bluuebunny/crossref_metadata_2025 huggingface dataset:
High frequency magnetic field sensors based on the Faraday effect in garnet thick films
Authors: Wolfe R. , Gyorgy E. M. , Lieberman R. A. , Fratello V. J. , Licht S. J. , Deeter M. N. , Day G. W.
Published: July 2002

The Faraday effect in the thick epitaxial films of magnetic garnets of the type used in magneto-optic isolators can be used as the basis for a fiber-optic magnetic field sensor. These films have uniaxial anisotropy perpendicular to the surface and they contain bismuth to enhance the Faraday rotation. The typical magnetic domain pattern of meandering stripes changes in response to an applied field perpendicular to the film and this changes the polarization of infrared light propagating perpendicular to the film. Theory and experiment show that the speed of operation is limited by relaxation or resonance effects to upper frequencies between 106 and 109 Hz. Maximum sensitivity requires low magnetic moment and large thickness, in conflict with the requirements for high speed.
Superconducting and optical properties of ultrathin films of Bi2(Sr,Ca)3Cu2Ox formed at 673 K
Authors: Yanase Akihisa , Mori Masami , Liu Ziyuan , Kawai Maki
Published: July 2002

Electronic properties of ultrathin films of Bi2(Sr,Ca)3Cu2Ox, successively formed on MgO(100) at a substrate temperature of 673 K using atomic layering deposition of metals followed by oxidation with a 8×10−7 Torr NO2 are studied. It was revealed that the film formed at 673 K showed a semiconductive property, whereas the film annealed at 1093 K with 760 Torr O2 shows a superconducting transition with the onset Tc of 90 K and the zero-resistance Tc of 40 K. Optical absorption and x-ray diffraction studies indicate that the electronic structure of Bi2(Sr,Ca)3Cu2Ox ultrathin film changes from charge-transfer type semiconductor to a superconductor with an in-gap band, due to the increase in carrier concentration caused by annealing with O2.
Wavelength demultiplexing optical switch
Authors: Ünlü M. S. , Demirel A. L. , Strite S. , Taşiran S. , Salvador A. , Morkoç H.
Published: July 2002

A novel wavelength demultiplexing optical switch (WDMOS) with completely optical input/output capabilities is demonstrated. The WDMOS input elements can be applied to optical logic circuits in which discrete wavelengths are utilized as an added dimension to the intensity levels of the optical signals. The WDMOS can be viewed as a resonant cavity-enhanced heterojunction phototransistor vertically integrated with a quantum well light emitting diode. The resulting device is an N-p-n-p optical switch situated in an optical cavity which serves to combine the wavelength selective spectral response of the optical cavity with the bistable switching characteristics of the N-p-n-p structure.
Bend-induced even and odd modes in picosecond electrical transients propagated on a coplanar waveguide
Authors: Alexandrou Sotiris , Sobolewski Roman , Hsiang Thomas Y.
Published: July 2002

A picosecond time separation between the two sides of a single electrical transient propagated on a bent coplanar waveguide has been observed using a subpicosecond electro-optic sampling system. The separation corresponds to the geometrical path difference introduced by a 90° coplanar waveguide bend. Contrary to the straight waveguide where the transient propagates in the odd mode only, the bend forced the signal to emerge as a superposition of both the odd and even waveguide modes. Introduction of proper local grounding in the bend area, by wirebonding the ground lines on both sides of the transmission line, suppressed the unwanted even mode while preserving the standard odd-mode propagation.
Destruction of the quantum well structure of thin silicon-germanium superlattices by ion implantation
Authors: Freiman W. , Beserman R. , Dettmer K. , Kessler F. R.
Published: July 2002

Thin SimGen superlattices (SLs) have been implanted with dopant and neutral ions and annealed at low temperature (600 °C) during a short time (30 min). Intermixing between the two species takes place when the SL has been rendered amorphous. This effect is due to disorder only and no dopant impurity influence could be seen in contrast to the case of III–V SLs.
Demonstration of vacuum field emission from a self-assembling biomolecular microstructure composite
Authors: Kirkpatrick D. A. , Bergeron G. L. , Czarnaski M. A. , Hickman J. J. , Chow G. M. , Price R. , Ratna B. L. , Schoen P. E. , Stockton W. B. , Baral S. , Ting A. C. , Schnur J. M.
Published: July 2002

We report the first demonstration of vacuum field emission from an electron source fabricated from self-assembling biomolecular composite microstructures. Diacetylenic lipid DC8,9PC is used to form hollow, 0.5 μm diam, ≳50 μm long, tubelike structures that are subsequently plated with metal and formed into an aligned composite in an epoxy matrix. The composite material is thin-sectioned across the axis of alignment and then etched to expose the plated tubules. The sharp edges of the exposed metal tubules produce a very large local electric field enhancement, allowing for the vacuum field emission of significant current densities at relatively low applied macroscopic fields (≤60–80 kV/cm).
Observation of a super-periodic feature on gold with a scanning tunneling microscope
Authors: Wilkins M. J. , Davies M. C. , Jackson D. E. , Roberts C. J. , Tendler S. J. B. , Williams P. M.
Published: July 2002

In this letter we present the first reported images of a super-periodic hexagonal lattice observed on gold in air by scanning tunneling microscopy. The surface features presented extend over large areas (up to 1.0×105 nm2) with an average periodicity of 8 nm, and a corrugation of 1 nm. The impact of comparable results on highly oriented pyrolytic graphite suggests the need for some caution when using gold in biomolecular scanning tunneling microscopy studies.
Periodic filaments in reflective broad area semiconductor optical amplifiers
Authors: Tamburrini M. , Goldberg L. , Mehuys D.
Published: July 2002

