bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of the impurities in production rates of radiation-induced defects in silicon materials and solar cells
Authors: Khan Aurangzeb , Yamaguchi Masafumi , Ohshita Y. , Dharmarasu N. , Araki K. , Abe Takao , Itoh Hisayoshi , Ohshima T. , Imaizumi M. , Matsuda S.
Published: July 2002

The present extensive systematic study of defect introduction rates as a function of boron, gallium, oxygen, and carbon concentrations by means of deep level transient spectroscopy has drawn a quite complete picture towards the identification of the dominant radiation-induced defects in Si. The radiation-induced defect EV+0.36 eV has been identified as Ci–Oi complexes. The absence of an EC−0.18 eV complex center in gallium-doped samples and the linear dependence of its introduction rates on both the boron and oxygen content fixed its identification as the Bi–Oi complex in boron-doped Si. One of the technologically important results of present study is that the gallium appears to strongly suppress the radiation induced defects, especially hole level EV+0.36 eV (Ci–Oi), which is thought to act as a recombination center as well as the dominant compensating center at EC−0.18 eV (Bi–Oi). As a result, the effects of lifetime degradation and carrier removal could be partially offset to higher radiation fluences by using Ga as a dopant instead of boron in Si space solar cells. The anneal out of the new hole level EV+0.18 eV in gallium-doped samples at around 350 °C, together with recovery of free carrier concentration, suggests that this level may act as a donor-like center which compensates free carrier concentration in gallium-doped Si.
Nanoscale control of ferroelectric polarization and domain size in epitaxial Pb(Zr0.2Ti0.8)O3 thin films
Authors: Paruch P. , Tybell T. , Triscone J.-M.
Published: July 2002

We demonstrate that atomic force microscopy can be used to precisely manipulate individual sub-50 nm ferroelectric domains in ultrahigh density arrays on high-quality epitaxial Pb(Zr0.2Ti0.8)O3 thin films. Control of domain size was achieved by varying the strength and duration of the voltage pulses used to polarize the material. Domain size was found to depend logarithmically upon the writing time and linearly upon the writing voltage. All domains, including those written with ∼100 ns pulses, remained completely stable for the 7 day duration of the experiment.
Degenerate dynamical systems
Authors: Saavedra Joel , Troncoso Ricardo , Zanelli Jorge
Published: July 2002

Dynamical systems, whose symplectic structure degenerates, becoming noninvertible at some points along the orbits, are analyzed. It is shown that for systems with a finite number of degrees of freedom, like in classical mechanics, the degeneracy occurs on domain walls that divide phase space into nonoverlapping regions, each one describing a nondegenerate system, causally disconnected from each other. These surfaces are characterized by the sign of the Liouville flux density on them, behaving as sources or sinks of orbits. In this latter case, once the system reaches the domain wall, it acquires a new gauge invariance and one degree of freedom is dynamically frozen, while the remaining degrees of freedom evolve regularly thereafter.
Reactive ion etching of silicon carbide in SF6 gas: Detection of CF, CF2, and SiF2 etch products
Authors: Chabert P. , Cunge G. , Booth J.-P. , Perrin J.
Published: July 2002

We have detected by laser-induced fluorescence the radicals SiF2, CF, and CF2 produced during the reactive ion etching of SiC substrates in a pure SF6 plasma. Spatially and temporally resolved measurements were used to distinguish between gas phase and etched surface radical production. Whereas CF and CF2 are produced directly at the etched surface, the SiF2 radicals are produced in the gas phase (probably by electron-impact dissociation of SiF4). We attribute this difference to the formation of a carbon-rich layer on the SiC substrate surface, the removal of which produces CFx (x=1,2,3) radicals. The CF2 radical represents up to 20% of the total carbon etch products under our conditions.
Overview: Unsolved problems of noise and fluctuations
Authors: Abbott Derek
Published: July 2002

Noise and fluctuations are at the seat of all physical phenomena. It is well known that, in linear systems, noise plays a destructive role. However, an emerging paradigm for nonlinear systems is that noise can play a constructive role—in some cases information transfer can be optimized at nonzero noise levels. Another use of noise is that its measured characteristics can tell us useful information about the system itself. Problems associated with fluctuations have been studied since 1826 and this Focus Issue brings together a collection of articles that highlight some of the emerging hot unsolved noise problems to point the way for future research.
Direct observation of nanometer-scale Mg- and B-oxide phases at grain boundaries in MgB2
Authors: Klie R. F. , Idrobo J. C. , Browning N. D. , Regan K. A. , Rogado N. S. , Cava R. J.
Published: July 2002

Here we describe the results of an atomic resolution study of the structure and composition of both the interior of the grains, and the grain boundaries in polycrystalline MgB2. We find that there is no oxygen within the bulk of the grains but significant oxygen enrichment at the grain boundaries. The majority of grain boundaries contain BOx phases smaller than the coherence length, while others contain larger areas of MgO sandwiched between BOx layers. Such results naturally explain the differences in connectivity between the grains observed by other techniques.
Resistivity of RMn12−xFex alloys
Authors: Stankiewicz Jolanta , Bartolomé Juan , Morales Magali , Bacmann Madeleine , Fruchart Daniel
Published: July 2002

