bluuebunny/crossref_metadata_2025 huggingface dataset:
CO2 laser assisted particle removal threshold measurements
Authors: Lee S. J. , Imen K. , Allen S. D.
Published: July 2002

Laser removal of particulates from solid surfaces was achieved using an energy transfer medium which preferentially adsorbs in the capillary spaces under and around the particulates on the contaminated surface. Subsequent laser irradiation causes explosive evaporation of the energy transfer medium and propels the particles off the substrate much like a small rocket engine. In our experiments, a TEA CO2 (10.6 and 9.6 μm) laser was used to remove 9.5 μm Al2O3, 5 μm Al2O3, and 1 μm polystyrene particles from Si surfaces using water as the energy transfer medium. At these wavelengths the laser energy is absorbed predominantly in the water not in the substrate. The threshold fluence for particle removal was found to follow a degenerate threshold model with measured thresholds significantly below the substrate damage threshold. The temperature rise in the energy transfer medium was estimated using energy conservation, suggesting that superheating of the adsorbed water is a reasonable mechanism for water assisted laser particle removal.
Analysis of normal-incident absorption in p-type quantum-well infrared photodetectors
Authors: Man P. , Pan D. S.
Published: July 2002

Normal-incident absorption in the recently-demonstrated, p-type quantum-well infrared photodetectors is analyzed with the k⋅p theory, under the envelope-function approximation. A first-principles calculation of the infrared-absorption spectra is performed with no adjustable parameter. The responsivity is evaluated from the calculated normal-incident absorption and the experimentally-derived photoconductive gain. Good agreement is obtained with measurements at λ<λc. The bandwidths of the infrared-absorption spectra are found to be limited by spin-orbit splitting as well as the overlap integrals.
Nonuniform photobleaching of dyed polymers for optical waveguides
Authors: Moshrefzadeh R. S. , Misemer D. K. , Radcliffe M. D. , Francis C. V. , Mohapatra S. K.
Published: July 2002

An experimental technique for calibrating the photobleaching process in a nonlinear optical material is presented. The technique depends on the existence of a sharp interface between the bleached and unbleached layers of the material which travels across the film but otherwise has a constant shape. The sharp interface of constant shape is a feature of a general model and is consistent with our experimental results. By determining the dependence of the velocity on the bleaching intensity, the order of the photobleaching kinetics is determined.
Selective reactive ion etching of InGaAs/InAlAs heterostructures in HBr plasma
Authors: Agarwala Sambhu , Adesida Ilesanmi , Caneau Catherine , Bhat Rajaram
Published: July 2002

A reactive ion etching process using HBr plasma has been developed for the selective removal of InGaAs on InAlAs. Etch rates of 110 and 0.67 Å/min are obtained for InGaAs and InAlAs, respectively, at a plasma self-bias voltage of −100 V, a chamber pressure of 120 mTorr, and a HBr flow rate of 10 sccm. This translates to an etch selectivity of over 160 which is the highest that has been obtained for this material system. The etch stop mechanism on the InAlAs is deduced from x-ray photoelectron spectroscopy to be due to involatile Al2O3 that is formed by residual O2 and/or H2O vapor in the chamber. It is shown that the surface of the etched InAlAs can be restored to the state prior to HBr etching by sequential rinsing in dilute HCl and H2O. This process should be useful for the fabrication of InAlAs/InGaAs heterostructure field-effect transistors.
Polycrystalline silicon solar cells with a mechanically formed texturization
Authors: Bender H. , Szlufcik J. , Nussbaumer H. , Palmers G. , Evrard O. , Nijs J. , Mertens R. , Bucher E. , Willeke G.
Published: July 2002

Polycrystalline (Wacker SILSO) silicon has been mechanically textured using a conventional dicing saw and beveled blades for V-groove formation. The minimum optical reflectivity achievable is limited by the blade tip radius and surface roughness after damage etching. Solar cells were prepared using a conventional diffusion and screen printed metallization. Grooved cells without an additional antireflection coating (jsc=31.8 mA/cm2, Voc=536 mV, FF=69%, η=11.8%) showed a 20% increase in jsc and a 1.1% absolute efficiency improvement as compared to a nongrooved reference cell with an antireflexion coating (jsc=26.4 mA/cm2, Voc=547 mV, FF=74.1%, η=10.7%). In grooved cells the efficiency is found to be limited mainly by the fill factor due to a nonoptimized front grid design.
Spiral growth of C60
Authors: Fujita J. , Kuroshima S. , Satoh T. , Tsai J. S. , Ebbesen T. W. , Tanigaki K.
Published: July 2002

We have observed the spiral growth of C60 grown on cleaved graphite using atomic force microscopy. Triangular terraces in the spirals consist of a monolayer of C60 having a 10 Å step height which agrees well with (111) lattice constant of fcc-C60. One of the characteristic features of the C60 spiral is the presence of a line defect running from the spiral core and crossing the spiral terraces. As a result, the original helicoid plane transforms into a stack of terraces. We think the C60 spiral growth is terminated by the introduction of a line defect at the early stages of the film growth, resulting from the weak van der Waals forces.
Photonic integrated tunable receivers with optical preamplifiers for direct detection
Authors: Chuang Z. M. , Mondry M. J. , Young D. B. , Cohen D. A. , Coldren L. A.
Published: July 2002

