bluuebunny/crossref_metadata_2025 huggingface dataset:
The pure rotational spectrum of CaNH2 and CaND2 (X̃ 2A1): Additional proof of planarity
Authors: Brewster M. A. , Ziurys L. M.
Published: July 2002

The pure rotational spectrum of CaNH2 in its X̃ 2A1 ground electronic state has been recorded using millimeter/submillimeter direct absorption methods in the frequency range 320–537 GHz as well as that of CaND2. The species were created by Broida-oven techniques. Eleven rotational transitions were observed arising from the v=0 and v6=1 states of CaNH2, and eight transitions were recorded for the v3=1 and v4=1 levels. For CaND2, eight transitions (v=0) were also measured. For the majority of these transitions, Ka doublets corresponding to Ka=0–5 were observed and fine structure splittings were resolved in every component. These spectra were analyzed using an S-reduced Hamiltonian; rotational, centrifugal distortion, and spin–rotation parameters were determined for CaNH2, CaND2, and the three observed vibrationally excited states. An r0 structure has also been calculated. The data are consistent with calcium amide being a planar molecule with C2v symmetry and having predominately ionic bonding, as indicated by previous optical studies.
A note on the intermediate region in turbulent boundary layers
Authors: Barenblatt G. I. , Chorin A. J. , Prostokishin V. M.
Published: July 2002

We demonstrate that the processing of the experimental data for the average velocity profiles obtained by J. M. Österlund presented in Phys. Fluids 12, 1–4 (2000) was incorrect. Properly processed these data lead to the opposite conclusion: They confirm the Reynolds-number-dependent scaling law and disprove the conclusion that the flow in the intermediate (“overlap”) region is Reynolds-number-independent.
Effects of hydrogen on the growth of nanocrystalline silicon films by electron-beam excited plasma chemical vapor deposition
Authors: Imaizumi Mitsuru , Yamaguchi Koji , Okitsu Kazuhiko , Yamaguchi Masafumi , Hara Tamio , Ito Tadashi , Konomi Ichiro , Jones Kim M. , Al-Jassim Mowafak M.
Published: July 2002

It has been shown that nanocrystalline silicon films can be grown from silane gas without hydrogen dilution by electron-beam excited plasma chemical vapor deposition (EBEP–CVD). A high density of atomic hydrogen, which is derived from the dissociation of silane molecule, is confirmed in the plasma by optical emission spectroscopy. This fact is thought to be a reason for the growth of nanocrystalline silicon films without the introduction of hydrogen gas. Transmission electron spectroscopy reveals that crystallites are not distributed uniformly, but rather form the mosaic-like clusters in an amorphous silicon matrix in the film. Hydrogen gas is introduced into the EBEP–CVD silicon film growth so as to study the effects of the hydrogen gas. The growth rate increases proportionally to the hydrogen flow rate, and it is about 2.5 times greater than when no hydrogen gas is introduced. Also, a decrease in both the hydrogen content and the density of dangling bonds in the film is confirmed. These results imply that the generation of dangling bonds is suppressed by the introduction of hydrogen. The rate constants of dissociation reaction of silane molecules in the EBEP are estimated, and the change in density of radicals in the plasma by introducing hydrogen gas is calculated. A growth model is proposed that assumes the sticking coefficient of SiH3 precursor radical increases in proportion to atomic hydrogen flux. Using the calculation results and the model, the effects are explained to be due to an increase in the contribution ratio of SiH3 radicals to the growth, on account of the increase in the introduced hydrogen gas flow rate.
Particle generation and thin film surface morphology in the tetraethylorthosilicate/oxygen plasma enhanced chemical vapor deposition process
Authors: Fujimoto Toshiyuki , Okuyama Kikuo , Shimada Manabu , Fujishige Yousuke , Adachi Motoaki , Matsui Isao
Published: July 2002

Particle generation by gas-phase nucleation in the plasma enhanced chemical vapor deposition process and its effects on thin film surface morphology were studied experimentally for a conventional radio frequency plasma reactor using tetraethylorthosilicate (TEOS) vapor and oxygen gases. The particles suspended in the plasma space and deposited on the film were observed simultaneously by in situ laser light scattering methods and an ex situ scanning electron microscopic method. The generated particles were trapped in the plasma/sheath boundary under all four experimental conditions, in which TEOS concentrations were 0.5 and 5.0 vol % and reactor pressures were 66.7 and 533.3 Pa (0.5 and 4.0 Torr). The size and amount of particles and the film morphology were found to depend on the TEOS concentration and the reactor pressure. Under the conditions in which highly concentrated particles were generated in plasma, dome-like structures of 50–400 nm in diameter were observed on the thin film surface. The average size of the dome-like structure was comparable to that of the particles generated in plasma.
The melting of Ar54–HF: A canonical parallel tempering simulation
Authors: Ghayal Madhavi Rajan , Curotto E.
Published: July 2002

A classical canonical Monte Carlo computation for Ar54–HF between 1 and 50 K is performed. The results demonstrate that the Ar–HF exchange is significantly different in Ar54–HF compared to what has been found for Ar12–HF. The HF molecule in Ar54–HF does not leave the center of the cluster prior to the melting onset within the walk length used here. Additionally, the melting of the cluster is affected significantly by the presence of the chromophore.
Indecomposable representations of the nonlinear Lie algebras
Authors: Ruan Dong , Chen Linhong , Ruan Wei
Published: July 2002

