bluuebunny/crossref_metadata_2025 huggingface dataset:
Energy transfer from radio frequency sheath accelerated CF+3 and Ar+ ions to a Si wafer
Authors: Kersten H. , Snijkers R. J. M. M. , Schulze J. , Kroesen G. M. W. , Deutsch H. , de Hoog F. J.
Published: July 2002

The thermal energy flux which a rf plasma delivers to a silicon surface has been studied by a calorimetric method. The energy flux appears to be proportional to the product of the average ion energy and the ion flux, which was calculated from the Bohm criterion using measured plasma parameters. Furthermore, the value and energy dependence of the kinetic energy transfer efficiency (about 0.5) suggests that the microscopic interaction of impinging ions in the eV range with a silicon surface can be described by a binary collision model.
High Schottky barrier height of the Al/n-GaAs diodes achieved by sputter deposition
Authors: Chen C.-P. , Chang Y. A. , Huang J.-W. , Kuech T. F.
Published: July 2002

Thermally stable Al/n-GaAs Schottky contacts, up to annealing temperature at 500 °C for 20 s, have been realized by sputter deposition. The Schottky barrier height was 0.75 eV (0.9 eV) when using the current-voltage (I-V) [capacitance-voltage (C-V)] method with an ideality factor of 1.09 for the as-deposited samples. The Schottky barrier height increased to 0.97 eV (1.06 eV) with an ideality factor of 1.07 after annealing at 400 °C for 20 s. The discrepancy between I-V and C-V measurements was attributed to deep levels existing in the GaAs substrate. A (200) dark-field cross-section transmission electron microscopy image of the contact after annealing at 600 °C showed that the (Ga,Al)As phase formed at the interface and the enhancement of the Schottky barrier height was due to the formation of this phase.
Epitaxial YBa2Cu3O7−δ thin films on SrRuO3/Pt/MgO
Authors: Tiwari P. , Wu X. D. , Foltyn S. R. , Le M. Q. , Campbell I. H. , Dye R. C. , Muenchausen R. E.
Published: July 2002

Epitaxial YBa2Cu3O7−δ (YBCO) thin films were deposited on (100) MgO using platinum and SrRuO3 (SRO) buffer layers by pulsed laser deposition. The films were (001) textured normal to substrate surface with a high degree of in-plane orientation with respect to the substrate’s major axes. YBCO films showed superconducting transition temperature (Tco) at 91 K and critical current densities were found to be 2–3×106 A/cm2 at 77 K and zero field. An ion beam minimum channeling yield of 16% was obtained for YBCO films, indicating high crystallinity. The orientation relationship for this epitaxial multilayer structure was found to be (100) YBCO∥(100) SRO∥(100)Pt∥(100) MgO. This result showed that high-quality superconducting thin films can be deposited on metal with an appropriate buffer layer.
Direct measurements of lattice parameter variations and relaxation kinetics in strained Si1−xGex/Si heterostructures
Authors: Sardela M. R. , Hansson G. V.
Published: July 2002

Lattice parameter variations in strained Si1−xGex/Ge (x<0.23) induced by high-temperature annealing in the range 700–1000 °C, were determined by x-ray high-resolution reciprocal lattice mapping of the crystal structure. In the range 700–800 °C, the strain relaxation was found to increase by one order of magnitude owing to glide propagation of misfit dislocations, with an activation energy of 2.3 eV. In the range 850–1000 °C, relaxation was still high but the increase with the temperature was limited by dislocation interactions.
Transient behavior and memory effect of a PbZrxTi1−xO3/YBa2Cu3O7−x three-terminal device
Authors: Lin H. , Wu N. J. , Xie K. , Li X. Y. , Ignatiev A.
Published: July 2002

The transient behavior of a ferroelectric PbZrxTi1−xO3 and superconducting YBa2Cu3O7−x three-terminal device has been investigated. Four-state behavior, that is, two polarization states of the PbZrxTi1−xO3 gate and superconducting and normal states of the YBa2Cu3O7−x layer, has been observed. It was shown that the biased superconducting channel can be switched from superconducting state to the normal state by the flowing charge during the polarization switching of the PbZrxTi1−xO3 gate. The nonvolatility of this device based on the different polarization states of the ferroelectric gate has also been demonstrated.
Electrical tuning of the kinetic inductance of high temperature superconductors
Authors: Cho S. , Erlig H. , Kain A. Z. , Fetterman H. R. , Liang G.-C. , Johansson M. E. , Cole B. F. , Withers R. S.
Published: July 2002

A current controlled delay in the time of flight of electrical picosecond pulses in a YBa2Cu3O7 spiral delay line has been investigated using optoelectronic sampling techniques. The transmission line is a microwave stripline on the LaAlO3 substrate and is passivated with the contact pads open. The measured delay time clearly shows a squared dependence on the applied current, in good agreement with Ginzburg–Landau theory for the case of a uniform current density through a thin film.
Optical transition properties of β-FeSi2 film
Authors: Wang Lianwei , Qin Linhong , Zheng Yuxiang , Shen Wenzhong , Chen Xiangdong , Lin Xian , Lin Chenglu , Zou Shichang
Published: July 2002

