bluuebunny/crossref_metadata_2025 huggingface dataset:
Epitaxial growth and properties of YBa2Cu3O7−δ/NdGaO3/YBa2Cu3O7−δ trilayer structures
Authors: Boikov Yu. , Brorsson G. , Claeson T. , Ivanov Z. G.
Published: July 2002

We have used laser deposition to make YBa2Cu3O7−δ/NdGaO3/YBa2Cu3O7−δ trilayer structures. NdGaO3 films grow epitaxially on well lattice-matched substrates, like SrTiO3 (100), and on c-axis oriented YBa2Cu3O7−δ films. Epitaxial YBa2Cu3O7−δ films were grown on top of the NdGaO3 films, and there was no significant difference in critical temperature between top and bottom layers of the trilayer structures. The resistivity of a 300-nm-thick NdGaO3 interlayer was as high as 108 Ω cm at 300 K.
Superconducting YBa2Cu3O7−δ thin films on Si (100) substrates with CoSi2 buffer layers by an in situ pulsed laser evaporation method
Authors: Kumar Ashok , Narayan J.
Published: July 2002

We have prepared high-quality c-axis oriented superconducting YBa2Cu3O7−δ thin films on Si (100) substrates with CoSi2 buffer layers by in situ pulsed laser ablation processing. The films were characterized by x-ray diffraction, four-point ac electrical resistivity, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques. YBa2Cu3O7−δ films were found to be textured with c axis perpendicular to the substrate. A plot of normalized resistance against temperature exhibited a metallic behavior followed by an onset superconducting transition at 91 K with zero resistance temperature (Tc0) of 83 K. Cross-sectioned TEM results showed quite smooth interface between CoSi2 and Si with little interdiffusion; however, a reacted zone was observed between CoSi2 and YBa2Cu3O7−δ layers.
Reactive ion etching of copper in SiCl4-based plasmas
Authors: Howard B. J. , Steinbrüchel Ch.
Published: July 2002

Copper may become an alternative to aluminum as an interconnect material in ultralarge scale integration multilevel metallization schemes if it is possible to pattern Cu by dry etching in a manufacturable process. Here we report results on the reactive ion etching of Cu in SiCl4/Ar and SiCl4/N2 plasmas. Etching has been investigated as a function of gas composition, pressure, and substrate temperature. We have obtained etch rates as high as 850 Å/min using SiCl4/N2 and a substrate temperature of ∼ 220 °C, with excellent etch selectivity of Cu relative to polyimide and SiO2. We demonstrate that it is feasible to pattern Cu anisotropically using polyimide as a high-temperature etch mask.
Rayleigh backscattering measurement of single-mode fibers by low coherence optical time-domain reflectometer with 14 μm spatial resolution
Authors: Takada Kazumasa , Yukimatsu Ken-ichi , Kobayashi Masaru , Noda Juichi
Published: July 2002

An optical time-domain reflectometer (OTDR) with −136 dB minimum detectable reflectivity and 14 μm spatial resolution is developed based on low coherence interference. The high sensitivity was accomplished by using a high-power superluminescent diode module with a 1.5 mW fiber output and a new system configuration, both for effectively operating the balanced heterodyne detection. The reflectivity of −136 dB is only 6 dB above the shot noise limit. The first observation of 1.3 μm wavelength Rayleigh backscattering in single-mode fibers was successfully made by the OTDR with a 17 dB dynamic range and 14 μm spatial resolution.
Y1Ba2Cu3O7−x and LaAlO3 composite thin films by off-axis magnetron sputtering
Authors: Cukauskas Edward J. , Allen Laura H. , Holm R. T. , Sherrill Gregory K.
Published: July 2002

Thin-film composites of co-sputtered Y1Ba2Cu3O7−x and LaAlO3 have been deposited by off-axis magnetron sputtering. Scanning electron microscopy (SEM) and x-ray diffraction studies suggest that LaAlO3 precipitates along the grain boundaries of the Y1Ba2Cu3O7−x grains. The normal state conductivity, transition temperature, and critical current density systematically decreased with increasing LaAlO3 composition, consistent with a decrease in the coupling between Y1Ba2Cu3O7−x grains. Inductive transition widths were only a few degrees wide for all LaAlO3 compositions, indicating homogeneous materials. Initial photoresponse measurements show bolometric behavior near Tc and increased response for greater LaAlO3 compositions.
Size dependence of optical nonlinearity of CdSSe microcrystallites doped in glass
Authors: Shinojima Hiroyuki , Yumoto Junji , Uesugi Naoshi
Published: July 2002

This paper investigates the size dependence of the effective nonlinear cross section σeff and the carrier recombination time on the size of CdS0.12Se0.88 microcrystallites with average radii of 10, 30, 50, and 100 Å by degenerate four-wave mixing (DFWM) experiments. The decay curves of the DFWM signal as a function of the probe delay time have fast and slow components. As the microcrystallite size decreases, the fast component becomes dominant and a carrier recombination time of 2 ps was observed in the 10-Å microcrystallites. The diffraction efficiency of DFWM is almost the same for all microcrystallites, that is, σeff has a weak size dependence. Smaller microcrystallites show smaller magnitudes of the third-order nonlinear susceptibility ‖χ(3)‖, which is calculated from the measured effective nonlinear cross section and the carrier recombination time.
Reproducible growth of high quality YBa2Cu3O7−x film on (100) MgO with a SrTiO3 buffer layer by pulsed laser deposition
Authors: Cheung Jeffrey T. , Gergis Isoris , James M. , DeWames Roger E.
Published: July 2002

