bluuebunny/crossref_metadata_2025 huggingface dataset:
Superconducting Josephson arrays as tunable microwave sources operating at 77 K
Authors: Martens J. S. , Pance A. , Char K. , Lee L. , Whiteley S. , Hietala V. M.
Published: July 2002

High-temperature superconducting arrays of Josephson junctions have been fabricated and tested as millimeter-wave oscillators at 77 K. Power levels in the microwatt range have been detected in the range of 90–160 GHz from arrays using from 350 to almost 60 000 YBa2Cu3O7 junctions. Monolithic log-periodic spiral antennas as well as quasioptical resonators have been used to enable power coupling. The arrays were also found to be bias tunable over ranges limited by the receiving apparatus.
Columnar defects in YBa2Cu3O7−δ induced by irradiation with high energy heavy ions
Authors: Wheeler R. , Kirk M. A. , Marwick A. D. , Civale L. , Holtzberg F. H.
Published: July 2002

Defect microstructures in three YBa2Cu3O7−δ single crystals irradiated with different high energy heavy ions show dramatically different damage morphologies. For Sn and Au projectiles with total energies of 580 MeV and 1.0 GeV, respectively, highly aligned tracks are observed which extend for many microns in the crystals. However, irradiation with 1.4 GeV Br ions results in the formation of spherical damage regions widely separated along the ion path through the entire crystal. The continuity of damage along the ion path for the different projectiles varies with the magnitude of the electronic energy loss.
Boron delta-doped Si metal semiconductor field-effect transistor grown by molecular-beam epitaxy
Authors: Wu S. L. , Carns T. K. , Wang S. J. , Wang K. L.
Published: July 2002

A working p-type Si metal semiconductor field-effect transistor structure, utilizing a boron delta-doped layer as the conducting channel, has been successfully fabricated. Based on Hall measurements, a hole mobility of 120 (180) cm2 V−1 s−1 at 300 (77) K has been obtained. The sheet carrier density of the delta layer was estimated to be about 1.8×1012 cm−2. It is shown that the delta field-effect transistor exhibits an extrinsic transconductance of 640 μS/mm for a gate length of 5 μm, and a high gate to drain breakdown voltage (≳18 V). By reducing the gate length to 1 μm, a transconductance of up to 3.2 mS/mm is expected.
Photoconductance measurements on InTlSb/InSb/GaAs grown by low-pressure metalorganic chemical vapor deposition
Authors: Staveteig P. T. , Choi Y. H. , Labeyrie G. , Bigan E. , Razeghi M.
Published: July 2002

We report infrared photoconductors based on InTlSb/InSb grown by low-pressure metalorganic chemical vapor deposition on semi-insulating GaAs substrates. The photoresponse spectrum extends up to 8 μm at 77 K. The absolute magnitude of the photoresponse is measured as a function of bias. The specific detectivity is estimated to be 3×108 Hz1/2 cm W−1 at 7 μm wavelength.
Detection of in-plane and out-of-plane ultrasonic displacements by a two-channel confocal Fabry–Perot interferometer
Authors: Cand A. , Monchalin J.-P. , Jia X.
Published: July 2002

Simultaneous detection of in-plane and out-of-plane ultrasonic displacements by a two-channel confocal Fabry–Perot optical receiver is described. Accuracy is tested by measuring the in-plane and out-of-plane displacements produced by Rayleigh surface waves generated by a piezoelectric transducer and a laser.
Temporal and spatial evolution of laser ablated plasma from YBa2Cu3O7
Authors: Harilal S. S. , Radhakrishnan P. , Nampoori V. P. N. , Vallabhan C. P. G.
Published: July 2002

YBa2Cu3O7 target was laser ablated, and the time-of-flight (TOF) distributions of Y, Y+, and YO in the resultant plasma were investigated as functions of distance from the target and laser energy density using emission spectroscopy. Up to a short distance from the target (≂1.5 cm), TOF distributions show twin peaks for Y and YO, while only single-peak distribution is observed for Y+. At greater distances (≳1.5 cm) all of them exhibit single-peak distribution. The twin peaks are assigned to species corresponding to those generated directly/in the vicinity of target surface and to those generated from collisional/recombination process.
Anisotropy, birefringence, and optical phase retardation related to intersubband transitions in multiple quantum well structures
Authors: Kaufman D. , Sa’ar A. , Kuze N.
Published: July 2002

It is well known that the selection rules for intersubband transitions in quantum well structures require that the infrared light be polarized parallel to the growth direction. As a result, the induced intersubband susceptibility tensor becomes highly anisotropic and the crystal becomes birefringent. We have studied the effect of induced birefringence at the midinfrared range of the spectrum using a number of experimental techniques, including Fourier transform infrared absorption spectroscopy and optical phase retardation measurements using a tunable CO2 laser and a cross polarizer setup. We have observed that linearly polarized light becomes almost circularly polarized due to optical phase retardation between the ordinary and the extraordinary directions over a short optical path length of the order of 20 μm near the resonance (but not at the resonance). The real and the imaginary parts of the induced extraordinary refractive index were measured and have been found to be of the same order of magnitude. We also show that a solution of the Fresnel equation, modified to take into account both the imaginary and the real parts of the susceptibility tensor, is in good agreement with our experimental results.
Effect of hydrostatic pressure on strained CdSe/ZnSe single quantum wells
Authors: Hwang S. J. , Shan W. , Song J. J. , Zhu Z. Q. , Yao T.
Published: July 2002