Optical transition of properties of β-FeSi2 film have been investigated by optical transmittance absorption measurement, spectroscopic ellipsometry and reflectivity. Optical transmittance absorption measurement ranging from 0.5 to 1.1 eV revealed the direct transition at E0=0.84 eV, while absorption curve obtained from the spectroscopic measurement in the range of 1.5–4.5 eV implied additional transition at E′=1.05 eV, it is suggested that such additional transition originates from spin–orbit splitting at Γ (center of Brillouin’s zone). Reflectivity goes to the maximum value near Eg, indicating that the joint density of states in the transition at Eg is very high. Another peak which is related with the transition at E′ was also observed in the reflectivity spectra.
Spatial profiling of ion and neutral excitation in noble gas electron cyclotron resonance plasmas
Authors: Rhoades R. L. , Gorbatkin S. M.
Published: July 2002

Optical emission from neutrals and ions of several noble gases has been profiled in an electron cyclotron resonance plasma system. In argon plasmas with a net microwave power of 750 W, the neutral (696.5-nm) and ion (488-nm) emission profiles are slightly center peaked at 0.32 mTorr and gradually shift to a hollow appearance at 2.5 mTorr. Neon profiles show a similar trend from 2.5 to 10.0 mTorr. For the noble gases, transition pressure scales with the ionization potential of the gas, which is consistent with neutral depletion. Studies of noble gas mixtures, however, indicate that neutral depletion is not always dominant in the formation of hollow profiles. For Kr/Ar, Ar/Ne, and Ne/He plasmas, the majority gas tends to set the overall shape of the profile at any given pressure. For the conditions of the current system, plasma density appears to be more dominant than electron temperature in the formation of hollow profiles. The general method described is also a straightforward, inexpensive technique for measuring the spatial distribution of power deposited in plasmas, particularly where absolute scale can be calibrated by some other means.
High mobility InAs grown on GaAs substrates using tertiarybutylarsine and trimethylindium
Authors: Watkins S. P. , Tran C. A. , Ares R. , Soerensen G.
Published: July 2002

We report transport measurements on a series of high purity InAs epilayers grown on GaAs substrates by metalorganic chemical vapor deposition using tertiarybutylarsine and trimethylindium. Perfectly specular surfaces were obtained by a two step growth method consisting of a 400 °C prelayer followed by deposition of the thick bulk layer at higher growth temperatures. Temperature dependent Hall measurements between 1.8 and 293 K showed a competition between bulk and surface conduction, with average Hall mobilities of up to 1.2×105 cm2/V s at 50 K. Large changes in the temperature dependent transport data are observed several hours after Hall contact formation and appear to be due to passivation of the surface accumulation layer by native oxide formation.
Complete polarization control of 8×8 vertical-cavity surface-emitting laser matrix arrays
Authors: Yoshikawa T. , Kosaka H. , Kurihara K. , Kajita M. , Sugimoto Y. , Kasahara K.
Published: July 2002

Polarization of 8×8 vertical cavity surface emitting laser (VCSEL) arrays is completely controlled. These index-guided VCSELs have a 6×5 μm rectangular poststructure consisting of DBR mirrors. All 64 VCSELs emit fundamental single-mode and linearly polarized light with a polarization angle deviation of only 2.9°. Their light output characteristics are almost the same as those of conventional 6×6 μm polarization-uncontrolled VCSELs.
Temperature-dependent threshold and modulation characteristics in InGaAs/GaAs quantum-well ridge-waveguide lasers
Authors: Hu S. Y. , Corzine S. W. , Chuang Z. M. , Law K.-K. , Young D. B. , Gossard A. C. , Coldren L. A. , Merz J. L.
Published: July 2002

The observed temperature dependence of threshold currents in InGaAs/GaAs quantum-well ridge-waveguide lasers is modeled. This method incorporates both experimental data and theoretical gain calculations. The results show that lateral leakage currents must be included in the ridge-waveguide laser models. Based on the same model, the temperature-dependent modulation characteristics for InGaAs/GaAs quantum-well ridge-waveguide lasers are also investigated.
Element-specific vector magnetometry with magnetic circular dichroism
Authors: Chakarian V. , Idzerda Y. U. , Meigs G. , Chaban E. E. , Park J.-H. , Chen C. T.
Published: July 2002

The use of soft x-ray magnetic circular dichroism in two-dimensional (2D) element-specific vector magnetometry is demonstrated by investigating a thin Fe(001) single-crystal film grown on ZnSe(001). By measuring element-specific magnetic hysteresis curves along directions parallel and perpendicular to an applied magnetic field, the 2D behavior of the in-plane magnetization vector M is described as a function of the applied magnetic field. The use of this method to obtain element-specific 3D vector magnetometry in magnetic materials that exhibit both in-plane and out-of-plane magnetization is also discussed.
Application of layered synthetic microstructures to high-temperature plasma diagnostics (invited)
Authors: Day Robert H. , Barbee Troy W.
Published: July 2002

Layered synthetic microstructures (LSM’s) are a new type of man-made x-ray diffracting element which can be applied to a broad variety of diagnostic applications. The ability to use the synthesis process to engineer the properties of the LSM allows the designer of x-ray diagnostics to construct many novel instruments. In this paper, we review the state of the art in LSM fabrication and will describe some unique spectrometers that have been designed and fielded to provide measurements which are unachievable with conventional designs. We have also begun an experiment to understand the properties of LSM’s under intense heat loads. We will describe the experiments to date and our plans for further work in this area.
Ultrafast turnoff laser triggered gating system for microchannel-plate intensified x-ray spectrometers
Authors: Christie D. J. , Nilson D. G. , Wiedwald J. D. , Wilcox R. B.
Published: July 2002

