonstrated the existence of a second more slowly dissociating fraction that apparently results from the presence of endohedral complexes.
Prediction of density limits in tokamaks: Theory, comparison with experiment, and application to the proposed Fusion Ignition Research Experiment
Authors: Stacey Weston M.
Published: July 2002

A framework for the predictive calculation of density limits in future tokamaks is proposed. Theoretical models for different density limit phenomena are summarized, and the requirements for additional models are identified. These theoretical density limit models have been incorporated into a relatively simple, but phenomenologically comprehensive, integrated numerical calculation of the core, edge, and divertor plasmas and of the recycling neutrals, in order to obtain plasma parameters needed for the evaluation of the theoretical models. A comparison of these theoretical predictions with observed density limits in current experiments is summarized. A model for the calculation of edge pedestal parameters, which is needed in order to apply the density limit predictions to future tokamaks, is summarized. An application to predict the proximity to density limits and the edge pedestal parameters of the proposed Fusion Ignition Research Experiment is described.
Temperature change effect on minority species rf heating
Authors: Swanson D. G.
Published: July 2002

Although the idea of using the two-ion hybrid resonance to heat the minority species has been around for a long time and been in use in many experiments, the effects of the changing temperature of the minority species on the mode conversion process has not been carefully examined. In this paper it is shown that the behavior of the mode converted ion Bernstein wave not only changes quantitatively as the minority temperature changes, but changes qualitatively, so that the ion Bernstein wave switches sides and changes from a backward wave to a forward wave (or vice versa). While the absorption may not change dramatically, any potential use of the mode converted wave for current drive may change dramatically as the location of the driven current changes as the minority–majority temperature ratio changes.
Evolving perspectives during 12 years of electrical turbulence
Authors: Winfree A. T.
Published: July 2002

This Focus issue describes a problem in electrical dynamics which has fascinated generations of physiologists. There are today so many views of fibrillation that only the rarest generalization can embrace all of them. Fifty-two prominent investigators collaborate here to present aspects of the problem in these eighteen articles (including this introduction) tailored for readers whose principal expertise lies elsewhere. In “The High One’s Lay” (Norse Runes, ca. 800) Odin remarks, “Much too early I came to many places: the beer was not yet ready, or was already drunk…” but to this one we come at very nearly the right time in 1998. This introduction attempts to guide newcomers by noting the changed or multiple meanings of novel technical terms while sorting the key facts and ideas into an order that facilitates comparison and contrast with those of a dozen years ago. This Focus issue is authored by some of the foremost innovators of both theory and experiment in this area. By assimilating their presentations the readers of Chaos can become well poised to appreciate and evaluate the definitive evidence expected in the next few years.
Residence-time distributions for chaotic flows in pipes
Authors: Mezić Igor , Wiggins Stephen , Betz David
Published: July 2002

In this paper we derive two rigorous properties of residence-time distributions for flows in pipes and mixers motivated by computational results of Khakhar et al. [Chem. Eng. Sci. 42, 2909 (1987)], using some concepts from ergodic theory. First, a curious similarity between the isoresidence-time plots and Poincaré maps of the flow observed in Khakhar et al. is resolved. It is shown that in long pipes and mixers, Poincaré maps can serve as a useful guide in the analysis of isoresidence-time plots, but the two are not equivalent. In particular, for long devices isoresidence-time sets are composed of orbits of the Poincaré map, but each isoresidence-time set can be comprised of many orbits. Second, we explain the origin of multimodal residence-time distributions for nondiffusive motion of particles in pipes and mixers. It is shown that chaotic regions in the Poincaré map contribute peaks to the appropriately defined and rescaled axial distribution functions.
Semiclassical quark model of the nuclear matter response
Authors: Melendez W. , Horowitz C. J.
Published: July 2002

The longitudinal response function R(q,w) of nuclear matter is calculated in a semiclassical quark model. The model has a many-body string-flip potential that confines quarks into hadrons and avoids color van der Waals forces. Molecular dynamics simulations are used to calculate R(q,w) in one space dimension for a variety of momentum transfers q and excitation energies w. The response function decreases with density (compared to a free hadron response) because of quark exchange between hadrons. © 1995 American Institute of Physics.
Computational grids: On-demand computing in science and engineering
Authors: Foster Ian , Kesselman Carl
Published: July 2002

