bluuebunny/crossref_metadata_2025 huggingface dataset:
Application of scattering chaos to particle transport in a hydrodynamical flow
Authors: Jung C. , Tél T. , Ziemniak E.
Published: July 2002

The dynamics of a passive particle in a hydrodynamical flow behind a cylinder is investigated. The velocity field has been determined both by a numerical simulation of the Navier–Stokes flow and by an analytically defined model flow. To analyze the Lagrangian dynamics, we apply methods coming from chaotic scattering: periodic orbits, time delay function, decay statistics. The asymptotic delay time statistics are dominated by the influence of the boundary conditions on the wall and exhibit algebraic decay. The short time behavior is exponential and represents hyperbolic effects.
Characteristic zonal winds and long-lived vortices in the atmospheres of the outer planets
Authors: Beebe Reta
Published: July 2002

The cameras on board the NASA Voyager spacecraft provided a survey of cloud systems within the atmospheres of the giant planets and allowed determination of zonal wind patterns, which constrain long-lived cloud systems. The basic atmospheric circulations are compared and long-lived cloud features are reviewed. The basic structure of the Great Red Spot is reviewed and the tendency of the spot to drift at −4 m s−1 or −2 m s−1 is presented.
Pathological tremors: Deterministic chaos or nonlinear stochastic oscillators?
Authors: Timmer J. , Häussler S. , Lauk M. , Lücking C.-H.
Published: July 2002

Pathological tremors exhibit a nonlinear oscillation that is not strictly periodic. We investigate whether the deviation from periodicity is due to nonlinear deterministic chaotic dynamics or due to nonlinear stochastic dynamics. To do so, we apply various methods from linear and nonlinear time series analysis to tremor time series. The results of the different methods suggest that the considered types of pathological tremors represent nonlinear stochastic second order processes. Finally, we evaluate whether two earlier proposed features capturing nonlinear effects in the time series allow for a discrimination between two pathological forms of tremor for a much larger sample of time series than previously investigated.
Hybrid Monte Carlo method for off-lattice simulation of processes involving steps with widely varying rates
Authors: Clark M. M. , Raff L. M. , Scott H. L.
Published: July 2002

A hybrid Monte Carlo simulation method consisting of kinetic and equilibrium moves is presented. The method is applicable to any system involving N different processes whose rates may vary by orders of magnitude. We show that the method easily permits the propagation of the system through macroscopic time scales by application to a study of chemical vapor deposition diamond-film growth. The application is an off-lattice simulation utilizing CH3 as the growth species on a diamond [111] surface, and incorporating a computationally expensive, many-body potential surface. We show that, by using our method, it is possible to simulate a continuous system of several thousand atoms, with no underlying grid and with a realistic potential for times on the order of milliseconds. The growth rate of the simulated surface is consistent with experimental growth rates, and the simulation sheds light on possible morphologies during the early stages of diamond film formation. © 1996 American Institute of Physics.
Conduction mechanism of high-resistivity polycrystalline silicon films
Authors: Saito Yoji , Mizushima Ichiro , Kuwano Hiroshi
Published: July 2002

The electrical properties of polycrystalline silicon films deposited by low-pressure chemical vapor deposition and doped by boron, phosphorus, or arsenic with ion implantation, are investigated, and it is found that the resistivity versus donor concentration curve has a peak point for the completely depleted samples. An improved conduction model for the high-resistivity polycrystalline silicon films is proposed. The theoretical results are in reasonable agreement with experiment. It is shown that the trap level located at the grain boundary exists at 0.51 eV above the valence-band edge and that the hole current dominates the whole current through the films for all of the lightly doped samples, even for the donor-doped samples.
Growth and structure of titanium silicide phases formed by thin Ti films on Si crystals
Authors: Bentini G. G. , Nipoti R. , Armigliato A. , Berti M. , Drigo A. V. , Cohen C.
Published: July 2002

The silicide formation with a titanium film deposited on 〈100〉 single-crystal silicon, has been studied by using nuclear microanalysis, x-ray diffraction, and transmission electron microscopy. The presence of interfacial defects and their possible role in the early stages of the reaction has been evidenced. The phase composition was dependent on the annealing temperature and time: at 550 °C only TiSi2 is observed; at higher temperatures (>600 °C), a thin TiSi2 layer at the interface is again observed, but Ti-rich silicides grow on top of this layer by increasing the annealing time. For longer annealing times, all the reacted layer progressively transforms into TiSi2. The amount of reacted silicon grows with a (time)1/2 law; the activation energy of 1.8 eV reported for the growth of TiSi2 onto amorphous Si may be appropriate even in this case. The reaction proceeds at a rate of one order of magnitude higher than previously reported for reaction between silicon and an oxygen saturated titanium film. The kinetics seems to be controlled by silicon diffusion through the TiSi2 interfacial layer.
Ferromagnetic resonance studies in the bilayer system Ni0.80Fe0.20/Mn0.50Fe0.50: Exchange anisotropy
Authors: Scott J. C.
Published: July 2002

