bluuebunny/crossref_metadata_2025 huggingface dataset:
Improved step edges on LaAlO3 substrates by using amorphous carbon etch masks
Authors: Yi H. R. , Ivanov Z. G. , Winkler D. , Zhang Y. M. , Olin H. , Larsson P. , Claeson T.
Published: July 2002

We report a technique for the fabrication of sharp and straight step edges on LaAlO3 (LAO) substrates by ion milling. An electron beam lithography defined amorphous carbon film was used as an etch mask. It had very low ion milling rate and was easily prepared and removed. Atomic force microscopy was used to determine the step profile. YBa2Cu3O7 step edge junctions fabricated at the LAO steps show promising results. An IcRn product of 1 mV was obtained at 30 K. A Fraunhofer-like magnetic field dependence of Ic was obtained up to ±2 Φ0. One weak link or possibly identical weak links in series for these step edge junctions were observed from the current-voltage (I-V) curves as well as from the magnetic field dependence of the I-V curves.
High repetition rate traveling wave optical parametric generator producing nearly bandwidth limited 50 fs infrared light pulses
Authors: Petrov V. , Seifert F. , Noack F.
Published: July 2002

A 1 kHz Ti:sapphire femtosecond regenerative amplifier system is used to pump a lithium triborate optical parametric generator in a type II noncritical phase matching configuration and a β-barium borate parametric amplifier. Infrared pulses near 1460 nm as short as 50 fs are achieved with a pulse duration/bandwidth product of only 0.44.
Near field emission scanning tunneling microscopy
Authors: Sáenz Juan José , García Ricardo
Published: July 2002

The close proximity between probe and sample in a scanning tunneling microscope interface may produce unwanted modifications of the interface. This is particularly severe when working with soft materials, as molecular films or biomolecules. Here, we propose the operation of the scanning tunneling microscope in the near field emission regime as an effective method to overcome those problems. A theoretical description of the probe–sample interface in the near field emission regime predicts subatomic resolution in the direction normal to the surface and lateral resolution of 3 nm for tip–sample separations of 3–5 nm. Furthermore, atomic resolution is demonstrated by imaging steps of carbon atoms.
Theoretical study of field emission from diamond
Authors: Huang Z.-H. , Cutler P. H. , Miskovsky N. M. , Sullivan T. E.
Published: July 2002

The electron field emission from diamond surfaces is investigated theoretically using a model consisting of the projection of the energy band surfaces in the 〈111〉, 〈110〉, and 〈100〉 emission directions. The effect of the negative electron affinity, the band bending, the image interaction, and surface states is examined in detail. It is found that the conventional theory of electron field emission applied to crystalline diamond cannot explain the measured high-current emission at low fields. We postulate two subbands in the intrinsic band gap, which may be generated by defects or impurities. With reasonable band parameters, the calculated I-V characteristics agree with experimental data.
Determination of the bonding of carbon acceptors in InxGa1−xAs for x<0.1
Authors: Pritchard R. E. , Newman R. C. , Wagner J. , Maier M. , Mazuelas A. , Ploog K. H. , Lane P. A. , Martin T. , Whitehouse C. R.
Published: July 2002

The local environment of CAs acceptors in InxGa1−xAs has been determined from the localized vibrational modes (LVMs) of both isolated CAs impurities and H–CAs pairs using infrared (IR) absorption and Raman scattering techniques. In as-grown layers, a single LVM due to CAs was observed which broadened and shifted to lower energies with increasing x. The introduction of hydrogen led to the formation of H–CAs pairs and a single antisymmetric A1− mode (stretch) and a single symmetric A+1 mode (XH) were observed for all samples. All the LVMs were identified with carbon in CAsGa4 cluster configurations implying that less than 5% of the detectable carbon atoms are present in clusters incorporating one or more CAs–In bonds.
First-principles calculations for zinc-blende AlInN alloys
Authors: Wright A. F. , Nelson J. S.
Published: July 2002

First-principles calculations have been performed for ordered and disordered zinc-blende Al0.5In0.5N alloys including full relaxation of bond lengths and bond angles. The disordered alloy is predicted to have a mixing enthalpy of +39 meV/atom and a bowing parameter of +2.53 eV at the Γ-point transition. The similarity of the bulk zinc-blende and wurtzite Γ-point transitions also allows an estimate to be made of the energy gap versus composition for wurtzite alloys. In particular, the wurtzite AlInN alloy lattice matched to GaN is predicted to have an energy gap of 5.0 eV.
Room-temperature backbond oxidation of the porous silicon surface by oxygen radical irradiation
Authors: O’Keeffe Patrick , Aoyagi Yoshinobu , Komuro Shuji , Kato Takashi , Morikawa Takitaro
Published: July 2002

Backbond oxidation of the porous silicon (PS) surface as a result of irradiation by oxygen radicals (O*) from an electron cyclotron resonance plasma has been successfully achieved at room temperature. Increasing the O* irradiation time enhances both the photoluminescence (PL) intensity, and the oxygen related absorption in the 2000–2300 cm−1 wave number range obtained from Fourier-transform infrared spectroscopy (FTIR). Analysis of the FTIR spectra correlates oxidation of the outermost backbonded Si in the form H2Si–O2, HSi–O3 bonding structures with increasing PL intensity. Furthermore, these results show that oxidation of the backbonded Si network on the PS surface is the main mechanism responsible for the enhancement of the PL intensity and suppression of the PL fatigue. This enhancement and stabilization of the PL properties of PS at such low temperatures is explained in terms of the high sticking coefficient of O* and soft O* irradiation induced oxidation.
Bolometric diagnostics in JET
Authors: Mast K. F. , Krause H. , Behringer K. , Bulliard A. , Magyar G.
Published: July 2002

