bluuebunny/crossref_metadata_2025 huggingface dataset:
Generation of static pressures above 2.5 megabars in a diamond-anvil pressure cell
Authors: Goettel Kenneth A. , Mao Ho-kwang , Bell Peter M.
Published: July 2002

A static pressure of 2.75 Mbars has been generated in a diamond-anvil pressure cell. This pressure is 1 Mbar higher than the highest static pressure previously produced in a laboratory, 1.72 Mbar by Mao and Bell [Science 200, 1145 (1978)]. Improvements in the geometry of the cut of beveled anvil surfaces, selection of diamond anvils for a high concentration of nitrogen platelets, and modifications in the design of the supporting cell for the diamond anvils resulted in the attainment of 2.75 Mbars. Pressures from 1 bar to 1.85 Mbar were measured by the ruby fluorescence method. The ruby fluorescence, however, was found to diminish in intensity with increasing pressure and to become undetectable at 1.85 Mbar. Pressures above 1.85 Mbar were calculated on the assumption of elastic behavior for the diamond anvils in two ways: (1) by extrapolation of the relationship between central pressure and force applied to the anvils, and (2) by extrapolation of radial pressure profiles. Three lines of evidence confirm that the diamond anvils behaved elastically, rather than deforming plastically, to the highest pressure achieved. The design improvements reported in this paper should result in the acquisition of a wide range of data in diamond cells at pressures above 1 Mbar, pressures at which virtually no static data have been obtained. Pressures substantially above 2.75 Mbars are probably attainable with the present design of the diamond-cell apparatus.
Neutron spectrometry at JET (invited)
Authors: Jarvis O. N. , Gorini G. , Hone M. , Källne J. , Sadler G. , Merlo V. , van Belle P.
Published: July 2002

Measurements of the energy spectra of fusion neutrons is accorded a prominent position in the neutron diagnostics program at JET. The nature of the information on plasma properties which it is hoped will be obtained is discussed, as is the availability of suitable instruments and techniques for spectrometry on thermonuclear plasmas. Of these instruments, only the 3He ionization chamber has, so far, been successfully exploited; the lessons learned regarding its performance are outlined and the results obtained for ohmically and ICRF-heated plasmas are presented. It is shown that the deuterium ion energy distributions appear to be Maxwellian for all plasmas studied, that central ion temperatures have been obtained on a shot-by-shot basis which agree well with corresponding values obtained by neutral particle analysis and that the deuteron-to-electron density ratio in the plasma is approximately 0.5.
Effects of internal and external magnetic fields on the characteristics of a magnetic multipole plasma source
Authors: Tanaka Shigeru , Akiba Masato , Horiike Hiroshi , Matsuoka Mamoru , Ohara Yoshihiro , Okumura Yoshikazu
Published: July 2002

Influences of an externally produced axial magnetic field and the field produced by the filament current on the performance of a magnetic multipole plasma source were experimentally studied using a high-proton-yield ion source developed for the JT-60 NBI. It was shown that both of the fields give significant effects on the arc discharge characteristics, the arc efficiency, and the plasma uniformity. The probe measurement showed that the change of the arc efficiency caused by the field is closely related to the change of the ion saturation current density distribution on the extraction grid. The change of the distribution can be explained by the effect of the magnetic field on the orbits of the primary electrons emitted from the filaments. On the basis of the experimental results, a permissible level of the external field in the source was evaluated to be ±5 G.
Two new planar coil designs for a high pressure radio frequency plasma source
Authors: Munsat T. , Hooke W. M. , Bozeman S. P. , Washburn S.
Published: July 2002

Two planar coil designs for a high pressure rf plasma source are investigated using spectroscopic techniques and circuit analysis. In an Ar plasma a truncated version of the commonly used ‘‘spiral’’ coil is found to produce improvements in peak electron density of 20% over the full version. A coil with figure-8 geometry is found to move plasma inhomogeneities off of center and produce electron densities comparable to the spiral coils. Both of these characteristics are advantageous in industrial applications. Coil design characteristics for favorable power coupling are also determined, including the necessity of closed hydrodynamic plasma loops and the drawback of closely situated antiparallel coil currents.
CAMAC time-of-flight analyzer for molecular beam diagnostics
Authors: Huisken Friedrich , Pertsch Thomas
Published: July 2002

Time-of-flight (TOF) analysis of supersonic molecular beams is accomplished by a computer-controlled TOF analyzer incorporated into a CAMAC module. The measured arrival times are stored in a LeCroy histogramming memory module and transferred to a minicomputer for further processing. The system features four independent multichannel analyzers which can be selected by program. Each unit has 4096 24-bit channels. Dwell times are programmable between 1 and 255 μs and the maximum counting rate is 1 MHz. The system is intended for ordinary single pulse or pseudorandom TOF analysis and can also be used in photodissociation experiments employing pulsed lasers. The calibration of the TOF analyzer is described and exemplary measurements are presented.
Comparison of trapping–detrapping properties of mobile charge in alkali contaminated metal-oxide-silicon carbide structures
Authors: Raynaud C. , Autran J. L. , Briot J. B. , Balland B. , Bécourt N. , Billon T. , Jaussaud C.
Published: July 2002

