bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical vapor deposition of copper from Cu+1 precursors in the presence of water vapor
Authors: Gelatos A. V. , Marsh R. , Kottke M. , Mogab C. J.
Published: July 2002

Copper films have been deposited by low pressure chemical vapor deposition from mixtures of the Cu+1 precursor copper hexafluoroacetylacetonate vinyltrimethylsilane and water vapor. The addition of water vapor at the optimum concentration more than doubles the deposition rate and substantially reduces the nucleation time without adversely affecting the copper film resistivity, but excess amounts of water vapor significantly increase the copper resistivity. Auger electron spectroscopy analysis detects no impurities in copper films deposited under optimum water conditions, but detects oxygen in films deposited under excess water conditions, suggesting copper oxide formation.
Quantitative analysis of low-energy Xe+ ion bombardment damage of Si(100) surfaces using x-ray photoelectron spectroscopy
Authors: Lu Z. H. , Mitchell D. F. , Graham M. J.
Published: July 2002

In situ x-ray photoelectron spectroscopy has been used to analyze the nature and extent of damage to the Si(100) surfaces bombarded with xenon ions in the energy range 0.25–2 keV. Dramatic changes in the Si 2p core levels were found upon ion bombardment. A curve-fitting analysis of the core level shows that an amorphous silicon overlayer is formed on the Xe+ ion bombarded surface. The results indicate that these low-energy Xe+ ions amorphize the surface in a layer-by-layer manner and that the depth of damage increases rapidly for ion doses between 1013 and 1015 ions cm−2. At about 1015 ions cm−2 the damage depth reaches a saturation for all ion energies studied. The saturated damage depth is found to increase linearly with ion energy.
Internal emission metal-semiconductor-metal photodetectors on Si and GaAs for 1.3 μm detection
Authors: Liu Mark Y. , Chou Stephen Y.
Published: July 2002

Si and GaAs metal-semiconductor-metal photodetectors with finger spacing as small as 0.25 μm are studied for 1.3 μm wavelength operation. It was found that the detectors have an external quantum efficiency as high as 0.5% for 1.3 μm light and a low dark current at room temperature. Increasing the Schottky barrier height reduces the responsivity of the detectors, but reduces the dark current more significantly and increases the responsivity-to-dark-current ratio. The condition for maximum signal-to-noise ratio was derived. Finally, the dependence of the detector’s responsivity on the finger spacing was studied. Both the field-enhanced injection and charge-carrier screening were found to significantly affect the detector’s responsivity.
Shear force microscopy with capacitance detection for near-field scanning optical microscopy
Authors: Leong J-K. , Williams C. C.
Published: July 2002

Shear force microscopy is very useful for distance regulation in near-field scanning optical microscopy (NSOM). However, the optical method used to detect the shear force can cause problems when imaging photosensitive materials, i.e., the shear force detection beam can optically pump the sample. We present here a new approach to shear force detection based upon capacitance sensing. The design, operation, and performance of the capacitance detection are presented. Shear force topographic images of hard and soft surfaces are shown using tungsten and NSOM fiber tips. The closed loop vertical sensitivity achieved is 0.01 nm/√Hz.
LiNbO3 optical waveguides by Zn diffusion from vapor phase
Authors: Herreros B. , Lifante G.
Published: July 2002

Fabrication of optical waveguides on LiNbO3 by Zn diffusion from the vapor phase has been demonstrated, using a specially designed diffusion apparatus. The planar waveguides on z-cut samples support both TE and TM propagations, indicating an increase of refractive indices for n0 and ne. Energy dispersive x-ray analysis measurements confirm the diffusion of Zn into the crystal, and analysis of the content of Zn as a function of diffusion depth for samples treated at different temperatures indicates much higher diffusion coefficients than those obtained for Ti diffusion in LiNbO3. The technique is versatile, easy to operate, and allows fabrication of waveguides at temperatures as low as 600–700 °C, thus preventing Li outdiffusion.
Correlation between optical properties, composition, and deposition parameters in pulsed laser deposited LiNbO3 films
Authors: Afonso C. N. , Gonzalo J. , Vega F. , Dieguez E. , Cheang Wong J. C. , Ortega C. , Siejka J. , Amsel G.
Published: July 2002

The correlation between the optical properties and composition of lithium niobate films is investigated in films deposited by laser ablation of single-crystal LiNbO3 and Li enriched LiNbO3 sintered targets under different oxygen pressures and laser fluences. The results show that the variation of the film refractive index is in many cases related to the deposition process itself, rather than to a variation of the film composition. The experimental conditions to produce stoichiometric films with optical properties similar to those of the bulk material are discussed.
Speed control characteristics and digital servosystem of a circular traveling wave motor
Authors: Hatsuzawa Takeshi , Toyoda Kouji , Tanimura Yoshihisa
Published: July 2002

The rotational speed control characteristics of a circular traveling wave motor are investigated. This motor is an ultrasonic motor driven by a specially designed piezoelectric vibrator. There are various parameters for controlling rotational speed due to the influence of friction and resonance between rotor and stator. In this paper the dependence of rotational speed on these parameters is explored by using an experimental instrument. A digital servosystem to control the rotational position of the motor is then assembled, using the experimental results as a guide. The angular resolution of the motor is 5.4′, sufficient as a driver of a standard rotary table.
Device to measure friction coefficients and contact resistance inside a scanning Auger microscope
Authors: McDonald T. G. , Peebles D. E. , Pope L. E. , Peebles H. C.
Published: July 2002

