bluuebunny/crossref_metadata_2025 huggingface dataset:
Localized epitaxial growth of tetragonal and hexagonal WSi2 on (111)Si
Authors: Lin W. T. , Chen L. J.
Published: July 2002

Both epitaxial tetragonal and hexagonal WSi2 (t-WSi2 and h-WSi2) were grown locally on (111)Si. The best epitaxy was obtained in 600–1100 °C two-step annealed samples. The orientation relationships between t-WSi2 and Si are [110]WSi2∥[111]Si and (004)WSi2∥(2̄02), whereas those between h-WSi2 and Si are [0001]WSi2∥[111]Si and (202̄0)WSi2∥(202̄)Si. Interfacial dislocations, 80 Å in spacing, were identified to be of edge type with (1/6)〈112〉 Burgers vectors. Two step annealings were found to be effective in improving the epitaxy and relieving the island formation of WSi2 on Si. Significant intermixing of W and Si atoms during the preannealing is proposed to account for the effects.
The effect of temperature on viscoplastic pore collapse
Authors: Carroll M. M. , Kim K. T. , Nesterenko V. F.
Published: July 2002

The hollow-sphere model, with temperature-dependent viscoplastic material response, is used to investigate thermal effects in shock compaction of metal powders. Model calculations show very good agreement with experimental shock rise times only if the temperature dependence is considered. The results also suggest that the dynamic compaction may be qualitatively different depending on whether viscoplastic or inertial effects dominate the pore collapse process.
Photoluminescence spectra of undoped GaAs grown by molecular-beam epitaxy at very high and low substrate temperatures
Authors: Kudo Kazuhiro , Makita Yunosuke , Takayasu Ichiro , Nomura Toshio , Kobayashi Toshihiko , Izumi Tomio , Matsumori Tokue
Published: July 2002

The incorporation mechanisms of residual impurities in GaAs layers grown by molecular-beam epitaxy has been investigated by high-resolution photoluminescence (PL) spectroscopy at 2 K. A systematic study of near-band-edge emissions of undoped GaAs layers grown at a wide range of growth temperatures (Tg), 470–750 °C, demonstrates that PL spectra related with residual impurities are significantly dependent upon Tg. It was found that maximum emission intensity of free exciton is obtained at Tg ∼550 °C, and the minimum impurity incorporation is established at Tg of 550–650 °C.
Excimer laser etching of polymers
Authors: Srinivasan V. , Smrtic Mark A. , Babu S. V.
Published: July 2002

The ablative decomposition of polyimide, poly(methylmethacrylate), and TNS2 photoresist at high excimer laser (ArF and KrF) fluences (>1 J/cm2) is investigated. It is found that the mechanism of etching is both photochemical and thermal in nature at these fluences. A model, in which a thermal contribution to etching is added to the photochemical contribution derived from low fluence measurements, has been found to represent the experimental data satisfactorily. It is also shown that feature sizes as small as 0.4 μm can be delineated on polymeric materials in a self-developing manner using 193-nm laser pulses and contact-printing techniques.
Microstructurally engineered, optically transmissive, electrically conductive metal films
Authors: Aspnes D. E. , Heller A. , Porter J. D.
Published: July 2002

Using standard multilayer and effective medium models, we determine microstructures that optimize the near-IR-visible normal-incidence optical transmittance of electrically conducting metal films intended for use as semitransparent contacts for semiconductor devices such as photodetectors or photoelectrochemical converters. Various conditions are considered, including unpolarized and linearly polarized light and electrical conduction both parallel and perpendicular to the surface. For linearly polarized light, the optimum microstructure consists of parallel metal lines of nominally square cross section oriented perpendicular to the polarization vector of the incident light, regardless of the direction of electrical conduction. The line separation and cross-sectional dimensions must both be small compared to the wavelength λ. For unpolarized radiation, the optimum microstructure depends on the direction of electrical conduction. For conduction parallel to the surface, the optimum microstructure again consists of parallel lines with the lines oriented perpendicular to the residual linear polarization, if any, of the incident flux. For conduction perpendicular to the surface, the optimum microstructure consists of cylindrical metal posts of dimension small compared to λ. Expressions are derived that allow the thicknesses and refractive indices of protective antireflection coatings to be calculated to first order in the thicknesses of the metal films. The more general case of antireflection coatings for anisotropic structures is briefly discussed.
Study of excitons in an arbitrarily shaped GaAs/Al0.3Ga0.7As single quantum well in the presence of static transverse electric field
Authors: Hong Songcheol , Singh Jasprit
Published: July 2002

A method is developed to calculate exciton parameters in an arbitrarily shaped quantum well by using numerical methods in conjunction with the variational method. We solve the Schrödinger equation of the relevant system both by the Monte Carlo method and by the ordinary differential equation solving method, and find that the two approaches yield similar results. Our technique is readily applied to arbitrarily shaped GaAs/AlGaAs quantum wells, and allows us to study the variation of exciton parameters with respect to transverse electric field. We report the results for exciton binding energies, electron and hole tunneling rates, and exciton volumes, which are essential to predicting electro-optical properties of quantum well. Results are presented for the square, graded, and asymmetric quantum wells, and the effects of the shape of the well on exciton properties are discussed. We find that there is only small dependence of the exciton binding and emission energy on the well shape, but a strong dependence of the electron and hole tunneling rates and hence of the dynamical aspects of excitonic properties on the well shape.
Optical properties of gas-evaporated metal particles: Effects of a fractal structure
Authors: Niklasson G. A.
Published: July 2002

