bluuebunny/crossref_metadata_2025 huggingface dataset:
Plastic analysis of cylinder oxidation
Authors: Rafferty C. S. , Dutton R. W.
Published: July 2002

A plastic flow model is used to calculate the stress generated during thermal oxidation of silicon cylinders. The analysis is used to estimate stress as a function of thickness, radius of curvature, and temperature. The oxidation stress is much lower than previous analyses.
Optical spectroscopy: An i
n s
i
t
u diagnostic for pulsed laser deposition of high T
c superconducting thin films
Authors: Wu X. D. , Dutta B. , Hegde M. S. , Inam A. , Venkatesan T. , Chase E. W. , Chang C. C. , Howard R.
Published: July 2002

High oxygen partial pressure has been found to be an important parameter for the pulsed laser deposition of as-deposited superconducting thin films with high Tc and Jc. The optical emissions from both elemental and oxide species ejected from the target of YBa2Cu3O7−x during the pulsed laser deposition process increase with the oxygen pressure, with the oxide emission showing a stronger pressure dependence than the elemental emission. The dynamics of the interaction between the oxygen atoms and the species in the laser-produced plume were studied by a wavelength and time-resolved measurement. The results are qualitatively explained using a simple model based on optical emission arising from inelastic and recombination collision between the elemental species and electronically excited oxygen atoms. The formation of oxides in the plume is shown to be essential for the production of higher quality superconducting films, indicating the value of optical spectroscopy as a diagnostic tool.
High hole mobility in Si/Si1−xGex/Si p-type modulation-doped double heterostructures
Authors: Wang P. J. , Meyerson B. S. , Fang F. F. , Nocera J. , Parker B.
Published: July 2002

High quality Si/Si1−xGex/Si p-type modulation-doped double heterostructures with x=0.12 and 0.15 have been grown by the ultrahigh vacuum/chemical vapor deposition technique. Hole mobilities as high as ∼3700 cm2/V s at 14 K have been obtained for heterostructures with x=0.12, at a sheet carrier concentration of ∼8×1011 cm−2. This is the highest hole mobility ever reported for p-type Si material at these carrier concentrations. The electrical properties of these heterostructures at low temperatures are those expected of a two-dimensional hole gas at Si/SiGe and SiGe/Si heterointerfaces. The high hole mobility is indicative of excellent interfacial properties. Peak mobilities were observed to depend on the level and proximity of remote B dopant species, as well as the Ge content of the alloyed layers.
Laser beam deflection as a probe of laser ablation of materials
Authors: Sell Jeffrey A. , Heffelfinger David M. , Ventzek Peter , Gilgenbach Ronald M.
Published: July 2002

Helium-neon laser beam deflection is used to study excimer laser ablation of polymers and a YBa2 Cu3 O7−x superconductor. Density gradients above pulsed laser heated or ablated samples deflect the He-Ne laser beam and this is measured using a position sensitive detector. The technique permits the determination of the laser fluence threshold for ablation both in a vacuum and in air, and the velocity of the ablation products in a vacuum. A model of the thermal deflection at low fluence was developed which enables measurements of thermal diffusivity of the air.
Microscopic imaging of residual stress using a scanning phase-measuring acoustic microscope
Authors: Meeks Steven W. , Peter D. , Horne D. , Young K. , Novotny V.
Published: July 2002

A high-resolution scanning phase-measuring acoustic microscope (SPAM) has been developed and used to image the near-surface residual stress field around features etched in sputtered alumina via the acoustoelastic effect. This microscope operates at 670 MHz and has a resolution of 5–10 μm, depending upon the amount of defocus. Relative velocity changes of sample surface waves as small as 50 ppm are resolved. Images of the stress field at the tip of a 400-μm-wide slot etched in alumina are presented and compared with a finite element simulation. The SPAM uses an unconventional acoustic lens with an anisotropic illumination pattern which can measure anisotropic effects and map residual stress fields with several μm resolution and a stress sensitivity of 1/3 MPa in an alumina film.
Epitaxy of Y-Ba-Cu-O thin films grown on single-crystal MgO
Authors: Ramesh R. , Hwang D. , Ravi T. S. , Inam A. , Barner J. B. , Nazar L. , Chan S. W. , Chen C. Y. , Dutta B. , Venkatesan T. , Wu X. D.
Published: July 2002

The epitaxy of a thin-film Y-Ba-Cu-O (YBCO) superconductor deposited on a single-crystal [001] MgO substrate was examined by transmission electron microscopy. The large lattice mismatch (8–10%) in the basal plane of YBCO and MgO is accommodated mainly by the formation of a polycrystalline, mosaic structure. The grain boundaries correspond to unique crystallographic interfaces, determined by the crystal symmetry of the substrate and the thin film.
Sn incorporation into InP grown by molecular beam epitaxy: A secondary-ion mass spectrometry study
Authors: Panish M. B. , Hamm R. A. , Hopkins L. C.
Published: July 2002

Secondary-ion mass spectrometric analysis of InP/Ga0.47In0.53As heterostructures incorporating Sn-doped regions has been used to study the distribution of Sn in InP during molecular beam epitaxy. Depending upon the flux conditions, up to a monolayer of Sn can accumulate on the growing InP surface, and the surface accumulation mediates the incorporation of Sn into the growing layer. The surface to bulk distribution ratio of Sn per monolayer grown is less than 10−3. Once the surface has been saturated all additional Sn in the beam is incorporated and concentrations exceeding 1020 cm−3 can be achieved.
Flexible superconducting whiskers of the Li-doped Bi-Sr-Ca-Cu oxide
Authors: Matsubara Ichiro , Tanigawa Hideo , Ogura Toru , Yamashita Hiroshi , Kinoshita Makoto , Kawai Tomoji
Published: July 2002

