bluuebunny/crossref_metadata_2025 huggingface dataset:
A 19-channel fast grating polychromator for ECE measurements in the MTX tokamak (abstract)
Authors: Guharay S. K. , Boyd D. A. , Ellis R. F. , Stauffer F. J. , Lasnier C. J.
Published: July 2002

A 19-channel grating polychromator is developed to measure the temporal evolution of the electron cyclotron emission spectrum in the second and third harmonics in the MTX tokamak with an aim to determine the electron temperature in ohmically heated thermal plasmas as well as the electron energy distribution function in gyrotron and free-electron laser-pumped nonthermal plasmas. The spectrometer can cover a spectral range of about 0.3 to 1.4 mm and deliver a maximum spatial resolution of about 1 cm radially. A combination of a 90° off-axis paraboloidal mirror as the collimating element and a toroidal mirror to focus the diffracted beam yields images on the exit slits with a modest astigmatic distortion. Liquid-helium-cooled InSb detectors are installed in nine channels and associated electronics are optimized for a very low noise and fast response time (∼2 μs). A faster detector element, with response <100 ns, is envisioned for the remaining ten channels.
Current profile studies in ITER via dual-polarization reflectometry (abstract)
Authors: Pavlichenko O. S. , Skibenko A. I.
Published: July 2002

The poloidal field of current in a tokamak influences the propagation of the upper extraordinary EM wave (UXW) in a plasma. Calculations show that in an ITER plasma [B=4.9 T, I=22 MA, n(0)=1×1020 m−3] the current profile changes result in a noticeable shift Δr of the UXW cutoff layer (COFL) position in the region of the current density gradient (Δr=0.2–0.3 m). Simultaneous measurements of the ordinary (O) and extraordinary (X) wave COFL positions via dual-polarization reflectometry in the frequency bands of 50–100 GHz (O wave) and 110–220 GHz (X wave) will allow us to reconstruct the magnetic field radial profile with an accuracy 3–5% if the COFL position is measured with an accuracy of 1 cm. Current profile in a tokamak plasma can be reconstructed from these data and magnetic field measurements outside the plasma.
A high-resolution Lidar–Thomson scattering diagnostic for JET
Authors: Fajemirokun H. , Gowers C. , Nielsen P. , Salzmann H. , Hirsch K.
Published: July 2002

A LIDAR–Thomson scattering system with better than 5 cm spatial resolution to resolve edge electron temperature and density gradients in H-mode operation in JET is needed. A dynamic range in measurable electron temperature of 0.1–1.5 keV and a minimum detectable electron density of 1019/m3 are required. To achieve these levels of performance, it is planned to use a modified section of the existing JET LIDAR–Thomson scattering system. A new detection system, consisting of a streak camera and an intensifier unit, will be used. Spectral dispersion is to be performed by a three-channel edge filter spectrometer. Recording and digitization of the scattered signal will be performed by a CCD camera read out by a personal computer. The system is described and results of experiments to determine the minimum visible light levels using a commercial streak camera, intensifier unit, and CCD camera and a pulsed laser diode light source are briefly presented. In addition, simulations of expected signal-to-noise ratio performance are discussed.
Studies of a permanent magnet type sheet plasma source
Authors: Oka Yoshihide
Published: July 2002

A rectangular formed plasma (that is, a flat plasma sheet) has been developed by making use of a new arrangement of a permanent magnet to compact the source. The new arrangement of the magnet was found to be able to generate a quasi-uniform magnetic field approximately over a rectangular space. The size of the plasma sheet was ∼8 cm wide, and ∼1 cm thick. The plasma density was on the order of 1010 ions/cm3 . The permanent magnet type sheet plasma source (PERMSPS) may be applicable to develop a compact sheet plasma source appropriate for a large area hydrogen/deuterium negative ion source.
A tensile testing machine for stress oxidation kinetic studies in well-controlled conditions
Authors: Schmitt J. F. , Pacia N. , Pigeat P. , Weber B. , Bouhay M.
Published: July 2002

We describe here a tensile testing machine suitable for severe conditions imposed by ultrahigh vacuum and for the different surface analysis techniques associated with it. The apparatus allows to apply a gradually tensile force to a sample ribbon heated to a high temperature by the Joule effect. It gives the experimenter the possibility to rotate the stressed specimen and to adjust its position in front of different requisite analyzers (Auger electron spectrometer, for instance). This tensile testing machine can be used for carrying out kinetic studies on the stress oxidation of metals and alloys at high temperatures in well-determined conditions.
First results with a high-imaging speed scanning electron microscope
Authors: Fishbine B. H. , Macy R. J.
Published: July 2002

We have built a scanning electron microscope (SEM) capable of ≳1 kHz framing rate, with the large depth of focus and high resolution which make SEM generally superior to light microscopes. SEM also permits submicron mapping of voltages or magnetic field lines on integrated circuits or observation of flux lattice processes in high temperature superconductors. Increasing framing rate by 101–104 times that presently available (so-called TV rate−30–50 Hz) permits a variety of new dynamic microscopy studies. We refer to this microscope as a fast-scan electron microscope, or FSEM.
A model for negative ion extraction and comparison of negative ion optics calculations to experimental results
Authors: Pamela Jérôme
Published: July 2002