Ultrafine metal particles produced by evaporation in an inert gas connect into large clusters that can be described by a fractal dimension at length scales less than a correlation length. An effective medium theory for fractal structures is developed for the case where both the particles and the surrounding medium percolate. A structural parameter which can be related to the fractal dimension is present in the theory. Comparisons to experimental results on the optical properties of gas-evaporated coatings show very good agreement for the case of oxide-coated metal particles. For electrically conducting gold blacks the shapes of theoretical and experimental curves are in qualitative agreement.
Quantum-confined Stark effect in graded-gap quantum wells
Authors: Hiroshima Tohya , Nishi Kenichi
Published: July 2002

Exciton states in AlxGa1−xAs graded-gap quantum well structures with an electric field perpendicular to the layer have been calculated. The calculations show that, for the ground-state heavy-hole exciton in this quantum well structure, the dependence of Stark shift and the oscillator strengths on the external electric field is quite different from the case of the usual square-shaped quantum well structure, whereas for the ground-state light-hole exciton there is no significant difference between these two quantum well structures. These results can be interpreted in terms of the difference between the heavy-hole effective mass and the light-hole one.
Photoluminescence investigation of InGaAs-InP quantum wells
Authors: Moroni D. , André J. P. , Menu E. P. , Gentric Ph. , Patillon J. N.
Published: July 2002

The properties of InGaAs-InP single quantum wells have been studied by using the photoluminescence technique. Samples were grown by atmospheric pressure metalorganic vapor phase epitaxy. The photoluminescence of nominally undoped quantum wells is studied as a function of temperature and excitation power. The role of an excitonic process in 4-K radiative recombinations is pointed out. The best linewidth obtained for a 140-Å well is 4.5 meV, fairly close to the limit imposed by alloy fluctuations in the InGaAs thick layers. Radiative recombination is more and more efficient with decreasing well thickness and higher than in InGaAs bulk material.
Tunneling microscopy, lithography, and surface diffusion on an easily prepared, atomically flat gold surface
Authors: Schneir J. , Sonnenfeld R. , Marti O. , Hansma P. K. , Demuth J. E. , Hamers R. J.
Published: July 2002

We show that a gold surface with atomically flat terraces as large as (150 nm)2 can be easily prepared in air by melting a gold wire with an oxyacetylene torch. Features with characteristic dimensions as low as 10 nm can be written and observed on these terraces with a scanning tunneling microscope. The features are appreciably distorted by diffusion within an hour.
1
3C-doped diamond: Raman spectra
Authors: Chrenko R. M.
Published: July 2002

Gem-quality diamonds have been grown with 13C contents up to 89 at. %. First- and second-order Raman spectra of these crystals indicate that the second-order Raman lines reported for natural diamonds are, indeed, due to carbon lattice modes and not some impurity. Also, the equivalent of a sharp line at 2667 cm−1 in natural diamonds is present in these 13C-doped crystals. Other findings are reported.
Two-photon pumped CO B-A laser
Authors: Tiee J. J. , Quick C. R. , Loge G. W. , Wampler F. B.
Published: July 2002

An optically pumped CO laser that involves a two-photon excitation of the B state is described. A photon conversion efficiency of 15% is determined for the 0-1 and 0-2 vibraonic transitions of the B-A system. It appears that the major portion of the emitted light is the result of amplified spontaneous emission due to the high gain of the transition.
Correlation of the concentration of the carbon-associated radiation damage levels with the total carbon concentration in silicon
Authors: Ferenczi G. , Londos C. A. , Pavelka T. , Somogyi M. , Mertens A.
Published: July 2002

The dominant carbon-related radiation damage center in silicon was studied in detail by deep level transient spectroscopy. Samples with different carbon and oxygen content were implanted with gradually increasing proton fluence. Two energetically closely spaced levels were revealed and tentative identities were assigned. One at ET+EV=0.344 eV (σp=1.1×10−16 cm2) is assigned as the C+Oi complex, and that at ET+EV=0.370 eV (σp=8×10−18 cm2) is assigned as the Cs-Sii-Cs complex. It was shown that the concentration of these defects is correlated to the total concentration of carbon in the crystal.
Effects of magnetic surface anisotropy near the (110) Fe/MnF2 interface
Authors: Tang H. , Qiu Z. Q. , Du Y. W. , Stern G. P. , Walker J. C.
Published: July 2002

Epitaxial (110)56 Fe samples have been grown on (111) Ag and then covered with MnF2 in ultrahigh vacuum. Three 57 Fe layers have been placed at various depths from the Fe/MnF2 interface to permit Mössbauer spectroscopy. A linear temperature dependence of the hyperfine field for 57 Fe layers up to at least 10 layers into the sample is observed. This persistence of surface magnetic effects into the deep layers of the (110) Fe sample can be understood within the framework of a classical spin-wave calculation by Rado.
Crystallization process of Sb-Te alloy films for optical storage
Authors: Fujimori Susumu , Yagi Shogo , Yamazaki Hiroki , Funakoshi Nobuhiro
Published: July 2002

