bluuebunny/crossref_metadata_2025 huggingface dataset:
Soft proton exchange on periodically poled LiNbO3: A simple waveguide fabrication process for highly efficient nonlinear interactions
Authors: Chanvillard L. , Aschiéri P. , Baldi P. , Ostrowsky D. B. , de Micheli M. , Huang L. , Bamford D. J.
Published: July 2002

We report a simple fabrication process for realizing waveguides on periodically poled lithium niobate which preserves both the nonlinearity and the domain inversion. This so-called soft proton exchange has been used to generate highly efficient optical parametric fluorescence in the 1.48–2.01 μm region using a pump around 830 nm. The measured normalized efficiency is 130% W−1 cm−2 for an effective interaction length of 1.3 cm. This experimental figure is very close to the maximum theoretically predicted value of 140% W−1 cm−2.
Deep levels in high-energy proton-irradiated tin-doped n-type Czochralski silicon
Authors: Simoen E. , Claeys C. , Neimash V. B. , Kraitchinskii A. , Krasko N. , Puzenko O. , Blondeel A. , Clauws P.
Published: July 2002

A deep level transient spectroscopy study of defects created by 61 MeV proton irradiation of tin-doped n-type Czochralski silicon is reported. A comparison is made with the deep levels observed in irradiated p–n junction diodes fabricated in n-type float-zone silicon, without tin doping. The main conclusions are that in Sn-doped material, at least two additional deep radiation centers are introduced at 0.29±0.01 and 0.61±0.02 eV below the conduction band. From annealing experiments, it is concluded that these electron traps dissociate below 120 °C, which is lower than observed before for Sn–V related levels. It is demonstrated that the introduction rates of the well-known radiation defects are significantly smaller in Sn-doped material.
Nano-oxidation of silicon surfaces by noncontact atomic-force microscopy: Size dependence on voltage and pulse duration
Authors: Calleja Montserrat , Garcı́a Ricardo
Published: July 2002

Local oxidation of silicon surfaces by noncontact atomic-force microscopy is an emerging and promising method for patterning surfaces at the nanometer scale due to its very precise control of the feature size. Here, we study the voltage and pulse duration conditions to generate a motive of a given height with the minimum lateral size. We find that for a fixed tip–sample separation, the combination of short pulses and relatively high voltages (∼20 V) produces the highest height:width ratio. The application of relatively high voltages produces a fast growth rate in the vertical direction while the lateral diffusion of oxyanions is inhibited for short pulses. The above results are applied to generate lines of tens of microns in length with an average width at half maximum of about 10 nm.
Experimental investigation of particle heating in a strongly coupled dusty plasma
Authors: Quinn R. A. , Goree J.
Published: July 2002

Highly charged dust particles in a plasma can be strongly coupled when their kinetic temperature is low. This temperature is determined by a balance of heating and gas cooling. The heating is believed to be electrostatic, although its exact nature is still under investigation. Experiments in a multiple-layer plasma crystal were conducted to test proposed heating mechanisms. A method for measuring small-amplitude, low-frequency fluctuations in ion density was developed and, using this, very low-frequency electrostatic fluctuations were found upstream of the particles. These fluctuations should propagate with the ions towards the particles and heat them. However, the fluctuations were uncorrelated with, and too weak to account for, the observed particle temperatures. In the experiment, the temperature increased and then decreased with gas pressure; this result is only partly consistent with an ion wake heating mechanism. These negative findings help narrow the range of possible explanations for the observed temperatures.
Viscous flow in a slightly asymmetric channel with a sudden expansion
Authors: Hawa Takumi , Rusak Zvi
Published: July 2002

The effect of a slight asymmetry in the channel geometry on the flow transition from symmetric to nonsymmetric states in a long channel with a sudden expansion is presented. The asymptotic analysis is based on a study of the unsteady Navier–Stokes equations around the critical Reynolds number, Rec, where a bifurcation of asymmetric states in a symmetric channel occurs. It results in an ordinary, nonlinear, nonhomogeneous, first-order differential equation (similar to the Landau equation) which describes the evolution of the perturbation’s amplitude as function of Re near Rec and of the asymmetry of the channel, τ. It is found that channel asymmetry changes the pitchfork bifurcation diagram of a flow in a symmetric channel into two separate branches of equilibrium states. The primary branch describes a gradual and stable change of the flow states from symmetric to non-symmetric as Re is increased across Rec. The secondary branch appears at a certain modified critical Reynolds number, Recτ>Rec, and describes two additional non-symmetric flow states for each Re>Recτ which are disconnected from the primary branch. The large-amplitude asymmetric states along the secondary branch are also stable whereas the small-amplitude states are unstable. In the surroundings of Rec, the asymptotic results show an agreement with the results from numerical simulations using the Navier–Stokes equations. The asymptotic results also demonstrate an agreement with the available experimental data for Re near Rec. When Re increases above Rec, the second-order effects which are neglected in the asymptotic analysis become more dominant and are responsible for the deviation of the asymptotic results from the numerical and experimental results. The analysis clarifies the sensitive nature of the flow around Rec to geometry or flow asymmetries in both the experiments and the numerical computations and sheds more light on the nonlinear transition of a viscous flow in an expanding channel from symmetric to asymmetric states.
A shear cell for aligning and measuring birefringence of bow-shaped (banana) liquid crystals
Authors: Rastegar A. , Wulterkens G. , Verscharen H. , Rasing Th. , Heppke G.
Published: July 2002

