bluuebunny/crossref_metadata_2025 huggingface dataset:
Visible light emission from quantized planar Ge structures
Authors: Venkatasubramanian R. , Malta D. P. , Timmons M. L. , Hutchby J. A.
Published: July 2002

Visible photoluminescence has been observed near 1.9 eV at 300 K from quantized planar Ge structures. This is the first observation of luminescence in Ge and is similar to the recently reported luminescence from porous Si. The quantum structures are prepared from bulk Ge substrates, and both n- and p-type Ge produce luminescence at room temperature. These structures are fabricated by plasma-assisted etching using a CF4/O2 gas mixture.
Engineering of ultrathin barriers in high T
C, trilayer Josephson junctions
Authors: Klausmeier-Brown M. E. , Virshup G. F. , Bozovic I. , Eckstein J. N. , Ralls K. S.
Published: July 2002

Josephson junctions with ultrathin (25–40 Å) barriers were fabricated using high TC, trilayer films grown by atomic layer-by-layer molecular beam epitaxy (ALL-MBE). The films consisted of top and bottom electrodes of Bi2Sr2CaCu2O8, separated by a single molecular layer of a metastable compound, Bi2Sr2(Ca, Sr, Bi, Dy)n−1CunO2n+4, with n=5 to 11. Systematic variation of Bi or Dy doping on Ca sites in the barrier layer provided four orders of magnitude of tuning of both the junction critical current and the normal state resistance, while keeping their product approximately constant, near 0.5 mV. Barrier and junction engineering, on an atomic length scale, has been demonstrated for the first time.
Electron-phonon decoupling in the photoresponse of YBaCuO granular films at low temperature
Authors: Maneval J.-P. , Chibane F. , Bland R. W.
Published: July 2002

Granular YBaCuO films in their current-induced dissipative state were exposed to light pulses of small fluence and the decay of the photoresistance was observed on the nanosecond time scale in the range 1 K<T<35 K. The response appears bolometric down to 10 K. Below, we resolve a second decay rate having a temperature dependence characteristic of the electron-phonon interaction. Using the known lattice specific heat as a reference, we deduce the Sommerfeld coefficient (γ=2.5 mJ/K2 mol) of the electronic specific heat.
Adhesion studies of Cu-Cr alloys on Al2O3
Authors: Chan Chin-Jong , Chang Chin-An , Farrell Curtis E. , Schrott Alex G.
Published: July 2002

Adhesion of Cu-Cr alloys to c-axis sapphire wafers has been studied. A large increase in peel strength was observed when the Cr content exceeded 15 at. % for the as-deposited alloy films. The high measured peel strength can be attributed to Cr that segregates to the sapphire-alloy interface due to its high free energy in the metastable alloy structure. Heat treatment was found to greatly enhance the adhesion of low Cr containing (15 at. %) Cu-Cr alloys to c-axis sapphire. Cr was found to segregate to the sapphire-alloy interface or separate as spherical precipitates in the Cu matrix upon appropriate thermal treatment. Increase in peel strength between sapphire and the low Cr alloy interface was observed at annealing temperatures as low as 200 °C.
Time resolved 3.10 eV luminescence in germanium-doped silica glass
Authors: Gallagher Matt , Österberg Ulf
Published: July 2002

In this letter we present time resolved measurements of the 3.10 eV (400 nm) photoluminescence in germainum-doped silica. The 3.10 eV band arises from a triplet to singlet transition in a GeO defect. We find that the photoluminescence decays with a time constant of around 100 μs. There is a delay roughly 10 μs in duration between excitation and the appearance of maximum photoluminescence intensity. This is evidence that an additional energy state contributes to the radiative decay of the triplet state. This state can exist within the same defect or it can exist in another defect and transfer energy to the GeO.
Electrical properties and poling of BaTiO3 thin films
Authors: Lu H. A. , Wills L. A. , Wessels B. W.
Published: July 2002

Dielectric and ferroelectric properties were measured for both highly a-axis textured and randomly oriented BaTiO3 thin films deposited on Pt coated MgO substrates via metal-organic chemical-vapor deposition. Dielectric constants on the order of ε∼10 and an absence of ferroelectric hysteresis were generally observed for the as-deposited films. Upon applying an electric field exceeding a threshold value of ∼50–100 kV/cm across the film, both the dielectric constant and the ferroelectric hystersis were enhanced significantly as a result of poling. The dielectric constant increased to ε∼100, and the spontaneous polarization of the a-axis textured film reached Ps≥15 μC/cm2. The measured dielectric and ferroelectric properties of the BaTiO3 thin films depended on the microstructure of the films.
Cholesteric reflective display: Drive scheme and contrast
Authors: Yang D. K. , Doane J. W. , Yaniv Z. , Glasser J.
Published: July 2002

We studied the electro-optical response of a bistable cholesteric texture (BCT) display to ac voltage pulses. The material can be driven into states where planar and focal conic textures coexist at zero field and gray scale memory is achieved. According to the properties of the BCT display we designed two drive schemes; one for binary operation and the other for gray scale operation. We made a 320×320 pixel reflective display with a resolution of 80 lines/in. on a passive matrix. Measurement in an integration chamber showed that the display has higher contrast and better viewing angle than a reflective super twisted nematic display.
Limitation due to three-photon absorption on the useful spectral range for nonlinear optics in AlGaAs below half band gap
Authors: Kang Jin U. , Villeneuve Alain , Sheik-Bahae Mansoor , Stegeman George I. , Al-hemyari Kadhair , Aitchison J. Stewart , Ironside Charles N.
Published: July 2002