Sb-Te alloy films are developed as rewritable optical recording materials based on amorphous crystalline phase transformations. The crystallization process of Sb-Te sputtered films is systematically studied through measurement of recording characteristics to solve the trade-off problem between data (amorphous) stability and erasing sensitivity. Sb2Te3 is shown to be the best practical phase change medium, having room-temperature stability in amorphous states, short erasing times, and potentially good reversibility. The carrier-to-noise ratio of 50 dB in writing and a decrease in the carrier level of over 30 dB in erasing are achieved in dynamic measurement with a single beam optical head. These favorable properties are attributable to the wide composition margin for a single phase formation in the Sb-Te alloy system.
On the role of oxygen and hydrogen in diamond-forming discharges
Authors: Mucha J. A. , Flamm D. L. , Ibbotson D. E.
Published: July 2002

Plasma emission actinometry has been used to study the mechanism by which small additions of oxygen (∼0.5%) enhance the rate of diamond deposition in a dilute (4%) CH4/H2 discharge at high temperature (900–1300 K). Increasing amounts of CH4 in the feed depress [H], while increasing the O2 concentration, up to ∼5%, produces a fivefold increase in atomic hydrogen in the discharge zone. Invoking a mechanism where diamond growth competes with the formation of an amorphous/graphitic inhibiting layer, these results and earlier studies suggest that oxygen (1) increases [H] which selectively etches amorphous/graphitic carbon, (2) accelerates reaction of this layer with molecular hydrogen, and (3) may itself act as a selective etchant of nondiamond carbon. As a result, the number of active diamond growth sites is increased and enhanced growth rates are observed. We also have grown diamond by alternating a CH4/He discharge with a H2/O2/He discharge and results are consistent with this mechanism. Instantaneous growth rates are very high (45 μm/h) and codeposition of nondiamond allotropes is less. The H2/O2/He discharge removes the inhibiting carbon layer more effectively, while the CH4/He plasma presumably is richer in diamond-forming precursors. Thermochemical calculations suggest that these precursors are likely to be C2H2, C2H, C2, or C atoms rather than methyl radicals (CH3) as others have postulated.
Flow profile above a quartz crystal vibrating in liquid
Authors: Martin Bret A. , Hager Harold E.
Published: July 2002

The particle velocity distribution on an AT-cut quartz crystal oscillating in water is used to model the liquid flow profile near the crystal surface. The nonuniform particle velocity on the quartz surface results in vertical motion in the bulk liquid. This causes a pressure wave to be launched from the quartz surface. This wave is used to measure the velocity of sound in the liquid.
Self-consistent model of transport in quantum well tunneling structures
Authors: Pötz W.
Published: July 2002

We present a fully self-consistent model for the current-voltage characteristic of quantum well tunneling structures. Our approach is based on the independent particle approximation and incorporates both screening of the carrier potential and the response from the contacts. It is shown that a self-consistent treatment of charge supply from the contacts is essential for meaningful description of the system far from equilibrium. Results are presented for GaAs-AlGaAs double-barrier structures. Compared to standard calculations, this approach leads to strong quantitative changes in the I-V characteristic. In particular, peak and valley currents increase and current peaks shift to higher voltages. Doping effects on the I-V characteristic are discussed.
The effects of dopants on surface-energy-driven secondary grain growth in silicon films
Authors: Kim H.-J. , Thompson C. V.
Published: July 2002

The effects of phosphorus, arsenic, and boron on surface-energy-driven secondary grain growth (SEDSGG) in thin polycrystalline silicon films have been investigated. At concentrations at or above 5×1020 cm−3, phosphorus and arsenic were found to markedly enhance SEDSGG while boron had little effect. However, codoping with phosphorous and boron or arsenic and boron lead to compensation (reduction or elimination) of the enhancement effect. The kinetics of SEDSGG were analyzed using transmission electron microscopy. In order to identify electronic as well as segregation effects of dopants on the kinetics of SEDSGG, electron concentrations in the Si films were determined from Hall measurements and dopant segregation was directly measured using scanning transmission electron microscopy and energy-dispersive x-ray analysis. Analogous to normal grain growth, dopant-induced enhancement of SEDSGG can be explained in terms of an increased grain-boundary atomic mobility due to changes in point-defect concentrations resulting from changes in the Fermi level. The effects of codoping on segregation of dopants at grain boundaries was found to have no appreciable effect on the rate of SEDSGG.
Oxygen precipitation and thermal donor formation in Czochralski-grown silicon doped with carbon and tin
Authors: Wijaranakula W.
Published: July 2002

The effect of carbon and tin on the oxygen precipitation and the thermal donor formation in Czochralski-grown silicon after an extended isochronal anneal in the temperature range between 400 and 900 °C has been studied. The experimental results indicate that the oxygen precipitation in both carbon- and tin-doped silicon is enhanced. In carbon-doped silicon, the formation of the thermal donors is suppressed. No effect of tin on the thermal donor formation is observed. Based upon the hard-sphere model, it is hypothesized that the lattice strain arising from the size misfit between the doping impurities and silicon atoms can play an important role in the oxygen precipitation in a heavily doped silicon.
Measurements of the optical constants of solid and molten gold and tin at λ=10.6 μm
Authors: Brückner M. , Schäfer J. H. , Schiffer C. , Uhlenbusch J.
Published: July 2002

