bluuebunny/crossref_metadata_2025 huggingface dataset:
Film structure and magnetic properties of ferromagnetic amorphous Bi2O3-Fe2O3-PbTiO3 films prepared by rf-reactive sputtering
Authors: Kajima A. , Kaneda T. , Ito H. , Fujii T. , Okamoto I.
Published: July 2002

Amorphous-like oxide films of the Bi2O3-Fe2O3-PbTiO3 ternary system prepared by rf-reactive sputtering exhibit ferromagnetism and ferroelectricity simultaneously well above room temperature. In this paper, we have investigated the relation between the film structure and the magnetic properties of the films by means of x-ray diffractometry, transmission electron microscopy, magnetization measurement with a vibrating-sample magnetometer, and Mössbauer spectroscopy. The film composition used in the study is 0.16Bi2O3-0.74Fe2O3-0.10PbTiO3, which attains the maximum magnetization in this ternary system. It is revealed that ferromagnetism originates from the amorphous part in the films.
Thermal behavior of fluorine in SiO2 and Si investigated by the  19F(p,αγ) 16O reaction and secondary-ion mass spectrometry
Authors: Yu Byoung-gon , Konuma Naoki , Arai Eiichi , Ohji Yuzuru , Nishioka Yasushiro
Published: July 2002

Thermal changes of implanted fluorine distributions in a SiO2 film and a (100)-oriented Si single crystal were investigated by the 19F(p, αγ) 16O reaction and secondary-ion mass spectrometry. Fluorine in the Si accumulates to a damaged region (consistent with a Monte Carlo simulation) after annealing above 700 °C for 30 min. This effect is not observed in the SiO2. Once the fluorine is trapped by the damaged region, nearly 80% of the fluorine stays in the silicon after annealing at 800 °C. In contrast, only 10% of implanted fluorine remains in the SiO2 after annealing at 800 °C. These effects are explained by assuming the difference in the natures of imperfections in these samples. Above 1000 °C, most of the fluorine diffuses out of both systems.
Interpretation of dislocation propagation velocities in strained GexSi1−x/Si(100) heterostructures by the diffusive kink pair model
Authors: Hull R. , Bean J. C. , Bahnck D. , Peticolas L. J. , Short K. T. , Unterwald F. C.
Published: July 2002

Experimental measurements of misfit dislocation velocities, obtained from in situ transmission electron microscope observations of strained GexSi1−x/Si(100) heterostructures, are compared with predictions of the diffusive double-kink (or ‘‘kink pair’’) model of dislocation propagation. Good agreement is observed between experiment and theory for buried strained layers with applied stresses in the range of hundreds of MPa. For very thin uncapped strained layers, the diffusive double-kink model does not describe experimental data well. In these structures better agreement between experiment and theory is obtained if we model single-kink nucleation at the epilayer free surface. We compare our experimental data to those of other groups, and show how our modeling can reconcile apparently disparate trends deduced by these other groups.
Extra ‘‘strange’’ modes in ion implanted lithium niobate waveguides
Authors: Zhang L. , Chandler P. J. , Townsend P. D.
Published: July 2002

An extra ‘‘strange’’ mode has been observed in the extraordinary index mode spectrum of certain optical waveguides produced by He+ ion implantation in LiNbO3. This behaves differently to the normal modes contained within the main optical well of the waveguide, for example when observed at varying wavelengths or after surface polishing. The mode has been shown to be a real guided-wave mode, and has been attributed to a subsidiary optical well located beyond the main nuclear damage optical barrier. It is suggested that this well is produced by the radiation-enhanced diffusion of Li+ towards the nuclear damage barrier, and the mechanism is compared with that responsible for the well on the near side of the barrier which causes the previously reported ‘‘missing’’ modes.
Structural and electrical properties of YBa2Cu3O7−x films on SrTiO3(110) substrates
Authors: Zheng J. P. , Dong S. Y. , Bhattacharya D. , Kwok H. S.
Published: July 2002

The structural and electrical properties of in situ laser deposited thin films of YBa2Cu3O7−x on SrTiO3(110) substrates were studied as a function of deposition temperature. It was found that at low temperatures, grains with the 〈110〉 axis perpendicular to the substrate surface dominated. At higher temperatures, 〈103〉 perpendicular films were obtained. The Jc was found to be extremely anisotropic. For 〈103〉 perpendicular films at 70 K, the Jc’s were found to be 0.85×106 A/cm2 and 5×102 A/cm2 along the substrate 〈100〉 and 〈110〉 directions, respectively.
Electron-optical-phonon scattering rates in a rectangular semiconductor quantum wire
Authors: Kim K. W. , Stroscio M. A. , Bhatt A. , Mickevicius R. , Mitin V. V.
Published: July 2002

One-dimensional electron-optical-phonon interaction Hamiltonians in a rectangular quantum wire consisting of diatomic polar semiconductors are derived under the macroscopic dielectric continuum model. The scattering rates calculated in a GaAs square quantum wire show that when the quantum wire is free-standing in vacuum, the interaction by the surface-optical phonon modes is very strong and may dominate over other scattering processes, especially with dimensions of about 100 Å or less. When the wire is embedded in a polar semiconductor (AlAs to be specific), the scattering rates by the surface-optical phonon modes become generally smaller, but yet comparable to those by the confined longitudinal-optical modes as the wire dimension shrinks. A considerable decrease in the total scattering rate for optical phonons as a result of simple reduction in dimensionality is not observed in this study.
A real time study of the growth of microcrystalline silicon on transparent conducting oxide substrates
Authors: Fang M. , Drevillon B.
Published: July 2002