We present a special shear cell for aligning unconventional liquid crystals and performing high temperature optical studies. Sample thicknesses of 1–100 μm in the temperature range of 20–200 °C with a shear amplitude as large as 1 mm are achievable with this cell. The shear cell was used to align banana-shaped liquid crystals and to measure their optical anisotropy in the B2, B3, and B4 phases which was not possible before. The optical anisotropy of the B2 phase slowly increases by cooling and jumps to a low value at the transition to the B3 phase. The optical rotation is almost constant in the B2 phase and increases sharply at the transition to the B3 phase. The B3 and B4 phases are distinguishable by their optical anisotropy.
Kinetics, mechanism, and dynamics of the gas-phase H(D) atom reaction with adsorbed D(H) atom on Pt(111)
Authors: Kim Jae-Young , Lee Jihwa
Published: July 2002

We have investigated the kinetics of the abstraction reaction H(D)+Dad(Had)/Pt(111) at 100 K and saturation coverage (θsat=0.95±0.06 ML) using an H(D) atom beam, in which the angle-integrated and angle-resolved product desorption rates were simultaneously monitored with two mass spectrometers. HD molecules are formed by the abstraction reaction as well as by the secondary hot atom (s-HA) reactions, Ds*(Hs*)+Had(Dad)→HD, where Ds*(Hs*) is a collisionally excited surface D(H) atom. The two reaction components of HD show quite distinct angular distributions; while the former component is sharply forward-peaked to be represented by cos12(θf−3°), the latter component preferentially desorbs at large desorption angles centered at θf∼45°. The two HD formation reactions also exhibit distinct kinetics, which could be separately identified by properly selecting the desorption angle. Concurrent desorption of D2(H2) formed by a homonuclear s-HA reaction was also observed with a relatively large yield amounting to 37%(31%) of the initially adsorbed D(H) atoms. The angular distribution of D2 is very similar to that of HD formed by the s-HA reactions. Varying the beam incidence angle has no effect on the reaction rate constants and the product branching ratio. From a kinetic analysis, we estimate a cross section σabst=1.30±0.07(1.49±0.11) Å2 for HD formation by abstraction in H(D)-on-Dad(Had) reaction. For D2(H2) formation, an effective cross section for generating reactive Ds*(Hs*) atom is estimated as σ*=1.87±0.08(1.61±0.24) Å2. These values can be translated into the probabilities Pabst=0.19(0.21), Pex=0.27(0.23), Pads=0.73(0.67), and Pscatt=0.08(0.12) for abstraction reaction, s-HA generation, adsorption, and scattering of an incident H(D) atom, respectively. The isotope effects are small and the corresponding cross sections differ at most by 15%. The mechanism-dependent product angular distributions are discussed in terms of the different reaction dynamics from the view points of the surface potential corrugation experienced by the energetic hydrogen atoms (incident, primary, and secondary hot atoms) and the extent of the parallel momentum conservation in their reactions.
Energetics of hydrogen chemisorbed on Cu(110): A first principles calculations study
Authors: Bae ChinSung , Freeman David L. , Doll J. D. , Kresse G. , Hafner J.
Published: July 2002

In the current study we present a potential energy surface(PES) for atomic hydrogen chemisorbed on Cu(110) at Θ=18 monolayer (ML) obtained from a plane-wave, gradient-corrected, density functional calculation. This PES is markedly different from and significantly more complex than that predicted by empirical embedded atom method (EAM) calculations. Our results, for example, suggest strongly that the hollow (HL) site is not the preferred binding site for this system. In our calculations, both the short bridge (SB) and pseudo-threefold sites are energetically more favorable than the hollow (HL) site. Energetically, we find the SB site to be slightly lower (30 meV) than the pseudo-threefold site. We also find, however, that the calculated vibrational frequencies for the pseudo-threefold site agree more closely with experimental electron energy loss data than for the SB site. In view of the relatively flat region between adjacent pseudo-threefold sites along the cross-channel [001] direction, we speculate that the hydrogen atom motion at low coverages may be two-dimensional rather than quasi-one-dimensional in character.
Equation of state and temperature measurements for shocked nitromethane
Authors: Winey J. M. , Duvall G. E. , Knudson M. D. , Gupta Y. M.
Published: July 2002

A thermodynamically consistent equation of state (EOS) was developed for unreacted liquid nitromethane (NM). The specific heat cv, the coefficient of thermal pressure (∂P/∂T)v, and the isothermal bulk modulus BT, were modeled as functions of temperature and volume using existing experimental data. To test our EOS predictions, temperature measurements using time-resolved Raman spectroscopy were obtained from NM subjected to stepwise loading. In contrast to previous EOS developments, calculations using our EOS show good agreement with the measured temperatures. Comparison with previous EOS models shows that simplifying assumptions, such as holding (∂P/∂T)v or Γ/v constant, lead to significant inaccuracies in temperature predictions for shocked NM. The assumption that the Gruneisen parameter Γ is a function of volume only is not consistent with our EOS.
Spectral parameters of Nd-doped yttrium orthovanadate crystals
Authors: Xia H. R. , Meng X. L. , Guo M. , Zhu L. , Zhang H. J. , Wang J. Y.
Published: July 2002

