bluuebunny/crossref_metadata_2025 huggingface dataset:
Novel infrared detector concept utilizing controlled epitaxial doping profiles
Authors: Liu H. C. , Noël J.-P. , Li Lujian , Buchanan M. , Simmons J. G.
Published: July 2002

A novel infrared detector concept is proposed and experimentally demonstrated. Because of the flexibility provided by modern epitaxial growth techniques, we use thin heavily doped Si layers for infrared absorption via free-carrier-related processes, and the active region is sandwiched in a p-n junction. Silicon-based materials for long-wavelength infrared applications are highly desirable because of the possibilities for advanced Si circuit technology.
Analysis of an electron-wave Y-branch switch
Authors: Palm Thomas , Thylén Lars
Published: July 2002

An electron-wave Y-branch switch, analogous to the integrated optics Y-branch or digital switch, is proposed and analyzed using the beam propagation method. It is shown that this switch allows considerably wider electron velocity spectra than interferometric devices, such as the directional coupler. Furthermore, the Y-branch switch does not require single-mode electron waveguides.
Controlled preparation of oxygen deficient YBa2Cu3Ox films
Authors: Osquiguil E. , Maenhoudt M. , Wuyts B. , Bruynseraede Y.
Published: July 2002

We describe a simple method based on the oxygen pressure-temperature phase diagram to prepare oxygen deficient YBa2Cu3Ox thin films. Systematic critical temperature and x-ray diffraction experiments clearly show that films with different oxygen contents (6.6≤x≤7) are obtained in a controlled, reproducible, and reversible way.
New method for epitaxial heterostructure layer growth
Authors: Mantl Siegfried , Bay Helge L.
Published: July 2002

A new method for the fabrication of compound thin films inside single-crystalline matrices is demonstrated. It differs from all known techniques by the combination of epitaxial growth of the host material and the controlled deposition of a precipitating compound. A subsequent thermal treatment leads to a coalescence of the precipitates, resulting in a continuous buried layer. We call this method allotaxy. As an example we demonstrate the growth of buried epitaxial CoSi2 layers in Si(100).
Direct photoetching of polymer films using vacuum ultraviolet radiation generated by high-order anti-Stokes Raman scattering
Authors: Wada Satoshi , Tashiro Hideo , Toyoda Koichi , Niino Hiroyuki , Yabe Akira
Published: July 2002

High-order anti-Stokes Raman pulses of the vacuum ultraviolet were successfully utilized for ablation of polymer films. Efficient anti-Stokes conversion of the fourth harmonics of a conventional Nd:YAG laser provided fluences as large as 0.4 J/cm2 for a sixth-order anti-Stokes pulse at 160 nm. The selection of irradiation wavelength by a ready choice of scattered orders of Raman waves could verify critical wavelength dependence of ablation effect, which turned out that only the light at 160 nm made it possible to ablate polytetrafluoroethylene (PTFE) film with such low fluences.
Dopant compensation effects on impurity trapping and electrical resistivity of ion implanted amorphous silicon
Authors: Coffa S. , Poate J. M.
Published: July 2002

The implantation of B and P in ion-implanted amorphous Si has been investigated by measurements of spreading resistance and depth distribution of Pd trapped at defects. For concentrations of B or P in the range 0.2–1 at. %, the resistivity is reduced by an order of magnitude and the Pd trapping is retarded by the presence of B and enhanced by P. When B and P are present together at comparable concentrations the resistivity and the trapping efficiency of amorphous Si return to the undoped value. These compensation effects are explained in terms of the dopants changing the Fermi level position and hence the charge state and trapping efficiency of the defects. It is argued that most of the defects (∼1 at. %) are chargeable. These results provide a clue for understanding the dopant compensation phenomena observed in the rate of epitaxial crystallization of amorphous Si.
Anisotropic Si(100) etching induced by high translational energy Cl2 molecular beams
Authors: Teraoka Yuden , Nishiyama Iwao
Published: July 2002

Si(100) has been etched by high speed Cl2 molecular beams, generated by seeding in He. The translational energy dependence for etch rates has been measured by changing the gas mixing ratio and nozzle temperature. The two methods provided the same results. A 2.1 eV energy threshold was observed at 530 °C substrate temperature. The Cl+/Cl+2 intensity ratio, directly monitored by a quadrupole mass spectrometer, was independent of the nozzle temperature. These facts indicate that the etch rate enhancement is not attributed to Cl radicals or vibrationally excited Cl2 molecules. Owing to the translational energy induced etching, anisotropic etching profiles are realized at 670 °C substrate temperature.
Influence of phase separation on electron mobility in high-purity GaxIn1−xAsyP1−y (0≤y≤1)
Authors: Chen Z. , Bimberg D.
Published: July 2002

A strong contribution of the phase separation to the alloy scattering potential is determined for the first time in the composition range from y=0.4 to y=1.0 in high-purity GaxIn1−xAsyP1−y alloys. The composition fluctuation leads to a sharp increase in the alloy scattering potential at y=0.7, in perfect agreement with yet unexplained experimental electron mobility determinations.
Ultraviolet laser fabrication of ultrastrong optical fiber gratings and of germania-doped channel waveguides
Authors: Mizrahi Victor , Lemaire Paul J. , Erdogan Turan , Reed W. A. , DiGiovanni David J. , Atkins Robert M.
Published: July 2002

