bluuebunny/crossref_metadata_2025 huggingface dataset:
Excitonic transitions in InGaP/InAlGaP strained quantum wells
Authors: Schneider R. P. , Bryan R. P. , Jones E. D. , Lott J. A.
Published: July 2002

Excitonic transitions in metalorganic vapor phase epitaxially grown InxGa1−xP/In0.48(Al0.7Ga0.3)0.52P strained single quantum-well structures are characterized using low-temperature photoluminescence and photoluminescence excitation (PLE) spectroscopies. The structures consist of several uncoupled quantum wells with thicknesses between 1.2 and 11.3 nm, and compositions x of 0.48 (nominally lattice matched) and 0.56 (∼0.6% biaxial compressive strain). The photoluminescence spectra exhibit intense peaks over the wavelength range 550–650 nm, with linewidths between 7 and 23 meV depending on the well thickness. The PLE spectra reveal strong heavy-hole and light-hole transitions, as well as higher-order (n=2) transitions in the thicker wells. The heavy-hole/light-hole splitting shows little dependence on well thickness in the strained structures, indicating a relatively large conduction band offset of ΔEC∼0.75ΔEG.
Improved performance of quantum well infrared photodetectors using random scattering optical coupling
Authors: Sarusi G. , Levine B. F. , Pearton S. J. , Bandara K. M. S. , Leibenguth R. E.
Published: July 2002

We demonstrate that a random scattering reflector on top of a quantum well infrared photodetector increases the optical coupling (i.e., increases the infrared absorption, responsivity, and detectivity) by an order of magnitude compared with a one-dimensional grating or 45° angle of incidence geometry.
Shock wave velocity and shock pressure for low density powders: A novel approach
Authors: Dijken D. K. , De Hosson J. Th. M.
Published: July 2002

A novel approach is presented to predict the shock wave velocity as well as the shock wave pressure in powder materials. It is shown that the influence of the specific volume behind the shock wave on shock wave velocity and shock pressure decreases with decreasing initial powder density. The new model is compared with experimental data of various materials: Fe, Cu, Al, C, UO2, Ce2O3, SiO2 (quartz), NaCl, and polystyrene. It is concluded that the model holds in particular for initial powder densities less than 50% and for flyer plate velocities up to 5 km/s.
Low temperature formation of Si(111)7×7 surfaces from chemically prepared H/Si(111)-(1×1) surfaces
Authors: Vinh Le Thanh , Eddrief M. , Sébenne C. A. , Dumas P. , Taleb-Ibrahimi A. , Gunther R. , Chabal Y. J. , Derrien J.
Published: July 2002

Reflection high energy and low energy electron diffraction, along with high resolution photoemission studies reveal that ideally H-terminated Si(111) surfaces, H/Si(111)-(1×1) prepared by wet chemical etching, transform in ultrahigh vacuum into atomically clean Si(111)7×7 surfaces upon hydrogen desorption at temperatures as low as 550 °C.
Characterization of a microwave plasma jet containing Ar-CH4 gas mixture
Authors: Thomas L. , Jauberteau J. L. , Aubreton J. , Catherinot A. , De Souza A. R. , Cinelli M. J.
Published: July 2002

This work is devoted to the study of the expansion of a Ar-CH4 microwave plasma. Diagnostics have been performed within the reactor using both an electrostatic Langmuir double probe and spatially resolved emission spectroscopy. We have proven that the plasma jet results from electromagnetic surface wave propagation (ne≥nec=3.6×1011 cm−3, Te∼23 000–46 000 K) and have shown that injection of methane into the jet decreases ne and Te, and thus limits the striking conditions. Such an expanding plasma finds applications in plasma enhanced chemical vapor deposition technology. It can be used to create simple radicals close to a substrate and thus limits their destruction on the reactor walls.
Very long wavelength InxGa1−xAs/GaAs quantum well infrared photodetectors
Authors: Gunapala S. D. , Bandara K. M. S. V. , Levine B. F. , Sarusi G. , Sivco D. L. , Cho A. Y.
Published: July 2002

We demonstrate a long wavelength (λc=20 μm) quantum well infrared photodetector using nonlattice matched InxGa1−xAs/GaAs materials system. High optical gains (low capture probabilities) were achieved by using GaAs as a barrier material in this system. A detectivity of D*=9.7×1010 cm√Hz/W at T=10 K has been achieved.
Fabrication of vertical-microcavity quantum wire lasers
Authors: Arakawa T. , Nishioka M. , Nagamune Y. , Arakawa Y.
Published: July 2002

A strained InGaAs quantum wire laser with a vertical microcavity structure was fabricated for the first time. In this laser structure, quantum wires with a lateral width of about 10 nm were grown by a selective metalorganic chemical vapor deposition technique. The length of the microcavity was 4λ(λ=883 nm), with AlAs/AlGaAs distributed Bragg reflectors. The cavity effect was demonstrated by the measurement of photoluminescence with and without the cavity. Lasing oscillation was observed at 77 K by optical pumping.
Leakage current behaviors in rapid thermal annealed Bi4Ti3O12 thin films
Authors: Cho H.-J. , Jo W. , Noh T. W.
Published: July 2002

