bluuebunny/crossref_metadata_2025 huggingface dataset:
High vacuum feedthrough for angular, linear, and rotary motion
Authors: Scime E. E. , Kline J. L. , Mathess D. , Weber C.
Published: July 2002

An angular motion feedthrough capable of supporting a large diameter linear motion feedthrough has been designed and built for the large experiment on instabilities and anisotropies at West Virginia University. With a combination of linear, angular, and rotary motion, a probe can be positioned in the vacuum chamber within a cone-shaped volume.
Layer by layer removal of Au atoms from passivated Au(111) surfaces using the scanning tunneling microscope: Nanoscale “paint stripping”
Authors: Keel J. M. , Yin J. , Guo Q. , Palmer R. E.
Published: July 2002

Layer by layer removal of gold atoms from the (111) surface of gold has been performed using the scanning tunneling microscope. The process is made possible by a chemisorbed self-assembled monolayer (SAM) of dodecanethiol molecules on the surface, which gives rise to a reduced bonding strength between the top two layers of gold atoms. The gold atoms and associated adsorbed molecules are peeled off and displaced laterally by the STM tip, and the size of the modified area (down to ∼10×10 nm) is more or less determined by the scan size.
Solid–fluid coexistence of the Lennard-Jones system from absolute free energy calculations
Authors: Barroso M. A. , Ferreira A. L.
Published: July 2002

The thermodynamic properties of coexisting solid and fluid phases are computed for the Lennard-Jones system. We make absolute Helmholtz free energy calculations for fluid and solid reference thermodynamic states and we compute differences in free energy relatively to these states in order to obtain thermodynamic properties in a range of temperatures and densities. For the free energy difference calculations we use a previously developed method [A. L. Ferreira and M. A. Barroso, Phys. Rev. E 61, 1195 (2000)]. Our results are compared with others available in the literature. Furthermore, we present absolute values of the Helmholtz free energy along solid–fluid coexistence lines.
Single spatial mode experiments on initial laser imprint on direct-driven planar targets
Authors: Nakai M. , Azechi H. , Miyanaga N. , Shigemori K. , Kawasaki T. , Nagaya T. , Nishikino M. , Kanai Y. , Ohnuki D. , Nishimura H. , Shiraga H. , Maegawa O. , Ishizaki R. , Nishihara K. , Takabe H. , Yamanaka T.
Published: July 2002

Flat plastic targets were directly irradiated and accelerated by partially coherent light from the GEKKO XII laser [Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] with the wavelength of 0.53 μm in order to investigate initial laser imprinting. The growth of the perturbation imprinted on the target by an initial foot pulse modulated with a single spatial frequency was observed by the face-on x-ray backlight technique. Imprint levels produced by the foot beam with a stationary intensity modulation of the illumination profile and with a dynamically changing modulation were successfully obtained by an image relay technique and the improved two-wavelength Young’s interference method. Simple analytic models are proposed and compared with the experimental results. Stationary imprinting with perturbation wavelength longer than the target thickness is found to be well described by a simple incompressible model. The dynamic dependence of the imprint on the time scale of the temporal illumination profile is found to be qualitatively explained by linear perturbation analysis.
The significance of cluster lifetime in nucleation theory
Authors: Barrett Jonathan C.
Published: July 2002

Collisions between vapor monomers and small clusters may create short-lived states that will decay before undergoing equilibriating collisions with other (vapor or gas) molecules. As the vapor pressure (and hence the number of monomer–cluster collisions) increases, the number of such decays will increase, in contrast to the usual assumption that cluster decay rates are independent of the external vapor pressure. Such short-lived clusters should therefore be excluded from consideration in nucleation theory. The effect of excluding clusters with lifetimes less than a specified value τ is investigated by evaluating the partition function for clusters of 2, 3, and 4 molecules interacting via a Lennard-Jones potential. Calculations are performed by Monte Carlo integration, with a molecular dynamics simulation performed at each Monte Carlo point to determine whether the monomers remain within a specified distance of their center of mass a time τ later. Results are compared with those from other cluster definitions, including classical theory and constant volume clusters. Values are approximately independent of τ provided it is not too small, and exhibit a stronger decrease with increasing temperature than those from other cluster definitions. Making classical nucleation theory consistent with the population of long-lived small clusters (instead of with the monomer population) would therefore reduce the temperature dependence of theory.
On transport across a barotropic shear flow by breaking inertia-gravity waves
Authors: Staquet C. , Huerre G.
Published: July 2002

We investigate the interaction of an inertia-gravity wave packet with a barotropic dynamical barrier, by means of three-dimensional direct numerical simulations of the Boussinesq equations in a rotating reference frame. A simple model is used for the barrier, namely a barotropic shear layer with a horizontal shear. We show that the increase of the intrinsic frequency Ω of the wave packet by Doppler shifting may result in the breaking of the wave packet, in the neighborhood of a trapping plane where Ω=N(N is the Brunt–Väisälä frequency of the fluid and is constant in the present study). The breaking process triggers a turbulent diffusive transport of mass and momentum across the barrier, with a turbulent Prandtl number of order 1.
Centrifugal instability of semidilute non-Brownian fiber suspensions
Authors: Gupta V. K. , Sureshkumar R. , Khomami B. , Azaiez J.
Published: July 2002