Negative ion extraction is described by a model that includes electron diffusion across transverse magnetic fields in the sheath. This model allows a two-dimensional approximation of the problem. It is used to introduce electron space charge effects in a 2-D particle trajectory code, designed for negative ion optics calculations. Another physical effect, the stripping of negative ions on neutral gas atoms, has also been included in our model; it is found to play an important role in negative ion optics. The comparison with three sets of experimental data from very different negative ion accelerators, show that our model is capable of accurate predictions.
Index of refraction measurement at low temperatures
Authors: DeFranzo A. C. , Pazol B. G. , Wheeler C. E. , McCarthy K. A.
Published: July 2002

An apparatus is described for measuring the index of refraction as a function of temperature throughout the visible wavelength region. The apparatus has an accuracy of 1×10−4 in determining the index and has the flexibility to be modified to measure indices at nonvisible wavelengths. The performance and theory of operation are discussed.
Hydrogen gas circulating Raman shifter
Authors: Yagi Takashi , Lou Qihong
Published: July 2002

High-pressure hydrogen Raman frequency shifter with a gas flowing capability was developed, and stable Raman frequency conversion was obtained for a KrF pump beam at a 250 Hz repetition rate.
Cylindrically symmetric extractors with space charge dominated flow
Authors: Cavenago Marco , Bisoffi Giovanni
Published: July 2002

The design of a charged particle extraction system in cylindrical symmetry is discussed in the ideal case when the radial extension of the system is unlimited. A parallel beam equilibrium is derived for a diode case. The ideal shape z(r) of the cylindrically symmetric focusing electrode is determined exactly near the beam edge, that is for r < 2rh, where rh is the beam radius: differently from the planar gun theory, only at the beam edge this profile is at 67.5° angle with the beam axis z; an asymptotic formula, corrected up to the fourth order in r/rh is given for the rest of the focusing electrode, resulting in a 74.17° angle with the beam axis at infinity (r→∞). Numerical simulations performed by a particle tracking code are shown, after briefly discussing a few numerical algorithms used. The code validation with the well-known Pierce planar gun theory is performed, showing an adequate precision to check whether a beam propagates parallel in a long gap. The ideal focusing electrode exhibits the expected beam parallelism and improves the gun perveance with respect to a simple 67.5° cone.
Low-frequency nuclear magnetic resonance and nuclear quadrupole resonance spectrometer based on a dc superconducting quantum interference device
Authors: Fan N. Q. , Clarke John
Published: July 2002

A sensitive spectrometer, based on a dc superconducting quantum interference device, for the direct detection of low-frequency pulsed nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR), is described. The frequency response extends from about 10 to 200 kHz, and the recovery time after the magnetic pulse is removed is typically 50 μs. As examples, NMR spectra are shown from Pt and Cu metal powders in a magnetic field of 6 mT, and NQR spectra are shown from 2D in a tunneling methyl group and 14N in NH4ClO4.
Unlocked detection of SQUID signals: Theory and design
Authors: Dubuc C. , Benhida K. , Bloyet D.
Published: July 2002

We describe the principle and implementation of a new unlocked processing of SQUID signals. A digital interpolation is achieved by using the periodicity of the voltage-flux transfer characteristic. The method is analyzed and the choice of the main parameters is discussed. A practical implementation under CPU control with its self-calibrating procedure is described and the main performances are reported. The magnetometer particularly exhibits an improved ruggedness against some forms of spurious noise as compared to standard servomagnetometers. This method can be easily extended to optical interferometry. The use of this detection scheme is suggested as an example for Mach–Zehnder interferometers.
Data analysis on TFTR using the SNAP transport code
Authors: Towner H. H. , Goldston R. J. , Hammett G. W. , Murphy J. A. , Phillips C. K. , Scott S. D. , Zarnstorff M. C. , Smithe D.
Published: July 2002

This paper describes the between shots data analysis on TFTR using the one-dimensional equilibrium kinetic analysis code SNAP. SNAP accepts as input data: the measured plasma size and current, toroidal field, surface voltage, plasma composition (total Zeff and Zeff contribution from metallic impurities), edge neutral density, auxiliary heating power data (neutral beam power, energy, injection geometry and/or rf power and frequency), and measured profiles of Te(R), ne(R), Ti(R), Vφ(R), and Prad(R). SNAP iteratively calculates: (1) the mapping of profile data to a minor radius grid, (2) the magnetic topology including Shafranov shifted circular flux surfaces, (3) neutral beam attenuation and deposition profiles, (4) unthermalized beam ion density and beam power density delivered to thermal plasma species from a numerical solution to the Fokker–Planck equation, (5) the neutral density profile, (6) local heat and particle transport coefficients consistent with the measured profiles and calculated source terms, (7) ICRF power profiles from a reduced order full wave analysis and isotropic Stix quasilinear model, and (8) total neutron emissivity and plasma stored energy. Several ion heat transport models (including neoclassical χi and χi∝χe) are available to calculate an expected Ti(r) profile in the absence of measurements.
A standing-wave flow measurement system for small diameter pipes using long acoustic waves
Authors: Ikpe E. S. , Scarrott G. , Weight J. P. , Grattan K. T. V.
Published: July 2002