A detailed real time ellipsometry study of the growth of microcrystalline silicon (μc-Si) films on transparent conducting oxide (TCO) substrates is presented. Indium tin oxide and ZnO substrates are compared. μc-Si films prepared either from a high power (SiH4,H2) plasma or by alternating the SiH4 and H2 plasmas (layer-by-layer technique) are considered. Insights into the mechanisms of the TCO/μc-Si interface formation are obtained. A strong chemical reduction of the TCO substrate is observed during the early stage of exposure to the (SiH4,H2) plasma. Then the ellipsometric measurements reveal an induction period of about 1 min before the nucleation of microcrystallites. μc-Si films deposited by the layer-by-layer technique display a different behavior, in particular the chemical interaction at the ZnO/μ-Si interface is not observed in this case.
A dynamic simulation of particle rearrangement in powder packings with realistic interactions
Authors: Yen K. Z. Y. , Chaki T. K.
Published: July 2002

A computer simulation of evolution of random structures of spherical particles has been performed by solving Newton’s equations of motion. The forces considered are gravity, Hertz contact force, frictional force, and van der Waals interaction (VDWI). 948 monosized particles were placed without overlapping inside a rigid cylindrical container by generating the coordinates of the centers of the particles with the help of a random number generator. The initial packing density was only 0.363. The particles were allowed to settle under gravity. When the coefficient of friction (μ) among the particles and between the particle and the wall of the container was 0.3, the packing density reached a value of 0.578. If there is no friction, the density reached 0.633 which is comparable to the random close-packed density obtained in the random structures of steel ball bearings. For small particles, VDWI can reduce the packing density by agglomeration of particles into local clusters. For example, with VDWI and μ of 0.3, the random structures of particles with diameter 100 and 50 μm had packing densities of 0.528 and 0.420, respectively.

When μ was increased to 0.7, the packing density of 100-μm particles with VDWI was 0.505, compared to 0.528 in the case of μ equal to 0.3. The average velocity of the particles initially increased, and after reaching a maximum, started to decrease due to collisions amongst the particles. During the dynamic simulation, the trajectories of a few selected particles were traced. To study the rearrangement process, the average displacement of a few particles in a direction normal to the direction of gravity and the average angle of rotation of the straight line joining the centers of a few selected pairs of particles were calculated at various instants of time. It is seen that the rearrangement of 50-μm particles was smaller than that of 100-μm particles because of VDWI. The radial distribution functions of the computer-generated close-packed structure is similar to that of Finney’s close-packed structure of steel balls. In the case of 50-μm particles with VDWI, there were additional peaks close to the first peak, due to agglomerating effect of VDWI. The cumulative number of contacts was computed as a function of the radial distance and, in the case of 100-μm particles without friction and VDWI, it agreed with Mason’s data for steel balls.
Opto-optical switching in ion-implanted poly(methyl methacrylate)-waveguides
Authors: Kulisch J. R. , Franke H. , Irmscher R. , Buchal Ch.
Published: July 2002

Implantation of 1-MeV and 2-MeV He+ in bulk poly-(methyl methacrylate) (PMMA) leads to the formation of monomode and multimode lightguides in the range of 1012–1014 ions/cm2. The waveguide profiles are measured in pure PMMA and in PMMA doped with some wt% of the azo dye Methyl-Red. Although parts of the dye molecules are destroyed in the implanted region, a residual dye concentration is maintained to obtain photoinduced TRANS-CIS isomerization, a change between two spatial forms of the molecule, in the guide area. This is demonstrated by switching the coupling intensity of the guided light by an exposure to blue light in the coupling zone of a prism coupler.
Reactive codeposition of in situ Y-Ba-Cu-O superconducting films using dilute mixtures of ozone in oxygen
Authors: Kubinski D. J. , Hoffman D. W. , Soltis R. E. , Logothetis E. M.
Published: July 2002

This investigation reports the effect of dilute additions of ozone in molecular oxygen on the limiting reactive gas pressures required for in situ deposition of YBa2Cu3O7−x thin films. Thermodynamic analysis indicates that the high oxidizing potential of ozone assures stability at equilibrium under virtually all experimental conditions of ozone pressure and substrate temperature. Thus the generation of a minor fraction of ozone in oxygen enables in situ deposition to be carried out without further enrichment at gas pressures well below those required in pure molecular oxygen. In situ superconductor deposition at various rates using coevaporated metals revealed a lower limit at an ozone-to-copper ratio of approximately unity. Superconducting films deposited at O3/Cu flux ratios above this threshold were highly (00l) oriented with critical temperatures of 87–90 K and critical currents of 2×106 A/cm2 that exhibited only small or ambiguous trends with increasing ozone above the threshold. Films deposited at O3/Cu ratios below the threshold were visually dissimilar (transparent-brown), semiconducting, and marked by conspicuous disappearance of the characteristic x-ray spectra. This threshold is a nonthermodynamic limit below which the supply of ozone is insufficient to maintain stoichiometry during continuous deposition. Since ozone molecules donate only single oxygen atoms in reaction, the observed limiting O3/Cu flux ratio supplies no more than one-half the total oxygen required to form tetragonal YBa2Cu3O6, which is the entry level phase for in situ deposition. It follows that molecular oxygen continues to function as a principal oxidant in reactive deposition even at reduced operating pressures given the stabilizing presence of ozone at a sufficient flux to elevate copper to its higher oxidation state.
Temporal relaxation measurements of photoinduced nonequilibrium in superconductors
Authors: Bluzer Nathan
Published: July 2002