A device is described for in situ, rotary pin-on-disk wear studies in a commercial scanning Auger microscope. This device is mounted on a single 8-in. vacuum flange and can be installed in place of the normal sample mounting manipulator. The device allows simultaneous measurement of contact resistance and friction coefficient under controlled atmospheric conditions as wear progresses. The surface composition and topography of the wear track are measured without exposure of the surface to contaminating environments or removal of the pin from the wear track. Modifications made to the vacuum system to facilitate atmospheric control are also described.
Photoluminescence and electroluminescence of SiGe dots fabricated by island growth
Authors: Apetz R. , Vescan L. , Hartmann A. , Dieker C. , Lüth H.
Published: July 2002

We present a study of photo- and electroluminescence of SiGe dots buried in Si and compare them with structures containing smooth SiGe layers. The SiGe dot structures were fabricated by low-pressure chemical vapor deposition using the Stranski–Krastanov growth mode (island growth). We show that the localization of excitons in the dots leads to an increase of the luminescence efficiency at low excitation compared to smooth SiGe layers (e.g., quantum wells). At higher excitation the efficiency decreases which is attributed to nonradiative Auger recombination processes in the dots.
A multiprocessor data acquisition and analysis system for scanning tunneling microscopy
Authors: Hoeven A. J. , van Loenen E. J. , van Hooft P. J. G. M. , Oostveen K.
Published: July 2002

A new data acquisition and analysis system for scanning tunneling microscopy has been developed. With a single system, topography studies and current imaging tunneling spectroscopy can be performed, nanometer-scale indentations can be made, and the off-line analysis can be done. The system is based on the parallel use of several processors allowing for simultaneous data acquisition, processing, and display. User interfacing is done only via a host computer, a UNIX system with three-dimensional display capabilities, while the measurements and indentations are done via a second processor with optimal real-time characteristics.
Hard x-ray microprobe with total-reflection mirrors
Authors: Suzuki Yoshio , Uchida Fumihiko
Published: July 2002

A hard x-ray microprobe with a grazing-incidence total-reflection mirror system is developed. The optical system has a pair of elliptical mirrors arranged in a crossed mirror geometry (Kirkpatrick–Baez configuration) and forms demagnified images of an x-ray source. A focused spot size of 3.5 μm×4.8 μm is obtained at a wavelength of 2.3 Å. A focusing test with an x-ray source determined by a pinhole generates a finer microbeam. Preliminary experiments on scanning x-ray microscopy are performed using the focused x-ray beam.
Atomic-scale formation of ultrasmooth surfaces on sapphire substrates for high-quality thin-film fabrication
Authors: Yoshimoto M. , Maeda T. , Ohnishi T. , Koinuma H. , Ishiyama O. , Shinohara M. , Kubo M. , Miura R. , Miyamoto A.
Published: July 2002

The atomically ultrasmooth surfaces with atomic steps of sapphire substrates were obtained by annealing in air at temperatures between 1000 and 1400 °C. The terrace width and atomic step height of the ultrasmooth surfaces were controlled on an atomic scale by changing the annealing conditions and the crystallographic surface of substrates. The obtained ultrasmooth surface was stable in air. The topmost atomic structure of the terrace was examined quantitatively by atomic force microscopy and ion scattering spectroscopy as well as a theoretical approach using molecular dynamics simulations.
Application of modulated photothermal radiometry to infrared transparent samples
Authors: Walther H. G. , Seidel U. , Karpen W. , Busse G.
Published: July 2002

For the correct interpretation of modulated photothermal radiometric signals both the absorptive and IR-emmissive properties of the sample under test have to be taken into account. Therefore we derived a formula for layered samples and compared the theoretical predictions to measurements performed on a paint layer on brass.
Intense diagnostic neutral beam development for ITER
Authors: Rej D. J. , Henins I. , Fonck R. J. , Kim Y. J.
Published: July 2002

For the next generation, burning tokamak plasmas such as in the International Thermonuclear Experimental Reactor (ITER), diagnostic neutral beams and beam spectroscopy will continue to be used to determine a variety of plasmas parameters such as ion temperature, rotation, fluctuations, impurity content, current density profile, and confined alpha particle density and energy distribution. Present-day low-current, long-pulse beam technology will be unable to provide the required signal intensities because of higher beam attenuation and background bremsstrahlung radiation in these larger, higher-density plasmas. To address this problem, we are developing a short-pulse, intense diagnostic neutral beam. Protons or deuterons are accelerated using magnetic-insulated ion-diode technology, and neutralized in a transient gas cell. A prototype 50-kA, 100-kV, 1-μs accelerator is under construction at Los Alamos. Initial experiments will focus on ITER-related issues of beam energy distribution, current density, pulse length, divergence, propagation, impurity content, reproducibility, and maintenance.
A method for the measurement of the cathode surface temperature for a high-current free-burning arc
Authors: Haidar J. , Farmer A. J. D.
Published: July 2002