The electrical resistivity of RMn12−xFex (R=Er,Ho) polycrystalline system with x=0, 4, 5, and 6 was measured over the temperature range of 4 to 300 K. The resistivity increases sharply near the Néel temperature TN for x=4, 5, and 6 which, according to existing theories, can be ascribed to the formation of superzone gaps. Then, the resistivity increase should be proportional to the staggered magnetization m′ below TN, whereas we find experimentally that it is quadratic in m′. Thermal smearing of the gaps can lead to such a dependence. There is no evidence for superzone effects in x=0 compounds. A combination of spin disorder, phonon, and impurity scattering gives a good account for the experimental data.
Compressibility effects on the Rayleigh–Taylor instability of an ablation front
Authors: Piriz A. R.
Published: July 2002

The influence of the compressibility of the ablating plasma on the Rayleigh–Taylor instability of an ablation front has been analyzed by means of an extension of a previous analytical model. As a result, it is found that the effect of the compressibility is to increase the instability growth rate and to enlarge the range of perturbation wavelengths for which the front is unstable. The magnitude of such effects depends on the values of the Mach and Froude numbers and, for conditions relevant to inertial fusion, the instability may be considerably enhanced.
Infrared response of vitreous titanium dioxide films with anatase short-range order
Authors: Scarel G. , Hirschmugl C. J. , Yakovlev V. V. , Sorbello R. S. , Aita C. R. , Tanaka H. , Hisano K.
Published: July 2002

The polarization-dependent optical response of vitreous titanium dioxide films was determined by infrared reflection–absorption spectroscopy (IRAS). The predominant nearest-neighbor coordination (short-range order) in the films was characteristic of crystalline anatase. A dielectric function ε(ν) was constructed, based on random orientational disorder of anataselike, octahedral TiO6 units relative to the substrate. This dielectric function, which is the directional average of the dielectric function for an anatase crystal in the E⊥c and E∥c orientations, was used to calculate energy loss functions from which theoretical IRAS spectra were obtained. Experimental absorption band frequencies are in good agreement with peaks in the calculated transverse optic loss function, Im[ε(ν)], at 261 and 436 cm−1, and in the calculated longitudinal optic loss function, Im[−1/ε(ν)], at 840 cm−1. Agreement (i.e., polarization-dependent behavior, band frequency, and relative intensity) between the experimental and theoretical IRAS spectra indicates that orientational disorder of TiO6 units is the important factor governing infrared reflection–absorption behavior of the films.
Luminescence of nanocrystalline ZnSe:Cu
Authors: Suyver J. F. , van der Beek T. , Wuister S. F. , Kelly J. J. , Meijerink A.
Published: July 2002

A chemical synthesis is described in which ZnSe:Cu particles slowly grow to a final size of ∼3.5 nm radius in 4 h reaction time. During particle growth, samples are extracted to study the luminescence as a function of particle size and temperature. Quantum size effects are observed to influence both the ZnSe and the Cu2+ luminescence. Temperature-dependent measurements on the luminescence intensity, lifetime, and peak positions are reported and discussed.
A method of noncontact suspension of rotating bodies using electromagnetic forces
Authors: Filatov Alexei V. , Maslen Eric H. , Gillies George T.
Published: July 2002

We propose and demonstrate a method of noncontact dynamically stabilized suspension which utilizes a combination of static interaction between permanent magnets and dynamic interaction between room-temperature conductors and magnets. The suspension features a combination of properties that are not collectively provided by any of the prior technologies, including load capacity and stiffness sufficient for many applications, low rotational loss, high efficiency, high reliability, and robustness to the system parameter variations and external disturbances. The rotational loss is expected to be virtually zero if only axial loading is applied: a condition which is very easy to satisfy in stationary applications if the rotation axis is vertical. The suspension is stable for any speed above a certain critical value. The validity of this method has been demonstrated by building and testing a prototype in which noncontact suspension of a 3.2 kg rotor is achieved when it rotates at spin speeds above 18 Hz.
Three-dimensional simulations of ultrasmall metal–oxide–semiconductor field-effect transistors: The role of the discrete impurities on the device terminal characteristics
Authors: Gross W. J. , Vasileska D. , Ferry D. K.
Published: July 2002

We present results for the fluctuations in the threshold voltage and electron drift velocity in ultrasmall devices due to different numbers and distribution of impurity atoms in the device active region. We find that fluctuations in the threshold voltage VT are due to both the actual number and position of the dopant atoms. For the devices being considered, the correlation of the threshold voltage (average drift velocity) to the number of dopant atoms in a 10 nm range at various depths shows that the atoms in the top 15–20 nm (top 8 nm) beneath the channel have the most impact.
The asymptotic region of the Kohn–Sham exchange potential in molecules
Authors: Della Sala Fabio , Görling Andreas
Published: July 2002

The Kohn–Sham exchange potential is shown to approach on nodal surfaces of the energetically highest occupied orbital different asymptotic limits than in other regions. This leads to strong anisotropies and barrier–well structures in the near-asymptotic region. Effective exact-exchange potentials, like the one obtained in the recently introduced localized Hartree–Fock method, exhibit the correct asymptotic limits and the accompanying structures in the near-asymptotic region. An efficient, accurate method for the calculation of the Slater potential and of effective exact-exchange potentials in the asymptotic region is presented. The method is based on an asymptotic continuation of Kohn–Sham (KS) orbitals and is numerically stable up to arbitrary large distances from the molecule. It can easily be implemented in existing quantum chemistry codes employing Gaussian basis sets. The asymptotic region of effective exact-exchange potentials is shown to be different from the various asymptotically corrected exchange-correlation functionals and to strongly affect unoccupied KS orbitals. Results for small- and medium-size molecules are presented.
Depth-dependent investigation of defects and impurity doping in GaN/sapphire using scanning electron microscopy and cathodoluminescence spectroscopy
Authors: Sun X. L. , Goss S. H. , Brillson L. J. , Look D. C. , Molnar R. J.
Published: July 2002

