bluuebunny/crossref_metadata_2025 huggingface dataset:
Infrared study of the Si-H stretching band in a-SiC:H
Authors: Koropecki R. R. , Alvarez F. , Arce R.
Published: July 2002

Amorphous silicon carbide (a-Si1−xCx:H) samples having x ≤ 0.4 were studied by infrared and visible spectroscopy. Treatment by factor analysis of the 2000–2100 cm−1 absorption band of the spectra allows us to interpret this particular vibrational mode in terms of only two independent contributions. The analysis shows that polarization inductive shifting is not significant. An IR study of the evolution of this band during oxidation of porous samples was also performed. All the experimental evidence indicates that the growth of free volumes induced by the presence of carbon plays the most important role in the behavior of the 2000–2100 cm−1 band upon stoichiometric variations.
Microstructure of amorphic diamond films
Authors: Collins C. B. , Davanloo F. , Jander D. R. , Lee T. J. , Park H. , You J. H.
Published: July 2002

It has been previously reported that layers of amorphic diamond can be grown in a UHV environment free from hydrogen with a laser plasma source. Some advantages are offered by this technique which produces films that adhere more readily to materials for which there are important applications. Theory has recently suggested a structure for amorphic diamond that comprises nodules of carbon atoms linked by sp3 bonds in a matrix of other polytypes and the purpose of this article is to communicate strong evidence in support of that hypothesis. Extensive examinations of a variety of films with a scanning tunneling microscope show a clearly prevalent structure composed of dense nodules. Grain size is about 1000 Å and the diamond character is attested by the agreement of morphology, high density, optical properties, soft x-ray spectroscopy, hardness, and lack of appreciable hydrogen. Measurements agree in supporting a fraction of about 75% diamond contents. The principal conclusion is that this material prepared with a laser plasma source has the structure expected for amorphic diamond.
Slow response and Eu2+-related trapping states in CaS:Eu thin-film electroluminescent devices
Authors: Ando M. , Abe Y. , Ono Y. A.
Published: July 2002

In order to clarify causes of the slow buildup of the optical output, i.e., slow optical response, in red-emitting CaS:Eu thin-film electroluminescent devices, Eu2+ concentration and temperature dependence of the response time of transferred electrons were measured. It was found that the response time increased exponentially with the increase in Eu2+ concentration and temperature. To understand these results, trapping states in CaS:Eu phosphor layer were studied by measuring temperature dependence of the following electro-optical characteristics with Eu2+ concentration as a parameter; (i) decay profile of trapped electrons, (ii) photoluminescent intensity, and (iii) photoinduced charge density. From these measurements, it was found that there existed two kinds of shallow states in the band gap of CaS. One was electron trapping states located at approximately 0.15 eV below the conduction-band minimum. These states were considered to be generated by Eu2+ clusters. The other was located at 0.06–0.08 eV below the conduction-band minimum. These states were considered to be 5d-excited states of isolated Eu2+ activators. Based on these experimental results, an energy band model for CaS:Eu thin film was proposed and causes for the slow optical response were discussed.
Density variation of tungsten films sputtered over topography
Authors: Tait R. N. , Dew S. K. , Smy T. , Brett M. J.
Published: July 2002

Density and resistivity of sputtered tungsten films are directly measured as a function of angle-of-vapor incidence. The film density is found to drop off quickly at deposition angles greater than 50°, and the resistivity rises sharply at angles greater than 70°. These deposition angle effects in films deposited over topography can be predicted using simulation by ballistic deposition (SIMBAD), a two-dimensional computer simulation of thin-film growth using ballistic deposition of hard disks. Simulated film structure and density is in good agreement with real tungsten films deposited over vias. To confirm density predictions, etch rate measurements made on planar films are presented which confirm the dependence of etch rate on film density. The results of the measurement are used to develop an etching algorithm using SIMBAD density predictions. Films deposited over vias are etched to reveal the presence of low-density regions of film covering the via sidewalls, showing excellent agreement with the simulation results.
Efficient solutions for scattering from strips and slots in the presence of a dielectric half-space: Extension to wide scatterers. I. Theory
Authors: Tsalamengas John L. , Fikioris John G.
Published: July 2002

A very efficient, simple, and rapidly convergent algorithm for solving the Carleman-type singular integral and integro-differential equations formulating a variety of problems related to scattering by strips and slots in the presence of a dielectric half-space is presented. The method, based on Neumann’s expansion of the Hankel-function kernel of the integral equations, is particularly suited to the case of wide strips or slots where well-known problems of decimal cancellation and slow convergence are now completely avoided. The algorithm can easily be extended to the case of strips inside or on the surface of dielectric slabs. Numerical comparisons with classical results of scattering by very wide strips in free space, and under all possible angles of incidence, bring to light the power, simplicity, and accuracy of the new algorithm.
Structure and magnetic properties of aerosol synthesized barium ferrite particles
Authors: Kaczmarek W. A. , Ninham B. W. , Calka A.
Published: July 2002

The aerosol synthesis technique has been employed to produce barium ferrite particles. X-ray and electron diffraction, scanning and transmission microscopy methods were used to find detailed information on crystallography, morphology and chemical composition of as prepared and annealed powders. A detailed study has been made of the correlation between magnetic hysteresis parameters and the inner structure of submicrometer ferrite particles.
Effects of the energy distribution of fast electrons on H2 vibrational excitation in a tandem negative ion source
Authors: Fukumasa Osamu
Published: July 2002

