bluuebunny/crossref_metadata_2025 huggingface dataset:
Precise measurement of dielectric properties at frequencies from 1 kHz to 100 MHz
Authors: Kakimoto Akira , Etoh Akihiro , Hirano Kaoru , Nonaka Satoshi
Published: July 2002

This paper describes an improved apparatus to measure dielectric constants and dissipation factors using a resonance technique. The measurements can be made rapidly and accurately without appreciable systematic error in the wide frequency range from 1 kHz to 100 MHz. This apparatus uses the half power-gap variation method or the half power-varying gap-immersion method for solid-plate specimens and the solid-plate displacement method for liquid specimens. The electrode system is 30 mm in diameter and has a shield ring to avoid the edge capacitance effect, guards against surface current leakage, and variable air capacitors to set the electrode gap at any arbitrary value. To detect a very small power loss, the resonance voltages in circuits with Q≂100 are stabilized to −86 dB at a constant ambient temperature. We use phase detectors so that the electrode gap and the voltage at resonance can easily be read from the digital panel meter and the digital voltmeter. No corrections are necessary even at a high frequency of 100 MHz. The accuracy of measurements made using the half power-varying gap-immersion method is within 0.2% for the dielectric constant and 3% for the dissipation factor without marked degradation over the entire frequency range.
Design of a calorimeter capable of measuring heats of adsorption on single-crystal surfaces
Authors: Kyser D. A. , Masel R. I.
Published: July 2002

This paper describes the design of the first calorimeter capable of measuring heats of adsorption of gases on single-crystal surfaces in ultrahigh vacuum. The calorimeter is of the quasi-adiabatic type, and measures the temperature rise as gas adsorbs. The calorimeter has been used to measure the heat of adsorption of CO and C2H4 on Pt(111). The calorimeter seemed to perform quite well in these experiments, and yielded results that are reasonable. Thus, it is suggested that a calorimeter would be a useful addition to a surface scientist’s arsenal.
Ring wire anemometer—Part I: Calibrations and cooling laws
Authors: Giovanangeli Jean-Paul , Chambaud Pierre , Mestayer Patrice
Published: July 2002

A hot-wire anemometer probe with a circular shape has been developed in order to measure the magnitude of the instantaneous velocity vector. The theoretical cooling law and calibration curves show that a ring wire is less sensitive to the lateral components of the velocity, i.e., less sensitive to positioning errors than straight wires. The theoretical considerations agree rather well with experimental data.
Optical properties of GaN epitaxial films grown by low-pressure chemical vapor epitaxy using a new nitrogen source: Hydrazoic acid (HN3)
Authors: Bu Y. , Lin M. C. , Fu L. P. , Chtchekine D. G. , Gilliland G. D. , Chen Y. , Ralph S. E. , Stock S. R.
Published: July 2002

We report results of our growth and characterization of GaN films using low-pressure chemical vapor epitaxy with a new nitrogen source, hydrazoic acid (HN3). This growth technique allows for low-temperature deposition, low III/V ratios, and increased deposition rates (up to ∼2–3 μm/h). The deposited films show Ga:N atomic ratios of 1±0.25 based on our x-ray photoelectron spectroscopy analyses, and the He(II) UPS (ultraviolet photoelectron spectroscopy) spectra compare favorably with the semi-ab initio calculations for the GaN valence bands and with the reported UPS data for single crystal GaN films. X-ray and Raman spectra show deposited films crystallized in the expected wurtzite structure. We find these epitaxial films to be efficient light emitters in the blue or yellow region of the spectrum, depending upon growth conditions. Our photoluminescence time-decay kinetics confirm the excitonic nature of the blue emission. Lastly, far infrared time-domain spectroscopy shows the low carrier concentration of this material.
Effect of mechanical agitation on fuse opening switch efficiency
Authors: Lee W. M. , Ford R. D.
Published: July 2002

It is demonstrated that an exploding wire fuse opening switch comprising aluminum wire in water can be made more efficient by mechanically agitating the wire while it is being exploded. The electrical current flowing through the wire collapses faster, generating a higher voltage output when the arrival time of the agitating source at the wire material is well selected. The agitation appears to facilitate the dispersion of the molten metal within the water tamper so that the electrical energy input necessary to open the switch is reduced.
Improved direct sampling electron impact fluorimetry apparatus for combustion studies
Authors: Peterson Richard B.
Published: July 2002

This note describes an improved laboratory apparatus for performing direct sampling electron impact fluorimetry (DSEIF) experiments on combustion systems. In comparison with previous work, the new apparatus is a dedicated diagnostic tool having greater optical access to the fluorescence region and uses a fully controllable electron gun residing in a separate vacuum chamber. These features account for an estimated factor of 10 increase in S/N ratio over the previous setup. The new apparatus is expected to allow time-resolved concentration measurements of major species during transient combustion events.
Vacuum emissivity meter for thermal emittance measurements of coatings
Authors: Rao G. Mohan , Mohan S.
Published: July 2002

The problems in measuring thermal emittance by steady-state calorimetric technique have been analyzed. A few suggestions to make it more accurate, simple, and rapid have been discussed and results are presented.
Principle of a new reflectometer for measuring dielectric film thickness on substrates of arbitrary surface characteristics
Authors: Sopori B. L.
Published: July 2002

