bluuebunny/crossref_metadata_2025 huggingface dataset:
Key elements for a sensitive 77 K direct current superconducting quantum interference device magnetometer
Authors: Lee L. P. , Teepe M. , Vinetskiy V. , Cantor R. , Colclough M. S.
Published: July 2002

We have made sensitive dc superconducting quantum interference device (SQUID) magnetometers that operate at 77 K have been made. By using bicrystal grain boundary Josephson junctions and a single layer of YBa2Cu3O7 thin film with optimized processing and an optimized directly coupled design, we have produced magnetometers with very low noise and a large transfer function. At 77 K, the transfer function is 100 μV/Φ0; the white field noise of the magnetometer is less than 10 fT/√Hz above 10 kHz, rising to 26 fT/√Hz at 1 Hz. The corresponding white noise energy has the low value of 2×10−31 J s; a value very similar to that of commercial Nb SQUIDS. Key elements required to achieve this performance are discussed.
Charge accumulation effects and microwave absorption of coplanar waveguides fabricated on high–resistivity Si with SiO2 insulation layer
Authors: Pfeifer T. , Heiliger H.–M. , Stein von Kamienski E. , Roskos H. G. , Kurz H.
Published: July 2002

Microwave attenuation of coplanar waveguides fabricated on high–resistivity silicon substrates with SiO2 insulation layer is investigated from 10 GHz up to 600 GHz by optoelectronic time–domain measurements. They are performed directly on the wafer employing a freely positionable photoconductive switch for picosecond–electric–pulse injection and an electro–optic crystal for pulse detection. The attenuation is significantly altered over the whole frequency range by free–carrier absorption resulting from inversion and accumulation effects at the Si/SiO2 interface.
Experimental procedures for the observance of shear band formation during low velocity impacts
Authors: Woody D. L.
Published: July 2002

This paper describes in detail the experimental procedures and apparatus involved in experiments that observe the real-time formation of shear bands in NaCl crystals during deformation due to impact. The crystals, impacted at low velocities of 5–20 m/s, emit rapid (30 ns) infrared emissions. An array of fast responding infrared detectors formed images which indicated that the shear bands form within a few tens of nanoseconds.
A versatile flash photolysis apparatus
Authors: Beischel Charles J. , Moore Stacie K. , Crouch Rosalie K. , Knapp Daniel R.
Published: July 2002

A flash photolysis apparatus and sample cell suitable for photoaffinity labeling experiments are described and compared to a conventional continuous wave source using potassium ferrioxalate actinometry and activation of a model aryl azide photoaffinity label. The flash lamp enclosure is designed to minimize the potential hazards from UV exposure, lamp explosion and electrical shock. The sample cell design with three concentric annular chambers allows for maximum exposure of the sample to the light sources, use of wavelength selecting filter solutions and temperature control. The flash apparatus delivers 105 greater photon flux per unit time and activates the model photoaffinity label four times more efficiently (in terms of total photons) than the continuous wave source which results in a total exposure time using the flash source of 2.5×10−6 that needed using the continuous wave source.
Modified sample holder for low-temperature deep-level transient spectroscopy, current-voltage and capacitance-voltage measurements
Authors: Myburg G. , Meyer W. E. , Auret F. D.
Published: July 2002

This note describes the design, construction, and test results of a modified sample holder used during low-temperature deep-level transient spectroscopy, current-voltage and capacitance-voltage measurements. This improved sample holder allows temperature scan rates of up to 6 K/min with a temperature shift of less than 1 K. High electrical isolation makes this sample holder also suitable for low-temperature current-voltage and capacitance-voltage measurements.
Improvement of sensitivity of photothermal deflection spectroscopy by a double pass method
Authors: Horita Susumu , Miyagoshi Eiji , Ishimaru Masahiko , Hata Tomonobu
Published: July 2002

In order to improve the sensitivity of photothermal deflection spectroscopy, we propose a double pass method, in which a pump beam is passed twice through the sample using a total reflector set behind the sample. A one-dimensional theoretical analysis of this method is developed and is verified by the measurement results of Si and InP wafers. Also, it is shown theoretically and experimentally that this method can determine lower optical absorption coefficients than conventional ones.
Inexpensive plasma discharge source for molecular emission spectroscopy with application to 15N analysis
Authors: Hoult D. I. , Preston C. M.
Published: July 2002

The assaying of nitrogen isotope abundance using emission spectroscopy commonly requires a plasma discharge in a sample of N2 gas at low pressure (∼0.5 kPa) in a sealed glass tube. Expensive high-power (≳20 W) radio-frequency or microwave amplifiers are often used for this purpose. However, with correct design, a simple and inexpensive, single transistor, 100 MHz, 1 W oscillator can be used to produce a bright plasma discharge in a low-pressure sample of nitrogen in a 6 mm diameter by 10 cm tube. The device utilizes optimal impedance matching to minimize the power requirements. The principles and limitations of the matching are outlined, and a simple feedback circuit is also described which, with the aid of a phototransistor, enables the emission intensity to be controlled. Ignition of discharge by friction or with the help of a simple piezoelectric gas lighter is also described, and construction details are given.
A mass-selective neutral particle energy analyzer with background rejection
Authors: van Blokland A. A. E. , Grimbergen T. W. M. , van der Ven H. W.
Published: July 2002

