bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic trapping and self-assembly of multicomponent nanowires
Authors: Tanase M. , Silevitch D. M. , Hultgren A. , Bauer L. A. , Searson P. C. , Meyer G. J. , Reich D. H.
Published: July 2002

Magnetic nanowires suspended in fluid solutions can be assembled and ordered by taking advantage of their large shape anisotropy. Magnetic manipulation and assembly techniques are demonstrated, using electrodeposited Ni nanowires, with diameter 350 nm and length 12 μm. Orienting suspended nanowires in a small magnetic field H≈10 G promotes self-assembly of continuous chains that can extend over several hundred μm. The dynamics of this process can be described quantitatively in terms of the interplay of magnetic forces and fluid drag at low Reynolds number. In addition, a new technique of magnetic trapping is described, by which a single magnetic nanowire can be captured between lithographically patterned magnetic microelectrodes. The use of three-segment Pt–Ni–Pt nanowires yields low resistance, Ohmic electrical contacts between the nanowires and the electrodes. This technique has potential for use in the fabrication and measurement of nanoscale magnetic devices.
In situ ordered polycrystalline FePt L10 (001) nanostructured films and the effect of CrMn and Zn top layer diffusion
Authors: Jeong Sangki , Ohkubo T. , Roy Anup G. , Laughlin D. E. , McHenry M. E.
Published: July 2002

The nanostructure and magnetic properties of in situ ordered polycrystalline FePt thin films (9 nm) have been studied. Films were deposited with a MgO underlayer onto Si and glass substrates using conventional rf diode sputtering. Perpendicular anisotropy was obtained when the substrate temperature exceeded 490 °C. The maximum order parameter (S) was estimated to be ∼0.9. The coercivities (Hc) ranged from 5 to 12 kOe. Observed high values of the coercive squareness (S*) indicate the existence of exchange coupling. High resolution transmission electron microscopy indicates a defective region which might be associated with defect-related localized incoherent nucleation, thereby inducing low values of Hc. Zn and CrMn top layers at ambient temperature were deposited after the deposition of FePt films at elevated temperatures. Rapid thermal annealing of these samples at 180–450 °C for 1 min resulted in a decrease of S* from 0.8–0.85 to ∼0.5–0.6.
Exchange coupling characteristics of bottom-type synthetic ferrimagnet based spin valves
Authors: Park Gun Hyung , Lee Seong-Rae , Kim Young Keun
Published: July 2002

Giant magnetoresistance (MR) and effective exchange coupling field (Hex) variations in bottom-type synthetic ferrimagnet based spin-valve (B–SV) films consisting of sputter-deposited Ta 5/seedlayer (NiFe, Cu, or Ru) 2/IrMn 9/CoFe (P1) 1.0–1.5/Ru 0.7/CoFe (P2) 3/Cu 2.8/CoFe 1.6/NiFe 3.2/Ta 5 (in nanometers) multilayers have been investigated. In particular, a focus was given on understanding the magnetotransport changes when the thickness difference between P2 and P1 layers, Δt(=tP2-tP1), was varied. These results were compared with those from similarly structured top spin-valve (T–SV) samples. When characterizing the subpeak profiles of MR transfer curves, we found that the subpeak shape of a B–SV with Δt=1.5 (=3.0–1.5) nm was different from that of a T–SV with the same Δt but was remarkably similar to that of a T–SV with Δt=2.0 (=3.0–1.0) nm. The degree of interfacial mixing (estimated to be in the order of 0.5 nm) during deposition at IrMn/CoFe (P1) appears higher for the B–SV: this resulted in an increase in effective Δt (or a decrease in effective P1 thickness). Hence, the effective thickness difference (Δteff) caused by intermixing has to be considered for designing B–SV structures. Annealing also induced changes in subpeak profiles, Hex, and MR ratios resulting from interdiffusion. In overall, a B–SV consisting of a NiFe seedlayer exhibited higher thermal stability than others.
Fabrication of oriented L1-FePt and FePd nanoparticles with large coercivity
Authors: Sato Kazuhisa , Bian Bo , Hirotsu Yoshihiko
Published: July 2002

Oriented L10-FePt and FePd nanoparticles with coercivities as large as 5 kOe (FePt) and 3 kOe (FePd) were fabricated by alternating deposition of Pt(or Pd) and Fe nanoparticles and their annealing at the temperatures between 773 and 873 K on single crystal NaCl and MgO. Atomic ordering reactions and degrees of order towards the L10-structure formation in these nanoparticles were investigated by high resolution electron microscopy and electron diffraction, and magnetic coercivities at low temperature were also measured. The long range order parameter of the FePt nanoparticles was ∼0.56 even after annealing at 873 K for 24 h. The coercivity of the FePt nanoparticles at 100 K was as high as twice the room temperature value. The low degree of order in the L10-structure formation and the thermal effect on magnetization have been found in the present FePt and FePd nanoparticles. These are closely concerned with the origin of the coercivity values which are very small in comparison with those expected from the single magnetic domain theory.
Correlation between plasma expansion dynamics and gold-thin film structure during pulsed-laser deposition
Authors: Irissou Eric , Le Drogoff Boris , Chaker Mohamed , Guay Daniel
Published: July 2002

