bluuebunny/crossref_metadata_2025 huggingface dataset:
Digital spectropolarimeter for the measurement of optical polarization
Authors: Lozykowski H. J. , Li T. , Akir Z. I.
Published: July 2002

A computerized setup for optical polarization measurements is described. The heart of this setup is a photoelastic modulator (PEM) whose retardation phase can be kept constant when the wavelength of modulated light is scanned in a wide range, and a dual-channel gated photon counter which has the capability of compensating the variation of excitation intensity with time and wavelength. Unlike conventional analog setups, where the difference of two perpendicularly polarized light components (I+ − I−) and the average of these components 1/2(I+ + I−) are extracted electronically and the ratio 2(I+ − I−)/(I+ + I−) is recorded as degree of polarization, this spectropolarimeter directly records the I+ and I− components (for circular polarization) or I∥ and I⊥ components (for linear polarization) of the analyzed light signal. Once the spectra of the two components are stored as a numerical file in the computer, they can be processed to extract the degree of polarization as a function of wavelength, temperature, etc. The curvature and asymmetry of the modulator response are taken into account exactly in data processing. The spectropolarimeter has proved to be very accurate due to the capability of compensating the fluctuation in excitation source and of electronically tracking the modulation wavelength.
Electron optical analysis of a high-resolution electron energy loss spectrometer with a retarding Wien filter
Authors: Tsuno K.
Published: July 2002

The transfer matrix up to the second-order aberrations has been formulated for an electron optical systems of a monochromator and an energy analyzer. Both of these instruments have two magnetic round lenses and a retarding Wien filter. The filter consists of a deceleration lens, a Wien filter, and an acceleration lens. The optimum excitation of the round lens is found to be that which provides parallel exit of electrons from the acceleration lens. The excitation of the Wien filter must be adjusted to focus the beam on the slit. The computed results are useful for finding the optimum operating conditions and for explaining experimental results of the high-resolution electron energy loss spectrometer.
Dielectric waveguide spectrometer for absorption spectroscopy of reactive vapors at microwave frequencies
Authors: Longo I.
Published: July 2002

Experiments of microwave spectroscopy of gases at low pressures are performed with some advantages using dielectric waveguide cells. The construction of an improved version of a dielectric waveguide spectrometer is described. Details on the experimental methods utilized for gas handling and for the observation of some absorption lines of HNO3, O3, and H2O in the 18–26.5-GHz frequency band, and of the CS radical at 49 GHz are given.
Instrument for the remote determination of viscosity and density in hostile environments
Authors: Li K. K. , Schneider A. , Abraham R. L.
Published: July 2002

A continuous bubble-rise-velocity (BRV) viscometry method was developed for Newtonian fluids which is based upon the remote determination of the rise velocity of a helium bubble. The bubble rise velocity was remotely determined by using a helium-leak detector to measure the rise time of a bubble passing through a constant distance. The density of the fluid was simultaneously obtained from differential pressure measurements in the bubble launch tubes. Empirical equations were developed which allow for calculation of the absolute viscosity and density from several remotely measurable variables: helium gas pressures in the bubble generation and launching system, liquid temperature, and helium concentrations at the liquid/air interface as a function of time. BRV viscometry results for highly viscous liquids (1 Pa s<viscosity <40 Pa s) correlated within ±10% with data obtained with capillary or rotational viscometers. An integrated probe was conceived for the on-line monitoring of viscosity, density, temperature, and liquid level, especially in a hostile environment.
Gravimetric capillary method for kinematic viscosity measurements
Authors: Rosenberger Franz , Iwan J. , Alexander D. , Jin Wei-qing
Published: July 2002

A novel version of the capillary method for viscosity measurements of liquids is presented. Viscosity data can be deduced in a straightforward way from mass transfer data obtained by differential weighing during the gravity-induced flow of the liquid between two cylindrical chambers. Tests of this technique with water, carbon tetrachloride, and ethanol suggest that this arrangement provides an accuracy of about ±1%. The technique facilitates operation under sealed, isothermal conditions and, thus can readily be applied to reactive and/or high vapor pressure liquids.
Voltage monitors for high-power 10–20 MV pulsed electron accelerators
Authors: Sanford T. W. L. , Halbleib J. A. , Lorence L. J. , Kelly J. G. , Griffin P. J. , Poukey J. W. , Mock R. C. , McAtee W. H. , Mikkelson K. A.
Published: July 2002

Four monitoring techniques that can determine peak voltage (Vp) to a precision of ∼5% for high-intensity, pulsed electron accelerators operating in the 10 to 20 MV range are discussed and applied to the 14-TW HERMES III accelerator. The techniques utilize parapotential flow theory, the range of H− ions, the bremsstrahlung from electron interactions with an electron target, and the photoneutron fluence from neutrons generated in a bremsstrahlung target. Application of these techniques to HERMES III shows that when the accelerator is operating under nominal conditions, Vp=(18.7±0.7) MV.
Scintillator studies with MeV charged particle beams
Authors: Tuszewski M. , Zweben S. J.
Published: July 2002