The index of refraction, the extinction coefficient, and the absorptance for gold and tin were measured in a temperature range from room temperature up to the melting point for the wavelength λ=10.6 μm. All measurements were performed under ultrahigh-vacuum conditions using a photometric infrared ellipsometer with a rotating analyzer. Measurements verify a discontinuous jump of the absorptance at the solid-to-liquid phase transition from 3.5 to 6.5% in the case of gold and from 4.9 to 9.2% in the case of tin. The experimental results derived for the clean solid surface are in good agreement with the theoretical prediction by a Drude model, if additionally appropriate effective masses and the anomalous skin effect are taken into account. This theory is much less accurate if applied to the molten state of gold and tin, as was already shown previously for liquid aluminum and copper.
Semiconducting low-pressure, low-temperature cesium plasma with unidirectional conduction
Authors: Svensson Robert , Holmlid Leif , Lundgren Lennart
Published: July 2002

In a low-temperature, low-pressure cesium plasma environment, special conditions have been found which exhibit unidirectional conduction of a current over a physical interelectrode space of a size up to 1 mm between two plane parallel electrodes. The spacing is determined by the need to maintain a high enough cesium pressure in the present setup. The cesium emitter has a temperature of 800 K or lower. Current densities of 100–200 A cm−2 during steady state and up to 500 A cm−2 under non-steady-state conditions are reported. The experiments give a semiconducting resistivity between the electrodes as low as 10−3 Ω m, usually around 10−2 Ω m. The special plasma conditions are probably due to excited states of cesium atoms, which condense to form an excited state of matter. Such a type of matter has been predicted to exist on theoretical grounds by Manykin et al. and was stated to have metallic electrons. We propose that the conduction observed involves electron transfer from the cold electrode, through the excited matter on the surface of this electrode and through a very thin plasma gap to the hot foil electrode.
Preparation and characterization of the NdFe10T2Nx (T=Mo,V) compounds with the ThMn12 tetragonal-type structure
Authors: Anagnostou M. , Christides C. , Pissas M. , Niarchos D.
Published: July 2002

The dramatic changes in the magnetic properties observed in the R2Fe17 alloys upon nitrogen absorption have also been observed in the NdFe10T2Nx (T=Mo,V). The nitrides, prepared at T=773 K and 21/2 atm pressure of N2, showed an increased anisotropy HA ≳ 5 T at RT compared to the HA = 0 for the non-nitrogenated materials. The Curie temperatures increase about 44% and the observed volume expansion is 3.6% for Mo and 2.8% for the V compound although the structure remains the same. A coercive field of 0.97 and 0.45 T has been observed at 4.2 K for NdFe10Mo2Nx and NdFe10V2Nx compounds, respectively.
Raman scattering study of thermal interdiffusion in InGaAs/InP superlattice structures
Authors: Yu Soon Jae , Asahi Hajime , Emura Shuichi , Gonda Shun-ichi , Nakashima Kiichi
Published: July 2002

Interdiffusion process of InGaAs/InP superlattice structures by thermal annealing of 700–850 °C is studied by Raman spectroscopy. Peak intensities and peak energies of InAs-, GaAs-, and InP-like longitudinal optical (LO) phonon modes change with thermal annealing temperature and time. Depth profiles of the group III and group V atoms are estimated quantitatively by measuring the variations of the peak energies of the LO phonon modes and the ratios of the mode intensities. The energy shift of the GaAs-like LO peak showing a small broadening, the existence of nonenergy shift InP LO phonon peak and the emerging of InP-like LO peak in the lower energy region indicate that the interdiffused superlattice consists of uniform compositional InGaAsP well and InP barrier layers and sharp interfaces. It is found that the resulting InGaAsP quaternary alloy is roughly lattice-matched to InP (<±0.5%). It is also found that the diffusion coefficient in the well region is larger than that in the barrier region, and that the interdiffusion coefficient D0 and activation energy Ea are 8.56×1010 cm2/s and 5.82 eV, respectively. The interdiffusion in this superlattice is determined by the diffusion in the InP region.
Photoluminescence quenching in a polymer thin-film field-effect luministor
Authors: Dyreklev P. , Inganäs O. , Paloheimo J. , Stubb H.
Published: July 2002

We report the observation of photoluminescence quenching in thin films of poly(3-hexylthiophene) and Langmuir–Blodgett films of poly(3-hexylthiophene)/arachidic acid by the injection of positive charges in the polymer. Charge injection was made in a polymer field effect transistor, used in what we name the luministor mode. The quenching is discussed in terms of polarons/bipolarons acting as recombination centra for the excitons, suppressing the photoluminescence. The inverse phenomenon, luminescence enhancement by depletion of charges, has also been achieved.
Motion of a magnetic domain wall traversed by fast-rising current pulses
Authors: Berger L.
Published: July 2002

A Bloch wall is predicted to undergo finite displacements when traversed by a current pulse with short rise time ≤20 ns and long fall time, in thin films of metallic ferromagnets. In Ni–Fe films of thickness 85–150 nm, pulses with peak current density ≂1×107 A/cm2 are expected to induce wall displacements of order 0.1–1 μm. This effect originates from the s-d exchange interaction. It is phenomenologically similar to the well-known ‘‘wall streaming’’ motion of Bloch walls subjected to fast-rising pulses of hard-axis magnetic field. The effect is related to the existence of a novel, current-induced, term in the expression for the momentum of a magnetic domain wall.
Microhardness and Young’s modulus of diamond and diamondlike carbon films
Authors: Savvides N. , Bell T. J.
Published: July 2002