An exploratory investigation, using laboratory fabricated acoustic components, of standing-wave flow measurement techniques for liquids and gases in pipes of diameter up to about 25 mm was undertaken, using long acoustic waves. The results show a linear sensitivity based on the ‘‘sing-around’’ technique, often associated with contrapropagating time-of-flight flowmeters. A repeatability test at a volume flow rate of 1.5 ℓ per minute indicates that, within the 95% confidence limit, only 5% of the readings will lie outside the range of 1.1–1.9 ℓ per minute. The transducer used in the above investigation comprises a section of the pipe wall which acts as part of a resonating transmitter or detector of long waves in a fluid. The measurement cell is closed and generates a known standing-wave pattern. The results obtained suggest that, in the future, the initial accuracy obtained in this study can be significantly enhanced with further improvements to the transducers, the measurement cell, the electronics, and test procedures, on which work is continuing, to produce a device competitive with those using other technologies.
A capacitive antenna for measurement of the dispersion relation of capillary waves on water
Authors: Barter J. D.
Published: July 2002

A noninvasive sensor has been developed to monitor the complex wave number of capillary waves on water (λ≊1 cm). It has been successfully employed to monitor surface tension and wave damping of varying surface conditions with surface tension resolution δγ≊0.25 mN m−1 and imaginary wave-number resolution δki≊0.0055 cm−1. The principle of detection is based on the capacitance between an rf driven metallic plate in proximity to the water surface as modulated locally by the presence of surface water waves. Results are found to be in good agreement with a companion surface slope detection method. This new method is simpler, more portable, and measures the complex wave number directly whereas most conventional devices either do not measure both components of the wave number or rely on shallow or restricted water surface containers or measure only static surface tension and elastic modulus.
Single chord far-infrared polarimetry experiment on RFX
Authors: Gadani G. , Parini A. , Zilli E. , O’Leary P. , Prunty S. L. , Sexton M. C.
Published: July 2002

This paper summarizes the work of the authors in the realization and testing of a pilot single chord polarimetry experiment on the RFX (reversed field experiment) machine, at the far-infrared wavelength of 118.8 μm. The fundamental purpose of this experiment is to demonstrate the feasibility of a Faraday rotation angle measurement on RFX, with the required resolution, and to clarify all the aspects which may be useful for the final six-chord version of the diagnostic. The apparatus which has been developed is described, with emphasis on some of the modifications which proved essential in order to obtain a satisfactory measurement, in spite of the hostile environment of the machine. Typical results of Faraday angle measurements are presented and discussed, and the reliability of the measurement is demonstrated. In particular, the required ±0.2° accuracy is achieved and the results are consistent with magnetic field profiles similar to the ones predicted by the Bessel function model. Suitable design considerations are formulated in order to guarantee the required performance in the six-chord version, even when the machine moves into full regime.
D-T radiation effects on TFTR diagnostics (invited)
Authors: Ramsey A. T.
Published: July 2002

For a 50%-50% deuterium-tritium plasma, the neutron production is 80× higher and the total-energy release is 200× higher than the same plasma composed only of deuterium. With this increase in radiation, diagnostics which see only negligible amounts of noise during DD operation may find themselves overwhelmed during DT. The neutrons are not only more numerous, but have 6× as much energy, which causes the calculated 2.5× increase in the gamma flux per neutron near TFTR. Here the effects of this increased radiation on the TFTR diagnostics set are reported. The most noticeable effects are luminescence and transmission losses in fiber-optic signal cables. Silicon detectors show signs of neutron interactions as well as gamma response, and microchannel electron multipliers show an increased background due to the gamma flux. Bolometers show n and γ heating, and the Thomson scattering intensifier gate spark gap was unreliable until the gas pressure was adjusted. All of these effects were anticipated, and in many cases shielding or compensation techniques were used. Compensation fibers work satisfactorily at these radiation levels, and the rapid falloff of the radiation as one moves away from the machine makes relocation of fibers and other sensitive components very useful. Conventional shielding attempts worked when streaming through signal penetrations was properly dealt with. In the next generation of DT campaigns and new tokamaks, such problems will be more severe. The implications for these machines are discussed.
Design of an optimal Ross filter system for x-ray spectra measurements in the range of 8.98–88 keV
Authors: Khutoretsky I. V.
Published: July 2002

This article describes wide-band Ross filter spectrometers for short-pulse plasma devices. The spectrometer consists of a number of channels, each representing a Ross filter pair in conjunction with x-ray detectors. Sensitivity bands of these channels cover the energy interval of interest without gaps. We consider as optimal the spectrometer whose channels have constant response within their sensitivity ranges and minimal response outside them. The main innovation is the addition of light material into one filter of the Ross pair, which reduces significantly (up to 5 times) the response outside the sensitivity range. Examples are presented of the optimal six-channel (8.98–18.99–29.2–38.92–50.24–67.42–88 keV) spectrometers with three types of detectors: Pb calorimeters, CsI scintillators, and Al2O3 thermoluminescent detectors and filters of readily available materials. The effect of uncertainty in x-ray cross sections and material thicknesses and the effect of filter-scattered photons hitting the detector on the accuracy of measurements are calculated.
Cryogenic linear ion trap for accurate spectroscopy
Authors: Poitzsch M. E. , Bergquist J. C. , Itano W. M. , Wineland D. J.
Published: July 2002