The effect of hydrostatic pressure on the quantum confined transition in CdSe/ZnSe single quantum wells grown by molecular beam epitaxy has been studied by low-temperature photoluminescence measurements. Samples with layer thicknesses of CdSe from 1 to 4 monolayers were used. Strong excitonic emissions associated with the lowest Γ-Γ interband transitions were observed in these highly strained quantum well samples. The pressure coefficients of the interband transitions are found to depend on well thickness with the numerical value decreasing as the well width increases. Pronounced sublinear pressure dependence of the excitonic emissions was observed in the samples with 3 and 4 monolayer CdSe wells, indicating the degradation of the samples due to strain relaxation. Our results suggest that the critical thickness for the CdSe layer pseudomorphically grown on ZnSe is less than 4 monolayers.
500 GHz optical short pulse generation from a monolithic passively mode-locked distributed Bragg reflector laser diode
Authors: Arahira Shin , Oshiba Saeko , Matsui Yasuhiro , Kunii Tatsuo , Ogawa Yoh
Published: July 2002

A 500 GHz optical short pulse train was generated from a passively mode-locked distributed Bragg reflector laser diode (DBR-LD). The repetition frequency was thirteen times the fundamental round trip frequency in the LD, and harmonic mode-locking occurred. The pulse duration was 700 fs and the time-bandwidth product was 0.51, very close to the transform-limited value of a Gaussian waveform, 0.44. To our knowledge, this is the first report on the harmonic mode locking of a monolithic passively mode-locked laser diode.
Experiments with back side gas cooling using an electrostatic wafer holder in an electron cyclotron resonance etching tool
Authors: Meyer J. A. , Kirmse K. H. R. , Jenq J.-S. , Perez-Montero S. Y. , Maynard H. L. , Wendt A. E. , Taylor J. W. , Hershkowitz N.
Published: July 2002

Wafer temperature, etch rate, and etch uniformity measurements of SiO2 wafers were made to characterize the use of back side helium cooling with an electrostatic wafer holder in an electron cyclotron resonance etching tool. The etch rate was found to be independent of the wafer temperature in the range between 20 and 110 °C. A 7% increase in etch nonuniformity (3σ) at higher backside pressures was attributed to helium, which leaked around the edge of the wafer, displacing the etchant gas. A back side pressure of 2–3 Torr provides a balance between wafer temperature control and helium leak rates.
Raman spectroscopy using a fiber optic probe with subwavelength aperture
Authors: Tsai Din Ping , Othonos Andreas , Moskovits Martin , Uttamchandani Deepak
Published: July 2002

Raman spectroscopy with subwavelength spatial resolution of a diamond sample was recorded using a tapered fiber optical probe in conjunction with a conventional Raman spectrometer. The experiment demonstrates the potential of suboptical wavelength resolution analytical spectroscopy. The tapered fiber optical probe with an aperture of around 100 nm, served as the means for delivering pump radiation while simultaneously collecting the Stokes radiation from the diamond specimen. Comparing the magnitude of the Raman scattering measured with the submicron single mode fiber probe to similar signals obtained with a nontapered probe made of the same type of fiber, illustrates the potential increase in effective optical aperture resulting from the close approach of the fiber to the surface.
Phase-matching property optimization using birefringence tuning in solid solutions of KTiOPO4 isomorphs
Authors: Cheng L. K. , Cheng L. T. , Bierlein J. D. , Parise J.
Published: July 2002

We report here the linear and nonlinear optical properties of the solid-solutions KTiOPxAs1−xO4 and Cs1−xKxTiOAsO4. Single domain crystals of these solid solutions were grown using a high temperature solution growth technique. By varying the compositional parameter x, the optical birefringence of these crystals was tuned to achieve noncritically phase-matched type II frequency doubling of the 1.064 and 1.32 μm lines of Nd:YAG. Near optimal compositions for these two applications, and their associated phase-matching angles, temperature bandwidths and angular acceptances are presented. The birefringence of KTiOPxAs1−xO4 exhibits a Vegard dependence on x, and the phase-matching property optimization amounts to an accurate determination of the partition coefficients for P and As suitable for crystal growth. For the Cs1−xKxTiOAsO4 solid solution, a non-Vegard dependence of the crystal birefringence and the cell constants was observed. This is believed to be due to the preferential occupation of the larger K(2) site by Cs.
Wide terrace formation during metalorganic vapor phase epitaxy of GaAs, AlAs, and AlGaAs
Authors: Shinohara Masanori , Tanimoto Masafumi , Yokoyama Haruki , Inoue Naohisa
Published: July 2002

GaAs, Al0.35Ga0.65As, and AlAs surface terrace structures formed during metalorganic vapor phase epitaxy (MOVPE) on vicinal (001) surfaces are investigated. The minimal terrace width for two-dimensional (2-D) nucleation for AlGaAs is almost equal to that for GaAs. In contrast, for AlAs it is reduced and the growth mode becomes three dimensional at temperatures below 580 °C. Monolayer step-flow growth without 2-D islands and terraces about 1 μm wide are obtained above 630 °C for all materials. These results are very different from those by molecular beam epitaxy and suggest that MOVPE is superior to grow wide uniform heterointerfaces for GaAs/AlAs and GaAs/AlGaAs.
Effect of faceting on the band gap of ordered GaInP
Authors: Friedman D. J. , Horner G. S. , Kurtz Sarah R. , Bertness K. A. , Olson J. M. , Moreland J.
Published: July 2002