Linear stability of the Taylor–Couette (TC) flow of semidilute non-Brownian suspension is investigated by utilizing the fiber orientation model developed by Hinch and Leal [J. Fluid Mech. 76, 187 (1976)] in conjunction with a quadratic and hybrid closure proposed by Advani and Tucker [J. Rheol. 34, 367 (1990)]. It is found that irrespective of the closure approximation used the fiber additives suppress the centrifugal TC instability, i.e., the critical Reynolds number (Re) increases with the fiber volume fraction and aspect ratio as well as the interfiber interaction coefficient. This increase in the critical Re is significantly larger than that in the total viscosity, except for very small values of the volume fraction and the interaction coefficient. The enhanced stabilization can be attributed to the fact that the suspension develops negative first and second normal stresses in the TC flow when the inner cylinder rotates and the outer one is stationary, i.e., the fluid is in a state of compression. Moreover, the interfiber interactions result in alignment of the fiber orientation tensor with respect to the rate of deformation tensor. This coupling enhances the ability of the fluid elements to resist the amplification of radial velocity disturbances that give rise to the centrifugal instability. This mechanism is substantiated based on a rigorous energy analysis, demonstrating that the coupling between the fiber orientation and perturbation radial velocities gives rise to fiber-induced perturbation shear stresses that are dissipative. Specifically, the coupling of fiber-induced perturbation shear stresses with the base flow velocity leads to a compressive force that dissipates energy leading to the suppression of the centrifugal instability.
Carbon 1s photoelectron spectroscopy of CF4 and CO: Search for chemical effects on the carbon 1s hole-state lifetime
Authors: Carroll Thomas X. , Børve Knut J. , Sæthre Leif J. , Bozek John D. , Kukk Edwin , Hahne Jeffrey A. , Thomas T. Darrah
Published: July 2002

Carbon 1s photoelectron spectra for CF4 and CO have been measured at several photon energies near the carbon 1s threshold. The spectra have been analyzed in terms of the vibrational structure and the natural linewidth. For CO the vibrational structure shows evidence for anharmonicity in both the energy spacing and the intensity. Analysis of the results using an anharmonic model gives an equilibrium bond length for core-ionized CO that is 4.85 pm shorter than that of neutral CO. For CF4, the vibrational structure is very weak, and the analysis shows that the change in equilibrium CF bond length upon ionization is no more than 0.54 pm. Ab initio theoretical calculations give results in accord with these bond-length changes. The unusually small bond-length contraction in CF4 can be understood in terms of nonbonded fluorine–fluorine repulsion. The natural linewidth for core-ionized CO, 95±5 meV, is essentially the same as that of CH4. This result is in contrast with expectations based on the one-center model of Auger decay and earlier predictions based on semiempirical molecular orbital theory. More recent calculations indicate, however, that there is only a small difference between CO and CH4, in agreement with the observed result. For CF4, the natural linewidth is 77±6 meV. This value differs from that for CH4 in the direction expected from the electronegativities of hydrogen and fluorine, but is greater than the prediction based on semiempirical theory. The natural linewidth for CO with a carbon 1s electron excited to the 2π resonance is 83 meV, which is significantly less than is found for core-ionized CO. Although this difference is supported by theoretical calculations, the direction of the difference is counterintuitive. An overview is presented of the current state of experimental and theoretical knowledge on carbon 1s linewidths.
Semiclassical mechanics of bound chaotic potentials
Authors: Dahlqvist Per
Published: July 2002

Semiclassical methods for determining quantum eigenvalues in chaotic systems are discussed. A recent calculation for an open scattering system with Axiom-A properties serves as a starting point for the discussion. How deviation from Axiom-A properties, such as intermittency and occurrence of small stability islands, normally arise in bound Hamiltonian systems, and how these deviations complicate the calculation of semiclassical eigenvalues are demonstrated. It is also stressed that since such deviations are typical of bound Hamiltonian systems, they might be of crucial importance for the statistical properties of the energy levels.
Oxidation-enhanced diffusion of ion-implanted boron in silicon in extrinsic conditions
Authors: Miyake Masayasu
Published: July 2002

Oxidation-enhanced diffusion (OED) of ion-implanted boron has been studied in extrinsic conditions, i.e, in a high boron concentration range by a new isoconcentration method using secondary ion mass spectroscopy (SIMS). In the isoconcentration method, 10B has been used as a tracer and 11B as a base, considering the SIMS measurement sensitivity. For isoconcentration diffusion at 950 and 1000 °C, diffusion coefficients both in N2 ambient and in dry O2 ambient increase with boron concentration in extrinsic conditions. The diffusion coefficient in dry O2 is larger than that in N2, i.e., OED is observed for boron concentration from intrinsic conditions to 1020 cm−3. The increment in the diffusion coefficient due to OED is constant for the boron concentration range of 2×1019–1×1020 cm−3, and is 2–3.5 times larger than that in intrinsic conditions. On the other hand, for boron implantation into intrinsic substrates, i.e., nonisoconcentration diffusion at 950 and 1000 °C, OED decreases with the dose and disappears at a 1015 cm−2 dose which has a peak boron concentration of about 4×1019 cm−3. The OED disappearance at the 1015 cm−2 dose is attributed to the loss of silicon interstitials by the residual damage due to implantation.
Selective focusing of different ion species produced by magnetically insulated ion beam diodes
Authors: Dreike P. L. , Miller P. A.
Published: July 2002

