bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic system for the detection of transient liquid/gas interfaces using the pulse-echo technique
Authors: Matikainen L. , Irons G. A. , Morala E. , Chang J-S.
Published: July 2002

An ultrasonic method has been chosen to examine liquid/gas interfacial areas in closed systems. Although commercial equipment was used for the transducer and ultrasonic analyzer, commercial transient memory devices were inadequate. Consequently, a real-time data analysis and transient memory (DATM) unit was designed and constructed. A series of flight times for a succession of 1024 signals are calculated and recorded in the transient memory. The system clock operates at 10 MHz and increments a 12-bit binary counter. The counter is capable of measuring return signal times as long as 212 μs (4.096 ms) with a 1-μs resolution. The data are available as analog voltages for display on an oscilloscope or the digital data may be directly transferred to a microcomputer for analysis, display, or archival storage. The DATM device was successfully applied, collecting data for the analysis of rising bubbles in metallurgical systems and two-phase flow in horizontal tubes.
Densitometer for absolute measurements of the temperature dependence of density, partial volumes, and thermal expansivity of solids and liquids
Authors: Craubner H.
Published: July 2002

A densitometer device is described which can be used for rapid absolute determination of the temperature dependence of density, partial volumes, and thermal expansivity of condensed matter. The instrument is based on the hydrostatic method. It employs a two-chamber measuring system and an electronic balance. It can be used at both low (down to −100 °C) and high (up to 300 °C) temperatures. A small, polished buoyancy body of fused silica serves as a calibration standard. The theoretical foundations of hydrostatic density measurements are reviewed and pilot experiments are reported. Samples investigated are, e.g., silicon, LD polyethylene, n-hexane, methanol, and toluene. The information obtained refers among others to the stirrup buoyancy, the time course of thermodynamic equilibration after change of temperature, the temperature dependence of density and specific volume of methanol, etc. The results demonstrate that the instrument can be used for precise, rapid densitometric investigations of small samples of solids (5–700 mg) and liquids (5–100 cm3), independent of form and shape, at both low and high temperatures. The measurements can also be carried out dynamically by use of scanning techniques so that thermally deduced density changes can be observed directly in continuous fashion. For a self-consistent relative density determination relative to the calibration standard itself, the onset of inaccuracy is in the fifth decimal (<±0.01%), whereas for direct absolute measurements it is, at present, in the fourth decimal (<±0.1%).
Multiple track Doppler-shift spectroscopy system for TFTR neutral beam injectors
Authors: Kamperschroer J. H. , Kugel H. W. , Reale M. A. , Hayes S. L. , Johnson G. A. , Lowrance J. L. , Shah P. A. , Sichta P. , Sleaford B. W. , Williams M. D. , Zucchino P. M.
Published: July 2002

A Doppler-shift spectroscopy system has been installed on the TFTR neutral beam injection system to measure species composition during both conditioning and injection pulses using short and long pulse ion sources. Two intensified vidicon detectors and two spectrometers are utilized in a system capable of resolving data from up to 12 ion sources simultaneously. By imaging the light from six ion sources onto one detector, a cost-effective system has been achieved. Fiber optics are used to locate the diagnostic in an area remote from the hazards of the tokamak test cell allowing continuous access, and eliminating the need for radiation shielding of electronic components. Automatic hardware arming and interactive data analysis allow beam composition to be computed between tokamak shots for use in analyzing plasma heating experiments. Measurements have been made using lines of sight into both the neutralizer and the drift duct. Analysis of the data from the drift duct is both simpler and more accurate since only neutral particles are present in the beam at this location. Comparison of the data taken at these two locations reveals the presence of partially accelerated particles possessing an estimated 1/e half-angle divergence of 15° and accounting for up to 30% of the extracted power from the short pulse ion sources. Operation with long pulse ion sources indicates a higher atomic composition, fewer partially accelerated particles, and somewhat reduced neutralization line densities.
Generation of a high-power rf pulse in a rectangular waveguide
Authors: Friedman M. , Serlin V.
Published: July 2002

High-power rf radiation with a frequency of 800 MHz was extracted from a modulated intense relativistic electron beam into a rectangular waveguide. The rf extraction was limited to a rf power below 500 MW. Problems which prevent generation of higher power were identified and solutions offered.
Probe design aspects of ruby decay-time fluorescent sensors
Authors: Ghassemlooy Z. , Grattan K. T. V. , Lynch D.
Published: July 2002

This paper describes the design, construction, and testing of fiber-optic probes for temperature monitoring. Results obtained over a temperature range of 20–160 °C demonstrate the usefulness of crushed crystal ruby, in several different configurations, as a means of temperature measurement.
Resonant modes and laser spectrum of microdisk lasers
Authors: Frateschi N. C. , Levi A. F. J.
Published: July 2002

A theory for quantitative analysis of microdisk laser emission spectra is presented. Conformal mapping is used to determine the radial and azimuthal eigenvalues and eigenvectors corresponding to leaky optical modes in the disk. The results are compared with experimental data obtained from a 0.8 μm radius InGaAs/InGaAsP quantum well microdisk laser.
High counting rate gaseous x-ray detectors for synchrotron radiation applications (invited)
Authors: Lewis R. A. , Fore N. S. , Helsby W. , Hall C. , Jones A. , Parker B. , Sumner I. , Worgan J. S. , Budtz-Jo/rgensen C.
Published: July 2002