Pulsed-laser deposition of Au thin films has been achieved by ablating a gold target with a KrF excimer Laser in various conditions of ambient Ar gas pressure (from 10−5 to 4 Torr) and target-to-substrate distance (from 1.0 to 11 cm). The dynamics of the plasma plume were measured in the same conditions. Highly oriented Au (111) thin films are obtained for pressure-distance deposition conditions such that the neutral Au species have a typical velocity larger than 2 km s−1, while a polycrystalline powder is obtained when the typical velocity is smaller than 0.8 km s−1.
Time-resolved spectroscopic measurements of ∼1 keV, dense, subnanosecond X-pinch plasma bright spots
Authors: Shelkovenko T. A. , Pikuz S. A. , Sinars D. B. , Chandler K. M. , Hammer D. A.
Published: July 2002

Bright, ∼1 μm x-ray sources (micropinches) produced within exploding wire X pinches are found to be near solid density and ∼1 keV electron temperature. For example, with a Ti X pinch, a 90 ps lifetime, 1.5–1.8 keV electron temperature, ∼1023/cm3 electron density plasma was observed. These plasma characteristics were determined using time-resolved x-ray spectra produced by 2- and 4-wire X pinches and collected by an x-ray streak camera with <10 ps time resolution. Together with a spherically bent mica crystal spectrograph, the streak camera recorded the 1–10 keV radiation emitted from X pinches made from different wire materials. Some spectra were dominated by continuum and others by line radiation. Spectral features varied on time scales ranging from 10 to 300 ps, depending on the wire material. Results are presented that demonstrate the necessity of time-resolved data for determining plasma conditions from micropinch x-ray spectra.
Observation of memory effect in germanium nanocrystals embedded in an amorphous silicon oxide matrix of a metal–insulator– semiconductor structure
Authors: Choi W. K. , Chim W. K. , Heng C. L. , Teo L. W. , Ho Vincent , Ng V. , Antoniadis D. A. , Fitzgerald E. A.
Published: July 2002

The memory effect of a trilayer structure (rapid thermal oxide/Ge nanocrystals in SiO2/sputtered SiO2) was investigated via capacitance versus voltage (C–V) measurements. The Ge nanocrystals were synthesized by rapid thermal annealing of the cosputtered Ge+SiO2 films. The memory effect was manifested by the hysteresis in the C–V curve. Transmission electron microscope and C–V results indicated that the hysteresis was due to Ge nanocrystals in the middle layer of the trilayer structure.
An improved thermodynamic energy estimator for path integral simulations
Authors: Glaesemann Kurt R. , Fried Laurence E.
Published: July 2002

A new path integral energy estimator is presented that improves upon the thermodynamic energy estimator via a free particle projection. This centroid thermodynamic estimator significantly reduces the numerical noise of the thermodynamic estimator. The debate as to which estimator is better (virial, centroid virial, or thermodynamic) is partially resolved. The centroid estimators are found to be significantly better than their noncentroid analogues. The new centroid thermodynamic estimator has accuracy close to the centroid virial estimator, and may have particular advantages when derivatives of the potential are expensive to evaluate.
Dielectric relaxation of chained ferrofluids
Authors: Murashov Vladimir V. , Camp Philip J. , Patey G. N.
Published: July 2002

Molecular and Brownian dynamics simulations are used to investigate the frequency-dependent dielectric relaxation of ferrofluids, with the objective of identifying features characteristic of dipolar chain formation at low densities. It is shown that the presence of chains gives rise to a high frequency band associated with the vibrational motion of dipoles within the chains. This band serves as a “signature” of association and is not present in dipolar fluids at higher, liquid-like densities. A simple theory that traps the basic features of the relaxation behavior is also presented.
Relativistic effects on linear and nonlinear polarizabilities studied by effective-core potential, Douglas–Kroll, and Dirac–Hartree–Fock response theory
Authors: Norman Patrick , Schimmelpfennig Bernd , Ruud Kenneth , Jensen Hans Jo/rgen Aa. , Ågren Hans
Published: July 2002

Relativistic calculations of electric dipole moments, linear polarizabilities, and first- and second-order hyperpolarizabilities have been carried out for the isovalent group VI dihydrides (O–Po) and group VII monohydrides (F–At) at three different levels: the time-dependent Dirac–Hartree–Fock approximation, the time-dependent Hartree–Fock approximation with a Douglas–Kroll transformed one-component Hamiltonian, and the time-dependent Hartree–Fock approximation with effective-core potentials. These calculations are compared with nonrelativistic time-dependent Hartree–Fock results in order to elucidate the role of relativistic effects on these properties and to investigate the extent to which the Douglas–Kroll approach and the effective-core potentials—both of which neglect spin-dependent terms but are computationally less demanding—are able to reproduce the 4-component Dirac–Hartree–Fock results. The results show that qualitatively correct relativistic corrections in most cases can be obtained with the more approximative methods, but that a quantitative agreement with 4-component calculations is often not obtained.
Prediction of trapping rates in mixtures of partially absorbing spheres
Authors: Kansal Anuraag R. , Torquato Salvatore
Published: July 2002