Ferromagnetic resonance of Permalloy in the bilayer system Ni0.80Fe0.20/Mn0.50Fe0.50 has been used as a probe of the exchange anisotropy at the interface between the ferromagnetic Permalloy layer and the antiferromagnetic manganese iron. For rotation of the applied magnetic field in the plane of the film, the resonance condition exhibits a unidirectional anisotropy which relates directly to the exchange bias field, as measured, for example, by the shift of the hysteresis loop. In the perpendicular orientation, and for Permalloy layer thicknesses greater than about 400 Å, one or more standing spin wave modes are seen in addition to the uniform FMR. The indexing of these modes permit an evaluation of the boundary condition at the ferromagnet/antiferromagnet interface, in terms of partial spin pinning.
Injection-enhanced annealing of InP solar-cell radiation damage
Authors: Yamaguchi Masafumi , Ando Koushi , Yamamoto Akio , Uemura Chikao
Published: July 2002

This paper demonstrates that minority-carrier injection due to forward bias and light illumination under low current density and short-time injection conditions at room temperature can lead to enhanced recovery of radiation-induced defects in p-InP and radiation damage in InP n+-p junction solar cells. Deep-level transient spectroscopy analysis shows that the major defect centers H4 (EV +0.37 eV) and E2 (EC −0.19 eV) in p-InP exhibit injection-enhanced annealing which is a recombination-enhanced effect with a reduced activation energy of 0.133 eV. The marked recovery of the InP n+-p solar-cell radiation damage due to minority-carrier injection mainly results from recovery in minority-carrier diffusion length and decrease in recombination current. These mainly originate from the annihilation of the major defect centers H4 and E2 in the p-InP layer due to injection.
Spectroscopic ellipsometry and x-ray photoelectron spectroscopy studies of the annealing behavior of amorphous Si produced by Si ion implantation
Authors: Vasquez R. P. , Madhukar A. , Tanguay A. R.
Published: July 2002

The dielectric functions of a-Si prepared by Si ion implantation in Si and of subsequently thermally annealed a-Si have been measured by means of spectroscopic ellipsometry. Differences are observed that may be accounted for only partially by differences in density, recrystallization during preparation of the anneal-stabilized a-Si state, or differences in the surface condition of the samples. Intrinsic changes in the bond polarizability are thus indicated. Comparison of the x-ray photoemission results for the Si 2p core levels and the valence band states of the as-implanted and anneal-stabilized a-Si samples reveals measurable changes in the valence charge distribution sufficient to substantiate a change in the bond polarizability.
Semi-insulating properties of Fe-implanted InP. II. Deep levels of Fe from the study of p+-semi-insulating-n+ diodes
Authors: Cheng Julian , Forrest S. R. , Tell B. , Wilt D. , Schwartz B. , Wright P.
Published: July 2002

The properties of semi-insulating (SI) Fe-implanted InP are studied via the electrical and optical properties of p+-SI-n+ InP diodes. The current-voltage-temperature characteristics reveal a rich variety of transport processes in which the deep levels of Fe play a prominent role, including tunneling and field-assisted thermionic emission from these levels, and space-charge-limited double-injection current effects. From the analysis of these currents, different experimental estimates of the position of the deep levels have been obtained. These are compared with a direct experimental determination of their position from the measurement of the photocurrent spectra of the p+-SI-n+ diodes. These results establish the position of the iron acceptors at a level lying between 0.60–0.65 eV below the conduction band minimum. Capacitance spectroscopy of the p+-SI-n+ diodes revealed additional defect levels and carrier freeze-out effects at low temperatures.
Simulation of thermally stimulated currents in dielectrics: Effect of thermal expansion
Authors: Vanderschueren J. , Ladang M. , Niezette J. , Corapci M.
Published: July 2002

The influence of thermal expansion on thermally stimulated currents has been studied by means of model calculations based on the bistable model of Fröhlich, considering especially the case of materials characterized by expansion coefficients markedly different above and below the relaxation range. A good qualitative and quantitative agreement has been obtained between theory and experiment in elastomeric materials (styrene-isoprene-styrene and isoprene-styrene-isoprene block copolymers) showing that thermal expansion is the main factor responsible for the appearance of current reversals in thermally stimulated polarization processes.
Scattering of ultrasonic waves by oblate spheroidal voids of high aspect ratios
Authors: Lakhtakia Akhlesh , Varadan Vasundara V. , Varadan Vijay K.
Published: July 2002

The scattering of ultrasonic waves by oblate spheroidal voids of very high aspect ratios (a:b=1:20) is analyzed using the T-matrix method. By using an iterative Gram–Schmidt orthogonalization procedure, and by enforcing the unitarity and the symmetry properties of the T matrix at each iteration, numerical results are presented for normalized frequencies kpb up to 15.0. Aspect ratios up to 1:20 and such high frequencies were previously not amenable to computations using the conventional T-matrix procedure. Scattering by smooth as well as rough voids having periodically corrugated surfaces is studied. All computations were carried out on a DEC VAX 11/730 minicomputer.
Propagation of a mildly relativistic electron beam at sub-Torr pressures
Authors: Smith J. R. , Schneider R. F. , Rhee M. J. , Uhm H. S. , Namkung W.
Published: July 2002

