bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical filters for the gravitational waves detector VIRGO: Performance of a two-stage suspension
Authors: Braccini S. , Bradaschia C. , Del Fabbro R. , Di Virgilio A. , Ferrante I. , Fidecaro F. , Flaminio R. , Gennai A. , Giazotto A. , La Penna P. , Losurdo G. , Palla F. , Pasqualetti A. , Passuello D. , Poggiani R. , Zhang Z.
Published: July 2002

Mechanical filters using cantilever springs as elastic elements have been developed for the seismic isolation system of the VIRGO gravitational wave detector. A two-stage suspension has been built in order to study how the attenuation performances of individual filters combine when the filters are cascaded. An attenuation ⩾80 dBin the vertical direction and ⩾110 dBin the horizontal direction has been attained for frequencies above 10 Hz.
Compact sputter source for deposition of small size-selected clusters
Authors: Hall S. G. , Nielsen M. B. , Robinson A. W. , Palmer R. E.
Published: July 2002

We report on the development of a caesium ion sputter source for the production of small mass-selected atomic clusters. It has been designed to be compact and portable, enabling it to be attached to ultrahigh vacuum (UHV) systems for use in deposition experiments. The sputter source, developed from a high energy (∼20 keV) atomic ion beam source, has been modified by introducing a beam extraction section, resulting in a cluster beam energy of 1.5 kV. This allows mass selection to be performed with a compact Wien velocity filter, greatly reducing the dimensions of the source. The source produces sufficient intensities of small clusters (1 – 15 atoms/cluster) for UHV deposition experiments, for example, a deposition rate of 0.002 monolayers/min for Al7− focused onto a 1 cm2 area has been obtained. It is possible to produce beams of many materials, especially the noble metals and carbon. We show mass spectra for Agn −, Aln− , and Cn− clusters.
Data acquisition system to interface between imaging instruments and the network: Applications in electron microscopy and ultrasound
Authors: Kapp Oscar H. , Ruan Shengyang
Published: July 2002

A system for data acquisition for imaging instruments utilizing a computer network was created. Two versions of this system, both with the same basic design, were separately installed in conjunction with an electron microscope and a clinical ultrasound device. They serve the functions of data acquisition and data server to manage and to transfer images from these instruments. The virtues of this system are its simplicity of design, universality, cost effectiveness, ease of management, security for data, and instrument protection. This system, with little or no modification, may be used in conjunction with a broad range of data acquiring instruments in scientific, industrial, and medical laboratories.
Thickness and conductivity determination of thin coatings on ferromagnetic substrates in the case of cylindrical symmetry
Authors: de Halleux B. , Ptchelintsev A. , de Limburg Stirum B.
Published: July 2002

An eddy current method allowing the determination of parameters of a thin nonmagnetic conductive coating on a ferromagnetic conductive substrate is reported. At a single operating frequency, two independent quantities can be determined: a permeability-to-conductivity ratio of the substrate and a thickness-conductivity product of the coating. Thus, thickness or conductivity of the coating can be determined independent of variations of the substrate magnetic and electrical parameters. A simple theoretical formula for the normalized electrical impedance of the test coil is obtained using asymptotic expansions of Bessel functions. The method was applied to the evaluation of electrogalvanized wires in the frequency range 100 kHz–1 MHz. A set of low carbon steel wires with diameter around 2.2 mm, coated with zinc layers having thicknesses in the range 2.7–64.6 μm, was investigated using two long coils. Experimental data of the electrical impedance were compared to those predicted. Agreement between theory and experiment is excellent for coatings thicker than 12 μm. Despite discrepancies between theory and experiment for very thin layers arising from various imperfections of the coating and interfaces, the method was applied successfully in the thickness range below 12 μm. To do this, two parameters: an apparent conductivity of the coating and a thickness offset, were introduced. The mathematical inversion of the experimental data with the two-variable Newton–Raphson method and the asymptotic formula is extremely fast. The technique developed has an extremely low sensitivity to variations of the ferromagnetic substrate conductivity and magnetic permeability. A magnetizing field of 0–23 000 A/m, producing large variations in the substrate magnetic permeability, does not significantly influence results of the coating thickness determination. The agreement between measured thickness and that obtained by a chemical method is excellent, typically within 0.5 μm. An uncertainty of the thickness or conductivity determination better than 1% is obtained.
Development of infrared focal plane arrays for space
Authors: Wu Jian , Forrest William J. , Pipher Judith L. , Lum Nancy , Hoffman Alan
Published: July 2002

Space astronomy requires large-area cryogenic infrared focal plane arrays (FPAs) with high quantum efficiency, extremely low dark current, low power dissipation, and background limited noise performance. To meet these requirements, especially at temperatures of 5–15 K, Santa Barbara Research Center designed and fabricated a new multiplexer, CRC-744. The FPAs made by bonding InSb detector arrays to CRC-744 multiplexers were evaluated at the University of Rochester. The best array achieved the read noise of 5 e − with 12 s integration and 7 e − with 200 s integration with Fowler-64 sampling at 15 K, the average dark current of <0.2 e−/ s at both 15 and 29 K, and the average quantum efficiency of 87% at both 15 and 29 K. The 10%–90% rise time was 4 μs driving a 600 pF external load. The power dissipation was 0.3–0.4 mW when running flat-out (100% duty cycle). The full well capacity was 105 e− (230 mV) with 400 mV of applied bias. The above test results demonstrate that the FPAs meet background-limited space experiment requirements. The CRC-744 multiplexer works well down to at least 5 K (the lowest temperature of our tests).
A flexible surface-coil-type resonator using triaxial cable
Authors: Hirata Hiroshi , Ono Mitsuhiro
Published: July 2002