We propose and demonstrate a photonic integrated tunable receiver which cascades a traveling-wave optical preamplifier, a passive tunable grating-assisted codirectional coupler filter, and a waveguide photodetector. The devices contain three strained InGaAs quantum wells and operate around λ=0.98 μm. The spectral responses have been measured using the broadband spontaneous emission from the integrated amplifier. Optical filters ∼4-nm wide, ∼10-nm apart with grating pitches ranging from 7.4 to 10.6 μm were observed. Wavelength selective photodetection of a channel ∼3-nm wide, tunable over 4.3 nm with a reverse bias is in relatively good agreement with theory.
Reversible changes of the charge state of donor/hydrogen complexes initiated by hole capture in silicon
Authors: Seager C. H. , Anderson R. A.
Published: July 2002

The effect of light-injected holes on phosphorus/hydrogen pairs has been examined in silicon. Previous studies have shown that light soaking appears to debond H from phosphorus, thereby returning it to the positive charge state. Here, we demonstrate that this charge state change is partially reversible if samples are held in electronic equilibrium for periods of hours to days. Since this recovery process can be delayed for days by depleting the light-soaked region, it appears that freed hydrogen is not merely returning to donors, but that the original hole capture event is merely creating a different charge state of the P⋅H pair. We also demonstrate that the kinetics of the hole-induced conversion process is markedly different in depletion than in zero bias and suggest that this is due to the presence of the recovery process which can only occur in the presence of free electrons.
Investigation of the stresses in continuous thin films and patterned lines by x-ray diffraction
Authors: Kuschke W.-M. , Arzt E.
Published: July 2002

Strains and stresses in aluminum thin films and patterned lines were measured using x-ray diffraction. Measurements were performed on pure aluminum and on ion-implanted aluminum, as annealed and six months after an annealing treatment. The results suggest that stresses in passivated lines, starting from an unequitriaxial state of stress, show the tendency to relax in the direction of an equitriaxial state of stress, depending on the ratio of grain size and linewidth or film thickness. The relaxation is particularly rapid in ion-implanted aluminum lines, in contradiction to the expected strengthening effect. Possible implications for electromigration resistance are discussed.
InAsSb/AlAsSb double-heterostructure diode lasers emitting at 4 μm
Authors: Eglash S. J. , Choi H. K.
Published: July 2002

Double-heterostructure InAsSb/AlAsSb diode lasers emitting at 4 μm have been fabricated. The laser structure was grown on GaSb substrates by molecular beam epitaxy. The devices exhibit continuous wave operation at temperatures up to 80 K, and pulsed operation up to 155 K. The lowest threshold current density is 33 A/cm2 obtained at 50 K, but the characteristic temperature is only 17 K.
Lattice relaxation of nanostructured semiconductor pillars observed by high-resolution x-ray diffraction
Authors: Sluis Paul van der , Verheijen Martin J. , Haisma Jan
Published: July 2002

High resolution x-ray diffraction is used to obtain two-dimensional reciprocal space maps from two-dimensional periodic arrays of small (<250 nm) semiconductor pillars. The pillars were made by etching an (001) oriented Si wafer that was epitaxially overgrown with Si1−xGex. The pillars were etched to such a depth that they have a Si bottom and a Si1−xGex top. The shape of the pillars and the lattice parameters in the pillars are determined by comparison of the measured maps with kinematical diffraction model calculations using separate Fourier transformation of the shape of the Si and Si1−xGex parts of the grating. It was found that in the pillars the Si1−xGex lattice was totally relaxed, whereas it was compressively strained prior to etching.
Observation of a negative electron affinity for heteroepitaxial AlN on α(6H)-SiC(0001)
Authors: Benjamin M. C. , Wang Cheng , Davis R. F. , Nemanich R. J.
Published: July 2002

This study demonstrates the presence of a negative electron affinity (NEA) surface on AlN was grown on α(6H)-SiC. Heteroepitaxial AlN was grown on α(6H)-SiC(0001) substrates by molecular beam epitaxy techniques. The surface electronic states were characterized by ultraviolet photoemission obtained at surface normal. The observation of a sharp spectral feature at the lowest energy of the emitted electrons is an indication of a surface with a negative electron affinity. In addition, the trend of the NEA feature was examined as a function of annealing. The surface Fermi level is found to be near the middle of the AlN gap, and a possible band alignment between the AlN and SiC is presented.
Micromachined millimeter-wave photonic band-gap crystals
Authors: Özbay E. , Michel E. , Tuttle G. , Biswas R. , Sigalas M. , Ho K.-M.
Published: July 2002

We have developed a new technique for fabricating three-dimensional photonic band-gap crystals. Our method utilizes an orderly stacking of micromachined (110) silicon wafers to build the periodic structure. A structure with a full three-dimensional photonic band gap centered near 100 GHz was measured, with experimental results in good agreement with theoretical predictions. This basic approach described should be extendable to build structures with photonic band-gap frequencies ranging from 30 GHz to 3 THz.
1.09-eV Schottky barrier height of nearly ideal Pt/Au contacts directly deposited on n- and p+n-Al0.48In0.52As layers
Authors: Fricke A. , Stareev G. , Kummetz T. , Sowada D. , Mähnss J. , Kowalsky W. , Ebeling K. J.
Published: July 2002