Filaments with a regular spacing of the order of 25 μm are experimentally observed in double-pass broad area GaAlAs amplifiers for near normal injection angle. Their formation is attributed to nonlinear interaction between counterpropagating beams and Talbot self-imaging.
Schlieren visualization of acoustic phase conjugate waves generated by nonlinear electroacoustic interaction in LiNbO3
Authors: Ohno M. , Takagi K.
Published: July 2002

The acoustic phase conjugate wave was generated at 56 MHz by nonlinear electroacoustic interaction in LiNbO3 and its field was visualized with the schlieren technique. The field distribution of the phase conjugate wave was observed to be very close to that of the incident wave, and the time-reversal property of the phase conjugate waves was experimentally confirmed for the first time.
Reflection and refraction of ballistic electrons through different carrier concentration regions
Authors: Fukai Yoshino K. , Tarucha Seigo , Hirayama Yoshiro , Tokura Yasuhiro , Saku Tadashi
Published: July 2002

Transmission and reflection characteristics of ballistic electrons are studied in a macroscopic four-terminal square device with a strip Schottky gate placed so as to bisect the device. Since the gate is negatively biased, a bend resistance peak at zero magnetic field, which is induced by ballistic electron injection into an opposite voltage probe, varies from positive to negative, and a magnetic focusing peak shifts to a lower field. These phenomena arise from the reflection of ballistic electrons crossing regions of different electron densities. The transmission and reflection probabilities are determined as a function of gate voltage, and are related to the change in the refractive index of ballistic electrons.
Highly selective sputtering of silicon from TiSi2 at elevated temperature
Authors: Harper J. M. E. , Motakef S. , Moy D.
Published: July 2002

We demonstrate almost 100% selective sputtering of silicon from TiSi2 using a combination of low energy ion bombardment and elevated temperature. TiSi2 was prepared by annealing 1000-Å-thick Ti on (100)Si in He at 635 °C for 30 min to produce 2300-Å thick TiSi2. Ion beam etching was carried out using 300 eV argon with a flux of 0.27 mA/cm2 at temperatures from 33 to 700 °C. In situ sheet resistance measurements were used to monitor the decrease in silicide thickness as a function of time. Near room temperature, ion etching causes normal sputtering of the silicide. However, at temperatures of 500–700 °C, the sheet resistance remains almost unchanged during ion beam etching. Analysis by Rutherford backscattering, with and without Xe markers, shows that Si atoms sputtered from the surface of these high-temperature samples are continuously replaced by Si diffusing from beneath the silicide layer. The thickness and composition of the silicide remain almost unchanged, but the dramatic change in sputtering behavior shows that the surface is enriched in Si. Compared with the room-temperature values, the absolute sputtering yield of Ti at 500–700 °C is decreased by a factor of 5, and the yield of Si is increased by a factor of 2. The net result is almost 100% selective sputtering of silicon.
Buried heterostructure laser fabricated using reactive ion etching and gas source molecular beam epitaxy
Authors: Liévin J.-L. , Le Gouézigou L. , Bonnevie D. , Gaborit F. , Poingt F. , Brillouet F.
Published: July 2002

Buried heterostructure lasers fabricated using reactive ion etching for stripe definition and gas source molecular beam epitaxy for blocking layer regrowth are presented for the first time. The structure design includes, in particular, a nonselective epitaxial regrowth step as well as a III-V material lift-off. Preliminary results show continuous wave operation with threshold currents of 43 mA and maximum output power of 17 mW per facet. This process is, in particular, very well suited for integration purposes and high yield 2 in. wafer processing.
Oxidation induced AlAs/GaAs superlattice disordering
Authors: Chang J. C. P. , Kavanagh K. L. , Cardone F. , Sadana D. K.
Published: July 2002

Rapid interdiffusion occurs at thin-film SiGe/GaAs interfaces when samples are annealed in oxygen containing ambients. Secondary ion mass spectroscopy and AlAs/GaAs superlattice disordering indicate that Ge and/or Si diffuse to depths of 200 nm after oxidation at 800 °C for 30 min. Negligible diffusion is detected for anneals in forming gas. Dissociation, out-diffusion, and oxidation of the GaAs substrate at the surface are associated with the phenomenon.
Novel and nonintrusive optical thermometer
Authors: Guidotti Daniel , Wilman John G.
Published: July 2002

We have developed a novel thermometer based on the small temperature-induced changes in the optical reflectivity of metals and semiconductors. A nulling optical bridge has been constructed which reduces the temperature measurement to the shot noise limit of the detector. Under ideal laboratory conditions, we have demonstrated a temperature resolution of 0.2 °C.
Robust electrically tunable 1.5 μm mode-locked fiber-external-cavity laser
Authors: Iannone Patrick P. , Raybon Gregory , Koren Uziel , Prucnal Paul R.
Published: July 2002

We demonstrate a robust, broadly tunable pulse source operating near 1.55 μm wavelength consisting of a silica fiber external cavity coupled to an antireflection-coated InGaAsP two-section distributed-Bragg-reflector laser. The laser is actively mode locked at a repetition rate of 1.92 GHz to produce nearly transform-limited pulses with full width at half-maximum as low as 24 ps and can be electrically tuned over a wavelength range exceeding 8 nm.
Terahertz pulses from semiconductor-air interfaces
Authors: Pedersen J. E. , Balslev I. , Hvam J. M. , Keiding S. R.
Published: July 2002

We report an unexpected observation of strong terahertz pulses, radiated perpendicular to semiconductor-air interfaces illuminated by femtosecond laser pulses at normal incidence. Symmetry arguments preclude radiation emitted strictly along the direction of the surface electric field and the dipoles, normal to the interface. We attribute our observations to the strong interface-induced angular redistribution of the radiation being collected by a small dielectric lens. For detection, a small symmetry breaking displacement within the terahertz diffraction spot is sufficient.
Generation of ultralong pulse ArF emission in dynamic mixtures of He plasma jet with Ar/F2 neutral gas
Authors: Sato F. , Sunada Y. , Okamoto S. , Kannari F.
Published: July 2002

