bluuebunny/crossref_metadata_2025 huggingface dataset:
Chemical vapor deposition of the superconducting YBa2Cu3O7−x phase using halides as metal sources
Authors: Ottosson M. , Andersson T. , Carlsson J.-O. , Hårsta A. , Jansson U. , Norling P. , Niskanen K. , Nordblad P.
Published: July 2002

It is shown for the first time that the superconducting YBa2Cu3O7−x phase can be deposited by chemical vapor deposition using the halide precursors YCl3, BaI2, and CuCl as metal sources and an O2/H2O gas mixture. Sintered calcium stabilized zirconia plates were used as substrates. The superconductor was obtained upon deposition without the need for post-annealing. An ideal (001) texture was always found to prevail.
Observations of nanocrystals in thin TbFeCo films
Authors: Li Z. G. , Smith David J. , Sickafus K.
Published: July 2002

Observations of thin films of amorphous TbFeCo by electron microscopy with a resolution limit of better than 0.2 nm invariably reveal the presence of very fine microcrystals (sizes ∼2–5 nm). Bright field imaging, in both plan view and in cross section, indicates that these nanocrystals have the crystal structure of α-Fe or Co. In contrast, crystals of Tb metal (or Tb oxides) have not been observed. Similar observations of FeCo thin films, prepared under identical experimental conditions, reveal much larger crystals (typically 10–50 nm). It is concluded that the presence of the rare earth element Tb is crucial to the microstructure displayed by this kind of material.
Electronic analog of the electro-optic modulator
Authors: Datta Supriyo , Das Biswajit
Published: July 2002

We propose an electron wave analog of the electro-optic light modulator. The current modulation in the proposed structure arises from spin precession due to the spin-orbit coupling in narrow-gap semiconductors, while magnetized contacts are used to preferentially inject and detect specific spin orientations. This structure may exhibit significant current modulation despite multiple modes, elevated temperatures, or a large applied bias.
Effect of deposition rate on properties of YBa2Cu3O7−δ superconducting thin films
Authors: Wu X. D. , Muenchausen R. E. , Foltyn S. , Estler R. C. , Dye R. C. , Flamme C. , Nogar N. S. , Garcia A. R. , Martin J. , Tesmer J.
Published: July 2002

Superconducting thin films of YBa2Cu3O7−δ on (100) SrTiO3 are prepared in situ by a pulsed laser deposition technique at deposition rates from 1 to 145 Å/s. Crystallinity of the films is examined by Rutherford backscattering in the channeling mode using a 2.2 MeV He+ ion beam. The backscattering minimum yield (χmin) increases with the deposition rate. A χmin of 3% is observed in the films deposited at the lowest deposition rate. Even at a deposition rate of 145 Å/s, the films show good crystallinity with χmin of 15%, indicating epitaxial growth. The x-ray diffraction measurements show that the films have strong c-axis orientation normal to the substrates. The films have metallic resistance versus temperature behavior with zero resistance temperatures of 90 K. The results indicate that the pulsed laser deposition technique could be used to deposit large-area films efficiently with adequate substrate movement.
Detection of a stimulated emission process as an inverse thermal lens signal
Authors: Terazima Masahide , Azumi Tohru
Published: July 2002

A stimulated emission process is detected by applying the transient thermal lens (TL) technique developed recently. The observed inverse TL signal compared with the conventional TL signal indicates that a convex thermal lens is created in the solution by the stimulated-emission process. The sensitivity and the advantages of this method are discussed.
Effect of scattering on the longitudinal mode spectrum of 1.3 μm InGaAsP semiconductor diode lasers
Authors: Peters Frank H. , Cassidy Daniel T.
Published: July 2002

The scattering of stimulated emission within InGaAsP semiconductor diode lasers has been measured and correlated with the measured spectral output of the lasers. It is found that the spectral output of the diode lasers is strongly dependent on internal scattering. It is also found that the amount of scattering is characteristic of the laser structure. A theoretical model has been developed which demonstrates the effect of scattering on the spectral output, and which explains the differences observed in the spectral output of different structures in terms of the internal scattering.
Synthesis of polymer-metal composite thin films by pulsed excimer laser coablation
Authors: Gitay Madhavi , Joglekar Bharati , Ogale S. B.
Published: July 2002

Polymer(polyamide)-metal(Sn) composite thin films have been deposited by a new pulsed excimer laser copulation method. The composite character of the films has been established by the combined use of infrared transmission, x-ray diffraction, Mössbauer spectroscopy, and scanning electron microscopy combined with energy dispersive analysis of x rays.
Dynamics of excimer laser-ablated aluminum neutral atom plume measured by dye laser resonance absorption photography
Authors: Gilgenbach Ronald M. , Ventzek Peter L. G.
Published: July 2002

