bluuebunny/crossref_metadata_2025 huggingface dataset:
Interferometric determination of optical anisotropy in fibers 1- homogeneous fibers
Authors: Hamza A. A. , Sokkar T. Z. N. , Shahin M. M.
Published: July 2002

This article describes a method for the measurement of refractive indices and birefringence of fibers. It is used to overcome difficulties in measuring refractive indices of immersion liquids as well as the corrections for dispersion and temperatures. Two fibers are used for each measurement. One is of known refractive index and dispersion properties and the other is of unknown refractive index. A modified mathematical formula is used with a two-beam interference microscope. This technique is applied to two groups of fibers having different ranges of refractive indices. The first group contains seven different products of nylons and the second group contains five different products of polyesters. The calculated refractive indices using this method is compared with those obtained using the established method. Illustrations are given using microinterferograms.
Influence of the interface quality on the elastic properties of Co/Au multilayers investigated by Brillouin light scattering
Authors: Hillebrands B. , Krams P. , Spörl K. , Weller D.
Published: July 2002

We have determined the set of elastic constants of polycrystalline Co/Au multilayers by means of Brillouin light scattering. Annealing the samples enhances c33 by 14% and c55 by 30%, but leaves c11 unchanged. Increasing the modulation wavelength of the multilayers, c33 increases, but c11 and c55 remain unchanged. These results are discussed in the light of the known phenomena of chemical and geometrical interface modifications of the multilayered structures as a function of annealing temperature and time.
Measurement of the electrogyratory coefficient in photorefractive Bi12SiO20 crystal
Authors: Nakagawa Kiyoshi , Kajita Nobuyuki , Chen Jing , Minemoto Takumi
Published: July 2002

The electrogyratory effect in the Bi12SiO20 (BSO) single crystal has been investigated by measuring the change of the polarization state of a light passing through a thick BSO single-crystal plate. The linear electrogyratory coefficient η41 in the BSO crystal has been determined as (1.8±0.4)×10−9 mm/V.
Second generation, high-power, fundamental mode large-orbit gyrotron experiments
Authors: Irwin K. , Destler W. W. , Lawson W. , Rodgers J. , Scannell E. P. , Spang S. T.
Published: July 2002

Experimental studies of a large-orbit gyrotron device operating at the fundamental of the cyclotron frequency have been conducted. Based on results of initial investigations at the University of Maryland a linear beam facility was retrofitted to produce rotating beams and a second experiment has been conducted. Experimental operation of this second device, aimed at the generation of rf radiation at ∼650 MHz corresponding to a tangential intersection of the beam-waveguide dispersion curves is described.
Dislocation formation related with high oxygen dose implantation on silicon
Authors: Stoemenos J. , Reeson K. J. , Robinson A. K. , Hemment P. L. F.
Published: July 2002

The generation of dislocations in silicon implanted by oxygen (SIMOX) is studied by transmission electron microscopy. In an effort to separate the effects of displacement damage caused by ion implantation from the dynamic structural transformation which occurs due to the insertion of oxygen into the lattice, two special experiments were designed. The first consisted of a series of low dose oxygen implantations in which the energy was either ramped up or down in small steps. This served to expand the region in which oxygen was implanted, permitting a more detailed study of the defects. The second experiment involved the implantation of oxygen into a (111) wafer in order to study the influence of the crystallographic orientation on the generation of dislocations. Both experiments reveal the important role of the surface in the generation of dislocations. It is concluded that most of the threading dislocations are formed during the high-temperature anneal and have their origin in a defect-rich zone near the surface. These defects are attributed to Si-interstitial migration to the surface which results from the formation of SiO2. Consequently, epitaxial growth takes place on the surface and due to the growth defects generated there, dislocations are extended to the Si overlayer during the high-temperature annealing. Dislocations are also formed in the Si overlayer near the interface with the SiO2 buried layer. These dislocations are pinned by the SiO2 precipitates and are either consumed or dragged by them to the oxide interface during subsequent high-temperature annealing. The effect of surface contamination on the generation of dislocations in the early stage of implantation is discussed and factors which yield a better quality SIMOX material are presented.
Fluorine-containing species on the hydrofluoric acid etched silicon single-crystal surface
Authors: Takahagi T. , Ishitani A. , Kuroda H. , Nagasawa Y.
Published: July 2002

The chemical structure and property of fluorine-containing species on the hydrofluoric acid (HF) etched Si surface was examined by use of x-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The fluorine content on the surface was found to increase with increase of HF concentration. A silicon surface etched by 50% HF has fluorine of 2.6×1014 atoms/cm2 as Si–F. Most of the Si–F bondings are rapidly hydrolyzed to Si–OH by rinsing the wafer in water. Thus prepared Si–OH groups are found to be useful as active sites for chemical modification of the bare silicon single-crystal surface. The Si–F was observed not to influence the oxidation rate of HF etched silicon surface.
Optical thickness mapping of InGaAsP/InP layers
Authors: Sartorius B. , Brandstättner M. , Wolfram P. , Franke D.
Published: July 2002

A two-wavelengths transmission method is presented for measuring the thickness of epitaxial layers with a resolution of better than 10 nm. The measuring speed is high which for the first time makes possible an imagelike presentation of thickness inhomogeneities in layers. A calibration scheme is described which allows quantitative thickness measurements. By the example of measuring buried layers inside a heterostructure the versatile use of the method is demonstrated.
Critical current enhancement in proton-irradiated Tl2CaBa2Cu2O8 films
Authors: Weaver B. D. , Reeves M. E. , Chrisey D. B. , Summers G. P. , Olson W. L. , Eddy M. M. , James T. W. , Smith E. J.
Published: July 2002

