bluuebunny/crossref_metadata_2025 huggingface dataset:
Schottky barrier height and interface chemistry of annealed metal contacts to alpha 6H-SiC: Crystal face dependence
Authors: Waldrop J. R. , Grant R. W.
Published: July 2002

The electrical properties and interface chemistry of unannealed and annealed Ni, Ti, and Al contacts to both Si (0001) and C (0001̄) terminated faces of 6H-SiC are compared by using x-ray photoemission spectroscopy, current-voltage, and capacitance-voltage data. For annealing temperatures in the 400 to 600 °C range Ni and Ti contacts have significantly more dissociation of interface SiC and formation of reaction products for the C-face than the Si-face. The chemical reactivity of the Al contact was limited and equal for both faces. Stability of the Schottky barrier height with annealing, which has a wide variation according to metal and face, is not correlated with the degree of metal/6H-SiC interface chemical reactivity
Evidence for the spectral dependence of nonequilibrium picosecond photoresponse of YBaCuO thin films
Authors: Semenov A. D. , Goghidze I. G. , Gol’tsman G. N. , Sergeev A. V. , Gershenzon E. M.
Published: July 2002

The transient voltage photoresponse of current biased YBaCuO thin films to 20 ps laser pulses of 0.63 and 1.54 μm wavelengths is measured for temperatures around the superconducting transition region. The fast picosecond decay of the response is followed by a slow nanosecond relaxation which is associated with the bolometric effect. The magnitude of the fast component of the response varies in proportion to the square root of wavelength that plausibly reflects multiplication processes of photoexcited electrons via electron–electron scattering and interaction with high energy phonons.
Accurate monocrystal miscut angle determination by x-ray diffraction on a wedge
Authors: Gailhanou M.
Published: July 2002

Semiconductor crystal miscut angles may be determined with high precision by a new method, based on the measurement of the Bragg angle shift for a highly asymmetric reflection. X-ray diffraction on a cleaved wedge has the particularity that the asymmetry is different for the cleavage plane and for the surface whose miscut angle is to be determined. Therefore, a rocking curve gives rise to two diffraction peaks. The angular difference between the two peaks is very sensitive to the miscut angle for high asymmetry of the reflection relative to the measured surface.
Growth of In1−xTlxSb, a new infrared material, by low-pressure metalorganic chemical vapor deposition
Authors: Choi Y. H. , Besikci C. , Sudharsanan R. , Razeghi M.
Published: July 2002

We report the growth of In1−xTlxSb, a new III-V alloy for long-wavelength infrared detector applications, by low-pressure metalorganic chemical vapor deposition. In1−xTlxSb with good surface morphology was obtained on both GaAs and InSb substrates at a growth temperature of 455 °C. X-ray diffraction measurements showed resolved peaks of In1−xTlxSb and InSb films. Infrared absorption spectrum of In1−xTlxSb showed a shift toward lower energies compared to InSb spectrum. Hall mobility data on In1−xTlxSb/InSb/GaAs structure showed enhanced mobility at low temperatures compared to InSb/GaAs structure.
High-resolution electron microscopic study of the interface between diamond film and its substrate
Authors: Jiang N. , Zhang Z. , Sun B. W. , Shi D.
Published: July 2002

A high-resolution electron microscopic (HREM) study of the interface structure between diamond film and its silicon substrate has been carried out. The HREM images reveal that there is an amorphous layer between diamond film and its substrate for a sample grown by the hot filament chemical vapor deposition. β-SiC crystallites are embedded in this amorphous layer. The HREM images of cross-sectional specimens reveal that the diamond crystallites can nucleate directly on either the intermediate amorphous layer, the β-SiC crystallites, or at some scratches of the Si substrate.
On the role of Cu and Nb in the formation of nanocrystals in amorphous Fe73.5Nb3Cu1Si13.5B9
Authors: Ayers J. D. , Harris V. G. , Sprague J. A. , Elam W. T.
Published: July 2002

Extended x-ray absorption fine structure analysis of amorphous and partially crystallized samples of the soft magnetic alloy Fe73.5Nb3Cu1Si13.5B9 reveals that, even before heat treatment, a portion of the Cu is present in the form of tiny, close packed clusters. Analysis of the Nb-free alloy Fe76.5Cu1Si13.5B9 shows that the Cu clusters are not present in the quenched ribbons, but that fcc Cu precipitates form during heat treatment. Results suggest that the Cu clusters act to catalyze nucleation of Fe-rich nanocrystals, but that these clusters are formed on a finer scale when Nb is added to the alloy, perhaps because it helps to lower the solubility of Cu in the amorphous phase.
Photoluminescence study of strong interdiffusion in CdTe/CdMnTe quantum wells induced by rapid thermal annealing
Authors: Tönnies D. , Bacher G. , Forchel A. , Waag A. , Landwehr G.
Published: July 2002

Thermally induced interdiffusion in CdTe/CdMnTe quantum wells was investigated by photoluminescence spectroscopy. The single quantum well structures were grown by molecular beam epitaxy annealed by rapid thermal annealing for 1 min at temperatures between 380 and 520 °C. A blue shift close to the barrier energy was observed indicating an almost perfect interdiffusion between the well and the barrier material. We derive an activation energy of 2.8 eV for the interdiffusion process from a Fickian diffusion model applied to our experiments.
Short wavelength intersubband transitions in InGaAs/AlGaAs quantum wells grown on GaAs
Authors: Chui H. C. , Martinet E. L. , Fejer M. M. , Harris J. S.
Published: July 2002

