bluuebunny/crossref_metadata_2025 huggingface dataset:
Correlation between magnetic properties of layered ferromagnetic/dielectric material and tunable microwave device applications
Authors: Salahun Erwan , Quéffélec Patrick , Tanné Gérard , Adenot Anne-Lise , Acher Olivier
Published: July 2002

Layered dielectric / ferromagnetic materials are extensively explored for microwave applications. Indeed, these materials combine the large saturation magnetization of ferromagnetic material with the low loss of dielectrics. Here, our aim was to integrate a layered ferromagnetic composite in a microwave propagation structure since the main advantage of such a material is the large impedance for one polarization. Thus, in order to predict the transmission response of the device, we carried out an electromagnetic analysis to determine how the field pattern of a microstrip line and the microwave-induced demagnetizing fields disturb the material behavior. We also explored the use of the propagation structure in two dc magnetic field-dependent devices: a tunable band stop filter and a magnetic switch. The stop-band function presented a large tunability of more than 50% with a minimal insertion loss of 3 dB when 250 Oe field was applied. Moreover, a magnetic switch using a dc field perpendicular to the easy axis of the ferromagnetic material was manufactured.
High-temperature effects of AlGaN/GaN high-electron-mobility transistors on sapphire and semi-insulating SiC substrates
Authors: Arulkumaran S. , Egawa T. , Ishikawa H. , Jimbo T.
Published: July 2002

The high-electron-mobility transistors (HEMTs) have been demonstrated on both sapphire and semi-insulating (SI) SiC substrates, and the dc characteristics of the fabricated devices were examined at temperatures ranging from 25 to 500 °C. The decrease in drain current and the transconductance with the increase of temperature have been observed. The decrease ratio of transconductance and drain current was similar for both the HEMTs on sapphire and SI–SiC substrates at and above 300 °C. The HEMTs on SiC substrates showed better dc characteristics after being subjected to thermal stress up to 500 °C. Although the SiC-based HEMTs showed better characteristics up to the temperature of 300 °C, compared with the sapphire-based HEMTs, similar dc characteristics were observed on both at and above 300 °C. For high-temperature applications (⩾300 °C), additional cooling arrangements are essential for both devices.
Anomalous detonation velocities following type II deflagration-to-detonation transitions in pentaerythritol tetranitrate
Authors: Gifford M. J. , Tsembelis K. , Field J. E.
Published: July 2002

The detonation velocity following type II deflagration-to-detonation transitions (DDT) has been observed to be markedly different to that which would be expected were the charges directly initiated. In charges of pentaerythritol tetranitrate (PETN) velocities as high as 5.6 mm μs−1 have been observed compared to 3.7 mm μs−1 which is both predicted and measured for the charge were it to be directly initiated. Experiments have also been carried out that attempt to measure the temperature within columns of PETN prior to a type II DDT event. Other experiments and hydrocode simulations have been carried out that attempt to isolate the possible causes of the anomalous detonation velocity and as a result determine what the critical factors that determine the velocity are. These studies have led to a greater understanding not only of the reasons behind the change in detonation velocity, but also of the stages that occur in the build up to type II DDT.
Closely spaced and separately contacted two-dimensional electron and hole gases by in situ focused-ion implantation
Authors: Pohlt M. , Lynass M. , Lok J. G. S. , Dietsche W. , Klitzing K. v. , Eberl K. , Mühle R.
Published: July 2002

Separately contacted layers of a two-dimensional (2D) electron gas and a 2D hole gas have been prepared in GaAs, which are separated by AlGaAs barriers down to 15 nm thickness. The molecular-beam-epitaxial growth was interrupted just before growth of the double-layer structure in order to use in situ focused-ion-beam implantation to pattern contacts which extend underneath the barrier. The two charge gases form upon biasing the p- and n-type contacts underneath and above the barrier in the forward direction and show independent transistor-like behavior.
Maximum entropy method analysis of thermal motion and disorder in thermoelectric clathrate Ba8Ga16Si30
Authors: Bentien A. , Iversen B. B. , Bryan J. D. , Stucky G. D. , Palmqvist A. E. C. , Schultz A. J. , Henning R. W.
Published: July 2002

Multitemperature (15, 100, 150, 200, 300, 450, 600, 900 K) single crystal neutron diffraction data on the type I clathrate Ba8Ga16Si30 are reported. For the framework atoms reciprocal space structural refinements give total occupancies in the unit cell of Ga/Si=3.8/2.2, 1.8/14.2, 10.2/13.8 for the 6c, 16i, and 24k sites respectively, thus showing that Ga avoids the tetrahedral 16i positions. The guest atom displacement parameters obtained from structure factor fitting are analyzed with semianharmonic Einstein models giving Einstein temperatures (ΘE) of 69(1), 98(7), and 124(2) K for Ba(2)(100), Ba(2)[100], and Ba(1), respectively. The analysis furthermore suggests that all guest atoms are structurally disordered, and the disorder appears to be temperature dependent with increased host-guest interaction at high temperatures. The structure factors are subsequently used in the maximum entropy method calculations to obtain direct space nuclear densities. These are modeled with anharmonic one-particle potential models to fourth order. Even at elevated temperatures anharmonicity is limited indicating that the low thermal conductivity of the clathrate has a different origin.
Vibration of self-organized silver nanocrystals
Authors: Courty A. , Lisiecki I. , Pileni M. P.
Published: July 2002

