bluuebunny/crossref_metadata_2025 huggingface dataset:
Measuring the escaping beam ions from a tokamak plasma
Authors: Buchenauer D. , Heidbrink W. W. , Roquemore L. , McGuire K.
Published: July 2002

A new technique using a silicon surface barrier (SSB) diode has been developed for measuring the escaping fast ion flux from a tokamak plasma. Calibration of the detector with an ion beam showed that at a fixed energy the diode’s output current varied linearly with the incident deuteron flux. The diode was mounted inside the PDX vacuum vessel with collimating apertures designed to admit the spiraling orbits of 50-keV deuterons expelled from the plasma by MHD instabilities. Results from PDX indicated that relative measurements of the escaping fast ion flux due to several plasma instabilities could be made.
Excess noise of the R 928 photomultiplier
Authors: Köchel M. , Hirsch K. , Salzmann H.
Published: July 2002

The noise factor of the HAMAMATSU R 928 circular cage photomultiplier has been measured. It is demonstrated that the optimum mode of operation with respect to the noise is the one with constant interstage voltage distribution. Different effects contributing to the overall noise factor have been identified.
Hα laser fluorescence diagnostic on the Tara Tandem Mirror experiment
Authors: Guss W. C. , Yao X. Z. , Pócs L. , Mahon R. , Casey J. , Post R. S.
Published: July 2002

A laser fluorescence diagnostic has been used for measuring the neutral hydrogen density in the central cell of the Tara thermal barrier tandem mirror. Experiments have been performed using laser-induced, resonance fluorescence detection of Hα (6563-Å) radiation. Measurements were made at a number of radial positions with 1-cm resolution, from the magnetic axis to near the plasma limiter. Stray laser light contributions to the signal were eliminated with a double-pulse technique. For comparison, the chord-averaged plasma Hα radiation was analyzed under the identical conditions for which laser fluorescence data were taken.
Optical Ranicon detectors for photon counting imaging. I
Authors: Clampin Mark , Crocker Jim , Paresce Francesco , Rafal Marc
Published: July 2002

We discuss the design and development of Ranicon detectors for optical photon counting imaging on ground-based telescopes. The significant factors which determine the performance of these detectors are found to be the proximity focusing stage, the microchannel-plate stack (MCP), and the signal processing electronics. For applications in optical astronomy, the low photon counting efficiency typically found with optical MCP-based detectors, due to ion barrier films, presents an additional consideration. We review the performance of each stage of the Ranicon detector and the techniques for achieving optimal performance. A new approach to the signal processing electronics reduces nonlinearity, while achieving increased processing speeds and a position error corresponding to <21 μm FWHM. A significant improvement in detector performance is achieved with an advanced Ranicon incorporating a reduced proximity focusing gap and an unfilmed input plate in the MCP stack. The theoretical spatial resolution of both standard and advanced Ranicon designs is derived and compared to the experimentally determined values. For the advanced Ranicon, this spatial resolution is shown to be typically 40 μm FWHM at ∼650 nm. The point spread function of the Ranicon system is shown to be stationary over the active imaging area, principally due to the removal of nonlinearities and noise sources from the signal processing electronics.
Practical definition of the plasma sheath edge for modeling planar glow discharges
Authors: Wang Yicheng
Published: July 2002

While the parallel-plate capacitive model is often employed to describe the electrical behavior of a plasma sheath, the simple question of how far apart the two plates are for a given plasma cannot be easily answered yet because of the lack of a workable definition of the sheath edge. The sheath edge estimated with the Child–Langmuir equation may misplace as much as 40% of the total space charge outside the sheath. An alternative practical definition of the sheath edge is proposed that includes almost all space charge within the sheath.
Broadband microwave absorption spectrometer for liquid media
Authors: Mukherjee Pritish , Gosnell Timothy R. , Bigio Irving J.
Published: July 2002

A broadband, continuous-sweep microwave spectrometer has been constructed for measurements of the absorption coefficient of aqueous solutions and other liquid media. The spectrometer makes use of the phase fluctuation optical heterodyne technique, which provides a direct measure of the microwave power deposited in the sample. Consequently, in contrast to the standard dielectrometric techniques that indirectly determine the absorption coefficient via separate measurements of the real and imaginary parts of the dielectric constant, this spectrometer directly measures the microwave absorption coefficient. Broadband spectra are obtained using a transmission line to couple microwave power into the liquid sample. The absorption spectrum for deionized water in the range 3–20 GHz is presented as an example and shows excellent agreement with calculated values of the absorption coefficient based on previously published dielectric data.
Formation of Al-Cu via/interconnect by low-pressure collimated sputtering
Authors: Joshi R. V. , Dalal H. M. , Filippi R.
Published: July 2002

This paper describes the effect of low-pressure collimated sputtering (LPCS) on deposition rates, step coverages, and electrical properties of Al-Cu. The LPCS deposition is achieved in a magnetron sputter deposition system with a hollow cathode and collimator. The deposition results show that as the via or line size reduces, a complete fill requires a monotonic increase in the aspect ratio of the collimator which limits the throughput for a thick deposition, especially at high pressures (≳1 mT). The benefit of the LPCS is the improved deposition rate (scaled to power) of 1.5–2× compared to the conventional high-pressure collimated deposition. The integration of LPCS process to fabricate a two-level Al-Cu metal structure with submicron Al-Cu studs (aspect ratio of 2) shows excellent via and electromigration resistances.
Theoretical analysis of ultrafast pump-probe experiments in semiconductor amplifiers
Authors: Girndt A. , Knorr A. , Hofmann M. , Koch S. W.
Published: July 2002

