bluuebunny/crossref_metadata_2025 huggingface dataset:
A video data-acquisition system for quantitative low-energy electron diffraction studies
Authors: Guo T. , Atkinson R. E. , Ford W. K.
Published: July 2002

We have developed an easy to use and inexpensive low-energy electron diffractometer. The system is based on an Apple Macintosh II microcomputer and uses a high-resolution CCD video camera. The video interface is a single plug-in imaging board which digitizes the video signal in real time. No expensive auxiliary video processing devices are required. The system is of moderately high speed. A typical set of 16 IV curves with 125 data points in each curve can be generated from images summed over 16 frames in less than 4 min. Spot profile measurements are also routinely made. A description of the apparatus and the capabilities of the system are presented, illustrated using measurements of the epitaxial growth of bismuth films on III-V semiconductor surfaces.
Recent advances in heavy ion beam probe diagnostics (invited)
Authors: Crowley T. P. , Aceto S. C. , Connor K. A. , Heard J. W. , Hickok R. L. , Lewis J. F. , McLaren P. E. , Ouroua A. , Schatz J. G. , Schoch P. M. , Schwelberger J. , Simcic V. J. , Zielinski J. J.
Published: July 2002

Heavy ion beam probes (HIBPs) have proven to be a unique tool for measuring fluctuations and particle transport in tokamaks. They have been used to measure fluctuations in density, electric potential, and magnetic vector potential. The density and potential fluctuation measurements have determined the particle flux due to electrostatic turbulence in the TEXT and ISX-B tokamaks. In these measurements, the frequency spectra (0–500 kHz) of the phase between density and potential, the wave numbers of the fluctuations, and the fluctuation level are obtained. Three topics are discussed in this paper. We present measurements of magnetic fluctuations during MHD activity using the TEXT HIBP. Analysis of these measurements indicates that the diagnostic is primarily sensitive to the local value of Aφ in the sample volume unless the local Aφ is small. In addition, we discuss instrumental effects associated with wave number measurements. We will discuss the effects of sample volume size on the wave number measurements and report the results of experiments in which the sample volume size is reduced by passing the primary beam through an aperture. Finally, a brief description of the new design issues addressed in constructing the 2 MeV HIBP for TEXT-Upgrade and 160 kV ATF HIBP will be presented.
On the formation of epitaxial CoSi2 from the reaction of Si with a Co/Ti bilayer
Authors: Zhang S.-L. , Cardenas J. , d’Heurle F. M. , Svensson B. G. , Petersson C. S.
Published: July 2002

In spite of much work, the formation of epitaxial CoSi2 from Ti/Co on (100) Si remains something of a mystery. It has been proposed that epitaxy occurs via the formation of an intermediate phase of CoSi with a (311) preferred orientation. In the absence of sufficient information it is impossible to validate or to invalidate the specific original claim. However, one shows that the formation of preferably oriented CoSi is not a necessary condition for the subsequent growth of epitaxial CoSi2. Careful measurements of diffraction intensities reveal the probable, temporary formation of a metastable form of CoSi2, based on a diamond cubic rather than the usual CaF2 structure.
High T
c superconducting levitation motor with a laser commutator
Authors: Weeks David E.
Published: July 2002

A high Tc superconducting levitation bearing driven by an optically switched solenoid is described. The bearing uses flux pinning in the new high Tc superconductors for stability. A simple liquid nitrogen supply system is described that greatly improves the ease with which high Tc superconductors can be maintained at 77 K for extended periods of time in small styrofoam dishes. A force versus height curve is given and is used to determine the design limits of the levitation bearing. Alternate motor designs are discussed.
Photoluminescence lifetime microscope spectrometer based on time-correlated single-photon counting with an avalanche diode detector
Authors: Louis T. A. , Ripamonti G. , Lacaita A.
Published: July 2002

A photoluminescence lifetime microscope spectrometer (PLμS) based on time-correlated single-photon counting (TCSPC) with a single-photon avalanche diode (SPAD) detector was developed for the investigation of the microscopic spatial fluctuations of the minority-carrier lifetime and other material parameters in gallium arsenide (GaAs) and related compound semiconductors. The high sensitivity of the TCSPC technique is essential for time-resolved photoluminescence (TRPL) measurements with a spatial resolution of the order of a few micrometers. The spatial resolution of the PLμS is compatible with the diffusion length in GaAs substrates or the dimensions of small, highly integrated GaAs devices. The PLμS is the first instrument of its kind based entirely on solid-state components, i.e., a gain-switched diode laser for pulsed excitation and an avalanche diode for single-photon detection. It is explained why, in samples dominated by nonradiative linear recombination, the relatively large excitation pulse width of the diode laser compared to a synchronously pumped dye laser does not adversely affect the timing accuracy of the measured decay time constants. It was previously shown that, by using nonlinear least-squares iterative convolution analysis, a TCSPC instrument with an instrumental response width of 70 ps (FWHM) is capable of accurately measuring fluorescence decay time constants down to 10 ps with ±2 ps timing accuracy. The PLμS is designed to take full advantage of the high repetition rates, up to 100 MHz, typical for mode-locked laser sources or gain-switched diode lasers. The data-acquisition time for a complete decay curve containing typically several hundred thousand counts is thus reduced to a few seconds. Hence, the PLμS is, in principle, suitable for scanning operation and topographical imaging.
Dispersion compensation high-resolution electron energy-loss spectrometer for time-resolved surface studies
Authors: Wu K. J. , Peterson L. D. , Elliott G. S. , Kevan S. D. , Gibson K. D. , Hinch B. J. , Dubois L. H.
Published: July 2002

