bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanism of stress transmission from an electrorheological fluid to the electric plates
Authors: Miyamoto Tetsuo , Ota Motonori
Published: July 2002

We propose a new mechanism of stress transmission from an electrorheological fluid (ERF) to the electric plates. Employing the cubic particle chain model, we have calculated the force acting on the particle of chains spanning the electric plate gap. In a linear region between stress and strain, we have found that the friction force between the plate and the adjacent particle is very important to induce stress from an ERF. The friction force is also a key factor to determine which phenomena occur first, the particle chain breaks up or it begins to move on the plate.
Band-offset determination for GaInP-AlGaInP structures with compressively strained quantum well active layers
Authors: Dawson Martin D. , Duggan Geoffrey
Published: July 2002

(AlGaIn)P-on-GaAs structures incorporating compressively strained Ga1−xInxP (x≳0.48) quantum well active layers have been studied by low-temperature photoluminescence excitation spectroscopy. The splitting between the lowest energy heavy- and light-hole excitonic transitions is observed to be only weakly dependent on well width over the range 25–300 Å, for sample sets with x=0.56 and x=0.59. Envelope function approximation fitting, based on bulk valence band dispersion calculations which include the strain-induced interaction with the spin split-off band, shows this splitting behavior to be a sensitive function of the heterojunction band offset. Conduction band discontinuities, ΔEc, of 0.67ΔEg (x=0.56) and 0.85ΔEg (x=0.59) provide the best fit to these and all higher lying transitions for the full range of structures examined, indicating that poor hole confinement is a limiting factor in practical compressive strain (AlGaIn)P laser device performance.
Epitaxial growth of SrTiO3/YBa2Cu3O7−x heterostructures by plasma-enhanced metalorganic chemical vapor deposition
Authors: Liang S. , Chern C. S. , Shi Z. Q. , Lu P. , Safari A. , Lu Y. , Kear B. H. , Hou S. Y.
Published: July 2002

We report heteroepitaxial growth of SrTiO3 on YBa2Cu3O7−x/LaAlO3 substrates by plasma-enhanced metalorganic chemical vapor deposition. X-ray diffraction results indicated that SrTiO3 films were epitaxially grown on a (001) YBa2Cu3O7−x surface with [100] orientation perpendicular to the surface. The film composition, with Sr/Ti molar ratio in the range of 0.9 to 1.1, was determined by Rutherford backscattering spectrometry and energy dispersive spectroscopy. The thickness of the SrTiO3 films is 0.1–0.2 μm. The epitaxial growth was further evidenced by high-resolution transmission electron microscopy and selected area diffraction. Atomically abrupt SrTiO3/YBa2Cu3O7−x interface and epitaxial growth with [100]SrTiO3∥[001]YBa2Cu3O7−x were observed in this study. The superconducting transition temperature of the bottom YBa2Cu3O7−x layer, as measured by ac susceptometer, did not significantly degrade after the growth of overlayer SrTiO3. The capacitance-voltage measurements showed that the dielectric constant of the SrTiO3 films was as high as 315 at a signal frequency of 100 KHz. The leakage current density through the SrTiO3 films is about 1×10−6 A/cm2 at 2-V operation. Data analysis on the current-voltage characteristic indicated that the conduction process is related to bulk-limited Poole-Frenkel emission.
Photochemically formed refractive index profiles in nonlinear optical polymer thin films
Authors: Kim Jang-Joo , Zyung Taehyoung , Hwang Wol-Yon
Published: July 2002

A simple but realistic kinetic model has been developed to describe the refractive index profile formed by photochemical reaction in nonlinear optical polymers. The effects of the absorption due to the unconvertible reactant and the photoproduct are included in the model. The experimental results are consistent with the model. The parameters required in the model are obtained from a simple transmission experiment. The rate of the bleached depth change with time becomes slower as the bleaching proceeds, while the shape of the index profile was kept nearly the same. Small absorption of bleaching light due to the photoproduct has a significant effect on the resulting refractive index profiles.
Decay dynamics of laser-induced gratings in LiNbO3:Zn
Authors: Deng Jiachun , Wen Jinke , Wu Zhongkang , Wang Huafu
Published: July 2002

The light-induced grating erasure technique has been used to measure the photorefractive properties of LiNbO3:Zn. The results show that the photoinduced hole carriers increase when Zn content exceeds the concentration threshold. The charge relocation rate at high Zn doping content increases significantly, while the concentration of the photoinduced charge carriers has no obvious change.
Positive charging of buried SiO2 by hydrogenation
Authors: Vanheusden K. , Stesmans A.
Published: July 2002

Simple hydrogen annealing of the buried oxide (BOX) of state-of-the-art separation by implanted oxygen material in the range 450–700 °C was found to introduce net positive charge in the BOX with areal densities up to 5×1012 elem. charges cm−2, while H2 annealing in the range 700–1000 °C was observed to activate a neutral state. Both processes appeared reversible upon appropriate vacuum annealing. The positive charge in the BOX is detected using electron spin resonance of a positive BOX-charge-induced signal in Si. The results are interpreted in terms of a two-state model which describes the trapping of hydrogen at a reactive site yielding an either positively charged (activation temperature TA≊450 °C) or neutral (TA≊715 °C) state, based on hydrogen incorporation into oxygen vacancies (Si—Si bonds).
New approach to the growth of low dislocation relaxed SiGe material
Authors: Powell A. R. , Iyer S. S. , LeGoues F. K.
Published: July 2002