The combined effects of diffusion and reaction in heterogeneous media govern the behavior of a wide variety of physical and biological phenomena, including the consumption of nutrients by cells and the study of magnetic relaxation in tissues. We have considered the so-called “trapping problem,” in which diffusion takes place exterior to a collection of fixed traps while reaction occurs at their surface. A simulation technique for predicting the overall trapping rate for systems of partially absorbing spherical traps based on the first-passage spheres method is presented. Using data obtained by applying this simulation technique, we then consider the problem of mixtures of partially absorbing traps. By hypothesizing a method for reducing a general mixture of traps to a mixture of perfect absorbers and perfect reflectors (i.e., reducing the dimensionality of the space of variables), we are able to accurately predict the effective surface rate constant and the trapping rate for an arbitrary mixture of partially absorbing traps. Remarkably, we find that a single, nearly universal curve allows accurate predictions to be made over a wide range of trap volume fractions and even for different trap distributions.
Ordering of island-like FePt L1 thin films
Authors: Kim Mu-Gyeom , Shin Sung-Chul , Kang Kyongha
Published: July 2002

We report the island growth morphology of 50-nm-thick FePt thin films prepared on MgO substrates by dc magnetron sputtering. In-depth high-resolution transmission electron microscopy studies showed that the island had a very flat facet in a dome shape and was composed of two distinct structures. The island contained FePt grains with an average size of 5–7 nm within about 10 nm from the film surface, whereas an ordered L10 phase was established below the island. The L10 structure was compressively strained along the film plane, generating {111} twins and stacking faults. The strained structure also affected the region where agglomeration between islands occurs.
Effects of cathode materials and arc current on optimal bias of a cathodic arc through a magnetic duct
Authors: Zhang Tao , Chu Paul K. , Brown Ian G.
Published: July 2002

A negatively biased collecting plate was used to collect the ion current of the cathodic arc plasma transported through a curved magnetic duct. The optimal duct bias at which the duct has the maximum efficiency for plasma transport was measured for C, Ti, Mo, and W plasmas as a function of the arc current and guiding magnetic field. The optimal bias decreased with the magnetic field and was almost steady when the field was above 400 G. The optimal bias at 400 G and above increased with the arc current for C plasma but the opposite relationship was observed for Ti, Mo, and W plasmas. The effects of the plasma density, ion mass, ion kinetic energy, and magnetic field on the optimal bias are discussed.
Ionization of organic molecules with ultraviolet lasers: A technique for generating large, well-defined ionized volumes
Authors: Woodworth J. R. , Green T. A. , Frost C. A.
Published: July 2002

In this paper we report a technique for generating a large, homogeneous volume of ionized gas and for making time-resolved measurements of its electron density. We also report absolute photoionization coefficients for a number of molecules. These coefficients will allow calculation of peak electron densities obtained in other ionization-related experiments. In our technique, the beam from a rare-gas halogen laser photoionizes organic molecules that have been seeded into a buffer gas. Ionization is accomplished by the absorption of two photons. We have analyzed the electron densities produced by photoionization with a microwave interferometer that measures the electron density in the ionized gas with a time-resolution of a few nanoseconds. Some of the organic molecules photoionized in this work produce electron-ion pairs with an efficiency more than five orders of magnitude higher than commonly used laboratory ionization sources such as ArF laser photoionization of NO. We have also studied the effect of attaching gases on the ionized mixtures and have demonstrated that addition of as little as 10 Torr of SF6 can reduce the peak electron density observed by a factor of 103.
Identification of defect centers in Hg1−xCdxTe using their energy level composition dependence
Authors: Myles Charles W. , Williams P. Frazer , Chapman R. A. , Bylander E. G.
Published: July 2002

We have extended the Kobayashi, Sankey, and Dow [Phys. Rev. B 25, 6367 (1982)] theory of deep levels in Hg1−xCdxTe to include (vacancy, impurity) nearest-neighbor pairs. In qualitative agreement with the results obtained by these workers for isolated point defects, we find that the composition dependences (dE/dx) of the defect energy levels associated with such complexes depend on the site occupied by the impurity atom. Furthermore, we find that the composition dependences of some of the defect levels produced by such a complex are very different than the dE/dx of levels associated with the corresponding isolated point defects. We thus suggest that this theory can often be used as an aid in the identification of the defect center producing an observed energy level. In particular, it can be used to obtain site information about an observed level and, in favorable cases, to distinguish between levels produced by isolated point defects and those produced by complexes. As an example, we compare our theoretical predictions for the dE/dx of levels associated with (vacancy, impurity) pairs to the experimental slopes of the energy levels observed in deep level transient spectroscopy by Jones, Nair, and Polla [Appl. Phys. Lett. 39, 248 (1981)] and find that the theory lends support to these workers’ interpretation of their data. In addition, we present new photoluminescence data on both a previously observed and identified acceptor and on an unknown center in Hg1−xCdxTe. As a further example of the usefulness of our theory, we compare the theoretical slopes of energy levels associated with (vacancy, impurity) pairs with the composition dependences of the defect levels extracted from the photoluminescence data. The results of both of the theoretical-experimental comparisons show that the theory can be used successfully, in conjunction with experimental data, to aid in the identification of the defect center which produces an observed energy level.
Spectroscopy of tetracene submonolayers using phonon emission
Authors: Dietsche W. , Rapp Th. , Basso H. C.
Published: July 2002