It has been shown that under certain growth conditions the pseudobinary semiconductor alloy GaInP shows cation site ordering into the Cu-Pt structure, and that this ordering results in a lowering of the band gap Eg from that of the disordered alloy. The Eg lowering is known to depend on growth conditions, including the orientation of the substrate. We study the dependence of Eg on epilayer thickness for GaInP grown by metal-organic vapor-phase epitaxy. For epilayers grown on singular (100) substrates under growth conditions conventionally used to produce ordered material, Eg decreases dramatically with increasing epilayer thickness: Eg for a 10-μm-thick epilayer is ∼40 meV lower than for a 1-μm-thick epilayer. This dependence of Eg on thickness can be understood in terms of the recently observed faceting of the GaInP growth surface.
In situ monitoring of strain relaxation during antimony-mediated growth of Ge and Ge1−y Cy layers on Si(001) using reflection high energy electron diffraction
Authors: Osten H. J. , Klatt J.
Published: July 2002

Ge and Ge0.99C0.01 layers were grown pseudomorphically on Si(001) and investigated during growth with reflection high energy electron diffraction (RHEED). We show that the RHEED technique permits dynamic monitoring of the in-plane lattice spacing of the growing layer by measuring the distances between diffraction features during growth and applying an appropriate mathematical algorithm. The onset of plastic relaxation in these layers as a function of growth temperature was investigated. Lower growth temperature increases the critical layer thickness. We estimated an overall activation energy of around 0.1 eV. Adding 1% carbon to the Ge layer delays the onset of relaxation. But the Ge1−yCy layer does not behave identically to a pseudomorphic Ge film with an artificially reduced strain. It should rather be considered as a new material.
Carrier deep-trapping mobility-lifetime products in poly(p-phenylene vinylene)
Authors: Antoniadis H. , Abkowitz M. A. , Hsieh B. R.
Published: July 2002

In order to estimate the deep-trapping mobility-lifetime (μτ) product for holes and electrons in poly(p-phenylene vinylene) (PPV), trap-free space-charge-limited current, and time-of-flight measurements were performed on bilayer devices comprising of a PPV layer and a trap-free molecularly doped polymer layer. μτ products of about 10−9 and 10−12 cm2/V were found for holes and electrons respectively, corresponding to an average range of 1 μm for holes and 10 Å for electrons under an electric field of 105 V/cm. The low μτ value for electrons is attributed to severe deep trapping of electrons in PPV, which effectively reduces their range. Implications on the efficiency of electroluminescence devices are discussed.
TASERs: Possible dc pumped terahertz lasers using interwell transitions in semiconductor heterostructures
Authors: Korotkov A. N. , Averin D. V. , Likharev K. K.
Published: July 2002

We have carried out a theoretical analysis of a possibility to generate coherent continuous-wave terahertz radiation using double-quantum-well heterostructures. The lasing should take place due to inversed population of the wells, created by electron flow through the structure under the effect of applied dc voltage. Estimates show that, e.g., 3 THz radiation with a relatively narrow line (Δf/f≲10−5) and power of the order of 0.1 mW may be generated using structures with area as small as ∼100 μm2, at temperatures up to ∼30 K. For the experimental implementation of this opportunity, a special design is suggested to reduce absorption of terahertz radiation.
Air stabilized (001) p-type GaAs fabricated by molecular beam epitaxy with reduced surface state density
Authors: Yan D. , Look E. , Yin X. , Pollak Fred H. , Woodall J. M.
Published: July 2002

We present a contactless electromodulation study of undoped/p+ GaAs (001) structures, fabricated by molecular beam epitaxy (MBE), which exhibit reduced surface state densities and surface Fermi level values closer to the band edge in relation to other p- or n-type GaAs (001) surfaces. The temperature dependence of the measured barrier height has been explained by a modified current-transport equation which contains two ‘‘pinning’’ levels (0.25 and 0.5 V relative to the valence band). Measurements were carried out in air and also in situ in the ultrahigh vacuum environment of a MBE chamber soon after growth and before the sample was removed to air.
Theory for the apertureless near-field optical microscope: Image resolution
Authors: García N. , Nieto-Vesperinas M.
Published: July 2002

We present a theory that should explain the operation of the apertureless near-field optical microscope in the limit of smooth variations of both the refractive index and the corrugation of the object. Special emphasis is made on ultimate resolution and the recent experiments by F. Zenhausern, M. P. O’Boyle, and K.H. Wickramasinghe [Appl. Phys. Lett. 65, 1623 (1994)]. We show that, in order to obtain resolution better than 7 nm, the variation of the object refractive index has to satisfy severe conditions.
Molecular beam epitaxial growth of high quality Zn1−xCdxSe on InP substrates
Authors: Dai N. , Cavus A. , Dzakpasu R. , Tamargo M. C. , Semendy F. , Bambha N. , Hwang D. M. , Chen C. Y.
Published: July 2002

High quality, lattice matched Zn1−xCdxSe has been grown on InP substrates by molecular beam epitaxy. The quality of the epilayers was monitored by reflection high energy electron diffraction, and by low temperature photoluminescence and transmission electron microscopy (TEM). The use of an As flux during the pregrowth substrate treatment followed by a low initial growth temperature were needed to optimize the growth. TEM images of samples grown under these conditions show abrupt interfaces and good crystalline quality. Epilayers exhibit excellent optical properties, indicated by a very narrow, high intensity near-band-edge excitonic emission peak (full width at half maximum of 10 meV), and almost negligible deep level emission.
High saturation behavior of the four-wave mixing signal in semiconductor amplifiers
Authors: Mecozzi A. , D’Ottavi A. , Cara Romeo F. , Spano P. , Dall’Ara R. , Guekos G. , Eckner J.
Published: July 2002