A mass-discriminating neutral particle spectrometer has been developed for the Rutherford scattering diagnostic at the TEXTOR tokamak. The analyzer is equipped with a momentum preselector and a triple-coincidence time-of-flight detection system providing a rejection capability for background events. Entering neutral particles are stripped by means of a thin carbon foil. Electrons emitted from a second carbon foil are used to give the time-zero signal. Calibration has been performed for hydrogen and helium particles in the energy range from 10 to 90 keV. The energy loss inside the carbon foils, the absolute efficiency, and the resolution of the analyzer have been investigated. The momentum preselector has a bandwidth of ±12.5% with respect to its adjustable central momentum. For both hydrogen and helium, the energy resolution is 2.5% for energies above 30 keV. Calculations show that the analyzer can still operate in the highly radiative environments of nuclear fusion devices.
X-ray microdiffractometer using synchrotron radiation
Authors: Hirano Tatsumi , Higashi Fumika , Usami Katsuhisa
Published: July 2002

An x-ray diffractometer using synchrotron radiation (SR) has been constructed and its performance was evaluated. Its characteristics are (1) a fine and highly intense x-ray beam from focusing SR x rays on a sample using two spherical mirrors which are arranged in the Kirkpatrick–Baez configuration and (2) a high detection efficiency of the cylindrical bent imaging plate (IP). A focused beam size of 10×11 μm2 and intensity of more than 107 photons/s were obtained at a wavelength of 1.38 Å. Accuracy of the lattice parameters, δa/a, was 2×10−4 estimated from measuring a superconductor YBa2Cu3O7−δ powder. The developed microdiffractometer was applied to measure diffraction images from a specific region on the NbTi metal superconducting wire which consisted of many NbTi fine wires buried in a Cu matrix. Diffraction peaks from a NbTi fine wire of 30 μm diameter were clearly observed and were distinct from the Cu matrix. The developed microdiffractometer can be applied to measurements of as-received samples in the micro-order specific region.
NMR data acquisition, data processing, and spectrometer control with an IBM PC compatible
Authors: Humbert F. , Retournard A. , Mischler E. , Brondeau J. , Canet D.
Published: July 2002

This article describes a system implemented on an IBM compatible personal computer (PC) for acquisition and processing of NMR data and for the spectrometer control. The homemade hardware includes a 12-bit analog-digital conversion board and a simplified pulse sequence controller. The software, written in assembly language and in Turbo Pascal, handles these two boards and, thanks to a versatile pulse generator, allows easily to run most of the modern NMR experiments in simple or in quadrature detection with spectral widths up to 25 000 Hz. Owing to its simplicity, its low cost, and its versatility, this system is specially suited for upgrading old NMR spectrometers or can be considered as the basis of a routine spectrometer.
High quality single and double two-dimensional electron gases grown by metalorganic vapor phase epitaxy
Authors: Chui H. C. , Hammons B. E. , Simmons J. A. , Harff N. E. , Sherwin M. E.
Published: July 2002

We demonstrate the metalorganic vapor phase epitaxy (MOVPE) growth of AlGaAs/GaAs two-dimensional electron gases (2DEGs) with mobilities as high as 786 000 cm2/V s at a carrier density of 3.0×1011 cm−2 at 0.3 K. The mobility figures of merit (μ/n3/2) for these 2DEGs are the highest reported to date for MOVPE materials. These 2DEGs also exhibit the fractional quantum Hall effect (FQHE) with minima in longitudinal resistance corresponding to Landau level filling factors 2/3, 4/3, and 5/3. The temperature dependence and carrier density dependence of mobility were characterized, and the mobility was found to vary linearly with carrier density, implying that the mobility is probably limited by background ionized impurity scattering. A delta-doped 2DEG was also compared with uniformly doped 2DEGs and was found to have a slightly higher mobility. Finally, we obtained high mobility in a coupled double 2DEG structure for 2D to 2D tunneling applications.
High-sensitivity optical microphone for photoacoustics
Authors: de Paula M. H. , Vinha C. A. , Badini R. G.
Published: July 2002

We show that with the optical microphone the sensitivity of the photoacoustic gas-phase microphone detection technique is improved by four orders of magnitude and that temperature variations of 10−9 °C at the sample surface can be detected with a conventional lock-in detection scheme.
Alternating current losses in Bi2Sr2Ca1Cu2O8+δ/Ag tapes at power frequencies
Authors: Pitsakis M. N. , Haugan T. , Wong F. C. H. , Patel S. , Shaw D. T.
Published: July 2002

Measurements of transport alternating-current (ac) losses in Bi2Sr2CaCu2O8+x powder-in-tube Ag-sheathed tapes at 4.2 and 65 K and at 20, 60, 200, and 400 Hz were carried out and comparisons to the theoretically predicted hysteretic loss plus ohmic loss were made. The measured loss, albeit larger than predicted, was found to agree with Bean’s critical state model. The loss, having a linear dependence on the frequency of the alternating transport current and increasing with decreasing critical current density, confirms hysteresis as the dominant source of power dissipation at both 4.2 and 65 K. However, at 4.2 K, the loss varies as the square of the amplitude of the transport current, which is not consistent with the model.
Control of gas permeation through the solid–solid interface of piezoelectric films by use of an applied electric field
Authors: Seto Takatoshi
Published: July 2002