On the two-state Heisenberg–Weyl basis, the indecomposable representations of the nonlinear Lie algebras of vector type, Rνλ (ν,λ=0,±1), one of which is generated by two angular momentum operators J0, J2 and any component of an irreducible tensor operator of rank 1, T(1νλ) (ν,λ=0,±1), of an SO(3) group, are studied in detail. We give the explicit expressions for the infinite-dimensional indecomposable representations of Rνλ, which further subduce the infinite-dimensional indecomposable representations on the invariant subspaces and induce the finite-dimensional or infinite-dimensional (indecomposable, irreducible) representations on the quotient spaces. As special cases, the standard angular momentum representations of Rνλ are given also.
Experimental study of amplitude–frequency characteristics of high-transition-temperature radio frequency superconducting quantum interference devices
Authors: Zeng X. H. , Zhang Y. , Chesca B. , Barthel K. , Greenberg Ya. S. , Braginski A. I.
Published: July 2002

We measured the amplitude–frequency characteristics of radio frequency superconducting quantum interference devices (rf SQUIDs) over a temperature range between 65 and 79 K. Using the expressions derived from the recently developed rf SQUID theory, valid also at large thermal fluctuations, we determined from these data the basic parameters of high-transition-temperature superconductor (HTS) rf SQUIDs. These parameters were: (a) the high-frequency coupling coefficient between the rf SQUID and the tank circuit resonator, k, (b) the SQUIDs hysteretic parameter, β, (c) the critical current of the Josephson junction, Ic, (d) its normal resistance, Rn, and (e) its noise parameter, Γ. We found a good agreement with the values of β(Ic) and Rn determined directly after destructively opening the SQUID loop. In accordance with the theoretical predictions, our experimental results show that at large thermal fluctuation levels (T≅77 K), rf SQUIDs with large loop inductance operate in nonhysteretic mode up to β values exceeding 3. Furthermore, we have shown that the optimal energy sensitivity is attained in the nonhysteretic mode at a value of β distinctly higher than 1. A quantitative comparison of white noise predicted by the theory with that obtained from the experiment showed a reasonable agreement. We also discussed the contribution of the phase information to the SQUID’s signal and noise at optimum operation conditions, when a mixer was used as a signal detector.
Validating a polarizable model for the glass-forming liquid Ca0.4K0.6(NO3)1.4 by ab initio calculations
Authors: Ribeiro Mauro C. C. , Almeida Luiz C. J.
Published: July 2002

Ab initio calculations have been performed in order to investigate a recently proposed polarizable model [M. C. C. Ribeiro, Phys. Rev. B 61, 3297 (2000)] for molecular dynamics (MD) simulation of the molten salt Ca0.4K0.6(NO3)1.4. On the basis of the electronegativity equalization method, polarization effects in the MD simulations have been introduced by a fluctuating charge (FC) model for the nitrate ion. Partial charges in the nitrate ion are obtained by ab initio calculations at several levels of theory, and compared with previously proposed models for MD simulations of nitrate melts. Charge fluctuation is achieved in the ab initio calculations by using positive probe charges placed around a nitrate ion. The parameters of the FC model are corroborated by comparison of the ab initio partial charges with the ones obtained directly by the electronegativity equalization method. Simulated annealing of a cluster including two double-charged cations and two nitrate ions shows that very different structures are obtained depending on whether the FC model or its nonpolarizable counterpart is considered. Ab initio calculations show that the structure of this cluster is strongly dependent on polarization effects in the nitrate ions.
Infrared imaging video bolometer
Authors: Peterson B. J.
Published: July 2002

A new concept for an infrared imaging bolometer is proposed which provides full video (two-dimensional) imaging of the radiated power from the plasma. This concept preserves all the advantages (compared to conventional metal foil resistive bolometers) of the previously proposed and tested segmented mask infrared imaging bolometer (SIB). It avoids the problems associated with the copper mask of the SIB, while giving a full frame video image of the plasma radiation with improved experimental flexibility regarding the pixel size. Analysis of the noise equivalent power shows that compared to a SIB with the same pixel area, the infrared imaging video bolometer is 2–5 times more sensitive with improved spatial resolution. These benefits are gained at the expense of the mechanical support, which the mask provides for the foil in the SIB. A numerical algorithm is used to solve the two-dimensional heat diffusion equation for the foil and determine the time-dependent spatial distribution of incident power on the foil from the infrared (IR) video camera measurements of the foil temperature. Testing the algorithm using a Gaussian model of the incident power shows that it can accurately reproduce the Gaussian model to within 6%. A simple scheme to absolutely calibrate the entire foil is described and several design points are detailed pointing out the range and experimental flexibility of the diagnostic using currently available IR camera technology.
Influence of electrons reflected from a target on the operation of triode-type electron sources
Authors: Engelko V. , Kuznetsov V. , Viazmenova G. , Mueller G. , Bluhm H.
Published: July 2002