Multiwire gas proportional detectors have been used for many years on synchrotron radiation experiments and offer unrivaled dynamic range and detection efficiency but have been somewhat limited in count rate performance. We report here recent test results from two new rapid data acquisition systems developed at Daresbury and in addition the results of comparative tests on a new design of gas detector, the Microgap, and a gas Microstrip detector. Both designs appear capable of high rate ≳100 kHz/mm2 operation and combined with the new acquisition systems should begin to alleviate the count rate problems for some types of experiment.
Vertical inertial piezoelectric translation device for a scanning tunneling microscope
Authors: Agraït N.
Published: July 2002

We report a new type of inertial translation device that uses a single piezoelectric tube. In contrast to previous inertial translation devices which must operate in horizontal position, this new design can operate in any position, even vertical. This makes possible the construction of a compact high-stability thermally compensated low temperature scanning tunneling microscope, specially suited to designs that allow for a very short tip and sample change time.
European Synchrotron Radiation Facility (ESRF)
Authors: Haensel R.
Published: July 2002

The European Synchrotron Radiation Facility (ESRF), at present being built in Grenoble, France, is a state-of-the art synchrotron radiation facility open as of 1994 to users primarily from the 12 member countries. ESRF is funded for 30 beam lines, out of which 7 are to be opened in 1994 and the remainder step-by-step during the years to follow. The ESRF storage ring contains a total of 32 straight sections out of which 29 are available for insertion devices. So far the first set of 18 beam lines has been defined. Most of the ESRF beam lines will be on insertion devices, however additional beam lines on bending magnets can be installed by interested groups from the member countries by special arrangement.
Slip systems in C
60 single crystals
Authors: Tachibana M. , Sakuma H. , Michiyama M. , Kojima K.
Published: July 2002

A behavior of plastic deformations of C60 single crystals was examined using the microindentation technique. Not only slip lines but also dislocation etch pits were observed around the indentation on the crystal surface. It is confirmed that the slip systems in C60 single crystals are {111}〈110〉 in a temperature range of 240 K to 450 K. This means that, even in a simple cubic phase below a phase transition temperature of ∼260 K, the slip systems are the same as a face-centered-cubic phase.
A fiber drop analyzer: A new analytical instrument for the individual, sequential, or collective measurement of the physical and chemical properties of liquids
Authors: McMillan N. D. , Fortune F. , Finlayson O. , McMillan D. D. G. , Townsend D. , Daly D. , Fingleton M. , Dalton M.
Published: July 2002

A new instrumental method has been devised for the individual, sequential, or collective measurement of the physical and chemical properties of liquids. The instrumental theory for the fiber drop analyzer (FDA) has been developed for the measurement of surface tension, viscosity, refractive index, and chemical composition of a liquid. An empirical theory is suggested for the measurement of pH in a limited range. The analytical theory for the fiber drop analyzer has been established, a prototype constructed and tested for measuring individually surface tension, viscosity, refractive index, and the chemical composition on a restricted set of test solution. The instrument is shown to have the capability to simultaneously measure the above measurands, but in addition can in individual measurement procedures, measure all these quantities. The instrument perhaps is also potentially capable of measuring specific gravity and pH in its existing form, and other optical properties of liquids with some basic modification. The laboratory FDA has been used to test a series of samples from a large cane sugar manufacturer’s process and these measurements demonstrate that this technology has the potential to be used as a remote optrode industrial process monitor for sucrose manufacture and very possibly, elsewhere in other industrial applications.
Construction of a transform-limited picosecond time-resolved Raman spectrometer
Authors: Iwata Koichi , Yamaguchi Shoichi , Hamaguchi Hiro-o
Published: July 2002

A pump-probe picosecond time-resolved Raman spectrometer has been constructed using a dye laser synchronously pumped by a cw mode-locked Nd:YAG laser and a high repetition rate (2 kHz) dye amplifier pumped by the frequency doubled output from a cw Nd:YAG regenerative amplifier. Transform-limited picosecond pulses with 3.5 cm−1 wave number width and 3.2 ps temporal width are obtained at the wavelength of 588 nm. The second harmonic of these pulses is generated at 294 nm and is used for pumping, while the remaining visible pulses are used for probing resonance Raman scattering. The cross-correlation time between the pump and probe pulses is 4.1 ps. The temporal profile of the laser pulse is found to be very close to the sech2 shape. The wave number resolution of the system is estimated to be 3.5 cm−1 according to the Tailor criterion. The time resolution is estimated to be 2.2 ps using a criterion newly proposed in the present paper. Time-resolved Raman spectra of S1 trans-stilbene and S1 p-terphenyl are presented to demonstrate the capability of the constructed spectrometer.
High-resolution capacitive pressure gauges
Authors: Adams E. Dwight
Published: July 2002

Design, construction, methods of measurement, and uses of high-resolution capacitive pressure gauges in low temperature applications are reviewed. Pressure gauges for use from 10−3 to over 107 Pa, with a resolution of as high as 1×10−8 are described. Many uses that have been made of these gauges are mentioned with emphasis on 3He melting pressure thermometry.
New high-resolution phonon spectroscopy using impulsive stimulated Brillouin scattering
Authors: Kinoshita S. , Shimada Y. , Tsurumaki W. , Yamaguchi M. , Yagi T.
Published: July 2002

