bluuebunny/crossref_metadata_2025 huggingface dataset:
VUV laser absorption spectrometer system for measurement of H0 density and temperature in a plasma
Authors: Stutzin G. C. , Young A. T. , Schlachter A. S. , Stearns J. W. , Leung K. N. , Kunkel W. B. , Worth G. T. , Stevens R. R.
Published: July 2002

A system to determine the density and temperature of ground-state hydrogen atoms in a hydrogen plasma by measurement of the absorption of Lyman-beta or Lyman-gamma radiation is described. The Lyman-series radiation is generated by resonant four-wave sum-frequency mixing in mercury vapor. A wide range of hydrogen atom densities can be measured by employing these two transitions. A sample measurement on a H− ion-source discharge is presented. Extensions to Lyman-alpha and other vacuum-ultraviolet wavelengths are discussed.
Discharge suppression system for a double focusing, atmospheric pressure ionization mass spectrometer
Authors: Grange Andrew H. , O’Brien Robert J. , Barofsky Douglas F.
Published: July 2002

An electrical discharge suppression system for a medium throughput (∼2  l/s) pumping line has been devised that works up to potentials of ±15 kV. This device permits atmospheric pressure ionization sources to be interfaced to high-resolution, magnetic sector mass spectrometers with source potentials of 6–10 kV.
Longitudinal discharge N2 laser with automatic preionization using an LC inversion circuit
Authors: Furuhashi H. , Goto T.
Published: July 2002

A four-segmented longitudinal discharge low pressure N2 laser (337 nm) is reported in which automatic spark preionization and an LC inversion-charge transfer excitation circuit are employed. Its laser output power was nearly doubled when the techniques developed here were used. The characteristics of the peak laser output powers are interpreted qualitatively, with the electron densities calculated from the observed discharge voltages and currents.
High-speed gated x-ray imagers (invited)
Authors: Kilkenny J. D. , Bell P. , Hanks R. , Power G. , Turner R. E. , Wiedwald J.
Published: July 2002

Single- and multiframe gated x-ray images with time resolution as fast as 150 ps are described. These systems are based on the gating of microchannel plates in a stripline configuration. The gating voltage comes from the avalanche breakdown of a reverse biased p–n junction producing high-power voltage pulses as short as 70 ps. Results from single- and four-frame x-ray cameras used on Nova are described.
Multiple charge reaction cell for studies of primary explosives
Authors: Miron G. , Bar I. , Heflinger D. , Tzuk Y. , Rosenwaks S.
Published: July 2002

A reaction cell for the detonation of primary explosives is described. The cell is 250 mm in diameter and contains 30 samples, which can be initiated consecutively using a laser beam. A manually driven mechanism is used to locate each charge in its turn in a central firing position without having to break the vacuum. Eight 3-in. observation windows and four 0.25-in. feedthrough ports allow recording and analysis of the emission resulting from the detonation products. The design provides a means for protection against accidental explosion. The cell is currently being used for spectroscopic studies of the gaseous reaction products obtained from the detonation of lead azide.
Miniaturized capacitive transducer for detection of broadband ultrasonic displacement signals
Authors: Kim Kwang Yul , Niu Lin , Castagnede Bernard , Sachse Wolfgang
Published: July 2002

This article describes a miniaturized version of the capacitive transducer for the detection of broadband, ultrasonic displacement signals at the surface of a specimen. The overall size of the capacitive transducer is a cylinder of 11.11 mm in diameter and 22.86 mm in length, in which four different sizes of the sensing area of the capacitive electrode have been successfully tried, ranging from 1 to 5 mm in diameter. Examples of detected waveforms resulting from such excitations as a glass capillary fracture and the formation of cracks on the surface of a specimen are provided using the specimens of glass and epoxy plates, respectively. The amplitudes of the detected signals are shown to be proportional to the displacements normal to the surface of the specimen. These small transducers are especially well suited for measurements on a laboratory specimen which requires several of them to study an acoustic emission source, to characterize an elastic (or a viscoelastic) behavior of the material, or simply to study the wave propagation.
Combined microstructure x-ray optics
Authors: Barbee Troy W.
Published: July 2002

Multilayers are man-made microstructures which vary in depth and are now of sufficient quality to be used as x-ray, soft x-ray, and extreme ultraviolet optics. Gratings are man-made in-plane microstructures which have been used as optic elements for most of this century. Joining of these two optical microstructures to form combined microstructure optical elements has the potential for greatly enhancing both the throughput and the resolution attainable in these spectral ranges. The characteristics of these new optic elements will be presented and compared to the experiment with emphasis on the unique properties of these combined microstructures. The results reported are general in nature and not limited to the soft x-ray or extreme ultraviolet spectral domains and also apply to neutrons.
A single-shot autocorrelator for the ultraviolet with a variable time window
Authors: Szatmári S. , Schäfer F. P. , Jethwa J.
Published: July 2002

A single-shot autocorrelator for the ultraviolet based on multiphoton ionization of gases has been developed. It makes use of a modified Mach–Zehnder interferometer and a segmented two-photon-ionization chamber as a spatial square-of-intensity detector. The device has in principle a continuously variable temporal detection range from ∼50 fs to 50 ps.
High pressure rolling-ball viscometer of a corrosion-resistant type
Authors: Sawamura Seiji , Takeuchi Nobuo , Kitamura Kiyoshi , Taniguchi Yoshihiro
Published: July 2002