Nd-doped yttrium orthovanadate (Nd:YVO4, abbreviated as NYV) crystal has been grown using a modified Czochralski method. Its main structural parameters and optical and laser properties are all presented. The absorption spectrum of Nd3+ ions doped in NYV in a wavelength range from 190 to 900 nm and that of free Nd3+ ions in HCl solution of 0.2 mol in the range of 190–900 nm have both been measured. The width of the absorption band around 808 nm to match the laser diode pumping is about 28 nm, which is approximately three times broader than that of Nd-doped yttrium aluminum garnet crystal. The line intensity of the absorption spectrum of NYV has been calculated. The calculated luminescence parameters of NYV are also listed.
Numerical simulation of current crowding phenomena and their effects on electromigration in very large scale integration interconnects
Authors: Yeh Everett C. C. , Tu K. N.
Published: July 2002

Two types of current crowding structures were simulated in this work. In each structure, both the pattern of current crowding and the magnitude of the associated current density gradient were examined. Factors like line width, curvature, and conductivity, which affect the crowding behavior, were analyzed. The numerical magnitude of the gradient, which changes to a driving force when a potential in the gradient is defined, was found to be high enough to affect the atomic rearrangement during electromigration. It induces void formation in the low current density region of an interconnect, and it causes precipitates to link together rather than to ripen in a two-phase alloy. Also, we found that as the line width scales down, the effects of current crowding become more and more significant.
Integrable evolution systems based on Gerdjikov–Ivanov equations, bi-Hamiltonian structure, finite-dimensional integrable systems and N-fold Darboux transformation
Authors: Fan Engui
Published: July 2002

A spectral problem and the associated Gerdjikov–Ivanov (GI) hierarchy of nonlinear evolution equations is presented. As a reduction, the well-known GI equation of derivative nonlinear Schrödinger equations is obtained. It is shown that the GI hierarchy is integrable in a Liouville sense and possesses bi-Hamiltonian structure. Moreover, the spectral problem can be nonlinearized as a finite dimensional completely integrable system under the Bargmann constraint between the potentials and the eigenfunctions. In particular, an explicit N-fold Darboux transformation for the GI equation is constructed with the help of a gauge transformation of spectral problems and a reduction technique. Some explicit solitonlike solutions of the GI equation are given by applying its Darboux transformation.
Anomalous skin effect and collisionless power dissipation in inductively coupled discharges
Authors: Cunge G. , Crowley B. , Vender D. , Turner M. M.
Published: July 2002

In this article we present an experimental study of the electron electrodynamics in an inductively coupled argon discharge. The discharge is configured in a re-entrant geometry and operates in the stochastic heating regime at pressures below 10 mTorr. The radial distribution of the induced rf electric field E and current density J were determined for a wide range of plasma parameters in argon gas from the measurement of the radial distribution of the magnetic field components and its spatial derivatives. The results show an anomalous skin effect at low pressure and high plasma densities that is characterized by a nonmonotonic spatial decay of the electromagnetic field E and current density J along with phase reversal and bifurcation of E and J and negative power absorption regions. These features are interpreted to be a result of nonlocal electrodynamics due to the electron thermal motion (which causes spatial dispersion in the conductivity). The electron thermal motion in the inhomogeneous rf induced electric field induces a phase randomization that leads to collisionless heating. The relative ratio of ohmic collisional heating to collisionless heating is estimated by comparing the total and collisional (deduced from an estimation of the electron-neutral collision frequency) power fluxes absorbed by the plasma electrons. This shows that collisionless heating dominates ohmic heating for pressures below 5 m Torr. These results are compared with the previously published work of Godyak et al. [V. A. Godyak, R. B. Piejak, and B. M. Alexandrovich, Phys. Rev. Lett. 80, 3264 (1998)] and show a surprisingly good agreement (at constant gas pressure and plasma density) despite the differing chamber geometry.
Numerical study of tilt stability of prolate field-reversed configurations
Authors: Belova E. V. , Jardin S. C. , Ji H. , Yamada M. , Kulsrud R.
Published: July 2002

Global stability of the field-reversed configuration (FRC) has been investigated numerically using both three-dimensional magnetohydrodynamic and hybrid (fluid electron and δf particle ion) simulations. The stabilizing effects of velocity shear and finite ion Larmor radius (FLR) on the n=1 internal tilt mode in the prolate FRCs have been studied. Sheared rotation is found to reduce the growth rate, however a large rotation rate with Mach number of M≳1 is required in order for significant reduction in the instability growth rate to occur. Kinetic effects associated with large thermal ion orbits have been studied for different kinetic equilibria. The simulations show that there is a reduction in the tilt mode growth rate due to FLR effects, but complete linear stability has not been found, even when the thermal ion gyroradius is comparable to the distance between the field null and the separatrix. The instability existing beyond the FLR theory threshold could be due to the resonant interaction of the wave with ions whose Doppler shifted frequency matches the betatron frequency.
Modeling of the depletion of the amorphous-silicon surface during hemispherical grained silicon formation
Authors: Sallese J. M. , Ils A. , Bouvet D. , Fazan P. , Merritt Chris
Published: July 2002