Permeation of gases such as helium and oxygen through the interface of aluminum evaporated polyvinylidene fluoride films was found to change with the strength of an applied direct current electric field. This method promises, to a small extent, a better separation factor than that predicted based on the Knudsen diffusion. The surface morphology was investigated to understand the nature of aperture involved in the diffusion.
Laser blow-off lithium beam probing with high temporal resolution for edge plasma diagnostics
Authors: Sasaki S. , Takamura S. , Uesugi Y. , Ohkouchi Y. , Kadota K.
Published: July 2002

Laser blow-off neutral lithium beam probing with high temporal resolution has been developed to measure edge electron density profiles in a plasma. A new electron density reconstruction method, taking account of the transport of a laser blow-off beam in the plasma, improves the accuracy of the density measurement. The use of a camera system with a gate function makes it possible for us to measure the density profile with a high temporal resolution of 10–50 μs. The optimum condition for shutter timing and period to observe the Li i emission profile is discussed from the viewpoints of the beam penetration into the plasma and the accuracy of measurement. A rapid temporal evolution of the edge electron density profile during limiter biasing in a small tokamak HYBTOK-II was successfully obtained by this system.
Compact flash x-ray source producing high average powers in nanosecond pulses
Authors: Pouvesle J. M. , Cachoncinlle C. , Robert E. , Viladrosa R. , Collins C. B. , Davanloo F.
Published: July 2002

X-ray diodes driven by repetitively pulsed Blumleins have been shown to be able to deliver high dose rates of x rays in pulses of nanosecond duration. Reported here is a study of the scaling of such devices conducted to isolate the primary factors limiting performance. Low residual gas pressure in the output diode together with the critical alignment of the electrodes were found essential for enhanced output. Optimizations served to increase the x-ray yield by an order of magnitude and the resulting performance is reported. At the output window, dose rates exceeding 1.4 kR min−1 were obtained in nanosecond pulses from the finished device of table top size at a charging voltage of 30 kV and a pulse repetition rate of 50 Hz.
Phase-modulated ellipsometer using a Fourier transform infrared spectrometer for real time applications
Authors: Canillas A. , Pascual E. , Drévillon B.
Published: July 2002

A new Fourier transform infrared phase-modulated ellipsometer is presented. It combines the high frequency provided by a photoelastic modulator (37 kHz) with the low frequency of the Fourier transform infrared spectroscopy (<1 kHz), by means of a numerical data acquisition system. A full spectrum recording (from 900 to 4000 cm−1) can be achieved in 2 s. Thus, it allows its adaptation for kinetic in situ studies. The optical setup and the data reduction procedure are presented. In particular, a self-consistent spectral calibration procedure is described in detail. The precision in Ψ and Δ increases from 0.3° to 0.02° when increasing the integration time from 2 to 760 s. The examples shown in this article illustrate the high sensitivity to identify and analyze the absorption vibration variations of ultrathin films (a few angstroms thick).
Inversion of time domain signals from a Balle–Flygare type microwave spectrometer
Authors: Campbell Edward J.
Published: July 2002

The method of sine and cosine Fourier transforms with a phase correction, well known in NMR and traveling wave Fourier transform microwave spectroscopy, is examined for the pulsed beam Fabry–Perot cavity. The validity of this approach is closely related to the result, noted previously elsewhere [J.-L. Le Gouët and P. R. Berman, Phys. Rev. A 20, 1105 (1979), and F. Rohart and B. Macke, J. Phys. 41, 837 (1980)] that only the polarization spatial harmonic that projects onto the driven fundamental mode of the cavity contributes appreciably to the free induction decay signal. When the full signal is recorded after a short polarization pulse, an absorption line shape function in the low power limit for a single nondegenerate transition can be recovered as an angular distribution weighted integral over the coordinate θ between the nozzle axis and a point on the cavity axis of Doppler-shifted Voight profiles. Passage of the beam through the transverse Gaussian profile of a TEM00q mode contributes an effective line broadening temperature. These results are a direct extension of a semiclassical derivation given earlier [E. J. Campbell, L. W. Buxton, T. J. Balle, and W. H. Flygare, J. Chem. Phys. 74, 813 (1981), and E. J. Campbell, L. W. Buxton, T. J. Balle, M. R. Keenan, and W. H. Flygare, J. Chem. Phys. 74, 829 (1981)]. Analytical results are derived using simplified cavity mode functional forms. Calculations using the exact mode expressions are reported. The relation between this approach and the direct absorption method is discussed.
Low resistance ohmic contact for p-type ZnTe using Au electrode
Authors: Ohtsuka Takeo , Yoshimura Masashi , Morita Katsuhiko , Koyama Masataka , Yao Takafumi
Published: July 2002

We report low-resistive Au ohmic contact for a molecular beam epitaxy grown nitrogen doped p-type ZnTe (p-ZnTe:N) layer with high thermal stability, where the p-ZnTe surface is treated by oxygen plasma and HCl solution prior to Au film deposition. C contamination and native oxide layers of ZnTe are removed by oxygen plasma and HCl treatment, respectively, from the surface. As a result, a Te-rich layer is formed on the surface. The annealing temperature dependence of specific contact resistance is investigated. The specific contact resistance of Au ohmic contact for p-ZnTe:N with carrier concentration of 2×1018 cm−3 treated by oxygen plasma and HCl solution reaches as low as 5.8×10−6 Ω cm2 at an annealing temperature of 350 °C. This specific contact resistance value is the same as that of the reported Pd/(Pt)/Au contact for p-ZnTe:N with carrier concentration of 3×1019 cm−3, and clearly shows higher thermal stability.
A double-crystal x-ray monochromator in antiparallel position with a sagittally bent crystal
Authors: Hrdý Jaromír
Published: July 2002