Research in light-ion-driven inertial-confinement fusion is emphasizing high-voltage, nonprotonic ions to obtain improved magnetic stiffness. Target preheat by coaccelerated proton impurities is a serious concern. A method is described which should essentially eliminate protonic preheat for applied magnetic field, magnetically insulated (applied-B) ion diodes. Briefly, the charge state of the principal ion species is changed by passing through a thin foil in the applied magnetic field. Due to the change in canonical angular momentum, the ions’ closest approach to the axis of an axisymmetric diode is different from that of the proton contaminant. This difference provides effective separation of protons from the principal species.
Calculation of the electron velocity distribution in high electron mobility transistors using an ensemble Monte Carlo method
Authors: Wang T. , Hess K.
Published: July 2002

The electron velocity distribution is calculated for an idealized model of the high electron mobility transistor using a many-particle Monte Carlo model and a self-consistent two-dimensional Poisson solver. Hot electron effects, nonstationary effects, and real space transfer are analyzed. The results show that significant velocity overshoot, 2.8×107 cm/s at 300 K and 3.7×107 cm/s at 77 K exists under the gate and that the velocity overshoot is limited by both k-space transfer and real-space transfer. The values of the overshoot velocities are much smaller than those obtained from the more conventional drift-diffusion model.
Transmission electron microscope and transmission electron diffraction observations of alloy clustering in liquid-phase epitaxial (001) GaInAsP layers
Authors: Norman A. G. , Booker G. R.
Published: July 2002

Transmission electron microscope examinations performed on liquid-phase epitaxial GaInAsP layers grown on (001) InP substrates showed a coarse tweed structure (∼150-nm scale) and a fine granular structure (∼15-nm scale). Transmission electron diffraction patterns revealed main spots with associated satellite spots, indicating the presence of periodic variations in lattice parameter along the [100] and [010] directions and of wavelength corresponding to the fine granular structure. The particular behavior depended on the alloy layer composition. Both structures are attributed to alloy clustering arising from spinodal decomposition.
A comparison of rapid thermal annealing and controlled atmosphere annealing of Si-implanted GaAs
Authors: Kanber H. , Cipolli R. J. , Henderson W. B. , Whelan J. M.
Published: July 2002

The chemical and electrical characteristics were measured of 100-keV Si+-implanted GaAs at doses of (6 – 10)×1012 cm−2 after rapid thermal annealing (RTA) for times of 5–40 s at temperatures between 850 and 975 °C. Optimal conditions were 5 s at 930 °C in either Ar or Ar–H2 atmospheres. Purity of the gas ambient was critical at the higher temperatures. Surface degradation was minimal for face-to-face annealing, as compared to exposed SiO2 encapsulated surfaces. Essentially identical electrical characteristics were obtained by the preferred RTA conditions as compared to 30-min conventional furnace annealing under optimum conditions at 850 °C using the controlled atmosphere technique. The markedly different RTA annealing times with comparable electrical characteristics are attributed to the differences in the host lattice damage recovery resulting from heat transfer and the actual duration to reach the desired anneal temperature.
Surface-wave propagation along the boundary between sea water and one-dimensionally anisotropic rock
Authors: Pan Wei-Yan
Published: July 2002

New formulas for the components of the electromagnetic surface wave propagating along the boundary between sea water (Region 1) and a one-dimensionally anisotropic rock (Region 2) have been obtained. The conductivity of the rock is taken to be σx=σy=σT, σz=σL, where z is perpendicular to the boundary. Both σL and σT are constant. When σL=σT, the new formulas coincide with those of Wu and King [Radio Sci. 17, 521, 532 (1982); J. Appl. Phys. 54, 507 (1983)] for an isotropic medium. When σL≠σT, the lateral-wave part of the field is separated into two terms of which the first is of electric type with the wave number k2=kL, and the second is of magnetic type with k2=kT. The new formulas can be used to interpret recent measurements of the oceanic crust.
Heavy metal gettering in silicon-on-insulator structures formed by oxygen implantation into silicon
Authors: Kamins T. I. , Chiang S. Y.
Published: July 2002

Gettering of chromium and copper metal impurities to the damaged regions surrounding an implanted buried oxide has been investigated. Cr tends to segregate to the surface Si-SiO2 interface; only a small fraction moves to the damaged regions surrounding the buried oxide. Cu segregates to the damaged regions more readily; in addition, a large fraction of the implanted Cu moves to a location several micrometers beneath the buried oxide layer. The buried oxide does not appear to stop the movement of the Cu.
Investigation of the nonlinearity in the luminescence of GaAs under high-density picosecond photoexcitation
Authors: Von Lehmen A. , Ballantyne J. M.
Published: July 2002

We report extensive experimental measurements of the nonlinearity in the band-band recombination luminescence in GaAs both broadband and as a function of wavelength, doping, and photoexcitation density. The results of a simple rate equation model which includes the bimolecular term show good qualitative agreement with the data. The implications of the nonlinearity for pump-probe-type time-resolved measurements are discussed.
Vibrational spectra of polysilane alloys
Authors: Furukawa Shoji , Matsumoto Nobuo , Toriyama Takeshi , Yabumoto Norikuni
Published: July 2002