Thin scintillators used as detectors of escaping fusion products in the TFTR tokamak are studied with Van de Graaf beams of 3-MeV protons and 3.5-MeV alphas. ZnS scintillators are found generally adequate for the D–D experiments performed up to now, marginal for near-term D–T experiments because the emitted light saturates at alpha fluxes greater than 1010 cm−2 s−1, and totally inadequate for future ignited plasmas. Other scintillators have been tested that have lower light efficiencies but much better properties at high fluxes. In particular, the P46 scintillator appears to be an excellent choice for future experiments.
Compact standalone data acquisition system for submicrosecond time-resolved Fourier transform spectroscopy
Authors: Berg P. A. , Sloan J. J.
Published: July 2002

We report the development of a data acquisition system which can be used with any commercial Michelson interferometer to carry out time-resolved Fourier transform spectroscopy with a time resolution of one microsecond. The sensitivity and spectral resolution of the experiment are limited only by the interferometer. The instrument occupies one slot on a conventional VME enclosure (6U height). It includes all hardware and firmware to control the experiment which generates the spectral transients and to collect the time-resolved interferograms. We are presently transferring this design to a single 6U height printed circuit board (with a mezzanine), in order to make it available as a standalone system for use with any VME platform.
A fiber-optic light-scattering spectrometer for dark-colored solutions of macromolecules
Authors: Chu Benjamin , Ying Qicong , Dhadwal Harbans S.
Published: July 2002

A fiber-optic light-scattering spectrometer with simultaneous operation at wavelengths of 488 and 790 nm is described. The spectrometer can perform both static and dynamic light-scattering measurements, down to a scattering angle of 8°, from dark-colored solutions of macromolecules.
Active voltage biasing of very low impedance devices
Authors: Dolabdjian C. , Robbes D. , Lesquey E. , Monfort Y.
Published: July 2002

This note presents an active electronic circuit which controls the voltage applied to a device under test of very low input impedance. Performances and applications of this circuit are given in the superconducting field.
High-intensity x-ray line focal spot for laboratory extended x-ray absorption fine-structure experiments
Authors: Sakurai Kenji
Published: July 2002

Use of an intense and narrow linear-shaped x-ray source is essential to improve the quality of the extended x-ray absorption fine-structure measurements in a laboratory. To this end, an x-ray generator with a large rotating anode, designed for dedicated use of point-shaped focal spot, was modified to provide a linear-shaped focal spot of ∼0.1 mm in width at an exit angle of 6°. The maximum allowable current was 600 mA, which has never been realized so far using a conventional x-ray linear focal spot.
Apparatus for the mass spectrometric analysis of detonation products quenched by adiabatic free expansion
Authors: Blais N. C. , Fry H. A. , Greiner N. R.
Published: July 2002

We describe an apparatus that enables mass spectral analysis of the reacting chemical mixtures that drive detonation. Laboratory-scale (∼0.1 g) explosive pellets are detonated in a high-vacuum chamber, and rapid cooling by adiabatic free expansion quenches the chemical reactions. The instrument records a series of 95 mass spectra of the quenched reaction mixtures from one pellet. The spectra cover the mass range m=1 to m=300 and are recorded every 12 μs, which provides a mass analysis for every 20 μm of the detonation wave. This expansion of the time scale occurs because after expansion a 20-μm layer takes 12 μs to pass the mass spectrometer ionizer. The series of spectra give a molecular characterization of the chemical processes that drive detonation.
High frequency measurement technique for patterned soft magnetic film permeability with magnetic film/conductor/magnetic film inductance line
Authors: Senda Masakatsu , Ishii Osamu , Michikami Osamu
Published: July 2002

This article describes a new technique in the 1 MHz to 1 GHz range for measuring the permeability of patterned soft magnetic films. An inductance line with a magnetic film/conductor/magnetic film structure makes it possible to measure permeability at frequencies of up to 1 GHz because of the low stray capacitance and high resonance frequency of the electric circuit. The magnetic film pattern is designed so that the demagnetizing field can be ignored, and the absolute permeability value is estimated by analyzing the magnetic circuit. No anomaly, which may be caused by a magnetic charge at the pattern edge or a dimensional resonance, is observed using this pattern. Also, the relative permeability μr′(0) and ferromagnetic resonance frequency fk measured with this technique, are confirmed to be in good agreement with the values calculated from static magnetic properties.
Thermal diffusivity measurements using linear relations from photothermal wave experiments
Authors: Salazar A. , Sánchez-Lavega A.
Published: July 2002

We present a methodology to retrieve the thermal diffusivity of bulk homogeneous samples based on a set of simple linear relations that exist between two measurable magnitudes in modulated photothermal experiments. The influence of the photothermal parameters involved (exciting beam radius and height and radius of the probe beam) is evaluated to assert the validity of the linear relations. Specifically, we discuss the thermoreflectance and mirage techniques and their more convenient use and method, depending on the kind of sample to analyze (solid, liquid, gas), to obtain the thermal diffusivity.
Deconvolution of unchopped time-of-flight waveforms
Authors: Cameron Brett R. , Harland Peter W.
Published: July 2002

A reliable method for deconvolving badly convoluted molecular beam time-of-flight waveforms using Fourier transform and Wiener filtering techniques is presented. The devised method places no restrictions on the functional form of any factors affecting the shape of the measured time-of-flight distribution, but rather uses an accurately determined distribution to estimate an overall response function for the system. The estimated response function may then be used to deconvolve any convoluted time-of-flight waveform measured under similar experimental conditions. The mathematical details of the method are discussed and examples of its application to the deconvolution of time-of-flight waveforms measured in unchopped pulsed supersonic beams of argon, krypton, CHCl3, and CH3Cl are presented.
Space charge measurement in thick dielectric materials by pulsed electroacoustic method
Authors: Li Ying , Aihara Mitsugu , Murata Koichi , Tanaka Yasuhiro , Takada Tatsuo
Published: July 2002