A new high-resolution electron energy-loss spectrometer based on the dispersion compensation (DC) concept has been designed, built, and tested. The parallel processing inherent in DC has allowed us to attain signal levels two orders of magnitude in excess of conventional designs while operating at comparable resolution. This is consistent with expectations based on simple model calculations. The resolving power of the spectrometer is not as good as theoretically predicted probably due to uncontrolled beam angle effects. Initial tests on a variety of systems are presented. We analyze the strengths and weaknesses of the design and suggest future improvements.
Observation of strong contrast from doping variations in transmission electron microscopy of InP-based semiconductor laser diodes
Authors: Hull R. , Stevie F. A. , Bahnck D.
Published: July 2002

We report strong transmission electron microscope (TEM) contrast between p-, i-, and n-doped InP layers in semiconductor laser diodes. For doping concentrations ∼1018 cm−3, contrast levels on the order 30% are observed between p- and n-type layers. A critical feature of these experiments is that the samples imaged in the TEM are relatively perfect, plane-parallel sided membranes fabricated with a focused ion beam. This technique offers the ability to detect and map doping variations with nm-scale resolution, simultaneously with the other compositional and defect information inherent to TEM.
A versatile substrate heater for use in highly oxidizing atmospheres
Authors: Estler R. C. , Nogar N. S. , Muenchausen R. E. , Wu X. D. , Foltyn S. , Garcia A. R.
Published: July 2002

We report the design, construction and performance of a versatile substrate heater that meets the severe design constraints of heating substrates to high temperatures (≤900 °C) in relatively high pressures (hundreds of Torr) of oxidizing gases. The heater has been used to heat substrates by both thermal conduction via a conductive high temperature cement and by direct radiation. In particular, the production of high-quality YBa2Cu3O7−δ thin films grown on radiatively heated LaAlO3 substrates is demonstrated using the pulsed laser deposition (PLD) technique.
Measurement of position-dependent detection efficiencies for two quadrupole mass spectrometers with electron-impact ion sources
Authors: Hall J. , Zorić I. , Rinnemo M. , Kasemo B.
Published: July 2002

Measurements have been carried out of the position-dependent detection efficiencies of two quadrupole-type commercial mass spectrometers with electron-impact ion sources. Contours of constant detection efficiencies for different ion source parameters were determined by scanning a collimated argon beam of 1-mm diameter across the ion source. The measured results show clearly how different ion source settings influence the detection efficiency and the size of the active volume within the ion source. Furthermore it is found that the optimal performance of the instrument in the molecular-beam mode as well as in the residual gas mode occurs at the same ion source settings. The absolute value of the detection efficiency, for this particular ion source setting, is Dmax = 0.88 × 10−5. A simple model is developed connecting the conventional sensitivity factor with the measured position-dependent detection efficiency contour plots. The agreement between the measured and calculated sensitivity factors is good.
A VISAR with a multireflection étalon and its application in interior ballistics research
Authors: Wang Shengyou , Cao Caizhi , Sun Jiangzheng
Published: July 2002

A VISAR (velocity interferometer system for any reflector) with a new type delay leg is described, which uses multireflection in the étalon for increasing the delay time τ. When the incident angle is changed, the sensitivity of the VISAR can be changed. A few step values of the sensitivities can be selected for different applications. Experimental results for measuring the bullet’s motion in the 7.62-mm gun are presented.
A charge pumping method for rapid determination of interface-trap parameters in metal-oxide-semiconductor devices
Authors: Chen Wenliang , Balasinski Artur , Ma T.-P.
Published: July 2002

We present a new implementation of charge pumping for rapid characterization of interface-trap parameters, especially geometric mean of electron and hole capture cross sections, in metal-oxide-semiconductor field-effect transistors (MOSFETs). With the help of an HP8116A (or equivalent) function generator operated in the voltage-controlled-oscillator mode, this method enables measurement of the charge pumping current as a function of frequency with one continuous sweep of the frequency. Data analysis can be performed on an HP4145B (or equivalent) parameter analyzer by defining user functions. The measurement setup can be readily assembled with standard instruments without the need of a computer. It allows fast measurements without compromising the accuracy. The improved measurement speed has led to new observations revealing the rapid change of the capture cross sections of the interface traps shortly after Fowler–Nordheim hot-carrier injection.
High-speed signal averaging system for periodic signals
Authors: Black A. , Apte R. B. , Bloom D. M.
Published: July 2002

A high-speed emitter coupled logic system for fast averaging is described. This system may be used to extract signals from broadband background noise, while preserving harmonic content. Each captured waveform may consist of up to 1024 sample points, and up to 16 kilowaveforms may be accumulated in one cycle. A 20 kilowaveform per second averaging rate is achieved on signals in a 20-kHz to 10-MHz band. The system is used to process the intermediate frequency output of an electro-optic sampling probe in order to recover 14.4-GHz, nonsinusoidal, periodic waveforms from a GaAs integrated circuit.
A sensitive oxygen measuring system developed for determining oxygen evolution rates in cyanobacteria with low photosynthetic activity
Authors: Rane S. S. , David K. A. V.
Published: July 2002