A laser triggered photoconductive switch based microchannel-plate (MCP) gating system has been developed. The gating pulse provided to the MCP has a fall time on the order of 200 ps. Use of this system has resulted in increased signal-to-noise ratio on three MCP intensified x-ray spectrometers during recent x-ray experiments at the Novette laser facility. The x-ray signals of interest have a duration of approximately 300 ps while background in the same spectral region continues for several nanoseconds. As a result, signal-to-noise ratio is maximized by turning the MCP off just after the signals of interest are recorded. The MCP’s are turned on by charging to approximately 1 kV with a slow rise-time (500 ns) pulse and rapidly gated off by a photoconductive switch connected to the MCP through transmission lines. Staggering the turnoff times of three microstrip lines across the MCP by 250 ps provides some time resolution. Details of the system, including pulse charging system, trigger beam delivery optics, and system diagnostics will be discussed.
Development of an intense neutral beam for the injected internal target technique, (IT)2, diagnostic system (abstract)
Authors: Quon B. H. , Moses K. G. , DiVergilio W. F.
Published: July 2002

The (IT)2 diagnostic beam probe will be used to measure the hot electron density and temperature profiles in the thermal barrier and MHD anchor regions of the TARA tandem mirror experiment. The measurement requires a high-quality beam with current densities >50 mA/cm2 at beam energies of 50–100 keV. The design of the extractor/accelerator configuration was done using the ORNL ion optic beam code1, and studies using the code indicate a beam divergence, Δθ≲0.5°. The beam will be extracted from a rf generated dense plasma source; and space-charge neutralization of the beam will be accomplished by plasma formed by another rf discharge in the vicinity of the extractor, prior to the charge exchange cell. Measurements of the plasma source performance and details of the design will be presented.
Meyer–Neldel rule for liquid semiconductors
Authors: Fortner J. , Karpov V. G. , Saboungi Marie-Louise
Published: July 2002

The fact that the Meyer–Neldel rule is obeyed in many liquid semiconductors has led to the examination of its origin. An explanation based on a statistical shift of the Fermi energy with temperature is shown to be unrealistic. Multiphonon hopping is suggested as an explanation of the temperature and composition dependence of the electrical conductivity. This mechanism has the advantage of being universally valid for amorphous, crystalline, and liquid semiconductors.
Vacuum-operated digital wavelength meter
Authors: Bränberg Agneta , Nylén Per
Published: July 2002

A vacuum-operated digital wavelength meter for measurement of laser light has been designed, built, and tested. Special considerations have been paid to the mechanical stability and ease of use. The rigid design, small dimensions, and small weight of the instrument makes it possible to move it between different experimental setups without troublesome realignment. The operation in vacuum also eliminates the need for the air-to-vacuum correction.
Picosecond optical response of Tl2Ba2CaCu2O8 and Tl0.5Pb0.5Sr2(Ca0.8Y0.2)Cu2O7 high T
c superconductor films
Authors: Lai Y. S. , Liu Y. Q. , Cao W. L. , Lee Chi H. , Shen Zhi-Yuan , Pang Philip , Kountz Dennis J. , Holstein William L.
Published: July 2002

We have investigated the optical response of 700 nm optically thick Tl2Ba2CaCu2O8 and Tl0.5Pb0.5Sr2(Ca0.8Y0.2)Cu2O7 high Tc superconductor films activated by a few mJ/cm2 laser pulses. We have systematically studied the dependence of optical response on temperature and laser intensity. Fast and slow components can be clearly identified. A 70 ps electric transient has been obtained when activated by a 3.3 mJ/cm2 laser at 80 K or by a 10 mJ/cm2 laser at 50 K.
Photoresponse and fast optical readout for a PbZrxTi1−xO3/YBa2Cu3O7−x thin-film heterostructure capacitor
Authors: Lin H. , Wu N. J. , Geiger F. , Xie K. , Ignatiev A.
Published: July 2002

The low-temperature photoresponse properties for a PbZrxTi1−xO3/YBa2Cu3O7−x thin-film heterostructure capacitor are reported. The fast optical readout effect measured for the device while the YBCO bottom electrode was superconducting indicates a fall time dependent on YBCO state. A simple equivalent circuit model confirmed that the temperature dependence of the YBCO electrode resistance is responsible for the variation of the fall time of the optical readout signal. Such heterostructures can be used to fabricate high power, radiation-hard optical sensors which cover the whole visible range.
Comparison of a glass thermometer against a nuclear orientation thermometer in high magnetic fields
Authors: Reijntjes P. J. , van Rijswijk W. , Vermeulen G. A. , Frossati G.
Published: July 2002

We have compared the low-frequency capacitance of a glass thermometer made of very pure SiO2 doped with ∼1200 ppm OH− with a 60CoCo single-crystal γ-ray anisotropy primary thermometer in the range of 15–40 mK in magnetic fields up to 6 T. Within our temperature accuracy of ±5% no shift of the capacitance due to the applied fields was observed.
Investigation of systematic noise in stochastic linear system analysis
Authors: Blümich B.
Published: July 2002

In stochastic system analysis, transfer functions are retrieved from experimental data by cross correlation. A well-known linear cross correlator is the Michelson interferometer used in Fourier transform infrared spectroscopy. Due to the noise excitation, the transfer functions are inherently contaminated by systematic noise. It is shown, that in the limit of observation periods which are long compared to the maximum time shift in the cross correlation, the systematic noise decreases in proportion to the inverse square root of the data-acquisition time. Experimental data from stochastic NMR spectroscopy illustrate that the resolution of the transfer function can be optimized independent of the observation period.
Millimeter-wave spectroscopy with a solid-state IMPATT oscillator source
Authors: Isaacs N. A. , Russell D. K.
Published: July 2002