Radiation losses from the JET plasma are measured (temporally and spatially resolved) with three pin-hole cameras which observe one poloidal plasma cross section from underneath (one vertical camera with 14 bolometers) and from the side (two horizontal cameras with 10 bolometers each). In addition, eight collimated single bolometers monitor toroidal symmetry of plasma emissivity. An improved metal resistor bolometer capable of surviving at least 5000 D–T pulses in JET is composed of two identical foils (4-μm-thick gold absorber, 7.5-μm-thick Kapton substrate, and 0.1-μm-thick gold resistor), mounted one behind another in one housing. The rear foil serves as a reference bolometer in a bridge circuit. With an integration time constant of 20 ms a detection limit of 70 μW/cm2 was measured in JET. Examples of measuring results in JET are presented: strong poloidal asymmetries of the radiation density as precursor signals of a density limit disruption and the formation of a poloidally symmetric, cold plasma mantle before a disruption.
Fusion gamma diagnostics
Authors: Medley S. S. , Cecil F. E. , Cole D. , Conway M. A. , Wilkinson F. J.
Published: July 2002

Nuclear reactions of interest in fusion research often possess a branch yielding prompt emission of gamma radiation in excess of 15 MeV which can be exploited to provide a new fusion reaction diagnostic having applications similar to conventional neutron emission measurements. Conceptual aspects of fusion gamma diagnostics are discussed with emphasis on application to the Tokamak Fusion Test Reactor (TFTR) during deuterium neutral beam heating of D–T and D–3He plasmas. Recent measurements of the D (T, γ)5He, D(3He, γ)5Li, and D(D, γ)4He branching ratios at low center-of-mass energy (30–100 keV) and of the response of a large volume Ne226 detector for gamma detection in high neutron backgrounds are presented. Using a well-shielded Ne226 detector during 20 MW–120 kV deuterium beam heating of a tritium plasma in TFTR, the D(T, γ)5He gamma signal level is estimated to be 3.5×105 cps.
Design of a tubular reactor instrumentation assembly for conducting thermal decomposition studies
Authors: Rubey Wayne A. , Carnes Richard A.
Published: July 2002

A thermal instrumentation assembly which uses a high-temperature tubular reactor for conducting gas-phase thermal decomposition studies of organic substances has been designed. This thermal reactor assembly uses a counterflow heat exchanger in conjunction with a narrow-bore quartz tubular reactor to obtain precise control over physical factors, such as exposure temperature, mean residence time, and gas-phase residence-time distribution. By virtue of the design of this quartz-ware assembly, gaseous species are subjected to essentially a square-wave thermal pulse as they pass through the thermal reactor.
Monte-Carlo error analysis in x-ray spectral deconvolution
Authors: Shirk Donald G. , Hoffman Nelson M.
Published: July 2002

The deconvolution of spectral information from sparse x-ray data is a widely encountered problem in data analysis. An often-neglected aspect of this problem is the propagation of random error in the deconvolution process. We have developed a Monte-Carlo approach that enables us to attach error bars to unfolded x-ray spectra. Our Monte-Carlo error analysis has been incorporated into two specific deconvolution techniques: the first is an iterative convergent weight method; the second is a singular-value-decomposition (SVD) method. These two methods were applied to an x-ray spectral deconvolution problem having m channels of observations with n points in energy space. When m is less than n, this problem has no unique solution. We discuss the systematics of nonunique solutions and energy-dependent error bars for both methods. The Monte-Carlo approach has a particular benefit in relation to the SVD method: It allows us to apply the constraint of spectral nonnegativity after the SVD deconvolution rather than before. Consequently, we can identify inconsistencies between different detector channels.
E parallel to B energy analyzer for measurement of end-loss ions from the Mirror Fusion Test Facility-B
Authors: Kirkwood R. K. , Higgins L. L. , Munch J. , Wuerker R. F.
Published: July 2002

An instrument is being designed and constructed to measure the mass and energy spectrum of ions lost from the end cells of the Mirror Fusion Test Facility (MFTF-B) experiment. The mass and energy analyzer is of an E parallel to B type and is being designed to resolve protons and deuterons in an energy range of 2–200 keV to within ±2% or 200 eV. The magnet is designed to be small and high field (1.2 T) so that it will fit into a radial array on the MFTF-B end dome. To achieve this large energy range in a small magnet, careful attention is paid to the trimming of the poles and electrode near the input edge. The input slit size is adjusted by fast variable apertures to increase the dynamic range. Also, the electronics is designed to be compatible with the high neutron flux rate in the MFTF-B environment. Detailed calculations on particle trajectories and magnet trimming will be presented, as well as detector and electronics design.
Space and time-resolved measurements of plasma density by a lithium neutral beam probe in NBT-1M
Authors: Iguchi H. , Kadota K. , Takasugi K. , Shoji T. , Hosokawa M. , Fujiwara M. , Ikegami H.
Published: July 2002