Low-frequency Raman spectra are performed on silver nanocrystals self-organized on a hexagonal compact array on highly oriented pyrolytic graphite (HOPG) substrate. In addition to the well-known Raman scattering by the nanoparticle quadrupolar vibration mode, two lower intensity bands at larger frequency shifts are observed. They are attributed to acoustic phonons confined in the nanocrystals corresponding to the fundamental breathing mode and its first harmonic. Their observation was made possible because of the high crystallinity and the narrow size distribution of the silver nanoparticles. The coated particles organized in 2D superlattices appear thus to behave as isolated particles dispersed in matrix.
Signal interferences from turbulent spin dynamics in solution nuclear magnetic resonance spectroscopy
Authors: Huang Susie Y. , Lin Yung-Ya , Lisitza Natalia , Warren Warren S.
Published: July 2002

Artifacts arising from aperiodic turbulent spin dynamics in gradient-based nuclear magnetic resonance (NMR) applications are comprehensively surveyed and numerically simulated by a nonlinear Bloch equation. The unexpected dynamics, triggered by the joint action of radiation damping and the distant dipolar field, markedly deteriorate the performance of certain pulse sequences incorporating weak pulsed-field gradients and long evolution times. The effects are demonstrated in three general classes of gradient NMR applications: solvent signal suppression, diffusion measurements, and coherence pathway selection. Gradient-modulated solvent transverse magnetization can be partially rephased in a series of self-refocusing gradient echoes that blank out solute resonances in the CHESS (chemical-shift-selective spectroscopy) and WATERGATE (gradient-tailored water suppression) solvent suppression schemes. In addition, the discovered dynamics contribute to erratic echo attenuation in pulsed gradient spin echo (PGSE) and PGSE stimulated echo diffusion measurements and produce coherence leakage in gradient-selected DQFCOSY and HMQC experiments. Specific remedies for minimizing unwanted effects are presented.
Formation of voids in a doped polymethylmethacrylate polymer
Authors: Day Daniel , Gu Min
Published: July 2002

We report on the formation of submicrometer voids within a doped polymethylmethacrylate (PMMA) polymer under multiphoton absorption excited by an infrared laser beam. An ultrashort pulsed laser beam of pulse width 80 fs at a repetition rate of 82 MHz and a wavelength of 800 nm is focused into a PMMA-based photorefractive polymer consisting of 2,5-dimethyl-4(p-nitrophenylazo)anisole, 2,4,7-trinitro-9-fluorenone, and N-ethylcarbazole. The large change in refractive index associated with a void allows confocal reflection microscopy to be used as a detection method. Voids can be arranged in a multilayered structure for read-only high-density optical data storage.
Elastic and piezoelectric fields in substrates GaAs (001) and GaAs (111) due to a buried quantum dot
Authors: Pan E.
Published: July 2002

In this article we present a rigorous study on the elastic and piezoelectric fields in substrates GaAs (001) and GaAs (111) due to a buried quantum dot (QD) using an efficient and accurate continuum mechanics model. It is based on a Green’s function solution in anisotropic and linearly piezoelectric half space combined with the generalized Betti reciprocal theorem. To address the effect of material anisotropy, two other substrates, Iso (001) and Iso (111), are also examined and they are assumed to be elastically isotropic. For a point QD with hydrostatic misfit strain γ*=0.07 in volume va=4πa3/3 where a=3 nm, and at depth h=10 nm below the surface, we have observed the following features. (1) The simplified elastically isotropic model should, in general, not be used for predicting elastic and piezoelectric fields in the semiconductor GaAs. (2) The magnitude of the QD-induced piezoelectric potential on the surface of GaAs (111) or GaAs (001) is comparable to, or even larger than, the direct potential. (3) Large horizontal and vertical electric fields, on the order of 106 V/m, can be induced on the surface of GaAs (001) and GaAs (111). (4) The elastic field induced on the surface of GaAs (001) has rotational symmetry of order C4 (i.e., the elastic field remains the same after rotation of 2π/4 around the [001] axis), while the corresponding piezoelectric field has rotational symmetry of order C2. On the other hand, both the elastic and piezoelectric fields on the surface of GaAs (111) have rotational symmetry of C3 around the [111] axis. (5) The magnitude of the elastic and piezoelectric quantities on the surface of GaAs (111) is, in general, larger than that of the corresponding quantities on the surface of GaAs (001). (6) Under different electric surface conditions (insulating or conducting), the surface piezoelectric fields induced are quite different.
Nanoindentation-induced deformation of Ge
Authors: Bradby J. E. , Williams J. S. , Wong-Leung J. , Swain M. V. , Munroe P.
Published: July 2002

The deformation mechanisms of crystalline (100) Ge were studied using nanoindentation, cross sectional transmission electron microscopy (XTEM) and Raman microspectroscopy. For a wide range of indentation conditions using both spherical and pointed indenters, multiple discontinuities were found in the force–displacement curves on loading, but no discontinuities were found on unloading. Raman microspectroscopy, measured from samples which had plastically deformed on loading, showed a spectrum shift from that in pristine Ge, suggesting only residual strain. No evidence (such as extra Raman bands) was found to suggest that any pressure-induced phase transformations had occurred, despite the fact that the material had undergone severe plastic deformation. Selected area diffraction pattern studies of the mechanically damaged regions also confirmed the absence of additional phases. Moreover, XTEM showed that, at low loads, plastic deformation occurs by twinning and dislocation motion. This indicates that the hardness of Ge measured by indentation is not primarily dominated by phase transformation, rather by the nucleation and propagation of twin bands and/or dislocations.
Car–Parrinello molecular dynamics simulation of liquid water: New results
Authors: Izvekov Sergei , Voth Gregory A.
Published: July 2002