Epitaxial YBa2Cu3O7−x(YBCO) films were grown on SrTiO3-buffered (100) MgO substrates by pulsed laser deposition. The SrTiO3 layer of about 500 Å thick serves a dual purpose to provide a better lattice match to the YBCO films as well as a diffusion barrier to prevent interaction between YBCO and MgO. These YBCO films exhibit excellent structural, electrical, and microwave properties with Tc≳89 K and Tc=2.9×106 A/cm2 at 77 K (1×106A/cm2 at 84 K). X-ray pole figure measurements showed that over 99.92% of the volume fraction of the c-axis oriented film has the a-b axis aligned parallel to the [010] and [001] direction of the substrate.
GaAs/AlGaAs superlattice miniband detector with 14.5 μm peak response
Authors: Bandara K. M. S. V. , Choe J.-W. , Francombe M. H. , Perera A. G. U. , Lin Y. F.
Published: July 2002

Extended long wavelength infrared detection with a miniband-type AlGaAs/GaAs superlattice structure is reported. The experimental response band of the detector is peaked near 14.5 μm in good agreement with the theoretical response, provided that electron-electron interactions are taken into account. The detector operates at a low bias voltage, which could lead to important advantages in application to IR focal plane arrays.
Thermal quenching of Er3+-related luminescence in In1−xGaxP
Authors: Neuhalfen A. J. , Wessels B. W.
Published: July 2002

Thermal quenching of the characteristic intracenter luminescence from trivalent Er ions in In1−xGaxP layers was investigated. The Er-doped InGaP alloys were prepared by metalorganic vapor phase epitaxy with compositions ranging from x=0 to 0.31. A thermally activated luminescence quenching was observed with an activation energy that depended on the alloy composition. From measurements of the thermal quenching of the photoluminescence, the energy level of an erbium-related trapping center in the alloys was determined. The variation of the position of the Er-related energy level as a function of alloy composition is explained in terms of a vacuum-referred binding energy model.
Excimer laser ablated strontium titanate thin films for dynamic random access memory applications
Authors: Roy D. , Peng C. J. , Krupanidhi S. B.
Published: July 2002

Thin films of SrTiO3 were deposited on platinum coated silicon and bare silicon by excimer laser (248 nm) ablation at 400 and 500 °C or ex situ crystallized. Films deposited at 500 °C showed good crystallinity and were characterized for dielectric constant, dielectric loss, leakage current and C-V characteristics. The films showed a dielectric constant of 240, a dissipation factor of 0.02, a leakage current of 2×10−9 A/cm2, and a charge storage density of 42 fC/μm2 at a bias of 5 V. The C-V behavior of both metal-insulator-metal (MIM) and metal-insulator- semiconductor (MIS) structures indicated bulk dielectric permittivity in the accumulation region and also good Si/SrTiO3 interfaces.
Two-dimensional exciton dynamics in InGaAs/GaAs quantum wells
Authors: Takahashi Yutaka , Owa Soichi , Kano Satoru S. , Muraki Koji , Fukatsu Susumi , Shiraki Yasuhiro , Ito Ryoichi
Published: July 2002

We have investigated the exciton dynamics in InGaAs/GaAs single quantum wells using time-resolved photoluminescence spectroscopy. The temperature dependence of the decay time shows that the scattering rate of two-dimensional excitons is reduced in the narrower wells compared with that of AlGaAs/GaAs quantum wells. The results suggest the dominant contribution of the alloy disorder scattering to the exciton scattering processes over the interface roughness scattering.
Atomic probe imaging of β-SiC thin films grown on (100) Si
Authors: Steckl A. J. , Mogren S. A. , Roth M. W. , Li J. P.
Published: July 2002

Atomic-scale imaging has been achieved on β-SiC surfaces using scanning tunneling microscopy in air. SiC films were grown on Si (100) substrates by chemical vapor deposition using the carbonization reaction of the surface with C3H8, followed (for films thicker than 100 nm) by the reaction of C3H8 and SiH4. For a relatively thick SiC (∼6 μm) film, the average nearest-neighbor surface atomic spacing measured was 3.09 Å, which is very close to the nominal value of 3.08 Å. Several of the thinner (<100 nm) SiC films exhibited significantly larger atomic spacings, indicating the strong effect of the larger atomic spacing (nominally 3.84 Å) of the Si substrate.
Laser-assisted organometallic chemical vapor deposition of films of rhodium and iridium
Authors: Cohan Judson S. , Yuan Haojie , Williams R. Stanley , Zink Jeffrey I.
Published: July 2002

High purity (less than 1% carbon) thin films of rhodium and iridium metal have been obtained by laser-assisted organometallic chemical vapor deposition. Gaseous (η5-C5H5)M(C2H4)2 (M=Rh,Ir) was the organometallic precursor. Depositions were carried out in an atmosphere of He and H2 at room temperature and atmospheric pressure. Wavelength dependence studies of the rhodium precursor have shown that only irradiation into the compound’s charge transfer band causes deposition. Deposits can also be obtained thermally. The films were analyzed by x-ray diffraction and x-ray photoelectron spectroscopy.
C60 photoluminescence spectra related to gas adsorption
Authors: Zhao Tienan , Liu Jinqing , Li Yuliang , Zhu Daoben
Published: July 2002

The influence of surrounding gas pressure upon PL spectra of C60 is observed. The relationship between intensity of PL spectra and pressure agrees well with the Langmuir formula of a monomolecular adsorption layer. This phenomenon is attributed to the fact that the disturbance of molecules adsorbed on C60 lowers the symmetry of C60 and reduces the inhibition of the electronic transition, hence influencing PL emission.
Metamorphic In0.3Ga0.7As/In0.29Al0.71As layer on GaAs: A new structure for high performance high electron mobility transistor realization
Authors: Win P. , Druelle Y. , Cappy A. , Cordier Y. , Favre J. , Bouillet C.
Published: July 2002