A model, based on surface energy minimization under nonequilibrium conditions, is presented to describe the evolution of the amorphous silicon (a-Si) topography near the hemispherical grained silicon. The evolution of the depletion area can be explained by a combination between capture of silicon (Si) atoms at the grain boundary and energy minimization of the surrounding a-Si surface. Grain depletion dependence on annealing time was measured by means of transmission electron microscopy. The simulated results agree well with the real observations. This approach is presented as a first step in physically based modeling of HSG formation.
Identification of Mercier instabilities in Alcator C-Mod tokamak
Authors: In Y. , Ramos J. J. , Hastie R. J. , Catto P. J. , Hubbard A. E. , Hutchinson I. H. , Marmar E. , Porkolab M. , Snipes J. , Wolfe S. , Taylor G. , Bondeson A.
Published: July 2002

During current ramp-up discharges, highly localized magnetohydrodynamic (MHD) fluctuations were observed on the electron cyclotron emission diagnostics of Alcator C-Mod tokamak [I. H. Hutchinson et al., Phys. Plasmas 1, 1511 (1994)]. The electron temperature profile was hollow, while the density profile was weakly decreasing. Assuming that the equilibration time was short enough to quickly thermalize ions the pressure profile was also found to be hollow. Using this pressure profile as an additional constraint to the EFIT program, an equilibrium with reversed shear was constructed having a q(0)≫1. The localized MHD activity was observed near the inner q=5 rational surface in this reconstructed equilibrium, where the Mercier criterion for ideal MHD stability was violated because of the reversed pressure gradient (dp/dr>0), q>1 and moderate shear. When kinetic effects were added, the ideal Mercier mode was finite ion Larmor radius stabilized. However, ion Landau damping was found to be strong enough to drive a kinetic Mercier instability.
Recent progress of white light interferometric fiberoptic strain sensing techniques
Authors: Yuan Libo , Zhou Limin , Jin Wei , Chan C. C.
Published: July 2002

Strain, deformation, and temperature measurements constitute some of the most interesting parameters to be monitored in composite materials or structures. White light interferometry offers good performance even for long-term measurements of these parameters. Based on the Michelson interferometer, a fiberoptic localized extensometer and multiplexing strain-sensing techniques are demonstrated in this article. Related problems such as the effect of optical fiber coating on an embedded sensor and the dual use of one sensor are discussed. Finally, application examples of surface strain and internal strain (0–6000 microstrain) and temperature (22–36 °C) of concrete sample are given.
Depletion of charge produced during plasma exposure in aluminum oxide by vacuum ultraviolet radiation
Authors: Cismaru C. , Shohet J. L. , Lauer J. L. , Hansen R. W. , Ostapenko S.
Published: July 2002

A temporary increase in the conductivity of aluminum oxide sputter deposited on the surface of aluminum wafers was made by exposure to vacuum ultraviolet (VUV) radiation produced by a synchrotron light source. The oxide was charged, either positively or negatively, by exposure to a nonreactive inductively coupled plasma, under typical plasma processing conditions. We show the dependence of the conductivity on the energy of the incoming radiation, and conclude that only those photons whose energy is above the band gap of the oxide are capable of producing a temporary increase in the conductivity. By exposing localized regions of precharged oxide samples to the vacuum ultraviolet radiation, we produce regions of charge depletion in and around the exposed areas. We conclude that VUV radiation may be used to significantly decrease plasma-induced surface charging of dielectrics.
Determining the solvation correlation function from three-pulse photon echoes in liquids
Authors: Everitt K. F. , Geva E. , Skinner J. L.
Published: July 2002

The decay of three-pulse photon echo signals from a solute in a liquid solvent is sensitive to the solute’s transition frequency fluctuations, as characterized by its two-point time correlation function, otherwise known as the solvation correlation function. The most widely used method for determining this solvation correlation function from photon echo data involves the three-pulse photon echo peak shift (3PEPS) method. Using this method the long-time decay of the solvation correlation function can be obtained directly, but the determination of the short-time decay requires a difficult numerical fitting procedure. In this study we propose several alternative approaches to determining the solvation correlation function from echo data, the most promising and straightforward of which we call the S3PE (short-time slope of the three-pulse photon echo) method. The accuracy and efficacy of this approach is illustrated by extracting the solvation correlation function from “experimental” data obtained from classical molecular dynamics computer simulations.
Influence of oxygen impurities on the crystallization mechanism of NiZr2 metallic glasses
Authors: Boutet S. , Steele G. , Dikeakos M. , Altounian Z.
Published: July 2002

The influence of oxygen impurities on the crystallization mechanism of NiZr2 metallic glasses was studied. For this glass system, the first crystallization product is the metastable E93(cF96) cubic structure instead of the equilibrium C16(tI12) tetragonal structure. A possible mechanism for the formation of this metastable phase has previously been put forth. The hypothesis is that oxygen forms a semipermanent bond with Zr resulting in the oxygen atom being surrounded by six Zr atoms in octahedral configuration which act as nucleation sites for the E93 cubic phase. Hydrogenation of the amorphous composition eliminates the nucleation sites required for the formation of this metastable cubic phase, thereby allowing the glass to crystallize directly into the stable tetragonal C16 phase, and thus providing strong evidence in support of the proposed crystallization mechanism.
Accurate relative pKa calculations for carboxylic acids using complete basis set and Gaussian-n models combined with continuum solvation methods
Authors: Toth Ann Marie , Liptak Matthew D. , Phillips Danielle L. , Shields George C.
Published: July 2002