We have performed thermally stimulated ionic current measurements on aluminum-oxide-silicon carbide (3C and 6H polytypes) capacitors to study the trapping–detrapping properties of alkali mobile ions at the oxide interfaces. Two traps, at ∼1.0 and ∼1.4 eV, have been detected at the oxide/SiC interface; only one (at ∼1.0 eV) is present at the aluminum/oxide interface. Studies of the energy dependence of the oxide traps with the electric field are reported here for comparison with silicon structures. A numerical method has been used to calculate the energy distributions of these traps, which reveal some differences between the two kinds of structures.
Novel system for picosecond photoemission spectroscopy
Authors: Haight R. , Silberman J. A. , Lilie M. I.
Published: July 2002

This article describes a laser-based source and detection scheme for performing time-resolved photoemission studies of materials. The pulsed laser source produces intense picosecond pulses of coherent radiation that are nearly continuously tunable from the near infrared to photon energies up to 13 eV. To achieve high sensitivity, a novel multianode time-of-flight spectrometer has been built that generates an angularly resolved intensity versus kinetic energy spectrum with better than 100-meV resolution. The source and detector provide an opportunity to study the electronic dynamics of excited systems on a picosecond time scale.
Voltage offsets in (Pb,La)(Zr,Ti)O3 thin films
Authors: Pike G. E. , Warren W. L. , Dimos D. , Tuttle B. A. , Ramesh R. , Lee J. , Keramidas V. G. , Evans J. T.
Published: July 2002

Cooling (Pb,La)(Zr,Ti)O3 films from their pulsed laser deposition temperature in a reducing ambient yields a voltage offset in the polarization–voltage characteristics. Reversing the as-processed polarization at 120 °C nearly removes the offset. By reversing the polarization at room temperature and either heating the film at zero voltage or illuminating the film with UV light, the offset can be partially changed. All changes are recoverable using the same processes with opposite polarity polarization. This behavior is explained by a process-induced accumulation of oxygen vacancies at one interface, oxygen vacancy defect-dipole complexes throughout the film, and trapping of free electrons at the interface of positive polarization. Voltage offset and shift effects are not observed in films cooled in 1 atm of oxygen
Conception and performance of the new Lagrippa facility
Authors: Lamy Th. , Lamboley G. , Hitz D. , Andrä H. J.
Published: July 2002

A new Lagrippa facility has been constructed for the production of high quality beams of multicharged ions with energies of 1–25 q keV. The machine is based on the new 10 GHz, Caprice ECR-ion source which operates partially on the second harmonic. A new extraction optics for ECR sources with variable electrode distance has been employed which allows high currents at an emittance of less than 40 π mm mrad (corresponding to a beam spot of a diameter less than 4 mm with a divergence ≤±20 mrad). Together with an acceleration–separation–deceleration scheme this machine furnishes beam currents of 11 μA O7+ at 15 q keV, 80 pA Ar17+ at 20 q keV, 6 pA Ar17+ at 20 q keV, and a significant current of Kr31+. Further details of the conception of the machine, its performance, and the first experiments up to June 1989 will be presented.
Giant ion sources of neutral-beam injectors for fusion (invited)
Authors: Kunkel Wulf B.
Published: July 2002

All large tokamak fusion experiments today use auxiliary heating by multimegawatt beams of neutral isotopes of hydrogen injected with energies in the neighborhood of 100 keV per atom. This requires reliable operation of large ion souces, each delivering many tens of amperes of protons or deuterons, and soon even tritons. For meaningful experiments these sources must operate with pulse durations measured in seconds, although the duty factor may still be small. It is remarkable that the successful sources developed in Europe, Japan, and the U. S. are all very similar in basic design: the plasma is produced by diffuse low-pressure high-current discharges in magnetic multipole ‘‘buckets’’ with distributed thermionically emitting cathodes. This article briefly reviews the principal considerations and the basic physics of these sources, and summarizes the collective experience to-date and describes the impressive recent performance of the U. S. Common Long Pulse Source, as a specific example.
Direct injection supersonic cluster beam source for FT-ICR studies of clusters
Authors: Maruyama Shigeo , Anderson Lila R. , Smalley Richard E.
Published: July 2002

A miniaturized pulsed supersonic beam source has been developed using laser vaporization of a computer-controlled target disk, producing intense beams of cluster ions with excellent repeatability and control. Due to its small size and narrow pulse width, the entire source is adequately pumped by a single 170 ℓ /s turbopump. The resultant vacuum quality permits this source to be attached to a Fourier transform ion cyclotron resonance apparatus (FT-ICR) such that the supersonic cluster ion beam is directly injected. The result is a powerful but simple FT-ICR instrument of wide applicability. The new source is suited as well for a variety of other uses such as molecular beam epitaxy.
Motional Stark effect polarimetry for a current profile diagnostic in DIII-D
Authors: Wróblewski D. , Burrell K. H. , Lao L. L. , Politzer P. , West W. P.
Published: July 2002

Motional Stark effect produces large net linear polarization of Hα emission from neutral beams in tokamaks. Measurement of the polarization direction permits determination of the local magnetic field pitch angle. Design of a single point, spatially scannable, high-sensitivity polarimeter installed on DIII-D is described. Excellent signal-to-noise ratio with good temporal and spatial resolution was obtained in preliminary measurements of magnetic field pitch angle.
Large ion volume time-of-flight mass spectrometer with position- and velocity-sensitive detection capabilities for cluster beams
Authors: de Heer Walt A. , Milani Paolo
Published: July 2002