In this growth process a new strain relief mechanism operates, whereby the SiGe epitaxial layer relaxes without the generation of threading dislocations within the SiGe layer. This is achieved by depositing SiGe on an ultrathin silicon on insulator (SOI) substrate with a superficial silicon thickness less than the SiGe layer thickness. Initially, the thin Si layer is put under tension due to an equalization of the strain between the Si and SiGe layers. Thereafter, the strain created in the thin Si layer relaxes by plastic deformation. Since the dislocations are formed and glide in the thin Si layer, no threading dislocation is ever introduced in to the upper SiGe material, which appeared dislocation free to the limit of the cross sectional transmission electron microscopy analysis. We thus have a method for producing very low dislocation, relaxes SiGe films with the additional benefit of an SOI substrate.
High efficiency chemical etchant for the formation of luminescent porous silicon
Authors: Kelly Michael T. , Chun Jonathan K. M. , Bocarsly Andrew B.
Published: July 2002

Hydrofluoric acid solutions containing high concentrations of the ion NO+ produce an etchant capable of reproducibly generating a porous silicon layer on both single-crystal and polycrystalline silicon surfaces. Room-temperature photoluminescence from porous silicon that has been chemically etched in such solutions has been observed. The photoluminescent intensity is superior to that obtained using HNO3/HF based stain etches. Reproducibility with respect to etch induction time, and the quality of the porous silicon layer are also improved when compared to classic stain etchants. Although, prior work has suggested that HNO2 is the active oxidant in silicon stain etching processes, the present work points to NO+ as the active species.
Isolation of fulleride phases by distillation
Authors: Poirier D. M.
Published: July 2002

A technique for the synthesis of phase pure alkali-metal fullerides is demonstrated. The fulleride compounds are distilled from mixed phase samples or from other pure phases by the preferential evaporation of either fullerenes or alkali-metal atoms. Distillation has been used to form K3C60, K4C60, RbC60, and Rb4C60 which exhibit core level photoemission spectra that are consistent with bulk structure measurements. The KxC70 system, for which structural information has not been reported, was also examined and the compounds KC70, K3C70, and K4C70 were found.
Application of x-ray interference method for residual strain measurement in low energy Ar ion-bombarded Si (001)
Authors: Tsai Cho-Jen , Vreeland Thad , Atwater Harry A.
Published: July 2002

We have employed the x-ray interference method for measurement of the residual strains in Si (001) surfaces bombarded by low energy Ar+. This method, combined with transmission electron microscopy, permits determination of the average residual strain in very thin bombarded layers. The residual strain in the bombarded layers was found to monotonically increase as the density of pointlike defects increases and saturates upon the formation of extended defects. Annealing data also suggest that defects formed by low energy ion bombardment at moderate temperature (≊450 °C) require high temperature (≳800 °C) annealing for their removal.
Study of diffusion and trapping of a fluorinated hydrocarbon in ion beam irradiated poly(styrene) by nuclear resonance reaction analysis
Authors: Umezawa Kenji , Nakanishi Shigemitu , Gibson Walter M. , Frisch Harry L. , Kitamura Akira
Published: July 2002

The swelling of a poly(styrene) (PS) glass by sorption of a fluorinated hydrocarbon, 3,5-bis (trifluoromethyl) aniline (TFMA) is considered in a regime characterized by so called case II diffusion. Attention is focused on diffusion and trapping of vapor into ion beam irradiated glassy PS by using nuclear resonance reaction analysis. The diffusion coefficient for the TFMA is dramatically decreased on irradiation with a 30 keV H+ with 5×1013–1×1014 atoms/cm2 at 22.5 °C. These ion beam irradiation effects are similar to temperature effects on diffusion. As an application of the observed effect, trapping the TFMA was carried out between two different ion beam irradiation regions into PS at room temperature. This feature may allow development of new kinds of devices for applications.
Simulations of crystal growth: Effects of atomic beam energy
Authors: Gilmer George H. , Roland Christopher
Published: July 2002

We have simulated silicon molecular beam epitaxy on (100) and (111) substrates using molecular dynamics methods. We find that the kinetic energy of the atomic beam has a dramatic effect on the crystalline ordering in the deposit. Energetic beams form a crystalline film at less than half the absolute temperature required for a thermal beam. Our simulations show that crystallization is facilitated by the transient atomic motion just after the impact of an atom from the beam.
Nonlocal electron kinetics in a low-pressure inductively coupled radio-frequency discharge
Authors: Kolobov V. I. , Beale D. F. , Mahoney L. J. , Wendt A. E.
Published: July 2002

The Boltzmann equation for electrons is analyzed for a low-pressure inductively coupled rf discharge in argon driven by a planar coil. Spatially resolved probe measurements of the electron distribution function (EDF) indicate that the total energy of electrons is an argument of the EDF. Pressure dependence of the light emission distribution is explained on the basis of nonlocal electron kinetics.
Laser-induced phase transformation from amorphous to perovskite in PbZr0.44Ti0.56O3 films with the substrate at room temperature
Authors: Lu X. M. , Zhu J. S. , Huang X. F. , Lin C. Y. , Wang Y. N.
Published: July 2002

