bluuebunny/crossref_metadata_2025 huggingface dataset:
Deposition and physical characterization of thin films of lithium niobate on silicon substrates
Authors: Baumann Robert C. , Rost Timothy A. , Rabson Thomas A.
Published: July 2002

Thin films (0.1–0.6 μm) of LiNbO3 have been deposited on silicon substrates by reactive rf sputtering. Under optimized deposition conditions the resulting thin films of LiNbO3 were optically transparent and adhered well to the silicon substrates. X-ray diffraction showed the films were oriented polycrystalline with the c axis normal to the silicon surface. Rutherford backscattering and Auger electron spectroscopy were used to evaluate the physical properties of these films. Potential applications of this technology include nonvolatile electronic and optical memories, and optical detectors.
Diffusion of Zn into GaAs and AlGaAs from isothermal liquid-phase epitaxy solutions
Authors: Algora C. , Araújo G. L. , Martí A.
Published: July 2002

In this work we present results of zinc diffusion in GaAs using the liquid phase epitaxy technique from liquid solutions of Ga-As-Zn and Ga-As-Al-Zn. Using silicon-doped n-GaAs substrates, working at a diffusion temperature of 850 °C, and introducing a dopant concentration ranging 1018–1019 cm−3, the most important findings regarding the diffusion properties are as follows: (a) zinc concentration in the solid depends on the square root of zinc atomic fraction in the liquid; (b) the diffusion is dominated by the interstitial-substitutional process; (c) the diffusivity D varies as about C3 in the form D=2.9×10−67C3.05; (d) aluminum plays the role of the catalyst of the diffusion process, if it is introduced in the liquid solution, since it is found that D varies as (γAsXlAs)−1; (e) the zinc interstitial is mainly doubly ionized (Zn++i); (f) the zinc diffusion coefficient in Al0.85 Ga0.15 As is about four times greater than in GaAs; (g) by means of all these results, it is possible to control zinc diffusion processes in order to obtain optimized depth junctions and doping levels in semiconductor device fabrication.
A helium discharge with neutral gas flow: Theoretical calculations
Authors: Karditsas Panayiotis J.
Published: July 2002

This study carries out numerical calculations using the ‘‘theory for rf ionization of noble gases with turbulent flow based on a two-electron group model,’’ which was developed in order to investigate the problem of ionizing a high speed neutral gas by the application of an external rf electric field. The plasma model is described by the electron energy and the particle balance equations and accounts for the high-speed neutral gas flow through the turbulent diffusion coefficient and the convection loss term. The calculated results based on the two-electron group model demonstrate that the I-V curves are affected by the magnitude of the turbulent diffusion coefficient, the high-speed flow affects the discharge parameters through the turbulent diffusion coefficient and through the convection loss term, and as the electron density is increased the electron-electron interactions became more intense and the distribution function approaches a Maxwellian at a single electron temperature. The numerical evaluation of the energy exchange terms between the two groups of electrons show that the bulk electrons attain their temperature primarily by the balance between the energy gain due to the electric field and the energy loss due to the elastic collisions with the neutrals and ions, and the tail electrons gain energy primarily by the electron-electron collisions and by the bulk to tail conversion due to the applied electric field, and loose energy primarily by the excitation from the ground level and by the tail to bulk electron conversion due to elastic collisions. The results of calculations for two particular cases indicate that for pressure in the range of 400–510 Torr, temperature in the range 480–511 K, velocity in the range 449–485 m/s, ionizer tube diameter of 0.022 m, one can attain electron densities in the range 1017–1018 m−3 with the application of moderate rf electric fields in the range of 200–400 V/cm.
Characteristics of erbium implants in silicon-on-insulator
Authors: Tang Y. S. , Sealy B. J.
Published: July 2002

The characteristics of erbium implants in a silicon-on-insulator structure were studied by photoluminescence and electrical activation measurements. The results indicate that a correlation exists between the luminescence energy or the lattice configuration and the electrical activation of the erbium in the implanted materials. Meanwhile, this work suggests a new way to enhance the luminescence efficiency of the erbium implanted materials.
Multikilowatt Pockels cell for high average power laser systems
Authors: Weaver L. F. , Petty C. S. , Eimerl D.
Published: July 2002

We describe in detail the design and performance of a multikilowatt Pockels cell for use in high average power laser systems. The Pockels cell is a gas-cooled, transversely excited electro-optic switch based on KD*P as the electro-optic material. Matched pairs of crystals with different crystallographic orientations are used to make the switch performance insensitive to the operating point and ambient temperature. Excellent switching performance and low-wave-front distortion have been achieved at average power levels in excess of 1 kW.
Electron-stimulated desorption of fluorine from barium fluoride films deposited on silicon substrates
Authors: Sharma J. K. N. , Chakraborty B. R. , Shivaprasad S. M.
Published: July 2002

The desorption of fluorine from barium fluoride thin films deposited on silicon substrate has been observed due to the incidence of electron beam during Auger electron spectroscopic (AES) studies. Slow electron energy loss spectroscopy (SEELS) has been employed to observe changes in core levels and color center formation. The desorption cross section for fluorine and the critical electron beam dose necessary to initiate electron-stimulated desorption have been estimated. The results are envisaged to provide information to investigators performing AES on such materials to choose parameters so as to eliminate or reduce beam damages. Since the desorption of fluorine results in metalliclike barium on the surface, it can also be a technique to deposit clean Ba layers on cathode materials to achieve work-function reduction.
High-frequency response of p-substrate buried crescent InGaAsP lasers
Authors: Weber A. G. , Ronghan Wu , Bimberg D.
Published: July 2002

