bluuebunny/crossref_metadata_2025 huggingface dataset:
Validating cylindrical Langmuir probe techniques
Authors: Rogers J. H. , De Groot J. S. , Hwang D. Q.
Published: July 2002

Several methods for estimating the plasma potential and density using cylindrical Langmuir probes are compared to the self-consistent solutions of the Vlasov–Poisson equations calculated by Laframboise (J. G. Laframboise, Ph. D. dissertation, University of Toronto, 1966). Measurements are made during the decay of a magnetic-field-free plasma in which the mean-free path of the electron is shorter than the dimensions of the vacuum vessel (the electrons, therefore, have a Maxwellian velocity distribution). The measurements are made in a parameter range in which exact analytical solutions do not exist for the ion and electron saturation currents, 0.5≤R/λDe≤5, where R is the probe radius and λDe is the electron Debye length (kTe/4πne2)1/2. An iterative procedure is used to fit the data at probe voltages both above and below the plasma potential while constraining the curves to be continuous at the plasma potential. The measured curves could be represented extremely well by the numerical results. It is therefore assumed that the plasma parameters used to fit the numerical results to the measurements are correct. The systematic errors which result from using several analysis techniques which assume R/λDe≪1 are also presented, and it is shown that empirical corrections to these errors can be described which compensate for the finite probe radius.
ECR ion source using slow wave structures
Authors: Baskaran R. , Jain S. K. , Ramamurthi S. S.
Published: July 2002

In this ECR ion source, the possibility of maintaining the plasma by slow wave structures (SWS), helical coil, and slotted line antennas, in the region where wce, wpe ≫ wrf (wce, wpe, and wrf are electron cyclotron, plasma, and microwave frequencies, respectively) is exploited. The plasma parameters, plasma density, and electron temperature are maximized by coupling microwave (frequency: 2.45 GHz; power: 650 W) at two places in a magnetic mirror machine (mirror ratio Rm ≂ 1.45) to obtain higher beam current. Initially, the plasma is produced by coupling microwave to SWS at the mirror throat. The microwave is coupled by exciting the dominant slow wave field component of SWS, using an E-plane horn antenna. Then the plasma is brought to the region wce, wpe ≫ wrf at the mirror throat by increasing the magnetic field. Simultaneously, the ECR region is shifted from mirror throat to the center where second microwave coupling is done at the resonant region using another horn antenna. The characterization of plasma parameters are presented for both helical coil and slotted line antennas. Enhancement of plasma parameters are observed in the present scheme. Also, the SLA is found to produce better plasmas (ne ∼ 7 × 1012 cm−3 and Te ∼ 12 eV) than the helical coil and hence the SLA is chosen for the ion beam characterization. The extracted ion beam current density in the present scheme is ∼25 mA/cm2 at 2-kV extraction voltage.
The NSLS: Representative science from 0.2 meV to 320 MeV
Authors: Gmur N. , Hulbert S. , Lazarz N. , McWhan D. B.
Published: July 2002

An overview of the research performed at the National Synchrotron Light Source (NSLS) is given. (AIP)
An angle-resolving photoelectron spectrometer for the simultaneous measurement of cross sections and asymmetry parameters using synchrotron radiation
Authors: Feldhaus J. , Erlebach W. , Kilcoyne A. L. D. , Randall K. J. , Schmidbauer M.
Published: July 2002

We describe an angle-resolving photoelectron spectrometer for atoms and molecules which uses the magic angle geometry in combination with multidetection such that cross sections and asymmetry parameters can be determined simultaneously. The instrument is based on the cylindrical mirror analyzer (CMA) design with the cylinder axis and the light beam collinear. Only the photoelectrons which are emitted in the ‘‘reverse’’ direction at the magic angle reach the ring-shaped position-sensitive detector. The complete system also incorporates a conical effusive gas source, in order to maintain cylindrical symmetry, and very efficient differential pumping between target and electron spectrometer. Results from the C 1s photoionization of CO2 demonstrate the kind of precision attainable.
Band edge discontinuities between microcrystalline and amorphous hydrogenated silicon alloys and their effect on solar cell performance
Authors: Xu X. , Yang J. , Banerjee A. , Guha S. , Vasanth K. , Wagner S.
Published: July 2002

We have used internal photoemission measurements to determine the electrical band gap of microcrystalline p-type layers used in a-Si:H alloy solar cells, and the band edge discontinuities of the conduction and the valence bands between μc-Si:H and a-Si:H alloys. The band gap ofμc-Si:H is found to be around 1.6 eV, and the discontinuities at the conduction and the valence band edges are −0.02 and 0.26 eV, respectively. Use of these parameters in the numerical simulation of single-junction a-Si:H alloy solar cells is found to accurately predict the experimental results of solar cell performance.
Variable-metric diffraction crystals for x-ray opticsa)
Authors: Smither Robert K. , Fernandez Patricia B.
Published: July 2002