Radio-frequency-sputtered amorphous as-grown PbZr0.44Ti0.56O3 (PZT) thin films were prepared on glass substrates from a PZT ceramic target with excess PbO. They were subsequently treated with a laser-induced phase transformation technique to achieve a pure perovskite structure. The optimal conditions for the process were determined. During the whole fabrication process, the substrate was kept at room temperature. This technique was also compared with traditional oven and rapid thermal processing after-deposition treatments.
New crystalline structure for nanometer-sized Ge microcrystallites prepared by plasma enhanced chemical vapor deposition
Authors: Jiang Jiangong , Chen Kunji , Huang Xinfan , Li Zhifen , Feng Duan
Published: July 2002

Crystallized Ge films have been produced in a plasma enhanced chemical vapor deposition system by the decomposition of H2-diluted GeH4 gas source while using the H2 plasma treatment. Structural analyses of the films using x-ray diffraction and transmission electron microscopy techniques revealed a new crystalline structure in the Ge microcrystallites with a diameter of about 5 nm, which is different from the normal diamond structure of crystalline Ge. This new nanometer crystalline structure has been explained to be a metastable nanometer-sized atomic configuration formed in the film deposition process.
Fabrication of a silicon quantum wire surrounded by silicon dioxide and its transport properties
Authors: Nakajima Y. , Takahashi Y. , Horiguchi S. , Iwadate K. , Namatsu H. , Kurihara K. , Tabe M.
Published: July 2002

A novel fabrication method for ultrafine silicon wires is presented. To achieve electron physical confinement with a high potential SiO2 barrier, the SIMOX (separation by implanted oxygen) technique, electron beam lithography, anisotropic chemical etching, and thermal oxidation are used. The size of the wires is controlled by the lithography, the thickness of the top silicon layer and the thermal oxidation for narrowing the patterned silicon wire. The steplike structure in the conductance versus gate voltage curve, which remains up to higher temperatures for a smaller wire, suggests that a strong one-dimensional transport effect occurs in this silicon wire.
High quality AlxGa1−xN grown by metalorganic chemical vapor deposition using trimethylamine alane as the aluminum precursor
Authors: Khan M. Asif , Olson D. T. , Kuznia J. N.
Published: July 2002

We report the first low pressure (76 Torr) metalorganic chemical vapor deposition of AlxGa1−xN using trimethylamine alane (TMAAl) as the aluminum source. AlxGa1−xN epilayers deposited using TMAAl exhibited an excellent surface morphology and very strong room temperature photoluminescence. For AlN layers (using TMAAl as the aluminum precursor) we obtained a total carbon contamination level as low as 1017 cm−3.
Helium bubbles in silicon: Structure and optical properties
Authors: Siegele R. , Weatherly G. C. , Haugen H. K. , Lockwood D. J. , Howe L. M.
Published: July 2002

Silicon samples were implanted with 20 keV He at various temperatures. The damage and the size of the He bubbles created during the implantation were measured with Raman spectroscopy and transmission electron microscopy. Room temperature implantation with 2.5×1017 He atoms/ cm2 produced an amorphized layer with a high density of small voids (∼5 nm). After annealing at 923 K the amorphous layer was recrystallized, but still contained extended defects. The He bubbles coalesced forming large bubbles in the implanted region. Implantation at 723 K left the Si essentially crystalline, but with a large number of defects. The He bubbles created at this temperature were larger than after room temperature implantation. Light emitting properties of this porous material are briefly discussed.
Acousto-optic technique: A new nondestructive technique to evaluate thin layered structures
Authors: Wevers M. , Devolder S. , De Meester P. , Leroy O.
Published: July 2002

On laboratory scale a new nondestructive technique has been elaborated for the quality control of layered structures. This technique is called the ‘‘acousto-optic technique’’ and it measures the modulation of ultrasound reflected by a layered material optically in amplitude and phase using laser beams crossing the ultrasonic beams (incident and reflected). The most important characteristics of layered structures which have been investigated are the thickness and the thickness variations within a layer and the presence of artificial defects. Only when the ultrasound is incident in the Rayleigh angle of the substrate material, the phase differences measured obtain important information on the quality of the layered structure. The experimental results underline the results already obtained from the theoretical models elaborated for this technique.
High etch rates of GaN with magnetron reactive ion etching in BCl3 plasmas
Authors: McLane G. F. , Casas L. , Pearton S. J. , Abernathy C. R.
Published: July 2002

Magnetron reactive ion etching of GaN in BCl3 plasmas was investigated as a function of cathode power density, flow rate, and pressure. GaN etch rates were achieved (350 nm/min), which were twice the highest etch rate previously reported, and at low cathode bias voltages (<100 V). Auger electron spectroscopy measurements revealed the etched surfaces to be Ga deficient to a depth of 10 nm, with a surface chlorine residue of <1 at. %. Magnetron dry etching appears well suited to applications such as mesa definitions for photonic devices in the GaN materials system.
Fast multichannel heterodyne radiometer for electron cyclotron emission measurement on stellarator W VII-A
Authors: Hartfuss H. J. , Tutter M.
Published: July 2002