The relaxation oscillation frequency of p-substrate buried crescent InGaAsP lasers is measured as a function of the output power in the switched-on state. The lasers are excited by a steplike current pulse at room temperature. The highest resonance frequency observed for a 350-μm long cavity is 12.1 GHz equivalent to an intrinsic 3-dB cutoff frequency of 18.8 GHz at an optical power of 9 mW/facet according to an injection current of 3.8 times threshold current, this is so far the best ever published value for a p-substrate laser.
The effect of charge state on the local vibrational mode absorption of the carbon acceptor in semi-insulating GaAs
Authors: Fischer D. W. , Manasreh M. O.
Published: July 2002

We use infrared absorption spectroscopy to study both the electronic excitation and the local vibrational mode (LVM) of the carbon acceptor in semi-insulating GaAs as a function of EL2 photoquenching. The behavior of the far-infrared electronic lines shows that the normally compensated carbon becomes neutralized (i.e., changes its charge state from singly negative to neutral) when the EL2 absorption is photoquenched. At the same time, the LVM absorption band shows no change in spectral form or vibrational frequency of its fine structure after photoquenching which indicates that, contrary to expectations, a charge-state change has no measurable effect on this band.
The nonlinear description of a plasma maser
Authors: Murukesapillai K. , Hamza A. M.
Published: July 2002

A plasma–microwave system was proposed by one of the authors for the production of microwave radiation. The device exploits the electromagnetic instabilities of nonequilibrium plasmas. During single-mode operation of the plasma maser, the resonant particles become trapped and cease to radiate before a substantial fraction of the energy available could be extracted from the plasma in the form of radiation. (This is not true for multimode operation. During multimode operation, the total energy available is distributed over a large number of resonant lines and the amplitudes of the various frequency components of the waves are not at all large enough to cause particle trapping and subsequently saturation. Thus, the linear theory remains valid until the anisotropy disappears due to radiation.) One should, therefore, consider the interaction of the bulk plasma with the nonresonant monochromatic electromagnetic wave in order to estimate the total energy transferred from the plasma to the wave. In the framework of the linear treatment, due to the resonant nature of the instability considered in previous work by one of the authors, the transfer of energy from the nonresonant plasma to the wave is zero. Consequently, the efficiency of the device during single-mode operation can only be evaluated after considering the nonlinear evolution of the plasma–microwave system. In this paper we describe in some details the nonlinear evolution of the plasma–wave system using a single particle analysis. The current density J is calculated using the second moment of the particle distribution function (evaluated using Liouville’s theorem of conservation of phase space density along particle orbits), and the energy balance equation is solved numerically.
Anomalous ion channeling in InGaAs/GaAs strained heterojunction
Authors: Wu Chunwu , Yin Shiduan , Zhang Jingping , Xiao Guangming , Liu Jiarui , Zhu Peiran
Published: July 2002

An ion beam with different incident energies E was used to analyze a 500-Å-thick In0.25Ga0.75As strained epitaxial film grown on GaAs (100) by molecular beam epitaxy. Ion channeling angular scans about 〈110〉 axis were carried out in (100) plane. When E is 5.8 MeV, the angular misalignment between 〈110〉 channels of the top layer and the substrate was 0.90°. We can calculate the planar strain of the epilayer, which is 1.62%. When incident ion energy was decreased, anomalous phemomena were observed in the angular scan profiles of the substrate. When E is 3.0 MeV, a serious asymmetry appeared in axial scan profile of the substrate; When E is 1.2 MeV, the angular misalignment reduced to 0.60°, and the critical angle for channeling of the substrate is 1.25° which is much larger than that of the epilayer, 0.95°. The physical mechanism giving rise to these phenomena is discussed, and the causes and conditions for these phenomena taking place were pointed out.
Single and multiple AlGaAs quantum-well structures grown by liquid-phase epitaxy
Authors: Chen Jiahn-Ann , Wang Chin-Kun , Lin Hao-Hsiung , Wang Way-Seen , Lee Si-Chen
Published: July 2002

The Al0.05Ga0.95As/Al0.35Ga0.65As single- and multiple-quantum-well structures with well widths less than 20 Å have been successfully fabricated by liquid-phase epitaxy using low-temperature, two-phase, and dummy wafer methods. The transmission electron microscope cross-section technique is applied to study the thickness variation of quantum well and the transition width at the heterojunction interface. An interesting phenomenon observed during liquid-phase epitaxy growth is that the interface of Al0.05Ga0.95As grown on Al0.35Ga0.65As is rather flat and sharp whereas the opposite growth sequence gives rise to a wavy interface. It is believed that the flat Al0.05Ga0.95As/Al0.35Ga0.65As interface is due to a tendency to deposit the epilayer when the Al0.05Ga0.95As solution is in contact with the Al0.35Ga0.65As substrate and the wavy Al0.35Ga0.65As/ Al0.05Ga0.95As interface is due to a tendency to dissolve the substrate when the Al0.35Ga0.65As solution is in contact with the Al0.05Ga0.95As substrate. The transition width is less than 10 Å at the Al0.05Ga0.95As/Al0.35Ga0.65As interface but is about 30–50 Å at the inverted Al0.35Ga0.65As/ Al0.06Ga0.95As interface. These values are about the same as those reported in the recent literature. The peak energy of the photoluminescence spectrum reveals the quantum size effect.
A thermionic energy converter with an electrolytically etched tungsten emitter
Authors: Gubbels G. H. M. , Metselaar R.
Published: July 2002