Impulsive stimulated Brillouin scattering is applied to a new high-resolution phonon spectroscopy, where phonons created by two crossing pump pulses are observed using diffraction of a cw probe light in both time and frequency domains. In time domain, real-time behavior can be detected sensitively using a digital oscilloscope, while in frequency domain, measurements with high resolution are attainable by means of a spherical Fabry–Perot interferometer. Several examples of the measurements on liquid samples are demonstrated for clarifying various aspects of the phonon generation by the present method: the mechanism of the generation under pulsed light irradiation, the propagation of the generated phonon, the resonance excitation, and the interference with the other nonlinear optical processes. The relation with the ordinary light scattering is also discussed.
Novel gas target for use in laser harmonic generation
Authors: Peatross J. , Meyerhofer D. D.
Published: July 2002

A novel gas target was developed for use in laser-atom harmonic-generation experiments. It operates on the principles of free molecular flow rather than those of fluid flow as does a gas jet. This allows much lower gas pressures to be achieved. The device is a small, cylindrical, double-ended hole through which the focused laser beam passes. Gas enters from the middle of the cylindrical wall and quickly disperses as it emerges out the hole openings. As with the gas jet, the purpose of the gas target is to provide a very narrow and localized distribution of gas for laser interaction. Some of the advantages of the target relative to the jet are that it is easier to systematically align to the laser beam and it can operate at much lower pressures. Results of a Monte Carlo simulation of the gas density and flow rate within the target and experimental measurements of the density profile made by imaging the recombination emission are presented herein. It is found that the gas density decreases rapidly once outside the target hole openings along the symmetry axis. The calculations are in good agreement with experimental measurements. The gas target continues to function without serious deviation at pressures up to ten times above the molecular flow range.
Scattering of reflectometer signals from rippled surfaces
Authors: Conway G. D.
Published: July 2002

Transverse coherent density fluctuations at the plasma cutoff layer are modeled by a rippled conducting surface. Two simulations are presented which give the reflectometer back scattered power as functions of ripple wavelength, amplitude, and phase. Results from an experimental simulation of the STOR-M tokamak geometry and a numerical simulation using the Helmholtz integral and a paraxial Gaussian probe beam, agree in showing three ripple wavelength (Λ) sensitivity regions defined by beam radius (w): Short wavelengths Λ/λ≪2w/λ experience large Bragg scattering. Long wavelengths Λ/λ≫10w/λ experience no scattering. Intermediate wavelengths experience complex scattering with strong modulation of reflected power at twice ripple frequency.
An optical detection low temperature atomic force microscope at ambient pressure for biological research
Authors: Mou Jianxun , Yang Jie , Shao Zhifeng
Published: July 2002

A low temperature atomic force microscope, based on the optical lever detection method and operated in liquid nitrogen vapor at ambient pressure, has been constructed. The experimental results show that atomic resolution images can be obtained on both mica and highly oriented pyrolytic graphite at temperatures down to 79 K with sufficient thermal stability. In liquid nitrogen vapor, no surface contamination was observed after many hours of continuous operation, which demonstrates that such an approach is ideal for biological applications for its lower cost and easy maintenance.
Valence subband structures of wurtzite GaN/AlGaN quantum wells
Authors: Uenoyama Takeshi , Suzuki Masakatsu
Published: July 2002

Valence subband structures of wurtzite GaN/AlGaN quantum wells have been studied, using the k⋅p method in which the parameters are derived by first-principles calculations. Since wurtzite GaN and AlN have the small spin-orbit splitting energies (≤20 meV), the mixing among the six bands including the spin-orbit split band should be considered to obtain the subband states correctly. According to our parameters for the GaN/AlGaN quantum well, the hole carrier confinement in the two-dimensional systems does not lead to a significant reduction of hole masses, and so the threshold current density of wurtzite GaN/AlGaN quantum well laser diodes is not decreased.
Nondestructive measurement of large objects with electron paramagnetic resonance: Pottery, sculpture, and jewel ornament
Authors: Ikeya Motoji , Yamamoto Masahiro , Ishii Hiroshi
Published: July 2002

A cylindicral cavity of TE111 mode with an aperture of 3 mm in diameter has been used to measure the electron paramagnetic resonance (EPR) spectrum of a large object placed over the aperture. EPR spectra of a precious fossil of a dinosaur tooth piece and a fossil bone of the Machikane Alligator were measured nondestructively in addition to a jadeite sculpture, a pearl and turquoise necklace, a large turmaline, a star ruby, and ceramic pottery. Thus, EPR can be a nondestructive tool to detect forgery and to test the authenticity in art as well as to allocate ancient objects in archaeological provenance study.
High-T
c three-axis dc SQUID magnetometer for geophysical applications
Authors: Dantsker E. , Koelle D. , Miklich A. H. , Nemeth D. T. , Ludwig F. , Clarke J. , Longo J. T. , Vinetskiy V.
Published: July 2002