A lithium neutral beam probe has been improved for space and time-resolved measurements of plasma density in NBT-1M. A lithium neutral beam (4 keV, 10–30 μA) is injected into the plasma and photon flux emitted from the injected lithium atoms by electron impact excitation is detected. This cross section is not sensitive to the electron temperature in a wide range (10 eV<Te <200 eV) and the photon flux intensity is proportional to the electron density. Typical spatial and temporal resolutions are 1 cm and a few milliseconds, respectively. Beam attenuation is not severe for plasmas with n1<1014 cm−2 unless the ion temperature is very high (Ti >1 keV), where the attenuation through charge-exchange process becomes dominant. This method is not influenced by the magnetic field and can be applied to plasmas in any magnetic field configuration.
Computer-controlled four-gun multisubstrate sputtering system for the preparation of composition-modulated structures
Authors: Yang H. Q. , Jin B. Y. , Shen Y. H. , Wong H. K. , Hilliard J. E. , Ketterson J. B.
Published: July 2002

We describe a four-gun sputtering system which has been used successfully to prepare composition-modulated structures consisting of amorphous semiconductors and superconducting alloys or binary compounds. The substrates are mounted in ovens which can be individually heated to over 1000 °C. The ovens are mounted on a wheel which is driven by a computer-controlled stepping motor. With appropriate programming of the movement of the stepping motor, the deposition sequence is determined.
Fast, controlled stepping drive for D2 filament ejection
Authors: Amenda W. , Lang R. S.
Published: July 2002

Centrifugal pellet injectors are required to refuel plasma machines. The pellet feed into the centrifuge should, if possible, be direct to keep the exit angle divergence small. The D2 filaments used are first stored in a cryostat and then rapidly transported to the intake region of the centrifuge. An intermittent drive for fast, controlled ejection of D2 filaments is described here. Mean filament speed of up to 0.6 m/s per step (1.2 mm) are achieved for the centrifugal pellet injector which refuels the ASDEX tokamak at Garching. The timing of the (81) step shifts can be synchronized with the rotor motion. The drive allows rates of up to 50 pellets per second. The drive method also seems to be suitable for direct feeding of other known centrifugal pellet injectors.
Noninvasive optical fiber photoacoustic microprobe
Authors: Lai Edward P. C. , Chan Becky L. , Wylie Ian W.
Published: July 2002

A microprobe has been designed for the noninvasive detection of photoacoustic signals. It is made up of a fused silica optical fiber which has a core diameter of 600 μm and is coupled to a piezoelectric ceramic transducer. It can detect the laser-induced photoacoustic waves in a 5×10−5 M aqueous ferroin solution, though its sensitivity is approximately 70 times less than that of a typical photoacoustic cell. The probe makes a good contact with any curved surface, and can be easily moved all over a cell to tap signals at many points. Thus, surface profiling of signal intensities is allowed. Other application advantages and design improvements are also discussed.
Miniature, self-contained, Penning ionization gauge using a samarium–cobalt magnet
Authors: Vanderschmidt G. F. , Candidus Edward S.
Published: July 2002

A variant of the self-contained Penning gauge, utilizing an integral, internal, samarium–cobalt magnet offers advantages in simplicity of construction and small size. Using available commercial material, a field of 570 G between 2.54-cm-square pole pieces separated by 0.9 cm is readily achieved with a 2.54×1.14-cm rectangular bar of samarium–cobalt magnetized across its thickness of 0.32 cm. A gauge so constructed begins operation at a pressure of 200 Torr and continues to supply useful pressure information to below 10−4 Torr when operated with a supply voltage of 2 kV.
Temperature variable high-pressure cell and assembly for Raman spectroscopic studies of aqueous systems
Authors: Wong P. T. T.
Published: July 2002

A temperature variable high-pressure optical cell and the assembly for pressure generation and measurement are described. The water corrosion problem of the steel cell at high pressure is eliminated by using a quartz sample holder to isolate the water from the inner bore of the steel cell. The cell and the assembly have been tested by measuring the pressure dependence of the endothermic phase-transition temperature between the liquid crystalline and the gel phase of aqueous DPPC.
Dual homodyne detection system for measuring asymmetric spectra in the far-infrared regime
Authors: Tsukishima T. , Nishida I. , Nagatsu M. , Inuzuka H. , Mizuno K.
Published: July 2002

A dual homodyne detection system for measuring scattered radiation from plasmas has been fabricated. The system is operative in the far-infrared regime, and with it the power spectral distribution of the scattered radiation in the upper and lower sidebands with respect to the frequency of the incident wave can be obtained. Theory of operation and experimental results for simulated radiation fields are given.
High-speed digital image processing system, MFIP, with bus-oriented architecture
Authors: Sugimoto Satoshi A. , Ichioka Yoshiki
Published: July 2002

A general purpose high-speed digital image processing system with bus-oriented architecture has been developed using a time-shared multiframe data bus with the data transferring rate of 80 Mbytes/s. This system is equipped with special purpose hardware for executing frame-to-frame operation, 2-D convolution, and 2-D recursive filtering, allowing image processing of dynamic scenes can be performed in real time. The architecture and hardware of the developed system are presented, and the manufacture of special purpose hardware is described. Experimental results have demonstrated the ability to accomplish image processing of moving objects in real time, and 2-D convolution and 2-D recursive filtering at high speed.
An instrument for measuring turbulent pressure fluctuations
Authors: Papadimitrakis Yiannis Alex , Hsu En Yu , Street Robert L.
Published: July 2002