Infrared (IR) absorption and Raman spectra are measured for glow-discharge-produced, wide-optical-gap binary Si:H alloys containing a number of polysilane (SiH2)n groups (polysilane alloys). The highly resolved IR stretching band revealed double peaks, at 2100 and 2122 cm−1, which correspond to an exterior SiH2 and an interior SiH2, respectively, in a 3/4 Si(SiH2)nSi 3/4 group. This result provides evidence for the existence of (SiH2)n (n≥3) groups. Nonlinearity of the (SiH2)n wagging absorption strength with the number of SiH2 units in the alloy is observed in the IR spectra. This is related to a change in the polymerization degree of a (SiH2)n chain. Raman scattering intensity in the 50–400 cm−1 range is lower than that for conventional hydrogenated amorphous silicon alloys, suggesting a reduction in the number of Si loops arising from (SiH2)n chain formations. The change in the polymerization degree as a function of substrate temperature during deposition and the annealing temperature are also discussed.
Investigation of the kinetic mechanism for the ion-assisted etching of GaAs in Cl2 using a modulated ion beam
Authors: McNevin S. C. , Becker G. E.
Published: July 2002

There is increasing technological interest in using Cl2 and Cl-containing compounds in the dry plasma etching of III–V semiconductors. This paper presents a study of the ion-assisted etching of GaAs by Cl2 using a modulated ion beam technique to gain insight into the kinetic mechanism of this process. The etching rate increases with increasing ion energy (0.3–3 kV) and depends linearly on ion flux (1.0–10.0×1014 ions cm2 s). The etching rate increases with increasing Cl2 pressure up to a saturation limit near 2×10−6 Torr. This saturation limit is independent of the ion flux coincident on the surface within the range studied. The ion-enhanced etching rate decreases with increasing sample temperature over the range 300–500 K. Major etch products are AsCl3 and GaCl2 (and possibly GaCl), and the time dependence of the increase in these mass spectrometer signals following the initiation of the ion pulse is consistent with all of the products having a most probable translational energy of ∼0.14 eV. There is an additional delay in the appearance of the AsCl3 signal which roughly corresponds to a first order reaction with an associated time constant of 1.1 ms. One possible kinetic mechanism for the ion-enhanced etching is proposed which involves the surface reactions of Ga and AsCl with adsorbed chlorine. In this model, the ∼1 ms delay in the appearance of the AsCl3 is attributed to the lifetime of potential energy excitation caused by the ion.
K
u-band radiation produced by a relativistic backward wave oscillator
Authors: Leifeste Gordon T. , Earley Lawrence M. , Swegle John A. , Poukey James W. , Miller R. Bruce , Crist Charles E. , Wharton Charles B. , Ballard William P.
Published: July 2002

Reported in this paper are the results of an experiment to produce high-power Ku-band (12–18 GHz) microwave radiation from a backward wave oscillator (BWO) driven by a relativistic electron beam. Experimentally measured output power was about 250 MW at 12.5 GHz and 100 MW at 14 GHz. A description of the slow wave structure is given along with theoretical predictions of the vacuum waveguide dispersion relations. The diagnostics to determine the frequency and power of the device are described. Finally, comparisons between the experimentally measured frequency and power, and the analytic and numerical simulations of the BWO are made.
Oxygen precipitation retardation and recovery phenomena in Czochralski silicon: Experimental observations, nuclei dissolution model, and relevancy with nucleation issues
Authors: Tan T. Y. , Kung C. Y.
Published: July 2002

We report experimental results of an oxygen precipitation study carried out using Czochralski silicon wafers. A two-step anneal scheme was employed: a lower-temperature step (at 650 or 750 °C for 0–128 h) for SiO2 precipitate nucleation and a higher temperature step (at 1050 °C for 0–64 h) for growth. The oxygen precipitation rate is monitored by measuring the interstitial oxygen (Oi) concentration in the silicon lattice. We have found that (i) a precipitation retardation phenomenon exists for wafers that received prolonged nucleation annealing treatment (from 2 to 16 h), and (ii) this retardation phenomenon gives way to a precipitation recovery phenomenon for wafers that received still longer nucleation annealing treatment (for 8–128 h). We also describe a nuclei dissolution model to explain the retardation/recovery phenomena. The dissolution proceeds against an Oi supersaturation which would normally drive the nuclei into growth.

The most important aspects of the model are (i) the dissolution occurs at the onset of the high-temperature growth anneal step, (ii) the factor directly opposing the Oi supersaturation and leading to the nuclei dissolution process is attributed to a large supersaturation of silicon self-interstitials (I supersaturation), essentially also generated at the onset of the growth anneal step, (iii) the generation of the I supersaturation is associated with a nuclei/precipitate polymorph change again occurring at the onset of the growth anneal step. The fundamental physical cause leading to these phenomena is the exigent-accommodation volume (or exigent volume) associated with precipitate growth. This model can explain the present results and is consistent with many other experimental results. We then examine the relevance of the exigent-volume factor with nucleation issues such as its effect on ramping, the effect of carbon, the existence of multiple polymorphs of SiO2, multiple nucleation paths, and a nucleation incubation phenomenon. We believe contributions of the exigent-volume factor to the nucleation phenomena generally exist.
Stability of transverse self-sustained discharge-excited long-pulse XeCl lasers
Authors: Coutts J. , Webb C. E.
Published: July 2002