The bare work functions of etched and unetched plasma-sprayed tungsten were found to be 4.8 and 4.5 eV, respectively. The electron emission of plasma-sprayed tungsten, both etched and unetched, was measured over a wide range of temperatures in a cesium atmosphere. Work functions were derived from the saturation current densities. In the ignited mode, current-voltage (I-V) characteristics were measured. The influence of the emitter, collector, and cesium reservoir temperatures on the I-V characteristics was investigated. Barrier indexes of 2.06 and 2.30 eV were found for etched and unetched tungsten emitters, respectively. At an emitter temperature of 1400 °C, in the case of an unetched tungsten emitter a power density of 1.5 W/cm2 was found, while for an etched tungsten emitter it was 4.5 W/cm2. This increased power density could be attributed to a lower collector work function. The lower cesiated collector work function resulted from the evaporation of oxygen, as WO3, from the etched tungsten emitter.
Two semiempirical expressions for condensed-phase heat capacities
Authors: Tsao J. Y.
Published: July 2002

We propose two semiempirical expressions for representing condensed-phase heat capacities over a wide temperature range. Both can be integrated analytically to give closed-form expressions for entropies and enthalpies. As examples, we use the expressions to represent the molar heat capacities, entropies, and enthalpies of 〈Si〉 and 〈Al〉.
Electrical and optical properties of defect states induced by air plasma process in n/n+ epitaxial silicon
Authors: Wang F. P. , Xu J. G. , Sun H. H.
Published: July 2002

The electrical and optical properties of radio frequency (rf) air plasma process-induced defect states in 50 Ω cm n/n+ epitaxial silicon are investigated by junction capacitance techniques. Capacitance-voltage measurements reveal the presence of a thin oxide layer of about 180 Å on the 30-min plasma treated silicon sample. Deep level transient spectroscopy shows the existence of various defects in the sample. These consists of a dominant bulk electron trap labelled as E(0.46) at 0.46 eV below the conduction band, as well as continuously distributed interface states. The spectral dependence of the optical cross section for the defect levels were measured by deep level optical spectroscopy. A simple analysis indicates that a phonon mode (ℏωp=28 meV) couples to the defect E(0.46). Its electron-phonon coupling strength is rather weak with a Franck–Condon shift of 0.04 eV. Defect E(0.46) anneals out at a fairly low temperature of about 120 °C. Etching off the oxide layer in a diluted HF solution was found to eliminate the E(0.46) defect level. This is tentatively explained as due to passivation of the defect E(0.46) by hydrogen from the HF solution.
Measurement of the intrinsic bond strength of brittle thin films on flexible substrates
Authors: Guo Q. , Osaki H. , Keer L. M. , Wheeler D. R.
Published: July 2002

The brittle cracking and subsequent debonding of nickel films deposited on polymer substrates subjected to uniaxial strain is investigated. Stress analyses for a film/substrate system are performed. Based on the analysis, the interfacial bond strength between brittle thin films and flexible substrates can be evaluated in terms of the tensile strength of the coating and the length of the largest segment that first debonds. Experiments were performed on Ni films with different thicknesses evaporated on polyethylene terephthalate substrates and the intrinsic bond strength was evaluated. The interfacial bond strengths were shown to be relatively independent of the film thickness for the range studied.
The C̆erenkov free-electron laser for the relativistic electron beam with a slow rotating equilibrium
Authors: Kim Sun-Kook , Choi Duk-In , Choi Jeong-Sik
Published: July 2002

In a dielectric-loaded waveguide a slow rotating equilibrium of a relativistic electron beam which interacts with the electromagnetic waves is investigated in a self-consistent way. General dispersion relations for the fundamental transverse magnetic modes in the presence of the external magnetic field are derived using the cold fluid Maxwell equations and the appropriate boundary conditions. For slow space charge and slow cyclotron modes an algebraic equation is obtained from the dispersion relation by using a tenuous beam approximation. Solutions of the resulting equation are obtained for variations of several parameters, such as the external magnetic field, the dielectric constant, the thickness of the dielectric material, and the gap between beam and dielectric materials. With the beam-dielectric gap satisfying the stability condition, the growth rate of the space charge and the slow cyclotron instabilities show the same behavior as previous results for the no gap case [IEEE Trans. Plasma Sci. PS-17 576 (1989)]. Finally, emphasis in the analysis is given to the effect of the finite gap between the beam and dielectric and the comparison to the previous study of a no-gap case. From this analysis it is also shown that as the gap width increases, the growth rate, ωic decreases due to the finite geometric effect related to the gap width.
Reproducible leaky tube diffusion of Cd in InP at 500 °C
Authors: Wheeler C. B. , Roedel R. J. , Nelson Randall W. , Schauer Stephan N. , Williams Peter
Published: July 2002

We report for the first time the successful application of the leaky tube method to diffuse elemental Cd into InP at 500 °C. Specular surfaces are consistently realized while additional phosphorus in the ambient is not required. Free-carrier concentration profiles and junction depths were experimentally determined for times ranging from 20 min to 21/2 h. A reproducible surface concentration of ionized acceptors is ∼1×1018 cm−3 (T=300 K). A concentration dependent diffusion coefficient ranging from approximately 1×10−14 to 1×10−10 cm2/s is calculated for the conditions under investigation. Secondary ion mass spectroscopy analysis shows the atomic Cd concentration to be very similar to that of the ionized acceptors, with the atomic surface concentration approximately two times greater than the surface hole concentration.
Single-mode operation of a hybrid optically pumped D2O pulsed far-infrared laser
Authors: Yuan D. C. , Siegrist M. R.
Published: July 2002