A new technique, transient photoimpedance response (TPR), has been formulated and was used to measure the nonequilibrium relaxation process in YBCO and Niobium. The TPR method dispenses with the need for weak link structures and temporal relaxation measurements are made directly on unpatterned thin films. With a dc current bias, voltage signals are produced in response to photoabsorbed short (300 fs) laser pulses producing a transient impedance change. Nonequilibrium excitation lifetimes are related to the temporal dependence of the voltage signal produced by transient changes in the superconductor’s impedance. With the TPR technique excitation lifetimes in the normal, transition, and superconducting state are observed on each sample. Data interpretation is facilitated by measuring and comparing the TPR signal in all three states. Typically the normal- and transition-state TPR signals in YBCO and Nb are bolometric and correspond to resistive impedance changes. However, the relaxation signal’s time constants in the normal and transition states are different and are dominated by phonon trapping and the relaxation of the order parameter, respectively. In the zero-resistance superconducting state the TPR signal is due to kinetic inductance changes and the nonequilibrium’s relaxation is a manifestation of quasiparticle generation and recombination processes strongly influenced by phonon trapping in the sample. Qualitive and quantitative aspects of the TPR method are presented with some experimental results on YBCO and Nb.
Evidence for the recombination-enhanced dissociation of a hydrogen-carbon complex in silicon
Authors: Kamiura Yoichi , Yoneta Minoru , Nishiyama Yoshihide , Hashimoto Fumio
Published: July 2002

We have recently found that hydrogen injected into n-type crystalline silicon by chemical etching not only passivated phosphorus but also electrically activated substitutional carbon by forming a hydrogen-carbon complex with a donor level at Ec−0.15 eV. This article shows that the complex was annihilated by above-gap excitation near and below room temperature only outside the depletion layer of the Schottky structure under the application of various reverse bias voltages. This clearly proves that the hydrogen-carbon complex is dissociated via the recombination-enhanced defect reaction.
Modeling of physical etching based on the two-dimensional velocity distributions of ions and fast neutrals using the Boltzmann equation
Authors: Tokonami Tadashi , Makabe Toshiaki
Published: July 2002

A numerical model based on the Boltzmann equation is proposed to simulate the physical etching by energetic particles in the sheath region of the discharge. The local profiles of the two-dimensional velocity distributions of ions and fast neutrals in the gas phase are calculated in a radially uniform discharge, under a set of collision cross sections, for external parameters: sheath voltage and width, ion current density, and pressure. A case study is performed in a dc abnormal glow discharge in Ar having a masked Al electrode. The time evolution of the etching profile is simulated as a result of the physical interaction between the surface and energetic particles from the gas phase. This enables the estimation of the etch rate and anisotropy for ions and fast neutrals. A great advantage of the present numerical procedure is that it is free from stochastic fluctuations and the lengthy central processing unit time found in particle simulations.
The effect of heat treatment on the SrTiO3 thin films prepared by radio frequency magnetron sputtering
Authors: Nam Seung-Hee , Kim Ho-Gi
Published: July 2002

Strontium titanate thin films have been prepared on p-type Si(100) substrates by radio frequency (rf) magnetron sputtering. The films were deposited at 400 °C and annealed at various temperatures. The thin films were polycrystalline and the crystallinity of films was increased by annealing. The SrTiO3 thin films were composed of three regions; an external surface layer, a main layer, and an interface layer. The composition and the width of the interface layer were not changed by annealing below 600 °C. The composition ratio of films, as analyzed by the Rutherford backscattering technique, was 1, 1.1, and 3 for Sr, Ti, and O, respectively. The electrical properties of SrTiO3 films were dramatically controlled by annealing. The SrTiO3 film annealed at 600 °C had ideal capacitance-voltage characteristics and maximum effective dielectric constant.
Analysis of double injection transients in amorphous silicon p-i-n diodes
Authors: Hack M. , Street R. A.
Published: July 2002

In this article we present results of both experimental and computer modeling studies of transient double injection currents in amorphous silicon p-i-n diodes. After the application of a forward bias step pulse, the current decays until there is a sudden sharp rise, often by two to three orders of magnitude. The delay time for this current increase varies from microseconds to many milliseconds, and it is found to be strongly dependent on the pulse repetition rate, applied bias, degradation state of the sample, and illumination. Our results are in good agreement with computer simulations of these phenomena. The sudden current rise is associated with a change in transport mechanism from electron space-charge limited current flow to bipolar recombination limited current flow. Experimentally and theoretically it is found that in a degraded device the delay time is also very dependent on the spatial position of the metastable defects, with those near the n+ contact having a much more dominant effect than those near the p+ contact.
Magnetic hysteresis in thin ferromagnetic films
Authors: Nowak J.
Published: July 2002