A variable-metric (VM) crystal is one in which the spacing between the crystalline planes changes with position in the crystal. This variation can be either parallel to the crystalline planes or perpendicular to the crystalline planes of interest and can be produced by either introducing a thermal gradient in the crystal or by growing a crystal made of two or more elements and changing the relative percentages of the two elements as the crystal is grown. A series of experiments were performed in the laboratory to demonstrate the principle of the variable-metric crystal and its potential use in synchrotron beam lines. One of the most useful applications of the VM crystal is to increase the number of photons per unit bandwidth in a diffracted beam without losing any of the overall intensity. In a normal synchrotron beam line that uses a two-crystal monochromator, the bandwidth of the diffracted photon beam is determined by the vertical opening angle of the beam which is typically 0.10–0.30 mrad or 20–60 arcsec. When the VM crystal approach is applied, the bandwidth of the beam can be made as narrow as the rocking curve of the diffracting crystal, which is typically 0.005–0.050 mrad or 1–10 arcsec. Thus a very large increase of photons per unit bandwidth (or per unit energy) can be achieved through the use of VM crystals. When the VM principle is used with bent crystals, new kinds of x-ray optical elements can be generated that can focus and defocus x-ray beams much like simple lenses where the focal length of the lens can be changed to match its application. Thus both large magnifications and large demagnifications can be achieved as well as parallel beams with narrow bandwidths.
A combined continuous-wave and pulsed microwave copper chloride discharge
Authors: McColl W. , Passow M. , Brake M. L.
Published: July 2002

Pulsed and continuous-wave microwaves at 2.45 GHz combined in an Asmussen resonant cavity are used to vaporize, dissociate, and excite copper chloride discharges. Steady state microwaves from 50 to 150 W sustain a microwave discharge which heats and dissociates the copper chloride to a sufficient vapor pressure. A variable frequency (2.45 to 2.60 GHz) pulsed microwave source with pulse widths ranging from 0.5 to 2 ms, repetition rates of 500 to 5000 Hz and a peak output power of 4,500 W then excites the copper atomic states. The two microwave signals are superimposed using a hybrid junction before input into the resonant cavity. Microwave frequencies of the pulsed portion of the signal around 2.50 GHz provided maximum absorption by the discharge. This device is being examined as a potential pump source for a copper vapor laser.
Apparatus with an elastic barrier for radial compression of liquid supported monolayers
Authors: Bohanon T. M. , Mikrut J. M. , Abraham B. M. , Ketterson J. B. , Jacobson S. , Flosenzier L. S. , Torkelson J. M. , Dutta P.
Published: July 2002

We have constructed an apparatus that radially compresses monolayers on the surface of water. This mode of compression prevents the anisotropy that is sometimes observed in films that are compressed uniaxially. The area is changed using an elastic band stretched around 12 fingers which move synchronously. The ratio of maximum to minimum diameter of the elastic barrier is ∼7:1, so that the compression ratio is ∼50:1. The apparatus can accommodate dishes of various sizes up to 8 in. in diameter. The temperature is controlled by circulating water under the dish. Isotherms obtained using this apparatus illustrate the difference between uniaxial compression and radial compression for a fatty acid monolayer.
Band-gap reduction and valence-band splitting of ordered GaInP2
Authors: Ernst P. , Geng C. , Scholz F. , Schweizer H. , Zhang Yong , Mascarenhas A.
Published: July 2002

Low-temperature photoluminescence excitation spectra are used to determine the order-dependent parameters: valence-band splitting and band-gap reduction in spontaneously ordered GaInP2. Effects due to composition fluctuations between different samples and the associated strain, as well as the excitonic binding energies, have been properly taken into account to yield accurate band-gap reduction and valence-band splitting values. The results from recently published ab initio band structure calculations are used to extrapolate the band-gap reduction from the strongest experimentally realized degree of ordering to perfect ordering. We find a total band-gap reduction of 471±12 meV, which is very close to recent theoretical predictions.
Versatile ultrahigh-vacuum compatible sample holder allowing in situ rotation of the sample around its surface normal
Authors: Germar R.
Published: July 2002

A versatile sample holder for ultrahigh vacuum is described allowing cooling and heating of the sample as well as in situ rotation around its surface normal which is perpendicular to the axis of rotation of the sample holder itself.
Combination of multichannel detection and fast time response in a multichord spectrometer
Authors: Bamford R. A. , Carolan P. G. , Bunting C. A.
Published: July 2002

A high resolution spectrometer has been used to measure simultaneously plasma impurity ion temperatures and rotational velocities, with submillisecond temporal resolution. The dual requirements of detailed spectral detection and fast time response are satisfied by having two detection systems viewing the same dispersed spectrum. The first is a multichannel system (e.g., a two-dimensional charge coupled device camera, for multichord detection) and the other an assembly comprising of three photomultipliers. A matched double spectrometer (f=1.26 m) is used to disperse the spectrum and giving an overall inverse dispersion of 0.04 nm/mm. The dispersive power is about 20× greater than the more conventional systems and has a corresponding increase in etendu, or light throughput, for the same resolution. The combination has been successfully used for magnetohydrodynamics mode locking experiments on COMPASS-C tokamak where velocity shifts of ∼30 km−1 were measured to an accuracy of ∼1 km s−1 with a 40 μs time resolution.
CO2 laser interferometer for electron density measurement in JT-60U tokamak
Authors: Kawano Yasunori , Nagashima Akira , Ishida Shinichi , Fukuda Takeshi , Matoba Tohru
Published: July 2002