We show by a simple model that, in semiconductor amplifiers, the functional dependence of the four-wave mixing signal on the output power of pump and probe depends on the underlying optical nonlinearity. The observation, at different pump-probe detunings, of a different dependence of the conjugate power on pump and probe output permits the identification of the dominant optical nonlinearity at a given detuning.
SPARTUVIX: A time-resolved XUV transmission grating spectrograph for x-ray laser research
Authors: Bourgade J. L. , Combis P. , Louis-Jacquet M. , Le Breton J. P. , de Mascureau J. , Naccache D. , Sauneuf R. , Thiell G. , Keane C. , MacGowan B. , Matthews D.
Published: July 2002

A transmission grating streaked spectrograph (SPARTUVIX) has been developed at the Centre d’Etudes de Limeil-Valenton for measuring the temporal evolution of soft-x-ray spectra in laser-produced plasmas. In this article the ideas behind the instrument are described as well as a description of the actual working diagnostic and its relevant components. This diagnostic has been used to look at the time behavior of x-ray laser emission, and a number of very interesting results have been obtained. A representative sample of these results will also be shown.
Fast cerium magnesium nitrate (CMN) thermometer for the low millikelvin temperature range
Authors: Greywall Dennis S. , Busch Paul A.
Published: July 2002

The construction details and the performance of a CMN susceptibility thermometer of novel design are discussed. The device features a response time of 30 s at 3 mK and less than 2 s at 10 mK. When operated as part of a simple self-inductance bridge circuit at a drive level sufficient to obtain a resolution of one part in 104, the power dissipation is only 10 pW and the self-heating is negligibly small. This new thermometer makes possible a new class of experiments in the low mK regime.
High reflectivity 1.55 μm (Al)GaAsSb/AlAsSb Bragg reflector lattice matched on InP substrates
Authors: Lambert B. , Toudic Y. , Rouillard Y. , Gauneau M. , Baudet M. , Alard F. , Valiente I. , Simon J. C.
Published: July 2002

We report the molecular beam epitaxy growth of (Al) GaAsSb/AlAsSb Bragg reflectors around the 1.55 μm wavelength region. Mirrors with 96% reflectivity have been achieved by using ten pairs of quarter wavelength layers. This demonstrates the capability of the (Al) GaAsSb/AlAsSb system to achieve efficient Bragg mirrors lattice matched to InP substrates.
An atomic oxygen environmental cell for a transmission electron microscope
Authors: Rodriguez N. M. , Oh S. G. , Downs W. B. , Pattabiraman P. , Baker R. T. K.
Published: July 2002

The capabilities of the transmission electron microscope have been extended to enable in situ studies of the interaction of atomic oxygen with various solids to be performed. This has been accomplished by modifying the specimen chamber region of a JEOL 200CX TEM/STEM electron microscope to accommodate a specially designed environmental cell and specimen heating stage. With this arrangement it is possible to continuously observe changes in the appearance of a specimen as it undergoes reaction with a beam of atomic oxygen. In this paper a description of the technique will be presented together with some applications which highlight its advantages over conventional transmission electron microscopic post-reaction examinations.
How methanol affects the surface of blue and red emitting porous silicon
Authors: Rehm J. M. , McLendon G. L. , Tsybeskov L. , Fauchet P. M.
Published: July 2002

The effects of liquid methanol on the photoluminescence intensity and FTIR spectra of red and blue emitting porous silicon were investigated. Hydrogen passivated red emitting samples exhibit quenching and recovery of photoluminescence intensity and broadening of the Si-Hx stretch bands upon exposure to liquid methanol. Oxygen passivated red emitting samples exhibit no photoluminescence quenching. The sensitivity of the red emitting sample is due to the microstructure of porous silicon at the surface and the ability of methanol to penetrate the pores. The blue photoluminescence of thermally oxidized samples is quenched upon exposure to methanol. This is attributed to the solvent’s ability to change the surface passivation which modifies existing traps and introduces competitive recombination channels for electrons.
Nanosecond switching using power MOSFETs
Authors: Baker R. J. , Pocha M. D.
Published: July 2002

It is shown that using the secondary breakdown effect of a bipolar transistor, often called an avalanche transistor, the large input capacitance of a power MOSFET may be charged very quickly. A power MOSFET driven by an avalanche transistor is used to generate electrical pulses of >800 V into 50 Ω with rise times of approximately 3 ns. The output pulse amplitude can be varied by adjusting the drain-source voltage of the power MOSFET. The trigger delay of this circuit is approximately 5 ns, with jitter of <100 ps. This circuit has been used to generate pulses at a repetition rate of greater than 1 kHz.
Generation of terahertz radiation using electro-optic crystal mosaics
Authors: Carrig Timothy J. , Rodriguez G. , Sharp Clement Tracy , Taylor A. J. , Stewart Kevin R.
Published: July 2002

We describe the generation of terahertz radiation by optical rectification in an electro-optic crystal mosaic. The mosaic is constructed from four single crystals of the organic salt dimethyl amino 4-N-methylstilbazolium tosylate and is approximately 1 cm2 in area. We characterize both the optical rectification efficiency and the spatial and temporal profiles of the generated terahertz beam, and find that the mosaic performs as well as a single crystal.
Inverse staggered polycrystalline and amorphous silicon double structure thin film transistors
Authors: Aoyama Takashi , Ogawa Kazuhiro , Mochizuki Yasuhiro , Konishi Nobutake
Published: July 2002