A new technique for the optical spectroscopy of adsorbed molecules is introduced. It is based on the detection of the phonons emitted during nonradiative relaxation. A high sensitivity was achieved by using superconducting tunnel junctions as detectors. A light power of the order of 1 μW was sufficient for the spectroscopy of submonolayers of tetracene. Molecules deposited on a cold substrate had a spectrum similar to the one of isolated molecules in a solvent. Deposition, or annealing, at room temperature, however, yielded spectra like those of single crystals.
Pulsed photothermal modeling of layered materials
Authors: Balageas D. L. , Krapez J. C. , Cielo P.
Published: July 2002

Exact analytical solutions of the heat-diffusion problem encountered in the pulsed photothermal evaluation of layered materials are presented. The analysis relates to the long-time decay of the front face temperature following the absorption of a surface heat pulse. The configuration of a coating on a substrate is analyzed, and the parameters governing the temperature evolution are identified with a particular emphasis on the thermal contact resistance term. This model provides a new method of measuring the quality of the interface. Previously published data and new experiments with laminated materials and living tissues are analyzed using the proposed analytical solutions.
Piezoelectricity in three-phase systems: Effect of the boundary phase
Authors: Ueda Hiroyoshi , Fukada Eiichi , Karasz Frank E.
Published: July 2002

The influence of electrical conductivity on the piezoelectricity of polymers was studied using a three-phase model. The model consists of a continuous nonpiezoelectric phase (phase 1) surrounding a spherical piezoelectric phase (phase 2), which is itself bounded by an electrically conductive shell (phase 3). The piezoelectric constants for the system can be expressed as d=d2KPKT and e=e2KPKS, where d2 and e2 are the piezoelectric strain and stress constants of phase 2, respectively, and KP is a function of the dielectric constants of phases 1, 2, and 3. KT and KS are expressed as functions of the elastic constant of each phase. The piezoelectric constants d and e decrease with decreasing elastic constant of phase 3 and with increasing dielectric constant of phase 3. The three-phase system shows a Maxwell–Wagner piezoelectric relaxation with a relaxation time given by τ=(2ε1+ε2+ηε3)/(2σ1+σ2+ησ3), where η=2δ/a. In these expressions εi and σi are the dielectric constant and the electrical conductivity of phase i, respectively, a is the radius of the sphere (piezoelectric phase), and δ is the thickness of the electrically conductive shell around the piezoelectric phase. When τ1(=ε1/σ1)>τ2[=(ε2+ηε3)/(σ2+ησ3)], the functional dependence of KP on frequency implies the occurrence of a relaxation process. Conversely, when τ1<τ2, a retardation process is observed.
The optogalvanic effect in a 13.56-MHz chlorine discharge
Authors: Kramer Jerry
Published: July 2002

Irradiation of the bulk plasma region in a 13.56-MHz Cl2 discharge with an XeCl laser increased the current through the discharge. The perturbed current waveform had the shape of an amplitude modulated waveform with a period long with respect to the rf cycle. This optogalvanic effect has been attributed to the photodetachment of electrons from Cl−, which perturbs the electron density. The optogalvanic signal depended on the square root of the pressure and was almost independent of the discharge current. The optogalvanic current has been correlated with the dependence of the Cl− density on pressure and discharge current as well as the changes in the electric field induced by the perturbation. Saturation of the signal at high laser intensity has been accounted for by the impedance mismatch induced by the increased electron density. From the relationship between the saturation and the impedance mismatch, the ratio of Cl− to the electron density was calculated. Probing various parts of the discharge with a laser beam having a smaller cross section than the discharge did not reveal any significant spatial variations in the discharge.
Substrate-orientation dependence of GaN single-crystal films grown by metalorganic vapor-phase epitaxy
Authors: Sasaki Toru , Zembutsu Sakae
Published: July 2002

Gallium-nitride single crystals were grown on (0001)- and (011̄2)-oriented sapphire substrates by metalorganic vapor-phase epitaxy. Smooth-surfaced layers with fine ridgelike facets can be obtained on the (011̄2) sapphire. They have lower carrier concentrations than the layers on the (0001) sapphire. Deep centers responsible for blue (∼425 nm) and yellow (∼560 nm) emissions from undoped layers are reduced on the (011̄2) substrates, as compared with the (0001) substrates. On the other hand, the layers on the (0001) sapphire have better crystallinity and higher Zn-incorporation efficiency than those on the (011̄2) sapphire. Growth kinetics of GaN layers are discussed by developing a tentative model.
Simple electrodes for quadrupole ion traps
Authors: Beaty Earl C.
Published: July 2002

Quadrupole traps for charged particles often involve electrodes with portions carefully machined to the shape of hyperboloids. It is shown here that the more important features of such traps can be achieved using electrode shapes which are much easier to fabricate. Detailed numerical calculations are reported on some sample electrodes. The numerical method can be easily extended to other shapes which accommodate specialized laboratory situations.
Determination of dopant and deep imperfection profiles in p-type CdTe by improved constant capacitance-voltage transient measurements
Authors: Shiau Jeng-Jye , Fahrenbruch Alan L. , Bube Richard H.
Published: July 2002