The population distribution of vibrationally excited hydrogen molecules H2(v″), and the H− production are investigated theoretically by solving numerically a set of particle balance equations in a steady-state pure hydrogen plasma. In particular, the enhancement of the H2(v″) distribution is discussed for different energy distributions of fast electrons ef. Whether the energy distribution for ef is a delta function type or a plateau type, collisional excitation of H2(v″) caused by ef is very effective to enhance the H− production and a resultant vibrational distribution becomes the plateau distribution. Besides these, if ef with energies higher than 30–40 eV are present, both H2(v″) excitation and then H− yield hardly depend on the form of the energy distribution of ef.
Numerical calculation of hybrid magneto-electric states in an electron waveguide
Authors: Chaudhuri S. , Bandyopadhyay S.
Published: July 2002

We have performed a numerical calculation of the energy dispersion relation of hybrid magneto-electric states (both propagating and evanescent) in an electron waveguide subjected to a magnetic field. Our results are considerably different from those obtained through the Bohr–Sommerfield quantization condition. We have also calculated the density of the magneto-electric states as a function of energy and the velocity versus energy relationships. Finally, we show how the wavefunctions of these states evolve with increasing magnetic field from particle in a box states to edge states. These results are useful in the analysis of numerous recent magnetotransport experiments performed in electron waveguides.
Temperature dependent photoluminescent properties of InAsxP1−x/InP strained-layer quantum wells
Authors: Storch D. R. , Schneider R. P. , Wessels B. W.
Published: July 2002

Thermal quenching of photoluminescence from InAsxP1−x/InP strained-layer quantum wells has been investigated over the temperature range of 20–295 K. Structures with compositions of x=0.67 and x=1.0 and quantum well thicknesses of 1–17 monolayers were evaluated using Fourier transform photoluminescence spectroscopy. For InAs/InP heterostructures, the activation energy for thermal quenching depended on well thickness. Luminescence quenching was attributed to thermalization of free excitons from the well, and subsequent nonradiative recombination. Addition of phosphorus to the wells alters the recombination process responsible for luminescence quenching.
Breakdown delay time in phototriggered discharges
Authors: Legentil M. , Pasquiers S. , Puech V. , Riva R.
Published: July 2002

The breakdown delay times of phototriggered discharges have been measured and calculated for binary neon/xenon and neon/HCl mixtures as well as for the ternary neon/xenon/HCl mixtures used in XeCl lasers. The study has been performed for minor gas concentrations in the range 10 ppm–10% at total pressures up to 6 bars and for reduced electric fields between 4 and 40 Td. The agreement between the predicted values and the experimental results is quite good. The analysis of the results points out that the breakdown delay times are mainly determined by the direct ionization from the ground-state atoms and molecules, except when the reduced electric field and the concentration in minor gases have simultaneously low values. In such cases, the breakdown delay times are determined by the Penning effects. A transition between a resistive phase, dominated by the microscopic processes, and an inductive regime, which is circuit limited, is also reported.
Influence of roughness on magnetic surface anisotropy in ultrathin films
Authors: Chang Ching-Ray
Published: July 2002

A magnetostatic model for shape anisotropy of an ultrathin film with surface roughness is presented. Apart from the usual volume anisotropy, an additional perpendicular surface anisotropy results from the surface roughness. For a continuous film, the shape anisotropy follows the famous 1/t behavior. By considering the correlation between the surfaces, the perpendicular surface anisotropy can be further increased. When the film thickness is less than a certain value, the magnetic layer may become a discontinuous or island-like structure and the shape anisotropy is proportionally lower with decreasing film thickness. With a nonzero quality factor (Q=Kc/2πMs2), a marked kink in the dependence Kefft on the film thickness gradually appears with increasing roughness. Observed results agree qualitatively with predictions based on the present model.
Structural and optical properties of hydrogenated amorphous silicon carbide deposited by glow discharge from C3H8-SiH4-H2 mixture
Authors: Park Jang-Ho , Kwon Hyuk-Sang , Lee Jai-Young
Published: July 2002

Films of hydrogenated amorphous silicon carbide (a-SiC:H) have been prepared by a glow discharge decomposition from gas mixtures of C3H8-SiH4-H2 and CH4-SiH4-H2, in order to examine the effect of hydrocarbon gases on the structural and optical properties of these films. To study the influence of hydrogen on those properties of the propane-based films, the properties of the films deposited at different substrate temperatures (Ts) are systematically investigated using infrared (IR) and ultraviolet-visible absorption spectroscopies. By observing the change of intensities of IR absorption peaks with substrate temperature, the hydrogen bonding responsible for the absorption peaks could be assigned more accurately. When Ts is increased up to 300 °C, intensities of CH3 and SiH2 groups are reduced, indicating the formation of a dense network structure. At the same carbon concentration in gas mixtures, propane allows more carbon and hydrogen atoms to be effectively incorporated into the film than methane. The IR spectra reveal that the structure of a propane-based film has the characteristics of that of two kinds of films, methane- and ethylene-based films. It is found that the chemical bonding nature of the hydrocarbon gas strongly affects the bonding structure and the composition of the films. From these results, it is proposed that the use of propane is suitable for the fabrication of high-quality a-SiC:H with a wide optical gap (≳2.0 eV) and a deposition rate of ∼2 Å/s.
Study of photocarrier generation mechanism in a layered photoreceptor: Triphenylamine trisazo pigment/molecularly doped polymer
Authors: Umeda Minoru , Hashimoto Mitsuru
Published: July 2002