The magnetic hysteresis in thin ferromagnetic films with in plane anisotropy is described using a simple modification of the Stoner–Wohlfarth model of coherent rotations. Introducing an additional internal field results in very realistic shapes of hysteresis loops and removes the nonphysical singularities characteristic for coherent rotations. This additional field originates from the domain structure and represents the effect of incoherent rotations occurring during the magnetization process. The component of this field parallel to the external magnetic field determines the width of the hysteresis loop, while the perpendicular component defines the slope of the hysteresis loop and its squareness.
An equilibrium model of the semiconductor heterojunction diode based on kinetic theory
Authors: Le Coz Y. L. , Tiersten H. F.
Published: July 2002

A mathematical model for a semiconductor heterojunction diode at equilibrium based on kinetic theory of inhomogeneous systems is presented. A generalized Boltzmann equation for variable effective mass is obtained from Marshak and van Vliet’s extended Wannier–Slater Hamiltonian [Solid-State Electron. 21, 417 (1978)]. An Ehrenfest correspondence procedure has shown that only forces due to variation in band-edge energy and electric potential energy arise; the supposed force arising from the spatial gradient of effective mass does not exist. The diode model consists of three separate regions: two regions of homogeneous material composition and a finite interface region of inhomogeneous composition. Boltzmann’s equation is solved in each region as a function of arbitrary electric potential. Physically reasonable boundary and continuity conditions are also established. Closed-form analytical solution of our model equations does not appear to be possible because of the coupling with Poisson’s equation. To demonstrate the implications of our model without resorting to a numerical investigation, we make some reasonable simplifying assumptions to derive a new built-in potential formula. The formula suggests that an error exists in the currently accepted formula. The error is particularly large when carrier effective density-of-states ratios across the diode are appreciably greater than unity.
Models for the stray field from magnetic tips used in magnetic force microscopy
Authors: Wadas A. , Hug H. J.
Published: July 2002

This letter presents a theoretical approach for calculating the stray magnetic field of the tiny tip used in magnetic force microscopy (MFM). We consider several models for the tip. We demonstrate the advantage of using nonmagnetic tips covered by a magnetic thin film to improve lateral resolution of MFM. The analysis is quantitative and can be directly applied to a real tip that conforms to the shape limitations of our model. The same analysis can be applied to the case of a superconducting sample.
Study of epitaxial platinum thin films grown by metalorganic chemical vapor deposition
Authors: Kwak B. S. , First P. N. , Erbil A. , Wilkens B. J. , Budai J. D. , Chisholm M. F. , Boatner L. A.
Published: July 2002

The metalorganic chemical vapor deposition technique has been successfully applied to the growth of epitaxial platinum thin films on (100) surfaces of single-crystal potassium tantalate (KTaO3) and strontium titanate (SrTiO3). Platinum thin films grown on KTaO3 (100) at a rate of 70 nm/h showed strong Rutherford backscattering spectroscopy (RBS)/channeling effects with a χmin of 4%. In-plane φ and θ-2θ scan x-ray diffraction analysis demonstrated the three-dimensional epitaxial alignment of the platinum film with the KTaO3 substrate. Transmission electron micrographs viewed in cross section provided additional information regarding the nature of the epitaxial Pt-KTaO3 interface. The room-temperature resistivity of a 60-nm-thick Pt film on KTaO3 (100) was 12.0 μΩ cm. X-ray diffraction and pole-figure analysis showed that in the case of Pt films deposited on either fused quartz or Si (100) surfaces, the resulting films were polycrystalline and were fully textured with <111≳ orientations perpendicular to the substrate surfaces.
Piezoelectric wave dispersion curves for infinite anisotropic plates
Authors: Syngellakis S. , Lee P. C. Y.
Published: July 2002

Plane-wave propagation in an infinite plate is analyzed by the linear three-dimensional theory of piezoelectricity. The general dispersion relation, valid for any degree of anisotropy and for the commonly applicable electrical boundary conditions, is formulated. The general equation yielding the surface wave velocities is also derived. A numerical algorithm, potentially applicable to piezoelectric plates of any material symmetry, is developed. Results are obtained for particular crystal cuts of practical interest and waves propagating in the coordinate directions. Comparison with corresponding predictions by the purely elastic theory allows assessment of the effect of electromechanical coupling as well as of the accuracy of the computed dispersion relationships.
Magnetic and conversion electron Mössbauer spectroscopy studies in Fe/Ta multilayers
Authors: Shringi S. N. , Piramanayagam S. N. , Prasad Shiva , Venkatramani N. , Patni M. J. , Krishnan R. , Tessier M.
Published: July 2002

We have prepared Fe/Ta multilayers by rf sputtering. A small 1-cm2 chip of 57Fe was placed on the Fe target. We studied the magnetization (M) and M-H loops and also carried out conversion electron Mössbauer spectroscopy (CEMS). The in-plane loops are rectangular with a lowest coercivity of 2.6 Oe. Magnetization studies indicate a dead Fe layer about 5 Å thick at each interface. CEMS spectra for samples with t(Fe)≥54 Å showed a typical six-line pattern, indicating the presence of bulk Fe. No other Fe sites could be detected. However, for t(Fe)=24 Å, where almost 50% of Fe is nonmagnetic, CEMS spectra showed the presence of a strong paramagnetic doublet.
Magnetoresistance of the random anisotropic Co70.4Fe4.6Si15B10 alloy
Authors: Machado F. L. A. , Lopes da Silva B. , Montarroyos E.
Published: July 2002