Pt/Au Schottky contacts on AlInAs lattice-matched to InP have been fabricated using effective cleaning of the semiconductor surface with low-energy (30 eV) Ar+ ions prior to the metal deposition. A short-time annealing of the contacts at moderate elevated temperatures in the range of 230 to 430 °C was employed in order to eliminate eventual postbombardment defects. Subsequently, an increase of the effective Schottky barrier height from 0.85 to 1.09 eV was observed. This improvement is probably due to the heteroalignment between PtAs2 and AlAs phases which easily appears if intimate contacts are considered. Conventionally prepared wafers (without ion-beam treatment) exhibit a barrier height of 0.82 eV which remains unchanged during annealing. The initial breakdown voltage in ion-etched samples rises from −18 to −28 V and the reverse current density at −10 V diminishes by more than two orders to less than 8×10−7 A cm−2. An ideality factor n very close to unity was obtained from the slope of forward current-voltage characteristics of contacts to homogeneously and shallow Zn-doped substrates.
Surface roughness during chemical beam etching and its remedy by enhanced cation diffusion
Authors: Chiu T. H. , Williams M. D. , Ferguson J. F. , Tsang W. T. , Kapre R. M.
Published: July 2002

Reflection high-energy electron diffraction has been used to monitor the layer-by-layer removal of GaAs during chemical beam etching. The etching is accomplished by injecting AsCl3 gas directly into the growth chamber at a temperature typical for the growth. The development of a spotty pattern provides an early indication of surface roughness. A roughening mechanism of the etched surface due to a sluggish cation diffusion is identified. A migration enhanced etching method has been investigated in the etching of InP using AsCl3, which results in mirror like morphology. A two-dimensional etching mechanism and a in situ monitoring technique at atomic scale are essential for a true monolayer etching technology.
Controlled high-rate localized shear in porous reactive media
Authors: Nesterenko V. F. , Meyers M. A. , Chen H. C. , LaSalvia J. C.
Published: July 2002

It is demonstrated that controlled high-strain-rate plastic deformation of heterogeneous reactive porous materials (Nb+Si, Mo+Si+MoSi2) produces shear localization. Within the shear bands, having thicknesses 5–20 μm, the overall strains (γ≤100) and strain rates (γ̇≤107 s−1) result in changes in particle morphology, melting, and regions of partial reaction. The shear band thickness is smaller than the initial characteristic particle size of the porous mixture (≤44 μm). This ensures quenching of the deformed material structure in the same time scale as the deformation time (10−5 s). In the shear localization region, two types of patterning are observed: (a) a characteristic shear fracture which subdivides the Nb particles into thin parallel layers and (b) the formation of vortices.
Frequency modulation of the superconducting parallel-plate microwave resonator by laser irradiation
Authors: Tsindlekht M. , Golosovsky M. , Chayet H. , Davidov D. , Chocron S.
Published: July 2002

We have studied the effect of chopped laser irradiation (λL=514 nm) on the resonant frequency (f0≊5.4 GHz) of a superconducting parallel-plate resonator (PPR) consisting of two thin epitaxial YBa2Cu3O7−x films. We demonstrate that laser irradiation shifts the resonant frequency of the PPR with negligible change of quality factor. Photoinduced deviation of f0 strongly depends on the chopping frequency and increases linearly with light intensity. The effect of illumination is attributed to the photoinduced change of the kinetic inductance due to laser heating. This effect may be used to produce phase modulation of the superconducting transmission lines.
Evidence for compositional heterogeneities in hydrogenated amorphous silicon nitride films
Authors: Fritzsche H.
Published: July 2002

It is found that the negative effective correlation energy (−U) model for the K defects in hydrogenated amorphous silicon nitride (a-SiNx:H) cannot explain the observed subgap absorption in the optical spectra. An alternative model which describes a-SiNx:H as a compositionally heterogeneous material with spatial band-gap fluctuations is suggested. This model allows a qualitative explanation of the experimental results without having to assume a negative sign for the defect correlation energy. Other semi-insulating amorphous semiconductors, such as a-SiOx:H, also show evidence for compositional heterogeneities.
Crystallographic texture change during abnormal grain growth in Cu-Co thin films
Authors: Harper J. M. E. , Gupta J. , Smith D. A. , Chang J. W. , Holloway K. L. , Cabral C. , Tracy D. P. , Knorr D. B.
Published: July 2002

The addition of 0.4–8.6 at. % Co to Cu thin films strongly influences the temperature evolution of microstructure, stress, and resistivity. For concentrations near 1 at. % Co in coevaporated Cu-Co on oxidized Si, normal grain growth begins at about 75 °C, about 50 °C lower than in pure Cu. There is an abrupt decrease in resistivity and stress at a temperature which increases with Co content from 120 °C (0% Co) to 250 °C (8.6 at. % Co), and coincides with precipitation of Co within Cu grains. A dramatic change in texture is observed in both coevaporated and electroplated Cu-Co films upon annealing above 250 °C. As-deposited films have a three-component texture of (111) fiber, (200) fiber, and random but annealed films have a dominant (200) fiber texture. This ‘‘cube’’ texture differs from the dominant (111) texture of annealed pure Cu, and appears to be coupled to an abnormal grain growth process since many grains are observed to be larger than ten times the film thickness. It is proposed that segregation of Co to external surfaces or to Cu grain boundaries may favor this (200) texture by selectively affecting grain-boundary mobility or the surface energy driven grain growth.
In-plane aligned CeO2 films grown on amorphous SiO2 substrates by ion-beam assisted pulsed laser deposition
Authors: Zhu Shen , Lowndes Douglas H. , Budai J. D. , Norton D. P.
Published: July 2002