An instrument is described for laboratory measurements of the fluctuating static pressure in the turbulent boundary layer above progressive water waves. It consists of a disk-shaped sensing head properly designed to minimize the dynamic pressure variation to an acceptable level, a commercially available piezocrystal transducer housed inside a casing, and a forward-bent connecting tube. Pressure fluctuations sampled by the disk are converted into an electrical signal by the piezocrystal transducer. Through low-pass filtering, only the frequency range of interest is retained. The instrument was tested successfully for frequency response, dynamic and mechanical noise sensitivity, and response to spurious pressure fluctuations (produced when operating in a Eulerian wave-following mode) inside a cylindrical chamber and in a wind–wave facility, and some sample results along with the calibration procedures and data analysis are presented.
Converting an AM radio into a high-frequency lock-in amplifier in a stimulated Raman experiment
Authors: van Exter Martin , Lagendijk Ad
Published: July 2002

We describe an AM detection method and show that a normal radio has a nonlinear response for weak signals. Introducing an extra carrier and using a double modulation technique makes our detection unit sensitive to the phase of the rf signal. In this way, the radio combination becomes equivalent to a high-frequency lock-in amplifier and we are able to distinguish between the gain and depletion of the laser beams in a stimulated Raman experiment. Another important aspect is the retrieval of the linearity of the detection unit.
New video-enhanced contrast infrared topograph apparatus for evaluation of GaAs crystals
Authors: Katsumata Tooru , Fukuda Tsuguo
Published: July 2002

A new IR transmission topograph apparatus in which video image contrast is enhanced greatly by digital processing is developed for fast and nondestructive evaluation of GaAs wafers. Clear topographs of IR (1 μm) absorption in 2-in.-diam GaAs wafers, resulting from the distribution of the native defect EL2, and birefringence, resulting from residual stress, are obtained with good contrast and high signal/noise ratio.
Soft x-ray beam line for surface EXAFS studies in the energy range 60≤hν≤11 100 eV at the Daresbury SRS
Authors: MacDowell A. A. , Norman D. , West J. B.
Published: July 2002

The characteristics of the beam line used for surface EXAFS (extended x-ray absorption fine structure) studies at the Daresbury Synchrotron Radiation Source (SRS) are described. Monochromatic photons are available in the energy range 60≤hν≤11 100 eV. This has been achieved using a monochromator with a combination of crystal and grating optics. The radiation is focused through the monochromator by a toroidal premirror at 0.5° grazing angle. Three pairs of crystals and a plane grating with focusing mirror are available which can be interchanged under ultrahigh vacuum (UHV). The plane grating/mirror monochromator has two ranges of zero-order angles, 6.4° and 2°, giving photon energy ranges of 60–550 eV and 600–2000 eV, respectively, with a 1200 l mm−1 grating. The crystals in use are InSb(111), Ge(111), and Ge(220) having photon energy ranges of 1745–7360 eV, 2000–8430 eV, and 3260–11 100 eV. The performance of the gratings and crystals in respect to intensity, resolution, scattered light, and higher orders is discussed, and some representative results from the beam line are given. Detailed consideration has been given to thermal effects on the crystal and grating optics. The grating can be exposed to a maximum power density of 9 W cm−2 and has so far withstood the intense radiation. The Ge crystals, which can see power densities of up to 150 W cm−2, have survived, but exit beam movement and energy scale shifts are observed. Efforts to reduce these beam movement effects have been successful inasmuch as the instrument is usable. InSb crystals suffered some radiation damage, and eventually surface melted. Beryl and quartz crystals have been tried but did not survive. The crystal part of the monochromator is in routine use, but the grating part has yet to be proved successful for surface EXAFS experiments.
Pulsed free jet expansion system for high-resolution fluorescence spectroscopy of capillary gas chromatographic effluents
Authors: Pepich Barry V. , Callis James B. , Danielson J. D. Sheldon , Gouterman Martin
Published: July 2002

A method for detection of capillary gas chromatographic (C-GC) effluent using supersonic jet spectroscopy is described. A novel concept is introduced which overcomes four major obstacles: (i) high temperature of the GC; (ii) low GC flow rate; (iii) low dead volume requirement; and (iv) duty factor mismatch to a pulsed laser. The effluent from the C-GC flows into a low dead volume antechamber into which a pulsed valve, operating at 5 Hz, discharges high-pressure inert gas for 600 μs. The antechamber feeds through a small orifice into a high-vacuum chamber; here an isentropic expansion takes place which causes marked cooling of the GC effluent. The fluorescence of the effluent is then excited by a synchronously pulsed dye laser. With iodine vapor in helium (2 ml/min) modeling the GC effluent, the fluorescence of the cooled molecules is monitored with different delay times between opening of the pulsed valve and firing of the laser. With a glass wool plug inserted in the antechamber to promote mixing between the high-pressure pulse gas and the iodine, the observed pressure variation with time follows a simple gas-dynamic model. Operating in this pulsed mode it is found that the effluent concentration increases by a factor of 7 while the rotational temperature drops from 373 to 7 K. The overall fluorescence intensity actually increases nearly 30-fold because the temperature drop narrows the absorption bands. Tests on acenaphthene chromatographed on a 15-m capillary column show that the antechamber does not degrade resolution and that the high-pressure pulses act to reduce C-GC retention times, presumably through a Venturi effect. The antechamber can be operated with GC effluent temperatures above 200 °C without adversely affecting the pulsed valve.
Test pattern for fluorescence microscopy
Authors: Janssen G. C. A. M. , Rousseeuw B. A. C. , van der Voort H. T. M.
Published: July 2002