The double-crystal x-ray monochromator (spectrometer) in (+,+) setting is high-resolution equipment. Focusing and a considerable increase of the x-ray monochromatic flux without any lowering of resolution may be reached if one of the crystals is properly bent into conical shape. The parameters of the bending are dependent on the wavelength. This ideal conical bending may be replaced by an easier-realizable cylindrical bending where the virtual source and the focus are located on the axis of the cylinder. In this case the higher monochromatic flux, as compared with the flat crystals, may be reached only for Bragg angles from about 35° to about 60°. The highest flux is for the Bragg angle θ=45° and its nearest neighborhood.
Deposition of high dielectric constant materials by dual spectral sources assisted metalorganic chemical vapor deposition
Authors: Singh R. , Alamgir S. , Sharangpani R.
Published: July 2002

The development of new high dielectric constant materials is essential for the development of advanced silicon integrated circuits. In this letter, we report preliminary results of lanthanum doped lead zirconate titanate (PLZT) films deposited by dual spectral sources (DSS) rapid isothermal processing (RIP) assisted metalorganic chemical vapor deposition (MOCVD) system. The dielectric constant and leakage current density data reported in this letter represents the best results reported to date. The use of high energy photons play an important role in the deposition of high quality dielectric films
A new method for measuring the retardation of a photoelastic modulator using single photon counting techniques
Authors: Cline R. A. , Westerveld W. B. , Risley J. S.
Published: July 2002

We present a new method to measure in situ the amplitude of the retardation for a photoelastic modulator polarimeter using single photon counting techniques. The method allows the simultaneous measurement of linear and circular polarization of light without the need for a separate calibration procedure. Comparison with measurements made with a λ/4-retarder polarimeter show excellent agreement, confirming the method used.
Signal averaging with a stabilized dual beam Mach Zehnder interferometer: Monitoring changes in gas density
Authors: Tardy D. C.
Published: July 2002

A traditional Mach Zehnder interferometer has been fitted with a feedback loop that maintains a constant and known phase difference between the two optical beams. This stabilization is necessary so that signal averaging will not distort the signal. To increase sensitivity for small phase shifts and determine absolute phase shifts when large phase shifts are involved a dual beam technique, which uses circularly polarized monochromatic light, is implemented. In one arm of the interferometer a phase shift of 90° between the two polarization orientations is introduced via a quarter wave plate. Two photodiodes independently detect the polarized light beams that maintain a 90° phase difference. One of these signals provides the input for the stabilization while the other (with enhanced sensitivity) is used to monitor the density. Unambiguous phase shifts are calculated from the information contained in both signals. The interferometer is being used to monitor gas density changes resulting from vibrational to translational energy transfer.
Microchannel plate modal gain variations with temperature
Authors: Slater David C. , Timothy J. Gethyn
Published: July 2002

Measurements of the modal gain of two high-gain curved-channel microchannel plates (MCPs) at various operating temperatures are presented. Both MCPs were fabricated from Galileo Electro-Optics Corporation Long LifeTM glass with 12-μm diam channels on 15-μm centers. The modal gain was found to decrease with increasing temperature at a rate of −0.1% (°C)−1. This reduction of gain with temperature is attributed primarily to an axial temperature gradient along each MCP channel creating a nonuniform electric field within the channel that lowers the effective output gain. A lowering of the secondary electron yield resulting from increased phonon scattering of secondary electrons released within the walls of the MCP channels was also assessed, but was found to have a negligible contribution to the drop in gain with temperature.
Dynamic scanned-probe lateral-force determination
Authors: Wetsel G. C. , Drummond Roby M. A.
Published: July 2002

A continuum-mechanical model of the dynamics of a scanned probe is described that includes intrinsic losses as well as the effect of a lateral force on the end of the probe. A method for the determination of calibrated lateral force is experimentally evaluated and the sensitivity of the method is analyzed.
Lower T
c barriers at high angle boundaries in the (BiPb)2Sr2Ca2Cu3Ox system
Authors: Yan Y. , Lo W. , Evetts J. E. , Campbell A. M. , Stobbs W. M.
Published: July 2002

The structure of high angle boundaries in the (BiPb)2Sr2Ca2Cu3Ox system, which is compositional and structurally modulated along the boundaries, was investigated by high resolution electron microscopy. These compositional variable boundaries tend to facet onto the (001) plane, leaving steps of height equal c/2 for the (BiPb)2Sr2CuOx and (BiPb)2Sr2Ca1Cu2Ox phases with amorphous material at the corners of these steps. These data suggest a weak link is formed at high angle boundaries where there are such lower Tc or insulating phases.
Crystallization of colonies of locally aligned grains during thallination of spray-pyrolyzed TlBa2Ca2Cu3Ox thick films
Authors: Goyal A. , Specht E. D. , Kroeger D. M. , Tkacyzk J. E. , Briant C. L. , DeLuca J. A.
Published: July 2002