Ultralong pulse (≳40 μs) fluorescence of ArF excimer molecules at 193 nm has been generated by dynamically mixing a pulse discharge excited He jet with neutral Ar/F2 gas located downstream in a vacuum chamber. Rapid cooling of the high temperature He plasma through neutral gas collisions and efficient energy transfer to Ar gas create Ar metastable atoms, which form ArF excimer molecules through harpoon reactions with F2, in relatively field-free space. The fluorescence intensity increased with increasing F2 concentration up to ∼10% F2 in Ar with 2-atm backing pressure. In a preliminary experiment with an ArF probe laser, this mixture showed an amplification gain.
Diamond crystallite formation on Si(100) from the gas phase: Seeding or heterogeneous nucleation?
Authors: Molinari E. , Polini R. , Tomellini M.
Published: July 2002

Well separated particles of diamond have been obtained on Si(100) surface by the hot filament chemical vapor deposition technique after scratching by diamond paste. Consecutive depositions, one at a higher and one at lower temperature, or at different CH4 contents of the gas mixture, together with a kinetic analysis based on the particle size distribution function, allow one to decide about the relative importance of heterogeneous nucleation and of seeding.
Reduction of recombination-enhanced diffusion of Be in InGaAs strained layer
Authors: Uematsu Masashi , Wada Kazumi
Published: July 2002

An InGaAs strained layer introduced into the p-n junction of Esaki tunnel diodes has been found to reduce the current-induced degradation of the diodes, that is, recombination-enhanced impurity diffusion (REID) of Be. The Be REID coefficients for diodes with the InGaAs strained layer are about two orders of magnitude smaller than those without the strained layer. This suggests that the strained layer reduces the recombination-enhanced process, which is consistent with the results for InGaAs strained-layer lasers.
Minority carrier lifetime and diffusion length in HgTe/CdTe superlattices by molecular beam epitaxy
Authors: Shin S. H. , Arias J. M. , Zandian M. , Pasko J. G. , Bajaj J. , DeWames R. E.
Published: July 2002

Transient minority carrier lifetime and steady state diffusion length measurements have been performed on n-type HgTe/CdTe superlattices grown on CdZnTe(100) substrates. The n-type (100) superlattice sample shows a lifetime of 90–100 ns at 77–160 K which then decreases with increasing temperature down to 50 ns near 300 K. p-type HgTe/CdTe superlattices show normal behavior for temperature-dependent lifetimes. The measured lifetime is approximately 20 ns at 77 K and increases continuously to 85 ns at 300 K. An independent measurement of minority carrier diffusion length in a p-type HgTe/CdTe superlattice has led to an excellent agreement with a transient lifetime value of 66 ns at 200 K. The minority carrier diffusion length in a direction parallel to the interfaces indicates that the lateral transport properties are not much different from the transport properties of bulk HgCdTe.
Laser-induced hole-burning and flow visualization in the cloud of products of detonated lead azide
Authors: Tzuk Y. , Bar I. , Rosenwaks S.
Published: July 2002

Utilizing a pulsed beam of a Nd:YAG laser, hole burning through the opaque cloud of products formed following the detonation of lead azide is demonstrated. The characteristics of the hole and of the expanding cloud are monitored in real time by a HeNe beam and by high-speed framing photography. The hole is carried with the cloud and propagates at a constant velocity of 0.5–2.8 km/s, depending on the time and location of burning. The hole burning is a result of eliminating solid particles from the cloud. The application of a laser to burn a hole in the detonation products from a solid explosive is demonstrated for the first time. This technique may serve as a method for flow visualization in an aerosol medium.
Transmission electron diffraction study of C70 phase transformation at low temperature
Authors: Tomita M. , Hayashi T. , Gaskell P. , Maruno T. , Tanaka T.
Published: July 2002

C70 grown on a NaCl substrate is observed by transmission electron microscopy (TEM) at low temperature (104 K). New spots that appear reproducibly in the electron diffraction (ED) at low temperature can be indexed as (m±1/2, n±1/2, 0) (m, n: integer) in a [001]hcp projection. The lattice constant a is lower at low temperature and the reduction ratio is a104 K/a300 K=1.02/1.06 nm=0.96±0.02, which is much lower than the value reported for C60. The ED of the low-temperature phase is observed below about 260 K, and an intermediate state is also detected in this temperature range.
Periodic index separate confinement heterostructure InGaAs/AlGaAs quantum well lasers grown by temperature modulation molecular beam epitaxy
Authors: Hong M. , Chen Y. K. , Wu M. C. , Vandenberg J. M. , Chu S. N. G. , Mannaerts J. P. , Chin M. A.
Published: July 2002

Solid-source molecular beam epitaxy with substrate temperature modulation has produced periodic index separate confinement heterostructure InGaAs/AlGaAs quantum well lasers with greatly improved performance. These lasers in a broad area geometry are under room-temperature continuous wave operation and have low threshold current density of 300 A/cm2, high internal quantum efficiency of 91%, low internal waveguide loss of 2.2 cm−1, a reduced transverse beam divergence of 30°, and a high characteristic temperature of 187 K.
Composition dependent transport properties of strain relaxed InxGa1−xAs(x<0.45) epilayers
Authors: Chen Jianhui , Fernandez J. M. , Wieder H. H.
Published: July 2002