We have observed linear ‘‘crystals’’ of up to tens of laser-cooled 199Hg+ ions in a linear rf ion trap. The trap operates at liquid-He temperature and is designed for use as a prototype 40.5 GHz frequency standard with high accuracy and stability.
Mammography imaging studies using a Laue crystal analyzer
Authors: Chapman D. , Thomlinson W. , Arfelli F. , Gmür N. , Zhong Z. , Menk R. , Johnson R. E. , Washburn D. , Pisano E. , Sayers D.
Published: July 2002

Synchrotron-based mammography imaging experiments have been performed with monochromatic x-rays in which a Laue crystal placed after the object being imaged has been used to split the beam transmitted through the object. The X27C R&D beamline at the National Synchrotron Light Source was used with the white beam monochromatized by a double crystal Si(111) monochromator tuned to 18 keV. The imaging beam was a thin horizontal line approximately 0.5 mm high by 100 mm wide. Images were acquired in line scan mode with the phantom and detector both scanned together. The detector for these experiments was an image plate. A thin Si(111) Laue analyzer was used to diffract a portion of the beam transmitted through the phantom before the image plate detector. This ‘‘scatter free’’ diffracted beam was then recorded on the image plate during the phantom scan. Since the thin Laue crystal also transmitted a fraction of the incident beam, this beam was also simultaneously recorded on the image plate. The imaging results are interpreted in terms of an x-ray schliere or refractive index inhomogeneities. The analyzer images taken at various points in the rocking curve will be presented.
Thomson scattering stray light reduction techniques using a CCD camera
Authors: Nilson D. G. , Hill D. N. , Evans J. C. , Carlstrom T. N. , Hsieh C. L. , Stockdale R. E.
Published: July 2002

The DIII–D Thomson scattering system has been expanded to measure divertor plasma temperatures from 1 to 500 eV and densities from 0.05 to 8×1020 m−3. To complete this system, a difficult stray light problem was overcome to allow for an accurate Rayleigh scattering density calibration. The initial stray light levels were over 500 times higher than the expected Rayleigh scattered signal. Using a charge-coupled device (CCD) camera, various portions of the vessel interior were examined while the laser was fired through the vessel in air at atmospheric pressure. Image relaying, exit window tilting, entrance and exit baffle modifications, and a beam polarizer were then used to reduce the stray light to acceptable levels. The CCD camera gave prompt feedback on the effectiveness of each modification, without the need to reestablish vacuum conditions required when using the normal avalanche photodiode detectors (APD). Once the stray light was sufficiently reduced, the APD detectors provided the signal time history to more accurately identify the source location. We have also found that certain types of high reflectance dielectric coatings produce 10–15 times more scatter than other types of more conventional coatings. By using low-scatter mirror coatings and these new stray light reduction techniques, we now have more flexibility in the design of complex Thomson scattering configurations required to probe the central core and the new radiative divertor regions of the DIII–D vessel.
In situ observation of infrared spectra of some molecular fragments and products in rf discharge plasmas generated in an absorption cell of a Fourier transform infrared spectrometer
Authors: Iinuma K. , Sasaki N. , Takahashi T. , Fujisawa M. , Suzuki J. , Satoh K. , Furukawa K. , Satoh Y.
Published: July 2002

We have developed a Fourier transform infrared spectrometer, the absorption cell of which is utilized as a plasma reactor by winding the rf coil around it to couple directly the rf power. The infrared absorption spectra of some fragmented and synthesized molecules produced in the rf glow-discharge plasma are observed by employing five source gases: CO2, CD4, CF4 (in Kr), SF6, and a N2/O2 mixture. The measurements are made at 0.5 cm−1 apodized resolution on 7.5 and 7.8 MHz rf frequencies with the input rf power ranging between 30–75 W. The products assigned at present are: carbon monoxide in CO2 plasma, CD2H2 in CD4 plasma, and nitrous oxide (N2O) in a N2/O2-mixture plasma. A strong but not clearly assigned spectrum of fragmented molecules in SF6 plasma can also be observed.
The effect of using silicon based diffusion pump fluid on spectral quality in an electrospray ionization ion trap/time-of-flight mass spectrometer
Authors: Purves Randy W. , Gabryelski Wojciech , Li Liang
Published: July 2002

The formation of adducts resulting from interactions between protein ions and residual gases in an electrospray ionization ion trap/time-of-flight mass spectrometer is reported. This instrument utilizes diffusion pumps to achieve high vacuum, and we found that when silicon based diffusion pump fluids were used, characteristic adduct peaks appeared in the mass spectra. These adduct peaks were not detected, however, when a polyphenyl ether (Santovac 5) was used as the diffusion pump fluid. In switching the diffusion pump fluid to Santovac 5, a rigorous cleaning procedure capable of removing residual silicon pump fluid from the instrument was a critical step. This cleaning procedure can also be used for routine cleaning of the ion trap and other source components.
Modeling of negative ion transport in a plasma source (invited)
Authors: Riz David , Paméla Jérôme
Published: July 2002

A code called NIETZSCHE has been developed to simulate the negative ion transport in a plasma source, from their birth place to the extraction holes. The H−/D− trajectory is calculated by numerically solving the 3D motion equation, while the atomic processes of destruction, of elastic collision with H+/D+ and of charge exchange with H0/D0 are handled at each time step by a Monte Carlo procedure. This code can be used to calculate the extraction probability of a negative ion produced at any location inside the source. Calculations performed with NIETZSCHE have been allowed to explain, either quantitatively or qualitatively, several phenomena observed in negative ion sources, such as the isotopic H−/D− effect, and the influence of the plasma grid bias or of the magnetic filter on the negative ion extraction. The code has also shown that, in the type of sources contemplated for ITER, which operate at large arc power densities (>1 W cm−3), negative ions can reach the extraction region provided they are produced at a distance lower than 2 cm from the plasma grid in the case of volume production (dissociative attachment processes), or if they are produced at the plasma grid surface, in the vicinity of the extraction holes.
An ultrahigh vacuum cryogenic scanning tunneling microscope with tip and sample exchange
Authors: Harrell L. E. , First P. N.
Published: July 2002