We have achieved single-mode operation in a pulsed hybrid optically pumped D2O far-infrared laser. The active volume of the resonator was divided into two sections separated by a thin plastic foil. The larger section served as the main gain medium and the shorter section as the mode selective element. The vapor pressure in the smaller volume was either very low or alternatively about three times higher than the pressure in the main part. In both cases single-mode operation was achieved without any reduction of the total output energy.
Efficient time integration of a viscoplastic model for shock waves
Authors: Rubin M. B.
Published: July 2002

An unconditionally stable numerical procedure is developed to integrate the stiff differential equation associated with the flow rule for viscoplasticity used by Swegle and Grady [J. Appl. Phys. 58, 692 (1985)] to predict shock structure. Following the work of Rubin [J. Appl. Math. Phys. ZAMP 40, 846 (1989)] the flow rule is integrated implicitly and is converted into a scalar equation. It is shown that for the Swegle–Grady model this scalar equation reduces to a quadratic equation that can be solved without iteration.
Characterization of thin CdS films grown by the gradient recrystallization and growth technique
Authors: Hernández J. L. Rivera , Gracia-Jiménez J. M. , González R. Silva , Montes G. Martínez
Published: July 2002

For the first time the growth of polycrystalline CdS films by the gradient recrystallization and growth technique on silicon, quartz, and glass substrates is reported. X-ray diffraction, photoluminescence, scanning electron microscopy, and microprobe studies were used for their characterization. This preliminary study shows that this technique is suitable for growing CdS films with larger grain sizes than those obtained by conventional evaporation methods. The photoluminescence studies show that the emission spectrum of the films deposited on silicon is comparable to single-crystal CdS.
Ferromagnetic resonance studies on Ho0.85Tb0.15Fe2Hx and Dy0.73Tb0.27Fe2Hx systems
Authors: Annapoorni S. , Markandeyulu G. , Rao K. V. S. Rama
Published: July 2002

The ferromagnetic resonance studies were carried out at room temperature on fine powders of Ho0.85Tb0.15Fe2Hx (x=0–3.1) and Dy0.73Tb0.27Fe2Hx (x=0–3.3) at X and Q bands. The g values were found to decrease with increasing hydrogen concentration in both the systems. This data along with the earlier magnetization and Mössbauer data have been used to explain the observance of Tcomp in the hydrogenated samples of Ho0.85Tb0.15Fe2.
Abrupt Mg doping in thin graded base GaAs/GaAlAs heterojunction bipolar transistors
Authors: Tews H. , Neumann R. , Humer-Hager T. , Treichler R.
Published: July 2002

Abrupt Mg doping profiles have been realized in npn GaAs/GaAlAs heterojunction bipolar transistor (HBT) structures with compositional grading in the base region. The layers were grown by metalorganic vapor-phase epitaxy (MOVPE). Acceptor concentrations in the base are 1×1019 cm−3. Mg is also incorporated in the emitter and cap layers due to the Mg memory effect, and in the collector layer due to dopant diffusion. The incorporation of Mg is found to depend on the Si-donor concentration in these layers. Annealing experiments at 840 °C show only little broadening of the Mg doping profile. High-temperature process steps will consequently not change the Mg concentration significantly. We will demonstrate that neither the Mg memory effect nor Mg dopant diffusion limits the use of Mg for MOVPE-grown HBT layer sequences.
An optimized prismatic cover design for concentrator and nonconcentrator solar cells
Authors: Zhao J. , Wang A. , Green M. A.
Published: July 2002

Recently, the performance of both solar cells and photovoltaic systems have been considerably improved by the use of a prismatic cover applied to cell surfaces. This cover steers light away from the metal contact fingers on the top surface of the cell that would normally obscure the cell surface. Although the experimental advantages of this approach are now well documented, there is no published analytical treatment of these covers. This paper investigates their design for both concentrating and nonconcentrating application and clarifies the potential and limitations of the approach.
Laser-produced reduction of pentavalent vanadium in aqueous solutions and V2O5 powder
Authors: Khawaja E. E. , Khan M. A. , Al-Adel F. F. , Hussain Z.
Published: July 2002

The reduction of pentavalent vanadium ions in aqueous solutions upon laser irradiation has been confirmed by using optical absorption and fluorescence techniques. X-ray photoelectron spectroscopy (XPS) study revealed that V2O5 was reduced to lower oxides upon laser treatment. Furthermore, the presence of reduced valence states of vanadium has been detected through XPS in vanadium-containing solids such as V2O5/P2O5 glass, thin films prepared separately from V2O5 powder and the glass.
Properties of amorphous hydrogenated carbon films from ArF laser-induced C2H2 photolysis
Authors: Dischler B. , Bayer E.
Published: July 2002

Amorphous hydrogenated carbon films (a-C:H) have been deposited using 193-nm ArF laser-induced photolysis. The source gas was C2H2 (5%), diluted in argon (95%). The substrate temperature was varied between 150 and 350 °C in steps of 50 °C. Infrared spectroscopic analysis yields results on hydrogen content and sp3/sp2 carbon bond ratio. For the H/C atomic ratio values near 1.0 and for the sp3/sp2 bond ratio values near 10 are obtained. The corresponding values for plasma-deposited a-C:H films from C2H2 are distinctly lower. Electrical resistivity, refractive index, optical gap, and microhardness have also been determined.
Optical characterization of Cd1−xMnxTe epilayers grown by liquid-phase epitaxy
Authors: Lee Y. R. , Alonso R. G. , Suh E.-K. , Ramdas A. K. , Li L.-X. , Furdyna J. K.
Published: July 2002