Cathodoluminescence (CL) imaging and temperature-dependent cathodoluminescence spectroscopy (CLS) have been used to probe the spatial distribution and energies of electronic defects near GaN/Al2O3 interfaces grown by hydride vapor phase epitaxy (HVPE). Cross sectional secondary electron microscopy imaging, CLS, and CL imaging show systematic variations in defect emissions with a wide range of HVPE GaN/sapphire electronic properties. These data, along with electrochemical capacitance–voltage profiling and secondary ion mass spectrometry provide a consistent picture of near-interface doping by O out-diffusion from Al2O3 into GaN over hundreds of nanometers. Low-temperature CL spectra exhibit a new donor level at 3.447 meV near the interface for such samples, characteristic of O impurities spatially localized to the nanoscale interface. CLS emissions indicate the formation of amorphous Al–N–O complexes at 3.8 eV extending into the Al2O3 near the GaN/sapphire interface. CLS and CL images also reveal emissions due to excitons bound to stacking faults and cubic phase GaN. The temperature dependence of the various optical transitions in the 10–300 K range provides additional information to identify the near interface defects and impurity doping.
Impact of thermal strain on the dielectric constant of sputtered barium strontium titanate thin films
Authors: Taylor T. R. , Hansen P. J. , Acikel B. , Pervez N. , York R. A. , Streiffer S. K. , Speck J. S.
Published: July 2002

Barium strontium titanate thin films were deposited by sputtering on Pt/SiO2 structures using five different host substrates: magnesium oxide, strontium titanate, sapphire, silicon, and vycor glass. These substrates were chosen to provide a systematic change in thermal strain while maintaining the same film microstructure. All films have a weakly textured microstructure. Temperature dependent dielectric measurements from 100–500 K determined that decreasing thermal expansion coefficient of the host substrate (i.e., larger tensile thermal strain) reduced the film dielectric permittivity. The experimentally determined Curie–Weiss temperature decreased with increasing tensile thermal strain and the Curie–Weiss constant increased with tensile strain as predicted by Pertsev et al. [J. Appl. Phys. 85, 1698 (1999)].
Improved thermal stability of synthetic ferrimagnetic media with enhanced exchange coupling strength
Authors: Inomata A. , Abarra E. N. , Acharya B. R. , Ajan A. , Okamoto I.
Published: July 2002

The effect of the antiferromagnetic interlayer exchange coupling strength J between the initial or stabilization magnetic layer L1 and the top magnetic layer L2 on the thermal stability of synthetic ferrimagnetic media (SFM) is investigated. Enhanced J is achieved by the insertion of a thin Co-rich hexagonal close-packed layer between the Ru layer and L1, and such a structure did not change the read/write properties significantly. The contribution of the anisotropy energy of L1 to the thermal stability of SFM is improved by increasing J. However, a significant increase in the contribution of L1 to the thermal stability is achieved at relatively low J values (0.14 erg/cm2) which translate into only a 3–4% increase in the switching field H0.
Comments on the use of the Einstein equation for transport diffusion: Application to argon in AlPO4-5
Authors: Tepper H. L. , Briels W. J.
Published: July 2002

Two methods to calculate corrected collective diffusion coefficients in zeolites are compared. The meaning of the center-of-mass coordinate that occurs in the usual Einstein expression for the corrected diffusivity is discussed. The use of unfolded particle trajectories in the expression is shown to be only valid for periodic systems and only if the entire box is taken as the control volume. A wave vector-dependent Einstein expression is derived, equivalent to the Green–Kubo form that was derived in an earlier study [J. Chem. Phys. 113, 6875 (2000)]. The box size dependence of the diffusivities calculated from the usual Einstein equation is reproduced for small k-values when the new expression is applied to a large box.
A generalized scaling of a chiral index for molecules
Authors: Solymosi Miklos , Low Robert J. , Grayson Martin , Neal Maureen P.
Published: July 2002

We propose a scaling of an intrinsic molecular chirality index calculated from atomic positions. Its application to the design of chiral molecules through a consideration of atomic or group chiral indices is discussed for a range of molecules from small molecules to liquid crystal molecules. It is found to indicate the trend in change of chirality of a molecule caused by an atom or group substitution. Comparison is made between the method of scaling and an analytic calculation of the index for an orthogonal tetrahedron. We investigate the effect of substitution of atoms and groups in real liquid crystal molecules by application of the generalized chiral index.
Terahertz conductivity of anisotropic single walled carbon nanotube films
Authors: Jeon Tae-In , Kim Keun-Ju , Kang Chul , Oh Seung-Jae , Son Joo-Hiuk , An Kay Hyeok , Bae Dong Jae , Lee Young Hee
Published: July 2002