The concentration and mobility of the two-dimensional electron gas present at the interface between strain-relaxed, lattice matched, InyAl1−yAs/InxGa1−xAs(x < 0.45), modulation doped heterojunctions grown by means of compositionally step-graded buffer layers on GaAs substrates, were measured at room temperature and at 77 K. The composition dependence of the electron density is attributed to the dependence of the band-gap energy of InxGa1−xAs and that of InyAl1−yAs on x, with a conduction band offset, ΔEc∼0.67ΔEg. The room temperature electron mobility increases from 9×103 cm2/V s for x=0.07 to 1.05×104 cm2/V s for x=0.45. Such strain-relaxed heterostructures have higher electron mobilities than similar pseudomorphic structures with the same sheet electron concentration.
Observation of the focusing of x-ray transition radiation using cylindrical optics
Authors: Piestrup M. A. , Boyers D. G. , Pincus C. I. , Li Qiang , Ho A. H. , Maruyama X. K. , Snyder D. D. , Skopik D. M. , Silzer R. M. , Moran M. J. , Rothbart G. B.
Published: July 2002

We have measured the profile of x rays generated by a transition radiator and focused by simple cylindrical optics. Soft x rays with photon energies between 1 and 4 keV were generated by a 93-MeV electron beam striking a stack of eight foils of 3.5-μm-thick mylar. These x rays were emitted in an annular cone and were collected by a quartz cylinder which focused the x rays to a 0.5-mm-diam spot at a distance of 1.35 m from the transition radiator.
Visible photoluminescence of Zn-doped CuAlS2
Authors: Aksenov Igor , Sato Katsuaki
Published: July 2002

The observation of a very intense blue and green photoluminescence from low-resistivity CuAlS2 crystals, grown by chemical vapor transport and subsequently doped with Zn, is reported. The emission is strong even at room temperature, the color of emission being dependent on Zn-doping conditions. Results obtained suggest that the CuAlS2 compound can be considered as a perspective material for blue and green light-emitting device realization.
Enhancement in critical current density of Y1Ba2Cu3O7−δ thin films on hastelloy with TiN buffer layers
Authors: Kumar Ashok , Narayan J. , Chen X.
Published: July 2002

We have prepared high quality superconducting Y1Ba2Cu3O7−δ (YBCO) thin films on hastelloy (C) with titanium nitride (TiN) buffer layers. The hastelloy (C) is a nickel based superalloy with excellent high-temperature properties and corrosion resistance. The superconducting and TiN buffer layers were deposited sequentially at 600 °C using pulsed excimer laser irradiation of the respective targets. TiN has been suitably chosen owing to matching of thermal expansion coefficient (∼8.0–9.0×10−6/K) with hastelloy (∼9.0×10−6/K) and YBCO (∼12–13×10−6/K). X-ray diffraction, four point ac electrical resistivity and scanning electron microscope studies were performed on these films for correlations between crystal structure, microstructure, and superconducting properties. Auger electron spectroscopy (AES) was used to determine the extent of interdiffusion in metal-TiN and TiN-Y1Ba2Cu3O7−δ interfaces. These films exhibited a characteristic metallic conductivity followed by an onset of superconductivity at 91 K with a zero resistance temperature (Tco) of 85 K. Critical current density (Jc) for these films (77 K and zero magnetic field) was determined to be ∼9.0×104 A/cm2 for thin films on metallic substrates.
Nonspecular x-ray scattering from the amorphous state in W/C multilayers
Authors: Jiang Xiaoming , Metzger T. H. , Peisl J.
Published: July 2002

The nonspecular x-ray scattering distribution from an amorphous W/C multilayer structure has been examined close to low order Bragg reflections. The scattering distribution is explained as coherent atomic scattering from amorphous W and C layers having a periodicity in growth direction. This layer periodicity results in scattering intensity streaks in reciprocal space perpendicular to the one-dimensional order. In addition, sharp intensity modulations appear, whenever the incident or exit angle equals the first order Bragg angle of the multilayer. They can be understood in terms of a dynamical interaction between the x-ray standing wave and the atomic scattering in the layers.
Composition change of SiCx (x=1–2) films due to variation of film precursors in the Si2H6/C2H2 chemical vapor deposition reaction system
Authors: Hong Lu-Sheng , Shimogaki Yukihiro , Egashira Yasuyuki , Komiyama Hiroshi
Published: July 2002

Silicon carbide (SiC) films have been deposited on a silicon substrate by the chemical vapor deposition method using the Si2H6 and C2H2 gas system. The carbon content in the films was dependent on the volume-to-surface ratio (V/S) of the reactor. Study of the film formation mechanism indicated that the change in film composition was caused by V/S-dependent contributions of three film precursors. Films formed by surface reaction of Si2H6 gave a composition of SiC2, while films formed by gaseous species, most plausibly, SiH2 and SiH3C≡CH, showed a stoichiometric composition of SiC.
Modulated thermoreflectance imaging of hidden electric current distributions in thin-film layered structures
Authors: Welsch E. , Reichling M. , Göbel C. , Schäfer D. , Matthias E.
Published: July 2002

Thermal imaging of hidden electric current distributions with a resolution of several ten micrometers is demonstrated. It is shown that the thermoreflectance technique is capable of monitoring current-induced temperature variations on as well as beneath the surface of thin layered structures. A temperature pattern was generated by Joule heating using an ac current in a 2.5 μm thick structured gold film that was evaporated on a glass substrate and covered by a TiOx layer. The current density distribution in the gold film is revealed by the measured photothermal pattern, provided that both laser beam diameter and thermal diffusion length are smaller than the desired lateral resolution.
Effects of substrate temperature on the microstructure of YBa2Cu3O7−δ films grown on (001) Y-ZrO2 substrates
Authors: Alarco J. A. , Brorsson G. , Ivanov Z. G. , Nilsson P.-Å. , Olsson E. , Löfgren M.
Published: July 2002