An external magnetic field between the electron source and a target causes the reflected electrons to move along the magnetic force lines towards the source region. There they get reflected back to the target by the electric field of the source. These electrons distort the electric field in the source region, and change the source’s operational parameters. Penetration of reflected electrons back into the source region reduces essentially the space charge limited emission current density of a cathode and the minimum current density to form a potential minimum and a virtual cathode. How much the emission current density decreases depends on the target material’s atomic number, Z, which determines the reflection coefficient and the energy spectrum of the reflected electrons. The calculations are in good agreement with experimental data. The analysis shows that reflected electrons must be considered for a correct calculation of the beam parameters at the target for the distribution of the energy density deposited into the target, and for a better understanding of the electron source operation.
Multimegawatt solid state rf driver for generating rotating magnetic fields
Authors: Slough J. T. , Miller K. E. , Lotz D. E. , Kostora M. R.
Published: July 2002

A radio frequency (rf) system using solid state switching has been designed and constructed that is capable of driving a pair of loop antenna with a circulating power of 60 MW for millisecond pulses. The primary application of this system is to produce an oscillating magnetic field in the frequency range of 0.2–0.7 MHz, to generate and sustain a large plasma current. The maximum power transfer from the rf source was measured to be greater than 10 MW. The driver consisted of 12 insulated gate bipolar transistor modules driven in parallel, and was capable of switching 20 kA at 1700 V. A sinusoidal current waveform with large circulating currents was obtained on the antenna by incorporating the antenna in a high Q (60), parallel LCR resonant circuit. The low impedance switch driver was matched to the antenna load through a 20:1 step-up air core transformer with a coupling efficiency of 99%.
Size control of erbium-doped silicon nanocrystals
Authors: John John St. , Coffer Jeffery L. , Chen Yandong , Pinizzotto Russell F.
Published: July 2002

This work describes the effects of pyrolysis oven length and erbium precursor on the preparation of discrete erbium-doped silicon nanoparticles. These doped nanoparticles were prepared by the co-pyrolysis of disilane and the volatile complex Er(tmhd)3 (tmhd=2,2,6,6-tetramethyl-3,5-heptanedionato). The particle sizes and size distributions were determined using high resolution and conventional transmission electron microscopy. Erbium-doped silicon nanoparticles exhibit a selected area electron diffraction pattern consistent with the diamond cubic phase and a distinctive dark contrast in the transmission electron microscope. The presence of erbium is confirmed by x-ray energy dispersive spectroscopy. In general, the mean diameter of the individual nanoparticles increases as the length of the pyrolysis oven used during their preparation is increased.
Different types of chaos in an optically injected semiconductor laser
Authors: Krauskopf Bernd , Wieczorek Sebastian , Lenstra Daan
Published: July 2002

With advanced tools from bifurcation theory routes to chaos via period doubling and the break-up of tori are identified. This allows us to distinguish between different types of chaos in terms of the output characteristics of the laser. We also find locking to a periodic solution inside a region of chaos. This information is important for applications requiring chaotic signals, such as encryption schemes.
Phonon mediated lifetimes in intersubband terahertz lasers
Authors: Menon Vinod M. , Goodhue W. D. , Karakashian A. S. , Ram-Mohan L. R.
Published: July 2002

We present a detailed study of the electron-LO phonon interaction in a triple quantum well structure, which acts as the active region in an intersubband terahertz emitter. The phonon modes of the heterostructure were calculated using a transfer matrix method within the framework of the dielectric continuum model. Unlike earlier calculations that approximate phonon emission rates using bulk-like phonon modes, we exploit the presence of specific interface and layer-confined phonon modes. The electronic levels are designed to be in resonance with one of the phonon modes for optimizing phonon-scattering rates and to enhance device performance. Our calculations indicate that it is beneficial to utilize the higher energy interface phonon modes rather than the confined phonon modes for faster depopulation in a three level lasing scheme. Scattering rates for two different designs were computed to establish the above result.
In situ conductivity study of the phase transition in Sb-doped C60
Authors: Li Xiang , Tang Y. J. , Zhao H. W. , Zhan W. S. , Wang Haiqian , Hou J. G.
Published: July 2002

C 60 /Sb bilayers were prepared on the substrate of mica, and their electrical properties were investigated by in situ dc conductivity measurements. The results indicate that the Sb doping in C60 significantly affects the critical temperature (Tc) for the orientational order–disorder transition of C60. The Tc of Sb-doped C60 increases to about 278 K, ∼18 K higher than that of the pristine C60. This transition is sensitive to Sb content and disappears upon annealing. A possible mechanism of such a phase transition is discussed.
Stable stratification alteration in a thermal diffusion cloud chamber
Authors: Schaeffer N. , Utheza F. , Garnier F. , Lauriat G.
Published: July 2002

The formation of clouds resulting from the homogeneous condensation of vapor phase diluted in a background or carrier gas was studied numerically. The effect of the background gas on the nucleation process in a cloud chamber heated from below is discussed. The computations were performed using 1-propanol as the condensable gas and helium, hydrogen, nitrogen, and argon, respectively, as carrier gases. Results of the simulation conducted show that large differences appear in the cloud formation when operating with hydrogen or helium, and with argon or nitrogen for which the onset of convective motions are predicted. Therefore, the isothermal patterns and streamlines are similar to those obtained in the case of Rayleigh–Bénard instabilities. The influence of the thermal Rayleigh number on the nucleation process is also considered, and it is shown that supersaturation isolines exhibit complex distortions for supercritical thermal Rayleigh numbers. As a consequence, only small zones of important nucleation rate are observed.
Low leakage current characteristics of YMnO3 on Si(111) using an ultrathin buffer layer of silicon oxynitride
Authors: Rokuta E. , Hotta Y. , Tabata H. , Kobayashi H. , Kawai T.
Published: July 2002