An eight-channel radiometer for simultaneous measurement of electron temperatures at different radii via electron cyclotron emission is described. It is divided into two parts, the interchangeable front end and the filter section. By replacing the front end, both first and second-harmonic electron cyclotron emission measurements are possible in the range of 50–180 GHz. The instrument is absolutely calibrated with an accuracy estimated to be within ±10%. The spatial resolution ΔR/R is of the order 10−3, the temporal resolution 20 μs.
Microchannel plate streak camera
Authors: Wang C. L. , Medecki H. , Hale C. P. , Leipelt G. R. , Thomas S. W. , Wiedwald J. D.
Published: July 2002

The development of a streak camera using a microchannel plate electron multiplier as the cathode is presented. Potential applications to γ-rays, low-energy x-rays, and charged particles are described. Preliminary test shows that 150-ps resolution can be obtained.
Tomographic analysis of the evolution of plasma cross sections
Authors: Holland A. , Navratil G. A.
Published: July 2002

A diagnostic has been developed for measurements of the evolution of plasma density distributions in two dimensions using the principles of computed emisson tomography. The system measures the near-infrared emission along several chords through the plasma cross section and the emission profile is then reconstructed using a maximum entropy based algorithm. This paper will present details of the reconstruction algorithm, the data collection system, the verification of the diagnostic using both physical and numerical phantom sources, evidence for the correlation between n2 and the infrared emission intensity, and initial measurements on a tokamak plasma.
Novel electromagnetic technique for repositioning of coolant tube spacers in CANDU nuclear reactors
Authors: Dableh Joseph H.
Published: July 2002

A novel electromagnetic technique to reposition the coolant tube spacers in the fuel channels of CANDU nuclear reactors was successfully developed in the fall of 1983 at Ontario Hydro Research Division. The need to reposition dislocated spacers in noncommissioned reactors was discovered subsequent to the rupture of a pressure tube in one reactor at the Pickering Nuclear Generator Station in Ontario. A contributing factor to the failure of the tube was the fact that the annular spacers (garter springs), used to maintain the coaxial configuration between the pressure tube and its surrounding calandria tube, had been displaced longitudinally for a number of years. Subsequent to this finding, it was discovered that a number of garter springs in noncommissioned nuclear reactors were displaced due to vibration induced by various sources during the construction stage. Since the garter springs are not directly accessible by mechanical means, extensive dismantling of the fuel channels would have been necessary to reposition the springs in their designated locations. This paper describes a novel method to reposition the garter springs without dismantling the fuel channels. The method consists of exerting a force on the springs in the direction of the required displacement by applying a large electromagnetic impulse (generated by a 200-kJ capacitor bank) to a drive coil inserted into the pressure tube opposite the spacer. The repositioning of displaced garter springs in five new reactors in Ontario has been carried out successfully in 1984. The saving in reactor repair cost, interest charges, and replacement energy cost was on the order of hundreds of millions of dollars. Equally large benefits and savings will be realized if the need to use this technique in commissioned reactors arises. Also, the related development of strong compact coils and low-resistance pulse power cable have significant implications and advantages in various other applications related to the pulse power industry, in general, and to electromagnetic metal forming and fusion technologies, specifically.
Diagnostics for TFTR neutral beam species measurement
Authors: Kugel H. W. , Eubank H. P. , Gammel G. , Grisham L. R. , Kaita R. , Kamperschroer J. H. , Kozub T. A. , Langley R. A. , Medley S. S. , O’Connor T. , Prichard B. , Roquemore A. L. , Williams M. D.
Published: July 2002

Five diagnostic systems were used for initial species measurements during tokamak fusion test reactor (TFTR) neutral beam test stand operations involving four ion sources, as well as several different configurations and operating conditions. Initial results were obtained for total neutral species fractions at the beamline input and the beamline output, differential radial profiles of species fractions, angular divergences of species components, species radial power density profiles, and beam impurity components for various conditions.
Fourier transform infrared spectrometer for a single aerosol particle
Authors: Grader Gideon Sageev , Flagan Richard C. , Seinfeld John H. , Arnold Stephen
Published: July 2002

A spectrometer is reported here for obtaining the infrared spectrum of a single aqueous aerosol particle by a Fourier transform technique. The particle is held in an electrodynamic balance and irradiated simultaneously by the infrared output from a Michelson interferometer and the visible light from a dye laser. The size of the particle is modulated by chopping the IR beam, and the resulting visible scattered light fluctuation is detected at 90° with a photomultiplier tube. The amplitude of the scattered light fluctuation is measured with a lock-in amplifier at each interferometer mirror position. The electronic circuitry for stepping the interferometer mirror is presented and discussed. Inverting the lock-in signal by a discrete fast Fourier transform routine (FFT) yields the particle absorption spectrum. The resulting spectrum for an (NH4)2SO4 droplet is presented.
New apparatus for measuring steady-state diffusion
Authors: Mikati Nabil
Published: July 2002