We have demonstrated intersubband transition energies as high as 580 meV (2.1 μm wavelength) in InGaAs/AlGaAs quantum wells (QWs) grown on GaAs substrates. The well width dependence of intersubband transition energies in both In0.5Ga0.5As/Al0.45Ga0.55As QWs and In0.5Ga0.5As/AlAs QWs have been determined. Good agreement of the intersubband transition energies to a single band effective mass model with band nonparabolicity included is found. Experimental studies of buffer and QW growth parameters for optimized intersubband absorption have also been performed.
High repetition rate operation of a long pulse excimer laser
Authors: Sato Yukio , Inoue Mitsuo , Haruta Kenyu , Nagai Haruhiko , Murai Yutaka
Published: July 2002

The high repetition rate operation of a long pulse XeCl laser is demonstrated. The laser is found to work successfully when the reverse voltage mode operation of a spiker-sustainer circuit is employed. This produces the steep voltage rise between the main electrodes resulting in an initiation of a homogeneous discharge and supplies excitation energy from the sustainer circuit with no time delay. These features enable the laser to operate at a repetition rate of greater than 500 Hz with a long pulse duration of 340 ns. An average power of 505 W is achieved.
Low-noise YBa2Cu3O7 -PrBa2Cu3O7 multiturn flux transformers
Authors: Keene M. N. , Goodyear S. W. , Chew N. G. , Humphreys R. G. , Satchell J. S. , Edwards J. A. , Lander K.
Published: July 2002

Epitaxial thin-film YBa2Cu3O7 flux transformers with multiturn input coils have been constructed on 1 cm2 MgO substrates using PrBa2Cu3O7 as an insulator. By coupling these to high-temperature superconducting quantum interference devices (SQUIDs) using a flip-chip technology, several low-noise magnetometers and a gradiometer have been constructed. The yield of fully working flux transformers on 1 cm2 substrates exceeds 80%, and field sensitivities at 77 K of (520±30)fT/√Hz at 1 Hz and (165±8)fT/√Hz above 10 Hz have been achieved. No evidence for excess low-frequency noise above that of the uncoupled SQUID has been found in the flip-chip magnetometers.
Theory of nonlinear optical absorption in coupled-band quantum wells with many-body effects
Authors: Pereira M. F. , Binder R. , Koch S. W.
Published: July 2002

Nonlinear optical absorption spectra and refractive index changes are computed for coupled-band semiconductor quantum wells by numerically solving the interband polarization equation. The theory combines band-structure engineering with many-body techniques and is applied to lattice-matched GaAs-AlGaAs and strained InGaAs-GaAs systems with carrier densities ranging from the excitonic to the gain regimes. Good agreement with recent experimental results is found.
High-efficiency silicon doping of InP and In0.53Ga0.47As in gas source and metalorganic molecular beam epitaxy using silicon tetrabromide
Authors: Jackson Steven L. , Fresina Michael T. , Baker Judith E. , Stillman Gregory E.
Published: July 2002

Efficient vapor source Si doping of InP and In0.53Ga0.47As have been demonstrated using SiBr4 as the Si source for both gas source (GSMBE) and metalorganic molecular beam epitaxy (MOMBE). Net electron concentrations ranging from n=2×1017 to 6.8×1019 cm−3 and from 9×1016 to 3×1019 cm−3 have been obtained for InP and In0.53Ga0.47As, respectively. Comparison of these data with those for Si2H6 indicate that the Si incorporation efficiency with SiBr4 is more than 10 000 times greater than with Si2H6 for substrate temperatures in the range of 475≤Ts≤500 °C. Specular surface morphologies were obtained, even for the most heavily doped samples. While [Si] as high as 1.8×1020 cm−3 was obtained in InP, the net electron concentrations and 300 K Hall mobilities decrease with increasing [Si] for [Si]≳6.8×1019 cm−3. Contact resistances as low as Rc=3×10−8 Ω cm2 were obtained using a nonalloyed Ti/Pt/Au contact to InP layers doped to n=6.3×1019 cm−3. During GSMBE growth, an increased Si background concentration ([Si]∼2×1017 cm−3) was observed after extended use of the SiBr4 source for these heavy doping concentrations. This increased background was not observed in MOMBE-grown material. Depth profiles of pulse-doped structures indicate the absence of memory effects for structures grown by MOMBE.
Fabrication of polymer light-emitting diodes using doped silicon electrodes
Authors: Parker I. D. , Kim Helen H.
Published: July 2002

We report the fabrication of light-emitting diodes from the semiconducting conjugated polymer poly[2-methoxy,5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene], using doped silicon (both n and p type) as an electrode material. Light emission at low voltages is clearly demonstrated. The presence of a thin SiO2 layer at the silicon interface modifies the device characteristics compared to devices fabricated on indium-tin-oxide substrates. An interesting consequence of this is the ability to align the Fermi level of the silicon electrode with the lowest unoccupied molecular orbital of the polymer allowing hole injection in forward bias and electron injection in reverse bias.
Strong accumulation of As precipitates in low temperature InGaAs quantum wells grown by molecular beam epitaxy
Authors: Cheng T. M. , Chin Albert , Chang C. Y. , Huang M. F. , Hsieh K. Y. , Huang J. H.
Published: July 2002