We have grown YMnO3 (YMO) thin films on Si(111) using silicon oxynitride (SiON) as a buffer layer. Thickness of SiON buffer layer was well controlled within 2 nm. High resistance of ultrathin SiON layer (dSiON∼0.7 nm) to Si oxidation was confirmed by x-ray photoelectron spectroscopy (XPS). Using the ultrathin SiON layer, we obtained c-axis oriented ferroelectric phase of YMO. Although capacitance–voltage curves of Al/YMO/SiON/Si(111) showed hystereses attributed to ferroelectricity of the YMO films, the memory window was not sufficient (0.2 V), seemingly due to poor crystallinity of the YMO films. On the other hand, leakage current characteristic was good enough for application. The typical value of leakage current density was 10−8 A/cm2 at a drive voltage of ±5 V. In this article, the details of the characterization elucidated by using x-ray diffraction, atomic force microscopy, and XPS will be shown as well.
Ion-implantation-induced densification in silica-based glass for fabrication of optical fiber gratings
Authors: Fujimaki Makoto , Nishihara Yoshitaka , Ohki Yoshimichi , Brebner John L. , Roorda Sjoerd
Published: July 2002

Ion implantation induces a refractive index increase in silica-based glass, which is mainly due to densification of the glass. The refractive index increase can be used to fabricate optical fiber gratings that are formed with periodic refractive index modulation in the core of an optical fiber. In this article, the generation mechanism of the densification has been investigated through measurements of thickness changes of silica glass induced by proton and He2+ ion implantation. Furthermore, fabrication of the optical fiber grating using the refractive index increase has been demonstrated. From the result, ideal implantation conditions to fabricate the gratings are discussed.
Colossal magnetoresistance in La0.7Ba0.3MnO3 thin films prepared by spray pyrolysis
Authors: Studenikin S. A. , Golego Nickolay , Cocivera Michael
Published: July 2002

Barium–lanthanum–manganite (La0.7Ba0.3MnO3) thin films that exhibit a colossal magnetoresistance (CMR) effect have been prepared by spray pyrolysis of solutions of aqueous nitrates. Structural, optical, and magnetotransport properties of the films were studied as a function of growth conditions and postgrowth treatments. In a magnetic field of 600 mT, the maximum CMR effect amounted to a 15% decrease in resistivity relative to zero field value. Instead of decreasing at lower temperature, the value of the CMR continued to increase as the temperature decreased to 100 K. This behavior is attractive for practical applications.
Excluded volume effects on the diffusion-influenced reaction: The many-particle kernel approach
Authors: Lee Juhyeok , Sung Jaeyoung , Lee Sangyoub
Published: July 2002

In most theories of diffusion-influenced reactions, the reaction system is assumed to consist of a central reactant molecule surrounded by the other reactant molecules that pass each other freely. That is, excluded volumes among the like reactant molecules are neglected. We use the many-particle kernel formalism to investigate the effect of excluded volumes on the diffusion-influenced reaction. We obtain approximate analytic expressions for the many-particle kernel and the time profile of the survival probability of reactant molecules. The result is shown to be in good agreement with the Brownian dynamics simulation.
Simulations of C28 chemisorption on diamond (001)-(2×1) surface: The comparison between cluster–cluster interaction and cluster–surface interaction
Authors: Zhu W. J. , Pan Z. Y. , Ho Y. K. , Wang Y. X.
Published: July 2002

In this article, the dynamic behavior of C28 chemisorption on diamond (001)-(2×1) surface was investigated by molecular dynamics simulation. The many-body Brenner potential was employed to describe the interaction between carbon atoms. With the incident energy ranging from 25 to 40 eV, the single C28 was found to have more than 50% of the probability to be chemisorbed on a diamond surface and to form two C–C bonds with one dimer of the surface. Then the chemisorption of two C28 clusters was simulated at the above energy range. The cluster–cluster interaction was found to hinder the next incident cluster to be chemisorbed. Besides, the juxtaposition configuration of two C28 on the surface was observed when their impact points were along the same dimer row. For multicluster impacting, when two or three clusters formed a nucleation site, the forthcoming cluster was easily to be adsorbed close to it. The growth of the C28 cluster assembled film is typically a three dimensional island mode. Our study also showed that within the energy range the C28 clusters retained their cage structure after chemisorption. This is in agreement with experimental results.
Delayed melting at the substrate interface of amorphous Ge films partially melted with nanosecond laser pulses
Authors: Vega F. , Solis J. , Siegel J. , Afonso C. N.
Published: July 2002

The dynamics of melting-rapid solidification of amorphous Ge films on transparent substrates upon irradiation with nanosecond laser pulses has been analyzed by means of real time reflectivity measurements performed both at the air-film and film-substrate interfaces. The effect of the heat flow conditions on the rapid solidification process has been studied by comparing the behavior of films with thicknesses ranging from 50 to 180 nm on substrates with different thermal conductivities like glass, quartz, and sapphire. The films deposited onto substrates of low thermal conductivity (glass and quartz) undergo a local delayed melting process in the vicinity of the film-substrate interface, the process being dependent on the film thickness and/or the laser fluence. This delayed melting process is never observed in films deposited on sapphire. The comparison of the results suggests that the solidification heat released from the primary melt is responsible for the delayed melting process at the film-substrate interface whenever the heat-transfer ratio to the substrate is low enough.
Comment on “An ab initio cluster study of the structure of the Si(001) surface” [J. Chem. Phys. 112, 2994 (2000)]
Authors: Hess J. S. , Doren D. J.
Published: July 2002