We have developed and tested a high-performance time-of-flight mass spectrometer for clusters in a molecular beam. Several important improvements over conventional designs have been implemented that include a large ionization volume, a perfected ion steering system and a large area efficient ion detector. Cluster ions that are produced within the 200-cm3 ion volume can be simultaneously detected over a size range of from 1 to about 10 000 amu with a resolution of about 1000. The mass spectrometer can also be operated in a position-sensitive mode for cluster beam deflection measurements, and in a velocity-sensitive mode to determine the cluster velocities. The performance of the spectrometer is demonstrated with Al and Fe clusters. We present mass spectra of cluster beams and also velocity, and magnetic and electric deflection measurements of collimated iron and aluminum cluster beams.
A high-resolution x-ray fluorescence spectrometer for near-edge absorption studies
Authors: Stojanoff V. , Hämäläinen K. , Siddons D. P. , Hastings J. B. , Berman L. E. , Cramer S. , Smith G.
Published: July 2002

A high-resolution fluorescence spectrometer using a Johann geometry in a backscattering arrangement was developed. The spectrometer, with a resolution of 0.3 eV at 6.5 keV, combined with an incident beam, with a resolution of 0.7 eV, form the basis of a high-resolution instrument for measuring x-ray absorption spectra. The advantages of the instrument are illustrated with the near-edge absorption spectrum of dysprosium nitrate.
Seeded supersonic alkali cluster beam source with refilling system
Authors: Bewig L. , Buck U. , Mehlmann Ch. , Winter M.
Published: July 2002

A supersonic sodium cluster beam source with a refilling system is described in detail. Due to the external refilling system a new loading of the oven, which is designed for high-temperature application at 800 °C, is accomplished very fast and interrupts the measuring process only for 1–2 h. Additional purification of the alkali metal in the reservoir allows the usage of standard quality sodium samples.
High-field, high-pressure, and low-temperature magneto-optical apparatus using a diamond anvil cell
Authors: Matsuda Y. , Kuroda N. , Nishina Y.
Published: July 2002

An optical system equipped with a diamond anvil cell is constructed for studying the optical properties of materials under the simultaneous conditions of high magnetic field, high pressure, and low temperature. As an application of this apparatus, the magnetophotoluminescence due to the exciton state in Cd0.9Mn0.1Se is measured at 4.2 K under 1.25 GPa in the presence of magnetic fields up to 23 T.
Aircraft-borne, laser-induced fluorescence instrument for the in situ detection of hydroxyl and hydroperoxyl radicals
Authors: Wennberg P. O. , Cohen R. C. , Hazen N. L. , Lapson L. B. , Allen N. T. , Hanisco T. F. , Oliver J. F. , Lanham N. W. , Demusz J. N. , Anderson J. G.
Published: July 2002

The odd-hydrogen radicals OH and HO2 are central to most of the gas-phase chemical transformations that occur in the atmosphere. Of particular interest is the role that these species play in controlling the concentration of stratospheric ozone. This paper describes an instrument that measures both of these species at volume mixing ratios below one part in 1014 in the upper troposphere and lower stratosphere. The hydroxyl radical (OH) is measured by laser induced fluorescence at 309 nm. Tunable UV light is used to pump OH to the first electronic state (Ã 2Σ+(v′=1) ← X̃2Π3/2 (v″=0)) near 282 nm. The laser light is produced by a high-repetition rate pulsed dye-laser powered with all solid-state pump lasers. HO2 is measured as OH after gas-phase titration with nitric oxide. Measurements aboard a NASA ER-2 aircraft demonstrate the capability of this instrument to perform reliably with very high signal-to-noise ratios (≳30) achieved in short integration times (< 20 sec).
State of the art of radio-frequency ion sources for space propulsiona)
Authors: Groh K. H. , Loeb H. W.
Published: July 2002

After 30 years of research, development, and qualification work of radio-frequency ion thrusters (RIT), the RIT 10 engine has now been tested successfully in space onboard the European Retrievable Carrier (EURECA). RIT 10 produces a thrust of 10 mN and is designed for north–south stationkeeping of geosynchronous satellites. Besides, the European Space Agency (ESA/ESTEC) plans to implement ion propulsion in their technological satellite ARTEMIS, where ion thrusters shall be used operationally for north–south stationkeeping. In parallel, development and tests of a scaled-up 50 mN engine RIT 15 have been continued successfully with xenon and krypton as propellants. A large ion engine with a 35 cm ionizer diameter, the RIT 35, has been developed for primary propulsion of interplanetary probes aiming at a thrust level in the 250 mN range. A laboratory prototype has been subjected to extensive testing and performance mapping. Recently, this work has been continued in European cooperation due to a redirection of contracts. The ion source diameter has been reduced to 26 cm but the performance should be kept using a British high perveance grid at the German rf-ion source.
Optical design and performance of the inelastic scattering beamline at the National Synchrotron Light Source
Authors: Kao C.-C. , Hamalainen K. , Krisch M. , Siddons D. P. , Oversluizen T. , Hastings J. B.
Published: July 2002

Phase I of the X21 beamline at the National Synchrotron Light Source was commissioned during 1993. The research program at the X21 beamline is focused on the study of electronic excitations in condensed matter with total energy resolution of 0.1–1.0 eV. The source is a 27-pole hybrid wiggler. A water-cooled horizontal focusing Si(220) monochromator and a spherically bent Si(444) analyzer were installed and commissioned. At 8 keV the energy resolution of the monochromator is about 0.7 eV, and the energy resolution of the analyzer is about 0.1 eV. Results from several selected experiments are also discussed.
Growth of metastable Ge1−xSnx/Ge strained layer superlattices on Ge(001)2×1 by temperature-modulated molecular beam epitaxy
Authors: Gurdal O. , Hasan M.-A. , Sardela M. R. , Greene J. E. , Radamson H. H. , Sundgren J. E. , Hansson G. V.
Published: July 2002