Epilayers of Cd1−xMnxTe grown on CdTe substrates by liquid-phase epitaxy (LPE) are characterized by x-ray, modulated (piezo- or photo-) reflectivity, and Raman spectroscopy. The epilayers are found to be of excellent structural quality, having sharp excitonic signatures in the reflectivity spectra and highly uniform Mn concentrations. Intentional introduction of In donors during LPE growth of Cd1−xMnxTe has been verified by spin-flip Raman signals which show large Raman shifts with a Brillouin function behavior characteristic of donors in diluted magnetic semiconductors. During the LPE growth we also encountered the formation of large-area, free-standing platelets of Cd1−xMnxTe. They have been similarly characterized with x-rays, as well as modulation and Raman spectroscopy.
A plasma etching-induced defect state in electron-irradiated n-type bulk section
Authors: Wang F. P. , Sun H. H.
Published: July 2002

Defect states induced by radio frequency air plasma etching process in n-type bulk silicon have been studied. Deep level transient spectroscopy shows that a deep center with a small electron capture cross section σtn =1.3×10−20 cm−3 and an energy level at 0.41 eV below the conduction band was induced by plasma treatment of previously electron-irradiated Si samples. The spectral dependence of optical cross sections for this defect level was measured by deep level optical spectroscopy, showing that the defect has a strong electron-phonon coupling with a Franck–Condon shift of about 0.4 eV, and that the defect core is repulsive for electrons. The defect anneals out above 400 K, and is also slightly unstable at room temperature.
Parameter studies for a coaxial saturable inductor magnetic switch
Authors: Power A. J. , Choi P. , Dolan J. E.
Published: July 2002

The physical properties of a coaxial saturable inductor magnetic switch have been examined as a stand-alone unit and as a component in a pulse forming circuit. A methodology for optimizing the performance of this type of switch for which voltage holdoff and saturated inductance are specified is presented. It is shown that the volume and hence cost of the switch can be reduced by 20% with an appropriate choice of switch dimensions. Additional cost reduction may be achieved by a considered choice of core material. It is also shown that, for a single-stage compression circuit with compression less than 10, further significant cost reduction can be achieved by designing the switch to close at a fraction of the theoretical maximum holdoff voltage and by choosing the switch saturated inductance appropriately.
Visible Y-junction diode laser with mixed coupling
Authors: van der Poel C. J. , Opschoor J. , Valster A. , Drenten R. R. , Andre J. P.
Published: July 2002

An experimental study and theoretical analysis of a phase-locked, visible, λ=670 nm, 2-3 Y-junction semiconductor laser array are presented. In a ridgetype 2-3 Y-junction, AlInGaP/InGaP array, both in-phase and anti-phase array modes are observed to lase simultaneously. The experimental results are discussed in the framework of a model based on the beam propagation method. The influence of the presence of both interferometric and evanescent coupling on the array modes is analyzed.
Transient decay of persistent photoconductivity in Al0.3Ga0.7As
Authors: Dobson T. W. , Scalvi L. V. A. , Wager J. F.
Published: July 2002

Transient decay of persistent photoconductivity (TDPPC) measurements were performed and analyzed in terms of models in which the TDPPC is associated with thermally activated electron capture into DX and a modification of the ionized impurity density, and hence the mobility, concomitant with electron capture. Quantitative agreement between theory and experiment was possible when Chadi and Chang’s model for DX [Phys. Rev. Lett. 61, 873 (1988); Phys. Rev. B 39, 10063 (1989)] was employed in conjunction with a photo-induced shallow donor.
Electrical resistivities of single-crystalline transition-metal disilicides
Authors: Hirano Toshiyuki , Kaise Masatsugu
Published: July 2002

Single crystals of the group IVa to VIII transition-metal disilicides, namely TiSi2, VSi2, CrSi2, MoSi2, αFeSi2, and CoSi2, have been successfully grown by a floating-zone method. Temperature and crystallographic dependencies of the resistivity have been measured in the temperature range from 4.2 K to room temperature. The resistivity of all the disilicides show a positive temperature dependence and some anisotropy. The thermal component of the resistivity changes systematically with the group number of the metal elements and correlates well with the d band density of states at the Fermi energy.
Optical activity of incommensurate state of [N(CH3)4]2CuCl4
Authors: Saito K. , Sugiya H. , Kobayashi J.
Published: July 2002

By applying the HAUP (high-accuracy universal polarimeter) method, [N(CH3)4]2CuCl4 was found to be optically active in its incommensurate phase, e.g., g23=3.9×10−5 at 24 °C. The temperature dependence of g23 was obtained. By making use of the fact that the commensurate phase of [N(CH3)4]2CuCl4 is ferroelastic and centrosymmetric, the temperature dependence of the soliton density in its incommensurate phase was deduced by this optical measurement. It is suggested that the HAUP method will become a new and direct method for measuring soliton densities of incommensurate states.
Transverse electric field scattering by a Kerr media deposited on a conducting planar surface
Authors: Peterson P. , Gavrielides A. , Sakurada E.
Published: July 2002