High-quality YBa2Cu3O7−δ films grown on (001) single-crystal Y-ZrO2 substrates by pulsed laser deposition have been studied as a function of substrate temperature using transmission electron microscopy. A transition from epitaxial films to c-axis oriented polycrystalline films was observed at 740 °C. An intermediate, polycrystalline, BaZrO3 layer was formed from a reaction between the film and the substrate. A dominant orientation relationship of [001]YBCO//[001]int. layer//[001]YSZ and [110]YBCO//[110]int. layer//[100]YSZ was observed. The formation of grain boundaries in the films resulted in an increased microwave surface resistance and a decreased critical-current density. The superconducting transition temperature remained fairly constant at about 90 K.
Saturation fields in Co-Fe/Cu multilayers with giant magnetoresistance: In-plane uniaxial magnetic anisotropy effects
Authors: Inomata K. , Saito Y.
Published: July 2002

Magnetization processes are investigated by calculation and experiments for Co-Fe/Cu multilayers with giant magnetoresistance, which are prepared on MgO(110) substrates using ion beam sputtering and have in-plane uniaxial magnetic anisotropy (Ku). The experiments show the metamagnetic transition from antiferromagnetic spin structure to ferromagnetic one for an easy axis external field. This is supported by calculation of the magnetic phase diagram for stable magnetization configurations, which shows the metamagnetic transition to occur for (J12/d)/Ku≤1, where J12 is antiferromagnetic layer interaction and d is magnetic layer thickness. The saturation fields from antiferromagnetic to ferromagnetic spin structures are substantially decreased by induction of the in-plane uniaxial anisotropy. The relation Hsh − 2Hse = 2Ku/Ms, found for the saturation fields by the calculation, is confirmed experimentally for the multilayers, where Ms is the saturation magnetization, and Hse and Hsh are the saturation fields for the external field parallel to the easy and hard axes, respectively.
Oxidation effects on cleaved multiple quantum well surfaces in air observed by scanning probe microscopy
Authors: Howells S. , Gallagher M. J. , Chen T. , Pax P. , Sarid D.
Published: July 2002

Atomic force microscopy (AFM) and scanning tunneling microscopy (STM) of quantum well structures can give an independent method of measuring superlattice spacing and uniformity without having to resort to more involved techniques requiring intricate sample preparation. We present the first AFM images of cleaved InGaAs/InP multiple quantum wells and compare them with STM images taken of the same heterostructure. The images were stable in air for over a day. Based on our results, we propose that the mechanism for contrast in our images is due to an oxide layer that grows primarily on the InGaAs wells and not on the InP barriers. Both STM and AFM clearly resolve the individual wells of the heterostructure, although STM measured a larger corrugation than an AFM. STM also exhibited superior lateral resolution of about 2 nm while AFM had a lateral resolution of approximately 6 nm.
Time resolved nonequilibrium phonon dynamics in the nonradiative decay of photoexcited forsterite
Authors: Demos S. G. , Buchert J. M. , Alfano R. R.
Published: July 2002

Information on the nonequilibrium phonon dynamics of the 225 cm−1 and 335 cm−1 modes on forsterite has been obtained using time resolved Raman scattering. The observed nonequilibrium phonon population is associated with the overall complex nonradiative decay following the excitation of the impurity ion.
Tm3+-related emissions in III-V semiconductors grown by metalorganic vapor phase epitaxy
Authors: Pressel K. , Weber J. , Hiller C. , Ottenwälder D. , Kürner W. , Dörnen A. , Scholz F. , Locke K. , Wiedmann D. , Cordeddu F.
Published: July 2002

Layers of InP:Tm, GaAs:Tm, GaP:Tm, and GaInP:Tm have been grown by metal-organic vapor phase epitaxy at atmospheric pressure using tris(isopropylcyclopentadienyl)thulium as a liquid Tm source. Electrical measurements revealed no characteristic influence of Tm on the electrical properties of the semiconductor host. Tm3+-related 4f emissions at 1.2 and 1.9 μm are observed both in GaAs and GaInP. In GaAs, the Tm3+ 4f luminescence at 1.2 μm consists of a series of very sharp lines. In GaInP samples, the Tm3+-related luminescence at 1.2 μm is much stronger than in the GaAs samples and is still observable at room temperature.
Characterization of InxGa1−xAs/GaAs strained-layer superlattices by transmission electron microscopy and convergent beam electron diffraction
Authors: Wei X. L. , Fung K. K. , Feng W. , Zhou J. M.
Published: July 2002

Four InxGa1−xAs/GaAs strained-layer superlattices grown by molecular beam epitaxy have been studied by transmission electron microscopy (TEM) and convergent beam electron diffraction (CBED). Cross-section TEM images show that the interfaces are sharp and the superlattice layers are uniform. Misfit dislocations are also observed at the superlattice substrate interface. Diffraction disks of reflections in plan-view CBED patterns show the presence of satellite sidebands due to periodic modulations of the superlattices. The separation and intensities of the sidebands depend sensitively on the structural parameters of the superlattices. Accurate values of the elastic strains and thicknesses of the superlattice layers have been obtained by matching the observed and kinematically calculated sideband intensities based on a square wave model of the strain profile in the superlattice.
Electrochemical capacitance-voltage depth profiling of nanometer-scale layers fabricated by Ga+ focused ion beam implantation into silicon
Authors: Mogul H. C. , Steckl A. J. , Webster Gyles , Pawlik M. , Novak S.
Published: July 2002

The electrochemical capacitance-voltage (ECV) profiling technique is employed to measure the active carrier concentration in nanoscale layers fabricated by focused ion beam (FIB) implantation of 3 to 10 keV Ga+ ions into crystalline Si. The carrier concentration profiles obtained by ECV indicate the ability of this technique to probe depths as shallow as 2–3 nm and with a nanometer-scale depth resolution. The carrier concentration obtained by ECV matches well with the Ga atomic concentration profile detected by secondary-ion mass spectroscopy, but is almost an order of magnitude higher than that provided by the spreading resistance profile technique.
High power single mode operation of long cavity GaAlAs lasers with nonabsorbing mirror buried twin ridge substrate structure
Authors: Naito H. , Imafuji O. , Kume M. , Shimizu H. , Kazumura M.
Published: July 2002