New Car–Parrinello molecular dynamics simulations of the structural and dynamical properties of liquid water are reported. The calculated radial distribution functions are in excellent agreement with most recent both x-ray and neutron diffraction scattering experiments. The simulated self-diffusion properties are also in good agreement with experimental data.
Effects of sulfur passivation on Ti/Al ohmic contacts to n-type GaN using CH3CSNH2 solution
Authors: Song June O , Park Seong-Ju , Seong Tae-Yeon
Published: July 2002

We investigate the effect of CH3CSNH2 solution treatment on Ti/Al ohmic contacts to n-GaN:Si (3×1018 cm−3). It is shown that the sulfide treatment results in a drastic increase in the photoluminescence intensity, compared with that of the untreated sample. Current-voltage (I–V) results show that the sulfide treatment significantly improves the specific contact resistance. The annealing of the sulfide-treated sample (at 700 °C) results in a specific contact resistance of 3.1×10−6 Ω cm2. X-ray photoemission spectroscopy (XPS) results show that the Ga 2p core levels shift toward the higher-binding energy side by 0.2 eV for the sulfide-treated sample and by 0.4 eV for the annealed (sulfide-treated) sample, compared with that of the untreated one. It is further shown that the intensity of O 1s core level decreases with the sulfide treatment. Based on the I–V and XPS results, the sulfide and annealing treatment dependence of the specific contact resistance is discussed.
Field emission characteristics of carbon nanofiber improved by deposition of boron nitride nanocrystalline film
Authors: Sugino Takashi , Yamamoto Tomohide , Kimura Chiharu , Murakami Hirohiko , Hirakawa Masaaki
Published: July 2002

An improvement in field emission characteristics of a graphite nanofiber (GNF) has been attempted. Boron nitride (BN) films are synthesized by plasma-assisted chemical vapor deposition. It is demonstrated that electron emission occurs at a low anode voltage due to depositing the BN nanocrystalline film on flat Si substrates. Deposition of the BN nanocrystalline film is applied to the GNF to improve the field emission characteristics of the GNF. In addition to a reduction in the average turn-on electric field, the emission current increases by two orders of magnitude in comparison with that of an as-grown GNF.
Metalorganic vapor-phase epitaxial growth of vertically well-aligned ZnO nanorods
Authors: Park W. I. , Kim D. H. , Jung S.-W. , Yi Gyu-Chul
Published: July 2002

We report metalorganic vapor-phase epitaxial growth and structural and photoluminescent characteristics of ZnO nanorods. The nanorods were grown on Al2O3(00⋅1) substrates at 400 °C without employing any metal catalysts usually needed in other methods. Electron microscopy revealed that nanorods with uniform distributions in their diameters, lengths, and densities were grown vertically from the substrates. The mean diameter of the nanorods is as narrow as 25 nm. In addition, x-ray diffraction measurements clearly show that ZnO nanorods were grown epitaxially with homogeneous in-plane alignment as well as a c-axis orientation. More importantly, from photoluminescence spectra of the nanorods strong and narrow excitonic emission and extremely weak deep level emission were observed, indicating that the nanorods are of high optical quality.
Template-catalyst-free growth of highly ordered boron nanowire arrays
Authors: Cao L. M. , Hahn K. , Scheu C. , Rühle M. , Wang Y. Q. , Zhang Z. , Gao C. X. , Li Y. C. , Zhang X. Y. , He M. , Sun L. L. , Wang W. K.
Published: July 2002

Well-aligned boron nanowire arrays were grown vertically on silicon substrates over areas up to several tens of square centimeters using radio-frequency magnetron sputtering of highly pure boron. During growth and self-assembly of boron nanowire arrays, no template or catalyst was needed. The morphology, structure, and composition of the self-organized boron nanowires were characterized in detail using scanning electron microscopy, transmission electron microscopy, and electron energy-loss spectroscopy. Our results might provide insight into the controllable formation of a wide variety of ordered nanostructures with advanced properties.
Interchain interaction and Davydov splitting in polythiophene crystals: An ab initio approach
Authors: Bussi Giovanni , Ruini Alice , Molinari Elisa , Caldas Marilia J. , Puschnig Peter , Ambrosch-Draxl Claudia
Published: July 2002

The crystal-induced energy splitting of the lowest excitonic state in polymer crystals, the so-called Davydov splitting Δ, is calculated with a first-principles density-matrix scheme. We show that different crystalline arrangements lead to significant variations in Δ, from below to above the thermal energy kBT at room temperature, with relevant implications on the luminescence efficiency. This is one more piece of evidence supporting the fact that control of interchain interactions and solid-state packing is essential for the design of efficient optical devices.
Enhanced transparency ramp-type Josephson contacts through interlayer deposition
Authors: Smilde Henk-Jan H. , Hilgenkamp Hans , Rijnders Guus , Rogalla Horst , Blank Dave H. A.
Published: July 2002