Absorption and dispersion of singlewalled carbon nanotube films were measured using an optoelectronic THz beam system for THz time-domain spectroscopy. The anisotropically aligned nanotube films were prepared through simple mechanical squeezing with a bar coater. The angle-dependent absorption and dispersion values were then measured. Results indicate that the index of refraction decreases with increasing frequency (0.1–0.8 THz), whereas the real conductivity increases with increasing frequency. The real conductivity measured is not congruent with the simple Drude model, but it follows a Maxwell–Garnett model, where the nanotubes are embedded in a dielectric host.
Effect of chemical stress on diffusion in a hollow cylinder
Authors: Wang W. L. , Lee Sanboh , Chen J. R.
Published: July 2002

The effect of chemical stress on diffusion in a hollow cylinder for plane strain and zero axial force has been investigated. Two diffusion processes of constant surface stress and constant surface potential are studied. No matter what the plane strain or zero axial force is the influence of chemical stress on the diffusion process of constant surface potential is similar to that of constant surface stress. Chemical stress enhances both the diffusion coefficient and the concentration. For a given time, the level of concentration becomes lower with a greater ratio of outer radius to inner radius for constant surface potential with given FXf and for constant surface stress with given FXi. F=2EV̄/[9(1−v)RT] where E, V̄, R, and T are the Young’s modulus, partial molal volume, gas constant, and absolute temperature, respectively; Xi and Xf are the initial and final mole fractions at boundary surfaces. The results are also compared with those in thin plates and solid cylinders reported in the literature.
New analytical potential energy surface for the CH4+H hydrogen abstraction reaction: Thermal rate constants and kinetic isotope effects
Authors: Espinosa-Garcı́a J.
Published: July 2002

A modified and recalibrated potential energy surface for the gas-phase CH4+H→CH3+H2 reaction and its deuterated analogs is reported and tested, which is completely symmetric with respect to the permutation of the four methane hydrogen atoms, and is calibrated with respect to updated experimental and theoretical stationary point (reactants, products, and saddle point) properties, and experimental forward thermal rate constants. The forward and reverse rate constants are calculated using variational transition-state theory with multidimensional tunneling effect over a wide temperature range, 300–2000 K. The theoretical results reproduce the available experimental data, with a small curvature of the Arrhenius plot which indicates the role of the tunneling in this reaction. Five sets of kinetic isotope effects are also calculated. In general, they agree with experimental values within the experimental errors. This surface is then used to analyze dynamical features, such as reaction-path curvature, the coupling between the reaction-coordinate and vibrational modes, and the effect of the vibrational excitation on the rate constants. It is found qualitatively that excitation of the CH4 stretching and umbrella modes enhance the forward rate constants, and only the CH3 umbrella mode in the product appear vibrationally excited.
Winding number formula for Maslov indices
Authors: Robbins Jonathan
Published: July 2002

A formula for the Maslov index of closed curves on Lagrangian manifolds is derived. The index is expressed as the number of times the plane tangent to the curve winds around it. Applications include unstable periodic orbits, in which case the Lagrangian manifolds are the stable or unstable manifolds of the orbits, and cycles on the invariant tori of integrable systems, in which case the manifolds are the tori themselves.
Upright, correlated random walks: A statistical-biomechanics approach to the human postural control system
Authors: Collins J. J. , De Luca C. J.
Published: July 2002

The task of maintaining erect stance involves a complex sensorimotor control system, the output of which can be highly irregular. Even when a healthy individual attempts to stand still, the center of gravity of his or her body and the center of pressure (COP) under his or her feet continually move about in an erratic fashion. In this study, we approach the problem of characterizing postural sway from the perspective of random-walk theory. Specifically, we analyze COP trajectories as one-dimensional and two-dimensional random walks. These analyses reveal that over short-term intervals of time during undisturbed stance the COP behaves as a positively correlated random walk, whereas over long-term intervals of time it resembles a negatively correlated random walk. We interpret this novel finding as an indication that during quiet standing the postural control system utilizes open-loop and closed-loop control schemes over short-term and long-term intervals, respectively. From this perspective, our approach, known as stabilogram-diffusion analysis, has the advantage that it leads to the extraction of COP parameters which can be directly related to the steady-state behavior and functional interaction of the neuromuscular mechanisms underlying the maintenance of erect stance.
Nondestructive defect detection in laser optical coatings
Authors: Marrs C. D. , Porteus J. O. , Palmer J. R.
Published: July 2002

Defects responsible for laser damage in visible-wavelength mirrors are observed at nondamaging intensities using a new video microscope system. Studies suggest that a defect scattering phenomenon combined with lag characteristics of video cameras makes this possible. Properties of the video-imaged light are described for multilayer dielectric coatings and diamond-turned metals.
Flux-flow-type Josephson oscillator for millimeter and submillimeter wave region. III. Oscillation stability
Authors: Nagatsuma T. , Enpuku K. , Sueoka K. , Yoshida K. , Irie F.
Published: July 2002