The new application of pulsed electroacoustic (PEA) method to measure space charge profiles in several millimeters thick polymers such as power transmission cable was proposed. In this method, space charge profiles are detected as acoustic wave signals that are generated by the space charge profiles existing in the sample under stimulation of an electric pulse. In most polymer samples, such as cross-linked polyethylene (XLPE) widely used in XLPE cable (CV cable), however, the acoustic wave form is obviously distorted as it propagates through the thick polymer. The acoustic wave distortion cannot be negligible when applying this method directly to very thick samples (several millimeters thick). To recover the wave form and obtain the accurate space charge profiles, it is necessary to study the attenuation and dispersion characteristics of the sample and remove their effects to the propagating acoustic wave. So-called ‘‘deconvolution processing’’ using ‘‘Jacobi method’’ was employed in this report to obtain the undistorted wave form. The principle of the data processing method is introduced and some examples for recovering the wave form are given to verify the effectiveness of the data processing method.
Synchronized shock tubes for wave reflection studies
Authors: Skews B. W.
Published: July 2002

The usual method for the study of shock wave reflections, and particularly Mach reflection, is by allowing a plane shock wave, generated in a shock tube, to impinge on a wedge situated in the tube. It is now generally accepted that the boundary layer growth on the wedge surface effectively acts as a mass sink, so that the flow direction behind the point of reflection does not have to satisfy the boundary condition of being parallel to the wall. This means that the classical reflection geometry for inviscid flow, as given in textbooks, cannot be achieved in the laboratory. However, a very much closer approximation to the ideal reflection geometry can be experimentally achieved by having two plane shocks mutually reflecting in free space. In the current tests this is achieved by having two shock tubes inclined to each other at twice the requisite wedge angle so that two plane shocks meet at the tube’s intersection. The difficulty with this setup is ensuring that the two waves arrive simultaneously at the intersection point. This paper describes attempts at obtaining the requisite synchronization, and the degree of success achieved. An experimental facility has been successfully implemented for the generation of two plane shock waves synchronized to arrive at a given position within 1 μs of each other. Photographs of ‘‘ideal’’ reflections have been obtained for a 20 degree wedge angle which confirm that the transition from regular to Mach reflection does not persist beyond the theoretical limits, as is found experimentally in tests using a solid wedge.
An improved system for measuring the lateral conductance of Langmuir monolayers
Authors: Cavalli Ailton , Oliveira Osvaldo N.
Published: July 2002

A special arrangement of electrodes and a differential system were employed for measuring the lateral conductance of Langmuir monolayers. Such an experimental system obviates the major difficulties inherent in this type of measurement which may have prevented the enhanced conductance from being observed in recently published data. It is shown unequivocally that both dc and ac conductances of monolayers increase when the monolayer is compressed beyond a critical density, thus resolving a controversy from the literature.
A low-cost, high-speed, near-infrared hygrometer
Authors: Wilson A. C. , Barnes T. H. , Seakins P. J. , Rolfe T. G. , Meyer E. J.
Published: July 2002

We describe a simple near-infrared hygrometer based on a broadband light-emitting diode (LED) centered at 1320 nm. Light from the LED is collimated and passes through a rotating optical-filter assembly and a sample cell. The water vapor concentration is measured using a synchronous detection scheme. This compact and robust instrument has a response time of 0.15 s and can reliably detect short-term absolute humidity changes as small as 0.6 mg/L (which equate to 0.02% absorption); the long-term stability of the absolute humidity measurement over a period of 4 days is approximately 1 mg/L. These performance characteristics are particularly well suited to measurements associated with human respiration, and we present results in this humidity regime.
Optimal geometry for neutral-beam-based optical diagnostics in tokamaks
Authors: Goldston Joshua E. , Goldston Robert J.
Published: July 2002

The key to obtaining good spatial resolution for neutral-beam-based optical diagnostics in tokamak plasmas is that the narrow optical sightline must cross the wide neutral beam path at a point where the sightline is tangent to the toroidal direction. For a single one-dimensional pinhole camera arrangement, this condition can be met at two points of interest in the plasma, such as the magnetic axis and the plasma edge. The camera location required to provide optimized spatial resolution is calculated. We find that the camera must be placed closer to the plasma edge as the neutral beam is aimed more tangentially.
Beam diagnostic techniques for a small-size high-efficiency radio-frequency ion source
Authors: Zakhary S. G.
Published: July 2002

The use of both a small discharge volume and magnetic mirror fields allow sequential ionization and an increased efficiency of this ion source. The extracted ion current can reach 12 mA at an extraction voltage=3 kV and discharge pressure=20 mTorr. In this paper a description of the techniques which are used for measuring the important parameters to evaluate this ion source is presented. These parameters are: beam profile, beam emittance, energy spread, and charge spectra of the beam. The source is found to have a beam emittance of 150 mm m rad, and energy spread of 30–60 eV, and a content of Ar+4 reaching ≂20% of the total extracted ion current.
Development of a chamber for in situ polarized total-reflection fluorescence x-ray absorption fine structure spectroscopy
Authors: Shirai Masayuki , Nomura Masaharu , Asakura Kiyotaka , Iwasawa Yasuhiro
Published: July 2002