We report measurements of the spectral dispersion and the magnitude of three-photon absorption in Al0.18Ga0.82As for photon energies between one half and one third the band gap and show that a two-parabolic-band model is valid in this material. These results indicate that there is a limited spectral range below half the band gap in AlGaAs (and presumably all semiconductors) in which the bound electronic optical nonlinearity can be used without significant multiphoton absorption.
Correlation between the band gap of semiconductors and thermal activation parameters of plasticity
Authors: Siethoff H.
Published: July 2002

Two characteristic activation energies of the plasticity of semiconductors depend on the minimum band gap: the kink energy deduced from the lower yield point and the diffusion energy derived from the first recovery stage of stress-strain curves. There is a clear distinction between the elemental semiconductors Si and Ge and the III-V compounds. In addition, both activation energies are correlated only differing by a constant factor. The results corroborate a former conclusion, that an elementary diffusion step might be involved in the process of kink formation and migration.
Molecular design of hole transport materials for obtaining high durability in organic electroluminescent diodes
Authors: Adachi Chihaya , Nagai Kazukiyo , Tamoto Nozomu
Published: July 2002

The molecular design of hole transport materials (HTMs) for producing high durability in organic layered electroluminescent (EL) diodes was elucidated. The durability tests were examined using fourteen hole transport materials in the cell structure of an anode/hole transport layer (HTL)/emitter layer (EML)/cathode. The ionization potential (Ip) of HTLs was found to be the dominant factor for obtaining high durability in organic EL devices. The formation of the small energy barrier at the interface of a HTL/anode was required for high durability. Moreover, no straightforward relations between melting point, glass transition temperature of the HTMs, and durability of the EL devices were observed. The EL device using the HTM having a low Ip (5.08 eV) showed an especially remarkable stability. In this case, the half-life period of the initial luminance was beyond 500 h.
Electron and hole mobility in tris(8-hydroxyquinolinolato-N1,O8) aluminum
Authors: Kepler R. G. , Beeson P. M. , Jacobs S. J. , Anderson R. A. , Sinclair M. B. , Valencia V. S. , Cahill P. A.
Published: July 2002

We have measured the drift mobility of electrons and holes in thin, vapor-deposited films of tris(8-hydroxyquinolinolato-N1,O8) aluminum using a time of flight photoconductivity technique. The drift of mobility of both carriers is dispersive and strongly electric field and temperature dependent. At ambient temperature and an electric field of 4×105 V cm−1, the effective mobility of electrons and holes is 1.4×10−6 and 2×10−8 cm2 V−1 s−1, respectively, in a 400 nm thick sample.
X-ray characterization of extremely high quality (Sr,Ba)TiO3 films grown by pulsed laser deposition
Authors: Qadri S. B. , Horwitz J. S. , Chrisey D. B. , Auyeung R. C. Y. , Grabowski K. S.
Published: July 2002

Thin films of Sr0.5Ba0.5TiO3 have been grown on MgO (100), SrTiO3 (100), and LaAlO3 (012) substrates using pulsed laser deposition. These films were characterized by a variety of x-ray diffraction techniques. Deposited films exhibited true single crystal morphology. X-ray rocking curves for the (002) reflection as measured by double and triple crystal spectrometers showed unusually narrow full width at half-maximum (FWHM) values of 72 arcsec for films grown on LaAlO3, and 140 arcsec for films deposited onto SrTiO3. The FWHM for films deposited on MgO were significantly broader (∼2500 arcsec). While the quality of the epitaxial films is related to the lattice mismatch between the film and the substrate, extremely well aligned films can be grown on substrates with a relatively large lattice mismatch.
Effect of ion speed distribution on the spectral shape of the 2.5-MeV neutron line produced by DD fusion
Authors: Slaughter Dennis
Published: July 2002

Ion mean energy may be determined from Doppler broadening of the 2.5-MeV neutron line in Maxwellian deuterium plasma. Since many plasmas are non-Maxwellian a Monte-Carlo simulation has been used to predict the spectral shape produced by a variety of simple speed distributions with mean energies in the range 1–100 keV. In the case of isotropic ions considered here, the results are Gaussian to high order and their width varies as the square root of the mean ion energy. However, the linewidth varies substantially among different ion speed distributions with the same mean energy. The similarity in shape of these spectra prevent the determination of the speed distribution type from detailed measurements of the neutron spectrum, unlike the situation where co-counter beams produce anisotropic ion distributions.
Two-color interferometry for fusion plasma diagnostics
Authors: Lehecka T. , Peebles W. A. , Luhmann N. C. , Carlstrom T. N.
Published: July 2002

Radial view interferometers on large fusion devices have experienced difficulty in compensating for large vibration-induced phase shifts. This compensation has previously been achieved using common path visible or near infrared interferometers. However, the high rate of phase change observed by the compensation interferometer combined with deterioration of reflecting surfaces located close to the harsh plasma environment limit the resolution and usefulness of such systems. This article describes laboratory tests of a vibration-compensating interferometer that operates at two wavelengths of the CO2 laser: 9.2 and 10.6 μm. It is particularly well suited for application to CIT or other devices with either high density or large plasma dimensions.
Measurement of contact placement errors in the van der Pauw technique
Authors: Koon Daniel W. , Bahl Arshad A. , Duncan Edward O.
Published: July 2002