The complete basis set methods CBS-4, CBS-QB3, and CBS-APNO, and the Gaussian methods G2 and G3 were used to calculate the gas phase energy differences between six different carboxylic acids and their respective anions. Two different continuum methods, SM5.42R and CPCM, were used to calculate the free energy differences of solvation for the acids and their anions. Relative pKa values were calculated for each acid using one of the acids as a reference point. The CBS-QB3 and CBS-APNO gas phase calculations, combined with the CPCM/HF/6-31+G(d)//HF/6-31G(d) or CPCM/HF/6-31+G(d)//HF/6-31+G(d) continuum solvation calculations on the lowest energy gas phase conformer, and with the conformationally averaged values, give results accurate to 12 pKa unit.
Synchronization experiments with an atmospheric global circulation model
Authors: Lunkeit Frank
Published: July 2002

Synchronization in a chaotic system with many degrees of freedom is investigated by coupling two identical global atmospheric circulation models. Starting from different initial conditions, the two submodels show complete synchronization as well as noncomplete synchronization depending on the coupling strength. The relatively low value of the coupling strength threshold for complete synchronization indicates the potential importance of synchronization mechanisms involved in climate variability. In addition, the results suggest synchronization experiments as a valuable additional method to analyze complex dynamical models, e.g., to estimate the largest Lyapunov exponent.
Polymeric contributions to entropic surface forces
Authors: McCoy John D. , Teixeira Melody A. , Curro John G.
Published: July 2002

Density functional theory is applied to hard site chains between hard walls. The wall separation is varied and the normal pressures, surface excesses, and surface tensions are recorded. At low bulk density, a density depletion near the wall dominates the thermodynamic behavior. At high bulk density, the thermodynamic properties develop a damped oscillatory behavior with a period of approximately one site diameter and a range of roughly six site diameters.
Spatial ordering of stacked quantum dots
Authors: Lee C.-S. , Kahng B. , Barabási A.-L.
Published: July 2002

We investigate the growth conditions necessary to form an ordered quantum dot crystal by capping spatially ordered quantum dots and growing a new layer of dots on top of the capping layer. Performing Monte Carlo simulations and developing analytic arguments based on the stress energy function, we demonstrate the existence of an optimal capping layer thickness, external flux, and temperature for the formation of quantum dot crystals.
The threshold of the instability in miscible displacements in a Hele–Shaw cell at high rates
Authors: Lajeunesse E. , Martin J. , Rakotomalala N. , Salin D. , Yortsos Y. C.
Published: July 2002

For sufficiently large viscosity ratios and injection rates, miscible displacements in a vertical Hele–Shaw cell at high rates become unstable, leading to three-dimensional (3D) fingering patterns. Below the instability threshold, the base state is 2D in the form of a “tongue” of constant thickness. We apply the long wave Saffman–Taylor stability analysis to find an expression for the threshold of instability as a function of the viscosity ratio and the injection rate. The results are in agreement with the experimental data.
A Monte Carlo test of the Fisher–Nakanishi–Scaling theory for the capillary condensation critical point
Authors: Dillmann Oliver , Janke Wolfhard , Müller Marcus , Binder Kurt
Published: July 2002

Extending the Swendsen–Wang cluster algorithm to include both bulk (H) and surface fields (H1) in L×L×D Ising films of thickness D and two free L×L surfaces, a Monte Carlo study of the capillary condensation critical point of the model is presented. Applying a finite-size scaling analysis where the lateral linear dimension L is varied over a wide range, the critical temperature Tc(D) and the associated critical field Hc(D) are estimated for 4⩽D⩽32 lattice spacings, for a choice of the surface field H1 small enough that the dependence of Hc(D) on H1 is still linear. It is shown that the results are consistent with the power laws predicted by Fisher and Nakanishi [M. E. Fisher and H. Nakanishi, J. Chem. Phys. 75, 5857 (1981)], namely Tc(∞)−Tc(D)∝D−1/ν, Hc(D)∝D−(Δ−Δ1)/ν, where ν is the bulk correlation length exponent of the three-dimensional Ising model, and Δ, Δ1 are the corresponding “gap exponents” associated with bulk and surface fields, respectively. As expected, the order parameter of the thin film near its critical point exhibits critical behavior compatible with the universality class of the two-dimensional Ising model.
Quantized vibrational modes of nanospheres and nanotubes in the elastic continuum model
Authors: Kahn Daniel , Kim K. W. , Stroscio Michael A.
Published: July 2002

The properties of nanoscale spheres and tubes are of recent interest due to the discovery of the fullerene molecule and the carbon nanotube. These carbon structures can be modeled as nanoscale spherical or cylindrical shells. In this article, these nanostructures are treated in the thin shell approximation with the elastic properties taken to be those of the graphene sheet. A quantization prescription is applied to the classical elastic modes to facilitate the first calculations of the quantum-mechanical normalizations of selected modes. These modes are shown to be amenable to the study of electron-phonon interactions. Indeed, electron-phonon interaction Hamiltonians are derived. Moreover, it is shown for such a tube of finite length that the electron-phonon interaction strength depends on the axial position. As a special case it is shown that the dispersion relation for the clamped tube depends on the length of the tube. In this article we consider both the vibrational frequencies and the mode quantization for both spherical shell and the nanotube using realistic material parameters.
Band alignments and photon-induced carrier transfer from wetting layers to Ge islands grown on Si(001)
Authors: Wan J. , Jin G. L. , Jiang Z. M. , Luo Y. H. , Liu J. L. , Wang Kang L.
Published: July 2002