Research groups at Argonne National Laboratory and the University of Southern California are developing a set of key technologies to support grid development and programming. A large-scale prototype of such future computational grids called the Globus Ubiquitous Supercomputing Testbed or GUSTO, is designed. GUSTO comprises of supercomputers and other computer systems at national laboratories and other institutions across this country and Europe. (AIP) © 1998 American Institute of Physics.
Using Java for scientific programming and electromagnetics
Authors: Martin Jared , Long Lyle N. , Morooney Kevin M.
Published: July 2002

The advantages and disadvantages of Java for scientific programming are explored through the development of a Java applet for computational electromagnetics (JACE). Due to the complexity of systems modeled by computational electromagnetics, JACE is a good measure of performance for scientific programming. Java’s integration of graphics capabilities and numerical computations facilitates the development of graphical simulations and user interfaces. Further, Java’s object-oriented architecture and absence of pointers provide enhanced program flexibility and traceability, decreasing development time. © 1998 American Institute of Physics.
Vacuum surface flashover: A high-pressure phenomenon
Authors: Gray Eoin W.
Published: July 2002

Desorbed gases from insulator surfaces may be much more important in flashover initiation than properties of the dielectric surface. Ambient neutral densities, immediately above the insulator surface, in the initial stages of flashover have been calculated to lie in the range from 2×1017/cm3 to 2×1021/cm3 with a mean of about 1×1019/cm3, whether flashover occurred on surfaces in air at atmospheric pressure or in vacuum as low as 10−6 Torr. The evidence presented indicates that, for dc and microsecond pulse voltages, surface flashover is a local, relatively high-pressure phenomenon. Comparison of field strengths of surface flashover for various insulating materials perpendicular to the electrodes, operating pressures, and voltage waveforms appears to indicate that flashover values range well within an order of magnitude (∼18–80kV/cm). A filamentary nature of the flashover discharge is shown and is consistent with gas breakdown phenomena. Ionization wave front velocities are examined and these compare favorably with those obtained from gaseous breakdown studies.
Annealing of ion-implanted resistors reduces the 1/ f  noise
Authors: Vandamme L. K. J. , Oosterhoff S.
Published: July 2002

The conductivity fluctuations in 1-MeV, boron-implanted layers in silicon have been investigated at room temperature with the anneal temperature as a parameter. The 1/ f  noise parameter α has been calculated from conductance, Hall voltage, and noise experiments. Annealing of the implants causes, in addition to an increase in the number of electrically active impurities, a decrease in the 1/ f  noise parameter α by a factor of at least 50. The α value is proportional to eΔE/kTan, with an annealing activation energy ΔE=1.1 eV in a temperature range of 722 K <Tan<1022 K. The annealing affects the quality of the crystal, the scattering mechanism, the temperature dependence of the mobility, and the value of α. The better the crystal, the lower the 1/ f  noise parameter α.
Generation of very high-frequency ultrasonic waves using thin films of vinylidene fluoride-trifluoroethylene copolymer
Authors: Kimura Kuniko , Ohigashi Hiroji
Published: July 2002

Electromechanical properties of thin films of vinylidene fluoride-trifluoroethylene copolymer [P(VDF-TrFE)] and their application to ultrasonic transducers were studied in the frequency range of 50–250 MHz at room temperature. A 5-μm-thick P(VDE-TrFE) film resonating at 250 MHz in thickness extensional mode exhibited a large electromechanical coupling factor of 0.26. The dielectric and elastic constants were also studied in this frequency region. A transducer using a 3-μm-thick film exhibited a large conversion efficiency (6.5 dB at 150 MHz), and good impulse response (30 ns ring-down time width) in water. A concave transducer transmitted a well-focused ultrasonic beam (35-μm beamwidth).
Influence of the substrate on the early stage of the growth of hydrogenated amorphous silicon evidenced by kinetic ellipsometry
Authors: Antoine A. M. , Drevillon B.
Published: July 2002

Fast real-time ellipsometry is used to study in situ, as a function of the substrate, the growth of the first tens of monolayers of hydrogenated amorphous silicon (a-Si:H) deposited by a rf glow discharge of SiH4. The high sensitivity of this technique is illustrated and the early stage of the growth is found to strongly depend upon the nature of the substrate. A nucleation mechanism followed by incomplete coalescence is observed on metal and hydrogenated amorphous germanium (a-Ge:H) substrates. On the contrary, fused silica (SiO2) and tin dioxide (SnO2) are superficially reduced:  this reduction creates at the interface a mixed layer of a-Si:H and silicon oxide on the silica substrate, and produces elemental tin at the surface of the SnO2 substrate. In this last case, tin is found to diffuse in the further a-Si:H growing film. On crystalline silicon (c-Si), the a-Si:H growth shows incomplete coalescence followed by homogeneous growth, probably together with the reduction of the native c-Si oxide layer.
Optical investigations of ion implant damage in silicon
Authors: Hummel R. E. , Xi Wei , Holloway P. H. , Jones K. A.
Published: July 2002