An ultrahigh vacuum, cryogenic scanning tunneling microscope (STM) has been developed for imaging and current–voltage spectroscopy. Design details and results from initial studies are presented. The microscope design is based on the Besocke “beetle” style STM with some significant modifications. In particular, the placement of the tip and sample have been interchanged to facilitate in-vacuum transfer of tips and samples. The STM operates in a cryostat submerged in liquid helium or liquid nitrogen. Imaging of the 22×3 reconstruction of the Au(111) surface and atomic resolution of graphite are demonstrated. A current versus voltage spectrum showing Coulomb charging features and level quantization in a 29 000 amu Au nanocrystal is also presented to show the spectroscopic capability of the instrument.
Multiple-frequency continuous wave ultrasonic system for accurate distance measurement
Authors: Huang C. F. , Young M. S. , Li Y. C.
Published: July 2002

A highly accurate multiple-frequency continuous wave ultrasonic range-measuring system for use in air is described. The proposed system uses a method heretofore applied to radio frequency distance measurement but not to air-based ultrasonic systems. The method presented here is based upon the comparative phase shifts generated by three continuous ultrasonic waves of different but closely spaced frequencies. In the test embodiment to confirm concept feasibility, two low cost 40 kHz ultrasonic transducers are set face to face and used to transmit and receive ultrasound. Individual frequencies are transmitted serially, each generating its own phase shift. For any given frequency, the transmitter/receiver distance modulates the phase shift between the transmitted and received signals. Comparison of the phase shifts allows a highly accurate evaluation of target distance. A single-chip microcomputer-based multiple-frequency continuous wave generator and phase detector was designed to record and compute the phase shift information and the resulting distance, which is then sent to either a LCD or a PC. The PC is necessary only for calibration of the system, which can be run independently after calibration. Experiments were conducted to test the performance of the whole system. Experimentally, ranging accuracy was found to be within ±0.05 mm, with a range of over 1.5 m. The main advantages of this ultrasonic range measurement system are high resolution, low cost, narrow bandwidth requirements, and ease of implementation.
An instrument for the collection of simultaneous small and wide angle x-ray scattering and stress–strain data during deformation of polymers at high strain rates using synchrotron radiation sources
Authors: Hughes D. J. , Mahendrasingam A. , Martin C. , Oatway W. B. , Heeley E. L. , Bingham S. J. , Fuller W.
Published: July 2002

A fully integrated system has been developed which allows the study of the deformation of synthetic polymers by simultaneous small- and wide-angle x-ray scattering (SAXS/WAXS) and stress–strain techniques at synchrotron radiation sources. Two-dimensional x-ray data collection is achieved via two charge coupled device based area detectors which provide video signal outputs. A video extensometer provides sample strain and cross-section data during deformation. All three video signals are processed by a powerful Synoptics i860 processor based video framegrabber, with no loss of data. With this data collection strategy a temporal resolution of 40 ms is possible. In order to study the mechanical yield of the sample, a bridge-type strain gauge is used which reveals the sample loading. An electronic trigger mechanism provides accurate synchronization of the x-ray data, sample video data, sample loading information and controls the onset of deformation. Two experiments are highlighted showing the drawing of polyethylene at an overall rate of ≈10 s−1. By analysis of the sample video data it is possible to correlate the SAXS and WAXS data with specific points upon the true stress–strain curve. This novel system is shown to be a useful tool for the investigation of the deformation of polymers at rates that are relevant to industrial processing.
Normal-incidence strained-layer superlattice Ge0.5Si0.5/Si photodiodes near 1.3 μm
Authors: Huang F. Y. , Zhu X. , Tanner M. O. , Wang K. L.
Published: July 2002

Ge0.5Si0.5 strained-layer pin photodiodes, in which multiple strained layers serve as the absorption region, have been fabricated. These devices exhibit an optical response at wavelengths beyond 1.3 μm at normal incidence. The measured external quantum efficiencies at an applied bias of 4 V are 17% at 0.85 μm and 1% at 1.3 μm, respectively. Excellent electrical characteristics evidenced by the avalanche breakdown at 20 V have also been demonstrated.
Subharmonic-pumped continuous-wave parametric oscillator
Authors: Schiller S. , Breitenbach G. , Paschotta R. , Mlynek J.
Published: July 2002

We have operated a doubly resonant optical parametric oscillator (OPO) whose pump wave is generated in the OPO cavity itself by resonant frequency doubling of an injected subharmonic wave. The subharmonic-pumped oscillator employs a miniature monolithic MgO:LiNbO3 resonator and is pumped by a single-frequency Nd:YAG laser at 1064 nm. The threshold power was 120 mW at 1064 nm, and an efficiency of 7% for the conversion from 1064 to 1063/1065 nm via the nonresonant 532 nm wave was reached at 300 mW infrared input power. Single-frequency operation for up to one-and-a-half hours was observed.
Novel millimeter-wave near-field resistivity microscope
Authors: Golosovsky Michael , Davidov Dan
Published: July 2002