A sensitive system has been developed to measure the evolution rate of the photosynthetic oxygen produced by cyanobacteria. The system was built around a Clark oxygen probe. The circuit diagram of the polarizing voltage unit and amplifier, methods for calibration, and the flow chart of the computer program are given. The circuitry of the amplifier allows sensitivity up to 0.072 nmole/ml/mm as compared to 0.31 nmole/ml/mm of commercially available oxygraphs. Oxygen evolution rates of four different strains of cyanobacteria are reported. The system was tested for cultures having chla range between 2.75 and 0.0275 μg/ml with an O2 rate of 239 μmole O2 mg chla−1 h−1.
Influence of the rf excitation on the low energy broad ion beam characteristics
Authors: Engemann J. , Korzec D. , Ningel K.-P. , Zrnc G.
Published: July 2002

Influence of the rf excitation in a capacitively coupled filamentless broad ion beam source with radial electrode configuration on the ion beam properties has been examined. Ion energy distribution was measured by use of a retarding field energy analyzer connected to a computer controlled data acquisition system. Influence of working conditions on the average ion energy and on the ion energy spread in the beam is described. Energy spread has typical values between 8 and 25 eV. Average ion energy can change due to variations of ion source working conditions (at constant extraction voltages) up to 60 eV. Increase of both the average ion energy and ion energy spread is observed with increasing rf power coupled to the plasma (20–100 W). This correlates to the increasing amplitude of plasma floating potential oscillation. Average ion energy decreases with increasing magnetic induction (0–75 mT) and with increasing pressure in the vacuum chamber (2×10−4–1.8×10−3 mbar) due to decreasing cathode oscillation amplitudes. Average ion energy decreases with increasing distance from the broad beam axis because of chromatical and spherical aberrations of the source extraction optics. Multiple peaks in the ion energy spectrum are observed. Their occurrence can be explained by charge exchange effects in the rf oscillating plasma sheath.
Histogramming data acquisition system for an (e,2e) coincidence experiment
Authors: Bennett M. A. , Smith P. A. , Waterhouse D. K. , Ford M. J. , Flexman J. , Williams J. F.
Published: July 2002

A four-dimensional histogramming data acquisition system has been developed for use on an 80386 IBM-compatible computer. The method has a large data storage capacity providing good experimental resolution and system flexibility. A custom-built analog-to-digital board generates a memory address in hardware from the incoming data which permit the use of a simple and elegant histogramming algorithm. The system is used to collect and analyze data from (e,2e) experiments. Results from coplanar symmetric (e,2e) experiments on argon, at an incident energy of 3 keV, are presented to demonstrate the performance of the instrument. The method is applicable to experiments where data from several sources have to be combined and then histogrammed in real time.
Measurement of long-pulse relativistic electron beam perpendicular- to-parallel velocity ratio by Cerenkov emission and radiation darkening on a glass plate
Authors: Choi J. J. , Gilgenbach R. M. , Spencer T. A. , Menge P. R. , Ching C. H.
Published: July 2002

We report measurements of the ratio of the perpendicular velocity to the parallel velocity, α= v⊥ /v∥, of a relativistic electron beam gyrating in a magnetic field by the use of (1) Cerenkov emission from a glass plate, detected by a gated microchannel plate image intensifier camera, and (2) electron-beam-induced radiation darkening pattern on the same glass plate. The measurements are based on a direct determination of the Larmor radius of an electron beam of known energy. Experiments were performed on a long-pulse electron beam accelerator with e-beam diode parameters: VD = 0.6–0.9 MV, pulse length=0.5–1 μs, ID = 1–10 kA. The experimental value of α agrees with simulation results from particle trajectory codes as well as theoretical predictions from Busch’s theorem and adiabatic theory.
A method for determining the column density from the pressure-broadened resonance lines
Authors: Ueda K. , Sonobe O. , Chiba H. , Sato Y. , Namioka T. , Ito K.
Published: July 2002

We have developed a method for determining metal-atom number-density integrated over a line-of-sight (i.e., the column density) by measuring the optical depth in the wings of the pressure-broadened resonance lines. This method is capable of monitoring the column density in situ during photoelectric absorption measurement of metal vapors in a synchrotron radiation beamline. The present method requires measuring the reduced absorption coefficients of the metal–metal and metal–buffer-gas collisional quasimolecules γMM and γMG and the effective vapor length l before its use. We thus describe also the procedure for obtaining γMM, γMG, and l using He-buffered Yb vapor as a specific example.
Improvement of beam lifetime by optics modification at the Photon Factory storage ringa)
Authors: Katoh M. , Hori Y. , Kitamura H. , Mitsuhashi T.
Published: July 2002