A fluorescent test pattern with submicron dimensions has been produced. With this test pattern the optical characteristics of a confocal scanning laser microscope can be determined. The fabrication procedure of the test pattern and the raw data obtained in a measurement of the transfer function of the confocal scanning laser microscope are presented.
New simultaneous thermogravimetry and modulated molecular beam mass spectrometry apparatus for quantitative thermal decomposition studies
Authors: Behrens Richard
Published: July 2002

A new type of instrument has been designed and constructed to measure quantitatively the gas phase species evolving during thermal decompositions. These measurements can be used for understanding the kinetics of thermal decomposition, determining the heats of formation and vaporization of high-temperature materials, and analyzing sample contaminants. The new design allows measurements to be made on the same time scale as the rates of the reactions being studied, provides a universal detection technique to study a wide range of compounds, gives quantitative measurements of decomposition products, and minimizes interference from the instrument on the measurements. The instrument design is based on a unique combination of thermogravimetric analysis (TGA), differential thermal analysis (DTA), and modulated beam mass spectroscopy (MBMS) which are brought together into a symbiotic relationship through the use of differentially pumped vacuum systems, modulated molecular beam techniques, and computer control and data-acquisition systems. A data analysis technique that calculates partial pressures in the reaction cell from the simultaneous microbalance force measurements and the modulated mass spectrometry measurements has been developed. This eliminates the need to know the ionization cross section, the ion dissociation channels, the quadrupole transmission, and the ion detector sensitivity for each thermal decomposition product prior to quantifying the mass spectral data. The operation of the instrument and the data analysis technique are illustrated with the thermal decomposition of contaminants from a precipitated palladium powder.
Automatic Langmuir probe plasma diagnostic
Authors: Hopkins M. B. , Graham W. G. , Griffin T. J.
Published: July 2002

The hardware implementation of a computer-based Langmuir probe technique is described. The technique, which is applicable in a wide range of dc plasma conditions, allows a full range of plasma parameters to be measured efficiently.
Shock tube powder dispersal unit
Authors: Decker Leon J. , Cohen Arthur , Donnelly Emmett
Published: July 2002

A simple device for producing a dusty gas at the end wall of a shock tube prior to the arrival of the test shock wave has been produced and tested. It is readily adapted to existing equipment, with minimal modifications.
Compact axial flow gas transport system for a coaxial CO2 discharge laser
Authors: Seguin V. A. , Seguin H. J. J. , Capjack C. E.
Published: July 2002

The design and construction of an axial flow gas transport system for a coaxial CO2 laser discharge is described. The system features a novel annular flow geometry, which yields a compact, cylindrical package. Flow velocities of up to 50 m/s have been obtained in the device. Measurements of active medium working temperature and gain profiles are also presented.
Technique for high-pressure electrical conductivity measurement in diamond anvil cells at cryogenic temperatures
Authors: Erskine David , Yu Peter Y. , Martinez Gerard
Published: July 2002

A technique is described for making four-probe electrical conductivity measurements on bulk samples in a diamond anvil cell. The technique has been successfully applied up to 48 GPa and at temperatures below 4.2 K to measure the superconducting transition temperatures (Tc, of Pb, GaP, and Si. A method for analyzing the resistance versus temperature curve in the vicinity of the superconducting transition is also described. This method is applied to determine the pressure dependence of Tc in Si in the region where Tc varies rapidly with pressure.
Photoinduced changes in the refractive index of azo-dye/polymer systems
Authors: Ivanov M. , Todorov T. , Nikolova L. , Tomova N. , Dragostinova V.
Published: July 2002

The photoinduced isotropic and anisotropic changes in the refractive index of dye/polymer guest-host systems are investigated. The values obtained are compared to the diffraction efficiencies of scalar and polarization holographic gratings, recorded in the same polymer systems. It is concluded that the induced anisotropy is related to the dye molecules involved in the photoprocesses, whereas the isotropic changes, which are much stronger, are related to the polymer matrix as well.
Simple and compact low-energy Mott polarization analyzer
Authors: Dunning F. B. , Gray L. G. , Ratliff J. M. , Tang F.-C. , Zhang X. , Walters G. K.
Published: July 2002

A UHV compatible Mott polarization analyzer is described that employs electron accelerating voltages of ∼20 kV. The efficiency of the analyzer, ∼3×10−5, is competitive with those provided by other polarimeters. The present analyzer is considerably simpler and more compact than earlier designs and can be used to undertake energy- and angle-resolved polarization measurements with input beam currents below ∼10−14 A.
Versatile, disturbance-free, electromagnetically driven, supersonic beam source
Authors: Sanna G. , Nardi M. , Cardoni P. , Tomassetti G.
Published: July 2002

A nozzle valve having a programmable opening time has been realized and tested. Its working principle differs from those used before in similar devices. In a preliminary version, the valve has been shown to be able to deliver gas pulses having a rise time of about 45 μs and a variable time length from 250 μs (FWHM) to continuum. It can also be operated as a beam chopper with frequency in the range 0–270 Hz and a variable duty factor. The valve does not generate either rf disturbances or appreciable current spikes in the ground network. It is a simple construction device and does not require a critical setup.
Low-cost apparatus for high-pressure optical spectroscopy at low temperatures
Authors: Riesen Hans , Kindler Ueli , Güdel Hans U.
Published: July 2002