Single-crystal metastable diamond-structure Ge1−xSnx/Ge strained-layer superlattices (SLS) with x up to 0.24 (the equilibrium solid solubility of Sn in Ge is <0.01) have been grown on Ge(001)2×1 substrates using temperature-modulated molecular-beam epitaxy with maximum growth temperatures Ts≤150 °C. In situ reflection high energy electron diffraction combined with postdeposition high-resolution x-ray diffraction (HR-XRD) and cross-sectional transmission electron microscopy results show that the Ge1−xSnx(001)2×1 alloy and Ge(001)2×1 spacer layers are commensurate. In fact, the alloy layers are essentially fully strained with an average in-plane lattice constant mismatch of (1±2)×10−5 and an average tetragonal strain in the growth direction of (1.39±0.03)×10−2 as determined from HR-XRD reciprocal-space lattice maps obtained using asymmetric (113) reflections. ω broadening of the zero-order SLS peak was only 30.1 arc sec FWHM, indicating that the degree of mosaicity in these structures is negligible. The intensities and positions of the satellite reflections and finite-thickness interference fringes in HR-XRD 004 rocking curve ω-2θ scans are in good agreement with simulated patterns obtained using a dynamical scattering model.
The electromagnetic modes of a helical resonator
Authors: Diehl Robert , Wheatley David M. , Castner T. G.
Published: July 2002

The electric fields of the helical resonator, both of the fundamental frequency and the odd harmonics up to the eleventh, have been probed using metallic copper and heavily doped Si:P disks by measuring the relative frequency shift Δf/f and the change in quality factor Δ(1/Q) with a network analyzer after insertion of the disk as a probe mounted on a dielectric support rod which could be translated along the z axis of the helix with a micrometer drive. The magnetic field component Hz was probed using the paramagnetic free radical DPPH and a simple transmission electron spin resonance (ESR) spectrometer. The Δf/f results were compared with calculated results using the Bethe–Schwinger expression and the plasma result for the change in dielectric response, while the Δ(1/Q) results were compared with a standard loss expression. The results, except for the role of the short but including the metallic disk thickness and diameter dependence, agree with the fields given by Pierce for an infinite helical current sheet, when adapted to the standing wave form. The ESR results demonstrate the optimum position for a paramagnetic sample. The ESR amplitude versus probe insertion depth is in qualitative agreement with an expression by Wilmshurst et al., but also exhibits an unexplained sign change.
Microwave differential dilatometer measures 10−12 m, at 1 Hz
Authors: Aschero G. , Mango F. , Gizdulich P.
Published: July 2002

To check and measure the converse piezoelectric effect in bone samples, we had to detect displacements in the range of 1–100 pm with three kinds of restrictions: (1) the biological nature of the samples imposes severe limits in selecting a suitable device and method; (2) such a method has to take into account some clinical applications to which the experiment is devoted; (3) the piezoelectric behavior of bone samples is particularly interesting at low frequencies, around 1 Hz. For such reasons we modified an existing dilatometer based on a microwave differential spectrometer. A 14 GHz klystron, linearly modulated in frequency by a triangular 50 Hz voltage applied to the repeller, is connected, via magic T, to two identical cavities tunable around 14 GHz and whose resonance curves are recorded by crystal detectors. When one of the two cavities changes its height according to the length variations of the sample, its resonance frequency varies resulting in a shift of the resonant curve with respect to the resonance curve of the other cavity acting as reference. The comparison between the cavities’ responses is performed by a pulse technique transforming the frequency shifts into time intervals, that are then converted into dc voltages. The differential character of this measurement avoids the need for the microwave source stabilization. The relative shift in frequency is measured with an accuracy better than 500 Hz. This accuracy allows us to measure displacements smaller than 7 nm in the cavity’s height. After 2 h of warmup, thanks to the differential arrangement of the system, thermal or other drifts are not detectable within a lapse of time of 12 h. This feature allows coherent signal averaging over long periods. With a piezoelectric ceramic stack moving 100 pm in square wave fashion at 50 mHz we found that the signal to noise ratio was 20 dB after 1000 cycles of signal averaging, when our bandpass filter was tuned at 1 Hz. In conclusion, this system can detect periodic displacements as small as 1 pm in a short time and reliably. Due to the operational simplicity and stability, at room temperature and humidity, the device is suitable for dilatometric measurements on biological samples.
A framed monochromatic x-ray microscope for ICF (invited)
Authors: Marshall F. J. , Oertel J. A.
Published: July 2002