We report the fabrication of low loss (<0.2 dB) fiber Bragg gratings of 10 nm reflection bandwidth, and of 19 nm bandwidth lossy gratings. With this technology we also demonstrate the direct writing of channel waveguides in commercial germania-doped wafers without the use of photoresist and etching.
Crystallized mixed-phase silicon films for thin film transistors on glass substrates
Authors: Voutsas Apostolos T. , Hatalis Miltiadis K.
Published: July 2002

The low temperature crystallization of mixed-phase silicon films deposited by low pressure chemical vapor deposition was investigated. The mixed phase consists of crystalline regions embedded in an amorphous matrix, with the crystalline fraction being a function of the deposition temperature and the deposition rate. In this material, the nucleation rate of new crystallites during annealing is higher than in a completely amorphous film, resulting in a shorter crystallization time and a smaller average grain size. To compensate for the reduction in the grain size, a composite structure was proposed consisting of two successive layers; a mixed-phase layer and an amorphous layer. Crystallized mixed-phase films were used for the fabrication of polysilicon thin film transistors on new Corning (Code 1735) glass substrates at a maximum processing temperature of 560 °C. A field-effect mobility of 20 cm2/V s and a threshold voltage of 5.1 V were obtained even before hydrogenation.
Generation of electrochemically deposited metal patterns by means of electron beam (nano)lithography of self-assembled monolayer resists
Authors: Sondag-Huethorst J. A. M. , van Helleputte H. R. J. , Fokkink L. G. J.
Published: July 2002

Submicron metal patterns have been produced by galvanic deposition in openings in a monolayer resist generated by electron beam (e-beam) lithography. The monolayer resist is a self-assembled docosanethiol (C22H45SH) layer adsorbed on gold. Proper removal of the thiol requires an e-beam dose of 10–100 mC cm−2. The positive resist pattern was used to selectively deposit galvanic copper. The size of the Cu patterns is affected by the galvanic deposition time and the CuSO4 concentration in the electrolyte solution. The smallest Cu patterns produced were about 75 nm in width.
Real time spectroellipsometry study of the interaction of hydrogen with ZnO during ZnO/a-Si1−xCxH interface formation
Authors: An Ilsin , Lu Yiwei , Wronski C. R. , Collins R. W.
Published: July 2002

Using real time spectroellipsometry (SE), we have studied the interfacial interactions that occur when i- and p-type hydrogenated amorphous silicon-carbon alloys (a-Si1−xCx:H) are deposited from hydride-containing plasmas onto transparent, conducting films of ZnO. The SE spectra collected during the nucleation of a-Si1−xCx:H onto ZnO reveal a widening of the near-interface optical gap of ZnO by ∼0.1 eV, an effect attributed to the penetration of atomic H from the plasma. The SE data, along with ex situ secondary ion mass spectrometry, reveal that the H diffuses into ZnO to depths ≳200 Å. The defects that result from H incorporation in ZnO (e.g., O vacancies) lead to a shift in the near-interface Fermi level higher into the ZnO conduction band and to an estimated enhancement in the electron concentration by ∼1020 cm−3.
Control of structure and electrical properties of lead-zirconium-titanate-based ferroelectric capacitors produced using a layer-by-layer ion beam sputter-deposition technique
Authors: Auciello O. , Gifford K. D. , Kingon A. I.
Published: July 2002

It is demonstrated that the structure and electrical properties of Pb(ZrxTi1−x)O3(PZT)-based capacitors, involving RuO2 electrodes, can be controlled by depositing intermediate PbTiO3 (PT) layers at the PZT/electrode interfaces. Three different PZT-based capacitor systems were studied, namely: (a) RuO2/PZT/RuO2/(100)MgO, (b) RuO2/PZT/PT/RuO2/(100)MgO, and (c) RuO2/PT/PZT/PT/RuO2/(100)MgO. Electrical characterization of capacitor (a), without a PT layer, shows about 71% reduction in remanent polarization, while those with one (b) or two (c) PT layers present only 34% and 29% decrease in remanent polarization, after 1010 switching cycles. Electrical conduction measurements (current density versus time) have shown that ion beam sputter-deposited PZT-based capacitors with or without PT layers present about an order of magnitude (∼6×10−9 A/cm2, at 100 s) smaller dc leakage current, for comparable physical and electrical parameters, than dc leakage characteristic of PZT sol-gel-based capacitors with RuO2 electrodes produced in our laboratory. Intermediate PT layers may help eliminate the formation of undesirable second nonferroelectric phases and/or charged defects at the PZT-electrodes interface in ion beam sputter-deposited PZT-based capacitors, which in turn results in improved electrical properties.
CeO2: An alternative insulator material for superconducting field effect devices
Authors: Walkenhorst A. , Schmitt M. , Adrian H. , Petersen K.
Published: July 2002

The properties of high-Tc superconducting field-effect devices using CeO2 as an insulating layer have been studied. The dielectric constant and hence the achieved charge transfer for constant gate voltage and equivalent geometry is smaller as compared to the established SrTiO3 dielectric. This is mostly compensated by better insulating properties. The observed field effects for a fixed amount of charge transfer are very similar to those obtained with the SrTiO3 dielectric, indicating that the observed field effects are truly due to changes in the charge carrier density and not due to field-induced stresses in the multilayer structure.
Novel chemical routes to silicon-germanium-carbon materials
Authors: Kouvetakis John , Todd Michael , Chandrasekhar D. , Smith David J.
Published: July 2002