Bi4Ti3O12 thin films have been grown on indium-tin-oxide coated glass by pulsed laser deposition. Films are rapidly thermal annealed at 650 °C in three kinds of atmospheres such as O2, N2, and air. The annealing atmosphere is found to be an important growth parameter which determines the crystallization, microstructures, and the leakage current behaviors. The film annealed in oxygen has a columnar grain structure with an amorphous phase, and its leakage current behavior is in agreement with the prediction of the space-charge-limited conduction model. The film annealed in nitrogen has polycrystalline porous structure, and its high field conduction is well explained by the thermoionic emission model, called the Poole–Frenkel emission. On the other hand, the film annealed in air has both the columnar and porous structures, and its electrical behavior shows characteristics of both models.
Observation of a negative persistent photoconductivity effect in In0.25Ga0.75Sb/InAs quantum wells
Authors: Lo Ikai , Mitchel W. C. , Kaspi R. , Elhamri Said , Newrock R. S.
Published: July 2002

We have observed a negative persistent photoconductivity effect in In0.25Ga0.75Sb/InAs quantum wells with Shubnikov–de Haas measurements. The saturated reduction of the electron density in the InAs well was about 10%. The electron effective mass was found to be (0.048±0.004) m0 for an electron density of 18.0×1011 cm−2. The electron quantum lifetime decreased as the electron density was reduced by the negative persistent photoconductivity effect due to electron-hole interaction.
Pressure dependence of the photoluminescence spectra of nitrogen-doped ZnSe: Evidence of compensating deep donors
Authors: Chen Anthony L. , Walukiewicz Wladek , Haller Eugene E.
Published: July 2002

We have measured the photoluminescence spectra of nitrogen-doped ZnSe under hydrostatic pressure. From the pressure dependence of the peak positions of the acceptor-bound exciton and donor-acceptor-pair emissions, we show that highly doped samples have two donor-acceptor-pair transitions, one involving shallow and one involving deep donors. Our results confirm that one mechanism limiting the free hole concentration is compensation from this deep donor.
Silicon wafer-to-wafer bonding at T<200 °C with polymethylmethacrylate
Authors: Eaton William P. , Risbud Subhash H. , Smith Rosemary L.
Published: July 2002

A versatile method for low temperature (T<200 °C) bonding of silicon and oxidized silicon wafers is reported using spun cast films of polymethylmethacrylate (PMMA) as the bonding material. The PMMA films are thermoplastic, transparent, dielectric, planarizing, and photopatternable. Bonding was achieved with both unpatterned and patterned, 1-μm-thick films. Tensile bond strengths of 3.12 MPa were typical (although the strongest bond had a strength of 5.85 MPa) and thin film stresses of 10 MPa (tensile) were measured. Photopatterned PMMA films exhibited approximately 14% lateral pattern smear after bonding.
Frequency limitations of negative differential mobility in vertical conduction in superlattices
Authors: Lei X. L. , Horing N. J. M. , Cui H. L. , Thornber K. K.
Published: July 2002

The frequency-dependence of the carrier drift velocity in superlattice miniband conduction in response to a small signal ac electric field is investigated for laterally unconfined and one-dimensionally confined (2D) superlattices biased in the negative differential mobility regime. Numerical calculations show that in both systems there exists a mobility-transition frequency of order of 100 GHz, above which the differential mobility becomes positive. This frequency in a 2D superlattice is about three times that in an unconfined system, owing to enhanced carrier scattering. In a domain-driven microwave oscillator, the mobility-transition frequency is expected to be relatively small compared to the oscillator frequency. Nonetheless, the higher mobility-transition frequency in the 2D superlattice would render it more advantageous for use in negative differential mobility microwave oscillators.
Scanning tunneling microscopy of InAs/Ga1−xInxSb superlattices
Authors: Lew A. Y. , Yu E. T. , Chow D. H. , Miles R. H.
Published: July 2002

Cross-sectional scanning tunneling microscopy and spectroscopy have been used to characterize InAs/Ga1−xInxSb strained-layer superlattices grown by molecular-beam epitaxy. Monolayer roughness of the InAs/Ga1−xInxSb interfaces is visible in atomically resolved images of the epitaxial layers. An asymmetry in electronic structure between interfaces in which InAs has been grown on Ga1−xInxSb and those in which Ga1−xInxSb has been grown on InAs has also been observed in these images. Current-voltage spectra obtained while tunneling into the epitaxial layers are found to be strongly influenced by extended superlattice electronic states.
Liquid metal undercooled below its Curie temperature
Authors: Platzek D. , Notthoff C. , Herlach D. M. , Jacobs G. , Herlach D. , Maier K.
Published: July 2002

Electromagnetic levitation has been used to undercool an alloy of Co80Pd20 below the Curie temperature of the solid α phase. If the temperature of the undercooled liquid decreases below the Curie temperature an attractive force between the sample and an external permanent magnet was observed. This may indicate the existence of a metallic liquid showing magnetic ordering.
Maskless patterning of silicon surface based on scanning tunneling microscope tip-induced anodization and chemical etching
Authors: Sugimura Hiroyuki , Yamamoto Takuma , Nakagiri Nobuyuki , Miyashita Masayuki , Onuki Tetsuji
Published: July 2002

A microprocessing method for silicon (Si) without photolithography is proposed. The method consists of only two processes. Hydrogen-terminated Si surfaces (Si-H) were first locally anodized using scanning tunneling microscopy (STM). The non-anodized surfaces were then etched chemically in potassium hydroxide solution. The anodic oxide produced with the first process performed as an etching mask. The height of the etched pattern of approximately 50 nm was much larger than the thickness of the anodic oxide. Humidity effect on STM tip-induced anodization of Si-H is also shown. The area of the anodization was enlarged with increasing humidity, and the spatial resolution became worse.
Wet oxidation of amorphous and crystalline Si1−x−yGexCy alloys grown on (100)Si substrates
Authors: Atzmon Z. , Bair A. E. , Alford T. L. , Chandrasekhar D. , Smith David J. , Mayer J. W.
Published: July 2002