We have measured changes in the superconducting transition temperature Tc and critical current density Jc of epitaxial Tl2CaBa2Cu2O8 films upon exposure to 2 MeV protons. Jc was measured inductively at 4.2 and 77 K and in fields of H=0 and 0.2 T. At 77 K and H=0, Jc decreases monotonically with increasing fluence Φ. The rate of decrease is about 1.8 times greater than for YBa2Cu3O7 films, even though the rate of change of Tc with Φ is comparable. At 4.2 K, Jc is initially enhanced, even at H=0. The maximum observed increase is 34% (to 8 MA/cm2) at Φ≊1016 protons/cm2 and H=0.2 T. This enhancement is attributed to pinning of magnetic flux lines by proton-induced defects.
Modeling and optimization of high-T
c superconducting bolometers: The effect of film thickness
Authors: Neff H.
Published: July 2002

The performance of thin-film, YBa2Cu3O7−x-based, transition edge bolometers at high and moderate degrees of thermal isolation has been modeled. Using standard formulas in connection with a parametrized representation of available empirical data, i.e., transition temperature Tc, resistance temperature coefficient β, and resistivity ρ, both the detectivity D* and responsivity ‖S‖ of the detectors have been evaluated as a function of film thickness d. The model calculations reveal that ‖S‖ scales inversely with film thickness and conductivity, respectively, and peaks at a thickness of approximately 100 Å. In turn, the detectivity D* degrades rapidly for smaller values, suggesting to compromise on both figures in the same range. These results, in part, rely on recent findings on flicker noise in thin metal films, as discussed in the literature. The model also shows that the performance at moderate degrees of thermal isolation compares well with existing thermal detectors operating at ambient temperature, but is expected of being superior for small, fast detector configurations at high degrees of thermal isolation.
Metal-oxide semiconductor transistors fabricated on Si/Al2O3/Si structures
Authors: Ishida M. , Yamaguchi S. , Masa Y. , Nakamura T. , Hikita Y.
Published: July 2002

Metal-oxide semiconductor field effect transistors (MOSFETs) were fabricated by polycrystalline-Si gate process on double heteroepitaxially grown Si(100)/Al2O3(100)/Si(100) structures in order to characterize the Si on insulator (SOI) structures. To realize the SOI structures, at first, the epitaxial Al2O3(100) film was grown on a 2-in. Si(100) wafer, and then, Si epitaxial film was grown on the Al2O3/Si by the chemical vapor deposition method. The SOI wafers were able to be handled in the same way as Si wafers during the device fabrication process. From ID-VD and ID-VG properties of the MOSFET, the transistor action was confirmed, and the threshold voltage of 0.4 V and the effective mobility of 540 cm2/V s at VG − VT = 4.0 V were obtained. The epitaxial Si layer was p-type, and the impurity concentration was considered to be 5×1015 cm−3. These results were very similar to those obtained from Si on sapphire epitaxial films.
Structural study of tin and carbon coimplanted silicon
Authors: Mei P. , Schmidt M. T. , Yang E. S. , Wilkens B. J.
Published: July 2002

The alloy system Six(SnyC1−y)1−x was investigated. The purpose is to form material with reduced strain at silicon heterojunctions. In this work, samples were prepared by coimplantation of tin and carbon ions into silicon wafers within the dosage range 1015–1016 cm−2, followed by rapid thermal annealing. Rutherford backscattering and channeling, Auger sputter profiling, and secondary-ion-mass spectrometry were employed to study the crystallinity, chemical composition, and depth profiles. A near-perfect crystallinity for 0.5 at. % of tin and carbon was achieved. For high-dose implanted samples, tin segregation was observed. This work demonstrates promising features of group-IV semiconductor synthesis by ion implantation.
Effect of zinc diffusion on impurity profiles of carbon- and beryllium-doped thin GaAs layers grown by chemical beam epitaxy
Authors: Tokumitsu E. , Chiu T. H. , Luftman H. S. , Ha N. T.
Published: July 2002

A significant difference between beryllium and carbon distribution in GaAs after zinc diffusion is presented. It is shown that grown-in carbon is stable and remains localized even after zinc diffusion, whereas grown-in beryllium diffuses very rapidly in the presence of diffusing zinc. This effect can be attributed to the difference in the crystal lattice site which the dopant occupies.
Aging of zinc oxide varistors subjected to partial discharges in sulfur hexafluoride
Authors: Bui A. , Khedim A. , Loubière A. , Kourdi M. B.
Published: July 2002

The behavior of zinc oxide varistors subject to partial discharges in sulfur hexafluoride is studied with respect to their protective coating (glass and epoxy resin). Sulfur hexafluoride (SF6) is used as an insulating medium for the electrical equipment because of its high dielectric strength and good heat transfer properties. The decomposition of SF6 and residual impurities can considerably influence the varistor current-voltage characteristics essentially in the ohmic region. An analysis of the phenomenon shows that the degradation is due to a conducting deposit around the varistors and a physical corrosion of the coating.
Modification of aggregate formation in arachidic-acid–cyanine-dye complex Langmuir–Blodgett films by substituent groups
Authors: Saito Kazuhiro , Ikegami Keiichi , Kuroda Shin-ichi , Saito Mitsuyoshi , Tabe Yuka , Sugi Michio
Published: July 2002