The vertical acceptance of the Photon Factory storage ring had been limited by a narrow vacuum chamber at an insertion device. To increase the acceptance, the vertical betatron function at the device was reduced. This modification resulted in an increase of the beam lifetime by a factor of 1.5 and enabled one to operate the ring continuously for 24 h without a beam injection. The effects of the optics modification on the beam lifetime, beam injection, betatron tune shifts produced by the insertion devices, and the brilliance of the synchrotron light are presented.
Small-angle x-ray scattering/diffraction system for studies of biological and other materials at the Stanford Synchrotron Radiation Laboratorya)
Authors: Wakatsuki S. , Hodgson K. O. , Eliezer D. , Rice M. , Hubbard S. , Gillis N. , Doniach S. , Spann U.
Published: July 2002

A versatile small-angle x-ray diffraction/scattering system has been developed at Stanford Synchrotron Radiation Laboratory for studies of biological and other materials. The system includes two sets of collimation slits separated by an ionization chamber, a sample holder cooled by a circulation bath, a vacuum/He scattering path after the sample holder and a detector, either a linear one-dimensional position-sensitive proportional counter or a position-sensitive quadrant detector. Data aquisition is controlled by a VAXstation through a CAMAC interface. Menu-driven data acquisition and on-line analysis software has been developed. The system can be used to collect small- to intermediate-angle x-ray scattering and diffraction data. Monochromatic, anomalous, and time-resolved scattering/diffraction experiments are possible. A time-resolved spectrophotometer using photodiode arrays has also been developed for simultaneous measurements of optical absorption spectra and x-ray scattering/diffraction.
Automated pressure and temperature control apparatus for x-ray powder diffraction studies
Authors: So P. T. C. , Gruner S. M. , Shyamsunder E.
Published: July 2002

A system for performing x-ray diffraction on biological samples as a function of pressure and temperature is described. It is capable of operating in a pressure range of 1 bar–3 kbar (0.1–300 MPa) and in a temperature range of −30 to 80 °C. The system incorporates microprocessor-based pressure and temperature controllers which provide automated control with excellent stability characteristics: Fluctuations in pressure and temperature can be maintained within ±1 bar (0.1 MPa) and ±0.05 °C, respectively. Use of the apparatus is illustrated by application to a pressure-induced phase transition in a lipid-water liquid crystal.
A combined optical and magneto-optical measurement system
Authors: Geerts W. J. M. A. , Lodder J. C. , Popma Th. J. A.
Published: July 2002

A magneto-optical (MO) Kerr tracer based on an ellipsometer was developed for studying the surface magnetic properties of thin films. This system can be used to measure the optical properties n and k, which are strongly related to the magneto-optical parameters θk and ηk. In order to carry out measurements on materials having a small θk we have developed a multiple reflection sample holder which gives an enhancement of the rotation. The behavior of the sample holder is explained in terms of Jones matrices. The optical and magneto-optical properties for a thickness series of Co-Cr films were measured. Comparative measurements on other systems gave similar results.
Two low-cost robust electro-optic hybrid current sensors capable of operation at extremely high potential
Authors: Ning Y. N. , Liu T. Y. , Jackson D. A.
Published: July 2002

Two very simple electro-optic hybrid schemes which convert the output from a conventional current transformer to an optical signal are presented. These systems may be used to indicate the presence of and/or measure the magnitude of large currents at very high potential. The first scheme would be very useful for indicating whether the conductor was carrying current or for making measurements within an accuracy of ∼10% at extremely high potentials. Whilst the second scheme, with a demonstrated minimum detectable signal of 0.32 A/√Hz, provides a simple and low-cost way for accurate current measurement in high potential locations. The optical signals from the measurement scheme can be transferred for subsequent demodulation via multimode fibers hence greatly reducing the electrical insulation required for safe operation of the current transformer thereby offering a significant cost saving in its manufacture.
A dusty plasma device for producing extended, steady state, magnetized, dusty plasma columns
Authors: Xu Wenjun , Song Bin , Merlino Robert L. , D’Angelo Nicola
Published: July 2002

We describe a rotating-drum dust-dispersal device, which we have used, in conjunction with an existing Q machine, to produce extended, steady state, magnetized plasma columns. The dusty plasma device (DPD) is to be used for the investigation of waves in dusty plasmas and of other plasma/dust aspects. The device is capable of generating dusty plasmas in which as much as ∼90% of the negative charge is attached to dust grains of 1–10 μm size.
Runaway electrons as a diagnostic of magnetic fluctuations (invited)
Authors: Bengtson Roger D. , Freeman M. R. , Wootton A. J. , Wang P. W. , Myra J. R. , Catto Peter J.
Published: July 2002

The transport of runaway electrons in a hot plasma can be comparatively easily measured by perturbation experiments which provide a runaway electron diffusivity D. The diffusion can be interpreted in terms of a magnetic fluctuation level, from which an electron thermal diffusivity can be deduced. We find the runaway electron diffusion coefficient is determined by intrinsic magnetic fluctuations rather than electrostatic fluctuations because of the high energies involved. The results presented here demonstrate the efficacy of using runaway transport techniques for determining intrinsic magnetic fluctuations.
High-performance, low-noise digital controller for inchworm piezoelectric translators
Authors: Chen X. , Cousins B. , McEllistrem M. , Hamers R. J.
Published: July 2002