The oxidation of amorphous Si0.65Ge0.27C0.08 and single-crystal Si0.63Ge0.36C0.01 in wet ambient at 700 and 900 °C has been studied using Rutherford backscattering spectrometry and transmission electron microscopy. A reference sample of Si0.63Ge0.37 was also oxidized in order to determine the influence of carbon on the oxidation behavior. The low C content alloy behaved similar to the SiGe alloy: uniform Si1-xGexO2 was obtained at 700 °C whereas SiO2 was formed at 900 °C, and Ge piled up underneath the oxide. In both cases, carbon was not detected in the oxide layer. The amorphous Si0.65Ge0.27C0.08 alloy behaved significantly different at both oxidation temperatures in comparison with the crystalline Si0.63Ge0.36C0.01 and Si0.65Ge0.37. Negligible oxidation occurred at 700 °C whereas SiO2 was obtained at 900 °C and the rejected Ge distributed uniformly throughout the SiGeC alloy. It is proposed that fast Ge diffusion during oxidation at 900 °C resulted from diffusion at grain boundaries, since crystallization of the amorphous SiGeC layer occurred in conjunction with oxidation, leading to nucleation of nanocrystals (∼5 nm diam). The oxidation/annealing treatment has thus provided a useful mechanism for increasing the relative Ge concentration in the SiGeC alloy.
Atomic ordering of GaInP studied by Kelvin probe force microscopy
Authors: Leng Y. , Williams C. C. , Su L. C. , Stringfellow G. B.
Published: July 2002

The atomic ordering of GaInP has been established and studied by a variety of methods, including transmission electron microscopy, cathodoluminescence, and photoluminescence. In this work, a Kelvin probe force microscope (KPFM) has been employed to image several GaInP samples previously characterized by these established techniques. The results of our study clearly show that the KPFM is capable of distinguishing between ordered and disordered regions in GaInP, and that the KPFM contrast strongly depends on the amplitude of the applied ac bias voltage of the KPFM. The measurements indicate that ordering in GaInP modifies the density and/or lifetime of the surface states.
Defects responsible for gray tracks in flux-grown KTiOPO4
Authors: Scripsick M. P. , LoIacono D. N. , Rottenberg J. , Goellner S. H. , Halliburton L. E. , Hopkins F. K.
Published: July 2002

Electron paramagnetic resonance (EPR) has been used to identify the primary electron and hole traps responsible for ‘‘gray tracks’’ in flux-grown KTiOPO4(KTP). Ionizing radiation (x rays) was used to produce the gray-track effect. During an irradiation at 0 °C, a broad absorption band peaking near 500 nm is introduced, the EPR spectra from a series of Ti3+ centers appear, and the dominant EPR spectrum associated with Fe3+ ions decreases significantly. Following the irradiation, the decay of the optical absorption and the Ti3+ centers, along with the growth of Fe3+ centers, were monitored over a period of 20 h at room temperature. Changes in the EPR spectra of the Ti3+ and Fe3+ centers during the anneal correlated with the decay of the induced optical absorption (i.e., gray track). These results demonstrate that Fe3+ centers are the primary hole trap and Ti4+-VO complexes are the primary electron trap responsible for gray track formation in flux-grown KTP crystals.
Near field optical latent imaging with the photon tunneling microscope
Authors: Marchman Herschel M. , Novembre Anthony E.
Published: July 2002

We present a simple optical technique for measuring features formed in radiation sensitive materials (photoresists) after exposure. The monitoring of photoresist patterns after exposure, but before development is known as latent imaging. Optical techniques used in the past for latent image detection have really only sensed scattered intensity levels from periodic patterns and not spatially resolved images of the features themselves. The application of photon tunneling microscopy to imaging of latent resist patterns exposed using point-source x-ray and midultraviolet illumination will be demonstrated.
Site-controlled growth of nanowhiskers
Authors: Sato T. , Hiruma K. , Shirai M. , Tominaga K. , Haraguchi K. , Katsuyama T. , Shimada T.
Published: July 2002

The metalogranic vapor-phase epitaxy (MOVPE) growth of site-controlled nanowhiskers having a single preferential growth direction is accomplished by using a SiO2 window mask. A small window size (200×200 nm in this experiment) is essential for growing a single whisker from a single Au- seed cluster formed inside each window of the mask. The presence of the SiO2 mask greatly influences the MOVPE growth process, especially the growth direction and resultant diameter of the whiskers. This influence may be due to surface migration of the source materials or source gas diffusion near the surface from the masked region to the window region.
Double-fused 1.52-μm vertical-cavity lasers
Authors: Babić Dubravko I. , Dudley James J. , Streubel Klaus , Mirin Richard P. , Bowers John E. , Hu Evelyn L.
Published: July 2002

We demonstrate a novel long-wavelength vertical-cavity laser structure employing two AlAs/GaAs mirrors and a strain-compensated InGaAsP quantum-well active region. The lasers have been fabricated by wafer fusion and have the lowest room-temperature pulsed threshold current density of 3 kA/ cm2 at 1.52 μm. Eight laser sizes ranging from 9 to 60 μm were fabricated with threshold currents as low as 12 mA. Single transverse mode operation was observed on the 9 μm device, while other devices lased multimode. The maximum pulsed output power was 7 mW.
Current density dependence of electromigration failure of submicron width, multilayer Al alloy conductors
Authors: Oates A. S.
Published: July 2002