Water-soluble cyanine dye derivatives can be adsorbed from aqueous solution to an arachidic acid monolayer at the air-water interface. Interface-adsorbed complex Langmuir–Blodgett films of arachidic acid and four different derivatives of thiacarbocyanine dyes were fabricated using this method, and their optical properties were examined employing a linearly polarized incident. Clear differences in both spectral shape and in-plane anisotropy were found among the films of different derivatives, each associated with an aggregate form characteristic of the substituent group. They can be classified as a dimer with Davydov splitting, a monomer, and a J aggregate. Estimation of the configuration of the molecules in the dimers and measurement of the photoluminescence spectrum for the J aggregate were performed to clarify the nature of aggregates. The results suggest the possibility of systematic control of aggregate formation in the system by introducing substituent groups for dyes.
Mathematical model of internal temperature profile of GaAs during rapid thermal annealing
Authors: Third C. E. , Weinberg F. , Young L.
Published: July 2002

In previous studies it was reported that GaAs samples which were rapid thermal annealed exhibit bright bands adjacent to the surfaces in cathodoluminescence images of the cross sections. It is possible that the presence and depth of these bright bands are related to thermal stresses in the GaAs resulting from thermal gradients during heating and cooling. To investigate this possibility, a one-dimensional mathematical model was developed to predict the temperatures through the thickness of the GaAs. Calculations of the thermal stress field show that the thermal stresses do not correlate with the depth of the bright bands.
A method for the phase measurement of the multipacting electrons
Authors: Noori Majid T. , Harmon Gerald S.
Published: July 2002

At high frequency in a low pressure electrical discharge, multipacting electrons are believed to be responsible for the gas breakdown. The multipacting theory predicts that these electrons arrive at the end plate of the discharge tube while the phase of the rf field is within a particular range. Although there exist some indirect verification of phase pile-up of multipacting electrons, it was felt that a direct measurement of the phase angle distribution was needed. A simple and practical method is presented in this paper for performing the task. This method was employed for such a measurement and the outcome is in a good agreement with the theoretical predictions.
Characterization of epitaxial yttria-stabilized zirconia/Si interface by ion beam channeling
Authors: Fukumoto H. , Yamamoto M. , Osaka Y.
Published: July 2002

Yttria-stabilized zirconia (YSZ) films which have high crystalline quality and no dislocation near the YSZ/Si interface, have been epitaxially grown on Si(100) in spite of the relatively large lattice mismatch between YSZ and Si. The formation of the SiO2 layer at the YSZ/Si interface during the YSZ deposition takes an important part as a buffer layer in the epitaxial growth of YSZ films on Si.
Heteroepitaxy and characterization of Ge-rich SiGe alloys on GaAs
Authors: Venkatasubramanian R. , Timmons M. L. , Mantini M. , Kao C. T. , Parikh N. R.
Published: July 2002

Growth of SiGe alloys on GaAs substrates at temperatures as low as 590 °C is described. The growth has been accomplished using the pyrolysis of disilane (Si2H6) and germane (GeH4) at such temperatures. The layers were characterized electrically and show n-type conduction with carrier concentrations of ∼1×1018 cm−3. The high quality of the SiGe layers is evident in the Rutherford-backscattering/channeling results on SiGe/GaAs structures. A χmin of 5.6% has been obtained for a Si0.05Ge0.95 layer on GaAs. χmin increases with increasing silicon content in the SiGe layers. The SiGe alloy layers were also studied by x-ray diffraction, and the composition was determined assuming coherent, tetragonally distorted growth of SiGe on GaAs. The distortion calculations, based on theoretical elastic constants, were confirmed using Auger electron spectroscopy to determine alloy composition.
Formation of p+-p-n junctions in gallium arsenide by a two-step diffusion process
Authors: Heath L. S. , Bisberg J. E. , Chin A. K. , Meehan K.
Published: July 2002

A two-step, open-tube diffusion process has been developed to form p+-p-n junctions in GaAs. n-type GaAs substrates were zinc diffused at 550 °C to form a p+ layer, capped with thermally deposited silicon nitride, and annealed in an open-tube furnace. The zinc redistributes during the anneal, forming a p layer adjacent to the p+ layer. The peak carrier concentration of the p+ and p layers and the depth of the p+-p and p-n junctions are controlled by the time and temperature of the anneal. The anneal time was varied from 30 to 180 min and the temperature range was 700–850 °C. Both the p+-p and p-n junction depths show a square root dependence on annealing time. Diffusion coefficients and activation energies for the zinc diffusion which occurs during the anneal are determined.
Low-energy ion-assisted epitaxy of InGaAsSb on InP (100)
Authors: Kaspi R. , Barnett S. A.
Published: July 2002

InGaAsSb alloys were grown within the solid-phase miscibility gap, lattice matched to InP (100) substrates, using ion-assisted deposition. The alloy structure and properties were strongly dependent upon the energy E of Ar ions bombarding the growing film. Films deposited with E≤16 eV exhibited multiple (400) x-ray diffraction peaks and relatively low electron mobilities, indicating that there was significant alloy decomposition. Increasing E to 19–21 eV yielded single, sharp (400) x-ray peaks and increased the electron mobility, showing that ion irradiation suppressed decomposition. E≳22 eV resulted in ion damage as indicated by decreased mobilities and broadening of the x-ray peaks.
Hydrogen redistribution and gettering in AlCu/Ti thin films
Authors: Marwick A. D. , Liu Joyce C. , Rodbell K. P.
Published: July 2002