The scattering of a transverse electric plane wave incident from a linear media by a nonlinear Kerr film deposited on a good conductor is studied. Self-focusing and self-defocusing are included both above and below the critical angle. The solution to the complex second-order nonlinear differential wave equation is constrained at the nonlinear/conductor planar interface by mixed boundary conditions and at the linear/nonlinear interface by the continuity of the tangential electric and magnetic fields. A potential-well approach is employed to classify and isolate the various solutions. Several examples illustrate the two nonlinear analogies of the evanescent and harmonic field solutions. Additionally, we obtain the surface-wave solutions and the transitional, hybrid, fields. Finally, we show that the reflectivity is multistable with respect to the incident intensity and that the reflected intensity is multistable as the incident angle changes for a constant input intensity.
Penetration and equilibration of injected electrons into a high-current hydrogen pseudospark-type plasma
Authors: Bauer H. R. , Gundersen M. A.
Published: July 2002

The penetration and equilibration of the velocity distribution function of an initially monoenergetic electron beam with energies of 50, 100, and 500 eV which is injected into a Maxwellian ‘‘bulk’’ hydrogen pseudospark or back-lighted thyratron plasma ( j≊104 A/cm2, Te≊1 eV, ne=1–3×1015 cm−3) is evaluated using a Fokker–Planck equation. The electron beam considered here is the part that is produced during the conductive phase by the electric field in the cathode fall. The beam is estimated to traverse the electrode gap without equilibration with the background plasma if the plasma density is ≤2.5×1015 cm−3.
Micromagnetic calculations of 180° surface domain-wall magnetization profiles with comparison to measurements
Authors: Blue James L. , Scheinfein M. R.
Published: July 2002

We compare measurements of magnetization profiles across 180° surface domain walls in a permalloy ferromagnet with calculations from micromagnetic models. The models were solved both by relaxation and by a time-evolution calculation. The measurements were made using scanning electron microscopy with polarization analysis. We obtain good agreement without postulating any surface anisotropy effect. This is the first successful comparison between experiment and a time-evolution calculation of domain walls.
Influence of water vapor in the chemically excited oxygen flow generated from the reaction of Cl2 with alkaline H2O2
Authors: Tokuda T. , Fujii N. , Yoshida S. , Sawano T. , Shimizu K. , Tanaka I.
Published: July 2002

The estimation for the water vapor included in chemically generated excited oxygen flow and the influence of the water vapor on the excited oxygen species are presented. The concentration of the water vapor in the flow was changed by altering the temperatures of the solution and the cold trap and then, it was estimated by measuring the the pressure change and by measuring the concentration of the excited oxygen molecules. The fraction of O2(1Δ) to the total oxygen did not change with the water vapor pressure, but the concentration of O2(1Σ) changed significantly. Applying the high sensitivity of O2(1Σ) concentration to H2O, the estimation of a small quantity of water vapor concentration was available in the system.
Analysis of orientation distribution in YBa2Cu3O7−x polycrystals by electron channeling patterns
Authors: Kang W. J. , Yoshimi K. , Hanada S. , Saito S. , Murayama Y. , Hayashi S. , Nagata A.
Published: July 2002

A unit standard map for YBa2Cu3O7−x superconductors was constructed and indexed from a series of electron channeling patterns (ECPs). (001) pole figures of YBa2Cu3O7−x tapes and bulk specimens with various values of critical current density (Jc) were drawn by using the map covering [001-1̄1̄0-1̄10] stereographic quadrant and ECPs taken from individual grains of the specimens. It was found that preferred orientation of (001) formed in the tape with a decreasing thickness of the tape, which raised Jc significantly. It is concluded that the ECP technique is very useful for the analysis of orientation distribution in small-sized YBa2Cu3O7−x specimens such as tapes or thin films.
Boundary-condition refinement of the Child–Langmuir law for collisionless dc plasma sheaths
Authors: Farouki Rida T. , Dalvie Manoj , Pavarino Luca F.
Published: July 2002

An exact solution to the problem of collisionless, space-charge-limited flow of cold ions across a one-dimensional (planar) dc plasma sheath of negligible electron density is derived for general values of the presheath ion velocity v0 and electric field E0. For a given ion current density J and sheath thickness d, the exact solution reduces to the classical Child–Langmuir model in the case that v0=0 and E0=0. When either v0 or E0 is sufficiently large, however, the exact solution may differ appreciably from the Child–Langmuir law. The existence of a closed-form expression for the spatial variation of the sheath potential is shown to be contingent upon the satisfaction of a simple inequality relating v0 and E0 to J. When v0 obeys the Bohm criterion and the magnitude of E0 suggests that the Bohm energy is acquired over a distance not less than one Debye length, this inequality is indeed satisfied.
Optically detected magnetic resonance of cubic SiC grown by chemical vapor deposition on Si
Authors: Kennedy T. A. , Freitas J. A. , Bishop S. G.
Published: July 2002

Two distinct spectra are reported from an optically detected magnetic resonance study of epitaxial films of cubic SiC. The first is a Lorentzian, single line with g=2.0065±0.0015, which is strong in Al-doped SiC. This line is attributed to residual donors. The second spectrum, observed in both Al-doped and undoped samples, is dominated by a pair of exchange-split lines with g=2.0024 and a=0.095 cm−1. Although a definite assignment of this spectrum cannot be made, spectral dependence studies show it is associated with a defect-related luminescence band in the energy range from 1.6 to 1.9 eV.
Nondestructive characterization of silicon-on-insulator structures using infrared spectroscopic ellipsometry
Authors: Ferrieu F. , Dutartre D.
Published: July 2002