We demonstrate a technique for contactless mapping of resistivity or dielectric constant of surfaces and films with a spatial resolution better than 100 μm. This technique may be used for the nondestructive testing of semiconducting wafers, conducting polymers, oxide superconductors, and printed circuits. The principle of operation consists of the scanning of a tiny millimeter-wave antenna at a very small height above an inhomogeneous conducting surface and measuring the intensity and phase of the reflected (transmitted) wave. We use a specially designed resonant slit antenna and achieve subwavelength spatial resolution of λ/50.
Brillouin spectroscopy on dried sonogels
Authors: García-Hernández M. , Jiménez-Riobóo R. J. , Prieto C. , Fuentes-Gallego J. J. , Blanco E. , Ramírez-del-Solar M.
Published: July 2002

The elastic properties of organically modified silicates prepared by ultrasonics aided polycondensation of Tetraethoxysilane and Polidimethylsiloxane is studied by means of high resolution Brillouin spectroscopy. Our results evidence the microseparation of the organic and inorganic phases for the systems with high content of polymer. We propose a mechanical model that qualitatively explains the observed variation of the elastic constant c11 vs molar fraction of dimethylsiloxane in these vitreous materials and develop a structural model that accounts for the observed dynamical behavior.
Detection of hot electron current with scanning hot electron microscopy
Authors: Vázquez F. , Kobayashi D. , Kobayashi I. , Miyamoto Y. , Furuya K. , Maruyama T. , Watanabe M. , Asada M.
Published: July 2002

Scanning hot electron microscopy (SHEM) has been proposed as an experimental technique which allows for detection of hot electrons emitted from a subsurface semiconductor structure, thus making it possible to obtain the spatial distribution of hot electrons in a device. Here we present the experimental evidence of SHEM operation. Hot electrons with energies of 3 eV are injected by means of a Si/CaF2/Au heterostructure and subsequently detected at the tip of a scanning tunneling microscope in the SHEM configuration. The measured hot electron current was approximately 4 pA for a tunnel current of 5 nA. These results, although still of a preliminary nature, show the potential of SHEM as a technique suitable for the visualization of electron wave effects in semiconductor structures.
N incorporation in GaP and band gap bowing of GaNxP1−x
Authors: Bi W. G. , Tu C. W.
Published: July 2002

We report a study on the N incorporation in GaP grown by gas-source molecular beam epitaxy using a N radical beam source. Contrary to theoretical predictions under thermoequilibrium conditions, GaNP with N concentration as high as 16% has been obtained without showing any phase separation, but increasing the growth temperature will result in a decrease of N incorporation. These results indicate that using nonequilibrium growth techniques can achieve GaNP alloys with a N concentration far greater than the thermal equilibrium solubility limit. Optical absorption measurements reveal that although the band gap energy of GaNxP1−x decreases with increasing N concentration, it is still positive for x up to 16%, indicating that the material is not a semimetal but a semiconductor, contrary to theoretical predictions based on the Van Vechten’s quantum dielectric model.
Rapid solid phase crystallization of nanocrystalline silicon deposited by electron cyclotron plasma chemical vapor deposition
Authors: Holgado S. , Martínez J. , Garrido J. , Morant C. , Piqueras J.
Published: July 2002

Nanocrystalline silicon films were deposited in an electron cyclotron resonance plasma of Ar+H2+SiH4 on (100) and (111) oriented Si substrates without external heating. Before deposition, the substrates were cleaned in situ in an Ar+H2 plasma. This cleaning process caused surface roughness particularly on (100) substrates. Apparently, the excessive roughness of the interface with (100) Si surface prevented complete crystallization of the subsequently deposited films. In contrast, rapid solid phase crystallization of the films deposited on (111) surfaces occurred at around 1000 °C.
Ferromagnetic artificial pinning centers in superconducting Nb0.36Ti0.64 wires
Authors: Rizzo N. D. , Wang J. Q. , Prober D. E. , Motowidlo L. R. , Zeitlin B. A.
Published: July 2002

We used ferromagnetic artificial pinning centers in superconducting NbTi wires to achieve a large critical current density (Jc) in a magnetic field. Four wires were fabricated that contained nanometer-sized arrays of Ni or Fe pins inside micron-sized filaments of Nb0.36Ti0.64 alloy. A ferromagnetic pin volume of only 2% Ni produced Jc’s (e.g., 2500 A/mm2 at 5 T, 4.2 K) that were comparable to those of commercial wires that have a pin volume of ∼20% Ti. We conclude that ferromagnetic artificial pins are more effective than nonmagnetic pins for a given volume percent.
A composite quantum well field-effect transistor
Authors: Yang M. J. , Wang Fu-Cheng , Yang C. H. , Bennett B. R. , Do T. Q.
Published: July 2002

We have investigated the transport properties of a field-effect transistor (FET) with a composite quantum well, which consists of two adjacent semiconductor quantum wells, GaSb and InAs, sandwiched by AlSb barriers. This FET shows a novel V-shaped transfer characteristic, which is a direct result of the switching between electron and hole channels.
Wavelength control in II–VI laser diodes with first order distributed Bragg reflectors
Authors: Eisert D. , Bacher G. , Legge M. , Forchel A. , Nürnberger J. , Schüll K. , Faschinger W. , Landwehr G.
Published: July 2002