We report the first dye laser resonance absorption photographs of a single species of aluminum ground-state neutral atoms in the plume ablated from solid aluminum by KrF excimer laser radiation. Aluminum ground-state neutral atoms were diagnosed by illuminating the ablated plume with a dye laser tuned to the 32P1/2–42S1/2 transition at 394.4 nm. Measurements have been performed in vacuum as well as in argon and air environments. Streaming velocities measured for neutral aluminum atoms in vacuum ranged from 0.5×106 cm/s at low excimer laser fluences of 1–2 J/cm2 to 3.4×106 cm/s at high fluences of 7 J/cm2. Dye laser resonance absorption photography measurements of ablated aluminum in argon and air showed slower expansion at 50 and 200 Torr, while observations at 760 Torr indicate turbulent mixing of aluminum neutrals near the surface. Differences between data in argon and air may be due to oxidation of neutral aluminum atoms.
Current imaging of cleaved silicon pn junctions with an ultrahigh vacuum scanning tunneling microscope
Authors: Kordić S. , van Loenen E. J. , Walker A. J.
Published: July 2002

Current imaging of cleaved two-dimensional silicon pn junctions with an ultrahigh vacuum scanning tunneling microscope is presented. In order to be able to distinguish between p-type material, n-type material, and the depletion region a voltage ramp is applied to the p side of the junction, while the voltage on the n side is constant. At the same time standard topography and stabilization current plots give no indication of the presence of the pn junctions. The IV characteristics measured over different parts of the junctions are explained. The influence of the shape of the cleaved surface on the measurements is discussed.
Growth of GexSi1−x alloys on Si(110) surfaces
Authors: Hull R. , Bean J. C. , Peticolas L. , Bahnck D.
Published: July 2002

We have studied the growth of GexSi1−x alloys on Si(110) surfaces. For this growth normal, there are only two inclined {111} glide planes intersecting the interfacial plane. Both intersections are along the same in-plane [11̄0] direction, thus classic a/2〈110〉{111} glide misfit dislocations can form along only one interfacial direction. This produces an orthorhombic unit cell following strain relaxation by misfit dislocations. At sufficiently high stresses, previously unobserved misfit dislocation structures are activated. The critical thickness for misfit dislocation introduction is found to be shifted to lower Ge compositions with respect to growth on the (100) surface, consistent with a higher angular factor resolving the interfacial component of the dislocation Burgers vector in the (110) system.
High speed, nondestructive readout from thin-film ferroelectric memory
Authors: Thakoor Sarita
Published: July 2002

High speed, polarization direction dependent photoresponse from ferroelectric lead zirconate titanate (PbZr0.53Ti0.47O3) thin films, sandwiched between conducting electrodes to form a memory capacitor, is reported. Laser pulses with a full width at half maximum of ∼10 ns at 532 nm wavelength are utilized to readout the photoresponse signal from individual polarized elements. Such readout is repeated over a million times, with no detectable degradation in the photoresponse or the remanent polarization, suggesting its potential as a nondestructive readout (NDRO) of nonvolatile polarization state in thin-film ferroelectric memories. In principle, both electronic as well as thermal mechanisms could be triggered by such photon exposure of ferroelectric thin films. A comparison of the photoresponse from capacitors with semitransparent and opaque top electrodes suggests that the observed NDRO signal is primarily due to thermally triggered mechanisms.
Real-time monitoring of a surface reaction in germanium film growth
Authors: Eres Djula , Sharp J. W.
Published: July 2002

Epitaxial germanium film growth by a surface reaction was investigated using a pulsed molecular jet. Time-resolved reflectometry was utilized for in situ monitoring of both the formation and the evolution of a chemisorbed layer of digermane. The rate of chemisorption was independent of temperature. Evolution of the adsorption layers occurred by a temperature dependent first order process, believed to be molecular hydrogen desorption. Digital growth of germanium films was demonstrated by periodically refilling the active surface sites liberated by molecular hydrogen desorption between two successive gas pulses. Epitaxial germanium films over 150 nm thick were grown on Si (100) substrates.
Ellipsometry for rapid characterization of Si1−xGex layers
Authors: Racanelli M. , Drowley C. I. , Theodore N. D. , Gregory R. B. , Tompkins H. G. , Meyer D. J.
Published: July 2002

We report on the ability of ellipsometry to rapidly determine the germanium content and the film thickness of Si1−xGex layers deposited on silicon substrates. The technique is used to evaluate thickness on single- and for the first time, double-layer Si/SixGe1−x films. We estimate the refractive index of Si1−xGex from ellipsometry measurements and find that only the real part differs significantly from that of silicon for 0<x<0.30. We examine the sensitivity of ellipsometry to changes in germanium content and film thickness. We find that sensitivity is cyclical with film thickness and, in the best case, ellipsometry can be used to determine germanium content within ±1 at. % or thickness within ±20 Å for x∼0.10.
Electronic structure of chiral graphene tubules
Authors: Saito R. , Fujita M. , Dresselhaus G. , Dresselhaus M. S
Published: July 2002