A tangential chord CO2 laser interferometer for electron density measurement in the JT-60U tokamak is described. To compensate for a phase shift due to mirror vibrations, an IR-HeNe laser interferometer is introduced. Probe beams of the CO2 and the IR-HeNe lasers travel in a similar form for a distance of 100 m by utilizing relay optics. The effective phase resolution of the system is estimated to be 1/68 fringe, which corresponds to a line integrated density of 3.1×1018 m−2. An ultra-accurate phase comparator which has a 1/104 fringe resolution is proposed to improve the capability of present and future interferometers.
The TEXT upgrade vertical interferometer
Authors: Hallock G. A. , Gartman M. L. , Li W. , Chiang K. , Shin S. , Castles R. L. , Chatterjee R. , Rahman A. S.
Published: July 2002

A far-infrared interferometer has been installed on TEXT upgrade to obtain electron density profiles. The primary system views the plasma vertically through a set of large (60-cm radial×7.62-cm toroidal) diagnostic ports. A 1-cm channel spacing (59 channels total) and fast electronic time response is used, to provide high resolution for radial profiles and perturbation experiments. Initial operation of the vertical system was obtained late in 1991, with six operating channels.
A differential absorption spectrometer for bremsstrahlung diode voltage measurement
Authors: Riordan J. C. , Faulkner J. E. , Goyer J. R. , Kortbawi D. , Meachum J. S. , Mendenhall R. S. , Roth I. S. , Whitton B. A.
Published: July 2002

An indirect voltage measurement of a relativistic electron beam diode can be deduced from the high energy tail of its bremsstrahlung spectrum. Our spectrometer contains seven silicon pin diode detectors with filters optimized to cover the 0.5–2 MV range. Theoretical response functions were calculated using the CYLTRAN Monte Carlo transport code with the next event estimator method. Diode voltage measurements performed with the spectrometer on the PITHON x-ray simulator are in good agreement with the standard electrical measurement.
Quick sample exchange manipulator for dual molecular beam and scanning tunneling microscopy experiments
Authors: Sullivan Daniel J. D. , Kummel Andrew C.
Published: July 2002

Here we describe the design, construction, and operation of an ultrahigh-vacuum manipulator for combined molecular beam and scanning tunneling microscopy experiments. The manipulator allows (1) sample transfer, (2) liquid-nitrogen cooling, (3) electron beam heating, (4) rotation about the vertical and horizontal axes, and (5) electrical isolation of the sample. The unique features of the design are (a) direct transfer of a 3/8-in.-diam sample to a load-lock sample carrier without the use of a second transfer arm and (b) sample mounting and electron beam heating systems that permit the sample to be several hundred degrees hotter than the sample mounting plate, thus minimizing sample contamination.
Introduction of cesium vapor into the arc chamber of a high-brightness H−/D− volume source and resulting beam characteristics (abstract)
Authors: Debiak T. W. , Gammel G. , Kuehne F. , Ng Y. , Sredniawski J.
Published: July 2002

Addition of cesium vapor to H−/D− multicusp volume sources has been shown to result in significantly increased extracted ion current density. However, using a cesium oven, the initial introduction of Cs vapor causes high-voltage breakdowns that persist for extended periods. In the extreme case, source operation may no longer be possible without shutting down and thoroughly cleaning source components. If operation can be recovered, the increase in extracted ion current density persists for many days, usually until filament burn-out or other failure unrelated directly to Cs introduction. We have refined the procedure for Cs introduction to produce less catastrophic initial source operation and shorter recovery times to consistent operation. The new procedure has produced consistent H− currents of 35–42 mA at 30 keV. Higher currents, up to 64 mA, have been achieved for short periods soon after recovery. These data were obtained for a 6.4-mm-diam emission aperture using a modified Pierce geometry. In this paper, the new procedure for introduction of Cs will be described with the associated recovery characteristics. This paper will compare the emittance changes as a function of H− current, equivalent current, and plasma electrode bias. The behavior of the output over many days and shutdown-operation-shutdown cycles also will be described.
Low-noise lumped-element timing filters with rise-time invariant crossover times
Authors: Nowlin C. H.
Published: July 2002

Herein are described low-noise, lumped-element pulse-shaping filters that produce output pulses with zero-crossing times that are invariant with changes in input pulse amplitude and invariant with changes in input pulse rise time for input pulses with linearly increasing leading edges. Design equations and circuit diagrams are given. In addition, equations are derived that show that, in general, the noise-caused timing variance is inversely proportional to the crossover time, provided the crossover time occurs during the linearly increasing leading edge. The noise-caused timing variances of these lumped-element filters are only a few percent worse than the best that can be achieved for the same crossover time with a conventional delay-line constant-fraction filter in cascade with a resistance-capacitance low-pass filter. Neither delay lines nor delay-line approximates are used in these filters.
A femtosecond autocorrelator with internal calibration
Authors: Oksanen J. A. I. , Helenius V. M. , Korppi-Tommola J. E. I.
Published: July 2002

We describe an autocorrelator which allows measurement of femtosecond pulse profiles in real time. The autocorrelator output is displayed on an oscilloscope screen. This profile contains all the information needed to measure the pulse duration. The autocorrelator is based on collinear second-harmonic generation optical arrangement. It allows for convenient alignment of high repetition rate femtosecond lasers in real time.
A multipurpose scanning probe microscope
Authors: Sander M.
Published: July 2002