We report the use of novel molecular precursors and ultrahigh vacuum chemical vapor deposition techniques to synthesize solid solutions of cubic SiC-GeC and diamond-structure Si1−x−yGexCy materials. Thin films with composition Si0.37Ge0.13C0.50 were deposited on Si by thermal decomposition of Ge[Si(CH3)3]4 at 650–700 °C. Electron microscope observations showed a polycrystalline zinc-blende-type structure and infrared (IR) analyses revealed carbide-type Si-C and Ge-C vibrations. The Si1−x−yGexCy (y≳2%) alloys were deposited at 550–600 °C on Si and SiO2 by interactions of (1) C(SiH3)4 and GeH4; (2) CH3GeH3 and SiH4; and (3) CH3GeH3 with mixtures of GeH4 and SiH4. A homogeneous alloy phase of composition Si56Ge30C14 with diamond cubic structure was obtained from reaction 1. Reactions 2 and 3 produced films with carbon compositions ranging from 2 to 27 at. %. The materials containing less than 10% carbon appeared to be exclusively diamond cubic, whereas those with greater carbon compositions showed mixtures of diamond cubic and carbide phases as indicated by vibrational and structural characterization. Secondary ion mass spectrometry experiments revealed that all materials had excellent chemical purity.
Deposition of intrinsic, phosphorus-doped, and boron-doped hydrogenated amorphous silicon films at 50 °C
Authors: Cabarrocas Pere Roca i
Published: July 2002

We report the optical and electronic properties of intrinsic and doped hydrogenated amorphous silicon films deposited at 50 °C. Comparison of the film properties in the as-deposited and annealed states (1 h at 200 °C) suggests that dense and ordered films can be deposited at 50 °C. Moreover, the effects of post-deposition annealing support the hypothesis that at low substrate temperature hydrogenated amorphous silicon grows in a metastable state. Annealing produces a decrease of the metastable defect density in the intrinsic films and the activation of dopants in doped films. Our results suggest that the suppression of plasma and surface polymerization reactions, which usually result in the deterioration of the films deposited at 50 °C, is of critical importance in obtaining high-quality films.
Debris-free single-line laser-plasma x-ray source for microscopy
Authors: Rymell L. , Berglund M. , Hertz H. M.
Published: July 2002

A debris-free, narrow-bandwidth, single-line laser-plasma soft x-ray source has been developed suitable for water-window microscopy using zone-plate optics. The 10 Hz table-top source utilizes microscopic ammonium hydroxide droplets as target. The N VI emission at λ=2.88 nm is ∼1×1012 photons/(sr pulse). As an alternative to ammonium hydroxide, it is demonstrated that urea dissolved in water also produces strong emission from nitrogen ions, thereby extending the applicability of the droplet x-ray source to a new range of target materials.
Extended x-ray absorption fine structure analysis of the difference in local structure of tantalum oxide capacitor films produced by various annealing methods
Authors: Kimura Hidekazu , Mizuki Jun’ichiro , Kamiyama Satoshi , Suzuki Hiroshi
Published: July 2002

Extended x-ray absorption fine structure (EXAFS) above the Ta L3 edge on tantalum oxide capacitor films has been measured. Tantalum oxide films were prepared by low-pressure chemical vapor deposition (CVD) using a Ta(OC2H5)5 and O2 gas mixture. Four kinds of tantalum oxide films were studied: as-deposited (amorphous), N2 annealed (crystalline), dry O2 annealed (crystalline), and O2-plasma annealed (amorphous). From EXAFS analysis, differences in the local structures of tantalum oxide capacitor films, in terms of oxygen deficiency around Ta, were observed in the various annealed films. The leakage current characteristics of tantalum oxide capacitors correspond to the differences in the local structures around Ta.
Y2O3 inclusions in YBa2Cu3O7−δ thin films
Authors: Verbist K. , Vasiliev A. L. , Van Tendeloo G.
Published: July 2002

Nanoprecipitates in YBa2Cu3O7-δ (YBCO) thin films have been identified by high resolution electron microscopy (HREM) as Y2O3 inclusions; they correspond to two different types of epitaxial relationships namely [001] or [110] parallel to the YBCO c-axis. The [001] precipitates are situated near the YBCO surface, in the bulk and on the YBCO film/substrate interface. The [110] precipitates have only been observed at the surface. Literature data have been reinterpreted.
Neutral pressure and gas flow instrumentation for TFTR
Authors: LaMarche P. H. , Dylla H. F. , Owens D. K. , Arnold N. D. , Hojsak W. J. , Rauch W. A. , Thompson M. E.
Published: July 2002

The design and operation of instrumentation included in the gas injection system of the Tokamak Fusion Test Reactor (TFTR) for torus pressure and gas flow measurements are described. Magnetically shielded ion gauges, located on the torus boundary, are used for fast (1 kHz) torus pressure measurements over the range 10−7–10−3 Torr. Gas injection assemblies comprising an array of piezoelectric gas injection valves are situated at three toroidal locations. The gas injection valves are programmed for various discharge conditions including feedback control from the torus pressure gauges and plasma density measurement. Gas flow through the injection valves is monitored by strain-gauge-type pressure transducers on each injection valve. The resulting gas flow measurements are used for gas fueling, particle balance, and recycling studies.
Effects of intense ultraviolet radiation on electrostatic energy analyzers
Authors: Mathew J. , Jennings W. C. , Hickok R. L. , Connor K. A. , Schoch P. M. , Hallock G. A.
Published: July 2002