A new high electron mobility transistor (HEMT) using InAlAs/InGaAs grown on GaAs has been successfully realized. This structure, with an In content close to 30%, presents several advantages over conventional pseudomorphic HEMT on GaAs and lattice matched HEMT on InP. To accommodate the mismatch between the active layer and the GaAs substrate, a metamorphic buffer has been grown. High electron mobility with high two-dimensional electron gas density (20 700 cm2/V s with 4×1012 cm−2) and high Schottky barrier quality (Vb=0.68 V with η=1.1) have been obtained. A 3 μm gate length device has shown intrinsic transconductance as high as 530 mS/mm.
Laser-deposited PrGaO3 films on SrTiO3 substrates and in YBa2Cu3O7/PrGaO3/YBa2Cu3O7 trilayers
Authors: Brorsson G. , Nilsson P. Å. , Olsson E. , Wang S. Z. , Claeson T. , Löfgren M.
Published: July 2002

PrGaO3 films were successfully grown by laser deposition at temperatures between 730 and 785 °C. The minimum full width at half maximum value of the (004) x-ray diffraction peak was 0.14°, for films deposited on SrTiO3 substrates at 760 °C. The optimum temperature for deposition of PrGaO3 in YBa2Cu3O7/PrGaO3/YBa2Cu3O7 trilayers was found to be 760 °C. Three distinct layers were observed, and the PrGaO3 exhibited two orientations with respect to the c-axis oriented bottom layer; either the [001] or the [110] direction parallel to the YBa2Cu3O7 c axis. Two orthogonal in-plane orientations were observed for each of these cases. The highest resistivity (at 100 K) of the PrGaO3 layer was 105 Ω cm. Considerable interaction occurred between the PrGaO3 and the YBa2Cu3O7 bottom layer at 785 °C, where the two bottom layers deteriorated.
Chiral thin solid films: Method of deposition and applications
Authors: Azzam R. M. A.
Published: July 2002

Chiral thin solid films (CTSFs) can be deposited on a solid substrate in vacuum by letting a vapor stream of film material impinge on the substrate at oblique incidence and rotating the substrate during deposition. The direction of substrate rotation determines the handedness of the resulting helical structure which resembles that of a cholesteric or twisted-nematic liquid crystal layer. CTSFs are useful in making new optical rotators and beam splitters that separate the orthogonal circular polarization components of light. A quadrant-detector ellipsometer that uses chiral and achiral obliquely deposited thin films is described for measuring the state of polarization of light.
Mechanism of chemical erosion of sputter-deposited C:H films
Authors: Schenk A. , Biener J. , Winter B. , Lutterloh C. , Schubert U. A. , Küppers J.
Published: July 2002

The mechanism of thermally activated chemical erosion of sputter-deposited C:H films of a few atomic layer thickness is investigated using thermal desorption spectroscopy. Methane, CH3 radicals, and various C2Hj species of molecular and radical nature desorb as gaseous products above 600 K competitively to H2. C-CiHj bond breaking is determined to be the rate limiting step of hydrocarbon production. The reaction is of first order with respect to CiHj precursors in the films with a distribution of activation energies, 56±5 kcal/mol for methane production. CH3 radical desorption occurs predominantly from the very surface of the C:H films.
Effect of proton exchange on the nonlinear optical properties of LiNbO3 and LiTaO3
Authors: Hsu Wei-Yung , Willand Craig S. , Gopalan Venkatraman , Gupta Mool C.
Published: July 2002

The effect of proton exchange carried out using benzoic and pyrophosphoric acid on the nonlinear optical coefficient (d) of LiNbO3 and LiTaO3 was studied using a second-harmonic generation reflectance technique. Significant degradation in the d coefficient of LiNbO3 and LiTaO3 was observed as a result of proton exchange with either benzoic or pyrophosphoric acid under the conditions studied. Some recovery only in the short time proton-exchanged sample (0.5 h at 180 °C) of LiNbO3 was observed under thermal annealing at 350 °C for 1 h. Results of in situ measurement of second-harmonic signal recovery under thermal annealing are reported. Results are also presented on theoretical and experimental variations of second-harmonic generation intensity with an incident polarization angle.
Amphoteric behavior of germanium in In0.5Ga0.5P grown by liquid phase epitaxy
Authors: Lee Jong Boong , Kim In , Kwon Ho Ki , Choe Byung-Doo
Published: July 2002

Properties of Ge-doped In0.5Ga0.5P grown by liquid phase epitaxy were investigated by Hall effect, capacitance-voltage, photoluminescence, and electroluminescence measurements. The Ge dopant in InGaP shows amphoteric behavior with a compensation ratio (Na/Nd) of about 0.4. The activation energies of donor and acceptor were measured to be 47 and 58 meV, respectively. The deep acceptor transition related to Ge complex is also observed by luminescence measurements.
Theoretical analysis of extremely small linewidth enhancement factor and enhanced differential gain in modulation-doped strained quantum-well lasers
Authors: Yamanaka Takayuki , Yoshikuni Yuzo , Lui Wayne , Yokoyama Kiyoyuki , Seki Shunji
Published: July 2002

The possibilities of extreme reduction in the linewidth enhancement factor α and of chirpless operation are theoretically investigated in InGaAs/InGaAsP quantum-well lasers. First, the condition for lasing operation at the peak of the differential gain spectrum is derived. Lasing characteristics are then calculated taking into account the effects of strain on the valence subband structure. It is shown that by appropriate application of detuning and p-type modulation doping to a compressive-strained quantum well, it is possible to reduce the α factor to virtually zero while keeping the laser operating in the region of positive gain.
Photoluminescence from narrow InAs-AlSb quantum wells
Authors: Brar Berinder , Kroemer Herbert , Ibbetson James , English John H.
Published: July 2002