Recent microstructural studies of high-Jc, Tl-1223, spray-pyrolyzed thick films have shown that the high-Jc and reduced weak-link behavior can be ascribed to the presence of a unique microstructure, wherein the film is divided into ‘‘colonies’’ of biaxially aligned regions. In an effort to understand the nucleation and growth of Tl-1223 as well as the formation of the colony microstructure, several sets of films quenched from various stages of the high-temperature thallination process were examined using electron microscopy, x-ray diffraction and electron backscatter diffraction (EBSD). It is found that the crystallization of the 1223 phase is associated with formation of a liquid phase which contains significant amounts of all oxides. Furthermore, it is found that the film nucleates at the substrate on the side closest to the thallium source. The growth front then moves up through the thickness and along the length of the film. X-ray microdiffraction measurements show that local biaxial alignment or the formation of colonies starts to occur at the onset of 1223 crystallization.
Anomalous bias-stress-induced unstable phenomena of hydrogenated amorphous silicon thin-film transistors
Authors: Tai Ya-Hsiang , Tsai Jun-Wei , Cheng Huang-Chung , Su Feng-Cheng
Published: July 2002

Thin-film transistors (TFTs) with different silicon nitride (SiNx) gate compositions and various hydrogen concentrations in their amorphous silicon films (a-Si:H) have been stressed with positive and negative biases to realize the instability mechanisms. For both stress polarities, it is found that the threshold voltage shifts significantly increase due to the trap sites in the SiNx gate. As the effects of the trapped charges in the SiNx films are reduced, the anomalous threshold voltage shifts under negative stress voltage are observed. The creation of the states near the conduction band in the a-Si:H films can be enhanced according to the defect pool concept and stimulated by the hydrogen contents in the a-Si:H films, which can be confirmed by the subthreshold swing change. Therefore, the negative threshold voltage shifts caused by the hole trapping in the SiNx gate are positively compensated by the created states, reflecting the turnaround behaviors for the threshold voltage shifts. As for the positive stress, the state creation in the a-Si:H films can be suppressed via the defect pool mechanism and thus the threshold voltage shifts are dominantly affected by the electron trapping in the SiNx gates.
High-resolution imaging gamma-ray spectroscopy with externally segmented germanium detectors
Authors: Callas J. L. , Mahoney W. A. , Varnell L. S. , Wheaton Wm. A.
Published: July 2002

Externally segmented germanium detectors promise a breakthrough in gamma-ray imaging capabilities while retaining the superb energy resolution of germanium spectrometers. An angular resolution of 0.2° becomes practical by combining position-sensitive germanium detectors having a segment thickness of a few millimeters with a one-dimensional coded aperture located about a meter from the detectors. Correspondingly higher angular resolutions are possible with larger separations between the detectors and the coded aperture. Two-dimensional images can be obtained by rotating the instrument. Although the basic concept is similar to optical or x-ray coded-aperture imaging techniques, several complicating effects arise because of the penetrating nature of gamma rays. The complications include partial transmission through the coded aperture elements, Compton scattering in the germanium detectors, and high background count rates. Extensive electron–photon Monte Carlo modeling of a realistic detector/coded–aperture/collimator system has been performed. Results show that these complicating effects can be characterized and accounted for with no significant loss in instrument sensitivity.
The frequency response of porous silicon electroluminescent devices
Authors: Peng C. , Fauchet P. M.
Published: July 2002

Under a constant forward bias, porous silicon light-emitting devices (LEDs) produce stable electroluminescence (EL) that is detectable at applied voltages as low as 5 V and visible in daylight at higher voltages. The recombination dynamics of the EL are studied and correlated to the photoluminescence properties of light-emitting porous silicon (LEPSi). The EL efficiency is related to the LEPSi properties and the device configuration. LEPSi LEDs with an EL efficiency of 0.01% have been achieved. The frequency response of the EL to a modulating ac bias is measured. For metal/LEPSi LEDs, the −3 dB frequency is determined by the carrier transit time which must be larger than the carrier lifetime to achieve efficient EL. For LEPSi pn junction LEDs, the −3 dB frequency is determined only by the carrier lifetime and can be in excess of 200 kHz.
Optical system to detect fracture of glass materials
Authors: Medrano R. E. , Ikesawa L. E.
Published: July 2002

One of the most important properties of brittle materials is static fatigue. To measure this property, the specimen is loaded under constant stress and the fracture occurs after an elapsed period of time. The scatter in this time is large, and to obtain a good statistical representation it is necessary to test a large number of samples (over 20). Due to this scatter, the time for some of the tests could be large, and a period of several months might be necessary to test all the samples. In this article we describe an automatic optical detector for fracture that was employed to study the static fatigue of transparent materials. The main advantages of this instrument are (i) automatic registration of fracture for long periods of time, (ii) application on bending tests (this reduces the testing space) of low strength materials, and (iii) the cost is low and the number of samples can be increased with practically no increase in cost.
Experimental observation of vertical cavity with polarization birefringence using asymmetric superlattice
Authors: Vakhshoori D. , Leibenguth R. E.
Published: July 2002