Temperature- and excitation-power-dependent photoluminescence measurements were carried out for the multilayer structure of Ge islands grown on a Si(001) substrate by gas-source molecular-beam epitaxy. When the excitation power increases from 10 to 400 mW, the photoluminescence peak from the Ge islands showed a large linear blueshift of 34 meV while that of the wetting layers did not change much. These two different power dependences are explained in terms of type-II and type-I band alignments for the islands and the wetting layers, respectively. When the sample temperature increased from 8 to 20 K, an anomalous increase of photoluminescence intensity for islands was accompanied by a rapid decrease of that from the wetting layers, implying that a large portion of photon-induced carriers in the wetting layer was transfered to the neighboring islands and the Si layer, respectively, thus resulting in an increase of photoluminescence intensity of the islands.
The spin-valve transistor: Fabrication, characterization, and physics (invited)
Authors: Jansen R. , van ’t Erve O. M. J. , Kim S. D. , Vlutters R. , Anil Kumar P. S. , Lodder J. C.
Published: July 2002

An overview is given of the fabrication, basic properties, and physics of the spin-valve transistor. We describe the layout of this three-terminal ferromagnet/semiconductor hybrid device, as well as the operating principle. Fabrication technologies are discussed, including vacuum metal bonding. We characterize properties of the device relevant for possible applications in magneto-electronics, such as relative magnetic response, output current, and noise behavior. Furthermore, we illustrate the unique possibilities of the spin-valve transistor for fundamental studies of the physics of hot-electron spin transport in magnetic thin film structures.
A model of spatial algebraic growth in a boundary layer subjected to a streamwise pressure gradient
Authors: Tumin Anatoli
Published: July 2002

Steady three-dimensional disturbances are considered within the scope of the linearized boundary layer equations. The disturbances are assumed to be periodic in the spanwise direction, and their spanwise scale is assumed to be much larger than the boundary layer thickness. The model is an extension of Luchini’s theory [J. Fluid Mech. 327, 101 (1996)] to the Falkner–Skan boundary layer.
Bright blue electroluminescence from an InGaN/GaN multiquantum-well diode on Si(111): Impact of an AlGaN/GaN multilayer
Authors: Dadgar A. , Christen J. , Riemann T. , Richter S. , Bläsing J. , Diez A. , Krost A. , Alam A. , Heuken M.
Published: July 2002

We present an electroluminescence test structure which consists of an InGaN/GaN multiquantum well as active region on the top of an AlGaN/GaN multilayer grown by metalorganic vapor phase epitaxy on Si(111) substrate. The integral room-temperature electroluminescence spectrum reveals a peak emission wavelength of 467 nm and a significantly higher brightness than an identical reference structure on sapphire substrate. In microelectroluminescence imaging, two emission peaks at 465 and 476 nm can be separated originating from locally different areas of the diode. Cathodoluminescence measurements in cross section and high-resolution x-ray diffraction measurements show that the structure is less strained than a sample without the AlGaN/GaN multilayer. The AlGaN/GaN multiple layer sequence which has a total thickness of 1.5 μm causes lattice relaxation during growth after a thickness of around 0.9 μm as directly visualized by cathodoluminescence line scans across the diode.
Pulsed laser deposition of silk protein: Effect of photosensitized-ablation on the secondary structure in thin deposited films
Authors: Tsuboi Yasuyuki , Goto Masaharu , Itaya Akira
Published: July 2002

Silk fibroin is a simple protein expected to have functional applications in medicine and bioelectronics. The primary structure of this protein is quite simple, and the main secondary structures are β-sheet crystals and amorphous random coils. In the present study, we investigated pulsed laser deposition (PLD) of fibroin with the β-sheet structures as targets. The primary and secondary structures in films deposited were analyzed using infrared spectroscopy. Normal laser deposition at 351 nm using neat fibroin targets produced thin films of fibroin with a random coiled structure. Ablation was triggered by two-photonic excitation of the peptide chains, which resulted in the destruction of β-sheet structure in PLD. In order to avoid the two-photonic excitation, we adopted a PLD method utilizing anthracene (5–0.1 wt %) in a photosensitized reaction involving doped fibroin targets. Laser light (351 or 355 nm) was absorbed only by anthracene, which plays an important role converting photon energy to thermal energy with great ablation efficiency. Thin fibroin films deposited by this method had both random coil and β-sheet structures. As the dopant concentration and laser fluence decreased, the ratio of β-sheet domain to random coil increased in thin deposited films.
Si-rich/SiO
2
nanostructured multilayers by reactive magnetron sputtering
Authors: Gourbilleau F. , Portier X. , Ternon C. , Voivenel P. , Madelon R. , Rizk R.
Published: July 2002

Silicon-rich (SR)/SiO2 multilayered systems were produced by reactive magnetron sputtering, through an approach based on the ability of hydrogen, when alternatively mixed to the argon of the plasma, to reduce the oxygen originated from the SiO2 target. Optimum values of both hydrogen partial pressure (45 mTorr) and deposition temperature (500 °C) have led to the highest incorporation of Si in the SR layer which crystallizes after annealing. The SR/SiO2 superlattices grown with such conditions showed that the size of the Si nanocrystals is limited by the thickness of the SR layer. Considering the difference observed between the photoluminescence peak position and the predicted band gap for Si nanocrystals, the results suggest that we deal with a quantum-size confinement assisted by a Si–O vibration located at the interface.
Effects of dielectric materials on electromigration failure
Authors: Doan J. C. , Lee S. , Lee S.-H. , Flinn P. A. , Bravman J. C. , Marieb T. N.
Published: July 2002