A high pressure rolling-ball viscometer was designed for use with corrosive solutions such as electrolytes, using a glass inner cell with a glass cylinder and its piston. The viscosities of water and 2.55-m sodium chloride aqueous solution were measured up to 375 MPa at 25 °C with an error of less than ±1%.
A new probe for measuring small electric fields in plasmas
Authors: Stenzel R. L.
Published: July 2002

A dipolar double probe has been developed for in situ measurements of small electric fields in laboratory plasmas. The probe measures dc to ac electric fields (0≤f≲20 MHz) with high sensitivity (Emin≂10 μV/cm) and responds to both space charge electric fields (Esc(Esc= −∇φp) and inductive electric fields (Ei = −∂A/∂t). Using voltage-to-frequency conversion, the probe signal is obtained free of errors and loading effects by a transmission line. Various examples of useful applications for the new probe are presented, such as measurements of (i) dc ambipolar fields, (ii) ac space-charge fields of ion acoustic waves, (iii) ac inductive fields of whistler waves, and (iv) mixed inductive and space-charge electric fields in current-carrying magnetoplasmas.
ALTAIR: An infrared laser scattering diagnostic on the TORE SUPRA tokamak
Authors: Truc A. , Quéméneur A. , Hennequin P. , Grésillon D. , Gervais F. , Laviron C. , Olivain J. , Saha S. K. , Devynck P.
Published: July 2002

A collective laser light scattering diagnostic ALTAIR (a french acronym for local analysis of anomalous transport using infrared light), using a CO2 laser beam (λ=10.6 μm) has been realized to measure plasma density fluctuations in the TORE SUPRA tokamak. This article describes in detail the optical setup, the signal processing, acquisition, and control systems required for this experiment. As the density fluctuations propagating in tokamaks have small wave numbers and require small scattering angles, such scattering experiments are considered as having no resolution along the beam. However, taking advantage of the pitch angle variation of the magnetic field lines around the magnetic axis along a vertical chord, it has been possible to obtain partial spatial localization of the scattering volume by rotating the direction of the analyzed wave vector in a horizontal plane. Heterodyne detection is used to determine the fluctuations propagation direction. The experiment has been tested on acoustic waves and the first results obtained on TORE SUPRA indeed show the existence of a spatial resolution.
Dependence of electron effective mass on alloy composition of InAlGaAs lattice matched to InP studied by optically detected cyclotron resonance
Authors: Chen Y. F. , Dai Y. T. , Fan J. C. , Lee T. L. , Lin H. H.
Published: July 2002

The electron effective mass of InAlGaAs lattice matched to InP has been determined as a function of Al content. The electron effective mass is obtained from far-infrared optically detected cyclotron resonance (ODCR). In ODCR, the carriers are provided by optical pumping, and hence no doping is necessary. Unlike previous reports, we are able to detect the cyclotron resonance signal of a thin intrinsic epilayer at low temperature. Thus corrections of nonparabolicity are not required. In addition, from photoluminescence measurement, we determine the band-gap energy. Both the effective mass and band-gap energy show a nonlinear variation with Al composition.
A simple microwave plasma source for diamond deposition
Authors: Khachan J. , Pigott J. R. , Brand G. F. , Falconer I. S. , James B. W.
Published: July 2002

We describe a simple microwave-produced plasma source that has been constructed for plasma-assisted chemical vapor deposition of diamond thin films. Microwave power from a 700 W domestic microwave oven magnetron is fed into a water-cooled cylindrical stainless steel vacuum vessel. A methane/hydrogen gas mixture introduced into the vessel is excited by the microwaves to produce a well-defined plasma ball which does not interact with the walls of the vessel. The position of the plasma ball in the vessel can be predicted by cold cavity calculations of the axial electric field profile. The vessel has several diagnostic ports which do not alter its resonant condition. Diamond has been deposited on various substrates, placed beneath the plasma ball on a graphite-capped quartz pedestal. Some of these results are presented and discussed.
Simultaneous real-time spectroscopic ellipsometry and reflectance for monitoring thin-film preparation
Authors: An Ilsin , Nguyen H. V. , Heyd A. R. , Collins R. W.
Published: July 2002

An expansion of the capabilities of high-speed, multichannel spectroscopic ellipsometry (SE) is described that involves simultaneous measurement of the reflectance spectrum along with the two spectra in the ellipsometric angles (ψ, Δ). Previously, a novel rotating-polarizer spectroscopic ellipsometer has been perfected that employs a photodiode array detector for high-speed acquisition of (ψ, Δ) spectra, designed for real-time studies of thin-film growth. For a polarizer angular rotation frequency of ω0, the (ψ, Δ) values at a given photon energy are deduced from the 2ω0 Fourier components of the detector irradiance, normalized by the dc component. A third parameter, the weighted reflectance RA, can be obtained from the dc component and from a calibration based on the known optical properties of the substrate measured prior to film growth. With (ω0/2π)=12.5 Hz, three-parameter data sets, [ψ(hν), Δ(hν), RA(hν); 1.5≤hν≤4.5 eV], can be acquired with a time resolution as short as 40 ms. Although RA provides complementary information to (ψ, Δ), it has yet to be exploited in conjunction with real-time SE until this study. A resilient analysis approach, based on mathematical inversion and least-squares fitting of the real-time three-parameter data sets, is designed to yield the film dielectric functions and thicknesses independently at each time during the early stages of thin-film growth. The three-parameter approach has been applied successfully in studies of amorphous silicon (a-Si:H) thin films prepared by plasma-enhanced chemical vapor deposition, and aluminum and silver films prepared by physical vapor deposition. For the a-Si:H films, RA(hν) exhibits deviations as large as ∼3% from that predicted in modeling (ψ, Δ) alone. The deviations result from light scattering by plasma particulates, and we show how additional information can be extracted from the spectral dependence of the scattering loss.
Thermal stability of the midgap acceptor rhodium in indium phosphide
Authors: Näser A. , Dadgar A. , Kuttler M. , Heitz R. , Bimberg D. , Hyeon J. Y. , Schumann H.
Published: July 2002