Flexible Li-doped Bi-Sr-Ca-Cu-O superconducting whiskers have been prepared by heating a glassy melt-quenched plate in a stream of O2 gas. The whiskers show a resistance drop at 110 K with a zero resistance at 81 K. These values are higher than those of the Pb-doped Bi-Sr-Ca-Cu-O whiskers by 5 and 11 K, respectively. The doping of Li is effective to raise Tc for both the 2212 phase and the 2223 phase. The Jc values of the Li-doped whiskers are 30 000 A/cm2 at 77 K and 300 000 A/cm2 at 66 K in a zero magnetic field.
Optical absorption and carrier-induced bleaching effect in quantum wire and quantum box structures
Authors: Sakaki Hiroyuki , Kato Keishi , Yoshimura Hisao
Published: July 2002

The optical absorption spectra of quantum wires and boxes are studied theoretically to evaluate the carrier-induced bleaching effect. It is found that the absorption coefficients of these highly confined systems (HCSs) and their changes with the introduction of carriers can be far greater than those of less-confined systems (LCSs) such as quantum wells (films) and bulk semiconductors. In addition, the carrier-induced bleaching effect of HCS is found to remain very high at room temperature while that of LCS is substantially weakened by the thermal distribution of carriers.
Scanning tunneling microscopy of the surface morphology of YBa2Cu3Ox thin films between 300 and 76 K
Authors: Moreland John , Rice Paul , Russek S. E. , Jeanneret B. , Roshko A. , Ono R. H. , Rudman D. A.
Published: July 2002

Scanning tunneling microscopy (STM) images of YBa2Cu3Ox (YBCO) thin films show different growth mechanisms depending on the deposition method and substrate material. We present images of YBCO films sputter deposited onto MgO and SrTiO3, and laser ablated onto LaAlO3 showing screw dislocation and ledge growth mechanisms. At room temperature we observed an anomalous tunneling conductance near the edge of growth steps which causes a large apparent step-edge height in the STM image. This effect decreases with decreasing temperature, so that the step height approaches the expected value for one unit cell of 1.2 nm at 76 K. This phenomenon reflects changes in either the surface tunneling barrier or tunneling density of states upon cooling.
Synthesis of ferromagnetic Bi-substituted yttrium iron garnet films by laser ablation
Authors: Kidoh Hideo , Morimoto Akiharu , Shimizu Tatsuo
Published: July 2002

Bismuth-substituted yttrium iron garnet (Bi:YIG) films were deposited on gadolinium gallium garnet substrate by laser ablation using the ArF excimer laser. This is the first report on the preparation of Bi-substituted YIG films by laser ablation. Films have a garnet single phase above the substrate temperature of 490 °C, and the film composition does not deviate largely from the target composition and it is almost constant in the temperature range between 490 and 580 °C. The saturation magnetization of the film is 1500 G at room temperature. Faraday rotation angle θF at a wavelength of 830 nm at room temperature is −0.3×104 °/cm.
Target modification in the excimer laser deposition of YBa2Cu3O7−x thin films
Authors: Foltyn S. R. , Dye R. C. , Ott K. C. , Peterson E. , Hubbard K. M. , Hutchinson W. , Muenchausen R. E. , Estler R. C. , Wu X. D.
Published: July 2002

Under conditions used for pulsed laser deposition (308 nm, 20 ns, 2–8 J/cm2) of Y-Ba-Cu-O superconducting thin films, we have measured a pronounced decrease in deposition rate with cumulative laser exposure of the target. This decay in rate is accompanied by evolution on the target surface of microscopic columnar structures, having yttrium-enriched surfaces, which are aligned in the direction of the incident laser beam (45°). Neither the vapor plume direction nor film stoichiometry is affected by the presence of these oriented, chemically altered surface features.
Demonstration of an x-ray ring-aperture microscope for inertial-confinement fusion experiments
Authors: Ress D. , Lerche R. A. , Da Silva L.
Published: July 2002

We are investigating the use of annular (ring) apertures to image high-energy x-ray emission (≳4 keV) from inertial-confinement fusion targets. In our scheme, a coded image is formed on a detector (such as x-ray film) by x rays that pass through a narrow annulus cut in a sheet of high-Z material such as gold. Signal-to-noise ratio calculations show a factor of 10 advantage of ring-aperture imaging over conventional pinhole imaging. Simultaneous pinhole and ring-aperture images of small (≊20 μm diam), laser-driven, x-ray sources were obtained in recent experiments. We used a 10-μm-wide, 1-mm-diam annulus in a 6-μm thickness of gold; a 10-μm-diam pinhole was in the center of the annulus. Unfolds of the coded images have signal-to-noise ratios a factor of 20 larger than the pinhole images. The ring-aperture microscope is a promising new technique to image inertial-confinement fusion targets and other compact sources of high-energy x rays.
Interface roughness scattering and electron mobility in quantum wires
Authors: Motohisa J. , Sakaki H.
Published: July 2002