The microhardness, H, and Young’s modulus, E, of a polycrystalline diamond film and several amorphous diamondlike carbon (DLC) films were determined from force-displacement curves obtained using an ultralow-load microhardness instrument (UMIS-2000). Measurements were made at a constant loading rate of 3 mN/s, to a maximum applied force of 67 and 100 mN with contact force of 0.06 and 1.07 mN, respectively. The diamond film had a surface morphology typical of microwave plasma chemical vapor deposition films (crystallite size 0.5–3 μm), and the force-displacement curves showed nearly complete elastic behavior. The average values of hardness (80–100 GPa) and modulus (500–533 GPa) are comparable to those of natural (001) diamond reference standards (H=56–102 GPa, E=1050 GPa). The DLC films were prepared by low-energy ion-assisted unbalanced magnetron sputtering. By varying the bombarding ion energy, five films were prepared having different sp3/sp2 bonding ratios (3–6), optical gaps (1.2–1.6 eV), and hydrogen concentrations (4–20 at %). The force-displacement measurements are characterized by substantial elastic recovery, and individual films show a very narrow range of hardness and modulus values. It is found that high hardness and improved modulus in DLC films correlate with increasing ion energy, sp3/sp2 bonding ratio, and energy gap. Individual films have mean values of hardness and elastic modulus in the range 12–30 GPa and 62–213 GPa, respectively.
Absolute H-atom concentration profiles in continuous and pulsed rf discharges
Authors: Tserepi Angeliki D. , Dunlop James R. , Preppernau Bryan L. , Miller Terry A.
Published: July 2002

Absolute concentrations of ground state atomic hydrogen are determined by two-photon absorption laser-induced fluorescence in a pure hydrogen rf discharge. Axial concentration profiles obtained across the interelectrode space show a relatively constant concentration (of the order of 1014 atoms/cm3) in the region around the center of the discharge until it decreases sharply within 3–4 mm of each metal electrode surface. In addition, the temporal evolution of the atomic concentration is monitored by means of a pulsed discharge from short times to the establishment of a steady-state concentration. We present a model according to which the formation and decay of the distribution of atomic hydrogen is dominated by diffusion from the production regions towards both the center of the discharge and the metallic electrode surfaces where H atoms are absorbed.
Comparison of high vacuum and ultra-high-vacuum tantalum diffusion barrier performance against copper penetration
Authors: Clevenger L. A. , Bojarczuk N. A. , Holloway K. , Harper J. M. E. , Cabral C. , Schad R. G. , Cardone F. , Stolt L.
Published: July 2002

We demonstrate that depositing Ta diffusion barriers under ultra-high vacuum conditions without in situ oxygen dosing allows for variations both in microstructure and in the concentration of chemical impurities that severely degrade barrier performance. The effects of deposition pressure, in situ oxygen dosing at interfaces, hydrogen and oxygen contamination, and microstructure on diffusion barrier performance to Cu diffusion for electron-beam deposited Ta are presented. 20 nm of Ta diffusion barrier followed by a 150 nm Cu conductor were deposited under ultra-high vacuum (UHV, deposition pressure of 1×10−9 to 5 ×10−8 Torr) and high vacuum (HV, deposition pressure of 1×10−7 to 5×10−6 Torr) conditions onto 〈100〉 Si. In situ resistance furnace measurements, Auger compositional depth profiling, secondary ion mass spectrometry, and forward recoil detection along with scanning and transmission electron microscopy were used to determine the electrical, chemical, and structural changes that occurred in thin-film Ta diffusion barriers upon annealing. Undosed HV deposited Ta barriers failed from 560 to 630 °C, while undosed UHV barriers failed from 310 to 630 °C. For UHV Ta barriers, in situ oxygen dosing during deposition at the Cu/Ta interface increased the failure temperatures by 30–250 °C and decreased the range of failure temperatures to 570–630 °C. Undosed UHV Ta barriers have no systematic relationship between failure temperature and deposition pressure, although correlations between breakdown temperature, oxygen and hydrogen concentrations, and microstructural variations were measured.
Multilayer x-ray mirrors: Interfacial roughness, scattering, and image quality
Authors: Spiller Eberhard , Stearns Daniel , Krumrey Michael
Published: July 2002

Scattering of the multilayer coatings used for our normal incidence soft x-ray telescope at λ=63.5 Å has been measured at λ=1.54 Å and grazing angles of incidence and at soft x rays near normal incidence. Furthermore, the edge of the moon is used as a known test target to estimate the amount of scattering in the arcsec range from images obtained on the date of the solar eclipse on July 11, 1991. The internal surfaces of the coating are inspected by high-resolution electron microscopy. A theoretical model describing the evolution and replication of roughness from layer to layer throughout the structure, which is in agreement with all experimental data is presented. We find that practically all roughness caused by the growth of the multilayer structure occurs at spatial frequencies which are too high to produce scattering. The substrate roughness is replicated at lower spatial frequencies which might produce scattering within the field of view of an instrument. However, roughness in this range is below the 0.5 Å level again resulting in insignificant amounts of scatter.
Optical characterization of KTiOPO4 periodically segmented waveguides for second-harmonic generation of blue light
Authors: Eger D. , Oron M. , Katz M.
Published: July 2002