We report on photoluminescence spectra from narrow InAs-AlSb quantum wells. Strong, clearly resolved peaks for well widths from 2 to 8 monolayers were observed. Transmission electron micrographs show direct evidence for the structural quality of the quantum well structures. The transition energies of the narrowest wells suggest a strong influence of the AlSb X-barrier on the electronic states in the conduction band.
Resonant tunneling through mixed quasibound states in a triple-well structure
Authors: Brown E. R. , Parker C. D. , Calawa A. R. , Manfra M. J.
Published: July 2002

A triple-well resonant-tunneling structure made from the In0.53Ga0.47As/AlAs material system yields a broad negative differential resistance (NDR) region without the precipitous drop in current that occurs in single-well structures. This NDR characteristic is attributed to resonant tunneling through mixed quasibound states. A diode made from this structure is used to generate a nearly constant power of 0.5 mW up to 16 GHz.
Polycrystalline AlN films of fine crystallinity prepared by ion-beam assisted deposition
Authors: Yang Jie , Wang Chen , Yan Xinshui , Tao Kun , Liu Baixin , Fan Yudian
Published: July 2002

Aluminum nitride films were synthesized by electron gun (e-gun) evaporation of aluminum onto Si(111) wafer and glassy carbon, with simultaneous bombardment by 5–20 keV nitrogen ions. Under specific experimental conditions, polycrystalline AlN films of fine crystallinity were obtained by this method. The correlation between experimental parameters and the resulted structure as well as the stoichiometry of the AlN films is also discussed.
Observation of random-telegraph noise in resonant-tunneling diodes
Authors: Ng Sze-Him , Surya Charles , Brown Elliott R. , Maki Paul A.
Published: July 2002

We report the observation of random-telegraph noise in GaAs/Al0.4Ga0.6As resonant tunneling diodes. Measurements made on our devices from 57 to 70 K revealed discrete switching events with step heights ranging from 6 to 20 μV. Our studies indicated that the 20-μV switching sequences correspond to two-state thermally activated processes involving a single trap. At a bias of −0.4 V, the capture and emission activation energies of this trap are 81 and 51 meV, respectively, implying that the trap is located in the barrier. Our results suggest that the noise arises from transmission coefficient fluctuations due to hopping conduction of carriers through the barrier.
Sb/GaSb heterostructures and multilayers
Authors: Golding T. D. , Dura J. A. , Wang W. C. , Vigliante A. , Moss S. C. , Chen H. C. , Miller J. H. , Hoffman C. A. , Meyer J. R.
Published: July 2002

We have successfully synthesized heterojunctions and elementary multilayered structures of the semimetal-semiconductor system Sb/GaSb using molecular beam and migration enhanced epitaxies. The study is motivated in part by the potential for producing an indirect narrow-gap semiconductor, in which a confinement-induced positive energy gap in the Sb layers will lead to highly attractive properties for nonlinear optical switches operating in the infrared. One may also be able to exploit the long mean free path in Sb (up to 2 μm) in studying quantum transport phenomena. X-ray diffraction confirms the ordered growth of GaSb/Sb/GaSb multilayers, and field-dependent magnetotransport measurements yield electron and hole mobilities ≥3×104 cm2/V s in Sb thin films.
Er luminescence centers in GaAs grown by migration-enhanced epitaxy
Authors: Taguchi Akihito , Kawashima Minoru , Takahei Kenichiro , Horikoshi Yoshiji
Published: July 2002

Er-doped GaAs has been grown by migration-enhanced epitaxy. The samples were grown at 300, 400, and 500 °C. Secondary ion mass spectroscopy measurements showed that the Er concentration in the grown epitaxial layer does not depend on the growth temperature between 300 and 500 °C. All samples showed luminescence due to the Er intra-4f-shell transition from the 4I13/2 excited state to the 4I15/2 ground state, but the spectra change drastically when the growth temperature is increased from 300 °C to 400 or 500 °C. The photoluminescence spectra of the samples grown above 400 °C are simpler than that of the sample grown at 300 °C. The spectrum of the sample grown at 300 °C became broad after annealing, whereas the spectra of the samples grown at 400 °C and above showed only changes in the relative intensity of the main luminescence lines. Some thermally stable Er luminescence centers seem to be preferentially formed at 400 and 500 °C.
Direct detection of atomic arsenic desorption from Si(100)
Authors: Alstrin April L. , Strupp Paul G. , Leone Stephen R.
Published: July 2002

Application of the 118 nm single photon laser ionization technique to a molecular beam epitaxy machine is used for the first time to demonstrate direct desorption of As atoms from Si(100). Both As2 and As are the desorbing species from 1 ML of arsenic on silicon above 1000 K. This is in contrast to previously reported models that considered only dimer desorption. With a continuous flux of As4, the scattered and desorbing arsenic species from Si(100) are examined as a function of surface temperature (650–1200 K). Atomic desorption is large, 75%±19%, above 1000 K, and complete conversion of As4 to As2 and As occurs at 1200 K. The species selectivity of laser ionization time-of-flight mass spectroscopy has broader implications for GaAs growth.
Dependence of InAs phonon energy on misfit-induced strain
Authors: Yang M. J. , Wagner R. J. , Shanabrook B. V. , Moore W. J. , Waterman J. R. , Yang C. H. , Fatemi M.
Published: July 2002