A reflectometer is described that can make accurate measurements of the thickness of a dielectric film on a large-area substrate. The measured value does not depend on the surface characteristics of the substrate. Two basic principles that the new reflectometer invokes are: (i) the wavelength dependence of the integrated reflectance exhibits a minimum at a wavelength which can be related to the film thickness; and (ii) the reciprocity principle for integrated reflectance (i.e., the sample is illuminated with a light of wide angular distribution and the component of light reflected normal to the sample is measured). The instrument has applications in semiconductor industry in general and, in particular, in solar energy device fabrication. This instrument can also be used to measure the absolute reflectance.
Design of magnets inside cylindrical superconducting shields
Authors: Rigby K. W.
Published: July 2002

We discuss the design of magnets inside closed, cylindrical, superconducting shields. We give the Green function for the magnetic vector potential for cylindrically symmetric currents inside such a shield. The magnetic field everywhere inside the shield can be obtained from this function, which includes the effects of the induced shield currents exactly. We give the field for a thin solenoid as an example and discuss the convergence of the series solution for this case. The shield can significantly reduce the strength and improve the homogeneity of a magnet. The improvement in homogeneity is of particular importance in the design of correction coils. These effects, and the maximum field on the shield, are examined for a typical solenoid. The results given are also useful, although not exact, for long shields with one or two open ends.
Frequency analysis of reflection high-energy electron diffraction intensity oscillations during molecular beam epitaxial growth of GaAs on nominally oriented (111)B substrates
Authors: Garcia B. J. , Fontaine C. , Muñoz-Yagüe A.
Published: July 2002

Frequency analysis of reflection high-energy electron diffraction (RHEED) intensity oscillations during GaAs growth by molecular beam epitaxy on nominally-oriented (111)B substrates is reported. Double frequency oscillations have been observed and analyzed in a wide range of substrate temperatures. Because the growth rate deduced from RHEED frequency analysis was found to be independent of substrate temperature, no Ga loss from the sample surface seems to take place during growth under conditions which allow RHEED intensity oscillations.
600 fs 10.6 μm infrared pulse generation with radiation-damaged GaAs reflection switch
Authors: Elezzabi A. Y. , Meyer J. , Hughes M. K. Y.
Published: July 2002

Ultrafast infrared laser pulses at 10.6 μm as short as 600±200 fs have been produced using optical semiconductor switching. This is achieved by using GaAs damaged with a 180 keV H+ dose of 1×1016 cm−2 as an optical–optical switch. Cross-correlation measurements are used to obtain the pulse shapes. We find that the generated infrared reflectivity pulse widths are proportional to the H+ ion dose to the power −0.4. This allows a precise control over the generated pulse durations.
Nucleation of misfit dislocations in In0.2Ga0.8As epilayers grown on GaAs substrates
Authors: Chen Y. , Liliental-Weber Z. , Washburn J. , Klem J. F. , Tsao J. Y.
Published: July 2002

Misfit dislocation arrays in In0.2Ga0.8As epilayers grown on GaAs substrates tilted 2°–10° away from exact (001) toward varied directions have been studied by transmission electron microscopy. A method has been developed to determine the glide plane and the Burgers vector of each misfit dislocation in the tilted InGaAs/GaAs interfaces. Based on experimental observations and theoretical analyses, it is proposed that a stacking fault surrounded by a 30° partial is at first generated by a growth error, followed by thermally activated nucleation of a 90° partial dislocation that removes the stacking fault and forms a 60° dislocation. From the frequency of nucleation events versus the dislocation glide force, the energy barrier for dislocation nucleation of α and β 90° partial dislocations was determined to be equal to 1.5 and 1.4 eV, respectively.
Synchrotron microtomography of supported catalysts
Authors: Nichols M. C. , Kinney J. H. , Johnson Q. C. , Saroyan R. A. , Bonse U. , Nusshardt R. , Pahl R.
Published: July 2002

Synchrotron microtomography is a new technique which is capable of elemental, chemical, and structure sensitive imaging in three dimensions at resolutions better than 15 μm. This paper describes the first application of this new technique to the investigation of the morphology and elemental distribution of a supported catalyst. Using this new tool it was possible to obtain three-dimensional information from regions of the catalyst away from the vicinity of the damaged surface region of the sample. The technique allows the use of both computed tomographic (CT) cross sections as well as the development of a three-dimensional rendering of elements in a material, each of which allows visualization of different areas that would go unnoticed in normal radiographic or CT investigations.
Powder diffraction facilities at Daresbury Laboratory
Authors: Pattison P. , Cernik R. J. , Clark S. M.
Published: July 2002