The photocarrier generation mechanism has been studied in a highly sensitive layered organic photoreceptor for laser beam printers. A series of experiments has been carried out on a layered photoreceptor which has a carrier generation layer (CGL) containing a triphenylamine trisazo pigment as the main component. As a result, we have found that (1) excitons are produced in the bulk of the CGL by photon absorption, (2) the excitons dissociate into free carriers (negative electrons and positive holes) at the interface between the CGL and a carrier transport layer (CTL), and (3) all positive holes are immediately injected into the CTL. The mechanism of photocarrier generation is considered to be based on a photoinduced electron transfer reaction from the ionization potential level of the carrier transport material in the ground state to the ionization potential level of the photoexcited carrier generation material.
Characterization of hot wall epitaxy grown ZnTe layers
Authors: Link P. , Schmidt Th. , Bauer S. , Wagner H. P. , Leiderer H. , Gebhardt W.
Published: July 2002

Single cyrstalline ZnTe layers have been successfully grown on (001) GaAs substrates by hot wall epitaxy at substrate temperatures between 280–370 °C. The vapor phase near the substrate surface was investigated by a quadrupole mass spectrometer. Transmission electron microscopy, reflectivity, and photoluminescence were used for growth optimization, impurity identification, and strain determination. The biaxial inplane strain is about ε∥=−0.5% at the interface and ε∥ (320 °C)=−0.06% at the surface for thicknesses of 1–5 μm. Two luminescence peaks can be assigned to As and N.
Morphologies of discontinuous gold films on amorphous polymer substrates
Authors: Kunz Martin S. , Shull Kenneth R. , Kellock Andrew J.
Published: July 2002

Transmission electron microscopy was used to analyze the effects of annealing treatments on the morphologies of discontinuous gold films evaporated onto polystyrene or poly(2-vinylpyridine) substrates. For polystyrene substrates the average size of discrete gold particles increases significantly during a long-term annealing treatment at 179 °C. The size distribution is well approximated by a log normal distribution function, consistent with a coalescence mechanism for particle growth. The fluid character of the polymer substrates at the annealing temperature of interest allows us to control this coalescence rate, thereby providing a unique method for controlling the microstructure of discontinuous metal films. Cross-sectional transmission electron microscopy showed that the coalescence rate for gold particles in a poly(2-vinylpyridine) matrix is much less than the coalescence rate for gold particles in a polystyrene matrix, indicating that polymer/metal interactions play an important role in the determination of the coalescence rate.
Design of self-biased hexaferrite waveguide circulators
Authors: Tsankov Mincho A. , Milenova Lyudmila G.
Published: July 2002

Self-biased millimeter-wave circulators can be built using hexaferrite materials with high internal anisotropy field, thus avoiding the use of large and heavy permanent magnets. The design principles of these devices are considered thoroughly in the article for both below- and above-resonance circulators. The article treats the classical structure of a half-wave-long ferrite cylinder, two dielectric spacers, and two metal transformers. A simple microwave technique for the measurement of the necessary parameters of the hexaferrite material is used. The choice of an adequate material with a proper value of the internal anisotropy field is discussed. An accurate procedure for the dimensioning of the ferrite insert and the spacers that eliminates the tedious cut-and-try work is described. A way to find the effective internal magnetic field is shown. Simple relations for the calculation of the matching elements are also given. Results on an above-resonance 33 GHz self-biased circulator that support the theory are presented.
Distribution of magnetic moments in Co/Pt and Co/Pt/Ir/Pt multilayers detected by magnetic x-ray absorption
Authors: Schütz G. , Stähler S. , Knülle M. , Fischer P. , Parkin S. , Ebert H.
Published: July 2002

Circular magnetic x-ray dichroism (CMXD) was observed at the Pt and Ir L2,3 edges in the multilayered structures 25⋅(4 Å Co+30 Å Pt) and 25⋅(4 Å Co+11 Å Pt+8 Å Ir+11 Å Pt). The samples were prepared by sputtering and show a large perpendicular anisotropy. The magnetic absorption at the Pt and Ir L2,3 edges was measured in an external magnetic field of 0.15 T perpendicular to the surface. The results indicate a significant spin polarization of the Pt and Ir layers. By comparison with the corresponding CMXD signals of Pt and Ir impurities in a ferromagnetic iron host we estimated the local spin and orbital moments. The results show that the innermost three monolayers in both systems couple ferromagnetically to the Co layers with an average magnetic moment of about 0.01 μB.
Composition dependence of photoinduced and thermally induced bleachings of amorphous Ge-S and Ge-S-Ag films
Authors: Kawaguchi Takeshi , Maruno Shigeo , Tanaka Keiji
Published: July 2002