Low temperature InGaAs strained quantum wells have been grown by molecular beam epitaxy and annealed at 600–900 °C for 10 min. For an optimized annealing condition, arsenic precipitates can be successfully confined in the InGaAs wells and completely depleted in the GaAs barriers. The strong accumulation of As precipitates shows that the phenomena are not due to the strain effect but may be explained by the difference of interfacial energy between precipitate and matrix. The ability to control the As precipitates into two-dimensional quantum wells in LT materials has unique applications in a wide variety of devices.
Growth of high-quality 3C-SiC epitaxial films on off-axis Si(001) substrates at 850 °C by reactive magnetron sputtering
Authors: Wahab Q. , Sardela M. R. , Hultman L. , Henry A. , Willander M. , Janzén E. , Sundgren J.-E.
Published: July 2002

Single crystal 3C-SiC films of thickness ∼10 μm were grown by reactive magnetron sputtering on off-axis Si(001) at 850 °C. The film quality was comparable to the best chemical vapor deposited 3C-SiC as characterized by x-ray diffraction, transmission electron microscopy, and photo- luminescence (PL). The lattice mismatch and difference in thermal contraction between SiC and Si resulted in complete arrays of misfit dislocations at the film/substrate interface and a residual in-plane strain of (−6.9±1)×10−4, respectively. The full width at half-maximum (FWHM) of the 3C-SiC(004) peak was 59 arcsec in ω-2θ direction. The structural defects in the SiC film were planar faults on {111} planes and no voids or plastic deformation in the Si substrate were observed. PL spectra of SiC films showed characteristic appearances with N bound-exciton (N-BE) lines with a FWHM value of 3.4 meV. The deposition conditions leading to low defect-density 3C-SiC films are discussed in terms of low-energy ion-surface interactions.
Blue electroluminescence from porous silicon carbide
Authors: Mimura Hidenori , Matsumoto Takahiro , Kanemitsu Yoshihiko
Published: July 2002

The possibility of a new blue light emitting diode (LED) using porous SiC as a luminescent material is described. The porous SiC is electrochemically formed on a single crystalline 6H-SiC substrate fabricated by the Acheson method. The diode structure is a Schottky-like junction between indium tin oxide (ITO) and porous SiC. The ITO/porous SiC junction shows a rectification behavior and a blue electroluminescence (EL) under the forward direction.
Optical monitoring of the growth of heavily doped GaAs by chemical beam epitaxy and of the in situ etching of GaAs using CBr4
Authors: Joyce T. B. , Bullough T. J. , Farrell T.
Published: July 2002

We report the in situ optical monitoring of the growth of heavily doped GaAs by chemical beam epitaxy. The normal incidence reflectance of a 670 nm semiconductor laser was monitored in real time using dynamic optical reflectivity (DOR). Oscillations in the reflectance of the growing film arising from small changes in the refractive index due to doping were observed for carbon doping in the range 2×1019–6×1020 cm−3. No oscillations were obtained for samples with carbon or sulphur doping levels in the range 1018–1019 cm−3. A reduction in growth rate was observed for carbon concentrations above 1020 cm−3 and this was attributed to etching by the CBr4 dopant source. In situ etching of GaAs layers by CBr4 prior to growth was also monitored using DOR.
Effect of intrinsic growth stress on the Raman spectra of vacuum-arc-deposited amorphous carbon films
Authors: Ager Joel W. , Anders Simone , Anders Andre , Brown Ian G.
Published: July 2002

Amorphous carbon (a-C) films grown by vacuum-arc deposition techniques contain substantial amounts of compressive, residual, growth stress (over 10 GPa). The magnitude of the stress can be controlled by changing the incoming energy of the ions. It is observed that stress shifts the Raman scattering feature in these films to higher frequency by as much as 20 cm−1. The Raman spectra of adhering and delaminated films are used to measure the magnitude of the stress-induced shift, which is −1.9 cm−1/GPa for compressive biaxial stress. The observed value is compared to that expected from disordered diamond and graphite structures.
Femtosecond optical absorption measurements of electron-phonon scattering in GaAs quantum wells
Authors: Turner K. , Rota L. , Taylor R. A. , Ryan J. F. , Foxon C. T.
Published: July 2002

We present a combined experimental and theoretical investigation of intra- and intersubband carrier relaxation in GaAs/AlAs quantum wells following femtosecond laser excitation at low density. Time-resolved optical absorption has been measured using 125 fs pulses from a tunable Ti:sapphire laser which allows carriers to be excited preferentially into different subbands. The experiments have been analyzed using a multi-subband Monte Carlo simulation which contains all the important scattering mechanisms. Electron-phonon scattering rates obtained from dielectric continuum theory have been used, and we find excellent agreement with the experiment. The dominance of interface phonons in intrasubband relaxation is confirmed.
Modification to the HP 4274/75A LCR meters for investigation of device admittance under heavy forward bias conditions
Authors: Bach H. G. , Dressler W.
Published: July 2002