By constant capacitance-voltage transient measurements we are able to determine the dopant and deep imperfection density versus distance profiles, regardless of either the absolute density of imperfection levels, or their density relative to the dopant density. The data analysis of the method is similar to the well-known capacitance versus voltage measurement, which is very convenient compared to other imperfection profiling methods.
Effects of cathode surface roughness on the quality of electron beams
Authors: Lau Y. Y.
Published: July 2002

The effects of the roughness of the cathode surface on the emittance of an electron beam are examined. Tentative scaling laws are suggested which yield the bounds on the beam emittance due to surface roughness for both temperature-limited and space-charge-limited regimes. These formulas are found to be consistent with numerical integration of electron trajectories over a wide range of parameters. In general, roughness-induced beam emittance may be reduced by a factor of 2–5, if the cathode is operated in the space-charge-limited regime rather than in the temperature-limited regime.
High speed deposition of high-quality ferrite films from aqueous solution at low temperatures (≤90 °C)
Authors: Abe M. , Tamaura Y. , Goto Y. , Kitamura N. , Gomi M.
Published: July 2002

We have plated polycrystalline CoxFe3−xO4 (x=0 and 0.43) films on PET and glass substrates at 80–90 °C in an aqueous solution by new three methods: (1) spraying, (2) spin coating, and (3) thin liquid-film methods. The reaction solution is (1) sprayed, (2) spin coated, and (3) flowed through a gap between the substrate and a glass plate, respectively, making a thin (5–400 μm) coating of the solution on the substrate. Since the solution flows off, the composition of the solution on the substrate does not significantly change during the plating, and the ferrite particles formed in the solution are washed away. This improves the film quality compared to previous methods. We have further improved the film quality by introducing CH3COO− buffer ions into the solution, and also by filtering the solution. By the thin liquid-film method, we have obtained maximum deposition rates of ∼160 and ∼300 Å/min by the spraying and the thin liquid-film methods, respectively. The films of Fe3O4 and CoxFe3–xO4 (x=0.43) plated by the thin liquid-film method exhibited a preferential texture of (100) and (111) planes, respectively, parallel to the surface. Both films had a columnar structure normal to the surface, but the magnetization lies in the surface plane.
Evidence for recombination-controlled electroluminescence in alkaline-earth sulfides
Authors: Crandall Richard S. , Ling Mildred
Published: July 2002

Thin-film alkaline-earth-sulfide electroluminescent devices exhibit, under voltage-step excitation, an unexpected decrease in the light output if the voltage is abruptly increased at some time after the beginning of the step. We use this phenomenon to demonstrate that the dynamics of the light emission is controlled by field-dependent trapping and eventual recombination at empty activators rather than impact excitation of activators.
An analysis of time-dependent magnetization and coercivity and of their relationship to print-through in recording tapes
Authors: Flanders P. J. , Sharrock M. P.
Published: July 2002

Time-dependent magnetic phenomena in oxide particulate recording materials are observed by measuring the change of magnetization with time in the presence of a constant field or by measuring the dependence of the hysteresis loop on the field sweep rate. Either type of experiment yields a measured value of the coercivity as a function of the characteristic measurement time. For a constant-field experiment, this time is simply the interval needed for the applied field to reduce the magnetization from saturation remanence to zero. A corresponding time, approximately inverse to the sweep rate, can be associated with the coercivity measured in a swept-field experiment. A time-dependence parameter that measures the strength of the dependence of magnetization on time at constant field and also that of coercivity on sweep rate in a swept-field experiment can be determined. This parameter can be interpreted, using simple kinetic theory, to estimate the volume of the magnetic switching unit. Volumes estimated in this way correlate reasonably well over 2 orders of magnitude with particle volumes determined by electron microscopy. The amount of print-through in recording tapes is found to correlate well with the time-dependence parameter for tapes made from a variety of iron oxide particles both with and without added cobalt.
The kinetics and mechanism of oxide layer formation from porous silicon formed on p-Si substrates
Authors: Yon J. J. , Barla K. , Herino R. , Bomchil G.
Published: July 2002

The formation of oxide layers from porous silicon layers formed on P substrates which present different and well-controlled porous textures is studied in detail. It is shown that the overall process leading to oxides with properties similar to standard thermal oxides consists of two steps: the oxidation of silicon in the porous layer and the densification of silica. The first step does not depend upon the initial texture of the layer, but is mostly determined by the porosity of the sample and the temperature of the oxidation sequence. The second step, oxide densification, which takes place at temperatures higher than 1000 °C, is very sensitive to the porous texture of the layer, the densification times increasing sharply with the average pore size. The densification process has a high activation energy, which can be related to the activation energy for the viscous flow of silica.
Growth of single-crystal TiN/VN strained-layer superlattices with extremely high mechanical hardness
Authors: Helmersson U. , Todorova S. , Barnett S. A. , Sundgren J.-E. , Markert L. C. , Greene J. E.
Published: July 2002