We have theoretically investigated the influence of interface roughness on the scattering and mobility of electrons in very thin quantum wires, where all the electrons are in the lowest subband. In particular, the magnitude and electron concentration dependence of mobility are studied and shown to depend sensitively on the correlation length Λ and amplitude Δ of roughness. It is found that interface roughness scattering is drastically suppressed as the electron concentration increases, as in the case of impurity scattering when a realistic set of roughness parameters is chosen for edge quantum wire structures. General criteria to achieve ultra-high mobility in various quantum wire structures are also discussed.
Effect of microvoids on initial and light-degraded efficiencies of hydrogenated amorphous silicon alloy solar cells
Authors: Guha S. , Yang J. , Jones Scott J. , Chen Yan , Williamson D. L.
Published: July 2002

Using a combination of infrared absorption and small-angle x-ray scattering on hydrogenated amorphous silicon alloy films and efficiency measurements of solar cells with intrinsic layers prepared under nominally identical conditions to those for the deposition of the films, we observe a correlation between microstructure in the films and solar cell performance. With increasing microvoid density, both the initial and light-degraded performance of solar cells are found to deteriorate.
Temporal profile of optical transmission probe for pulsed-laser heating of amorphous silicon films
Authors: Park Hee K. , Xu Xianfan , Grigoropoulos Costas P. , Do Nhan , Klees Leander , Leung P. T. , Tam Andrew C.
Published: July 2002

The transient temperature field development during heating of an amorphous silicon (a-Si) film, deposited on a fused quartz substrate by pulsed excimer laser irradiation is studied. Experimental optical transmission data are compared with heat transfer modeling results. The temperature-dependence of the material complex refractive index through the thin film thickness is taken into account.
Giant magnetoresistance in heterogeneous AgCo alloy films
Authors: Carey M. J. , Young A. P. , Starr A. , Rao D. , Berkowitz A. E.
Published: July 2002

Giant magnetoresistance in heterogeneous, sputtered AgCo thin films is reported. The films consist of Co-rich precipitates in an Ag-rich matrix. Δρ/ρ values as high as 55% at 4.2 K and 20% at room temperature are observed. The magnetoresistance is shown to depend on the Co concentration as well as the particle size. Upon annealing, Δρ/ρ first increases, then decreases. Δρ, however, decreases monotonically with annealing.
Model for conductance in dry-etch damaged n-GaAs structures
Authors: Rahman M. , Johnson N. P. , Foad M. A. , Long A. R. , Holland M. C. , Wilkinson C. D. W.
Published: July 2002

A model for the effects of dry-etch damage on the conductances of etched structures is developed. Expressions for defect distribution are obtained for top-surface and sidewall damage. The expression for sidewall damage is used in the calculation of wire conductances. The model accounts accurately for changes in experimentally measured conductances of SiCl4-etched n+-GaAs wires with variations in material carrier concentration, epilayer thickness, and etch time/depth. The analysis indicates that defects are created at a significant rate at sidewalls as compared to top surfaces.
Textured growth of diamond on silicon via in situ carburization and bias-enhanced nucleation
Authors: Wolter S. D. , Stoner B. R. , Glass J. T. , Ellis P. J. , Buhaenko D. S. , Jenkins C. E. , Southworth P.
Published: July 2002

Ordered diamond films have been deposited on single-crystal silicon substrates via an in situ carburization followed by bias-enhanced nucleation. Textured diamond films with greater than 50% of the grains oriented D(100)//Si(100) and D〈110〉//Si〈110〉 were grown in both a horizontal and vertical microwave plasma chemical vapor deposition reactor. Separate diamond films from each of the two reactors were analyzed both by scanning electron microscopy and Raman spectroscopy. The in situ carburization is speculated to form an epitaxial SiC conversion layer, thus providing an economical alternative to obtaining epitaxial diamond films on single-crystal SiC.
Relative free energies of Si surfaces
Authors: Follstaedt D. M.
Published: July 2002

Cavities are formed by ion implanting (001) Si with He and annealing at 800 °C to enlarge and to remove the He. Subsequent annealing at 600 °C results in cavities with well-defined facets as seen in [110] cross section with transmission electron microscopy. The most frequently observed facets are {111} planes. A rounded surface is seen about the [001] direction of all cavities, and (11̄0) facets are seen less frequently. The cavities allow the equilibrium crystal shape of Si to be examined and the relative free energies of the observed planes to be measured. The surface free energies of {001} and {110} planes are found to be 1.09±0.07 and 1.07±0.03 times that of {111} planes, respectively.
Excimer laser ablated barium strontium titanate thin films for dynamic random access memory applications
Authors: Roy D. , Krupanidhi S. B.
Published: July 2002

Polycrystalline thin films of Ba0.5Sr0.5TiO3 were deposited by excimer laser (248 nm) ablation. Films deposited near 575 °C exhibited good crystallinity, a dielectric constant of 330, a dissipation factor of 0.02, a leakage current density of 2×10−7 A/cm2, a charge storage density of 36 fC/μm2, and breakdown time of 3700 s at an applied electric field of 0.125 MV/cm. The C-V (capacitance-voltage) behavior of both MFM (metal-ferroelectric-metal) and MFS (metal-ferroelectric-semiconductor) structures were studied and the estimated dielectric permittivity in the accumulation region of MFS structure nearly indicated the bulk value, suggesting a reasonably good Ba0.5Sr0.5TiO3/Si interface.
Optical differentiator using symmetric self-electro-optic effect devices
Authors: Hosoda Makoto , Kawashima Kenji , Inai Makoto , Yamamoto Teiji , Fujiwara Kenzo
Published: July 2002

