bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of epitaxial GaAs and AlxGa1−xAs layers doped with oxygen
Authors: Goorsky M. S. , Kuech T. F. , Cardone F. , Mooney P. M. , Scilla G. J. , Potemski R. M.
Published: July 2002

Intentional oxygen doping (≳1017 cm−3) of GaAs and Al0.30Ga0.70As epitaxial layers was achieved during metalorganic vapor phase epitaxy through use of an oxygen-bearing metalorganic precursor, dimethylaluminum methoxide (CH3)2AlOCH3. The incorporation of oxygen and very low levels of Al (AlAs mole fraction <0.005) in the GaAs layers leads to the compensation of intentionally introduced Si donors. Additionally, deep levels in GaAs associated with oxygen were detected. The introduction of dimethyl aluminum methoxide during AlxGa1−xAs growth did not alter Al mode fraction or degrade the crystallinity of the ternary layers, but did incorporate high levels of oxygen which compensated Si donors. The compensation in both GaAs and Al0.30Ga0.70As indicates that high resistivity buffer layers can be grown by oxygen doping during metalorganic vapor phase epitaxy.
Calibration of the isolated oxygen interstitial localized vibrational mode absorption line in GaAs
Authors: Skowronski M. , Neild S. T. , Kremer R. E.
Published: July 2002

A series of isochronal annealing experiments have been performed on bulk GaAs crystals doped with oxygen. Two centers induced by oxygen, the isolated oxygen interstitial (Oi) and the gallium-oxygen-gallium (Ga-O-Ga) defect, most likely due to oxygen interstitial-arsenic vacancy complex, were monitored using localized vibrational mode absorption. The Ga-O-Ga center dissociates at temperatures above 650 °C resulting in an increase of the Oi concentration. Using the known oscillator strength of Ga-O-Ga transition, the calibration factor between integrated absorption and concentration of isolated oxygen interstitial was determined to be 8×1016 cm−1. The observed increase of absorption bands of both defects after high-temperature annealing indicates that other types of oxygen-containing defects are present.
Experimental evidence and interpretation of dopant–point defect pair diffusion
Authors: Orlowski Marius
Published: July 2002

Experimental verification along with detailed simulation of up-hill dopant diffusion in the vicinity of a damage layer consisting of dislocation loops is presented. The effect of dopant up-hill diffusion, predicted on the basis of the so-called dopant–point defect pair diffusion model, is explained by the additional dopant current driven by the gradient of point defect concentration. The gradient of point defects (self-interstitials, in the present case) is caused by the strong absorption of self-interstitials by dislocation loops in the damage layer. The present simulation of phosphorus diffusion in preamorphized silicon crystal shows that the pertinent phosphorus profiles, displaying the up-hill diffusion, allow reliable extraction of parameters governing the coupled phosphorus and self-interstitial diffusion dynamics. Three different derivations of the pair diffusion model are investigated. It is shown that the pair diffusion model is consistent with a derivation of transport equations from the master equation assuming that the elementary jump frequency Γ0 is enhanced locally by the presence of self-interstitials according to Γ0(CI/C*I). It is also shown that the same assumption made on the level of the final diffusion equation leads to incomplete formulation of the relevant dynamics.
Blue-green surface-emitting second-harmonic generators on (111)B GaAs
Authors: Vakhshoori D. , Fischer R. J. , Hong M. , Sivco D. L. , Zydzik G. J. , Chu G. N. S. , Cho A. Y.
Published: July 2002

Passive devices capable of generating coherent blue-green light radiated in a surface emitting geometry is realized on (111)B GaAs substrates. This substrate orientation is required by the symmetry of the III–V crystals for the particular nonlinear counterpropagating interaction under consideration. The visible light output power versus the fundamental optical power is measured and shown to agree with the theory. This result demonstrates the feasibility of active visible surface emitting generators in the milliwatt output power range on (111)B substrate.
Excellent thermal stability of superconducting properties in YBa2Cu3O7 films irradiated by pulsed excimer lasers
Authors: Singh Rajiv K. , Bhattacharya D. , Harkness S. , Narayan J. , Diwari P. , Jahncke Catherine , Sparks R. , Paesler M.
Published: July 2002

We have investigated the microstructure and superconducting properties of YBa2Cu3O7 films irradiated by nanosecond pulsed excimer lasers. The superconducting YBa2Cu3O7 thin films were deposited in situ on (100) LaAlO3 substrates using the pulsed laser evaporation technique. The virgin unirradiated YBa2Cu3O7 films exhibited excellent superconducting properties with Tco (temperature for zero resistance) of 90 K and critical current densities Jc (at 77 K and zero magnetic fields) of approximately 5.0 × 106 A/cm2. The films were further irradiated by a pulsed excimer XeCl laser (λ=308 nm, τ=45×10−9 s) with energy density varying from 30 to 300 mJ/cm2. Excellent thermal stability was observed for YBa2Cu3O7 films on LaAlO3 substrate for laser irradiation at all energy densities between 30 and 300 mJ/cm2, with no deterioration in the Tco values (90±0.3 K). An improvement in the Jc of the films was observed at low-energy density irradiation, however, for energy densities above the melt threshold the Jc values decreased sharply. The Raman measurements for laser irradiated films showed improvement in the crystallinity of the film with stronger Raman peaks at 140 and 340 cm−1, thus correlating the improvement in Jc to better crystallinity of the films.
Direct type II–indirect type I conversion of InP/GaAs/InP strained quantum wells induced by hydrostatic pressure
Authors: Gerling M. , Pistol M.-E. , Samuelson L. , Seifert W. , Fornell J.-O. , Ledebo L.
Published: July 2002