Pump-probe experiments in semiconductor amplifiers are analyzed theoretically. On the basis of Maxwell–Semiconductor–Bloch equations it is shown that the probe signal exhibits dominant oscillatory interference-like structures. These structures are superimposed on the pump and probe intensity dependent features. The calculations are qualitatively similar to experimental results.
Surface sources of piezoelectric transduction
Authors: Liu Yuan
Published: July 2002

Recently, a complete formulation of the transient surface excitation problem for piezoelectric materials has suggested the existence of a type of electrical sources on the surface not traditionally considered in piezoelectric transduction. This letter shows that these additional sources correspond to electric current dipoles. It is shown that the wave forms, or the frequency dependence, of waves generated by these sources are different from those generated by traditionally studied sources such as mechanical stresses and electric currents. These characteristics can be used to identify the contribution of such sources. Schottky and p-n junctions on the surface of a semiconductive material are suggested as the experimental implementation of the new sources. In addition to piezoelectric transduction, current dipoles can also be used to generate electromagnetic waves in a nonpiezoelectric medium.
Method to calibrate an ionization chamber for measuring indoor radon concentrations with standard gamma-ray sources
Authors: Matsumoto Yuzuru , Tokumori Kenji , Iwata Toru , Sakae Takeji , Ishibashi Kenji , Katase Akira
Published: July 2002

Most instruments for measuring radon concentrations in the air should be calibrated using air with known radon concentrations, obtained from a solution of radium. However, safe handling of such a solution of alpha-active elements can be troublesome. Standard gamma-ray sources of low activity are handled more safely and typically used to obtain the absolute detection efficiency of a Ge detector with high accuracy. A new method has been developed to calibrate a radon detector with such sources. A radon exhalation rate for a substance containing a small amount of radium is measured with the radon detector to be calibrated. After this, the vessel containing the radium is sealed so that the radon does not escape from it. The buildup of the activity of  214Bi in it is obtained from gamma-ray measurements and gives the radon exhalation rate on the basis of the activity of the standard sources. From the comparison between the two values of the exhalation rate, the radon detector is calibrated. A plane multiwire-electrode ionization chamber is used as a radon detector, and its detection efficiency is calculated from its geometrical form. The radon exhalation rate computed from the calculated efficiency agrees with that determined from the activity of the standard gamma-ray sources within their specified 6% error.
An inexpensive mirror furnace
Authors: Gabršček S. , Holc J.
Published: July 2002

This note describes the surface treatment of a mirror furnace, made from a block of aluminum. The method offers an inexpensive way to obtain temperatures up to 2100 °C.
A pulsed alkali-ion gun for time-of-flight secondary ion mass spectrometry
Authors: Hues Steven M. , Colton Richard J. , Wyatt Jeffrey R. , Schultz J. Albert
Published: July 2002

A pulsed alkali-ion gun for use in time-of-flight secondary ion mass spectrometry (TOF-SIMS) has been constructed and tested. The ion pulses are formed by rastering a continuous ion beam from a thermionic emitter source across a 0.13-mm slit. The pulses consist of 100–1000 alkali ions having a full-width-at-half-maximum temporal distribution of less than 2.4 ns and a spot size of approximately 1×2 mm. In addition, the angular beam divergence of this ion gun is less than 0.5°, making it also suitable for TOF ion scattering and direct-recoil spectroscopy. The ion gun has been used to obtain a series of cluster ion spectra which show a mass resolution of about 2000 and a mass range of nearly 9000 amu.
Refractive index and thickness of films using a double parallel-plate refractometer
Authors: Giuliani J. F.
Published: July 2002

A parallel-plate refractometer has been developed which can be used to measure the refractive index of liquid and solid films with an accuracy of 0.4%. The refractometer, which is a modification of the Pfund single-plate refractometer, provides the ability to measure film thicknesses which range between 0.1 and several millimeters.
A system for automatically scanning tissue culture dishes to detect fluorescently labeled cell colonies
Authors: Goldstein Seth R. , Guan-Xiong Zhou , Siegel Ruth E. , Brownstein Michael J.
Published: July 2002

A microprocessor-controlled system has been developed to automatically scan tissue culture dishes in order to detect and locate fluorescently labeled cell colonies for subsequent cloning. An X-Y recorder mechanism moves an 80-mm-diam dish in a raster scan through a stationary laser beam adjacent to a photomultiplier tube equipped with an emission filter. Front-end electronics processes the PMT signal to screen out small-scale fluorescent artifacts of selectable size (e.g., <0.2 mm). Appropriate signals are input to the computer which then interrupts the raster scan to perform a limited fine scan of the dish to accurately localize the fluorescent spot position. An additional artifact test using a different filter is then performed. The underside of the dish is scribed at the location of spots that pass this test. Using fluorescein as a label, fluorescence as low as 25% above intrinsic cell background fluorescence can be detected. The fluorescence signal level threshhold can be set (e.g., 70% above intrinsic cell background) to within an accuracy of approximately 15% of intrinsic cell background fluorescence, and the system will reliably find colonies with a signal exceeding that level. With the above typical values, the number of false positives is typically less than five per dish and the time to completely scan an 80-mm-diam tissue culture dish is 2–4 min.
Small-angle scattering technique with a simplified angle selection
Authors: Küttel O. M.
Published: July 2002