We have newly developed a 350 μm long cavity GaAlAs laser with nonabsorbing mirror buried twin ridge substrate structure, in order to obtain highly reliable high power single mode operation. It is found that the long cavity stabilizes lateral mode at powers higher than conventional maximum values because the carrier density is reduced to well suppress spatial hole-burning effect. The fundamental spatial mode operation is confirmed up to 210 mW and the maximum output power as high as 380 mW is obtained. The lifetime at 100 and 200 mW at 25 °C are expected to be 170 000 and 24 000 h, respectively, from the aging test results.
Improvement of punchthrough-induced gate-oxide breakdown in n-channel metal-oxide-semiconductor field-effect transistors using rapid thermal nitridation
Authors: Huang M. Q. , Lai P. T. , Ma Z. J. , Wong H. , Cheng Y. C.
Published: July 2002

Gate-dielectric breakdown in small n-channel metal-oxide-semiconductor field-effect transistors has been investigated. It is found that such breakdown is accelerated by large channel current when the devices operate in punchthrough conditions. The situation can be greatly improved by rapid thermal nitridation (RTN) of the gate oxide in the transistors. In addition, the time-dependent dielectric breakdown of the devices operating beyond punchthrough is also considerably improved by RTN. The results indicate that the charge to breakdown Qbd is increased by three orders of magnitude as compared to conventional-oxide devices. All these improvements can be attributed to the nitridation-induced hardening of SiO2/Si interface.
Raman scattering study of strain in ZnxCd1−xTe/CdTe superlattices
Authors: Trofimov I. E. , Petrov M. V. , Balakirev F. F. , Milokhin A. E. , Kuzmin V. D.
Published: July 2002

The strain configuration in ZnxCd1−xTe/CdTe strained-layer superlattices (SLS) has been determined by Raman scattering. We have shown that SLS with an individual layer width below the critical thickness are lattice matched to their substrate.
Optical anisotropy of YBa2Cu3O7−δ films on NdGaO3(001) substrates: A comparison with single domain crystals
Authors: Zibold A. , Widder K. , Geserich H. P. , Scherer T. , Marienhoff P. , Neuhaus M. , Jutzi W. , Erb A. , Müller-Vogt G.
Published: July 2002

We have investigated the spectral reflectance of thin YBa2Cu3O7−δ films deposited on twin-free NdGaO3(001) substrates. Using polarized light in the spectral range between 50 meV and 6 eV, we found a significant a-b anisotropy near the plasma edge. On the basis of a Lorentz–Drude model we have calculated the tensor components of the dielectric function parallel to the a and to the b axis, respectively. The obtained results are compared with the a-b anisotropy of single domain crystals.
Surface microroughness observed by scanning tunneling microscope and improved device characteristics of GaAs/Si grown with AlGaAs/AlGaP intermediate layers
Authors: Egawa T. , Jimbo T. , Umeno M.
Published: July 2002

Scanning tunneling microscope images show that a smoother surface and heterointerface can be obtained in a GaAs/Si grown with Al0.5Ga0.5As/Al0.55Ga0.45P intermediate layers (AlGaAs/AlGaP ILs), which result from a two-dimensional growth at an initial stage. By using the AlGaAs/AlGaP ILs, the device characteristics are improved; a saturation electron velocity of 1.6×107 cm/s for a GaAs metal-semiconductor field-effect transistor, and an internal quantum efficiency of 83%, an intrinsic mode loss coefficient of 23 cm−1, a differential gain coefficient of 1.9 cm/A, and a transparency current of 266 A/cm2 for a single quantum-well laser diode.
Correlation between ultraviolet-induced refractive index change and photoluminescence in Ge-doped fiber
Authors: Duval Yan , Kashyap Raman , Fleming Simon , Ouellette François
Published: July 2002

The refractive index change arising following the UV exposure of a Ge-doped fiber was obtained by measuring the change in the far-field width of the fiber mode in the infrared. Simultaneous measurements showed a gradual decrease in the visible photoluminescence from the fiber which can be directly correlated to the photoinduced index change.
Electronic configuration of tantalum in 1T-LiTaS2
Authors: Eibschutz M. , Murphy D. W. , Zahurak S. , Waszczak J. V.
Published: July 2002

High resolution Mössbauer effect (ME) of the 6.2 keV γ rays of 181Ta has been observed in a lithiated single crystal of 1T-LiTaS2. The isomer shift of 105.2 mm/s is 35 mm/s larger than that of 2H-TaS2 and comparable to that of 2H-LiTaS2. The ME in 1T-TaS2 is not observable because of the presence of a nearly commensurate charge density wave (CDW). The observation of the ME in 1T-LiTaS2 shows that the CDW is suppressed and also reflects a change in the electronic configuration from Ta4+ (5d1) toward Ta3+ (5d2). A value of 45 mm/s per e− has been derived for the IS change due to charge transfer from Li to Ta.
Electrical properties of Sb implanted Si1−xGex alloy layers
Authors: Atzmon Z. , Eizenberg M. , Shacham-Diamand Y. , Mayer J. W. , Schäffler F.
Published: July 2002