Ion implantation damage in silicon has been studied utilizing a new optical technique (differential reflectometry). It has been demonstrated that differential reflectometry can be used to identify whether an implanted layer is crystalline, damaged crystalline, or amorphous. The intensity of interband transitions can be used to determine the thickness of a damaged crystalline layer over a submerged amorphous layer. Interference effects were utilized to determine the thickness of an amorphous layer. Thus, differential optical reflectance has far-reaching potential for characterizing implanted substrates.
Hydrogen and ammonia response of metal-silicon dioxide-silicon structures with thin platinum gates
Authors: Spetz A. , Armgarth M. , Lundström I.
Published: July 2002

The hydrogen and ammonia sensitivity of metal-oxide-semiconductor (MOS) structures with platinum gates between 3 and 70 nm thick was investigated. The response to these gases was measured as a shift in the capacitance-voltage (C-V) curve of the MOS structure along the voltage axis. The measurements were made at an elevated temperature, mainly at 150 °C, where chemical reactions take place on the surface of the catalytic metal. The main purpose of the investigation was to determine if hydrogen and ammonia are detected by similar mechanisms. It is concluded that hydrogen molecules are dissociated and hydrogen atoms give rise to a dipole layer at the metal-oxide interface, similar to the behavior of hydrogen in hydrogen sensitive MOS structures with thick catalytic metal, normally Pd, gates. Ammonia, on the other hand, appears to be detected through surface potential changes of the Pt film, which are capacitively coupled to the semiconductor surface through voids in the thin metal film.
Kinetics of dry oxidation of silicon. II. Conditions affecting the growth
Authors: Wolters D. R. , Zegers-van Duynhoven A. T. A.
Published: July 2002

In part I, the kinetics of dry oxidation of silicon has been investigated and a new model based on the classical oxidation theory including space-charge effects is proposed. In part II, the power-of-time law is shown to fit to the experimental results and the major conditions affecting the growth are investigated. The dependence on crystallographic orientation, the ‘‘crossover’’ effect, the nonlinear oxygen pressure dependence, the enhancing anneal effect, the peculiar growth on 2-D structures, and the silicon surface pretreatment effect are examined. As a practical application the model predicts the location of structural thin spots in the gate oxide of a metal-oxide-silicon capacitor.
Electron acceleration in a relativistic electron plasma wave
Authors: Mora P. , Amiranoff F.
Published: July 2002

The acceleration of electrons in a relativistic electron plasma wave is computed analytically and numerically. The electron acceleration is first computed as an expansion in powers of the electric field amplitude. A relation between the first- and second-order terms is derived, which corresponds to the relativistic Landau damping effect. Energy conservation in the wave frame enables one to obtain the maximum energy gain for a given injection energy. Optimum lengths are similarly calculated.
Linear theory of a field-emitter-array distributed amplifier
Authors: Ganguly A. K. , Phillips P. M. , Gray H. F.
Published: July 2002

A small-signal theory of a field-emission-array distributed amplifier consisting of two microstriplike transmission lines is developed to calculate the premodulation in the input channel and the gain in the output channel. A first-order perturbation analysis is used to treat the beam-wave coupling in this device within the framework of a cold fluid model. The dependence of the linear gain on frequency, beam voltage, beam current, and the circuit parameters is derived to determine the parameter range for operation of the device. It is found that the height of the circuit is restricted to lie between 80 and 120 μm to maintain high electronic gain and low loss arising from the finite conductivity of the metal surfaces. In an output line having a substrate with a relative dielectric constant, εr=4, a net gain of 7 dB/cm is calculated with a beam voltage of 60 V and a beam current of 2.14 A/cm in each wedge of a seven-wedge emitter array. As the beam voltage is increased in the range 60–100 V, the net gain decreases from 7.0 to 3.0 dB/cm, while the frequency for maximum gain increases from 50 to 80 GHz with a corresponding increase in the bandwidth. The small-signal instantaneous bandwidth is in excess of 60%.
A low energy limit to boron channeling in silicon
Authors: Lever R. F. , Brannon K. W.
Published: July 2002