A prototype three-axis magnetometer has been developed, intended for geophysical applications, involving high-transition temperature dc superconducting quantum interference devices (SQUIDs). Each SQUID was fabricated from a thin film of YBa2Cu3O7−x deposited on a SrTiO3 bicrystal to form two Josephson junctions, and was directly coupled to a single-turn pickup loop patterned in the same film. The three orthogonally mounted sensors were immersed in liquid nitrogen in a fiberglass Dewar and operated in separate flux-locked loops. In nominally zero ambient magnetic field, the best magnetic field resolution was 170 fT Hz−1/2 in the white noise, increasing to 225 fT Hz−1/2 at 1 Hz. The dynamic range was ±1.6×106 Hz1/2 in the white noise, and the highest slew rate achieved was 1.6 mT s−1, at 900 Hz. The 3 dB point in the frequency response was about 90 kHz. The three channels were mutually orthogonal to about 1%. The three-axis magnetometer was also operated outside the laboratory in the presence of 60 Hz and radio-frequency noise.
An improved fast-response microthermocouplea)
Authors: Beckman P. , Roy R. P. , Velidandla V. , Capizzani M.
Published: July 2002

An improved wire-type chromel–alumel microthermocouple with a disk-shaped junction is described. In this design, the 20 μm diameter thermocouple wires are installed taut between two 127 μm diameter prongs, one of chromel and the other of alumel. The disk junction, of 0.1 mm diameter and 4 μm thick, is located approximately midway between the prong tips. Time constants of two microthermocouples are reported. The two microthermocouples differ from each other primarily in the length of the prongs. The microthermocouple with the longer prongs exhibits faster response, its time constant in turbulent flow of liquid Refrigerant-113 (a poor conductor of heat) being less than 2 ms.
Design principles of a variable temperature scanning tunneling microscope
Authors: Bott Michael , Michely Thomas , Comsa George
Published: July 2002

We report on the construction of a variable temperature scanning tunneling microscope (STM) operating from 20 to 700 K in UHV, which routinely allows one to image dense packed metal surfaces in atomic resolution down to the lowest temperature. Central problems in designing a variable temperature STM are discussed in some detail. Methods to achieve efficient vibration isolation between the cryostat and the STM are presented. Furthermore, a sample and sample holder assembly is described, which ensures long-term mechanical stability and STM imaging, while subject to extreme temperature variations. The temperature response of the STM while cooling and heating the sample is measured and will be discussed.
Analysis of piezo actuators in translation constructions
Authors: Holman A. E. , Scholte P. M. L. O. , Heerens W. Chr. , Tuinstra F.
Published: July 2002

A translation stage has been developed for generating displacements with nanometer accuracy and a dynamic range of 10 μm. The stage uses piezo stacks as actuators and is equipped with capacitive sensors which are able to measure displacements with subnanometer resolution. Because the measurements are very accurate, the displacement properties of the piezo actuator used in the translation stage can be recorded with high precision. This allows us to investigate the displacement response of the piezo actuator when sinusoidal and triangular voltages are applied to it. These measurements will be used to model the hysteresis behavior of the piezo actuator. It is observed that the branches of the hysteresis curves can be described by a third-order polynome and that the hysteresis curve has point symmetry properties. Also a model is presented for describing the general behavior of a piezo actuator in a translation stage.
Nonorthogonal twinning in thin film oxide perovskites
Authors: Fahey K. P. , Clemens B. M. , Wills L. A.
Published: July 2002

We have observed nonorthogonal twinning in thin film oxide perovskites. This twinning geometry is equivalent to a 60° rotation of the twinned crystallites about the [111] direction in an [001] oriented film. This twinning is not detectable by the standard x-ray tests for film quality (a radial θ–2θ scan and a φ scan at a chi of 45°). In this study we observe this twinning in films of PbZrxTi1−xO3, BaTiO3, and SrRuO3 grown by sputtering and MOCVD on MgO and SrTiO3. These twins are observed in films deposited on a substrate with which there is a large lattice mismatch and in films that are deposited in an oxygen deficient environment. We propose that these twins result from plastic deformation associated with misfit accommodation and discuss the twin geometry and the nature of the twin interface.
Initialization of plasma density profiles from reflectometry
Authors: Varela P. , Manso M. E. , Silva A. , Fernandes J. , Silva F.
Published: July 2002

The contribution of the initial plasma to density profiles reconstructed from the dφ/df vs f curve obtained with reflectometry is studied. It is shown that the initial phase information determines to a great extent the accuracy of the inverted profiles at the edge. As it is difficult to measure the edge contribution models are required to initialize the profile evaluation. A novel method is presented that uses the phase information from the lowest frequency waves to obtain dφ/df below the first probing frequency F1, by imposing the continuity with the measured dφ/df characteristic and its derivative at F1. An approximate shape of the edge profile is obtained because low-frequency waves are sensitive to the initial plasma where they propagate without reflection. The accuracy of the inverted profiles is thereby improved, as shown by simulation studies performed for profiles with an exponential-like decay and with an edge density plateau (typical of H-mode regimes during ELMs). It is found that the contribution from the initial plasma decreases with density (or frequency); for densities of the order of 10× the first probed density ne1 it is reduced to values less than 10% in the case of a profile with a flat edge and 2% for a peaked one. For ne≳10ne1 the profiles can be absolutely calibrated from reflectometry data alone with an accuracy of ±2 mm independent of the initialization model. The numerical study also shows that profile deviations resulting from insufficient phase derivative data, e.g., due to discrete probing, can be more significant than those originated by the initialization process.
A simple, ultrahigh vacuum compatible scanning tunneling microscope for use at variable temperatures
Authors: Mugele F. , Kloos Ch. , Leiderer P. , Möller R.
Published: July 2002