Both (001)- and (111)-oriented CeO2 thin films have been grown on amorphous fused silica (SiO2) substrates by ion-beam assisted pulsed laser ablation of a polycrystalline CeO2 target. Using 200 eV Ar+ ions incident at 55° to the substrate normal, the preferred orientation for CeO2 film growth is (001) at room temperature, but changes to (111) for temperatures ≥300 °C. Furthermore, the ion-beam assisted CeO2 films exhibit strong in-plane crystallographic alignment. In contrast, CeO2 films grown without ion-beam assistance exhibit a mixture of polycrystalline orientations with the relative amounts depending on growth temperature. Under optimum conditions, off-normal-incidence Ar+ ions produce a (111)-oriented crystalline CeO2 film that is aligned with respect to a single in-plane axis, on an amorphous substrate.
Possible lifetime-limiting defect in 6H SiC
Authors: Son N. T. , Sörman E. , Chen W. M. , Kordina O. , Monemar B. , Janzén E.
Published: July 2002

We reveal and investigate a possible lifetime-limiting defect in as-grown 6H SiC by optical detection of magnetic resonance (ODMR). This defect is shown to be a deep level center (with an energy level at about Ec−1.1 eV), evident from the related deep photoluminescence emission and a photo-excitation spectrum of the ODMR signal. The fact that this defect has been observed in both bulk crystals and epilayers, regardless of their doping type, indicates that this must be a common and basic defect in 6H SiC.
Chemical segregation in CoNiPt(SiO2) alloy film
Authors: Murayama Akihiro , Miyamura Masao , Kondoh Shinji
Published: July 2002

Chemical segregation in SiO2-added CoNiPt alloy films for high-density longitudinal recording media have been studied by high-resolution transmission-electron microscopy-energy dispersive spectroscopy with a spatial resolution of 20 Å. Sputtered CoNiPt(SiO2) films consist of well-separated grains with diameters less than 200 Å. Si is clearly detected only in a grain boundary region with the width from 12 to 30 Å. Oxygen concentration in the grain boundary is also much higher than that inside the grain. X-ray photoelectron spectroscopy shows that Si atoms in the film are in the form of SiO2. Therefore, it is concluded that SiO2 is segregated to the grain boundary in the CoInPt films. The development of the grain separation due to this chemical segregation explains the excellent magnetic and recording properties of the CoInPt(SiO2) films, such as high coercivity beyond 2400 Oe and low media noise. Inhomogeneity of CoNiPt alloy elements are also discussed.
Optical properties of ternary and quaternary IV–VI semiconductor layers on (100) B
a
F
2 substrates
Authors: McCann Patrick J. , Li Lin , Furneaux John E. , Wright Robert
Published: July 2002

Fourier transform infrared (FTIR) absorption spectra and photoluminescence (PL) spectra for PbSe0.78Te0.22 and Pb0.95Sn0.05Se0.80Te0.20 layers grown by liquid phase epitaxy on (100) BaF2 substrates are reported. FTIR absorption edges varied from 213 to 275 meV (between 4 and 300 K) for the ternary alloy and from 118 to 200 meV (between 10 and 300 K) for the quaternary alloy. PL energies were 174 meV at 5 keV for the ternary alloy and 100 meV at 7.1 K for the quaternary alloy. The differences between the low temperature FTIR absorption edge energies and the PL energies are attributed to the Burstein–Moss effect.
Sputter cleaning and smoothening of GaAs(001) using glancing-angle ion bombardment
Authors: Labanda J. G. C. , Barnett S. A. , Hultman L.
Published: July 2002

Flat, clean, essentially defect-free GaAs(001) surfaces were produced at 570 °C in an As4 overpressure using 1 keV Ar ion bombardment at an impingement angle φ of 15° from the surface plane and a dose of 2.3×1016 ions/cm2. Ion bombardment smoothened the surfaces leading to minimum roughness values of ≊0.3 nm and reflection high-energy electron diffraction (RHEED) patterns that showed streaks with a 2×4 reconstruction. GaAs films grown by molecular beam epitaxy on the sputter cleaned surfaces exhibited strong RHEED oscillations. Cross-sectional transmission electron microscope images showed that the epitaxial layers and substrates were defect-free except for 2–3-nm diam dislocation loops observed 10–20 nm below the substrate surface, separated by ≳100 nm along the interface.
Time-resolved surface expansion of metals under picosecond laser illumination
Authors: Levy Ady , Amer Nabil M.
Published: July 2002

Picosecond photothermal displacement experiments were performed to resolve the rise time of the actual surface expansion of laser-illuminated metals. A rise time of ∼100 ps was resolved for Ni, in agreement with the predictions of a hydrodynamic model. The applicability of the photothermal effect to time-resolved scanning probe microscopies is addressed.
TFTR diagnostic control and data acquisition system
Authors: Sauthoff N. R. , Daniels R. E. ,   PPL Computer Division
Published: July 2002

General computerized control and data-handling support for TFTR diagnostics is presented within the context of the Central Instrumentation, Control and Data Acquisition (CICADA) System. Procedures, hardware, the interactive man–machine interface, event-driven task scheduling, system-wide arming and data acquisition, and a hierarchical data base of raw data and results are described. Similarities in data structures involved in control, monitoring, and data acquisition afford a simplification of the system functions, based on ‘‘groups’’ of devices. Emphases and optimizations appropriate for fusion diagnostic system designs are provided. An off-line data reduction computer system is under development.
Edge diagnostics for tandem mirror machines (invited)
Authors: Allen S. L. ,   TMX-U Experimental Team
Published: July 2002