The electronic structure for graphene monolayer tubules is predicted as a function of the diameter and helicity of the constituent graphene tubules. The calculated results show that approximately 1/3 of these tubules are a one-dimensional metal which is stable against a Peierls distortion, and the other 2/3 are one-dimensional semiconductors. The implications of these results are discussed.
Simulation of three-dimensional director structures in twisted nematic liquid crystal displays
Authors: Lien A.
Published: July 2002

The three-dimensional simulation of the liquid crystal director deformation profile and the electric field distribution for the twisted nematic liquid crystal display has been carried out for the first time. The result gives us a complete understanding about liquid crystal deformation profile inside a pixel and the locus of the disclination line pair across the entire pixel area. This would not be possible in the case of the two-dimensional (2D) simulation [A. Lien, Proceedings of the 10th International Display Research Conference (vde-verlag gmbh, Berlin und Offenbach, 1990), p. 248; G. Haas, H. Wohler, M. W. Fritsch, and D. A. Mlynski, ibid., p. 252; A. Lien and R. A. John, IBM J. Res. Devel. 36, 51 (1992)], since the 2D simulation result is accurate only for the region which is far away from the corner area of a pixel.
Electronic structure of aluminum nitride: Theory and experiment
Authors: Loughin S. , French R. H. , Ching W. Y. , Xu Y. N. , Slack G. A.
Published: July 2002

We report the results of a vacuum ultraviolet (VUV) study of single crystal and polycrystalline AlN over the range 4–40 eV and compare these with theoretical optical properties calculated from first principles using an orthogonalized linear combination of atomic orbitals in the local density approximation. The electronic structure of AlN has a two-dimensional (2D) character indicated by logarithmic divergences at 8.7 and 14 eV. These mark the centers of two sets of 2D critical points which are associated with N 2p→Al 3s transitions and Al=N→Al 3p transitions, respectively. A third feature is centered at 33 eV and associated with N 2s→Al 3d transitions.
Steric variation of the cerium valence in Ce2Fe14B and related compounds
Authors: Capehart T. W. , Mishra R. K. , Meisner G. P. , Fuerst C. D. , Herbst J. F.
Published: July 2002

Through measurements of the near-edge Ce L3 x-ray absorption structure we have investigated the influence of site volume on the cerium valence in Ce2Fe14B, Ce2Fe14BHx, and Ce2Fe17. The crystal structures of these compounds are isomorphic with those of technologically important permanent magnet materials. Confirming other experiments, we find that the Ce ion in Ce2Fe14B is in a strongly mixed-valent α-like state which is incompatible with a local 4f moment. Comparison of the spectroscopically determined valences of the three materials demonstrates a shift toward a γ-like cerium state, which supports a magnetic moment, as the steric volume of the Ce site(s) increases. Our results strongly suggest that the volume of the rare-earth site is the principal factor controlling the Ce chemical valence in these systems.
Use of quantum-well superlattices to obtain a high figure of merit from nonconventional thermoelectric materials
Authors: Hicks L. D. , Harman T. C. , Dresselhaus M. S.
Published: July 2002

Currently, the materials with the highest thermoelectric figure of merit (ZT) are one-band materials. The presence of both electrons and holes lowers ZT, so two-band materials such as semimetals are not useful thermoelectric materials. However, by preparing these materials in the form of two-dimensional quantum-well superlattices, it is possible to separate the two bands and transform the material to an effective one-carrier system. We have investigated theoretically the effect of such an approach and our results indicate that a significant increase in ZT may be achieved. This result allows the possibility of using a new class of materials as thermoelectric refrigeration elements.
Alloy scattering limited transport of two-dimensional carriers in strained Si1−xGex quantum wells
Authors: Venkataraman V. , Liu C. W. , Sturm J. C.
Published: July 2002

The mobility of two-dimensional electron systems in strained Si1−xGex quantum wells was studied at low temperatures as a function of the germanium content in the well. While mobilities exceeding 30 000 cm2/V s have been achieved for pure Si layers, they dropped to less than 3000 cm2/V s for Si0.88Ge0.12 wells, demonstrating the effect of strong alloy disorder scattering. This was confirmed by the relatively weaker dependence of mobility on carrier concentration in gating experiments. By accounting for valley degeneracy effects in the standard two-dimensional alloy scattering model, an effective scattering potential Valloy=0.8±0.1 eV has been derived for electrons. Using a weaker potential, it is shown that the maximum low temperature mobilities for holes reported in literature are also consistent with the alloy scattering model.
High performance InGaAs/GaAs quantum well infrared photodetectors
Authors: Gunapala S. D. , Bandara K. M. S. V. , Levine B. F. , Sarusi G. , Park J. S. , Lin T. L. , Pike W. T. , Liu J. K.
Published: July 2002