We have designed and constructed a spectrometer for the observation of high-resolution absorption spectra in the millimeter wave region using a solid-state IMPATT oscillator as a source. Details of the spectrometer are presented, together with the first results obtained using the new instrument.
Apparatus for low-energy ion scattering spectroscopies: Imaging angular distributions and collecting angle-resolved energy spectra
Authors: Yarmoff Jory A. , Williams R. Stanley
Published: July 2002

An apparatus for using low-energy ion scattering to study surface crystallography is described. The ion source can produce highly collimated beams of either noble gas or alkali metal ions with energies up to 30 keV. A versatile manipulator has been built that enables the entire UHV chamber to be translated and rotated in order to easily orient it with respect to the ion beam. The sample is mounted on a manipulator with two independent rotations, three translations, and a tilt, and can be oriented such that the sample normal or an arbitrary bulk crystal axis may be parallel to the incident ion beam within 0.1°. Ions that have scattered from a single crystal surface are detected with either a large solid angle two-dimensional imaging detector or with a high-resolution angle-resolving electrostatic analyzer. The backscattered ion image on the large area detector may be viewed in real time and with the aid of a video digitization system to determine the bulk stereogram of a crystal, and provide information about the near surface atomic structure. The electrostatic analyzer position is rotatable with respect to the incident ion beam direction, allowing scattering angles from 0° to 166° to be achieved. Examples of data collected with the instrument are presented.
Glass calorimeter for spatially resolved studies in arc lamps
Authors: Pearson J. B. , Curzon F. L.
Published: July 2002

The construction of an arc vessel designed to measure the axial profile of thermal wall loading in a vortex-stabilized arc lamp is described. The cooling jacket, which surrounds the quartz arc tube is made of glass and is partitioned so that the axial profile of wall loading can be measured by continuous flow calorimetry. A notable feature is that, if required, the inner tube can easily be removed and replaced. Procedures for the calibration of the calorimeter are outlined and checks which were made for systematic errors in the apparatus are also reported. A profile, obtained with the calorimeter, is presented for a 17-kW arc operating in argon at a pressure of 5 1/2 atm and with a dc current of 225 A.
Johnson noise in SQUID magnetometers
Authors: Savicki Joseph P.
Published: July 2002

Conducting tubes threading the pick-up coils in SQUID magnetometers may generate magnetic flux noise larger than the intrinsic SQUID noise. A method for calculating the level of this noise is presented which can aid in the design of low noise systems. Application to a system in this lab predicts a noise level of 0.001 fluxoids rms/(Hz)1/2, in good agreement with the observed level of 0.001 fluxoids rms in a 1-Hz bandwidth.
Laser speckle measurements of flow velocity in a simplified gas jet
Authors: Pearson J. B. , Hilko B. , Houtman H. , Curzon F. L.
Published: July 2002

The double exposure laser speckle photography technique has been used to measure the radial velocity profile in a simple gas jet. In order to achieve operation in the speckle regime, the flow was seeded with a high density (1.35×107 cm−3) of 0.6-μm-diam aerosol droplets. At low Reynolds number, the measurements yield a velocity profile which agrees well with theory. At high Reynolds number, where the flow is turbulent, the small-scale turbulence destroys the correlation between the two exposures. While this precludes the measurement of the mean velocity, it suggests that this technique may be a sensitive means of detecting the onset of turbulence.
Computer-controlled data-acquisition system for an x-ray spectrometer
Authors: André J. M. , Cardinaud C. , Chargelegue P. , Marcelet F. , Sénémaud C.
Published: July 2002

A data-acquisition system, controlled by an Apple IIe microcomputer, designed for a bent crystal, vacuum spectrometer is described. A specific interface performing the photon counting via a programmable counter timer and the detector position encoding through a 12-bit analog-to-digital converter is coupled to the microcomputer bus by an 8-bit parallel interface. An outline of the software in advanced and machine language is given.
Electrodeless method for the measurement of ionic conductivity of RbAg4I5
Authors: Ishida T. , Monden K. , Nakada I.
Published: July 2002

An electrodeless method has been developed for measuring an ionic conductivity of a superionic conductor. This technique allows us to obtain an intrinsic ionic conductivity, free from the ambiguous electrode–specimen interface problem. In principle, the application of alternating magnetic field to the pelletized RbAg4I5 specimen induces ionic current. The ionic conductivity of the specimen can be evaluated from the magnetic field generated by the ionic current. A AgI specimen is used to calibrate the measuring system. The ionic conductivity of RbAg4I5 measured by this method is in good agreement with those of earlier works.
Use of glass foils for e-beam excitation
Authors: Mandl A.
Published: July 2002

The use of glass as a foil material for systems using e-beam excitation has been examined. A 1-mil glass bubble structure has been developed which can efficiently transmit high-energy e-beam currents ∼12 A/cm2 while holding off an atmosphere of pressure.
CO2 laser stabilization using an external cavity locked to a reference HeNe laser
Authors: Adam A. G. , Gough T. E. , Isenor N. R.
Published: July 2002