A high-pressure cell with sapphires as Bridgman anvils and a simple flow tube cryostat for optical spectroscopy are described. Temperatures down to 10 K and pressures up to 50 kbar are easily obtained.
Multipoint Thomson scattering diagnostic for DIII-D
Authors: Hsieh C. L. , Chase R. , DeBoo J. C. , Evanko R. G. , Gohil P. , Snider R. T. , Stockdale R. E.
Published: July 2002

The multipoint Thomson scattering diagnostic for DIII-D has been in operation since early 1987. Its capability of measuring electron temperatures as low as 50 eV at densities of a few times 1012 cm−3 and a spatial resolution of 1.4 cm in the plasma edge region has been essential in the study of H-mode plasmas. The major components of the diagnostic system consist of a 10-J ruby laser, many stages of funnel-shaped beam baffles, stacks of razor blades for viewing and stray light dumps, two wide-angle lenses for the collection of scattered light through reentrant window ports with protection shutters, 88 fiber bundles 15 m in length for light transmission to an f/1.9 spectrometer, an intensified CCD camera system capable of single-photon detection, and a VAX computer for hardware control and data processing. The input end of the fiber bundle is made demountable so the view locations can be reconfigured to optimize the spatial resolution for the plasma region of interest.
Atomic resolution ultrahigh vacuum scanning tunneling microscopy of epitaxial diamond (100) films
Authors: Stallcup R. E. , Aviles A. F. , Perez J. M.
Published: July 2002

We report atomic resolution images of chemical vapor deposition grown epitaxial diamond (100) films obtained in ultrahigh vacuum (UHV) with a scanning tunneling microscope. A (2×1) dimer surface reconstruction and amorphous atomic regions are observed. The (2×1) unit cell is measured to be 0.51±0.01×0.25±0.01 nm2. The amorphous regions are identified as amorphous carbon. A radial structure 1.5 nm in diameter is observed on a plane at a 20° slope to the (2×1) surface. Tunneling current versus voltage spectra in UHV and Raman spectra are also obtained.
Free carrier density profiling by scanning infrared absorption
Authors: Boone Jack L. , Shaw Michael D. , Cantwell Gene , Harsch William C.
Published: July 2002

A prototype instrument for making contactless measurements of free carrier concentration as a function of the surface coordinates has been developed. The instrument requires minimal sample preparation and the measurements are nondestructive. Measurements are based upon the free carrier absorption of photons at a wavelength of 10.6 μm. The measurement sensitivity is determined by the ability to resolve small variations in the transmitted wave. These variations can be significantly influenced by changes in sample thickness. A scheme has been devised which eliminates thickness variations by rotating the sample through small angles to achieve a transmission maximum at each data point. Preliminary results indicate that system drift limits the sensitivity of the prototype system to measurements of the order of 1015 free carriers per cm3. Data on CdS samples indicate accurate measurements for free electron densities greater that 1016 cm−3. Refinements in the instrument should reduce this level to 1014 cm−3 or less.
Reliable and versatile scanning tunneling microscope
Authors: Kaiser W. J. , Jaklevic R. C.
Published: July 2002

A new scanning tunneling microscope (STM) system is described that has been operated in several environments for both topographic imaging and tunnel spectroscopy. This STM shows high resistance to the effects of vibration and thermal drift. The device is unique in its simplicity and has only four moving parts. In addition, the critical tip–sample approach mechanism is inherently reliable and precise. The STM system accommodates a wide range of sample geometries and requires no special sample holder.
Quantum efficiency of gold photocathodes (2–8 keV) and EXAFS in its secondary electron yield and in the detection currents of a microchannel plate and a silicon surface barrier detector
Authors: Cho T. , Yamaguchi N. , Kondoh T. , Hirata M. , Miyoshi S. , Aoki S. , Maezawa H. , Nomura M.
Published: July 2002

The quantum efficiency of gold photocathodes has been investigated by using synchrotron radiation from 2–8 keV; in particular its detailed structure near the M absorption edge region is obtained. The secondary electron conversion efficiency of gold has been calculated by using the mass absorption coefficient given by a relativistic Hartree-Slater model and by the semiempirical values of Henke et al., respectively. These data are compared with the published data at some discrete energies, and we add several new data points, especially for the gold M edge region (2–4 keV). X-ray absorption fine structure (EXAFS) has been observed in the secondary electron current of the gold photocathode as well as in the detection current responses of a microchannel plate and a silicon surface barrier detector.
Low background-rate detector for 40-keV ions using a conversion dynode and a microchannel-plate electron multiplier to reject low-energy ions, electrons, and photons
Authors: Friedman Peter G. , Bertsche Kirk J. , Michel Maynard C. , Morris Donald E. , Muller Richard A. , Tans Pieter P.
Published: July 2002