The transverse-optical (TO) phonon energy in strained InAs quantum wells has been investigated by using far-infrared absorption. We observe that the TO phonon energy decreases when the misfit-induced biaxial tension in the InAs single quantum well is increased. Our result shows a stronger phonon energy dependence on the strain than the one reported by Cerdeira et al. [Phys. Rev. B 5, 580 (1972)]. The discrepancy may be explained by stress relaxation near the surface in their experiment. The application of our result will be discussed.
Aharonov–Bohm effect and one-dimensional ballistic transport through two independent parallel channels
Authors: Simpson P. J. , Mace D. R. , Ford C. J. B. , Zailer I. , Pepper M. , Ritchie D. A. , Frost J. E. F. , Grimshaw M. P. , Jones G. A. C.
Published: July 2002

We have developed a new technique to contact a submicrometer metal dot gate independently of surrounding gates. With this we have made two ballistic channels in parallel on a GaAs-AlGaAs heterostructure. Independent control over all the gates allows unprecedented flexibility to adjust both the size of the dot and the widths of the channels. In a perpendicular magnetic field we can obtain extremely large Aharonov–Bohm oscillations and a double-frequency oscillation indicative of edge state charging in an open system. At low magnetic fields we see no evidence for any interaction between the one-dimensional subbands in the two channels.
Midwave (4 μm) infrared lasers and light-emitting diodes with biaxially compressed InAsSb active regions
Authors: Kurtz S. R. , Biefeld R. M. , Dawson L. R. , Baucom K. C. , Howard A. J.
Published: July 2002

Heterostructures with biaxially compressed, As-rich InAsSb are being investigated as active regions for midwave infrared emitters. InAs1−xSbx/In1−xGaxAs (x≊0.1) strained-layer sublattices (SLSs), nominally lattice matched to InAs, were grown using metalorganic chemical vapor deposition. An SLS light-emitting diode was demonstrated which emitted at 3.6 μm with 0.06% efficiency at 77 K. Optically pumped laser emission at 3.9 μm was observed in a SLS/InPSb heterostructure. The laser had a maximum operating temperature of approximately 100 K.
Laser spectral linewidth dependence on waveguide loss measurements using the Fabry–Perot method
Authors: Yu L. S. , Liu Q. Z. , Pappert S. A. , Yu P. K. L. , Lau S. S.
Published: July 2002

The critical role of the optical source spectral linewidth in semiconductor low loss waveguide measurements using the Fabry–Perot resonance method is analyzed. For 5-mm-long GaAs/AlGaAs waveguides with losses in the 1 dB/cm range, a frequency stabilized single mode laser with a linewidth of less than 0.01 Å is required to obtain a loss value accurate to within 5%.
GaAs/InGaAs/AlGaAs optoelectronic switch in avalanche heterojunction phototransistor vertically integrated with a resonant cavity
Authors: Huang F. Y. , Morkoç H.
Published: July 2002

An optoelectronic switch with high sensitivity based on avalanche multiplication is demonstrated in a GaAs/InGaAs/AlGaAs heterojunction bipolar phototransistor (HPT) with an integrated resonant cavity. The device, similar to a resonant-cavity enhanced HPT, consists of a four layer n+-p+-i-n structure. Excellent electrical switching characteristics with a high control voltage efficiency (Vs/Vh) of 1.8 have been obtained when the device is operated in the dark. The device can be switched optically at a selected wavelength owing to the integrated resonant cavity. By exploiting the inherent high optical gain, an extremely high optical control sensitivity (∂Vs/∂P0), exceeding 6 V/μW, has been achieved.
Time-to-frequency converter for measuring picosecond optical pulses
Authors: Kauffman M. T. , Banyai W. C. , Godil A. A. , Bloom D. M.
Published: July 2002

We present a new technique for measuring the intensity I(t) of optical pulses using a temporal optical system. A diffraction grating pair followed by a microwave-driven, optical phase modulator configured as a time lens is used to uniquely map the pulse shape from the time domain to the frequency domain, allowing measurement of the pulse shape with a spectrometer. We discuss the theory of operation and present experimental results illustrating 3 ps time resolution.
Thermodynamic effects in depth profiling and ion-beam mixing without invoking thermal spikes
Authors: Kelly Roger , Miotello Antonio
Published: July 2002

Various studies on ion-beam mixing suggest that the extent of mixing is sensitive to the sign and magnitude of the heat of mixing, ΔHm. This implies a role, not only for random motion, but also for chemical driving forces of the type where the total diffusion flux is modified by the factor [1−αi(1−αi) 2hmp/RT(1+p)]. Here α1 is the atomic fraction of component i, αi(1−αi)hm is the heat of mixing of a regular solution, and p is the ratio of the diffusivities for chemically guided defect motion to those for random motion of all types. The parameter p has never been evaluated for any system and we wish to evaluate it first by analyzing the profiling experiments of Marton, Fine, and Chambers on multilayers of Ni-Ag. We then obtain further values of p from ion-beam mixing experiments on bilayers and multilayers. It is shown that it is possible to understand a variety of experimental results relating to profiling and to ion-beam mixing in terms of chemical driving forces and, moreover, to do so without invoking thermal spikes.
Anomalous laser-induced voltages in YBa2Cu3Ox and ‘‘off-diagonal’’ thermoelectricity
Authors: Testardi Louis R.
Published: July 2002

Large anomalous laser-induced voltages observed in YBa2Cu3Ox are explained as the result of ‘‘off diagonal’’ thermoelectricity, an uncommon phenomenon which may only occur in low symmetry environments. The effect is accompanied by a large electrical impedance transformation and the coupling of electrical and thermal currents in orthogonal directions. It thus offers new thin film applications for power generation, cooling, heat pumping, heat flow measurement, and the fast self-powered sensing of optical and other radiation energy absorbed in thin layers.
Correlation between photoluminescence and surface species in porous silicon: Low-temperature annealing
Authors: Tsybeskov L. , Fauchet P. M.
Published: July 2002