Longitudinal magnetoresistance measurements in Co70.4Fe4.6Si15B10 are reported for applied magnetic fields H varying from 0 to ±15 Oe. Two regimes were observed: one which increases with H2 and another which decreases with M2 for higher fields. The maximum in the magnetoresistance is observed for H=2.4 Oe for samples annealed for 15 min at 573 K in a transverse magnetic field of 2 kOe. The measured variation in R(H) from H=0 to 2.4 was about 0.2%. The value of H=2.4 is nearly the same field where a field-induced transition in the magnetization was observed. For samples annealed in the absence of the magnetic field the H2 term is the only one observed. The present results can be accounted for by the rotational model for uniaxial transverse anisotropy and the results are also in agreement with the random anisotropy model used to discuss the irreversibility and the field-induced transition.
Laser-enhanced synthesis and processing of diamond films from liquid hydrocarbons
Authors: Singh Jogender , Vellaikal M. , Narayan J.
Published: July 2002

We report synthesis of diamond films by pulsed laser irradiation on copper substrate immersed into liquid benzene. It is envisaged that carbon released from benzene at the liquid–solid interface is converted into diamond as a result of rapid quenching from a high temperature. The diamond crystallites were characterized using high resolution transmission electron microscopy imaging and electron diffraction techniques. Growth of thicker diamond films by subsequent chemical vapor deposition has been investigated by transmission and scanning electron microscopy techniques. Thin diamond film deposited during liquid phase provided seed for diamond growth during subsequent chemical vapor deposition.
Fracto-emission from high density polyethylene: Bond breaking versus tribological stimulation
Authors: Dickinson J. T. , Jensen L. C. , Dion R. P.
Published: July 2002

We reexamine the emission of electrons and positive ions from high density polyethylene (HDPE) during tensile deformation at strain rates on the order of 30% s−1. Earlier reports have suggested that electron emission due to bond scissions accompanying deformation of HDPE have been observed. Here we focus on the role of small frictional effects on the polymer at the edges of the clamps due to slippage during elongation. We show that when slippage is eliminated, the deformation-induced particle emission vanishes. Thus, the prefailure electron and positive ion emission is apparently not due to bond scissions as a result of tensile deformation of the polymer but to slippage of the polymer in the grips. We discuss the processes occurring during tribological loading which produce intense, longer lasting emission during and after stimulation. We present evidence that the emission due to tribological loading involves charge transfer upon contact between metal and polymer, mechanical separation of charge, and subsequent dynamic stimulation of the polymer surface due to energetic charge motion (surface flashover).
Thomson scattering measurements of electron temperature and density in an electron cyclotron resonance plasma
Authors: Bowden M. D. , Okamoto T. , Kimura F. , Muta H. , Uchino K. , Muraoka K. , Sakoda T. , Maeda M. , Manabe Y. , Kitagawa M. , Kimura T.
Published: July 2002

Electron temperature Te and density ne in the source region of an electron cyclotron resonance discharge have been measured by incoherent Thomson scattering of the beam from a 0.5 J yttrium aluminum garnet laser. This is the first experiment in which this technique, routinely used on fusion plasmas, has been applied to a processing plasma. Measurements were made in an argon discharge at pressures from 0.3 to 2 mTorr and microwave powers from 250 to 1000 W. Velocity distributions were measured both parallel and perpendicular to the magnetic field and a slight anisotropy of electron temperature was observed for low-pressure discharges. Temperatures in the range of 1–5 eV and densities in the range of 2–10×1017 m−3 were measured. Te and ne were found to strongly depend on pressure but only weakly on the input power and discharge magnetic field. No deviations from a Maxwellian velocity distribution were observed.
Luminescence due to lattice-mismatch defects in ZnTe layers grown by metalorganic vapor phase epitaxy
Authors: Naumov A. , Wolf K. , Reisinger T. , Stanzl H. , Gebhardt W.
Published: July 2002

Two sharp and intense emission bands with the maxima of 2.185 and 2.150 eV and a weak phonon coupling were investigated in the heteroepitaxial ZnTe layers. The study of the ZnTe layers grown on different substrates with thicknesses of 0.5–3.2 μm has shown that this luminescence is produced in the interface region that contains a high density of structural defects. The temperature dependence of these bands reveals the excitonic character of the recombination. We propose that the observed bands originate from the recombination of excitons localized at structural defects such as dislocations and associated defects.
Inelastic electron tunneling spectroscopy and atomic force microscopy investigation of ultrathin sputtered amorphous silica films on gold
Authors: Mallik R. R. , Butler T. , Kulnis W. J. , DeVier B.
Published: July 2002

Ultrathin amorphous SiO2 films are radio frequency sputter deposited onto thin film gold electrodes and incorporated as the insulating barrier in metal/insulator/metal tunnel junctions of the type Au/SiO2/Pb. Inelastic electron tunneling spectra (IETS) recorded at 4.2 K reveal characteristic zero bias anomalies associated with rapid variations in the Pb density of states on either side of the superconducting gap which shows unequivocally that tunneling is the primary conduction mechanism through the junctions at this temperature. Full IET spectra reported are essentially identical to those previously recorded for similar SiO2 films on aluminum. Atomic force and scanning tunneling microscope images of the SiO2 and underlying gold films are also presented; these data confirm that the SiO2 films are sufficiently uniform and continuous for IETS.
The low-temperature photochromic response of bismuth silicon oxide
Authors: Hart D. W. , Hunt C. A. , Hunt D. D. , Martin J. J. , Harris Meckie T. , Larkin John J.
Published: July 2002