Redistribution and uptake of hydrogen was found to occur during anneals in forming gas (90% N2+10% H2) of thin-film AlCu/Ti/AlCu sandwich layers deposited on a thin layer of SiO2. Annealing at 350 or 400 °C for 30 min caused the Ti-containing layer to getter hydrogen, which came from both the upper and lower interfaces of the SiO2 and from the gas. The uptake kinetics from the gas were surface limited. The hydrogen distribution was influenced by the formation of TiAl3, in which the solubility of hydrogen was found to be negligible. Hydrogen in partly reacted layers was found to be associated with unreacted titanium.
Optical properties of AgGaSe2 and AgGaSe2:Co2+ single crystals
Authors: Hahn Suk-Ryong , Kim Wha-Tek , Kim Yong-Geun , Kim Hyung-Gon
Published: July 2002

The temperature dependence of the optical energy gaps in AgGaSe2 and AgGaSe2:Co2+ single crystals has been investigated. The impurity optical absorption of AgGaSe2:Co2+ has also been studied. In the temperature dependence of the energy gaps, the temperature coefficients (dEg/dT) are measured to be 1.8×10−4 eV/K (10–60 K) and −3.2×10−4 eV/K (95–300 K) for the AgGaSe2, and 8.9×10−5 eV/K (10–60 K) and −1.0×10−4 eV/K(80–300 K) for the AgGaSe2:Co2+, respectively. In the optical-absorption spectrum of the AgGaSe2:Co2+, three absorption bands of 1.54, 0.72, and 0.51 eV are observed. It is identified that these impurity absorption peaks are attributed to the electronic transitions between the split energy levels of Co2+ ion with Td symmetry sites of the AgGaSe2 host lattice.
Effects of thermal annealing on oxygen related centers in GaAs
Authors: Skowronski M. , Kremer R. E.
Published: July 2002

Infrared absorption measurements in the 600–1300 cm−1 range of oxygen doped bulk GaAs crystals are presented. Nine different absorption bands have been observed and the effect of thermal treatment on their intensity investigated. Short term annealing (5 min) followed by quenching resulted in either partial or complete disappearance of absorption lines located at 604.8, 730.8, 794.3, 1084.2, 1092.0, and 1114.3 cm−1 and have been interpreted as being due to the dissolution of the complexes involving oxygen atoms. In parallel to this dissolution, there was a corresponding increase of concentration of isolated interstitial oxygen released from those complexes. In particular, it has been determined that the oxygen related center responsible for the 730.8 cm−1 triplet dissociates with an activation energy of 3.8 eV. The results of long term annealing (14 h) are consistent with the above interpretation. The concentration of simple defects, interstitial oxygen, and Ga-O-Ga(1) center, is decreasing in the temperature range of 600–700 °C due to formation of complexes with other impurities and defects. In the same temperature range, the intensity of high energy lines: 1084.2, 1092.0, and 1114.3 cm−1, lines increased by about 50%. These lines most likely originate from silicon-oxygen and/or aluminum-oxygen pairs.
Activation energy enhancement during initial silicon-oxide growth in dry oxygen
Authors: Kamohara Shiroo , Kamigaki Yoshiaki
Published: July 2002

Silicon oxidation enhancement in the thin oxide region is investigated by studying activation energy dependence on SiO2 thickness using the Arrhenius plot of oxidation rates. The enhancement of the activation energy is found to occur at approximately 30 Å SiO2 thickness. The change of the oxidation-limiting process from surface reaction enhancement to oxidant diffusion retardation can provide an explanation of this activation energy enhancement. This model also provides a consistent view of previous experiments in the thin region.
Time and temperature influence over graded band-gap AlxGa1−xAs layers
Authors: Algora Carlos , Gavand Marc
Published: July 2002

Graded band-gap AlxGa1−xAs layers were grown using isothermal liquid phase epitaxy techniques together with saturated solutions. The effects of time and temperature of contact between liquid solutions and solid substrates over grown layers are studied. The Al depth profiles, as measured by secondary ion mass spectroscopy analysis, show that: (a) the thickness of the grown layer increases rapidly at the contact starting moments and it saturates in a few minutes, (b) the Al surface concentration increases with the contact time at the beginning of the process and then it saturates, (c) the thickness of the layer decreases if the temperature increases. Finally, for this last new find we develop a tentative explanation based on an etch-diffusion-regrowth mechanism.
A stress-induced diffusion model for failure of interconnects in microelectronic devices
Authors: Guo Q. , Whitman C. S. , Keer L. M. , Chung Y.-W.
Published: July 2002

Voiding and open-circuit failures from cracking of interconnects in microelectronic devices are often observed during isothermal aging and thermal fatigue tests with or without electric current flow. Although the effects of many factors on the failure rate have been investigated experimentally, it is not yet known how to extrapolate the results of accelerated tests to normal operating conditions. Theoretical failure models for isothermal aging and thermal fatigue tests are constructed from diffusion theory and fracture mechanics in this paper. The results from many investigations can be incorporated into this model to explain many of the observed phenomena, for example, effects of the aging temperature, interconnect stress, linewidth, line thickness, passivation, interlayer dielectric stress, etc. Patterned Al-Cu interconnects were thermally cycled in air. It was found that the failure mechanisms of interconnects under isothermal aging and thermal fatigue are the same. Effects of hold time, frequency, and thermal fatigue temperatures on failure rate were studied both experimentally and theoretically. The predicted results according to the present failure model show excellent agreement with experiments.
An approach to two-dimensional vector thermal radiative transfer for spatially inhomogeneous random media
Authors: Jin Ya-Qiu
Published: July 2002