We have constructed a chamber for the in situ structural study of metals and metal oxides supported on single-crystal surfaces by polarized total-reflection fluorescence x-ray absorption fine structure (PTRF-XAFS) spectroscopy. This chamber makes it possible to measure in situ PTRF-XAFS spectra under a variety of conditions; from high vacuum (1×10−9 Pa) to high pressure (1×105 Pa) and from low temperature (100 K) to high temperature (800 K). A wide degree (100°) of rotation of the sample along the x-ray light axis can be attained in order to measure the asymmetric or anisotropic structure of active sites on the single-crystal substrates in two different directions—parallel and perpendicular to the surface. The chamber is mounted on XYZ and rotation tables to achieve total-reflection conditions of the incident x ray to the sample. The advantage of this in situ PTRF-XAFS technique has been demonstrated by measuring extended x-ray absorption fine structure spectra of Pt/α-Al2O3(0001) and x-ray absorption near-edge structure spectra of vanadium oxide on ZrO2(100) under reaction conditions
Charge and mass resolved time of flight observations of 140 fs laser produced ions
Authors: Guethlein G. , Bonlie J. , Price D. , Shepherd R. , Young B. , Stewart R.
Published: July 2002

Ions from this plasma are self-extracting with energies of 0.1 to 100 keV, the extraction potential being one of the desired observables. The charge/mass (z/μ, μ is mass in AMU) separation is provided by a static magnetic field (B⋅L=1280 G cm, FWHM=14 mm) located 5 cm from the linear (1−d) detector. Displacement along the detector axis is thus proportional to z/μ(1/v). The detector is a gold cathode MCP with a fast (sub-ns) phosphor. The phosphor output is coupled into a streak camera (typical sweep 8.5 or 24 μs total) through a coherent fiber bundle. Streak images are grabbed with a 14-bit CCD. The signature of any specific ion is a straight line of slope proportional to z/μ. Since there are usually more than one charge state of a given ion, integer multiple slopes appear. Thus z and m can be found. Absolute calibration is taken from the slope of the proton streak, which is always present with our plasmas. While providing the same information as a Thomson parabola, the straight line images are easier to extract information from and offer resolution with less energy dependence. By providing mass and time of flight information, the product of z⋅Te can be determined unambiguously during the hydrodynamic acceleration of the plasma.
Acceleration experiments for an intense H− ion beam
Authors: Ando A. , Takeiri Y. , Kaneko O. , Oka Y. , Tsumori K. , Asano E. , Kawamoto T. , Akiyama R. , Kuroda T.
Published: July 2002

Intense H− beams have been extracted from a large multicusp plasma source operated with cesium seeding. The H− beams were accelerated up to 100 keV by a single-stage or a two-stage electrode system. Spatial profiles of the beams are measured calorimetrically and the beam divergence angle is obtained from half of the e-folding width. A minimum beam divergence angle of 5 mrads is achieved at a H− current density of 30 mA/cm2 with a beam energy of 100 keV. The ratio of acceleration current to H− current increases abruptly when a H− current saturates in the space charge limited region. This enhancement is mainly due to secondary electrons caused by the intersection of H− beams with an extraction grid. When the operating gas pressure decreases, the ratio of the acceleration current to the H− current decreases. This is related to a stripping loss of H− ions in the electrodes. A beam divergence angle reaches a minimum when a ratio of Vacc to Vext is set at an optimum value of 1.6 in the single-stage acceleration. This ratio is almost the same as that in the double-stage acceleration, where the optimum ratio of Eaccl/Eext is 1.5. In the optimum Eaccl/Eext ratio the divergence angle is not affected by Vacc2. The divergence angle can be reduced by changing Vacc2 even if the ratio of Eaccl/Eext is not optimized. The beam steering effect by permanent magnets buried in an extraction grid is observed in nine beamlets experiments. A simple calculation of a single particle trajectory gives a good approximation of the beam deflection angle.
A simple and compact synchrotron radiation x-ray exposure system in a vacuum for ultrafine pattern fabrication
Authors: Horiuchi T. , Deguchi K. , Ishiyama T. , Oda M.
Published: July 2002

This paper describes a simple and compact manual synchrotron radiation x-ray exposure system for fundamental research on ultrafine pattern fabrication with x-ray lithography. Special requirements for printing ultrafine patterns are investigated, and a step-and-repeat exposure system that includes a new gap-setting, a soft-contact mechanism in a vacuum, and a rough alignment mechanism is developed. All the mechanisms are neatly packed into a small vacuum chamber and are manually remote controlled. The system can be used for various fundamental studies. It is especially useful for experiments to print ultrafine patterns using x-ray cross-sectioned and phase-shifting masks. The success of a variety of experiments verifies the good performance and usefulness of this system.
A formal presentation and comparative study of low-frequency noise reduction techniques for direct current superconducting quantum interference devices
Authors: Lam Chok Sing M. , Dolabdjian C. , Gunther C. , Bloyet D. , Certenais J.
Published: July 2002