X-ray powder diffraction measurements using synchrotron radiation are currently being carried out on three experimental stations on the SRS at Daresbury Laboratory. Station 9.1 contains a general purpose powder diffractometer for angular dispersive measurements. The instrument is sited on the wiggler beamline, which provides radiation with a critical energy of 12 keV. A Si(111) water-cooled, channel-cut monochromator gives useful flux over an energy range from 6 to 30 keV. A cryostat and furnace are available for experiments requiring special environments, while a curved position sensitive detector can be used for time-resolved measurements. The wiggler white beam is employed on Station 9.7 for energy dispersive powder diffraction experiments. Various sample stages for kinetic experiments are in use on this station, and examples are shown of recent high-pressure work. A new high resolution powder diffractometer has been built and commissioned on Station 8.3, using bending magnet radiation. The diffractometer is based on the Parrish and Hart design, in which long, parallel foils are used to define the angular divergence accepted by the detector. In this way, large synchrotron beam cross sections can be employed while maintaining high angular resolution.
Fast measuring system of energy dispersive x-ray diffraction intensity for synchrotron radiation (abstract)
Authors: Yoshizawa M. , Sugawara H. , Jyohtake K. , Yamagishi S. , Fukamachi T. , Kawamura T. , Nakajima T.
Published: July 2002

We have developed a fast measuring system of energy dispersive x-ray diffraction intensity. A solid state detector (SSD) has been used to measure the energy dispersive x-ray diffraction intensities. The energy resolution of SSD is almost ten times higher than that of a scintillation counter or proportional counter. For full use of SSD, a fast processing system of the signal is needed, especially when x rays from synchrotron radiation (SR) are used. When SSD is used for x rays from SR, however, we have two problems. One is that the dead time of conventional signal processing system is long, which prevents the efficient use of synchrotron radiation source. The other is that a fast data recording system is needed, because the number of data of a single diffraction spectrum is large. To solve these two problems, we have designed a new measuring system. The system consists of a personal computer and an interface board of multichannel analyzer function. The interface consists of peak hold, fast ADC, memory, add one, and DMA. (1) Improvement of the dead time. We adopted a successive approximation ADC to shorten the conversion time. The dead time is then 2 μs in the present system, which is much shorter than that of the Wilkinson ADC (about 40 μs). (2) Fast data recording. In most conventional MCA, the memory of MCA is separated from that of computer and the data are transferred between MCA and computer. In this case, the data are transferred by GP-IB or RS232C, and the data transfer time is several ten seconds. In the present system, the same memory is accessed by MCA and computer and the data transfer time is zero. This fast measuring system has already been installed at Photon Factory, KEK and utilized to measure the energy dispersive diffraction intensities. We have observed Pendellösung fringe induced by x-ray resonant scattering to make use of this system.
X-ray diffraction by moving objects: A new application of synchrotron radiation
Authors: Ihringer J. , Wroblewski T.
Published: July 2002

A parallel-beam geometry with analyzer crystal is used for x-ray diffraction experiments on fast-moving machine parts. With this method in rotating samples, like turbine blades, strain can be measured in different directions with respect to the acting force by appropriate choice of the diffraction plane. Stroboscopic gating of the counter allows position-resolved strain examination. Further applications are diffraction experiments on fluids and melts.
Device for the studies of deformations of polycrystalline materials in shock compression using x-ray diffraction of SR (abstract)
Authors: Mytnichenko S. V. , Lyakhov N. Z. , Sheromov M. A. , Smirnykh V. V. , Tolochko B. P.
Published: July 2002

The diffraction investigations of polycrystalline materials allow one to receive information about microdeformations of the crystalline lattice. It is known that the chemical activity of solid states increases as a result of mechanical deformation. The x-ray diffraction experiments contribute to the studies of this increase. There is no doubt that the use of SR gives advantages to these diffraction experiments over the traditional sources of radiation. The high intensity of SR allows one to decrease the time necessary for a diffraction pattern to be exposed and to investigate the mechanical deformation in situ. A new device for the study of polycrystalline materials in shock compression using x-ray diffraction of SR was designed. This device has some advantages over the old one. It is worth noting, first of all, that we used an automatic machine for a very fast change of the samples (10 s). Just as before, the shock compression was performed by a steel projectile with a spherical end. We used flat polycrystalline samples. At the moment of collision the stresses achieved several kBars. Detection electronics allow the diffraction patterns with a resolution time of about 1 ms to be received.
Single electron charging at temperatures above 4 K in ultrasmall lateral quantum dots patterned on shallow GaAs/AlGaAs heterostructures
Authors: Borsosfoldi Z. , Rahman M. , Larkin I. A. , Long A. R. , Davies J. H. , Weaver J. M. R. , Holland M. C. , Williamson J. G.
Published: July 2002

We demonstrate single electron charging in fully controllable nanoscale quantum devices at temperatures above 4 K. Hitherto, single electron devices operating at ‘‘high’’ temperatures have been two-terminal, having no control electrode, whereas fully tunable structures such as quantum dots have only shown charging effects at temperatures of 4 K or less. We have fabricated ultrasmall quantum dots on modulation doped heterostructures where the two-dimensional electron gas is less than 30 nm from the surface. Dots with lithographic diameter 150 nm show Coulomb oscillations up to temperatures of 7 K. Higher temperature operation allows potential applications to be considered without the need, for example, of a dilution fridge.
Wavefront imaging of plasma by means of computerized tomography
Authors: Ohe K. , Naito A. , Iwama N.
Published: July 2002