Instability mechanisms discussed to date are unable to account for the behavior of long-pulse self-sustained discharge-pumped XeCl devices. We develop theoretical arguments supporting the concept that halogen donor depletion during the discharge pulse is the principal cause of discharge collapse and the termination of lasing. The theoretical prediction that the duration of the glow phase should vary as the inverse square of the initial halogen donor concentration is verified by experimental results furnished by a study of a resistively stabilized long-pulse xenon chloride laser.
Real-time characterization of the photoresist/substrate interface
Authors: Hager Harold E. , Escobar Glenn A. , Verge Peter D.
Published: July 2002

The use of a piezoelectric crystal as the substrate for a photoresist film provides unique resist characterization capabilities. In particular, the photoresist near the substrate is probed in real time. The basis of this measurement technique is described, emphasizing the physical phenomena responsible for observed piezoelectric crystal response behavior. Demonstration of this analysis to a gelatin-based resist is given. The influence of solvent drying is readily distinguishable from the effects of photohardening reactions.
Magnetic insulation of extraction Applied-B ion diodes
Authors: Slutz Stephen A. , Seidel David B.
Published: July 2002

The difference in the operation of extraction geometry versus radial geometry Applied-B ion diodes is explained through the use of a general magnetic insulation condition for cylindrically symmetric ion diodes which is expressed in terms of the magnetic stream function. We find that Applied-B extraction geometries attempted so far have suffered from a magnetic field configuration defect which explains their rather poor performance. We present solutions to the extraction Applied-B ion diode problem, as well as 2D, electromagnetic particle-in-cell simulations of an example solution.
Optimization of BF2+ implanted and rapidly annealed junctions in silicon
Authors: Wu I-W. , Fulks R. T. , Mikkelsen J. C.
Published: July 2002

The electrical properties and defect characteristics of shallow junctions fabricated by using BF2+-ion implantation and followed by either furnace or rapid thermal annealing (RTA) have been investigated. The RTA temperature-time cycle was optimized in terms of leakage current, junction depth, and sheet resistivity of junctions. Specifically, shallow p+ junctions (∼180 nm) with low leakage current (∼2 nA/cm2 at −5 V) were obtained with 49-keV, 2×1015-cm−2 BF2+ implantation and RTA at 1050 °C for 15 s. The effects of a Si+ preamorphizing implant and pre- or post-RTA low-temperature furnace anneal were also studied. p+/n diodes fabricated with a preamorphizing implantation exhibit about 3 orders of magnitude higher leakage current than the diodes without preimplantation. The excessive leakage current of the preamorphized junctions arises from a band of post-annealing defects located in the depletion region of the n well (from ∼220 to 420 nm). Samples without the Si+ implant have very shallow and narrow defect bands (from ∼70 to 120 nm) located inside the heavily doped p+ region. The depth distribution of post-annealing defects corresponds to the partially amorphized (heavily damaged) regions near the as-implanted crystalline/amorphous interfaces. Furthermore, a low-temperature furnace anneal (550 °C for 1 h) before or after RTA treatment reduces leakage current for diodes without preimplantation. This reduction of leakage current by the two-step annealing coincides with the relaxation of the implant-induced stress in the junction, as measured by substrate curvature. The post-RTA anneal is found to be more effective than the pre-RTA anneal, both in terms of leakage current and the amount of stress relief. Channeling tails were observed in secondary-ion mass spectrometry boron profiles of BF2+-implanted samples, and Si+ preamorphization eliminates them. However, identical carrier concentration profiles are obtained by spreading carrier-resistance measurements for samples with or without preamorphization, which suggests that the channeled boron atoms remain in the interstitial sites after RTA and hence are inactive.
Line-broadening analysis of synchrotron x-ray diffraction data
Authors: Huang T. C. , Hart M. , Parrish W. , Masciocchi N.
Published: July 2002

The advantages of using monochromatic and parallel synchrotron x rays for the microstructure analysis of polycrystalline materials have been studied. Analysis of line broadening from Pd powers showed encouraging results. Warren–Averbach analysis [J. Appl. Phys. 21, 595 (1950)] with respect to the three major crystal axes [111], [100], and [110] was done using 1-Å x rays. Crystallite sizes and microstrains relative to the [111] direction were obtained using three different reflection pairs (111)-(222), (111)-(333), and (111)-(444). The fixed symmetrical instrument profile shape has major advantages in the correction of instrumental broadening and the determination of a low level (10−4 range) of stacking-fault probabilities.
Tunable cw laser operation in the 1.45–2.16 μm range based on F+2-like centers in O−2 doped NaCl, KCl, and KBr crystals
Authors: Wandt D. , Gellermann W. , Luty F. , Welling H.
Published: July 2002