A versatile scanning probe microscope is described that offers the combination of use for imaging in ambient atmosphere, under a liquid, and in ultrahigh vacuum. In contrast to any home-built or commercial instruments available at present, these features are realized here in a single instrument. A compact size instrument is achieved by a piezoelectrically driven sample approach mechanism. The sample or the tip can be scanned providing two separate scanning modes which cover a total scan range from 20 Å to 10 μm. An area of 30 mm2 can be scanned without breaking the tip/sample contact. Exchangeable tip mounts facilitate an easy change between prealigned tips. The design of the scanning force microscope is based on the optical deflection method for imaging in the contact mode. The microscope can be used as a scanning tunneling microscope as well.
A low-power-dissipation broadband cryogenic preamplifier utilizing GaAs MESFETs in parallel
Authors: Lee Adrian Tae-Jin
Published: July 2002

A voltage sensitive preamplifier design is presented for operation at 1.6 K. The active device is a Sony 3SK164 dual-gate GaAs metal-semiconductor field-effect transistor (MESFET), which was chosen for its low-frequency noise performance, stability against oscillations, and the inclusion of a gate protection diode. Active devices made from GaAs operate at cryogenic temperatures without carrier ‘‘freeze out.’’ The main design goal was to keep the power dissipation in the cryostat minimal, while maintaining high bandwidth and low noise. This was achieved by operating four parallel MESFETs at cryogenic temperatures in cascode with a room-temperature Si JFET. Parallel operation gives a higher transconductance-to-power dissipation ratio than with a single device. The input cascode is followed by high-speed, low-noise operational amplifiers. The low-frequency noise corner occurs at 100 kHz. The white voltage noise of the preamplifier referred to the input is <0.9 nV/Hz1/2 at 1 MHz with 2 mW dissipated in the cryogenic stage. The power dissipation can be reduced to 1 mW with a moderate increase in noise. The preamplifier noise was found to be dominated by the cryogenic stage. There are two 50-Ω outputs with gains of 39 dB and 59 dB, and the −3 dB points occur at 500 Hz and 10 MHz. The design of the preamplifier is discussed in detail. Noise measurements under a variety of bias conditions are presented along with an analysis of the different noise sources.
Measurement of the microwave dielectric constant for low-loss samples with finite thickness using open-ended coaxial-line probes
Authors: Jiang G. Q. , Wong W. H. , Raskovich E. Y. , Clark W. G. , Hines W. A. , Sanny J.
Published: July 2002

This work addresses the effect of finite sample thickness on microwave dielectric constant measurements for thin, planar, low-loss samples using the open-ended coaxial-line probe method. Detailed measurements of the dielectric constant were carried out on a wide range of thicknesses of air samples which were backed by infinitely thick teflon and alumina dielectric media. The measurements were made at room temperature for various (50 Ω) coaxial-line dimensions, microwave frequencies 4–8 GHz, and power levels near a fraction of a mW. The results provide strong support for previously published theoretical calculations based on a boundary value problem which uses a spectral domain formulation for the aperture fields. From thin, planar samples, values of 10.4±0.5 and 25.9±1.3 were obtained at 5 GHz and 300 K for the bulk dielectric constant of MgO and LaAl2O3, respectively. The applicability of a simple empirical model based on an exponential fit is discussed.
Simple determination of the frequency response of piezoelectric tubes
Authors: Tao L. , Maps J.
Published: July 2002

A simple technique for measuring the relative extension or response of a piezoelectric tube as a function of frequency is presented. The method clearly identifies resonant modes of the system. This information is useful in tuning feedback control systems in scanned probe microscopes.
Optically guided large-nanostructure probe
Authors: Marchman Herschel M. , Wetsel Grover C.
Published: July 2002

A large-nanostructure probe with optically guided macroscopic scanning has been developed for high-resolution imaging and characterization of nanostructures. The novel optical viewing system allows placement of the imaging tip to within 1 μm of a desired site on the sample during coarse positioning. Fine positioning and imaging are accomplished with nanometer-scale resolution using a segmented-tube piezoelectric scanner. High-resolution images of identifiable quantum dots have been obtained to demonstrate the efficacy of the method.
Simultaneous measurements of enthalpy and heat capacity of a thermosetting polymer during the curing process
Authors: Cassettari M. , Papucci F. , Salvetti G. , Tombari E. , Veronesi S. , Johari G. P.
Published: July 2002

We report a new microcalorimetric technique which allows simultaneous measurements of the heat capacity and the rate of enthalpy release during the chemical reaction in a substance under quasi-isothermal conditions. The basic features of the instrument are presented together with brief experimental results on the polymerization of diglycidyl ether of bisphenol A mixed with ethylene diamine. The instrumentation is an advance for studies of both synthetic and biological formation of macromolecules, for now it becomes possible to measure the heat capacity of a time-variant system and to characterize its vitrification transition occurring at constant temperature, as the growth of the macromolecule by chemical reaction increases the sample’s viscosity. The abrupt decrease observed in the heat capacity curve corresponds to the vitrification transition, which cannot be observed in the corresponding enthalpy release curve. The present calorimeter has an important use in both technological assessment and in understanding the fundamental aspects of the vitrification phenomenon.
High accuracy Kerr effect measurement technique
Authors: Shelton D. P.
Published: July 2002