The effects of dielectric layers on electromigration failure were studied in situ using a high-voltage scanning electron microscope and at the wafer level using conventional accelerated testing. Several different passivation layers were deposited on wafers with A1 interconnect test structures. Prior to the deposition of the final dielectric, the wafers were processed identically and, whenever possible, simultaneously. Interconnects encapsulated with compliant polymer and very thin (0.1 μm) SiO2 layers demonstrated substantial lifetime extensions over those with more rigid (1 μm thick) SiO2 layers. Unpassivated lines behaved dramatically differently and failed much sooner than those covered with only 0.1 μm of SiO2. As expected, increasing the passivation thickness from 0.5 to 4 μm increased the electromigration lifetime for SiO2 covered specimens. The fabrication of silicon dioxide dielectrics using electron-cyclotron-resonance chemical-vapor deposition (CVD) and silicon nitride dielectrics via plasma-enhanced CVD damaged the interconnects. This damage nearly completely removed the barrier to void nucleation during electromigration.
Electron beam interaction with lower hybrid waves at Cherenkov and cyclotron resonances
Authors: Volokitin A. S. , Krafft C.
Published: July 2002

Cyclotron and Cherenkov resonant interactions between a radially confined electron beam spiraling in a magnetoplasma and a quasi-monochromatic lower hybrid wave are considered. The main physical process consists of the nonlinear self-organization of part of the beam electrons, forming dynamically stable bunches that are continuously decelerated or accelerated while keeping resonance with the emitted wave. For the Cherenkov and anomalous Doppler resonances, such bunches exist during an infinitely long time; the main difference between both cases is that, for the cyclotron resonance, the gain of energy supplied by the longitudinal motion of the beam electrons is mainly spent to increase their perpendicular energy, and only a small part of it, proportional to the ratio of the wave frequency to the electron gyrofrequency, is given for wave radiation. For the normal Doppler resonance case, electron bunches also appear during the nonlinear wave-particle evolution. However, electrons lose perpendicular energy and are accelerated along the longitudinal direction. As formed bunches do not have a high stability, the interaction of the beam electrons with the wave weakens rather quickly, whereas the wave radiation decreases as a function of the distance from the injector.
Enhanced K-shell x-ray line emissions from aluminum plasma created by a pair of femtosecond laser pulses
Authors: Nakano Hidetoshi , Nishikawa Tadashi , Uesugi Naoshi
Published: July 2002

The influence of an ultrashort prepulse on K-shell x-ray line emissions from Al plasma produced by 100 fs Ti:sapphire laser pulses is studied. By introducing an independent 100 fs prepulse, a more than 20-fold enhancement in K-shell emission was achieved. We could experimentally optimize Kα and Heα line emissions. In case of oblique incidence, resonance absorption made it possible to maximize Kα emission while keeping pulse duration short. On the other hand, Heα line emission was maximized when a separation between two laser pulses was large, resulting in pulse broadening (∼30 ps).
Cycloaddition chemistry of thiophene on the silicon (111)-7×7 surface
Authors: Cao Y. , Yong K. S. , Wang Z. H. , Deng J. F. , Lai Y. H. , Xu G. Q.
Published: July 2002

The mechanism of the cycloaddition reaction between thiophene and Si(111)-7×7 has been investigated using thermal desorption spectroscopy (TDS), high resolution electron energy loss spectroscopy (HREELS), electronic electron energy loss spectroscopy (EELS), scanning tunneling microscopy (STM), and PM3 semiempirical calculations. The results show that thiophene binds on Si(111)-7×7 through a [4+2] cycloaddition reaction between the 2, 5 C-atoms of thiophene and the adjacent adatom-rest atom pairs on Si(111)-7×7. Semiempirical PM3 calculations based on the cluster model further confirm this di-σ bonding configuration. A stepwise surface diradical mechanism has been proposed to account for the regioselective [4+2] cycloaddition reaction.
Nonlinear charge and current neutralization of an ion beam pulse in a pre-formed plasma
Authors: Kaganovich Igor D. , Shvets Gennady , Startsev Edward , Davidson Ronald C.
Published: July 2002

The propagation of a high-current finite-length ion beam in a cold pre-formed plasma is investigated. The outcome of the calculation is the quantitative prediction of the degree of charge and current neutralization of the ion beam pulse by the background plasma. The electric and magnetic fields generated by the ion beam are studied analytically for the nonlinear case where the plasma density is comparable in size with the beam density. Particle-in-cell simulations and fluid calculations of current and charge neutralization have been performed for parameters relevant to heavy ion fusion assuming long, dense beams with length lb≫Vb/ωb, where Vb is the beam velocity, and ωb is the electron plasma frequency evaluated with the ion beam density. An important conclusion is that for long, nonrelativistic ion beams, charge neutralization is, for all practical purposes, complete even for very tenuous background plasmas. As a result, the self-magnetic force dominates the electric force and the beam ions are always pinched during beam propagation in a background plasma.
Generation of circularly polarized light by superposition of coherent transition radiation in the millimeter wavelength region
Authors: Shibata Yukio , Sasaki Satoshi , Ishi Kimihiro , Takahashi Toshiharu , Matsuyama Tomochika , Kobayashi Katsuhei
Published: July 2002