A method using two-wavelength pyrometry has been developed for the measurement of the cathode surface temperature of high-current free-burning arcs. The method measures the total thermal radiation flux emitted from the cathode and the surrounding plasma and subtracts the derived plasma component using a modified Abel-inversion transformation. The effects associated with the plasma radiation reflected by the cathode are minimized by using measurements near the cathode edges. Experimental data are used to account for the dependency of the cathode emissivity on wavelength. In this paper the details of this technique are discussed and measurements of cathode surface temperature are presented for pure and thoriated tungsten cathodes.
Fast-acting piezoactuator and digital feedback loop for scanning tunneling microscopes
Authors: Lapshin Rostislav V. , Obyedkov Oleg V.
Published: July 2002

The design of a sectional piezoactuator is described, and the principle of operation of a tunnel junction digital stabilization system is given. The total settling time of the system while the least significant section is in operation is 1 μs at 0.01-nm resolution (in the Z direction). The application of the sectional piezoactuator permitted an increase in operating frequency and also eliminated errors caused by the piezoceramics hysteresis. Introduction of a fast-acting ALU as a digital accumulator of regulation errors made it possible to achieve high stability of the loop operation at high operating frequencies. The system suggested can adapt the speed of the loop operation depending on the relief steepness values. The blunting of the tip and sample destruction is avoided because there is a mechanism of smooth approach of the tip to the nominal scanning height.
Combinations of point source electron beams and simple electrostatic lenses: Initial demonstrations of micron-scale lenses
Authors: Shedd G. M. , Schmid H. , Unger P. , Fink H.-W. , Dubner A. D.
Published: July 2002

This paper presents results stemming from the incorporation of micron- and millimeter-scale electrostatic lenses into an electron projection microscope, wherein the lenses can be used to focus and otherwise influence electron beams emitted from electron point sources. Topics discussed include the impetus for adding lenses to a normally lensless microscope, details of the lens design and fabrication techniques (including two novel methods for making micron-scale lenses and apertures), descriptions of the test procedures and conditions, and the observed results and their possible implications. The advantage of using a millimeter-scale lens to increase the magnification of projected images is illustrated. Then the microfabrication of two-electrode lenses measuring 1 μm in diameter and 1.7 μm in length is described. Although less than ideal, one of these structures performed sufficiently well to create what may be the first electron beam focused by a truly micron-scale lens. The materials and construction procedures used to build lenses by hand with diameter of 20 μm and electrode spacings of 8 μm are described. Two-electrode lenses of this type have demonstrated the capacity to withstand applied biases of over 500 V, and to send an electron beam through crossover with relatively little distortion.
Continuous energy diffraction spectroscopy: A newd-space matching technique for energy dispersive synchrotron radiation diffraction
Authors: Lee P. L. , Beno M. A. , Knapp G. S. , Jennings G.
Published: July 2002

In this article, a new technique, continuous energy diffraction spectroscopy (CEDS) is described, for diffraction experiments using a synchrotron energy dispersive polychromatic beamline. This type of beamline uses a curved crystal monochromator (polychromator) to focus a range of x-ray energies (bandwidth ∼1 keV) into a narrow (100–120 μm) line image. With a sample at this image point, using an 2D detector, we are able to measure diffracted intensities for the entire energy range of the incident beam simultaneously with limited or no motion of the sample. This method allows the collection of anomalous scattering and diffraction anomalous fine structure (DAFS) data faster and more accurately than with conventional methods. Because of the speed with which these types of diffraction experiments can be done, this method creates new options for time resolved diffraction experiments and provides new data collection strategies.
Flush-mounted probes in the divertor plates of Tokamak de Varennes
Authors: Gunn James P. , Boucher Claude , Stansfield Barry L. , Savoie Sylvio
Published: July 2002

Arrays of 12 flush-mounted Langmuir probes have been installed in both the upper and lower outboard divertor plates of TdeV (Tokamak de Varennes). Measurements of electron temperature and density are obtained using a novel method of analysis which assumes that charge collection is dominated by the finite size of the electrostatic sheath. The technique is validated by comparing measurements from a cylindrical and a flush probe which are operated simultaneously in the same plasma.
Novel high-temperature Calvet-type calorimeter for investigating metal-water reactions
Authors: Bradford Michael C. , Phillips Jonathan , Klanchar Martin
Published: July 2002

The initial operation of a Calvet-type calorimeter is reported. The instrument has been designed specifically to study lithium and lithium compound reactions with water at an elevated temperature. Additionally, the calorimeter test section incorporates an environment that resembles actual application conditions. Calibration procedures are explained for three important parts of the instrument, including (1) introduction of the water sample, (2) analysis of the effluent gas, and (3) measurement of the heat of reaction. Ten measurements of the heat of the lithium oxide-water reaction yielded values from 110 to 140 kJ/mol H2O and averaged 124 kJ/mol H2O. The average is in perfect agreement with the theoretical heat value computed utilizing JANAF thermochemical data.
Quasidivergency-free extraction of a slow positron beam from high magnetic fields
Authors: Gerola D. , Waeber W. B. , Shi M. , Wang S. J.
Published: July 2002