We investigated the thermally induced redistribution of Rh in low pressure MOCVD grown InP structures by means of secondary-ion-mass-spectroscopy. Analogous measurements for InP:Fe structures serve as reference. On alternately Rh-doped/undoped InP structures an upper limit for the diffusion coefficient of DRh(800 °C)≤1×10−14 cm2/s is established much smaller than DFe(750 °C)=1×10−11 cm2/s. No exchange reactions are observed at the interface of p-InP/InP:Rh structures. Only Rh implanted into InP shows defect induced redistribution into amorphous areas. Rh is superior to Fe as far as thermal stability is concerned.
A merging preaccelerator for high current H− ion beams
Authors: Inoue T. , Miyamoto K. , Mizuno M. , Okumura Y. , Ohara Y. , Ackerman G. D. , Chan C. F. , Cooper W. S. , Kwan J. W. , Vella M. C.
Published: July 2002

The high power ion beams used in the next generation thermonuclear fusion reactors require high current negative ion beams accelerated to high energy, with high efficiency. One way to meet these requirements is to merge multiple low current density H− beamlets into a single high current beam. The feasibility of a high current merging preaccelerator was demonstrated in this experiment by merging 19 beamlets of H− ions distributed over a circular area 80 mm in diameter from a Japan Atomic Energy Research Institute negative ion source. H− ions were extracted at a current density exceeding 10 mA/cm2 at the ion source which operates at 0.13 Pa (1 mTorr), with a low arc power density (70 V×250 A). Spherically curved grids (with built-in magnetic electron suppression) were used in the preaccelerator to focus the extracted beamlets into a single 104 mA, 100 keV beam. The merged beam has a diameter of 23 mm and a converging angle of ±30 mrad at the beam envelope. The rms emittance of the 104 mA merging beam was 1.00 π mrad cm, which is a condition acceptable to the electrostatic quadropole accelerator for further acceleration.
Topography feedback mechanism for the scanning electrochemical microscope based on hydrodynamic forces between tip and sample
Authors: Ludwig Markus , Kranz Christine , Schuhmann Wolfgang , Gaub Hermann E.
Published: July 2002

The distance between microelectrode and sample is a crucial parameter in scanning electrochemical microscopy. Here we report on a technique where the hydrodynamic coupling between tip and sample is employed to measure and control this distance. We built an apparatus, where a microelectrode is vibrated laterally and the damping of the amplitude upon approach to the surface is measured optically. We show that amplitudes of up to 5 μm are easily obtained in an aqueous environment and that amplitudes below 1 nm can be detected with phase sensitive amplifiers. We measured the different vibration modes of the electrodes and identified the ones best suited for distance measurements. On hard surfaces we found the characteristic decay length of the coupling to be less than 1 μm and, within our measured range, independent of frequency and amplitude of the vibration. Measurements on an elastic surface of known spring constant revealed that the vibrating electrode exerts a repulsive normal force on the sample which may displace the surface and result in an increased apparent decay length of several μm. Under typical conditions this frequency- and amplitude-dependent force is in the order of several 100 μN. In parallel electrochemistry experiments we found that the reduction current at the microelectrode was only slightly increased by the vibration of the electrode and was a linear function of the amplitude.
Nonlinear optical tagging and laser induced fluorescence
Authors: Skiff F. , Curry J. J.
Published: July 2002

Optical test-particle diagnostics based on laser induced fluorescence are typically performed in the regime of weak optical pumping or in the regime of a short tagging pulse. In such cases, it is usually possible to construct a linear transfer function to describe the effect of tag-beam optical pumping on search beam fluorescence. The regime where particle dynamics plays a role in the optical pumping and laser induced fluorescence processes is explored. In this new regime, the diagnostic signal is nonlinearly related to the pump beam amplitude, and it becomes necessary to consider the time-dependent process of optical pumping on each particle orbit. The possibilities of techniques based on this extension are illustrated by a simple example which shows how ion Fokker–Planck diffusion can be measured with a single laser beam.
A time-of-flight spectrometer for measuring inelastic to elastic differential cross-section ratios for electron-gas scattering
Authors: LeClair L. R. , Trajmar S. , Khakoo M. A. , Nickel J. C.
Published: July 2002

We describe a crossed electron beam-atomic beam apparatus which utilizes a pulsed electron gun and field free drift tube to obtain time-of-flight (TOF) spectra of electrons scattered from atoms and molecules. This apparatus was constructed for the purpose of obtaining inelastic-to-elastic differential cross-section (DCS) ratios in the energy range extending from threshold to several eV above the threshold of the inelastic channel. The TOF approach eliminates the need for complicated calibration procedures required when using conventional electrostatic electron energy-loss spectroscopy (EELS) at these low energies. The characteristics of the apparatus will be given, along with representative TOF spectra from carbon monoxide. From those spectra we obtained DCS ratios at 90° scattering angle for excitation of the a3Π state of CO, in the impact energy range of 6–15 eV. These ratios were measured with uncertainties as small as ±4%, which represents a substantial improvement over previous measurements in this energy range. This demonstrates the feasibility of using the TOF technique to measure DCS ratios which in turn can serve as secondary standards to normalize other inelastic DCSs obtained from measurements with EELS.
Nonlinear absorption and refraction in an organic dye functionalized main chain polymer waveguide in the 1.5 μm wavelength region
Authors: Asobe M. , Yokohama I. , Kaino T. , Tomaru S. , Kurihara T.
Published: July 2002