Electromigration failure of Al alloy metallization systems is one of the main concerns for integrated circuit reliability as feature sizes are reduced into the submicron regime. One of the most important aspects of electromigration failure is the current density dependence of the failure time. Many studies have been conducted for widths above 1 μm and the consensus of these studies indicates that a current density exponent, n=2, describes microstructure related failure of the metallization. There is very little data available, however, for feature sizes close to 0.5 μm, particularly for metallizations consisting of Al alloys clad by refractory layers. In this letter we investigate the current density dependence of microstructure related failure for narrow (0.6 μm) conductors with multilayer TiN refractory layers, and correlate this dependence with void formation by electromigration. We show that the current density dependence of microstructural failure in such narrow conductors differs significantly from that observed for widths above 1 μm. At 0.6 μm n as low as 1 is obtained compared with n=2 at 1.2 μm for microstructure-related failure of long, multilayer stripes. The number of voids formed during accelerated testing and their average nucleation rate appear to be independent of the current density for 0.6 μm stripes, contrary to findings for wider stripes. It is suggested that growth of voids determines the failure kinetics of narrow stripes.
Silicon doping of GaN using disilane
Authors: Rowland L. B. , Doverspike K. , Gaskill D. K.
Published: July 2002

The n-type doping of GaN by organometallic vapor phase epitaxy using Si2H6 on sapphire has been demonstrated. The electron concentration depended linearly on Si2H6 to trimethylgallium mole fraction ratio. State-of-the-art values of 300 K electron mobility were obtained for electron concentrations from 1×1017–4×1019/cm3 with no apparent increase in compensation at either the lowest or highest concentrations studied. Electron concentrations obtained using a given concentration of disilane were constant with growth temperature in the range 980–1040 °C.
Energy distribution of output electrons from a microchannel plate
Authors: Koshida Nobuyoshi , Hosobuchi Masato
Published: July 2002

The output energy spread of a microchannel plate has been studied experimentally in a wide range of operating conditions. The energy distribution is found to consist of a sharp main peak with the full width at half-maximum of a few electron volts and a long tail extending over a wide energy range. These two components are presumably caused by two distinct regions of the potential distribution near the output end produced by the electrode penetrating into a certain depth within the microchannels. The tail component shows a significant change, particularly in the unsaturated operation mode. The resultant variation in the relative number of high-energy output electrons may have a detrimental effect on the spatial resolution of the image intensifier.
Determination of experimental tokamak plasma profiles using maximum-entropy analysis
Authors: Cottrell G. A. , Fairbanks E. S. , Stockdale R. E.
Published: July 2002

The diagnostician commonly faces the problem of extracting the maximum information on plasma spatial profiles from only a very limited and noisy data set. Conventionally, functional forms (e.g., a parabola raised to a power) are fitted to the measured data using nonlinear least-squares regression. This immediately biases the interpretation and constrains results to a narrow family of curves for which there may be no real evidence in the data. In this paper, we examine the consequences of abandoning this assumption and, instead, seek the constrained maximum entropy (ME) profile making no such assumptions. Results are compared with conventional analysis. The ME method has the inherent advantages of (i) yielding only positive (and therefore physically meaningful) profiles, (ii) suppression of noise on the data, and (iii) producing a profile which contains the least amount of spurious detail. The method is illustrated with reference to measured chord-average CO2 laser interferometer data taken on the Doublet III tokamak.
Acousto-optic rf spectrum analyzer for plasma diagnostics (abstract)
Authors: Irby James H. , Beals David
Published: July 2002

An acousto-optic rf spectrometer (AOS) has been designed and constructed for use on the Constance B and TARA mirror experiments at Massachusetts Institute of Technology (MIT). The AOS is , in essence, a preprocessor of data that can come from a variety of sources including rf probes and microwave/laser scattering experiments. The output of the AOS is the Fourier transform amplitude of the input in a parallel format suitable for computer acquisition. The spectrometer, having a bandwidth of 500 MHz, together with its receiver, is capable of looking at fluctuations anywhere in the frequency range of a few MHz up to 4 GHz. Power levels of a few nanowatts can be detected. Complete 500-MHz-wide spectrums can be processed and acquired at the rate of 1 every 10 μs. The optical components, receiver, and data-acquisition interface will be discussed and initial data taken on the Constance B experiment will be shown.
High-frequency gyrotron scattering diagnostic for instability studies on TARA
Authors: Woskoboinikow P. , Cohn D. R. , Gerver M. , Mulligan W. J. , Post R. S. , Temkin R. J. , Trulsen J.
Published: July 2002

A 1- to 10-kW,>30-ms pulsed, narrow linewidth (<1 MHz), 137-GHz gyrotron is being fabricated for collective Thomson scattering plasma diagnostics on the TARA tandem mirror experiment. The drift cyclotron loss cone, the axial loss cone, harmonics of these instabilities, and the ion two stream instability in the TARA plugs will be studied with this diagnostic.
m=1/n=1 density fluctuations in currentless high-β plasma in heliotron E
Authors: Zushi H. , Motojima O. , Kaneko H. , Mizuuchi T. , Wakatani M. , Iiyoshi A. , Uo K.
Published: July 2002