Inverse staggered polycrystalline silicon (poly-Si) and hydrogenated amorphous silicon (a-Si:H) double structure thin film transistors (TFTs) are fabricated based on the conventional a-Si:H TFT process for the application to liquid crystal display panels with peripheral driver circuits integration. After depositing a thin (20 nm) a-Si:H using the plasma chemical vapor deposition technique at 300 °C, Ar+ and XeCl (300 mJ/cm2) lasers are irradiated on the peripheral driver circuits areas, and then thick a-Si:H (200 nm) and n+Si layers are deposited again. Field effect mobilities of 10 and 0.5 cm2/V s are obtained for the laser annealed poly-Si and the a-Si:H (without annealing) TFTs, respectively.
Cryogenic cooling of monochromators
Authors: Marot G. , Rossat M. , Freund A. , Joksch S. , Kawata H. , Zhang L. , Ziegler E. , Berman L. , Chapman D. , Hastings J. B. , Iarocci M.
Published: July 2002

In this paper, we report on the design and x-ray diffraction properties of cryocooled silicon single crystals exposed to the following wiggler beams: power density: 150 W/mm2, total power: 75 W and power density: 0.5 W/mm2, total power: 100 W. First, thermomechanical and engineering aspects of low-temperature crystal cooling are discussed, leading to two basic cooling geometries: internal cooling and side cooling. Experimental tests of both these cooling schemes at NSLS on beam lines X25 and X17 are then described and discussed. Finally, engineering problems related to the integration of cryogenic cooling on ESRF beam lines are presented.
X-ray photoemission study of the interface formation between calcium and self-assembled alkanethiol monolayers
Authors: Razafitrimo H. , Ettedgui E. , Guo L.-H. , McLendon G. L. , Gao Y.
Published: July 2002

We have investigated the interface formation of Ca with an alkanethiol CH3(CH3)17SH monolayer self-assembled onto gold-coated silicon. Deposited Ca neither diffused into nor interacted chemically with the monolayer. Core-level shift and work function changes were observed in the monolayer as soon as Ca was deposited and they were stabilized after 8 Å of Ca coverage. The shifts are interpreted in terms of charge transfer from Ca to the monolayer, creating a dipole layer at the interface.
Effects of electron cyclotron resonance plasma thermal oxidation on the properties of polycrystalline silicon film
Authors: Lee Jung-Yeal , Han Chul-Hi , Kim Choong-Ki , Kim Bok-Ki
Published: July 2002

The optical and electrical properties of polycrystalline silicon (poly-Si) film with electron cyclotron resonance (ECR) plasma oxidation have been investigated. Density of dangling bonds in the poly-Si film was decreased significantly after oxidizing by ECR oxygen plasma. It was found that oxygen ions generated during the ECR plasma oxidation process diffuse into the poly-Si film, and passivate the dangling bonds. Also, it was found that the poly-Si film with ECR plasma oxidation has better thermal stability than hydrogen-passivated poly-Si film, which can be explained by the higher energy of Si–O bond than that of Si–H.
The Gaseous Electronics Conference radio-frequency reference cell: A defined parallel-plate radio-frequency system for experimental and theoretical studies of plasma-processing discharges
Authors: Hargis P. J. , Greenberg K. E. , Miller P. A. , Gerardo J. B. , Torczynski J. R. , Riley M. E. , Hebner G. A. , Roberts J. R. , Olthoff J. K. , Whetstone J. R. , Van Brunt R. J. , Sobolewski M. A. , Anderson H. M. , Splichal M. P. , Mock J. L. , Bletzinger P. , Garscadden A. , Gottscho R. A. , Selwyn G. , Dalvie M. , Heidenreich J. E. , Butterbaugh Jeffery W. , Brake M. L. , Passow M. L. , Pender J. , Lujan A. , Elta M. E. , Graves D. B. , Sawin H. H. , Kushner M. J. , Verdeyen J. T. , Horwath R. , Turner T. R.
Published: July 2002

A ‘‘reference cell’’ for generating radio-frequency (rf) glow discharges in gases at a frequency of 13.56 MHz is described. The reference cell provides an experimental platform for comparing plasma measurements carried out in a common reactor geometry by different experimental groups, thereby enhancing the transfer of knowledge and insight gained in rf discharge studies. The results of performing ostensibly identical measurements on six of these cells in five different laboratories are analyzed and discussed. Measurements were made of plasma voltage and current characteristics for discharges in pure argon at specified values of applied voltages, gas pressures, and gas flow rates. Data are presented on relevant electrical quantities derived from Fourier analysis of the voltage and current wave forms. Amplitudes, phase shifts, self-bias voltages, and power dissipation were measured. Each of the cells was characterized in terms of its measured internal reactive components. Comparing results from different cells provides an indication of the degree of precision needed to define the electrical configuration and operating parameters in order to achieve identical performance at various laboratories. The results show, for example, that the external circuit, including the reactive components of the rf power source, can significantly influence the discharge. Results obtained in reference cells with identical rf power sources demonstrate that considerable progress has been made in developing a phenomenological understanding of the conditions needed to obtain reproducible discharge conditions in independent reference cells.
Particle simulation of ion optics and grid erosion for two-grid and three-grid systemsa)
Authors: Peng Xiaohang , Ruyten Wilhelmus M. , Friedly Verlin J. , Keefer Dennis , Zhang Quan
Published: July 2002