The edge plasma in a tandem mirror machine shields the plasma core from cold neutral gas and impurities. A variety of diagnostics are used to measure the fueling, shielding, and confinement of the edge plasma in both the end plug and central-cell regions. Fast ion gauges and residual gas analyzers measure the gas pressure and composition outside of the plasma. An array of Langmuir probes is used to measure the electron density and temperature. Extreme ultraviolet (EUV) and visible spectroscopy are used to measure both the impurity and deuterium densities and to estimate the shielding factor for the core plasma. The linear geometry of a tandem mirror also allows direct measurements of the edge plasma by sampling the ions and electrons lost out of the ends of the machine. Representative data obtained by these diagnostics during operation of the Tandem Mirror Experiment (TMX) and Tandem Mirror Experiment-Upgrade (TMX-U) experiments are presented. Diagnostics that are currently being developed to diagnose the edge plasma are also discussed.
Analog delay line based multichannel digitizer
Authors: Cosso F. , Zweben S. J.
Published: July 2002

An inexpensive high-speed multichannel digitizing system was constructed based on Reticon analog delay lines. In the present configuration the system was capable of recording 512 successive samples at a 1.6-MHz sampling rate for each of 64 separate channels.
Linear high-voltage ramp generator for use in selective field ionization of Rydberg atoms
Authors: Fuqua W. L. , MacAdam K. B.
Published: July 2002

An electronic circuit has been constructed that generates a positive 3-kV linear ramp at adjustable slopes 125–500 V/μs, extendable to at least 1800 V/μs, for use in time-resolved selective field ionization of highly excited Rydberg atoms. Its principle of operation is as follows: An inductor, the primary of a 10:1 pulse transformer, is precharged with magnetic flux. The primary circuit is then opened and the collapse of flux is controlled by an integrator circuit with feedback from the secondary. An output circuit eliminates irregularities during the startup of the output pulse. The quiescent output is less than 40 mV. The output ramp, which can be fired at up to 1-kHz repetition rate and can drive typical capacitor-plate loads, has a slope that is constant within 2% from bottom to top, adjustable over a 4:1 range by a single potentiometer. The circuit has been extensively used for the detection and resolution of final-state ensembles in Rydberg spectroscopy and collision experiments.
Toward improved temporal resolution in electron coincidence experiments
Authors: Best P. E. , Zhu Hong
Published: July 2002

The two major contributions to the time spread of electrons detected after energy analysis in coincidence techniques are from the angular spread in the spectrometers and energy dispersion. We describe a compensation technique for each of these contributions. To compensate for the angular spread we would couple the first hemispherical electron spectrometer with an identical one, by means of an electron lens with a magnification of −1. Compensation for the energy spread is possible because in the spectrometers faster electrons have longer transit times, while the opposite is the case for electrons in field-free space and in electron lenses. In each case there is a linear relationship between the time spread and the spread in kinetic energies.
Precise temperature controller for resistance thermometers
Authors: Bruschi L. , Storti R. , Torzo G.
Published: July 2002

We describe here a stable and sensitive temperature controller to be used with resistance thermometers. The temperature resolution provided by this instrument was ΔT≂20 μK at room temperature and ΔT≂1 μK at liquid 4He temperature.
Plastic third sound resonator and low-temperature pressure gauge
Authors: Volz S. , Gillis K. , Mochel J. M.
Published: July 2002

A robust plastic third sound resonator has been developed which permits a wide range of experiments to be carried out on superfluid helium films. At room temperature the cell can be filled by diffusion with a wide range of gases including He, Ne, Ar, N2, and CO2 to form both substrate and experiment. The highly flexible walls allow in situ pressure measurements with a resolution of 10−6 Torr. Third sound can also be detected with capacitor plates within this cell.
High-resolution pressure–volume measurements by a strain gauge technique
Authors: Batlogg B. , Boppart H.
Published: July 2002

An experimental technique is described which employs resistive strain gauges to measure the pressure–volume relationship of solids up to∼50 kbar. The strain resolution is better than 10 ppm with a dynamical range up to 20 000. Two examples are presented to illustrate the sensitivity and the reliability of this technique.
Electro-optic voltage measurement in a high-power excimer laser
Authors: Osborne M. R. , Hutchinson M. H. R.
Published: July 2002

A novel electro-optic technique for measuring the voltage between the discharge electrodes of a high peak power excimer laser is described. The accurate measurement of this rapidly varying (>100 MHz) high voltage (>20 kV) in the immediate vicinity of very large rates of change of currents (>1012 A/s) is of importance in laser research but presents considerable difficulties when using conventional measuring techniques.
Optical and UV/x-ray imaging diagnostics for imploding plasma experiments
Authors: Lee P. H. Y. , Price R. H. , Reay J. , Pecos J. , Seagrave J. , McGurn J. , Cochrane B. , Anderson B.
Published: July 2002

We report on a fast framing camera designed to image imploding foils driven by inductive storage drivers. The camera has several front ends which are disposable, they allow for imaging in either the visible, UV, or x-ray regions; it also has very large dynamic range which allows it to record sequences of events where the brightness changes by many orders of magnitude.
Plane multiwire-electrode ionization chamber for measurements of radon concentration in air
Authors: Katase Akira , Matsumoto Yuzuru , Nagao Yasunori , Sakae Takeji , Tanabe Kenichi , Ishibashi Kenji
Published: July 2002