We have measured the optical and transport properties of In0.2Ga0.8As/GaAs quantum well infrared photodetectors based on bound-to-bound, bound-to-quasibound, and bound-to-continuum intersubband transitions. Excellent hot electron transport and high detectivity D*=1.8×1010 cm√Hz/W (at λp=16.7 μm) were achieved at temperature T=40 K.
Polyperinaphthalene film formation by pulsed laser deposition with a target of perylenetetracarboxylic dianhydride
Authors: Yudasaka M. , Tasaka Y. , Tanaka M. , Kamo H. , Ohki Y. , Usami S. , Yoshimura S.
Published: July 2002

Thin films of polyperinaphthalene (PPN) have been obtained by Nd:YAG pulsed laser deposition with a target of perylenetetracarboxylic dianhydride. Components of the films depend on the power and wavelength of the laser light, which is verified by absorption spectra, Raman scattering spectra, and in situ mass spectra. The optimum conditions for the PPN film formation is 10 mJ cm−2 at 266 nm.
Extended x-ray absorption fine structure investigation on buried InAsP/InP interfaces
Authors: Lamberti C. , Bordiga S. , Boscherini F. , Pascarelli S. , Schiavini G. M.
Published: July 2002

As K-edge extended x-ray absorption fine structure has been carried out on the 2–3 monolayers thick interface of ad hoc grown InAsP/InP expitaxial multistructures deposited by low pressure metalorganic vapor phase epitaxy. The goal was to characterize the local structure of the unwanted, strained interface layers of InAsP produced by the exposure of the InP surface to AsH3 as occurs during the growth of InP/InGaAs heterostructures. We observed that the first shell environment of As at these interfaces is identical to that found in bulk InAs. In particular, we measure a constant As—In bond length, independently of As concentration at the interface; this implies that epitaxy with InP is accompanied by local structural distortions which accommodate the constant As—In bond length.
Organic-inorganic heterostructure electroluminescent device using a layered perovskite semiconductor (C6H5C2H4NH3)2PbI4
Authors: Era M. , Morimoto S. , Tsutsui T. , Saito S.
Published: July 2002

Using the combination of a layered perovskite compound (C6H5C2H4NH3)2PbI4 (PAPI), which forms a stable exciton with a large binding energy owing to its low-dimensional semiconductor nature and exhibits sharp and strong photoluminescence from the exciton band, and an electron-transporting oxadiazole derivative, we fabricated an organic–inorganic heterostructure electroluminescent (EL) device. The EL spectrum of the device corresponded well to the photoluminescence spectrum of the PAPI film; the emission was peaking at 520 nm and half-width of the emission was about 10 nm at liquid-nitrogen temperature. Further, highly intense EL of more than 10 000 cd m−2 was performed at 2 A cm−2 at liquid-nitrogen temperature in the device.
Abrupt Si/Ge interface formation using atomic hydrogen in Si molecular beam epitaxy
Authors: Ohta G. , Fukatsu S. , Ebuchi Y. , Hattori T. , Usami N. , Shiraki Y.
Published: July 2002

Compositional abruptness of strained Si/Ge heterointerfaces grown by solid source Si molecular beam epitaxy under supply of atomic hydrogen (AH) was investigated using secondary ion mass spectrometry and reflection high-energy electron diffraction. Systematic variation of growth temperature and AH exposure pressure revealed that Ge segregation length is a steadily decreasing function of AH coverage on the growth surface.
Enhancement mode metal-semiconductor field effect transistors using homoepitaxial diamonds
Authors: Kawarada Hiroshi , Aoki Makoto , Ito Masahiro
Published: July 2002

Enhancement mode-type metal-semiconductor field effect transistors using diamond have been fabricated. The transistor operation is based on the control of surface p-type conduction of a hydrogen terminated homoepitaxial layer. Boron doping was not used for the conduction. An aluminum contact is used for the Schottky gate and gold ohmic contacts are used for the source and drain. The obtained transconductance is 20–200 μs/mm using aluminum gates of 10–40 μm in length. The active region on the homoepitaxial layer is thin enough for the total depletion of carriers when the gate bias is zero.
Segregation and trapping of erbium during silicon molecular beam epitaxy
Authors: Serna R. , Lohmeier M. , Zagwijn P. M. , Vlieg E. , Polman A.
Published: July 2002

Erbium surface segregation is observed during growth of Er-doped Si by molecular beam epitaxy on Si(100) at 600 °C. Once a critical Er surface areal density of 2×1014 Er/cm2 is reached, enhanced Er trapping is observed, possibly due to the formation of silicide precipitates. Er segregation on Si(100) is fully avoided when growth is performed in an oxygen background pressure of ∼10−10 mbar, due to the formation of Er-O complexes. No Er segregation is observed on Si(111), which is attributed to the formation of epitaxial Er3Si5 precipitates.
Iron diffusivity in silicon: Impact of charge state
Authors: Koveshnikov Sergei V. , Rozgonyi George A.
Published: July 2002