A steady concentration gradient is maintained in a narrow vertical diffusion channel making it possible to determine the concentration dependence of the diffusion coefficient in one single experiment. The gradient is sustained by a simple transport system and is observed interferometrically. The apparatus is tested using calcium chloride and sugar. The method is rapid and the results agree fairly well with those reported in the literature. Analyses of the flow velocity and the time to reach the steady state are given.
Spatial Fourier transform method for evaluating SQUID gradiometers
Authors: Ribeiro P. Costa , Bruno A. C. , Paulsen C. C. , Symko O. G.
Published: July 2002

A simple method of measuring the spatial transfer function of a gradiometer, consisting of a flux transformer coupled to a SQUID, is presented and it is compared with theoretical predictions. Based, on this approach, a new method of reporting a gradiometer’s performance is proposed; the rejection factor is expressed in decibels obtained directly from the transfer function plot.
Gas-handling system of a gas chromatograph for the purity control of tritium gas
Authors: Schober T. , Dieker C.
Published: July 2002

The gas-handling system of a simple, inexpensive gas chromatograph is described suitable for the safe and fast purity analysis of tritium gas.
Reply to ‘‘Comments on ‘Improved algorithm for the discrete Fourier transform’ ’’ [Rev. Sci. Instrum. 5
8, 714 (1987)]
Authors: Froeyen M. , Hellemans L.
Published: July 2002

The difference between Sorella and Ghosh’s approach [Rev. Sci. Instrum. 55, 1348 (1984)] and ours [M. Froeyen and L. Hellemans, Rev. Sci. Instrum. 56, 2325 (1985)] to obtain an expression for the Fourier transform of discrete data is highlighted. A practical advantage of our algorithm over Sorella’s is stressed.
Drive mechanism for a surface force apparatus
Authors: Luesse Clifford , Van Alsten John , Carson George , Granick Steve
Published: July 2002

A technique is described for micropositioning a surface forces apparatus with low mechanical and thermal drift. The technique is less exacting and more stable than competing ones.
Precision vacuum X
Y
Z adjustable laser mirror mount
Authors: Gilmartin M. , Williamson B. , Campbell N.
Published: July 2002

A laser mirror mount is described for use in a vacuum enclosure which will allow for horizontal and vertical movement and, in addition, offer linear travel of around 1 cm with micron accuracy. This design is relatively simple and easy to produce and has proven both rugged and reliable in day-to-day use. Such a mount has great potential in applications such as color center lasers where operation at 77 K is required, thus necessitating a vacuum enclosure.
Detection of oxygen using a low-power diode laser
Authors: Auerbach A. , Doersam D.
Published: July 2002

This article describes a novel approach to gas detection. A low-powered diode laser is used to produce a hot spot on the surface of a thin film. When oxygen is present, specific reaction with the film occurs, and a reaction site is formed. The altered optical character of the site is detected and is representative of the oxygen concentration.
Efficient 30-W, 140-MHz rf amplifier for cw CO2 waveguide laser excitation
Authors: Hochuli U. E. , Haldemann P. R.
Published: July 2002

Details of a 30-W, 140-MHz rf amplifier for cw CO2 waveguide laser excitation are presented. The amplifier delivers 30 W into a 50-Ω load while requiring only 40 W of dc power from a 28-V supply and 100 mW of rf drive power for an overall efficiency of 75%. A coupling-starting network design theory is given that provides the initiation over voltage for the discharge plasma from an rf power source of limited output voltage capability. The network then matches the drive circuit to the new input impedance of the operating discharge without any adjustments. This design theory applies to the whole class of networks whose losses can be approximated by a loss conductance in parallel with the gas discharge.
Laser power meter with an integral alignment module
Authors: Inoue Takemi , Endo Michiyuki , Yokoshima Ichiro , Kawahara Kiyohiko
Published: July 2002

A reliable, fast-beam alignment method for a thermal-type laser-power meter is proposed. The thermopile-type power meter that has been developed and manufactured consists of a main-sensor and a pinhole on the target, and a fast-response sub-sensor behind it. The alignment can quickly be performed by monitoring the beam-power density of the incident-laser beam. The method has been found to be very effective for beam alignment.
Cryogenic vacuum window
Authors: Adams G.
Published: July 2002

A procedure is described for assembly of an inexpensive, easy to assemble waveguide window that has both low microwave losses and small reflectivity. This window is vacuum, superfluid-helium-tight, and withstands repeated thermal cycling to helium temperatures.
Special purpose computer system for Ising models
Authors: Taiji Makoto , Ito Nobuyasu , Suzuki Masuo
Published: July 2002

The special purpose processor for Ising spin systems, which is named the m-TIS, megaspin model of the Tokyo University Ising spin machine, is designed and constructed by the present authors. The m-TIS can treat several millions of Ising spins per second when it is connected to an appropriate host computer. For example, the speeds in the case of square and cubic models are 1.8 and 1.5 million spins/s, respectively. The maximum ability is 107/s. This machine can treat the Ising spin systems having one translation invariant direction in the lattice and having local Hamiltonians, including less than 13 spins–for example, Ising models with external field, ±J spin glasses, and ±H random field models.
Design of a scanning tunneling microscope for electrochemical applications
Authors: Dovek Moris M. , Heben Michael J. , Lang Christoph A. , Lewis Nathan S. , Quate Calvin F.
Published: July 2002