In a hybrid slow positron beam, extraction of the positrons from the magnetic field (∼1 T for the PSI beam) to field-free space is a necessary operation. A theoretical and experimental demonstration is given which shows that the following proposed beam extraction method works as predicted: magnetic transport of the slow positrons down to field strengths of ∼100 G and passage through an aperture grid of ∼10 cm diameter in a field termination shield followed by some brightness enhancement stages. The simulation and measurement of the magnetic-field distributions along the beam axis show a steep drop down of the field from ∼100 G to a few gauss within 1 cm of shield thickness and a quasiuniform spreading of the transverse field strength across the grid opening. Measurement of transmission and divergency (transverse energy) of the beam exiting the extraction aperture confirmed theoretical estimations and ray tracing calculations for the aperture design used to be of the order of 75% and 20 eV, respectively. These data as a function of field strength and beam energy are used for optimization of the final extraction aperture design (≳85% transmission) to be used in the PSI high intensity beam facility.
Formation of rectilinearly wide plasmas by a slotted waveguide under electron cyclotron resonance
Authors: Ishii S. , Wakatsuchi M. , Kato Y. , Tani F. , Sunagawa M.
Published: July 2002

A plasma source was developed for ion implanters capable of irradiating large-area substrates. Microwave discharge is performed by electron cyclotron resonance (ECR). A rectilinearly wide flux of magnetic induction is formed with two long permanent magnets with oppositely facing poles. The ECR zone formed inside a vacuum chamber is elongated in the direction along the pole faces. A waveguide slotted along its E plane is inserted between the magnets. The long slot radiates microwaves into the vacuum chamber through dielectric materials. These materials play the role of waveguide. Plasmas are uniformly generated in the direction along the slotted waveguide when it is terminated with a short plunger. This mechanism is analyzed by calculating radiation patterns of the slotted waveguide.
Design and performance of a new spectroscopic photon emission microscope system for the physical analysis of semiconductor devices
Authors: Chan D. S. H. , Phang J. C. H. , Chim W. K. , Liu Y. Y. , Tao J. M.
Published: July 2002

This article describes the design and performance of a new spectroscopic photon emission microscope system with panchromatic imaging and continuous wavelength spectroscopic capabilities. Very low levels of light emissions from biased devices can be detected and high resolution spectral characteristics can be analyzed because of the highly efficient light collection and transmission optics. Results shown include those metal oxide semiconductor transistors biased in saturation, forward and reverse biased p-n junctions, and oxide leakage. The potential use of the ‘‘defect fingerprinting’’ technique, whereby a unique spectral signature is assigned to each failure mechanism, is also discussed.
Ultracentrifuge apparatus to generate a strong acceleration field of over 1 000 000 g at a high temperature in condensed matter
Authors: Mashimo Tsutomu , Okazaki Satoru , Shibazaki Shirou
Published: July 2002

An ultracentrifuge apparatus to generate a strong acceleration field of up to or higher than 1 000 000 (1×106) g at high temperature for long times has been developed for sedimentation of atoms in condensed matter. The system consists of a high-temperature air turbine motor with oil-floating bearing and a specimen rotor made of a titanium alloy. It was confirmed that the ultracentrifuge experiment could be performed for a maximum rotating speed greater than 220 000 rpm with a rotor inner diameter of 40 mm. The specimen could be heated to over 300 °C for durations of several days. The maximum acceleration field achieved was higher than 1.1×106 g for temperatures ≳200 °C. This apparatus can be used for strong acceleration field (mega-gravity field) science in solids and liquids at high temperature.
Low temperature calibration of Manganin pressure gauges
Authors: Andersson O. E. , Sundqvist B.
Published: July 2002

High pressures are often measured using the resistance of Manganin wires. However, the pressure coefficient of resistance is known to depend on temperature. We have measured this temperature dependence by comparing the output from a Manganin gauge with that of a well calibrated Zeranin gauge and determined a correction factor which enables us to measure the pressure at any temperature between 150 and 300 K with a temperature dependent error well below 0.5%.
A four-point surface conductivity probe suitable for
in situ
ultrahigh vacuum conductivity measurements
Authors: Wiegenstein Christopher G. , Schulz Kirk H.
Published: July 2002

A simple design for a four-point probe suitable for precision surface conductivity measurements is described. Our design makes use of small, commercially available spring contact probes which are mounted in a custom built MACOR ceramic probe head. The design is suitable for use in ultrahigh vacuum applications, and the custom-built parts can be fabricated in any machine shop. Very reproducible values were obtained using this probe for surface conductivity measurements on a MoS2(0001) model catalyst, a sputter deposited indium-tin oxide thin film and a doped silicon wafer.
Temperature programmed desorption-mass spectrometer with supersonic molecular beam inlet system
Authors: Danon Albert , Avraham Ifat , Koresh Jacob E.
Published: July 2002

A novel atmospheric temperature programmed desorption-mass spectrometer (TPD-MS) device based on supersonic molecular beams (SMB) is demonstrated. The coupling between SMB and TPD-MS enables one to obtain highly sensitive TPD measurements with very fast time response (less than 1 s), that makes it possible to distinguish between desorptions from energetically neighboring sites. Quantitative adsorption measurements of adsorbing gas and vapors could be easily done. High detection sensitivity of 4 ng/s for H2O16 and 100 pg/s for H2O18 is achieved. The high sensitivity TPD measurements are demonstrated by the ability to monitor simultaneous physical adsorption of nitrogen, oxygen, and water on various sites on carbon fibers at room temperature.
Surface dimerization induced CuPtB versus CuPtA ordering of GaInP alloys
Authors: Zhang S. B. , Froyen Sverre , Zunger Alex
Published: July 2002