Photoinduced and thermally induced bleachings of as-deposited GexS100−x and (Ge0.3S0.7)100−yAgy films were systematically studied in the ranges of 21≤x≤42 and 0≤y≤67 using optical transmission measurement. The bleachings for the Ge-S system show a maximum at around the stoichiometric composition GeS2, whereas that for the Ge-S-Ag system become smaller with an increase of the Ag content and vanish above 40 at. %. The composition dependence for the Ge-S system can reasonably be explained by an increase in the Ge-S bond density and subsequent decrease of short- and medium-range disordering. The bleaching rates, which are relatively small for Ge-rich films, are considered to be associated with the flexibility of the local network structure. The photo-oxidation phenomenon, which is observed for the films illuminated in air, also shows a maximum at around GeS2. The composition dependence for the bleaching of Ag-containing Ge30S70 films can be understood in a similar way to the Ge-S system. The vanishing at y≂40 is associated with a thermodynamically stable phase at that composition for the Ge-S-Ag system.
The lattice strains in a specimen (cubic system) compressed nonhydrostatically in an opposed anvil device
Authors: Singh Anil K.
Published: July 2002

A general expression has been derived using anisotropic elasticity theory for the lattice strain which corresponds to the x-ray diffraction measurement on the polycrystalline specimen (cubic system) compressed nonhydrostatically in an opposed anvil device. The expressions for the various diffraction geometries emerge as the special cases of this equation. The strain calculated using isotropic elasticity theory corresponds to the macroscopic strain in the specimen, and can be obtained from the present equation by letting the anisotropy factor 2(S11−S12)/S44=1. Further, it is shown that the ratio of the lattice strain to the macroscopic strain (in the direction of the lattice strain) produced by the deviatoric stress component depends on the Miller indices (hkl) of the lattice planes and the elastic anisotropy factor. This ratio is unity only if the crystallites constituting the specimen are elastically isotropic, and increases with increasing anisotropy of the crystallites.
Interdiffusion in InGaAs/GaAs quantum well structures as a function of depth
Authors: Gillin W. P. , Dunstan D. J. , Homewood K. P. , Howard L. K. , Sealy B. J.
Published: July 2002

Interdiffusion in InGaAs/GaAs quantum wells has been studied using photoluminescence to follow the development of the diffusion with time in a single sample. Two distinct regimes are seen; a fast initial diffusion and a second steady-state diffusion. The steady-state diffusion was found to be dependent on the depth of the quantum well from the surface and to correlate with published data on the indiffusion of gallium vacancies into gallium arsenide.
A method of pulsed-laser desorption of hydrogen
Authors: Boivin R. , Ross G. G. , Terreault B.
Published: July 2002

An apparatus and an experimental procedure, mainly designed to investigate the thermodynamics and kinetics of hydrogen evolution in materials, are described. Employing a 30 ns ruby laser pulse as a heat source, this method probes H behavior at higher temperatures and on a much shorter time scale than classic thermal desorption. Precise calibration techniques for the laser fluence and the desorption yield have been developed. The absolute calibration agrees well with a measurement of the H content by elastic recoil detection. Particular attention has been paid to lateral uniformization of the laser intensity, to allow valid one-dimensional modeling of laser heating and H evolution, and extraction of the activation energies and kinetic factors. As an example, a cursory study of intrinsic H in Be is presented. The method is also applicable to other volatile dopants.
The propagation of a radar pulse in sea water
Authors: King Ronold W. P. , Wu Tai T.
Published: July 2002

The propagation in sea water of an electromagnetic field in the form of a semi-infinite wave train or a radar pulse generated by an electric dipole is investigated analytically for low frequencies. The frequency-domain formula for the downward-traveling field of a horizontal electric dipole excited by a sinusoidally modulated electric-current pulse is Fourier transformed to obtain an explicit expression for the field at any distance in the time domain. Specific application is made to a wave packet of 25.5 cycles in a time duration of 1 s. The amplitude and phase velocity of the wave packet are determined together with the amplitudes of the initial and final transients. Graphs are displayed and discussed for a range of distances; these show that the amplitude of the wave packet decays more rapidly than the amplitudes of the transients. Possible application to remote sensing in the ocean is considered.
Interdiffusion of GaAs/Ga1−xInxAs quantum wells
Authors: Taylor W. J. , Kuwata N. , Yoshida I. , Katsuyama T. , Hayashi H.
Published: July 2002

We report results of an investigation of interdiffusion in GaAs/Ga0.82In0.18As strained single quantum wells. Wells of width 12–100 Å, grown by organometallic vapor phase epitaxy, were subjected to 10 s rapid thermal anneals of 830–950 °C, and shifts in the electron-to-heavy-hole transition energies were detected by 4 K photoluminescence. We employed a powerful computer model to relate postdiffusion well shape to changes in photoluminescence energies, enabling estimation of diffusivity. Interdiffusion rates of 1×10−16–2×10−14 cm2/s and activation energies of 3.1–3.8 eV were obtained.
Magnetization image reconstruction from magnetic force scanning tunneling microscopy images
Authors: Mayergoyz I. D. , Adly A. A. , Gomez R. D. , Burke E. R.
Published: July 2002

The problem of magnetization image reconstruction from magnetic force scanning tunneling microscopy images is discussed. The reconstruction problem is reduced to some convolution-type integral equations and analytical solutions to these equations are obtained by using the standard Fourier transform technique. The theoretical discussion is illustrated with some numerical examples.
Interdiffusion in alloys of the GaInAsP system
Authors: Cohen R. M.
Published: July 2002