Apparatus and techniques are demonstrated which allow gas phase dc electro-optic Kerr effect measurements to be made with 0.1% absolute accuracy and nanoradian sensitivity. Measurements of the electric-field-induced birefringence of a gas are calibrated against a liquid Kerr cell, which is in turn calibrated absolutely in situ. Some of the problems addressed in this work are control of stray birefringence in order to obtain an extinction ratio below 10−10, a simple method for calibration of space charge effects in the CS2 reference Kerr cell, construction of electrodes with accurately calculable fields, and an investigation of the sources of systematic errors and drifts and means to eliminate them.
Electron optical analysis of a retarding Wien filter for electron spectroscopic imaging
Authors: Tsuno K.
Published: July 2002

A new Wien filter has been designed for electron spectroscopic imaging. The shape of the electrodes and the magnetic pole pieces of the filter has fourfold symmetry and therefore the Wien condition giving a straight optical axis is satisfied even in the fringing field region. The second-order aberration coefficients of the filter are formulated in a simple form. The filter is applied to a spectroscopic low-energy reflection electron microscope in a retarding condition. The optics of the image-forming lens system is analyzed using the transfer matrix method. The achromatic focus is achieved when the distances of the objective plane and the imaginary image plane to the filter are equal. A condition for obtaining the image free from second-order aberrations is found. The total magnification of the instrument is 3000–14000 times; energy resolution of 2 eV is attained for an initial beam divergence angle of 10 mrad.
A simple apparatus for time-resolved x-ray diffraction biostructure studies using static and oscillating pressures and pressure jumps
Authors: Mencke Andrés , Cheng An-chi , Caffrey Martin
Published: July 2002

A beryllium rod with an internal bore diameter of 1.5 mm and a wall thickness of 2.4 mm constitutes an x-ray compatible cell for hydrostatic pressures rated up to 1800 bar (180 MPa, 26 000 psi) at temperatures up to 90 °C. The system can be used to produce static and oscillating pressures, pressure ramps, and pressure jumps. Pressure is generated by compressing water, the pressure medium, in a syringe-type high-pressure pump. Commercially available pressure valves serve to produce sinusoidal pressure oscillations and pressure jumps for any initial and final pressure between atmospheric pressure and 1800 bar. Typical rise times for a minimally damped and damped pressure jump from atmospheric pressure to 1600 bar are ∼2 and 5 ms, respectively. A depressurization jump from 450 bar to atmospheric has a decay time of order 5 ms. This equipment has the advantage of being relatively easy to build and to operate. However, it does not provide the fastest possible pressure jumps. The assembly of thermocouples and wire feedthroughs for operation under high pressure is detailed. The apparatus described here has been used in time-resolved x-ray diffraction studies of lipid phase transitions using synchrotron radiation. We anticipate using it to collect static and slow kinetic data on a conventional x-ray source.
Determination of dead-space volumes having two different temperatures by the gas expansion method
Authors: Suzuki Isao
Published: July 2002

A new gas expansion method is described to determine dead-space volumes having a temperature contrast boundary. The observed volumes obtained agreed with those obtained from the conventional gas expansion method and the water filling method.
A selected ion flow tube-laser induced fluorescence instrument for vibrationally state-specific ion-molecule reactions
Authors: Kato Shuji , Frost Michael J. , Bierbaum Veronica M. , Leone Stephen R.
Published: July 2002

A selected ion flow tube apparatus is coupled with laser induced fluorescence (LIF) detection for the selective monitoring of ion vibrational states and their reactions. Mass selected ions are injected into a flow tube with a venturi inlet using He carrier gas. A 200 Hz dye laser system provides sensitive LIF detection of the injected ions at densities as low as 1×105 cm−3 for N+2. The rotational temperatures of the N+2 ions are estimated to be ≊300 K using the LIF detection, while the vibrational temperatures can be high and may be varied by the injection potentials. Vibrationally state-selected ion-molecule reactions of N+2(v=0, 1, and 2) are studied with N2, Ar, and O2 at thermal kinetic energies (Elab<0.1 eV), where translation-to-vibration energy transfer is negligible. Isotopically specific charge-transfer reactions of 15N+2(v) with 14N2 are also studied. The ability to mass select ions and characterize their vibrational states and those of their reaction products allows novel studies of state-to-state ion chemistry.
Electron spin detector for spin-resolved x-ray photoelectron spectroscopy
Authors: Klebanoff L. E. , Campen D. G. Van , Pouliot R. J.
Published: July 2002

A low-energy diffuse scattering electron spin detector for spin-resolved x-ray photoelectron spectroscopy (SRXPS) is described. The detector is coupled to a commercial 152-mm mean radius, 150° spherical sector electrostatic electron energy analyzer. Electron optics are described for both the transport of photoelectrons from the energy analyzer exit slit to the gold scattering target, and from the gold target to the spin analyzer electron detectors. The spin detector has an effective Sherman function of 0.078±0.008, with a figure of merit of approximately 4×10−5. The electron optical phase space acceptance EAΩ of the detector is 623 eV mm2 sr. The SRXPS apparatus performance is demonstrated with SRXPS spectra from ferromagnetic Fe and a cobalt-based ferromagnetic glass.
The Novolever: A new cantilever for scanning force microscopy microfabricated from polymeric materials
Authors: Pechmann R. , Köhler J. M. , Fritzsche W. , Schaper A. , Jovin T. M.
Published: July 2002