Both experimental profiles and Monte Carlo simulations have shown that a channeling tail is unavoidable in the implantation of boron into silicon at 5 keV, even though high-index channeling does not occur. A model is proposed to explain this disappearance of high-index channeling at low energies, based on simple geometrical considerations of ion deflections predicted by a binary collision potential.
Chemical etching-induced defects in phosphorus-doped silicon
Authors: Yoneta Minoru , Kamiura Yoichi , Hashimoto Fumio
Published: July 2002

We have found with deep-level transient spectroscopy that chemical etching introduced three electron traps, E1(0.11), E2(0.13), and E3(0.15), in the near-surface region of phosphorus-doped crystalline silicon. The results on depth profiles of these traps and carriers suggested the donor character of the traps, but they hardly exhibited the Poole–Frenkel effect. From their correlations with carbon and oxygen, we propose a tentative identification that E1 and E2 traps arise from two kinds of hydrogen-oxygen-carbon complexes and the E3 trap arises from a hydrogen-carbon complex. Hydrogen is assumed to be adsorbed on the silicon surface during chemical etching and diffuse into the interior of the crystal during the subsequent evaporation and sample storage processes to be trapped at two kinds of oxygen-carbon complexes and substitutional carbon to form the traps. The annealing behavior of E2 and E3 traps in the dark were studied in detail. Their densities were increased at temperatures of 70–90 °C and subsequently were decreased at higher temperatures obeying first-order kinetics. The increase in trap densities is interpreted to be due to the further formation of the traps by capturing mobile hydrogen by oxygen-carbon complexes and substitutional carbon. This hydrogen is assumed to be released at temperatures of 70–90 °C by the dissociation of the hydrogen-phosphorus complex that was also formed by in-diffusing hydrogen during the evaporation and sample storage processes. The subsequent decrease in trap densities is attributed to the thermal dissociation of the traps at higher annealing temperatures and the subsequent loss of hydrogen at sinks. The illumination of band-gap light above 230 K annihilated the traps. The annihilation of the traps occurred only outside the depletion region of the Schottky structure. This effect is ascribed to the recombination-enhanced reaction, in which the electronic energy released by the electron-hole recombination at a trap level is converted into local vibrational energy to induce the thermal dissociation of the traps.
Pulsed laser deposition of epitaxial BaFe12O19 thin films
Authors: Carosella C. A. , Chrisey D. B. , Lubitz P. , Horwitz J. S. , Dorsey P. , Seed R. , Vittoria C.
Published: July 2002

Epitaxial thin films of barium hexaferrite (BaFe12O19) have been fabricated by the pulsed laser deposition technique on basal plane sapphire. Structural studies reveal the films to be predominantly single phase and crystalline, with the c axis oriented perpendicular to the film plane. The magnetic parameters deduced from vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are close to the parameters associated with bulk materials. Post annealing of the films reduced the FMR linewidth by more than a factor of 3 so that it compares reasonably well with single-crystal films. The derivative FMR linewidth was measured to be 66 Oe at 58 GHz and 54 Oe at 86 GHz. Spin-wave-like modes have been observed for the first time in barium ferrite films. The deduced exchange stiffness constant of 0.5×10−6 ergs/cm is in reasonable agreement with recent calculations.
Experiments on a current-toggled plasma-opening switch
Authors: Mendel C. W. , Savage M. E. , Zagar D. M. , Simpson W. W. , Grasser T. W. , Quintenz J. P.
Published: July 2002

Plasma-opening switches have been used to improve pulsed-power wave shapes for over a decade. These switches have used the inertia of the plasma to hold the switch closed. This results in conflicting requirements when long hold-off time and fast opening are required, and also results in variation in opening current due to variation in initial plasma fill. The current-toggled plasma-opening switch attempts to overcome these problems by using external magnetic fields rather than inertia to control the plasma conductor. Data will be presented showing several features of the operation of this switch. These data will be compared to models used to design the switch. The comparisons indicate that the mass can be measured approximately from fast coil data and that the slow coil flux does set the opening level of the current. They also indicate that the opening current is somewhat dependent upon plasma mass, and that the design of the field coils that provide the control fields must be done more carefully to provide a switch that opens satisfactorily.
Indium doping of CdTe and Cd1−xZnxTe by molecular-beam epitaxy: Uniformly and planar-doped layers, quantum wells, and superlattices
Authors: Bassani F. , Tatarenko S. , Saminadayar K. , Magnea N. , Cox R. T. , Tardot A. , Grattepain C.
Published: July 2002