This note describes a newly developed flexible surface-coil-type resonator (FSCR) used for electron paramagnetic resonance (EPR) measurements. A conventional FSCR has used a balanced transmission line made by coaxial lines. The new resonator uses triaxial cable in order to avoid anisotropy of flexure of the transmission line. Experimental results show that the EPR signal measured with the triaxial FSCR is 35% stronger than that measured with the conventional FSCR.
Sample shuttle for fluorescence-yield x-ray absorption detector maintains sample chamber purge atmosphere
Authors: Weesner Forrest J. , Bohne Harold , Bleam William F.
Published: July 2002

X-ray absorption measurements of low-Z elements (Z<20) are feasible when performed under a He atmosphere. We describe a sample shuttle for use with a popular fluorescence detector that maintains a stable He-purged atmosphere and allows rapid exchange of samples with reproducible positioning. No waiting time is needed following sample exchange and fluorescence intensity variations due to sample chamber gas composition changes are minimized.
A high gravity chemical vapor deposition apparatus
Authors: Abe Yoshiyuki , Maizza Giovanni , Sone Noboru , Nagasaka Yuji , Suzuki Tetsuya
Published: July 2002

A high gravity centrifuge facility in which thin films can be produced, especially from gas phase, was developed. The centrifuge facility allows high gravity materials processing up to 100g (g denotes the terrestrial gravity acceleration). With a minor modification, not only thin films from gas phase but also bulk materials could be produced in the facility. For the first demonstrative attempt in this facility, diamond thin films were grown under high gravity conditions up to 100g by means of the direct current-plasma chemical vapor deposition method, in which diamond was deposited on a molybdenum substrate in a moderate pressure condition (27 kPa) of the gas flow of hydrogen-methane mixture (methane 1 vol %). The details of the facility are described, and the preliminary results on the high gravity diamond synthesis are presented.
Developments on the KSU-CRYEBIS, a user facility for low energy, highly charged ions
Authors: Stockli M. P. , Abdallah M. , Chen C. Y. , Cocke C. L. , De Paola B. D. , Fry D. , Gibson P. E. , Richard P. , Tipping T. N. , Walch B. , Winecki S. , Eastman B. , Gebel Th. , Langer E. , Lehnert U. , Preusse H. , Ullmann F. , Gorges A. , Ramassamy M.
Published: July 2002

The KSU-CRYEBIS, a CRYogenic electron beam ion source, supplies experiments with low-energy, highly charged ions of numerous species. The supplied charge states cover the range from 1+ to 52+, with typical beam currents of a nA for low charge states and a few pA for the highest charge states. The ion energies cover the range from 0.3 to 165 keV per charge. This is an unusually broad range of final ion energies and hence requires an unusual dynamic ion transport system. This paper presents advances made with respect to the CRYEBIS ion beam transport, diagnostics, and identification. In addition, an update on the developments of ion beams with very high duty cycles is given.
Vacuum arc ion source for heavy ion fusion
Authors: Liu F. , Qi N. , Gensler S. , Prasad R. R. , Krishnan M. , Brown I. G.
Published: July 2002

Heavy ion fusion is one approach to the problem of controlled thermonuclear power production, in which a small DT target is bombarded by an intense flux of heavy ions and compressed to fusion temperatures. There is a need in present HIF research and development for a reliable ion source for the production of heavy ion beams with low emittance, low beam noise, ion charge states Q=1+ to 3+, beam current ∼0.5 A, pulse width ∼5–20 μs, and repetition rate ∼10 pulses per second. We have explored the suitability of a vacuum arc ion source for this application. Energetic, high current, gadolinium ion beams were produced with parameters as required or close to those required. The performance parameters can all be improved yet further in an optimized ion source design. Here we describe the ion source configuration used, the experiments conducted, and the results obtained. We conclude that a vacuum arc based metal ion source of this kind could be an excellent candidate for heavy ion fusion research application.
Argon ion laser-induced fluorescence with diode lasers
Authors: Severn G. D. , Edrich D. A. , McWilliams R.
Published: July 2002

Diode lasers have been used for ion temperature measurements in ArII plasmas by finding new laser-induced fluorescence (LIF) schemes suited to the present range of available wavelengths. The new LIF schemes require excitation at 664, 669, and 689 nm, all near industry-standard wavelengths. Conventional LIF measurements performed by dye lasers in ArII use 611.66 nm in vacuum, shorter than any commercially available red diode laser line, and depend on the population of the 3d′ 2G9/2 metastable state. The metastable state density of the conventional LIF scheme was found to be larger than the populations of the other metastable states by an order of magnitude or less. A master oscillator power amplifier diode laser was used both in a Littman–Metcalf cavity and as an optical amplifier for a low power diode laser which was in a Littman–Metcalf cavity. Both systems provided intensity of up to 500 mW, continuously tunable over 10 nm centered at 666 nm, and were used to obtain high resolution ion velocity distribution functions.
High-performance beamline for vacuum-ultraviolet-excited material processing
Authors: Akazawa H. , Takahashi J.
Published: July 2002