Using a valence force field approach and ab initio pseudopotential calculations, we examine the role of subsurface strain in the ordering of Ga0.5In0.5P alloys. We show that depending on the orientation of the surface phosphorus dimers, these alloys can have (i) a CuPtA ordering for 1×2 or c(4×4) reconstruction; (ii) a CuPtB ordering for 2×1 or β2(2×4) reconstruction; and (iii) a triple period ordering for 2×3 or c(8×6) reconstruction. These results are in good agreement with recent experiments of Gomyo et al. [Phys. Rev. Lett. 72, 673 (1994); Jpn. J. Appl. Phys. 34, L469 (1995)].
Nanometer-scale field-induced oxidation of Si(111):H by a conducting-probe scanning force microscope: Doping dependence and kinetics
Authors: Teuschler T. , Mahr K. , Miyazaki S. , Hundhausen M. , Ley L.
Published: July 2002

Hydrogen-terminated Si(111) was patterned on the nanometer scale by field-induced oxidation using a biased conducting-probe scanning force microscope. The kinetics of oxide growth as well as its dependence on doping are investigated. Field-induced oxidation is observed for voltages exceeding a doping dependent threshold above which oxidation kinetics follows a power law.
A broadband pulsed radio frequency electron paramagnetic resonance spectrometer for biological applications
Authors: Murugesan Ramachandran , Afeworki Mobae , Cook John A. , Devasahayam Nallathamby , Tschudin Rolf , Mitchell James B. , Subramanian Sankaran , Krishna Murali C.
Published: July 2002

A time-domain radio frequency (rf) electron paramagnetic resonance (EPR) spectrometer/imager (EPRI) capable of detecting and imaging free radicals in biological objects is described. The magnetic field was 10 mT which corresponds to a resonance frequency of 300 MHz for paramagnetic species. Short pulses of 20–70 ns from the signal generator, with rise times of less than 4 ns, were generated using high speed gates, which after amplification to 283 Vpp, were deposited into a resonator containing the object of interest. Cylindrical resonators containing parallel loops at uniform spacing were used for imaging experiments. The resonators were maintained at the resonant frequency by tuning and matching capacitors. A parallel resistor and overcoupled circuit was used to achieve Q values in the range 20–30. The transmit and receive arms were isolated using a transmit/receive diplexer. The dead time following the trailing edge of the pulse was about 450 ns. The first stage of the receive arm contained a low noise, high gain and fast recovery amplifier, suitable for detection of spin probes with spin-spin relaxation times (T2) in the order of μs. Detection of the induction signal was carried out by mixing the signals in the receiver arm centered around 300 MHz with a local oscillator at a frequency of 350 MHz. The amplified signals were digitized and summed using a 1 GHz digitizer/summer to recover the signals and enhance the signal-to-noise ratio (SNR). The time-domain signals were transformed into frequency-domain spectra, using Fourier transformation (FT). With the resonators used, objects of size up to 5 cm3 could be studied in imaging experiments. Spatial encoding of the spins was accomplished by volume excitation of the sample in the presence of static field gradients in the range of 1.0–1.5 G/cm. The spin densities were produced in the form of plane integrals and images were reconstructed using standard back-projection methods. The image resolution of the phantom objects containing the spin probe surrounded by lossy biologic medium was better than 0.2 mm with the gradients used. To examine larger objects at local sites, surface coils were used to detect and image spin probes successfully. The results from this study indicate the potential of rf FT EPR for in vivo applications. In particular, rf FT EPR may provide a means to obtain physiologic information such as tissue oxygenation and redox status.
A novel approach for doping impurity in thin film in situ by dual-beam pulsed-laser deposition
Authors: Ong C. K. , Xu S. Y. , Zhou W. Z.
Published: July 2002

Doping techniques are of great importance in developing new materials and devices. We present here a novel approach for doping impurity in thin film by using dual-beam pulsed-laser deposition technique that allows in situ controlling doping under a wide range of conditions. We demonstrated doping Ag in situ in YBa2Cu3O7−δ thin films and for the first time observed long bar-like Ag structures with a length up to 150 μm in the as-deposited films, which may have important application in the fabrication of superconductor-normal metal-superconductor Josephson junctions.
The beam emission spectroscopy diagnostic on the DIII-D tokamak
Authors: McKee G. , Ashley R. , Durst R. , Fonck R. , Jakubowski M. , Tritz K. , Burrell K. , Greenfield C. , Robinson J.
Published: July 2002

A beam emission spectroscopy system has been installed on DIII-D to provide localized density fluctuation measurements for long-wavelength turbulent modes with k⩽3 cm−1 which are typically associated with anomalous radial transport. High signal-to-noise fluctuations measurements are accomplished through use of high speed electronics to maintain a frequency response of over 500 KHz and cryogenically cooled amplifiers and detectors to reduce electronic noise. The optics and neutral beam-sightline geometry have been optimized to allow for spatial resolution of Δr⩽1 cm. In addition, a half-scale two-dimensional (2D) fiber array to measure the 2D turbulent density field, necessary to measure the full S(kr,kθ) wavenumber spectra, has been implemented and initial results obtained.
Tokamak Fusion Test Reactor charge exchange atom spectrometry using a natural diamond detector
Authors: Krasilnikov A. V. , Medley S. S. , Gorelenkov N. N. , Budny R. V. , Ignatyev O. V. , Kaschuck Yu A. , Petrov M. P. , Roquemore A. L.
Published: July 2002