We have designed and constructed a high-performance, low-noise digital controller for ‘‘inchworm’’ piezoelectric translators. The controller features a maximum output voltage of 700 V, an rms noise level of less than 2 mV, and is capable of driving inchworms at speeds of up to 0.23 mm/s. The controller offers substantially better performance in terms of resolution, noise, speed, and cost than commercial controllers, and is suitable for atomic resolution scanning tunneling microscopy and atomic force microscopy applications.
Determination of silicon evaporation rate at 1200 °C in hydrogen
Authors: Zhong Lei , Fujimori Hiroyuki , Shimbo Masaro , Kashima Kazuhiko , Matsushita Yoshiaki , Aiba Yoshiro , Hayashi Kenro , Takeda Ryuji , Shirai Hiroshi , Saito Hiroyuki , Matsushita Jun-ichi , Yoshikawa Jun
Published: July 2002

Separation by implanted oxygen silicon wafers have been investigated with cross-sectional transmission electron microscopy after annealing at 1200 °C in argon as well as in hydrogen. It is observed that the buried oxide has experienced little change in the thickness, which is ascribed to the low hydrogen solubility in the crystal (about 3×1015 cm−3) and provides a natural mark to measure the thickness variation of the top silicon directly. The evaporation rate as determined in this method is less than 0.1 nm/min with an accuracy of ±0.1 nm/min, at least two orders of magnitude lower than reported in previous investigations.
A comparison of experiment and simulation for neutron guidance through glass polycapillary fibers
Authors: Xiao Q. F. , Chen H. , Mildner D. F. R. , Downing R. G. , Benenson R. E.
Published: July 2002

The transmission efficiency and exit divergence of cold neutrons guided through straight and bent polycapillary fibers made of borosilicate glass have been measured. Experimental results have been compared with a ray-tracing simulation. Good agreement between the two has been obtained by considering in the simulation only reflectivity losses due to absorption. Therefore, we conclude that the influence of other loss mechanisms on reflectivity, such as surface roughness and waviness, are not significant compared with absorption loss for the borosilicate polycapillary fibers we have measured. Using the same simulation program, we have characterized the performance of a neutron focusing lens placed at the end of a 58Ni guide tube and optimized for a neutron spectrum from a cold source at a temperature of 65 K. An order of magnitude increase in neutron intensity within a submillimeter focal spot is predicted.
Bandpass photon detector for inverse photoemission spectroscopy
Authors: Yokoyama K. , Nishihara K. , Mimura K. , Hari Y. , Taniguchi M. , Ueda Y. , Fujisawa M.
Published: July 2002

The performance of the bandpass photon detector for inverse photoemission spectroscopy has been significantly improved. The detector basically consists of a simple combination of a SrF2 entrance window and a commercial Cu–BeO photomultiplier. RbCl (KBr) evaporation onto the SrF2 window realizes a FWHM of 0.51 eV (0.58 eV), at the sacrifice of sensitivity. On the other hand, KCl evaporation onto the first dynode of the photomultiplier provides good characteristics for the photon detector not only with respect to the FWHM but also in terms of the sensitivity. The new detector has a FWHM of 0.47 eV with a maximum response at a photon energy of 9.4 eV. The sensitivity is improved by about one order of magnitude.
A fast pressure monitor for pulsed laser vaporization cluster sources
Authors: Woenckhaus J. , Becker J. A.
Published: July 2002

A fast and low cost pressure monitor is presented that can easily be mounted on pulsed molecular beam sources and allows one to measure the pressure pulse in the source during operation. The pressure monitor has a time resolution of 10 μs and is especially suited for the control of gas dynamics and nucleation in pulsed laser vaporization cluster sources.
A microchopper for neutral beams
Authors: Kuhnke K. , Kern K. , David R. , Lindenau B. , Comsa G.
Published: July 2002

A mechanical beam chopper with small dimensions is presented. The shape of the generated neutral beam pulses is calculated and experimental results are discussed. The microchopper is based on the operation principle of neutron choppers. It is operated in vacuum and generates molecular beam pulses at a repetition rate of 10 kHz with pulse lengths easily adjustable between 5 and <1 μs. The chopper can be used for time-of-flight applications and inherently acts as a high velocity pass filter.
Sensitivity analysis of junction field effect-pressure Halltron
Authors: Wen Dianzhong
Published: July 2002

In this paper the pressure-magneto-electric effect of a junction field-effect transistor (JFET) is discussed by using standard relaxation techniques. A theoretical evaluation of the pressure sensitivity and Hall sensitivity of n-channel silicon JFET with various geometries(W/L), gate voltages(VCS), and drain voltages (VDC) is made. The results show that supposing W/L≤1/2−1, a junction field-effect pressure sensor with high stability and low noise is designed.
A high power current pulse generator using an insulated-gate bipolar transistor
Authors: Park Kijun , Kim Jin J.
Published: July 2002

A simple and reliable high power current pulse generator using a commercially available insulated gate bipolar transistor has been designed and constructed. This device generates current pulses up to 650 A at up to 990 V with the pulse length adjustable over 0.6 μs—1 ms with a rise time <0.5 μs.
In situ measurement of large piezoelectric displacements in resonant atomic force microscopy
Authors: Hudlet S. , Saint Jean M. , Royer D. , Berger J. , Guthmann C.
Published: July 2002