We have developed and tested an inexpensive ion detector with dark-count rates below 10−4 s−1 and excellent background rejection. Each 40-keV ion that strikes a grazing-incidence Al2O3 conversion dynode ejects a few tens of secondary electrons, which enter separate pores of a microchannel plate and are independently multiplied to saturated pulse height. The pulses are summed to produce an output signal that is proportional to the number of secondary electrons. This permits pulse-height discrimination against backgrounds of low-energy ions, electrons, and photons. We have successfully tested the detector with C+, Na+, K+, Rb+, and Cs+ at 5–40 keV, and with 36-keV C− and CH−. It should detect ions and neutrals of all species, at energies above 5–10 keV, with good efficiency and excellent background discrimination. Counting efficiency and background discrimination improve with higher ion energy. The detector can be operated at pressures up to at least 2×10−7 Torr and be exposed to air repeatedly without requiring reactivation. The maximum ion count rate is 3×106 s−1 in pulse-counting mode and 6×109 s−1 in current-integrating mode. Detection of 40-keV ions at rates below 10−2 s−1 was required in development of a 10-cm radius 40-keV cyclotron dedicated to high-sensitivity radioisotope dating by accelerator mass spectrometry (AMS). In the cyclotron, the detector suppresses to 6×10−4 s−1 the background count rate from the presence of low-energy ions, photons, and electrons.
Broadband measurement of electron cyclotron emission in TFTR using a quasioptical light collection system and a polarizing Michelson interferometer
Authors: Stauffer F. J. , Boyd D. A. , Cutler R. C. , Diesso M. , McCarthy M. P. , Montague J. , Rocco R.
Published: July 2002

For the past four years, a Fourier transform spectrometer diagnostic system, employing a fast-scanning polarizing Michelson interferometer (FMI), has been operating on the TFTR tokamak at the Princeton Plasma Physics Laboratory. It is used to measure the electron cyclotron emission (ECE) spectrum over the range 2.5–18 cm−1 (75–540 GHz), with a resolution of 0.123 cm−1 (3.7 GHz), at a rate of 72 spectra per second. The quasioptical system for collecting the light and transporting it through the interferometer to the detector has been designed using the concepts of both Gaussian and geometrical optics. The commercial FMI was custom made for this project and is the state of the art for this type of specialized instrument. The diagnostic system is described and an error propagation analysis of the absolute calibration process is given. Examples of ECE spectra measured in two polarization directions are given and electron temperature profiles derived from each of them are compared.
Design and characterization of a 1200 °C entrained flow, gas/solid reactor
Authors: Gullett Brian K. , Blom John A. , Gillis George R.
Published: July 2002

The design and characterization of a 1200 °C flow reactor for studying noncatalytic, gas/solid reactions are presented. The reactor system is designed for high-temperature, isothermal operation in a developing, laminar flow regime. The process gas is raised to the reaction temperature by flowing through a tubular preheat furnace fitted with sequential alumina honeycombs for increased convective and radiative surface area. The preheat furnace eliminates typical use of a flame burner to reach these high temperatures, thereby preventing the existence of combustion gases that may affect the reaction of interest. The reactive solid is introduced into the flow reactor by a water-cooled injection probe. Reacted solids are collected by a stainless-steel, water-cooled probe capable of axial movement. Solids residence times can be varied between ∼50 and 250 ms, dependent upon process gas flow rate and collection probe height in the reactor. Sample results are presented for the calcium oxide/sulfur dioxide (CaO/SO2) reaction at varying times and temperatures.
Watt-level millimeter-wave monolithic diode-grid frequency multipliers
Authors: Hwu R. J. , Jou C. F. , Luhmann N. C. , Lam W. W. , Rutledge D. B. , Hancock B. , Lieneweg U. , Maserjian J. , Streit D. C.
Published: July 2002

Watt-level cw solid-state sources in the millimeter-wave region are needed for plasma diagnostics. Monolithic metal-grid arrays containing in excess of 1000 Schottky diodes have produced watt-level output at 66 GHz in a doubler configuration, in excellent agreement with the large-signal predictions of the frequency multiplication. Current efforts are concentrated on fabricating and developing arrays of a novel barrier-intrinsic-N+ (BIN) diode which promise increased performance in a tripler configuration. Initial tests will be made for a configuration where a tripling efficiency of 35% at an output frequency of 100 GHz is predicted. Eventual goals are monolithic BIN diode grids operating at 1 THz.
Reflectometry systems for the DIII-D tokamak
Authors: Lehecka T. , Peebles W. A. , Luhmann N. C. , Burns S. R. , Olson E. , Group DIII-D
Published: July 2002

A seven-channel reflectometer system has been installed on the DIII-D tokamak. This diagnostic will be used to investigate electron density profiles and fluctuations during both L- and H-mode operation. The reflectometer is configured as a narrow-band FM radar system utilizing analog electronics and compound modulation. These techniques have been tested in the laboratory yielding a spatial accuracy of ±1 cm and temporal resolution of ∼1 ms.
Magnetic field measurement techniques with heavy ion beam probes
Authors: Crowley T. P.
Published: July 2002

Spatially (0.1 cm3) and temporally (1 μs) resolved magnetic field measurement techniques using a heavy ion beam probe as a test particle source are described. The measurement of both steady-state and time-varying fields is discussed. The plasma flux function can be determined by measuring the toroidal velocity of the beam ion in an axisymmetric device, because the canonical angular momentum of a particle, Pφ=qψ+MνφR, is conserved in an axisymmetric system. Corrections due to nonaxisymmetry can be significant in tokamaks and must be taken into account for the current profile and fluctuation measurements. The requirements and design of a toroidal velocity detector are discussed. The signals expected in experiments using the Texas Experimental Tokamak (TEXT) heavy ion beam probe with a velocity detector have been calculated, and they are at least two orders of magnitude higher than the amplifier noise for dc measurements of poloidal and ergodic magnetic limiter fields and for sawtooth and MHD oscillations. Low-level turbulence is expected to produce signals below the noise level.
Performance of a gas spring harmonic oscillator
Authors: Del Fabbro R. , Di Virgilio A. , Giazotto A. , Kautzky H. , Montelatici V. , Passuello D.
Published: July 2002