We present a comparative study of existing low-frequency noise reduction techniques for dc superconducting quantum interference devices (SQUIDS). These methods are essential to applications involving high-Tc SQUIDS because they dramatically reduce the 1/f noise to useful low-frequency noise levels. We propose a formal presentation of the problem and explain mathematically the working principles of these noise reductions methods, particularly for fluctuations arising from the critical current of the junctions. An increase in the white noise level is generally observed when a sinusoidal lock-in detection is used for these methods and we give here a mathematical explanation for this peculiar effect. Finally, noise measurements made on high-Tc grain boundary dc SQUIDS are presented; the experimental results are in close agreement with theory.
Liquid-jet target for laser-plasma soft x-ray generation
Authors: Malmqvist L. , Rymell L. , Berglund M. , Hertz H. M.
Published: July 2002

We describe a new liquid-target system for low-debris laser-plasma soft x-ray sources. The system is based on a microscopic liquid jet and is experimentally evaluated for 0.7–1 keV proximity lithography and water-window x-ray microscopy applications. Compared to an existing liquid-droplet target, this target system has the same low debris emission, high x-ray photon flux, and narrow spectral bandwidth. The advantages of the liquid-jet target include improved x-ray flux stability, increased range of suitable target liquids, and elimination of the need for temporal synchronization, thereby allowing less complex laser systems to be used.
Nonadiabatic scanning calorimeter
Authors: Yao Haruhiko , Ema Kenji , Garland Carl W.
Published: July 2002

A high-resolution computerized calorimeter capable of fully automatic operation in either ac or relaxation modes is described. Emphasis is given to a new version of the relaxation technique in which the heater power is ramped linearly in time. This improvement results in superior performance and convenience in studying both first- and second-order phase transitions and allows quantitative evaluation of latent heats as well as pretransitional heat capacity variations. Examples are given for the use of this calorimeter in the study of liquid crystal phase transitions.
Rotating-compensator multichannel ellipsometry: Applications for real time Stokes vector spectroscopy of thin film growth
Authors: Lee Joungchel , Rovira P. I. , An Ilsin , Collins R. W.
Published: July 2002

A multichannel spectroscopic ellipsometer based on the rotating-compensator principle was developed and applied to measure the time evolution of spectra (1.5–4.0 eV) in the normalized Stokes vector of the light beam reflected from the surface of a growing film. With this instrument, a time resolution of 32 ms for full spectra is possible. Several advantages of the rotating-compensator multichannel ellipsometer design over the simpler rotating-polarizer design are demonstrated here. These include the ability to: (i) determine the sign of the p-s wave phase-shift difference Δ, (ii) obtain accurate Δ values for low ellipticity polarization states, and (iii) deduce spectra in the degree of polarization of the light beam reflected from the sample. We have demonstrated the use of the latter spectra to characterize instrument errors such as stray light inside the spectrograph attached to the multichannel detector. The degree of polarization of the reflected beam has also been applied to characterize the time evolution of light scattering during the nucleation of thin film diamond by plasma-enhanced chemical vapor deposition, as well as the time evolution of thickness nonuniformities over the probed area of the growing diamond film. In this article, a detailed description of calibration and data reduction for the new instrument is provided. Future applications of this instrument are expected for real time characterization of film growth and etching on patterned surfaces for microelectronics and on thick transparent substrates for large area displays and photovoltaics.
Self-aligning optical particle sizer for the monitoring of particle growth processes in industrial plants
Authors: Bassini A. , Musazzi S. , Paganini E. , Perini U. , Ferri F.
Published: July 2002

We describe a diffraction based optical particle sizer to be used on-line in an industrial plant for monitoring the growth process of polystyrene beads in the range (400 μm–4 mm). The instrument has been designed to perform elastic light scattering measurements at very small angles (from 8×10−5 to 8×10−3 rad) and is provided with an active servo system that controls the beam alignment during operations.
A new data processing method to determine accurate density and size distribution of defects by bright field infrared laser interferometer (optical precipitate profiler)
Authors: Nakai Katsuhiko , Matsumura Atsuki , Harada Hirofumi
Published: July 2002

We have addressed essential problems for the determination of the size distribution and volume density of crystal defects by bright field infrared laser interferometer [optical precipitate profiler (OPP)]. By taking into consideration the influences of the intensity profile and phase shift of the incident laser beam along the optical axis, we developed a new statistical data processing method to determine the true size distribution and volume density of the crystal defects from the raw OPP data. Using this method we evaluated the size distribution and volume density of oxygen precipitates introduced in a CZ–Si wafer and the validity of the new method was confirmed by comparing the obtained results with those obtained by the etching method and transmission electron microscopy.
Wavelength calibration of the charge exchange recombination spectroscopy system on the DIII-D tokamak
Authors: Gohil P. , Burrell K. H. , Groebner R. J. , Holtrop K. , Kaplan D. H. , Monier-Garbet P.
Published: July 2002