We have examined the nonlinear optical properties of a main chain organic polymer waveguide in the 1.5 μm wavelength region. The nonlinear absorption coefficient was estimated to be α2=0.8–2×10−11 m/W in the 1.48–1.61 μm wavelength range. The wavelength dependence of the nonlinear absorption coefficient suggests that the strong nonlinear absorption originates from two step absorption through overtones of C–H vibrational absorption. The nonlinear refractive index was estimated to be n2=2.8(±0.3)×10−18 m2/W at a wavelength of 1.55 μm. The nonlinear absorption would restrict the applicability of the waveguide to all-optical switching in this wavelength region.
Piston–cylinder apparatus for high-pressure impedance spectroscopy
Authors: Hinrichs R. , da Jornada J. A. H.
Published: July 2002

A simple piston–cylinder apparatus was developed for impedance spectroscopy at pressures up to 3 GPa and temperatures up to 500 °C. The apparatus is of the compound cylinder type, with the innermost cylinder made of a commercially available low-cost alumina-based ceramic, with pistons of hard metal that allow electric connections. Cell electrical resistance was higher than 1 MΩ at T<300 °C and higher than 100 kΩ at 400 °C. The inductivity in the wires and pistons was about 2 μH. The sample was enclosed in a h-BN capsule, which insured a good hydrostaticity without disturbing the measurement. The equipment proved to be very useful in determining the activation volume of the conduction process in several ionic conductors.
Logarithmic current-to-voltage converter for local probe microscopy
Authors: Dürig U. , Novotny L. , Michel B. , Stalder A.
Published: July 2002

A quasilogarithmic current–voltage converter has been built which allows currents spanning an exceptionally broad range from 10 pA to 10 mA with a bandwidth greater than 2 kHz to be measured. The converter is based on the virtual ground scheme employing semiconductor diodes as nonlinear elements in the feedback path. It is ideally suited for studying local interactions in scanning tunneling microscopy.
High-pressure cell for measuring the zero-shear viscosity of polymer melts
Authors: Mattischek Johann-Peter , Sobczak Rudolf
Published: July 2002

The pressure dependence of viscosity of polymer melts is investigated insufficiently at present, the main reason being the requirements for high-duty viscometers. Only a few high-pressure viscometers are available and these are working with several disadvantages. The critical parts of rotating viscometers are seals and capillary types pose problems with pressure gradients and dissipation. Falling ball viscometers, according to Stokes’ law, allow measurements without problems with rotating parts, pressure gradients, and dissipation. The disadvantages of this method are very long measuring times at high viscosities. Unfortunately, polymer melts are not sufficiently stable at temperatures above the melting point, thermal degradation follows and unreliable data are the result. The magnetoviscometer, developed at the University of Linz, circumvents long measuring times by replacing the gravitational field by a much stronger magnetic field, which acts on an iron sphere in the molten polymer. As a new device for the magnetoviscometer a high-pressure cell, capable of 1000 bar and 523 K, is developed for measuring the zero-shear viscosity of polyolefine melts. The advantages and features of the high-pressure cell are described.
H
−
measurement in the magnetically filtered region of the large negative ion source
Authors: Hamabe M. , Oka Y. , Tsumori K. , Osakabe M. , Takeiri Y. , Kaneko O. , Kuroda T.
Published: July 2002

H- ion density in the extraction region of a volume-production-type ion source is measured, using the photodetachment method, and directly compared to H− ion beam extracted from the ion source in order to understand the effective production of H− ions. It is observed that there is qualitative similarity between H− density and extracted H− beam current, as expected. Characteristics of H− ion production under two values of magnetic strength are compared to study the effect of the filter field. It was found that the weaker magnetic field of 750 G cm is not sufficient for the filter field since high energy electrons can come into the extraction region across the magnetic field.
Heterodyne detection of ultrasound from rough surfaces using a double phase conjugate mirror
Authors: Delaye Philippe , Blouin Alain , Drolet Denis , Monchalin Jean-Pierre
Published: July 2002

We present an improved version of the classical heterodyne interferometer for ultrasound detection, which includes a double phase conjugate mirror (DPCM) in the detection arm. The DPCM performs wave front adaptation to plane wave of the speckled beam scattered by the rough surface of the sample. The performances of the system are analyzed regarding the transmission (≊30%) and fidelity (≊70%) of the phase conjugation and the response time and étendue of the device. An example of application to the detection of laser generated ultrasound is also presented.
In situ measurements of the solubility of crystals under high pressure by an interferometric method
Authors: Suzuki Yoshihisa , Sawada Tsutomu , Miyashita Satoru , Komatsu Hiroshi
Published: July 2002

Using a two-beam interferometer and a high-pressure cell with transparent windows, we measured the solubility of crystals under high pressure in situ. This method enabled us to observe in situ the transitional process of equilibration with a small quantity of specimens. We applied this method to measure a pressure dependence of the solubility of NH4Cl in water and compared with the previous data obtained by other techniques. It was found that this method is precise and suitable to measure the solubility of rare and expensive materials such as proteins.
Current density profile measurement on the Texas Experimental Tokamak using a heavy ion beam probe
Authors: Schwelberger J. G. , Crowley T. P. , Connor K. A. , Schoch P. M.
Published: July 2002