The HP 4274A and HP 4275A LCR meters are widely used in the fields of semiconductor device characterization and component test. A bias voltage can be applied to the test samples either from an external power supply or from the built-in HP-IB controllable voltage source. The total series resistance of the bias filtering circuit should be in the range of about 100 Ω (HP 4275A). Detailed measurements and checking the measuring circuit diagrams revealed that the effective series resistance can be much higher, depending on the measuring range of the bridge. Therefore, admittance measurements on low-ohmic samples, especially Schottky or pn junctions under heavy forward bias conditions, are seriously affected by bias voltage reduction between the front HI/LOW terminals. Thus, e.g., a reduced apparent capacitance is measured. Consequently, the doping concentration near the pn junction will be determined erroneously. To avoid these effects, a bias regulating circuit is inserted into the LCR meters to guarantee the feedthrough of the bias voltage without any attenuation. Examples of admittance vs frequency and doping profiles near the pn junction of quaternary (Ga0.046In0.954As0.1P0.9) diodes are given for explanation.
Application of silicon surface barrier detector for fast neutral particles
Authors: Miura Y. , Takeuchi H. , Ohara Y. , Konagai C. , Kimura H.
Published: July 2002

A design study of a small-size neutral particle analyzer using a silicon surface barrier detector (SSD) is performed. The SSD is very sensitive to x rays or photons, so that a pair of 45° sector magnets to separate a reionized neutral from x rays and photons will be used for this analyzer. In order to examine the performance, the SSD was applied to measure the species ratio of the prototype neutral beam injector for JT-60. It was confirmed that the energy resolution was 12% at 40 keV and the linear relation between the incident energy of particles and the pulse height was held over the energy range from 16.7 to 100 keV. The species ratio measured by the SSD was in good agreement with that by the Doppler-shift spectrometer. The SSD has a sufficient capability for the energy analysis of fast neutrals.
Ion temperature measurement in a plasma column using pulsed CO2 collective scattering and coherent detection
Authors: Lachambre Jean-Louis , Decoste Réal
Published: July 2002

We describe a pulsed CO2 laser scattering apparatus set up to measure the ion temperature of a magnetically stabilized arc plasma (ne ≂1021 m−3, Te ≂5 eV). Sensitivity and spectral resolution considerations led us to use heterodyne detection with a separate local oscillator and a multichannel rf frequency analyzer. The forward scattering angle is chosen to be 5° in order to match the expected ion feature spectrum to the receiver bandwidth and also to eliminate spontaneous fluctuations from the small-k, large-amplitude signal. Experimental scattering spectra illustrate the apparatus sensitivity to discharge current. The ion temperature appears to be determined to ±10%. Applications to high-temperature fusion plasmas are discussed.
Low-frequency digital lock-in amplifier
Authors: Probst P. A. , Collet B.
Published: July 2002

A digital lock-in amplifier which simultaneously measures in phase and in quadrature components at a reference frequency and at twice this frequency is described. It is drift free, insensitive to harmonics, has a very high gain stability (25 ppm/K), and operates up to 1250 Hz with no limitations on the low-frequency side.
Microchannel-plate pinhole camera for 20–100-keV x-ray imaging
Authors: Wang C. L. , Leipelt G. R. , Nilson D. G.
Published: July 2002

We present the design and construction of a sensitive pinhole camera for imaging suprathermal x rays. Our device is a pinhole camera consisting of four filtered pinholes and microchannel-plate electron multiplier for x-ray detection and signal amplification. We report successful imaging of 20-, 45-, 70-, and 100-keV x-ray emissions from the fusion targets at our Novette laser facility. Such imaging reveals features of the transport of hot electrons and provides views deep inside the target.
Calorimetric measurements of single-pulse high-power microwaves in oversized waveguides
Authors: Wharton C. B. , Earley L. M. , Ballard W. P.
Published: July 2002

A method for measuring the peak power of a single microwave pulse in an oversized circular waveguide is presented. This measurement technique uses a new circular waveguide calorimeter to measure the total energy of the microwave pulse. The peak power is determined from the total energy and by measuring the pulse shape with a fast diode detector connected to a circular waveguide directional coupler. Measurements have been made at 3.15 GHz for power levels up to 200 MW. Pulse widths were varied between 5 and 50 ns giving pulse energies between 1 and 10 J.
Method for an accurate calibration of the flight-time-focused time-of-flight atom probe
Authors: Ren Duomin , Tsong T. T. , McLane S. B.
Published: July 2002

A method is devised to determine accurately the flight-path constant, the time-delay constant, and the pulse factor for the flight-time-focused time-of-flight atom probe field ion microscope. Using these constants, masses of ions can be determined routinely to the accuracy of ∼0.005 to 0.06 u for ions of mass 1–100 u with our present system. This system has a flight-path length of ∼250 cm. It is equipped with a time digital converter of 1-ns time resolution and supporting measuring instruments of very modest specifications. The accuracy of the system can be further improved by having better supporting instruments. The principle of this calibration method can be easily adopted for calibrating other types of mass spectrometers.
K
a
-band circular polarization analyzer
Authors: Gold Steven H.
Published: July 2002

A simple device is described to test the circular polarization of microwave radiation. It employs two matched apertures, opposite 45° twists, and a hybrid coupler to separate and measure the two circularly polarized components of an incident wave.
Delay line anodes for microchannel-plate spectrometers
Authors: Lampton M. , Siegmund O. , Raffanti R.
Published: July 2002