A thin interlayer is incorporated in ramp-type Josephson junctions to obtain an increased transparency. The interlayer restores the surface damaged by ion milling and has the advantage of an all in situ barrier deposition between two superconductors, leading to clean and well-defined interfaces. The method has been applied to Josephson junctions between high (YBa2Cu3O7−δ) and low temperature (Nb) superconductors, separated by a Au barrier. Transmission electron microscopy images of these junctions reveal crystalline YBa2Cu3O7−δ up to the interface with the Au barrier. The junctions have improved critical current density values exceeding 20 kA/cm2, normal state resistances of 3×10−8 Ω cm2 and IcRn products of 0.7 mV at 4.2 K. Furthermore, the junction properties can be controlled by varying the Au barrier thickness.
Electrostatic force microscopy using a quartz tuning fork
Authors: Seo Yongho , Jhe Wonho , Hwang Cheol Seong
Published: July 2002

We demonstrate an electrostatic force microscopy based on a quartz tuning fork with 50 nm spatial resolution and 1 pN force sensitivity. We use a tuning fork with a spring constant of 1300 N/m and a Q factor of 3000. A sharpened nickel tip is attached to a prong of the tuning fork as well as electrically connected to the electrode of the prong. By applying a dc bias to the tip, ferroelectric domain patterns are recorded and read out on piezoelectric thin film.
Images of synchronized chaos: Experiments with circuits
Authors: Rulkov Nikolai F.
Published: July 2002

Synchronization of oscillations underlies organized dynamical behavior of many physical, biological and other systems. Recent studies of the dynamics of coupled systems with complex behavior indicate that synchronization can occur not only in case of periodic oscillations, but also in regimes of chaotic oscillations. Using experimental observations of chaotic oscillations in coupled nonlinear circuits we discuss a few forms of cooperative behavior that are related to the regimes of synchronized chaos. This paper is prepared under the request of the editors of the special focus issue of Chaos and contains the materials for the lecture at the International School in Nonlinear Science, ‘‘Nonlinear Waves: Synchronization and Patterns,’’ Nizhniy Novgorod, Russia, 1995. The main goal of the paper is to outline the collection of examples that illustrate the state of the art of chaos synchronization.
Magnetic x-ray scattering studies of the rare-earth metal holmium (invited)
Authors: Gibbs Doon , Moncton D. E. , D’Amico K. L.
Published: July 2002

We present the results of recent magnetic x-ray scattering experiments on the rare-earth metal Ho performed using both a rotating anode source and synchrotron radiation. Specifically, we have measured the Ho(00l)+ magnetic satellites in the simple spiral antiferromagnetic phase between 132 and 20 K and in the conical phase below 20 K. Although the cross section for magnetic x-ray scattering is reduced from the usual Thomson cross section by a factor of ≊105, the incommensurate magnetic satellites are well separated from the main Bragg peaks. Thus, detection of the satellites is possible with a rotating anode source and extensive high-resolution studies of them are straightforward with synchrotron radiation. The assembled data are in good agreement with the results of magnetic neutron scattering published previously for different Ho samples.
Spin glass behavior of Cd1−xMnxTe below the nearest-neighbor percolation limit
Authors: Novak M. A. , Symko O. G. , Zheng D. J. , Oseroff S.
Published: July 2002

Magnetization measurements down to 10 mK of Cd1−xMnxTe for Mn concentrations 0.01≤x≤0.15 show spin glass behavior. Such behavior is attibuted to short-range exchange and dipolar interactions. Both interactions are used to explain the concentration dependence of the spin freezing temperatures for 0.01≤x≤0.6, the short-range exchange dominating at high concentrations, and the dipolar interaction at low concentrations.
Bismuth iron garnet films prepared by rf magnetron sputtering
Authors: Krumme J.-P. , Doormann V. , Willich P.
Published: July 2002

We report on the growth of highly bismuth-substituted iron garnet films by rf magnetron sputtering in a pure argon plasma. Under special conditions the target composition is fully reproduced in the films. Film homogeneity in the noncrystalline state is excellent. Crystallization on lattice-matched garnet substrates occurring during growth above 520 °C substrate temperature and by post-annealing above 650 °C yields the garnet phase, as inferred from the optical and magneto-optic spectra and the saturation magnetization. Residual imperfections appearing after crystallization need further elucidation. We cope with the extreme disparity in the elemental sputter yields of the mixture Gd-Bi-Fe-Al-Ga-O by (i) protecting the growing film from ion bombardment in using a magnetron source and (ii) binding Bi to a more slowly sputtering species, such as in BiFeO3.
Substrate-related effects on the optical behavior of a granular surface: The Maxwell Garnett theory revisited
Authors: Bosi Giulio , de Dormale Bernard
Published: July 2002

An approximate treatment, describing the influence of a dielectric substrate on the optical behavior of a granular surface, is reported. It shows that discrepancies between experimental results and predictions mainly based upon the Maxwell Garnett theory [Philos. Trans. R. Soc. London 203, 385 (1904); 205A, 237 (1906)] cannot be interpreted as substrate-related effects. The magnitudes and locations of the multiple images of the unperturbed dipole of a small metallic sphere have been carried out in an approximate, though reliable, way in the presence of polarizing fields both parallel and perpendicular to the substrate. The resulting dipole is introduced in a long-known optical model, describing a granular surface as a planar array of equal dipoles interacting with each other. Graphical results, showing the influence of substrates of various dielectric constants, are presented. A discussion of possible improvements of the available model is also reported.
Formation of Pt silicides: The effect of oxygen
Authors: Chang Chin-An
Published: July 2002