A simplified homodyne small-angle scattering technique for plasma fluctuation measurements is described. The local oscillator is produced by a beam splitter which lies just behind the scattering area in the main laser beam. The scattered radiation is reflected from the beam splitter and directed onto the detector. Meanwhile, the transmitted portion of the beam is reflected back to the same beam splitter and superimposed with the scattered light so as to act as a local oscillator. The proposed method has several advantages. No separate local oscillator path is necessary, and the alignment and selection of different scattering angles is easily done by two microprocessor-controlled step motors. With a variable attenuator the local oscillator power is adjustable to any desired value. Heterodyning is possible by adding an acousto-optic modulator which shifts the LO frequency. First results of measurements on microturbulences in a plasma are presented.
Sensitive contactless eddy-current conductivity measurements on Si and HgCdTe
Authors: Chen M. C.
Published: July 2002

A high-sensitivity high-spatial-resolution eddy-current apparatus has been set up for contactless conductivity measurements on Si and HgCdTe. The inductive sensitivity limit has been demonstrated, on Si slices, to a very low σt (product of conductivity and thickness) of 0.0004 Ω−1 and the spatial resolution was shown to be about 4 mm, both a threefold improvement over past published results. HgCdTe bulk slices and epitaxial films have been measured over a wide range of σt from 0.001 to 1 Ω−1 at 77 K. The conductivity mapping measurements on HgCdTe material were also demonstrated for the first time. The sensitivity of eddy-current probes consisting of miniature commercial rf coils were shown to be not only temperature independent, but also very stable after repeated thermal cyclings between 300 and 77 K. This feature makes the eddy-current method an ideal technique for routine contactless conductivity measurements on HgCdTe material at 77 K. We also show that both the sensitivity and the spatial resolution of eddy-current probes can be explained quantitatively by a simple theory which treats coils as magnetic dipoles.
High temperature magnetic sphere/needle rheometer
Authors: Chu Benjamin , Hilfiker Rolf
Published: July 2002

A magnetic sphere/needle rheometer, which is capable of measuring viscosities between ≂3×10−3 and 5×104 Pas at temperatures up to 380 °C, has been developed. The temperature dependence of the melt viscosity of a polyethylene sample is also reported.
Reply to ‘‘Comment on ‘Optical carriage for laser-induced fluorescence in a magnetized plasma’ ’’ [Rev. Sci. Instrum. 6
0, 3830 (1989)]
Authors: Anderegg F. , Paris P. J. , Skiff F. , Good T. N. , Tran M. Q.
Published: July 2002

The comments made by Goeckner and Goree are correct, in general, but they are not relevant to our experiment. The measurements made with the optical carriage represent an average over the diagnosed volume, and the laser power is low enough to avoid the effect due to saturation broadening.
Enhanced dc arc lamp performance for spectroscopic applications
Authors: Woodlee Randall L. , Fuh Ming-Ren S. , Patonay Gabor , Warner Isiah M.
Published: July 2002

The performance of a high-pressure xenon arc lamp is enhanced by application of a combination of two techniques which (1) reduces noise due to arc wander and (2) increases the lamp intensity. Fluctuations in lamp intensity due to arc wander are minimized by the superimposition of an alternating current (ac) on the direct-current (dc) source voltage in conjunction with detector averaging. Lamp intensity is increased by the application of a static magnetic field to the arc plasma. Arc stability and intensity are monitored indirectly by measuring arc-excited Rhodamine B fluorescence. Data illustrating the effects of each technique individually and in combination are presented. Lamp output is typically maintained to less than 1% relative standard deviation while intensity is increased by as much as 127%.
Exact solutions of balance equation governing ion-beam-induced composition changes and sputtering
Authors: Sigmund Peter
Published: July 2002

Analytic solutions have been found for a system of nonlinear integro-differential equations describing compositional changes and sputtering of materials under ion bombardment in planar geometry. These solutions refer to the stationary (high-fluence) limit and were found by adopting feasible expressions for intermediate quantities from which both input and output can be derived. Explicit examples include sputtering, collisional mixing, and relaxation, but the method allows inclusion of a wider variety of effects.
Charge transfer limitations in δ-doped AlGaAs/InGaAs pseudomorphic high electron mobility transistors
Authors: Jogai B.
Published: July 2002

The charge transfer between the δ-doped region and channel of an AlxGa1−xAs/InyGa1−yAs pseudomorphic high electron mobility transistor (p-HEMT) is explored theoretically. The model is based on a self-consistent solution of the k⋅p Hamiltonian and Poisson equation and explicitly accounts for surface states. It is shown that heavily doping the δ layer does not guarantee a large amount of electrons in the channel. At higher doping, an increasing number of electrons are retained in the δ-layer, reducing the charge-transfer ratio. It is further shown that charge transfer is drastically reduced when the cap layer is recessed to form the gate.
Structural studies of electrochemical interfaces with x rays
Authors: Abruña H. D. , White J. H. , Bommarito G. M. , Albarelli M. J. , Acevedo D. , Bedzyk M. J.
Published: July 2002