Van der Pauw resistivity measurements were performed on samples of six different shapes: circle, square, two circular cloverleafs, and two square cloverleafs, and the measurement error of the resistivity due to contact displacement was determined. Earlier predictions for this error were verified for the circle and square, and two circular cloverleafs, although significant higher-order corrections were found in all cases except the square. The three square shapes gave contact placement errors typically 10–100 times smaller than the errors in the corresponding circular shapes. All cloverleafs gave smaller errors than the corresponding nonclovered shapes, although this difference disappeared in the limit of large contact displacement.
Spiral growth of GaSb on (001) GaAs using molecular beam epitaxy
Authors: Brar Berinder , Leonard Devin
Published: July 2002

Atomic force microscopy is employed to obtain images of the surface of GaSb epilayers grown on (001) GaAs using molecular beam epitaxy. The images reveal a surface that consists of micron size mounds that are approximately 4 nm high. A stepped surface is clearly observed on the mounds with a single step edge that originates from a screw dislocation at the center of the mound and moves out to the edge in a spiral fashion. The surface structure of the spiral mounds is observed to depend on the growth temperature of the GaSb epilayer, presumably as a result of a shorter diffusion length of the group III adatoms for lower substrate temperatures.
Cross-sectional scanning tunneling microscopy study of GaAs/AlAs short period superlattices: The influence of growth interrupt on the interfacial structure
Authors: Smith A. R. , Chao Kuo-Jen , Shih C. K. , Shih Y. C. , Streetman B. G.
Published: July 2002

We report studies of GaAs/AlAs short period superlattices using cross-sectional scanning tunneling microscopy. In particular, we investigate the role of growth interrupt time on the resulting interfacial structure. Superlattices with repeated periods of four layers of GaAs and two layers of AlAs are resolved atom by atom. Superlattices grown using a 30 s growth interrupt time are observed while those grown with a 5 s growth interrupt time are not. We also discuss residual effects of the growth interrupt process on layers grown on top of the short-period superlattice.
Control of ionization in e-beam evaporators via optimum choice of focus-coil current
Authors: Bhatia M. S. , Patel K. , Joshi A. , Chatterjee U. K.
Published: July 2002

e-beam evaporation is accompanied by production of a significant ionic component, which is a result of interaction of electrons with residual gas atoms as well as vapor atoms. In this study we show that the interaction of primary beam electrons with vapor atoms can be controlled to a certain extent by choosing the correct magnetic lens current. This technique can be used to reduce or enhance the extent of ionization depending upon the application.
Electrodeposition of rhenium on tungsten hot plate used in Q plasma source
Authors: Paris P. J.
Published: July 2002

The brief note describes diverse aspects of the technique used for rhenium plating the hot plate used for contact ionization of barium in a Q plasma source. The rhenium plating optimizes the probability of barium ionization. Special care has to be taken in order to deposit a uniform layer of rhenium, for this purpose a slow rotation is given to the plate during deposition.
High-resolution VUV absorption spectroscopy with the 6-VOPE facility (invited)
Authors: Ito Kenji , Namioka Takeshi
Published: July 2002

A high-resolution VUV spectroscopic facility, called 6-VOPE, which consists of a 6.65-m vertical dispersion off-plane Eagle spectrometer and a zero-dispersion-type tandem concave grating predisperser system, was designed and installed at the Photon Factory. This facility attained a resolving power of >2.5×105 at ∼79 nm in the photographic detection mode and >1.5×105 at ∼88 nm in the photoelectric detection mode—the highest resolving power ever demonstrated, in both detection modes, for this spectral region. The nature and the level of the focused stray light in the 6-VOPE facility is discussed. Some examples of absorption spectra are presented to show the capability of the 6-VOPE facility.
Ion sources at the Novosibirsk Institute of Nuclear Physics (invited)
Authors: Belchenko Yu. I. , Davydenko V. I. , Derevyankin G. E. , Dimov G. I. , Dudnikov V. G. , Morosov I. I. , Roslyakov G. V. , Schabalin A. L.
Published: July 2002