Numerical as well as experimental studies have been made of the oscillation stability for the travelling-wave-type oscillator, which utilizes a vortex motion in a long Josephson junction, i.e., a flux flow. For the Josephson oscillator, a steep current step in a dc I-V characteristic improves the oscillation stability. Two kinds of effects which degrade the steepness of the current step have been investigated for the long junction of the overlap geometry. One is the self-field effect which makes the current step inclined, and the other is the resonant motion of the vortices which induces a staircaselike structure on the current step. We have discussed the method for the reduction of these effects and proposed a novel junction geometry without these effects, i.e., an overlap junction with a projection on one junction side. With the new geometry, we have obtained current steps whose slope is about one hundred times steeper than those obtained with the conventional overlap geometry and whose height attains about a half of the maximum critical current over the wide voltage region 0.1≤Vdc≤1.0 mV. The linewidth calculated from the current step is expected to be a few kHz.
Defect density reduction in epitaxial silicon
Authors: Rossi J. A. , Dyson W. , Hellwig L. G. , Hanley T. M.
Published: July 2002

We present results establishing a relationship between epitaxial layer defect density and starting substrate perfection for silicon p/p+ epitaxy. Using these results we demonstrate that control of the layer defect density at a level <20/cm2 is reproducibly accomplished. At this level, the defects are primarily S pits. The density of stacking faults and dislocations is kept at <1/cm2.
Leaky Lamb waves in fibrous composite laminates
Authors: Chimenti D. E. , Nayfeh Adnan H.
Published: July 2002

Results of experimental measurements and theoretical calculations on ultrasonic leaky Lamb-wave propagation in fiber-reinforced, unidirectional composite laminates are presented. With the Lamb wave vector oriented parallel to the fiber direction, dispersion curves of phase velocity versus frequency and plate thickness have been constructed from measurements of ultrasonic reflection from fluid-loaded composite plates. The experimental results are supported by a theoretical model of Lamb-wave propagation in the composite plate. The model begins with an approximate calculation of the effective, homogeneous, transversely isotropic elastic behavior of a unidirectional composite laminate in the long-wavelength limit, using a two-step procedure based on alternating layered media. This intermediate continuum result is then incorporated into a calculation of the ultrasonic reflection coefficient of a fluid-loaded anisotropic plate, which is assumed to approximate the fibrous composite laminate. Good quantitative agreement with the model is found if the fiber volume fraction is taken to be an adjustable parameter. However, not all portions of the dispersion curves predicted by the model can be observed in the data. It is conjectured that relative differences in mode coupling account for this discrepancy.
Implant-dose dependence of grain size and {110} texture enhancements in polycrystalline Si films by seed selection through ion channeling
Authors: Kung K. T.-Y. , Reif R.
Published: July 2002

This work outlines an optimized seed selection through ion channeling (SSIC) process for enhancing the grain size and {110} texture of polycrystalline Si films grown by low-pressure chemical vapor deposition on SiO2. These films, 0.44 μm thick, were self-implanted at normal incidence to various doses (1–20 × 1014 cm−2) and subsequently recrystallized at 600 °C. An enhanced average grain diameter resulted after implantation and annealing, ranging from 0.10 to 2.0 μm (versus the as-deposited 0.080 μm) and increasing with the implant dose. The grain size versus implant dose behavior may be explained by a previously proposed stochastic model. An enhanced {110} texture was also observed after processing for implant doses of 6–14 ×1014 cm−2. The optimal dose was 11 × 1014 cm−2, for which the {220} diffracted x-ray intensity was 30 times the as-deposited value, and the 〈110〉 directions were confined to within ±4° (versus the as-deposited ±20°) of the surface normal. This experiment demonstrates the effectiveness of SSIC in growing strong {110}-textured polycrystalline Si films on amorphous insulators.
Spectroscopic ellipsometry: A new tool for nondestructive depth profiling and characterization of interfaces
Authors: McMarr P. J. , Vedam K. , Narayan J.
Published: July 2002

The ability of spectroscopic ellipsometry to analyze the multilayer surface structure of an implanted semiconductor with 1–2 Å resolution has been demonstrated. Spectroscopic ellipsometric data from 1.5 to 4.5 eV on a number of self-ion-implanted silicon samples have been analyzed using the regression analysis technique. It is shown that such a procedure can yield information nondestructively and in a nonperturbing manner: (i) on the depth profile of multilayer structures; (ii) quantitative information on the thicknesses of each layer (within 90% confidence limits); (iii) the structure (whether crystalline or amorphous) as well as the degree of crystallinity in the region; (iv) characterize the oxide layer if present on specimen; and (v) microroughness of the surface, if present. Furthermore, it is shown that these results are in excellent quantitative agreement with the completely independent results obtained on the same specimens using cross-section transmission electron microscopy.
Characteristics of the discharge current in the nanosecond-pulse breakdown
Authors: Sakurai Takeki , Watanabe Toshimitsu
Published: July 2002

The rise time and the peak of a pulsed discharge current are measured under various experimental conditions such as the change in capacitances of both storage and peaking condensers. It is shown that the peak of the discharge current can be determined by the law of the second voltage-time area. The relation between the rise time and the peak is also made clear.
Roughness studies of ion beam processed molybdenum surfaces
Authors: Bu-Abbud George H. , Mathine David L. , Snyder Paul , Woollam John A. , Poker David , Bennett Jean , Ingram David , Pronko Peter P.
Published: July 2002