A design for a scanning tunneling microscope that is well suited for electrochemical investigations is presented. The construction of the microscope ensures that only the tunneling tip and the sample participate in electrochemical reactions. The design also allows rapid replacement of the tip or sample, and enables facile introduction of auxiliary electrodes for use in electrochemical experiments. The microscope utilizes stepper motor driven approach mechanics in order to achieve fully remote operation and to allow reproducible coarse control of tip/sample spacings for electrochemical experiments. Highly ordered pyrolytic graphite images at atomic resolution in air and aqueous solutions can be obtained with this microscope.
Multislit streak photography for plasma dynamics studies
Authors: Tou T. Y. , Lee S.
Published: July 2002

A microscope slide with several transparent slits installed in a streak camera is used to record time-resolved two-dimensional information when a curved luminous plasma sheath traverses these slits. Applying this method to the plasma focus experiment, the axial run-down trajectory and the shapes of the plasma sheath at various moments can be obtained from a single streak photograph.
Bolometers for CIT
Authors: Schivell J.
Published: July 2002

Designing bolometers for Compact Ignition Tokamak presents difficult, perhaps insurmountable, challenges. Detector environment will be quite harsh, viewing access will be severely limited, and, most importantly, the heating of detectors by neutron and gamma radiation will be larger than that by the radiation losses to be measured. Furthermore, the radiation losses themselves will no longer be dominated by impurity radiation as in earlier machines, but will be a combination of impurity radiation, bremsstrahlung, and synchrotron radiation. Possible approaches to a design have been developed, based on optimizing the response to VUV- and x-radiation, possible local shielding, subtraction of the n and γ heating, constant in situ calibration, and deployment of the detectors in a tangentially viewing array. The array makes it possible to cover the plasma cross section, as well as to see into the divertors. Estimates indicate that it should be possible to make successful measurements of the two-dimensional radiation loss profile.
Plasma diagnostics for the CIT (invited)
Authors: Medley S. S. , Young K. M. , Team CIT Diagnostics
Published: July 2002

The primary mission of the Compact Ignition Tokamak (CIT) is to study the physics of alpha-particle heating in an ignited D–T plasma. A burn time of about 10 τE is projected in a divertor configuration with base-line machine design parameters of R=2.10 m, a=0.65 m, b=1.30 m, Ip=11 MA, BT=10 T, and 10–20 MW of auxiliary rf heating. Plasma temperatures and density are expected to reach Te(0)∼20 keV, Ti(0)∼30 keV, and ne(0)∼1×1021 m−3. The combined effects of restricted port access to the plasma, the presence of severe neutron and gamma radiation backgrounds, and the necessity for remote handling of in-cell components create challenging design problems for all of the conventional diagnostics associated with tokamak operations. In addition, new techniques must be developed to diagnose the evolution in space, time, and energy of the confined alpha distribution as well as potential plasma instabilities driven by collective alpha-particle effects. The design effort for CIT diagnostics is presently in the conceptual phase, with activity being focused on the selection of a viable diagnostic set and the identification of essential research and development projects to support this process. A review of these design issues and other aspects impacting the selection of diagnostic techniques for the CIT experiment will be presented.
Data-acquisition system of the reversed field pinch device REPUTE-1
Authors: Tsuzuki N. , Aoki H. , Shinohara H. , Toyama H. , Morikawa J.
Published: July 2002

The new, compact data-acquisition system of the reversed field pinch device, REPUTE-1, is reported. Its distinctive feature is high flexibility and easy handling. The interface between the computer and measurement devices is CAMAC. The computer and the CAMAC devices are connected to a CAMAC byte serial highway that transmits setup parameters and acquisition data. The computer carries out setup of CAMAC devices and data acquisition automatically by use of CAMAC parameters and the acquisition data base. The maintenance tools for the data base are also provided. The computer system, which consists of a ‘‘TOSBAC DS-600,’’ has been in operation for REPUTE-1 since 1985.
q-profile measurement in tokamaks using fueling pellets
Authors: Durst R. D. , Phillips P. E. , Rowan William L.
Published: July 2002

Fuel pellets ablating in a hot, magnetically confined plasma generate cold, self-luminous filaments which seem to orient themselves along the local magnetic field direction. This distinctive ablation pattern has been used for local measurements of the q profile. In the Texas Experimental Tokamak (TEXT), this technique was investigated experimentally, and the results were compared to other q-profile measurements to examine limits of applicability. It is found that the technique may be applied only to limited regions of the plasma. Although the mechanism which causes the filaments to align along the magnetic field lines is not completely understood, comparisons between this technique and other techniques tend to support its use. Inclination angle profiles for the local magnetic field and q profiles obtained on TEXT by this technique are presented. The q profiles are compared with predictions based on various resistivity models, specifically classical, neoclassical, and q-clamped.
Utilization of charge exchange recombination spectroscopy for the study of metallic ion transport in TFTR
Authors: Knize R. J. , Fonck R. J. , Howell R. B. , Hulse R. A. , Jaehnig K. P.
Published: July 2002