A review of investigations in the physics and technology of ion sources, developed in the Institute of Nuclear Physics in Novosibirsk is presented. Distinctive features of physical processes and technical characteristics of plasma sources of gaseous ions, negative ion surface-plasma sources, electrohydrodynamic (liquid metal) ion sources are considered. In original design plasma sources, ion beams with a current of up to 90 A and energies 1–30 keV are formed by four-electrode multislit extraction systems from highly ionized, high brightness plasma flux, generated by an high-current arc discharge with a cold cathode in a small cross-section diaphragmed channel, and directed with a magnetic field of a special configuration. Plasma jet expansion for a very low ion temperature (0.1 eV) production is used. In surface plasma sources, the fluxes of negative ions are produced when electrons are captured from the electrode surface at the electron affinity level of sputtered and reflected particles. A discharge of a special type in a gas-cesium mixture with in a thin plasma layer between the negative ion emitter and emission holes is used. A number of versions of SPS with different types of discharges are considered: SPS which operate in pulse mode with H− beam current up to 11 A, with current 0.1 A, and high brightness for accelerators, for continuous mode operation. Specific features of physical processes in electrohydrodynamic (EHD) ion emitters are studied and the technology of production of different ions is worked out. The production of ion beams with high brightness from the dielectric melt in the EHD-emission regime is developed. The dynamics of spontaneous oscillation excitation with a quasidiscrete spectrum in the frequency range of up to 108 Hz, transient processes occurring at the emission disturbances, emission stability at low current, a physical model for calculating the emission surface dimensions, and the evolution of the ion momentum distribution function for the ion motion are studied. The utilization of the designed EHD sources in the ion microscope, in submicromachining and in high voltage accelerators are discussed.
A simple artificial light system for solar simulated irradiation of polymeric materials
Authors: Foyle V. P. , Guillet J. E.
Published: July 2002

A simple, inexpensive device for artificial simulation of sunlight is described. The illumination system is composed of a 275-W sunlamp and a 500-W mercury discharge/tungsten filament industrial lamp. The device has a fan for cooling and a motorized turntable for uniform sample irradiation. Calibration of the intensity in the 300–400-nm region of the ultraviolet by three actinometric systems showed that a 13-h exposure in the simulator was comparable to a 1-day exposure to Toronto summer sunshine.
Luminescent barometry in wind tunnels
Authors: Kavandi Janet , Callis James , Gouterman Martin , Khalil Gamal , Wright Daniel , Green Edmond , Burns David , McLachlan Blair
Published: July 2002

A flexible and relatively inexpensive method and apparatus are described for continuous pressure mapping of aerodynamic surfaces using photoluminescence and imaging techniques. Platinum octaethylporphyrin (PtOEP) has a phosphorescence known to be quenched by oxygen. When dissolved in a silicone matrix, PtOEP may be distributed over a surface as a thin, uniform film. When the film is irradiated with ultraviolet light, the luminescence intensity provides a readily detectable, qualitative surface flow visualization. Moreover, since the luminescence intensity is found to be inversely proportional to the partial pressure of oxygen, a quantitative measure of pressure change may be obtained using a silicon target vidicon or a charge-coupled device video sensor to measure intensity. Luminescent images are captured by a commercial frame buffer board. Images taken in wind tunnels during airflow are ratioed to images taken under ambient ‘‘wind-off’’ conditions. The resulting intensity ratio information is converted to pressure using calibration curves of I0/I vs p/p0, where I0 is the intensity at ambient pressure p0 and I is the intensity at any other pressure p. The result is a two-dimensional static pressure plot for the surface of interest. It is shown that the pressure plots predicted by luminescence intensity compare favorably with pressure plots made by conventional pressure measuring devices.
Recent developments in microwave reflectometry at JET (invited)
Authors: Costley A. E. , Cripwell P. , Prentice R. , Sips A. C. C.
Published: July 2002

The latest developments in microwave reflectometry work at JET are described. A multichannel reflectometer system which can measure either the spatial profile of the electron density, or the propagation of rapid density perturbations, is described and some illustrative results are presented. The possible use of reflectometry as a technique for determining the total internal magnetic field is discussed and the results of an experiment to test the basis of this method are presented. Finally, a new technique, correlation reflectometry, which has been developed specifically for studying density fluctuations is described and some preliminary results are presented.
Errors caused by baseline offset and noise in the estimation of exponential lifetimes
Authors: Dowell L. J. , Gillies G. T.
Published: July 2002

We have investigated errors and their sources in exponential-parameter estimation. This investigation was part of ongoing research in thermal metrology using the temperature-dependent fluorescence lifetime of rare-earth-doped ceramic phosphors. We have found that noise and baseline offset are the dominant sources of error in our experiments. In this note, we present the dependence of errors in exponential-lifetime estimates upon baseline offset and noise, as determined by the Monte Carlo simulation of Marquardt least-squared-error algorithms. These simulation results are validated by a Kullback–Leibler stochastic-distance model. We also demonstrate the necessity of estimating the baseline for accurate lifetime estimation.
A new design for a multitechnique ultrahigh vacuum surface analysis chamber with high pressure capabilities
Authors: Campbell R. A. , Goodman D. W.
Published: July 2002

An ultrahigh vacuum (UHV) surface analysis chamber coupled with a high pressure cell (HPC) is described. The UHV chamber has been designed using an octagonal format to utilize several surface analytical techniques. In addition, the single-level surface analysis chamber design allows simple access to the HPC for carrying out kinetic studies at elevated pressures (≳1 atmosphere) with in situ transfer from the UHV chamber. The UHV-compatible HPC has been designed to facilitate the exchange of the sample or repair of the sample holder while maintaining the analysis chamber at UHV conditions.
Laminated gaskets for absorption and electrical measurements in the diamond anvil cell
Authors: Leong D. , Feyrit H. , Prins A. D. , Wilkinson V. A. , Homewood K. P. , Dunstan D. J.
Published: July 2002