A continuous measuring system has been developed, which uses a plane multiwire-electrode ionization chamber and obtains radon concentrations by measuring in situ alpha energy spectra due to alpha-active nuclei in the air. The chamber has three rigid plane multiwire electrodes in a box of aluminum plates which have holes for the air to flow freely through them. The concentration measurements do not disturb the distribution of radon in the air. Values of concentration are obtained with good statistical errors because of the use of a large volume for the ionization chamber. The slow rise-time pulses of alpha particles from the chamber are analyzed with a specially designed analog-to-digital converter which is controlled with a microcomputer. The energy spectra have been obtained with a FWHM of about 600 keV. Time variations of radon concentrations have been measured in a room in a ferroconcrete building.
Teflon cell arrangement in high-pressure studies with a temperature programmer
Authors: Shubha V. , Ramesh T. G.
Published: July 2002

A precision analog temperature programmer is presented for use with the Teflon cell technique which is extensively used in high-pressure studies. The stability of temperature control is within ±0.1°C of the setpoint value. Linear temperature versus time ramps selectable from 1°C/min to 20°C/min are also possible in this system. This instrument facilitates automatic data acquisition of electronic transport properties under high-pressure conditions.
Electron-cyclotron-resonant microwave plasma system for thin-film deposition
Authors: Mejia S. R. , McLeod R. D. , Kao K. C. , Card H. C.
Published: July 2002

A new microwave plasma method for the fabrication of solid films is presented. Microwave power is efficiently transferred to the plasma, resulting in minimal power requirements. Uniform silicon films have been fabricated with a wide range of optical and electronic properties, at high deposition rates and low substrate temperatures. In a magnetically well-confined plasma operating in the vicinity of electron-cyclotron-resonance (ECR) conditions, film properties are strongly dependent upon the intensity of the externally applied dc magnetic field. The departure of the plasma chemistry from that associated with conventional rf systems is manifested in the observation of some opposite trends in the growth of the films.
Bourdon gauge absolute manometer
Authors: Jiménez-Domínguez H. , Figueroa-Lara F. , Galindo S.
Published: July 2002

It is suggested how an ordinary differential Bourdon gauge can easily be transformed into an absolute manometer.
Microprocessor-controlled electron impact ion source operated at constant discharge current and voltage
Authors: Ahn J. , Lawson R. P. W. , Stromsmoe K.
Published: July 2002

An electron impact ion source using a solid charge was interfaced with A/D and D/A units which are connected to a microprocessor control unit. A PID (proportional, integral, and derivative) control algorithm was implemented to control the ion source. The power fed to the ion source filament and furnace filament are controlled so as to keep both the discharge voltage and current constant. With this controlled ion source, the result shows a steady ion current. For example, with Pb+ ions, an initial ion current of 13 μA stayed within ±1.5 μA for 60 min; with no control, the ion current fell steadily and had to be manually reset three times every 20 min over a 60-min run. Similar results have been obtained with Mg+, Al+, Zn+, and Sn+ ions.
Velocity distribution and energy diagnostics in intense guided relativistic electron beams
Authors: Avivi P. , Cohen Ch. , Friedland L.
Published: July 2002

A novel experimental method to measure both the velocity distribution and the relativistic factor γ of intense guided electron beams is described. The method is based on the use of a magnetic hill to discriminate the electrons with different transverse velocity components. Analysis of the current reflected by the hill as a function of the height of the hill yields the above mentioned beam characteristics.
Optical shot-noise-limited detection: A single-sideband technique with flexible modulation frequencies
Authors: Anfinrud Philip , Struve Walter S.
Published: July 2002

A multiple modulation detection scheme offering near shot-noise-limited performance with facile, independent variability of both rf modulation frequencies is reported. This method enables efficient tailoring of the modulation frequencies to empirical laser and technical noise spectra.
Two-parameter data-acquisition system for slit-scan chromosome analysis
Authors: Weier Heinz-Ulrich , Eisert Wolfgang G.
Published: July 2002

Transient digitizers based on RCA flash converters are used to record two-parameter data for chromosome analysis.
Pulsed metastable atomic beam source for time-of-flight applications
Authors: Kohlhase A. , Kita S.
Published: July 2002

A metastable atomic beam source was developed utilizing pulsed helium and argon nozzle beams. A coaxial electron gun, which can be used in a pulsed as well as in a continuous mode, excites the noble gases to their metastable states by electron bombardment in the direction of propagation of the ground-state atoms. In contrast to former work, the electron beam is controlled and accelerated by a combination of three hemispherically shaped tungsten grids. With continuous electron gun operation the source produces a metastable flux of about 1015 atoms/sr s for helium and argon under optimum expansion conditions. Applying short electrical pulses to a control grid yields supersonic metastable atom pulses, with velocity distributions having a relative width as low as 3.8% for helium and 6.5% for argon ( FWHM ) with a 100% modulation of the metastable beams. These features make the source applicable for velocity analyzed scattering experiments using the time-of-flight technique.
Laser beam profile measurement by a thermographic technique
Authors: Baba Tetsuya , Arai Teruo , Ono Akira
Published: July 2002

A thermal method to measure laser beam profiles has been developed. A laser beam is absorbed by a heat-resisting film and transformed into heat. A profile of the temperature increment over the receiving film is radiometrically detected by a thermographic instrument. The method is demonstrated by one-dimensional profile measurements of a pulsed YAG laser beam whose energy density is several J per cm2.
Electrohydraulic fatigue apparatus for testing in ultrahigh vacuum and controlled environments
Authors: Lee Won-Jong , Chung Yip-Wah , Fine Morris E. , Baker James P.
Published: July 2002