Periodically segmented waveguides were fabricated by the ion exchange process in KTiOPO4. The waveguides were characterized by measuring the spectra of the transmitted and reflected guided infrared light and of the second-harmonic-generated power. The near-field distribution of the fundamental and second-harmonic wave was also investigated. Infrared to blue light conversion efficiency up to 250% W−1 cm−2 was obtained. Waveguide characteristics were calculated by replacing the segmented structure with an equivalent continuous waveguide. Good agreement between the calculated and measured values was obtained.
Interfacial reactions in Pt/InP contacts
Authors: Mohney S. E. , Chang Y. A.
Published: July 2002

Interfacial reactions in Pt/InP contacts were examined by transmission electron microscopy and Auger depth profiling. A solid state amorphization reaction occurred after the contacts were annealed for 60 s at 325 °C. Crystallites were observed in the amorphous layer near the boundary between the amorphous phase and the remaining Pt upon annealing at 350 °C. The predominant phase formed upon crystallization was polycrystalline Pt5InP. A cubic phase, which is most likely a supersaturated solution of phosphorus in Pt3In, also formed. As the annealing temperature was increased, the reaction proceeded with the formation of phases that were richer in In and P. For 60 s anneals at temperatures of 500 °C or greater, Pt-In phases and textured PtP2 were observed, and the film/InP interface exhibited roughness on the scale of tens of nanometers. Both the Pt-In phases and PtP2 were present at the film/InP interface.
Determination of interfacial roughness correlation in W/C multilayer films: Comparison using soft and hard x-ray diffraction
Authors: Savage D. E. , Phang Y.-H. , Rownd J. J. , MacKay J. F. , Lagally M. G.
Published: July 2002

Interfacial roughness correlation in W/C multilayer films with periods of 23, 30, and 37 Å is examined with x-ray diffraction using λ in the 10–13 Å range and λ=1.54 Å. Transverse scans through multilayer Bragg reflections are analyzed to determine the magnitude and lateral correlation length of the component of interfacial roughness that is perfectly correlated through the multilayer stack. The results are independent of wavelength, even though hard x rays sample much more deeply into the film, indicating that interfacial roughness is not changing through these films.
A novel hard magnetic material for sintering permanent magnets
Authors: Shen Bao-gen , Wang Fang-wei , Kong Lin-shu , Cao Lei , Zhan Wen-shan
Published: July 2002

We have discovered that the substitution of Ga or Si for Fe in Sm2Fe17Cx helps the formation of high-carbon rare-earth iron compounds with 2:17-type structure. We have succeeded in preparing Sm2Fe15M2Cx (M=Ga, x=0, 1.0, 2.0, and 3.0; M=Si, x=0, 0.5, 1.0, and 1.5) compounds with Th2Zn17-type structure by arc melting. The carbides are single phase except for Sm2Fe15Ga2C3.0, which contains a few percent of α-Fe. The Curie temperature TC of Sm2Fe15Si2Cx compounds is found to increase from 550 to 590 K, as x increases from 0 to 1.5. For Sm2Fe15Ga2Cx, TC increases with x from 565 K for x=0 to 635 K for x=2.0, and then decreases with x. Room-temperature saturation magnetization of these carbides is in excess of 100 emu/g and has a small dependence on carbon content. All compounds of Sm2Fe15M2Cx studied in this work except for Sm2Fe15Si2 exhibit an easy c-axis anisotropy at room temperature and show an anisotropy field of higher than 90 kOe for x≥1.0. The present work suggests the possibility of producing high-performance 2:17-type sintering permanent magnets.
Magnetic properties of carbon-coated, ferromagnetic nanoparticles produced by a carbon-arc method
Authors: Brunsman E. M. , Sutton R. , Bortz E. , Kirkpatrick S. , Midelfort K. , Williams J. , Smith P. , McHenry M. E. , Majetich S. A. , Artman J. O. , De Graef M. , Staley S. W.
Published: July 2002

The Krätschmer–Huffman carbon-arc method of preparing fullerenes has been used to generate carbon-coated transition metal (TM) and TM-carbide nanocrystallites. The magnetic nanocrystallites were extracted from the soot with a magnetic gradient field technique. For TM=Co the majority of nanocrystals exist as nominally spherical particles, 0.5–5 nm in radius. Hysteretic and temperature-dependent magnetic response, in randomly and magnetically aligned powder samples frozen in epoxy, correspond to fine particle magnetism associated with monodomain TM particles. The magnetization exhibits a unique functional dependence on H/T, and hysteresis below a blocking temperature TB. Below TB, the temperature dependence of the coercivity can be expressed as Hc=Hc0[1−(T/TB)1/2], where Hc0 is the 0 K coercivity.
Nonlinear morphological instabilities in directional solidification—an integral approximation
Authors: Hsieh Jin-Yuan , Hwang Chi-Chuan
Published: July 2002

In this article, we derive a strongly nonlinear evolution equation by using the integral method to study the instabilities in a directionally solidified binary mixture. This equation can not only describe the interfacial behaviors of all the long-wave limits, but can also provide the possibility of strongly nonlinear instability analyses. Weakly nonlinear analyses proceeded from the critical conditions are undertaken to investigate the two-dimensional bifurcation types and a transition curve separating subcritical and supercritical ranges is obtained.
Investigation of hot electrons in electron-cyclotron-resonance ion sources
Authors: Barué C. , Lamoureux M. , Briand P. , Girard A. , Melin G.
Published: July 2002