Charge exchange recombination spectroscopy has been used to observe transitions originating from hydrogen-, helium-, and lithiumlike charge states of medium-Z metallic impurities in TFTR. The temporal and spatial densities of these ions were measured in ohmic and neutral beam heated plasmas. These preliminary results agree with predictions of a transport code.
Continuously space-resolved x-ray spectroscopy at JET
Authors: Schumacher U. , Källne E. , Morsi H. W. , Rupprecht G.
Published: July 2002

Application of a double-crystal Bragg device with the one crystal swiveling additionally around the x-ray optical axis between the two crystals allows continuous spatial scanning of x-ray line emission from high-temperature plasmas. The main components and physical properties of the monochromator are described, and first results of measurements of spatial profiles of the emission shells of several nickel ionization stages at JET are given.
A variable-volume infrared cell for high-pressure studies
Authors: Suppes Galen J. , McHugh Mark A.
Published: July 2002

A variable-volume IR cell is described which can operate to 400 bar and 150 °C. The wetted metal surfaces of the cell are coated with a high-temperature fluoropolymer and the movable piston, which allows for continuous adjustment of the internal volume of the cell, has a solid teflon adapter which contacts the contents in the cell. With this cell it is possible to perform IR studies with supercritical fluids over wide ranges of fluid densities.
A fast infrared scanning technique for nondestructive testing
Authors: Hartikainen Jari
Published: July 2002

A simple and fast thermal NDT measurement system is described and its usefulness is demonstrated using a honeycomb structure as a test sample. The sample is heated with a hot air jet and the surface temperature differences due to subsurface defects are detected with a single HgCdTe detector. An image of the sample is formed by scanning over the sample surface with a deflection mirror in the y direction while moving the sample in the x direction. The measurement time is typically 6 s per image and several images are averaged to improve signal to noise ratio. The main advantages of this system compared to conventional infrared camera techniques are considerably reduced cost and the ease with which the system can be modified to various applications.
Deflection-type energy analyzer for energetic electron beams in a beam-plasma system
Authors: Michel J.-A. , Hogge J.-P.
Published: July 2002

An energy analyzer for the study of electron beam distribution functions in unmagnetized plasmas is described. This analyzer is designed to avoid large electric fields that are created in multigrid analyzers and to measure directly the beam distribution function without differentiation. As an example of an application, results are presented on the propagation of an energetic beam (Eb : 2.0 keV) in a plasma (no : 1.×1010 cm−3, Te : 1.4 eV).
USX and SX radiation measurement of tokamak plasma by microchannel plate
Authors: Kálvin S. , Bakos J. S. , Bürger G. , Kardon B. , Petravich G. , Zoletnik S.
Published: July 2002

A new method is described for the measurement of soft x-ray (SXR) and ultrasoft x-ray (USXR) radiation of fusion plasmas. The system applies the microchannel plate (MCP) detector and can be used to measure the emitted radiation along 12 chords in different energy ranges. The operation of the MCP in the measurement is discussed in detail. Some results are included which demonstrate the capabilities of the device.
Simple computer-supported photoelectrochemical instrument for studies of ultrathin films on transparent electrodes
Authors: Blanchet Pierre -F. , Tessier Alain , Paquette André , Côté Dominique
Published: July 2002

The construction and characteristics of a photoelectrochemical cell, a potentiostat, and a monochromator-microcomputer interface are described. The three-electrode system is designed for photoelectrochemical studies on transparent electrodes of metals and semiconductors and is capable of detecting photocurrents in the nanoampere range on various thin-film modified electrodes. The cell can also be used for the gathering of absorption spectroscopic data. A comparison with another system is made, with emphasis on the advantages of our system. Examples of typical results are given. An integrated and flexible software, whose main features are briefly described, is used for the control of the setup.
Optical measurement of temperature with single-crystal silicon
Authors: Friberg Ari T. , Kajanto Isko
Published: July 2002

The principle of a temperature sensor based on the absorption properties of an indirect semiconductor is presented. In particular, single-crystal silicon with a GaAs-LED source is analyzed as a representative example. A potential temperature range is obtained that is substantially wider than is possible with direct semiconductors. It is also insensitive to the source spectral width and can be efficiently varied by altering the Si layer thickness.
Analysis of the energy consumption of LaB6 cathodes in SEM applications
Authors: Chen De-sen , Wang Bin , Xi Wei-guo
Published: July 2002

The power required to heat a lanthanum hexiboride cathode for use in scanning electron microscopes (SEM) has been calculated and found to be in close agreement with experimental measurements. The analysis indicates that direct heating of the LaB6 by the heater current, and efficient heat transfer to the cathode from the heated supports, results in low power consumption. The operating temperature of the cathode support material must be carefully designed to avoid poisoning of the LaB6 by excessive metal evaporation and deposition on the cathode. The LaB6 cathode developed here is well suited to the small heater power supply of the SEM and improves the picture quality over the traditional tungsten filament cathodes.
Cylindrical position-sensitive x-ray detector for fast powder diffractometry
Authors: Hashizume H. , Minato I. , Kusuhara H. , Yamanaka A.
Published: July 2002