A new force sensor element based on multilayer thin film technology and adapted for optical readout in a conventional scanning force microscope has been developed. The use of polymers as cantilever materials enables the introduction of mechanical properties otherwise not accessible with microfabrication based on Si technology. The fully batched fabricated cantilevered force transducer is based on the photoresist novolak and incorporates an integrated EBD tip. Bending experiments on microstructures indicate that the Young’s modulus of novolak is about two orders of magnitude lower than for Si. Therefore, in using a cantilever design similar to that with Si it is possible to fabricate more flexible structures from polymeric materials. The new force sensors have been tested and their performance has been evaluated on different samples.
The temperature dependence of the forward characteristics of 1N4007 silicon diode
Authors: Ota S. B. , Nanda K. K.
Published: July 2002

The temperature dependence of the forward voltage of 1N4007 Si diode is reported in the temperature range 10–300 K. The forward voltage for a current of 200 μA was found to vary linearly at a rate of −2.4 mV/K for temperatures above 60 K. This temperature dependence of the forward voltage was found to change to −3.6 mV/K when the current was changed to 10 nA. It is observed that the forward voltage for a current of 200 μA, first increased rapidly below a temperature (T*) of about 21 K and then gradually with further reduction in temperature. T* was found to reduce linearly with ln(I).
Measurement of surface reflection coefficients via multiple reflection of microwaves
Authors: Conway G. D. , Schott L. , Hirose A.
Published: July 2002

Multiple reflection of a microwave beam between a horn antenna and a smooth target in the antenna near field produces an interference effect in the received power. This effect can be described by modeling the antenna and target as a closely coupled system with ‘‘coherent’’ reflection coefficients. This model shows better agreement with experimental data than models based on isotropic antenna ‘‘backscatter.’’ Measurement techniques are derived from this new model, which permit, by sampling the interference pattern, the remote sensing of the reflection coefficient of an unknown surface. From the reflection coefficient the dielectric constant or surface roughness can be obtained. A simple diagnostic apparatus is described together with possible industrial/laboratory applications.
Design and three dimensional calibration of a measuring scanning tunneling microscope for metrological applications
Authors: Jusko O. , Zhao X. , Wolff H. , Wilkening G.
Published: July 2002

A scanning-tunneling microscope (STM) of the scanning-sample type with transducers for the measurement of the position in all three axes has been developed. Motions in the X-, Y-, and Z-axis are straight and rectangular to a high degree and the capacitance transducers are calibrated in situ by plane mirror laser-interferometry. With these qualities as part of the design, the Abbe error may be minimized. X-Y-capacitance transducers and X-Y-piezo actuators are part of analog servo loops, thus providing positioning in the X-Y-plane to a desired coordinate. The STM is mainly built from commercially available parts.
Liquid EXAFS cells for measurements in transmission and fluorescence mode of corrosive samples
Authors: Marcos Enrique Sánchez , Gil Manuel , Martínez José M. , Muñoz-Páez Adela , Sánchez Marcos Antonio
Published: July 2002

The design of two small, compact and portable cells for EXAFS measurements of liquids is presented. One of the cells has been optimized for transmission measurements and the other for fluorescence. The sample chamber of both cells has been designed metal free to avoid corrosion by acids or bases. Materials and construction of the cell are such that their cost is quite low. The cells have been tested by recording EXAFS spectra of ionic aqueous solutions.
Selection and design of ion sources for use at the Holifield radioactive ion beam facilitya)
Authors: Alton G. D. , Haynes D. L. , Mills G. D. , Olsen D. K.
Published: July 2002

The Holifield Radioactive Ion Beam Facility now under construction at the Oak Ridge National Laboratory will use the 25 MV tandem accelerator for the acceleration of radioactive ion beams to energies appropriate for research in nuclear physics; negative ion beams are, therefore, required for injection into the tandem accelerator. Because charge exchange is an efficient means for converting initially positive ion beams to negative ion beams, both positive and negative ion sources are viable options for use at the facility. The choice of the type of ion source will depend on the overall efficiency for generating the radioactive species of interest. Although direct-extraction negative ion sources are clearly desirable, the ion formation efficiencies are often too low for practical consideration; for this situation, positive ion sources, in combination with charge exchange, are the logical choice. The high-temperature version of the CERN-ISOLDE positive ion source has been selected and a modified version of the source designed and fabricated for initial use at the facility because of its low emittance, relatively high ionization efficiencies, and species versatility, and because it has been engineered for remote installation, removal, and servicing as required for safe handling in a high-radiation-level ISOL facility. The source will be primarily used to generate ion beams from elements with intermediate to low electron affinities. Prototype plasma-sputter negative ion sources and negative surface-ionization sources are under design consideration for generating radioactive ion beams from high-electron-affinity elements. The design features of these sources and expected efficiencies and beam qualities (emittances) will be described in this report.
2D imaging of an undulator source by phase circular Bragg–Fresnel lens
Authors: Tarazona E. , Elleaume P. , Chavanne J. , Hartman Ya. M. , Snigirev A. A. , Snigireva I. I.
Published: July 2002