We present the construction of a very compact scanning tunneling microscope (STM) which can be operated at temperatures between 4 and 350 K. The tip and a tiny tip holder are the only movable parts, whereas the sample and the piezoscanner are rigidly attached to the body of the STM. This leads to an excellent mechanical stability. The coarse approach system relies on the slip-stick principle and is operated by the same piezotube which is used for scanning. As an example of the performance of the device, images of a NbSe2 surface with atomic resolution are obtained.
Study of the thin-film palladium/hydrogen system by an optical transmittance method
Authors: Garcia Jose A. , Mandelis A.
Published: July 2002

The thin-film palladium/hydrogen system was studied using a novel all optical method. Isotherms at room temperature (25 °C) were obtained for palladium films with different thicknesses. The measured isotherms included the α, α-to-β, and β phase regions. A decrease of the phase transition region was observed as the palladium film thickness was decreased. This optical method has good potential for use in studying the equilibrium and kinetic aspects of any thin-film/gas system.
A low-frequency vibration isolation table using multiple crossed-wire suspensions
Authors: Barton Mark A. , Kanda Nobuyuki , Kuroda Kazuaki
Published: July 2002

A practical low-frequency one-dimensional vibration isolation system has been developed exploiting a previously developed crossed wire suspension technique. A table is supported by two such suspensions so as to be stiff in 5° of freedom but with a very long period in one horizontal direction. The rotation of the suspended mass in the original system is eliminated and the transfer function at high frequencies is greatly improved. Periods of 10 s were achieved in experimental tests, giving isolation of 40 dB at 1 Hz and up to 60 dB at 10 Hz. The system is suitable for one-dimensional optics experiments or as a base for further stages of vibration isolation.
Photon-assisted tunneling in a resonant tunneling diode: Stimulated emission and absorption in the THz range
Authors: Drexler H. , Scott J. S. , Allen S. J. , Campman K. L. , Gossard A. C.
Published: July 2002

The dc I–V characteristic of a triple-barrier resonant tunneling diode (RTD) integrated in a bowtie antenna and driven by THz radiation displays up to five additional resonant tunneling channels. These channels appear as additional peaks in the I–V characteristic whose voltage positions vary linearly with frequency in the investigated range between ν=1.0 and 3.4 THz. We attribute these peaks to photon-assisted tunneling processes corresponding to absorption and stimulated emission of up to three photons. The experiments suggest that such a device can be utilized to detect and generate THz radiation.
Vacuum ultraviolet rare gas excimer light source
Authors: Wieser J. , Murnick D. E. , Ulrich A. , Huggins H. A. , Liddle A. , Brown W. L.
Published: July 2002

A dc electron beam at 20 keV is used for the excitation of pure rare gases at pressures up to 1.7 bar. The well known second excimer continua of argon, krypton, and xenon observed under these excitation conditions provide an efficient light source in the vacuum ultraviolet spectral region between 120 and 200 nm. Thin (300 nm) SiNx foils are used as entrance windows for the low energy electron beam. Due to the flexibility of the production process of the thin foils one can consider various shapes and sizes of the light emitting region to be manufactured. Efficiencies of ∼30% are observed for the conversion of electron beam energy into light.
A new pure ion plasma device with laser induced fluorescence diagnostic
Authors: Anderegg F. , Huang X.-P. , Sarid E. , Driscoll C. F.
Published: July 2002

We describe a new apparatus for magnetic confinement of a pure ion plasma, with laser diagnostics to measure test particle transport across the magnetic field. In addition to the axisymmetric trapping potential, rotating electrostatic wall perturbation is used to counteract the plasma loss processes, giving steady-state ion confinement for weeks. Electronic spin polarization of the ion ground states is used to label the test particles; this spin orientation is controlled by direct optical pumping. The laser-induced fluorescence (LIF) technique is used to nondestructively measure the ion velocity distribution; and an absolute calibration of the charge density is obtained from the LIF measurement of the plasma rotation velocity. Two new technological improvements compatible with ultrahigh vacuum systems have been used: a semirigid Teflon insulated coaxial cable has low microphonic noise, and an antireflective coating is used to reduce reflection of ultraviolet light inside the vacuum chamber.
Repetitively operated plasma opening switch using laser produced plasma
Authors: Akiyama H. , Katschinski U. , Nagata E. , Katsuki S. , Kohno S.
Published: July 2002

A plasma opening switch using laser produced plasma is successfully operated at repetition rates up to 3.3 pulses per second. It is shown that the switch performance has good reproducibility without any maintenance. Reliability tests indicate that the switch lifetime is limited by the volume of the target material and the lifetime of the energy storage capacitor.
Production of highly charged ion beams from electron cyclotron resonance ion sources (invited)
Authors: Xie Z. Q.
Published: July 2002