An approach to two-dimensional vector thermal radiative transfer equation for a layer of spatially inhomogeneous, random scattering medium is developed. By using the Fourier transformation and matrix expression, one-dimensional radiative transfer equation of the spectrum of the Stokes vector is derived. Employing an iterative approach in the approximation of small albedo, the zeroth- and first-order solutions from the integral radiative transfer equation are obtained. Numerical results of polarized brightness temperature of atmospheric precipitation and vegetation canopy with a Gaussian and periodic fractional volumes, respectively, are obtained. The functional dependence of brightness temperature to inhomogeneous scale, frequency, polarization, dielectric properties of the underground medium, etc. are discussed.
Electrical transport and superconductivity in a PrBa2Cu3O7-GdBa2Cu3O7 composite system
Authors: Lin J. J.
Published: July 2002

Composite samples of PrBa2Cu3O7-GdBa2Cu3O7 have been fabricated with the nominal GdBa2Cu3O7 volume fraction φ ranging from 0.00 to 1.00. Resistivity and magnetization measurements performed on the samples are interpreted in terms of sample structure composed of GdBa2Cu3O7 and PrBa2Cu3O7 grains embedded in a Gd1−xPrxBa2Cu3O7 matrix. The Pr concentration x as a function of φ is established by inferring it from the superconducting transition temperature Tc. In particular, both the resistivities and magnetizations show drastic changes when φ exceeds about 0.6. This is the value of φ at which x first exceeds a critical value of about 0.5 and where the Gd1−xPrxBa2Cu3O7 matrix first superconducts. The Gd1−xPrxBa2Cu3O7 phase is presumably formed during the high temperature (900 °C) firing process which results in mutual substitution between the Gd and Pr atoms.
Electrical properties of β-SiC metal-oxide-semiconductor structures
Authors: Chaudhry M. I.
Published: July 2002

Using conductance and capacitance data for metal-oxide-semiconductor (MOS) structures on n-type β-SiC, the density of states at the β-SiC/SiO2 interface, their location in the bandgap of β-SiC, and the electron capture probability are obtained. The MOS structures were fabricated by oxidizing β-SiC in wet oxygen. It is found that interface-state density of the order of 1011 states/(cm2-eV) is located between 0.28–0.40 eV below the conduction-band edge of β-SiC. The electron-capture probability is in the range from 4.2×10−9 to 8.4×10−8 cm3/s. This study shows that the electrical properties of β-SiC MOS structures are similar to that of Si MOS structures.
The effect of InP buffer layer on the electron transport properties of epitaxial In1−xGaxAs
Authors: Dosluoglu T. , Solanki R.
Published: July 2002

Carrier concentration and mobility of undoped InGaAs layers grown on InP via organometallic vapor phase epitaxy have been investigated. The mobility limits imposed by various scattering mechanisms were studied over the temperature range 40 to 300 K. Electrons in InGaAs epilayers grown on semi-insulating InP substrates without any InP buffer layer had a lower 77 K mobility than others grown with an undoped InP buffer layer. This is attributed to a higher acceptor compensation in the unbuffered layers (as determined from temperature dependent carrier concentration data) and to significant ionized-impurity scattering in these more compensated samples.
Enhanced effects with scanning force microscopy
Authors: Howells S. , Chen T. , Gallagher M. , Yi L. , Sarid D.
Published: July 2002

We present a general theory that describes the operation of scanning force microscopy in the contact force regime. We find that force derivatives along the surface of a sample produce images that can be dramatically enhanced relative to those of surface topography. For scanning tunneling microscopy atomic force microscopy (STM/AFM) and AFM configurations, the spring constant of the cantilever and the force derivatives perpendicular to the surface of the sample determine the enhancement, respectively.
Photocarrier generation in metal-free phthalocyanines: Effect of the stacking habit of molecules on the photogeneration efficiency
Authors: Kanemitsu Yoshihiko , Yamamoto Aishi , Funada Hiroshi , Masumoto Yasuaki
Published: July 2002

The photocarrier generation mechanism in metal-free phthalocyanines (H2Pc) was studied by time-of-flight photoconductivity measurements. The quantum efficiencies of photogeneration of holes depend on the crystal structure of H2Pc. The photogeneration efficiencies in X- and τ-H2Pc are high compared with those of α- and β-H2Pc. The lifetimes of the precursor state of free carriers in X- and τ-H2Pc are between those of α-H2Pc and β-H2Pc. Moreover, infrared absorption and Raman spectra show that X- and τ-H2Pc are intermediate states between α-H2Pc and β-H2Pc. It is pointed out that the photogeneration dynamics of H2Pc is controlled by the intermolecular overlap of the π-electron wavefunctions and the stacking habit of molecules.
Study on the structural relaxation of vortex state due to the flux creep in high T
c superconductors
Authors: Li Xiao-Guang , Lai Rongji , Zhao Huazhang , Wang Zhongmin , Chen Lin , Zhang Yuheng
Published: July 2002

The deviation of magnetization (M) relaxation from logarithmic time dependence is due to both the low pinning potential influenced by the driving energy formed by the gradient of flux lines and the large thermal activation. Considering the structural relaxation of the vortex state under the action of the driving force and thermal activation, the dependence of M on time t can be obtained as M=A+Bt−β, where A, B, and β keep constant at a given field and temperature.
Normal spectral emittance of crystalline transition metal carbides
Authors: Mackie William A. , Carleson Pete , Filion Janice , Hinrichs C. H.
Published: July 2002