The Laser Fusion Experiments Groups from the Laboratory for Laser Energetics (LLE) and the Los Alamos National Laboratory (LANL) have jointly developed an instrument capable of simultaneously space-, time-, and spectrally resolving x-ray emission from inertial confinement fusion (ICF) targets. Uses of the instrument include framed imaging of line emission from fuel or shell dopants and monochromatic backlighting. The x-ray imaging is accomplished with a Kirkpatrick-Baez (KB)-type four-image microscope, which has a best spatial resolution of ∼5 μm and a sensitive energy range of ∼2–8 keV. Time-resolved x-ray images are obtained with a pair of custom framing cameras, each of which records two of the four images in two independent 80-ps time intervals. In addition, the energy range of the images can be restricted to a narrow (monochromatic) spectral range (∼10–100 eV) by the introduction of diffracting crystals. This technique has been demonstrated with an e-beam-generated dc x-ray source, and at the LANL Trident laser facility and the LLE OMEGA laser facility with x-rays from laser-produced plasmas.
Fast tokamak plasma flux and electron density reconstruction technique
Authors: Chiang K. L. , Hallock G. A. , Wootton A. J. , Wang L.
Published: July 2002

Density profiles in TEXT-U are obtained using a vertical viewing far-infrared (FIR) interferometer. To obtain the local (inverted) density, we have developed a simple analytic model of the plasma equilibrium configuration which is faster than EFIT (a flux surface reconstruction program) and can be easily computed between discharges. This analytic solution of the Grad–Shafranov equation is valid as long as the pressure p is a function of poloidal flux ψ, i.e., p=p(ψ). The procedure incorporates both magnetic and FIR density data to solve the Grad–Shafranov equation, and provides a density profile which is self-consistent with the reconstructed equilibrium flux surfaces. Examples are presented.
A versatile Kelvin probe for dynamic work function change measurements during gas adsorption and in situ film growth experiments
Authors: Schmidt M. , Nohlen M. , Bermes G. , Böhmer M. , Wandelt K.
Published: July 2002

In the present work, we describe a new Kelvin probe for dynamical work function change (ΔΦ) measurements in ultrahigh vacuum. The construction of the Kelvin probe is especially optimized to meet the experimental conditions for gas-adsorption experiments as well as for in situfilm growth investigations during metal deposition. This is realized by a new setup which enables a change of the geometrical orientation of the vibrating reference electrode with respect to the sample surface. The Kelvin probe combined with thermal desorption spectroscopy, Auger electron spectroscopy, and scanning tunneling microscopy facilities, forms a powerful tool for film growth analysis. The performance of the instrumentation is demonstrated with some representative test experiments for copper deposition on Pt(111).
Nuclear magnetic resonance in a diamond anvil cell at very high pressures
Authors: Pravica Michael G. , Silvera Isaac F.
Published: July 2002

We describe a novel design to study the nuclear magnetic resonance (NMR) properties of materials at high pressure in a diamond anvil cell. A split gasket is used to pressurize the sample and a single turn coil couples the rf field with the sample. Due to the large filling factor, this method has a significantly increased sensitivity compared to previously used techniques and should allow NMR study of materials in a diamond anvil cell into the megabar region. We demonstrate the system with a measurement of the spin-lattice relaxation (T1) of cyclohexane as a function of pressure at 79 K up to 9.7 GPa. We have also pressurized a sample of hydrogen to 26 GPa.
Electron cyclotron resonance sources: Historical review and future prospects (invited)
Authors: Geller R.
Published: July 2002

Low charge state electron cyclotron resonance ion source (ECRIS) work since 1965 and high charge state ECRIS since 1974. These ECR sources are categorized into three main sections: (1) Low charged ion (ECRIS) inside simple magnetic mirror or Bucket configurations. (2) High charged ion ECRIS inside min-B mirror configurations. (3) Short pulsed ECRIS with highly charged ions where the ion confinement is disturbed for a short while, which allows the extraction of intense ion pulses. Future prospects are based on rational scaling of the magnetic confinement including high B modes, by increasing the radio frequency (rf) frequency and ECR magnetic field. In this case, charge exchange has to be minimized and plasma instabilities have to be avoided. However, clever empirical tricks lead also to outstanding not always predicted improvements. Let us cite: optimized rf plasma coupling, electron guns, gas mixing, wall coating, biased electrodes, and more recently multiple ECR frequency heating. ECRIS have not yet achieved their optimal possibilities. Let us wait for the next generation of superconducting ECRIS and the possible use of subcentimeter waves.
Compact low-energy electron microscope for surface imaging
Authors: Adamec P. , Bauer E. , Lencová B.
Published: July 2002

A compact electrostatic low-energy electron microscope is described. The electron optical system of the microscope was optimized in order to reduce the number of correcting elements and thus to simplify construction and operation of the instrument. The lenses are biased so that the specimen can be kept close to ground potential. The electrostatic tetrode objective lens allows to achieve a resolution below 10 nm at 10 eV. For beam separation, a magnetic sector with small deflection angle was used. The separator requires only one coil winding for excitation and does not introduce significant aberrations. A three-lens projector system enables magnifications from 600 to 60 000 times. The microscope was built and tested. The weight of the whole mumetal shielded instrument is less than 20 kg so that it can be attached to almost any specimen chamber via a 6 in. Con-flat flange. The microscope was operated in the mirror, low-energy electron microscopy, and low-energy electron diffraction modes. In the experimental system without vibration damping, 30 nm resolution was demonstrated.
Divertor impurity monitor for the International Thermonuclear Experimental Reactor
Authors: Sugie T. , Ogawa H. , Nishitani T. , Kasai S. , Katsunuma J. , Maruo M. , Ebisawa K. , Ando T. , Kita Y.
Published: July 2002