CdTe and Cd1−xZnxTe layers and microstructures were doped with indium donors during their growth at low temperatures (200–220 °C) by molecular-beam epitaxy under Cd overpressure. Uniform and planar doping of layers and local doping of quantum wells and superlattices are presented. Characterization techniques include secondary-ion mass spectroscopy (SIMS), capacitance-voltage and Hall-effect measurements, optical spectroscopy, x-ray double diffraction, and x-ray photoelectron spectroscopy. In the range of indium concentrations 2×1016–1×1018 cm−3, the donor activation efficiency is 100% for uniform doping. A low-temperature carrier mobility of up to 5300 cm2/V s is obtained. The highest measured carrier concentration is 1.3×1018 cm−3; at a higher doping level, strong compensation occurs, related to dopant migration and cadmium vacancy formation. Planar doping also yields ≊100% activation efficiency for moderate values of sheet density (≊1011 cm−2) but has the same limit of about 1018 cm−3 for total carrier concentration. High-structural-quality planar-doped quantum wells and superlattices are obtained. Good localization of dopant is demonstrated by SIMS at low sheet density but at high concentration substantial migration of indium occurs.
Least-squares estimates of the nonlinear constants of piezoelectric crystals
Authors: Hruska Carl K.
Published: July 2002

The values of nonlinear constants of piezoelectric crystals are frequently calculated from overdetermined linear systems using the least-squares fit. In such systems, all nonlinear constants, whose values are known from earlier publications, are replaced with these values. The results of the least-squares fit, executed after the substitutions, are interpreted only mechanically, with no regard for the substitutions made. It is shown that this procedure frequently leads to a loss of valuable information and/or to unnoticed distortions and misinterpretations of the estimates of the nonlinear constants and of their standard errors. The reasons for these undesired phenomena and how to avoid them are explained. The calculation process should start with the least-squares fit with the substitutions to be made later, when their effect cannot be misunderstood. In a number of cases, however, the substitutions serve no useful purpose and should be avoided. A practical illustration is made for the nonlinear constants of quartz determined by the resonator method. The ideas and results of this paper apply generally to the determination of any material constants of crystals where the least-squares method is used.
Experimental demonstration of resonant interband tunnel diode with room temperature peak-to-valley current ratio over 100
Authors: Day D. J. , Yang Rui Q. , Lu Jian , Xu J. M.
Published: July 2002

This letter reports a recent experiment on resonant interband tunneling (RIT) diodes and the measured room temperature peak-to-valley (P/V) current ratio of 104:1 which represents the highest P/V ratio ever reported in any tunneling device. The RIT diode studied in this work consists of an InGaAs/InAlAs double-quantum well system embedded in a pn junction structure grown on InP.
Giant ac magnetoresistance in the soft ferromagnet Co70.4Fe4.6Si15B10
Authors: Machado F. L. A. , da Silva B. L. , Rezende S. M. , Martins C. S.
Published: July 2002

ac magnetoresistance (MR) measurements performed in thin ribbons of the amorphous soft ferromagnet Co70.4Fe4.6Si15B10 are reported with a longitudinal dc applied magnetic field H varying from 0 to ±15 Oe. The dependence of the MR with the frequency f of the measuring ac current was investigated for 0.4≤f≤100 kHz. No significant frequency dependence in the resistivity ρ for H=0 and H=±15 Oe was found. For intermediate values of H, ρ(H) presents a peak in H which increases linearly in frequency. The MR peak in H at room temperature varies from typical values of 0.13% in the low-frequency range to a giant value of 27% at 100 kHz. Two possible sources for the frequency dependence of the magnetoresistance in amorphous alloys are discussed.
Preparation of thin-film (Ba0.5,Sr0.5)TiO3 by the laser ablation technique and electrical properties
Authors: Yoon Soon-Gil , Lee Jai-Chan , Safari A.
Published: July 2002

The chemical composition and electrical properties were investigated for epitaxially crystallized (Ba0.5,Sr0.5)TiO3 (BST) films deposited on Pt/MgO and YBa2Cu3O7−x (YBCO)/MgO substrates by the laser ablation technique. Rutherford backscattering spectroscopy analysis shows that thin films on Pt/MgO have almost the same stoichiometric composition as the target material. Films deposited at 600 °C exhibited an excellent epitaxial growth, a dielectric constant of 430, and a dissipation factor of 0.02 at 10 kHz frequency. They have a charge storage density of 40 fC/μm2 at an applied electric field of 0.15 MV/cm. Leakage current density of BST thin films on Pt/MgO was smaller than on YBCO/MgO. Their leakage current density is about 0.8 μA/cm2 at an applied electric field of 0.15 MV/cm.
Suppression of interface-state generation in reoxidized nitrided oxide gate dielectrics
Authors: Krisch K. S. , Sodini C. G.
Published: July 2002