This recent paper uses multiconfiguration self-consistent field (MCSCF) wave functions to study the structure of Si(001). The results are at odds with density functional theory predictions and experiment. This comment shows that dynamic correlation, which is neglected in MCSCF calculations, is essential for reliable predictions of the geometry of Si(001). © 2000 American Institute of Physics.
Morphology of interfacial reaction between lead-free solders and electroless Ni–P under bump metallization
Authors: Jang J. W. , Frear D. R. , Lee T. Y. , Tu K. N.
Published: July 2002

The morphology of interfacial reaction products between four lead-free solder alloys on electroless Ni–P was characterized. The four Pb-free solders were 99.3Sn0.7Cu, 95.5Sn3.8Ag0.7Cu, 96.5Sn3.5Ag, and 96Sn2Ag2Bi (in wt%) alloys. After reflow, the interfacial intermetallics in the first two solders that contain Cu (99.3Sn0.7Cu and 95.5Sn3.8Ag0.7Cu) had good adhesion with electroless Ni–P. However, the 96.5Sn3.5Ag and 96Sn2Ag2Bi alloys formed interfacial intermetallics with a needle shaped morphology that spalled off the surface of electroless Ni–P. This difference is attributed to the role of Cu in the solders (which modified the chemical potential of the interfacial intermetallics), the volume change that occurs during intermetallic formation, and the interfacial properties of the compound. In solid state aging experiments, the consumption of electroless Ni–P by intermetallic growth was not significant (approximately 1 μm) and all the intermetallics had good adhesion to the electroless Ni–P. The electroless Ni–P exhibited some damage at the outer edge of the bond pad due to stress imposed during solid state aging. Large Ag3Sn and Cu6Sn5 intermetallics were observed in the bulk of the solders (except for SnAgBi solder), and these intermetallics are discussed in terms of soldering reaction at the interface and phase equilibrium.
On contrast parameters and topographic artifacts in near-field infrared microscopy
Authors: Palanker D. V. , Simanovskii D. M. , Huie P. , Smith T. I.
Published: July 2002

Near-field microscopy overcomes the diffraction limit through the partial conversion of the evanescent fields, formed around the subwavelength sources of light, into propagating waves by interactions between the probe and the sample. Contrast parameters in this imaging technique are quite different from those in conventional (far-field) optics. We study the mechanisms of image formation in the transmission mode of a near-field microscope in the mid-infrared part of the spectrum (6–10 μm). The amount of light propagating from a subwavelength aperture through a flat substrate (“allowed” light) is found to strongly increase as the tip approaches the sample, generating topographic artifacts in near-field images. Such artifacts can be eliminated by flat sample preparation techniques. The transmitted power is strongly influenced by the refraction index of the sample resulting in a substantial difference of the near-field spectrum from the far-field one. A model describing tunneling of light through a subwavelength aperture into the substrate has been developed and is in very good agreement with the experimental data. The model predicts that spectral sensitivity is enhanced with smaller tip diameters.
Comparison of Raman-scattering and Shubnikov–de Haas measurements to determine charge density in doped semiconductors
Authors: Cuscó R. , Artús L. , Ibáñez J. , Blanco N. , González-Dı́az G. , Rahman M. , Long A. R.
Published: July 2002

We have verified the accuracy of free-charge determinations from Raman scattering in doped semiconductors by comparing the results obtained from phonon–plasmon coupled-mode line-shape fits with the charge-density values extracted from the analysis of the Shubnikov–de Haas oscillations. The experiments were carried out on n-InP layers, and conduction band nonparabolicity was included both in the Lindhard–Mermin model used to fit the Raman spectra and in the Shubnikov–de Haas analysis. We find a very good agreement between Raman and magnetotransport results, which confirms the reliability of the charge-density determination from Raman-scattering measurements when the line-shape analysis is carried out using the Lindhard–Mermin model.
Positive charge instability during bidirectional stress on metal–oxide–silicon capacitors
Authors: Ziane Dj. , El-Hdiy A.
Published: July 2002

Bidirectional electron injections are made on metal–oxide–silicon capacitors under constant currents or constant voltages. It is shown that both stresses reveal the same generation mechanism of oxide defects and consequently confirm that the gate/oxide interface is more stress resistant than the oxide/silicon interface. It is also shown that the created positive charge is unstable during bidirectional stress. We characterize this instability by studying dielectric defect neutralization following a new procedure. Oxide field intensity and polarity are considered as the principal precursors of this instability. Without any applied field, the neutralization follows a logarithmic law; while under a nonstressing field it follows an exponential law. Both kinetic laws are linked, since the logarithmic law describes the saturation value of the exponential one, and hence both describe the same process. Results of both current and voltage stresses give a power law between the oxide field near the cathode during stress and the capture cross section measured from neutralization kinetics.
Localized surface plasmons on nanometric gold particles observed with an apertureless scanning near-field optical microscope
Authors: Adam P.-M. , Benrezzak S. , Bijeon J. L. , Royer P.
Published: July 2002