We have employed x-ray absorption spectroscopy, including surface EXAFS (extended x-ray absorption fine structure) and x-ray standing waves (XSW) in the in-situ structural study of electrochemical interfaces. The SEXAFS technique was used to study the structure of half a monolayer of copper underpotentially deposited on a Pt(111) electrode. From analysis of the data a Cu–Cu distance of 2.85 Å and a coordination number of six were determined, strongly suggesting that the deposit is largely composed of clustered sites. The electrosorption isotherm of iodide on a Pt(111) electrode surface was measured in situ using x-ray absorption spectroscopy, and it exhibited two plateaus which we ascribe to changes in packing density and surface structure. Using x-ray standing waves, we have studied the potential dependence of the adsorption of iodide onto a Pt/C LSM and have interpreted the results in terms of distributional changes in the vicinity of the electrode surface.
High-resolution Compton profile spectrometer for 29.5-keV x rays with a combination of crystal analyzer and imaging plate
Authors: Itoh F. , Sakurai M. , Sugawa T. , Suzuki K. , Sakai N. , Ito M. , Mao O. , Shiotani N. , Tanaka Y. , Sakurai Y. , Nanao S. , Kawata H. , Amemiya Y. , Ando M.
Published: July 2002

A high-resolution Compton spectrometer has been installed for 29.5-keV incident x rays from a vertical wiggler inserted in the 2.5-GeV storage ring of the Photon Factory at Tsukuba. This spectrometer consists of bent-crystal monochromator, a Cauchois-type bent-crystal analyzer, and an imaging plate as a position sensitive detector. The overall momentum resolution is 0.084 a.u. for the incident x-ray energy of 29.5 keV. High-resolution Compton profile measurements on Al, a quasicrystal Al-Li-Cu, and solid and liquid phase of Li are shown to demonstrate the performance of this spectrometer.
Monochromator and beamline for a laboratory synchrotron (abstract)
Authors: Tiit V. , Kuznetsov A. S. , Pill K. , Vilt E.
Published: July 2002

In recent years, at the Institute of Physics of the Estonian Academy of Sciences, a laboratory pulsed synchrotron radiation source with the electron orbit radius of 6 cm and the light pulse duration of about 30 ms1 has been devised. By now, a normal incidence vacuum monochromator operating in the spectral range 50–350 nm has been designed for the synchrotron. The monochromator has a nonclassical diffraction grating with the radius of the curvature 0.5 m and the spectral resolution about 0.05 nm. In the beamline, a toroidal mirror is used, which focuses the radiation on the electron orbit plane within a 110 mrad angle and directs it to the entrance slit of the monochromator. The absolute values of the SR radiation in the VUV region are determined with the help of a NO ion chamber. In the report, laboratory testing data are presented which show the possibilities of the application of the SR source in spectroscopic investigations.
Submicrometer-resolution photoelectron-spectroscopy at MAX Lab
Authors: Nyholm R. , Eriksson M. , Hansen K. , Sairanen O-P. , Werin S. , Flodström A. , Törnevik C. , Meinander T. , Sarakontu M.
Published: July 2002

The design of a photoemission microprobe beamline at the MAX laboratory is presented. The beamline will utilize the radiation from a 26 period undulator on the 550-MeV MAX storage ring. The beamline will be capable of providing about 1010 photons/s of monochromatized radiation (bandwidth better than 0.25 eV) in the energy range of 20 to 150 eV focused into a submicrometer focal spot. It will be used for scanning photoemission experiments with a lateral resolution better than 1 μm. The optical system is comprised of a plane-grating monochromator with a Kirkpatrick–Baez objective and a specially designed ellipsoidal focusing mirror.
High spatial resolution at very high sensitivity using synchrotron radiation excited XPS
Authors: Schaible M. , Petersen H. , Braun W. , Koch E.-E.
Published: July 2002

A dedicated surface analysis beamline with ‘‘small spot’’ XPS facilities is currently under construction at BESSY. When completed in 1989, it will serve as a primary means for the study of metal, semiconductor, and insulator surfaces via laterally resolved XPS and photoyield measurements. This report discusses the first results of this system as attached to a BESSY plane grating monochromator beamline. The data obtained to date clearly demonstrate the potential these two analytical techniques offer for the study of materials science. A further improvement of lateral resolution (now ≊150 μm) into the 1 μm or even submicron range is discussed.
Ultrahigh precision coupling of angular motion for a constant exit-height monochromator (abstract)
Authors: Rosenbaum G. , Schug J.
Published: July 2002

An ultrahigh precision coupling of the angular motion of the two axes in a double-crystal monochromator with constant exit height has been constructed. The coupling device is a double parallelogram similar to the kind used for drafting tables. Computer simulations have been used to minimize the angular motion in the joints of the parallelograms to less than ±5° for the entire Bragg-angle range from 10° to 71°. This allows the use of backlash-free and friction-free flexural pivots. The axis of the first crystal is controlled by a precision rotary table. The shaft of the second crystal stage is supported by a trolley riding on a translation stage. Bearings allow for free rotation of the shaft. The double parallelogram provides only for the exact angular position of the second axis but does not support any weight of the second crystal stage and freely follows the trolley. The trolley is positioned so that the beam from the first crystal is intercepted and reflected at the correct height. The device is ultrahigh vacuum compatible. This design, which fully separates the two demands for extremely precise angular tracking and for less precise positioning for constant exit height, has several advantages beyond its superior tracking accuracy. The stationary first axis allows efficient, in-vacuum cooling of the first crystal. A direct rotary drive can be used for the first axis thus providing direct linear Bragg-angle control. A heavy weight second crystal stage, e.g., for sagittal focusing, may be used without deforming the angular linkage mechanism since all weight is carried by the rugged translation stage. No high-precision machining such as grinding or lapping is needed for the double-parallelogram linkage. The arms of the parallelogram, i.e., the distance between the holes for the flexural pivots, need to be only of precisely the same length.