High-frequency density fluctuations with m=1/n=1 have been observed in a currentless high-β plasma. The line density was measured with a 5-ch FIR laser interferometer. A high-β plasma with 〈β〉∼2% was obtained with about 2-MW neutral beam injection into a currentless target plasma produced by second-harmonic ECRH. With weak gas puffing [β(0)≳1%], sawteeth-like oscillations accompanied by high-frequency fluctuations of about 2–5 kHz were observed on the line density. These fluctuations coincide with the soft x-ray fluctuations. From both signals the mode number of this instability is estimated to be m=1 and n=1. During the fluctuations, rapid enhancement (10%–20%) in the edge ion saturation current was also measured, which indicates that this instability causes particle loss from the bulk to the edge. The instability is quenched by a change in density profile from peaked to broad with intense gas puffing. This behavior is consistent with a theoretical analysis.
Far-infrared polarimetry/interferometry for internal magnetic field measurement on ZT-40M (abstract)
Authors: Erickson R. M. , Forman P. R. , Jahoda F. C.
Published: July 2002

An important aspect of this method is to measure the density simultaneously with the Faraday rotation in order to infer the magnetic field from the rotation. This measurement performed on several chords yields information on the density and poloidal field profiles. Heterodyne techniques are employed for the polarimetry as well as the interferometry because they are insensitive to spurious amplitude changes that can hamper other methods. On ZT-40M, amplitude changes exceeding 50% have been observed, thus precluding any other method for our application. We use a 185-μm laser, a rotating grating for heterodyning, and GaAs photoconductors and Schottky diodes for detection. An instrumental sensitivity of 3 mrad at a time resolution of 25 μs has been demonstrated, however vibration-induced structure limits the sensitivity to ∼50 mrad. Efforts to reduce each of these numbers are in progress. The simultaneous measurement has been made on ZT-40M, and effort is turning to system refinement and scaling up to multichord operation. Error propagation in the inversion process is being evaluated.
Design of a high energy x-ray imaging system for the Tandem Mirror Experiment-Upgrade (abstract)
Authors: Failor B. H. , Silver E. H. , Clauser J. F.
Published: July 2002

We want to image the hot, mirror-confined electrons produced by electron cyclotron resonant heating in the end cells of the Tandem Mirror Experiment-Upgrade. Preliminary spectroscopic measurements with NaI(Tl) detectors indicate tail electron temperatures in the range of 100–300 keV. Our goal is to image x-rays in the energy range 10–200 keV, for plasma densities as low as 1011 cm−3. A spatial resolution of one part in forty at framing rates of 200 Hz should be achieved. The imaging system will consist of an x-ray converter (phosphor or scintillator) and image intensifier (diode or microchannel plate), followed by a video readout (silicon intensifier tube). We will outline the steps we are taking to implement this system.
Application of InP:Fe photoconductors as a fast and sensitive soft x-ray detector and bolometer (abstract)
Authors: Kania D. R. , Jones L. A. , Shepherd R. L. , Maestas M. D. , Wagner R. S. , Hammond R. B. , Bradley J. M.
Published: July 2002

Recently we have demonstrated that InP:Fe photoconductors are fast (FWHM∼150 ps), sensitive (2.7×10−3 A/W), and flat response soft x-ray detectors using synchrotron radiation from the Stanford Synchrotron Radiation Laboratory.1 We have applied these to the measurement of the radiation emitted by a collapsing annular gas (argon) puff z-pinch plasma. The detector was used in two modes of operation: (1) a filtered soft x-ray detector as a pinch diagnostic and (2) a fast unfiltered bolometer to measure the total radiated power as a function of time. We will compare the performance of the photoconductors to other common fast x-ray detectors and bolometers.
High-resolution x-ray spectroscopy for plasma diagnostics (abstract)
Authors: Burkhalter P. G.
Published: July 2002

Techniques have been developed to acquire improved x-ray spectra from intense, hot laboratory plasmas. Spatially resolved high-resolution x-ray spectra is a valuable diagnostic for characterizing plasma sources.1 By mimimizing the plasma source size and with the utilization of selected x-ray diffraction crystals, x-ray line wavelengths can be measured with accuracies of 2–3 mÅ in the 10–15 Å region, provided calibration wavelengths are available or can be calculated. Dedicated experiments to determine line coincidences for x-ray laser studies is a recent application of high-resolution x-ray spectroscopy.2,3 Examples will be presented of results using laser-produced plasmas and the gas puff source for spectroscopy.
UHV universal manipulator with direct cooling
Authors: Wu N. J. , Ignatiev A.
Published: July 2002

An ultrahigh-vacuum compatible sample manipulator which incorporates rotation and a Dewar for sample cooling is described. The rotation is accomplished using a differentially pumped rotary seal made of two Teflon O rings and the temperature of the sample can be controlled from 30 K to over 1600 K.
Experimental method of measuring energy in the Bénard–Rayleigh problem
Authors: Zamora M. , Rey de Luna A.
Published: July 2002

The energy content, introduced by the thermodynamics of steady states, is measured in the Bénard–Rayleigh problem using a heat fluxmeter connection. We describe the experimental apparatus, which can turn around a horizontal axis, thus inducing or destroying convective structures. After calibration, we were able to measure the heat flux through the fluid layer as well as the structural energy of the convective cells. These structural energy values confirm that the energy content is a steady-state function.
Neutral beam species measurements using i
n s
i
t
u Rutherford backscatter spectrometry
Authors: Kugel H. W. , Kaita R. , Gammel G. , Williams M. D.
Published: July 2002