Interdiffusion experiments and results for InP-GaInAs(P) heterostructures are reviewed and discussed within a thermodynamic model. Important factors affecting interdiffusion in the GaInAsP system are shown to include the (1) miscibility gap, (2) different diffusivities on each sublattice in each material, (3) Fermi level or impurity induced changes in diffusivity and perhaps diffusion mechanism, and (4) experimental technique chosen. With a miscibility gap present, the activity coefficients and solubilities of all species vary near a heterojunction and cause the interdiffusion to become strongly composition dependent. At commonly used growth and annealing temperatures, many superlattices are expected to equilibrate as two quaternary superlattices rather than a homogeneous alloy. Different diffusivities on each sublattice in a superlattice can lead to either a widening or a narrowing of quantum wells. When this occurs, optical measurements of the band gap energy are likely to be misleading because of quantum size effects. Diffusivity on each sublattice can be changed by the presence of group II, IV, or VI dopants. Diffusion on the group III sublattice in p-type GaInAsP is found to be consistent with an interstitialcy mechanism, but the mechanism remains unknown with n-type doping and for the group V sublattice. Diffusion experiments performed in closed, open, and capped environments are discussed. Poorly designed and controlled experiments are found to be associated with large discrepancies in observed diffusivities, unreliable concentration profiles, and new condensed phases appearing in the solid. Experiments to date indicate that the Cu-Pt ordered structure often found in GaIn(As)P epilayers are unstable, and not strain stabilized, relative to the disordered structure at commonly used growth and annealing temperatures.
Photoquenching and thermal recovery of a thermally stimulated current peak in semi-insulating GaAs
Authors: Fang Z.-Q. , Look D. C.
Published: July 2002

A prominent thermally stimulated current peak T5 appearing in semi-insulating GaAs is shown to photoquench under infrared illumination, and then thermally recover at a rate r=2.0×108 exp(−0.26 eV/kT) s−1, exactly the same as that observed for EL2, within experimental error. Two possible explanations exist: (1) T5 and EL2 are microscopically very similar, probably each with an AsGa core; or (2) T5 is an electron trap that only appears to quench and recover with EL2 because EL2 controls the electron lifetime. Several other traps show similar quenching and recovery behavior.
Magneto-optical Faraday effect of porous films comprised of cobalt-substituted barium ferrite fine particles dispersed in a resin
Authors: Matsumoto Koji , Sasaki Satoshi , Haraga Ken’ichi , Yamaguchi Kazuhiro , Fujii Toshitaka , Okamoto Iwao , Kimura Takayuki , Fujii Itsuhiro
Published: July 2002

The magneto-optical Faraday effect of porous films comprised of cobalt-substituted barium ferrite (Co:BaM) fine particles fixed by a resin was investigated. The films were prepared by spin-on process of a magnetic ink involving Co:BaM particles on glass substrates. Porous films were formed when the particle concentration of the ink, f, was low, i.e., f<0.3, and the coated ink was dried while applying a dc magnetic field normal to the substrate plane. The pit size became bigger when the coated ink was thicker, or the field was stronger. The Faraday effect of the films underwent a drastic change caused by the formation of a porous structure. The Faraday rotation spectrum exhibited dispersion-type behavior and its center wavelength was shifted toward longer wavelength with increasing pit dimension. Rotation angle enhancement was observed, which is considered to be caused by the mode modulation of light due to the existence of the pits.
Complex magneto-optical Kerr rotation of Fe,FeCo/Cu multilayer films
Authors: Xu Y. B. , Jin Q. Y. , Zhai Y. , Lu M. , Miao Y. Z. , Bie Q. S. , Zhai H. R.
Published: July 2002

The complex magneto-optical Kerr rotation spectra of Fe/Cu and FeCo/Cu bilayers and compositionally modulated films (CMF) were studied experimentally and theoretically. In the bilayers, an enhancement of Kerr ellipticity εk by a factor of 5 was observed at long wavelength side, while the Kerr rotation θk can only be enhanced by a factor of 2 around the plasma edge of Cu. In the CMFs, εk was enhanced by 60% but no θk enhancement was observed. Theoretical analyses showed that both the magnitude of effective ε̃xye and the magnitude and signs of effective Ae and Be are important for magneto-optical enhancement.
Magnetic study of M-type doped barium ferrite nanocrystalline powders
Authors: Batlle X. , García del Muro M. , Tejada J. , Pfeiffer H. , Görnert P. , Sinn E.
Published: July 2002

We have studied the static magnetic properties of three different M-type doped barium ferrite compounds prepared by the glass crystallization method. The zero-field-cooled (ZFC) and field-cooled (FC) processes have been recorded at low field and they all show the typical features of a small particle system. The ZFC curves display a broad peak at a temperature TM, which depends on the distribution of particle volumes in the sample. Isothermal magnetization curves M(H) at several temperatures and saturation magnetization Ms as a function of temperature have been measured for the Co-Ti sample (BaFe10.4Co0.8Ti0.8O19). The dependence on temperature of the macroscopic magnetic parameters has been analyzed. The distribution of blocking temperatures is studied from the derivative of the remanent-to-saturation magnetization ratio with respect to temperature and it is fitted to a lognormal distribution, leading to a mean blocking temperature 〈TB〉=(81±40) K. The distribution of volumes of the magnetic unit is also obtained from this fitting. The dependence on temperature of the coercive field follows a Tk-law below 35 K. The value of the k exponent is discussed within the scope of two models: (i) the aligned case (k=0.5) and (ii) the random case (k=0.77).
Diffusion length variation and proton damage coefficients for InP/InxGa1−xAs/GaAs solar cells
Authors: Jain R. K. , Weinberg I. , Flood D. J.
Published: July 2002