An optical differentiation circuit with symmetric self-electro-optic effect devices is proposed and demonstrated. A novel method called global stability analysis of the differential photoresponse equation clearly shows the temporal dynamics of circuit operation.
Combustion chemical vapor deposition: A novel thin-film deposition technique
Authors: Hunt A. T. , Carter W. B. , Cochran J. K.
Published: July 2002

A new open-atmosphere chemical vapor deposition (CVD) technique has been developed that we term combustion chemical vapor deposition (CCVD). During CCVD a flame provides the necessary environment for the deposition of a dense film whose elemental constituents are derived from solution, vapor, or gas sources. Ag, YSZ, BaTiO3, YIG, YBa2Cu3Ox, and Y2BaCuO5 have been deposited via CCVD with the combustion of a sprayed, cation-containing, organic solution as the sole heat source. CCVD could, for some applications, be less expensive and more flexible than conventional CVD.
Spontaneous emission factor and its scaling in vertical cavity surface emitting lasers
Authors: Shtengel G. , Temkin H. , Uchida T. , Kim M. , Brusenbach P. , Parsons C.
Published: July 2002

We report room-temperature measurements of the spontaneous emission factor β in high-quality gain-guided GaAs/AlGaAs vertical cavity surface emitting lasers. In devices with 6-μm diameter we obtain β=2.8×10−3. The measured scaling of β with the cavity volume agrees well with classical electromagnetic model of dipole radiation. The magnitude of β exceeds that predicted by classical theory by approximately a factor of 2.
Cross-sectional scanning tunneling microscopy of doped and undoped AlGaAs/GaAs heterostructures
Authors: Gwo S. , Chao K.-J. , Shih C. K.
Published: July 2002

Scanning tunneling microscopy (STM) was used to study the (NH4)2S-passivated (110) cross-sectional surfaces of both doped and undoped Al0.3Ga0.7As/GaAs heterostructures on n+-substrates. The ex situ (NH4)2S treatment of the cross-sectional surfaces of heterostructures was found to be very stable against oxidation. STM images showed no appreciable deterioration of surface quality in vacuum after more than 40 days. The spectroscopic results on the undoped epilayer showed diodelike behavior, confirming that an undoped large band gap region can be imaged by STM through carrier injection from the conductive regions.
Neutron focusing lens using polycapillary fibers
Authors: Chen H. , Mildner D. F. R. , Xiao Q. F.
Published: July 2002

Multiple mirror reflection at small grazing angles from the smooth surfaces of the narrow channels of polycapillary fibers can be used to transport, bend, and focus thermal neutron beams. We report the results of the focusing of a polychromatic cold neutron beam using a compact lens of borosilicate fibers and with a focal distance of 57 mm. The intensity profile of the beam at the focus is approximately conical in shape with a full width at half-maximum of 0.49 mm, and with an average gain in intensity of about 20. These experimental results agree well with those obtained by computer simulation.
Electronic and mechanical properties of carbon nitride films prepared by laser ablation graphite under nitrogen ion beam bombardment
Authors: Ren Zhong-Min , Du Yuan-Cheng , Ying Zhi-Feng , Qiu Yuan-xun , Xiong Xia-Xing , Wu Jia-Da , Li Fu-Ming
Published: July 2002

Carbon nitride films have been formed on Si(100) substrates by laser ablation of graphite under a low energy nitrogen ion beam bombardment. Data of Raman shift and x-ray photoelectron spectroscopy indicate the existence of carbon-nitrogen bonds in the films. Time-of-flight measurements suggest the existence of paracyanogen-like materials, such as C4N4, in the films. High energy backscattering spectrometry has shown that the percentage of N content in the film is 41% or so. The x-ray diffraction and transmission electron micrograph measurements have also been taken to characterize the crystal properties of the obtained films. Qualitative tests indicate the films of high Vickers hardness Hv, and of good adhesion to the silicon substrates.
Etching effect on metal-organic molecular-beam epitaxy growth of GaSb using triethylgallium and trisdimethylaminoantimony
Authors: Liu X. F. , Asahi H. , Inoue K. , Marx D. , Asami K. , Miki K. , Gonda S.
Published: July 2002

Metal-organic molecular-beam epitaxy growth of GaSb is investigated for the first time by using the new precursor trisdimethylaminoantimony (TDMASb) together with triethylgallium (TEGa). An etching effect is observed when TDMASb is supplied to the (001) GaSb surface without precracking. The etching rate is dependent on the substrate temperature and TDMASb flow rate, while independent of the TEGa flow rate. GaSb layers can be grown when the TDMASb is precracked in the gas cracker cell. The etching mechanism is discussed in connection with the decomposition process of TDMASb on the surface.
Low-temperature epitaxial growth and photoluminescence characterization of GaN
Authors: Dissanayake A. , Lin J. Y. , Jiang H. X. , Yu Z. J. , Edgar J. H.
Published: July 2002

Epitaxial layers of GaN on sapphire substrates have been grown by metalorganic chemical-vapor deposition at a deposition temperature as low as 400 °C, which is the lowest temperature for successful epitaxial growth of GaN by any technique. This is achieved by controlling the low flow rate of the source gases and by first depositing an AlN buffer layer at 400 °C. Low-temperature photoluminescence measurements have been employed to study the optical properties of the films deposited at different temperatures.
Relaxation and H coverage of ammonium fluoride treated Si(111)
Authors: Copel M. , Culbertson R. J. , Tromp R. M.
Published: July 2002