Intense ultraviolet radiation from the plasma poses a significant problem for the implementation of heavy ion beam probe diagnostic systems on fusion-oriented confinement devices. The radiation enters the electrostatic energy analyzer used to detect secondary ions, resulting in both a distortion of the electric field inside the analyzer and noise generation in the detector channels. Data-acquisition procedures and mechanical design techniques have been developed to significantly reduce these effects. We have also been successful in modeling the electric field distortion and have developed a data correction procedure based on this model. Methods for approaching the problems anticipated in future devices are also suggested.
Neutron streak camera electron gun design
Authors: Close E. R. , Colonias J. S.
Published: July 2002

Representative values for electrode voltages, time compensation, and transmission efficiency are obtained by computer simulation for a preliminary design of an electron gun to be used in a neutron streak camera application. The calculations indicate a time resolution on the order of 20 ps and a transmission efficiency of about 10%.
Prototype studies of the MFTF-B far-infrared interferometer (abstract)
Authors: Zu Q. X. , Du Z. M. , Savage R. L. , Peebles W. A. , Luhmann N. C. , Monjes J. A. , Throop A. L. , Thomas S. R.
Published: July 2002

A far-infrared (FIR) laser interferometer operating at 185 μm (Difluoremethane) will be used to monitor line integrated plasma density in the high-density center-cell region of the MFTF-B device at the Lawrence Livermore National Laboratory. There are a number of unique physical constraints and performance goals requiring careful analysis. Therefore, at UCLA a series of prototype experiments have been conducted to establish the final system design. For example, detailed studies of dielectric waveguide propagation have been performed since the laser source will be located ∼20 m from the vacuum vessel. Other areas studied include the expected spatial resolution achievable in the 60-cm-diameter plasma located at the center of the 8-m-diameter vacuum vessel. In addition, the effects of phase front distortion, refraction, and vibration, together with feedback in a Michelson configuration have all been carefully addressed.
Measurement of the wall radiation in soft x-ray region in PDX (abstract)
Authors: Sesnic S. , Tenney F. H. , Bitter M. , Hill K. W. , von Goeler S.
Published: July 2002

A detector setup with three LN-cooled Si(Li) diodes is used to measure soft x-ray spectra (0.8–20 keV) emitted from the inside walls of the PDX vessel during the plasma discharge. The setup is part of a pulse-height-analysis system, which is used to measure the plasma and wall radiation simultaneously at five different radial positions. The wall and the plasma radiation are measured under different plasma conditions (e.g., OH and neutral beam heating). The wall radiation is very much increased during the neutral beam heating, with an enhancement factor of at least 10 over the OH wall radiation. Since we measure the plasma and the wall radiation at the same time, the measurements allow the conclusion that the wall radiation can be attributed essentially to fluorescence (line radiation, e.g., Ti-Kα) and scattering (continuum part of the wall radiation spectrum). The fluorescence and the scattering are both caused by soft x-ray radiation flux coming from the plasma. There seems to be no need to invoke other, more exotic causes for the wall radiation, for example, charge particle bombardment of the wall.
Current measurements by Faraday rotation in single-mode optical fibers
Authors: Chandler George I. , Jahoda Franz C.
Published: July 2002

Development of techniques for measuring magnetic fields and currrents by Faraday rotation in single-mode optical fibers has continued. We summarize the results of attempts to measure the toroidal plasma current in the ZT-40 reversed field pinch using multiturn fiber coils. The fiber response is reproducible and in accord with theory, but the amount and distribution of the stress-induced birefringence in this case are such that prediction of the sensor response at low currents is difficult if not impossible. The low-current difficulty can be overcome by twisting the fiber to induce a circular birefringence bias. We report the results of auxiliary experiments with a fiber that has been twisted with 15 turns per meter and then recoated to lock the twist in place.
Fast special purpose computer for Monte Carlo simulations in statistical physics
Authors: Condon J. H. , Ogielski A. T.
Published: July 2002

Design, hardware, and operating software of a special purpose computer built for the Monte Carlo simulations of a wide class of random Ising spin systems is described. The machine is quite versatile, easy to operate, and executes programs written in a high level C language. It is a 32-bit bus oriented system, with a very fast, dedicated Monte Carlo processor and a general purpose single-board computer sharing the 16-Mbyte address space. The former processor executes the basic Monte Carlo heat bath algorithm, and the latter performs required physical ‘‘measurements’’ on spin configurations and handles communication with a UNIX host machine. The host computer is used to compile and download programs and to receive small quantities of reduced data for permanent storage and further analysis.
Subnanosecond bunching of a positron beam
Authors: Crane W. S. , Mills A. P.
Published: July 2002

A simple scheme for bunching spatially distributed charged particles is described. In the present application, sub-nanosecond width pulses are obtained from a milliliter volume containing slow (≤2 eV) positrons. The utility of this technique is demonstrated by a qualitative observation of the temperature dependance of the surface state lifetime for positrons on aluminum.
Construction of a periodic electrode array
Authors: Shelton D. P.
Published: July 2002

A design for an electrode array for use in nonlinear optics experiments is presented. The array applies a spatially periodic transverse electric field (amplitude ∼ 3 kV/mm and period 4 mm) to a gas sample through which a laser beam is focused.
High-stability scanning tunneling microscope
Authors: van de Walle G. F. A. , Gerritsen J. W. , van Kempen H. , Wyder P.
Published: July 2002