We describe a photon-counting readout system for microchannel-plate spectrometers that uses a delay line and timing circuit for the wavelength coordinate and a wedge–wedge charge division system for the orthogonal spatial coordinate. A novel zigzag layout allows these two anode patterns to coexist on a common planar substrate and share the charge from each photoevent, thereby simultaneously localizing the photon in each of its two dimensions. Unlike wedge-and-strip or resistive anode encoders, the delay line offers a spatial resolution that is relatively independent of the format length. Unlike discrete anode systems, the delay line readout system’s complexity is also independent of the field of view size. These facts make the delay line readout system advantageous in large format detectors. We have assembled a testbed detector having a delay line propagation speed of 2.2 mm/ns and a time resolution of 33 ps FWHM. Ultraviolet testing shows a Gaussian event distribution having a 70 μm FWHM width; the readout system blur contribution is less than 50 μm FWHM.
Detuning of the gain and reflectivity spectra and its effect on the output characteristics of vertical cavity surface emitting lasers
Authors: McMahon C. H. , Bae J. W. , Menoni C. S. , Patel D. , Temkin H. , Brusenbach P. , Leibenguth R.
Published: July 2002

We have investigated the effect of mismatch between the reflectivity resonance and the gain spectra of vertical cavity surface emitting lasers. Detuning was caused by hydrostatic pressure and self-heating. Hydrostatic pressure shifts the gain peak towards shorter wavelengths with respect to the Fabry-Pérot (FP) resonance without modifying the gain spectrum. The threshold current remained unchanged for a positive mismatch of up to 18 nm. It increased four-fold for a negative mismatch of −13 nm at 0.5 GPa, where lasing disappeared. Increased threshold current and quenching of the emission are a consequence of the decrease of the gain at the FP resonance. A similar effect was observed when the gain peak was red-shifted with respect to the FP resonance by increasing the injected power. Increased mismatch is accompanied by a decrease of the gain at the emission wavelength which is responsible for the laser output quenching at high injected powers.
Deceleration ion optical system for sputtering measurements between 50 and 500 eV as function of angle of incidence
Authors: Liebl H. , Bohdansky J. , Roth J. , Dose V.
Published: July 2002

A deceleration system for a parallel ion beam in the energy range of 50 to 500 eV is described. The system is used for sputtering yield measurements as a function of the angle of ion incidence. Measured yield data for Cu and Au sputtered by 100- and 300-eV D+ ions are reported and compared to computer calculations. Experimental and calculated data show only a weak dependence on the angle of incidence. However, at glancing incidence the experimental values are larger up to a factor of 2 compared to the calculated ones. This is attributed to the surface roughness not included in the calculations.
High-precision portable instrument to measure position angles of a video camera for bird flight research
Authors: Delinger W. G. , Willis W. R.
Published: July 2002

A battery-powered portable instrument for research on the aerodynamics of bird flight has been built to automatically measure and record the horizontal and vertical angles at which a video camera is pointed as an operator videotapes a soaring bird. Each angle was measured to a precision of about 20 arc seconds or better. Two complete systems were constructed, and a triangulation method was used so the same bird in flight could be videotaped by two cameras at different locations to establish the radius vectors from an origin to the bird. The angle information was generated by rotary transducers attached to the camera mounts, and the angle values along with timing data were stored in the semiconductor memory of a single-board computer. The equipment has been successfully tested in the field and promises to have a wider application where a portable instrument is required to measure angles to high precision.
Dedicated microprocessor system to control laser Doppler velocimetry measurements and to reduce data
Authors: Srikantaiah D. V. , Philip T. , Wilson W. W.
Published: July 2002

A dedicated microprocessor system has been developed exclusively to control and reduce data from a two-component laser Doppler velocimeter (LDV) which uses counter-type signal processors. The system control and data-acquisition/validation software residing in the EPROMs has made the LDV system a stand-alone instrument. The measurements are initiated through a hex keypad where each key is programmed for a specific function including traverse of the optics. During measurements, blocks of 16 kbytes of raw data are transferred to a mass storage for detailed postmeasurement analysis. The system is also provided with a general purpose interface bus (GPIB) to enable access to a centralized data-acquisition network. The overall LDV system is portable and has been successfully used in field measurements at various magnetohydrodynamic (MHD) facilities and in other laboratory applications.
Dynamic response of the conical-tip thin-film thermometer
Authors: Hill Kenneth D.
Published: July 2002

The dynamic response of the conical-tip thin-film thermometer has been investigated through both experiments and numerical simulation. The numerical model extends the theoretical basis for the response from the simplified stagnation-region analysis to the cone geometry within the laminar flow regime, while taking into account the coupled thermal response of the fluid and the solid body. The experimental measurements, particularly the velocity scaling behavior, present useful information in their own right in addition to providing a check on the behavior of the model. This work confirms the shape of the dynamic response function and a velocity-independent spatial frequency response, a characteristic of the stagnation-region theory and an observed feature of hemispherical-tip probes. Previous authors have reported an empirically derived velocity dependence for the conical-tip sensor. In light of the work reported here, the validity of such empirical relationships must be seriously questioned.
Characterization of the piston gauge to assess the suitability of its use with several working fluids up to 5 MPa
Authors: Sharma J. K. N. , Jain Kamlesh K. , Bandyopadhyay A. K.
Published: July 2002