A wavelength calibration of all the detectors on the charge exchange recombination spectroscopy system is performed after every plasma discharge on the DIII-D tokamak. This is done to insure that the rest of the wavelength position of the C VI 5290.5 Å charge exchange line on the detector is accurately known so that the Doppler shift of the spectral line emitted during the discharge can be used for measurements of plasma rotation. In addition, this calibration provides a check on the spectral dispersion needed to determine the ion temperature. The reference spectra for the calibration are Ne I lines created by neon capillary discharge lamps contained within specially designed diffuse reflectors. The Ne I lines at 3520.4720, 5274.0393, 5280.0853, 5298.1891, and 5304.7580 Å are used in this work. The location of these lines on the linear detectors can be determined to an accuracy of 0.1 pixel, which corresponds to a plasma rotation accuracy of 1.2 and 0.7 km/s for the central and edge rotation measurements, respectively. Use of oppositely directed views of the plasma at the same major radius have been used to verify that the nominal 5290.5 Å wavelength of the C VI (n=8–7) multiplet is the correct wavelength for the line emitted owing to charge exchange excitation.
Mirror-image calibrator for resonant perturbation method in surface resistance measurements of high Tc superconducting thin films
Authors: Ong C. K. , Chen Linfeng , Lu Jian , Xu S. Y. , Rao Xuesong , Tan B. T. G.
Published: July 2002

In surface resistance measurement of high Tc superconducting (HTS) thin films, the conventional resonant perturbation methods have large uncertainties, because their calibrators usually have much larger surface resistance than HTS thin films. This article describes a new type of calibrator, mirror-image calibrator: when the open end of a dielectric resonator is connected to its mirror image, the resonant frequency and quality factor of the resonator are equal to those of the dielectric resonator when its open end is shorted by a perfect conductor. This principle is applied to modify the dielectric resonator method in surface resistance measurement of HTS thin films. The structures of the dielectric resonator for surface resistance measurement (Rs probe) and its mirror-image calibrator are explained in detail. Comparison is made between the present technique and the conventional perturbation technique, and results show that the accuracy and sensitivity of the resonant perturbation method are greatly improved by using the mirror-image calibrator.
Sub-micron photocurrent mapping of heterostructures by micro-probe optical-beam induced current
Authors: De Vittorio M. , Cingolani R. , Mazzer M. , Holt D. B.
Published: July 2002

Photocurrent mapping of heterointerfaces with sub-micron resolution has been successfully obtained in air by means of a specially designed optical-beam-induced-current setup. The experimental method is described and three important applications are presented and discussed.
High resolution surface plasmon resonance spectroscopy
Authors: Tao N. J. , Boussaad S. , Huang W. L. , Arechabaleta R. A. , D’Agnese J.
Published: July 2002

A method for detecting surface plasmon resonance with high resolution (∼10−5 degrees or ∼10−8 refractive index units) and fast response time (1 μs) is described. In the method, light is focused through a prism onto a metal film on which molecules to be detected are adsorbed. The total internal reflection of the incident light is collected with a bicell photodetector instead of a single cell or an array of photodetectors that are widely used in previous works. The ratio of the differential signal to the sum signal of the bicell photodetector provides an accurate measurement of shift in surface plasmon resonance angle caused by the adsorption of molecules onto the metal films or by conformational changes in the adsorbed molecules. Using the method, we have studied subtle conformational changes in redox protein, cytochrome c, due to an electron transfer reaction.
Optoelectronic feedback stabilization of current modulated laser diodes
Authors: Dellunde Jaume , Torrent M. C.
Published: July 2002

Optoelectronic feedback is proposed as a suitable method for output stabilization of current modulated laser diodes. Numerical simulations show low jitter operation with significant on/off ratios even beyond the relaxation oscillation frequency. Low frequency components in the output power spectra are efficiently suppressed.
Surfactant-mediated epitaxy of Ge on partially Ga-terminated Si(111) surfaces
Authors: Maruno S. , Fujita S. , Watanabe H. , Kusumi Y. , Ichikawa M.
Published: July 2002

Surfactant-mediated heteroepitaxy of Ge on Si(111) with Ga as surfactant has been studied using a recently developed apparatus of scanning reflection electron microscopy combined with scanning tunneling microscopy. It has been found that Ge film formation of 4.3 ML thickness on a Ga-terminated √3×√3 surface results in two-dimensional island growth in contrast with pseudomorphic growth on 7×7 surface. Irregular growth of Ge clusters along the lower sides of atomic step edges also takes place on the √3×√3 surface at an elevated substrate temperature. Ge film was also grown on partially Ga-terminated Si(111) with both Ga-adsorbed √3×√3 and Ga-desorbed 7×7 reconstruction areas on the surface. It has been found that self-organized Ge clustering occurs along the Ga-desorbed 7×7 area with stripe shape.
Study of the leakage field of magnetic force microscopy thin-film tips using electron holography
Authors: Frost B. G. , van Hulst N. F. , Lunedei E. , Matteucci G. , Rikkers E.
Published: July 2002

Electron holography is applied for the study of the leakage field of thin-film ferromagnetic tips used as probes in magnetic force microscopy. We used commercially available pyramidal tips covered on one face with a thin NiCo film, which were then placed in a high external magnetic field directed along the pyramid axis. Good agreement between simulated and experimental electron phase difference maps allows to measure the local flux from the ferromagnetic tips and therefore to evaluate the perturbation induced by the microprobe stray field on the sample area.
Magnetostriction characteristics of ultrathin permalloy films
Authors: Kim Y. K. , Silva T. J.
Published: July 2002