Using medium energy ion scattering and elastic recoil detection, we have studied silicon surfaces prepared by ex situ NH4F wet etching. We report direct measurements of relaxation and hydrogen coverage of the passivated Si(111)-(1×1) surface. For Si(111), nearly ideal, unreconstructed surfaces are obtained, terminated by a single atomic layer of hydrogen. Silicon backscatter yields agree closely with simulations of a bulk truncation, with an inward relaxation of the outermost layer of 0.075±0.03 Å. On the other hand, Si(001) prepared by NH4F solution shows severe roughening.
Quasibound states in two-dimensional quantum wires
Authors: Wang Jian , Wang Yongjiang , Guo Hong
Published: July 2002

We report detailed studies of quasibound states of a T-shaped two-dimensional quantum wire structure. While in the tunneling regime the peaks of the resonant transmission pattern correspond to quasibound states in the system, in the transmissive regime we show that the reflection peaks correspond to them. Furthermore, there is a one-to-one correspondence in energy and wave function between the quasibound states of the open structure and the bound state of the corresponding closed structure. We show that the quasibound states of the system can be unambiguously identified by the behavior of the electron dwell time.
Resistivity of boron and phosphorus doped polycrystalline Si1−xGex films
Authors: Bang David S. , Cao Min , Wang Albert , Saraswat Krishna C. , King Tsu-Jae
Published: July 2002

Sheet resistance, Hall mobility, and effective carrier concentration as a function of annealing parameters for boron or phosphorus ion implanted films of polycrystalline Si, Si0.75Ge0.25, and Si0.50Ge0.50 films are presented. The films were ion implanted with boron or phosphorus at dosages between 5×1014 and 4×1015 cm−2, and then thermally annealed between 550 and 650 °C from 0.25 to 120 min. Boron doped films showed decreasing minimum sheet resistance with increasing Ge fraction, while phosphorus doped films exhibited the reverse trend. Both boron and phosphorus doped films showed minima as a function of anneal time. This is attributed to the competing processes of damage annealing versus dopant segregation. Poly-Si0.50Ge0.50 films achieved minimum resistance faster than poly-Si films, and the lowest sheet resistances were measured in boron doped, poly-Si0.50Ge0.50 films.
In-plane photocurrent spectroscopy in GaAs-AlAs superlattices
Authors: Schrottke L. , Grahn H. T. , Klann R. , Fujiwara K.
Published: July 2002

The in-plane photoconductivity of GaAs-AlAs superlattices on GaAs substrates is experimentally studied as a function of the incident photon energy at different temperatures and light intensities. Superlattice and substrate are electrically isolated by a thick  Al0.3Ga0.7As barrier but connected through penetrating contacts. Depending on the transport properties of the two subsystems pseudo-negative photoconductivity can be observed, i.e., at the absorption maximum of the superlattice the photocurrent exhibits a minimum.
Construction and novel application of a flat flame burner facility to study hazardous waste combustion
Authors: Senser Dwight W. , Morse John S. , Cundy Vic A.
Published: July 2002

The construction and application of a flat flame facility specifically used in hazardous waste combustion studies are reported. The corrosive nature of the products formed during combustion of organic hazardous wastes requires special consideration in not only the design and selection of materials, but also in maintenance procedures. Sustained operational reliability, accurate measurement capabilities, and minimal human hazards were targeted as principal design considerations. Details are provided regarding the configuration of the laboratory scale burner chamber, the reactant feed systems, and the exhaust handling equipment, along with the probe arrangements used to collect experimental species and temperature data. A unique pumpless feed system capable of both metering and vaporizing liquid hazardous feed stocks is detailed. Special experimental constraints and the procedures followed to overcome these complexities are described. Test data for a dichloromethane/methane/air flame are provided.
TARA data-acquisition and physics analysis system (abstract)
Authors: Sullivan J. D. , Fredian T. W. , Irby J. H. , Karcher C. A. , McVey B. D. , Sevillano E. , Stillerman J.
Published: July 2002

The MIT data-acquisition and physics analysis system was designed to provide high throughput and ready access to data from any run. The system is based on a VAX 11/750 which is to be configured in a VAX cluster back-end network. The front end for the data system is a kinetic system CAMAC serial highway interface. Preexisting software packages have been combined into a coherent system which has required a minimum of new software development. The acquisition, archiving, basic analysis, and display of 1.5 Mbyte of data for every shot is accomplished once every 5–8 minutes with any shot being easily reanalyzed. A set of standard tools is provided for use in user-written programs several of which are incorporated into the production system. The range of interactive analysis options is illustrated by using the medium-energy x-ray diagnostic in one anchor as an example. The resulting physics analysis includes intercomparison with other diagnostics to compute Te, the fraction of hot electrons, and other plasma parameters.
CO2 laser interferometer array for Big Dee
Authors: Fairbanks E. S.
Published: July 2002

A 12 channel interferometer array is planned for obtaining electron density profiles on Big Dee. Each channel consists of coaxial CO2 and HeNe laser beams. The reference beam is formed by splitting off half of the laser power at each wavelength by using acousto-optic modulators which introduce a 40-MHz frequency shift in the reference beam. The detected interference signals from room-temperature visible and IR detectors are mixed with the 40-MHz drive for the acousto-optic cells. The quadrature mixer signals result in phase information due to vibration and phase-velocity variation in the plasma. Simultaneous solution of the two equations describing the phase shift at the two wavelengths yields the phase shift due only to the plasma effects. The arithmetic operations will be performed digitally in real time by a dedicated microprocessor in each channel. The execution speed of the microprocessor is expected to be sufficient for measuring line integral density in the presence of vibrations of 1-mm amplitude at 1 Hz or 10-μm amplitude at 100 Hz. Phase resolution for each channel is 2π/64 and time between samples is 25 μs. Density profiles are derived from chordal line integral density data by computer tomography.
Infrared emission as a diagnostic for a collapsing gas shell Z-pinch (abstract)
Authors: Jones L. A. , Kania D. R. , Shepherd R. L. , Maestas M. D.
Published: July 2002