The effect of iron charge state on its diffusion in p-type Si near room temperature has been investigated by C–V and depth dependent deep-level transient spectroscopy measurements. The migration enthalpies of both positively charged and neutral iron were found to be 0.92 and 0.56 eV, respectively. Disagreement between the theoretical predictions and experimentally observed trend in iron diffusion is briefly discussed in terms of diffusion path, elastic strain, and Coulombic interaction versus impurity charge state.
Characterization of growing thin films by i
n s
i
t
u ellipsometry, spectral reflectance and transmittance measurements, and ion-scattering spectroscopy
Authors: Netterfield R. P. , Martin P. J. , Sainty W. G. , Duffy R. M. , Pacey C. G.
Published: July 2002

A versatile ultrahigh-vacuum thin-film deposition and analysis system is described. Films are deposited by electron beam evaporation with the possibility of ion beam bombardment of the growing film. Measurements of the reflectance and/or transmittance of the coating surface can be made simultaneously at 16 wavelengths across the visible or infrared spectrum. Ellipsometric measurements can also be made in situ, at a single wavelength and single angle of incidence, by an ellipsometer which can operate in either an automatic rotating analyzer mode or a manual nulling mode. The system is also equipped with an ion gun producing a submillimeter spot, and with a hemispherical sector, ion energy analyzer for ion scattering spectroscopy studies of the film surface. Results obtained during the deposition of a gold film are presented to demonstrate the capability of the system.
Dielectric measurements with helical resonators
Authors: Deri R. J.
Published: July 2002

A method for measuring dielectric properties with helical resonators is presented and analyzed. The procedure is based on an equivalent circuit model which treats the helix as a length of transmission line; an experimental approach for determination of the model parameters is demonstrated. Typical experimental results are also presented.
Acousto-optic color spectrometer
Authors: Hallikainen J. , Parkkinen J. , Jaaskelainen T.
Published: July 2002

A computerized spectrophotometer using an acousto-optic tunable filter is described. The equipment operates between 400 and 700 nm and is applied, for example, to reflected color measurement.
Automated capacitance bridge
Authors: Cavicchi R. E. , Silsbee R. H.
Published: July 2002

The design of a computer-automated capacitance-conductance bridge is described. The bridge operates in the frequency range 40 Hz–40 kHz with a resolution better than 0.1% at signal levels as low as 400 μV and is most useful for studying the complex impedance of nonlinear devices as a function of the test signal amplitude, frequency, and waveform. Of particular interest is the stability problem associated with feedback during the self-balancing process for the two impedance phases.
Technique for impedance matching at two ultrasonic frequencies simultaneously
Authors: Johnson E. C.
Published: July 2002

Situations arise where it would be advantageous if ultrasonic measurements could be performed at two distinct frequencies simultaneously. Such a scheme is hampered by the need for a method whereby the sample impedance at both frequencies can be matched to that of the driver electronics. Such a method is presented in this note.
Measurement of the current density profile in the Alcator C tokamak using lithium pellets
Authors: Marmar E. S. , Terry J. L. , Lipschultz B. , Rice J. E.
Published: July 2002

High-speed lithium pellets have been injected into Alcator C tokamak plasmas in order to measure the internal magnetic field, and thus current density profiles. In the pellet ablation cloud, intense visible line radiation from the Li+ ion (λ≊5485 Å, 1s2s 3S−1s2p 3P) is polarized due to the Zeeman effect, and measurement of the polarization angle yields the direction of the total local magnetic field. A ‘‘snap shot’’ of the q profile is obtained as the pellet penetrates from the edge into the center of the discharge, in a time of about 300 μs. The spatial resolution of the measurement is about 1 cm. At a toroidal field of BT=10 T, the emission in the unshifted π component of the Zeeman triplet is more than 80% polarized, and q profiles have been obtained. The pellets are perturbative (〈Δne〉/〈ne〉≊1), but the total pellet penetration time is at least a factor of 1000 smaller than the classical skin time. It can thus be anticipated that the current density profile should not be perturbed significantly during the time of the measurement. With some relatively straightforward modifications and refinements, precision approaching 10% for the measurement of q profiles should be achievable. The technique appears viable, using Li, as long as the toroidal field is ≳4 T.
UHV compatible compact double-crystal monochromator at BEPC diffraction and scattering beamline 4B9A
Authors: Shu D. , Wang M. , Liu W. , Xie Q. , Wang W. , Cong Z. , Zhang Y. , Liu J. , He W.
Published: July 2002