Single-crystal TiN/VN strained-layer superlattices (SLS’s) with layer thicknesses lTiN =lVN =λ/2 (where λ is the period of the superlattice) ranging from 0.75 to 16 nm have been grown on MgO(100 ) substrates by reactive magnetron sputtering. Cross-sectional transmission electron microscopy (TEM) and x-ray diffraction examinations showed that the films were single crystals exhibiting coherent interfaces and several orders of superlattice reflections. There was no evidence in either plan-view or cross-sectional TEM analyses of misfit interfacial dislocation arrays. The primary defects observed were dislocation loops with a diameter of 8–10 nm extending through several layers and small defects with a diameter of 1–2 nm that were confined within single layers. Microindentation hardness values H, measured as a function of λ in films with a total thickness of 2.5 μm, increased from 2035±280 kg mm−2 for Ti0.5V0.5N alloys (i.e., λ=0) to reach a maximum of 5560±1000 kg mm−2 at λ=5.2 nm and then decreased rapidly to 3950±550 kg mm−2 at λ=7.5 nm. Further increases in λ resulted in a slower decrease in H to 3640±550 kg mm−2 at λ=32 nm. The large error bars in the H values for the SLS samples were due to the difficulty in measuring such extremely high hardnesses in thin films. (H for pure single-crystal TiN and VN films were 2200±300 and 1620±200 kg mm−2, respectively.) SLS samples grown with constant λ=6.5 nm, but different lTiN /λ ratios, exhibited a maximum hardness at lTiN /λ≂0.3.
Characterization of deep levels in zinc oxide
Authors: Simpson J. C. , Cordaro J. F.
Published: July 2002

An electron trap of 0.3 eV depth was characterized in hydrothermally grown, single-crystal zinc oxide using deep-level transient spectroscopy. Specimens were fabricated with Ag Schottky contacts on (0001) surfaces. The capture cross section was determined to be 2.6×10−14 cm2. The defect is a native donor and is attributed to a singly ionized oxygen vacancy V•O.
Magnetization buckling in elongated particles of coated iron oxides
Authors: Aharoni Amikam
Published: July 2002

The whole eigenvalue spectrum is investigated for the nucleation of the magnetization reversal in an infinite circular cylinder, which has a uniaxial anisotropy (parallel to the cylinder axis) only in a cylindrical shell, on the surface. Numerical solution for the buckling mode is carried out for the physical parameters of acicular γ-Fe2O3 particles, coated with CoFe2O4, and show that it is the curling mode which takes place in the experiments on such particles. The best fit to the available experimental data yields an exchange constant A≂9×10−8 erg/cm for γ-Fe2O3.
Production of high-quality amorphous silicon films by evaporative silane surface decomposition
Authors: Doyle J. , Robertson R. , Lin G. H. , He M. Z. , Gallagher A.
Published: July 2002

High-quality hydrogenated amorphous silicon films (a-Si:H) have been produced by decomposition of low-pressure silane gas on a very hot surface with deposition on a nearby, typically 210 °C substrate. A high-temperature tungsten filament provides the surface for heterogeneous thermal decomposition of the low-pressure silane and subsequent evaporation of atomic silicon and hydrogen. These evaporated species (primarily) induce a-Si:H growth on nearby substrates which are temperature controlled using a novel substrate holder. The light and dark conductivities, optical band gap, deposition rates, and light-soaking effects of preliminary films are reported. The decomposition-evaporation process has been examined using a mass spectrometer to directly detect the decomposition rate and the evaporated radical species. Based on this data and other information, a simplified model for the deposition process is suggested. The excellent film quality and the attributes of the deposition process make this technique, which was originally suggested by Wiessman, viable for the fast rate, large-area deposition of a-Si:H for solar cells and other applications.
Wave dispersion theory in a plasma column bounded by a cylindrical waveguide
Authors: Uhm H. S. , Nguyen K. T. , Schneider R. F. , Smith J. R.
Published: July 2002

A unified theory of the electromagnetic wave propagation in a plasma column immersed in an axial magnetic field is developed, including the important influence of finite geometrical effects on wave dispersion properties. The analysis is carried out within the framework of a macroscopic cold fluid model. Coupled eigenvalue equations for the electromagnetic perturbations are obtained for an arbitrary density profile. For a flat-top density, a closed algebraic dispersion relation of the electromagnetic wave is obtained without any prior approximation. This transcendental dispersion relation is analytically solved in special cases of (a) uniform plasma, (b) infinite magnetic field, (c) zero magnetic field, (d) electrostatic perturbations, and (e) the low-frequency whistlerlike mode. In order to demonstrate the important influence of finite geometrical effects, the low-frequency whistlerlike mode is rigorously investigated for axisymmetric waves in a completely filled waveguide. From the analysis, it is shown that the whistlerlike mode propagates in the axial direction only when the total electron line density exceeds a critical line density. Moreover, the conventional dispersion relation of the low-frequency whistler mode is recovered only for a large plasma radius. Otherwise, the plasma geometrical effects play a pivotal role in wave propagation.
Temperature dependence of interface anisotropy in Ni/Mo multilayers
Authors: Pechan Michael J.
Published: July 2002

Equal layer thickness Ni/Mo multilayer samples ranging in Ni layer thickness d from 14 to 340 Å have been investigated by x-band ferromagnetic resonance at temperatures between 4 and 293 K. The dependence of anisotropy (less demagnetization) Ha upon d clearly indicates the interface anisotropy plays a significant role in these samples. Interface (Ks) and volume (Kv) contributions to the anisotropy are extracted at each temperature using an approximate form of Ha=2(Kv+2Ks/d)/M. The Ks temperature dependence is shown to be inconsistent with a simple mean field model and indicates that interface strain due to the Ni-Mo lattice mismatch is largely responsible for the origin of Ks.
The enhanced magnetic moment and structural study of Fe/MgO multilayered films
Authors: Koyano T. , Kuroiwa Y. , Kita E. , Saegusa N. , Ohshima K. , Tasaki A.
Published: July 2002