Using an apertureless scanning near-field optical microscope, we obtained wavelength dependent images of an isolated gold nanometric particle laid on a quartz substrate. The images show a sharp resonance around λ=488 nm. The far-field surface plasmon resonance of the spherical particles (diameter is 40 nm) in solution is centered at λ=530 nm. Atomic force microscope images give evidence that the particles spread on the substrate. The near-field blueshift of the resonance is thus explained by excitation of a surface plasmon resonance along the minor axis of an oblate spheroid shaped particle.
The effect of optical prepulse on direct-drive inertial confinement fusion target performance
Authors: Boehly T. R. , Fisher Y. , Meyerhofer D. D. , Seka W. , Soures J. M. , Bradley D. K.
Published: July 2002

The effect of optical prepulses on the performance of imploding inertial confinement fusion (ICF) targets has been measured. The neutron yields from nearly identical spherical targets imploded by the OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] laser were measured as a function of prepulse fluences in the drive laser. These experiments indicate that the cumulative prepulse fluence on target must be less than ∼0.2 J/cm2, which corresponds to a prepulse intensity contrast of ⩾107. This effect is the result of damage to the Al barrier layer used on OMEGA ICF targets. To verify this, the effect of low-intensity irradiation on these Al layers was observed on planar targets using the time-resolved reflectivity and the time-integrated transmission measurements. These experiments show that damage to the Al layers begins at ∼0.1 J/cm2, consistent with the implosion performance results.
Disorder effects in reduced dimension: Indium–phosphide-based resonant tunneling diodes
Authors: Weaver B. D. , Jackson E. M. , Summers G. P. , Seabaugh A. C.
Published: July 2002

Disorder alters the current–voltage characteristics of low-dimensional devices such as resonant tunneling diodes (RTDs) differently than conventional electronic devices, because of the increasing importance of quantum effects. There are now enough experimental data, including new measurements presented here, for the basis of a detailed model of radiation effects in RTDs to be developed. A model is presented in which the reduced dimensionality in the density of states of RTDs renders scattering of charge carriers from atomic defects highly effective in removing the carriers from resonance.
Indium enrichment in Ga1−xInxP self-assembled quantum dots
Authors: Johansson Jonas , Zwiller Valery , Thelander Claes , Gustafsson Anders , Seifert Werner , Samuelson Lars , Svensson Chatrin , Malm Jan-Olle , Falk Lena
Published: July 2002

Quantum dots of Ga1−xInxP on GaP (001) have been grown by low-pressure metalorganic vapor phase epitaxy at 650 °C with varying (Ga,In)P coverages. The quantum dots were extensively characterized by transmission electron microscopy (TEM), atomic force microscopy, energy dispersive x-ray spectroscopy, and temperature-dependent photoluminescence spectroscopy (PL). With increasing coverage the dots develop first as flat, extended hills with more or less pronounced {113} facets. Subsequently, on top of these hills, smaller, well-faceted, In-rich dots are formed. The PL intensity emitted from these dots is first constant and then increases with increasing temperature towards a maximum at about 200 K before it decreases. We present a model which explains the experiments, assuming In-rich dots surrounded by Ga-rich barriers. No evidence of alloy ordering was found in the TEM measurements.
Whistler turbulence at the magnetopause: A nonlinear generation mechanism
Authors: Cai C. L. , Cao J. B. , Zhou G. C. , Wang D. J.
Published: July 2002

The plasma maser effect in the existence of enhanced kinetic Alfvén wave turbulence is investigated as the generation mechanism of the whistler turbulence at the magnetopause. The numerical results of the growth rate show that on the scale of neither the ion inertial length nor the electron inertial length, the whistler waves can be excited, and the peak of the maximum growth rate occurs on the scale of the effective ion Larmor radius. The kinetic Alfvén wave dynamics associated with the scale length of the effective ion Larmor radius is intrinsically important in the magnetic reconnection and leads to the generation of whistler turbulence. The theoretical model of the generation of whistler turbulence is useful for explaining the observations of intense electromagnetic fluctuations at the magnetopause.
Nonlinear effects of physisorption on static friction
Authors: Gao G. T. , Zeng X. C. , Diestler D. J.
Published: July 2002

The effects of a physisorbed film on the force of static friction in a model contact (monatomic adsorbate confined between plane-parallel walls) were investigated by Monte Carlo simulation. At fixed coverage the friction curve (shear yield stress vs normal stress) exhibits a marked nonlinearity, which results from a competition between adsorbate–wall interactions that predominate at low loads and wall–wall interactions that set in beyond a threshold load, which increases with coverage. Previous proximal-probe and computer experiments, carried out at high coverages, see only the initial (low-load) linear portion of the friction curve.
Metal–insulator transition temperature dependence on lead and oxygen content in La1−xPbxMnO3±y thin films
Authors: Yamada Y. , Kusumori T. , Muto H.
Published: July 2002