This work describes a new in situ method for measuring the neutral particle fractions in high-power deuterium neutral beams, used to heat magnetically confined fusion plasmas. Deuterium beams, of variable energies, pulse lengths, and powers up to 47 keV, 100 ms, 1.6 MW, were Rutherford backscattered at 135° from the TiC inner neutral beam armor of the PDX, and detected using an electrostatic analyzer with a microchannel plate. Complete energy scans were made every 20 ms and data were obtained simultaneously from five different positions across the beam profile. The neutral particle fractions were measured to be D0(E):D0(E/2):D0(E/3)=53:32:15. The corresponding neutral power fractions were P0(E):P0(E/2):P0(E/3)=72:21:7, and the associated ionic fractions at the output of the ion source were D+1 (E):D+2 (E):D+3 (E)=74:20:6. The measured neutral particle fractions were relatively constant over more than 70% of the beam power distribution. A decrease in the yield of the full-energy component in the outer regions of the beam was observed.
Barium ion Zeeman and space potential diagnostic
Authors: Wickham M. , Lazar N. H. , Rynn N.
Published: July 2002

A diagnostic has been developed to simultaneously determine the magnetic field and space potential in fusion-like plasmas.1 In Fig. 1, we show schematically the diagnostic concept. The magnetic field is determined by a measurement of the Zeeman resonance absorption pattern of an energetic (<30 keV) barium ion beam (10 μA). The spectrum is obtained by laser-induced fluorescence. In our approach, similar to a technique developed at UC Irvine,2 the absorption spectrum of the barium ion beam is measured as the frequency of a narrow-linewidth dye laser is scanned over the Doppler-shifted Zeeman-split resonance transition. The resonantly scattered light at 4934.1 Å is collected without frequency processing other than a narrow-band filter to reduce background plasma light. Space potentials are determined by a measurement of the Doppler shift due to a change in beam energy, E=E0−eφp(E0 is the beam energy, φp is the plasma potential). The laser is injected tangentially to the ion beam to take advantage of the narrow Doppler spread in the direction of the beam.
Low-temperature, high-pressure apparatus for nuclear-magnetic-resonance experiments
Authors: van der Putten D. , Prins K. O. , Trappeniers N. J.
Published: July 2002

A description is given of a liquid-helium cryostat containing a high-pressure NMR probe, suitable for hydrostatic pressures up to 15 kbar. The tail of the cryostat is designed to fit between the poles of a conventional electromagnet. Hydrostatic helium gas pressure is generated by means of a commercially available two-stage gas compressor. The apparatus is designed for performing nuclear-magnetic-resonance (NMR) experiments on samples subjected to pressure, in a temperature range from 2 to 100 K.
Optimization of H− production in a magnetically filtered multicusp source
Authors: Leung K. N. , Ehlers K. W. , Pyle R. V.
Published: July 2002

Different techniques to increase the H− yield in a multicusp source have been investigated. It is shown that the extracted H− current can be enhanced by optimizing the discharge voltage, the neutral gas pressure, or by employing a magnetoelectrostatic containment scheme. A factor of 6 increase in H− output has been achieved by placing the extractor very close to the magnetic filter. It is also found that the extracted electron current is much reduced at this optimum geometry.
Rapid response microcalorimeters for biochemical experiments
Authors: Kodama Takao , Woledge Roger C.
Published: July 2002

Calorimeters have been constructed for measuring heat changes accompanying biochemical reactions in samples of small volume. They can measure heat changes of 0.05 mJ in reaction volume of 1 or 2 ml with a time resolution better than 1 s. The instruments have proven useful in studies of some biochemically interesting reactions, where high sensitivity and good time resolution are required.
Photonic methods of high-speed analog data recording
Authors: Chang James , Filter William F. , Lockwood Grant J. , Neyer Barry T.
Published: July 2002

We have developed a photonic high-speed analog data recording system that, when compared with conventional oscilloscope-based systems, offers greater economy, higher bandwidth, electrical isolation, and compactness. The basis of this approach is to record analog photonic signals rather than analog electrical signals. A key component is the prototype high-speed multi- channel data recorder. Initial demonstrations of this photonic system in pulsed power experiments have already shown its versatility and usefulness. We describe the system and its integration with newly developed photonic sensors and discuss its overall impact in diagnostic technology.
Design and performance of a double-pass high-resolution electron energy loss spectrometer
Authors: Stroscio Joseph A. , Ho W.
Published: July 2002

The design, characterization, and performance of a high-resolution electron energy loss spectrometer for surface studies is described. The spectrometer is based on a double-pass 127° cylindrical deflector analyzer for both the monochromator and analyzer stages. An overall resolution of 4 meV is obtained with a current of 5×10−11 A measured at the sample. The resolving power of the double-pass deflector, in the specific geometry utilized, is significantly greater than that of either deflector. The observed energy resolution on metal and semiconductor surfaces is contrasted; it is found that electronic excitations lead to noninstrumental broadening on semiconductor surfaces.
Principles of a new electron spectrometer for angular-resolved photoemission using a magnetic deflector
Authors: Lévêque G.
Published: July 2002

We describe the principle of a new electron spectrometer combining a magnetic torroidal deflector and a simple electrostatic focuser. The electrons are dispersed according to their energy and polar angle, along two orthogonal axes of a plane detector. This bidimensional (E, θ) display is very convenient for band-structure studies and for rapid acquisition of the data.
Comprehensive approach for diagnosing intense single-pulse microwave sources
Authors: Earley L. M. , Ballard W. P. , Roose L. D. , Wharton C. B.
Published: July 2002