We have found that Fe atoms in Fe/MgO multilayered films prepared in the UHV condition have a magnetic moment larger than that for bulk α-Fe. The magnetization of Fe atoms in Fe/MgO (10 Å/15 Å) film is about 240 emu/g at 4.2 K. The hyperfine field is 350 kOe at 4.2 K, which is also larger than that of bulk α-Fe.
Monte Carlo simulations of plasma-deposited amorphous silicon
Authors: Shaw John G. , Tsai C. C.
Published: July 2002

Estimates of the effective deposition probability for plasma-deposited amorphous silicon (a-Si:H) films were obtained from computer simulations using a Monte Carlo technique. Randomized scattering events are tracked to simulate the deposition of a-Si:H along etched trenches under a metallic shadow mask. The resulting film thickness profiles are consistent with scanning electron micrographs obtained from step coverage experiments. Device quality materials tend to have effective deposition probabilities lower than 0.01 and are associated with CVD-like deposition involving SiH3 radicals. Defective materials are found to have deposition probabilities near unity and are associated with a PVD-like process involving SiH and SiH2 radicals.
Effect of target-substrate distance on the growth and properties of rf-sputtered indium tin oxide films
Authors: Vasant Kumar C. V. R. , Mansingh Abhai
Published: July 2002

Indium tin oxide films have been deposited by rf sputtering an oxide target (90% In2O3+10% SnO2). Transparent conducting films have been obtained on room-temperature substrates without any post-deposition annealing. The effects of target-substrate separation on the growth characteristics and film properties have been studied. The virtual-source formation of the sputtered neutrals in the gap between the target and substrate has been observed. The effect of sputtering parameters on the position of the virtual source has been studied. It has been observed that the films deposited onto substrates kept below and above the virtual source have different properties. The films on substrates kept above the virtual source have (222) preferred orientations, with a direct optical band gap of 3.7 eV, an electron effective mass of 0.51 m, and a figure of merit ∼14×10−3 Ω−1. The films on substrates below the virtual source have preferred orientations along (440) and (400), with a band gap of 3.5 eV, an effective mass of 0.2 m, and a higher figure of merit ∼40×10−3 Ω−1.
Underdetermined system theory applied to qualitative analysis of response caused by attenuating plane waves
Authors: Sano Yukio
Published: July 2002

A qualitative analysis of the mechanical response of rate-dependent media caused by a one-dimensional plane smooth wave front and by a continuous wave front attenuating in the media is performed by an underdetermined system of nonlinear partial differential equations. The analysis reveals that smooth strain, particle velocity, and stress profiles, which the smooth wave front has, are not similar and that the wave front is composed of some partial waves having different properties. The property is represented by a set of strain rate, acceleration, and stress rate. The wave front derived here from the analysis is composed of four different partial waves. The front of the wave front is necessarily a contraction wave in which strain, particle velocity, and stress increase with time, while the rear is a rarefaction wave where they all decrease with time. Between these two wave fronts there are two remaining wave fronts. We call these wave fronts mesocontraction waves I and II. Wave front I is a wave in which stress decreases notwithstanding the increase in strain and particle velocity with time, which is followed by the other, i.e., wave front II, where with time, particle velocity, and stress decrease in spite of the increase in strain. The continuous wave front having continuous and nonsmooth profiles of strain, particle velocity, and stress can also be composed of four waves. These waves possess the same property as the corresponding waves in the smooth wave front mentioned above. The velocities at three boundaries that the waves have are discontinuous. Therefore, these four wave fronts are independent waves, just as a shock wave and a rarefraction wave. Specifically, the front wave, i.e., a contraction wave front is being outrun by a second wave front, the second one is being outrun by a third wave front, and the third is being outrun by a fourth wave front, i.e., a rarefaction wave. We call the second wave front degenerate contraction wave I. We also call the third one degenerate contraction wave II. The stress-strain path and the stress-particle velocity path at a position in a rate-dependent medium which is passed by the continuous wave front are schematically shown.
Qualitative analysis of degradation processes of attenuating plane waves by underdetermined system theory
Authors: Sano Yukio
Published: July 2002

A qualitative analysis of the mechanical response caused by smooth attenuating wave fronts and by continuous attenuating wave fronts degrading in rate-dependent media is performed by an underdetermined system of equations, that is, by equations of conservation of mass and momentum only. Degradation is defined as the decrease of the number of partial waves in a smooth wave front or of independent waves in a continuous wave front. For the smooth wave front the inceptive wave front with which the degradation commences is a wave that is composed of four partial waves found previously and named a contraction wave, mesocontraction waves I and II, and a rear rarefaction wave. The analysis reveals one possible degradation process that is caused by another rarefaction wave which first follows the rear wave and then outruns the rear wave, mesocontraction waves II and I in sequence. The continuous wave degrades from the inceptive continuous wave front which is composed of four independent waves found previously and named a contraction wave, degenerate contraction waves I and II, and a rear rarefaction wave. The analysis indicates that degradation from the inceptive wave front to the contraction wave is possible to progress in six different patterns. In short, the degradation can occur through six different processes. Each process gives rise to four different sets of strain, particle velocity, and stress profiles, and accordingly four different types of stress-strain paths and four different types of stress-particle velocity paths. The stress-strain paths induced during some of the processes are similar to the paths in sandstone computed by Seaman using the Lagrangian analysis. The stress-particle velocity paths induced during some of the processes are also similar to the paths in LASL graphite computed by Seaman.
A two-dimensionally focusing, quasi-optical antenna for millimeter-wave scattering in plasmas
Authors: Idehara T. , Tatsukawa T. , Brand G. F. , Fekete P. W. , Moore K. J.
Published: July 2002