This report presents observations on propagation of a mildly relativistic electron beam (γ=2.4) in several different gases (air, He, N2, and Ar) at low pressure (10–320 mTorr). At such low pressures, and with beam currents of several kiloamperes, beam-induced ionization may result in self-focusing of an electron beam. Beams propagating under this condition are said to be in the ion-focusing regime of propagation. The injected beam has an rms radius of 0.7 cm and a transverse temperature of 35 keV. Beam transport efficiency was measured for He, N2, and Ar. A simple calculation was performed to determine the space-charge neutralization fraction as a function of time. Using the results of this calculation, the charge-transport efficiency is found and compared with the experimentally measured quantity.
Bonding and electronic structures of amorphous SiNx:H
Authors: Hasegawa S. , Tsukao T. , Zalm P. C.
Published: July 2002

The bonding properties and annealing effects for glow-discharge amorphous silicon nitride (GD a-SiNx:H; x=0–0.33) have been investigated by means of x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and optical measurements. After annealing, a fraction of the N atoms were effused from the film. Shifts of the XPS spectra (Si2p and N1s lines) toward higher binding energy with x are observed. The opposite and large shifts are also observed in the AES spectra (SiLVV and NKLL lines). The peak binding energy EB(Si2p) of the Si2p is connected with a weighted average coordination number nav at a Si site in the SiNn (n=0,...,4) configurations, and the chemical shift per Si–N bond in the Si2p core level is 0.7 eV. For EB(Si2p) and the peak kinetic energy EK(SiLVV), a linear reduction in (EB+EK) with x is found. This result implies that the approach of the N atoms to the Si–Si bonds serves to shift the Si3p native bonding states downward. This model is consistent with the changes of the optical gap and slope B in the Tauc equation as a function of x. A reduction in EB(N1s)+EK(NKLL) with x is also found, indicating that the shifts of the N1s and NKLL are chemical shifts.
Transparent carbon film prepared by mass-separated negative-carbon-ion-beam deposition
Authors: Ishikawa Junzo , Takeiri Yasuhiko , Ogawa Kiyoshi , Takagi Toshinori
Published: July 2002

A carbon film was deposited by mass-separated negative-carbon-ion-beam deposition in the energy range of 25–1000 eV. The carbon film deposited by a C− ion beam was optically transparent (the maximum optical gap was 0.96 eV) and served as an electrical insulator (the maximum electrical resistivity was 1.5×108 Ω cm). The film property strongly depended on the ion-beam energy for deposition and, the film obtained at the deposition energy of 115–215 eV was the most transparent and the best insulator. Its atomic density was also the highest and was almost the same as that of diamond. The carbon film deposited at room temperature was amorphous and showed no IR absorption. On the other hand, the film deposited at a substrate temperature of 800 °C showed graphitelike rings in reflection high-energy electron-diffraction patterns and an IR absorption such as graphite. Its electrical resistivity was much lower. The property of the film deposited by a C−2 ion beam was more strongly dependent on the ion-beam energy than that of the film deposited by the C− ion beam (the maximum optical gap was 1.44 eV, and the maximum electrical resistivity 1.8×1010 Ω cm). The surface of the film deposited by the C− or the C−2 ion beam was smooth and chemically inert.
Film-edge-induced dislocation generation in silicon substrates. II. Application of the theoretical model for local oxidation processes on (001) silicon substrates
Authors: Vanhellemont J. , Amelinckx S. , Claeys C.
Published: July 2002

A theoretical model which allows prediction of the type and of the equilibrium configuration of dislocations generated or captured in fcc substrates at the edges of thin films is applied to local oxidation processes on (001) Czochralski silicon substrates. Nitride film structures aligned along the two most interesting crystallographic directions on the (001) surface, i.e., the 〈110〉 and the 〈100〉 directions, are studied by high-voltage electron microscopy. The model allows to explain the observed dislocation types including most of the previous reports in the literature. Some numerical examples are given which illustrate the strength of the model to obtain even quantitative information both on the film stresses and on the critical glide force from the observed equilibrium configuration of the defects. Good agreement is obtained between the observed shape and position of the defects and computer simulations based on the model.
Mapping of GaAs wafers by quantitative infrared microscopy
Authors: Dobrilla P. , Blakemore J. S.
Published: July 2002

A near-infrared transmittance mapping system, previously described for quantitative macroscale (∼1 mm) mapping of the midgap EL2 defect in thin semi-insulating GaAs wafers, has been modified to provide such quantitative data on a finer scale (∼50 μm). This allows EL2 mapping on both macro- and microscales to be compared, quantitatively; and these also to be compared with dislocation micromaps and microphotographs. The well-known cellular structures for both EL2 and dislocations are resolved, and it is possible to measure the optically detectable neutral EL2 concentration inside cells (where dislocations are fewest) and in the cell walls (where they are most numerous). Comparisons of micromaps for various small parts of a wafer, and with a macromap showing the broad low-resolution variations, indicates that the local EL2 values inside cells and at cell walls vary across a wafer with the same spatial trend as given by a low-resolution macromap. This is consistent with the hypothesis that EL2 simply getters around any dislocation as a Cottrell atmosphere, as contrasted with expectations from an alternative model which postulates that EL2 (or the point defects from which EL2 is able to construct itself) will be produced by dislocation climb.
Epitaxial growth and electric characteristics of cubic SiC on silicon
Authors: Nishino Shigehiro , Suhara Hajime , Ono Hideyuki , Matsunami Hiroyuki
Published: July 2002