For the first time, a heavy ion beam probe has been used to measure the poloidal magnetic flux in a tokamak. In this measurement, first proposed over 20 years ago, the toroidal displacement of the heavy ion beam probe particles is caused by the force of the poloidal magnetic field on the ion beam probe particles. In a nearly toroidally symmetric device such as the Texas Experimental Tokamak, the toroidal position of the ions at the detector consists of a part proportional to the poloidal magnetic flux at the sample volume and an integrated contribution of the poloidal magnetic flux along the trajectory. The local part in the relation between beam position and magnetic flux is used as a correction term in an iterative algorithm that calculates the poloidal magnetic flux. The q profile and the current density profile can be derived from the measured poloidal flux. Errors of the measurement can be due to uncertainties in the analyzer position and also in the knowledge of the location of the sample volume. Also uncertainties in the plasma current and position contribute to the error of the poloidal flux measurement. It is essential to know the magnetic field outside the plasma. The calculation of the outside field is difficult due to the presence of the iron core. The error in the measurement of the poloidal flux is on the order of 1%. The current profiles and q profiles were measured for discharges with on axis and off axis electron cyclotron resonance heating (ECRH), and with impurity injection. As expected, all current profiles peak in the center. With central ECRH, the measured current profiles are consistent with a prediction based on Spitzer resistivity and the measured electron temperature profile. In these plasmas, the safety factor has a central value of qc=0.95±0.1 and near the center of the plasma, the poloidal flux is observed to increase with time. The current profiles for off axis ECRH exhibit a larger current density in the wings of the distribution than comparable centrally heated ECRH plasmas. Results from plasmas with impurity injection yield qc=0.6 which is significantly lower than expected since these plasmas have m=2 activity.
Fast resistive bolometry
Authors: Spielman R. B. , Deeney C. , Fehl D. L. , Hanson D. L. , Keltner N. R. , McGurn J. S. , McKenney J. L.
Published: July 2002

Resistive bolometry is an accurate, robust, spectrally broadband technique for measuring absolute x-ray fluence and flux. Bolometry is an independent technique for x-ray measurements that is based on a different set of physical properties than other diagnostics such as x-ray diodes, photoconducting detectors, and P-I-N diodes. Bolometers use the temperature-driven change in element resistivity to determine the total deposited energy. The calibration of such a device is based on fundamental material properties and its physical dimensions. We describe the use of nickel and gold bolometers to measure x rays generated by high-power z pinches on Sandia’s Saturn and Z accelerators. The Sandia bolometer design described herein has a pulse response of ∼1 ns. We describe in detail the fabrication, fielding, and data analysis issues leading to highly accurate x-ray measurements. The fundamental accuracy of resistive bolometry will be discussed.
New design of a cryostat-mounted scanning near-field optical microscope for single molecule spectroscopy
Authors: Durand Yannig , Woehl Jörg C. , Viellerobe Bertrand , Göhde Wolfgang , Orrit Michel
Published: July 2002

Due to the weakness of the fluorescence signal from a single fluorophore, a scanning near-field optical microscope for single molecule spectroscopy requires a very efficient setup for the collection and detection of emitted photons. We have developed a home-built microscope for operation in a l-He cryostat which uses a solid parabolic mirror in order to optimize the fluorescence collection efficiency. This microscope works with Al-coated, tapered optical fibers in illumination mode. The tip-sample separation is probed by an optical shear-force detection. First results demonstrate the capability of the microscope to image single molecules and achieve a topographical resolution of a few nanometers vertically and better than 50 nm laterally.
Systematic and statistical errors in correlation estimators obtained from various digital correlators
Authors: Kojro Z. , Riede A. , Schubert M. , Grill W.
Published: July 2002

A number of commercially available digital correlators is discussed with respect to algorithms, systematic errors, and statistical errors. Special attention has been paid to the determination of an influence of the temporal integration of measured signals on autocorrelation functions measured in digital correlators. A calculation of the standard deviation for statistical errors in correlation estimators has been performed. The result is compared with the experiment. Favorable noise properties of the multiple-tau correlator which have been reported in the literature are not confirmed.
Characterization of neutral density profile in a wide range of pressure of cylindrical pulsed gas jets
Authors: Malka V. , Coulaud C. , Geindre J. P. , Lopez V. , Najmudin Z. , Neely D. , Amiranoff F.
Published: July 2002

The neutral density profile of cylindrical gas jets is measured with a Mach–Zehnder interferometer under a wide range of backing pressures. The sensitivity of this diagnostic together with the mathematical treatment of the data allows us to measure neutral densities for argon gas as low as 1017 cm−3 for a 5 mm diam gas jet.
A proposed new microstructure for gas radiation detectors: The microhole and strip plate
Authors: Veloso J. F. C. A. , dos Santos J. M. F. , Conde C. A. N.
Published: July 2002

A new type of microstructure device for a gas radiation detector is proposed. This microstructure, the microhole and strip plate structure, merges the structures of a gas electron multiplier and a microstrip plate in one single plate. This design allows two-multiplication stages and a separation of the sensitive and the detection regions, with full optical positive feedback suppression. Simulations for gas gain and electron transparency of the microstructure are presented. Different applications are discussed.
Schottky contacts on ternary compound semiconductors: Compositional variations of barrier heights
Authors: Mönch Winfried
Published: July 2002