In additively colored NaCl, KCl, and KBr crystals doped with O−2 anionic molecular impurities, a laser active defect is formed by optically induced association of F centers with oxygen-vacancy defect pairs. The formed defect has F+2 -like properties in terms of optical transition energies, Stokes shift, and optical gain. It can be regarded as an F+2 center attached in different possible configurations to a neighboring double negatively charged oxygen anion impurity which replaces a halide ion. Stable cw laser operation could be realized, so far, in the hosts NaCl, KCl, and KBr. Pumped with 10 W at 1.064 μm the NaCl center laser was tunable from 1.45 to 1.74 μm with 1.3 W peak output power at 1.60 μm. The KCl and KBr systems, both pumped at 1.32/1.34 μm, were tunable from 1.66 to 1.97 μm with 170 mW peak output, and from 1.86 to 2.16 μm with 30-mW peak output, respectively. Depending on the host material the laser crystals do or do not require auxiliary light exposure exciting the higher-energy transitions of the laser active center in the F center absorption range. The auxiliary F light produces and maintains, by induced F+2 center reorientation, the laser active defect configuration in NaCl and KBr, while in KCl it separates the F+2 center from the O−− impurity.
Cycle life, stability, and characteristics of color switching cells utilizing polythiophene films
Authors: Kaneto K. , Agawa H. , Yoshino K.
Published: July 2002

Cycle life, stability, and switching characteristics of a color switching device utilizing a conducting polymer, polythiophene film in an electrochemical cell are studied. Cycle life of more than 5×105 times has been achieved by operation with an appropriate rectangular voltage application in an electrolyte of Pb(ClO4)2/acetonitrile. A chronoabsorptometric measurement is carried out to inspect the kinetics of electrochemical cycle. The diffusion of charged species in the film is found to control the switching time and its constant is evaluated to be 10−12–10−10 cm2/s as a function of applied voltage. The doping mechanism and dopant distribution profiles in the film are proposed for various conditions of applied voltages. Stability and cycle life of the cell during switching, and memory state under an applied voltage are discussed in terms of the degradation of polythiophene film.
Sample size effect in coercivity measurement of epitaxial magnetic garnet films
Authors: Vértesy G. , Pardavi-Horváth M. , Tomás̆ I. , Půst L.
Published: July 2002

The full set of characteristic parameters of epitaxial garnet films was measured as a function of the sample size from about 2000 to 5 mm2. The type of domain structure, width of the stripe domain period, characteristic material length, domain wall energy, and anisotropy did not change within the error of measurement on reducing the sample size. The bubble domain collapse field decreased by about 2.5%, and the domain wall coercivity was measured and found to have decreased—almost by an order of magnitude. The experiments showed the lack of dependence of coercivity on the domain wall length. The coercivity and collapse field are suggested as being related to the sample dimensions via the sample-size-dependent derivatives of the total free energy with respect to the domain wall positions. The assumption of the direct effect of the free energy derivatives on the coercivity is supported by a model experiment.
Production of atomic or molecular nitrogen ion beams using a multicusp and a microwave ion source
Authors: Walther S. R. , Leung K. N. , Kunkel W. B.
Published: July 2002

Two small ion sources have been used to generate positive nitrogen ion beams. One is a multicusp ion source, the other is a compact microwave ion source which needs no magnetic field for operation. Both sources are operated with and without a magnetic filter to control the energetic electron population near the extraction region. Results for both ion sources, including current densities and ionic species mix are presented. The multicusp ion source can produce beams of nitrogen ions with greater than 90% of the ion species either N+ or N+2 with current densities of ∼8 and 2.5 mA/cm2, respectively. The microwave ion source can generate nitrogen ion beams composed of more than 85% N+2 with current densities of ∼30 mA/cm2.
All-electron study of c(2×2) S chemisorbed above magnetic Fe(001)
Authors: Chubb S. R. , Pickett W. E.
Published: July 2002

We have performed a first-principles study of the adsorption of sulfur above a magnetic Fe surface. Our results, derived from the all-electron, film full-potential augmented-plane-wave method applied to a seven-layer Fe film with and without c(2×2) overlayers of S, include determinations of the equilibrium sulfur height (heq) and vibrational frequency, as well as the associated electronic and magnetic structures. We find excellent agreement between our calculated value (1.12 Å) of heq with the earlier result (1.09±0.05 Å) derived by Legg et al. from a dynamical low-energy electron diffraction intensity analysis. The adsorption induces antibonding minority surface states immediately above and below EF which play an important role both in reducing the magnetic moment of the surface Fe atom (by ∼20%) and in the resulting calculated increase (0.86 eV) in work function. These states should be clearly resolvable in both integrated and angle-resolved spin-polarized photoemission and inverse-photoemission experiments. We present additional predictions, including the adsorption-induced changes in the hyperfine fields.
Low-temperature GaAs epitaxial growth using electron-cyclotron resonance/metalorganic-molecular-beam epitaxy
Authors: Tanaka Yoshimitsu , Kunitsugu Yasuhiro , Suemune Ikuo , Honda Yoshiaki , Kan Yasuo , Yamanishi Masamichi
Published: July 2002