In resonant atomic force microscopy (AFMR) the calibration of the tip–sample relative displacement remains a major problem. Commonly used PZT piezoceramics exhibit a nonlinear behavior response for large applied voltages. For low voltages applied to the piezoceramics (i.e., small corrugations), the calibration can be performed by measuring the height of known structures. For large displacements, the interferometric heterodyne detection used in the AFMR provides a relative tip–sample displacement up to 10 μm, without removing the piezo-tube from the microscope. From these measurements, it was established that the piezosensitivity is not a constant parameter. Its averaged value during an excursion depends linearly on the applied voltage. With this system, routine controls are very easy and an example is given of the displacement corrections related to the nonlinearity of the piezo-tube for the electrostatic interaction between the tip and a gold surface.
Design and performance of the Advanced Light Source double-crystal monochromator
Authors: Jones G. , Ryce S. , Lindle D. W. , Karlin B. A. , Woicik J. C. , Perera R. C. C.
Published: July 2002

A new ‘‘Cowan type’’ double-crystal monochromator, based on the boomerang design used at National Synchrotron Light Source (NSLS) beamline X-24A, has been developed for beamline 9.3.1 at the Advanced Light Source (ALS), a windowless ultrahigh vacuum beamline covering the 1–6 keV photon-energy range. Beamline 9.3.1 is designed to simultaneously achieve the goals of high energy resolution, high flux, and high brightness at the sample. The mechanical design of the monochromator has been simplified, and recent developments in technology have been included. Measured mechanical precision of the monochromator shows significant improvement over existing designs. In tests with x-rays at NSLS beamline X-23A2, maximum deviations in the intensity of monochromatic light were just 7% during scans of several hundred eV in the vicinity of the Cr K edge (6 keV) with the monochromator operating without intensity feedback. Such precision is essential because of the high brightness of the ALS radiation and the overall length of beamline 9.3.1 (26 m).
Wavelength-dispersive x-ray fluorescence detector
Authors: Kirkland J. P. , Kovantsev V. E. , Dozier C. M. , Gilfrich J. V. , Gibson W. M. , Xiao Qi-Fan , Umezawa K.
Published: July 2002

A wavelength-dispersive x-ray fluorescence detector system has been developed that can be used to discriminate fluorescent photon energies for practically any incident flux. The system uses a Kumakhov polycapillary lens to collimate fluorescent photons from a sample. The collimated photons are transmitted to a crystal-counter combination on a stepping motor driven θ–2θ stage. The stage diffracts the photon wavelength of interest and a photon-counting or current-mode counter is used to measure the photons. The system had a resolution of less than 150 eV at 8 keV using the (200) reflection from an abraded and etched LiF crystal, and was easily able to discriminate between Zn Kα (8.620 keV) and Cu Kβ (8.905 keV) x rays emitted from a brass sample. The LiF (400) reflection had a resolution of approximately 50 eV, but with ten times less intensity.
Correlation reflectometry: An experimental investigation of measurement capability
Authors: Rhodes T. L. , Taylor R. J. , Peebles W. A.
Published: July 2002

The correlation reflectometer was conceived as a method of determining the interior correlation length of plasma turbulence in a nonperturbing and localized manner. Currently, measurements on different machines have produced different lengths and tendencies. Theories have been used to interpret the data from this diagnostic, but the diagnostic and theories remain unverified by direct validation with other diagnostics. As part of its ongoing research program aimed at the understanding and full utilization of reflectometry, UCLA has initiated a direct comparison between turbulent correlation lengths as measured by reflectometry and Langmuir probes. This investigation is performed on the CCT tokamak at UCLA. Initial results show good agreement between the two diagnostics, with radial coherence lengths in the range 1.0–3.0 cm depending upon the frequency of the fluctuation. A detailed description of the experiment and initial results are presented.
A new technique for differentiating between diffusion and flow in granular media using magnetic resonance imaging
Authors: Kuperman V. Yu. , Ehrichs E. E. , Jaeger H. M. , Karczmar G. S.
Published: July 2002

We have shown that a simple nuclear magnetic resonance spin-tagging sequence for spatial encoding of the longitudinal magnetization, combined with an imaging sequence, can be used to measure flow and diffusion in granular materials. Using this technique, experiments have been performed to study flow and diffusion profiles during convection induced by the vertical shaking of a container (39 mm diameter) filled with a granular medium. We have shown that maximum diffusion and displacements occur in a thin boundary layer near the container’s walls. The observed flow profiles are predominantly flat with relatively small positive displacements across the container with the exception of the boundary layer, where increasingly negative displacements are observed as the container’s edges are approached.
Dichroic ultraviolet absorption of thin liquid crystal films
Authors: West John L. , Magyar Gregory R. , Kelly Jack R. , Kobayashi S. , Iimura Y. , Yoshida N.
Published: July 2002

Cyanobiphenyl liquid crystals absorb strongly in the ultraviolet. These absorption bands are highly dichroic. The dichroic ratio changes as a function of order parameter and orientation of the liquid crystals. Plots of the dichroic ratio as a function of film thickness demonstrate that the polymer alignment layer not only imposes an orientation on the liquid crystal director but also lowers the order parameter of the liquid crystal near the polymer surface. A sharp decrease in dichroic ratio occurs at film thicknesses near 35 nm, suggesting a phase transition which may be caused by the appearance of a biaxial phase or smectic layering at the air interface.
Broad spectrum optical phase retarder using three metallic mirrors for normal and Brewster’s angle of incidence ellipsometry
Authors: Wentink D. J. , Kuijper M. , Wormeester H. , van Silfhout A.
Published: July 2002