We have developed gaskets laminated from two layers of steel both for optical absorption and for electrical measurements in the diamond anvil cell. For absorption, these gaskets provide masking around the sample, avoiding the need for imaging of the gasket hole. For electrical measurements, laminated gaskets avoid the need for specially prepared diamonds as the feedthrough wires are not in contact with the anvils. Using argon as a pressure medium, both techniques have been used up to about 50 kbar at 300 and at 10 K.
Relaxed Si0.7Ge0.3 buffer layers for high-mobility devices
Authors: Mooney P. M. , Jordan-Sweet J. L. , Ismail K. , Chu J. O. , Feenstra R. M. , LeGoues F. K.
Published: July 2002

The minimum epitaxial layer thickness required to produce relaxed, thermally stable, Si0.7Ge0.3 buffer layer structures for high electron- and hole-mobility devices has been determined, using high resolution x-ray diffraction. A 1.4-μm-thick layer, step graded to x=0.35, is sufficiently thick so that the residual strain in a uniform composition Si0.33Ge0.67 layer grown on top of it is essentially independent of thickness or growth temperature of the layer. Such structures are stable when annealed at 750 °C.
Asymmetrically cut crystals for synchrotron radiation monochromators
Authors: Sánchez del Río M. , Cerrina F.
Published: July 2002

Asymmetrically cut crystals are interesting for use in synchrotron radiation monochromators because of their good energy resolution characteristics and their focusing properties. Ray tracing codes, such as SHADOW, are very efficient in the design and development of new optical devices. In order to determine the convenience of using asymmetrically cut crystals for x-ray monochromators, SHADOW has been extended to include these kinds of crystals. The physical approach to ray tracing asymmetrically cut crystals is based on the coexistence of two periodic structures. One of these is the bulk periodic structure of the Bragg planes. Such a structure determines the existence of a rocking curve near the Bragg condition, and is implemented in SHADOW following the Darwin–Prins formalism of the dynamical theory of diffraction. The second periodic structure is a one-dimensional grating on the crystal surface, formed by the truncation of the lattice planes with the surface. This grating is responsible for the focusing properties of these crystals and plays an essential role in determining the trajectory of the rays. The combination of an asymmetric crystal and a nonplanar surface can be easily achieved by bending (Johann case) to provide improved properties. More complex cases such as the ground-bent crystals (i.e., Johansson geometry) can be considered as a particular case of asymmetrical crystals in which the angle between the Bragg planes and the surface change along the crystal surface. All these cases have been implemented in SHADOW.
Optimization of the perturbation signal for electrochemical impedance spectroscopy in the time domain
Authors: Popkirov G. S. , Schindler R. N.
Published: July 2002

The choice of the perturbation wave form is of crucial importance for reliable electrochemical impedance spectroscopy measurements based on the fast Fourier transformation. Using numerical simulation, arguments and results are presented for the choice and the optimization of a perturbation signal constructed as a superposition of discrete sine waves with selected frequencies. Two possible ways to optimize the perturbation for better noise immunity are described: choosing proper values for the phases of the individual sine waves, minimal perturbation signal amplitudes can be obtained which improve the quality of impedance data by 25%. By introducing response-sensitive amplitudes an improvement in the quality of data by a factor of 4–5 can be reached in the low frequency range. A new technique for single-pulse measurements with continuous perturbations that assures a steady-state response and better accuracy at high capacitive and/or inductive samples is also described.
Tip sharpening by normal and reverse electrochemical etching
Authors: Fotino Mircea
Published: July 2002

This article deals with the characteristics and formation by electrochemical etching under ac voltage of very sharp metal tips usable in several applications and in particular in scanning probe microscopy [scanning tunneling microscopy (STM) and atomic force microscopy]. An exhaustive survey of other existing mechanical and physicochemical procedures for producing sharp tips is also included for background comparison. Because tip sharpness is central to the atomic or near-atomic resolution attainable by STM, yet appears to be so far incompletely studied or documented in the literature, it is argued that high-resolution evidence is required for proper tip characterization as a prerequisite toward adequate performance in the nanometer range. Although atomic-resolution imaging of two-dimensional (flat) surfaces by STM has been possible with tips of ill defined or large apex radii, comparable performance on three-dimensional (rough) surfaces requires the use of tips with sleek shanks and apex radii smaller than or at least commensurate with the desired resolution. The central role played in electrochemical etching under ac voltage by bubble dynamics in shaping the tip apex is analyzed. Experimental results embodied in high-magnification micrographs obtained by high-resolution transmission electron microscopy are presented to illustrate both the intrinsic limitation imposed by large apex radii usually obtained by electrochemical etching in normal configuration (tip oriented downward) and the greatly enhanced sharpening action of the reverse configuration (tip oriented upward) that produces ultrasharp tips of nanometer and subnanometer apex dimensions (nanotips).
Optical trapping and fluorescence detection in laminar flow streams
Authors: Wang W. , Liu Y. , Sonek G. J. , Berns M. W. , Keller R. A.
Published: July 2002

An optical laser trap with fluorescence excitation/emission capability has been integrated in a flow cytometric geometry for the study of microparticle confinement and off-axis fluorescence detection in laminar flow streams. Measurements of particle escape velocity, trapping efficiency, and fluorescence intensity are presented for 2 μm diameter dye-tagged latex microspheres in laminar flow streams having velocities of up to 12 mm/s. Experimental results are compared with theoretical values for flow velocity and fluorescence intensity and found to be in excellent agreement.
Generation of a large diameter intense relativistic electron beam for the triaxial relativistic klystron amplifier
Authors: Friedman M. , Serlin V.
Published: July 2002