We report on experiments to determine the normal spectral emittance of crystalline forms of five transition metal carbides: hafnium carbide, niobium carbide, tantalum carbide, titanium carbide, and zirconium carbide. These emittance measurements were taken at the commonly used pyrometer wavelength of 0.65 μm. The specimens were cylindrical with 0.10-cm-diameter blackbody holes drilled axially to a depth of 1.0 cm. The crystalline specimens were prepared from sintered stock by floating zone arc refinement and then centerless ground to the desired diameter. Measurements were made in vacuum in the temperature range 1200<T<2400 K. The emittance of HfC tends to increase slightly with temperature (εHfC=0.4322+1.065×10−4 T) while those of NbC, TaC, TiC, and ZrC decrease (εNbC=0.4913−6.6×10−5 T, εTaC=0.4662−5.084×10−5 T, εTiC=0.8192−1.66×10−4 T, and εZrC=0.715−1.174×10−4 T). Bulk stoichiometries of the samples were C/Hf=0.86±0.03, C/Nb=0.833±0.014, C/Ta=0.79±0.05, C/Ti=0.955±0.005, and C/Zr=0.917±0.015. As a check on the accuracy of the method and procedure, normal spectral emittance measurements were taken on molybdenum yielding values consistent with those accepted. The normal spectral emittance was determined to be isotropic with respect to crystal orientation within the uncertainty of our measurements.
Growth of InGaAsP/InP single-quantum-well and multiple-quantum well structures by low-pressure metal-organic chemical vapor deposition
Authors: McCrary V. R. , Lee J. W. , Chu S. N. G. , Slusky S. E. G. , Brelvi M. A. , Livescu G. , Thomas P. M. , Ketelsen L. J. P. , Zilko J. L.
Published: July 2002

InGaAsP/InP single-quantum well and multiquantum-well (MQW) structures have been successfully grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). The quantum wells grown consist of 1.3- and 1.5-μm composition InGaAsP, with barriers of InP. Layer thicknesses vary from 18 to 1300 Å for the various structures grown. Analysis of these structures by low-temperature photoluminescence reveals distinct, sharp luminescent peaks, with half-widths from 4.8 to 13 meV. Cross-sectional transmission electron microscopy (XTEM) and Auger spectroscopy of the quantum-well structures reveals extremely sharp interfaces and homogeneous composition, demonstrating the feasibility of LP-MOCVD for the growth of very thin epitaxial layers. This preliminary data indicates that the growth of MQW structures for the next generation of laser diodes (i.e., MQW-distributed-feedback lasers), with monolayer interfacial abruptness, is possible by LP-MOCVD.
Ambipolar diffusion theory of the rectangular positive column with quadratic ionization
Authors: Ingold J. H.
Published: July 2002

The ambipolar diffusion theory of the rectangular positive column with ionization rate proportional to the square of the electron density is discussed. In agreement with previous theoretical work and with observation, it is predicted that the positive column fills the rectangular cross section up to an aspect ratio of 3, after which there is no further spreading. The reason for this behavior is discussed. In disagreement with previous work, it is predicted that little (∼20%) increase in the production of resonance radiation at the same efficiency can be obtained by increasing the aspect ratio when ionization is proportional to the square of electron density
Order parameter spatial variation and anchoring energy for nematic liquid crystals
Authors: Barbero G. , Durand G.
Published: July 2002

A spatial variation of the nematic scalar order parameter leads to a surface anchoring energy renormalization. This renormalization is a consequence of torque conservation and of the ‘‘macroscopic’’ definition of the surface orientation. The order change comes from an assumed property of the boundary or from an external curvature constraint inducing surface melting. In both cases, the maximum effect leads to a surface extrapolation length comparable with the nematic-isotropic coherence length. Strong anchoring data should be remeasured and reinterpretated.
Nb/Ni and Ni/Nb bilayers on Si: Rapid thermal processing, phase separation, and ternary phase formation
Authors: Horache E. , Fischer J. E. , Van der Spiegel J.
Published: July 2002

Ni/Nb and Nb/Ni bilayers on Si(100), Ni/NbSi2/Si(100) and Nb/Ni/Si/SiO2/Si(100) were produced by rf sputtering and annealed by rapid thermal processing. Thereafter, phase sequence and morphology were deduced by Auger electron spectroscopy and x-ray diffraction. The first three cases lead to phase separation of the binary compounds NbSi2 and NiSi2. Conversely when SiO2 is used as a buffer to limit the consumption of Si, the ternary phase Nb4Ni4Si7 or Nb4Ni4Si7+NbSi2 can be produced depending on the amount of Ni available. These observations are consistent with the Nb-Ni-Si phase diagram, in which phase separation occurs in a Si-rich environment whereas the ternary phase is stable in a Si-poor environment.
Electrical transport and related properties of zone-melt-recrystallized silicon-on-insulator films
Authors: Thompson L. R. , Collins G. J. , Stein H. J.
Published: July 2002

Electrical transport properties of zone-melt-recrystallized Si films of Si-on-Insulator wafers were investigated using resistivity and Hall effect measurements between 77 and 300 K. Both graphite strip and cold cathode electron beam methods were used for zone melting which produced high resistivity (≳103 Ω cm at room temperature) recrystallized films. Phosphorus implantation into the silicon films to a dopant level of 1×1016 cm−3 and subsequent annealing at 1100 °C reduced the room-temperature resistivities to ∼1 Ω cm. Hall mobilities of 950 cm2/V s were observed at room temperature for both materials after the implant anneal sequence. However, for temperatures less than 150 K, the mobility is higher in graphite strip than in electron beam recrystallized films. This behavior is consistent with the relative crystalline qualities of the two films as determined by electron channeling and x-ray diffraction. It is noteworthy that a deep level was observed at 0.2 eV below the conduction band in the graphite strip recrystallized film but not in the electron beam recrystallized samples.
Electrostatic charging of two insulating powders
Authors: Schein L. B. , LaHa M. , Marshall G.
Published: July 2002