An optical phase retarder for the photon energy range of 1.5–5.5 eV (825–225 nm) is described. The use of metallic mirrors yields good transmission in the entire energy range and the smooth energy dependence of the phase shift is convenient for in situ spectroscopic ellipsometric applications. The optical properties of the retarder are in good agreement with its expected values. The retarder has proved to be a valuable improvement in ellipsometry measurements and enables the use of a conventional rotating polariser ellipsometer for normal incidence measurements.
Metal ion beam self-sputter deposition system
Authors: Gotoh Y. , Amioka T. , Tsuji H. , Ishikawa J.
Published: July 2002

A metal ion beam self-sputter deposition system, which requires no gas feeding, has been developed for film preparation under ultrahigh vacuum. A copper ion beam extracted from a liquid metal ion source is focused by an asymmetric lens system to impinge on the target which is made of the same material as the ion species. Deposition could be done under a pressure of 10−5Pa and the deposition rate of 2.5 nm/min at maximum was achieved. Crystallinity, impurity incorporation, and electrical properties of the deposited copper films were evaluated by x-ray diffraction, Rutherford backscattering spectrometry, particle induced x-ray emission, and a four point probe. The film properties were dominated by the deposition rate, and no significant dependence of the primary ion energy on the film properties was observed. The films with the resistivity of as low as 2.1μΩcm could be obtained at higher deposition rate.
Application of 6 MeV/n heavy-ion beams to biophysical experiments
Authors: Sato Y. , Tanaka A. , Furusawa Y. , Matsumoto S. , Murakami T. , Soga F. , Takeo K. , Fujita Y.
Published: July 2002

A new accelerator facility and two irradiation methods using 6 MeV/n heavy-ion beams are described along with preliminary results concerning their applications to biophysical investigations. The beams are obtained from the injector linac installed at the Heavy Ion Medical Accelerator in Chiba. Various ion species (He–Xe) having different charge states are accelerated to the same velocity, which is suitable for comparing the charge effects of heavy ions in the high linear energy transfer region. An attempt has been made to test the usefulness of the apparatus for studying track structure by using pBR322 plasmid DNA and spores as targets in vacuum. Newly constructed equipment with a molecular-beam source (water vapor) placed on this beam line is also described.
Assembly for Rutherford backscattering at exactly 180°
Authors: Ellmer H. , Fischer W. , Klose A. , Semrad D.
Published: July 2002

We describe a facility which allows us to measure projectiles scattered at an angle arbitrarily near 180°. The backscattered projectiles are deflected in the horizontal plane out of the incoming beam by a combination of electric and magnetic fields. The charged particles, which are spatially dispersed according to their energy, are detected by a cooled 300 mm2 ion implanted silicon detector. By a judicious choice of the relative strength of both fields we ensure that the essential parts of the spectrum will not be distorted due to an energy dependent percentage of projectiles missing the detector. As the projectiles are also dispersed according to their charge state we are able to distinguish between, e.g., singly and doubly charged He projectiles as they hit the detector at different positions. The detector can be moved in the vertical direction to continuously vary the backscattering angle between 180° and 178.5°. This experimental result shows for the first time the angular range to which the 180° enhancement is confined. Such a device is ideally suited for investigating single crystals by uniaxial channeling blocking.
Vacuum ultraviolet absorption spectroscopy in the spectral interval of Lyman-α of atomic hydrogen and deuterium in an ion source plasma
Authors: Wagner D. , Dikmen B. , Döbele H. F.
Published: July 2002

Atomic hydrogen and deuterium in the plasma of a magnetic multipole source are investigated with respect to the fraction of the atomic component and the energy distribution of the atoms. Information is obtained by analysis of the wings of the optically thick Lyman-α transitions, and by admixture of small amounts of the other isotope as a thermometer gas in order to warrant transparency in the center of the line. The atom to molecule density ratio is found to be around 15%; the analysis of the energy distributions yields a dominant cold component (Tcold∼400 K), a hot component (Thot≳2000 K) which comprises about 20% of the atoms, and a small but significant amount of fast atoms, described by Tfast with energies up to several eV; the relative amount of these atoms is below 1%.
Vehicle-mounted nephelometer for use in desert environments
Authors: Markham James R. , Cosgrove Joseph E. , Smith Wayne W. , Best Philip E.
Published: July 2002

Vehicles that are required to travel off-road in arid and semiarid conditions can be exposed to high levels of airborne particles. The airborne material, typically sand, can be detrimental to the performance of air-breathing engines and other mechanisms. The U. S. Army, for instance, has experienced the influence of airborne desert dust during testing of equipment at Yuma Proving Ground, and during critical operations at other desert locations. To enhance testing of equipment under loading of airborne desert dust, a laser-based nephelometer has been constructed which provides the real-time measurement of dust mass per unit volume. The instrument is sensitive and provides a linear response to dust concentration levels from 0.01 to above 25 g/m3. Important is that: (1) the light scattering technique is independent of particle size distribution in the sampling volume; and (2) the instrument is rugged to allow for mounting and operation on vehicles traveling off-road in the desert environment.
A highly automatic measurement system for three orthogonal magnetic moments of a permanent magnet block
Authors: Hwang C. S. , Yeh Shuting , Teng P. K. , Uen T. M.
Published: July 2002