A high-performance beamline dedicated to vacuum-ultraviolet (VUV)-excited semiconductor processing has been constructed on the compact electron storage ring “Super ALIS”. The first toroidal mirror accepts photons (emitted at a bending magnet) for 70 mrad in the horizontal direction, and the reflected parallel beam is focused onto the specimen surface by the second toroidal mirror. A brilliant VUV beam (with a photon density of 1.3×1016 s−1 mm−2 when the ring current is 300 mA) illuminates a circular field (10 mm in diameter) on the target surface. The eight 5-m-long differential pumping stages allow the reactant gas to be introduced into the reaction chamber at pressures up to 0.1 Torr. The processing is monitored in real time by using ultraviolet phase-modulated spectroscopic ellipsometry, and VUV-stimulated evaporation of SiO2 film has been demonstrated.
Fast exhaust channel optical absorption method and apparatus to study the gas exchange in large diesel engines
Authors: Vattulainen J. , Hernberg R. , Hattar C. , Gros S.
Published: July 2002

An optical absorption spectroscopic method and apparatus with shorter than 1 ms response time have been used to study the gas exchange processes in realistic conditions for a single cylinder of a large diesel engine. The method is based on measuring the differential line-of-sight optical uv absorption of the exhaust-gas-contained SO2 as a function of time in the exhaust port area just after the exhaust valves. The optical absorption by SO2 is determined from light transmission measurements at 280 and 340 nm performed through optical probes installed into the exhaust channel wall. The method has been applied to a continuously fired, large, medium speed production-line-type diesel engine with 990 kW rated power. The test engine was operated with standard light fuel oil (MDO Termoshell) and with light fuel oil treated with a sulfur additive {Di-Tert-Butyldisulfid [(CH3)3C]2S2}. The latter was to improve the optical absorption signals without increasing the fouling of the exhaust channel optical probes as in the case of heavier fuel oil qualities. In the reported case of a four-stroke diesel engine measurement results show that the method can provide time-resolved information of the SO2 density in the exhaust channel and thus give information on the single-cylinder gas exchange. During the inlet and exhaust valve overlap period the moment of fresh air entering into the measurement volume can be detected. If independent exhaust gas temperature and pressure data are available, the absorption measurements can readily be used for determining the burnt gas fraction in the exhaust channel. In this work the possibility of using the optical absorption measurement to determine the instaneous exhaust gas temperature was studied. Based on known fuel properties and conventional averaged SO2 measurements from the exhaust channel a known concentration of SO2 was assumed in the exhaust gas after the exhaust valves opening and before the inlet and exhaust valves overlap period. Together with an exhaust gas pressure measurement the optical absorption signal was used to determine the instaneous exhaust gas temperature. Due to the minimal modifications needed by the engine for optical access, and continuously fired operation with relevant power levels and realistic fuel qualities, this measurement method, with some further development, can be useful to obtain time-resolved data from the exhaust channel of real production-line-type diesel engines.
Design and implementation of a slope measuring instrument for measurement of charged particle temperatures
Authors: Rajput S. S. , Garg S. C.
Published: July 2002

This article reports the design considerations, implementation, and performance of an instrument, used to measure the slope of current–voltage (I–V) characteristics of ionospheric plasma, for onboard measurement of charged particle temperatures. The instrument measures the reflected ac signal in the probe current, when an ac voltage is superposed over the probe bias, and is designed for the slope measurement from 6.3×10−14 A/V2 to 6.3×10−9 A/V2 with full scale resolution of 0.2%.
Counting errors in a real-time multichannel scaler
Authors: Zieliński Marek , Dygdała Roman S. , Płóciennik Przemysław
Published: July 2002

In this article the problem of errors arising from a specific design of a real-time multichannel scaler is presented. The dead-times error, double-pulse error, and the error due to the gate width modulation are discussed. The absolute values of the systematic errors of the gate widths of a single channel are of the order of hundreds of picoseconds, making for a severe problem when the gate is small. The problem is overcome by a floating allocation of the gates. This method leads to a decrease in the differences between the variances of the number of counts for all time channels and as a consequence improves the precision of the measurements.
Improvement in time and space resolution of stroboscopic micrography using high power xenon flash
Authors: Miyake Momoko O. , Mogami Yoshihiro , Kataoka Eri , Kajita Eri , Baba Shoji A.
Published: July 2002

A circuit capable of regulating 300-W xenon flash tubes up to at 5000 flashes per second (fps) using an insulated gate bipolar transistor (IGBT) as a gating device is presented. This device enables the microscopic analysis of ciliary movement at very high temporal and spatial resolutions, revealing slow and fast phases of angular change during the effective stroke of a single cilium.
Microwave absorption for water plume density measurements
Authors: Boulais K. A. , Choe J. Y. , Irwin K. A. , Higdon C. E.
Published: July 2002

We describe an experimental method to measure the water density of a plume created from a shallow underwater explosion. Our approach is based on the attenuation characteristics of a microwave signal propagated through the plume. A unique correlation exists between the amount of attenuation and macroscopic quantities including the volume fraction of water in air. In this article, both the theory required for data analysis and the experimental arrangement used for measuring the highly attenuated microwave signal are discussed.
Production of 3d metal ion electron cyclotron resonance plasmas and ion beams using volatile compounds
Authors: Ullrich A. , Grübling P. , Zschornack G.
Published: July 2002