Circularly polarized light was generated in the millimeter wavelength region from superposition of forward transition radiation (TR) and backward TR emitted from two metallic screens placed along a trajectory of a short-bunch beam of electrons of 42 MeV. The degree of the circular polarization was analyzed to be 97% of the polarized radiation at λ=2.25 mm, using a Soleil’s compensator and a wire-grid polarizer. The geometry of the metallic screens was discussed from the point of the phase difference between the forward TR and the backward TR.
Small-angle neutron scattering from supercritical heavy water at off-critical densities
Authors: Bonetti M. , Calmettes P. , Bervillier C.
Published: July 2002

We report the results of small-angle neutron scattering measurements performed on supercritical heavy water at wave-number transfers between 0.07 and 0.36 Å−1. The data were collected along five different isochores at temperatures about 1.15, 2.20, and 5.50 °C higher than the measured critical temperature. The density, ρ, was in the range (ρc−0.062)<ρ<(ρc+0.082) g cm−3, where ρc is the critical density. The shape of the scattering spectra is represented by the expression previously used for those measured along the critical isochore [Bonetti et al., J. Chem. Phys. 112, 268 (2000)]. The temperature and density dependencies of the isothermal compressibility and the correlation length can be reasonably described using a parametric representation of the thermodynamic space and corrections to scaling that include odd terms to account for the asymmetry of the system.
Effects of transverse helium injection on hypersonic boundary layers
Authors: Auvity Bruno , Etz Michael R. , Smits Alexander J.
Published: July 2002

Results are presented on the control of a zero-pressure gradient Mach 8 boundary layer using low-momentum helium injection through a transverse slot. The boundary layer structure was visualized in three orthogonal planes using planar filtered Rayleigh scattering. Sequential images of the boundary layer were obtained using a new MHz imaging system and employed to construct three-dimensional representations of the instantaneous boundary layer behavior. The results indicate that low levels of helium injection into transitional and turbulent boundary layers can have a substantial effect on the boundary layer structure. Longitudinal structures develop downstream of the slot and persist for long times. They appear to be streamwise vortices, and it is speculated that they are formed near the injection slot due to local streamline concave curvature. The results may be important for aero-optic applications.
Diffusion of ion-implanted boron in germanium
Authors: Uppal Suresh , Willoughby Arthur F. W. , Bonar Janet M. , Evans Alan G. R. , Cowern Nick E. B. , Morris Richard , Dowsett Mark G.
Published: July 2002

The diffusion of boron (B) in germanium (Ge) is studied. B was introduced in Ge wafers by ion implantation, and concentration profiles after furnace annealing were obtained using secondary ion mass spectroscopy. The diffusion coefficient and solid solubility of B in Ge has been calculated to be 1.5(±0.3)×10−16 cm2/s and 5.5(±1.0)×1018/cm3, respectively, at 850 °C by fitting experimentally obtained profiles. This value of diffusion coefficient is at least two orders of magnitude lower than the minimum value reported in the literature for B diffusion in Ge. The results are significant as they question the general agreement about vacancy diffusion as the mechanism responsible for diffusion of B in Ge.
Cu(001) to HD energy transfer and translational to rotational energy conversion on surface scattering
Authors: Goncharova L. V. , Braun J. , Ermakov A. V. , Bishop G. G. , Smilgies D.-M. , Hinch B. J.
Published: July 2002

Intense peaks are observed in angular intensity distributions for HD scattering from the Cu(001) surface. These can be ascribed to coherent diffraction with translational energy transfers of ΔE=0, −11.0, or 33.11 meV to molecular rotational energy. Time-of-flight spectra, at other scattering angles, display inelastic peaks that are assigned to phonon creation or annihilation processes with either the HD rotationally elastic or inelastic transitions. The HD phonon dispersion curves suggest a strong HD coupling both with surface Rayleigh modes and with bulk phonon modes of the metal surface. Comparisons of both elastic and inelastic scattering intensities are also made with those reported for the Ni(001) surface. To explain an apparent anomalous diffraction peak intensity ratio for Ni, a preferential coupling for the HD J=0 rotational state into a predissociation channel above the Ni surface is proposed.
Determination of traps in poly(p-phenylene vinylene) light emitting diodes by charge-based deep level transient spectroscopy
Authors: Gaudin Olivier , Jackman Richard B , Nguyen Thien-Phap , Le Rendu Philippe
Published: July 2002

Charge-based deep level transient spectroscopy has been used to study the defect states that exist within poly(p-phenylene vinylene) (PPV), a semiconducting polymer with a band gap of about 2.4 eV. The technique allows the determination of activation energies, capture cross sections, and trap concentrations. In some circumstances, it is also possible to distinguish between minority and majority carrier traps. The structures investigated here consisted of indium–tin–oxide (ITO)/PPV/MgAg light emitting diode (LED) devices. Two types of trapping centers were found. The first type has activation energies in the range 0.49–0.53 eV and capture cross sections on the order of 10−16–10−18 cm2. It shows a Poole–Frenkel, field assisted–emission process. This level has been identified as a bulk acceptor-like majority carrier (i.e., hole) trap. The second type has activation energies in the range 0.40–0.42 eV and capture cross sections on the order of 10−19 cm2. This level has been identified as a minority carrier (i.e., electron) trap. This second trap type is therefore expected to limit minority carrier injection into the PPV layer within the LED, and hence reduce electroluminescence under forward bias conditions.