We built and tested a new electron beam generator that is capable of generating a 66 cm diameter annular intense relativistic electron beam of energy of 450 keV and current of 60 kA. The new generator incorporates a coaxial-to-triaxial mode converter which allows us to generate and (in the future) to propagate the electron beam between two coaxially grounded conductors. We designed the beam transport system to minimize the axial magnetic energy needed to confine the electron beam. An even lower impedance device can be built by scaling up the size, generating a higher electron beam current. This beam geometry (sheet beam) is useful for efficient generation of high power microwaves.
Position control system for suspended masses in laser interferometer gravitational wave detectors
Authors: Winterflood J. , Blair D. G. , Schilling R. , Notcutt M.
Published: July 2002

We review and present an analysis of the major issues in the design of test mass control systems for laser interferometer gravitational wave detectors. Based on this analysis, we present a design for a computer controlled modular analog servo control system which is well suited to the control of a large number of degrees of freedom in long baseline instruments. The system has been tested on an interferometer using multistage cantilever spring isolators. The system enables simple monitoring, testing, and display of many channels simultaneously, while retaining the advantages of analog proportional-integral-derivative control electronics.
Correction for nonlinear behavior of piezoelectric tube scanners used in scanning tunneling and atomic force microscopy
Authors: Akila J. , Wadhwa S. S.
Published: July 2002

The piezoelectric tube scanners used in tunneling microscopy show nonlinear displacements in x, y, and z directions with applied voltage. A software technique to correct for this nonlinear behavior in x and y directions is proposed. The method calculates the voltages to be applied to the x and y quadrants of the piezotube during the scan, taking into consideration the variations of the x/y piezosensitivity with voltage. The technique is of importance in scans performed over large areas, typically in the micrometer range, where nonlinear behavior of the tube scanner causes distortions in the images obtained.
Production and optical properties of an unscreened but localized magnetic field
Authors: Read F. H. , Channing J. M.
Published: July 2002

A technique is described of using current carrying coils to produce a magnetic field that is well localized, falling off quickly with distance. The basis of the technique is that the first four magnetic multipole moments of the system are arranged to be zero. The deflection and electron optical properties of this type of field are then investigated. It is shown that a beam that initially converges to a point on the axis of symmetry of the field will be deflected in such a way that it still passes through the axis. Similarly, a beam originating at the axis will be asymptotically radial but with a changed direction.
Evanescent wave cavity ring-down spectroscopy with a total-internal-reflection minicavity
Authors: Pipino Andrew C. R. , Hudgens Jeffrey W. , Huie Robert E.
Published: July 2002

A miniature-cavity realization of the cavity ring-down concept, which permits extension of the technique to spectroscopy of surfaces, thin films, liquids, and, potentially, solids, is explored using a wave-optics model. The novel spectrometer design incorporates a monolithic, total-internal-reflection-ring cavity of regular polygonal geometry with at least one convex facet to induce stability. Evanescent waves generated by total-internal reflection probe absorption by matter in the vicinity of the cavity. Optical radiation enters or exits the resonator by photon tunneling, which permits precise control of input and output coupling. The broadband nature of total-internal reflection circumvents the narrow bandwidth restriction imposed by dielectric mirrors in conventional gas-phase cavity ring-down spectroscopy. Following a general discussion of design criteria, calculations are presented for square and octagonal cavity geometries that quantify intrinsic losses and reveal an optimal cavity size for each geometry. Calculated absorption spectra for the NO3 radical from 450 to 750 nm in a nitric acid solution are presented to demonstrate bandwidth and sensitivity.
Evaluation of thermal evaporation conditions used in coating aluminum on near-field fiber-optic probes
Authors: Hollars Christopher W. , Dunn Robert C.
Published: July 2002

The effects that the thermal evaporation conditions have on the roughness of aluminum-coated near-field fiber-optic probes were investigated using the high-resolution capabilities of atomic force microscopy. The coating conditions studied include the effects of background gas composition, base vacuum pressure, and aluminum evaporation rate. The effects of aging on the aluminum-coated tips were also evaluated. The results from topography measurements of the resulting aluminum film indicated that the most dramatic improvements in the tip coatings can be achieved using high aluminum evaporation rates at base vacuum pressures below 10−5 Torr. These results agree with other studies on thin aluminum films and reflect a decrease in oxide formation. For demanding applications of near-field microscopy requiring maximal resolution, the results presented here indicate that it may also be necessary to reduce oxygen and/or water from the vacuum chamber prior to coating.
Ion energy and mass analyzer at radio frequency electrode in a plasma chamber
Authors: Mizutani Naoki , Nagata Yasushi , Kubo Akira , Hayashi Toshio
Published: July 2002

There are two modes for ion energy analysis at a rf electrode in a plasma chamber. One is a dc mode in which the electric potential of the ion energy analyzer is constant in time, and another is a rf mode in which the electric potential of the analyzer oscillates with same frequency, amplitude, and phase as that of the rf electrode. For correct ion energy analysis at the rf electrode, the rf mode is necessary. For ion mass analysis in the rf mode, the electric potential of the ion mass analyzer also must oscillate. We fabricated such an ion energy and mass analyzer, and confirmed its performance.
Chemical vapor deposition diamond window for high-power and long pulse millimeter wave transmission
Authors: Kasugai A. , Sakamoto K. , Takahashi K. , Tsuneoka M. , Kariya T. , Imai T. , Braz O. , Thumm M. , Brandon J. R. , Sussman R. S. , Beale A. , Ballington D. C.
Published: July 2002