A UHV compatible compact double-crystal monochromator was designed and constructed for BEPC diffraction and the scattering beamline 4B9A. It is a compact device with a 325 ×250×250 mm3 vacuum chamber. A T-structure mechanism has been designed for allowing the monochromator to have a Bragg angle range from 5° to 70° and keep the exit beam position and direction fixed during wavelength tuning. The first crystal is cooled by a heat-pipe cooling system and a pair of PZT drivers provide a two-dimensional adjustment to optimize the alignment between two crystals. The design and operating principles are described in this paper.
VUV beamline (4–50 eV) with a 1 m Seya–Namioka monochromator for surface studies
Authors: Namba H. , Masuda M. , Kuroda H. , Ohta T. , Noda H.
Published: July 2002

Optical and mechanical design of a VUV beamline BL-7B in PF-KEK are presented. The optical characteristics are discussed by use of the data of gas absorption spectrum and those of photoelectron spectroscopy.
6-GeV synchrotron radiation project
Authors: Kamitsubo H. , Be S. H. , Hara M. , Nagaoka R. , Sasaki S. , Wada T.
Published: July 2002

This paper outlines the status of a 6-GeV synchrotron radiation designed at RIKEN. This facility consists of a main storage ring, a booster synchrotron, a 1.5-GeV preinjector linac, positron injection linacs, and others. The electronan GeV. The storage ring has a circumference of 1069.2 m and 7-m-long straight sections for insertion devices. The lattice of the main ring is a Chasman–Green-type one and has 36 periodicity. The low emittance (εx=8.2 nm rad) and large dynamic aperture are expected even with field errors and misalignments of magnetic elements. Three years of a preconstruction research and development period and 5 years of construction period are scheduled.
Novel broad-band excitation of Er3+ luminescence in chalcogenide glasses
Authors: Gu S. Q. , Ramachandran S. , Reuter E. E. , Turnbull D. A. , Verdeyen J. T. , Bishop S. G.
Published: July 2002

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopy carried out on bulk samples of Er2S3-doped Ge33As12Se55 glasses demonstrate that Er3+ is incorporated in optically active sites in the glass and gives rise to a broad ∼1500–1600 nm 4I13/2→4I15/2 PL spectrum similar to those observed in Er-doped oxide glasses. The novel PLE spectrum of the 1550 nm Er3+PL band comprises a superposition of relatively sharp peaks which are attributable to the characteristic 4I15/2→4I11/2 and 4I15/2→4I9/2 Er3+ absorption transitions at 810 and 980 nm, respectively, and a broad, below-gap PLE band characteristic of the weak defect or impurity absorption tails in chalcogenide glasses which decrease exponentially with decreasing photon energy. At high energy the exponentially rising Urbach absorption edge, which leads to competing nonradiative decay mechanisms, imposes an exponentially decreasing slope on the PLE spectrum.
Low energy multicycle injection in a superconducting electron storage ring
Authors: Nakayama K. , Gomei Y.
Published: July 2002

It is shown that multicycle injection in an electron storage ring with a superconducting bending magnet can, in principle, be possible at low energy because of short radiation damping time and long Touschek life time due to beam enlargement. We estimated possible beam current by multicycle injection for a circular ring: radius=0.5 m; field index=0.5; injection energy=15 MeV; injector current=50 mA, and found that beam current of about 1 A can be injected in 5 min if injected beam is stable. However, it should be noticed that threshold stored current due to beam instabilities go down with energy. We should further study beam instability in order to check the feasibility of low-energy multicycle injection.
Superconducting magnet of Aurora
Authors: Takayama T. , Group SHI Accelerator Research
Published: July 2002

The AURORA superconducting magnet system is composed of a cylindrical single-body magnet and a refrigeration system for superconducting coils. The magnet generates Bz=1 T on the central orbit at the 150 MeV electron beam injection energy and Bz=4.3 T at the 650 MeV storage energy. The diameter of the central orbit is 1 m. Iron poles and yokes are used for shielding the magnetic field, reducing the electromagnetic force between superconducting coils, and making the magnetic field distribution adequate for beam injection and storage.
Imaging of fluctuating domain shapes: Methods of image analysis and their implementation in a personal computing environment
Authors: Seul M. , Sammon M. J. , Monar L. R.
Published: July 2002

Methods for the analysis of digital images have been implemented on a personal computer, augmented with a 32-bit floating-point array processor located in its backplane. They are applied to derive a quantitative description of domain shapes and patterns, as well as dynamic shape fluctuations, based on series of images recorded on video disk or tape. This description relies on a variety of algorithms, in part developed in the context of optical character recognition, to extract and encode domain boundaries, and to evaluate moments and power spectra of momentary boundary configurations. Time-series analysis of principal axes directions and of selected, active Fourier modes in terms of suitable correlation functions permits the study of dynamic phenomena. Examples are discussed to illustrate the scope and versatility of the analytical procedures whose wide applicability in laboratory environments is facilitated by their implementation on a personal computer platform.
Data acquisition and control using National Instruments’ ‘‘LabVIEW’’ software
Authors: Kirkman I. W. , Buksh P. A.
Published: July 2002