Mechanically polished molybdenum samples have been irradiated with 150 keV molybdenum ions at fluences from zero to 16×1015 ions/cm2 to study the effects on surface smoothing. Both fluence and substrate temperature during irradiation (25, 250, and 500 °C) had considerable effects on the optical properties. Ellipsometry, profilometry, and Nomarski photography were used to characterize the surfaces. Multiple wavelength, multiple angle of incidence ellipsometry results were analyzed using effective medium approximation models, with molybdenum, molybdenum oxide, and voids as the principal constituents. Generally, we find that the reflectance calculated from the ellipsometric measurements increases continuously as a function of fluence. However, for high substrate temperature and short wavelength the reflectance as a function of fluence reaches a maximum and then decreases. Effective medium calculations indicate that there is a corresponding change in the surface roughness with fluence, and that effects due to oxides are minimal.
A study of CClF3/H2 reactive ion etching damage and contamination effects in silicon
Authors: Mu X. C. , Fonash S. J. , Oehrlein G. S. , Chakravarti S. N. , Parks C. , Keller J.
Published: July 2002

A comprehensive characterization of the damage and contamination produced in silicon by CC1F3/H2 reactive ion etching is presented. This highly selective SiO2-to-Si reactive ion etching process unfortunately produces all three of the deleterious damage-contamination layers that can result from dry etching exposure; viz., CC1F3/H2 reactive ion etching produces a residue layer on the Si surface, a permeated layer at the Si near-surface, and a layer of damaged Si. Various post-RIE-exposure, surface-recovery approaches are evaluated in this report. The results indicate that in order to restore the surface to a device-quality state, it is not sufficient to simply eliminate surface contamination. Damage incurred in the silicon bonding must be restored or removed. The latter can be accomplished by suitable treatments such as wet chemical silicon etch or silicide formation.
Titanium disilicide formation on heavily doped silicon substrates
Authors: Beyers Robert , Coulman Don , Merchant Paul
Published: July 2002

Titanium disilicide formation on heavily doped silicon substrates was investigated with sheet resistance measurements, elemental depth profiling, and transmission electron microscopy. As found in a previous study [H.K. Park, J. Sachitano, M. McPherson, T. Yamaguchi, and G. Lehman, J. Vac. Sci. Technol. A 2, 264 (1984)], the TiSi2 growth rate depended on the dopant concentration. The growth rate was highest on undoped substrates, intermediate on heavily phosphorus-doped substrates, and lowest on heavily arsenic-doped substrates. However, the critical dopant concentration effect reported by Park et al. was not observed. The uniformity of the titanium-silicon reaction was not seriously affected by heavy substrate doping. For heavily arsenic-doped substrates (3.0×1021 As/cm3), TiAs precipitates formed at C49 TiSi2 grain boundaries, and the C49-to-C54 transformation temperature increased to 850 °C. For heavily phosphorus-doped substrates (1.0×1021 P/cm3), no phosphides were unambiguously detected, and the C49-to-C54 transformation temperature remained below 800 °C. Discrete blocking layers at the silicide-silicon interface, such as the native silicon oxide or a dopant-rich phase, did not cause the reduction in silicide growth. Thus, it is concluded that dopant and knock-on oxygen atoms in solid solution in both the silicide and the silicon retard TiSi2 growth.
Flux-flow-type Josephson oscillator for millimeter and submillimeter wave region. IV. Thin-film coupling
Authors: Qin J. , Enpuku K. , Yoshida K.
Published: July 2002

Power emission from a flux-flow-type Josephson oscillator with a thin-film coupling method is studied experimentally. The thickness of one electrode of the oscillator is made thin enough to allow electromagnetic fields generated by the oscillator to be emitted through the thin-film electrode. Radiation power from the oscillator is detected with superconductor-insulator-superconductor detectors, which are fabricated on top of the oscillator. Experimental results show that sufficient power can be obtained from the oscillator by using the thin-film coupling method when the thickness of the electrode is comparable to the London penetration depth. The results obtained are in reasonable agreement with theoretical predictions. The thin-film coupling method will be useful when the oscillator is connected to external circuits, such as an impedance matching circuit.
Growth and characterization of AlGaInAs lattice matched to InP grown by molecular-beam epitaxy
Authors: Praseuth J. P. , Joncour M. C. , Gérard J. M. , Hénoc P. , Quillec M.
Published: July 2002

We present a complete investigation of crystalline, optical, and electrical properties of molecular-beam-epitaxial-grown AlGaInAs lattice matched to InP covering the whole range of concentrations. Using the two indium cells method, we show very easy control of lattice matching of this quaternary system which can be written as (Al0.48In0.52As)z(Ga0.47In0.53As)1−z. X-ray double diffraction profiles do not depend on the Al concentration and they show sharp diffraction linewidth. The PL full widths at half maximum are comparable to the narrowest reported. Transmission electron microscopy shows excellent crystallinity for z up to 0.60. Room-temperature electron mobility higher than 4000 cm2/V s for z up to 0.40 is comparable to that of InP and is the best result reported up to now for these quaternary alloys. This system is thus quite suitable for microwave and optical devices applications.
Transient, combined conduction and radiation in an absorbing, emitting, and isotropically scattering solid cylinder
Authors: Tsai J. R. , Özisik M. N.
Published: July 2002

Transient, combined conduction and radiation is solved in an absorbing, emitting, and isotropically scattering solid cylinder initially at uniform temperature and for times t>0 subjected to a constant temperature at the black cylindrical surface. The collocation method is used to solve the radiation part of the problem and the implicit finite difference scheme is used to solve the conduction part. The effects of the conduction to radiation parameter, the single scattering albedo, the optical thickness of the medium on the temperature distribution, and the heat flux are examined.
Laser-induced thermal desorption of moisture from a surface in atmospheric conditions
Authors: Tam A. C. , Schroeder H.
Published: July 2002