A particle simulation code has been developed to study ion optics and the effect of charge-exchange-induced grid erosion in electron bombardment ion thrusters. The code is based on the particle-in-cell method to simulate the beam extraction and ion optics and a Monte Carlo method to calculate the charge exchange collisions between fast beam ions and neutral particles. The space charge effects for both fast beam ions and slow charge exchange ions are included. Both two- and three-dimensional versions of this code have been developed for both two-grid and three-grid systems. The two-dimensional model provides a qualitative description of the details of the ion flow and the charge exchange collisions. The three-dimensional version has successfully predicted the experimentally observed erosion pattern in which the maximum erosion occurs at the geometric centers of accelerator grid apertures.
Electric field effect on ultrathin YBa2Cu3O7−δ grain boundary Josephson junctions
Authors: Petersen K. , Takeuchi I. , Talyansky V. , Doughty C. , Xi X. X. , Venkatesan T.
Published: July 2002

The effect of electric field on ultrathin YBa2Cu3O7−δ grain boundary Josephson junctions has been investigated. A conventional metal insulator superconductor field effect transistor structure consisting of a Pr0.55Y0.45Ba2Cu3O7−δ /YBa2Cu3O7−δ bilayer channel, a crystalline SrTiO3 dielectric, and an Au gate electrode is deposited on a SrTiO3 bicrystal substrate. At high bias current (Ibias≫Ic) the observed effect is compatible with a parallel resistor model using a value close to the bulk charge carrier density of YBa2Cu3O7−δ. At low bias current (Ibias≥Ic) an enhanced field effect not compatible with a parallel resistor model is observed. This enhanced effect is related to the field dependent dielectric properties of the crystalline SrTiO3 insulation layer.
Transient behavior of photorefractive gratings in a polymer
Authors: Malliaras G. G. , Krasnikov V. V. , Bolink H. J. , Hadziioannou G.
Published: July 2002

The transient behavior of photorefractive gratings in the polymer composite poly(N-vinyl carbazole) (PVK), 2,4,7-trinitro-9-fluorenone (TNF), and N,N-diethyl-para-nitroaniline (EPNA) doped with various amounts of 4-(diethylamino)benzaldehyde diphenylhydrazone (DEH) is presented. The influence on the hole drift mobility due to the change in the trap density induced by DEH, was directly measured.
Time domain terahertz impulse ranging studies
Authors: Cheville R. A. , Grischkowsky D.
Published: July 2002

We present time domain impulse scattering measurements of freely propagating terahertz radiation measured with subpicosecond resolution. This fast time response corresponds to a usable bandwidth of over 1 THz. Measured scattered fields from thin wire targets agree well with the calculated scattering for the early and late time response in both the time and frequency domains. Realistic ranging from scale model aircraft is demonstrated.
Real-time pole and probe assessment of orientational processes in electro-optic polymers
Authors: Michelotti F. , Toussaere E. , Levenson R. , Liang J. , Zyss J.
Published: July 2002

The electro-optic properties of polymer films are measured by an original technique whereby a periodic sequence of poling and probing steps permits alternation of the application of orientation and dephasing potentials. Relaxation dynamics of the electro-optic coefficient of Red–Acid–Magly crosslinkable polymer films is studied as a function of the temperature of the samples. The time constant of the decay τ as measured at several temperatures is found to follow a Vogel–Fulcher–Tamann—Hesse dependence, for temperatures above glass transition. Poling the samples in the presence of a pulsed electric field leads to a r33 electro-optic coefficient as high as 6 pm/V.
Thermally stable, low-resistance PdGe-based ohmic contacts to high–low doped n-GaAs
Authors: Kwak J. S. , Kim H. N. , Baik H. K. , Lee J.-L. , Kim H. , Park H. M. , Noh S. K.
Published: July 2002

Thermally stable, low-resistance PdGe-based ohmic contacts to high–low doped n-GaAs have been developed. The lowest contact resistance obtained is two times lower than that of previously reported PdGe ohmic contacts. The contacts are thermally stable even after isothermal annealing for 5 h at 400 °C under atmosphere ambient. X-ray diffraction results and Auger depth profiles show that the good PdGe-based ohmic contact is due to the formation of both AuGa and TiO compounds. The AuGa compound enhances the creation of more Ga vacancies, followed by the incorporation of Ge into Ga vacancies, and the TiO compound suppresses As outdiffusion from the GaAs substrate, respectively.
Hot-electron multiquantum well microwave detector operating at room temperature
Authors: Barbieri Stefano , Mango Francesco , Beltram Fabio , Lazzarino Marco , Sorba Lucia
Published: July 2002

A new multiquantum well hot-electron microwave detector is demonstrated. The GaAs–AlGaAs heterostructure was grown by molecular beam epitaxy and tested in the X and K bands. It showed room-temperature operation with responsivity of several 103 V/W. The operation of the device is based on enhanced thermionic current due to carrier heating by the incident in-plane polarized microwave electric field. This principle yields a broad frequency range of operation extending up to the millimeter band without significant degradation of the responsivity.
Thomson scattering in the corona of laser-produced gold plasmas
Authors: Glenzer S. H. , Back C. A. , Estabrook K. G. , MacGowan B. J.
Published: July 2002

Thomson scattering measurements of the electron temperature in laser-produced gold plasmas are presented. We irradiated a flat gold disk target with one laser beam of the Nova laser facility at an angle of 64° from the normal. A second laser beam probed the plasma at a distance of 500 μm with temporally resolved Thomson scattering. The electron temperature measurements are compared with hydrodynamic simulations using the code LASNEX for experiments applying smoothed and unsmoothed heater beams. In case of an unsmoothed heater beam the simulations predict temperatures which are about 40% higher than our measured data. Although the agreement is improved for a smoothed heater beam, discrepancies exist in the decay phase of the plasma. We discuss possible explanations for these observations.
A practical fiber optic air-ratio sensor operating by flame color detection
Authors: Yamaguchi T. , Grattan K. T. V. , Uchiyama H. , Yamada T.
Published: July 2002