Two-dimensional imaging of an undulator x-ray source at different photon energies has been observed by means of phase circular Bragg–Fresnel lens (BFL) at the ESRF ID6 beamline. The optical properties of the BFL in the energy range 6–18 keV have been studied. Imaging has been studied on various orders of diffraction and on various harmonics of the undulator spectrum. Good resistance to a heatload of 100 W and 12 W/mm2 in the white beam has been demonstrated.
Observation of strain effects in semiconductor dots depending on cap layer thickness
Authors: Pistol M.-E. , Carlsson N. , Persson C. , Seifert W. , Samuelson L.
Published: July 2002

We have investigated the photoluminescence emission energy of InP dots as a function of cap layer thickness. We find a strong blue-shift with increasing cap layer thickness. The strain tensor in the dot as well as in the surrounding matrix has been modeled using finite element methods and the band gap has been calculated using deformation potential theory. We find good agreement between calculation and experiment. For uncapped dots we find that the emission energy is lower than for biaxially strained InP, and is indeed close to unstrained InP.
Long-lifetime high-intensity GaAs photosource
Authors: Calabrese R. , Ciullo G. , Guidi V. , Lamanna G. , Lenisa P. , Maciga B. , Tecchio L. , Yang B.
Published: July 2002

We used a GaAs crystal operating in a negative electron affinity mode to produce an intense continuous electron beam by photoemission. The major drawback of photoemission from GaAs, i.e., rapid current decay, was overcome without continuously supplying cesium. After a little initial decay, the current remained constant at 1 mA over a few mm2, with no degradation. Seasoning of the vacuum chamber played a fundamental role in achieving this performance.
New apparatus for thermal diffusivity measurements of refractory solid materials by the periodic stationary method
Authors: Khedari J. , Benigni P. , Rogez J. , Mathieu J. C.
Published: July 2002

An apparatus for the thermal diffusivity measurement of refractory solids at high temperatures (800–1800 K) by the periodic stationary method is presented. A cylindrical geometry for the sample has been chosen. The radial heat flow through the measurement cell is sine modulated and induces a thermal sine wave over the lateral side of the sample. The thermal diffusivity is determined from the measurement of the phase change and the amplitude ratio between two points of the sample. Thus, the thermal diffusivity can be obtained in two manners. The difference between these results is a criterium for the validity of the measurement. Experimental results on a sample of a cordierite based sintered material (Cecorite 130P) are presented. They show good agreement with the results of the CODATA Task Group on Thermophysical Properties.
Video sampling: A new low-cost method of capturing fast repetitive processes
Authors: Möller M. , Bruns H.-J.
Published: July 2002

We present a method of synchronizing an external shutter for a video camera or light source that allows a slow-motion representation of fast repetitive processes with a time scaling factor of up to 1,000,000 or more. The method uses standard, unmodified CCIR or EIA video equipment, including video cassette recorders for low-cost recording.
Excimer laser induced electron beams on an Al target: Plasma effect in a ‘‘nonplasma’’ regime
Authors: Beloglazov A. , Nassisi V. , Primavera M.
Published: July 2002

Experiments on electron-beam generation from an Al target illuminated by XeCl and KrCl excimer lasers were carried out under plasma ignition threshold intensities. Direct experimental evidence of such a plasma formation under ignition threshold is given for the first time. By Langmuir-like probe measurements, positive potentials as large as 0.36 and 0.75 V at distances down to about 2 μm from the grounded target over the laser spot area were reproducibly observed during the XeCl and KrCl laser action, respectively. From this result and in absence of cathode voltage, an accelerating electric field on the target of about 375 kV/m was estimated. The highest positive charge density near the cathode that resulted was about 3.3 mC/m3. The strong electric field caused by the plasma formation modified the acceleration conditions for a space-charge dominated electron beam and it should be the main cause of the discrepancies between the experimental current values and the calculated ones.
An electro-optic-based RMS voltage measurement techniquea)
Authors: Paulter N. G.
Published: July 2002

A new electro-optic-based technique for measuring the rms value of an applied voltage is presented. The technique incorporates a ratiometric method whereby the requirement for absolute laser power information is unnecessary. Description, analysis, and experimental results of the prototype measurement system are presented.
A simple circuit for measuring C–V profiles at kilovolt voltages
Authors: Chudobiak Michael J.
Published: July 2002

A simple circuit for measuring the capacitance–voltage profiles of high-voltage diodes is presented. The circuit is designed such that only one component, a noncritical power supply decoupling capacitor, requires a voltage rating equal to the maximum dc diode bias. Aside from this capacitor’s voltage rating, there is no limit to the maximum dc bias that can be applied to the diode. C–V profiles generated using this circuit are presented for biases of 0–1000 V, and are compared to those obtainable with a commercially available low-voltage capacitance meter. Errors of less than 2% are observed.
A simple IEEE-488 bus tester
Authors: Borghesani A. F. , Delfitto G. , Sambo A.
Published: July 2002

We have developed a simple, low cost IEEE-488 bus tester useful as both a diagnostic instrument for interface troubleshooting and as a learning tool for a better understanding of the working principles of this interface system.
A compact, light weight, high resolution electron monochromator
Authors: Goembel L. , Doering J. P.
Published: July 2002