A simple implementation of well-resolved computerized tomographical imaging was designed using external and periodic excitation of a wave packet, and applied to the ionization wave in a helium positive column of a glow discharge. The wavefront revealed by pursuing the temporal evolution of the reconstructed image was convex such that the rays converged as the wave propagated in the direction of its phase velocity.
Space potential measurements with a continuously emitting probe
Authors: Mravlag E. , Krumm P.
Published: July 2002

Space potential measurements with a continuously emitting probe suffer from the difficulty of a potential drop across the probe tip. In this paper we derive a simple method to ensure that the measurements are accurate in spite of this potential drop. Experimental results obtained in a single-ended Q-machine confirm the theoretical findings and provide reassuring evidence that the potential drop does not disturb the space potential unduly.
Color imaging the magnetic field distribution in superconductors
Authors: Batalla E. , Zwartz E. G. , Goudreault R. , Wright L. S.
Published: July 2002

A magneto-optically active glass was used to image the magnetic field distribution in superconductors using the Faraday effect. Polarized white light illumination of the glass resulted in various colors depending on the setting of the analyzing polaroid. These colors are shown to be consistent with the known dependence of the Faraday rotation angle on the applied magnetic field, the temperature of the glass, and the wavelength of the light. This technique was used to observe field distributions in polycrystalline and single-crystal YBa2Cu3O7 samples. In the ceramic sample, the field was uniform within the resolution (50 μm) of this technique and field magnitudes were measured with a 10% accuracy. In the single crystal, the magnetic field distribution was not uniform showing field gradients imaged as color gradients on the pictures of the glass. Contours of constant magnetic field were drawn from these photographs and from these, a critical current density of 109 A/m2 was deduced in an external field of 136 mT.
Precision analysis and low-light-level measurements using a prototype four-detector photopolarimeter (FDP)
Authors: Azzam R. M. A. , Lopez Ali G.
Published: July 2002

A given uncertainty of the output current vector of the FDP leads to a corresponding uncertainty in the determination of the Stokes vector of incident light. Using an FDP instrument matrix measured free from imperfections in the calibration optics, and for a preset level of error for each current, the root-mean-square errors (RMSE) of the three normalized Stokes parameters (NSPs) are calculated as functions of the state of polarization of an assumed totally polarized incident beam. Experimental results are also presented that show the effect of reducing the power level of a light beam (from ∼0.2 mW to <60 nW, an attenuation range of 35 dBs) on the precision with which the NSPs are measured. The RMSE of each NSP is virtually independent of attenuation over an initial range of two decades and rises subsequently. However, it is the digitization (or quantization) error of the 12-bit analog-to-digital converter that sets the limit on precision in our FDP. The accuracy with which the NSPs are measured is also essentially independent of light level, provided that the adjusted operational-amplifier gains are correctly accounted for. The ability of our prototype FDP to resolve small changes of the state of polarization of light is tested directly by introducing known deliberate perturbations around several input states. Polarization states that are separated by 0.1° on the Poincaré sphere are found to be resolvable with an uncertainty of ∼0.03°.
A molecular beam time-of-flight mass spectrometer using low-energy-electron impact ionization
Authors: Hayden C. C. , Penn S. M. , Muyskens K. J. Carlson , Crim F. F.
Published: July 2002

We have constructed a versatile apparatus to study photoinitiated processes in molecular beams using a variety of generally applicable techniques. The instrument contains a pulsed, low-energy electron gun that delivers space-charge-limited electron beams into the ionization region of a time-of-flight mass spectrometer. The electron energy is tunable from 8 to 200 eV, and the electron energy distribution is relatively narrow (FWHM ∼0.3 eV), which allows us to ionize laser-excited species and their decomposition products selectively. We have used low-energy electron impact ionization and mass spectrometry to characterize molecular beams, to detect vibrationally excited molecules prepared by vibrational overtone excitation, and to detect primary photodissociation products in the presence of precursor molecules.
Multi-quantum-well zero-gap directional coupler with disordered branching waveguides
Authors: Shi S. , Li Kam Wa P. , Miller A. , Pamulapati J. , Cooke P. , Dutta Mitra
Published: July 2002

A nonlinear switch formed by the integration of an overmoded multi-quantum-well (MQW) section with disordered input and output branching waveguides is presented. The area-selective disordering of GaAs/AlGaAs MQWs is achieved by diffusion of group III vacancies generated by etching of the surface oxide. The absorption edge of the disordered MQW regions was shifted by 71 nm and the disordered ridge waveguides had a loss figure of 8 dB/cm. Time-resolved optical pump-probe measurements were performed on an integrated switch that had more than a 5:1 power split between the two output ports. The measured signal recovery of the switch had a time constant of 110 ps.
Demonstration of the proximity effect in YBa2Cu3O7−x edge junctions
Authors: Kleinsasser A. W. , Delin K. A.
Published: July 2002

We demonstrate that recent data on the length and temperature dependence of the critical current in Josephson junctions with YBa2Cu3O7−x electrodes coupled by Ca- and Co-substituted YBa2Cu3O7−x interlayers are consistent with the conventional theory of the proximity effect.
Two-channel surface-normal wavelength division demultiplexer using substrate guided waves in conjunction with multiplexed waveguide holograms
Authors: Li Maggie M. , Chen Ray T.
Published: July 2002