Electron cyclotron resonance ion source (ECRIS) development has progressed with multiple-frequency plasma heating, higher mirror magnetic fields, and better technique to provide extra cold electrons. Such techniques greatly enhance the production of highly charged ions from ECRISs. So far at continuous wave (CW) mode operation, up to 300 eμA of O7+ and 1.15 emA of O6+, more than 100 eμA of intermediate heavy ions for charge states up to Ar13+, Ca13+, Fe13+, Co14+, and Kr18+, and tens of eμA of heavy ions with charge states to Kr26+, Xe28+, Au35+, Bi34+, and U34+ were produced from ECRISs. At an intensity of at least 1 eμA, the maximum charge state available for the heavy ions are Xe36+, Au46+, Bi47+, and U48+. An order of magnitude enhancement for fully stripped argon ions (I⩾60 enA) were also achieved. This article will review the ECR ion source progress and discuss key requirement for ECRISs to produce the highly charged ion beams.
A 2.45 GHz ECR ion source for production of medium charge states ions
Authors: Wutte D. C. , Leitner M. A. , Williams M. D. , Leung K. N. , Gough R. A. , Saadatmand K. , Benveniste V.
Published: July 2002

At the Lawrence Berkeley National Laboratory we are constructing an ECR ion source test facility for nuclear science as well as industrial applications experiments. For these purposes, a single-stage 2.45 GHz electron cyclotron resonance ion source has been designed and constructed. It features an axial magnetic field with a mirror ratio of up to six and a hexapole field produced by a simple Nd–Fe–B permanent magnet assembly. In order to enhance the ion confinement time, the source plasma volume has been enlarged as much as possible while still maintaining a high mirror ratio. This paper describes the design of the ion source, the extraction system and the test stand. First, operational experience and experimental results with an argon discharge are presented.
A direct method of extracting surface recombination velocity from an electron beam induced current line scan
Authors: Ong Vincent K. S.
Published: July 2002

The extraction of diffusion length and surface recombination velocity in a semiconductor with the use of an electron beam induced current line scan has traditionally been done by fitting the line scan into complicated theoretical equations. It was recently shown that a much simpler equation is sufficient for the extraction of diffusion length. The linearization coefficient is the only variable that is needed to be adjusted in the curve fitting process. However, complicated equations are still necessary for the extraction of surface recombination velocity. It is shown in this article that it is indeed possible to extract surface recombination velocity with a simple equation, using only one variable, the linearization coefficient. An intuitive feel for the reason behind the method was discussed. The accuracy of the method was verified with the use of three-dimensional computer simulation, and was found to be even slightly better than that of the best existing method.
Modeling of tunnel diode oscillators and their use for some low temperature investigations
Authors: Gevorgyan S. G. , Movsesyan G. D. , Movsisyan A. A. , Tatoyan V. T. , Shirinyan H. G.
Published: July 2002

The simple method of modeling of tunnel diode (TD) oscillators’ work is described, and may be applied also to the other types of negative-differential conductance oscillators. In particular, the calculation of the harmonic oscillation amplitude is performed by the energy balance method, based on TD measured the current–voltage characteristic’ (I–V curve), using only one fitting parameter—the tunnel diode’s measured bias at which oscillations are quenched by means of which the oscillator’s effective total losses are determined also. The formula for calculation of the TD generator’s frequency is derived; it agrees with experiment and permits determination of its dependence on the radiotechnical scheme’s elements and TD I–V curve’s shape. The results of the calculation in comparison with the experiment are reported for the oscillators of various constructions operating at different conditions. For this, more attention is given to the constructive solutions applied in the low temperature experiments. Examples of the TD oscillators’ use in cryogenic techniques as well as in the superconducting detectors of particles and radiation are presented. The oscillators described generate, under the certain conditions, low-amplitude (<40 mV) sinusoidal signals with a highly stable frequency (not worse than ΔF/F=10−9/min at liquid-helium temperatures) and low intensity of higher harmonics in the soft mode. The power released is less than 10 μW and the measuring rf magnetic field’s amplitude at a sample, placed inside or near the oscillator coil, is less than 1 mOe. Using designed facilities we have already detected normal-to-superconducting phase transitions of tin grains with diameters of about 2 μm and phase transitions in micrometer thick and 20 μm2 high-Tc superconducting films.
Polarized electroluminescence from rubbing-aligned poly(2,5-dinonyloxy-1,4-phenylenevinylene) films
Authors: Hamaguchi Maki , Yoshino Katsumi
Published: July 2002

Polarized light emission was observed in conjugated polymer electroluminescent diodes comprising rubbing-aligned poly(2,5-dinonyloxy-1,4-phenylenevinylene) as the emissive layer. By using 2-(4-biphenyly1)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole dispersed in polystyrene as the electron-transporting/hole-blocking layer, the electroluminescence efficiency and the dichroic ratio of the electroluminescent light increased, resulting in polarized electroluminescence with a dichroic ratio of 4.0.
Determination of the optical constants of thin films in the visible by static dispersive Fourier transform spectroscopy
Authors: Harvey A. R.
Published: July 2002