This article discusses the development of a simple fiber-optic sensor used to detect the air-ratio in a premix type gas boiler, by monitoring and appraising the color of the flame emission, including the effect of radical emissions. Such boilers with a multi-port plate burner show an improved thermal efficiency, with the environmentally friendly effect of a reduction in both NOx and CO in the exhaust gas. The sensor is used to monitor and maintain the air-ratio in order to enable effective feedback control, and a low-cost, durable and small sensor solution is presented. Tests carried out show the potential of the sensor for use outside the laboratory and image processing techniques are used to analyze the spectral features of the emissions seen to confirm the spectral regions of use of the fiber-optic sensor.
Pulsed single-mode dye laser for coherent control experiments
Authors: Corless John D. , West James A. , Bromage Jake , Stroud C. R.
Published: July 2002

We describe a pulsed single-mode dye laser whose output characteristics satisfy the stringent requirements of coherent control experiments. This simple, low cost laser exhibits 1.6× transform-limited frequency performance with a single-shot linewidth of 58 MHz, and a time averaged linewidth of 240 MHz. The spatial mode is nearly Gaussian and has a beam quality parameter M2=1.2. We modified the pulse shape using saturable absorption in the dye amplifier. The resultant pulses are temporally smooth and have a duration of approximately 20 ns.
New sequential method to process noisy temperature response from flash experiment measured by infrared camera
Authors: Mourand David , Gounot Jean , Batsale Jean-Christophe
Published: July 2002

The estimation of a thermal diffusivity map of a surface can be performed with an infrared camera by processing thermal images in response to a pulse of radiant energy. Indirectly, it is then possible to map other properties (humidity, density, etc.). One of the first requirements of this kind of device is to take into account the thermal measurement noise. When the thermal diffusivity varies by a small amount around a nominal value, a new method of sequential estimation based on an asymptotic expansion is proposed. The confidence interval of this method has been analytically compared with success, to the moment method and the method of logarithmic transformation. An experiment demonstrated that thickness variations of 50 μm can be detected on a plate 5 mm thick for a sample of polyvinyl chloride.
High repetition rate far-infrared p-type germanium hot hole lasers
Authors: Bründermann E. , Röser H. P. , Heiss W. , Gornik E. , Haller E. E.
Published: July 2002

We have studied the influence of high repetition rates, up to 300 Hz, on four pulsed p-type germanium lasers. The maximum electric input power which terminates laser action via heating is a characteristic value for each crystal. We show magnetic field sweeps and introduce a diagram which connects the dynamical behavior of light and heavy holes to optical phonons and impurity states. We find that temperature is an essential key for the understanding of the laser action. High repetition rates or continuous wave operation may be achieved with proper design of the crystal and its cooling environment.
Photon-assisted cryoetching of III–V binary compounds by Cl2 at 193 nm
Authors: Lin J.-L. , Freiler M. B. , Levy M. , Osgood R. M. , Collins D. , McGill T. C.
Published: July 2002

We compare low-temperature, excimer-laser-induced etching of GaAs, GaSb, InAs, and InSb surfaces covered with 1–2 monolayers of condensed Cl2. The etch properties and a relative etch rate of GaAs∼GaSb<InAs<InSb are obtained. In addition, the etch rate of GaSb is characterized as a function of various system parameters, i.e., substrate temperature, chlorine pressure, and laser fluence. Spatially well resolved, anisotropic etching of 0.5 μm features has been achieved.
Influence of hydrogen on chemical vapor deposition of tungsten on sputter-deposited TiN layers
Authors: Zhang S.-L. , Palmans R. , Keinonen J. , Petersson C. S. , Maex K.
Published: July 2002

Tungsten (W) films are deposited on sputter-deposited TiN adhesion layers in a cold-wall chemical vapor deposition reactor, initiated with the deposition of a W nucleation layer by SiH4 reduction of WF6. H2 is also introduced in the reactor for some depositions. The electrical resistivity and mechanical stress of the W films are found to be dependent on the underlying TiN layers as well as on the presence of H2 during W nucleation layer deposition. A higher resistivity is obtained when the W is deposited on the TiN prepared at 250 °C than on the TiN prepared at 450 °C. For the W deposited on the low-temperature TiN, the resistivity is reduced by adding H2 to the reactants during W nucleation layer deposition; while for the W deposited on the high-temperature TiN, the resistivity is almost insensitive to the H2 addition. More oxygen and fluorine are found at the W–TiN interface for the W deposited on the low-temperature TiN than on the high-temperature TiN. Introduction of H2 to the reactants during W nucleation layer deposition reduces the concentrations of interfacial fluorine and oxygen, in agreement with thermodynamic predictions. A lower film stress is obtained for the W deposited on the high-temperature TiN layers and/or with H2 addition. The W films become less textured when H2 is introduced to the reactants during W nucleation layer deposition.
Filtered x-ray diode diagnostics fielded on the Z accelerator for source power measurements
Authors: Chandler G. A. , Deeney C. , Cuneo M. , Fehl D. L. , McGurn J. S. , Spielman R. B. , Torres J. A. , McKenney J. L. , Mills J. , Struve K. W.
Published: July 2002