We report a wavelength division demultiplexer (WDDM) using collinear surface-normal input and output coupling. The reported device employs polymer-based multiplexed waveguide holograms in conjunction with substrate guided waves. A two-channel WDDM device operating at 700 and 738 nm with diffraction angles of 45° and 50° are demonstrated. The peak diffraction efficiencies of 80% and 77% are measured for these two channels. A crosstalk of −31 dB between the two channels is measured. Variations of the diffraction efficiencies and of the bandwidths as a function of film thickness and index modulation are further considered. A good agreement between theoretical analysis and experimental results is obtained.
X-ray crystal truncation rod scattering measurement of AsH3-exposed InP/InPAs/InP single heterostructures
Authors: Takeda Yoshikazu , Sakuraba Yoshiyuki , Fujibayashi Kei , Tabuchi Masao , Kumamoto Takayuki , Takahashi Isao , Harada Jimpei , Kamei Hidenori
Published: July 2002

The atomic-level heterointerface structures of InP samples that contain growth interrupted and AsH3-exposed surface, with 20 Å thick cap layer, were revealed by x-ray crystal truncation rod scattering measurement. The As atom distribution, the thickness of the cap layer, and the tetragonal distortion of the lattices were obtained from the samples that have only single modified layer in the whole InP wafer. The calculated total amounts of As matched well with the value obtained by fluorescence x-ray analysis.
Use of super Schottky diodes in a cryogenic radio frequency superconducting quantum interference device readout
Authors: Mück M. , Becker Th. , Heiden C.
Published: July 2002

We describe the fabrication and characterization of super Schottky diodes which are used in the cryogenic part of a 3 GHz radio frequency superconducting quantum interference device (rf SQUID) readout electronics. The diodes were prepared on silicon wafers with an n-doping level of 5×1024 m−3. They exhibited sensitivities of 1500 V−1 at 4.2 K, and a noise equivalent power of 2×10−15 W/√Hz was measured at 2.1 GHz. Using planar niobium 3 GHz rf SQUIDs and a cooled rf amplifier, experiments have been performed to investigate the feasibility of these super Schottky diodes for demodulation of the SQUID rf signal voltage. A simple cryogenic rf SQUID readout, employing two transistors and one super Schottky diode is described and investigated. Flux noise measurements in an open loop have been performed using this readout.
The loss of signal to noise due to imperfect isolation between the channels of a quadrature nuclear magnetic resonance probe
Authors: Tropp James , Derby Kevin
Published: July 2002

We consider a quadrature nuclear magnetic resonance (NMR) probe with imperfect isolation between the two channels arising from a parasitic mutual impedance, and show that the theoretically achievable signal-to-noise ratio is reduced by a factor of (1+η2)−1/2, relative to that of a probe with perfect isolation, where −20 log η is the isolation in dB; provided that all relevant receiver components are matched to a common impedance. The theoretical result is verified by experimental determination of the response of actual NMR imaging probes when driven with coherent signal, and the response of model circuits simulating actual probes when driven with sources of excess noise; the simulated circuits are needed to reduce extraneous interference in the noise measurements. The theory is also confirmed by computer simulations of noise response in coupled resonator circuits.
Development of a fast responsive directional energy analyzer
Authors: Honzawa Tadao
Published: July 2002

A directional energy analyzer, capable of quickly responding to fast signal changes as well as having a good angular resolution, is developed. Results have shown that owing to a current amplifier prepared in it, the analyzer can respond to a small and rapidly changing ion current with a rise time as short as 2 μs, as observed in plasma shock experiments.
Instrumentation for gas electron diffraction employing a pulsed electron beam synchronous with photoexcitation
Authors: Ewbank John D. , Faust Walter L. , Luo Jing Y. , English Jeffrey T. , Monts David L. , Paul David W. , Dou Qun , Schäfer Lothar
Published: July 2002

A novel instrument is described capable of recording gas electron diffraction (GED) patterns of excited molecular states or transient species with pulsed electron beams. The system incorporates (1) a pulsed optical beam for electronic excitation of materials under study, (2) a synchronously pulsed source of 30–50 keV electrons in a space-charge-limited beam, (3) necessary vacuum environment and sample-handling capabilities, and (4) detection and signal processing equipment using an on-line procedure developed at the University of Arkansas. Data obtained for several test gases demonstrate successful operation of the instrument. The 193 nm laser photofragmentation of carbon disulfide, CS2, is described in detail. In agreement with a recent time-of-flight mass spectrometric study of the same process, carbon monosulfide was observed as the reaction product. This study is the first quantitatively successful joint exercise of on-line multichannel GED data recording and a stroboscopic electron source. The method is expected to be generally useful in determining the structures of excited molecular states or reactive species, and it may enable studies of time-dependent phenomena. The current time resolution is ∼20 ns.
Compact ion/electron analyzer for spaceflight or laboratory use
Authors: McGarity J. O. , Huber A. , Pantazis J. , Oberhardt M. R. , Hardy D. A. , Slutter W. E.
Published: July 2002