The shape and absolute intensity of the infrared emission as a function of wavelength can yield information about the conditions in a plasma. This diagnostic technique has been reviewed by Zwicker,1 who gives several examples of its application to low density plasmas. We have applied this diagnostic, for the first time, to a high density (∼1020 cm−3) plasma, a collapsing gas (argon) shell Z pinch. Using a fast Au doped Ge detector and infrared notch filters we have scanned the emitted spectrum from ∼0.5 to 8.2 μm with l-ns time resolution. This spectral range encompasses the optically thin-to-thick transition as well as the plasma frequency at the time of peak compression. We will present this data along with an interpretation which allows us to follow the development of the pinched column during the thermalization stage.
MIRI: A multichannel far-infrared interferometer/polarimeter for TFTR (abstract)
Authors: Park H. , Mansfield D. K. , Johnson L. C. , Ma C. H.
Published: July 2002

A double path multichannel far-infrared interferometer/ polarimeter employing retroreflectors for density and current profile determination has been developed for TFTR. The system containing about 400 optical components is mounted on a 70 000-lb. vibration-free stand which encircles TFTR. Optically pumped cw CH3OH (λ=110 μm, p≂100 mW) twin lasers with a frequency separation of l MHz are employed as a source. Quasioptical Schottky diodes (NEP≂l0−9 W(Hz)1/2) are used as detectors. Considerable efforts are devoted to have remote control capabilities for future D–T operation. The detailed design characteristics of this system together with preliminary results of chord averaged density information will be presented. Also the theoretical aspects of Faraday rotation for TFTR plasma will be discussed.
Development of high power, twin frequency far-infrared lasers for fusion diagnostics (abstract)
Authors: Lehecka T. , Zu Q. X. , Du Z. M. , Dworak R. , Savage R. L. , Peebles W. A. , Luhmann N. C. , Semet A.
Published: July 2002

Recent developments in plasma diagnostics such as multichannel collective scattering and phase imaging dictate the use of high-power, stable radiation sources in the far-infrared (FIR) spectral region. Towards this end, an optically pumped, twin frequency laser has been developed at UCLA. The CO2 pump laser produces greater than 100 W in a single mode over the majority of the CO2 wavelength range (9–11 μm). The twin frequency FIR laser utilizes a single cavity with two separate dielectric waveguides. The difference frequency (λ=185 μm) is tunable from 0–5 MHz with a short-term stability Δf≤±20 kHz. EH11 spatial modes are routinely achieved with output powers of 100 mW.
Fast multichannel electron temperature diagnostic for TFTR using x-ray imaging
Authors: Kiraly J. , Bitter M. , Goeler S. von , Hill K. W. , Johnson L. C. , McGuire K. , Sesnic S. , Sauthoff N. R. , Tenney F. , Young K. M.
Published: July 2002

The TFTR x-ray imaging system (XIS) is an array of 64-Si surface barrier diodes which image the plasma poloidally. Special absorber foils have been installed to permit measurement of electron temperature Te with <100-μs time resolution along 10–30 chords. The technique uses the ratio of x-ray fluxes transmitted through two different foils, which depend mainly on Te. Simulations show that strong line radiation can change this ratio. To correct for these effects, special beryllium–scandium filters are employed to select the line-free region between 2 and 4.5 keV. Separate filter pairs allow correction for strong L line radiation as well as Ti or Ni Kα emission. The Te determination is based on simulations. Comparison of results with Te values from the electron–cyclotron emission and x-ray pulse height analysis diagnostics is presented.
Triton confinement and energy-loss studies with a time-resolved neutron detector (abstract)
Authors: Newman D. E. , Fisher R. K. , Thomas D. M.
Published: July 2002

The expected results are presented for a fast, selective 14-MeV neutron detector which should be capable of separately measuring the confinement and energy loss of fast tritons for the first time. The tritons, from D–D reactions in a deuterium plasma, are observed when they collide with deuterons while slowing down, producing a characteristic 14-MeV neutron. Triton experiments are an excellent test for the confinement of fusion-produced alphas in a self-sustained reactor, which is critically dependent on plasma heating by the alphas. The triton production rate is pulsed by injecting a burst of deuterium using a neutral-beam heating source. The temporal distribution of the 14-MeV neutron flux is determined by the confinement and slowdown rate of the tritons. The expected flux is calculated as a function of time for the predicted triton transport, anomalous particle losses, and anomalous energy-loss rates, thus demonstrating how the various effects can be separately determined.
Rapid measurement of inelastic electron tunneling spectra
Authors: Gajda G. J. , Weinberg W. H.
Published: July 2002

The design and the operation of a rapid (∼10 s), accurate (±1%), moderate resolution (∼50 cm−1) system for measuring inelastic electron tunneling spectra are described. The utility of this system is discussed, and an example of its use is presented.
Electron paramagnetic resonance at high pressure using a diamond anvil cell
Authors: Sakai Nobuko , Pifer Joe H.
Published: July 2002