Using conventional programming techniques for the production of data acquisition and control software can be a time-consuming procedure, and the code subsequently produced can often be inflexible and rather difficult to modify in the light of changing experimental requirements. A new generation of commercial software products have recently appeared which it is claimed can significantly reduce development times and give rise to more flexible code and improved user interfaces. An example of such a product is National Instruments’ ‘‘LabVIEW,’’ which presents a novel graphical approach based on Apple Macintosh computer platforms. Extensive use of LabVIEW has been made by the Soft X-ray Group at Daresbury Laboratory over the past two years, and its performance is reported on here. Several examples of experimental arrangements for which it has been used are described, and an evaluation of the product is made.
Negative ion production in a large semicylindrical ion source
Authors: Hanada M. , Inoue T. , Mizuno M. , Ohara Y. , Okumura Y. , Suzuki Y. , Tanaka H. , Tanaka M. , Watanabe K.
Published: July 2002

A large semicylindrical negative ion source, whose dimensions are 34 cm in diameter and 104 cm in length, has been developed. By optimizing a chamber depth and a filter strength, a H− current of 650 mA (7.7 mA/cm2) was obtained at an arc condition of 1.3 Pa, 70 V, and 1200 A. In order to increase the H− current and to reduce an operating pressure, a small amount of Cs was injected. As a result, the H− current was increased from 550 mA (6.5 mA/cm2) to 850 mA (10 mA/cm2) under an arc power of 70 V×800 A. The most significant feature of the cesium effect was the reduction of the operating pressure. With maintaining the sufficient current of 670 mA (8 mA/cm2), the operating pressure could be lowered to 0.03 Pa. At this pressure, the highest gas efficiency of 20% was achieved.
Magnetostriction measurements of ribbon samples using a fiber-optic interferometer
Authors: Gates L. , Stroink G.
Published: July 2002

We present an inexpensive, relatively simple optical method to measure the magnetostriction curve of single ribbons or bulk samples that can be as small as a few millimeters. The device is small enough to be placed between the poles of an electromagnet. It uses a single-mode bidirectional fiber coupler as a beam splitter for the operation of a Fabry–Perot interferometer. Both longitudinal (λ∥) and transverse (λ⊥) magnetostriction can be obtained. As an example, we present results on nickel, Fe80B20, and Terfenol-D.
A radiant flow reactor for high-temperature reactivity studies of pulverized solids
Authors: Chen John C. , Niksa Stephen
Published: July 2002

Our radiant two-phase flow reactor presents several new possibilities for high-temperature reactivity studies. Most importantly, the thermal histories of the suspension and entrainment gas can be independently regulated over wide ranges. At low suspension loadings, outlet temperatures can differ by hundreds of degrees and gas temperatures are low enough to inhibit hydrocarbon cracking chemistry, so primary products are quenched as soon as they are expelled. With coal suspensions, tars were generated with the highest H/C ratio and lowest proton aromaticity ever reported. Alternatively, particles and gas can be heated at similar rates to promote secondary chemistry by increasing particle loading. Simply by regulating the furnace temperature, arbitrary extents of conversion of coal tar into soot were observed for fixed total mass loss. Under both circumstances heat fluxes are comparable to those in large furnaces, so relevant heating rates and reaction times are accessible. Suspensions remain optically thin even for the highest loadings of technological interest because they are only 1 cm wide. Consequently, the macroscopic behavior remains firmly connected to single-particle phenomena. Mass and elemental closures are rarely breached by more than 5% in individual runs, so interpretations are not subject to inordinate scatter in the data. The reactor is also well suited for combustion studies, as demonstrated by extents of carbon and nitrogen burnout from 50% to 100% for various gas-stream oxygen levels.
A normal incidence vacuum ultraviolet emission spectrometer
Authors: Tang Zizhou , Xu Zengli , Kevan Steve
Published: July 2002

A compact, normal incidence vacuum ultraviolet (VUV) fluorescence spectrometer for use with both electron and photon excitation in the energy range of 15–40 eV was built and tested. This 1-m concave grating spectrometer is described together with the performance of its microchannel plate-charge coupled device detector system. Results of the calibration of the system at the SURF-II synchrotron light source at the National Institute of Standards and Technology are given. Initial results of experiments using both photon and electron excitation are also presented.
Fabrication of ultrasmall tunnel junctions by electron-beam lithography
Authors: Koester S. J. , Bazán G. , Bernstein G. H. , Porod W.
Published: July 2002