Electrical properties of Sb implanted strained Si1−xGex alloy layers are reported. Two sets of Si1−xGex epilayers with compositions of x=0.08 and 0.18, MBE grown on (100)Si substrates, were implanted at room temperature with Sb+ ions at energies of 200 and 100 keV, respectively, and doses of 1013 and 1015 cm−2. Secondary-ion mass spectrometry and spreading resistance profiling measurements show that Sb implantation, with a dose below the critical value for amorphization (1013 cm−2), formed a p-type region upon annealing at 500 °C. Only higher temperature anneals transformed the implanted layer into the expected n-type doping. Maximal values of electrical activity (45±10%) and mobility were obtained in this case only at temperatures around 800–900 °C. For the high dose implantation (1015 cm−2), it was found that the highest activation efficiency at the implantation profile peak was obtained at 500–600 °C, while at the end-of-range region the activation efficiency was very low.
Angle and temperature tuning of phase-matched second-harmonic generation in N-(4-nitrophenyl)-N-methylaminoacetonitrile
Authors: Morita Ryuji , Vidakovic Petar V.
Published: July 2002

N-(4-nitrophenyl)-N-methylaminoacetonitrile is shown to be a very efficient nonlinear organic material. Angularly phase-matched second-harmonic generation efficiencies as high as 1.8×10−3, 2.0×10−4, and 1.2×10−4 W−1 at 1.064, 1.21, and 1.30 μm, respectively, have been measured by using cw Nd:YAG and semiconductor lasers as fundamental sources. Temperature-tuning sensitivities of phase-matched second-harmonic generation have been found to be among the largest ever measured. Values obtained at 1.064, 1.21, and 1.30 μm are −1.2, −1.2, and −1.4 mrad/°C, respectively.
Single mode potassium and silver ion-exchanged glass waveguides with low losses and high index increase
Authors: Helmers H. , Helleso O. G. , Benech P. , Rimet R.
Published: July 2002

An improved method for fabricating single mode, low loss optical waveguides using a two step potassium and silver ion exchange in glass is reported. The waveguides are compatible with optical fibers and butt coupling of diode lasers. Propagation losses, down to 0.4 dB/cm, are measured for a wavelength of 780 nm. In the single mode waveguide, an index increase of 1% is obtained, which allows small bending losses for curvatures with a radius down to 2 mm.
Photorefractive properties and self-pumped phase conjugation of tetragonal Fe-doped KTa1−xNbxO3 crystal
Authors: Wang Jiyang , Guan Qingcai , Liu Yaogang , Wei Jingqian , Wang Dadi , Lian Yingwu , Yang Huaguang , Ye Peixian
Published: July 2002

This letter reports the two-wave mixing experimental results of tetragonal Fe-doped KTa1−xNbxO3. A 7.3 cm−1 gain coefficient and 42% diffraction efficiency have been obtained. For the first time internally self-pumped phase conjugation is being observed in this crystal. At room temperature, the conjugate reflectivity measured is 21%.
Above- and below-band femtosecond nonlinearities in active AlGaAs waveguides
Authors: Hultgren C. T. , Dougherty D. J. , Ippen E. P.
Published: July 2002

Femtosecond optical pulses were used to study the gain and refractive index dynamics in a bulk AlGaAs diode laser. Experiments were performed at wavelengths above and below the band gap of the diode-laser active region. The above-band gain dynamics exhibit an ultrafast transient that has not been seen before in AlGaAs devices. We attribute this dynamic to spectral-hole burning and a delay in carrier heating. The below-band refractive index measurements demonstrate that carrier heating by free-carrier absorption is important and that there is a delay in the onset of this heating of approximately 120 fs.
Anomalous intense ultraviolet emission bands in the radio-frequency glow discharges of GeH4-fluorocarbon-H2 mixtures
Authors: Yagi Shigeru , Takahashi Noriyoshi
Published: July 2002

Anomalous intense ultraviolet emission bands in the region 320–370 nm with a maximum at 340 nm were observed in radio frequency glow discharges of CF4-H2 mixtures containing 0.3%–1% of GeH4. The system of emission bands is prominent also in the discharges of GeH4-C2F6-H2 mixtures but the corresponding emission system was not observed in the discharge spectra of GeH4-CH4-H2 and SiH4-CF4-H2 mixtures. From the vibrational analysis of the bands, it was found that the emission bands almost agree with the weak emission system of GeF2, which has been tentatively assigned in earlier work as the 3B1–1A1 transition.
Fractal analysis of leakage-current fluctuations of Si metal-oxide-semiconductor capacitors for the characterization of dry-etching damage
Authors: Miyano Takaya , Fujito Manabu , Fujimoto Kiwamu , Sanjoh Akira
Published: July 2002

Three categories of leakage-current fluctuations through the oxide layers of Si metal-oxide-semiconductor capacitors are observed in the 5 kHz frequency range. They are classified by the fabrication processes for the polycrystalline silicon gate electrodes of the capacitors: (1) wet etching, (2) dry etching using plasma generated by electron cyclotron resonance, and (3) reactive ion etching. Fractal dimensions of each category of the current fluctuations are evaluated to be: (1) 2.00 (standard deviation σ=0.01); (2) 1.87 (σ=0.10; and (3) 1.71 (σ=0.08), respectively. The results are analyzed in terms of Brownian motion. The decrease in the fractal dimension is ascribed to change in defect structure of the electron traps induced by each dry-etching process.
Buried single-crystal CoSi2 layers in SiGe alloys made by ion beam synthesis
Authors: Jebasinski R. , Mantl S. , Dieker Chr. , Crecelius G. , Dederichs H. , Vescan L.
Published: July 2002