The divertor impurity monitoring system of the International Thermonuclear Experimental Reactor has been designed. The main functions of this system are to identify impurity species and to measure the two-dimensional distributions of the particle influxes in the divertor plasmas. The wavelength range is 200–1000 nm. The viewing fans are realized by molybdenum mirrors located in the divertor cassette. With additional viewing fans seeing through the gap between the divertor cassettes, the region approximately from the divertor leg to the x point will be observed. The light from the divertor region passes through the quartz windows on the divertor port plug and the cryostat, and goes through the dog-leg optics in the biological shield. Three different type of spectrometers: (i) survey spectrometers for impurity species monitoring, (ii) filter spectrometers for the particle influx measurement with the spatial resolution of 10 mm and the time resolution of 1 ms, and (iii) high dispersion spectrometers for high resolution wavelength measurements are designed. These spectrometers are installed just behind the biological shield (for λ<450 nm) to prevent the transmission loss in fiber and in the diagnostic room (for λ⩾450 nm) from the point of view of accessibility and flexibility. The optics have been optimized by a ray trace analysis. As a result, 10–15 mm spatial resolution will be achieved in all regions of the divertor.
A high precision method for measuring very small capacitance changes
Authors: Ashrafi Ashkan , Golnabi Hossein
Published: July 2002

A novel method for measuring very small capacitance changes based on capacitance-to-phase angle conversion is introduced in this article. This new method is the improved or linearized version of the nonlinear capacitance-to-phase angle conversion method. The main features of this scheme are the very good linearity, extremely high stray immunity and a very high resolution. The experimental results of the prototype version of this scheme have also been reported. By using this prototype and a simple capacitive transducer, a minimum detectable distance of about 16 nm can be achieved. This means that a capacitance change of about 0.7 fF (0.7×10−15 F) in a capacitance of 22 pF can be resolved, so the minimum resolvable relative capacitance is about 32 ppm. By the theory it can be seen that the minimum resolvable relative capacitance of 2 ppm could be achieved by this method.
Improving the efficiency of a jet pump using an elliptical nozzle
Authors: Guillaume D. W. , Judge T. A.
Published: July 2002

This note presents a unique means of increasing the efficiency of a jet pump. Much research has been devoted to the study of elliptical nozzles on jets and their ability to increase the amount of fluid entrainment over round jets with equal perimeters. Since the efficiency of a jet pump is directly related to the ability of the primary jet to entrain fluid, a jet pump is an obvious potential application of these elliptical nozzles. In this study, the efficiency of a jet pump is measured using a jet with a round cross section and a jet with an elliptical cross section that has a 3:1 aspect ratio. At high flowrates, the jet pump using the elliptical jet is shown to have an efficiency that is approximately a factor of 6 greater than the pump using the round jet.
Common origin for stress-induced leakage current and electron trap generation in SiO2
Authors: Satake Hideki , Toriumi Akira
Published: July 2002

The origin of stress-induced leakage current in ultrathin SiO2 has been quantitatively investigated on the basis of the experimental results on temperature dependence of stress-induced leakage current. We found that stress-induced leakage current is dependent on stressing temperature, and that it is independent of measurement temperature. It has been quantitatively demonstrated for the first time that the activation energy of the appearance of stress-induced leakage current agrees well with that of electron trap generation so far reported. It is discussed quantitatively that stress-induced leakage current and electron trap generation have a common origin.
Mechanism for the anomalous degradation of Si solar cells induced by high fluence 1 MeV electron irradiation
Authors: Yamaguchi Masafumi , Taylor Stephen J. , Matsuda Sumio , Kawasaki Osamu
Published: July 2002

An anomalous increase in the short-circuit current Isc of n-on-p Si space solar cells, followed by an abrupt decrease in Isc and cell failure has been observed under high fluence (≳1016 cm −2) 1 MeV electron irradiation. A model to explain these phenomena by expressing the change in carrier concentration p, of the base region as a function of the electron fluence is proposed in addition to the well-known model where Isc decreases by minority-carrier lifetime reduction under irradiation. The reduction in p due to majority-carrier trapping by radiation-induced defects has two effects: broadening of the depletion layer which increases the generated photocurrent, and also an increase in the resistivity of the base layer, resulting in the abrupt decrease of Isc and failure of the solar cells.
Thin film diamond photodiode for ultraviolet light detection
Authors: Whitfield Michael D. , Chan Simon SM , Jackman Richard B.
Published: July 2002

A photodiode has been constructed from lightly boron doped, Si supported, thin film chemically vapor deposited (CVD) diamond which shows over five orders of magnitude discrimination between deep UV (≤220 nm) and visible light. A thin (10 nm) gold Schottky barrier with an associated Ti–Ag–Au ohmic contact was used to create a rectifying device with low (≤2 pA) dark currents when reversed biased. This structure showed a sharp cut off in photoresponse at 220 nm, the band gap energy of diamond. Conversely, a photoconductive device fabricated from similar (nominally undoped) material gave a broader UV photoresponse and displayed high dark currents; the superior performance of the diode structure on fine grain material is discussed.
Ultralow friction behavior of borided steel surfaces after flash annealing
Authors: Bindal C. , Erdemir A.
Published: July 2002