Testing the linkage shows the expected high accuracy. The maximum nonrepeatable deviation between the two axes is less than 5×10−5 degree (=0.2 arcsec). The tracking error for a 10−4 degree step is less than 1×10−5 degree, for a 10−3 degree step it is less than 2×10−5 degree. The maximum total deviation at any point within an interval of 0.1° is less than 1×10−4 degree (=0.4 arcsec). Repeatable and smooth long range deviations of a few arcseconds are compensated by feeding a predetermined corrective voltage to a piezo translator.
(2+1)-dimensional fundamental spatial dark soliton
Authors: Liu Shan-liang , Wang Wen-zheng , Xu Jing-zhi
Published: July 2002

We give the analytical fundamental dark soliton solutions of the (2+1)-dimensional nonlinear Schrodinger equation [(2+1)-D NSE]. The solutions reduce to (1+1)-D dark soliton solutions when the width of soliton in one transverse direction is much wider than that in the other direction, which is in good agreement with the experimental observation of the dark spatial solitons.
Perspectives on the use of very long undulators in high-energy storage rings (invited)
Authors: Coisson R.
Published: July 2002

A few electron storage rings exist (and possibly could be available in the future), with energy >10 GeV and with straight sections of the order of 100 m on which very long undulators could be installed. The exceptionally low emittance that these machines can reach when run at relatively low energies would allow highly degenerate radiation to be produced in the soft and medium x-ray range, with applications to biological imaging near the C and N K edges, holography, and nonlinear optics down to a few angstroms, pumping of soft x-ray ion lasers, picosecond or femtosecond resolution spectroscopy, etc.
Differential microcalorimeter for liquid samples
Authors: Barbini A. , Bertolini D. , Cassettari M. , Papucci F. , Salvetti A. , Salvetti G. , Veronesi S.
Published: July 2002

A microcalorimeter for liquid samples with high performance and low cost is described. It is essentially a differential apparatus in a ‘‘twin’’ configuration with two cylindrical cells. Two resistive sensors, put in a Wheatstone bridge, are wound on the cells to measure the temperature difference between them. Sensitivity, response time, and calibration procedure are reported. As illustrative example, the specific heat of some liquids at two temperatures has been measured.
Phase difference-to-voltage converter
Authors: Borghesani A. F.
Published: July 2002

A phase difference-to-voltage converter has been developed in order to measure and to monitor the phase angle φ between the rotating magnetic field and the disk magnetization in the recently developed rotating magnetic disk viscometer. The circuit described here shows a very good linearity (the nonlinearity has been experimentally found to be well ≤50 p.p.m.), high resolution (fractional phase changes as low as Δφ/φ≊10−4 can be detected), very high short-term stability (1/VφΔVφ/ΔT ≤10 p.p.m./°C), very good long-term stability (ΔVφ/Vφ ≤50 p.p.m. over several months), and a rapid response even at the low frequencies (0.5–30 Hz) used in the viscometer.
The superconducting x-ray lithography source program at Brookhaven (invited)
Authors: Williams G. P. , Heese R. N. , Vignola G. , Murphy J. B. , Godel J. B. , Hsieh H. , Galayda J. , Seifert A. , Knotek M. L.
Published: July 2002

A compact electron storage ring with superconducting dipole magnets, is being developed at the National Synchrotron Light Source at Brookhaven. The parameters of the source have been optimized for its future use as an x-ray source for lithography. This first ring is a prototype which will be used to study the operating characteristics of machines of this type with particular attention being paid to low-energy injection and long beam lifetime.
Polarization analysis of magnetic x-ray scattering (invited)
Authors: Gibbs Doon , Blume M. , Harshman D. R. , McWhan D. B.
Published: July 2002

In this paper we discuss polarization analysis in x-ray magnetic scattering experiments. The cross section for x-ray scattering is calculated, including magnetic terms, and three examples of magnetic structures are considered. It is shown that the contributions of the orbital- and spin-magnetization densities may be identified by analyzing the polarization of the scattered beam. We describe an instrument for performing linear polarization analysis in x-ray scattering experiments, and summarize its application in recent studies of holmium.
Spin-dependent K- and L-absorption measurements (invited)
Authors: Schütz G. , Frahm R. , Wienke R. , Wilhelm W. , Wagner W. , Kienle P.
Published: July 2002

Spin-dependent absorption spectroscopy with circularly polarized synchrotron radiation is presented as a new method to study magnetism in magnetic solids. In the near-edge absorption region, the spin-dependent absorption coefficient probes the spin density of unoccupied states of selected angular momentum at the absorber atom. The spin-dependent absorption effects as function of temperature contain information on the local magnetic coupling. A large spin-dependent part of the absorption of ∼+0.22 at the Pt L2 edges in PtFe is observed in transmission and fluorescence mode.
Spatial resolution characteristics of a GaAs-photocathode RANICON
Authors: Clampin M. , Paresce F.
Published: July 2002