The hot electrons in the plasma of an electron-cyclotron-resonance ion source are investigated by three passive diagnostics: bremsstrahlung, electron cyclotron emission, and diamagnetism. For this type of plasma the feasibility of the second diagnostic is an innovative development, as is the simultaneous use of two independent plasma diagnostics for either steady-state or transient experiments. In the steady-state experiments the bremsstrahlung and the electron cyclotron emission are interpreted by comparing the experimental spectra with simulated spectra calculated for the first time from a non-Maxwellian electron distribution. The ‘‘perpendicular temperatures’’ obtained by the two diagnostics are in good agreement. In the transient experiments the electron cyclotron emission and the diamagnetic signals are recorded to study the electron density and the electron lifetime. All these experiments performed using the Minimafios ion source working at 18 GHz with oxygen gas demonstrate trends and saturation effects when the gas injection pressure and the radio-frequency power are varied.
Chaotic responses in electric arc furnaces
Authors: King Paul E. , Ochs Thomas L. , Hartman Alan D.
Published: July 2002

This article reports the findings of ongoing research into the nature and extent of electric fluctuations occurring in electric arc furnaces (EAFs). These fluctuations are indicators of the state of the furnace system and may serve as precursors for use in predictive control of the system. Current and voltage wave forms taken from a small-scale, 200 lb capacity alternating current EAF are used to characterize the motion of the arc column. Wave forms were analyzed using nonlinear dynamics and digital signal processing techniques. Analysis indicates that the observed system behavior is suggestive of chaotic dynamics, with phenomena occurring on several time scales.
Particle size dependence of magnetic behavior and giant magnetoresistance in granular Fe—Ag films
Authors: Peng Chubing , Zhang Sheng , Li Guozhong , Dai Daosheng
Published: July 2002

We have studied the magnetic, and magnetotransport properties of a metallic granular FexAg1−x alloys (x=0–0.45), fabricated by using an electron-beam coevaporation technique. Observations with a transmission electron microscope confirmed that these alloys consist of small Fe particles embedded in an Ag matrix. Based on the superparamagnetic theory, the average number N of iron atoms in a particle, ranging from 102 to 816 as x=0.05–0.21, and, therefore, the average granular size of iron particles, has been determined by simulating the magnetization curves above the blocking temperature. At 1.5 K, the average magnetic moment of iron particles has been found to be reduced as N<400. At a low temperature, the temperature dependence of magnetization for samples with x≥0.21 follows Bloch’s T3/2 law. Moreover, giant magnetoresistance (GMR) has been observed at 1.5 K. Its magnitude is sensitively dependent on the size and density of the magnetic entities. As the granular radius is in the region of 8–13 Å, the GMR value is about 50%.
Coercivity of Fe-SiO2 nanocomposite materials prepared by ball milling
Authors: Giri Anit K. , de Julián C. , González J. M.
Published: July 2002

Samples containing Fe nanoparticles dispersed in SiO2 were prepared by high energy ball milling. We have studied the variation with the milling time of both the saturation magnetization and the coercive force of these samples. The rapid increase of coercivity with the decrease of temperature observed in the low temperature range suggested the presence of superparamagnetic particles in the samples. Nevertheless, our experimental data were in poor agreement with the well-known T1/2 law describing the coercive force of superparamagnetic particles. Coercivities as high as 540 and 850 Oe were obtained for samples with x=0.3 at room temperature and at 1.7 K, respectively. From the analysis of the temperature dependence of the saturation magnetization the spin wave stiffness constant was obtained. This quantity evidenced the enhancement of the thermal demagnetization associated with the reduction in size.
Determination of the optical constants of ZnSe films by spectroscopic ellipsometry
Authors: Dahmani R. , Salamanca-Riba L. , Nguyen N. V. , Chandler-Horowitz D. , Jonker B. T.
Published: July 2002

Spectroscopic ellipsometry was used to determine the real and imaginary parts of the dielectric function of ZnSe thin films grown on (001) GaAs substrates by molecular-beam epitaxy, for energies between 1.5 and 5.0 eV. A sum of harmonic oscillators is used to fit the dielectric function in order to determine the values of the threshold energies at the critical points. The fundamental energy gap was determined to be at 2.68 eV. The E0+Δ0 and E1 points were found to be equal to 3.126 and 4.75 eV, respectively. Below the fundamental absorption edge, a Sellmeir-type function was used to represent the refractive index. At the critical points, E0 and E0+Δ0, the fitting was improved by using an explicit function combining the contributions of these two points to the dielectric function.
Microstructures of (In,Ga)P alloys grown on GaAs by metalorganic vapor-phase epitaxy
Authors: Follstaedt D. M. , Schneider R. P. , Jones E. D.
Published: July 2002