To satisfy the electrical and thermomechanical requirements for a continuous wave millimeter wave beam transmission, a window assembly using a large size synthesized diamond disk has been developed. Such window systems are needed as a vacuum barrier and tritium shielding in future electron cyclotron heating systems for fusion plasma heating and noninductive electron cyclotron current drive. The diamond used in this study was manufactured by chemical vapor deposition (CVD) and consists of a polycrystalline diamond disk 96 mm in diameter and 2.23 mm thick. The disk was built into an assembly in which two Inconel tubes were bonded on both sides of the plate to provide vacuum shielding and water cooling to the edge of the disk, leaving an effective window aperture of 83 mm. It will be shown that, as a result of the high thermal conductivity and low dielectric loss exhibited by this grade of CVD diamond, the temperature increase of the window due to the absorption of high-power millimeter wave radiation could be minimized by simple water edge cooling at room temperature. During transmission of a focused Gaussian beam of 170 GHz, 110 kW, 10 s, the temperature increase at the center of the window reached a steady state condition at a value of approximately 40 K, in good agreement with calculated values. Water-edge-cooled CVD diamond windows promise to provide a practical technical solution for the transmission of continuous millimeter wave transmission in excess of 1 MW.
A sensitive and versatile torque magnetometer for use in high magnetic fields
Authors: Wiegers S. A. J. , van Steenbergen A. S. , Jeuken M. E. , Bravin M. , Wolf P. E. , Remenyi G. , Perenboom J. A. A. J. , Maan J. C.
Published: July 2002

We describe the design and construction of a sensitive dc torque magnetometer suitable for liquid as well as solid state samples. It can be used from room temperature down to very low temperatures (mK range) in magnetic fields produced either by superconducting or resistive magnets, in particular in the high fields (B≈30 T) produced by Bitter and hybrid magnets. The highest resolution that we have attained so far is about 0.3 pNm, which is mainly the result of a symmetric design. In typical laboratory conditions (at B=10 T) this corresponds to a magnetization resolution of about 3×10−11 emu. Other features include modularity, linearity, feedback and forward bias capabilities, and an in situ calibration of the signal.
An investigation of continuous-angle laser light scattering
Authors: Tsutsui Kazunori , Koya Keisuke , Kato Tadaya
Published: July 2002

A continuous-angle laser light scattering instrument has been developed that consists of an ellipsoidal mirror and a charge-coupled device detector. Continuous and simultaneous measurement for angular dependence of scattered intensity is achieved over the wide scattering angle with high angular resolution. Data acquisition by the instrument is quite rapid compared to conventional light scattering instruments and it takes less than 1 s in most cases. Characteristics of this instrument are evaluated and static light scattering data for linear polystyrene are presented.
YAG laser Thomson scattering diagnostic on the JT-60U
Authors: Hatae T. , Nagashima A. , Kondoh T. , Kitamura S. , Kashiwabara T. , Yoshida H. , Naito O. , Shimizu K. , Yamashita O. , Sakuma T.
Published: July 2002

A YAG laser Thomson scattering system has been developed to measure the time evolution of electron temperature (Te) and density (ne) profiles in the JT-60U. Presently this system provides Te and ne periodically every 100 ms (20 ms at the minimum) at 15 spatial channels. A six spectrum channel polychromator, which is a successive interference filter type, was designed to measure a wide Te range (20 eV–20 keV) by using five channels. The sixth channel is used for calibration by Rayleigh scattering. However, we also used the Rayleigh channel to measure Te and ne since the stray light level was very low. As a result, we were able to measure temperatures below 20 eV. The temperature of the silicon avalanche photodiode (APD) is stabilized by a Péltier element so that the gain is kept constant within ±0.5%. The stable performance of the APD enables accurate Te and ne measurement. During plasma operation, the electron temperature is measured over a wide range from the low temperature plasmas in the runaway plasma current tail generated by a killer pellet to the high temperatures of high performance negative shear plasmas.
Core reflectometer density profile measurements on DIII-D
Authors: Doyle E. J. , Rhodes T. L. , Peebles W. A. , Zeng L.
Published: July 2002

Measurements of core (normalized flux coordinate ρ⩽0.3–0.4) electron density profiles have been obtained on the DIII-D tokamak via a reflectometer system operating in the ordinary polarization (O mode). This system was developed and implemented for two primary reasons: first, there is a pressing need for core density profile measurements on DIII-D in plasmas with core transport barriers and centrally peaked profiles, and second, the measurements reported here further extend the demonstrated range of conditions in which reflectometry can provide reliable density profile measurements. As a test of the ability of reflectometry to measure such core profiles an existing DIII-D broadband frequency swept (FMCW) reflectometer system was converted to use O-mode propagation. This test system covers 50–75 GHz, corresponding to densities of 3.1–7.0×1019 m−3. Using this system, core access has been investigated in medium density discharges. Results demonstrate that adequate signals, and hence, accurate profiles, can in fact be obtained to the plasma center in discharges with centrally peaked profiles.
Spectroscopic diagnostics of an atmospheric microwave plasma for monitoring metals pollution
Authors: Woskov P. P. , Hadidi K. , Borrás M. C. , Thomas P. , Green K. , Flores G. J.
Published: July 2002