Longitudinal single mode emission from ZnSe-based laser diodes with first order distributed Bragg reflectors has been achieved. The emission energy could be varied in the green spectral range over more than 80 meV by changing the grating period from 97.7 to 102.2 nm. The variation of the lasing threshold current in this range is explained as a consequence of the optical gain spectrum of the structure. Wavelength fine tuning with a rate of Δλ/ΔT=2.9×10−2 nm/K was realized by temperature variation.
Secondary electron emission from boron-doped diamond under ion impact: Applications in single-ion detection
Authors: Kamiya Tomihiro , Cholewa Marian , Saint Andrew , Prawer Steven , Legge George J. F. , Butler James E. , Vestyck Daniel J.
Published: July 2002

The secondary electron emission from a 2 μm thick boron-doped diamond film under ion (4.6–7.7 MeV He+)impact is reported. The yield under ions impact is found to be remarkably high, stable over a period of many months, and independent of which side of the film (i.e., growth or substrate side) is exposed to the ion flux. By taking advantage of the high secondary-electron yield, the passage of each ion through the film could be detected with an efficiency of close to 100%, which to the best of our knowledge is the highest efficiency recorded to date for any thin-film window. This finding has an immediate application in single-ion irradiation systems where a thin vacuum window is required to allow extraction of an ion beam from the vacuum into air and at the same time offer 100% efficiency for the detection of the passage of the ion through the window.
Deactivation in heavily arsenic-doped silicon
Authors: Berding M. A. , Sher A. , van Schilfgaarde M. , Rousseau P. M. , Spicer W. E.
Published: July 2002

We have combined ab initio calculations with a general statistical theory to predict the properties of heavily arsenic-doped silicon. Although we find that a lattice vacancy surrounded by four arsenic (VAs4) is the dominant deactivating complex at high arsenic concentrations in equilibrium, vacancy clusters with fewer arsenic neighbors are present in significant quantities. These smaller complexes are essential not only to the establishment of equilibrium, since SiAs4 clusters are extremely rare, but can also explain deactivation even if VAs4 formation is kinetically inhibited. This suggests that materials with similar arsenic concentration and deactivation fractions can have different microscopic states, and therefore behave differently in subsequent processing. Good agreement is found between theory and experiment for the electronic concentration as a function of temperature and total arsenic concentration. We also show that for low arsenic concentrations, full activation is the equilibrium condition.
Spin-dependent conductance quantization in nickel point contacts
Authors: Oshima Hirotaka , Miyano Kenjiro
Published: July 2002

We have observed systematic change of the quantized conductance in point contacts of macroscopic nickel wires under varying external parameters, the temperature (above and below Tc) and the applied magnetic field. The observed quantized conductance can be explained by the number of the channels for electronic transport through the point contact and the spin-dependent transmission coefficient.
Excitation energy-dependent optical characteristics of InGaN/GaN multiple quantum wells
Authors: Cho Yong-Hoon , Song J. J. , Keller S. , Mishra U. K. , DenBaars S. P.
Published: July 2002

We have systematically studied the optical properties of InGaN/GaN multiple quantum wells (MQWs) at 10 K under different excitation conditions using photoluminescence (PL), PL excitation, and time-resolved PL spectroscopy. We found that the PL emission consists of a strong main peak at 2.80 eV and a much weaker and broader secondary peak at ∼2.25 eV. We observed that the peak position blueshifts and the spectral width narrows for the main peak when the excitation energies are varied from 3.81 eV (above the band gap of the AlGaN capping layer) to 2.99 eV (below the band gap of the GaN barrier layers). The intensity ratio of the main peak to the secondary peak also varied with excitation energy. The two observed emission peaks originate from different layers of the MQWs. Time-integrated and time-resolved PL revealed that the InGaN-related spontaneous emission processes are strongly affected by inhomogeneity and carrier localization in the MQWs. From these studies under varying excitation energies, we conclude that interface-related defects and roughness may play an important role in the InGaN-related emission mechanism during the carrier transfer between different layers of the MQWs.
Correlation between the surface defect distribution and minority carrier transport properties in GaN
Authors: Bridger P. M. , Bandić Z. Z. , Piquette E. C. , McGill T. C.
Published: July 2002

We have studied linear dislocations and surface defects in p- and n-type metalorganic chemical vapor deposition, hydride vapor phase epitaxy, and molecular beam epitaxy grown GaN films on sapphire with atomic force microscopy. The surface pits due to threading dislocations were found not to be distributed randomly but on the boundaries of growth columns. The dislocations are thought to be electrically active since the average distance between them (average column size) is comparable to minority carrier diffusion lengths as measured by electron beam induced current experiments on Schottky diodes fabricated with the same material. Diffusion lengths found for holes and electrons are on the order of Lp=0.28 μm and Le=0.16 μm which corresponded to the sizes of regions free from surface dislocations in both cases and can be described by a simple model of recombination on grain boundaries.
X-ray diffraction pole figure evidence for (111) sidewall texture of electroplated Cu in submicron damascene trenches
Authors: Lingk C. , Gross M. E. , Brown W. L.
Published: July 2002