Photoluminescence from thin strained layers of GaAs grown on InP has been studied under hydrostatic pressure. The structures are type II at atmospheric pressure. At higher pressures the structures change to type I with the lowest conduction band edge in the strained GaAs layer being the X minimum. This transformation is characterized by a drastic change in the pressure derivative of the emission energy and a rapid disappearance of the photoluminescence intensity at slightly higher pressures. A hydrostatic pressure derivative of less than one meV/kbar is measured for the valence band offset.
Surface recombination effects in soft x-ray efficiencies
Authors: Benitez E. L. , Husk D. E. , Tarrio C. , Schnatterly S. E.
Published: July 2002

We have measured the soft x-ray efficiencies of a silicon p-i-n photodiode and a La2O2S:Tm phosphor over a broad energy range. We have also measured the inelastic electron scattering spectra of the constituent materials and obtained values of optical absorption coefficients versus energy. The energy dependence of the efficiencies is well explained by a model based on surface recombination of electron hole pairs, and the quality of data which can now be obtained from synchrotrons makes possible quantitative fits from which we obtain diffusion length, surface recombination velocity, and bulk quantum efficiency.
Laser action in a KrF-laser-pumped Ta vapor
Authors: Yoshida H. , Ninomiya H. , Takashima N.
Published: July 2002

Ta vapor is generated from a Ta metal plate by irradiation of a pulsed YAG laser of a 2 J energy, and the Ta atoms are optically pumped by a KrF laser of 10 mJ energy. Ta laser oscillation has been obtained on five lines in the ultraviolet region; 292.5 nm (6F01/2−4P3/2), 322.7 nm (6F03/2−4P5/2), 328.1 nm (6F03/2−6D1/2), 330.4 nm (6F03/2−6D3/2), and 351.4 nm (6F01/2−2P1/2). The gains/cm on these laser lines are 0.35, 0.24, 0.09, 0.09, and 0.20, respectively. A maximum output power of 48 W has been obtained at 2.5 Torr of He buffer gas pressure.
Flux pinning and critical current density of a Y1Ba2Cu3O7−x superconducting thin film
Authors: Matsuura Takashi , Itozaki Hideo
Published: July 2002

The relation between the critical current density and the pinning potential of an epitaxial Y1Ba2Cu3O7−X thin film was investigated. The pinning potential was evaluated from the temperature dependence of the resistivity in various values of a magnetic field. The pinning potential was inversely proportional to the applied magnetic field and had the anisotropy in the direction of the magnetic field. Critical current density of the thin film was calculated using the obtained pinning potential. This calculated result was consistent with the critical current density measured by a four-probe method.
Self-aligned InGaAs/GaAs/InGaP quantum well lasers prepared by gas-source molecular beam epitaxy with two growth steps
Authors: Chen Y. K. , Wu M. C. , Kuo J. M. , Chin M. A. , Sergent A. M.
Published: July 2002

Index-guided self-aligned InGaAs/GaAs/InGaP quantum well lasers are fabricated by gas-source molecular beam epitaxy in two growth sequences on a GaAs substrate for the first time. The use of aluminum-free InGaP as cladding layers permits regrowth steps without the problem with the oxidation of aluminum alloys. A patterned n-InGaP current confinement layer is used to provide index guiding as well as current blocking. Preliminary results from coated 2.5-μm-wide and 508-μm-long devices show a room temperature continuous wave lasing threshold current of 12 mA with an external differential quantum efficiency of 0.68 mW/mA and a characteristic temperature of 130 K from 30 to 75 °C.
Electro-optics of electrically controlled birefringence liquid-crystal displays by 2×2 propagation matrix and analytic expression at oblique angle
Authors: Ong Hiap Liew
Published: July 2002

A new 2×2 propagation matrix for obliquely propagating light is used to compute the electro-optics of an electrically controlled birefringence liquid-crystal display, with arbitrary viewing angle. The results are the same as those obtained by the generalized geometrical optics approximation and are in good agreement with those computed by the 4×4 propagation matrix. By approximating the liquid-crystal medium as a homogeneous medium with a field-dependent orientation, a simple analytic expression is obtained for describing the optical transmission. The computed electro-optical transmissions at oblique angle show a good agreement between the simple formula and the full computation having the liquid crystal divided into 500 sublayers.
Polish-induced surface damage in nickel: Scanning acoustic microscopy and Brillouin scattering study
Authors: Sathish S. , Mendik M. , Kulik A. , Gremaud G. , Wachter P.
Published: July 2002

The angular dispersion of surface acoustic wave velocities on {100} planes of a nickel single crystal has been measured using continuous wave scanning acoustic microscope and Brillouin scattering. This dispersion is used to calculate the elastic constants. They are compared with bulk ultrasonic measurements performed on the same sample. Systematic differences have been observed in elastic constants and anisotropy. These are attributed to surface damage due to mechanical polishing of the specimen.
Photocurrent multiplication in amorphous silicon carbide films
Authors: Hiramoto Masahiro , Yoshimura Kanji , Nakayama Yoshikazu , Akita Seiji , Kawamura Takao , Yokoyama Masaaki
Published: July 2002

The photocurrent multiplication reaching 300 times was recently observed in amorphous silicon carbide (a-SiC:H) films using a simple cell configuration of SnO2/a-SiC:H/Au. This phenomenon, which appeared only under the irradiation of bulk-absorbed red light, is not due to Avalanche effects, but is thought to result from electron tunneling from SnO2 to a-SiC:H film through a thin insulating thin silicon oxide layer formed at the a-SiC:H/SnO2 interface in a high electric field built up by the photoaccumulated space charges of trapped holes near the interface.
Photoluminescence and secondary-ion mass spectrometry studies of rapid-thermal-annealed silicon coimplanted with phosphorus in GaAs
Authors: Marrakchi G. , Laugier A. , Guillot G. , Alaya S. , Maaref H.
Published: July 2002