The metal ions from volatile compounds method was used to produce metal ion electron cyclotron resonance (ECR) plasmas and metal ion beams. In detail, the production of iron, nickel, and cobalt plasmas and beams on the 14.5 GHz ECR ion source of the TU Dresden is reported using ferrocene, nickelocene, and cobaltocene, respectively. Besides the detection of ion charge state distributions in extracted ion beams with an analyzing magnet first wavelength dispersive x-ray spectra of 3d cobalt metal ions were measured. Thereby, the based on atomic structure calculations analysis of x-ray satellites allows it to get information on the ion charge state spectrum of the ions inside the ECR plasma.
Models of many-element electron cyclotron resonance plasmas
Authors: Marchetti M. T. , Cavenago M. , Pegoraro F.
Published: July 2002

It is a known fact that in electron cyclotron resonance ion sources, plasma impurities play a role in the formation of the ion charge state distribution (CSD). Writing the balance equations for the ion densities in a matrix form allows us to calculate CSD easily for plasmas containing an arbitrary number of elements, taking into account electron ionization, radiative recombination, charge exchange between ions, and ion flowing out of the magnetic trap. Moreover, by defining two global quantities—S0 and Sc—representative of charge exchange, the stationary case can be reduced to the resolution of only one nonlinear equation for S0 and Sc. Therefore plasma equilibria even with several species of impurity ions (carbon, oxygen, hydrogen, etc.) can be easily described and solved in this model. The application to the special case of no ion flow is discussed, to study a case similar to thermodynamic equilibrium. An additional factor exp{μ̃ i4/3}, where i is the charge state, is shown to be necessary to fit the CSD. The relationship between the ionization temperature as it appears from the CSD and the electron temperature is given.
Simulation of the low energy H− injector into the National Spallation Neutron Source radio frequency quadrupole accelerator
Authors: Leitner M. A. , Wutte D. C. , Leung K. N.
Published: July 2002

The low energy beam transport system (LEBT) for the National Spallation Neutron Source is required to transport 35 mA of a 65 keV H− ion beam from the ion source to the radio frequency quadrupole accelerator (RFQ) entrance with a normalized root-mean-square emittance < 0.15 pi mm mrad. At a later time, it is anticipated that this beam current will be increased to 70 mA. For this purpose a radio-frequency driven, magnetically filtered multicusp ion source is under development at LBNL. The H− beam extraction from the ion source is being simulated utilizing the three-dimensional (3D) computer code ARGUS. H− ion beam extraction from the ion source requires proper simulation of the extraction of both plasma electrons and the desired H− ions. The goal is to optimize the LEBT system so that the electrons are completely deflected between the first two electrodes and the desired H− beam is properly matched into the RFQ accelerator. The magnetic field in the extraction region is being optimized by using the 3D magnetic code OPERA3D. The performance of the all electrostatic LEBT for the transport of higher currents (>70 mA) is discussed.
New and versatile ultrahigh vacuum scanning tunneling microscope for film growth experiments
Authors: Wilms M. , Schmidt M. , Bermes G. , Wandelt K.
Published: July 2002

With the increasing popularity of the scanning tunneling microscope (STM) in surface science, many ideas for additional and new technical features have been proposed. The work herein contributes to this evolution with a special STM design. The STM described is part of an experimental apparatus for thin film growth investigations in ultrahigh vacuum. Besides the STM, the apparatus includes facilities for thermal desorption spectroscopy and Auger electron spectroscopy and a Kelvin probe for measuring dynamic work function changes. The Kelvin probe is optimized for gas adsorption experiments as well as for in situ film growth investigations during metal deposition. These added features combined with the STM and easy sample transfer yield a new powerful tool for in situ controlled preparation and extensive characterization of thin films. In the present work we describe the novel features of this STM and we demonstrate the efficiency of the whole system by giving a few representative results.
The unfolding of multichord Doppler spectrometry
Authors: Conway N. J. , Carolan P. G. , Tournianski M. R.
Published: July 2002

A 20-chord Doppler spectrometer is used on the START spherical tokamak to record charge-exchange recombination (CXR) spectra (C5+ 5291 Å, n=8→7). “Passive” radiation, mostly from near the plasma edge, is also present, and comes from electron-impact excitation of C5+ as well as C6+ CXR due to thermal neutrals. The relatively wide neutral beam, together with the blending of the passive and active emission, present difficult unfolding problems. These are overcome by imposing physics constraints such as constant ion temperatures on equilibrium magnetic flux surfaces. It is also necessary to model the beam-neutral atom density throughout the viewed equatorial plane. A nonlinear least-squares fitting code, using suitable profile parametrization, gives unfolded Ti(r) and vφ(r) profiles. These are presented along with estimates of the errors on the profiles.
Effect of incorporated nitrogen on the kinetics of thin rapid thermal N2O oxides
Authors: Green M. L. , Brasen D. , Feldman L. C. , Lennard W. , Tang H.-T.
Published: July 2002

We have grown ∼10 nm O2 and N2O-oxides on Si(100) by RTO (rapid thermal oxidation) over the temperature range 800–1200 °C. Although the growth rates of both oxides exhibit Arrhenius behavior over the entire temperature range, the N2O-oxides exhibit a large change in the Arrhenius preexponential factor for oxidation temperatures greater than 1000 °C. Above this temperature, N2O-oxides grow a factor of 5 slower than O2 oxides. Below this temperature, N2O-oxide growth rates approach those of O2-oxides. This growth rate inflection can be explained in terms of N incorporation, which increases with increasing oxidation temperature. The equivalent of one monolayer of N coverage is achieved at about 1000 °C, coincident with the inflection. The incorporated N retards the linear growth of the thin N2O-oxides either by occupying oxidation reaction sites or inhibiting transport of oxidant species to the vicinity of the interface.
Error analysis of Rijnhuizen tokamak project Thomson scattering data
Authors: Beurskens M. N. A. , Barth C. J. , Chu C. C. , Lopes Cardozo N. J.
Published: July 2002