A high resolution electron monochromator that incorporates Vespel polyimide plastic in its construction is described. A great saving in bulk can be realized by mounting the electron optical elements in Vespel tubes rather than mounting them by traditional means.
A video-based spin-polarized LEED data-acquisition system
Authors: Giergiel J. , Hopster H. , Lawrence J. M. , Hemminger J. C. , Kirschner J.
Published: July 2002

A video-LEED system for rapid measurement of spin-polarized low-energy electron-diffraction (LEED) data is described. The system is based on a special, high-dynamic-range camera but will also support TV-rate cameras for less demanding I/V LEED work. The capabilities of the system include LEED pattern recording, and data acquisition for asymmetry versus energy (A/V), intensity versus energy (I/V), and intensity versus time (I/T). The design and operation of the system is described and illustrated by asymmetry data for W(001).
Optical pulse radiolysis cell and apparatus designed to study reactions in supercritical fluids
Authors: Zhang Jianwei , Connery Karen A. , Strebinger Richard B. , Brennecke Joan F. , Chateauneuf John E.
Published: July 2002

The details of the construction of a high-pressure optical cell and flow apparatus for the study of pulse-radiolytically induced reactions in supercritical fluids are described. Application of pulse radiolysis and time-resolved absorption spectroscopy to near-critical dense gas and supercritical fluid allows for the generation and investigation of ionic transient species in these low dielectric media. Methodologies for sample preparation and pulse radiolysis of supercritical mixtures are described. Several aromatic carbocations have been generated in supercritical ethane and fluoroform and representative spectral and kinetic data are presented.
An apparatus for conducting experiments on solid-particle erosion
Authors: Inal O. T. , Bengisu M. , Morton B. , Richman R. H.
Published: July 2002

An apparatus that is capable of producing repeated impacts of erodent particles on a solid surface, in vacuum or controlled atmospheres, is described. It was developed specifically to correct the deficiencies of previous designs. It consists of an electromagnet, a laminated iron core, and an aluminum launcher (sabot), all contained in a sturdy frame that fits easily into a bell-jar vacuum system. Particle velocities can be readily varied over the range 3–100 m/s, with incidence angles from 10° to 90°. Such a device should find application in fundamental studies of solid-particle erosion.
Improved gating of microchannel plates for multiphoton ionization experiments
Authors: Gostein Michael , Sitz Greg O.
Published: July 2002

We have improved the high-voltage pulse circuit which we recently described for eliminating microchannel plate response to scattered laser light in our multiphoton ionization experiment [Rev. Sci. Instrum. 65, 3036 (1994)]. Our new design produces much less noise and is much more robust.
Narrow linewidth excimer laser for inscribing Bragg gratings in optical fibers
Authors: Othonos Andreas , Lee Xavier
Published: July 2002

A spectrally narrow linewidth KrF excimer laser has been developed for the application of writing Bragg gratings in optical fibers. Two air spaced etalons 80 and 6 cm−1 have been incorporated within the laser cavity resulting in a laser line with a linewidth of approximately 4 pm. A stable wavelength setting for writing Bragg gratings has been achieved without the necessity of a feedback mechanism. A study of the formation of Bragg grating in optical fibers with this narrow linewidth KrF excimer laser has been carried out. High quality gratings have been demonstrated in hydrogen sensitized fibers with a pulse energy density as low as 20 mJ/cm2. Limitations and various problems encountered in inscribing Bragg gratings (such as two simultaneous grating lines) with the narrow linewidth excimer laser source are also discussed.
Infrared electro-optical modulators based on field-induced Γ-L intervalley transfer
Authors: Meyer J. R. , Hoffman C. A. , Bartoli F. J. , Ram-Mohan L. R.
Published: July 2002

Electro-optical modulators based on intersubband transitions induced by normal-incidence radiation in GaSb-AlSb-family asymmetric double quantum wells are proposed. An applied field transfers electrons from Γ-valley states in one well to L-valley states in the other well, thereby radically altering the selection rules, resonance energies, and in-plane effective masses.
Production of a large diameter electron cyclotron resonance plasma using a multislot antenna for plasma application
Authors: Ueda Yoko , Tanaka Masayoshi , Shinohara Shunjiro , Kawai Yoshinobu
Published: July 2002

An electron cyclotron resonance plasma with large diameter, uniform, and high electron density is produced using a multislot antenna. The uniformity of the plasma is within 5% over 20 cm in diameter. The electron density of the helium plasma in front of a substrate is 7×1010 cm−3, while the electron density without the substrate is higher than the cutoff density for 2.45 GHz. The effect of the magnetic field configuration on plasma uniformity is investigated. Both of the R wave (electron cyclotron wave) and L wave are found to be excited in the plasma.
Semi-automatic atomic force microscope for imaging in solution
Authors: Mou Jianxun , Huang Gang , Shao Zhifeng
Published: July 2002

A semiautomatic atomic force microscope for imaging in solution is described. With this new design, the laser beam is focused into a fine line, and a rotating mirror is used to deflect the optical signal onto a fixed photodetector. The alignment is now operated with stepper motors. Combined with a three stepper motor sequential advancement for tip engagement, the operation of the atomic force microscope for imaging in solution is much simplified, and the crashing of the tip is largely avoided. Since all controls are now coupled with stepper motors, this system is fully compatible with automation and operation in a self sealed temperature controlled chamber. The design and the construction of this system is relatively simple and can be fitted into any existing system.