A highly automatic system with a three-angle rotation mechanism has been designed and constructed to measure several thousand permanent magnet blocks. The system’s main features include its high speed, highly automatic measurement, and the ease with which the different size magnet blocks can be installed and removed. This system provides precise and accurate measurements of the three orthogonal magnetic moment components to accurately characterize each block, as deemed necessary to assess the field quality of undulators and wigglers. A three-angle in rotation mechanism, together with a simple mathematical algorithm is used to measure and analyze the magnetic moments of the magnet block. The system includes the Helmholtz coil pair, block holder, the three-degree rotation mechanism, and the control and data acquisition system. A power train system consists of one motor coupled with a nonmagnetic stainless steel for 360° rotation and two motors individually coupled with two groups of nonmagnetic time belts for rotation angles of 0°, 180°, 0°, and 90°. The control system uses a microcomputer together with a stepping motor control card and a digital fluxmeter connected by the general purpose interface bus. The measurement speed of this system is 40 blocks per h. One reference magnet was measured, with those results verifying the long term precision of the order of 0.04% for the easy component and 0.02° for two minor components. The coil-pair geometry factor is calibrated via the voltage-field reciprocity principle, indicating that the system absolute accuracy is around 0.43%.
Greenspan acoustic viscometer for gases
Authors: Gillis K. A. , Mehl J. B. , Moldover M. R.
Published: July 2002

Double Helmholtz acoustic resonators, first proposed by Greenspan for measuring the viscosity of gases, were tested with helium, argon, and propane. Two different resonators were tested extensively with all three gases. For each of these instruments, the results for the viscosities of the three gases were consistent within ±0.5% at pressures spanning the range 25–1000 kPa. Without calibration, the viscosities deduced from one viscometer were systematically 1% larger than data from the literature; the viscosities from the second viscometer were systematically 3% larger than data from the literature. If the systematic differences were removed for each viscometer by calibration with a single gas at a single temperature and pressure, then nearly all the results for both instruments would have fallen within ±0.5% of the data from the literature. In these viscometers, the test gases are in contact with robust metal parts only; thus, these instruments are applicable to a very wide variety of gases over a very wide range of temperatures.
Compact design for real time in situ atmospheric trace gas detection based on mirage effect (photothermal deflection) spectroscopy
Authors: Zimering B. , Boccara A. C.
Published: July 2002

We present a compact and rugged setup for real time in situ trace gas detection based on photothermal deflection spectroscopy. The use of high quality Ge windows permits a true parallel geometry, resulting in a design resistant to ambient air motion while preserving the advantages of the technique such as good sensitivity, local probing, and open air measurement capability. Detection of ethylene within an enclosed sample cell has been performed in a N2 atmosphere, and we estimate the practical noise limited detection minimum to be 250 ppt, an order of magnitude improvement from a previous setup. We have measured absorption spectra of open laboratory air and real time ethylene exhaust from polymer and biological samples to investigate indus- trial, agricultural, and environmental applications.
Design of a ‘‘beetle-type’’ atomic force microscope using the beam deflection technique
Authors: Gasser B. , Menck A. , Brune H. , Kern K.
Published: July 2002

In the present article we describe a new setup for an atomic force microscope in the beetle-type geometry. The microscope consists of a compact head standing on three piezo legs with a fourth central piezo carrying the cantilever tip. We use the laser beam deflection method to detect the deflection of the cantilever. All optical components are integrated into the microscope head which has a diameter of 40 mm. This compactness results in a high mechanical stability, while the adjustment of the optical pathway is still easy to handle. The microscope can be used in UHV and in air. Measurements on KBr(100) in air show the capability of the microscope to obtain a resolution up to atomic corrugations.
Phenomenon of bipolar induction and development of a new rotation sensor
Authors: Kato Tetsuo , Kubono Takeshi , Mizuno Masashi
Published: July 2002

An apparatus was constructed for use in investigating bipolar induction phenomena, and related experiments were performed. A metal conductor was placed between a pair of bipolar magnets, and they were simultaneously rotated to induce a trapezoidal wave form ac voltage, whereas rotating the metal conductor alone caused a dc voltage to be induced. Rotation of the magnets alone caused a sinusoidal ac voltage to be induced. Drawing on their results, a new type of rotation detection sensor with an extremely simple construction was conceived, and its practical usefulness was confirmed.
Pulsed magnetically confined discharge for copper vapor lasers
Authors: Li Jun , Chen Qing-Ming , Zhang Wang , Xie Ming-Jie , Li Zai-Guang , Pan J. J.
Published: July 2002

An extended application of the magnetron sputtering discharge is described. The discharge, called a magnetically confined discharge in the experiments, is pumped in a pulse mode to produce and excite copper vapor atoms for laser operation. Copper atom densities adequate for laser action (∼1014 cm−3) are obtained in the discharge at temperatures below 400 K. Laser operation is expected in the experimental apparatus with fast-rise pulse pumping.