Indium phosphide solar cells are more radiation resistant than gallium arsenide and silicon solar cells and their growth by heteroepitaxy offers additional advantages leading to the development of lighter, mechanically strong and cost-effective cells. Changes in heteroepitaxial InP cell efficiency under 0.5 and 3 MeV proton irradiations have been explained by the variation in the minority-carrier diffusion length. The base diffusion length versus proton fluence has been calculated by simulating the cell performance. The diffusion length damage coefficient KL has also been plotted as a function of proton fluence.
Infrared study and characterization of Zn diffused InP
Authors: Borghesi A. , Guizzetti G. , Patrini M. , Caligiore A. , Chen R. C. , Pellegrino S.
Published: July 2002

Reflectance and transmittance spectra of p-type InP:Zn samples were measured by Fourier transform infrared spectroscopy (FTIR) in the spectral range from 40 to 700 cm−1. Zn was diffused into InP by an open-tube method, and a subsequent short annealing at different temperatures for the electrical activation of Zn diffused layers was performed. Free-carrier effects on vibrational structures around the restrahlen peak were evidenced. Concentration of electrically active Zn and free-hole damping constant were obtained by fitting reflectance spectra with a classical Drude–Lorentz dielectric function. The results confirmed the model for the electrical activation of the samples, based on outdiffusion of interstitial Zn by thermal annealing.
Novel magnetic applications of high-T
c bulk superconductors: Lenses for electron beams
Authors: Matsuzawa Hidenori
Published: July 2002

This paper presents a review on the latest state of the novel bulk devices, with an emphasis on lenses for electron beams. As one application of high critical-temperature (Tc) bulk superconductors, the author proposed the lenses (Supertrons) and his group has developed them. The principle of the lenses is simple: When one injects electron beams into narrow superconducting tubes, the tubes confine the self-magnetic field of the beams to the bore of the tubes because of the Meissner effect. The enhanced field accordingly focuses the beams into thinner ones. The first two sections outline high-Tc superconducting materials and fundamental characteristics of electron beams. In the body of this article, the lenses are evaluated according to the focusing of intense electron beams (∼340 keV, ∼1 kA, ∼10 ns) and assigned a figure of merit. Lenses were made from powder-pressed yttrium- (Tc=∼90 K), bismuth- (∼105 K), thallium- (∼120 K), and melt-processed yttrium-based superconductors. From the experimental results, one can say that powder-pressed lenses are suitable for short pulsed, low repetition-rate electron beams (a ferrite-core model) and that melt-processed lenses are, on the other hand, probably appropriate for continuous or slowly time-varying electron beams. In addition to the temperature-dependent focusing of the electron beams, a criterion for design of the lenses is discussed. To show the potential of the lenses, two applications of the lenses are described: a wiggler for free-electron lasers and an electron-beam guide for induction linear accelerators. Finally, other novel applications (current leads, magnets, and bearings) indicate the interest in bulk materials which are rapidly being developed. The review will provide fundamentals for potential applications of bulk superconductors.
Chain diffusion in ion crosslinked polystyrene gel
Authors: Calcagno L. , Percolla R. , Masciarelli D. , Foti G.
Published: July 2002

Concentration profiles and diffusion coefficients of deuterated polystyrene chains (27 000–104 000 amu) diffusing into hydrogenated polystyrene (h-PS) matrices (90 000 and 590 000 amu) were measured by forward recoil of 2.0 MeV He ions. This experimental procedure allows us to detect the diffusion coefficient in the range 3×10−15–3×10−13 cm2/s. The irradiation of the h-PS layer with ion beam changes the interdiffusion properties. The diffusion coefficient, measured in h-PS irradiated with 300 keV H+ in the 5×1011–2×1014 ions/cm2 fluence range, does not change at low fluence, instead it is reduced for a threshold fluence whose value depends on the matrix molecular weight. High fluence irradiation of h-PS decreases the polymer solubility because crosslinks between the original chains, produced by ion irradiation, yield a three-dimensional network (gel). By combining diffusion and solubility measurements, for both molecular weights, we observed that the diffusion process is slowed down when, in the irradiated h-PS is produced a gel fraction of 0.8, which corresponds to a polymer structure containing an average of 1.0 crosslink per chain. This result does not depend on the marker molecular weight.
Photoluminescence quenching study of the photocarrier generation mechanism in a layered photoreceptor containing azo pigment
Authors: Niimi Tatsuya , Umeda Minoru
Published: July 2002

Photoluminescence of the carrier generation layer (CGL) in a layered photoreceptor was examined. We found that the photoluminescence of a single CGL comprised of a fluorenone-based azo pigment can be extrinsically quenched at 56% by overcoating the CGL with the carrier transport layer, irrespective of the electric field including the zero field. The quenching efficiency was found to be well in accordance with the photocarrier generation efficiency of the higher electric field, therefore the quenching of the photoluminescence is considered for making the precursors of photocarriers. The photoluminescence quenching mechanism is presumed to be based on the photoinduced electron transfer from the carrier transport material to the photoexcited carrier generation material.
Photothermal measurements near a 90° edge. I. Mirage deflection by a free edge
Authors: Sánchez-Lavega A. , Salazar A.
Published: July 2002