We have developed an X-band electron resonance apparatus incorporating a diamond anvil cell to generate pressures up to 100 kbar. The system can operate down to 1.5 K and the pressure can be changed and calibrated via ruby fluorescence while at low temperature. The system differs from a conventional EPR cavity system in that the pressure gasket acts as the microwave resonator. For an initial application, the system is used to examine the pressure dependence of the magnetic properties of a chromium chalcogenide spinel, CdCr2Se4.
Laser resonant fluorescence scattering in the Toroidal Cusp Experiment (abstract)
Authors: Gao P. , Rhodes M. , Peebles W. A.
Published: July 2002

A dye laser induced resonant fluorescence scattering system has been installed on the Toroidal Cusp Experiment (TCX) at UCLA. This diagnostic has been employed to perform spatially and temporally resolved measurements of the neutral density and ion temperature. The local volume-average effect is used to decrease the fluctuation level in background radiation, thereby enhancing the signal-to-noise ratio. For Balmer alpha fluorescence measurements, the estimation of the neutral hydrogen density is based on either a coronal model or a time-dependent collisional radiative model depending on plasma parameters. By tuning the laser for broadband operation and using a narrow detection resolution, the ion temperature can be measured. The results are compared with other diagnostics.
Effects of neutron energy spectrum on the efficiency calibration of epithermal neutron detectors
Authors: Nieschmidt E. B. , England A. C. , Hendel H. W. , Hillis D. L. , Isaacson J. A. , Ku L. P. , Tsang F. Y.
Published: July 2002

The 235U epithermal neutron fission detector system at TFTR has been calibrated in situ, using three different neutron sources: 252Cf, a D-D, and a D-T neutron generator. These sources produced a continuous spectrum, a line spectrum at ∼2.5 MeV, and a line spectrum at ∼14 MeV, respectively. The toroidally averaged detection efficiencies are 4.61×10−9 (252Cf), 4.80×10−9 (D-D), and 5.42×10−9 (D-T) counts/neutron for a moderated 1.3-g 235U detector placed ∼4 m from the torus centerline. The effects of (n,2n) and (n,n′γ) reactions are discussed.
Thomson scattering at plasma densities below 1012 cm−3
Authors: Cobble J. A.
Published: July 2002

Major upgrades in the ruby-laser Thomson scattering system on the microwave-driven ELMO Bumpy Torus-Scale plasma have enabled routine and reliable measurements of the electron temperature and density along a plasma radius. Consisting of both signal-to-noise enhancement techniques and refined data handling procedures, these upgrades allow density determinations down to 2×1011 cm−3. Radial profiles of bulk electron parameters are essentially flat across the core plasma. Evidence is presented for a 1011-cm−3 density suprathermal distribution of electrons, which leads to an understanding of contradictory temperature measurements and of energy flow in the plasma.
Viscometer for low frequency, low shear rate measurements
Authors: Berg Robert F. , Moldover Michael R.
Published: July 2002

We describe a torsion-oscillator viscometer whose low frequency (0.5 Hz) and very low shear rate (0.05 s−1) are required for measurements of shear sensitive fluids such as microemulsions, polymer melts and solutions gels, and liquid mixtures near critical points. The viscometer has a resolution of 0.2% when used with liquid samples and a resolution of 0.4% when used with a dense gaseous sample. The viscometer operates under computer control and is compatible with submillikelvin temperature control.
Normal incidence grating spectrometer designed for inverse photoemission studies in the range 10–30 eV
Authors: Johnson P. D. , Hulbert S. L. , Garrett R. F. , Howells M. R.
Published: July 2002

We describe a normal incidence grating spectrometer for use in inverse photoemission studies of surfaces. We show that by operating in a configuration where the source and image are displaced from the Rowland Circle it is possible to construct a useful spectrometer that can be attached to any existing surface science chamber. The device covers the range 10–30 eV in photon energy with a typical energy resolution of 150 meV. Capable of operating with relatively low incident currents, this instrument will be an excellent choice for spin-polarized inverse photoemission experiments.
Directly heated lanthanum hexaboride cathode
Authors: Leung K. N. , Moussa D. , Wilde S. B.
Published: July 2002

A directly heated, cylindrical LaB6 cathode has been tested in a multicusp plasma generator. Magnetic fields generated by the heater and the discharge current are minimized by the special coaxial construction, thus enabling electron emission at very low discharge voltages. At higher discharge voltage, a discharge current greater than 100 A has been obtained from a single cathode unit in a steady-state plasma source operation. When the discharge current exceeds 25 A, the cathode can be operated without any heater current. The emission temperature is maintained just by ion bombardment from the discharge plasma.
Measurements of Faraday rotation in TFTR plasmas
Authors: Ma C. H. , Hutchinson D. P. , Vander Sluis K. L. , Mansfield D. K. , Park H. , Johnson L. C.
Published: July 2002

Recent results of simultaneous measurements of line electron density and poloidal field-induced Faraday rotation on the multichannel far infrared (FIR) interferometer/polarimeter on tokamak fusion test reactor (TFTR) are presented. The procedures and results of the calibration are described in detail. The effects of various errors in the measurement, as well as the problem of cross-coupling laser beams, are studied.
Probabilistic model of x-ray PHA data
Authors: Diesso M. , Hill K. W. , Sesnic S. , von Goeler S.
Published: July 2002