A low-temperature GaAs epitaxial growth method called electron-cyclotron resonance molecular-beam epitaxy was newly developed. Triethylgallium (TEGa) and triethylarsine (TEAs) were used as source gases and were introduced without thermal decomposition. The method has the advantage of cleaning the GaAs substrate at the growth temperature just prior to growth as well as to decompose metalorganics with the hydrogen plasma activated by the cyclotron resonance. The epitaxial GaAs film was successfully grown at a temperature as low as 300 °C. All samples grown at 400 °C exhibited p-type conductivity for (arsine/gallium) ratios between 4 and 13. The p-type carrier concentration was strongly dependent on the (arsine/gallium) ratio and was in the range of 1016 –1019 cm−3 .
Effect of polymer matrices on hole transport of 1,2-t
r
a
n
s-bis(9H-carbazole-9-yl) cyclobutane dissolved in a polymer binder
Authors: Sasakawa Tomoyoshi , Ikeda Tomiki , Tazuke Shigeo
Published: July 2002

Hole drift mobilities have been measured in films of solid solutions of trans-1,2-bis (9H-carbazole-9-yl) cyclobutane (DCZB) in various polymer binders. The hole drift mobilities differ by more than two orders of magnitude depending on the polymer binder used. In poly (methacrylates) films the hole drift mobility is large and the temperature dependence is small when the glass transition temperature of pure polymer is about 50 °C. The difference in rotational mobility of DCZB molecules is considered as the origin of this binder and temperature dependence on the hole mobility.
Measurements of temporal and spatial characteristics of electrohydrodynamic instabilities
Authors: Pregenzer Arian L. , Woodworth Joseph R.
Published: July 2002

Since an electrohydrodynamically (EHD) driven liquid-lithium ion source is being developed for experiments on the Particle Beam Fusion Accelerator II at Sandia National Laboratories, EHD experiments have been started with several liquids. In this paper, we present results of experimental studies of the behavior of the surface of water and ethanol in the presence of 15–40-kV/cm dc electric fields. Fields of this magnitude can produce unstable growth of surface perturbations with wavelengths in the 0.1–1.0 cm range. There is excellent agreement between theory and experiment for values of the wavelength of the dominant mode as a function of the applied electric field E0. Theoretical predictions about the temporal behavior of cusp formation are consistent with experiment. The experimental results are applicable, via scaling laws, to liquids in the presence of electric fields in the 1–50 MV/cm range, where unstable surface perturbations may produce field enhancements sufficient to field evaporate ions from the liquid surface.
A simple technique for determining the interface-trap distribution of submicron metal-oxide-semiconductor transistors by the charge pumping method
Authors: Hofmann F. , Krautschneider W. H.
Published: July 2002

The charge pumping method has been modified to simplify the experimental procedure and data evaluation. The width of a pulse section at midgap voltage was varied to scan the interface-state distribution within the band gap. A straight-forward analysis yields simple evaluation of interface-state distribution. The results obtained from a conventional and a submicron lightly doped drain metal-oxide-semiconductor transistor are presented.
Application of a semiempirical self-consistent-field band calculation to near-edge fine-structure analysis of core-shell electronic absorption edges
Authors: Ma H. , Skiff W. M. , Wu G. S. , Lin S. H. , Carpenter R. W.
Published: July 2002

A modified parametrization of the complete neglect of the differential overlap molecular orbital method is applied to energy-band calculations of solids. Results of the band calculation are used to calculate the near-edge fine-structure of core-shell electronic absorption edges in electron energy loss spectra. Preliminary application is made to silicon crystal.
Infrared photoluminescence of InAs epilayers grown on GaAs and Si substrates
Authors: Grober Robert D. , Drew H. D. , Chyi Jen-Inn , Kalem S. , Morkoç H.
Published: July 2002

We report the results of infrared photoluminescence and optical transmission measurements of InAs epilayers grown on both Si and GaAs substrates. Photoluminescence reveals four well-defined peaks associated with band-to-band transitions and impurity/defect associated transitions. The spectra of the epilayers grown on Si are red shifted by roughly 15 meV relative to that of the epilayers grown on GaAs. In addition, optical transmission measurements reveal two intrinsic absorption edges for the epilayers grown on Si. These data are interpreted in terms of biaxial strain induced between the epilayer and the substrate due to differing indices of linear thermal expansion.
Stability of frequency domain information bits in amorphous organic materials
Authors: Köhler W. , Zollfrank J. , Friedrich J.
Published: July 2002

We investigate the stability of frequency domain information bits as a function of time and temperature fluctuations. A large body of experimental results for a variety of organic materials is presented and analyzed in terms of phenomenological models on spectral diffusion and dispersive kinetics.
Small particle size distributions from mobility measurements
Authors: Sanders T. M. , Forrest S. R.
Published: July 2002

We report experiments performed on iron particles with radii in the range 40–100 Å, produced by pulsed evaporation from an electroplated tungsten filament in a cryogenic helium gas atmosphere. Flight times in electric fields of singly charged particles produced in the evaporation process yield values for gas velocity and charged particle mobility. Particle size distributions are determined both by electron microscopy and from the mobility. The latter method yields particle size distributions quickly and with good statistics, but with indicated radii larger by about 20 Å than those determined by electron microscopy. The discrepancy, which is most important for the smallest particles, is attributed to the effect of van der Waals interaction between the iron particles and the gas atoms. Comparison is made with theory, which connects the van der Waals interaction with the dielectric response functions. For particles in this size range, a van der Waals interaction determined from bulk iron data gives a satisfactory explanation of the discrepancy.
Numerical analysis of the spin-coating process
Authors: Shimoji Sadao
Published: July 2002