Exposing the photorefractive material bismuth silicon oxide (BSO) at low temperatures to 2.4–3.3 eV light produces photochromic absorption bands. In undoped and Fe-doped BSO these bands appear to consist of a series of overlapping bands ranging from around 1.5 eV in the infrared to near the band edge. The infrared component is always weaker than the visible range contributions. The infrared portion anneals just above 100 K; in some samples this anneal is accompanied by the appearance of additional structure in the visible region. In undoped BSO the major anneal of the photochromic bands takes place above 200 K. If iron is present the photochromic bands are weaker and an anneal stage in the 120–150 K range appears. Bleaching with either 1.51 or 2.28 eV laser light uniformly lowered the photochromic bands in both undoped and Fe-doped BSO. In BSO:Al the aluminum electronically compensates the deep donor centers responsible for the yellow coloration observed in undoped crystals. At low temperatures, photoexcitation using near band-edge light produces the same overlapping bands at 1, 1.38, and 2.45 eV that were observed in BGO:Al. These bands anneal together between 80 and 100 K. The [AlO4]0 center which causes the coloration observed in smoky quartz is a plausible model for the photochromic bands in BSO:Al.
Point defects in lithium triborate (LiB3O5) crystals
Authors: Scripsick M. P. , Fang X. H. , Edwards G. J. , Halliburton L. E. , Tyminski J. K.
Published: July 2002

Electron paramagnetic resonance (EPR), electron-nuclear double resonance, optical absorption, and thermoluminescence have been used to investigate radiation-induced point defects in a single crystal of lithium triborate (LiB3O5). Two prominent defects are observed after irradiation near liquid-nitrogen temperature with 60 kV x rays. A four-line EPR spectrum, with 12.2 G splittings, is assigned to a trapped-hole center, and another four-line EPR spectrum, with 120 G splittings, is assigned to a trapped-electron center. In each case, the nucleus responsible for the observed hyperfine is 11B. The trapped hole is localized on an oxygen ion and has a weak hyperfine interaction with one neighboring boron nucleus, whereas the trapped electron is localized primarily on a boron ion with a correspondingly larger hyperfine interaction. Both defects become thermally unstable near 125 K, and their decay (i.e., recombination) correlates with an intense thermoluminescence peak at this same temperature. An optical absorption peak at 300 nm is produced by the x rays and thermally decays at the same temperatures as the EPR spectra.
Dynamic processes in thin-film heads at frequencies up to 200 MHz
Authors: Shi X. , Kryder M. H.
Published: July 2002

In this article we present quantitative investigations of dynamic processes in 3380E and 3390 thin-film heads and the dynamic domain configurations of the 3380E head mapped at frequencies up to 200 MHz. The quantitative studies include measuring both the phase and the amplitude of wall motion and rotational magnetization. For a longitudinal domain wall near the back gap of the 3380E head, the phase lag, which was found to be a function of drive field, increases at a rate of 35° per 10 MHz initially. However, when the phase lag reaches the range from 35° to 45°, the wall jumps to a new position where the phase lag is smaller. This wall can still conduct magnetic flux even at 200 MHz. For the rotational process, significant damping was detected above 50 MHz.
Structural and electrical characteristics of SrTiO3 thin films for dynamic random access memory applications
Authors: Joshi P. C. , Krupanidhi S. B.
Published: July 2002

Polycrystalline SrTiO3 thin films having perovskite structure were prepared by the metallo-organic solution deposition technique on platinum coated silicon and bare silicon substrates. Crack free and crystalline films with uniform composition and thickness were fabricated by spinning and post deposition rapid thermal annealing at a low temperature of 550 °C for 60 s. The films exhibited good structural, dielectric, and insulating properties. The dielectric constant was found to depend on film thickness and annealing temperature. The small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 225 and 0.008, respectively, for a 0.8-μm-thick film annealed at 700 °C for 60 s. The frequency dependence of the dielectric constant and the dielectric loss was also studied. The measurement of the current-voltage (I-V) characteristics on films in metal-insulator-metal configuration indicated the conduction process to be bulk limited. The I-V characteristics were ohmic at low fields and space-charge limited at high fields. Room temperature resistivity of 1013 Ω cm and leakage current density of less than 10−8 A/cm2 were obtained for a 0.8-μm-thick film at an applied electric field of 200 kV/cm, establishing good insulating behavior. The interfacial properties of gold-strontium titanate-silicon structures were studied experimentally by measuring the capacitance-voltage (C-V) characteristics. The C-V curves exhibited anomalous frequency dispersion behavior and a hysteresis phenomenon. The hysteresis in the C-V curve was found to be about 0.8 V and of a charge injection type. The density of interface states recharged during the bias cycle in hysteresis measurement was estimated to be of the order of 8.3×1011 cm−2. The density of interface states at the flatband voltage was found to have a value of 1.38×1012 eV−1 cm−2. For a 0.5-μm-thick SrTiO3 film, a unit area capacitance of 3.5 fF/μm2 and a charge storage density of 36.7 fC/μm2 were obtained at an applied electric field of 200 kV/cm. These measured parameters place SrTiO3 as one of the suitable dielectric material for dynamic random access memory applications.
Hole-phonon scattering in strained SiGe quantum wells
Authors: Bhaumik K. , Ridley B. K. , Shacham-Diamand Y.
Published: July 2002