At the Rijnhuizen tokamak project a double pulse multiposition Thomson scattering diagnostic has been operational since 1996. It has been installed for the study of small scale structures in electron temperature (Te) and density (ne). This diagnostic measures Te and ne with high spatial resolution (3 mm full width at half maximum, i.e., 2% of the minor radius) and high accuracy (3%–4% of Te and 2%–3% of ne in the range of 50 eV–6 keV and ne=5×1019 m−3.) In this article an extensive error analysis is performed on both statistical and systematic deviations. It is found that the instrument function of the detection branch has a smoothing effect on the noise. This reduces the statistical error on the Te and ne measurements on each spatial position, because the resolution of the instrument is oversampled. The long tail of the instrument profile of the entire diagnostic has a significant effect on the systematic deviations in the Te and ne determination. However, it does not affect the relative size of the small scale structures on Te and ne, and for this this reason does not hamper the study of these structures.
Miniaturized nondestructive microwave sensor for chickpea moisture measurement
Authors: Abegaonkar Mahesh P. , Karekar R. N. , Aiyer R. C.
Published: July 2002

A miniaturized microstrip ring resonator (MRR) 1 in.×1 in. resonating at fro=10.27 GHz was used as a nondestructive moisture sensor for chickpea kernels (Cicer arietinum L.) for ease in loading and unloading. The change in the resonant frequency (Δfr) of the MRR is a measure of the amount of moisture in the overlaid kernel. The percentage of moisture (M) was varied from 0% (dry) to ∼50% (fully soaked) calculated on a wet weight basis. Δfr increased with M, although not linearly. Three regions were observed in the sensitivity curve. The first region extended from 0%–12%, the central region from 12%–43%, and the saturation region from 43%–50% in moisture content. In the central region the observed Δfr was 574 MHz, whereas in the first and third regions it was 44 and 55 MHz, respectively. The regions in the sensitivity curves indicate different dominant phenomena. A small scatter was observed in the first region, which increased with the increasing percent of moisture content.
Highly charged ions produced in a warm electron beam ion trap
Authors: Ovsyannikov V. P. , Zschornack G. , Grossmann F. , Landgraf S. , Ullmann F. , Werner T.
Published: July 2002

A compact electron beam ion trap (WEBIT) working at room temperature without any cryogenic components is described and experimentally investigated. The trap design is based on permanent magnet technology. For the formation of the electron beam a Pierce electron gun equipped with a cathode of high emissivity is used. The ion trap is created by a compressed electron beam passing through a drift tube system consisting of three sections with corresponding electrical trap potentials. X-ray spectra measured with a Si(Li) semiconductor detector indicate the production of Kr34+, Xe44+, Ce48+, Ir64+, and Hg66+ ions.
An isotopic labeling study of the growth of thin oxide films on Si(100)
Authors: Lu H. C. , Gustafsson T. , Gusev E. P. , Garfunkel E.
Published: July 2002

The mechanism of thin (<8 nm) oxide growth on Si(100) has been studied by high-resolution medium energy ion scattering in combination with oxygen isotope substitution in the T=800–900 °C and 0.1–1 Torr oxygen pressure regime. Isotopic labeling experiments demonstrate that the Deal–Grove model breaks down for these films. In addition to the traditional oxidation reaction at the Si/SiO2 interface, two other spatially specific reactions take place during thermal oxidation: an exchange reaction at the oxide surface and an oxidation reaction in the near-interfacial region.
Negative ion beam production by a microwave ion source equipped with a magnetically separated double plasma cell system
Authors: Tanaka M. , Amemiya K.
Published: July 2002

Filamentless negative ion beam production was investigated with a compact microwave ion source (2.45 GHz). One of the key points for negative ion production is the magnetic configuration. A magnetic filter field to lower electron temperature was generated in a negative ion production cell, which was shielded magnetically from a discharge cell with a magnetic field to couple microwave to plasma. Production of H− beam was studied with this source. H− was extracted through a grid slit (2×16 mm2) from plasma and accelerated to 20–40 keV. H− beam current was measured with a Faraday cup after magnetic mass separation. Continuous H− beam current of 73 μA (0.23 mA/cm2) was obtained with a magnetron power of 700 W. H− beam current was increased around 1.4 times by adding Xe gas to the H2 gas. Other negative ion species, which have a potential for applications to industrial ion beam processing with little charge-up problem, were also investigated. Carbon and hydrocarbon negative ion beams were produced using boron alkoxide (B(OCH3)3) and methane. C2H2− beams (22 μA) were obtained with the alkoxide. C2−(1.6 μA), C2H−(2.3 μA), C2H2−(0.6 μA), and H−(6.9 μA) beams were produced with methane. SiF4 and BF3 were used to generate F−, Si−, SiF3− and B− beams. Beam currents of these ion species were 17, 0.25, 1.5, and 0.03 μA, respectively.
Ultrahigh vacuum compatible all-glass high pressure reaction cell for accurate and reproducible measurement of small reaction rates
Authors: Reichl W. , Rosina G. , Rupprechter G. , Zimmermann C. , Hayek K.
Published: July 2002