The characteristics and the performances of a gas spring, to be used in the future in a three-dimensional multiple attenuation system, designed to support the heavy test masses for a low-frequency gravitational wave interferometric antenna, are presented. This multiple system is expected to attenuate 10−9 (10−11) at 10 Hz in the vertical (horizontal) direction. This experiment, in which masses up to 430 kg have been levitated, has shown that the height of the resonance peaks in the gas spring vertical and horizontal transfer functions should not prevent us from obtaining the required high attenuation factors. A gas temperature feedback system, for the gas volume control, has given satisfactory results.
Twenty-channel grating polychromator for millimeter wave plasma emission measurements
Authors: Cavallo A. , Cutler R. C. , McCarthy M. P.
Published: July 2002

A 20-channel grating instrument based on the Ebert–Fastie grating monochromator has been built to measure electron temperature profiles and electron temperature fluctuations in TFTR (tokamak fusion test reactor). Second-harmonic electron cyclotron emission for the plasma over the frequency range of 120–400 GHz is utilized; this corresponds to a central tokamak magnetic field of 2.9–5 T. System sensitivity is typically 10-eV rms for a 2.5-kHz bandpass with a 2.5-cm radial resolution and a 5-cm antenna spot size at the plasma center. The ratio of the largest to smallest plasma radius observed by the instrument can be as large as 1.65, which maximizes spatial coverage of the plasma. Emission is detected by 20 liquid-helium-cooled indium antimonide hot-electron bolometers mounted in a long hold cryostat. The 6.5-l helium reservoir must be filled every 19 days, while the liquid-nitrogen reservoir is filled automatically once a day. This instrument has about twice the number of channels and much better spatial resolution than other instruments of this type used for plasma diagnostics.
Space- and time-resolved measurements of ion temperature with the CVI 5292-Å charge-exchange recombination line after subtracting background radiation
Authors: Ida K. , Hidekuma S.
Published: July 2002

An ion temperature profile has been obtained with the CVI 5292-Å (n=8–7) charge-exchange recombination (CXR) line using a space- and wavelength-resolving visible spectrometer installed on the JIPP TII-U tokamak. Two sets of 50-channel optical-fiber arrays, one viewing a fast neutral hydrogen beam (CXR channels) and the other viewing off the neutral beamline (background channels), are arranged on the entrance slit of the spectrometer. This spectrometer is coupled to an image intensifier and CCD detector at the focal plane, and provides a temperature profile every 1/60 s. An ion temperature is derived from the Doppler-broadened line profile after subtracting the simultaneously measured cold component (background channels), which is due to electron excitation and/or charge-exchange recombination in the plasma periphery. An alternative approach to obtain the ion temperature profile without CXR is also demonstrated. This method is based on an Abel inversion technique for each wavelength separately.
Four-channel ZnS scintillator measurements of escaping tritons in TFTR
Authors: Zweben S. J.
Published: July 2002

A four-channel scintillation detector capable of measuring tritons, protons, and alphas escaping from a tokamak plasma was operated during the 1986 run period of the Tokamak Fusion Test Reactor (TFTR). Signals consistent with the expected 1-MeV triton behavior have been observed during deuterium operation. Backgrounds associated with neutrons/gammas and soft x rays have been evaluated in situ and are shown to be at the ≊10%–20% level for the present detector. Such a detector is capable of measuring escaping alphas in deuterium-tritium-fueled tokamaks such as TFTR.
An economical ultrahigh-vacuum probe of conductivity and mobility
Authors: Erickson J. W.
Published: July 2002

An ultrahigh-vacuum version of the four-point probe, commonly used in conductivity and mobility measurements, is described.
A versatile pattern generator for high-resolution electron-beam lithography
Authors: Nabity J. C. , Wybourne M. N.
Published: July 2002

A versatile, PC-based pattern generator for nanometer structure research applications has been developed. The pattern generator interprets data produced by a computer-aided design software package and controls the scanning and beam-blanking coils of a scanning electron microscope. The patterns are written using a vector scanning mode with each vector being written as a series of point exposures. By synchronizing the beam-blanking and the beam-scanning signals, a pattern is written in the steady state of the microscope and the pattern generator. This technique affords a high degree of accuracy and pattern perfection over a wide range of field sizes. At low magnification, patterns may be written over a large area (0.5×0.5 mm2 ), while at high magnification, delineation of nanometer scale circular arcs and straight lines of arbitrary angle is possible. We also demonstrate how the pattern generator can be used for registration to a resolution of better than 150 nm.
Low-energy electron transmission method for measuring charge trapping in dielectric films
Authors: Marsolais R. M. , Deschênes M. , Sanche L.
Published: July 2002

We describe a method for investigating the trapping of low-energy electrons in thin dielectric films and at their surfaces. It is based on the shift in the zero-energy reference produced by charge trapping in the low-energy electron transmission (LEET) spectra of dielectric films. We show that this energy shift or retarding potential is linearly related to the amount of accumulated charges and the trapping cross section. The method has the unique feature of being able to determine the dependence of the trapping cross section on the energy of the charging electron beam in the range 0–30 eV. Its characteristics are illustrated in the investigation of surface charging of multilayer Kr films partially covered with O2 molecules. The results confirm the capacitor model and serve, via the energy dependence of trapping cross section, to determine the precise mechanism responsible for charging in the range 3–10 eV.