A mathematical model of a single-arm x-ray pulse-height analyzer (PHA) system is developed. Given an assumption on the electron temperature and density profiles, a maximum likelihood technique is applied to calculate the peak electron temperature and enhancement factor of the plasma. This method is currently being used in the analysis of x-ray data from the tokamak fusion test reactor (TFTR); sample results are presented.
Review of tandem-linac projects
Authors: Bollinger Lowell M.
Published: July 2002

The paper is a brief review of superconducting linacs that are of interest for heavy-ion acceleration. Starting with the general features of the tandem-linac accelerator system, the mode of operation of the system is outlined and the main requirements for the tandem, the beam-bunching system, and the superconducting linac are mentioned. Following this introduction, the characteristics of the three tandem-linac systems now operating and the six other under construction are summarized. The technologies of two of these (the Argonne system based on niobium resonators and the Stony Brook system based on lead resonators) are compared, and differences in performance characteristics are related to differences in design choices. Some recent advances in the technologies related to superconducting heavy-ion linacs are summarized, including advances in helium refrigeration, liquid-helium distribution, beam diagnostics, and resonator design and performance. The final major topic of the paper is a brief discussion of the concept of a positive-ion superconducting injector linac being developed at Argonne as a replacement of the present tandem. Several probable applications of this new technology are mentioned. Most of the subject matter covered by the paper was included in another review paper.1 This work was supported by the U. S. Department of Energy, Nuclear Physics Division, under contract No. W-31-109-ENG-38.
Domain structures in magnetoresistive granular metals
Authors: Gavrin A. , Kelley M. H. , Xiao John Q. , Chien C. L.
Published: July 2002

We have imaged the magnetic domain structure of several heterogeneous CoxAg1−x alloys by using scanning electron microscopy with polarization analysis. These images show that extended domain structures exist in both the as-deposited samples and in samples annealed at moderate temperatures. This suggests that a significant fraction of the cobalt in these materials does not contribute to the giant magnetoresistance. Only those samples annealed at 600 °C and containing less than 40% cobalt by volume show no domain structure.
Interface between an oscilloscope and a multichannel analyzer
Authors: Weber P. M. , Smith D.
Published: July 2002

We describe a simple device for interfacing an oscilloscope with a sawtooth output to a multichannel analyzer. The apparatus works for low scan rates only (ms range), a limitation given by the timing requirement of the MCA.
Device to extrude indium wires
Authors: Ece M. , DeVito R. , Vidali G.
Published: July 2002

A homemade, versatile, low-cost device to extrude indium wire for vacuum seals is described. It has the advantage that no boule of indium has to be made in advance, thereby reducing the amount of poisonous indium vapors, and that wires of different sizes can be made.
Anisotropic pantograph
Authors: Houtman H.
Published: July 2002

A new scaling linkage is presented which allows arbitrary magnification or reduction of curves and drawings in the y direction while leaving dimensions in the x direction unchanged. The anisotropic pantograph represents a significant simplification over previously reported devices capable of this operation. Magnifications My in the range 1.05–80.0 and reductions Ry in the range 0.0125–0.95 are obtained using a single operation, and the tracking accuracy is <±150 μm. With the aid of a circle template or flat compass, the device may be used to draw arbitrary ellipses. A method for effecting arbitrary shears, and various methods for arbitrary scaling in two orthogonal directions are outlined.
Automated device for analyzing drug release kinetics from colloidal particles
Authors: Scholsky Kevin M. , Warner Robert J.
Published: July 2002

An automated device for determination of the kinetics of drug delivery from colloidal latex particles is described. The system utilizes ultrafiltration and spectrophotometric techniques simultaneously, allowing rapid, in situ, drug release profiles to be obtained without need for removal of the dispersed phase. The device has been used successfully in our laboratory for numerous drug delivery experiments.
Acousto-optic spectrum analyzer for plasma diagnostics
Authors: Irby J. H. , Beals D.
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 MIT. The AOS is an analog 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 and a resolution of 1 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 spectra 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.
Wave-vector imaging photoelectron spectrometer
Authors: Clarke A. , Jennings G. , Willis R. F.
Published: July 2002

We have developed an imaging photoelectron spectrometer based on a simple electrostatic immersion lens with the capability of measuring photoemission intensity as a function of the parallel component of electron wave vector throughout the Brillouin zone. The image is a simple rectilinear mapping of the k∥ component of the wave vector in reciprocal space. Using a retarding field-energy selection system, it is possible to energy select and image the various states below the Fermi energy. We obtain an energy resolution of 0.3 eV and a k∥ resolution of 0.04 Å−1. The distribution of photocurrent is amplified onto a phosphor screen by a channel electron multiplier array. The image on the screen is then picked up with a charge-coupled device (CCD) camera so that the digitized image can be both position and energy analyzed. The performance of the system is demonstrated by imaging the photoelectron distribution from a Cu(001) single crystal. We find that the intensity distribution of emission in k space reflects the dispersion of the projected bulk energy band structure.
Realization of an electron spectrometer using a toroidal magnetic deflector
Authors: Lévêque G. , Robin J.
Published: July 2002

We present some aspects of the realization of a new angular resolved photoemission spectrometer using a magnetic deflector. The photoelectrons are dispersed according to their energy and emission angle and focused onto a detector where the band structure appears in real time. The prototype has been realized around a toroidal magnetic field optimized by computer simulation. We discuss here the energy and the angle resolution of the whole system, related to some compromises in the technical realization as the field limit effects. The main result is that we obtain a complete display of the valence-band structure (in a plane) with a classical light source in an integration time of 10 s, which is shorter than the time needed by a classical spectrometer by several orders of magnitude.