We have evaluated the performance of the first RANICON to be processed with a GaAs photocathode. We discuss the design characteristics of this prototype detector and present experimental results showing an overall detector resolution of 76 μm FWHM, yielding a value for VR , the radial emission energy of a photoelectron, of 0.09 eV for the GaAs photocathode. On the basis of these figures, we discuss techniques for optimizing and improving the spatial resolution of GaAs-photocathode RANICONs.
Simulation studies on gas-to-particle conversion processes in the stratosphere by using ultraviolet SR (abstract)
Authors: Suzuki I. H. , Koike M. , Nakae S.
Published: July 2002

Since stratospheric particles have a possibility to make a large effect on the climate in a global scale, a number of observations have been carried out using different techniques.1 Those particles were found to consist of mainly sulfuric acid and to be 0.1–1.0 μm in size. Turco and co-workers proposed a model that the particles are formed through chemical and physical processes initiated by photodissociation of OCS (λ<2600 A).2 In order to examine this model, a simulation experiment in a laboratory system has been planned, in which ultraviolet components of SR are utilized. An optical system including a Seya-Namioka monochromator has been designed, constructed, and tuned precisely.3 In this system, the first prefocusing mirror (sphere) deflects the SR beam horizontally by 30°, and the second and the third ones (sphere) focus the beam vertically onto the entrance slit of the monochromator. The grating radius is 0.5 m. The monochromatized photon beam is reflected into the horizontal direction by the postfocusing mirror (toroid). A ray-tracing calculation was performed, and the obtained spot diagrams showed that the widths of the rays are about 100 μm at the two slits, and the spot size is 1.5×0.8 mm2 at the experimental point.

These calculated results were confirmed experimentally by using visible and ultraviolet components of SR. From an estimation on the rate of the particle formation using the data available in the literature, the rate determining step was found to be the photodissociation of OCS in the ultraviolet region. At first, the photoabsorption spectra (cross section) were measured at room temperature and at −80 °C (near to the stratospheric temperature). The spectrum is composed of a broad band centered at 2250 Å and of a number of small peaks. Photodissociation rates of OCS at several altitudes have been calculated using the present cross-section values, which indicated that the life of OCS is about 15 years at 20 km and two months at 30 km. It is known that CO and S are formed through the photodissociation of OCS. A computer-controlled mass spectrometer was made for pursuit of the time variation of CO density in the reaction cell, in which the sample gas, a few percent OCS in He, is introduced and irradiated by the photon beam. A chamber has been designed and constructed, in which a pseudostratospheric air is being irradiated by the ultraviolet radiation. A particle counter of laser-scattering type is being connected to this chamber in order to observe the particle number in it. The present study is the first examination applying SR to problems in the stratosphere as a simulated solar radiation. The obtained results have shown opening a new scientific opportunity in the utilization of SR.
An inexpensive net radiometer for multipoint spatial surveys
Authors: Granberg Hardy B. , Nadeau Andrew
Published: July 2002

The article describes an inexpensive net radiometer intended for multipoint spatial surveys. The radiometer employs plane polyethylene windows instead of domes. The use of plane windows eliminates the need for pressurizing and, because of the lesser air volume enclosed, reduces the potential for internal condensation. However, it also gives the radiometers an effective angle of view and a cosine response that both differ from those of domed instruments, and it may enhance effects of temperature differences between the upper and lower polyethylene shields in calm conditions. The new radiometer is easy to manufacture with uniform characteristics using readily available materials. Forty-four net radiometers were built, laboratory and field tested, and used with good success both under winter and summer conditions. Their sensitivity is 8.166 μV/W/sq m±7% in the thermal and 7.814 μV/W/sq m± 4% in the solar spectrum according to the laboratory tests, thus exhibiting a 4.5% greater sensitivity in the long than in the short wavelengths.
A simple endoscopic automatic vision system applied to monitoring of adhesive bonding
Authors: Grattan K. T. V. , Ning Y. N. , Palmer A. W. , Fox N. D.
Published: July 2002

A simple, endoscopic automatic vision system, using white-light illumination has been designed and is discussed. Results of an application to the monitoring of the laying of an adhesive strip in a robotically operated product assembly are illustrated.
A scanning tunneling microscopy/spectroscopy system for cross-sectional observations of epitaxial layers of semiconductors
Authors: Kato Takashi , Tanaka Ichiro
Published: July 2002

We have constructed a new scanning tunneling microscope (STM) using two mechanical stages. One (z stage) is for approaching the tip to the sample surface and the other (x stage) is for one-dimensional movement of the sample to observe a specific area of the sample surface. The stages move so precisely that the distance between the tip and the sample is constant during the sample movement. It enables us to find the specific area quickly. Another feature of the STM is a novel data accessing method which realizes high-speed scanning tunneling spectroscopy (STS) measurement. A great deal of data are accessed at high speed by a personal computer equipped with 32-megabyte random access memory (RAM). Using this system, STM and STS measurements of cleaved (110) surfaces of Ga0.47In0.53 As/InP multiquantum wells were performed in air.
Small, inexpensive apparatus for the determination of the density of powdered materials
Authors: Chern M. Y. , Mariani R. D. , Vennos D. A. , DiSalvo F. J.
Published: July 2002

An inexpensive apparatus for measuring the density of a small quantity of powdered material at an accuracy of 1% or better is presented. Since the working medium is a gas, the density of air or solvent sensitive samples can easily be measured with this apparatus in the ambient atmosphere of a glove box.
A 10-GHz frequency-domain fluorometer
Authors: Laczko Gabor , Gryczynski Ignacy , Gryczynski Zygmunt , Wiczk Wieslaw , Malak Henryk , Lakowicz Joseph R.
Published: July 2002