Natural diamond detectors (NDD) developed in Russia were used for fast charge exchange H0 atom spectrometry and flux dynamic measurements during Tokamak Fusion Test Reactor (TFTR) H+ minority ion cyclotron resonance heating (ICRH) experiments in deuterium plasma. For selected NDDs, the high energy resolution (∼2%–3%) and radiation resistance (5×1014 n/cm2) and low sensitivity to neutrons and gammas enable spectrometry of fast (0.2–3 MeV) atoms in TFTR radiation conditions. The NDD compact housing (∼2 cm+3) allowed noninterfering insertion into the particle charge exchange flight tube giving both systems similar views which allows comparison of their spectra and fluxes. A small NDD was chosen to limit count rates to 7×105 s−1. A spectroscopy amplifier operating with pileup inspection at such rates was developed, enabling measurement of the dependence of fast perpendicular proton energy spectra on ICRH heating power during sawtooth-free and sawtooth-crash times. The results agree with a model developed for sawtooth redistribution of fast particles.
Lower order blaze grating spectrometer of large diffraction angle
Authors: Koshkin Yu. S. , Mukhin E. E. , Razdobarin G. T. , Semenov V. V. , Shilnikov A. N. , Mihailovskij Yu. K. , Bakh L. I.
Published: July 2002

A new kind of large dispersion lower order blaze grating spectrometer is built. The design is based on the use of uncustomary large angles of incidence and diffraction approaching 80°. The double diffraction optical scheme is employed to fit the design conception. A set of compact size grating spectrometers of various focal lengths and grating ruled widths has been manufactured and explored. The measured grating efficiency related to different blaze angles shows the evidence for the instrument gainful operation. The spectrometer imaging properties are much promising to enable a fine spectral resolution to 0.005 nm under a short focal length ∼100 mm. The estimation of flux luminosity is made in comparison with Fabry–Perot interferometer.
A small-angle neutron scattering cell for the study of supercritical fluids at elevated pressure and high temperature: A study of heavy water
Authors: Bonetti M. , Ambroise J. P. , Calmettes P.
Published: July 2002

The main characteristics of a cell optimized for small-angle neutron scattering experiments on supercritical fluids are presented. The cell operates satisfactorily at pressures up to 300 bar at 400 °C and 750 bar at 90 °C. It has large apertures sealed by thick synthetic sapphire windows. The maximum forward scattering angle is 16° and the sample path length is 5.1 mm. It has been used to study scattering from supercritical heavy water close to its critical point at wave number transfers up to 0.34 Å−1.
Real-time multichannel scaler measurement of oscillator instabilities
Authors: Zieliński Marek , Dygdała Roman S. , Karasek Krzysztof , Zawadzka Anna
Published: July 2002

This article describes measurement of oscillator instabilities by a method using the real-time multichannel scaler (RTMS). A theoretical model for such application is also considered. The general problem of the oscillator instability measurements in time domain is discussed. The results of oscillator instability measurements using the real-time multichannel scaler and a time interval analyzer are compared. The full range of application of this method is up to 7E-7 and depends strongly on the RTMS construction. We present the results of oscillator instability measurements of the order of 3E-5, using the RTMS with a resolution of 3.13 ns and the range of operation 3.28 ms.
GaN linear electro-optic effect
Authors: Long X.-C. , Myers R. A. , Brueck S. R. J. , Ramer R. , Zheng K. , Hersee S. D.
Published: July 2002

Measurements of the linear (Pockels) electro-optical coefficient of wurtzite GaN are reported. The values for the electro-optic coefficients r33 and r31 are 1.91±0.35 and 0.57±0.11 pm/V at 633 nm, respectively, in agreement with extrapolations from measured second-harmonic generation coefficients (χ33(2)=−20±6 pm/V and χ31(2)=10±3 pm/V) suggesting that the dominant contributions are electronic in origin. Measurements were performed using a Mach–Zehnder interferometer with LiNbO3 as a reference material. Piezoelectric effects were also observed.
Magnetic phase transition in CeC2 crystals encapsulated in carbon nanocages
Authors: Yosida Yositaka , Oguro Isamu
Published: July 2002

An experimental study of magnetization process for CeC2 crystals encapsulated in carbon nanocages in the low-temperature antiferromagnetic region (T<30 K) in steady magnetic fields up to 15 T is reported. The magnetization curves show a dramatic change at a critical field Hc∼3.5 T. At a particular field Hs (<12±1 T), net magnetization levels off. The behavior at Hc is ascribed to a phase transition between an antiferromagnetic and a spin-flop state, and that at Hs to a phase transition between the spin-flop and a paramagnetic state. The magnetic phase diagram in the applied field and temperature plane is accurately determined based on the results of Hc(T) and Hs(T).
The effect of substrate misorientation on the photoluminescence properties of GaN grown on sapphire by metalorganic chemical vapor deposition
Authors: Grudowski P. A. , Holmes A. L. , Eiting C. J. , Dupuis R. D.
Published: July 2002

We report the growth and photoluminescence (300 and 4.2 K) characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates. The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on sapphire substrates using various growth conditions. The (0001) Al2O3 c-plane substrates are oriented exactly (0001) or misoriented either 2° towards the a plane (112̄0), 5° towards the m plane (101̄0), or 9° toward the m plane. A comparison of the 300 and 4.2 K optical characteristics of the samples grown on the different substrates indicates that a higher photoluminescence intensity is measured for the films on misoriented substrates.
Picosecond hot electron light emission from submicron complementary metal–oxide–semiconductor circuits
Authors: Tsang J. C. , Kash J. A.
Published: July 2002