The alignment of the electronic band structures at contacts between solids is defined by the continuum of interface-induced gap states and the charge transfer across the interface. The barrier heights of metal–semiconductor contacts as well as the band edge discontinuities of semiconductor heterostructures are primarily described by the zero-charge-transfer barrier heights. This characteristic semiconductor property equals the energy distance between the majority-carrier band edge and the charge-neutrality level of the interface-induced gap states. The compositional trends of barrier heights of Al1−xInxAs, In1−xGaxAs, and Al1−xGaxAs Schottky contacts and of valence-band offsets of Al1−xGaxAs/GaAs heterostructures are analyzed. The zero-charge-transfer barrier heights of ternary compounds are found to vary linearly as a function of the compositional parameter x.
Integrated micro-scanning tunneling microscope
Authors: Xu Y. , MacDonald N. C. , Miller S. A.
Published: July 2002

Two versions of micro-scanning tunneling microscopes (micro-STMs) have been fabricated. The integrated micro-STMs are fabricated from single crystal silicon using the high-aspect-ratio SCREAM process. Each micro-STM includes integrated xy comb drive actuators and a torsional z actuator with integrated cantilever and tip. One micro-STM measures approximately 200 μm on-a-side and is an example of a STM element for a STM array architecture. Another, larger micro-STM/atomic force microscope measures 2 mm on-a-side including a 1 mm long cantilever with a 20 nm diam tip. We demonstrate the operation of this larger STM by obtaining a STM image of a 200 nm metal conductor on a silicon chip.
High aspect ratio micromachining Teflon by direct exposure to synchrotron radiation
Authors: Zhang Y. , Katoh T. , Washio M. , Yamada H. , Hamada S.
Published: July 2002

Micromachining Teflon was achieved by direct exposure to synchrotron radiation and the microstructures made had the smallest surface detail down to 20 μm with structural height of more than 200 μm, that is, aspect ratio on the order of 10. The quality of micromachining Teflon by this process was found to be critically dependent on photon flux of the synchrotron radiation. Analysis of the mass distribution of gaseous species formed upon this process suggested that photochemical processes rather than pyrolytic processes may still dominate.
Cubic boron nitride synthesis in low-density supersonic plasma flows
Authors: Berns D. H. , Cappelli M. A.
Published: July 2002

We report on the growth of cubic boron nitride films on {100} silicon using a low density, supersonic plasma jet generated by a direct-current arc discharge expanded to low pressures. The arc discharge was operated on source gas mixtures of nitrogen and argon, with boron trichloride injected downstream of the expansion nozzle. The films were analyzed by infrared absorption and x-ray photoelectron spectroscopy. Phase selectivity was obtained by the application of a negative bias to the substrate so as to bombard the surface with energetic ions during deposition. The deposition process was found to be highly sensitive to substrate temperature and substrate bias voltage.
Low temperature processing of Nb-doped Pb(Zr,Ti)O3 capacitors with La0.5Sr0.5CoO3 electrodes
Authors: Al-Shareef H. N. , Tuttle B. A. , Warren W. L. , Dimos D. , Raymond M. V. , Rodriguez M. A.
Published: July 2002

The effect of crystallization temperature on the electrical properties of sol-gel derived Pb(Zr,Ti,Nb)O3 or PNZT capacitors with La0.5Sr0.5CoO3 (LSCO) electrodes has been investigated. It is demonstrated that LSCO//PNZT(4/30/70)//LSCO capacitors can be fabricated at temperatures as low as 550 °C without significant degradation in their ferroelectric and dielectric properties. Lowering the process temperature to 500 °C resulted in substantial degradation in capacitor properties. Nonetheless, all capacitors processed in the 500 °C to 675 °C range exhibited essentially no fatigue up to 5×109 switching cycles. The low temperature processing is significant as it indicates that this ferroelectric capacitor technology is compatible with high density nonvolatile memory architectures. In other words, these process temperatures are low enough to maintain plug integrity and to prevent degradation of the underlying CMOS circuitry in a high density ferroelectric memory.
Electrically detected magnetic resonance study of stress-induced leakage current in thin SiO2
Authors: Stathis J. H.
Published: July 2002

A spin-dependent trap-assisted tunneling current has been detected in a thin (44.5 Å) SiO2 film. An electron paramagnetic resonance signal, obtained from the tunnel current, provides the first microscopic information regarding the identity of defects responsible for stress-induced leakage currents in thin SiO2. The observed electrically detected magnetic resonance spectrum is anisotropic and does not correspond to any of the commonly known defects in the Si/SiO2 system. The change in current is 2.4±0.3×10−7 at resonance, which we explain in terms of a spin-dependent hopping process. Assuming that the signal corresponds to traps in the oxide, we estimate sensitivity to ∼1×109 defects/cm2.
Diffusion mediated chemical reaction in Co/Ge/Si(100) forming Ge/CoSi2/Si(100)
Authors: Prabhakaran K. , Sumitomo K. , Ogino T.
Published: July 2002