A method is described for stabilization of a cw CO2 laser by locking it to a modulated external cavity which is locked to a HeNe reference laser. This avoids the necessity of modulating the CO2 laser. Stability values of a few tens of kHz on the microsecond and minute time scales have been achieved.
Single-mode diode laser as a source of variable bandwidth, fixed center frequency optical fields
Authors: Camparo J. C.
Published: July 2002

A procedure of diode laser bandwidth control is investigated where bandwidth is primarily determined by adjusting the laser temperature and where compensating injection current changes are used to retune the laser to an atomic or molecular absorption resonance. A theoretical model shows that roughly an order of magnitude variation in the bandwidth of a fixed frequency field should be possible for a single ideal laser with this procedure and the concept is qualitatively justified by bandwidth measurements on two AlGaAs diode lasers tuned to the Rb D1 absorption resonance at 794.7 nm. However, since the largest observed bandwidth variation was only a factor of two, an expedient technique employing the temperature/injection current procedure with several lasers is demonstrated as a viable alternative to finding the single ideal laser.
Shutter ratio of a gated ITT F4128 microchannel-plate photomultiplier
Authors: Hirsch K. , Köchel M. , Salzmann H.
Published: July 2002

The shutter ratio of a proximity focused ITT F4128 microchannel-plate (MCP) photomultiplier is investigated for gated photocathode-to-MCP gap voltages. At counter potentials of greater than 3 V, the shutter ratio is better than 1013 for incident light with a wavelength longer than 600 nm.
Operation of a Dudnikov type Penning source with LaB6 cathodes
Authors: Leung K. N. , DeVries G. J. , Ehlers K. W. , Jackson L. T. , Stearns J. W. , Williams M. D. , McHarg M. G. , Ball D. P. , Lewis W. T. , Allison P. W.
Published: July 2002

The Dudnikov type Penning source has been operated successfully with low work function LaB6 cathodes in a cesium-free discharge. It is found that the extracted H− current density is comparable to that of the cesium-mode operation and H− current density of 350 mA/cm2 have been obtained for an arc current of 55 A. Discharge current as high as 100 A has also been achieved for short pulse durations. The H− yield is closely related to the source geometry and the applied magnetic field. Experimental results demonstrate that the majority of the H− ions extracted are formed by volume processes in this type of source operation.
Optical double-balanced quadrature mixer with applications to light-beating spectroscopy and photon counting
Authors: Burstyn H. C.
Published: July 2002

A doubly balanced optical quadrature mixer is proposed for use in light-beating spectroscopy. The technique allows one to examine asymmetric optical spectra. The ratio of the antisymmetric to symmetric spectral densities can be found directly. The use of the device in the photon-counting regime is also discussed. The instrument has direct applicability in the measurement of the dynamical properties of hydrodynamic systems out of equilibrium.
Microwave cavity reflection interferometer for single-pulse transient conductivity measurements
Authors: Eckstrom D. J. , Williams M. S. , Dickinson J. S.
Published: July 2002

A technique is described for measuring transient real and imaginary conductivity histories in a single pulse using the microwave cavity perturbation technique when the perturbations are large, that is, when the frequency shift is larger than the FWHM of the cavity resonance and/or when the cavity Q changes significantly. A demonstration of the use of the technique to measure laser photoionization yields in a high-pressure buffer gas is presented.
Magnetic field stabilizer for NMR imaging systems with resistive magnets
Authors: Weis J. , Jellúš V. , Frollo I.
Published: July 2002

The NMR stabilizer has been constructed for the purpose of magnetic field stabilization. The error signal for field correction is derived from the 1H resonance of pure H2O. A NMR transducer, operating in the pulse mode with time multiplexing, is connected to the transmit–receive radio frequency stage and yields information about the magnetic induction changes in the frequency form which is compared with the reference frequency. The frequency deviation is evaluated as a voltage that controls the power supply of the electromagnet coil. The stability achieved was slightly better than ±1 ppm.
Asymmetric double Langmuir probe: Small signal application
Authors: Uckan Taner
Published: July 2002

We discuss the asymmetric double Langmuir probe (ADLP) and demonstrate the possibility of using it to measure plasma temperature Te and density n when it is operated in the region of small signal response. The area of one of the ADLP collectors is considerably larger than the other. This probe can be operated at a relatively low applied voltage eVa/Te<1, and still provides sufficient information to determine the plasma Te and n. There is no need for a direct measurement of the ion saturation current, which can be on the order of a few amperes in large fusion devices. This reduces the requirements on the probe power supply.
Ultrahigh-vacuum system for surface studies using high-energy ion scattering and x-ray photoemission spectroscopy
Authors: Smith R. J. , Whang C. N. , Mingde Xu , Worthington M. , Hennessy C. , Kim M. , Holland N.
Published: July 2002

We describe a new ultrahigh-vacuum facility which is being used for studies of solid surfaces. The target chamber is attached via a differentially pumped beamline to a 2-MV Van de Graaff accelerator, and includes: (1) instrumentation for high-energy ion backscattering and channeling studies and nuclear reaction analysis, (2) a 100-mm radius hemispherical analyzer for photoemission studies, and (3) low-energy electron diffraction (LEED) optics.
Design of electromagnetic devices using commercial finite element programs
Authors: Johnson M. , Wands R. , Wolin E.
Published: July 2002