Preparation of the manganese oxide films with high Curie temperature (TC) above room temperature (RT) is essential for developing multilayered devices that work at RT. We have fabricated La1−xPbxMnO3±y (LPMO) thin films on LaAlO3–Sr2AlTaO6 (001) single-crystal substrates using a pulsed-laser ablation deposition method. Their metal–insulator transition temperature (TRmax), which nearly equals TC, is investigated as a function of the lead (Pb) and oxygen contents contained. The results in the following were obtained. X-ray diffraction indicates growth of epitaxial films with (001) orientation. Samples with high TRmax∼370 K can be prepared in deposition conditions with a substrate temperature (TS) of 600 °C and an oxygen pressure (PO) not less than 0.4 Torr. The TRmax decreases with increasing TS or decreasing PO. The former decrease in the TRmax is shown by electron-probe microanalysis to be ascribed to evaporation of Pb from the films at high TS. On the other hand, it is inferred that the latter decrease is due to a reduction in oxygen content in the films. The reduction of Pb and oxygen contents in the LPMO films, respectively, leads to a decrease in the number of conduction electrons and, consequently, results in a TRmax decrease of the films.
Top-interface-controlled fatigue of epitaxial Pb(Zr0.52Ti0.48)O3 ferroelectric thin films on La0.7Sr0.3MnO3 electrodes
Authors: Wu Wenbin , Wong K. H. , Choy C. L. , Zhang Y. H.
Published: July 2002

Epitaxial Pb(Zr0.52Ti0.48)O3/La0.7Sr0.3MnO3(PZT/LSMO) and LSMO/PZT/LSMO heterostructures have been grown on LaAlO3(001) substrates by pulsed-laser deposition. Three types of ferroelectric capacitors, i.e., Pt/PZT/LSMO (A), LSMO/PZT/LSMO (B), and Pt/PZT/LSMO (C) have been fabricated, where the Pt electrode was sputter deposited onto as-grown (capacitor A) and in situ annealed (capacitor C) PZT/LSMO films, respectively. It is found that the LSMO/PZT/LSMO capacitor shows a low coercive field and good fatigue endurance up to 1010 switching cycles. Similar properties are also obtained for capacitor A. However, the capacitor C, with the PZT film in situ annealed at reduced oxygen pressures, exhibits higher switching voltages and starts to fatigue rapidly at about 106 bipolar switching cycles. Lead deficiency at the surface of the annealed PZT films has been observed. Our results demonstrate that the fatigue performance of PZT/LSMO films, although affected greatly by the electrode configurations, is intrinsically determined by the interface property at the top electrode.
Theory of beat wave excitation in an inhomogeneous plasma
Authors: Ryutov A. D. , Cowley S. C. , Valeo E. J.
Published: July 2002

The theory of beat wave excitation in a slightly inhomogeneous plasma is presented. While the theory is general it applies directly to the experiments performed in Alaska by the ionospheric heating facilities HIPAS [High Power Auroral Simulation, Radio Sci. 25, 1269 (1990)] and HAARP [High Frequency Active Auroral Research Project, Geophys. Res. Lett. 25, 257 (1998)]. A ray tracing (WKB) formalism appropriate for computations is developed. The computational implementation of this formalism and extensive results will be presented in a follow up to this paper. Also the beat wave excitation of upper-hybrid waves is investigated analytically. The complicated trajectories of these waves in the plasma are described. When this beat wave reaches the plasma wave resonance it can, in the HIPAS–HAARP experiments, attain nonlinear amplitude. The electrostatic upper-hybrid waves are trapped around the density maximum of the ionosphere. This trapping is investigated in detail. Beat wave pumping of the trapped modes is possible using HAARP and HIPAS or with split beams from HAARP.
Numerical study of nonlinear forced magnetic reconnection
Authors: Browning P. K. , Kawaguchi J. , Kusano K. , Vekstein G. E.
Published: July 2002

Two-dimensional numerical simulations are used to investigate nonlinear aspects of forced magnetic reconnection in a zero β highly conducting plasma. This is representative of the solar corona, where reconnection may be induced by external perturbations, e.g., at the photospheric boundary of the corona. The aim is to investigate the energy dissipation by the reconnection, which may provide a mechanism for heating the coronal plasma. The field is taken to be initially a sheared force-free equilibrium in a slab, and the effects of applying a slow deformation to the boundaries are investigated. Previous analytical studies assuming small departures from the initial equilibrium have found that a current sheet forms during an initial ideal phase of evolution, which subsequently relaxes to a reconnected equilibrium, releasing some magnetic energy. The linear theory predicts that the energy release has a singularity when the field is marginally stable to the tearing mode. The nonlinear evolution of the field is calculated numerically, focusing on the energy release. In particular, the strongly nonlinear behavior is studied in the parameter regime in which the linear theory breaks down. It is found that nonlinearities become strong close to the marginal stability point, and for such highly sheared fields, the energy released by reconnection is large even for weak boundary deformations.
Nonlinear waves in dense dusty plasmas with high fugacity
Authors: Rao N. N. , Shukla P. K.
Published: July 2002

Nonlinear propagation of small, but finite, amplitude electrostatic dust waves has been investigated in the low as well as high fugacity regimes by deriving the corresponding Boussinesq equation which, for unidirectional propagation, reduces to the Korteweg–de Vries equation. The dust-acoustic wave (DAW) solitons are shown to correspond to the tenuous (low fugacity) dusty plasmas, while in the dense (high fugacity) regime the solitons are associated with the dust-Coulomb waves (DCWs). Unlike the DAW solitons which are (dust) density compressional and supersonic, the DCW solitons are (dust) density rarefactive and propagate with super-Coulombic speeds.
Ferromagnetic and freezing transitions in charged fermions: Metallic hydrogen
Authors: Ichimaru Setsuo
Published: July 2002