We have constructed a scanning tunneling microscope for operation under UHV conditions (10−8 Pa). With this instrument topographic measurements can be made on metal and semiconductor surfaces by means of a scanning tip electrode, driven by piezoelectric ceramic elements. The maximum area covered ranges up to 4000×4000 Å2 with a resolution better than 10 Å laterally and 0.15 Å rms perpendicular to the plane. Because of its compact design, the scan unit is very insensitive to vibrations and has a response time down to 0.3 ms. This allows a high scan rate to be used. In order to minimize temperature effects, special attention is paid to the geometry of the construction and the materials used, resulting in a drift ≤4 Å/min along the surface and 0.5 Å/min perpendicular.
Ultrahigh-vacuum hollow-cathode resonance lamp for He ii (40.8 eV) photoemission
Authors: Rowe J. E. , Christman S. B. , Chaban E. E.
Published: July 2002

A windowless ultrahigh-vacuum lamp for photoemission studies at ℏω=40.8 eV is described. This lamp has ∼3 times greater intensity at ℏω=40.8 eV than an improved microwave discharge lamp previously reported.
Personal-computer-based programmable temperature controller for general laboratory applications
Authors: Maclennan J. E. , Meadows M. R. , Handschy M. A. , Clark N. A.
Published: July 2002

A temperature controller for general laboratory applications in based on the Apple II computer.
Development of sequence and regular band lasers for use as local oscillators in Thomson scattering alpha particle diagnostics (abstract)
Authors: Bennett C. A. , Hutchinson D. P. , Vander Sluis K. L. , Staats P. A.
Published: July 2002

Heterodyne detection will be used to measure the scattered signal from a 100-MW pulsed CO2 laser Thomson scattered from energetic alpha particles. This measurement requires local oscillators displaced from the pump line by 6 to 21 GHz. We are developing cw sequence and regular band N2O and CO2 lasers which provide many lines in the required frequency range. The sequence lines are obtained by using a small in-cavity hot cell. Operating characteristics will be discussed for a variety of experimental arrangements.
Measurement of proton autoneutralization potential (abstract)
Authors: Garcia Manuel
Published: July 2002

A proton space charge having multi-MeV kinetic energy was injected through a thin ground plane to extract electrons and produce a time-dependent autoneutralization space potential. An electron-emitting floating-potential resistive divider was used to measure the space potential during 20 ns of the proton current pulse. During this time, proton kinetic energy fell from 10.6 to 8.5 MeV and thus the space potential (taken as 1.09× the floating potential) fell from 5.8 to 4.6 kV.
Bistatic LIDAR experiment proposed for the shuttle/tethered satellite system missions
Authors: McComas David J. , Spence Harlan E. , Karl Robert R. , Horak Henry G. , Wilkerson Thomas D.
Published: July 2002

A new experiment concept has been proposed for the shuttle/tethered satellite system missions, which can provide high-resolution, global density mappings of certain ionospheric species. The technique utilizes bistatic LIDAR to take advantage of the unique dual platform configuration offered by these missions. A tuned, shuttle-based laser is used to excite a column of the atmosphere adjacent to the tethered satellite, while triangulating photometric detectors on the satellite are employed to measure the fluorescence from sections of the column. The fluorescent intensity at the detectors is increased about six decades over both ground-based and monostatic shuttle-based LIDAR sounding of the same region. In addition, the orbital motion of the shuttle provides for quasiglobal mapping unattainable with ground-based observations. Since this technique provides such vastly improved resolution on a synoptic scale, many important middle atmospheric studies, heretofore untenable, may soon be addressed.
Simple, compact, high-repetition rate XeCl laser
Authors: Armandillo E. , Grasso G. , Salvetti G. , Penco E.
Published: July 2002

Operation of a compact, corona-preionized, XeCl excimer laser producing average output power in excess of 1 W at pulse repetition frequencies of up to 750 Hz is reported. This device is simple in construction and utilizes all commercially available components.
Isothermal study of rapid solid-state reactions by synchrotron radiation
Authors: Ayers J. D. , Elam W. T. , Vold C. L. , Qadri S. B. , Skelton E. F. , Webb A. W.
Published: July 2002

An experimental system is described with which exothermic solid-state phase transformations can be made to occur isothermally and their kinetics studied in times as short as 1 s. The system has been applied to the study of the crystallization rate of metallic glasses heated to temperatures well above their glass formation temperatures. Strips of the metallic glass 0.2 cm wide and 5 cm long are resistively heated over a portion of their length to the reaction temperature. They are heated within a 0.3-cm-i.d. tube through which flows a cooling gas. The gas flow rate and electrical current are controlled so as to maintain the sample at constant temperature during the reaction. The rate of reaction is measured by monitoring the intensity of diffraction peaks from the small crystallites which form within the ribbon. The x-ray flux from a bending magnet beam line at the Stanford Synchrotron Radiation Laboratory (SSRL) provides sufficient diffracted intensity to monitor the full development of the crystalline diffraction peaks in times as short as 1 s.
First results from Thomson scattering on JET (abstract)
Authors: Prentice R. , Nielsen P. , Gadeberg M.
Published: July 2002

The Single Point Thomson Scattering System uses a multipulse ruby laser to measure Te and ne up to twenty times during a JET plasma pulse. The scattering volume is on the equatorial plane and, between plasma pulses, can be relocated to any one of seven specific points on a major radius. The collection system employs multimirror arrays and a triple prism spectrometer is used to eliminate stray laser light and disperse the scattered light. Novel features include two optoelectronic feedback systems which maintain alignment within the laser input and the collection systems. Sensitive components are located outside the biological shield, and those inside are compatible with remote handling procedures. The entire diagnostic can be remotely controlled via the JET computer system. Initial results from the diagnostic are presented.
Measurement of the Ti X ion density in a theta pinch plasma utilizing a laser interferometer (abstract)
Authors: Datla R. U.
Published: July 2002