An abrupt and large increase in the absolute magnitude of λs in sputtered polycrystalline permalloy (Ni81Fe19) films for thicknesses below 7 nm was observed. Permalloy films maintain near-zero magnetostriction with film thicknesses above 7 nm. Film surface studies and microstructural characterizations suggest that the magnetostriction observed in this study is possibly due to an altered surface morphology of microstructural origin. This observation appears to be critical from the viewpoint of permalloy-based giant magnetoresistive or spin-valve sensor fabrication where typical permalloy film thicknesses are 3–10 nm. Because thin films with nonzero magnetostriction can induce an undesirable magnetoelastic anisotropy during sensor operation, the control and adjustment of the film composition seems necessary to minimize magnetostriction.
Observation of misfit dislocations at the InxGa1−xAs/GaAs interface by ballistic-electron-emission microscopy
Authors: Lee E. Y. , Bhargava S. , Chin M. A. , Narayanamurti V. , Pond K. J. , Luo K.
Published: July 2002

We report ballistic-electron-emission microscopy (BEEM) imaging and spatially resolved spectroscopy of InxGa1−xAs/GaAs misfit dislocations 800 Å below the surface. Majority-carrier scattering by a fraction of misfit dislocations was seen to locally reduce the BEEM current and to give logarithmic spatial dependence, which suggests charging of the dislocation cores.
Fabrication of high frequency nanometer scale mechanical resonators from bulk Si crystals
Authors: Cleland A. N. , Roukes M. L.
Published: July 2002

We report on a method to fabricate nanometer scale mechanical structures from bulk, single-crystal Si substrates. A technique developed previously required more complex fabrication methods and an undercut step using wet chemical processing. Our method does not require low pressure chemical vapor deposition of intermediate masking layers, and the final step in the processing uses a dry etch technique, avoiding the difficulties encountered from surface tension effects when wet processing mechanically delicate or large aspect ratio structures. Using this technique, we demonstrate fabrication of a mechanical resonator with a fundamental resonance frequency of 70.72 MHz and a quality factor of 2×104.
Single molecule spectroscopy with automated positioning
Authors: Ha T. , Chemla D. S. , Enderle Th. , Weiss S.
Published: July 2002

Rapid positioning of single molecules in the excitation volume of a confocal (or near-field) microscope is necessary for the successful spectroscopy of molecules with fluctuating emission properties. A computer controlled optical system which automatically and rapidly locates and performs spectroscopic measurements on single molecules was developed. Examples for such spectroscopies, performed on short-lived molecules, are given.
Dose dependence of microstructural development of buried oxide in oxygen implanted silicon-on-insulator material
Authors: Bagchi S. , Krause S. J. , Roitman P.
Published: July 2002

The effect of implantation dose on microstructural development of the buried oxide (BOX) of 200 keV oxygen implanted Si was studied by electron microscopy. A continuous BOX layer with a low density of Si islands was obtained for a dose of 0.45×1018 cm−2, following high temperature annealing. At a lower dose of 0.225×1018 cm−2 a layer did not form, but only disjointed, isolated, oxide precipitates developed. At a higher dose, 0.675×1018 cm−2, a continuous BOX layer with a high density of Si islands formed. Microstructures of intermediate-temperature annealed samples showed the formation of oxide precipitates at preferred depths, the morphology being dose dependent. The final microstructure of the BOX is strongly influenced by the evolution of the oxide precipitates during annealing. A qualitative mechanism is proposed for the dose-dependent behavior of BOX formation during the annealing process.
Highly efficient excitation of optical near-field on an apertured fiber probe with an asymmetric structure
Authors: Yatsui T. , Kourogi M. , Ohtsu M.
Published: July 2002

We propose and demonstrate a novel method to enhance the near-field optical intensity on the apertured probe with its foot removed asymmetrically by using a focused ion beam. The spatial distribution of the near-field optical intensity on the asymmetric probe was observed by scanning another sharpened symmetric probe over the aperture. The observed spatial distribution profile was in good agreement with a numerical result corresponding to the HE11 mode. Furthermore, compared with the symmetric apertured probe, a 10 times enhancement of the near-field optical intensity on the asymmetric apertured probe was observed.
Nonlinear optical properties of armchair nanotube
Authors: Xie Rui-Hua , Jiang Jie
Published: July 2002

The magnitude of the third-order nonlinear polarizability γ of armchair nanotube is theoretically studied. The calculated results for the C70 tube are consistent with those measured by Neher et al. [Opt. Lett. 17, 1491 (1992)]. The static and dynamical magnitudes of γ can be greatly enhanced by increasing the carbon number. When the carbon number is big enough, the major dynamical response peaks with large γ magnitudes are located at the optical frequency ω near the energy gap Eg (i.e., 3ω∼3Eg), and the highest peak magnitude is much larger than that of C70, which is important in practical use.
Enhanced unidirectional anisotropy of the Co90Fe10/CrMnPt system by the NiO capping layer
Authors: Soeya Susumu , Hoshiya Hiroyuki , Meguro Kenichi , Fukui Hiroshi
Published: July 2002