This paper describes the systematic studies carried out to characterize the controlled clearance piston gauge in the pneumatic pressure region up to 5.09 MPa by measuring its fall rate as a function of the jacket pressure (Pj) using different working fluids such as argon, nitrogen, helium, and hydrogen. It is also observed that a small ambient temperature fluctuation does not affect the overall uncertainty in the measured pressure. A relatively better reproducibility in the stall jacket pressure (Pz) values is obtained for helium and hydrogen as compared to that of argon and nitrogen; therefore it is shown that helium can also be used in addition to the commonly used nitrogen in the pneumatic pressure region. But the use of helium requires a higher value of Pj compared to that of nitrogen in order to get a good floating condition of the gauge. In addition, a detailed study is reported of the effective area of the simple piston gauge with different working fluids used during the calibration.
Probe for electrostatic wave measurements in plasmas
Authors: Wong K. L. , Akiyama H.
Published: July 2002

We present a probe arrangement for electrostatic wave measurements in plasmas. The probe picks up potential perturbation by capacitive coupling to a copper sensor. It has the advantages of high resolution (within 5 mm) and easy construction.
Use of laser-ablated fast particle beams for the measurement of n
e and T
e profiles in the TEXTOR boundary layer
Authors: Pospieszczyk A. , Ross G. G.
Published: July 2002

We have developed a source of suprathermal atoms consisting of a laser system, which ablates small portions of coating materials from the rear side of a glass substrate. The coating can be either a single species or a multilayer of several-thousand-angstrom thickness. Neutral particle beams produced by this method can have energies in the range of about 10 eV and penetrate into the plasma up to line densities of about nel=1×1013 cm−2. For the determination of the electron temperature we have chosen two elements, the ionization and excitation cross sections of which differ in the range up to 100 eV. For TEXTOR a two-component target with a C-LiF coating is used, which delivers a Li and C beam with about 5- and 15-eV energy, respectively, ablated by a ruby laser with 1-J energy. The beam attenuation is determined from the emitted light by using a camera with a Si-diode array system for spatial recording. The different attenuations and emission characteristics then allow the determination of radial electron density and temperature profiles over the spatial range from the liner into a few centimeters beyond the limiter.
High-pressure generation by a multiple anvil system with sintered diamond anvils
Authors: Ohtani E. , Kagawa N. , Shimomura O. , Togaya M. , Suito K. , Onodera A. , Sawamoto H. , Yoneda M. , Tanaka S. , Utsumi W. , Ito E. , Matsumuro A. , Kikegawa T.
Published: July 2002

High-pressure experiments using a multiple anvil high-pressure system with sintered diamond anvils are presented and discussed. Pressures in excess of 41 GPa were obtained, on the basis of the lattice constants of gold determined by the in situ x-ray diffraction technique using synchrotron radiation.
A simple monochromatic spark discharge light source
Authors: Chin O. H. , Wong C. S.
Published: July 2002

A compact spark discharge tube operated as a monochromatic light source at 587.5 nm is described. The device is powered by a small 25-kV, 3300-pF doorknob-type capacitor switched by an atmospheric air spark gap. The peak luminous intensity of the 587.5-nm line emission from the helium spark discharge operated at 23 kV and 900 mbar is estimated to be 2.1×103 Candela into 4π  radians.
High-current transistor-based regulator for the stabilization of 450-W xenon lamps
Authors: Policke Timothy. A. , Trexler Jack W. , Schreiner Anton F. , Knopp James A.
Published: July 2002

A stable high-current transistor-based regulator has been designed to stabilize 450-W dc xenon arc lamps. The circuit employs commercially available components. The regulator provides stabilization beyond that found in commercial optical instruments. The improvements using this circuit are a 0.20% ac-to-dc regulation representing a 44% decrease in the peak-to-peak ac ripple, achievement of nondrifting dc level, and being able to use the spectrometer immediately following lamp ignition.
Apparatus and experimental procedures for surface electron spectroscopies using incident ions, metastable atoms, and photons
Authors: Chaban E. E. , Hagstrum H. D. , Petrie P.
Published: July 2002

Two major additions to our multiexperiment apparatus are presented in this article. They are a metastable beam apparatus which produces 108 metastables per s and a sample manipulator that provides cooling of the sample to liquid-nitrogen temperature and flash heating to 1500 K following by rapid return to LN temperature. We also present new versions of our ion beam and photon beam apparatus. The ion beam source produces a 5×10−10A, focussed beam of noble gas ions at kinetic energies less than 10 eV. We discuss features of a K+ ion source, a Te evaporator, and our method of data presentation.
Nanosecond-pulse generator for laser diodes
Authors: Howard L. , Daneshvar K.
Published: July 2002

A high-current, nanosecond-pulse generator is described, ideal for driving low-impedance loads such as laser diodes. The generator utilizes step recovery diodes in a unique biasing scheme to produce 0.1–5 A pulses with pulse widths varying from 2 to 10 ns.
The use of graded-index fibers in fiber-optic laser-Doppler anemometry probes
Authors: Bopp S. , Tropea C. , Zhan L.
Published: July 2002

Fiber-optic laser-Doppler anemometry (LDA) probes based on the use of multimode, graded-index fibers are demonstrated. Conditions for fundamental transmission of laser light in these fibers are discussed, and an input coupling based on the use of SELFOC rod lenses is presented. The concept is demonstrated on several individual fiber links and on a two-component, backscatter LDA probe. The main advantages of this system lie in the simplicity and robustness of the input coupling mechanics while maintaining high transmitted power levels.
A new spectroscopic system for the measurement of hyper-Raman and Raman signals
Authors: Yamanaka Akio , Inoue Kuon
Published: July 2002