The interaction between holes confined in a strained Si1−xGex quantum well and acoustic and optical phonons is investigated in an effort to elucidate in-plane carrier transport. This treatment utilizes conventional deformation potential theory within the context of the momentum conservation approximation in the confinement direction to obtain analytical expressions for both acoustic and optical phonon scattering rates as functions of carrier energy. The optical phonon interaction explicitly accounts for the three vibrational modes: Si-Si, Si-Ge, and Ge-Ge by incorporating experimentally determined longitudinal optical (LO) phonon frequency shifts in the calculation of the matrix elements. The oscillator strengths for each of these LO (short wavelength) modes are approximated using a binomial distribution to describe the local atomic arrangement of a unit cell. The two-dimensional scattering rates are evaluated and compared with bulk scattering calculations for a well of fixed width and varying Ge content. It is found that the overall hole-phonon scattering rate in a SiGe well is higher than that of holes in strained SiGe layers due to the combined effects of similar two- and three-dimensional density of states and large inter-sub-band scattering. A qualitative description of high field transport within the well is obtained by calculating the relative contributions of particular optical phonon modes to the overall scattering rate at high carrier energies.
Strong Kα emission in picosecond laser-plasma interactions
Authors: Soom B. , Chen H. , Fisher Y. , Meyerhofer D. D.
Published: July 2002

Kα emission is observed from the interaction of a picosecond, 1.05 μm laser pulse at 4×1015 W/cm2 with a silicon target coated with various thicknesses of aluminum. Strong Kα emission requires a p-polarized, high-intensity-contrast laser pulse. At 7.1 Å, the Kα yield is 1.5×108 photons/sr with a duration of emission of ≤8 ps and a source area of 1.6×10−6 cm2. The radiance is ≥3×109 W/cm2 sr. Monte Carlo simulations have suggested that under these conditions Kα emission is a promising candidate for an efficient, ultra-short-duration x-ray source at ∼1.5 Å.
Microstructure based statistical model of electromigration damage in confined line metallizations in the presence of thermally induced stresses
Authors: Korhonen M. A. , Bo/rgesen P. , Brown D. D. , Li Che-Yu
Published: July 2002

Probability distributions are evaluated for electromigration induced open failures in narrow, passivated interconnects with a near-bamboo grain structure. Void formation is initiated at the cathode ends of the polycrystalline line segments or ‘‘grain clusters.’’ If these clusters are longer than a critical size Lc, they can accommodate enough atoms for voids to reach the critical size to fail the line. Obviously, the critical size Lc depends on the thermal stress: a cluster under a tensile stress is able to incorporate more atoms from the void than an unstressed cluster. In the case the clusters are shorter than Lc, atoms from the voids must be distributed also to bamboo sections, outside the clusters, in order for the voids to induce open failures. Based on this physical picture, failure probabilities are evaluated as a function of time. The predicted failure distributions and parametric dependencies compare well with the experiments.
Temperature limits on infrared detectivities of InAs/InxGa1−xSb superlattices and bulk HgxCd1−xTe
Authors: Young P. M. , Grein C. H. , Ehrenreich H. , Miles R. H.
Published: July 2002

Detailed theoretical calculations of Auger and radiative recombination rates for an optimized InAs/InxGa1−xSb superlattice (SL) and bulk HgxCd1−xTe (MCT) show that 300 K background limited operation for a 60° field of view can be theoretically achieved up to 130 K for the 11 μm SL and up to 185 K for 5 μm MCT. The SL structure is theoretically superior to MCT for 11 μm operation. The converse is true at 5 μm.
Determination of the mobility and transport properties of photocarriers in Bi12GeO20 by the time-of-flight technique
Authors: Ennouri A. , Tapiero M. , Vola J. P. , Zielinger J. P. , Moisan J. Y. , Launay J. C.
Published: July 2002

A direct measurement of a key material parameter in photorefractivity, the charge carrier mobility, has been achieved only recently by means of a holographic time-of-flight technique. In this paper we report, as far as we know, the first successful direct determination of electron mobility using the classical time-of-flight method. This consists in measuring the velocity of a sheet of excess carriers, created by a short-duration excitation pulse of strongly absorbed photons close to the surface. These carriers drift through the sample under the action of an applied electric field. However, the technique could not be used in its original configuration. A constant background illumination was required in order to saturate traps and to prevent space charge build up. Optimal illumination conditions (wavelength below 550 nm, suitable integrated number of photons) were found under which a quasifree, nondispersive, charge transport was observed. The mobility is limited by interaction with a shallow trap, the population of which can be modulated by the additional monochromatic illumination. An unexpected high value was found as compared to results published earlier. This value is probably very close to the microscopic collision-limited mobility. This explains the relatively small spread of the results obtained with different nominally undoped Bi12GeO20 (BGO) samples. The values lie in the range 0.2–1.0 cm2 V−1 s−1. They are in excellent agreement with that measured elsewhere in BSO using the holographic time-of-flight technique.
Temperature dependence of the photorefractive effect in undoped Bi12GeO20
Authors: Foldvari Istvan , Martin Joel J. , Hunt Charles A. , Powell Richard C. , Reeves Roger J. , Peter Agnes
Published: July 2002