Single crystals of cubic SiC were heteroepitaxially grown by chemical vapor deposition (CVD) using a SiH4-C3H8-H2 system on silicon substrates. To reduce the large lattice mismatch between cubic SiC and silicon, a buffer layer was made by carbonizing the surface of a Si substrate in the CVD system. An optimum condition for the buffer layer formation was determined by x-ray rocking curve measurements, reflection electron diffraction, and Auger electron spectroscopy. Electrical properties of the epitaxial cubic SiC layer were measured, and the mobilities on the Si(111) substrate were found to be larger than those on the Si(100) substrate. Diode characteristics of epitaxially grown p-n junctions were also investigated.
Domain structures in soft-ferromagnetic thin-film objects (invited)
Authors: van den Berg H. A. M.
Published: July 2002

A self-consistent domain theory, based on micromagnetic principles, is unfolded for two-dimensional solenoidal M distributions present in ideally soft-magnetic plane-parallel thin-film objects at zero external field and in the absence of conduction currents. Two types of domain configurations are distinguished: the basic structures in simply connected regions and the parallel configurations in special types of multiply connected regions—the parallel regions. A decomposition of the objects’s area into disjunct subregions, either simply connected or of the parallel type, whose union completely covers the object, is put forward. A procedure for constructing all feasible parallel regions is presented. In each region, the appropriate solenoidal M distribution is specified with which M is taken parallel to the subregion’s boundary. Thus, all the domain structures possible in thin-film objects with arbitrary lateral shapes can be constructed. Experimental examples are provided.
Schlieren and interferometric study of a laser triggered air spark in the nanosecond regime
Authors: Najafzadeh R. , Bergmann E. E. , Emrich R. J.
Published: July 2002

The growth of the plasma column and the electron density in an atmospheric air spark are studied by photographs. A 1-ns nitrogen laser provides the light source and the trigger. The relative timing is controlled by an adjustable light path length. It was found that the spark bridges the 0.5-mm gap during the first 5 ns. The plasma column diameter then grew linearly with time for 25 ns at a speed of 10.5 km s−1. The electron density in the ionized channel is found from interferograms; it reached a maximum value of 6.5×1019 cm−3 at 8 ns.
Nonlinear strain effects in ion-implanted GaAs
Authors: Paine B. M. , Speriosu V. S.
Published: July 2002

The nonlinear production of strain in (100) GaAs by room-temperature ion implantation has been studied. Ions of Ne, Si, and Te were used, with energies of 300, 300, and 500 keV, respectively. Doses ranged up to those required for amorphization. Strains were monitored by x-ray double-crystal diffractometry. Rocking curves were recorded about the (400) Bragg condition and detailed depth profiles of strain perpendicular to the sample surface, ε⊥(x), found by fitting the rocking curves with a kinematic model. These were compared with calculated profiles of the density of energy deposited in nuclear interactions, ρE(x). Rocking curves were also recorded about the (422) Bragg condition for selected samples, to monitor strain in the direction

parallel with their surfaces. At low doses, ε⊥(x) is a linear function of ρE(x). At doses sufficient to create strains exceeding about 0.3%, strong nonlinearities are evident and strain profiles depart significantly from the ρE(x) curves. For the Ne and Si implantations, the profiles tend to saturate at 0.4%–0.5% over a depth of ∼4000 Å. At higher doses a narrow (∼2000 Å), sharply peaked region develops, with strains up to 1.5%. At still higher doses this region becomes amorphous. The Te-implanted samples do not experience appreciable saturation; rather a sharply peaked profile develops, and grows with dose to amorphicity. Curves of ε⊥ vs ρE were extracted by comparison of ε⊥(x) and ρE(x) profiles. These demonstrated that for each ion species ε⊥ is a unique function of ρE at all depths. Although this function has the same general form for all three implantations, the curves differ from species to species. Above ε⊥=0.3%, ε⊥ increases sublinearly with ρE for all three implanted ions. For Ne and Si, ε⊥ becomes almost constant at 0.4%, beginning at ρE∼0.15 eV/Å3. The strain ε⊥ starts increasing again with ρE at about 0.7 eV/Å3 for Ne and 0.3 eV/Å3 for Si, until the GaAs goes amorphous. The curve for Te shows only a slight inflection at ε⊥∼0.3%, continuing to increase with ρE to amorphicity. Parallel strains in the Si-implanted samples were not more than 0.02% at all values of ρE.
Correlation between thermal and generation recombination noise sources: Analytical and Monte Carlo approaches
Authors: Macucci Massimo , Pellegrini Bruno , Terreni Pierangelo , Reggiani Lino
Published: July 2002

The autocorrelation function of current fluctuations caused by thermal scattering and trapping-detrapping phenomena is analytically evaluated within a simple semiconductor model and a statistical approach. The results, by accounting for the interaction between different sources of noise, are found to generalize existing approximate solutions. Analytical theory is finally compared with an appropriate Monte Carlo simulation obtaining a complete coincidence of the results.
Structure and properties of some novel ternary Fe-rich rare-earth intermetallics (invited)
Authors: Buschow K. H. J.
Published: July 2002