A two-dimensionally focusing, quasi-optical antenna having one elliptical reflector and one parabolic reflector has been built for use with a tunable gyrotron in order to carry out millimeter-wave scattering measurements on the TORTUS tokamak plasma at the University of Sydney. The advantages of this antenna are the following: (1) The elliptical reflector focuses the radiation beam in the toroidal direction, while the parabolic reflector focuses in the direction of major radius. This gives excellent two-dimensional focusing in the plasma region, and consequently excellent spatial resolution. (2) The focal point can be easily swept along the direction of major radius in the whole plasma region, simply by changing the angle of the parabolic reflector by a small amount. These features have been demonstrated experimentally using the tunable gyrotron source, GYROTRON III, and in computations of the radiated fields.
Propagation of high-power microwave pulses in air breakdown environment
Authors: Kuo S. P. , Zhang Y. S. , Kossey Paul
Published: July 2002

A chamber experiment is conducted to study the propagation of high-power microwave pulses through the air. Two mechanisms responsible for two different degrees of tail erosion have been identified experimentally. The optimum pulse amplitude for maximum energy transfer through the air has also been determined.
Effect of SiOxNy gage insulator on amorphous silicon thin-film transistors
Authors: Hiranaka Kouichi , Yamaguchi Tadahisa
Published: July 2002

The effect of the plasma chemical vapor deposition SiOxNy gate insulator on the threshold voltage for amorphous thin-film transistors was investigated, using different compositions of SiOxNy. The density of trapped charges responsible for the threshold voltage shift was found to be minimum at x/y=0.58. Photoluminescence measurements reveal that the peak energy in the photoluminescence in SiOxNy layers has a maximum value at x/y=0.58. The threshold voltage (Vth) was also found to increase with further increase of x/y. The observed threshold voltage shift is qualitatively interpreted in terms of energy band at the insulator-silicon interface.
Embryonic development of X
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s under static magnetic fields up to 6.34 T
Authors: Ueno S. , Shiokawa K. , Iwamoto M.
Published: July 2002

A possible influence of intense magnetic fields on the embryonic development of frogs was studied in reference to a potential hazardous problem in magnetic resonance imaging technology. Fertilized eggs of African clawed toads, Xenopus laevis, were cultured in Amphibian Ringer solution under static magnetic fields up to 6.34 T for varying lengths of time, and their cleavage and early embryonic development were followed to examine the possibility of teratogenic effects. Fertilized eggs cultured under the static magnetic field for 6 h followed normal course of cleavage and normally developed into feeding tadpoles. Results were unchanged even when fertilized eggs were cultured for 18 h from the cleavage stage to the neurula stage under a magnetic field of 4.5 T. We conclude that static magnetic fields up to 6.34 T do not affect appreciably the rapid cleavage and the following cell multiplication and differentiation in Xenopus laevis.
Relativistic recoil and the railgun
Authors: Allen J. E. , Jones T. V.
Published: July 2002

It is shown that the concept of electromagnetic momentum can be used to calculate the force acting on the projectile in a railgun, thereby refuting some recent papers on the subject.
Homogeneous nucleation in spatially inhomogeneous systems
Authors: Shi G. , Seinfeld J. H. , Okuyama K.
Published: July 2002

Homogeneous nucleation of a vapor in the presence of the loss of clusters by diffusion and thermophoretic drift is investigated. Analytical results are obtained for the cluster size distribution and the rate of nucleation by solving the modified kinetic equation for nucleation. The implications of cluster loss by diffusion and phoretic drift on the onset of the homogeneous nucleation of silicon vapor in the horizontal epitaxial chemical vapor deposition reactor is discussed. The range of conditions under which the loss of subcritical clusters by diffusion and drift becomes important for the interpretation of diffusion cloud chamber experimental data of the onset conditions of the homogeneous nucleation of vapors is also delineated.
Silane dissociation products in deposition discharges
Authors: Doyle J. R. , Doughty D. A. , Gallagher A.
Published: July 2002

Time-dependent production of higher-silane gases and a-Si:H film are measured relative to decomposed silane in rf and dc, hot and cold cathode, static-gas discharges. From the absence of higher-silane production in very low silane partial-pressure discharges, it is inferred that most higher silanes are produced by gas-phase SiH2-initiated reactions. The higher silanes are thus tracers of SiH2, while the film production traces the fraction of H, SiH, and SiH3 in the initial decomposition. From the measured stable product yields, we deduce that SiH4→SiH2+2H is the dominant electron-collisional dissociation channel.