A 1.5 kW, 2.45 GHz microwave sustained plasma in a flowing sample of stack exhaust gas has been shown in recent Department of Energy/Environmental Protection Agency testing to be an accurate monitor of trace hazardous metals (in the ppb range) such as lead, chromium, and beryllium. Optical-ultraviolet spectroscopic studies are being carried out to better understand this particular atmospheric pressure plasma torch. An experimental device has been modified with extra visible access for radial and axial profile measurements. Diffraction limited fiber optic plasma views and high-resolution grating spectrometer instrumentation for molecular rotational and atomic excitation temperature (Trot,Texc) measurements are being used for plasma studies. Initial chord averaged measurements have been made of the N2+(0,0) first negative system for Trot and Fe I levels for Texc in nitrogen and air plasmas, respectively.
Extraction of radio frequency from electromagnetic surface waves guided by metallic strips
Authors: Friedman M.
Published: July 2002

Pulses of rf radiation with power in the megawatt range was extracted from electromagnetic surface waves. These nonradiating waves propagated on a long and thin metallic strip with most of the wave energy confined to a distance of less than a half wavelength around the strip. The electromagnetic energy of the surface waves was first extracted into rectangular waveguides in a TE01 mode and then radiated into the atmosphere with an overall efficiency of 90%.
Experimental study of three-dimensional microfabrication by focused ion beam technology
Authors: Yongqi Fu , Kok Ngoi , Bryan Ann , Hung N. P. , Shing Ong Nan
Published: July 2002

Combined with experimental milling, three-dimensional (3D) microfabrication by focused ion beam (FIB) technology has been studied. Rules among limiting aperture size, dwell time, retrace time, tail of Gaussian distribution, etc., have been analyzed in terms of experimental results. Some phenomena are explained from the theoretical point of view. In addition, influence of redeposition for the sidewall root of microstructure in the process of milling is analyzed, and the avoidance methods are used in the meantime. It was proved by experiment that beam current (representing ion beam energy) and beam spot size play an important role in the etching process. Nonlinear variation of these parameters led to the broadening of edge periphery and redeposition at the root of the sidewall. On the other hand, milling order is vital for the 3D microfabrication result by FIB sputtering due to the redeposition effect and profile broadening effect.
Zinc-indium-oxide: A high conductivity transparent conducting oxide
Authors: Phillips Julia M. , Cava R. J. , Thomas G. A. , Carter S. A. , Kwo J. , Siegrist T. , Krajewski J. J. , Marshall J. H. , Peck W. F. , Rapkine D. H.
Published: July 2002

We report the fabrication and characterization of zinc-indium-oxide films with similar electrical conductivity and better transparency in both the visible and infrared compared with indium–tin–oxide, a widely used transparent conductor in many technological applications. Dramatically superior transmission properties in the 1–1.5 μm range in particular make zinc–indium–oxide attractive for use in infrared devices, where transparent electrodes are required. Resisitivities as low as 400 μΩ cm result from doping with small quantities of Sn; Al, Ga, and Ge are also effective dopants. Deposition on glass and quartz substrates as amorphous films by pulsed laser deposition and dc reactive sputtering is described.
Unity ratio of cross- to self-phase modulation in bulk AlGaAs and AlGaAs/GaAs multiple quantum well waveguides at half the band gap
Authors: Villeneuve A. , Kang J. U. , Aitchison J. S. , Stegeman G. I.
Published: July 2002

We have found the cross-phase modulation (XPM) for cross-polarized beams to be equal to the self-phase modulation (SPM) in bulk AlGaAs semiconductor waveguide at photon energies lower than half the band gap. For multiple quantum well (MQW) waveguide the ratio of the cross-phase modulation coefficient to the self-phase modulation coefficient is approximately one for the pump polarized perpendicular to the well plane (TM) and one-half for pump beams in the plane of the wells (TE).
Epitaxial growth of highly conductive RuO2 thin films on (100) Si
Authors: Jia Q. X. , Song S. G. , Wu X. D. , Cho J. H. , Foltyn S. R. , Findikoglu A. T. , Smith J. L.
Published: July 2002

Conductive RuO2 thin films have been heteroepitaxially grown by pulsed laser deposition on Si substrates with yttria-stabilized zirconia (YSZ) buffer layers. The RuO2 thin films deposited under optimized processing conditions are a-axis oriented normal to the Si substrate surface with a high degree of in-plane alignment with the major axes of the (100) Si substrate. Cross-sectional transmission electron microscopy analysis on the RuO2/YSZ/Si multilayer shows an atomically sharp interface between the RuO2 and the YSZ. Electrical measurements show that the crystalline RuO2 thin films are metallic over a temperature range from 4.2 to 300 K and are highly conductive with a room-temperature resistivity of 37±2 μΩ cm. The residual resistance ratio (R300 K/R4.2 K) above 5 for our RuO2 thin films is the highest ever reported for such films on Si substrates.