In this letter, we describe the ultralow friction mechanism of borided steel surfaces subjected to a short-duration, or ‘‘flash,’’ annealing procedure. In this procedure, a borided steel surface is exposed to high temperature (600 to 800 °C) for a short time (3 to 5 min) and then cooled to room temperature in open air. During the high-temperature exposure, boron atoms within the borided layer diffuse to the surface and react spontaneously with oxygen in air. The reaction product is a thin boron oxide film. During cooling, the boron oxide reacts spontaneously with moisture in the surrounding air to form a thin boric acid film. The sliding friction coefficient of a Si3N4 ball against this flash-annealed surface is about 0.06, but is 0.5 and higher against the unborided or borided-only surfaces. Mechanistically, we propose that the ultralow friction behavior of the borided and flash-annealed surface is due mainly to the layered-crystal structure of the boric acid film that forms on the sliding surface.
Dynamics of bound-exciton luminescences from epitaxial GaN
Authors: Eckey L. , Holst J.-Ch. , Maxim P. , Heitz R. , Hoffmann A. , Broser I. , Meyer B. K. , Wetzel C. , Mokhov E. N. , Baranov P. G.
Published: July 2002

Free- and bound-exciton luminescences of GaN epitaxial layers grown by a sublimation technique on 6H-SiC substrates were investigated using time-integrated and time-resolved photoluminescence measurements at low temperatures. Lifetimes were determined for the donor-bound exciton at 3.4722 eV and for two acceptor-bound excitons with energies of 3.4672 eV and 3.459 eV. On the basis of our results we obtain an upper limit of the free-exciton oscillator strength of 0.0046 for GaN. Luminescences between 3.29 eV and 3.37 eV are identified as due to excitons deeply bound to centers located near the substrate-epilayer interface. Free excitons are captured by these centers within 20 ps.
Effect of reactive ion etching–generated sidewall roughness on propagation loss of buried-channel silica waveguides
Authors: Bazylenko M. V. , Gross M. , Faith M.
Published: July 2002

Different mask materials (photoresist and amorphous silicon) and different sample temperatures can influence the roughness of sidewalls produced during reactive ion etching of silica. Buried-channel waveguides with different microroughness on the core sidewalls (corrugation periods less than 1 μm) have been fabricated and characterized for their propagation loss at 1.3 μm wavelength. An increase in the sidewall roughness amplitude of around 0.05 μm results in an increase in the propagation loss of 0.2 dB/cm. Sidewall roughness with a larger period appears to have smaller effect on loss.
Structural and mechanical properties of (B0.5−xSix)N0.5 films synthesized by dual-ion-beam deposition
Authors: Ong C. W. , Zhao X.-A. , Ng Y. M. , Chan K. F. , Tsang T. C. , Choy C. L. , Chan P. W.
Published: July 2002

The structural and mechanical properties of ion-beam deposited (B0.5−xSix)N0.5 films (0≤x≤0.5) were characterized by x-ray photoelectron spectroscopy, infrared absorption experiments, and nanoindentation tests. A single-layer BN film (x=0) has 70 vol. % in cubic phase (c-BN), and a hardness of 38 GPa. However, it peeled off very soon after deposition due to the high internal stress. If a buffer layer was deposited first, followed by a (B0.5−xSix)N0.5 film with x≊0.013, the whole configuration adhered very firmly to both quartz and silicon substrates. This improvement in adhesion was probably due to the formation of Si–N bonds, which served to release partly the stress inside the (B0.5−xSix)N0.5 films. Since the Si content was low, the film structure remained highly cubic, and there was no observable drop in hardness. For higher x, the cubic structure in (B0.5−xSix)N0.5 films disappeared rapidly and was replaced by a hexagonal structure. This structural change led to a rapid drop in hardness from 38 to 12 GPa. As x was further increased, more Si–N bonds were formed in the (B0.5−xSix)N0.5 layers. As a result, the hardness increased from the minimum value to a value ≊24 GPa.
Photoluminescence related to the two-dimensional electron gas at a GaN/AlGaN heterointerface
Authors: Bergman J. P. , Lundström T. , Monemar B. , Amano H. , Akasaki I.
Published: July 2002

We report photoluminescence (PL) spectra related to a two-dimensional electron gas confined at a GaN/AlGaN heterointerface. The recombination between electrons confined in the bottom of the interface potential and photoexcited holes causes a broad PL emission about 50 meV below the GaN exciton emissions. A second emission, attributed to the recombination of electrons in the first excited level at the interface, is also observed close to the excitonic band gap in GaN. The data agree with a self-consistent calculation of the energy levels and electron concentration at the interface.
Demonstration of a sub-picosecond x-ray streak camera
Authors: Chang Z. , Rundquist A. , Zhou J. , Murnane M. M. , Kapteyn H. C. , Liu X. , Shan B. , Liu J. , Niu L. , Gong M. , Zhang X.
Published: July 2002

A novel design, magnetically focused, x-ray streak camera was designed and tested using sub-20 fs soft-x-ray pulses generated by high harmonic emission in a gas. The temporal resolution of the camera was demonstrated to be under 0.9 ps throughout the ultraviolet to soft-x-ray wavelength region. Our streak camera represents the fastest x-ray detector developed to date.
Structure and properties of a complex crystal for laser diode frequency doubling: Cadmium mercury thiocyanate
Authors: Yuan Duorong , Xu Dong , Liu Mingguo , Qi Fang , Yu Wentao , Hou Wenbo , Bing Yonghong , Sun Suoying , Jiang Minhua
Published: July 2002