Coimplantation effects of phosphorus (P) are studied for Si-implanted GaAs by photoluminescence and secondary-ion mass spectrometry. P coimplantation decreases SiAs acceptor intensity. At high temperatures rapid thermal annealing causes As loss, which favors the formation of the SiAs-VAs complex. Diffusion of Si towards the GaAs bulk is not caused by P coimplantation but rather by the presence of carbon.
Role of buffer layers for superconducting YBa2Cu3O7−x thin films on GaAs substrates
Authors: Jia Q. X. , Lee S. Y. , Anderson W. A. , Shaw D. T.
Published: July 2002

High-temperature superconducting YBa2Cu3O7−x (YBCO) thin films were deposited on GaAs substrates by laser ablation. A double-buffer layer of yttrium-stabilized ZrO2 (YSZ)/Si3N4 was used to nucleate YBCO but also to prevent the degradation of the GaAs during YBCO film deposition. Superconducting YBCO thin films with a highly c-axis orientation perpendicular to the substrate surface, zero-resistance temperature of 85.5 K, and critical current density of 1.9×103 and 1.3×104 A/cm2 at 77 and 50 K, respectively, have been achieved in our experiments. These values are believed to be the best results reported so far for YBCO on GaAs.
Transistor characteristics in a three-terminal structure having YBa2Cu3O7−x electrodes on an insulating SrTiO3 substrate
Authors: Yoshida Akira , Tamura Hirotaka , Takauchi Hideki , Hasuo Shinya
Published: July 2002

Transistor characteristics in which both voltage and current gains exceeded one, were observed at 4.2 K in a three-terminal superconducting structure. A high critical-temperature superconducting YBa2Cu3O7−x emitter and collector were fabricated on a high-permittivity insulating SrTiO3 dielectric with a back-contact base electrode. The three-terminal structures were constructed on 500-μm-thick (100) single-crystal SrTiO3 substrates with a relative permittivity of 2×104 at 4.2 K. YBa2Cu3O7−x films were deposited on chemically cleaned substrates by laser ablation and base leads were constructed of silver paste.
Excimer laser-ablated bismuth titanate thin films
Authors: Maffei N. , Krupanidhi S. B.
Published: July 2002

Bismuth titanate thin films were deposited by the excimer laser ablation technique. Process parameters such as substrate temperature, laser fluence, and gas pressure were investigated and correlated to the resulting film properties. Results suggest an intrinsic bombardment effect on the growing film. The permittivity and dissipation factor measured at 100 kHz were 150 and 0.01, respectively. The ferroelectric properties exhibited a dependence on film orientation and films with preferred c-axis orientation yielded fully saturated hysteresis loops with Pr=7 μC/cm2 and Ec=20 kV/cm.
Room-temperature epitaxial growth of Ag(110)/GaAs(100) films
Authors: Nason T. C. , You L. , Lu T.-M.
Published: July 2002

Thin Ag films were deposited in a partially ionized beam vacuum system on undoped GaAs(100) substrates at room temperature. The x-ray pole-figure technique was used to characterize the crystal orientation. The epitaxial relationship observed was Ag(110)/GaAs(100) with Ag[100]//GaAs[1̄10]. The epitaxy was achieved at a vacuum in the 10−6 Torr range with no in situ cleaning. The substrates were prepared only by a HF dip immediately prior to deposition.
Reflection-high-energy-electron-diffraction intensity oscillations of Si(111) during gas source molecular beam epitaxy
Authors: Liu W. K. , Mokler S. M. , Ohtani N. , Zhang J. , Joyce B. A.
Published: July 2002

Reflection-high-energy-electron-diffraction (RHEED) intensity oscillations were used to monitor Si(111) growth during gas source molecular beam epitaxy using disilane. Intensity oscillations were measured as a function of both substrate temperature and disilane flow rate. Within the substrate temperature range of 490–560 °C where growth proceeded two dimensionally, well-defined intensity oscillations corresponding to bilayer growth could be observed along the [21̄1̄] and [11̄0] azimuths. The oscillation frequencies were found to increase with increasing substrate temperature as well as disilane flow rate. At lower temperatures where no dissociative adsorption of disilane occurred, intensity oscillations were not observed. At higher temperatures, growth entered the step flow regime and the intensity oscillations were weak or absent.
Side gating in δ-doped quantum wires
Authors: Feng Y. , Thornton T. J. , Harris J. J. , Williams D.
Published: July 2002

We have used a side gating technique to vary the width of narrow wires made from δ-doped GaAs. The wires show pronounced quantum interference effects which can be used to determine the wire width and electron phase coherence length as a function of gate voltage. At zero gate bias the depletion from the etched surfaces is very small because of the high electron density and the electrical width of the wires is therefore only slightly smaller than the physical width.
pnp resonant tunneling light emitting transistor
Authors: Genoe J. , Van Hoof C. , Fobelets K. , Mertens R. , Borghs G.
Published: July 2002

A pnp bipolar resonant tunneling transistor is realized using a base consisting of an n-type modulation doped quantum-well layer next to a double-barrier tunneling structure. Electrons are injected from the quantum-well base layer into the tunneling structure, leading to quantum-well light emission when they recombine with holes from the emitter. This optical output, which is modulated by the base voltage, persists in the negative differential resistance region of the current-voltage characteristics where the hole current is in oscillation. This opens possibilities for using this transistor as a high frequency electro-optical heterodyne convertor.
Two-color GaAs/(AlGa)As quantum well infrared detector with voltage-tunable spectral sensitivity at 3–5 and 8–12 μm
Authors: Kheng K. , Ramsteiner M. , Schneider H. , Ralston J. D. , Fuchs F. , Koidl P.
Published: July 2002