The crystallographic texture of electroplated Cu in damascene trenches has been examined by x-ray diffraction pole figure analysis. The influence of two post-plating treatments on the resulting orientation of (111) planes of the Cu inside the trenches are compared. When the as-deposited small-grained Cu is allowed to recrystallize at room temperature before chemical mechanical polishing of the overlying Cu, we observe only a (111) fiber texture of the Cu inside the trenches. In contrast, when the overlying material is polished away before recrystallization of the small-grained Cu, pole figures show evidence of sidewall texture of the (111) planes in addition to the (111) fiber texture in the as-deposited as well as the annealed state. The presence or absence of a sidewall texture component in the pole figures offers insight into the evolution of the microstructure of damascene Cu.
Impurity oxygen redistribution in a nanocrystallized Zr65Cr15Al10Pd10 metallic glass
Authors: Chen M. W. , Inoue A. , Sakurai T. , Ping D. H. , Hono K.
Published: July 2002

We report atom probe results on impurity oxygen dissolution in a Zr65Cu15Al10Pd10 metallic glass and its redistribution during nanocrystallization. Approximately 0.1 at. % impurity oxygen is detected from the as-melt-spun Zr65Cu15Al10Pd10 metallic glass. Oxygen redistribution occurs during annealing. In some crystallites, oxygen up to 4 at. % is detected, and virtually no oxygen is dissolved in the remaining amorphous phase. This result directly demonstrates that impurity oxygen promotes the crystallization by forming metastable phases containing high content oxygen and thereby influences the kinetics of crystallization.
Effects of interfacial layer growth on the electrical characteristics of thin titanium oxide films on silicon
Authors: Lee Byoung Hun , Jeon Yongjoo , Zawadzki Keith , Qi Wen-Jie , Lee Jack
Published: July 2002

Effects of interfacial layer growth on reactively sputter-deposited TiO2 films were studied. Leakage current was reduced to 10−8 A/cm2 at +1 V after annealing in oxygen ambient and showed tunneling-like temperature dependence. As the interfacial layer grew, interface states and hysteresis were improved significantly. However, the reliability was degraded as the annealing temperature increased.
Ordinary and extraordinary refractive indices for AlxGa1−xN epitaxial layers
Authors: Bergmann M. J. , Özgür Ü. , Casey H. C. , Everitt H. O. , Muth J. F.
Published: July 2002

Dispersion of the ordinary and extraordinary indices of refraction for wurtzite AlxGa1−xN epitaxial layers with x=0.00, 0.04, 0.08, 0.11, and 0.20 in the range of wavelengths 457<λ<980 nm were measured via a prism-coupled waveguide technique. The quantitative accuracy of x is ±10% and the accuracy of the refractive indices is ∼±0.01. The dispersion is found to be well described by a 1st-order Sellmeier dispersion formula. A simple functional form is presented that allows calculation of the refractive indices as functions of x and λ.
High-resistance buried layers by MeV Fe implantation in n-type InP
Authors: Gasparotto A. , Carnera A. , Paccagnella A. , Fraboni B. , Priolo F. , Gombia E. , Mosca R.
Published: July 2002

We performed 2 MeV Fe implantation at a temperature of 200 °C on n-type InP substrates with different background doping concentrations. We studied the activation of Fe atoms as compensating deep acceptors and the electrical properties of the implanted layers. Simulation of the current–voltage characteristics coupled with secondary ion mass spectrometry depth profiling was used to extract important parameters such as the activated Fe fraction, the resistivity, and the thickness of the compensated layers. Our results show that resistivities of the order of 107 Ω cm can also be obtained for background doping concentrations higher than 1×1018 cm−3, with active Fe concentration well above the known solid solubility limit.
Silicon-based single-electron memory using a multiple-tunnel junction fabricated by electron-beam direct writing
Authors: Dutta A. , Lee S. P. , Hatatani S. , Oda S.
Published: July 2002

Multiple-tunnel-junction-based nonvolatile single-electron-memory devices are promising for fast write/erase operation and long retention time. Fabrication of multiple-tunnel junctions with a predetermined number of barriers and islands is a major problem in realizing such devices. We have fabricated multiple-tunnel-junction-based single-electron devices by an electron-beam direct writing technique in a silicon-on-insulator layer. Using this technique, it is possible to fabricate multiple ultrasmall islands and tunnel barriers at a predetermined position, which is very important for reproducible device characteristics. Single-electron-memory devices based on multiple-tunnel junctions are fabricated. In these devices, a multiple-tunnel junction connects the gate electrode and a storage island. The Coulomb blockade across the multiple-tunnel junction acts as an energy barrier. Single-electron-memory operation is observed at 20 K. Retention time of at least 4 h has been observed.
Microstructural evolution induced by scanned laser annealing in Al interconnects
Authors: Hau-Riege C. S. , Thompson C. V.
Published: July 2002

A method has been developed for inducing controlled microstructural evolution in thin films patterned into lines, using scanned laser annealing (SLA). Experimental studies show at least three distinct types of microstructures resulting from SLA, depending on the scan rate and laser power. Starting with a polygranular initial microstructure, scanned laser annealing leads to either a large-grained polygranular structure, a bamboo structure, or an agglomerated structure. Microstructural evolution induced by SLA was found to lead to different evolution than conventional annealing, as well as to produce unique large-grained “bamboo” structures. Simulations of SLA further suggest the possibility of producing near-single crystal microstructures under properly controlled conditions.