The electrostatic charging characteristics of a mixture of two insulating powders with radii R and r such that R≫r are studied using a charge spectrometer which allows complete characterization of the charge and radius distribution function. The data are consistent with a natural extension of the surface-state theory which assumes, to first order, that the smaller radii powder particles share a fixed amount of charge determined by surface states on the larger radii particles. The challenges this result poses to microscopic theories of insulator contact charge exchange are discussed.
Studies of synchrotron radiation emission from the modified betatron accelerator
Authors: Smith T. J. , Golden J. , Kapetanakos C. A.
Published: July 2002

Numerical calculations of synchrotron radiation emitted from the modified betatron accelerator show that, for relativistic electron energies up to approximately 2 MeV, the single-particle intensity spectrum is characterized by a peak at the Doppler-shifted cyclotron frequency associated with the applied toroidal field. As the electron energy is increased above a few MeV, the calculated spectrum becomes comparable to that of an electron in purely circular motion. Measurements of the radiation using fixed-frequency heterodyne receivers indicate that the polarization, amplitude, and the temporal evolution of radiated power during the first few hundred microseconds of acceleration are in good agreement with the predicted single-particle spectrum. These observations have been used to confirm the energy evolution and provide information about the magnitude of the transverse velocity of the beam electrons. Late-time signal decay suggests that electrons are moving off the minor axis in a manner that is consistent with the excitation of the electron-cyclotron resonance.
Temperature dependence of magnetic field sensors using (Cd1−xMnx)Te and a light-emitting-diode light source
Authors: Mikami Noboru , Nagao Chie , Sawada Takao , Takahashi Hisamitsu , Furukawa Yoshinari , Aikawa Eiya
Published: July 2002

Verdet constants and optical transmissions of (Cd1−xMnx)Te solid solutions are determined as a function of Mn concentration, temperature, and wavelength. The sensitivity or modulation depth of magnetic field sensors using Faraday rotation in magneto-optical materials is analyzed using an effective Verdet constant. The effective Verdet constant is defined by a weighted average of normal Verdet constants. The average is over the spectral profile of the light source and is weighted by the intensity of transmitted light through the material and filter. The temperature dependence of the sensitivity in the sensors using (Cd,Mn)Te in various Mn concentrations and light-emitting-diode light sources is discussed.
The effects of a surface magnetic field on reactive ion etching
Authors: Han Haewook , Whang Ki-Woong
Published: July 2002

The effects of a surface magnetic field on reactive ion etching are described. The surface magnetic field is formed by the construction of a surface-multimagnetic mirror configuration (SURMAC) cage that consists of permanent magnets arranged inside the wall of a parallel plate rf discharge chamber. The experimental results of ion density, electron temperature, negative self-bias of an rf-generated N2 plasma, and etching of Si and SiO2 with a CF4 plasma are obtained with and without the SURMAC cage (rf power 40–520 W, gas pressure 20–100 mTorr). The results show that a surface magnetic field increases the etch rates of Si and SiO2 at high power (>250 W) and high pressure (100 mTorr), improves the Si to SiO2 selectivity at low power (<200 W) and decreases the magnitude of negative self-bias at all conditions.
Catalytic oxidation of silicon by cesium ion bombardment
Authors: Souzis A. E. , Huang H. , Carr W. E. , Seidl M.
Published: July 2002

Results for room-temperature oxidation of silicon using cesium ion bombardment and low oxygen exposure are presented. Bombardment with cesium ions is shown to allow oxidation at O2 pressures orders of magnitude smaller than with noble gas ion bombardment. Oxide layers of up to 30 Å in thickness are grown with beam energies ranging from 20–2000 eV, O2 pressures from 10−9 to 10−6 Torr, and total O2 exposures of 100 to 104 L. Results are shown to be consistent with models indicating that initial oxidation of silicon is via dissociative chemisorption of O2, and that the low work function of the cesium- and oxygen-coated silicon plays the primary role in promoting the oxidation process.
Charge collection in partially depleted GaAs test structures induced by alphas, heavy ions, and protons
Authors: El-Teleaty Shadia , Abdel-Kader W. G. , McNulty P. J. , Yaktieen M. H.
Published: July 2002

Charge-collection measurements on test structures were carried out for events induced by alphas, heavy ions, and proton-induced nuclear reactions over a variety of bias values and for two doping levels. Analysis of charge-collection pulse-height spectra provides the shape and dimensions of the sensitive volume associated with the single-event upset (SEU) sensitive junctions. The critical charge is determined by the circuit design. The critical charge and the dimensions of the sensitive volume are required by all the existing codes dealing with the calculation of SEU rates in natural space environments. The dimensions of the sensitive volume determined for some Rockwell GaAs test structures were used in simulations of charge collection by proton-induced nuclear reactions using the Clemson University Proton Interactions in Devices codes. Comparison of the results with experimental data yields agreement.
Donor bound-exciton structure observed by photoluminescence in very thin GaAs/In0.11Ga0.89As/GaAs single quantum wells
Authors: Kirby P. B. , Constable J. A. , Smith R. S.
Published: July 2002

Extremely narrow photoluminescence linewidths have been observed from 6-Å quantum wells of GaAs/In0.11Ga0.89As/GaAs. The quality of these spectra is such that structure involving higher-order donor-exciton transitions are observed.
High-quality GaAs layers on Si substrates grown by the hybrid method combining molecular-beam and liquid phase epitaxies
Authors: Yazawa Y. , Minemura T. , Unno T.
Published: July 2002