We report on a novel GaAs:Si/(AlGa)As multiquantum well photodetector structure which exhibits photoresponse maxima in both the 8–12 and 3–5 μm spectral regions. The relative intensity of these maxima strongly depends on the bias voltage, demonstrating the potential of such a structure as a tunable two-color intersubband detector.
Scanning Hall probe microscopy
Authors: Chang A. M. , Hallen H. D. , Harriott L. , Hess H. F. , Kao H. L. , Kwo J. , Miller R. E. , Wolfe R. , van der Ziel J. , Chang T. Y.
Published: July 2002

We describe the implementation of a scanning Hall probe microscope of outstanding magnetic field sensitivity (∼0.1 G) and unprecedented spatial resolution (∼0.35 μm) to detect surface magnetic fields at close proximity to a sample. Our microscope combines the advantages of a submicron Hall probe fabricated on a GaAs/Al0.3Ga0.7As heterostructure chip and the scanning tunneling microscopy technique for precise positioning. We demonstrate its usefulness by imaging individual vortices in high Tc La1.85Sr0.15CuO4 films and superconducting networks, and magnetic bubble domains.
Low-gas-pressure sputtering by means of microwave-enhanced magnetron plasma excited by electron cyclotron resonance
Authors: Yoshida Yoshikazu
Published: July 2002

A sputtering source utilizing both electron cyclotron resonance (ECR) microwave and dc planar magnetron plasmas is described. Microwave power is introduced into the plasma by a coaxial-type cavity. The magnetron cathode is placed on the open end of the inner conductor. The ECR magnetic field is applied in the open end by magnetron configuration magnets. The microwave propagation from the surface of the plasma column produces additional gas ionization resulting in a denser plasma at constant voltage. The operation pressure of this source is one-hundredth as low as that of a conventional magnetron source. The deposition rate of Cu is more than 130 nm/min for an argon gas pressure of 8×10−5 Torr, and microwave and dc powers of 500 and 200 W, respectively. Measured deposition uniformity is ±4.5% within a 10 cm diam for a 15-cm diam target.
Shortfall of defect models for amorphous silicon solar cell performance
Authors: von Roedern Bolko
Published: July 2002

It is suggested that the prevailing models for the Staebler–Wronski effect are incorrect because they ignore the effects of charged dangling bonds. The degradation behavior of material parameters such as photoconductivity or midgap defect densities does not allow us to predict either the magnitude or the kinetic behavior of solar cell degradation.
High-quality two-dimensional electron system confined in an AlAs quantum well
Authors: Lay T. S. , Heremans J. J. , Suen Y. W. , Santos M. B. , Hirakawa K. , Shayegan M. , Zrenner A.
Published: July 2002

We report the fabrication and characterization of a high-quality two-dimensional electron system in the X-point valley of an AlAs quantum well. The modulation doped structure has a density of ns=2.5×1011 cm−2 and low-temperature mobility μ=3×104 cm2/V s. Cyclotron resonance data reveal an effective mass mc=0.46m0, indicating that the X-point conduction valleys with heavy in-plane mass are occupied. In the magnetotransport data, we observe quantum Hall states at consecutive integral Landau-level fillings (ν), implying that the degeneracy of these valleys is lifted. Our data at high magnetic fields show well-developed fractional quantum Hall states at ν=1/3 and 2/3 with a gap of 1/3Δ=1.3K for the ν=1/3 state at B≊30 T.
Nonlinear refractive-index and two photon-absorption near half the band gap in AlGaAs
Authors: Villeneuve Alain , Yang C. C. , Stegeman George I. , Lin Chen-Hui , Lin Hao-Hsiung
Published: July 2002

The wavelength dependence of the nonlinear refractive index and two-photon absorption coefficient near half the band gap was measured in an AlGaAs waveguide. The two photon figure of merit for efficient nonlinear optics in AlGaAs is shown to be quite favorable for photon energies less than one half the band gap.
Polarization insensitive semiconductor laser amplifiers with tensile strained InGaAsP/InGaAsP multiple quantum well structure
Authors: Joma M. , Horikawa H. , Xu C. Q. , Yamada K. , Katoh Y. , Kamijoh T.
Published: July 2002

Data on semiconductor laser amplifiers with a small tensile strain in the wells of multiple quantum well structures are presented. Semiconductor amplifiers with a small strain of 0.2% exhibit polarization insensitive characteristics with a signal gain of 15 dB in the 1.5 μm wavelength range. The enhancement of TM mode gain due to tensile strain is studied by measuring the dependence of amplified spontaneous emission spectra on device length and tensile strain.
Acceptor doping in ZnSe versus ZnTe
Authors: Laks David B. , Van de Walle Chris G. , Neumark G. F. , Pantelides Sokrates T.
Published: July 2002

It is a long-standing puzzle that ZnSe is difficult to dope p type, while ZnTe—which is very similar to ZnSe—is very easily doped p type. We report ab initio calculations which show that the solubilities of Li and Na acceptors are much greater in ZnTe than the solubilities of the same acceptors in ZnSe. We trace the origin of this difference to the bonding properties of the acceptors with the neighboring chalcogens. Our results also explain the experimentally observed dependence on dopant concentration of the dislocation density in p-type ZnSe epilayers grown on GaAs.
Epitaxial YBa2Cu3O7 growth on KTaO3 (001) single crystals
Authors: Prusseit W. , Boatner L. A. , Rytz D.
Published: July 2002