Moisture adsorbed on a gold, copper, or silicon surface in atmospheric conditions can be detected by using a pulsed laser-induced heating of the surface (transient temperature rise ≲100 °C), and a continuous probe laser beam parallel to the surface to detect the transient refractive-index changes. The probe deflection signal can be interpreted as due to a compression pulse (produced by the heating and moisture desorption at the sample surface), followed by a rarefraction (produced by cooling and diffusional moisture readsorption). Using this interpretation of the transient probe deflection signal, the amount of moisture adsorbed at the samples for various surface temperatures and absolute moisture content in an ambient gas (e.g., nitrogen) can be monitored.
Electron and chemical kinetics in methane rf glow-discharge deposition plasmas
Authors: Kline Laurence E. , Partlow William D. , Bies William E.
Published: July 2002

Experimental measurements and theoretical modeling of methane deposition plasmas have led to the identification of the most likely homogeneous and heterogeneous reaction paths leading to the deposition of amorphous carbon thin films. Experimental measurements of the voltage, current waveforms, mass flow rates, and pressure are used as inputs to the model. The magnitude and flow-rate dependence of the discharge luminosity, film deposition rates, and downstream mass spectra are compared with the model predictions and used to identify the dominant reaction paths. The model uses Monte Carlo simulation of the electron kinetics to predict the electron impact dissociation and ionization rates. These rates provide input for a plug flow chemical kinetics model.
The corrosion and oxidation of Nd-Fe-B magnets
Authors: Dickens E. Douglas , Mazany Anthony M.
Published: July 2002

The susceptibility of Nd-Fe-B magnet powders to oxidation and corrosion is well known and presents problems in processing and in service. Although the oxidation of Nd-Fe-B magnet powders can lead to severe irreversible losses, such losses can be stemmed by the application of antidegradation coatings. The effects of oxidation on Nd-Fe-B magnet powders and magnets at elevated temperatures have been examined with respect to time, particle size, and treatment, using isothermal thermogravimetric analysis and long-term oven aging. The magnetic properties of each sample were then evaluated by hysteresis testing. The effects of corrosive agents were also examined, and although the oxidation and corrosion of Nd-Fe-B magnet powders may yield similar weight gains and losses in magnetic properties, each process exhibits a different magnetic hysteresis ‘‘signature.’’ The correlations between the weight gain and magnetic measurements have proven quite reliable. The application of coatings to magnet powders can reduce the weight gain due to degradation by more than 98%, while the losses in magnetic properties are reduced from over 75% (for uncoated powders) to less than 10% (for coated powders).
Numerical aspects on the simulation of I-V characteristics and switching times of resonant tunneling diodes
Authors: Jensen K. L. , Buot F. A.
Published: July 2002

The development of a more accurate numerical scheme for simulating double-barrier semiconductor structures has highlighted sensitivities of the computational results to numerical parameters for the different approximation schemes. In numerically evaluating the time evolution of the Wigner function, a second-order differencing scheme (SDS) was used instead of a simple up/down wind differencing scheme (UDS). In our investigations of the numerical aspects of these schemes, we have found: (a) the proximity of the ‘‘computational box’’ boundaries to the double-barrier region affects the peak-to-valley ratio of the I-V curve and the value of the bias at peak current; (b) the peak-to-valley ratio is larger for the SDS than it is for the UDS; (c) the current at the resonant bias for SDS is larger than that calculated using UDS; (d) the rise in the current in the nonresonant regions for both SDS and UDS is dependent on how the bias is applied; and (e) the presence of an accumulation of electrons in the first heterojunction of the first barrier provides a closer correspondence between simulation and experimentally observed I-V.
Potassium-assisted, facile oxidation of Si3N4 thin films
Authors: Blair D. S. , Rogers J. W. , Peden C. H. F.
Published: July 2002

X-ray photoelectron spectroscopy (XPS) was used to investigate potassium-assisted, facile oxidation of silicon nitride (Si3 N4 ) thin films on Si(100) substrates. The nitride films, 0.8–2.5 nm thick, were grown by heating the Si(100) crystal in hydrazine. Potassium (K) deposited onto the Si3 N4 surface at room temperature in a background of oxygen resulted in the formation of potassium peroxide (K2 O2 ) overlayers. Annealing the sample at 975 K for only 60 s decomposed the K2 O2 overlayer, desorbed K from the surface, and efficiently oxidized the underlying substrate. The XPS Si(2p) spectra indicate formation of silicon oxynitride on the surface. In the early stages of oxidation, up to 100% of the oxygen originally deposited as K2 O2 , was converted to silicon oxynitride after annealing. The enhanced oxidation rate under these conditions, relative to direct thermal oxidation, is attributed to the large concentration of reactive oxygen on the surface when the K2 O2 thermally decomposes.
The Fe/Si(100) interface
Authors: Gallego J. M. , Miranda R.
Published: July 2002