The structures and the magnetic properties of some novel ternary compounds were studied. These compounds have the approximate composition RFe10T2, where T represents Cr, V, Ti, Mo, W, or Si. The structure of all these compounds can be derived from the tetragonal ThMn12 structure type, but the crystallographic position occupied by the different T atoms is not the same. Most of the compounds have a homogeneity range represented by RFe12−xTx. This homogeneity range is fairly large in the case of T=V and strongly asymmetric for T=Ti and W. A structure determination is given for a representative member of the RFe10Si2 family. This structure determination is compared with results obtained previously for T=Mo and V, in which latter compounds the site occupancy of the T component is completely different from that in RFe10Si2. A survey is given of the magnetic and invar properties of RFe10T2 compounds. Special attention is paid to an analysis of the magnetocrystalline anisotropy in these materials.
Silicon and silicon dioxide thermal bonding for silicon-on-insulator applications
Authors: Black R. D. , Arthur S. D. , Gilmore R. S. , Lewis N. , Hall E. L. , Lillquist R. D.
Published: July 2002

There has been a good deal of interest recently in the applicability of thermal bonding to silicon-on-insultator (SOI) technology. Thermal bonding (also called direct bonding) is accomplished by mating polished, properly hydrolyzed silicon and/or silicon dioxide surfaces, which are then annealed to promote diffusion bonding. In order to produce high-quality SOI layers it must be demonstrated that the interface betweeen the wafers is void-free over the entire surface of the wafer (4-in. wafers in our study). We have found that the standard annealing step which has been used by other groups to form the wafer bond must be followed by a hyperbaric, high-temperature annealing cycle in order to produce interfaces which are completely void-free. In addition, we have found that mating the wafers in a controlled atmosphere is necessary to insure that voids do not remain after the thermal processing is complete. We shall present transmission electron micrographs which reveal the morphology of the bonded interface on an atomic scale. We shall submit C-scan acoustic micrographs and infrared transmission thermographs which display the areal nature of the bonding voids.
Self-consistent stochastic electron heating in radio frequency discharges
Authors: Goedde C. G. , Lichtenberg A. J. , Lieberman M. A.
Published: July 2002

Fermi acceleration is considered as an underlying mechanism for electron heating in rf discharges, in which the heating arises from the reflection of electrons from moving sheaths. By examining the dynamics of the electron collisions with the sheaths, the map that describes the electron motion is derived. For high-frequency discharges (ω/2π>50 MHz), the electron motion is shown to be stochastic. By combining these dynamics with collisional effects in the bulk plasma and incorporating self-consistent physical constraints, a self-consistent model of the discharge is developed. The model is used to calculate physically interesting quantities, such as the electron temperature and average lifetime, and to predict the minimum pressure necessary to sustain the plasma. The distribution of electron energies is shown to be non-Maxwellian. These results can be applied to experimentally interesting parallel-plate rf plasma discharges to predict the operating conditions necessary for stochastic heating to occur.
Study of intracavity absorption and laser behavior for C2H4, C2H6, CH3F, CH3Cl, and CH4/N2 by photoacoustic resonance spectroscopy
Authors: Röper J. , Neubrand A. , Hess P.
Published: July 2002

The first radial mode of a cylindrical resonator was excited in extracavity and intracavity configurations employing a modulated 3.39 μm HeNe laser. The resonance curves were measured as a function of pressure by a computer-controlled method and fitted to Lorentzian profiles. Measurements were performed for C2H4, CH3Cl, CH3F, C2H6, and CH4, where the optical absorption coefficient determined by transmission experiments increases from C2 H4 to CH4 . From the signal strengths and the Q factors of the resonances the so-called photoacoustic signal (PAS) was determined and compared with theory. Good agreement between theory and experiment was observed for all extracavity measurements and in the case of intracavity experiments with low optical losses in the laser resonator. In order to describe the large discrepancies between the experimentally determined PAS and the existing theory for high losses, improved models were developed, which are based on an inhomogeneous distribution of laser power in the optical cavity. Deviations from these models were found near threshold. The PAS observed above threshold is attributed to amplified spontaneous emission.
Depth-dependent imaging of dislocations in heteroepitaxial layers
Authors: Radzimski Z. J. , Jiang B. L. , Rozgonyi G. A. , Humphreys T. P. , Hamaguchi N. , Bedair S. M.
Published: July 2002

The generation and propagation of dislocations in GaAsP-InGaAs strained-layer superlattices have been studied using x-ray topography and electron-beam-induced current in the scanning electron microscopy. It is shown that three-dimensional information about dislocations in the substrate, as well as in subsequently grown epilayers, can be obtained via a one-to-one correlation of images obtained from these two techniques. Various types of threading and misfit dislocations are identified and their location specified.
Raman study of Si+-implanted GaAs
Authors: Wagner J. , Fritzsche C. R.
Published: July 2002

The effect of Si+ implantation on the allowed and forbidden first-order and on the resonantly excited second-order Raman spectrum of GaAs has been studied. The implantation dose was varied between 5×1011 and 1×1016 ions/cm2. For doses exceeding 1015 cm−2, the Raman spectrum of a completely amorphized surface layer was observed. In samples implanted with doses ≤1015 cm−2, which show a partly crystalline/amorphous mixed state, the relative intensities of amorphous and crystalline features in the Raman spectrum vary significantly for different exciting photon energies. This is explained by differences in the dispersion of the Raman susceptibility in amorphous and crystalline GaAs. Dipole-forbidden but defect-induced first-order scattering by longitudinal optical zone center [LO(Γ)] phonons shows an initial increase with implantation dose, which is, for excitation resonant with the E1 gap, followed by a saturation and even a decrease in intensity. This is understood in terms of an implantation-induced broadening and lowering of the E1 gap resonance in the Raman susceptibility which counteracts the increase in radiation defects. The intensity of resonantly excited 2LO(Γ) phonon scattering shows a monotonic decrease with increasing dose, which also indicates a broadening of the E1 gap resonance in the corresponding Raman susceptibility. These results demonstrate the sensitivity of resonant Raman scattering to radiation damage induced changes in the dielectric function and open the possibility for a sensitive assessment of implantation damage in GaAs.
Low-energy electron distribution in electron-beam-excited XeCl laser mixtures
Authors: Kannari F. , Kimura W. D.
Published: July 2002