Vertical cavity etalons with asymmetric superlattice claddings have been fabricated. As predicted earlier, the cavities with sawtooth superlattice claddings grown on (100) oriented substrate are birefringent with the new optical axes along (011) and (01̄1) directions. The difference in the resonant wavelengths of the cavity modes polarized along (011) and (01̄1) are measured to be about +0.3 and −0.3 Å for the two senses of our sawtooth superlattice structures. The change of the sign of the wavelength shift indicates that the observation is not due to an electro-optic effect of the incorporated p-n junction but is due to the reduction of the III-V crystalline symmetry by the presence of the asymmetric superlattice.
Sensitivity profile of the Storey–Purcell array
Authors: Hotz D. F. , Zavala S. A. , Villagómez R. , Camacho J.
Published: July 2002

The Storey–Purcell array is an arrangement of four coaxial coils, composed of a Helmholtz pair nested inside a larger opposing Helmholtz pair whose respective area–turns products are sufficiently closely balanced to cancel the dipole moment of the combination when the magnitude of series current is the same in each coil pair. Ideally, the external field will exhibit 25-pole character and falloff with distance as r−7. The array has desirable properties as a flux sensor because it is closely coupled to internal oscillating flux yet strongly decoupled to fluctuating external fields arising in distant sources. We have built an array and measured the external axial field component up to ten radii away. Our measurement technique relies on the principle of reciprocity for mutual inductance. Our analysis indicates area–turns unbalance of less than 500 ppm is required for the measured sensitivity profile to approach the calculated shape characteristic of a 25 pole. Comparison of measured field values to those calculated from the magnetic multipole expansion show our imperfect construction results in an area–turns unbalance of the order of 2.5% or 25 000 ppm.
A comparison between conventional photothermal frequency scan and the lock-in rate window method in measuring thermal diffusivity of solids
Authors: Munidasa Mahendra , Mandelis Andreas
Published: July 2002

A comparison between the conventional photothermal frequency scan method and the recently developed photothermal lock-in rate window technique for thermal diffusivity measurements of materials, is presented. In this comparison, a completely noncontact experimental configuration has been utilized based on infrared photothermal radiometry. This work shows that for thick materials with long thermal transport times across the sample where low-frequency measurements are required, the frequency scan method may be more appropriate due to its simplicity. The rate window method, however, gives superior signal-to-noise ratio (SNR) for materials with very short thermal transport times such as metal foils, which otherwise require high frequency, low SNR measurements. A further advantage of the pulse duration-scanned rate-window mode is that it does not require knowledge of the instrumental transfer function as an input.
Use of mechanical deflection to eliminate metallic vapor deposition on vacuum view ports
Authors: Grugel R. N. , Hightower J. , Hmelo A. B. , Wang T. G.
Published: July 2002

Metallic vapor emitted from a source can be deflected prior to depositing on an observation view port by imposing fans whose blades rotate perpendicular to the atoms flight path. The effectiveness of this technique is demonstrated with tin vapor in terms of relative rate deposition and visual examination as a function of the imposed rotation rate. The consequence of fan rotation on sample visibility is shown to be negligible.
Compact, semi-sealed-off, high-repetition-rate XeCl laser with a surface-wire-corona preionization
Authors: Komi Takao , Sugii Masakatsu
Published: July 2002

This paper describes the design and operating characteristics of a reasonably compact, semi-sealed-off, high-efficiency XeCl laser operating at prfs <170 Hz by a stable discharge system using a new type of surface-wire-corona preionizer. An efficient laser operation at a slope efficiency of 1.6% with an average power of 4.1 W (150 Hz) has been achieved from a discharge volume of 52 cc with an active length of 26 cm. With a small amount of H2 as additive, ≳2×106 shots have been achieved on a single gas fill and an estimated half-power lifetime of 3×107 shots made.
Injection power and wavelength dependence of an external-seeded gain-switched Fabry–Perot laser
Authors: Seo Dong-Sun , Liu Hai-Feng , Kim Dug Y. , Sampson David D.
Published: July 2002

We experimentally investigate a gain-switched Fabry–Perot semiconductor laser externally injection seeded with a narrow linewidth continuous wave laser. We determine the dependence of pulse width, side-mode suppression ratio, and timing jitter on seeding power and seeding wavelength. As external seeding power is increased up to a certain value, we observe negligible change in pulse width, a linear increase in side-mode suppression ratio, and a linear decrease in timing jitter. Exceeding a certain value leads to substantial pulse broadening. By tuning the seeding wavelength across a chirped mode of the laser, we observe the lowest timing jitter and the largest side-mode suppression when the seed wavelength is aligned with the center of the chirped spectrum of a desired mode.
Dual diode detector for homodyne EPR microwave bridges
Authors: Koscielniak Janusz , Berliner Lawrence J.
Published: July 2002

After low noise FET amplifiers found widespread use in both X-band and low-frequency systems, it became possible to use multidiode mixers for signal detection. Here, a novel dual diode mixer is described for use in homodyne microwave bridges for both cw and pulsed electron paramagnetic resonance spectrometers. The structure is composed of a 90° hybrid coupler and separate detectors in two arms. The device provides common mode rejection of noise-like regular balanced mixers but, by making diode dc currents accessible, offers big advantages for tuning of the bridge when low Q sample probes are used. Although the use of this detector does not affect sensitivity directly, tuning precision and increased long-term stability leads to unexpected improvements.
Blue frequency shift due to external light injection in a distributed-feedback laser diode
Authors: Inoue Kyo
Published: July 2002