The formation of iron silicides has been monitored by a variety of surface sensitive techniques such as Auger electron spectroscopy, electron energy loss spectroscopy, and low energy electron diffraction (LEED). The deposition of Fe onto Si(100) at room temperature results in layer-by-layer growth of polycrystalline Fe with some Si interdiffused into the growing film. The extent of the reaction of silicide formation is very limited at room temperature. These two observations contradict previous reports. Formation of iron silicide by solid phase epitaxy occurs at low temperature (325 °C). The first compound formed can be identified as FeSi—with an additional Si layer at the surface. At 450 °C the silicide film transforms to FeSi2, maintaining a layer of Si at the outer surface. In view of the low formation temperature and some LEED observations the disilicide is probably in the β-phase. We have determined the temperature range of stability of the FeSi2 film. Thermal treatments at temperatures around 600 °C produce the lateral disruption of the FeSi2 film. Iron disilicide can also be grown by evaporating Fe onto a Si substrate maintained at 350 °C.
A review of some aspects of ternary metal-metal-Si and metal-B-Si systems
Authors: Setton M. , Spiegel J. Van der
Published: July 2002

The reactions in both metal-metal-Si (M-M-Si) and metal-boron-Si (M-Bi-Si) are discussed in terms of compound formation, solid solubility, and thermodynamical equilibrium. In M-M-Si systems, the formation of stable ternary compounds is accessible via two routes: the reaction of Si with an intermetallic compound or the reaction of a metal with a silicide. From a literature survey, it is apparent that only a minority of systems contain ternary phases with high heats of formation, a condition necessary to avoid phase separation into binary phases. For alloys or bilayers interactions with Si, intermetallic compound formation is rare, probably because of the identity of the moving species and the energetically more favorable M-Si bonding. Physical parameters affecting stability and solubility of silicides are the differences in metallic radii, electronegativity and number of valence electrons. For structures consisting of a thin silicide film on B-doped Si, we show that part of the stability predictions based on data obtained for M-B, B-Si, and M-Si couples could be misleading and are invalidated when compared to previously established phase diagrams.
Molecular-beam epitaxial growth and characterization of ZnS-ZnxCd1−xS strained-layer superlattices
Authors: Karasawa Takeshi , Ohkawa Kazuhiro , Mitsuyu Tsuneo
Published: July 2002

ZnS-ZnxCd1−xS (x=0.56) superlattices with the same barrier (ZnS) thickness (47 Å) and varied well (ZnxCd1−xS) thicknesses (23–80 Å) were grown by molecular-beam epitaxy. Reflection high-energy electron diffraction patterns during the growth showed streaks, and superlattice structure was confirmed by the presence of satellites in the x-ray diffraction profile. Low-temperature photoluminescence (PL) peaks from near-band-edge emission shift to lower energy as the well thickness increases, suggesting that the emission is related to confinement in the wells. The full width at half maximum of PL lines increased with the increase in well thickness. A Raman spectrum from a single alloy layer showed two peaks (ZnS- and CdS-like) which also appeared clearly in superlattice spectra. The positions of these two superlattice peaks shift from the single alloy value to higher energy as the well thickness decreases.
A quantitative investigation of electron detrapping in SiO2 under Fowler–Nordheim stress
Authors: Zhang J. F. , Taylor S. , Eccleston W.
Published: July 2002

Detrapping of the trapped electrons from the acceptorlike trapping sites in SiO2 under Fowler–Nordheim (FN) stress has been quantitatively investigated using Al/SiO2/Si capacitor structures. Before FN stress, the traps were charged using the avalanche electron injection technique to enhance subsequent detrapping, and facilitate its distinction from trapping in subsequent studies. The quantity of electrons detrapped was assessed from the shift in the electrical field strength near the cathode. Under FN stress with an electrical field of 8 MV/cm or over, the probability of captured electrons remaining trapped was found to be less than 20%. This probability was insensitive to the number of electrons initially trapped in the oxide, decreasing as the stressing field strength increases. Within the experimental range of this study, the transient behavior of electron detrapping cannot be satisfactorily described by the dynamic balance model and a new model is developed based on the reactions occurring in the oxide under FN stress. It is found that there is more than one mechanism contributing to the electron detrapping and that the detrapping efficiency is unrelated to the initial capture cross sections of traps.
Parasitic effects of oxygen on the thermoelectric properties of Si80Ge20 doped with GaP and P
Authors: Cook B. A. , Harringa J. L. , Han S. H. , Beaudry B. J.
Published: July 2002

The presence of oxygen in silicon-germanium can have a significant effect on the sintering, microstructural, and transport properties of these alloys. A neutron activation study was performed to follow the total oxygen content during the preparation of mechanically alloyed n-type Si-20 at. % Ge alloys using either fine powders, polycrystalline Czochralski chunk, or single-crystal float zoned starting materials. The alloys were prepared with a nominal composition of Si0.747Ge0.187(GaP)0.016P0.034. The total oxygen concentration was measured in the starting materials, after 6 h of mechanical alloying in a helium environment, after hot pressing, and after a 3 h, 1100 °C heat treatment in fused silica ampoules. Alloys that contained oxygen levels in excess of 2.0 at. % exhibited low carrier mobility and low thermal conductivity, whereas those that contained less than 0.6 at. % oxygen possessed high mobility and thermal conductivity. The microstructure, as observed by optical metallography and scanning electron microscopy, was found to differ greatly with oxygen content as the low oxygen alloys showed relatively large, well-defined grains and the high oxygen alloys showed evidence of poor sintering and limited grain growth.