An ultrahigh vacuum preparation and analysis chamber with an externally attached high pressure reaction cell is described. The novel all-glass design of the reaction cell allows the study of reaction kinetics in a clean environment but under conditions close to those of conventional catalysis. Reactions on supported metals can be studied on pairs of “real” and “inverse” type model catalysts in the same experimental system under identical sample geometry. No supports or wires are connected to the catalyst while in the high pressure cell, and background activity can therefore be excluded. The experimental setup described required the construction of a special transfer mechanism for in situ manipulation of the samples. As a test reaction, CO hydrogenation has been studied on a transition metal oxide modified rhodium metal surface, and some initial results are presented.
A focused magneto-optical Kerr magnetometer for Barkhausen jump observations
Authors: Puppin E. , Vavassori P. , Callegaro L.
Published: July 2002

We describe a modified version of a magneto-optical Kerr magnetometer which allows measuring the hysteresis loop of a specific portion of the sample surface. The diameter of the sampled area can be optically tuned from several mm down to 15 μm. High quality hysteresis loops can be measured in a few seconds. Strong fluctuations are observed when the spot diameter is reduced to a few hundred microns or less. These fluctuations are related to the well-known Barkhausen noise here investigated for the first time in a systematic way using optical techniques. Preliminary data for epitaxial Fe grown on MgO are presented.
A two-axis micromachined silicon actuator with micrometer range electrostatic actuation and picometer sensitive capacitive detection
Authors: Ayela F. , Bret J. L. , Chaussy J. , Fournier T. , Ménégaz E.
Published: July 2002

This article presents an innovative micromachined silicon actuator. A 50-μm-thick silicon foil is anodically bonded onto a broached Pyrex substrate. A free standing membrane and four coplanar electrodes in close proximity are then lithographied and etched. The use of phosphorus doped silicon with low electrical resistivity allows the application of an electrostatic force between one electrode and the moving diaphragm. This plane displacement and the induced interelectrode variation are capacitively detected. Due to the very low electrical resistivity of the doped silicon, there is no need to metallize the vertical trenches of the device. No piezoelectric transducer takes place so that the mechanical device is free from any hysteretic or temperature dependance. The range of the possible actuation along the x and y axis is around 5 μm. The actual sensitivity is xn=0.54 Å/Hz1/2 and yn=0.14 Å/Hz1/2. The microengineering steps and the electronic setup devoted to design the actuator and to perform relative capacitive measurements ΔC/C=10−6 from an initial value C≈10−13 F are described. The elaborated tests and performances of the device are presented. As a conclusion, some experimental projects using this subnanometric sensitive device are mentioned.
Investigation of the propagation characteristics of excimer lasers using a Hartmann–Shack sensor
Authors: Schäfer Bernd , Mann Klaus
Published: July 2002

For wave front distribution measurements of excimer laser radiation, a Hartmann–Shack wave front sensor with 40×30 subapertures and a field of view adapted to the lateral laser beam profile was utilized. The peak-to-valley wave front resolution is λ/12 and the dynamic range 100λ per subaperture at 248 nm. Time-averaged propagation characteristics were determined for several combinations of resonator configuration and laser medium from the ns down to the fs pulse length regime. Above that, time-resolved measurements were carried out on a KrF excimer laser, showing a reduction of the beam divergence during the laser pulse by a factor of 1.6. This transient behavior is discussed on the basis of a simple geometrical model. The theoretical results are in qualitative agreement with the experiment.
Behavior of electromigration-induced gaps in a layered Al line observed by in situ sideview transmission electron microscopy
Authors: Okabayashi H. , Kitamura H. , Komatsu M. , Mori H.
Published: July 2002

We observed the detailed behavior of electromigration-induced gaps (voids that cause an open circuit) in a submicron-wide Al line layered on a Ti/TiN conductor by in situ sideview transmission electron microscopy. Two types of gaps were observed. The first type is characterized by extensive growth, which may make the Ti/TiN shunt ineffective under use conditions. The gap causes a decrease in the Al drift velocity upstream in the electron flow. This decrease probably results from mass transport through the exposed TiN surface into the gap. The second type of gap did not grow and later healed; therefore, the shunt seems to be effective. The gap had little influence on the drift velocity. Mass was transported directly from the cathode-side Al segment through the gap to the anode-side segment. These mass transport processes may be the causes of resistance oscillation in layered lines.
Enhancing the low field magnetoresistive response in perovskite manganites
Authors: Hwang H. Y. , Cheong S.-W. , Batlogg B.
Published: July 2002

We report significant improvement in the magnetoresistive (MR) response of perovskite manganites for small applied fields by the use of heterostructures with soft ferromagnets. At room temperature, a 5900-fold enhancement of the MR response at 10 Oe in La2/3Ca1/3MnO3 has been achieved using (Mn,Zn)Fe2O4 as the soft ferromagnet. By utilizing soft ferromagnets with various magnetic properties, this technique allows for enormous flexibility in ‘‘designing’’ a desired MR response for the manganites, particularly in low fields.
The dependence of the electrical characteristics of the GaN epitaxial layer on the thermal treatment of the GaN buffer layer
Authors: Lin C. F. , Chi G. C. , Feng M. S. , Guo J. D. , Tsang J. S. , Hong J. Minghuang
Published: July 2002