Nondestructive characterization of a large variety of silicon-on-insulator structures has been performed by infrared spectroscopic ellipsometry (IRSE). This technique is shown to be applicable over very wide ranges of Si and SiO2 thicknesses and thus is more adapted than visible reflectometry or spectroscopic ellipsometry when relatively thick films are analyzed. In addition, IRSE provides information on any possible interface roughness and thickness homogeneity of the layers.
Electrical properties of grain boundaries in Ba1−xKxBiO3 polycrystalline thin films
Authors: Enomoto Youichi , Moriwaki Kazuyuki , Tanabe Keiichi
Published: July 2002

Ba1−xKxBiO3 polycrystalline thin films are prepared on sapphire substrates by evaporation. In these films, grain boundaries affect the film resistivity in the normal state and I-V characteristics in the superconducting state. The temperature dependence of the resistivity is metallic for low-resistivity samples. On the other hand, that for high-resistivity is semiconductive and a bend is observed near 100 K. The I-V characteristics show series-connected tunneling Josephson junctions formed along a grain boundary. The ratio between the superconducting energy gap and Tc is estimated to be 3.5, equal to that of BaPb1−xBixO3. Using the resistively shunted junction model and Ambegaokar and Baratoff’s theory [Phys. Rev. Lett. 10, 486 (1963)], the tunneling resistance in a superconducting state is derived from the Josephson critical current densities and the hysteresis of the I-V curves. It increases with decreasing temperature at low temperatures and changes the junctions from weak link to tunneling.
Fabrication of low-loss zinc-selenide coated silver hollow waveguides for CO2 laser light
Authors: Matsuura Yuji , Miyagi Mitsunobu , Hongo Akihito
Published: July 2002

ZnSe coated Ag hollow waveguides transmitting CO2 laser light were developed. An inner ZnSe coating of good quality was obtained with high rf power and high translating speed in deposition by rf sputtering. The inner ZnSe layer was found to be amorphous by x-ray diffraction analysis; A layer structure (ZnSe-Ag) was observed by Auger electron spectroscopy analysis. Transmission properties of the short waveguides with 25 cm length were evaluated by measurements of loss spectra in the mid-IR region. As a result, ZnSe coated Ag waveguides showed lower loss than the Ge coated one fabricated previously, and the loss for CO2 laser light was predicted to be 0.021 dB/m. Furthermore, it was found that a ZnSe coated Ag waveguide is durable in practical use.
Field-induced anisotropic distribution functions and semiconductor transport equations with tensor-form coefficients
Authors: Chen Datong , Kan Edwin C. , Hess Karl
Published: July 2002

We propose a phenomenological method to extend isotropic nonequilibrium distribution functions in semiconductors into field-induced anisotropic forms. We show that the distribution functions which we derive for the Γ valley of GaAs compare favorably to more precise Monte Carlo simulations. A complete set of transport coefficients for the mancroscopic current continuity and energy flux equations is also derived. These transport coefficients should be helpful to study the range of applicability of various hydrodynamic models in ultrasmall devices.
A novel test structure for grating pitch determination with near-Angstrom accuracy
Authors: Peckerar M. C. , Rhee K. W. , Ho P.-T. , Goldhar J.
Published: July 2002

This communication describes a novel double-grating test structure which enables grating pitch-difference determination with angstrom accuracy. Edge acuity can also be estimated. The test structure is easily fabricated and rapidly evaluated with inexpensive equipment generally found in microstructure laboratories.
Radiation-induced frequency offsets and acoustic loss in AT-cut quartz crystals
Authors: Martin J. J.
Published: July 2002

Ionizing radiation and sweeping modify the defects present in quartz. According to relaxation theory the modification should produce a fractional frequency offset, Δf/f, equal to the negative of the sum of the changes in strength of the acoustic loss peaks with peak temperatures below the turnover. We have measured the acoustic loss and frequency versus temperature curves as functions of radiation dose, and alkali and hydrogen sweeping for AT-cut cultured quartz crystals with widely varying aluminum concentrations. The largest offsets were observed for the Na-swept crystals and the smallest for the H-swept samples. In addition, the smallest radiation-induced offsets were found in swept crystals with the lowest Al content. The magnitude of Δf/f was different from that predicted by relaxation theory. Instead, the observed Δf/f at the turnover consisted of: (1) the expected relaxation component, (2) a Δf/f at low temperatures in all samples studied, and (3) a change in the overall f(T) curve which appears only in Na-swept crystals. The low T offset is caused by T-independent changes in the elastic modulus. These must be due to the modifications of the interatomic forces brought about by the radiation-induced defect changes. Our general findings support the use of swept low-aluminum quartz in radiation environments.
Electron beam defined delamination and ablation of carbon-diamond thin films on silicon
Authors: Amaratunga Gehan A. J. , Welland Mark E.
Published: July 2002

Defined delamination of thin carbon-diamond films on Si using a focused electron beam of 0.5 kW/cm2 power density is reported. The films were deposited form a CH4/Ar rf plasma and were less than 1 μm thick with residual compressive stress of 1.0–0.5 GPa. At higher electron beam power densities ablation and crystallization of the films are observed. Analysis of buckling patterns in spontaneously delaminated films give estimates of 128 J m2, 91 GPa and 0.5 for the intrinsic interface toughness, Young’s modulus and Poissons ratio of the films.
Transport critical current density and microstructure in extruded YBa2Cu3O7−x wires processed by zone melting
Authors: Shi Donglu , Krishnan H. , Hong J. M. , Miller D. , McGinn P. J. , Chen W. H. , Xu Ming , Chen J. G. , Fang M. M. , Welp U. , Lanagan M. T. , Goretta K. C. , Dusek J. T. , Picciolo J. J. , Balachandran U.
Published: July 2002