A cylindrical position-sensitive x-ray gas detector has been designed, which allows a complete powder pattern to be recorded simultaneously from a specimen placed at the center of the detector circle. It covers an angular range 2θ of 120° at a 25-cm radius and works in the self-quenching streamer mode of gas ionization to provide 0.06° resolution in 2θ. Powder line positions can be determined with an accuracy of ±0.05°. The quality of detected patterns is well suited to profile analysis. Tests made at a classical x-ray source showed that recorded line profiles are describable by asymmetric Pearson VII functions. The designed instruments have successfully been applied to in situ powder data collection from a BaBiO3−x specimen at high temperatures and subsequent structure refinement by profile-fitting techniques. These features make the detector most suitable to the studies of fast structure changes like phase transitions with synchrotron radiation.
Photoacoustic detector for synchrotron-radiation research
Authors: Masujima T. , Yoshida H. , Kawata H. , Amemiya Y. , Katsura T. , Ando M. , Nanba T. , Fukui K. , Watanabe M.
Published: July 2002

Transient heat generation by absorption of x-ray and far-infrared beams was successfully detected by a photoacoustic detection method. The photoacoustic detectors of solid and gas phase for x rays and of solid materials for far-infrared light are shown together with its instrumentation. The x-ray photoacoustic signal showed a linear dependence on the ring current and ionization chamber current, both of which are the measure of the photon flux. Typical examples of photoacoustic signals were shown, and their characteristics were briefly discussed in relation to the physicochemical properties of the samples. The potential use of this detection method is discussed.
High-purity silicon radiation-sensor array for imaging synchrotron radiation in digital-subtraction angiography procedures
Authors: Audet Sarah A.
Published: July 2002

The possible integration of a recently fabricated high-purity silicon radiation-sensor array into experimental-instrumentation systems currently being developed for digital-subtraction angiography (DSA) procedures conducted with synchrotron radiation is discussed. In order to motivate the intended application of the sensor, the medical-imaging techniques of conventional coronary angiography and DSA are briefly reviewed followed by a summary of the different system and detector designs currently in use.
Soft x-ray beamline and a double-crystal monochromator of UVSOR (abstract)
Authors: Murata T. , Matsukawa T. , Naoe S. , Matsudo O.
Published: July 2002

The UVSOR is a 750-MeV dedicated electron storage ring in the Institute for Molecular Science at Okazaki, Japan. The ring was constructed mainly for the use of VUV photons. However, the intensity of the soft x-ray region around 10 Å region is not negligible. The ring is also equipped with a 4 T superconducting three-pole horizontal wiggler. We have constructed a beamline equipped with a monochromator in order to utilize the soft and normal x-ray photons from the ring. In order to separate the vacuum of the ring from that of the monochromator, a light tight Be foil of 10 μm in thickness is placed in the upstream of the monochromator in the beamline. The monochromator constructed is a high vacuum compatible with double crystal which provides constant offset of the output beam. The constant offset during the rotation of crystal plane was realized by a simple linkage of linear motions of the two crystals with two linear guides placed on both input and output beam levels. The mechanical movement was found to be very smooth through a full rotation of 60° (between 15° and 75° of Bragg angle). Monochromator crystals such as beryl (101̄0), quartz (101̄0), InSb(111), Ge(111), and Ge(220) whose 2d value is 15.965, 8.512, 7.481, 6.532, and 4.00 Å, respectively, are being used with a reasonable intensity and signal-to-noise ratio of output signal. The range of photon energy which can be used with this line is from 850 eV to 4 keV in the bending magnet section, and from 850 eV to 6 keV with a wiggler. Because of the comparatively low energy of 750 MeV of the electron, the heat load is not a severe problem, and no radiation damage was observed for the first beryl crystal during an exposure to the beam for several months.

We have measured the Na K-edge XANES spectrum of a thin film of NaCl which was evaporated in situ on a collodion film in the sample chamber at room temperature by using beryl as monochromator crystal. From the doublet separation of the spectrum, we can estimate the resolution better than 1 eV, which is sufficient for this energy range. With Ge(220) as monochromator crystal, K edge of potassium has been measured with a reasonable signal-to-noise ratio. Therefore, the practical limit of the energy attainable in this beamline of bending magnet section is about 4 keV.
Subpicosecond, resonant refractive index changes in germanium near 1.5 μm
Authors: Mak G. , van Driel H. M.
Published: July 2002

The refractive index changes have been time resolved in crystalline Ge near the direct-band-gap (0.8 eV, 1.55 μm) following femtosecond pulse excitation at room temperature. Measurements were made for 1.485<λ<1.55 μm using degenerate pump-probe transmission and reflection spectroscopy with 120 fs pulses from an optical parametric oscillator. Resonant excitation leads to large refractive index changes (≳10−3 for 1017 cm−3 carrier density) dominated by band filling and carrier screening effects. Unlike the much slower recovery observed in direct gap semiconductors, the refractive index change disappears with a time constant of 230 fs due to intervalley scattering of electrons to the lower energy L valley in this indirect-gap semiconductor.
New undulator and conventional lines at the Wisconsin Synchrotron Radiation Center (invited)
Authors: Margaritondo G.
Published: July 2002

We describe the recent, intensive construction program of new beamlines at the Wisconsin Synchrotron Radiation Center. In particular, we discuss technical features of new TGM lines, and the development of the advanced photoemission spectromicroscope MAXIMUM, based on undulator radiation.