Conventional dispersive Fourier transform spectrometry (DFTS) is a powerful tool for determining optical constants of materials. However, the refined and intrinsically high-cost mechanically scanned interferometers that are necessary are not well suited to use in hostile environments or for time-resolved operation. We describe here a novel approach to DFTS that employs a combination of a Wollaston prism and a linear detector array. It is ideally suited to the precision characterization of thin films with physical thicknesses of up to about 1000 wavelengths or typically about 1 mm. The simplicity and optical efficiency of conventional DFTS are combined with the inherent robustness, superior time resolution, and high repeatability of spatial interferometry. The technique offers an optical throughput that is an order of magnitude higher than spectrophotometry or spectral ellipsometry while accuracies of 1 part in 104 and repeatability of 1 part in 105 are possible for the measurements of the real part of the refractive index. The imaginary component of the refractive index of thick transparent samples has been measured with an absolute error of less than 2×10−4. The technique may be readily applied from the vacuum ultraviolet to the mid infrared. We present proof-of-principle measurements of optical constants at wave numbers between 9000 and 25 000 cm−1 for a self-supporting film of Melinex and for a thin film of ZnSe grown by molecular beam epitaxy onto a glass substrate.
Low-noise differentiator preamplifier for photogenerated signals
Authors: Rovati Luigi , Docchio Franco
Published: July 2002

A low-noise preamplifier to perform a derivative of photogenerated signals is proposed. The novel structure is based on an inductive feedback preamplifier which performs preamplification and a derivative of the photogenerated current in a single stage. A breadboard circuit implementation and noise measurements are presented. Comparative noise measurements show that the proposed architecture is competitive with the classical differentiator preamplifier
Temperature dependence of minority and majority carrier mobilities in degenerately doped GaAs
Authors: Lovejoy Michael L. , Melloch Michael R. , Lundstrom Mark S.
Published: July 2002

Measured minority and majority carrier mobility temperature dependencies in heavily doped n- and p-GaAs are compared. Majority carrier mobilities in heavily doped GaAs are essentially temperature (T) independent while minority carrier mobilities exhibit a roughly 1/T dependence. Majority carrier freezeout, which reduces both majority–minority carrier and ionized impurity scattering, is shown not to be responsible for the 1/T minority carrier mobility dependence. The difference in minority and majority carrier mobility T dependencies is explained in terms of the increased degree of degeneracy of majority carriers with decreased temperature, which decreases majority–minority carrier scattering.
A new scanning capillary tube viscometer
Authors: Cho Young I. , Kim Won-Tae , Kensey Kenneth R.
Published: July 2002

The present study introduces a new scanning capillary tube viscometer for measuring fluid viscosity continuously over a range of shear rates including a low shear regime. Using a charge-coupled device sensor array, one could measure the changes in fluid level in a rising tube h(t) from which viscosity and shear rate were mathematically calculated. The concept of the new scanning capillary tube viscometer was validated by measuring viscosities of Newtonian fluids and comparing the results with those obtained with reference data and a rotating viscometer. Furthermore, the present method overcomes one of the major drawbacks of the capillary tube viscometer, the inability to produce viscosity data in a low shear range, by extending the shear rate range as low as 5 s−1 for water and diluted glycerin solutions at room temperature.
Study of plasma uniformity on JT-60U negative ion source
Authors: Kawai M. , Grisham L. , Itoh T. , Kazawa M. , Kuriyama M. , Mogaki K. , Okumura Y. , Watanabe K.
Published: July 2002

The negative ion source developed at JAERI for the N-NBI was intended to accelerate a 500 keV, 22 A D− beam for 10 s. Two of these ion sources are mounted in the beamline. It has been found that the spatial uniformity of the source plasma is not as good as expected in the design phase of the negative ion sources for JT-60U. The source plasma uniformity has been estimated through measuring spatial distributions of the arc current flowing into each filament group and also the ion saturation current with Langmuir probes placed at ten positions around the extraction area of the plasma grid. We then altered the relative values of the arc current-limiting resistors to the eight filament groups in each source to balance the arc. As a result of the optimization of the arc resistors, the nonuniformity of the source plasma has been reduced.
GEO 600 triple pendulum suspension system: Seismic isolation and control
Authors: Plissi M. V. , Torrie C. I. , Husman M. E. , Robertson N. A. , Strain K. A. , Ward H. , Lück H. , Hough J.
Published: July 2002

In this article we describe aspects of the suspension system for each of the main optics (test masses) in the GEO 600 interferometric gravitational wave detector currently under construction in Germany. In particular we describe the triple pendulum, which is a key aspect of the overall system, discuss the details of the mechanical design, present transfer functions of the isolation performance, and display examples of impulse responses for the local control used to damp the low frequency modes of the triple pendulum. This local control is achieved using co-located sensing and feedback at the highest mass of the triple pendulum, providing a significant attenuation of local control noise to the fused silica test mass, the lowest mass of the triple pendulum. In order to enhance the vertical isolation, the triple pendulum will incorporate two stages of cantilever springs, and fused silica fibers will be used in the lowest pendulum stage in order to minimize thermal noise from the pendulum modes. It is expected that the thermal noise associated with the internal modes of the fused silica test mass (mass ∼6 kg) will set the sensitivity limit for GEO 600 from 50 to ∼200 Hz. The measured performance from individual stages of the prototype suspension system indicates that a seismic noise level which is a factor ∼3 lower than this thermal noise level at 50 Hz can be achieved.
A wide range linear electrometer
Authors: Acharya Y. B.
Published: July 2002