The increase in the radial line integral of the electron density in the NBS theta pinch plasma due to the ionization of titanium impurity has been measured with the use of a He–Ne laser heterodyne quadrature interferometer. Titanium is injected as an impurity into the base gas of hydrogen with the use of a coaxial gun discharge with titanium electrodes. The abundance of the Ti X ion density in the plasma is deduced in each discharge from the measured increase in electron density by knowing the temporal charge state distribution of Ti ions obtained by spectroscopic methods.
Improved calibration of DD neutron counters by activation of two indium disks in the Frascati 1-MJ plasma focus
Authors: Pedretti Edmondo , Rager Jean Pierre , Merlo Vittorio
Published: July 2002

Three Geiger counters made sensitive to DD neutrons by paraffin covers with interposed Ag, 109Ag, and Rh foils were calibrated by exposing them to 50 PF (plasma focus) shots and by recording counts while simultaneously irradiating two indium disks placed on the PF vacuum vessel. The ‘‘polar’’ disk came out to be about three times more activated than the ‘‘equatorial’’ disk, which was interpreted by assuming an extended focus instead of a point-like one as used in a previous work. The utilized formalism is reported and some minor discrepancies with counters calibration by removal of an Am/B source are discussed. Further refinements of the activation method are suggested.
Application of an E∥B spectrometer to PLT charge-exchange diagnostics
Authors: Roquemore A. L. , Gammel G. , Hammett G. W. , Kaita R. , Medley S. S.
Published: July 2002

A TFTR-type E∥B spectrometer was installed on the PLT to provide a wide energy range, mass resolving, horizontally scanning charge-exchange diagnostic. In ICRF heating experiments, the new analyzer has provided hydrogen minority high-energy ion tail measurements simultaneously with bulk deuterium ion temperatures over a range of equatorial viewing angles. Characteristics of the E∥B analyzer will be discussed. Data representative of the PLT operating regimes will be presented to illustrate the analyzer performance.
Measurement of electron density with combined technique of laser blowoff and laser-induced fluorescence
Authors: Kadota K. , Yamaoka H. , Tsuchida K. , Fujita J. , Matsuoka H. , Miyake S. , Usui T. , Oda T.
Published: July 2002

A method combining the techniques of laser blowoff and laser-induced fluorescence has been developed in order to measure the local electron density below 1013 cm−3. Characteristics of a Li0 beam produced by laser blowoff of a thin Li film are investigated using beam–plasma interactions and laser-induced fluorescence. Such a beam has a near-Maxwellian velocity distribution with a temperature around 4.5 eV and a density of the order of 1010 cm−3 at a distance of about 1 m from the film target. The feasibility of measuring electron density with this Li0 beam and a dye laser is demonstrated with an ECR plasma.
Digital temperature programmer for isothermal and thermal desorption measurements
Authors: Muha R. J. , Gates S. M. , Yates J. T. , Basu P.
Published: July 2002

A temperature programmer is presented for use with single crystals and other samples in vacuum. Linear temperature versus time ramps near 100 K and above, and single temperature tracking to ±0.35 K are both achieved with this instrument. A 12-bit digital ramp generator and a digital process controller form the basis of this design. Block diagrams and representative temperature ramps are shown.
Design and operation of a stable intense high-temperature arc-discharge source of hydrogen atoms and metastable trihydrogen molecules
Authors: Garvey James F. , Kuppermann Aron
Published: July 2002

We report a design for a stable intense beam source of hyperthermal hydrogen atoms. The basis for the design is an arc heater used first by Knuth for the generation of high-translational energy He–Ar beams. In the case of hydrogen atom generation this source is very unstable due to the corresponding higher temperatures which are generated by the plasma discharge. We have substantially eliminated these difficulties by the insertion of discharge-localizing insulators and the use of a tungsten nozzle mounted in the center of a 1-kG electromagnet. This source generates exceptionally high hydrogen atom beam intensities of ∼1022 atoms s−1 sr−1 with translational energy distribution functions which extend to 18 eV and whose peak occurs at energies as high as 13 eV. In addition metastable H3 molecules having an intensity between 1020 and 1021 molecules s−1 sr−1 are formed.
Processing and properties of Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films by pulsed laser deposition
Authors: Tantigate C. , Lee J. , Safari A.
Published: July 2002

In situ thin films of (1−x)Pb(Mg1/3Nb2/3)O3–xPbTiO3, (PMN-PT), with composition x=0.1, 0.3, 0.35, and 0.4, were deposited on MgO(100) substrates by pulsed laser deposition. The optimum conditions to form (100) oriented PMN-PT perovskite phase were at substrate temperatures in the range of 535 to 575 °C with an oxygen pressure of 200 mTorr. The Mg content in PMN-PT films was found to be essential to the formation of perovskite phase. Heterostructures of PMN-PT/La0.5Sr0.5CoO3 (LSCO) films were prepared on MgO(100) substrates to evaluate the dielectric properties of the films. The dielectric constant of PMN and PMN-PT films ranged from 1000 to 3800 at 10 kHz measured at room temperature. The highest dielectric constant was obtained from PMN films with 99% perovskite phase.
Simple low-cost microwave plasma source
Authors: Meiners L. G. , Alford D. B.
Published: July 2002

A generator-cavity system is described which is capable of delivering 0–600 W of microwave power at 2.45 GHz. The power generating section has been constructed from components contained in a portable home microwave oven and the cavity was assembled from easily machinable pieces. The cw magnetron source was mounted directly on a cylindrical microwave cavity. The plasma was contained in an on-axis 20-mm o.d. quartz tube. Design tradeoffs and operating information are discussed.
In situ calibrations of grazing incidence vacuum monochromators for x-ray laser research
Authors: Milchberg H. , Skinner C. H. , Suckewer S. , Voorhees D.
Published: July 2002