YBa2Cu3O7−x compounds were extruded into long wires with the diameter of 1 mm after sintering. The sintered wires were subsequently zone melted to develop a highly textured microstructure. Magnetization experiments at 77 K indicated a Jc value of 1×105 A/cm2 at 1 T. Transport measurements at 77 K showed a greatly enhanced field dependence of the critical current density. Transmission electron microscopy revealed an important grain-boundary feature which eliminated the weak-link behavior. Large amounts of dislocations have also been found in the zone-melted sample which may contribute to flux pinning in the system.
Magnetostatics of curling in a finite cylinder
Authors: Aharoni Amikam
Published: July 2002

The magnetostatic self energy is calculated for the magnetization curling mode in a finite cylinder, for the model proposed by Ishii and Sato [J. Appl. Phys. 65, 3146 (1989)]. It is shown that slight modifications of that model can eliminate all the cumbersome computations and allow all the integrations to be done analytically.
Characterization of GaAs/AlGaAs graded index-separate confinement heterostructure lasers by Raman scattering
Authors: Bradshaw J. , Shealy J. R.
Published: July 2002

We report the first use of Raman scattering to study GaAs/AlGaAs graded index-separate confinement heterostructure quantum-well lasers. We have used a forward scattering geometry in which the waveguide is endfired, and the light emerging from the opposite end facet is collected and spectrally analyzed. The probe is confined by the waveguide and thus interacts with the entire laser cavity. Because Raman scattering occurs in all regions of the heterostructure to which the optical mode is confined, this technique is a useful indication of the mode profile in waveguide heterostructures. We observe inhomogeneously broadened longitudinal and transverse optical phonons in the graded region.
Correlation between current-voltage and capacitance-voltage Schottky barrier height on (100) and (110) GaAs and (110) InP surfaces
Authors: Chin Vincent W. L. , Green Martin A. , Storey John W. V.
Published: July 2002

Recently, systematic studies of the electrical properties of both n- and p-type Schottky diodes formed by a large number of metals on GaAs of both (100) and (110) orientation and on (100)-oriented InP have been reported. Current-voltage (I-V) and capacitance-voltage (C-V) measurements were carried out and the barrier heights were evaluated in these studies. In this paper, these I-V zero-bias barrier heights have been correlated with the ideality factors of these diodes. Resulting from this modified barrier height approach is a more fundamental flat-band (zero-field) barrier which compares remarkably well with the reported values from the C-V measurements. In addition, the sum of the modified n- and p-type flat-band barrier heights for the GaAs (100) and InP (110) Schottky diodes is in better agreement with the band gap for each of the different metals used than the initially reported results.
Photochemical etching of n-InP as a function of temperature and illumination
Authors: Lowes Theodore D. , Cassidy Daniel T.
Published: July 2002

Photochemical (PC) etching of n-InP using an Ar+ laser and dilute phosphoric acid solutions was studied as a function of temperature, power, illumination frequency, and duty cycle. The etch rate was found to be independent of time and to increase fourfold by increasing temperature from 20 to 50 °C with an activation energy ≳0.34 eV. Thus the process is found to be reaction rate limited. The etch rate was observed to increase with power for low-power levels and then saturate near an irradiance of 200 W/cm2 at 20 °C. The photoetch rate, i.e., the etch rate divided by the fraction of time the Ar+ light is on, was affected by illumination duty cycle but not chopping frequency in the range 100–3200 Hz. These results are explained based on a rate equation model for material removal. Finally, a new application for PC etching is presented: sample preparation for transmission electron microscopy.
Isotope effects in amorphous silicon thin films produced by Ar-SiH4 -D2 plasma chemical vapor deposition method
Authors: Chen X. , Chang J. S. , Berezin A. A. , Ono S. , Teii S.
Published: July 2002

Ar-SiH4 -D2 gas mixture positive column plasmas and the deposition of (a-Si:D/H) thin films are investigated. Deuterated amorphous silicon thin films (a-Si:D/H) are produced in an Ar(95%)-SiH4(2.5%) -D2(2.5%) mixed gas plasma by employing dc positive column plasma chemical vapor deposition techniques. A twin probe electric field measurement is used to determine the plasma parameters. The reaction chamber wall temperature is measured by an infrared (IR) image camera. The results indicate that the uniformity of plasma is excellent; the wall temperature of the reaction chamber is nonuniform; and the deposition rate increases with increasing discharge power and gas pressure. The optical characteristics of isotopically different a-Si:H/a-Si:D films are also studied. The results show that the optical band gap of a film has a nonmonotonic thickness dependence with a significant isotope effect.
Effect of the pulse shape on self-phase-modulation-induced chirping of optical pulses in diode laser amplifiers
Authors: Dienes Andrew , Carr Lewis W.
Published: July 2002

Using the formalism of Agrawal and Olsson [Opt. Lett. 14, 500 (1989)] we calculate the output intensity and frequency chirp for different shape input pulses in semiconductor optical amplifiers. Gaussian pulses result in the least distortion and the most linear chirp, whereas a pulse with an extended leading edge is subjected to severe distortion and receives a chirp that is difficult to compensate. The applicability of this analysis to other laser amplifier systems is also discussed.