The presence of a 90° edge (corner) modifies substantially the photothermal signal generated by a focused and modulated laser beam incident on an opaque sample. A 3-D model has been developed in order to calculate the ac thermal fields in the sample and adjacent gas, as well as the mirage deviations in the gas. This model incorporates the effects introduced by the finite size of the Gaussian pump beam, and the height and size of the Gaussian probe beam. The experimental measurements of the mirage normal (φn) and transverse (φt) deflections confirm the theoretical predictions. The spatial symmetric forms, of both functions, relative to the exciting point, are broken by the thermal wave scattering produced by the edge. In particular, the inner (close to the edge) parts of φn and φt show an enhancement in their magnitude and phase. For imaging inspection (scanning the sample with probe and pump beams centered), there is an elevation in the magnitude of φn but a drop in its phase at distances smaller than the sample’s thermal diffusion length. However, the most prominent change takes place in φt (both in magnitude and phase), which gives the signature of the presence of the edge.
Permanent magnet film magneto-optic waveguide isolator
Authors: Levy M. , Scarmozzino R. , Osgood R. M. , Wolfe R. , Cadieu F. J. , Hegde H. , Gutierrez C. J. , Prinz G. A.
Published: July 2002

Recent advances in high-coercivity planar-magnetization film magnets and Bi-YIG (bismuth-substituted yttrium iron garnet) film technology have opened up the possibility of fabricating very small magneto-optic devices. In this article we demonstrate that these two technologies can be brought together to fabricate a high performance waveguide magneto-optic isolator for use in integrated optical circuits. The device operates at 1.55-μm wavelength and consists of a waveguide etched into a Bi-YIG film whose magnetization is saturated by a 22-μm-thick TbCu7-type SmCo magnet with a coercivity of 4 kOe. Isolation ratios of 25 dB have been obtained in the wavelength region between 1490 and 1555 nm.
Static critical properties of disordered ferromagnets studied by superconducting quantum interference device magnetometry and small-angle neutron-scattering techniques
Authors: Pouget S. , Alba M. , Nogues M.
Published: July 2002

CdCr(2−2x)In(2x)S4 is a highly frustrated magnetic system based on CdCr2S4, a well-known Heisenberg 3D ferromagnet. A study is presented of its static critical properties as a function of concentration, performed by low-field superconducting quantum interference device SQUID magnetometry and small-angle neutron-scattering SANS techniques. Samples were prepared from isotopic cadmium 114Cd with a low absorption cross section for thermal neutrons. Magnetic measurements performed with low dc fields in the temperature range 5–300 K allow one to determine the magnetic state of the samples, the reentrant temperature TG, the Curie temperature TC, and the critical exponent γ of the susceptibility above TC as a function of dilution in the domain 0<x<0.15. By directly measuring the critical magnetic fluctuations in zero field in SANS experiments, access is gained to the magnetic correlation length ξ, its exponent ν above TC, and another independent determination of γ. Whereas the pure compound exhibits exponents (γ=1.37, ν=0.70) compatible with a 3D Heisenberg ferromagnetic model, a pronounced increase of measured exponents with dilution was found, namely γ=1.97, ν=1.03. The results are compared to the ones of similar studies in the related system Eu(1−x)Sr(x)S and to the renormalization group treatment of strongly random ferromagnets, and possible mechanisms to explain how a small dilution can provoke large alterations in the critical behavior and move the system in the strong disorder region are discussed.
Magnetostriction, elastic moduli, and coupling factors of composite Terfenol-D
Authors: Sandlund L. , Fahlander M. , Cedell T. , Clark A. E. , Restorff J. B. , Wun-Fogle M.
Published: July 2002

Recently it was discovered that composites of Terfenol-D alloys with an insulating binder produce very large magnetostrictions. Resistivities of these composites reach high values, making them attractive for high-frequency applications which require small eddy current losses. In this paper the magnetostriction, magnetization, and Young’s moduli measurements made under constant magnetic field conditions and under constant flux conditions are reported. From these measurements, magnetomechanical coupling factors are calculated. The properties are compared to those of ordinary metallic Terfenol-D and nickel. Two different types of composites were investigated. In the first type the composite has an isotropic structure and in the second type, anisotropic. It is shown that the anisotropic type is more desirable since it possesses both higher magnetostriction and higher coupling factors. It is also clearly shown that the magnetization process for the anisotropic type can be explained by a 180° domain wall motion followed by a magnetization rotation.
Experimental testing of applicability of the Preisach hysteresis model to superconductors
Authors: Friedman G. , Liu L. , Kouvel J. S.
Published: July 2002

Applicability of the Preisach hysteresis model to superconductive hysteresis is tested on two types of materials using a vibrating sample magnetometer. The experiments are set up to check if the hysteresis displayed by the two samples satisfies the necessary and sufficient conditions for the applicability of the Preisach model. These conditions are wiping out of some field history by certain subsequent field extrema and congruency of minor hysteresis loops corresponding to the same field cycles, but having different histories. Observation of the measured minor hysteresis loops indicates that the two conditions are satisfied for the two samples tested. For this reason, it can be concluded that the Preisach model is a very accurate representation of superconductive hysteresis, at least for some superconducting materials.
Stability of the dimer structure formed on Si(100) by ultraclean low-pressure chemical-vapor deposition
Authors: Sakuraba Masao , Murota Junichi , Ono Shoichi
Published: July 2002