The synthesis of buried CoSi2 layers in Si0.91Ge0.09 alloys by the implantation of high doses of 100 and 150 keV Co+ ions and subsequent rapid thermal annealing at T≥1000 °C is studied by x-ray diffraction, Rutherford backscattering spectroscopy, He ion channeling, Auger electron spectroscopy, and transmission electron microscopy. After annealing, a buried single-crystal CoSi2 layer containing ≊1 at. % Ge is formed in the SiGe alloy. Silicide formation causes an outdiffusion of Ge leading to an increase in the Ge concentration of the adjacent SiGe layers. The remaining Ge within the silicide layer is found to be present as Si-Ge islands with the composition of the virgin Si0.91Ge0.09 alloy.
New class of Si-based superlattices: Alternating layers of crystalline Si and porous amorphous Si1−xGex alloys
Authors: Fathauer R. W. , George T. , Jones E. W. , Pike W. T. , Ksendzov A. , Vasquez R. P.
Published: July 2002

Superlattices consisting of alternating layers of crystalline Si and porous amorphous Si1−xGex have been fabricated. This is accomplished by first growing a Si/Si0.7Ge0.3 superlattice by molecular beam epitaxy, followed by Ar-ion milling to form mesa structures, and finally by immersion in HF:HNO3:H2O. This solution creates a porous structure similar to that created by anodic etching, and a high selectivity is observed for the conversion of the alloy layers relative to the Si layers. The degree of selectivity is found to depend on alloy layer thickness and strain. Superlattices have been fabricated from 1-μm wide mesas with Si0.7Ge0.3 layers fully converted to 5-nm thick porous amorphous material.
Young’s modulus of a thin film determined from the peak shifts of its membrane modes
Authors: Fartash A.
Published: July 2002

The perturbations of membrane modes of a circular film due to its plate rigidity is studied. A single mathematical expression valid for all orders of resonant modes is derived, and a new method for measuring the Young’s modulus is described that is based on finding the frequency shifts of thin-film membrane modes. The Young’s moduli of textured aluminum and nickel films are measured and found in good agreement with their calculated literature values [D. Baral, J. B. Ketterson, and J. E. Hilliard, J. Appl. Phys. 57, 1076 (1985)].
Stabilization of C-49 Ti(AlxSi1−x)2 observed from the reaction between TiSi2 and Al
Authors: Chung I. , Nam H. G. , Bene’ R. W.
Published: July 2002

The solid state reaction between aluminum and titanium silicide was studied over the temperature range of 450–800 °C. The phase formed from the reaction was different from Ti7Al5Si12, which has been frequently reported as the reaction product. Also, two other phases were reported nearly identical to those observed in terms of the similarity in the structure type and lattice parameters, namely, ternary C-49 Ti2AlSi3 and binary C-49 Ti(AlxSi1−x)2 which is the metastable C-49 TiSi2 with Al solid solution. Based on the detailed microscopic and spectroscopic analysis, it was suggested that the observed phase is likely the metastable C-49 Ti(AlxSi1−x)2 stabilized by substitution of Si with Al. Even though we did not find the maximum value of x, approximately 10% of Si was found to be substituted with Al for the sample annealed at 800 °C for 30 min.
Feature size effects on selective area epitaxy of InGaAs
Authors: Cotta M. A. , Harriott L. R. , Wang Y. L. , Hamm R. A. , Wade H. H. , Weiner J. S. , Ritter D. , Temkin H.
Published: July 2002

We demonstrate the use of an ultrathin (≊5 nm) Si layer deposited on InP substrates as a mask in selective area epitaxy of InGaAs by metalorganic molecular beam epitaxy. Patterns of varying shapes and sizes, from 5 to 0.5 μm, were written on the mask by focused Ga ion beam and etched by Cl2. The growth rate of InGaAs was studied by scanning force microscopy using stripes with guard rings spaced as close as 0.5 μm from the stripes. A small increase in the growth rate was detected only when the feature size was lower than 5 μm, and the growth rate was not affected by the presence of the guard rings. This shows that precursor material is being transferred from the slow growing {111}-planes to the (100)-plane, and that migration of species from the Si mask to the growing areas is negligible.
Epitaxial growth of strain-free Ge films on Si substrates by solid phase epitaxy at ultrahigh pressure
Authors: Ishiwara Hiroshi , Sato Takayoshi , Sawaoka Akira
Published: July 2002

A novel method to solve the thermal mismatch problem in heteroepitaxial growth has been presented, in which an amorphous film deposited on a single-crystal substrate is grown by solid phase epitaxy at ultrahigh pressure. It has been theoretically predicted in such systems as Ge/Si and GaAs/Si that the difference of the thermal expansion coefficient can be compensated by that of elastic strain generated by hydrostatic pressure. Experimentally, it has been found that the residual strain in Ge films on Si substrates is linearly decreased with increase of the pressure during annealing, while the defect density in the film is kept constant. It has been presumed from these results that a strain-free Ge film can be grown on a Si substrate by solid phase epitaxy at 2.5 GPa.
On the two-dimensional superstructure in the (001) plane of Bi-Sr-Ca-Cu-O superconductors
Authors: Zheng Jian-guo , Li Qi , Feng Duan , Yu Feng , Hong Jian-ming , Chen Xian-hui
Published: July 2002

The two-dimensional (2D) superstructure in the (001) plane of Bi-Sr-Ca-Cu-O superconductor was first proposed by Marshall et al. [Appl. Phys. Lett. 53, 426 (1989)]. Some results obtained in our experiments indicate that the apparent 2D superstructure modulation pattern results from two grains with a [001] twist boundary.
Ferroelectric phase transition in KTiOPO4: An optical second-harmonic generation study
Authors: Chu David K. T. , Hsiung Hui
Published: July 2002

The ferroelectric phase transition in a single-domain KTiOPO4 (KTP) crystal is studied with optical second-harmonic generation. The optical nonlinearity decreases continuously with increasing temperature and vanishes at the Curie point (TC=952 °C) and above. Over a broad temperature range in the ferroelectric phase, the nonlinear optical coefficient d33∝(TC−T)0.5. This behavior is in good agreement with the Landau theory for second-order ferroelectric phase transitions.