A closed-loop computer-interfaced electrohydraulic fatigue apparatus was constructed and installed in an ultrahigh-vacuum (UHV) scanning Auger microprobe for the study of environmental effects on fatigue. Load- or (total or plastic) strain-controlled fatigue tests can be performed in the push–pull mode between atmospheric pressure and UHV (below 6.5×10−8 Pa) under controlled gaseous environments. The specimen mounting allows access of an electron beam for Auger analysis, an ion gun for sputtering and a secondary-electron detector for imaging. There have been several important improvements made in the electronics.
Pulsed hot cathode (LaB6) discharge for uniform plasma production
Authors: Savas S. E. , Pyle R. V. , Berkner K. H.
Published: July 2002

A pulsed hot cathode hydrogen discharge of several milliseconds duration is used to produce a dense (<1014 cm−3), uniform plasma target for atomic collision studies. This plasma, whose cross section is determined by the cathode shape, is rectangular, since it is produced by a discharge (1500 V, ∼100 A) from a 2×11-cm2 rectangular LaB6 slab cathode along a 0.1-T magnetic field to a gas-fed anode. Background hydrogen (∼1 Pa) and contaminant gas (<10−2 Pa) are kept low by injecting H2 during the discharge into an evacuated (∼10−4 Pa) chamber. One drawback of this discharge for atomic physics applications is that at high plasma density (ne >2×1013 cm−3), sufficient fluxes of >1-keV x rays are produced to flood our solid-state detectors with background counts.
Molecular-beam epitaxial growth of CdTe(112) on Si(112) substrates
Authors: de Lyon T. J. , Rajavel D. , Johnson S. M. , Cockrum C. A.
Published: July 2002

High crystalline quality epitaxial CdTe(112)B/ZnTe films were deposited by molecular-beam epitaxy directly onto vicinal Si(112) substrates, without use of GaAs interfacial layers. The films were characterized with x-ray diffraction, optical microscopy, and wet chemical defect etching. Single crystal, twin-free CdTe(112)B films exhibit structural quality exceeding that previously reported for CdTe(112)B heteroepitaxy on GaAs/Si(112) or GaAs(112)B substrates. X-ray rocking curve full width at half-maximum of 72 arcsec for CdTe(224) reflection and near-surface etch pit densities (EPD) of 2×106 cm−2 have been observed for 8-μm-thick CdTe films. EPD depth profiles indicate that the threading dislocation density decreases with increasing II–VI epilayer thickness up to approximately 5 μm thickness and saturates at 2×106 cm−2 for thickness exceeding 5 μm. The CdTe epilayer orientation was observed to tilt 2° away from the Si(112) substrate orientation toward the [001] direction.
Simple time-resolving Thomson spectrometer
Authors: Rhee M. J. , Schneider R. F. , Weidman D. J.
Published: July 2002

We describe a simple time-resolving Thomson spectrometer system which can provide the temporal information of ions produced by a pulsed source, in addition to the time-integrated information. The electric field in a conventional spectrometer is modulated by a time-varying field. It is shown that from the resulting spectrogram, the time-resolved quantities associated with the ions can be deduced. Experimental results with plasma focus produced ions are given as an example.
Rotating sample holder for ESR studies of relatively high conductivity, thin samples
Authors: Zarifis V. G.
Published: July 2002

We have designed a low-loss dielectric sample holder for positioning very thin, metallic, semiconductor samples in a TE102 cavity for ESR studies at liquid-helium temperatures. The sample holder can be rotated ±15° from the center position, allowing accurate positioning of the high-conductivity sample at minimum electric field. This results in maximizing the Q factor and allowing symmetric excitation on both faces of the sample. We have also devised a method of setting the microwave phase to desired value to better than 0.3° by utilizing the hyperfine lines of a dilute As-doped Si sample.
Simple design for a frequency-independent voltage-controlled phase shifter
Authors: Bruschi L. , Storti R. , Torzo G.
Published: July 2002

A very simple general-purpose phase shifter is described here, that can be linearly voltage controlled in a wide frequency range. This device allows us to implement the standard lock-in amplifier into a vector tracking lock-in amplifier.
Plasma-materials interactions test facility
Authors: Uckan Taner
Published: July 2002

The Plasma-Materials Interactions Test Facility (PMITF) recently designed and constructed at Oak Ridge National Laboratory (ORNL) is an electron cyclotron resonance microwave plasma system with densities around 1011cm−3 and electron temperatures of 10–20 eV. The device consists of a mirror cell with high-field-side microwave injection and a heating power of up to 0.8 kW (cw) at 2.45 GHz. The facility will be used for studies of plasma-materials interactions and of particle physics in pump limiters and for development and testing of plasma edge diagnostics.
Photon statistical properties of visible laser diodes
Authors: Brown R. G. W. , Grant R. S.
Published: July 2002

We investigate the factorial moments and photon correlation properties of two Sharp Corporation 780-nm laser diodes and assess their suitability for use in photon counting and correlation experiments.
Construction of a two-photon photoacoustic spectrometer
Authors: Wilder J. A. , Findley G. L.
Published: July 2002

We describe a photoacoustic spectrometer optimized for the detection of nonradiative relaxation from molecular electronic states populated via two-photon excitation. The excitation source is a nitrogen-laser-pumped dye laser; the analog data-acquisition system automatically corrects the photoacoustic signal for pulse-to-pulse fluctuations in laser intensity; and the microcomputer interface is designed for universal communication to any microcomputer which supports an RS-232C I/O port. As an example of the capabilities of this spectrometer, we present two-photon photoacoustic spectra of CH3I and CD3I, covering small regions within the first s-Rydberg transitions, and show that the photoacoustic signal does indeed depend quadratically upon the incident laser intensity. These data represent the first direct detection of nonradiative decay from a molecular Rydberg state.
Precision ozone calibration system based on vapor pressures of ozone
Authors: Mauersberger K. , Hanson D. , Morton J.
Published: July 2002