Using a hybrid growth combining molecular-beam epitaxy (MBE) and subsequent liquid phase epitaxy (LPE), a high-quality GaAs layer having high crystallinity and no pits due to Si dissolution by Ga melt has been obtained over the entire Si substrate (40×20 mm2 ). Si dissolution was found to be caused by a partial As desorption from the surface of MBE-grown GaAs/Si during the preheating for LPE. It could be eliminated by keeping the LPE growth temperature (TL) below 750 °C. This had to be balanced with crystallinity which improved at higher TL temperatures. An optimum TL range for the hybrid growth was established around 750 °C. Furthermore, it was shown that high-crystallinity in MBE-grown GaAs/Si led to high quality in hybrid-grown GaAs/Si. Our results also indicate that further improvement in crystalline quality of GaAs/Si is possible by MBE-LPE hybrid growth.
Space-charge-limited currents in amorphous gallium sulfide thin films
Authors: Micocci G. , Tepore A. , Rella R. , Siciliano P.
Published: July 2002

The density N(E) of midgap states in vacuum-evaporated and thermally annealed amorphous GaS films has been deduced from space-charge-limited-current (SCLC) measurements. Specimens with an In/a-GaS/stainless-steel sandwich structure have been used to obtain current-voltage characteristics at room temperature. By using an analytical method the density N(E) over an energy range extending about 0.18 eV above the Fermi level at thermal equilibrium has been calculated. The conductivity data for variable-range hopping [log(σ)∝T−1/4] have also been studied, but the calculated values of N(E) are approximately one order of magnitude higher than those obtained by SCLC measurements.
Critical current density and microstructure of YBa2Cu4O8
Authors: Miyatake Takayuki , Yamaguchi Koji , Wada Takahiro , Suzuki Noburo , Willis J. O. , Yamauchi H. , Koshizuka Naoki , Tanaka Shoji
Published: July 2002

We investigated the intragranular critical current density Jc in YBa2Cu4O8 prepared by two routes with different oxygen pressures at various temperatures and applied fields. A relationship between the Jc’s and the microstructures observed by transmission electron microscopy is discussed. The magnitude of Jc for the low oxygen processed sample is higher by a factor of 5 than that for the high oxygen pressure sample. Transmission electron microscopy reveals that the sample prepared at high oxygen pressure shows an almost perfect stacking sequence, but the low oxygen pressure prepared one has a severely distorted structure. We conclude that the difference in Jc(H) for the samples must be related to the different microstructures. Jc at a fixed magnetic field shows an exponential temperature dependence similar to that seen in other high-Tc superconductors. The field dependence is Jc∝H−n with n between 0.5 and 1.5, and with the n value becoming larger at higher temperatures. This type of the behavior may arise from the two-dimensional character of YBa2Cu4O8.
Theoretical study of a high energy pulsed H2/SF6 nonchain first vibrational overtone HF chemical laser
Authors: Ashidate Shu-ich , Toshiaki Takashima , Kannari Fumihiko , Obara Minoru
Published: July 2002

A novel computer model of a pulsed H2/SF6 nonchain first vibrational overtone HF chemical laser has been constructed to investigate the competition between the overtone and fundamental laser performances. This model including the rotational relaxation process, can simultaneously simulate both fundamental and overtone lasing processes since undesirable fundamental lasing cannot completely be suppressed during experimental overtone oscillation. The relationship between resonator conditions and laser gains was studied. A He diluent gas up to 400 Torr is added to the basic gas mixture H2/SF6=12.5/87.5 (Torr) in order to suppress the fundamental small signal gain. Under this gas mixture the overtone output energy of 117 mJ/ℓ can be obtained, which is reduced to 63% compared with the one without diluent gas. The overtone output energy is found to be very sensitive to the residual reflectivity of the mirrors over the fundamental lasing band.
Physical properties of a heavy-ion-beam-excited supersonic jet gas target
Authors: Griegel Thomas , Drotleff Heinz W. , Hammer J. Wolfgang , Knee Heinrich , Petkau Knut
Published: July 2002

The profile, density, and temperature of a supersonic rare-gas jet was determined applying methods of nuclear physics and optical spectroscopy. The jet was produced in the windowless gas target facility RHINOCEROS and the heavy-ion particle beams were provided by the Stuttgart DYNAMITRON accelerator. Maximum densities in the range of 1017 to some 1018 particles/cm3 could be achieved in a gas jet of about 2.6 mm diam (FWHM). In a supersonic helium jet a cooling of the gas down to 45 K was observed. These results were compared with theoretical calculations.
The magneto-optical Kerr effect of bilayer films Nd-Fe/Cu and Nd-Fe/Al
Authors: Zhou S. M. , Lu M. , Zhai H. R. , Miao Y. Z. , Tian P. B. , Wang H. , Xu Y. B. , Huang H. B.
Published: July 2002

Bilayers Nd-Fe/Cu and Nd-Fe/Al made by vacuum evaporation were studied. The magneto-optical Kerr effect (MOKE) and reflectivity spectra were measured. For Nd-Fe/Cu with low Nd content and small thickness of Nd-Fe layer there is a peak in the MOKE spectrum and a broad MOKE enhancement. The position is located near the plasma edge of Cu. When the content of Nd exceeds 37 at. %, there is no Kerr peak in the MOKE spectrum of Nd-Fe/Cu. When the thickness of the magnetic layer is larger but still less than the light penetration depth, the position of the peak moves towards the long-wavelength side. For Nd-Fe/Al there is a broad enhancement in the short-wavelength region, but no Kerr peak occurs no matter how the magnetic layer changes. The results presented show that the necessary conditions for MOKE enhancement in bilayers are suitable values of n and k of the reflector, whether the reflector has a plasma edge or not, and the enhancement also depends on the properties of the magnetic layer.