The electron energy distributions for energies lower than 17 eV and their time-dependent evolution are calculated for electron-beam-excited Ne/Xe/HCl mixtures. A time-dependent Boltzmann equation including all interactions between electrons and ground– or excited-state species is solved together with a detailed full kinetics model for XeCl lasers. The effects of electron-electron collision, HCl concentration, and excitation rate on the steady-state electron energy distribution are examined. Under certain conditions, that is, for relatively high excitations and relatively low initial HCl concentrations, the low-energy electron distributions tend to be Maxwellian, and their average energies depend on various inelastic processes which cool down the electron energy. All electron reaction rates, especially those related to HCl vibrational excitation and dissociative attachment, are a function of the excitation rate and the transient HCl (v), Xe*, Xe**, and electron densities.
Magnetic pulse compression by metallic glasses
Authors: Smith C. H.
Published: July 2002

Domain models of dynamic magnetization in ferromagnetic metallic glasses are described in order to predict the behavior of metallic glasses in magnetic pulse compression systems. Formulas are developed relating basic magnetic properties of these materials to the design of saturable inductors for series resonant devices. Measurements of induced magnetic anisotropy energies between 50 and 920 J/m3 are given for several Fe- and Co-based metallic glasses together with measurements of dynamic magnetic losses and permeabilities versus time-to-saturation from 60 ns to 100 μs.
The microstructural and compositional influence upon HIREM behavior in Nd2Fe14B
Authors: Clemente G. B. , Keem J. E. , Bradley J. P.
Published: July 2002

Enhanced magnetically isotropic properties are observed in melt-spun flakes of the Nd2Fe14B(Si) type. The magnetic enhancement, referred to as HIREM, includes a remanent magnetization equal to 8–9.3 kG (with saturation magnetization measured between 15.2 and 15.7 kG), and an energy product up to 19 MGOe. Both of these properties are significantly above the conventional limits permissible for noninteracting magnetic grains. Microanalysis in an analytical electron microscope (AEM) indicates that there are two requirements for the HIREM phenomenon to arise: (1) a substantial absence of an intergranular phase between the 2-14-1 crystallites, and (2) a specific grain size range. These results support a model for the enhancement resulting from intergrain magnetic exchange coupling.
Film stress-related vacancy supersaturation in silicon under low-pressure chemical vapor deposited silicon nitride films
Authors: Ahn S. T. , Kennel H. W. , Plummer J. D. , Tiller W. A.
Published: July 2002

The effect of stress in silicon nitride films, deposited by the low-pressure chemical vapor deposition process, on the point defect concentrations in silicon has been studied. The stress level in the nitride film is varied by controlling the ratio of flow rates of reactant gases R=fSiH2Cl2/fNH3, from 1/6 to 6. The stress in the nitride film is tensile and its magnitude increases with decreasing R. During anneals at 1100 °C in Ar with a high stress in the nitride, phosphorus diffusion in silicon is retarded, antimony diffusion is enhanced, and extrinsic stacking faults shrink faster than with a low stress. These results suggest that a vacancy supersaturation and a self-interstitial undersaturation exist under the nitride and that the deviation from the equilibrium point defect concentrations are closely related to the stress level in the silicon nitride film. From the phosphorus junction profiles with varying shape width, an effective vacancy diffusivity of 3×10−10 cm2/s has been obtained.
Excited confined quantum states in CdMnTe-CdTe superlattices
Authors: Harper R. L. , Bicknell R. N. , Blanks D. K. , Giles N. C. , Schetzina J. F. , Lee Y. R. , Ramdas A. K.
Published: July 2002

The piezomodulated reflectivity spectra of CdMnTe-CdTe superlattices grown by photoassisted molecular-beam epitaxy reveal signatures associated with excited confined quantum states. The energies of these signatures are in excellent agreement with the predicted energies for heavy-hole and light-hole states calculated using a Kronig–Penney model in which strain effects are included. For comparison, we present calculations for the cases of a zero valence-band offset and a small valence-band offset which scales with Mn concentration.
Raman scattering in InGaAlP layers grown by molecular-beam epitaxy
Authors: Asahi Hajime , Emura Shuichi , Gonda Shin-ichi , Kawamura Yuichi , Tanaka Hidenao
Published: July 2002