The effects of solvent evaporation and non-Newtonian characteristics on the flow of polymer solutions on a flat rotating disk were analyzed theoretically and numerically. The solvent evaporation was evaluated from species conservation. The power-law and Carreau models were used for the non-Newtonian characteristics. The dependency of the dry-film thickness on the initial concentration of solute predicted by the Newtonian fluids agreed well with the reported experimental data. The thickness predicted decreased with the −0.658th power of spin speed for Newtonian fluids and decreased faster with the −2/(2n+1) power for power-law fluids, where n<1 is the power-law index, in contrast to most experimental values of about −0.5. The Carreau model predicted a similar value as for Newtonian fluids. To resolve the discrepancy between the theoretical prediction and experimental data, the mass transfer coefficient from liquid to vapor was assumed to increase the pth power of spin speed, as assumed by Meyerhofer [J. Appl. Phys. 49, 3993 (1978)]. The choice of the value of p then successfully explained various the experimental data.
Infrared reflection spectroscopy of the SiO2-silicon interface
Authors: Olsen J. E. , Shimura F.
Published: July 2002

An infrared reflection technique, devised to study the structure of very thin films on substrates of high refractive index, yields an optical spectrum amplification of three orders of magnitude. With the aid of an infrared polarizer, an unanticipated peak at 1240 cm−1 in the internal reflection spectrum of thin (5–100 Å) thermal SiO2 films on silicon has been identified as a longitudinal optical phonon peak. The unambiguous identification of this peak supports a similar interpretation of the 1230-cm−1 peak in oxygen-containing silicon first proposed by Hu in 1980.
Xerographic studies of charge trapping in layered organic photoconductors
Authors: Kanemitsu Yoshihiko , Funada Hiroshi , Imamura Shunji
Published: July 2002

Charge trapping in layered organic photoconductors consisting of a charge generation layer (CGL) and a charge transport layer (CTL) was studied by xerographic residual potential measurements. The residual potential builds up during repeated corona charging and light exposure cycles of photoconductors. The negative residual potential is proportional to the square of the CGL thickness and is linearly proportional to the CTL thickness. The square dependence is caused by the bulk trapping of electrons in the CGL, and the linear dependence is due to the negative charges on the CTL surface. From experimental results, it is concluded that the electron trapping in the CGL enhances the trapping of holes at the CGL/CTL interface, and consequently a fraction of negative corona charges remains on the CTL surface even after light exposure. The buildup of the residual potential during xerographic cycling is initiated by the electron trapping in the CGL. On the other hand, the decay rate of the residual potential after xerographic cycling depends on hole transport properties in the CTL. The activation energy for the decay of the residual potential is in good agreement with that for the drifting of holes through the CTL obtained from thermally stimulated current measurements. The decay rate of the residual potential is controlled by the surface charge neutralization process which involves the release of holes trapped at the CGL/CTL interface and the subsequent drifting of holes to the surface.
Transverse effects and enhanced dispersive optical bistability in a nonlinear Fabry–Pérot filled with a self-focusing medium
Authors: Reinisch R. , Vitrant G.
Published: July 2002

This paper is concerned with transverse effects arising from diffraction in a nonlinear Fabry–Pérot filled with a self-focusing medium. It is shown that the resulting bistable loop is ‘‘enhanced’’ with respect to the plane-wave one. This result contrasts with the self-defocusing case where optical bistability disappears when decreasing the width of the input beam.
On the effect of asymmetries on the jet from a linear shaped charge
Authors: Pack D. C. , Curtis J. P.
Published: July 2002

The jet from a linear-shaped charge is formed by the collapse of the wedge-shaped liner brought about by the passage of the detonation wave through the surrounding explosive. There is a variety of possible sources of asymmetry which can affect this process. The thickness distributions along each face of the liner may vary. The detonation wave may traverse the liner asymmetrically. The quantity or other properties of the explosive adjoining the liner arms may differ. In such situations the velocities imparted to opposite liner elements at equal distances from the intersection of the arms will in general be different. Thus a pair of liner elements which do meet will in general have started from different distances down their respective liner arms, and will not meet on the axis of symmetry of the charge. This effect causes the process of formation of the jet at the meeting point to occur asymmetrically. This paper presents an investigation of this phenomenon. We generalize the classical analysis of the symmetric steady-state collapse of a liner to include the asymmetries we have described. We present an extension of the classical jet formation theory to the asymmetric case by making several simple physical assumptions. We consider an example of a typical asymmetry in liner thickness and recover values for the off-axis velocity of the jet of the order observed in experiments.
Spectroscopic ellipsometry studies of crystalline silicon implanted with carbon ions
Authors: Nguyen N. V. , Vedam K.
Published: July 2002

The composition and structure of crystalline silicon implanted with carbon ions at high dose were studied using spectroscopic ellipsometry. A brief description of our spectroscopic ellipsometer system and the modeling method adopted for the analysis of the data are included. The crystal damage caused by carbon-ion implantation in the as-implanted sample was characterized as an amorphous region of atomic or chemical mixture of silicon and carbon atoms. The recrystallization of Si and the formation of crystalline silicon carbide on annealing these specimens at 800 °C and 1000 °C were investigated through similar spectroscopic ellipsometry studies.