The crystal structure of cadmium mercury thiocyanate [CdHg(SCN)4] is determined by means of a four circle diffractometer. The structural features and properties of the crystal are described. Blue-violet light output by frequency doubling of a 809 nm GaAlAs laser diode using a cadmium mercury thiocyanate crystal device that is 3 mm thick at the phase matching angle: θ=47.7°, φ=0°, is realized at room temperature with input power lower than 200 mW. A 404.5 nm light output power of 1.8 mW is also measured for a 576 mW input power of the GaAlAs laser diode.
Generation of ultraviolet light by frequency doubling of a red laser diode in a first-order periodically poled bulk LiTaO3
Authors: Mizuuchi Kiminori , Yamamoto Kazuhisa , Kato Makoto
Published: July 2002

Frequency doubling of a 684 nm laser diode in a first-order periodically poled LiTaO3 is presented. Controlling the side growth of the domain inverted region during high-voltage pulse application, a uniform nonlinear grating with a period of 1.7 μm and 50% duty cycle was fabricated over 10 mm interaction length in a 150 μm thick LiTaO3 substrate. A 342 nm wavelength of harmonic ultraviolet light was generated in a single pass through the domain-inverted structure.
Thermally stimulated currents in polycrystalline diamond films: Application to radiation dosimetry
Authors: Gonon P. , Prawer S. , Jamieson D.
Published: July 2002

Thermally stimulated currents (TSC) were studied in polycrystalline diamond films to gain information about the trap levels in this material. The TSC glow curve is composed of a dominant peak at 555 K with smaller overlapping peaks in the 400–500 K range. The analysis of the TSC isothermal decay at high temperatures shows that the peak at 555 K is related to a trap level at 1.86 eV. The dose response and the room temperature fading rate of TSC were measured in order to evaluate the potential of these films for UV radiation dosimetry. The TSC are found to increase sublinearly with the dose over three decades and to decay with the logarithm of the storage time at room temperature.
Thermally stimulated luminescence from x-irradiated porous silicon
Authors: Cooke D. W. , Bennett B. L. , Farnum E. H. , Hults W. L. , Muenchausen R. E. , Smith J. L.
Published: July 2002

We have measured thermally stimulated luminescence from light-emitting porous silicon that has been x irradiated at room temperature and heated to 400 °C. The glow curve exhibits peaks at 103, 155, 219, and 271 °C, with additional maxima occurring above 400 °C. Each of the peaks emits similar emission spectra characterized by a band with a maximum near 720 nm and 0.39 eV full width at half-maximum. Following x irradiation at room temperature, the sample exhibits well-known photoluminescence, but after heating to 400 °C, the loss of hydrogen renders the sample nonphotoluminescent. However, thermally stimulated luminescence can be repeatedly induced. Observation of thermally stimulated luminescence is unambiguous evidence for the existence of an insulating surface layer on porous silicon.
Correlation between the pretilt angle of liquid crystal and the inclination angle of the polyimide backbone structure
Authors: Arafune R. , Sakamoto K. , Ushioda S.
Published: July 2002

We have determined the inclination angle of the backbone structure of polyimide with alkyl side-chains in rubbed films. Four different polyimides with the same backbone structure but different lengths of alkyl side-chains were used in this study. The inclination angle of the backbone structure increases with the number of carbon atoms in the alkyl side-chains. We found a linear relation between the inclination angle of the backbone structure and the pretilt angle of liquid crystal (LC) that is in contact with the polyimide films. We conclude that the inclination of the polyimide backbone structure determines the pretilt angle of LC.
Impurity dependence on hydrogen and ammonia flow rates in InGaN bulk films
Authors: Piner E. L. , Behbehani M. K. , El-Masry N. A. , Roberts J. C. , McIntosh F. G. , Bedair S. M.
Published: July 2002

H, C, and O impurity concentrations in metalorganic chemical vapor deposition grown InGaN were found to be dependent on the hydrogen and NH3 flow rates. By increasing the hydrogen flow rate from 0 to 100 sccm, a decrease of greater than two orders of magnitude in the C and O impurity levels and one order of magnitude in the H impurity level was observed. Increasing the NH3 flow rate from 1 to 5 slm results in a decrease in the C concentration and an increase in the H and O concentrations indicating that high purity NH3 (99.999%) can be a significant source of O contamination. Additional studies show that when the InN percent in the InGaN films increases, the impurity concentrations increase regardless of changes in the growth conditions. The InGaN films were grown from 710 to 780 °C and the impurity concentrations were characterized by secondary ion mass spectrometry.
Evolution of stress relaxation and yellow luminescence in GaN/sapphire by Si incorporation
Authors: Lee In-Hwan , Choi In-Hoon , Lee C. R. , Noh S. K.
Published: July 2002

We report a systematic study accomplished with a series of undoped and Si-doped GaN epilayers grown on sapphire (0001) with the carrier concentration of 4.0×1017−1.6×1019 cm−3 in order to investigate the evolution of stress relaxation and yellow luminescence by Si incorporation. As the Si doping becomes higher, the bound exciton peaks are gradually shifted to lower energy due to relaxation of the thermal residual stress with the linear coefficient of ΔE/Δσ∥=42 meV/GPa. The present results show that both the full width at half maximum of double-crystal x-ray diffractometry and the photoluminescence intensity ratio of the yellow luminescence to edge emission gradually increase as the Si incorporation becomes heavier. We suggest that the Si doping in GaN epilayers induces overall defects and gives rise to stress relaxation during the cool-down process, and the yellow luminescence may be originated from a complex of VGa and the Si-induced defect.