Raman scattering from InGaAlP layers on (100) GaAs substrates grown by molecular-beam epitaxy (MBE) is studied. Compositional dependencies of Raman shifts show two-mode behavior for InAlP and partial three-mode behavior for InGaAlP. The empirical expressions for the compositional variations of LO and TO phonon frequencies are presented. Enhancement of the Raman peak intensities for AlP- and InP-like LO phonons is observed for the composition range when the direct band-gap E0 is close to the photon energy of the excitation light source. The ratio of valley depth to InP-like LO phonon peak height in the Raman spectrum of InGaP ranges from about 0.5 to 0.43, and correlates with the room-temperature photoluminescence peak energy (1.9–1.88 eV). The relationship between these is the same as for the metalorganic vapor-phase epitaxy (MOVPE) samples, although the depth-to-peak height ratios for the MBE samples coincide with the higher side values. The growth temperature dependence is also observed. These results indicate that the InGaP layers grown under the appropriate MBE-growth conditions show the ordered state, although the degree of the order is low. The InAlP layers show Raman spectra having well-resolved InP-like LO and TO phonon peaks. This differs from most of the reported results for MOVPE-grown InAlP layers, and suggests that the MBE-grown InAlP layers are very close to the disordered state alloy.
An elastic energy approach to the interstitial diffusion of 3d elements in silicon
Authors: Utzig J.
Published: July 2002

Evidence is presented that the elastic energy contribution to the migration enthalpies of interstitially dissolved 3d atoms in silicon cannot be neglected. The difference in elastic energy at the tetrahedral interstitial and the hexagonal interstitial site has been estimated in a hard-sphere model. The preexponential factor of diffusion D0 is evaluated within the framework of Zener’s D0 theory [C. Zener, in Imperfections in Nearly Perfect Crystals, edited by W. Shockley (Wiley, New York, 1952), p. 289]. Both migration enthalpy and preexponential factor, have been found to be in reasonable agreement with experimental findings.
Thermal magnetization noise as a function of frequency in amorphous ferromagnets
Authors: Prodi G. A. , Vitale S. , Cerdonio M. , Falferi P.
Published: July 2002

We report the observation of 1/frequency magnetization noise in toroidal strip-wound cores of amorphous ferromagnetic alloys at liquid-helium temperatures and in the frequency range 0.1 Hz–1 kHz. The materials tested are Co-based alloys, and exhibit very low magnetostriction and good soft magnetic properties. The experimental apparatus consists of a radio frequency SQUID magnetometer coupled to the sample by a superconducting flux transformer which is devised to allow measurements of its complex inductance. We show that the magnetization noise obeys in detail the fluctuation-dissipation theorem. A temperature-dependent partial roll-off of the complex permeability is found at ∼100 Hz, possibly linked to pinning wells for domain-wall motion. The link between 1/frequency noise and magnetic viscosity is briefly discussed.
On the flow of a thin liquid film over a rough rotating disk
Authors: Hwang J. H. , Ma F.
Published: July 2002

This study addresses the depletion of thin liquid films due to centrifugation. Equations describing the flow of a thin viscous film over a rough rotating disk are solved by either an analytical or numerical method. Depletion histories of the film are given for cases involving regular patterns of surface asperities. It is found that surface roughness markedly enhances the retention of a thin liquid film on a rotating disk. Moreover, different topographic structures of the surface roughness lead to different asymptotic limits of liquid retention.
Quantitative electron microprobe analysis of ultrathin gold films on substrates
Authors: Murata Kenji , Sugiyama Katsuya
Published: July 2002

The thickness of gold thin films of 0.1–100 nm on Si substrates has been measured with an electron probe microanalyzer. The analysis process is as follows. k ratio versus thickness calibration curves are produced through use of a Monte Carlo simulation of electron scattering based on the Mott cross sections for elastic scattering, where the exact film/substrate boundary condition is included. Then the thickness can be determined, corresponding to an observed k ratio from the samples. Prior to the analysis, the ionization cross sections for Au Mα and Lα x rays required in the simulation are obtained by measuring the x-ray intensity from very thin gold films as a function of incident electron energy. The measured thickness results agree very well with experimental ones, which are obtained with a quartz balance apparatus. The simulation model is discussed in comparison between theory and experiment. Also it is shown that the thickness detection limit of the present method can reach submonolayer films.
The effect of charge exchange processes on ion diode impedance
Authors: Desjarlais M. P.
Published: July 2002

A simple model of the effect of charge exchange processes on the steady-state ion current in a space-charge-limited ion diode is presented. The model is used to investigate the effect of charge exchange processes on ion diode impedance and virtual cathode motion.
Charge exchange effects in ion diodes
Authors: Pointon T. D.
Published: July 2002

A new one-dimensional particle simulation code has been developed to investigate the effect of charge exchange between the ions and background neutrals in a planar anode-cathode gap. The code has been used to study the effect of beam ions charge exchanging with neutrals in the anode plasma in an ion diode. Charge exchange creates a fast neutral population which expands into the gap much faster than the anode plasma itself. This flux quickly increases the neutral density throughout the gap. Furthermore, multiple charge exchanges reduce the ion flux and mean energy, and broaden the ion beam energy distribution. A description of the code and quantitative results of these effects are presented.
Concentration profiling using x-ray reflectivity: Application to Cu-Al interfaces
Authors: Chen Huaiyu , Heald S. M.
Published: July 2002