Filtered x-ray diode (XRD) detectors are used as primary radiation flux diagnostics on Sandia’s Z accelerator, which generates nominally a 200-TW, 2-MJ, x-ray pulse. Given such flux levels and XRD sensitivities the detectors are being fielded 23 m from the source. The standard diagnostic setup and sensitivities are discussed. Vitreous carbon photocathodes are being used to reduce the effect of hydrocarbon contamination present in the Z-machine vacuum system. Nevertheless pre- and postcalibration data taken indicate spectrally dependent changes in the sensitivity of these detectors by up to factors of 2 or 3.
Gridless ionized metal flux fraction measurement tool for use in ionized physical vapor deposition studies
Authors: Snodgrass T. G. , Booske J. H. , Wang W. , Wendt A. E. , Shohet J. L.
Published: July 2002

Ionized physical vapor deposition is a technique for sputtering metal into small trenches, by ionizing sputtered metal atoms so that their trajectories can be controlled by electric fields. To this date no one has quantified exactly what fraction of the metal vapor is ionized, although the trends of how ionization varies with input parameters is known. This article describes and demonstrates a new quartz crystal microbalance design, which can be used to measure the ionized metal flux fraction arriving at the substrate location. Instead of using grids to repel ions as similar devices do, this analyzer works by applying a voltage bias to the front surface of the crystal in order to repel ions. A magnetic field adjacent to the face limits electron current to the microbalance, minimizing its perturbation of the plasma. The measurement tool described in this article does not suffer from complications caused by placing grids in front of the monitor and is an attractive method for characterizing ionized physical vapor deposition systems. Ion and neutral metal fluxes as a function of ionizer power are presented for an argon/copper discharge.
Taber vibration isolator for vacuum and cryogenic applications
Authors: Chan H. W. , Long J. C. , Price J. C.
Published: July 2002

We present a procedure for the design and construction of a passive, multipole, mechanical high-stop vibration isolator. The isolator, consisting of a stack of metal disks connected by thin wires, attenuates frequencies in the kilohertz range, and is suited to both vacuum and cryogenic environments. We derive an approximate analytical model and compare its predictions for the frequencies of the normal modes to those of a finite element analysis. The analytical model is exact for the modes involving only motion along and rotation about the longitudinal axis, and it gives a good approximate description of the transverse modes. These results show that the high-frequency behavior of a multistage isolator is well characterized by the natural frequencies of a single stage. From the single-stage frequency formulas, we derive relationships among the various geometrical parameters of the isolator to guarantee equal attenuation in all degrees of freedom. We then derive expressions for the attenuation attainable with a given isolator length, and find that the most important limiting factor is the elastic limit of the spring wire material. For our application, which requires attenuations of 250 dB at 1 kHz, our model specifies a six-stage design using brass disks of approximately 2 cm in both radius and thickness, connected by 3 cm steel wires of diameters ranging from 25 to 75 μm. We describe the construction of this isolator in detail, and compare measurements of the natural frequencies of a single stage with calculations from the analytical model and the finite element package. For translations along and rotations about the longitudinal axes, all three results are in agreement to within 10% accuracy.
New mounting method of diamond monochromator for high brilliance synchrotron radiation
Authors: Takiya Toshio , Sugiyama Hiroshi , Zhang Xiaowei , Shimada Shoichi , Yamazato Kunihiko , Komura Akio , Ando Masami
Published: July 2002

We have studied a new and reliable cooling method for diamond crystals in third generation light sources. In order to reduce the strain from brazing between the diamond monochromator and its Cu block cooling device, another diamond platelet was introduced as an interface. Using a finite element method program based on numerical thermal analysis, the mounting strain was estimated at 0.6 arcsec. Then data was confirmed through preliminary x-ray characterization using laboratory x-ray sources. The strain in the area exposed to a 1 mm×4 mm synchrotron radiation beam (absorbed power 100 W) was estimated by simulation at an acceptable 1.0 arcsec. Applying the new cooling method, the diamond crystal can tolerate synchrotron radiation power up to 100 W.
Eight-channel x-ray spectrometer for 0.2–1.5 keV energy range with high time and energy resolution
Authors: Bessarab A. V. , Grigorovitch S. V. , Intyapin V. V. , Kundicov V. I. , Kunin A. V. , Tokarev V. A.
Published: July 2002

An eight-channel soft x-ray spectrometer has been developed, manufactured, and calibrated. Each channel consists of a calibrated bandpass filter, multilayer mirror, and vacuum x-ray diode. The accuracy of channel sensitivity calibration is ⩽ 15%. The time resolution of the spectrometer is Δt≈150 ps and energy resolution is E/ΔE⩾20.
A low-temperature ultrahigh vacuum scanning tunneling microscope with a split-coil magnet and a rotary motion stepper motor for high spatial resolution studies of surface magnetism
Authors: Pietzsch O. , Kubetzka A. , Haude D. , Bode M. , Wiesendanger R.
Published: July 2002

We present the design of a new ultrahigh vacuum scanning tunneling microscope (STM) which operates at T<20 K inside the bore of a 2.5 T superconducting split-coil magnet. The tip/sample region can easily be controlled visually, thus allowing safe and fast exchange of samples and tips while the microscope stays at low temperatures. A newly developed rotary motion stepper motor is presented which allows rotation of the sample by >270° about an axis perpendicular to the tip axis. This feature allows metal or molecular beam evaporation normal to the sample surface. Even more important, by means of this device tip and sample can be brought into a parallel or antiparallel magnetic configuration thus opening a novel approach to the study of magnetic phenomena on an atomic length scale. In addition, measurements of the magneto-optical Kerr effect can be carried out without removing the sample from the STM. Also a new tip exchange mechanism is described. The microscopic and spectroscopic performance of the new instrument is illustrated on Au(111)/mica, on Tb(0001)/W(110), and on Gd(0001)/W(110).