I n situ relative and absolute calibrations are described for two grazing incidence vacuum monochromators used in our ongoing x-ray laser experiments. The soft x-ray sources used in the calibrations are small plasmas produced by a specially constructed portable vacuum spark generator and by irradiating thin (∼100–300 μm diameter) carbon fibers with a high-power (1–5 GW, 1012–1013 W/cm2) CO2 laser. The absolute instrumental sensitivities have been determined using the method of branching ratios, while the relative calibrations have been done by simultaneously monitoring given ionic lines with each XUV instrument.
Study of the transit time of pressure propagation in an acoustic delay line
Authors: Song Yunn-Fang , Chen Ching-Iue , Chang Chu-Nan , You Jean-Luh , Hwang Fu-Kwun , Hsu Chih-Ying
Published: July 2002

A fast sensor was used as a vacuum gauge to measure the transit time of a gas pressure through an acoustic delay line (ADL). The results were compared with the predictions of two theoretical models. We found that in the rupture pressure range of 101 to 104 Pa, the predictions of Jean and Rauss’ model, based on the assumption that the flow of gas be a gas fluid, set lower boundaries for the observed transit times; while the predictions of our model, based on the molecular motion, set the upper ones.
Radial field discharge for high-flux ion extraction
Authors: Humphries S. , Len L. K.
Published: July 2002

Experimental results are described on a pulsed plasma source for the generation of intense beams of intermediate mass ions. The source used radial magnetic field and axial electric field to trap a high density of electrons on azimuthal orbits. A self-sustained discharge was maintained with high probability for ionization of injected gas. The large extraction area and narrow discharge gap allowed high current operation and effective extraction of ions. Up to 50 A of argon ions were generated over a 100-μs pulse. The total discharge current was 100 A and the voltage was 1000 V. A current density of 1 A/cm2 argon ions was measured 2 cm from the discharge gap.
Compact CdSe laser with microminiature cryogenic refrigerator
Authors: Valk B. , Olson D. J. , Salour M. M.
Published: July 2002

A microminiature refrigeration system allowing precise temperature control above 77 K has been tested successfully as a compact Dewar to achieve the necessary cryogenic temperatures to operate optically pumped semiconductor lasers in an external cavity. Using this system in a mode-locked CdSe laser resulted in a stable average output power of up to 10 mW. Tunability from 7015 to 7160 Å was achieved by changing the temperature from 77 to 111 K.
Improved feedback charge method for quasistatic C
V measurements in semiconductors
Authors: Mego Thomas J.
Published: July 2002

A method is described for the measurement of quasistatic CV characteristics in semiconductors which offers significant advantages over previous methods. Using a small voltage step across the device under test, a displacement charge is stimulated and measured. A feedback charge measurement circuit is used, reducing the effect of several significant error terms. This technique has the advantages of higher signal-to-noise ratio at the frequencies of interest, independence of signal size from measurement time, and ease of distinction of signal charge from error currents at the time of measurement. Results consistent with those of previous techniques have been obtained on silicon MOS capacitors and other devices using steps from 10 to 100 mV and delays between step and measurement of up to 200 s. Furthermore, the method has been extended to provide additional information useful in determining whether an equilibrium measurement is obtained and in diagnosing and correcting for errors due to dc leakage currents. With this method, it is also possible to measure quasistatic capacitance at fixed bias voltage using a square-wave test signal.
120-kV testing of a 10×40-cm prototype of the U. S. common long pulse neutral beam source
Authors: Weber P. D. , Owren H. M. , Paterson J. A. , Pincosy P. A. , Pyle R. V. , Wells R. P. , Vella M. C.
Published: July 2002

The 10×40-cm long pulse neutral beam source developed at Lawrence Berkeley Laboratory has been selected as the prototype for the design of the U. S. common long pulse source to be used on tokamak fusion test reactor (TFTR), Doublet-III, and mirror fusion test facility (MFTF-B). The long pulse source consists of a magnetic line cusp bucket with an actively cooled backplate electron dump and a four-grid accelerator using slot apertures and water-cooled molybdenum rails. Deuterium testing of the long pulse source at 120 kV and 53 A and with a 2-s pulse length has been completed on the neutral beam engineering test facility, including an 8-h 100-shot test to demonstrate the durability and reliability of the source. Maximum 2-s beam parameters obtained (not simultaneously) are 125 kV, 58 A (deuterium), and 7.1 MW. Beam pulse length has been extended to 5 s at 120 kV. Atomic species fractions in excess of 80% have been obtained, with a beam divergence (full energy, 1/e half-angle) of approximately 0.8×0.4°. Calorimetric measurements on the accelerator grids and backplate electron dump indicate heat loads consistent with predictions and within the design limits of the source. This testing has verified the design of the source and its ability to exceed the basic performance requirements.
Apparatus and technique for reconstruction of flaws using model-based elastic wave inverse ultrasonic scattering
Authors: Thompson D. O. , Wormley S. J. , Hsu D. K.
Published: July 2002