The low-temperature four-wave mixing (FWM) photorefractive response was investigated in undoped Bi12GeO20 (BGO) crystals. The FWM diffraction efficiency increases as the temperature is lowered until a local maximum is reached after which it decreases. The temperature where the maximum intensity FWM signal occurs depends on the write conditions. A model assuming both electron and hole gratings was used to describe the observations. Two shallow trap levels of 0.015 and 0.08 eV were identified as being responsible for the fast decay (<1 s) components of the FWM signal in undoped BGO.
Thermal stability of cobalt silicide thin films on Si(100)
Authors: Chen Bin-Shing , Chen Mao-Chieh
Published: July 2002

The thermal stability of blank and BF2−-implanted cobalt silicide (CoSi2) films annealed in a furnace with flowing nitrogen was investigated. It was found that BF2+ implantation can significantly stabilize thin silicide films during high-temperature annealing. This result can be attributed to an increase in surface and interface energy. For a CoSi2 film with a thickness of 350 Å, the silicide releases its high surface energy through low-energy silicon surface exposure at elevated annealing temperatures (≥800 °C). The optimal BF2+ implantation energy for a cobalt silicide layer 350 Å thick is 50 keV. At this energy, a dose of 2×1015 cm−2 is sufficient to improve the high-temperature stability of CoSi2 film. The highest annealing temperature without degrading the CoSi2 film can be increased by 100 °C using the optimal implantation conditions.
Finite element solution of the nonlinear Poisson equation for semiconductor devices using the fixed-point iteration method
Authors: Kobeissi H. , Ghannouchi F. M. , Khebir A.
Published: July 2002

The fixed-point iteration method is extended to the finite element solution of the nonlinear Poisson equation of semiconductor devices. The boundary value problem is derived and shown to have a global convergence. In addition, using explicit formulas to update the value of the electrostatic potential, the solution of simultaneous equations is avoided. A numerical example of a metal-oxide-semiconductor field-effect transistor at thermal equilibrium is presented.
Hydrogen atom recombination on tungsten and diamond in hot filament assisted deposition of diamond
Authors: Gat Roy , Angus John C.
Published: July 2002

A hot-filament chemical vapor deposition reactor in which the substrate is a heated wire was used to analyze the energy transport to the substrate during diamond deposition. In this reactor, radiation and convection contribute negligibly to substrate heating. Atomic hydrogen recombination to molecular hydrogen on the substrate surface accounts for ∼90% of the energy reaching the substrate. The atomic hydrogen recombination rate and the thermal accommodation coefficient for the energy released by atomic hydrogen recombination were estimated from in situ measurements for tungsten and diamond surfaces. The atomic hydrogen concentration gradient was estimated for simple geometries. The experimental conditions under which atomic hydrogen transport to the substrate is diffusion controlled were found. Addition of methane reduced the atomic hydrogen recombination rate on the substrate. An optimum pressure was found for the transport of atomic hydrogen to the substrate.
Absorption spectroscopy on room temperature excitonic transitions in strained layer InGaAs/InGaAlAs multiquantum-well structures
Authors: Hirayama Y. , Choi Woo-Young , Peng L. H. , Fonstad C. G.
Published: July 2002

The physical properties (transition energy, oscillator strength, linewidth, binding energy, and reduced effective mass) of room temperature excitons in compressively strained InGaAs/InGaAlAs multiquantum-well (MQW) structures as a function of the well width have been investigated for the first time by both absorption measurements and photomodulated transmittance measurements. Photomodulated transmittance spectroscopy has been successfully applied to clearly reveal critical transition points. Measured transition energies are in good agreement with a model which includes the heavy hole and light hole splitting due to the strain. For well widths of 2.5–7.5 nm, oscillator strengths are smaller for the strained layer MQWs than for the lattice-matched MQWs by 35%–45%. This is due to the larger exciton radius for the strained MQWs resulting from smaller in-plane reduced effective masses (0.031–0.038m0), which are 65% of those of the lattice-matched MQWs.
Magnetic properties of (Er,R)2Fe17Ny compounds (R=Y,Gd)
Authors: Wang J. L. , Lin W. G. , Tang N. , Li W. Z. , Gao Y. H. , Yang F. M.
Published: July 2002

Structural and magnetic properties of the interstitial (Er1−xRx)2Fe17Ny compounds with R=Y and Gd, x=0, 0.1, 0.25, 0.4, 0.5, 0.6, 0.75, and 1.0, 2<y<3, have been investigated. All the parent compounds crystallize in the Th2Ni17-type structure, except for Gd2Fe17 which crystallizes in the Th2Zn17-structure. All nitrides preserve the same structure as the parents. Introduction of nitrogen results in an increase in lattice constants a and c, and the expansion of unit-cell volume is about 6%. The Curie temperature was found to increase distinctly after nitrogenation. Nitrogen absorption leads to an increase in saturation magnetization, the values of the saturation magnetization increase monotonically with increasing Y or Gd concentration. Nitrogenation increases the uniaxial anisotropy of the Er sublattice, and causes a spin reorientation. The Y and Gd concentration dependencies of the spin reorientation temperature Tsr exhibit maxima. The tentative spin phase diagrams are presented.