When Pt silicides are formed in an ambient containing oxygen, or using Pt films containing an appreciable amount of oxygen, the formation rates of the silicides are reduced. In the latter case the reduced rates are attributed to the formation of an oxide layer, from the oxygen contained, between the surface Pt and the Pt2Si and PtSi phases. To remove such difficulties, we use Pt films containing little oxygen, and study the effect of oxygen on the formation of both Pt silicides in an oxygen ambient. It is shown that oxygen diffuses from the ambient into Pt during the stage of Pt2Si formation, and an oxide layer is formed under the surface when the front of the Pt2Si phase meets the oxygen in the film, which hinders further growth of the Pt2Si phase. Subsequent formation of the PtSi phase proceeds until it meets the oxide layer and is hindered from further growth. Accordingly, the oxide layer described has little effect on the bulk growth of these two silicides, and other mechanisms are needed to account for the reduced rates by oxygen for such systems, such as that described by the surface potential model.
Ellipsometric investigation of vanadium dioxide films
Authors: Swann J. T. , De Smet D. J.
Published: July 2002

Vanadium dioxide undergoes a transition at about 68 °C where the physical properties of the oxide, in particular the index of refraction and possibly the density, abruptly change values. In this work the indices of refraction of thermally grown films of vanadium dioxide on a vanadium substrate have been determined at room temperature and at 84 °C using the technique of ellipsometry. The index of refraction found for these films in this work is 2.82–0.317i at room temperature and 2.24–0.456i at 84 °C. In addition, our results indicate that there is a small increase in the thickness of each film upon heating through the transition.
Self-consistent T-matrix solution for the effective elastic properties of noncubic polycrystals
Authors: Middya T. R. , Basu A. N.
Published: July 2002

The multiple scattering theory has been a powerful tool in estimating the effective elastic properties of polycrystalline substances and different types of composite materials in terms of the component elastic properties. Both perturbative and self-consistent solutions within the framework of multiple scattering theory have been developed for cubic polycrystals by R. Zeller and P. H. Dederichs [Phys. Status. Solidi B 55, 831 (1973)]. Recently we have suggested [T. R. Middya, Mala Paul, and A. N. Basu, J. Appl. Phys. 58, 4095 (1985)] a perturbative method of calculation for all the noncubic polycrystals up to orthorhombic symmetry. Although the method has been quite successful in dealing with noncubic polycrystals with low anisotropy factors, it becomes too complex to handle the high anisotropy cases. Moreover, the results for many crystals for such cases with perturbation carried up to second order are inconsistent as they fall outside the well-known Hashin–Shtrikman (H–S) bounds. In order to overcome this difficulty, in this work we discuss a self-consistent T-matrix solution for the effective elastic properties of hexagonal, tetragonal, trigonal, and orthorhombic polycrystals. Within the approximation of multiple scattering of all orders from a single grain, we have obtained the self-consistent solution by exploiting the symmetry of each class. Next we have employed the formulas thus obtained to calculate the effective bulk and shear moduli of hexagonal, tetragonal, trigonal, and orthorhombic polycrystals. Finally the results are compared with our previous perturbative calculations, the H–S bounds and experiment. Unlike the previous calculations, all the self-consistent results fall within the H–S bounds. In addition to providing simple analytical formulas which can tackle polycrystals with arbitrary values of anisotropy factors, these formulas may also be used for evaluation of mechanical properties of composites having components belonging to different symmetries.
Multiple scattering theoretical and computer simulated dynamic model approaches to effective elastic properties of randomly disordered composites
Authors: Middya T. R. , Paul Mala , Basu A. N.
Published: July 2002

In the present investigation we have generalized the result obtained in the preceding paper [J. Appl. Phys. 59, 2368 (1985)] to treat composites containing crystallites of different crystal symmetries and arbitrary values of the elastic constants. This result has been used to discuss the existing theories intended to solve the same problem. An interesting finding of this analysis is that the present approach provides a single framework to discuss all the previous results which are particular cases of the general formulas derived here. Earlier all these cases were treated separately employing different approaches. Next we apply our results to six different binary composites and we find that our predictions compare quite favorably with experiment. For comparison we also calculate the same quantities by simulating the composite on a computer by the dynamic method originally developed by [T. R. Middya, A. N. Basu, and S. Sengupta [J. Appl. Phys. 57, 1844 (1985)] to discuss monocomponent polycrystal elastic properties. The two sets of results agree with each other for small differences in elastic properties of the components of a composite. But for larger differences, they diverge. Since the two approaches are based on widely different assumptions and the overall agreement of the effective-medium theory is distinctly superior, it appears that the existing experiments are consistent with the assumptions of the multiple scattering theory.
Capillary instabilities in thin films. II. Kinetics
Authors: Srolovitz D. J. , Safran S. A.
Published: July 2002