A precision ozone calibration system for stratospheric research has been developed and evaluated. Vapor pressures above solid ozone are mixed with a carrier gas (N2) to produce stratospheric ozone mixing ratios at total pressures of 1 to over 20 Torr. The uncertainty in the ozone mixing ratios is approximately ±1.5%, the stability of ozone is ±0.3%. Experiments to be calibrated may sample the gas mixture over a wide range of flow rates; the maximum throughput of gas with corrections of less than 1% to ozone is about 200 Torr l/min. A mass spectrometer system continuously monitors the purity and stability of the N2–O3 gas mixture.
Heat capacity of thick-film resistance thermometers below 1 K
Authors: Love M. S. , Anderson A. C.
Published: July 2002

Thick-film resistors, when used as thermometers below 1 K, have a heat capacity similar to that found in Matsushita carbon-composition resistors.
Small capacitor electrodes for microwave rotational spectroscopy in a supersonic expansion
Authors: Whitten W. B.
Published: July 2002

Nonresonant capacitive electrodes are shown to be convenient and effective for observing dielectric resonances in the microwave region where the sample size is small compared to the wavelength of the excitation. An example of rotational spectroscopy in a seeded supersonic expansion from a pulsed nozzle is presented.
Measurement of the spatial neutral deuterium temperature distribution in the HBTX1B reversed-field pinch by fluorescence scattering
Authors: Forrest M. J. , Trotman D. L. , Bamford R. , Lazaros A.
Published: July 2002

The spatial neutral deuterium temperature distribution has been made in the HBTX1B reversed-field pinch plasma device by Balmer-beta fluorescence scattering. This measurement is based on tuning a dye laser to the n=2–4 transition of deuterium and passing it through the deuterium plasma with sufficient power to saturate the selected transition. The technique, hitherto used to determine neutral densities and energies, has been extended by means of an optimized two-channel narrow-band interference-filter arrangement to analyze the scattered spectrum. Spatial resolution is achieved by a scanning Risley prism arrangement. Neutral temperatures in the range 20–150 eV have been measured and the spatial distribution is consistent with neutral particle analyzer results and an ion power balance model proposed for the reversed-field pinch.
2π-radian field-of-view toroidal electrostatic analyzer
Authors: Young D. T. , Bame S. J. , Thomsen M. F. , Martin R. H. , Burch J. L. , Marshall J. A. , Reinhard B.
Published: July 2002

We describe a new type of electrostatic charged particle analyzer based on toroidal geometry. The analyzer features a 360°×10° (polar×azimuthal) field of view and a focal length in the polar direction significantly longer than that of similar devices based on spherical geometry. Extended focal length is a requirement for matching the electrostatic energy spectrometer with a second, mass-resolving, analyzer. Laboratory tests show that the toroid design has a large geometric factor per unit of instrument weight, good energy-angle resolution in the particle deflection plane, and sharp (1.0° FWHM) resolution at focus in the polar angle direction. The analyzer is well suited for use in satellite-borne mass spectrometry and also as a stand-alone electrostatic analyzer.
Dark-field microscopy of transparent objects with a bright-field objective
Authors: Hartman A. W.
Published: July 2002

Described is a simple modification of a standard bright-field objective to produce dark-field imagery of transparent objects.
Investigation of leaks in fiberglass-reinforced pressure vessels by direct observation of hollow fibers in glass cloth
Authors: McAdams J.
Published: July 2002

A simple method of visual observation of hollow fibers within fiberglass cloth has been developed. This visualization can aid in determining the contribution these fibers make toward leaks observed in fiberglass-reinforced epoxy resin pressure or vacuum vessels. Photographs and frequency data of these hollow fibers are provided.
Variable-depth calorimetry of a layered material
Authors: Wang J. K. , Campbell J. H.
Published: July 2002

We have investigated the use of frequency variation in ac calorimetry in the measurement of thermal quantities within controllable distances of the sample heater and thermometer. This technique, useful in studies of heterogeneous samples where only a small part of the sample is of interest, e.g., surfaces, thin films, and interfaces, is applied to study the thermal properties of a test sample made from indium (In) sandwiched between layers of bulk gallium arsenide. We measure and analyze the frequency dependence of the thermal response of the sample, as well as the variation with frequency of the relative size of the anomaly observed at the In superconducting transition. The data are consistent with a model assuming a thermal diffusion-limited sampling volume.
Digitally timed boxcar averager for analog integration of portions of a video signal
Authors: Smith B. K. , Delaney P. A. , Passler M. A.
Published: July 2002

A new system for measuring video signal intensity over selected portions of a complete video scan has been developed and applied to acquisition of LEED IV data. Unlike other systems available, this system is not microprocessor driven, but relies on appropriately timed boxcar averaging such that interfacing to the computer is relatively simple, yet data acquisition is fast. Signal to noise is theoretically better for this system since the input to the analog to digital (A/D) converter can have a lower time constant.
Piezodriven scanner for cryogenic applications
Authors: La Comb Lloyd J. , Quate C. F.
Published: July 2002

A scanning microscope stage has been developed for use at cryogenic temperatures. The stage uses a piezoelectric driving element and circular flexure hinges to achieve a slow scan travel of greater than 10 μm and a near-resonance travel of 100 μm while immersed in liquid helium at 4.2 K. The scanner has been operated inside a pressure cell in a dilution refrigerator, where it dissipates less than 150 μW of heat at 100 mK.