The two-dimensional electrostatic modeling capability of the ANSYS finite element program is used in the design of the coax-to-parallel plate microwave transformer. Its two-dimensional axisymmetric capability is used in the design of a laser-triggered coaxial Blumlein spark gap. Finally, its three-dimensional magnetic modeling ability is used to model a large dipole magnet (the Chicago cyclotron magnet). The results of the calculations compare well with measurements for two of the above cases.
Precision capillary viscometer
Authors: Dhadwal H. S. , Chu Benjamin , Wang Z. , Kocka M. , Blumrich M.
Published: July 2002

A novel precision capillary viscometer which has a time resolution of ±0.001 s is reported. The viscometer has been utilized to demonstrate that estimates of intrinsic viscosity (to within 3% of the infinite dilution value for polystyrene in benzene) can now be made, over a wide range of polymer molecular weights, for solutions from a single polymer concentration.
Elimination of modulation effects in a tandem Fabry–Perot interferometer
Authors: Vanderwal J. J. , Walton D. , Hu Z.
Published: July 2002

Interétalon feedback in a tandem Fabry–Perot spectrometer will often be manifested by a frequency-modulated spectrum. This undesirable modulation can be removed in a simple and consistent manner without significant loss of signal.
Improved fast integrator for small ion currents (1 fA–1 mA)
Authors: Gardner R. J.
Published: July 2002

This fast, low-current integrator uses an active feedback circuit to eliminate the effects of reset/offset error and switch leakage. Sensitivity is 200 pC per volt, response time is <1 μs, input bias current (ib) is <0.5 fA, signal source background current can be subtracted and built-in calibration is provided. It is well suited to capacitance versus voltage measurements.
Nicolet data transfer to the AT&T 6300 computer
Authors: Christman S. B.
Published: July 2002

A hardware and software system transfers data between a Nicolet 1180/1280 computer and an AT&T 6300 computer over an RS-232 link.
Resonance-enhanced multiphoton ionization for diagnosis of a weakly ionized plasma
Authors: Bonnie J. H. M. , Granneman E. H. A. , Hopman H. J.
Published: July 2002

We describe an experimental setup in which resonance-enhanced multiphoton ionization (REMPI) is used for diagnosis of neutral particles (atoms or molecules) effusing from a plasma. Quantum-state-specific detection, achieved by selective ionization with the help of REMPI, yields the distribution over their internal degrees of freedom. Discrimination against nonlaser-produced ions is performed by means of the combination of an electric and a magnetic field. The applicability of the setup is demonstrated by the determination of the rotational temperature of ground-state hydrogen molecules in a multicusp ion source. Under nondischarge conditions a detection limit is achieved of ≊2×1010 state-selected hydrogen molecules/cm3, corresponding to a value of ≊7×108/cm3 at the analysis region. Under discharge conditions, this detection limit is deteriorated by the presence of metastable hydrogen molecules, which are ionized in a one-photon process.
Continuous and stopped flow EPR spectrometer based on a loop gap resonator
Authors: Hubbell Wayne L. , Froncisz Wojciech , Hyde James S.
Published: July 2002

A continuous and stopped flow EPR spectrometer based on a new loop gap resonator operating at X band is described. The important features of the instrument are: (1) very small amounts of material are consumed in both stopped and continuous flow modes of operation, (2) dead times on the order of 4 ms for stopped flow and 1 ms for continuous flow are realized with a very narrow age distribution in the sample compartment, and (3) the dead times and, hence, sample age are highly reproducible and independent of viscosity due to the use of a positive displacement syringe ram. The performance of the instrument is evaluated using the decay of ascorbate radical generated by Ce(iv) oxidation and reduction of nitroxides by ascorbic acid.
Small sample magnetometers for simultaneous magnetic and resistive measurements at low temperatures and high magnetic fields
Authors: Brooks J. S. , Naughton M. J. , Ma Y. P. , Chaikin P. M. , Chamberlin R. V.
Published: July 2002

We describe a very simple method for making measurements of the isotropic and anisotropic static magnetization of small samples which is especially useful in the limit of very low temperatures and high magnetic fields. The sensitivity of this technique can surpass that of commercial superconducting magnetometers in the high magnetic field limit. Methods for calibration are presented and magnetization measurements on several materials are shown to demonstrate the technique.
Sample rotation in diffuse reflectance Fourier transform infrared spectroscopy
Authors: Velapoldi Rance A. , Tvedt Jan E. , Christy Alfred A.
Published: July 2002

An apparatus for the rotation of sample and blank in diffuse reflectance Fourier transform infrared spectroscopy has been designed and fabricated. Spectra taken with sample rotation give data with better precision by a factor of 4 than without rotation. Additionally, sample rotation saves time by eliminating the need for taking three to five spectra followed by spectrum averaging as has been done in the past to obtain a representative spectrum of solids.
Method for the absolute calibration of photoacoustic cells
Authors: Benedetto G. , Maringelli M. , Spagnolo R.
Published: July 2002

A simple method is proposed for the absolute calibration of photoacoustic cells using a condenser microphone as a calibrated sound source. This method allows the measurement of acoustical transfer function of resonant and nonresonant cells. By correcting experimental data with the transfer function a good agreement with theoretical previsions has been achieved. The technique was tested on an optically opaque thermally thick sample.
Computerized apparatus for thermally stimulated current (TSC) measurements
Authors: Jackson John M. , Dutta Biprodas , Kinser Donald L.
Published: July 2002