We describe the design and performance of a 10-GHz harmonic-content frequency-domain fluorometer. The modulated excitation is provided by the harmonic content of a train of ps pulses. High-speed and/or high-frequency detection was attained with a triode-type microchannel plate photomultiplier tube (MCP PMT) from Hamamatsu, R-2566-6, with 6 μm channels. To minimize the cost of the electronic components, and to minimize the noise due to these components, the detection circuits consists of two frequency ranges, 10 MHz–2 GHz and 2–10 GHz. The upper frequency limit of 10 GHz is determined by the current MCP PMT, so the usual configuration includes a low-noise 2–10-GHz amplifier. This amplifier is easily replaced with a 2–18-GHz amplifier to allow operation to 18 GHz and the use of faster PMTs, should they become available in the future. Measurement of known optical delays demonstrates the accuracy of the instrument. For instance, a 1.69 ps optical delay was measured as 1.7±0.4 ps from 0.5 to 10 GHz, and 1.7±0.2 ps from 2 to 8 GHz, where the uncertainty indicates the maximum deviation from the expected value. The data were shown to be free of systematic errors by measurements on fluorophores with single exponential decays, with decay times ranging from 61 ps to 1.24 ns. Measurement of anisotropy decays with correlation times of 24 ps are shown and it is predicted that correlation times as short as 1 ps could be measured with this instrument. And finally, the sensitivity of the instrumentation was demonstrated by measurements of the very weak intrinsic tryptophan emission of deoxyhemoglobin, which displays decay times ranging from 2 to 820 ps.
Effect of hydrogen ion shower doping in polycrystalline silicon thin-film transistors
Authors: Mishima Y. , Takei M. , Matsumoto N. , Uematsu T. , Wakino U. , Kakehi T. , Okabe M.
Published: July 2002

We investigated the effect of hydrogen ion shower doping on polycrystalline silicon thin-film transistors (p-Si TFTs). Hydrogen atoms were introduced to the channel region of p-Si TFTs by PH3/H2 ion shower doping of the source/drain contact. Hydrogen concentration in the channel region can be controlled by altering the gate metal thickness. Hydrogen atoms affect the TFT’s threshold voltage shifts until it becomes negative, in n-type TFTs. The threshold voltage shift depends on the hydrogen content of the channel region in p-Si TFTs. This is explained by the existence of Si−3 trap states in the grain boundaries.
Relationship between diamond growth rate and hydrocarbon injector location in direct-current arcjet reactors
Authors: Dandy David S. , Coltrin Michael E.
Published: July 2002

A series of detailed calculations have been carried out using a stagnation flow model to examine the dependence of diamond growth rate on hydrocarbon injector location in dc arcjet reactors. It is predicted that, for methane feed, growth rate can be increased by as much as 75% by relocating the injector from a position near the plasma torch exit to one near the diamond surface, but outside the boundary layer. As the injector is moved towards the surface from the plasma torch, the concentrations of C and CH3 present at the surface increase. When the injector is located within the boundary layer, the lower atomic hydrogen concentration and short residence time leave most of the injected CH4 unreacted, causing growth rates to drop.
Short-external-cavity module for enhanced single-mode tuning of InGaAsP and AlGaAs semiconductor diode lasers
Authors: Cassidy Daniel T. , Bruce Douglas M. , Ventrudo Brian F.
Published: July 2002

The construction and single-mode tuning characteristics of a short-external-cavity (SXC) module for InGaAsP and AlGaAs semiconductor diode lasers are presented. The SXC system is a cost effective, simple, and rugged means to achieve single-mode tuning and complete spectral coverage over large spectral regions with normally multimode lasers. With AlGaAs lasers, complete spectral coverage in overlapping ∼5-cm−1 intervals over ∼400 cm−1 is obtained, while with InGaAsP diode lasers, complete spectral coverage in overlapping ∼5-cm−1 intervals of 100–200 cm−1 is obtained.
Hot carrier relaxation in GaAs V-groove quantum wires
Authors: Maciel A. C. , Kiener C. , Rota L. , Ryan J. F. , Marti U. , Martin D. , Morier-Gemoud F. , Reinhart F. K.
Published: July 2002

We have measured hot carrier relaxation in GaAs V-groove quantum wires using time-resolved photoluminescence. Relaxation between confined one-dimensional subbands is clearly observed on the time scale of several hundred picoseconds. A simulation of the experiment using a hybrid multisubband Monte Carlo method which includes hot phonon and degeneracy effects gives good agreement with the measurements.
Strain-compensated InGaAs/InGaAsP quantum well lasers lattice matched to GaAs
Authors: Park Seoung-Hwan , Jeong Weon-Guk , Choe Byung-Doo
Published: July 2002

The threshold current density and the characteristic temperature of strain-compensated InGaAs/InGaAsP/GaAs QW lasers are investigated theoretically. These results are also compared with those of uncompensated InGaAs/InGaAsP/GaAs QW lasers. From this calculation, it was confirmed that strain-compensated lasers have lower threshold current density and better performance at high temperature compared to uncompensated lasers. This is attributed to enhanced carrier confinement and weaker temperature dependence of Nth for strain-compensated lasers. The well number dependence of the characteristic temperature is dominant for lasers with relatively short cavity length.
High-performance camel-gate field effect transistor using high-medium-low doped structure
Authors: Lour Wen-Shiung , Liu Wen-Chau , Tsai Jung-Hui , Laih Lih-Wen
Published: July 2002