Photoluminescence (PL) and Fourier-transform infrared (FTIR) measurements have been performed on light-emitting porous silicon (LEPSi) after annealing at temperatures below 600 °C. Two different kinds of samples with different surface morphologies and different initial concentrations of chemically bonded hydrogen were studied. In hydrogen-rich samples we have observed an increase of PL intensity at temperatures up to 250 °C, which correlated with an increase of Si—H bond concentration. A correlation between PL peak wavelength and the ratio of Si—O bonds over Si—H bonds has been demonstrated.
Atomic vibration mediated electronic transport in amorphous silicon
Authors: Fortmann C. M.
Published: July 2002

A new electron transport framework for amorphous silicon is presented. This new description describes electrons as being localized on atomic sites with the dominate conduction path being a high probability tunneling process between adjacent sites. This tunneling process is mediated by atomic positions and vibrations which are treated as perturbations in which the tunneling frequency is that of the atomic vibration. This theory of electron transport describes a wide range of observations including the temperature and pressure dependence of the mobility.
Influence of the high voltage pulse shape on the plasma source ion implantation process
Authors: Speth R. R. , Emmert G. A. , Goeckner M. J.
Published: July 2002

Using a two fluid model, we investigate the effects on the ion impact energy, of varying the shape of a large, negative, finite rise time, voltage pulse to a planar target. Two pulse shapes are tested, one with exponential shutoff, and one with a powered linear shutoff. For pulse lengths under 50 μs, we find that pulse shaping can be used to make moderate changes in the energy distribution of the implanted ions. For pulse lengths over 50 μs, there is a negligible difference in the ion impact energy distribution for the pulse shapes tested.
Spatiotemporal characteristics determined by a relaxation continuum model of an inductively coupled plasma
Authors: Kondo Kenji , Kuroda Hidehiko , Makabe Toshiaki
Published: July 2002

The use of an inductively coupled plasma (ICP) in material processing reactors is of relatively recent origin. A new theoretical model has been developed, based on a relaxation continuum (RCT) model for a collision dominated ICP. The spatiotemporal behavior of the ICP is investigated at 0.3 Torr and 13.56 MHz in Ar under the influence of electric and magnetic fields. It is demonstrated that the plasma is mainly sustained near the wall sheath during the phase when the external magnetic field becomes weak. It is also shown that the dominant mechanism of the power deposition in the ICP is caused by the electron motion under an azimuthal electric field.
Growth and transducer properties of an acoustic superlattice with its periods varying gradually
Authors: Cheng Shi-de , Zhu Yong-yuan , Lu Ya-lin , Ming Nai-ben
Published: July 2002

Acoustic superlattices with periods varying gradually are grown by the Czochralski method. The transducer made of the acoustic superlattice is fabricated. The insertion loss measurement shows the transducer has a wide frequency response range.
Thin film composites of Au and YBa2Cu3O7−δ
Authors: Allen Laura H. , Cukauskas Edward J. , Fisher Michael A.
Published: July 2002

Using a novel bilayer deposition process, we have grown composite films of Au with YBa2Cu3O7−δ on various substrates. Our composites have well-segregated regions of Au and YBa2Cu3O7−δ, and we have not observed structural degradation of the grains or grain boundaries in the films. Transition temperatures and critical current density measurements have behaviors consistent with regions of weakened grain boundary coupling in the films. Photoresponse measurements are also reported. We believe that Au is diffusing into the grain boundaries and weakening the coupling between YBa2Cu3O7−δ grains. By varying the amount of Au in the films, the coupling can be adjusted. These Au/YBa2Cu3O7−δ composite films are promising materials for device applications relying on vortex motion.
Degradation of (Zn,Cd)Se quantum well heterostructures for blue/green light emitters under high optical injection
Authors: Hovinen M. , Ding J. , Nurmikko A. V. , Hua G. C. , Grillo D. C. , He Li , Han J. , Gunshor R. L.
Published: July 2002

Picosecond laser pulses were used to simulate current injection and generate dark defects in ZnSSe/ZnCdSe quantum well structures. The formation of the defects was monitored in situ with a photoluminescence microscope setup, with spatial resolution of about 1 μm. Dark defects are observed to form in the ZnCdSe quantum well, analogous to electrical injection in separate confinement heterostructure diode lasers. Transmission electron microscopy of the optically generated dislocation network gives further insight to the origin of the defect microstructure.
Microstructural features at the interface between laser ablated YBa2Cu3O7 films and LaAlO3 substrates
Authors: Guo L. P. , Tian Y. J. , Liu J. Z. , Xu S. F. , Li L. , Zhao Z. X. , Chen Z. H. , Cui D. F. , Lu H. B. , Zhou Y. L. , Yang G. Z.
Published: July 2002

The microstructure at the interface between YBa2Cu3O7(YBCO) thin film and (100)LaAlO3 substrate has been investigated by using transmission electron microscopy. It has been observed that two distinct microstructural features existed in the interface: (1) A thin transitional layer of Ba3Al2O6 was frequently observed and the YBCO thin film grown on it showed stacking faults. (2) Sharp interface with no transitional layer was also occasionally observed and the YBCO film grown on it was single crystalline. In rare cases, a low symmetry phase was observed near the surface of the LaAlO3 substrate, however, the distortion caused by the lattice mismatch between this phase and the YBCO did not affect the quality of the YBCO thin film.
Properties of industrial-grade platinum–cobalt resistance thermometers between 1 and 27 K
Authors: Sakurai H. , Besley L. M.
Published: July 2002