Optical emission consisting of pulses with temporal widths of less than 270 ps has been detected from fully functional silicon integrated circuits fabricated using submicron complementary metal– oxide–semiconductor (CMOS) logic gates. Emission is observed under normal bias conditions and occurs when the gates are switching. The emission arises from the hot electron populations created by the transient current pulses present in the transistors during switching. The speed and spectral characteristics of the emission suggest future applications in the measurement of timing in high speed CMOS circuits.
Investigation of CxSi defects in C implanted silicon by transmission electron microscopy
Authors: Werner P. , Eichler S. , Mariani G. , Kögler R. , Skorupa W.
Published: July 2002

Buried CxSi layers were produced by high-energy implantation of carbon into CZ silicon. The depth distribution of carbon, the morphology of the buried layers, as well as the precipitation of C were investigated as functions of rapid thermal annealing between 700 and 1300 °C, using transmission electron microscopy, secondary ion mass spectroscopy, and positron annihilation measurements. Different kinds of microdefects occur: below ≈800 °C there are vacancy agglomerates as well as metastable C–Si agglomerates (Φ≈2 nm), whereas at higher temperatures β-SiC precipitates are observed. Results are discussed in terms of the interaction between C atoms and radiation-induced defects.
Nanostructure patterns written in III–V semiconductors by an atomic force microscope
Authors: Magno R. , Bennett B. R.
Published: July 2002

An atomic force microscope has been used to pattern nanometer-scale features in III–V semiconductors by cutting through a thin surface layer of a different semiconductor, which is then used as an etch mask. Cuts up to 10 nm deep, which pass through 2–5 nm thick epilayers of both GaSb and InSb, have been formed. Lines as narrow as 20 and 2 nm deep have been made. Selective etchants and a 5 nm GaSb etch mask are used to transfer patterns into an InAs epilayer. The results are promising for applications requiring trench isolation, such as quantum wires and in-plane gated structures.
Low-temperature, flux-grown, Na-doped LaMnO3: Magnetic properties
Authors: Washburn Newell R. , Stacy Angelica M. , Portis Alan M.
Published: July 2002

Crystalline powders of Na-doped LaMnO3 have been precipitated from molten sodium hydroxide at 450 °C. Elemental analysis by wavelength dispersive spectroscopy indicates than Na substitutes for Mn giving LaMn1−xNaxO3+δ, with x=0.2. The pseudocubic lattice parameter of 3.916 Å is larger than that of the undoped material, consistent with substitution at the Mn site. Analysis of magnetic susceptibility gives a ferromagnetic Curie–Weiss temperature of 130 K, which is to be compared with the onset of weak ferromagnetism near 300 K. Low-temperature magnetization measurements suggest a model of canted antiferromagnetic clusters.
Relationship between storage media and blue photoluminescence for oxidized porous silicon
Authors: Loni A. , Simons A. J. , Calcott P. D. J. , Newey J. P. , Cox T. I. , Canham L. T.
Published: July 2002

Blue photoluminescence is observed, with nanosecond decay time, from rapid thermally oxidized porous silicon as a result of accelerated aging in plastic containers. Photoluminescence measurements, combined with chemical analyses of the “aged” porous silicon, indicate that the emission is a consequence of the incorporation of trace organic (hydrocarbon) contamination from the plastic containers as they outgas at a mildly elevated temperature (80 °C) and, albeit at a reduced rate, at room temperature. Such carbonaceous contaminants can subsequently be removed by high-temperature annealing, a process which also quenches the blue photoluminescence. Consequently, it is important to take into consideration the storage medium used when making comparative luminescent and compositional studies of porous silicon and, perhaps, porous materials in general.
Evidence for layered growth of (100) textured diamond films
Authors: Godbole V. P. , Sumant A. V. , Kshirsagar R. B. , Dharmadhikari C. V.
Published: July 2002

The growth of diamond films synthesized by the hot filament chemical vapor deposition method has been studied by scanning tunneling microscopy (STM). The smooth (100) faces of micron-sized diamond crystallites were found to exhibit pyramidal shaped architecture at the nano level. The STM data for chemical vapor deposited diamond is analyzed in the light of recently developed dynamical scaling approach. The value of the scaling exponent α≅0.85 signifies a growth primarily driven by the transport of reacting species on the surface rather than molecular diffusion in gas phase.
Favorable formation of the C49-TiSi2 phase on Si(001) determined by first-principles calculations
Authors: Yu B. D. , Miyamoto Yoshiyuki , Sugino Osamu , Sasaki T. , Ohno T.
Published: July 2002

Using first-principles total-energy calculations, we investigated the atomic structure of a very thin Ti film on Si(001) and their intermixing. Our calculations show that the Ti film forms a pseudomorphic body-centered-tetragonal structure on Si(001). We found that intermixing of Ti and Si atoms energetically favors the formation of a C49-TiSi2 phase. We propose a plausible explanation of how the C49-TiSi2 phase and the interfacial structure between C49 phase and Si(001) are formed. We discuss why the transformation of the C49 phase into the C54 phase is inhibited when the TiSi2 dimensions reach the submicron region.
Magnetoelastic coupling and magnetic anisotropy in La0.67Ca0.33MnO3 films
Authors: O’Donnell J. , Rzchowski M. S. , Eckstein J. N. , Bozovic I.
Published: July 2002