Epitaxial films of YBa2Cu3O7 have been grown on KTaO3 (100) single-crystal substrates by means of reactive thermal coevaporation at temperatures between 560 and 750 °C. The orientation of the YBa2Cu3O7 crystallographic c axis in these films was perpendicular to the substrate surface throughout the complete range of deposition temperatures even though the KTaO3 lattice constant represents a better match to the YBa2Cu3O7 c axis than to the a and b axes. Since the nucleation and growth of YBa2Cu3O7 films are known to be relatively sensitive to the formation of a-axis-oriented grains at imperfections on the substrate material, an investigation of the influence of the substrate surface finish on the film properties was carried out. Using substrates with appropriately prepared surfaces, YBa2Cu3O7 films exhibited a high degree of crystalline perfection, zero resistance at temperatures of 89 K and critical current densities up to 3×106 A/cm2.
Single-domain surface layers formed by heat treatment of proton-exchanged multidomain LiTaO3 crystals
Authors: Nakamura Kiyoshi , Tourlog Ailie
Published: July 2002

A space charge field model to explain the mechanism of a ferroelectric domain inversion phenomenon in proton-exchanged LiTaO3 has been proposed. This model predicts that single-domain layers could be formed on both surfaces of a proton-exchanged multidomain LiTaO3 plate without application of external electric fields. Experimental results demonstrating this prediction are reported. It is shown that the single-domain surface layers formed had spontaneous polarizations directed outward from the plate. This suggests the existence of a space charge field near the surfaces.
150% magnetoresistance in sputtered Fe/Cr(100) superlattices
Authors: Fullerton Eric E. , Conover M. J. , Mattson J. E. , Sowers C. H. , Bader S. D.
Published: July 2002

We report the epitaxial growth of Fe/Cr(100) superlattices onto MgO(100) single-crystal substrates by magnetron sputtering. Superlattices that are epitaxially oriented within 1° both in-plane and out-of-plane with the MgO substrate are achieved by initial growth of a Cr base layer at high temperature. Multiple superlattice diffraction peaks are observed in the low- and high-angle x-ray diffraction spectra. Three peaks are observed in the magnetoresistance associated with the oscillatory antiferromagnetic interlayer magnetic coupling as a function of Cr thickness. A maximum magnetoresistance of 150% at 4.2 K (28% at room temperature) is observed for a Cr(100 Å)/[Fe(14 Å)/Cr(8 Å)]50 superlattice.
Pulsed laser deposition of Ga-La-S chalcogenide glass thin film optical waveguides
Authors: Youden K. E. , Grevatt T. , Eason R. W. , Rutt H. N. , Deol R. S. , Wylangowski G.
Published: July 2002

Thin film optical waveguides of the chalcogenide glass Ga-La-S have been deposited on substrates of CaF2 and microscope glass by the technique of pulsed laser deposition. The chalcogenide properties of photobleaching, photodoping, and photoinduced refractive index changes have been observed and preliminary experiments carried out. The refractive index and thickness of the layer were verified using a waveguide ‘‘dark mode’’ analysis technique.
Comparison of the picosecond characteristics of silicon and silicon-on-sapphire metal-semiconductor-metal photodiodes
Authors: Wang Chia-Chi , Alexandrou Sotiris , Jacobs-Perkins Douglas , Hsiang Thomas Y.
Published: July 2002

The picosecond characteristics of silicon-based metal-semiconductor-metal (MSM) diodes with submicrometer finger spacing and width were studied. Diodes made on both bulk silicon and silicon-on-sapphire (SOS) substrates were measured by a subpicosecond electro-optic sampling system. The response of bulk-silicon MSM diodes was strongly dependent on the wavelength of the excitation light because of the change in penetration depth. The response of SOS diodes, on the other hand, had a weak dependence on wavelength since the thickness of the silicon layer limits the depth of photogenerated carriers. The response of a 200 nm SOS diode has a full-width at half-maximum of 4.5 and 5.7 ps with blue- and red-light excitations. The external quantum efficiency of SOS diodes was also determined at several selected wavelengths.
Large scale synthesis of single-shell carbon nanotubes
Authors: Lin X. , Wang X. K. , Dravid V. P. , Chang R. P. H. , Ketterson J. B.
Published: July 2002

We report on a novel technique for synthesizing large quantities of single-shell carbon nanotubes in a dc arc with a composite anode of graphite and copper. Based on systematic studies involving a varying diameter and distribution of copper rods inside the graphite anode, we have correlated the presence of copper to the formation of monolayer buckytubes. We speculate that copper atoms in the discharge disrupt the orderly formation of multilayer buckytubes observed in earlier experiments.
Atomic graphoepitaxy: A growth model for c-axis in-plane-aligned, a-axis oriented YBa2Cu3Ox thin films
Authors: Miyazawa Shintaro , Mukaida Masashi
Published: July 2002

The simple growth model of pure a-axis-oriented YBa2Cu3Ox thin films on (100)-oriented SrLaGaO4 substrates of a K2NiF4-type structure is proposed. This is called ‘‘atomic graphoepitaxy.’’ The model is based on an atomic-scale geometry of the (100) surface of K2NiF4-type substrates, which is characterized by atomic-scale grooves made of oxygen octahedra running along the 〈010〉 direction. These grooves are assumed to act as preferential nucleation sites of c-axis in-plane-aligned, a-axis-oriented YBa2Cu3Ox. Based on this hypothesis, the pure a-axis-oriented thin films are successfully obtained on (100)-oriented Nd2CuO4 substrates of K2NiF4-type structure.
High-temperature stable Ir-Al/n-GaAs Schottky diodes
Authors: Lalinský T. , Gregušová D. , Mozolová Ž. , Breza J. , Vogrinčič P.
Published: July 2002