A computer-controlled apparatus for thermally stimulated polarization and depolarization current (TSPC/TSDC) measurements over the temperature range −196 to 250 °C is described. The instrument is designed to combine state-of-the-art current sensitivity with computerized data acquisition and reduction. The apparatus is capable of detecting small (as low as 0.1 ppm) dipole concentrations (charge carriers) in solid dielectrics with the application of moderate electric fields (2–5 kV/cm).
Hollow cathode plasma source for active spacecraft charge control
Authors: Deininger William D. , Aston Graeme , Pless Lewis C.
Published: July 2002

A prototype plasma source spacecraft discharge device has been developed to control overall and differential spacecraft surface charging. Such charging phenomena have contributed to many satellite operating anomalies and systems malfunctions. The plasma source is based on a unique hollow cathode discharge, where the plasma generation process is contained completely within the cathode. This device can be operated on argon, krypton, or xenon and has a rapid cold start time of less than 4 s. The discharge system design includes a spacecraft-discharge/net-charge sensing circuit which provides the ability to measure the polarity, magnitude, pulse shape, and time duration of a discharging event. Ion currents of up to 325 μA and electron currents ranging from 0.02 to 6.0 A have been extracted from the device. In addition, the spacecraft discharge device successfully discharged capacitively biased plates, from as high as ±2500 V, to ground potential, and discharged and clamped actively biased plates at +5 V with respect to ground potential during ground simulation testing.
New device for measuring post-arc currents in circuit breakers
Authors: Vokurka V. , Ackermann U. , Schade E.
Published: July 2002

This paper describes a new technique for measuring post-arc currents in circuit breakers. The measurements are performed with a specially designed current monitor. In contrast to commonly used current monitors saturation of the core of the transformer at high pulses of current is prevented by shunting the turns of the transformer by antiparallel fast-recovery diodes. This new device offers several advantages in comparison to other known techniques for post-arc measurements: there is no galvanic coupling to the network, the system is easy to handle, and the costs of the components are low. The two post-arc-current monitors (PACM) described have a sensitivity of 0.1 V/A and 10 mV/A, and are linear within 1% in the range of ±4 and ±100 A, respectively. The first PACM has an upper cutoff frequency of 18 MHz, the second one 3.8 MHz and are designed for sinusoidal fault currents of 6.3 kA and 56 kA, respectively, at a frequency of 50 Hz. Examples of applications to axially blown arcs in SF6 and to vacuum circuit breakers are presented.
Dielectric measurements with a resonance method for comparing low-value three-terminal capacitors
Authors: Courteau R. , Bose T. K.
Published: July 2002

A resonance system for comparing low-value three-terminal capacitors with an active guard circuit based on an instrumentation amplifier is described in detail. The system is simple, easy to calibrate, and permits precise measurement of lossy three-terminal capacitors in the frequency range 50 Hz–10 MHz. Dielectric measurements made with this apparatus on 1-propanol at low temperatures are reported.
Simple gun for vapor deposition of organic thin films
Authors: Sato Naoki , Seki Kazuhiko , Inokuchi Hiroo
Published: July 2002

A simple evaporation gun for preparing organic thin films was fabricated using commercially available parts of an electron gun for a TV Braun tube. The device permits sample heating to be easily controlled because of the small heat capacity.
Computer-controlled system for investigating the hydrostatic piezoresistive effect as a function of temperature
Authors: Amin Ahmed
Published: July 2002

A system has been developed for investigating the piezoresistive effect in semiconducting solids and conductive polymers under different elastic and thermal boundary conditions. The system provides the necessary information needed for sensor design such as nonlinearity, hysteresis, and temperature dependence of the piezoresistance coefficient. The system operates under full computer control for both data acquisition and data reduction cycles. The temperature dependence of the hydrostatic piezoresistance coefficient of a donor-doped polycrystalline semiconducting barium titanate below and above its ferroelectric–paraelectric Curie point will be presented for the first time. The nonlinear and hysteretic behavior of an electrically conductive polymer over the pressure range of 0–30 MPa will also be demonstrated.
Rapid separation of fine particles with narrow size distribution
Authors: Aoki Ichiro , Shirane Kotaro , Tokimoto Takayuki , Kimura Masatugu
Published: July 2002

In a rotating tube with steady (laminar) flow (RSF) or with alternate flow (RAF) method for separation of fine particles, a simple and practical formula giving the relationship between the particle velocity (RSF velocity) along the tube length and parameter Aω0/V0 is derived, where A is the tube radius, ω0 is its angular velocity, and V0 is the sedimentation velocity of a particle. The chromatographic classification by these helical orbit sedimentation methods with laminar flow have been investigated with the formula in detail. In the flow methods the lowest size for biological and chemical samples with density ρ(≳1.05 g/cm3) is estimated as ∼10 μm when the tube with 2–4 mm i.d. and length L∼1 m is used.
Time response of small side-on photomultiplier tubes in time-correlated single-photon counting measurements
Authors: Meister Erich C. , Wild Urs P. , Klein-Bölting Peter , Holzwarth Alfred R.
Published: July 2002

The position-dependent time response of eight small side-on type photomultiplier tubes (Hamamatsu R928 and R955) has been investigated. Using the method of time-correlated single-photon counting relative transit times, single-photon response widths and relative quantum yields have been determined. This characterization provides the basis for the proper selection and use of fast photomultiplier tubes in single-photon counting experiments.
Optical alignment device for x-ray diffraction systems
Authors: Prawer S. , Wilkins S. W.
Published: July 2002

A device is described which enables x-ray diffraction systems to be aligned optically using a collimated laser beam to mimic the x-ray beam path through the system. Alignment using the device is faster and safer than the conventional procedures.
Cryogenic bathysphere for rapid variable-temperature characterization of high-T
c superconductors
Authors: Moreland John , Li Y. , Folsom R. , Capobianco T. E.
Published: July 2002