We report the occurrence of a diffusion mediated chemical reaction in the layered structure Co/Ge/Si(100) to form Ge/CoSi2/Si(100). This is possible due to the lower onset temperature of inward diffusion of Co in Ge(100) (∼150 °C) compared to that in Si(100) (∼300 °C). Deposition of ∼2 monolayer (ML) of Co at room temperature, onto a Ge covered (∼3 ML) Si(100) surface, mainly forms CoxGey species on the surface. However, annealing the sample at 400 °C, Co diffuses through the Ge layer and reacts with Si and forms buried cobalt silicide of the structure Ge/CoSi2/Si(100). X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), medium energy ion scattering (MEIS) are employed for the study. The results open up a possibility to fabricate metal/semiconductor heterostructures in a novel way.
Electrical properties of SrBi2Ta2O9 thin films and their temperature dependence for ferroelectric nonvolatile memory applications
Authors: Taylor D. J. , Jones R. E. , Zurcher P. , Chu P. , Lii Y. T. , Jiang B. , Gillespie S. J.
Published: July 2002

This letter addresses the temperature dependence of some of the electrical properties of 0.2-μm-thick SrBi2Ta2O9 capacitors with platinum electrodes on silicon wafers for nonvolatile memory applications. Investigations of the remanent polarization, the nonvolatile polarization and the coercive field with pulse amplitude were made at different temperatures. The endurance of the polarization as a function of temperature is reported. Up to 125 °C, the capacitors show less than a 10% reduction in polarization from their initial values following 1×1012 cycles.
Hard-x-ray radiation from short-pulse laser-produced plasmas
Authors: Chichkov Boris N. , Momma Carsten , Tünnermann Andreas , Meyer Susanne , Menzel Thomas , Wellegehausen Bernd
Published: July 2002

The generation of hard-x-ray radiation (ℏω≥25 keV) from short-pulse Ti:sapphire laser-produced plasmas is studied. Solid targets are irradiated by 0.2–10 ps laser pulses in the intensity range of 5×1013−5×1016 W/cm2. It is shown that the measured dose rates obey a simple scaling law.
Comparison of Si surface roughness measured by atomic force microscopy and ellipsometry
Authors: Fang S. J. , Chen W. , Yamanaka T. , Helms C. R.
Published: July 2002

Measurements of Si surface roughness by atomic force microscopy and ellipsometry have been performed over a wide range of conditions. Advanced methods of data analysis have been applied to both techniques leading to a quantitative comparison of root-mean-square (rms) roughness to the ellipsometric paramter Δ. Differences in Δ are observed for surfaces with the same rms roughness, but different roughness spectral densities, as expected from theory.
Optical probing of the temperature transients during pulsed-laser induced boiling of liquids
Authors: Park Hee K. , Grigoropoulos Costas P. , Poon Chie C. , Tam Andrew C.
Published: July 2002

The thermodynamics of the rapid boiling of a liquid on a solid surface heated by an excimer laser pulse is studied experimentally. The dynamics of bubble nucleation, growth, and collapse is detected by probing the optical specular reflectance. The transient temperature field is measured by monitoring the reflectance of a thin film with calibrated optical properties. The metastability behavior of the liquid and the criterion for the liquid-vapor phase transition in nanosecond time scale are obtained for the pressure from 1 atmosphere to 3.3 MPa.
Effect of hydrogen dilution on the deposition rate of hydrogenerated amorphous silicon films in a modified pulsed plasma discharge
Authors: Mukherjee C. , Anandan C. , Seth Tanay , Dixit P. N. , Bhattacharyya R.
Published: July 2002

Hydrogen dilution effects on the growth of a-Si:H films in a modified pulsed plasma discharge are studied for two different silane flow conditions with hydrogen dilution ranging from 0% to 80%. The increase of deposition rate (rd) due to hydrogen dilution is attributed mainly to changes in electron density (ne) and electron decay time constant (τe). Concurrently, it appears that hydrogen dilution mitigates the deleterious effects of secondary plasma reactions. Increasing the dwell time of the high power period under hydrogen dilution also increases rd, accompanied by an enhancement of photoconductivity (σph) as compared to films grown under similar conditions without dilution. The decrease in rd at dilution ≳25% is seen as the onset of a process of etching, presumably by atomic hydrogen, and this limits rd irrespective of the availability of the number of silane molecules at such dilutions. Time-resolved optical emission spectroscopy results for H* emission supports the above views.
Growth and characterization of K3Li2(TaxNb1−x)5O15 crystals for blue second-harmonic-generation applications
Authors: Furukawa Y. , Makio S. , Miyai T. , Sato M. , Kitayama H. , Urata Y. , Tamiuchi T. , Fukuda T.
Published: July 2002

Potassium lithium tantalate niobate, K3Li2(TaxNb1−x)5O15, or KLTN single crystals were grown by spontaneous crystallization method, and it has been demonstrated that the KLTN crystal has high potential as a nonlinear crystal for blue second-harmonic-generation (SHG) applications. Ta substitution for Nb site in K3Li2Nb5O15 crystal improves the transparency in the blue light region and decolorizes the material. Compared with K3Li2Nb5O15, the K3Li2Ta5O15 crystal exhibits a 60 nm blueshift of the absorption edge from 376 to 316 nm, and decreases its absorption coefficient from 2.3 to 0.3 cm−1 at 400 nm. The phase-matched frequency doubling of the Ti:sapphire infrared laser for blue SHG at room temperature has been demonstrated with the KLTN bulk crystal.
Monolayer control in the growth of (Al,Ga)Sb/GaSb single quantum wells: Application to the band offset and Γ–L crossover problems
Authors: Leroux M. , Massies J.
Published: July 2002