We report the results of magnetization measurements on pseudomorphic (fully strained) c-axis oriented colossal magnetoresistance manganite thin films grown by molecular beam epitaxy. We observe uniaxial magnetic anisotropy (hard axis/easy plane) with the easy plane being the film plane. Within the plane a weaker biaxial anisotropy is observed with [100] (Mn–O bond direction) easy axes. The magnetization dependence of the uniaxial anisotropy constant follows the predicted magnetization dependence of the magnetostriction constants within single-ion models indicating that the anisotropy energy is dominated by strain-induced anisotropy from the lattice constant mismatch with the SrTiO3 substrate. These results indicate a magnetostriction constant λ100≈+7×10−5, and an induced orbital moment of at least 0.02μb/Mn ion. We predict that by appropriate substrate selection an equilibrium out-of-plane magnetization can be produced.
Luminescence of as-grown and thermally annealed GaAsN/GaAs
Authors: Francoeur S. , Sivaraman G. , Qiu Y. , Nikishin S. , Temkin H.
Published: July 2002

We report a study of the luminescence properties of coherently strained GaAs1−xNx grown on GaAs by metalorganic molecular beam epitaxy. Well-defined photoluminescence was observed in samples with a nitrogen concentration up to 3%. Samples subjected to thermal anneals, investigated by x-ray diffraction and photoluminescence, show increased nitrogen incorporation and significant improvements in the luminescence efficiency. A band-gap reduction of more than 400 meV, compared to GaAs, is observed for a nitrogen concentration of ∼3%. For the range of nitrogen concentrations investigated here, the band gap follows predictions of the dielectric model of Van Vechten [J. A. Van Vechten and T. K. Bergstresser, Phys. Rev. B 1, 3351 (1970), and references therein].
Raman scattering in ion-implanted GaN
Authors: Limmer W. , Ritter W. , Sauer R. , Mensching B. , Liu C. , Rauschenbach B.
Published: July 2002

Raman measurements were performed on molecular beam epitaxially grown GaN before and after implantation with Ar+, Mg+, P+, C+, and Ca+ ions. With increasing ion dose, new Raman peaks arise at 300, 360, 420, and 670 cm−1, independent of the ion species. After rapid thermal annealing at temperatures between 900 and 1150 °C for 15 s, the intensities of the Raman modes decrease with increasing temperature with the exception of the 360 cm−1 mode which shows a maximum in intensity after annealing at 900 °C. The mode at 300 cm−1 is attributed to disorder-activated Raman scattering, whereas the other three modes are assigned to local vibrations of vacancy-related defects.
Nb/Al/AlO
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Josephson junctions for programmable voltage standards
Authors: Schulze H. , Behr R. , Müller F. , Niemeyer J.
Published: July 2002

We present a study of the microwave characteristics of Josephson junctions based on a superconductor–insulator–normal–insulator–superconductor sandwich, fabricated in Nb/Al/AlOx technology. With the nonhysteretic Shapiro steps and the small parameter spread observed, the junctions are suitable for programmable Josephson voltage standards. Their characteristic voltage Vc≈100 μV enables operation at microwave frequencies up to 100 GHz.
Atomic structures of hydrogen-terminated Si(001) surfaces after wet cleaning by scanning tunneling microscopy
Authors: Endo Katsuyoshi , Arima Kenta , Kataoka Toshihiko , Oshikane Yasushi , Inoue Haruyuki , Mori Yuzo
Published: July 2002

Scanning tunneling microscopy observations are performed on a H-terminated Si(001) surface treated with HF solutions and ultrapure water with very low dissolved oxygen and total organic carbon contents. Over a large area, row structures are observed in [110] and [11̄0] directions. Pyramidal-shaped etch pits are also observed, which are caused by anisotropic etching by OH ions. Detailed images clearly show 2×1 periodic structures. It is suggested that every other row of the ideally dihydride 1×1 surface is etched preferentially by OH ions. This explains the mechanism by which the smallest etch pits are formed.
Tapping-mode tuning fork force sensing for near-field scanning optical microscopy
Authors: Tsai Din Ping , Lu Yuan Ying
Published: July 2002

A tapping-mode tuning fork force-sensing method for near-field scanning optical microscope is reported. Use of the tapping-mode tuning fork with mechanically asymmetric excitation generates better stability and sensitivity than in the shear force mode. Comparison of force curves for the two methods demonstrate that the tapping-mode tuning fork method provides a simpler and more sensitive method for near-field measurements. The method is demonstrated by imaging a sample consisting of 500 nm standard polystyrene spheres on silica in both air and water.
Negative differential resistance due to single-electron switching
Authors: Heij C. P. , Dixon D. C. , Hadley P. , Mooij J. E.
Published: July 2002

We present the multilevel fabrication and measurement of a Coulomb-blockade device displaying tunable negative differential resistance (NDR). Applications for devices displaying NDR include amplification, logic, and memory circuits. Our device consists of two Al/AlxOy islands that are strongly coupled by an overlap capacitor. Our measurements agree excellently with a model based on the orthodox theory of single-electron transport.