An automated multiviewing ultrasonic apparatus and signal processing routine have been developed for utilization in nondestructive evaluation (NDE) of materials. The instrument has been developed to take advantage of recent advances in long and intermediate wavelength inverse scattering of elastic waves, and provides a 3-D reconstruction of a flaw. Although the reconstruction obtained does not contain fine details of the flaw’s structure, it provides sufficient information about the flaw (size, orientation, and selected materials properties) so that failure-predictive decisions can be made.
Quasi-elastic light scattering: Signal storage, correlation, and spectrum analysis under control of an 8-bit microprocessor
Authors: Glatter Otto , Fuchs Heribert , Jorde Christian , Eigner Wolf-Dieter
Published: July 2002

The microprocessor of an 8-bit PC system is used as a central control unit for the acquisition and evaluation of data from quasi-elastic light scattering experiments. Data are sampled with a width of 8 bits under control of the CPU. This limits the minimum sample time to 20 μs. Shorter sample times would need a direct memory access channel. The 8-bit CPU can address a 64-kbyte RAM without additional paging. Up to 49 000 sample points can be measured without interruption. After storage, a correlation function or a power spectrum can be calculated from such a primary data set. Furthermore access is provided to the primary data for stability control, statistical tests, and for comparison of different evaluation methods for the same experiment. A detailed analysis of the signal (histogram) and of the effect of overflows is possible and shows that the number of pulses but not the number of overflows determines the error in the result. The correlation function can be computed with reasonable accuracy from data with a mean pulse rate greater than one, the power spectrum needs a three times higher pulse rate for convergence. The statistical accuracy of the results from 49 000 sample points is of the order of a few percent. Additional averages are necessary to improve their quality. The hardware extensions for the PC system are inexpensive. The main disadvantage of the present system is the high minimum sampling time of 20 μs and the fact that the correlogram or the power spectrum cannot be computed on-line as it can be done with hardware correlators or spectrum analyzers. These shortcomings and the storage size restrictions can be removed with a faster 16/32-bit CPU.
New float flowmeter
Authors: Vallascas Rinaldo
Published: July 2002

A new float flowmeter design is presented based on the null method, with electric output signal and either manual or automatic current control in a coil to bring the float back to zero position. The instrument concerned is a constriction-type device and based on its theory a simple expression can be derived for describing the input–output relationship in quadratic terms. In addition to a description of the device, the static calibration curves using air at 295.16±0.50 K are also provided for volumetric flowrates ranging from 11 to 16 dm3/min and Reynolds numbers between 500 and 800. Typical inaccuracy is 1.8% of flowrate over this range.
Simple planar magnetron sputtering source
Authors: Rastogi R. S. , Vankar V. D. , Chopra K. L.
Published: July 2002

The design and performance of a simple and efficient planar magnetron sputtering source using demountable targets are described. The design of the source enables sputtering of magnetic and nonmagnetic materials with equal ease.
Subnanosecond high-voltage pulse generator
Authors: Brown David , Martin Don
Published: July 2002

We developed a pulse generator that uses high-voltage step recovery diodes to produce 400- to 500-V pulses with rise and fall times of 0.8 ns. The output pulse width is continuously adjustable. For a pulse width of 0.8-ns FWHM, the amplitude into 50 Ω is 400 V. With the pulse-width control set at maximum, the output pulse amplitude is about 500 V and the width is 3.5-ns FWHM. The delay of the output pulse with respect to the input trigger is 38 ns with a jitter of about ±30 ps. An unusual feature of the pulse generator is that the 38-ns delay time to the centroid of the output pulse is approximately constant and independent of the pulse width.
Microcomputer interface board for time-resolved multichannel scaling
Authors: Cobb Cathy L. , Martin Richard M.
Published: July 2002

A low-cost multichannel scaler and signal-averaging system with user selectable channel widths ranging from 1 to 255 μs has been developed for molecular beam time-of-flight (TOF) experiments. It has the ability to collect up to 255 channels and has a programmable delay of up to 0.65 s. On-board logic can accommodate a 15-MHz count rate. Completely contained on a 7×2 3/4 -in. Apple II prototyping board (with the exception of a 5-A, 5-V external power supply), the interface fits into a peripheral port of the Apple II. The interface was tested by measuring the TOF distribution of Ar metastables from a supersonic nozzle beam source.
Scaling up of a closed-cycle self-sustained discharge-excited CO laser
Authors: Saito Hideaki , Kanazawa Hirotaka , Watanabe Kenji , Taira Tatsuji , Sato Shun-ici , Fujioka Tomoo
Published: July 2002

Scaling of a CO laser device of closed-cycle self-sustained discharge-excited type has permitted the attainment of a maximum output power of 3.1 kW. The device incorporates two heat exchangers, operating, respectively, on freon R502 and liquid nitrogen. This permits regulation of the working gas temperature to any given level between room temperature and 120 K.
Quantitative microfluorometry of isolated living cells with pulsed excitation: Development of an effective and relatively inexpensive instrument
Authors: Vigo J. , Salmon J. M. , Viallet P.
Published: July 2002

Using a computer interfaced original apparatus, we can analyze the fluorescence decay time of a single living cell. This apparatus can measure rate constants in the range of one to few hundred nanoseconds. The smallest sample analyzed was 5×5×5 μm. We obtained enough sensitivity to measure the fluorescence of about 105 molecules of benzo(a)pyrene with a signal/noise ratio equal to 5. The signal was then defined with 300 points and experiment was 60 s long with a laser pulse frequency equal to 100 Hz. Distortions were less than 3% of the signal. Different kinds of information became accessible: statistical comparison on cellular populations and variation with time of studied parameters. As an example of applications, the intrinsic cell fluorescence has been analyzed in order to determine the amounts of bound and free NAD(P)H in single living cells.