This letter reports the growth by molecular beam epitaxy of AlxGa1−xSb/GaSb single quantum wells on GaSb substrates. Barrier compositions and well thicknesses are determined in situ using reflection high energy electron diffraction. The luminescence energies of wells with width increasing by a two monolayer increment, with either an odd or even number of monolayers, are intercalated, further evidencing the thickness control. For pseudomorphic AlxGa1−xSb/GaSb heterostructures, a heavy hole valence band offset in meV of (275±75)x is estimated. For an Al barrier composition of 0.31, the confinement induced Γ–L crossover occurs at a well thickness of 12 monolayers.
High efficiency in dry etching of Si for wavelengths around 120 nm
Authors: Streller U. , Krabbe A. , Schwentner N.
Published: July 2002

Microstructuring of Si with XeF2 can be optimized by increasing the contrast in choosing a wavelength with minimal nonselective etching. The efficiency of selective etching with optimal quality can be increased by factors of 100 and 500 by using wavelengths around 120 and 110 nm, respectively, in comparison to longer wavelengths around 200 nm. The high efficiency of typically 10 removed atoms per photon, the availability of optical materials for imaging and the potentially high spatial resolution at 120 nm compared to the conventional excimer laser and I-line wavelengths present a perspective for generating line densities required in the Gbit range.
Analysis of the transport mechanism in GaAs/AlGaAs quantum-well infrared photodetection structures using time resolved photocurrent measurements
Authors: Ehret S. , Schneider H. , Schönbein C. , Bihlmann G. , Fleissner J.
Published: July 2002

We show that the transient intersubband photocurrent in a GaAs/AlGaAs quantum-well infrared photodetector (QWIP) consists of two dynamical components, which are associated, respectively, with the drift motion of photoexcited carriers and with the extra injection current induced by the generated nonequilibrium space charges. The decay time τ of the latter component depends critically on the temperature of the sample and the applied bias voltage. For a temperature of T=22 K, decay times in excess of 15 μs are found. A simple model of the refilling process of the space charges is presented, showing, that the slow component corresponds approximately to the dielectric relaxation time of the structure along the growth direction. While the slow component in the present 8-period structure corresponds to about 50% of the total photocurrent, it is negligible in standard QWIP structures containing 40 or more periods, where ⩾99% of the intersubband photocurrent proceeds on a picosecond time scale.
Kinetics of processes in the Ti–Si1−xGex systems
Authors: Freiman W. , Eyal A. , Khait Yu. L. , Beserman R. , Dettmer K.
Published: July 2002

The kinetics of processes related to the formation of C49 and C54 Ti(Si1−yGey)2 germanosilicide phases in the two relaxed and strained Ti/Si1−xGex systems (x1=0.35 and x2=0.20) in the temperature range 600–800 °C are considered. These processes have been studied through Auger electron spectroscopy, secondary ion mass spectroscopy, x-ray diffraction, and Raman scattering spectroscopy supported by ion beam etching techniques. Si/Ge ‘‘intergrain’’ alloy has been found between the grains of the C49 or/and C54 phases, with a Ge-rich part Si1−zGez of z=2x–3x in the upper region. At higher temperatures, the Ge concentration in the Ge-rich alloy decreases and its volume increases. The temperature required for obtaining similar changes are higher when x2<x1. A kinetic electron-related model is proposed to explain the observed phenomena.
Band offset transitivity in AlGaAs/InGaP/InGaAsP heterostructures on a GaAs substrate
Authors: Cho Yong-Hoon , Choe Byung-Doo , Lim H.
Published: July 2002

The conduction-band offset ΔEc of Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2 lattice matched to a GaAs substrate was measured by capacitance-voltage analysis. To examine the transitivity of the band offset in the AlGaAs/InGaP/InGaAsP system, the band offsets of Al0.3Ga0.7As/In0.5Ga0.5P and In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2 were investigated. The value of ΔEc for the Al0.3Ga0.7As/In0.1Ga0.9As0.8P0.2 heterostructure, estimated by adding the measured ΔEc values in Al0.3Ga0.7As/In0.5Ga0.5P and in In0.5Ga0.5P/In0.1Ga0.9As0.8P0.2, agrees well with the value measured directly. We thus conclude that the transitivity rule holds well for the band offsets of an AlGaAs/InGaP/InGaAsP system lattice matched to a GaAs substrate.
Heteroepitaxial growth of KNbO3 single-crystal films on SrTiO3 by metalorganic chemical vapor deposition
Authors: Onoe Atsushi , Yoshida Ayako , Chikuma Kiyofumi
Published: July 2002

Potassium niobate (KNbO3) thin films have been deposited on silicon (Si) and strontium titanate (SrTiO3) substrates by metalorganic chemical vapor deposition. Stoichiometric KNbO3 films were obtained by adjusting the partial pressure of precursors. The crystallinity was examined by x-ray diffraction and reflection high-energy electron diffraction. Single-crystal (010) KNbO3 films with smooth surface were heteroepitaxially grown on (110)SrTiO3 substrate at 850 °C.
Transistor-based evaluation of conduction-band offset in GaInP/GaAs heterojunction
Authors: Faleh M. S. , Tasselli J. , Bailbe J. P. , Marty A.
Published: July 2002

The conduction-band discontinuity for GaInP/GaAs metalorganic chemical vapor deposition (MOCVD) HBTs has been determined from current–voltage characterization. The charge-control model used permits to compare the respective weights of collector current limitations due to the potential barrier effect and to the carrier diffusion mechanism in the low gap base region. A study of sensitivity to the main sources of error leads to a conduction-band offset value of ΔEC≊170±16 meV confirming the advantage of the resulting band lineup for the HBT.