A comprehensive approach to developing intense pulse microwave diagnostics for measuring the performance of a high-power microwave source is presented. Both conventional and new diagnostic techniques were used. Hence all measurements were made in a redundant fashion allowing small error bars in the measured data. The output power was diagnosed using four methods: two transmitting–receiving systems, two circular waveguide directional couplers, calorimetry, and gaseous breakdown. The operating frequency was measured using three methods: bandpass filters, a heterodyne receiver, and a homodyne receiver. The diagnostics were evaluated by using a 12-vane S-band inverted relativistic magnetron operating at 1 MV, 0.31 T, and 5 kA which reliably produced 3.15-GHz microwaves at powers of approximately 100 MW for pulse lengths variable from 5 to 70 ns. The microwave power pulse had a rise time of approximately 2 ns.
Microwave discharges in termination fixtures: An improved laboratory technique for exciting electrodeless discharges
Authors: Haugsjaa Paul O.
Published: July 2002

A new technique of exciting electrodeless discharges at microwave frequencies is described which involves a simply constructed device called a termination fixture. The termination fixture has been shown to allow operation of laboratory scale rare gas electrodeless discharges from atmospheric pressure down to pressures of 0.5 Pa (4 mTorr). The stability, tunability, efficiency, and flexibility of this technique represent an advancement beyond conventional means of exciting electrodeless discharges. This device is expected to provide improved spectroscopic light sources, a better technique of molecular dissociation, and a simplified method of providing electrodeless discharges for laboratory experiments.
Calibration system for electron detectors in the energy range from 10 eV to 50 keV
Authors: Marshall F. J. , Hardy D. A. , Huber A. , Pantazis J. , McGarity J. , Holeman E. , Winningham J. D.
Published: July 2002

A system has been developed to provide accurate calibration of electron detectors measuring in the energy range from approximately 10 eV to 50 keV. The principal component of the system is a large area (730 cm2), monoenergetic electron beam which is tunable in energy. This beam is produced by illuminating, in vacuum, a thin gold film deposited onto a quartz flat with ultraviolet light, such that photoelectrons are ejected from the gold surface. With the gold film floated at an adjustable negative voltage, the photoelectrons ejected from the surface are accelerated towards an electrically grounded screen which is positioned in front of the quartz flat. All high voltages in the beam system are guarded so as to eliminate any significant leakage current. The current leaving the gold surface which determines the beam intensity is measured using a specially designed picoammeter. Electron beam intensities of ∼106 electrons/cm2 s are produced by illuminating the gold photocathode with light from a 2-W mercury vapor lamp which has 90% of its output at 2537 Å. The resulting beam has an energy spread of 0.41 eV. Electron beam intensities of ∼107 electrons/cm2 s are produced with a 200 W medium pressure mercury arc lamp. For this case, the beam has a width in energy of 0.55 eV. Detectors to be calibrated are mounted within a set of computer-controlled rotational and translational tables. The tables allow the look direction of the detector to be oriented with respect to the beam in two orthogonal angles and two orthogonal directions. The entire calibration system operates within a set of Helmholtz coils that allow the Earth’s magnetic field to be canceled. The voltage on the gold surface, the angular and spatial positioning of the detector, and the accumulation and display of the data are all controlled by a minicomputer.
Multidetector grating spectrometer for infrared astronomy
Authors: Slingerland J.
Published: July 2002

A cryogenic grating spectrometer is described for astronomical use in the 8–13 μm atmospheric window with spectral resolving power near 200. Radiation is detected by means of an array of nine Si:As detectors located in the plane of dispersion. The instrument is controlled remotely by a microprocessor, which also handles data acquisition and storage. Some results of observations at the Arcetri telescope at Gornergrat are shown.
Universal CCD-controller system
Authors: Bortoletto F. , D’Alessandro M.
Published: July 2002

We describe a system capable of driving a variety of CCD (charge-coupled device) imagers in scientific applications. Although the system was designed and built for astronomical purposes, direct application to other fields is possible. A detailed description of the main parts and the selected design rules is given. To permit an easy duplication or update of the system particular care was taken to use, where possible, standard parts.
Piezodriven spindle for a specimen holder in the vacuum chamber of a scanning electron microscope
Authors: Hatsuzawa Takeshi , Tanimura Yoshihisa , Yamada Hirofumi , Toyoda Kouji
Published: July 2002

A rotating specimen holder device for use in the vacuum chamber of a SEM (scanning electron microscope) is developed by using a piezodriven mechanism. The mechanism consists of piezoelectric elements, clamps, and actuators that work as feeders to rotate the spindle. It is specially designed to eliminate the magnetic field influence of standard motors, and the holder can be placed just under the electron probe beam. In this article, the basic ideas, design, and instrumentation techniques are described. Then a servosystem is constructed for positioning the spindle. The angular resolution is 0.9° and the maximum rotation speed is 9.4 s/rotation.
Steady-state magnetized non-neutral ion plasma
Authors: Mulmargŏnde Kim S.
Published: July 2002

A steady-state dense non-neutral argon-ion plasma, confined radially by a strong uniform axial magnetic field (max 0.1 Wb/m2), has been generated to a density ∼1014/m3. The radial density profile of argon ions has been measured using a Langmuir probe. The dependence of the ion number density on the axial magnetic field has been observed.
Techniques for using emitting probes for potential measurement in rf plasmas
Authors: Wang E. Y. , Hershkowitz N. , Intrator T. , Forest C.
Published: July 2002