The stability at 20 K of five industrial-type platinum–cobalt resistance thermometers on thermal cycling has been studied together with their resistance-temperature characteristics between 1 and 27 K and their self-heating. The stability at 20 K on cycling between room temperature and 20 K is of the order of 10 mK and on cycling between 100 and 20 K is a few mK. Differences in the resistance-temperature relationships of the thermometers are very small, but the self-heating effects are relatively large, particularly below 4 K.
Electrode-holding devices with an incorporated contact pressure regulating system, designed for the switching effect in amorphous materials
Authors: Márquez E. , Esquivias L. , Villares P. , Jiménez-Garay R.
Published: July 2002

Two devices which can be used in switching experiments on bulk samples, capable of eliminating the instability in electrical contacts, as well as providing a means of regulating the contact pressure of the electrodes, are described. To clarify the utility of these devices, the results of a study on the dependence between the parameters electrical resistance and contact pressure are shown, as well as some results obtained from experiments based on the phenomenon of electrical switching.
Microchannel-plate photomultiplier applicability to the time-correlated photon-counting method
Authors: Yamazaki I. , Tamai N. , Kume H. , Tsuchiya H. , Oba K.
Published: July 2002

A microchannel-plate photomultiplier (MCP-PMT) has been applied to the time-correlated single-photon counting technique. Electrical and timing characteristics were investigated for the two types of MCP-PMT’s, nonproximity type (Hamamatsu R1264) and proximity type (R1564), which are different in distance between the photocathode and MCP. In the proximity type, the transit-time spread was found to be 60 ps, i.e., a factor of 4 shorter than that in conventional photomultipliers with a dynode string. It was concluded that both types of MCP-PMT’s are fully applicable to the single-photon counting method and that the proximity type MCP-PMT in particular leads to further improvements in the cathode transit-time difference and the wavelength effect of the timing properties. Some examples of experimental results are shown for fluorescence decay curves and picosecond time-resolved spectra.
Self-pressurizing liquid-nitrogen filler
Authors: Chumbley P. E. , Hulse M. M.
Published: July 2002

A self-pressurizing, two-level automatic liquid-nitrogen filler is described which utilizes the vapor from the natural evaporation of cryogen in both the research and supply Dewars to continuously pressurize the liquid-nitrogen reservoir. The system has greatly improved response time compared to other self-pressurizing systems while avoiding the disadvantages of using heating elements or external gas sources for pressurization.
Small mass spectrometer probe for analyzing hydrogen ion species
Authors: Leung K. N. , Guethlein G.
Published: July 2002

The characteristics of a small, water-cooled, 90° magnetic deflection mass spectrometer suitable for analyzing positive and negative hydrogen ion species is described.
Measurement of electron density profile by microwave reflectometry on tokamaks
Authors: Simonet F.
Published: July 2002

A new method for measuring the electron density spatial profile has been successfully tested on the tokamak of Fontenay aux Roses (TFR). This method is based on the total reflection experienced by a wave of frequency F on the layer where F=Fpe(r). The experimental results show that the maximum electron density in the discharge is also easily measured and that accurate determination of a density profile can be obtained with a time resolution of 5 ms. This diagnostic is well adapted to all fusion devices where access to the total plasma cross section is limited, particularly for large tokamaks.
X
Y recording of ultrasound pulse-echo frequency spectra in the presence of noise
Authors: Shell J. S. , Goldstein A. , Giesige R. J.
Published: July 2002

The experimental difficulties associated with recording the frequency spectra of ultrasound pulse-echo signals are discussed. In particular, the most troublesome sources of synchronous and asynchronous noise are reviewed. A simple interface circuit for XY chart recording of these frequency spectra is presented. We discuss its major advantages over conventional Polaroid hardcopy recording. These include its ability to discriminate against both synchronous and asynchronous noise and its ability to record multiple spectra on the same XY chart. A detailed discussion of our spectral amplitude calibration procedures is also included.
Furnace for high-temperature muon-spin-rotation measurements
Authors: Major J. , Fürderer K. , Herlach D.
Published: July 2002

A vacuum furnace has been developed, allowing muon-spin-rotation measurements between 300 and ∼1400 K. Excellent temperature homogeneity (±0.1 K over the sample volume) and temperature stability (±0.05 K) have been achieved. Incandescent halide lamps with elliptical reflectors were used for heating. The Pt-Pt10Rh thermocouples were calibrated around the Curie temperature of iron by specific heat measurements. The measured muon-spin precession frequencies in demagnetized ferromagnetic iron are directly proportional to the macroscopic spontaneous magnetization. Near the Curie temperature, an increase of the transverse relaxation of the muon-spin polarization shows that positive muons are trapped by vacancies in thermal equilibrium.
On-line computer to reduce response time in a viscometer system having analog feedback
Authors: McMillan Donald E. , Utterback Nyle G.
Published: July 2002

A bob-in-cup viscometer system is described that incorporates a guard ring to minimize surface effects at the fluid–air interface. Effectiveness of the guard ring requires that the torque-sensing member not rotate, and analog feedback from an angle sensor is used to supply electrical countertorque to maintain zero angle. The usual technique for determining the applied torque is to measure the electrical potential producing the countertorque. However, consistent with feedback systems in general, rapid changes in the torque being measured cause excursions from zero angle, producing overshoot in the countertorque. This effectively limits the system response time to signals (torque) changing more slowly than the overshoot time. The present system is unusual in utilizing an on-line computer to calculate the net torque directly from Newton’s second law through digital inputs of actual angular positions in time, electrical countertorque, and the moment of inertia. So long as the analog feedback system maintains angular excursions small enough for guard ring effectiveness, and within the limits of digital angle sampling rates for determination of acceleration, the net torque can be determined exactly in principle, even during overshoot in angle and countertorque. This technique should be applicable to other well-defined systems utilizing analog feedback where effective response time is limited by overshoot.
Implications of the Tevatron operating experience for 1000-W refrigerator systems (invited)
Authors: Rode C. H.
Published: July 2002