The microstructures of metalorganic vapor-phase epitaxy alloys of (In,Ga)P grown on GaAs substrates were examined using transmission electron microscopy. Alloys examined were grown at 600–775 °C on substrates at or near (001) or (113)A using growth rates of 0.69 and 0.17 nm/s. Two common semiconductor alloy phenomenon, ordering and phase separation, were studied over this range of growth conditions. The CuPt-type ordering reflections are sharpest for growth at 675 °C and more diffuse at 600 and 725 °C due to higher densities of antiphase boundaries. Order can be eliminated by growth at 750 °C or above to obtain the highest band gaps and optical emission energies. Detailed investigation of the microstructure for growth at 675 °C indicates that ordered domains are platelets consisting of thin (1–2 nm) lamella on (001) planes that alternate between the two {111}B ordering variants, in agreement with a model proposed by others. We have formed ‘‘unicompositional’’ quantum wells with sharply defined ordered layers between disordered barrier layers by changing growth temperature, which demonstrates that ordering is determined to a great degree by the conditions during growth. Phase separation is seen for the entire range of growth parameters, independently of ordering; its contrast shows modulations with a variable spacing ranging from a few nanometers to ∼100 nm. Implications of the coexistence of phase separation and ordering for growth models describing these phenomena are discussed.
Field effect measurements in doped conjugated polymer films: Assessment of charge carrier mobilities
Authors: Jarrett C. P. , Friend R. H. , Brown A. R. , de Leeuw D. M.
Published: July 2002

Conductivity and field-effect mobility measurements using metal-insulator-semiconductor field-effect-transistor devices and acceptor density measurements using metal-insulator- semiconductor (MIS) diodes are presented. The measurements were made on thin polymer films of the organic semiconductor, poly(β′-dodecyloxy-α,α′,-α′,α″terthienyl), which were doped to different conductivities using 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as an oxidizing agent. It is found that both the field-effect mobility and the conductivity of these films increases superlinearly upon doping while the transistor amplification, the on/off ratio, decreases. Acceptor densities as obtained from MIS diode measurements are in close agreement with the bulk charge density as calculated from the DDQ content. However, the product of this bulk charge density, field-effect mobility, and the elementary charge e is a factor of 100 larger than the polymer conductivity. This indicates that the average mobility for charge carriers in the bulk is considerably lower than the field-effect mobility. It is considered that the bulk charge carriers are trapped by the Coulomb interaction with their parent charge compensating counter-ions, whereas charges in accumulation have no associated counter-ions and, therefore, are more mobile.
Electrochromic vanadium–pentoxide–based films: Structural, electrochemical, and optical properties
Authors: Talledo A. , Granqvist C. G.
Published: July 2002

Crystalline VO2.5 films were prepared by reactive dc magnetron sputtering followed by annealing posttreatment. Lithium was inserted electrochemically from an electrolyte so that LixVO2.5 (0<x<1.5) was formed. The evolution of the electromotive force (EMF) was recorded during Li intercalation. For lithiated samples, structure by x-ray diffraction, optical properties by spectrophotometry in the 0.3–2.5 μm range, infrared reflectance by spectrophotometry in the 400–1200 cm−1 interval, and the mechanical stress by beam deflectometry were studied. Changes in lattice parameters, phonon spectra, and stress levels gave a consistent picture of the structural evolution. Measurements of optical absorption and EMF were interpreted within a conceptual model of interband transitions between the O 2p band and a split V 3d band. Durability and reversibility of the Li intercalation/deintercalation were verified by potentiodynamic measurements. For comparison, the properties of highly disordered films were also measured.
Increased voltage phenomenon in a resonance circuit of unconventional magnetic configuration
Authors: Ide Osamu
Published: July 2002

The behavior of an LCR (inductance-capacitance-resistance) circuit with a movable ferromagnetic core is discussed. The core is attracted by a magnetic field generated by an electric current resulting from the discharge of a capacitor in the closed LCR circuit. An unusual increase in recharge voltage, which was dependent on the magnetic configuration of the coil, was observed. This voltage increase does not conform to the mathematical simulation of the system. The possibility that a positive electromotive force was involved in this effect is discussed.
Depressed photoemission from Görlich cathodes at high laser light intensities
Authors: Boreham B. W. , Newman D. S. , Höpfl R. , Hora H.
Published: July 2002

The current density of electrons emitted from surfaces irradiated by light is known to follow either a linear or quadratic dependence with intensity for single- or double-photon absorption respectively or, at high incident light intensities, a square root dependence (depressed photoemission). In separate experiments, a Görlich (Cs3Sb) cathode was irradiated with the green (λ=5140 Å) and blue (λ=4880 Å) lines of an Ar+ laser at various intensities in an effort to determine over what range depressed photoemission continued above the current density threshold of about 10−5 A cm−2. The results have confirmed and extended the existence of depressed photoemission to intensities of up to five orders of magnitude higher than previously observed threshold values with no apparent evidence of saturation of the effect. The consequences of this are discussed in relation to surface traps and two-photon-plasmon excitation in the photocathode.
Transport properties in Se–Te–Ge glasses
Authors: El Mandouh Z. S.
Published: July 2002

Addition of germanium to the Se–Te alloy causes structural changes which modify the band structure and hence the electrical properties of the Se–Te alloy. In the present work, electrical, optical, and structural properties of Se–Te–Ge have been studied. The activation energies calculated from the dc resistivity measurements were changed from 0.15 to 0.39 eV with the change of germanium and thickness of the film. Refractive index n, extinction coefficient k, and dielectric constant ε of Se–Te–Ge alloy thin films showed significant change with light energy. Crystallization of the sample is achieved at 573 K. The amorphous Se–Te–Ge system is useful as a good photovoltaic material. The dc conductivity measurements were carried out from 294 to 555 K. The effect of heat treatment on optical absorption was investigated.