We consider the kinetic evolution of perturbations to thin films. Since all small (nonsubstrate intersecting) perturbations to the film surface decay, we consider the evolution of large perturbations, in the form of a single hole which exposes the substrate. For large holes, the hole radius increases at a constant rate under the assumption of evaporation/condensation kinetics. When the dominant transport mode is surface diffusion, large holes grow with a rate proportional to t−3/4[log3(t/ ρ4c) ]. Small holes with a radii less than  ρc shrink, where  ρc is the film thickness divided by the tangent of the equilibrium wetting angle. The growth of these holes eventually leads to hole impingement which ruptures the film, creating a set of disconnected islands. The relaxation time for these islands to go to their equilibrium shape and size ( ρeq) scales as  ρ2eq or  ρ4eq for evaporation/condensation or surface diffusion kinetics, respectively.
Low-energy ion irradiation during film growth for reducing defect densities in epitaxial TiN(100) films deposited by reactive-magnetron sputtering
Authors: Hultman L. , Helmersson U. , Barnett S. A. , Sundgren J.-E. , Greene J. E.
Published: July 2002

Transmission electron microscopy has been used to study the defect structure in epitaxial TiN(100) films as a function of the growth temperature (Ts=550–850 °C) and negative substrate bias (Vs=0–500 V) applied during reactive-magnetron sputter deposition onto cleaved MgO substrates. For the growth conditions used in these experiments, the energy per incident N ion (N+2 was the predominant ionic species) was ∼Vs/2 and the incident ion to thermal-atom flux ratio was ∼2. The results showed that the primary defects were dislocation loops whose number density nd decreased with increasing Ts for a given Vs. However, nd decreased much more rapidly with increasing Vs at constant Ts until a minimum defect density was attained at Vs=V*s after which nd increased with further increases in Vs. Low-energy ion irradiation during film growth played at least two primary roles: it resulted in the creation of additional point defects which then condensed into dislocation loops and it enhanced atomic mobilities thereby accelerating the rate at which defects were annealed out during deposition. The residual defect density was determined by a competition between these two effects. Films grown at Ts>750 °C and Vs=V*s were essentially free of dislocation loops. For comparison, the dislocation loop density in films grown with Vs=0 ranged from 5×1012 to 1.5×1010 cm−2 as Ts was increased from 550 to 850 °C.
Optical absorption in TiNxOy-compounds
Authors: Vogelzang E. , Sjollema J. , Boer H. J. , De Hosson J. Th. M.
Published: July 2002

Thin films of Ti, TiNx, and TiNxOy were prepared by dc reactive magnetron sputtering. The normal spectral reflectance and transmittance of films were measured in the spectral region of 0.4–25 μm. The free electron contribution to the optical properties has been determined from measurements of the Hall coefficient and the dc resistivity. Optical band-band transitions, that are found in TiNxOy, are compared to the calculated band structure of TiN and TiO.
An effective dipole theory for band lineups in semiconductor heterojunctions
Authors: Ruan Ying-Chao , Ching W. Y.
Published: July 2002

An effective dipole theory is presented to estimate the band lineups at the interface of a lattice-matched or nearly matched semiconductor heterojunction. The theory is based on the formation of an effective dipole at the interface which causes additional shift ΔEv in the difference of the band edges. A set of equations are derived from which δEv can be solved iteratively. The calculation requires the values of the top of the valence band and several bulk band-structure parameters of the constituent semiconductors as input. The dipole effect is evaluated by considering the charge transfer induced by the penetration of the effective mass electrons representing the bulk band states into the quantum barrier of the neighboring semiconductor. The theory is applied to predict the band offset values of more than 100 heterojunctions involving group IV, III-V, and II-VI semiconductors. Of the 30 heterojunctions for which the experimental data have been reported, the predicted values differ from the data by only about 0.1 eV on average. Extension of the present theory to several special interface systems is also discussed.
Atomic structures of several silicon surfaces: A direct field ion microscope observation
Authors: Liu H. M. , Tsong T. T.
Published: July 2002

Atomically resolved and well-ordered field ion images of several silicon surfaces have been obtained. For a carefully cleaned Si tip, after annealing at 800 °C for several minutes, very well-ordered atomic structures develop on high index planes such as the (230), (135), (124), (234), (123), (113), (115), and (317). Many of them are reconstructed. Two structures coexist for the (230) plane. Also, many two-dimensional defects can be seen.
Effect of magnetic ordering on phonon parameters for infrared active modes in ferromagnetic spinel CdCr2S4
Authors: Wakamura Kunio , Arai Toshihiro
Published: July 2002

Infrared reflectivity spectra of sintered crystal CdCr2S4 have been measured in the temperature range of 15–300 K. The frequencies of transverse and longitudinal phonon modes were determined from the spectra with the Kramers–Kronig relation. The temperature dependencies of those showed anomalously large shifts near the Curie temperature. The shifts for two modes on the higher-energy side increase and those for other two modes decrease with temperature. These shifts are described well by the terms of spin-correlation function and concluded to be originated from the spin-dependent force constant. The mode dependence of shifts is explained qualitatively from the relation between the linkage of super-exchange interaction and the direction of vibration of the ion. The effects of magnetic ordering were also observed on Szigeti effective charge, optical and static dielectric constants, and phonon damping constants. These are discussed from the viewpoint of the red shift of the absorption edge.
Thermomagnetic switching in amorphous rare-earth transition-metal alloys with high compensation temperature
Authors: Hansen P.
Published: July 2002