Investigations of the effects of rf on plasma potential measurements with electron emitting probes and methods for interpreting data are presented. Techniques correspond to the floating and inflection point methods of single-emitting and differential emitting probes, respectively. A simple method of measurement of plasma potential fluctuations is given which makes use of time-averaged emitting probe I–V characteristics.
Multigigahertz beam current and position monitor for relativistic electron beams
Authors: Carlson R. L. , Ridlon R. N. , Stout L. E.
Published: July 2002

A self-integrating magnetic-loop device having a rise time of less than 175 ps has been developed to monitor the temporal behavior of the current and position associated with an electron beam. Beam current and centroid position are measured with a 2-GHz bandwidth by combining the output of these loops with two 0°/180° hybrids. The improved monitors are essentially free of self-resonances and spurious responses at bandwidths extended to 2 GHz. The probes are economical and easy to produce in volume for a wide range of applications.
Improved method for the precise determination of the compressibility factor from refractive index measurements
Authors: Bose T. K. , St-Arnaud J. M. , Achtermann H. J. , Scharf R.
Published: July 2002

We show that the absolute determination of the refractive index when combined with an expansion technique for obtaining the higher-order coefficients of the Lorentz–Lorenz expansion leads to precise values of density. The compressibility factor of methane calculated with the first three coefficients of the Lorentz–Lorenz expansion is comparable to the best PVT values. The optical method for the determination of the compressibility factor is shown to be not only precise, but also has the ability to produce numerous experimental points in a short time as compared to other methods.
Silicon surface barrier detector for fusion neutron spectroscopy
Authors: Elevant T. , Hendel H. W. , Nieschmidt E. B. , Samuelson L. E.
Published: July 2002

The usefulness of the intrinsic 28Si(n,α)25Mg and 28Si(n, p)28Al reactions in silicon surface barrier detectors for measurements of ion temperatures in D-T fusion plasmas and of D-T fusion neutron flux has been investigated. For a 14-MeV neutron-generator narrow-energy-line source, the energy resolution (∼1.5%), detection efficiency, and useful count rates have been determined. Based on these results, for a 100-ms time bin, D-T plasma ion temperatures from 2 to 6 keV can be determined from the full-width half-maximum (FWHM) of the neutron-induced α spectral lines, with the error estimated to be 25% to 5%, respectively. The maximum intrinsic detection efficiency for a nominal 1500-μm-thick detector is ∼6×10−4.
Design of an ion temperature diagnostic based on neutral beam scattering
Authors: van Heesch E. J. M. , Hirose A. , Sarkissian A. , Skarsgard H. M.
Published: July 2002

Small-angle neutral beam scattering will be used on the STOR-M tokamak to obtain space and time-resolved measurements of the ion temperature. Advantages of the technique and experimental considerations leading to the design are discussed. It is expected that a 20–30-keV helium beam of 35–65-A/m2 current density together with a large area chevron channel-plate detector and automatic data handling will allow direct determination of ion temperatures at an accuracy of 10%, a temporal resolution of 40 μs, and a spatial resolution better than 1 cm.
New type of high-pressure apparatus and pressure measurement
Authors: Kawashima Y.
Published: July 2002

An apparatus has been devised, which generates high pressure by supplying thermal energy to a good electrical conductor ball surrounded by an electrical and thermal insulator. Its structure is simple and the pressure generation is not accompanied by a pressure leakage and a frictional force. A pressure-measurement technique of the apparatus in the presence of high temperature has been also devised. Then the generated pressure has been estimated by numerical calculation. As an example, the pressure of 4.9 GPa is produced by the apparatus. In conclusion, the estimated pressure is in good agreement with the experimental result of the pressure measurement.
Electroacoustic pulse source for high-resolution seismic explorations
Authors: Cannelli G. B. , D’Ottavi E. , Santoboni S.
Published: July 2002

We suggest an electroacoustic pulse source with frequency characteristics, directivity pattern, and energy suitable for high-resolution prospecting on land and underwater. The seismic wave is produced by a high-energy discharge, set in the focus of a parabolic aluminum reflector filled with insulating liquids. The acoustic pulse is transmitted to the soil via a neoprene diaphragm that couples the transducer to the earth. The discharge is primed by a low-energy preliminary spark, via a third electrode between the principal electrodes, which produces the liquid ionization. An important feature of the electroacoustic source is the variation of frequency spectrum of the impulse, by changing electrical parameters such as capacitance and inductance. The directivity pattern can be changed by inching the electrodes up or down with reference to the focus. First field measurements showed better penetration capacity of the seismic wave of the paraboloid in comparison with a traditional mechanical source. This electroacoustic source can be utilized on land, and even more successfully in underwater acoustic prospecting, by providing suitable electric insulation. In this latter application the frequency range is higher than that used for land prospecting.
Photopyroelectric thin-film instrumentation and impulse-response detection. Part I: A theoretical model
Authors: Power Joan F. , Mandelis Andreas
Published: July 2002

Thin-film pyroelectric effect detectors provide a simple means of measuring thermal properties of solid samples. The present work reports a time-delay theoretical model of thin-film pyroelectric detection which enables the recovery of thermal diffusivity and thermal conductivity information from the impulse response of the pyroelectric system.
New high-power arbitrary ratio power splitter at microwave frequencies
Authors: Ganguli A. , Baskaran R.
Published: July 2002

The details of a new, high-power, arbitrary ratio, waveguide power splitter at microwave frequencies are described. The experimental results, giving the coupled powers at the two output ports for different coupling ratios, are presented for input power levels of 1 and 3 kW (cw). The results are compared with the theory for such structures.