Free energies of metallic hydrogen consisting of itinerant electrons and protons in the fluid and the Wigner-crystalline phases are evaluated as functions of density and temperature at various degrees of proton-spin polarization, in a Born–Oppenheimer approximation stemming from substantial mass difference between the two constituents. Those equations of state applicable in quantum and classical regimes are then utilized for the construction of phase diagrams, describing solidification and spin magnetization for proton fluids. Nuclear ferromagnetism due to partial spin-alignment of protons is predicted in an extended parametric domain, including the vicinity of metal-insulator phase boundaries. A contact is made between the magnetic phase diagram so obtained and observed data on the surface magnetic fields and temperatures of magnetic white dwarfs.
Optical characterization of wide band gap amorphous semiconductors (a-Si:C:H): Effect of hydrogen dilution
Authors: Park Minseo , Teng C. W. , Sakhrani V. , McLaurin M. B. , Kolbas R. M. , Sanwald R. C. , Nemanich R. J. , Hren J. J. , Cuomo J. J.
Published: July 2002

The effect of hydrogen dilution on the optical properties of a wide band gap amorphous semiconductor (a-Si:C:H) was investigated. The samples were prepared by glow discharge decomposition of tetramethylsilane and were characterized primarily by optical techniques: spectroscopic ellipsometry, Raman scattering, infrared absorption, spectrophotometry, and UV photoluminescence. The deposition rate decreased with hydrogen dilution, while the silicon to carbon ratio remained constant with the addition of hydrogen. The optical band gap of this material increased as the hydrogen flow rate increased. Infrared absorption studies show that the concentration of hydrogen which is bonded to carbon decreases systematically upon hydrogen dilution. Hydrogen dilution appears to reduce the size and concentration of sp2 bonded carbon clusters, possibly caused by the etching of sp2 clusters by atomic hydrogen. The result was also supported by the shift of the Raman G peak position to a lower wave number region. Room temperature photoluminescence in the visible spectrum was observed with UV excitation.
Chain self-assembly and phase transitions in semiflexible polymer systems
Authors: Kindt James T. , Gelbart William M.
Published: July 2002

We present a phenomenological theory of the interplay between linear self-assembly, isotropic attractions, and orientation-dependent repulsions in determining the phase behavior of particles that reversibly polymerize into semiflexible chains. Important examples of such linearly aggregating systems include many proteins, micelles, and dipolar fluids. Four classes of phase diagrams are predicted, featuring coexistence regions between two isotropic phases, an isotropic and a nematic phase, or two nematic phases. We map out the evolution of phase diagrams with changing values of the chain persistence length and of the ratio of intrachain bond energy to isotropic attractive energy, and relate the behavior in equilibrium polymer systems to that of fixed-length polymer systems. In both cases our theory predicts that over a narrow range of persistence lengths, increasing the chain length leads first to the disappearance and then to the recovery of the isotropic–isotropic transition; this behavior is explained by a simple scaling argument.
Superadiabatic behavior of fast particles accelerated by ion cyclotron resonance heating
Authors: Bergeaud Vincent , Nguyen Frédéric , Bécoulet Alain , Eriksson Lars-Göran
Published: July 2002

This paper addresses the problem of superadiabatic motion of ions interacting resonantly with waves in the ion cyclotron range of frequency (ICRF). In the classical quasilinear treatment of ion cyclotron resonance heating, the phase difference between the wave and the cyclotron motion of the particles must be assumed to be completely uncorrelated between two resonance crossings. However, beyond a critical particle energy, the so-called adiabatic barrier, this assumption is no longer valid, and particles exhibit superadiabatic behavior. In order to study in detail the influence of superadiabatic motion on the efficiency of ICRF heating the MOKA code was developed. In the MOKA code, complete trajectories of fast particles in a toroidal plasma magnetic equilibrium modified by a realistic radio-frequency perturbation are calculated. This paper shows that the location of the adiabatic barrier depends strongly on the particle orbits. Also, the injected toroidal spectrum is of high importance for determining the correlation effects, while at high energies, collisions are found to play a negligible role. A realistic description of this adiabatic barrier is given for an ICRF minority heating pulse of Tore Supra [J. Pamela, Fusion Engineering and Design 46, 313 (1999)].
Viscoelastic liquid crystal colloids for the continuous processing of twisted nematic electro-optical cells
Authors: van Boxtel Marysia C. W. , Janssen Rob H. C. , Bastiaansen Cees W. M. , Broer Dick J.
Published: July 2002

Liquid crystal colloid materials are described based on the liquid crystal (LC) E7 and submicron sized poly(methyl methacrylate-co-divinylbenzene) particles. Application of a thermal treatment to the composite material produces a finely dispersed network of the internally crosslinked polymeric inclusions in the LC-E7. Dynamic rheological measurements on the LC colloids show that the presence of this network imposes pronounced viscoelastic behavior on the material, which may be exploited in the manufacturing of large-area twisted nematic (TN) electro-optical cells via continuous methods as an alternative to the currently available batchwise routes. The electro-optical characteristics of TN cells based on the composite material are approximately comparable to the electro-optical characteristics of a reference cell filled with pure LC E7, which ensures that the largely increased viscoelasticity of the composite does not lead to a degradation of electro-optical properties.