The thermomagnetic switching process in amorphous Tb-FeCo alloys has been investigated theoretically for typical compositions with a Curie temperature of 500 K and compensation temperatures ranging from 360 to 420 K. The temperature and radial dependence of the relevant magnetic parameters such as the saturation magnetization, the exchange constant, the uniaxial anisotropy, and the domain wall energy have been calculated in terms of the respective sublattice magnetizations inferred from the mean field theory and data obtained experimentally. The condition for domain stability has been derived and the radial dependence of the forces controlling the domain wall position is calculated yielding domain diameters for writing and erasure as a function of the applied field, the wall energy, and the laser-induced temperature. Heating above the Curie temperature is shown to offer an alternative possibility to control the domain diameter and to achieve high domain regularity at low applied magnetic fields.
Magnetic hardening of Pr2Co14B
Authors: Fuerst C. D. , Herbst J. F. , Pinkerton F. E.
Published: July 2002

By systematically varying composition in the Pr-Co-B phase diagram we have determined starting alloy formulations which yield melt-spun ribbons having technologically significant hard magnetic properties. In particular, energy products and coercivities as large as 5.5 MGOe and 25.0 kOe, respectively, have been observed in ribbons comprised principally of Pr2Co14B. We discuss the dependence of the magnetic characteristics on temperature as well as on composition.
Magnetic hysteresis in melt-spun Nd-Fe-Al-B-Si alloys with high remanence
Authors: Hadjipanayis G. C. , Gong W.
Published: July 2002

The large values of remanence observed in isotropic melt-spun R-Fe-Al-B-Si samples have been investigated by correlating the magnetic properties with the microstructure. Transmission electron microscope studies showed that the highest values of reduced remanence mR are obtained in samples with very fine Nd2Fe14B-type grains having a size of about 180 Å. The increased reduced remanence can be explained by the large interaction among the magnetic moments of neighboring grains which is caused by the large surface-to-volume ratio of the fine grains.
Bonding of silicon wafers for silicon-on-insulator
Authors: Maszara W. P. , Goetz G. , Caviglia A. , McKitterick J. B.
Published: July 2002

Several aspects of a new silicon-on-insulator technique utilizing bonding of oxidized silicon wafers were investigated. The bonding was achieved by heating in an inert atmosphere a pair of wafers with hydrophilic surfaces contacted face-to-face. A quantitative method for the evaluation of the surface energy of the bond based on crack propagation theory was developed. The bond strength was found to increase with the bonding temperature from about 60–85 erg/cm2 at room temperature to ≂2200 erg/cm2 at 1400 °C. The strength was essentially independent of the bond time. Bonds created during 10-s annealing at 800 °C were mechanically strong enough to withstand the mechanical and/or chemical thinning of the top wafer to the desired thickness and subsequent device processing. A model was proposed to explain three distinct phases of bonding in the temperature domain. Electrical properties of the bond were tested using metal-oxide-semiconductor (MOS) capacitors. The results were consistent with a negative charge density at the bond interface of approximately 1011 cm−2. A double-etch-back procedure was used to thin the device wafer to the desired thickness with ±20 nm thickness uniformity across a 4-in. wafer. The density of threading dislocations in the remaining silicon layer was 102 –103 cm−2, and the residual dopant concentration less than 5×1015 cm−3, both remnants of the etchstop layer. Complimentary metal-oxide-semiconductor (CMOS) devices made in the 20–100 nm silicon thick layers had subthreshold slopes of 68 mV/decade (both n- and p-channel MOS transistors). The effective carrier lifetime was 15–20 μs in 80- and 300-nm-thick Si films and the interface state density at the Si film-buried oxide interface was ≤5×1010 cm−2.
Stress from a parallelepipedic thermal inclusion in a semispace
Authors: Hu S. M.
Published: July 2002

Many problems concerning stress arising from the embedding of a foreign body in a semi-infinite matrix can be described as thermal inclusion involving a single or an assemblage of parallelepipedic elements. Because of its basic usefulness, we present an analytical solution to the problem of a parallelepipedic thermal inclusion in a three-dimensional semispace. Application of this solution to the currently important problem of trench isolations in integrated circuits will be presented separately elsewhere.
Rayleigh–Brillouin light scattering from multicomponent mixtures: The Landau–Placzek ratio
Authors: van der Elsken J. , Bot Arjen
Published: July 2002

In one-component fluids Rayleigh–Brillouin light scattering can be used to determine the equation of state of the fluid: A combination of the Brillouin shift and the Landau–Placzek ratio yields the isothermal compressibility. The same technique has been applied to multicomponent mixtures. We derive an expression for the Landau–Placzek ratio in a multicomponent mixture and show that it contains additional terms compared to the one-component case due to concentration fluctuations in the mixture. When we apply the expression to recent experiments on a five-component mixture of hydrocarbons, we show that the additional contribution cannot be neglected.
Bleustein–Gulyaev waves in gallium arsenide and other piezoelectric cubic crystals
Authors: Bright V. M. , Hunt W. D.
Published: July 2002