We report on the excellent thermal stability of Ir-Al/GaAs Schottky contact based on sequentially evaporated Ir-Al bimetallic system with an aluminum concentration of approximately 25 at. %. The contact system is stable up to 950 °C for 10 s (capless rapid thermal annealing) and exhibits an enhancement of the barrier height with the temperature of annealing.
Epitaxial lateral overgrowth of silicon by chemical vapor deposition on ultrathin oxide layers
Authors: Shih Y. C. , Liu J. B. , Oldham W. G. , Gronsky R.
Published: July 2002

Selective epitaxial growth followed by epitaxial lateral overgrowth (ELO) of silicon through windows in SiO2 in a hot-wall low-pressure chemical vapor deposition system has been used to fabricate silicon-on-insulator (SOI) structures. By careful ex situ and in situ surface cleaning and low-temperature processing, 2.5-μm-thick single-crystal silicon films have been successfully deposited over oxide layers as thin as 35 Å. Dislocation densities in these SOI films over thin oxides are higher than those found in SOI films deposited on thicker oxides. Nucleation of dislocations in the epitaxially grown film is attributed to pinhole expansion in the ultrathin oxide layers during ex situ cleaning, prebake treatment, or ELO processing. An unusual crystallographic defect with attributes of a microtwin-stacking fault complex are also observed in the ELO film appearing over thin oxide layers. A model is proposed to explain this class of defect structure and its formation mechanism.
Low-loss strain induced optical waveguides in strontium barium niobate (Sr0.6Ba0.4Nb2O6) at 1.3 μm wavelength
Authors: Marx J. M. , Tang Z. , Eknoyan O. , Taylor H. F. , Neurgaonkar R. R.
Published: July 2002

Low-loss optical waveguides have been produced in z-cut Sr0.6Ba0.4Nb2O6 (SBN:60) and electro-optic modulation has been demonstrated at a wavelength of 1.3 μm. The refractive index increase responsible for waveguiding results from a strain produced by a SiO2 film which has been deposited on the surface of the substrate at 320 °C. The waveguides are formed in the crystal by dry etching of channels in the strain film. The resulting optical waveguides support both polarizations. Propagation loss values of 0.7 dB/cm for TM polarization and 1.6 dB/cm for TE polarization were measured. Electro-optic modulation up to 22 MHz was performed on repoled samples using coplanar electrodes.
Q-band loop-gap resonator
Authors: Froncisz W. , Oles T. , Hyde James S.
Published: July 2002

The upper frequency for loop-gap resonators intended for use in electron-spin-resonance spectroscopy has been extended to Q band (35 GHz). A practical structure is described containing sample support, frequency tuning, and variable coupling. A typical sample volume is 39 nL. High-energy densities (15 GW−1/2) were achieved. As found previously at X band, Q-band loop-gap resonators permit observation of the dispersion with minimal demodulation of phase noise originating in the klystron. Theoretical calculations of the resonant frequency, Q, and the filling factor are found to be in good agreement with experiment.
Development of a high proton yield plasma source with multipole confinement and a magnetic filter
Authors: Holmes A. J. T. , Green T. S. , Newman A. F.
Published: July 2002

Proton yields in magnetic multipole sources can be increased by the creation of a magnetic ‘‘filter’’ within the discharge volume, although this may introduce nonuniformity in the plasma. We have investigated the properties of a filter which can satisfy the requirements of plasma uniformity and discharge electrical efficiency and creates a proton yield of 87% when a 60-A beam is extracted at 80 keV. A model describing the behavior of the filter is also described.
Design and characteristics of SIPPI, an ion source for a long-distance SIMS analysis of the Phobos surface
Authors: Pomathiod L. , Michau J. L. , Hamelin M.
Published: July 2002

The design, construction, and operating characteristics of SIPPI, a 2-mA, 3-keV krypton ion source, are described. This instrument will be part of a remote chemical analysis experiment of the surface of the Martian moon, Phobos. The composition of the surface will be evaluated at a distance of about 50 m by the mass analysis of ions ejected by the primary ion beam delivered by SIPPI. This long distance secondary ion mass spectrometry experiment is called DION and will be part of the Soviet space mission PHOBOS. The flight over Phobos is planned for the beginning of 1989. The ion source is based on a surface-wave-produced plasma from which the ions are extracted by means of a grid system. The ion beam is space-charge neutralized by the electrons emitted by heated tungsten filaments. SIPPI is composed of the ion source itself, its gas feed circuit, the power supplies for the discharge, the extraction system and neutralizing filaments, and the control and telemetry electronics. The dimensions of SIPPI are 45×32×13 cm; its mass is 10.7 kg.
A precision Bond method with SR
Authors: Ando M. , Hagashi Y. , Usuda K. , Yasuami S. , Kawata H.
Published: July 2002

A system for a very high precision absolute lattice spacing measurement has been developed. It employs, in principle, a bond method using a highly collimated and a very narrow bandwidth beam available from a monolithic (+, +) monochromator. Owing to the temperature stabilization of the hutch, where the equipment is installed, it has routinely achieved a precision of 2 parts in 106 in lattice spacing measurements.
Lateral force curve for atomic force/lateral force microscope calibration
Authors: Fujisawa Satoru , Kishi Eigo , Sugawara Yasuhiro , Morita Seizo
Published: July 2002

In this letter, a method to calibrate sensitivity for the three-dimensional displacement of X, Y, and Z directions by using the novel force curve, namely lateral force curve, as well as vertical force curve in atomic force/lateral force microscope (AFM/LFM) measurement is described. Furthermore, from quantized friction measurement based on the two-dimensional stick–slip model, it is experimentally confirmed that this lateral force curve calibration is reasonable.
Infrared thermography system on DIII-D
Authors: Petrie T. W. , Hill D. N. , Baptista J. , Brown M.
Published: July 2002