The effect of a capping layer on the exchange coupled Co90Fe10/CrMnPt system was investigated. The NiO capping layer is able to enhance the unidirectional anisotropy Ke of the Co90Fe10/CrMnPt system to ∼0.302–0.345 erg/cm2. This strong Ke is thought to be caused by large stress emancipation of the NiO film through thermal annealing, which assists spreading of the CrMnPt lattice distortion in a desirable direction. This lattice distortion, in turn, leads to the enhancement of the CrMnPt magnetocrystalline anisotropy. The NiO capped Co90Fe10/CrMnPt system exhibits the same high blocking temperature TB of ∼300 °C as the noncapped one, i.e., there is no TB reduction due to the amplification of the CrMnPt lattice distortion.
Electrofreezing effect and nucleation of ice crystals in free growth experiments
Authors: Braslavsky I. , Lipson S. G.
Published: July 2002

Electrofreezing is an effect where an electrostatically charged surface in contact with a supercooled liquid or an externally applied electric field significantly enhances nucleation of the solid phase. The electrofreezing effect has been used as a tool to nucleate ice and heavy ice crystals in free-growth experiments at supercooling greater than 1.5 °C. In order to nucleate ice crystals at smaller supercooling, we describe a device which uses a combination of a thermoelectric cooler and the electrofreezing effect. This system has been used to nucleate crystals at a supercooling down to 0.1 °C, but this figure is only limited by the temperature stability of the growth medium.
On determining the relevance of athermal nucleation in rapidly quenched liquids
Authors: Im James S. , Gupta Vikas V. , Crowder M. A.
Published: July 2002

When a liquid is quenched, classical nucleation theory asserts that at least a fraction of the solid must nucleate by way of the athermal mechanism. In this letter, we show that this fundamental issue regarding the relative rates of athermal and thermal nucleation during a quench can be readily addressed by comparing the instantaneous quench rate that is in effect at any point during the quench, −dT/dt, to kn*+/(∂n*/∂T) evaluated at the corresponding temperature. This and additional considerations permit the construction of a nucleation-mechanism diagram that maps out the thermal-mechanism-dominated and athermal-mechanism-dominated domains in the quench-rate–temperature parameter space. By projecting the thermal trajectory of a quench on the diagram, the relevance or irrelevance of the athermal mechanism, as well as the extent to which athermal mechanism participates in the transformation, can be assessed.
Electrical characterization of defects introduced in p-Si1−xGex during electron-beam deposition of Sc Schottky barrier diodes
Authors: Mamor M. , Auret F. D. , Goodman S. A. , Myburg G.
Published: July 2002

Scandium (Sc) Schottky barrier diodes were fabricated by electron-beam (EB) deposition on epitaxially grown p-Si1−xGex strained films with x=0.0–0.2. The EB deposition was performed either with or without shielding the Si1−xGex samples. The barrier height and the defects introduced during EB deposition have been investigated as a function of Ge composition. Our results showed that the barrier height decreased as the band gap changed with increasing Ge content. The defect properties were studied with deep-level transient spectroscopy. The most prominent defect observed in p-Si was a hole trap H(0.53) at Eν+0.53 eV. Increasing the Ge content led to a decrease in the activation energy of this defect and this decrease followed the same trend as the band-gap variation, suggesting that the main defect detected in p-Si1−xGex is the same as that observed in p-Si.
Electrical and physical characterization of deuterium sinter on submicron devices
Authors: Mogul H. C. , Cong L. , Wallace R. M. , Chen P. J. , Rost T. A. , Harvey K.
Published: July 2002

The impact of a deuterium (D2) sinter under two different annealing conditions, 450 °C/60 min and 450 °C/90 min, was studied and compared to the traditional forming gas (FG) sinter. Channel hot carrier (CHC) measurements indicated that while the D2 sinter for 60 min improves the lifetime of the devices by 10× over the FG sinter, an additional increase in the D2 anneal time actually has a negative impact on lifetime. DC current–voltage measurements also showed that samples sintered in D2 ambient for 60 min were the least prone to degradation under stress. Gated diode results showed no appreciable amount of difference in the initial interface state density among the different samples. Secondary ion mass spectroscopy indicated that neither poly nor salicide appears to be a complete barrier to D2 diffusion.
Effective band gap inhomogeneity and piezoelectric field in InGaN/GaN multiquantum well structures
Authors: Chichibu S. F. , Abare A. C. , Minsky M. S. , Keller S. , Fleischer S. B. , Bowers J. E. , Hu E. , Mishra U. K. , Coldren L. A. , DenBaars S. P. , Sota T.
Published: July 2002

The emission mechanisms of strained InxGa1−xN quantum wells (QWs) were shown to vary depending on the well thickness, L, and x. The absorption edge was modulated by the quantum confined Stark effect and quantum confined Franz-Keldysh effect (QCFK) for the wells, in which, for the first approximation, the product of the piezoelectric field, FPZ, and L exceed the valence band discontinuity, ΔEV. In this case, holes are confined in the triangular potential well formed at one side of the well producing the apparent Stokes-like shift. Under the condition that FPZ×L exceeds the conduction band discontinuity ΔEC, the electron-hole pair is confined at opposite sides of the well. The QCFK further modulated the emission energy for the wells with L greater than the three dimensional free exciton Bohr radius aB. On the other hand, effective in-plane localization of carriers in quantum disk size potential minima, which are produced by nonrandom alloy compositional fluctuation enhanced by the large bowing parameter and FPZ, produces a confined electron-hole pair whose wave functions are still overlapped (quantized excitons) provided that L<aB.