The GaN buffer layer was grown on the sapphire substrate by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) at 525 °C. The following 1.3 μm epitaxial GaN growth was carried out at 1025 °C. We varied the ramping rate from 12.5 to 100 °C/min to study the quality of the epitaxial GaN. It has been found that the x-ray peak width, photoluminescence (PL) linewidth, Hall mobilities, and carrier concentrations of GaN epitaxial layer strongly depend on the in situ thermal ramping rate. An optimum thermal ramping rate was found to be of 20 °C/min. The maximum mobility is 435 cm2/V s at carrier concentration of 1.7×1017 cm−3. The minimum full width at half maximum (FWHM) of x ray and PL were 5.5 min and 12 meV occur at a ramping rate of 20 °C/min. The decrease of the mobility at high and low ramping rate can be attributed to the thermal stress and the reevaporation of the GaN buffer layer.
Properties of NdBa2Cu3O7−δ thin film prepared by off-axis rf sputtering
Authors: Kim In-Seon , Lee Kyu Won , Park Yong Ki , Park Jong-Chul
Published: July 2002

Thin films of NdBa2Cu3O7−δ(NdBCO) were fabricated on SrTiO3 substrates by an off-axis rf sputtering. Disk shaped targets of 5 cm in diameter were prepared with stoichiometric composition of NdBCO by sintering at 1273 K in air. The sintered body was single phase and exhibited Tc(R=0)=92 K. The effects of several deposition parameters on the superconducting NdBCO thin films, e.g., gas pressure, substrate temperature, oxygen annealing process, and rf power were studied. The x-ray diffraction pattern showed the deposited thin films were highly c-axis oriented without any impurity phase. Thin films with Tc(R=0)=87 K could be obtained reproducibly at optimized conditions. Critical current density (Jc) of the patterned thin film was 106–107 A/cm2 at low temperature.
Thermal annealing characteristics of Si and Mg-implanted GaN thin films
Authors: Chan J. S. , Cheung N. W. , Schloss L. , Jones E. , Wong W. S. , Newman N. , Liu X. , Weber E. R. , Gassman A. , Rubin M. D.
Published: July 2002

In this letter, we report the results of ion implantation of GaN using 28Si and 24Mg species. Structural and electrical characterizations of the GaN thin films after thermal annealing show that native defects in the GaN films dominate over implant doping effects. The formation energies of the annealing induced defects are estimated to range from 1.4 to 3.6 eV. A 40 keV 1014 cm−2 Mg implant results in the decrease of the free-carrier concentration by three orders of magnitude compared to unimplanted GaN up to an annealing temperature of 690 °C. Furthermore, we have observed the correlation between these annealing-induced defects to both improved optical and electrical properties.
Explanation for the polarity dependence of breakdown in ultrathin silicon dioxide films
Authors: DiMaria D. J.
Published: July 2002

The polarity dependence observed for destructive breakdown of ultrathin silicon dioxide films is shown to be directly correlated to the oxide degradation caused by hot-electron-induced defect production. The probability of defect generation is also demonstrated to depend on the Fermi level position at the anode/oxide interface. The specific anode interface, whether substrate/oxide or gate/oxide, is shown to have no direct relationship to the degradation rate.
Emission from discrete levels in self-formed InGaAs/GaAs quantum dots by electric carrier injection: Influence of phonon bottleneck
Authors: Mukai Kohki , Ohtsuka Nobuyuki , Shoji Hajime , Sugawara Mitsuru
Published: July 2002

We studied the excitation-power dependence of photoluminescence (PL) spectra and the current dependence of electroluminescence (EL) spectra of self-formed InGaAs/GaAs quantum dots. We observed five peaks in the PL and EL spectra. From the size dependence of the peak interval and the carrier-density dependence of peak energy and peak intensity, we assigned the peaks to the discrete energy levels in the quantum dots. We simulated the EL spectra with rate equations, taking into account the carrier relaxation between the discrete levels, and found that the relaxation lifetime was about 10–100 ps.
Hall measurements and contact resistance in doped GaN/AlGaN heterostructures
Authors: Asif Khan M. , Shur M. S. , Chen Q.
Published: July 2002

We report on doped AlGaN/GaN heterostructures with very high values of the sheet electron concentration (up to approximately 1.5×1013 cm−2), high Hall mobility (on the order of 800 cm2/Vs) and high sheet concentration-mobility product (up to approximately 1016 1/Vs). Transmission line model measurements of the contact resistance to these layers show that series resistance is considerably reduced by doping the GaN channel. A contact resistance of 2.3 Ω mm is demonstrated for the structure with the highest sheet carrier concentration, which corresponds to ≊8.8×10−5 Ω cm2 specific contact resistance.
Theory of microwave intermodulation in a high-T
c superconducting microstrip resonator
Authors: Dahm T. , Scalapino D. J.
Published: July 2002

We calculate the intermodulation power for a superconducting microstrip resonator arising from the intrinsic microscopic nonlinearities. We focus on high-Tc superconductors where it is believed that the order parameter has dx2−y2 symmetry. A characteristic upturn of the intermodulation power is found at low temperatures. We discuss different ways to reduce intermodulations by changing the geometry of the microstrip.
Reliability of gate oxide grown on nitrogen-implanted Si substrates
Authors: Lin Chuan , Chou Anthony I. , Choudhury Prasenjit , Lee Jack C. , Kumar Kiran , Doyle Brian , Soleimani Hamid R.
Published: July 2002