We report an improved camel-gate field effect transistor using a high-medium-low doped channel. A 1000-Å-thick n=1×1017 cm−3 GaAs layer is employed to form the camel gate, which prevents the planar-doped barrier from being dropped abruptly. In addition to transition channel, a thin (200 Å) heavily doped (n=5×1017 cm−3) GaAs layer works as the main active channel to enhance the current drivability and transconductance. For our 1.5×100 μm2 device, the maximum current density of over 850 mA/mm was obtained. Moreover, an enhanced voltage-independent transconductance was also observed. Generally, the device exhibits a transconductance of 220 mS/mm which is compatible to that of MESFETs and is two- or threefold to that of reported camel-gate FETs. In addition, the proposed device demonstrates a large gate voltage swing for high transconductance operation. Due to the excellent device performance, our devices do hold promise for both large signal and digital circuits application, simultaneously.
Direct observation for the reduction of exciton binding energy induced by perpendicular electric field
Authors: Luo Kejian , Zheng Houzhi , Xu Shijie , Zhang Penghua , Zhang Wei , Yang Xiaoping
Published: July 2002

We experimentally study the effect of perpendicular electric field on the exciton binding energy using a specially designed step quantum well. From photoluminescence spectra at the temperature of 77 K, we have directly observed remarkable blueshift of the exciton peak due to the transition from spatially direct to spatially indirect excitons induced by electric field.
A methyl free radical source for use in surface studies
Authors: Peng Xiang-Dong , Viswanathan Rama , Smudde George H. , Stair Peter C.
Published: July 2002

A methyl radical source has been developed for use in high vacuum. Methyl radicals are produced through azomethane pyrolysis in a tubular reactor located inside an ultrahigh vacuum chamber. Other gas products include nitrogen from azomethane pyrolysis, and methane, ethane plus hydrogen from the reactions of methyl radicals on the walls of the reactor. Methyl yields as high as 42% have been observed.
High-temperature supersonic molecular-beam source
Authors: Auerbach D. J. , Rettner C. T.
Published: July 2002

We describe a supersonic molecular-beam source that can be heated to over 2300 K. Our design employs a commercially available tungsten tube which is resistively heated by passage of current along its length between two water-cooled copper clamps. The clamps are supported so as to minimize bending stresses on the tube while allowing for thermal expansion. Gas is supplied to the tube at one end using an o-ring connection and emerges from an orifice drilled about halfway along the length. The other end of the tube is welded closed. Temperature is measured by a thermocouple spot-welded adjacent to the orifice. The entire tube is surrounded by two tantalum heat shields which are split lengthwise for convenient assembly. These have large holes aligned with the beam axis. We present details of the design, assembly, and characterization of this source.
Growth of hydrogenated Si clusters using a quadrupole ion trap
Authors: Murakami Hirohiko , Kanayama Toshihiko
Published: July 2002

To investigate how stability of small Si clusters is affected by hydrogenation, SinH+xions (n=2–10) were grown from silane gas in a recently developed ion trap and the mass spectra were measured. Some compositions have been found to be particularly stable besides those already known for nonhydrogenated Si clusters such as Si6 and Si10. These clusters, Si5H10+, Si6H12+, and Si10H12–17+, are inferred to have the bulklike tetrahedrally coordinated structures whose dangling bonds are terminated by H atoms.
Optical high-sensitive field sensor using a Pockels crystal
Authors: Murooka Y. , Nakano T.
Published: July 2002

The sensitivity of an optical field sensor with a Pockels crystal of LiNbO3 for measuring a field distribution in a long-gap discharge has been much improved by using an intensity difference method with an intensity-modulated laser beam. The signal-to-noise ratio (S/N) is also improved by 37 dB from that without the above-mentioned method. The resultant sensitivity of the new field measuring system is 100 times higher than that of the previous one. Finally, it is possible to measure an electric field down to 7.5 V/cm in the long-gap discharge with high accuracy corresponding to the S/N ratio of 20 dB and 1.5 V/cm with the accuracy of 6.0 dB.
Interband transitions in Cd0.07Zn0.93Te/ZnTe strained single quantum wells grown by double-well temperature-gradient vapor deposition
Authors: Lee J. H. , Park H. L. , Kim T. W.
Published: July 2002

The electronic states in a Cd0.07Zn0.93Te/ZnTe strained single quantum well grown by the simple method of double-well temperature-gradient vapor deposition have been investigated both experimentally and theoretically. X-ray diffractometry measurements were performed to characterize the structural properties of the Cd0.07Zn0.93Te/ZnTe quantum well. Reflectivity and photoreflectance measurements showed several resonant excitations in the Cd0.07Zn0.93Te quantum well, and photoluminescence measurements on the strained quantum well structures showed that the sharp excitonic transition from the first electron subband to the first heavy-hole band. Interband transition energies in the Cd0.07Zn0.93Te were calculated by taking into account the strain effects, and these theoretical values are in reasonable agreement with the results from the experimental measurement. These results indicate that these Cd0.07Zn0.93Te/ZnTe strained quantum wells hold promise for the potential applications such as in optoelectronic devices in the blue-green region of the spectrum.