This paper presents an analytical solution to the boundary-value problem for the existence of a Bleustein–Gulyaev piezoelectric surface wave in cubic crystals. A general formulation of the boundary-value problem is first developed. The results are then used to demonstrate the existence of a Bleustein–Gulyaev wave in piezoelectric cubic crystals of 4̄3m and 23 symmetry classes. Numerical solutions are obtained for a number of commonly used materials such as GaAs, GaP, InSb, InAs, Bi12GeO20 and Bi4Ge3O12.
Charge-transfer collisions between He+2 ions and N2: Branching ratio into vibrational states
Authors: Kirkici H. , Bruno D. , Preiss J. , Schaefer G.
Published: July 2002

A plasma-mixing device in which a helium plasma beam is crossed with a molecular nitrogen beam was used to measure the branching ratio of the excitation of individual vibrational levels of the B2Σ electronic state of the molecular nitrogen ion in charge-transfer collisions between He+2 ions and ground-state N2 molecules. The branching ratio of the excitation of individual vibrational levels of the C3Π electronic state of the neutral nitrogen molecule due to the resonant energy-transfer collisions between argon metastables and ground-state nitrogen molecules was also measured using a plasma beam of a mixture of argon and helium. These results allow comparison of our measurements with results obtained using other techniques.
Observation of a current-induced force on Bloch lines in Ni-Fe thin films
Authors: Hung C.-Y. , Berger L. , Shih C. Y.
Published: July 2002

Finite displacements of Bloch lines, induced by current pulses directly traversing the sample, have been observed by the ferrofluid technique in Ni81Fe19 films of thickness 33–68 nm containing cross-tie domain walls. The pulses of duration ≤ 1 μs are normal to the wall. Bloch lines move along the wall whenever the current density exceeds a critical value ≊1×1012 A/m2. It is possible to partly control the sense of the central spin of Bloch lines by applying a field μ0H≊100 μT normal to the film during Bloch-line creation. The sense of the current-induced force on Bloch lines is found to depend on the sense of the central spin of Bloch lines, and agrees with the sense of the theoretically predicted s-d gyroscopic force which arises from s-d exchange. However, the average value of the force is about four times smaller than the predicted value for a one-band model.
Effects of noble gases on diamond deposition from methane-hydrogen microwave plasmas
Authors: Zhu W. , Inspektor A. , Badzian A. R. , McKenna T. , Messier R.
Published: July 2002

The deposition of diamond films by microwave plasmas has been studied in gaseous mixtures of methane, hydrogen, and noble gases. Plasma diagnostic results are compared with growth rates and Raman spectra of the films. The noble gases, which influence the degree of excitation or reactant molecules by energy transfer or charge transfer from their excited and ionic states, are active in the deposition process by inducing additional ion-molecule and excited atom-molecule reactions. As a result, enhanced deposition rates have been observed. Small oxygen additions along with the noble gases can suppress the formation of nondiamond carbon phases, leading to an effective way to rapidly deposit diamond films at high methane concentrations while still retaining minimal nondiamond carbon components in the films.
Gas evolution from hydrogenated amorphous carbon films
Authors: Jiang X. , Beyer W. , Reichelt K.
Published: July 2002

Gas evolution experiments have been performed on hydrogenated amorphous carbon (a-C:H) films prepared by plasma deposition. Two series of films are studied: in series I, C2H2 is used as a process gas at a fixed bias voltage while the gas pressure is varied, and in series II, CH4 is employed at a fixed gas pressure, and the bias voltage is changed. The results are compared to infrared absorption data and density measurements and support the presence of a void network in the amorphous material, the extent of the void network depending on the deposition conditions.
Refractive indices of InGaAlAs grown by molecular beam epitaxy
Authors: De Bernardi C. , Meliga M. , Morasca S. , Rigo C. , Sordo B. , Stano A.
Published: July 2002

The accurate determination of the refractive indices of InGaAlAs, grown by molecular beam epitaxy, is reported for the first time. The method used, modal, cutoff spectroscopy, is applied to InGaAlAs/InP single heterostructure waveguides, with compositions corresponding to band-gap wavelengths in the range of 1.02–1.12 μm. The refractive indices are determined at different wavelengths between 1.1 and 1.6 μm, with an accuracy better than 10−3.
The influence of interstitial Ga and interfacial Au2P3 on the electrical and metallurgical behavior of Au-contacted III-V semiconductors
Authors: Weizer Victor G. , Fatemi Navid S.
Published: July 2002

The introduction of a very small amount of Ga into Au contact metallization on InP is shown to have a significant effect on both the metallurgical and electrical behavior of that contact system. Ga atoms in the interstices of the Au lattice are shown to be effective in preventing the solid-state reactions that normally take place between Au and InP during contact sintering. In addition to suppressing the metallurgical interaction, the presence of small amounts of Ga is shown to cause an order of magnitude reduction in the specific contact resistivity. Evidence is presented that the reactions of GaP and GaAs with Au contacts are also drastically affected by the presence of Ga. The sintering behavior of the Au-GaP and the Au-GaAs systems (as contrasted with that of the Au-InP system) is explained as due to the presence of interstitial Ga in the contact metallization. Finally the large, two-to-three order of magnitude drop in the contact resistance that occurs in the Au-InP system upon sintering at 400 °C is shown to be a result of the formation of an Au2P3 layer at the metal-semiconductor interface. Contact resistivities in the 10−6 Ω cm2 range are obtained for as-deposited Au on InP when a thin (20 Å) layer of Au2P3 is introduced between the InP and the Au contacts.