Synchrotron radiation measurements were made using glancing-angle x-ray reflectivity to study Cu-Al thin-film interfaces. The reflectivity data contains information about film morphology, and its sensitivity to the concentration of an element can be improved by measuring above and below an absorption edge. An analysis routine for the reflectivity data was developed to extract a model of the concentration profile and roughness. The results are compared from Cu-Al interfaces prepared in an ultrahigh vacuum environment, with and without exposure to oxygen before Al deposition. The reactions caused by thermal annealing at temperatures ranging from 65 to 160 °C are also studied. Density profiles of the two samples after various anneals indicate that there are different levels of mixing at the interface, and the tendency to reach a similar level after high-temperature (140–160 °C) anneals. The low levels of reaction observed in this work are difficult to detect by other techniques, such as Rutherford backscattering spectroscopy. In view of the simplicity and the sensitivity of the glancing-angle x-ray reflectivity technique, it can be generalized to other thin-film systems.
Magnetic and magneto-optic properties of Bi-substituted garnet films crystallized by rapid thermal processing
Authors: Suzuki Takao , Sequeda Federico , Do Hoa , Huang Ting C. , Gorman Grace
Published: July 2002

A new technique to crystallize as-deposited, amorphous phase in (BiDy)3(FeGa)5O12 films is presented. This technique employs heat pulse annealing and leads to improved surface smoothness and smaller grains, in comparison with conventional oven anneal and also with in situ crystallization during deposition. Rapid thermal annealing was accomplished in a heat pulse apparatus with a ramp-up rate up to 50 °C/s. Upon heating for several seconds at about 650 °C, a single phase of garnet is formed. The samples were polycrystalline, but exhibit a perpendicular magnetic anisotropy of 104 erg/cm3, and a high squareness of Faraday hysteresis loops. The coercivity is typically 1–4 kOe. A systematic study of the effect of a ramp rate on a microstructure and magnetic properties has been made. The result indicates that the ramp-up rate is a key to controlling grain size and surface morphology.
Single-gate deep level transient spectroscopy technique
Authors: Pandian V. , Kumar V.
Published: July 2002

A new deep level transient spectroscopy technique is suggested which allows the deep level parameters to be obtained from a single temperature scan. Using large ratio t2/t1 of the measurement gate positions t1 and t2 and analyzing the steep high-temperature side of the peak, it is demonstrated that the deep level activation energy can be determined with high accuracy.
Charge retention of twisted nematic liquid-crystal displays
Authors: Yang K. H.
Published: July 2002

A simulated thin-film transistor (TFT) circuit has been built to drive the twisted nematic (TN) cell for the measurements of charge retention and the transmission versus peak voltage applied to the drain electrode of the simulated TFT using the gate pulse width as a parameter. The established rule that the transmission of the TN cell depends only on the rms voltage applied to the cell has been confirmed by calculating the rms voltage of the charge retention curves in correlation with the measured transmissions. The deviation of the decaying charge retention curves from the exponential behavior has been observed and can be qualitatively explained by a combination of the dielectric and transport properties of nematic liquid-crystal medium.
Growth kinetics of amorphous interlayers by solid-state diffusion in polycrystalline Zr and Hf thin films on (111)Si
Authors: Cheng J. Y. , Chen L. J.
Published: July 2002

The growth kinetics of an amorphous (a-)interlayer in polycrystalline Zr and Hf thin films on (111)Si have been investigated by cross-sectional transmission electron microscopy. The growth of the a-interlayer in group-IVb metals and silicon systems was found to exhibit similar behaviors. The growth was found to follow a linear growth law initially. The growth rate then slows down and deviates from a linear growth law as a critical thickness of the a-interlayer was reached. Crystalline silicide (ZrSi or HfSi) was found to nucleate at the a-interlayer/Si interface in samples after prolonged and/or high-temperature annealing. Silicon atoms were found to be the dominant diffusing species during the formation of amorphous alloys. The activation energy of the linear growth and maximum thickness of the a-interlayer were measured to be 1.4 eV, 17 nm and 1.2 eV, 27 nm in Zr/Si and Hf/Si systems, respectively. The correlations among the differences in atomic size between metal and Si atoms, growth rate and activation energy of the linear growth, critical and maximum a-interlayer thickness, the largest heat of formation energy for crystalline silicides, the calculated free-energy difference in forming amorphous phase, as well as the atomic mobility in Ti/Si, Zr/Si, and Hf/Si systems are discussed.
Material constants of new piezoelectric Ta2O5 thin films
Authors: Nakagawa Yasuhiko , Okada Takashi
Published: July 2002

The first measurement of the material constants of Ta2O5 thin films is described. x-axis-oriented Ta2O5 thin films were deposited on fused quartz using the dc diode sputtering method. The material constants were determined from the phase velocity and the electromechanical coupling constant of the bulk waves and the surface acoustic waves propagating on the layered substrate.
A microstructure based magnetization reversal model in sintered Fe-Nd-B magnets. I
Authors: Ramesh R.
Published: July 2002

A microstructure based magnetization reversal model is presented for sintered Fe-Nd-B magnets. The model makes use of a position dependent domain wall energy profile to correlate the intrinsic coercivity, iHc (and the nucleation field) to the magnetocrystalline anisotropy field. The inferences of the model are verified through the study of the effect of Dy and Ce additions on the iHc as well as by examining the temperature dependence of iHc and anisotropy field existing in published literature. It is inferred from this model that selective modifications of the interfaces could lead to appreciable improvements in the magnetic properties.