A bathysphere consisting of an inverted Dewar flask for submersible operation in cryogenic fluids is used to measure the resistance of superconductors, including high-Tc superconducting copper oxides, as a function of temperature from 4 to 300 K. We describe the cryostat incorporating the bathysphere and present data on NbTi (44% Ti) and YBa2Cu3O7−δ with respective superconducting transitions temperatures of 9.5 and 91.5 K. There are several advantages of the bathysphere method. The cryostat is of simple, compact design easily adapted to high-field applications where magnet bore size is a limiting factor. The sample and thermometer are thermolyzed in the dry vapor trapped at the top of the bathysphere. Temperature can be varied rapidly from 300 to 4 K at a rate of 1 K min with less than a 0.1 K thermal lag between the sample and thermometer.
X-ray diffractometer stage for i
n s
i
t
u structural analysis of thin films
Authors: Johnson R. W. , Johnson W. L.
Published: July 2002

A theta-two theta x-ray diffractometer stage has been developed for in situ structural characterization of thin-film samples. This stage integrates an ultrahigh vacuum dc ion-beam thin-film sample preparation chamber with the Siemens D500 x-ray diffractometer. In vacuo sample translation and manipulation is provided. The stage incorporates resistive heating to 900 K and liquid nitrogen cooling to 150 K. The sample theta rotation is transmitted into the vacuum chamber by a rotary feedthrough. X rays enter the vacuum chamber through a beryllium window with allowed reflection angles from 0 to +168° two-theta.
Novel automated micro batch analyzer
Authors: Sweileh Jamal A. , Lopez Jorge L. , Dasgupta Purnendu K.
Published: July 2002

An automated micro batch analyzer (AMBA) system is described. The sample is introduced into an air-tight reaction chamber (a polypropylene microcentrifuge tube) by a loop injector made from two three-way valves by flowing gas. Reagents/diluents are introduced into the chamber from pneumatically pressurized reservoirs provided with on-off valves. A microprocessor-controlled timer controls valve status and thus provides control of delivered volumes. Gas bubbles are introduced through the bottom of the chamber to perform mixing; the mixed liquid is then discharged into an optical detector via a bubble gate by superincumbent pressure. The bubble gate allows the data-acquisition system to collect data only when liquid is actually in the detection cell. For simple fast reactions, throughput rates of 210 samples/h could be obtained.
Multibeam receiver for millimeter-wave radio astronomy
Authors: Payne J. M.
Published: July 2002

An eight-beam receiver system for millimeter-wave radio astronomy is described. The receiver is designed to map spatially extended radio sources in both spectral line and continuum emission at a wavelength of 1.2 mm. This receiver is now in use on the 12-m radio telescope on Kitt Peak in Arizona.
Toroidal and poloidal soft x-ray imaging system on the DIII-D tokamak
Authors: Snider R. T. , Evanko R. , Haskovec J.
Published: July 2002

A toroidal soft x-ray imaging system is being added to the currently installed poloidal soft x-ray system on the DIII-D tokamak. The poloidal array is used to determine the poloidal mode structure and location of internal helical MHD perturbations in the plasma. The new array will add toroidal mode identification capability. The four detector arrays are toroidally spaced in a manner that allows identification of toroidal mode numbers up to 24. Beryllium vacuum windows separate the detectors from the tokamak vacuum and also serve as low-energy filters. The separate detector vacuum chambers can be filled with a gas that changes the low-energy cutoff of the system. By proper selection of the gas and pressure the low-energy cutoff can be chosen over the entire range of the detector sensitivity (500–1200 eV). This capability can be used to produce crude x-ray spectra for the entire imaging system or for gain control.
Profile correction to electron temperature and enhancement factor in soft-x-ray pulse-height-analysis measurements in tokamaks
Authors: Sesnic S. , Diesso M. , Hill K. , Holland A. , Pohl F.
Published: July 2002

Because soft-x-ray pulse-height-analysis spectra contain chordal information, the electron temperature and the radiation intensity (enhancement factor) measurements do not represent the local values. The correction factors for the electron temperature and the enhancement factor as a function of the temperature and density profile parameters and the energy are obtained. The spectrum distortion due to pulse pileup effects is also evaluated. A set of curves is given from which the distortion of the spectrum can be obtained if the electron temperature, the Be filter thickness, and the electronic parameters of the acquisition system are known.
Ion source for production of metastable He+(2S1/2) ions
Authors: Dunford R. W. , Dewey M. S.
Published: July 2002

The construction and performance of an electron bombardment ion source designed to produce a beam of low-energy (100–400 eV) singly ionized helium (He+) with a significant fraction of ions in the metastable 2S1/2 state is described. The source operates in the fringe field of a magnet and injects ions along the field lines into the center of the magnet. He+ currents of up to 70 μA with small beam energy spread (3 eV) are obtained. A typical metastable fraction is 0.08% for small He+ currents (2–5 μA).
Electronic device for the analysis of electron diffraction patterns
Authors: Trzynka A. , Takeo M.
Published: July 2002

Using a video camera, a video digitizer, and a microcomputer, an image processing system is assembled to determine the locations of electron diffraction spots on photographic negatives of electron diffraction patterns. This system can help to reduce the measurement time to one third when compared with conventional manual methods and produces results with better accuracy and less operator fatigue.