A blue frequency shift in a distributed-feedback laser diode (DFB-LD) induced by light injection is described. It is observed in an experiment that the lasing wavelength shifts toward the shorter wavelength and the carrier number increases when external light is injected into a DFB-LD in a particular condition. An F matrix analysis shows a similar behavior, where spatial distribution of the carrier density induced by the external light is taken into account.
Characterization of electron beam induced modification of thermally grown SiO2
Authors: Barnes J. R. , Hoole A. C. F. , Murrell M. P. , Welland M. E. , Broers A. N. , Bourgoin J. P. , Biebuyck H. , Johnson M. B. , Michel B.
Published: July 2002

We used local probe techniques to characterize electron beam (e-beam) induced changes in thin oxides on silicon. Primary effects of the 1 nm wide, 300 keV e beam included the formation of positive charges trapped in the SiO2, physical restructuring in the oxide, and deposition of carbonaceous compounds. Charges remained stable in thicker oxides (460 nm) and appeared as changes in the contact potential or microwave response with widths down to 100 nm. In thinner oxides (20 nm) the amount of charge was smaller and less stable; below 7 nm no charge was detected. Physical changes in the oxide, evident as a swelling of irradiated areas, accounted for the etching selectivity of these regions.
A density meter for solutions, solids, or dispersants
Authors: Bánó Mikuláš , Bán Jaroslav
Published: July 2002

A sensitive density meter for measuring the density of small amounts of solid, solution, or dispersed materials, e.g., biological systems in the liquid environment, is presented. The chamber for the measured sample is in the lower part of a glass buoy. It is closed by the glass stopper containing the permanent magnet. The buoy is immersed in the carrying liquid with the known density and is balanced by the magnetic force. The device enables the measurement at constant temperature as well as in the temperature scanning regime. The accuracy of measuring the liquid density is 1 mg/ℓ in a 1.5 ml chamber; the sensitivity of measuring the temperature is 1 mK. The volume of solids or dispersed systems of known weight is measured with an accuracy of 1.5 nl.
Two-dimensional intensified photodiode array detector for spaceflight use
Authors: Sahnow David J. , Feldman Paul D. , McCandliss Stephan R. , Mackey Edward F.
Published: July 2002

A two-dimensional, ultraviolet photon-counting detector suitable for spaceflight use, consisting of a microchannel plate intensifier coupled to a Reticon photodiode array, has been constructed and tested. The design is an extension of the one-dimensional detector flown on the Hopkins Ultraviolet Telescope. Extensive laboratory measurements have determined the operating characteristics of the detector and shown that it can successfully centroid with subdiode resolution. It was flown as part of an ultraviolet spectrometer on two sounding rockets, and successfully obtained long slit spectra of Comet Austin (1990 V) and the Io plasma torus surrounding Jupiter in the wavelength range of 1150–1850 Å. Details of the design, construction, testing, and flight performance of the detector are presented.
Modified crossed-beam apparatus for charge-transfer cross section measurement
Authors: Hashida M. , Sakabe S. , Izawa Y. , Nakai S. , Yamanaka C.
Published: July 2002

A modified crossed-beam apparatus to measure charge-transfer cross sections of metallic elements in wide impact-energy range (10–1000 eV) has been developed. The ion optics to extract charge-transferred ions from the primary neutral atomic beam was improved, and the background noise due to the collisions on residual gas and the charged particles produced by scattered laser light was reduced, and as the result, the S/N ratio of the charge-transferred ion signal was significantly improved to be ≳100 at 10 eV impact energy. The reduction of primary ions extracted from the ion source in the atomic beam at low impact energy was compensated for by the improvement of the S/N ratio, and the impact energy for which the cross section can be measured was extended to a lower energy (∼10 eV).
Factors which affect spatial resolving power in large array biomagnetic sensors
Authors: Flynn E. R.
Published: July 2002

A reduced chi-squared test has been used to evaluate factors that affect the spatial resolving power of large array biomagnetic sensors for the brain. Realistic array geometries are used and a classical description of spatial resolving power is applied to determine when two separate sources may be resolved. Array parameters such as sensor spacing, coil diameter, and gradiometer type are varied to determine their effect on spatial resolving power. The consequences of the number of sensors is considered and a comparison of existing systems is made. The effects of the vector nature of magnetic sources on spatial resolving power is also considered. It is shown that spatial resolving power is not strongly dependent upon individual sensor diameter, but that sensor spacing is important. It is also found that the instrumental spatial resolving power as a function of depth degrades much more quickly when planar gradiometers are used, as compared to axial gradiometers.
Digital frequency tripling circuit for third harmonic detection by lock-in amplifiers
Authors: Lee Seung-Min , Kwun Sook-Il
Published: July 2002

A new digital circuit for fast and stable frequency tripling was constructed. The frequency tripler covers the input frequency range from 0.1 Hz up to 5 kHz with a maximum phase shift less than 1 deg at the highest frequency. The tripler generates a stable signal synchronized to the input after just one input period. Since the circuit design is flexible, input frequency range and phase accuracy can be improved using faster integrated circuits.
Application of group theory on the nonlinear transport system following ion source
Authors: Qingchang Yu
Published: July 2002

The transfer group theory is used to study the nonlinear transport system that follows the ion source. The properties of the transfer group and the method of computing the phase-space contours, distribution functions, and moments of ion beams are studied. It is shown that the nonlinear element can be used to compensate for the aberration. As an example, a method of improving the quality of the beam extracted from an ion source by means of a nonlinear space-charge lens is discussed.
Plasma diagnostics in a metal vapor vacuum arc ion source (abstract)
Authors: Hao Wang , Jiyan Zou , Zhongyuan Cheng , Lichun Cheng
Published: July 2002