Reoxidized nitrided oxide gate dielectrics are characterized following electrical stress, in order to study the mechanism by which they are able to inhibit interface-state generation, as compared to silicon dioxide. It is found that the energy spectrum of the few interface states which are generated in reoxidized nitrided oxides differs from that of states generated in lightly nitrided oxides or in silicon dioxide. We have also measured interface-state generation as a function of stress time and stress polarity for different dielectrics, and observed two characteristic types of fluence dependencies. Interface states which are generated linearly with fluence are modeled using a simple first-order rate equation, which depends on the density of interface-state precursor sites. A sublinear fluence dependence is successfully modeled by including the effect of interfacial strain relaxation. Based on these results, we argue that the first type of interface-state generation, which follows a linear fluence dependence, is suppressed in electrically-stressed reoxidized nitrided oxides because the interface has fewer defect precursor sites.
Solute trapping of group III, IV, and V elements in silicon by an aperiodic stepwise growth mechanism
Authors: Reitano Riccardo , Smith Patrick M. , Aziz Michael J.
Published: July 2002

With rapid solidification following pulsed laser melting, we have measured the dependence on interface orientation of the amount of solute trapping of several group III, IV, and V elements (As, Ga, Ge, In, Sb, Sn) in Si. The aperiodic stepwise growth model of Goldman and Aziz accurately fits both the velocity and orientation dependence of solute trapping of all of these solutes except Ge. The success of the model implies a ledge structure for the crystal/melt interface and a step-flow mechanism for growth from the melt. In addition, we have observed an empirical inverse correlation between the two free parameters (‘‘diffusive speeds’’) in this model and the equilibrium solute partition coefficient of a system. This correlation may be used to estimate values of these free parameters for other systems in which solute trapping has not or cannot be measured. The possible microscopic origin of such a correlation is discussed.
Sensitivity and transient response of microwave reflection measurements
Authors: Schöfthaler Martin , Brendel Rolf
Published: July 2002

Microwave reflection measurements are widely used for the characterization of minority-carrier lifetimes in semiconductors. A theoretical description of the technique is presented. The approach is based on a dielectric multilayer model that accounts for experimental parameters such as microwave frequency, sample thickness and doping, and the distance to an optional reflector behind the sample. With a new definition of the sensitivity in transient microwave reflection measurements, the most sensitive configuration is investigated for a given semiconductor thickness and conductivity. Good agreement between the theoretical simulation and measurements is demonstrated. The model is also used for calculating microwave reflection transients from the excess carrier decay after pulsed laser excitation. It is found that the reflected microwave power mirrors the carrier decay if three criteria are fulfilled: The carrier generation must be homogeneous; low-injection conditions are required; and the reflector must be positioned appropriately for linear dependence of the microwave reflection on the carrier density.
Photoconductivity evolution due to carrier trapping by defects in 17 MeV-proton irradiated silicon
Authors: Amekura Hiroshi , Kishimoto Naoki , Saito Tetsuya
Published: July 2002

Damage concentration dependence of dark and photoconductivity has been studied in crystalline Si, irradiated with 17 MeV proton. The photoconductivity spectra consist of a broad peak due to a band-to-band transition and a tail spectrum on the lower energy side. Two kinds of tail spectra are observed in impurity-doped and/or damaged specimens, and the latter threshold is deeper than the former. While the main peak of the doped specimen does not greatly change up to a certain irradiation fluence φC, it steeply decreases beyond the φC, which depends on the shallow-impurity concentration. The tail spectrum of the shallow impurity simultaneously vanishes at the φC and another tail spectrum grows above the φC. As compared to fluence dependence of photocurrent decay time, it is clarified that the drastic decrease in the main peak results from a drop in the decay time or the carrier density, not in the carrier mobility. The defect density for the critical fluence φC has good correlation with the dopant concentration. It is concluded from these results that a competitive process between shallow impurities and deep defects dominates the optical transition and transport, and that the critical fluence φC corresponds to the damage concentration required to capture all the doped carriers. Mechanisms for the photoconductivity evolution and defect trapping efficiency are discussed as is a comparison with electron-induced damage.