A space qualified 260° spherical plate electrostatic analyzer has been developed as a plasma diagnostic tool. The use of nested spheres and unusually shaped microchannel plates has resulted in a sensor capable of measuring simultaneously the three-dimensional populations of ions and electrons in a plasma. High-current microchannel plates and a new packaging of a hybrid preamplifier discriminator are combined with an uncommon high-voltage circuit. The combination of these features yields an analyzer that is compact and lightweight, efficient in its power consumption, and has a broad dynamic range.
Thermally stimulated current measurements of SiO2 defect density and energy in irradiated metal-oxide-semiconductor capacitors
Authors: Reber Richard A. , Fleetwood Daniel M.
Published: July 2002

A modular system is described to measure thermally stimulated current (TSC) in irradiated metal-oxide-semiconductor (MOS) capacitors. Custom capacitor mounting allows accurate and convenient measurement of TSC with less than ∼0.1 pA error at temperatures up to ∼300 °C. These measurements are used to estimate the densities and energy levels of defects in the 1SiO2 layer of irradiated MOS capacitors with 45, 98, and 350 nm oxides. For capacitors irradiated under positive bias, TSC measurements provide accurate estimates of radiation-induced trapped-positive-charge density only if performed under negative bias. It is shown that space-charge effects and capacitance changes during TSC measurement can lead to incorrect estimates of the radiation-induced trapped-charge density. We demonstrate that, for n-substrate capacitors, these effects can be minimized if the bias applied during TSC measurement is more negative than the inversion-point voltage on a post-irradiation capacitance-voltage (C-V) curve. This improves prior practice in the literature. Improved estimates are provided for trapped hole energies in SiO2. Further, TSC measurements under proper bias conditions can be combined with conventional high-frequency C-V measurements to estimate hole- and electron-trap densities near the Si/SiO2 interface of irradiated MOS capacitors. To our knowledge, no other method can be used to quantitatively separate the effects of positive and negative oxide-trap charge on the radiation response of MOS devices. Finally, we show that irradiation with ∼10 keV x rays or ∼1.25 MeV Co-60 gamma rays leads to similar trapped-hole densities and energies in MOS capacitors with 350 nm nonradiation-hardened oxides.
A versatile low-cost Czochralski crystal growth system for nonlinear optical organic materials
Authors: Aggarwal M. D. , Wang W. S. , Shields Angela W. , Penn Benjamin G. , Frazier Donald O.
Published: July 2002

A versatile low-cost Czochralski system for pulling crystals from melt has been described. It is designed for low melting, transparent, and nonlinear optical materials. One of the most important novel feature of this crystal growth system is that the entire growth process including the solid–liquid interface can be viewed from any direction. Another is the use of an after-heater to reduce excess heat loss from the surface of the melt.
Work function measurements of dispenser cathodes by retarding potential method
Authors: Khairnar Rajendra S. , Chopra A. K.
Published: July 2002

The work function of dispenser cathode pellets has been determined by means of the retarding potential technique. A low-energy electron gun was fabricated which delivers a collimated beam of electrons on the pellet surface at normal incidence. The set up is calibrated by employing samples of known work function such as gold and tungsten, prior to determining the work function of the cathode pellets. This set up provides a rapid determination of the work function of cathode pellets.
High-speed resistance measurement of closing switches using a transmission line discharge technique
Authors: Podlesak Michael
Published: July 2002

Time-dependent resistance of a high voltage, high current, closing switch was measured via the discharge of a low impedance transmission line. With this technique, only the current waveform of the switch, the initial open circuit voltage, and the transmission-line characteristics need to be known to determine the switch resistance waveform. Under certain conditions a simple lossless transmission-line formula is sufficient for the calculation of the switch resistance waveform. However, if the transmission-line losses cannot be neglected a correction can be readily implemented through numerical signal processing. The bandwidth of this technique is limited to the bandwidth of the switch current record only. This is particularly useful in the measurement of the resistance of high voltage, high current switches where inductive pick-up noise in the switch voltage waveform is large and where high voltage probes of sufficiently high bandwidth are not readily available. In this article, both simulated and experimental examples are given, together with the method of calculation of switch resistance which takes into account practical transmission line losses. It was found that best results are obtained if the magnitude of the switch resistance is higher than or of a similar order as the characteristic impedance of the transmission line.
Quantum limited heterodyne detection in superconducting non-linear transmission lines at sub-millimeter wavelengths
Authors: Tong Cheuk-yu Edward , Blundell Raymond , Bumble Bruce , Stern Jeffrey A. , LeDuc Henry G.
Published: July 2002

A non-linear superconducting transmission line has been successfully employed in heterodyne detection of sub-millimeter waves. In our experiments an Nb/Al/AlOx/Nb tunnel junction, measuring 0.15×40 μm, with a critical current density of about 2500 A/cm2 is used as a distributed mixer element. We have demonstrated that quantum limited sensitivity can be achieved with this type of device. At 460 GHz, a Y-factor of 2.5 has been recorded, corresponding to a double-side-band receiver noise temperature of 80 K. The double-side-band conversion loss is about 1 dB and the mixer noise temperature is estimated to be 18(±10) K.
Formation of an intense pulsed beam of CH3Cl in the ‖111≳ state using a 2-m electrostatic hexapole field
Authors: Kasai T. , Fukawa T. , Matsunami T. , Che D.-C. , Ohashi K. , Fukunishi Y. , Ohoyama H. , Kuwata K.
Published: July 2002