We have developed a metal vapor vacuum arc ion source, which was used for film deposition. Based on this source, some experimental diagnostics of plasma parameters are presented in this paper. Characters of vacuum arc cathode spots, including number, size, motion, and lifetime, are studied using a high-speed photograph technique. Substrate bias voltage dependence of plasma microparameters, such as electron density and electron energy, are measured by a Langmuir probe measurement system. In conclusion, some discussion of experimental results are also presented.
Study of influence of pulsed gas admission and material of insulating ring on extracting ion current
Authors: Peng ZhuDong , Wang ShaoHu , Chen XingQian , Zhang XiaoDong
Published: July 2002

For heating the plasma of HT-6 Tokamak we have developed a multiampere ion source, which is able to provide positive ion current (pulsed 20 A). In this article we briefly introduce two significant studies we made while developing the big multicusp ion source. One is optimizing the pulse width of preadmission to obtain a uniform pulsed ion current; the other is making an insulating ring of two sorts of material to enhance the electrical character of the ring. Both of them made contributions to the extracted ion current.
Extension of the operation regime of an ion source (abstract)
Authors: Ortiz Tar , Muñoz Arturo
Published: July 2002

In this work we present a method to lengthen the operation life of ion sources, according to the peculiarities of the particle beam which is required by the user. To reach this goal we have modified Popov’s model and selected a fair variable that can be handled externally to prevent the break of the vacuum in the chamber. Our method could be applied to any kind of equipment containing an ion source, for instance, particle accelerators, ion implantors, neutron injectors, etc.
Ion sources for ion implantation and ion beam modification of materials (invited)
Authors: Sakudo Noriyuki
Published: July 2002

Industrial applications of ion beams began in the 1970s with their application in fabrication of semiconductor devices. Since electronic characteristics of semiconductors are very sensitive to the amount of doped elements and to the species, the ion beams should be precisely mass separated. Nowadays, ion implantation is expected to be used for surface modification of materials. For this the needed beam purity is lower, but the needed dose is higher, since mechanical and/or chemical characteristics of materials, which are less sensitive to the dose, should be improved rather than electronic ones. Mass resolution by a separator may be lowered to allow mixing of some neighboring elements and in some cases mass separation may be completely eliminated. Many ion sources have been developed for such applications; however, most were used for research work. In this paper, some of the typical ion sources are reviewed from the viewpoint of future industrial use.
Study of the improvement on the property and working life of Freeman source
Authors: Zheng Sixiao , Sun Guanqing , Wang Peilu , Liu Zhongyang , Jiang Jingyun , Liao Xiaodong
Published: July 2002

The improvement of the properties and working life of the Freeman source is described. The experimental results show that the magnetic mirror field caused by a pair of mild steel circular plates, 15 mm in diameter and 2 mm thick, placed outside the discharge chamber can increase the ionized efficency of the gas feed. The atom–ion ratio of nitrogen was increased from 66% to 81%, and the heating filament current was decreased about 30 A, from 130 A down to 100 A for a new filament of 2 mm in diameter at the same arc voltage, arc current, and external magnetic field condition. Additionally, a Mo shield cylinder 14 mm in diameter put behind the reflect cathode surrounding the BN insulator prevented the metallization of the BN insulators, and resulted in increasing the stability of the arc discharge until the end of the filament working life of the Freeman source. The improvement occurred because it restricted the deposition of the sputtered W and Mo atoms coming from the hot filament and reflect cathodes onto the BN insulator, hence maintaining a high resistance of 70 MΩ between the anode and cathode. The new design with a combination of the cathode shield cylinder and magnetic mirror field improved the running property of the Freeman source, the mass spectrum of nitrogen, and the working life of the Freeman source, to about 40 h.
New applications of arc discharge source
Authors: Chen M. , Zou Z. Y. , Huang J. M. , Ye B. N. , Qian W. G.
Published: July 2002

We describe some details of the production of 57Fe and C60 ions by the Nielsen source. Some application results are also given.
Domain observations of a durability tested TbFeCo magneto-optical disk using magnetic force microscopy
Authors: Kikukawa Atsushi , Awano Hiroyuki , Hosaka Sumio , Honda Yukio , Imura Ryo
Published: July 2002

Complex magnetic structures were observed on a durability tested TbFeCo magneto-optical disk. By considering the magnetic properties of the TbFeCo and the polarized microscopic image of the same region, it was concluded that those complex structures result from the decrement of the compensation temperature of the TbFeCo film at the track center. Samples that were exposed to static magnetic fields were also observed for the purpose of inspecting the changes in the coercive force of the damaged regions.
8.5 cm multipole ion source
Authors: Lu D. L. , Jiang S. F. , Yang J. F. , Guan C. L. , Wang D. T. , Zheng S. Q. , Liu M. Z.
Published: July 2002

An 8.5 cm multipole ion source for an MM-2U neutral beam injector has been developed. The source is operated with a discharge current of more than 200 A. The saturation ion current at the plasma grid is 300 mA/cm2. A hydrogen ion current of 9 A has been obtained at an accel. voltage of 25 kV with 50 ms pulse duration. This article describes the experiment apparatus and the experimental results.