Six infrared cameras measure temperature changes on the protective graphite armor inside the DIII-D vacuum vessel. Simultaneous time-dependent temperature measurements are made on armor tiles located on the centerpost and divertor regions, and on both outboard limiters. The nearly complete poloidal coverage is useful in measuring both the plasma heat flux distributions inside the vessel and the plasma power balance. Spatial resolution of each camera system is ≲1 cm, while the minimum resolvable time is 125 μs. Data from the IR TV systems are recorded on video tape, and are post-processed serially, using an image processor with an AT-compatible microcomputer. The processing system controls all VCRs, interprets DIII-D timing pulses, digitizes video data in the predetermined regions of interest, averages digitized signals to reduce noise, and constructs data files which are then stored as part of the permanent shot record.
Reflectometer density fluctuation measurements on DIII-D
Authors: Doyle E. J. , Lehecka T. , Luhmann N. C. , Peebles W. A. , Philipona R. , Burrell K. H. , Groebner R. J. , Matsumoto H. , Osborne T. H. ,   The DIII-D Group
Published: July 2002

An O-mode, homodyne reflectometer system utilizing seven discrete channels spanning 15–75 GHz is in operation on DIII-D. A frequency-tunable X-mode system is also used to take fluctuation data from reflecting layers lying between those of the fixed frequency, O-mode system. In order to demonstrate the power and flexibility of this diagnostic, results are presented from several different plasma regimes, including L to H transitions, ELMS, and high beta operation. One specific example is that at all L–H transitions, high-frequency (≥50 kHz) fluctuations are dramatically suppressed in a localized region near the edge of the plasma on a timescale of ≊100 μs.
Characterization of multilayer reflectors and position sensitive detectors in the 45–300 Å region
Authors: Yamashita K. , Takahashi S. , Kitamoto S. , Takahama S. , Tamura K. , Hatsukade I. , Sakurai M. , Watanabe M. , Yamaguchi A. , Nagata H. , Ohtani M.
Published: July 2002

Multilayer reflectors and position sensitive detectors have been developed in constructing imaging optical systems in the 45–300 Å region. Molybdenum-silicon (2d=140 Å, N=20) and nickel–carbon (2d=100 Å, N=20) multilayers were deposited on a spherical mirror (25 cm in diameter) for the normal incidence and on a segment of paraboloidal mirror (20 cm×10 cm) for 30° grazing incidence. Their optical characteristics were evaluated by using characteristic x rays and monochromatized synchrotron radiation in the 45–300 Å region. A position sensitive detector is made of a tandem microchannel plate (MCP) with a CsI photocathode and resistive plate, which is placed at the focal plane of each mirror. The detection efficiency and position resolution were measured by using characteristic x rays of CKα and monochromatized synchrotron radiation in the 45–200 Å region.
The theory of oscillator-coupled magnetic resonance with potential applications to molecular imaging
Authors: Sidles John A. , Garbini Joseph L. , Drobny Gary P.
Published: July 2002

This article describes systems in which the precession of a single particle spin is magnetically coupled to the excitation of an oscillator. The behavior of such systems resembles that of a ‘‘folded’’ Stern–Gerlach experiment, in which the linear spatial trajectory of the original Stern–Gerlach experiment is folded into the cyclic trajectory of an oscillator. Both quantum and semiclassical solutions to the equations of motion are derived. The results encompass any kind of oscillator which couples to a magnetic field. Examples include mechanical cantilevers with a magnetic source affixed to them, as well as inductor-capacitor resonant circuits. One potential application of oscillator-coupled magnetic resonance is the imaging of biological molecules. Some design issues relevant to molecular imaging are discussed.
Thermally stimulated current spectroscopy: Experimental techniques for the investigation of silicon detectors
Authors: Baldini Alberto , Bruzzi Mara
Published: July 2002

Radiation damage of silicon detectors can be investigated by means of several techniques. In a high-luminosity environment the thermally stimulated current (TSC) spectroscopy proves to be a good experimental method in order to analyze the deep defects induced by irradiation. Two different experimental systems for TSC spectroscopy, developed at the Energy Engineering Department of Florence, are examined in detail. The two systems differ in the cryogenic agent used to cool the silicon detectors: the first one utilizes a helium-gas closed-cycle Gifford–McMahon two-stage cryogenerator; the second one utilizes the helium vapors present inside a liquid helium Dewar. In the two systems two different heating procedures are used in order to perform the thermal scans necessary to carry on the TSC measurements: in the former system an electric heater performs the thermal scan, while in the latter one the heating process is achieved utilizing the temperature variation of the helium vapors inside the Dewar as a function of the height over the surface of the boiling helium. The main advantage of the electric heater is the possibility of obtaining heating rates β as high as 2.0 K/s, while the helium vapors ensure an excellent temperature matching between the temperature sensor and the sample (with the drawback of lower heating rates). The two methods used to get information by means of TSC spectroscopy, (variation of β and delayed heating) are briefly described together with an evaluation of the sensitivity of the measurement (no difference has been made between the two systems because the use of a different cryogenic agent does not affect sensitivity). Both systems proved satisfactory, even if the ease of operation of the helium gas makes it preferable in the temperature range examined by our measurements (120–200 K).
An automated research facility for measuring thermoluminescence emission spectra using an optical multichannel analyzer
Authors: Piters T. M. , Meulemans W. H. , Bos A. J. J.
Published: July 2002