An intense pulsed beam of CH3Cl in the ‖111≳ state without velocity selection was focused using a 2-m electrostatic hexapole field. The beam intensity was estimated to be ∼1×1013 molecules pulse−1, which is much greater than the similar beams in the earlier study of Gandhi et al. by at least two orders of magnitude. The beam had a 3-ms pulse width and was focused with an angular divergence of 0.7 mrad. The improvements in beam intensity and in the divergence of the beam can be mainly ascribable to the efficient pumping of the hexapole field through the cylindrical electrodes, which enables us to employ the helium seeding to have the fast stream velocity, the narrow distribution of velocity, and the aerodynamic effects. Those factors altogether made the velocity selection of the beam unnecessary.
High sensitivity photoelectron yield spectroscopy with computer-calculated electron optics
Authors: Schäfer J. , Ristein J. , Ley L. , Ibach H.
Published: July 2002

An improved spectrometer design for photoelectron yield spectroscopy is described. Basis of the new spectrometer is a computer-designed electron optics that images the emission spot into the electron multiplier and thereby improves the sensitivity for electrons emitted from the sample. The collection efficiency was experimentally determined to 98.3%. A background of stray electrons which limits the ultimate sensitivity of the method could be substantially reduced by minimizing multiple beam reflections and by coating critical surfaces with a high work function material such as platinum. As a result, photoyield spectra of Au with a dynamical range of ten orders of magnitude are routinely obtained.
A modular multifunctional Langmuir–Blodgett trough
Authors: Grunfeld F.
Published: July 2002

A review of Langmuir–Blodgett (LB) trough designs is given. A modular design of Langmuir–Blodgett trough is presented. This trough can be used for monolayer analysis, conventional deposition of LB films, and deposition of alternating LB films by adding different combination of pressure sensors and dipper mechanisms. Research results produced with this trough are referenced.
Generation and use of simulated sunlight in photochemical studies of liquid solutions
Authors: Faust Bruce C.
Published: July 2002

A new system illuminates liquid solutions with simulated sunlight, at constant temperature and with rapid mixing of the solution. Based on irradiance measurements, the relative spectral composition of the simulated sunlight is very similar to that of authentic sunlight at the earth’s surface.
Pressure measurements with a precision of 0.001 ppm in magnetic fields at low temperatures
Authors: Miura Y. , Matsushima N. , Ando T. , Kuno S. , Inoue S. , Ito K. , Mamiya T.
Published: July 2002

Pressure measurements made by an ac bridge technique with a precision of 0.001 ppm in magnetic fields at low temperatures using a Straty–Adams type gauge are described. In order to improve the sensitivity and the long-term stability of the bridge system, coaxial cables without dielectric insulator were developed, with a small cable capacitance temperature coefficient of the impedance. This pressure measurement system has a sensitivity of dP/P∼5×10−10 and a long-term stability of dP/P∼2.4×10−9 over 18 h. This is especially useful for measurements such as electric and magnetic susceptibility measurements in magnetic fields at low temperatures requiring a high precision.
Low threshold optical bistable switching in an asymmetric λ/4-shifted distributed-feedback heterostructure
Authors: Janz S. , He J. , Wasilewski Z. R. , Cada M.
Published: July 2002

The nonlinear optical response of an asymmetric λ/4-shifted distributed-feedback GaAs/AlAs heterostructure is investigated using numerical methods, and also demonstrated experimentally. This structure exhibited both optical switching and bistability at incident wavelengths near λ=884 nm. The observed bistability threshold of less than 1 kW cm−2 is more than an order of magnitude smaller than that of any previously measured distributed-feedback heterostructures.
Stigmatic spectrograph with a 2-D CCD detector for soft x-ray observations of laser produced plasmas
Authors: Villoresi P. , Nicolosi P.
Published: July 2002

Stigmatic spectroscopic observations of laser produced plasma have been performed in the 50–200 Å spectral interval. The purpose was to demonstrate the good instrumental performances of an intensified bidimensional detector installed on a stigmatic soft x-ray spectrometer. The latter is the combination of a grating spectrograph in Rowland circle mount and a toroidal mirror, both working at grazing incidence. The detector is composed of a scintillator on the spectrograph focal circle, an image intensifier, and a charge coupled device. The resulting spatial and spectral resolution are of 60 μm and 1000, respectively. The observations show a marked improvement in term of dynamic range, sensitivity, ease of operation, and real-time data presentation in comparison to both traditional photographic film and photodiode array detection technique.
Probe configurations for hot-dome anemometry
Authors: Thompson Brian E. , Couluris John P. , Pezelj Vladimir
Published: July 2002

Measurements were obtained in the Rensselaer transonic windtunnel with front and side sensors on block and domed configurations of hot-dome probes in the uniform freestream over the range Mach 0.42 to 0.82 and for pitch and yaw angles of up to 60 deg. Results are presented with two hot-dome probe configurations, a block probe and a domed probe, and quantify effects of probe geometry, angle sensitivity, and velocity up to transonic Mach numbers. Block probe showed turbulence generation in the vicinity of the hot-film sensors, probably associated with recirculating flow downstream of its sharp corners. The domed probe was designed with rounded front and side surfaces to realize benefits from aerodynamic contouring and effect reductions in blockage, probe interference, separation, and compressibility. The curved front sensor of the domed probe responded primarily to the normal component of cooling velocity, and this implies that the front sensor of domed probes can be used to obtain the magnitude of flow velocity. Responses of pitch and yaw sensors on the domed probe suggest angle calibrations similar to those for five-hole impact probes may be suitable for hot-dome probes.
Measuring the critical current of high temperature superconductors in liquid nitrogen as a function of temperature
Authors: Fournier P. , Aubin M.
Published: July 2002