A new and highly sensitive spectroscopic system which allows one to observe Raman and hyper-Raman scattering signals in a successive or simultaneous way has been developed for the first time. The present apparatus consists of a repetitively Q-switched Nd-yttrium aluminum garnet (YAG) laser, a single-grating monochromator supplemented with a premonochromator which is a double-grating monochromator of zero-dispersive type, and a gatable optical multichannel detector cooled below −40 °C. With this, a greatly improved sensitivity for hyper-Raman signals has been accomplished. For exciting hyper-Raman signals the original beam of the Nd-YAG laser was used, whereas the second-harmonic light of the laser was used for Raman signals. The second-harmonic light beam, collimated to the original one, was obtained from a phase-matched LiNbO3 crystal mounted on a kinematic mount. Thereby, either the original beam of the Nd-YAG laser or the second-harmonic one could excite the same portion of the sample, so that both hyper-Raman and Raman signals appeared in the same spectral region. Thus, it was demonstrated that the measurement of Raman and hyper-Raman scattering signals could be easily made by setting and unsetting the kinematic mount.
A computer-controlled turbidity apparatus
Authors: Nash R. J. , Fisch M. R.
Published: July 2002

A computer-controlled apparatus to measure the turbidity of optically transparent samples near second-order or nearly second-order phase transitions is described. The instrument can measure the turbidity with an accuracy of 0.001 cm−1 and a precision of better than 0.5%.
Dimensional considerations for small-bore water manometers
Authors: Guillaume D. W. , Norton M. , DeVries D.
Published: July 2002

When designing or experimenting with time-responsive slant manometers requiring small bore, the capillary effects which can change the height of the meniscus need to be considered. This article explores the governing manometer-design equations and investigates each design parameter’s role in causing a capillary height change. The most significant parameter is the tube’s degree of incline from the vertical. As the tube is inclined from this position, the capillary effect is lessened, but must still be considered. The design equations derived below yield straightforward guidelines for limitations on a manometer tube’s internal diameter.
Observation of soft x-ray radiation from Heliotron E plasmas by the absorption method for the measurement of electron temperatures
Authors: Kaneko H. , Tohda T. , Iiyoshi A.
Published: July 2002

An absorption method of soft x ray is applied to Heliotron E plasmas for measurement of the electron temperature. Nitrogen gas is used as an absorber for convenience, owing to its accurate, uniform, and easily controllable density. The general feature of the absorption method for measurement of the electron temperature is discussed using a model with two parameters: the generalized thickness of the absorber and the electron temperature. The energy resolution of this method is not sufficient as a general method for spectral analysis. Hence, it is necessary to assume in advance such a model spectrum as consists of bremsstrahlung, recombination radiation, and impurity line radiation. Since the spectrum is always assumed before the analysis, we should try to find the origins of deformation of the energy spectrum and to correct the contribution. The effect of line emission from impurity ions to the estimated electron temperature is evaluated as a function of the electron temperature and the energy of the line relative to the generalized absorber thickness used in the measurement. An actual spectrum is measured by a pulse-height analysis (PHA) of the soft x ray. The one clear line, from chlorine, is not significant in the present determination of the electron temperature by the absorption method. Another possible line from iron at energy less than 1 keV is included in the analysis. Using a convenient method for determination of local emissivity from a chord-integrated emissivity, the electron temperature is determined from the local emissivity. The observed broad electron-temperature profile might be an artifact due to recombination radiation of the highly ionized ion diffused out of the hot core of the plasma. It is confirmed that the absorption method gives absolute measurement of the electron temperature at the plasma center, when additional information on impurity lines are given by PHA. The estimated temperature is consistent with the PHA measurement. The absorption method combined with PHA provides an easy and inexpensive measurement of the electron temperature compared with a system fully constructed by PHA.
Efficiency and resolution of a new readout system for electro-optical devices
Authors: Dunham Mark E.
Published: July 2002

Results of a new experiment investigating fiber-coupled, astronomical CCD cameras as imaging systems for electro-optic devices are described. These results indicate that single-electron detection is achievable at 10-kV energy and that the resolution can exceed 35-μm FWHM. A system using such a camera to read a matched, high-resolution phosphor is described, and characterizations of the various component efficiencies are given. It is concluded that this system offers formidable competition to microchannel plate intensified systems with respect to dynamic range, absolute sensitivity, and cost.
Computer-assisted data acquisition on Josephson junctions
Authors: Pagano S. , Costabile G. , Fedullo V.
Published: July 2002

An automatic digital data-acquisition system for the test and characterization of superconducting Josephson tunnel junctions is presented. The key feature is represented by the high degree of interaction of the measurement system with the device under test. This is accomplished by an iterated sequence of data acquisitions, automatic analysis, and subsequent modifications of the control signals in the device. In this way, the basic calibration and the value of the relevant quantities involved with the Josephson junction are automatically determined. A connection with a host computer makes possible more complex data analysis, while the full control of the experiment by a dedicated computer allows the operator to perform nonroutine procedures.
Eddy current shielding and heating: Reduction of dissipation for very low-temperature experiments in the presence of magnetic field ripple
Authors: Meyer Eric S. , Silvera Isaac F. , Brandt Bruce L.
Published: July 2002