A facility for research into the mechanism of thermoluminescence (TL) is described. The facility comprises three units: an annealing oven, an irradiator, and a TL-emission spectrometer. Crystals or hot-pressed chips can be moved from and to the mentioned units by an automated sample changer. All units operate automatically and are controlled by a personal computer program. The spectrometer is based on a dispersive grating and an intensified diode array (512 active elements) and covers the 200–800-nm wavelength range. The wavelength resolution of the spectrometer is 6 nm when a 25-μm-wide entrance slit is used and 29 nm when a 1-mm-wide entrance slit is used. The sensitive spectrometer could measure emission spectra of CaSO4:Dy (TLD-200) irradiated at an absorbed dose as low as 3 mGy at a signal-to-noise ratio of 10:1 for LiF:Mg,Ti (TLD-100) this ratio was obtained at 75 mGy. A detailed description is given how measured data can be related to spectra predicted by a model, taking into account all system aberrations. Spectra of LiF:Mg,Ti (TLD-100) irradiated to an absorbed dose of 5 Gy are analyzed according to the Franck–Condon model for light emission. Two emission bands with peak energies of 3.01 and 2.60 eV at 463 K have been found.
Controllable pulse duration of a XeCl laser
Authors: Kim Dong Hwan , Chu Hong , Jhon Young Min , Choi Sang Sam
Published: July 2002

Long optical pulses have been generated in a XeCl excimer laser by using a simple capacitor-transfer discharge circuit consisting of storage capacitors charged at 26 kV and discharged through the electrodes, tightly coupled to the variable small peaking capacitors. By adjusting the [HCl] concentration and capacitance ratios, the typical pulse duration (20 ns) is stretched up to 150 ns (full width at half-maximum). The transfer behaviors of the pulse duration from short pulse to long pulse are presented and analyzed extensively by measuring the discharge voltage profile, output energy, overall efficiency, optical waveform, and pulse duration, as functions of [HCl] concentration and capacitance ratios.
Fabrication of large arrays of metallic nanowires on V-grooved substrates
Authors: Jorritsma J. , Gijs M. A. M. , Schönenberger C. , Stienen J. G. H.
Published: July 2002

Large arrays of Au nanowires down to 50 nm in width are fabricated on V-grooved InP substrates. Holographic laser interference exposure of photoresist and anisotropic etching are used to pattern the surface of InP(001) substrates into V-shaped grooves with a 200 nm period. Next, the patterned substrates are covered with a thin Au film, which is subsequently structured into nanowires using a well controlled wet etching process. Initial characterization confirms that the wires are electrically continuous.
Air operating atomic force-scanning tunneling microscope suitable to study semiconductors, metals, and biological samples
Authors: Cricenti Antonio , Generosi Renato
Published: July 2002

A scanning tunneling (STM)-atomic force microscope (AFM) operating at ambient pressure is described. A sound-isolated chamber contains the STM-AFM unit; the chamber can be evacuated or filled with inert gas, after the sample and tip (lever) are loaded, in order to reduce contamination on the sample. The STM-AFM unit consists of two separable cylindrical supports whose lower one contains the sample holder mounted on top of a piezoelectric scanner (movements 6×6×3 μm) that is contained in a motor controlled x–y–z stage (movements 8×8×1 mm). An I/V converter preamplifier for STM operation and a laser deflection circuit for AFM operation are separately mounted inside two different top cylinders. The STM top cylinder can be changed with the AFM one without removing the sample thus giving the possibility of looking at the same sample with STM and AFM. An optical microscope that can reach 120 enlargements allows us to position the tip or the lever on particular regions of the sample through the motor drives. A completely digitized feedback circuit allows fast sample-tip (lever) approach and simultaneous acquisition of constant force and lateral force images, for AFM operation, and constant current and barrier height ones, for STM operation. The same platinum grating has been imaged with STM and AFM. InGaAs wires onto a GaAs substrate and uncoated neurons have been imaged with AFM.
Reflectometer measurements of density fluctuations in tokamak plasmas (invited)
Authors: Nazikian R. , Mazzucato E.
Published: July 2002

Many anomalous features observed in reflectometer measurements of turbulent fluctuations in tokamak plasmas, such as loss of coherent reflection, large amplitude fluctuations, large angular divergence of the reflected waves, and correlation lengths of the order of the free-space wavelength of the probe beam, can be explained by modeling the plasma fluctuations as a poloidally varying random phase grating located at the cutoff with a phase magnitude given by 1D geometric optics. A key result of this analysis is that the turbulence spectrum cannot be inferred from phase measurements when large amplitude fluctuations are observed at the receiver. However, the turbulence spectrum may still be recovered from phase measurements by use of imaging optics and wide angle phase sensitive receivers.
Vertical chirp in grating pair stretcher and compressor
Authors: Zhang Zhigang , Harayama Sayaka , Yagi Takashi , Arisawa Takashi
Published: July 2002

We present a model to evaluate the vertical spectrum distribution of a laser beam in a grating pair stretcher or compressor at off-horizontal plane incidence. The vertical spectrum displacement or vertical chirp in the output pulse has been calculated and shown quantitatively as functions of the off-horizontal plane incident angle and the grating groove density. The resulting dispersion errors compared with that at horizontal incidence are also shown.
Degradation mechanism of AlGaAs/GaAs laser diodes grown on Si substrates
Authors: Egawa T. , Hasegawa Y. , Jimbo T. , Umeno M.
Published: July 2002

We have studied the rapid degradation of the AlGaAs/GaAs single quantum well laser diodes on Si substrates grown by metalorganic chemical vapor deposition. The dislocations propagate at velocities up to ∼75 μm/h along 〈100〉 and ∼20 μm/h along 〈110〉, which cause an increase in threshold current and a decrease in differential quantum efficiency. The degraded current–voltage characteristic resulted from the defect-assisted impurity diffusion. The degradation process occurs very rapidly due to the presence of a high density of defects and thermally induced strain.