A method of measuring the critical current of polycrystalline high temperature superconductors is described at various temperatures between 65 K and the transition temperature with the sample immersed in liquid nitrogen (LN2). The temperature of LN2 is varied following its phase diagram above the triple point (63.15 K). To increase the temperature of the nitrogen bath above 77 K, one increases the container gas pressure above 1 atm and pumps on the liquid to obtain temperatures below 77 K.
A simple two-axis ultraprecision actuator
Authors: Smith S. T. , Chetwynd D. G. , Harb S.
Published: July 2002

This paper describes a highly controllable, short-range translation and rotation mechanism. Two solenoid-magnet force actuators are applied to a simple elastic mechanism resulting in separable translation and rotation drive axes. To provide design rules and assess potential error sources, a theoretical model is discussed and experimentally evaluated. Two such actuators using monolithic aluminum and single crystal silicon flexures have been constructed and measured using stylus-based, optical and x-ray interferometric techniques. They are used to demonstrate both longer range motions of 80 μm and 3.6 mrad and higher precision motions, with resolution of better than 0.6 nrad over ranges of around 10 μrad across 1 μm displacement. Performance of these devices was limited primarily by the available drive electronics and measurement techniques, so it is expected that even better precision can be achieved.
Atomic collisions in negative ion beam simulation
Authors: Michaut C. , Bacal M.
Published: July 2002

Several types of collision processes (such as stripping of negative ions and neutrals and ionization of gas molecules and atoms by negative ions) have been introduced in a simulation code of the extraction, acceleration, and transport of negative ions. The energy spectra of neutral atoms formed in the accelerator, for various values of the pressure in the transport region, have been computed. It will be shown that most of the neutrals are formed in the neighborhood of the thick extraction electrode. The effect of these neutrals on the charge-state distribution in the beam and the effect of the positive ion formation in the transport region on the ion trajectories will be discussed.
An ion source with good beam current density uniformity for assisted deposition
Authors: Yuan-Zhu Kuang , Yu-Cai Feng , Zhi-Ping Lou
Published: July 2002

Recently, broad beam ion sources have been widely used for industrial applications. In order to obtain high quality thin films and process large workpieces, more uniform beam current density is needed. This article introduces a 10-cm-diam cusped ion source with good beam current density uniformity for assisted deposition. Its design characteristics and performance are described. The effects of operation parameters of ion source, the magnetic flux density and its distribution, the cathode shape and its location in the discharge chamber, and the configuration of grids on the uniformity of ion beam current density were experimentally investigated. For screen grid voltage of 300 V and beam current of 100 mA, a 0.93 beam current flatness parameter within a beam spot of 200 mm diameter at a distance of 300 mm downstream from the source was obtained.
Control of multipolar electron cyclotron resonance discharges using internal cavity impedance matching (abstract)a)
Authors: Asmussen J. , Mak P.
Published: July 2002

Recently, electron cyclotron resonance (ECR) discharges have been successfully applied to numerous ion source applications. These range from accelerator to etching and thin film deposition applications, and have strong potential for application in several commercial/industrial processes. Thus, new design requirements related to process automation and control are now imposed on plasma source design. Internal cavity tuning methods for excitation and impedance matching and ECR discharge control are presented. These impedance matching methods utilize a variable cavity end plate and an adjustable coupling probe to provide the two independent adjustments required to match the discharge loaded cavity applicator. Both end feed and side feed coupling create a well matched plasma source but the end feed excitation produces the most efficient (∼220–230 eV/ion) and most uniform (1σ=2.5%) discharge. Control of internal tuning can serve not only to match discharge impedance, but with the proper control can also avoid hysteresis and multiple steady states and jumps in plasma source outputs. Adjusting the internal cavity tuning to always produce a slight mismatch helps insure a stable and repeatable discharge operation.
Modeling the electromagnetic excitation of a compact ECR ion/free radical source (abstract)a)
Authors: Grotjohn T. A. , Tan W. , Gopinath V. , Srivastava A. K. , Asmussen J.
Published: July 2002

The electromagnetic excitation of a discharge inside a microwave plasma source has been numerically modeled in the time domain. The source is a cylindrical, single-mode microwave-excited cavity. The time-varying electromagnetic fields inside the resonant cavity, both inside and outside the discharge region, are obtained by applying a finite-difference time-domain method to solve Maxwell’s equations. The electromagnetic properties of the discharge load are described using a conductivity model. The spatial electric field patterns, natural frequencies, stored energy, and quality factor of a plasma-loaded, microwave-resonant cavity are simulated. Additionally, the simulated results for a simplified plasma source structure are compared to a known analytical solution to verify the simulation technique.