We have studied eddy current heating and shielding for conducting materials in a cylindrical geometry, and we have performed numerical calculations as a function of the important parameters. Results are presented in graphical form. Eddy current heating in OFHC copper at low temperatures and means of suppressing it have been studied in a Bitter magnet in a field of 15 T. Results show that it is possible to use conducting materials for experiments in high magnetic fields at temperatures below 1 K.
A parallel multiprocessor system for Monte Carlo simulations in statistical physics
Authors: Saarinen Jukka , Kaski Kimmo , Viitanen Jouko
Published: July 2002

Hardware architecture and operating software of a parallel multiprocessor system for various Monte Carlo simulations of models in statistical physics is described. The main parts of the multiprocessor systems are the host processor, three tightly coupled MIMD parallel processors, and their individual memories. Our multiprocessor system is flexible to operate, easy to expand and executes programs written in high-level tamc language which is a subset of the c programming language. The host computer is used to develop, compile, and down-load programs and transmit the results from work memory to mass memory for further analysis.
Worldwide census of synchrotron radiation facilities
Authors: Kobayakawa H. , Huke K.
Published: July 2002

Information has been compiled on the parameters of synchrotron radiation sources in twelve countries, including almost forty individual facilities. The data includes the energy of the beam, the characteristic photon energy, εC, of the bending magnet radiation, and details of the beam itself, and of beamlines, experimental stations, insertion devices, and photon energies.
SR x-ray fluorescence imaging by image reconstruction technique
Authors: Iida Atsuo , Takahashi Mamoru , Sakurai Kenji , Gohshi Yohichi
Published: July 2002

X-ray fluorescence imaging was made by the image reconstruction technique combined with synchrotron radiation. The monochromated synchrotron x-rays of line shape were used for the excitation of elements or the chemical state of an element. The sample was scanned with the rotational and translational motion, then the data was numerically transformed to the two-dimensional distribution of elements by the back-projection technique. In this method, the signal-to-background ratio was improved compared with the point scanning method. The application to the chemical state imaging of the sintered iron ore was demonstrated. The possibility of high resolution imaging was also studied using an asymmetric diffraction. A line-shaped x-ray beam as narrow as 4 μm was obtained.
Synthesized multilayer Fresnel X-ray optics (abstract)
Authors: Erko A. I.
Published: July 2002

The paper considers a diffraction model of a new type of focusing elements for x-ray optics based on profiled multilayer reflection structures. The characteristics of the focusing properties of synthesized Fresnel structures (SFS) were compared to those of conventional ‘‘transparent’’ zone plates. The latter were shown to exhibit fundamental resolution limits caused by the effects of volume diffraction in structures of real thickness. SFS x-ray optical elements are free from such limitations and display the properties of volume holographic lattices, namely, absence of chromatic aberrations, high efficiency and spatial resolution. The first experimental results of the investigation of SFS focusing properties in the soft x-ray wavelength range are reported. It is most advantageous to use SFS elements for controlling powerful synchrotron radiation beams, since they combine the temperature stability of multilayer mirrors with the possibility to obtain resolution below 0.1 μm.
Apparatus for time-resolved x-ray absorption spectroscopy using flash photolysis
Authors: Clozza A. , Congiu Castellano A. , Della Longa S. , Giovannelli A. , Bianconi A.
Published: July 2002

A system for time-resolved data acquisition is described. It is based on a Nd-YAG power laser, five NaI scintillators coupled with five photomultiplier tubes, a fast multichannel analyzer, a cryostat, and a Macintosh II computer (system controller and data acquisition). By means of this apparatus, time-resolved x-ray spectra of CO-myoglobin will be acquired using the synchrotron radiation emitted by a wiggler magnet.
Dynamical x-ray diffraction from a perfect crystal under grazing incidence conditions
Authors: Hashizume H. , Sakata O.
Published: July 2002

Synchrotron radiation obtained from the 6-T vertical-wiggler source at the Photon Factory has been used to study dynamical x-ray diffraction in a nearly perfect germanium crystal under total external reflection conditions. A specially designed goniometer has allowed independent control of the glancing angle and the deviation angle from exact Bragg incidence. The rocking-curve profiles observed from slightly asymmetric Bragg planes as a function of glancing angle were found to be quite different for both the diffracted and specular beams. These profiles show unusual features arising from the excitation or de-excitation of the wave fields in shallow surface layers of the bulk crystal. Furthermore, GeK fluorescence signals measured during the Bragg reflection showed characteristic modulations, demonstrating the feasibility of new standing-wave experiments for determination of interface structures.
Trial use of carbon-fiber-reinforced plastic as a non-Bragg window material of x-ray transmission
Authors: Nakajima T. , Koyama A. , Kuraoka Y. , Matsumoto K. , Yoshizawa M.
Published: July 2002

The carbon-fiber-reinforced plastic (CFRP) that can be used for window material in place of beryllium is a composite-type material comprising twisted carbon fibers and bisphenol-A plastic. Since the constituent elements of hydrogen, carbon, and nitrogen are thoroughly dispersed as a compound, the mass absorption coefficient of CFRP is somewhat larger than that of beryllium. The diffraction pattern of CFRP shows only a single halo pattern without a Bragg-like peak which is found in Mylar. Through x-ray diffraction, CFRP was confirmed to be practical for use as a non-Bragg window material with a moderately low mass-absorption coefficient and could be substituted for crystalline beryllium.