A linear electrometer capable of wide range current measurement is presented. Circuit analysis of the electrometer and an automatic gain switching system are described. The electrometer can measure currents from 100 pA to 15 μA. Experimental results of the range and rise time are also discussed.
Temperature-mediated phase selection during growth of GaN on (111)A and (1̄1̄1̄)B GaAs substrates
Authors: Yang J. W. , Kuznia J. N. , Chen Q. C. , Khan M. Asif , George T. , De Graef M. , Mahajan S.
Published: July 2002

GaN layers having the zinc blende and wurtzite structures can be selectively deposited on (111)A and (1̄1̄1̄)B GaAs substrates by varying the growth temperature. Using the growth temperature as a variable, layers having the two structures have been sequentially deposited. The as-grown structures have been examined by cross-sectional high resolution electron microscopy. Results indicate that the two phases once formed are structurally stable in the temperature range examined. Furthermore, the transition from GaN (zinc blende) to GaN (wurtzite) is sharp, whereas a faulted region is observed during the reverse transition. Arguments have been developed to rationalize these observations.
Spontaneous vitrification in the Au–Ta system with a small size difference
Authors: Pan F. , Chen Y. G. , Liu B. X.
Published: July 2002

Spontaneous vitrification was observed in the Au–Ta system, although the atomic size difference between Au and Ta is very small. It was found that among the various compositions studied, vitrification was only achieved at a composition of around Au23Ta77. Comparative data were obtained by ion mixing of Au–Ta multilayered films to support the spontaneous vitrification results. The amorphization mechanism was discussed in terms of competition between the amorphous phase against the nucleation and growth of the existing equilibrium compound, which explained the favorable composition range as well as the thermal stability of the obtained amorphous alloy.
Visualization of nanostructured porous silicon by a combination of transmission electron microscopy and atomic force microscopy
Authors: Teschke Omar
Published: July 2002

The observation of red-, near-infrared, and nonphotoluminescent porous silicon structures both by transmission electron microscopy as well as by atomic force microscopy provides a consistent structural picture of the species responsible for the visible luminescence observed in these samples. The topography of the tops are seen in detail by atomic force microscopy, while the valleys are better observed by transmission electron microscopy; the observation techniques are therefore complementary. By measuring the apex radius of curvature of the atomic force microscope tip, it is possible to determine the porous silicon particle size by simple geometrical arguments. For red-photoluminescent porous silicon, the measured particle diameter using atomic force microscopy was 55 Å and the particle height 4 Å. The corrected particle diameter of 17 Å is in close agreement with the 15 Å value measured by transmission electron microscopy.
Free-standing versus AlAs-embedded GaAs quantum dots, wires, and films: The emergence of a zero-confinement state
Authors: Franceschetti Alberto , Zunger Alex
Published: July 2002

Using a plane-wave pseudopotential method we investigate the electronic structure of free-standing and of AlAs-embedded GaAs quantum dots, wires, and films. We predict that (i) the confinement energy of the valence-band maximum (VBM) is larger in AlAs-embedded than in free-standing quantum structures, because of the zero-confinement character of the VBM wave function in the latter case; (ii) small GaAs quantum structures have an indirect band gap, whereas large GaAs quantum structures have a direct band gap; (iii) the conduction-band minimum of small free-standing quantum structures originates from the GaAs X1c valley, while it derives from the AlAs X1c state in AlAs-embedded quantum structures; (iv) the critical size for the direct/indirect crossover is larger in embedded quantum structures than in free-standing quantum structures.
Effect of hydrogen plasma precleaning on the removal of interfacial amorphous layer in the chemical vapor deposition of microcrystalline silicon films on silicon oxide surface
Authors: Park Young-Bae , Rhee Shi-Woo
Published: July 2002

Microcrystalline silicon(μc-Si) film deposited on silicon oxide in a remote plasma enhanced chemical vapor deposition (RPECVD) with disilane (Si2H6) and silicon tetrafluoride (SiF4) has been investigated. It was found that in situ hydrogen plasma cleaning of the substrate prior to deposition is effective to reduce the interfacial amorphous transition region. It is believed that hydrogen plasma cleaning generated adsorption and nucleation sites by breaking weak Si–O and Si–Si bonds and also removed oxygen/carbon impurity. Surface roughening was observed from the hydrogen plasma precleaning which helped nucleation and crystallization at the initial stage of the growth.
Photochemical removal of organic contaminants from silicon surface at room temperature
Authors: Fominski V. Yu. , Naoumenko O. I. , Nevolin V. N. , Alekhin A. P. , Markeev A. M. , Vyukov L. A.
Published: July 2002

Using in situ x-ray photoelectron spectroscopy we have investigated the possibility of photochemical organic contaminant removal from a silicon surface at room temperature in oxygen and fluorine containing atmospheres (O2, NF3/H2, O2/NF3/H2). In contrast to UV irradiation in O2 and NF3/H2 reagents, the possibility of complete organic contaminant removal has been observed in O2/NF3/H2 gas mixture.