Stability against air exposure of the dimer structure formed on Si(100) by ultraclean low-pressure chemical-vapor deposition was investigated. A 2×1-reconstructed dimer structure was clearly observed on the epitaxial Si film on Si(100) by reflection high-energy electron diffraction even after air exposure for 180 min. The dissociation process of the dimer structure and the oxidation process in the air depended on the cooling atmosphere in the reactor after chemical-vapor deposition as well as on the humidity of the air. It is proposed that the dissociation of the dimer structure in the air is suppressed by hydrogen adsorption and coincides with the oxidation of H-terminated or dangling bonds due to H2O adsorption.
Fe/Cr multilayers: Effect of annealing on the spin structure and magnetoresistance
Authors: Hahn W. , Loewenhaupt M. , Felcher G. P. , Huang Y. Y. , Parkin S. S. P.
Published: July 2002

The spin structure of antiferromagnetic Fe/Cr multilayers has been investigated by polarized neutron reflectivity. Measurements were taken on freshly sputtered films as well as films annealed at different temperatures. For annealing temperatures up to 350 °C adjacent Fe layers were found to remain antiferromagnetic, but the coupling strength gradually decreases. In multilayers annealed at higher temperature both antiferro- and ferromagnetic phases are present. In all cases the magnetoresistance is proportional to the amount of antiferromagnetism. The presence of off-specular, diffuse scattering around the antiferromagnetic Bragg peak indicates that the magnetic domains are laterally limited; however, their size is not correlated directly to the magnetoresistance.
Optical properties of GaAs/AlxGa1−xAs multiple quantum wells versus electric field including exciton transition broadening effects in optical modulators
Authors: Lin Chih-Hsiang , Meese J. M. , Chang Yia-Chung
Published: July 2002

A systematic study of the refractive index and absorption coefficient of GaAs/AlxGa1−xAs quantum wells as a function of electric field is presented. In this model, the effective-mass mismatches between GaAs and AlxGa1−xAs have been considered. For the interband optical absorption, we have considered the effect of the final-state interactions, and found an analytical function well describing this effect. The line-shape functions and their appropriate linewidths due to the inhomogeneous broadening mechanisms have been considered as a function of layer thicknesses, Al fraction, electric field, and residual doping density in the intrinsic multiple-quantum-well (MQW) region of a p-i-n optical modulator. The calculated absorption coefficient as a function of wavelength and electric field agrees very well with the experimental data. The calculated refractive index is indirectly verified by comparing the calculated reflectance spectra with the measured data of a MQW reflection modulator.
Tungsten etching in low-pressure SF6 plasma: Influence of the surface temperature
Authors: Petri R. , Henry D. , Francou J-M. , Sadeghi N. , Vayer-Besançon M.
Published: July 2002

The influence of the surface temperature on tungsten etching in a SF6 plasma diffusing from a helicon source has been studied in detail. The surface temperature dependence of the etching kinetics has been analyzed. The influence of the other parameters such as oxygen content of the plasma and ion energy have also been considered. The etching mechanism depends on the temperature range: the etching is partly spontaneous at higher temperatures (T≳−20 °C), becomes a chemical sputtering type at intermediate temperature (−20 °C<T<−40 °C), and a chemically enhanced physical sputtering at lower temperature (T<−40 °C). Surface analyses by x-ray photoelectron spectroscopy provide an understanding of how the surface chemistry is modified with temperature.
Tensor components of the magnetization in a twisted Fe-rich amorphous wire
Authors: Kraus L. , Kane S. N. , Vázquez M. , Rivero G. , Fraga E. , Hernando A. , Barandiarán J. M.
Published: July 2002

Four components of the susceptibility tensor of a high magnetostrictive amorphous Fe77.5Si7.5B15 wire are investigated by means of ac hysteresis loop measurements. The samples have been carefully annealed in order to eliminate the internal stresses produced during the quenching. When tensile stress and/or torsion are applied bistable magnetic behavior with a large Barkhausen jump is observed. The effect of applied torque on the longitudinal and circular components of remanence magnetization and on the longitudinal and circular coercive fields is studied for different constant values of tensile stress. With increasing torque the axial and circular components of remanence decrease and increase, respectively, approaching the limit value of 0.71 Ms. The axial coercive fields for the axial and radial magnetization components coincide. They are nearly constant at low torsion and above same threshold value, depending on applied stress, follow approximately a square-root dependence on applied torque. When tensile stress is applied the circular coercive fields show a well pronounced minimum at the same threshold torque. The experimental results are interpreted by taking into account the axial and helical components of magnetic anisotropy induced by magnetoelastic coupling.
Identification of tunneling emission in Si-SiO2 interfaces by multipoint correlation method with binomial weighting coefficients
Authors: Dmowski K. , Jakubowski A.
Published: July 2002

An analysis of the constant capacitance deep level transient spectroscopy method which shows the effect of tunneling emission processes from oxide traps is presented. It is based upon the correlation signal for a multipoint correlation method with binomial weighting coefficients, and includes the effect of a spatial distribution of oxide traps.