Direct nitrogen implant into Si substrate prior to gate oxidation has been proposed to grow multiple gate oxide thicknesses on a single wafer. In this letter, we have studied the reliability of gate oxide grown on nitrogen-implanted Si substrate. The effects of implant doses, sacrificial oxide thicknesses, and gate oxide thicknesses on gate oxide reliability have been investigated. It was found that there is a tradeoff between oxide thickness control and gate oxide reliability.
Effect of thermal annealing on optical emission properties of low-temperature grown AlGaAs/GaAs multiple quantum wells
Authors: Feng W. , Chen F. , Wang W. X. , Cheng W. Q. , Yu Y. , Huang Q. , Zhou J. M.
Published: July 2002

We have investigated the effect of thermal annealing on optical emission properties of low-temperature (LT) grown AlGaAs/GaAs multiple quantum wells (MQWs) by using photoluminescence (PL) spectroscopy. For comparison, the results on normal-temperature (NT) grown MQWs implanted with protons are also presented. The LT sample was grown by molecular beam epitaxy at 310 °C. The as-grown LT-MQWs show moderately strong PL. Upon annealing at 600 °C, the PL intensity of the LT-MQWs is dramatically quenched, in sharp contrast to the large increase in PL intensity of the implanted NT-MQWs. The quenching of PL intensity in the LT-MQWs is attributed to the formation of arsenic clusters that fast trap photoexcited carriers. In addition, an enhancement in the interface intermixing and roughening induced by thermal annealing has also been observed in the LT-MQWs.
Medium-wavelength, normal-incidence, p-type Si/SiGe quantum well infrared photodetector with background limited performance up to 85 K
Authors: Kruck P. , Helm M. , Fromherz T. , Bauer G. , Nützel J. F. , Abstreiter G.
Published: July 2002

The detector characteristics of a pseudomorphic p-type Si0.64Ge0.36/Si quantum well infrared photodetector are reported. The device exhibits a photoresponse between 3 and 8 μm with a peak responsivity of Rp=76 mA/W, at a peak wavelength of λp=5 μm, resulting in a detectivity as high as Dλ*=2×1010 cm√Hz/W at a temperature of T=77 K. Background limited infrared performance is achieved up to T=85 K. Investigation of the polarization dependence shows that in-plane polarized radiation produces the largest photoresponse, thus making normal-incidence detection feasible. The relevant optical transitions are analyzed on the basis of a self-consistent 6-band Luttinger–Kohn calculation including the in-plane dispersion.
Electron-beam induced crystallization transition in self-developing amorphous AlF3 resists
Authors: Chen G. S. , Boothroyd C. B. , Humphreys C. J.
Published: July 2002

Transmission electron microscopy is used to investigate electron-induced crystallization of thermally evaporated amorphous AlF3(a-AlF3). It is shown that this material undergoes a very complicated crystallization process with three crystalline substances (Al, AlF3, and Al2O3) formed as the dose increases. The sequence of the crystallization is highly sensitive to the presence of water, which inhibits radiolytic dissociation of a-AlF3 into Al and fluorine, reduces the dose required for the crystallization of a-AlF3, and causes the transformation of AlF3 into Al2O3.
Optical control of coherent optical phonons in bismuth films
Authors: Hase M. , Mizoguchi K. , Harima H. , Nakashima S. , Tani M. , Sakai K. , Hangyo M.
Published: July 2002

Interference of impulsively excited coherent phonons in semimetals has been studied by using a double-pulse pump–probe technique. Enhancement of the oscillation amplitude of an A1g mode is observed when the separation time of the double-pulse is matched to the period of the phonon oscillation, and a cancellation is observed when the separation time is adjusted to half the period of the phonon oscillation. The amplitude after the second pulse shows a sinusoidal dependence as a function of the separation time, and this dependence is explained in terms of a superposition of two coherent phonon oscillations. In addition, not only the A1g mode but also an Eg mode have been observed by electro-optic sampling.
Arsenic precipitation from thin surface layers of low-temperature grown GaAs
Authors: Kiehl R. A. , Yamaguchi M. , Ohshima T. , Saito M. , Yokoyama N.
Published: July 2002

Arsenic precipitation from a thin, 100-nm surface layer of GaAs grown at low temperature (LT) by molecular beam epitaxy is investigated. The precipitate depth distribution is examined for different rapid thermal annealing cycles. It is found that the precipitate distribution can tail a long distance into the underlying stoichiometric GaAs layer, depending on the peak annealing temperature. The distribution for an 800 °C anneal is virtually unaffected by a prior low temperature ‘‘soak’’ at 600 °C, thus showing that the precipitation is insensitive to the initial point defect concentrations in this temperature range. The relevance of these results to the precipitation process and to the use of thin LT layers in device applications is discussed.
Improved stability against light exposure in amorphous deuterated silicon alloy solar cell
Authors: Sugiyama S. , Yang J. , Guha S.
Published: July 2002

We have studied light-induced degradation in hydrogenated and deuterated amorphous silicon alloy solar cells. Replacing hydrogen with deuterium in the intrinsic layer of the cell improves stability against light exposure. Possible explanations for the improved stability are discussed.
Room-temperature near-band-edge photoluminescence from CuInSe2 heteroepitaxial layers grown by metalorganic vapor phase epitaxy
Authors: Chichibu Shigefusa
Published: July 2002

High purity CuInSe2 heteroepitaxial layers were successfully grown by low-pressure metalorganic vapor phase epitaxy. A certain amount of excitonic absorption was found in the optical absorption spectra even at room temperature (RT). A predominant near-band-edge photoluminescence peak was observed at RT for the first time from a (001) oriented epilayer grown on a GaAs(001) substrate. The epilayers were grown in order to carry out a systematic investigation of intrinsic defects and intentional dopants in the matrix.