The design principles and concepts for the Tevatron cryogenic system have been proven to be a viable way to deal with refrigeration maintenance and repair as well as magnet replacement. The operating experience and techniques are directly applicable for smaller systems (and also for larger ones like the proposed superconducting super collider).
First tests of the liquid-helium distribution line for the FSU linac
Authors: Frawley A. D. , Fox J. D. , Smith D. R. , Wright L. , Chapman K. R.
Published: July 2002

The liquid-helium distribution system for the FSU superconducting linear accelerator has been installed and a preliminary evaluation of the system performance has been made. A heat leak of about 30 W was anticipated for the entire system. With two of the five cryostats in place, we estimate an overhead heat leak for the piping system of about 37 W.
Improved vacuum seal-off device for cryogenic transfer lines
Authors: Noé J. W. , Lubicich T. M.
Published: July 2002

A design is given for a rugged and economical vacuum seal-off device for cryogenic transfer lines.
Experiments on an electron impact ionization ion source with phosphorus
Authors: Hoang Gia Tuong , Schneider Philippe , Remy Michel
Published: July 2002

An ion source using electron impact ionization is described and tested using phosphorus. An electron beam (600 eV, 10 mA) crosses a neutral flow of phosphorus vapor in the ionization chamber. The ions are extracted by multiaperture electrodes and a 800-μA ionic current can be obtained. Emittance diagrams of the source are drawn which lead to the value of ε4=4.8×10−7 rad2 m2.
Modeling light-emitting diode dynamic pressure transducers
Authors: Kruger A.
Published: July 2002

A model to describe a light-emitting diode as a dynamic pressure transducer is presented. This model is used to describe the measured current and voltage dependence of the sensitivity of the transducers. A method to determine an upper bound on the temperature dependence of the sensitivity and the rise time of the transducers is presented and is experimentally verified.
Four-point dc-resistance measurement apparatus for anisotropic crystals
Authors: Pfalzgraf B. W. , Spreckels H. , Müscher H.
Published: July 2002

We report on a four-point dc-resistance measurement apparatus to obtain the temperature dependence of the ratio of two components of the resistivity tensor of samples with hexagonal structure. We point out that this ratio, as well as the individual components, can be calculated. Problems arise for thin crystals having a small anisotropy. These can be solved by performing a resistance measurement with the technique of van der Pauw on the same sample. The achieved relative accuracy in the temperature-dependent anisotropy ratio is better than 1%. The absolute accuracy depends on the nonuniformity of the crystal thickness, and the determination of probe distances.
Status of the Yale–ESTU project
Authors: Parker P. D.
Published: July 2002

The Yale MP tandem accelerator was closed down on May 22, 1985, to begin the actual conversion process. The new accelerator pressure vessel (98 ft in length and 25 ft in diameter) was moved into the building on November 22, 1985. The new accelerator is projected to be operational at a terminal potential of 20 MV by October 1, 1986.
Recent work on superconducting QWRs at the Weizmann Institute (invited)
Authors: Ben-Zvi I. , Sokolowski J. S.
Published: July 2002

Recent work on superconducting quarter-wave resonators (QWR) at the Weizmann Institute of Science is reported. Two subjects are discussed: the performance of these resonators as particle acceleration devices in the booster module recently installed at the accelerator laboratory and new aspects of the electron multipactoring phenomenon in these resonators.
Noise characteristics of U. S. synchrotron radiation sources
Authors: Powers L.
Published: July 2002

Noise characteristics of the U. S. x-ray synchrotron sources are compared in the 0–2.5-kHz region. In general, little difference is found in the characteristic frequencies of the noise on focused and unfocused beamlines of a particular source, but the magnitude and white-noise levels differ. The National Synchrotron Light Source shows the least characteristic noise and the noise that is observed is small in magnitude (2–3 times the white-noise level).
Novel F2 detector for the gas monitor of an excimer laser
Authors: Hakuta Kohzo , Mukai Naruhiko , Miki Susumu , Takuma Hiroshi
Published: July 2002

A novel automatic F2 detecting method has been developed which uses the chemiluminescence emitted following a gas phase reaction between F2 and SiH4. The new method is shown to be sensitive enough to detect a ppm level of F2 mixed in rare gases, and the signal is linear in a broad range of F2 concentration. The use of such a detector in a rare gas fluoride excimer laser is discussed.
Retrievable UHV effusion cell for investigation of low melting point metals on solid surfaces
Authors: Castro T. , Reifenberger R.
Published: July 2002

The design and performance of an effusion cell used to deposit low melting point metals under UHV conditions is described. A novel feature of the cell is a transfer rod and pretreatment chamber that allow for the rapid loading and retrieval of crucibles containing low melting point source elements. This feature of our cell makes it ideal for depositing the highly reactive alkali metals. The performance of the effusion cell is evaluated for the deposition of the metal potassium.
Apparatus for simultaneous light scattering and microscopic video observation: Application to the growth of a droplet pattern
Authors: Perrot F. , Beysens D.
Published: July 2002

A simple apparatus is described which allows the simultaneous microscopic observation of a pattern and the analysis of the light scattered by it at low angles using a single video image. Applications are found any time a spatial Fourier analysis is needed in addition to a simple visualization. As an example, we report a preliminary study of the growth of ‘‘breath figures’’—a pattern formed by the condensation of vapor blown onto a cold surface.