Fabrication of a variety of ultrasmall tunneling structures is presented for possible applications in single electronics. Two main structures are described: (i) arrays of nanometer-scale metal dots and (ii) single and multiple linear tunnel junctions formed by overlapping lines. Very large, uniform particle arrays were fabricated by electron-beam lithography (EBL) with particle diameters as small as 25 nm. The advantage of our dot array system is its high degree of uniformity and very small junction size coupled with the use of isolated particles to reduce stray capacitance effects. Single and multiple linear tunnel junctions were fabricated by EBL using single-layer resist and angled evaporations. Our fabrication technique differs from previous ones in its ability to create very small tunnel junctions without the need for multilayer resist systems or precise knowledge of the angle of evaporation.
Development of an experimental system for optical characterization of large arbitrarily shaped particles
Authors: Sasse Ch.
Published: July 2002

A methodology is presented in order to optically characterize large, absorbing irregularly shaped particles. Two experimental systems were developed and implemented: a particle nephelometer which measures angular scattering from a single electrodynamically levitated particle at λ=514.5 nm, and an integrating sphere spectrometer which measures the spectral hemispherical reflectance of particulates in the wavelength range from 450 to 1959 nm. The particulates examined were spherical carbon particles and different oil shale particles. Measurements of phase function and cross polarization on individual particles indicate an increase in back scatter with increasing particle albedo. Criteria for particle discrimination are discussed.
A high performance scanning force microscope head design
Authors: Clark Steven M. , Baldeschwieler John D.
Published: July 2002

A stable and highly sensitive scanning force microscope head design is presented. The head provides an implementation of the optical lever detection method in which mechanical vibration noise has been minimized.
Production and storage of 2p2 3P ground state O2+ ions from iron oxide targets
Authors: Fang Z. , Kwong Victor H. S.
Published: July 2002

2p2 3P ground state O2+ ions are produced by laser ablation of solid Fe2O3 targets and stored in a radio frequency ion trap. The state of the O2+ ions is confirmed by comparing a known charge transfer rate coefficient for ground state O2+ ion and H2 with our measurement. The storage time is estimated to be about 10 s at the vacuum base pressure of 6×10−10 Torr.
Influence of azimuthal coil size variations on magnetic field harmonics of superconducting particle accelerator magnets
Authors: Ogitsu T. , Devred A.
Published: July 2002

The superconducting super collider (SSC) would have required dipole and quadrupole magnets with a very high field quality. The field quality is determined mainly by the dimensions of the magnet coils and their positions with respect to the iron yoke. It is thus very sensitive to manufacturing errors. A model is here developed to estimate the field distortions in a dipole magnet due to azimuthal coil size variations. This model is applied to the data collected during the fabrication and testing of a series of 5 cm aperture, 15 m long SSC dipole magnet prototypes. A clear correlation is observed between the predicted field distortions from the azimuthal coil sizes and the measured skew quadrupole and skew sextupole coefficients.
High quality epitaxial aluminum nitride layers on sapphire by pulsed laser deposition
Authors: Vispute R. D. , Wu Hong , Narayan J.
Published: July 2002

We have grown high quality epitaxial AlN layers on sapphire substrates by pulsed laser ablation of a stoichiometric AlN target. The AlN films deposited at 800 °C and laser energy densities in the range of 2–3 J/cm2 were found to be epitaxial with the c axis normal to the Al2O3(0001) surface. The x-ray rocking curve of epitaxial AlN films yielded a full width at half maximum of 0.21°. The selected area electron diffraction patterns and high resolution transmission electron microscopy also revealed that the films were epitaxial with an orientational relationship of AlN[0001]∥Al2O3[0001] and in-plain alignment of AlN[1̄21̄0]∥Al2O3[01̄10] and AlN[101̄0]∥Al2O3[2̄110]. This is equivalent to 30° rotation in the basal plane of the AlN film with respect to the sapphire substrate. The absorption edge measured by ultraviolet-visible spectroscopy for the epitaxial AlN film was sharp and the band gap was found to be 6.1 eV. The electrical resistivity of the films was about 5–6×1013 ohm cm with a breakdown field of 5×106 V/cm. At higher laser energy densities ≥10 J/cm2 and lower temperatures ≤650 °C, the deposited films were nitrogen deficient and contained free metallic aluminum, both of which degrade the microstructural, electrical, and optical properties of the AlN films.
The Oxford electron-beam ion trap: A device for spectroscopy of highly charged ions
Authors: Silver J. D. , Varney A. J. , Margolis H. S. , Baird P. E. G. , Grant I. P. , Groves P. D. , Hallett W. A. , Handford A. T. , Hirst P. J. , Holmes A. R. , Howie D. J. H. , Hunt R. A. , Nobbs K. A. , Roberts M. , Studholme W. , Wark J. S. , Williams M. T. , Levine M. A. , Dietrich D. D. , Graham W. G. , Williams I. D. , O’Neil R. , Rose S. J.
Published: July 2002

An electron-beam ion trap (EBIT) has just been completed in the Clarendon Laboratory, Oxford. The design is similar to the devices installed at the Lawrence Livermore National Laboratory. It is intended that the Oxford EBIT will be used for x-ray and UV spectroscopy of hydrogenic and helium-like ions, laser resonance spectroscopy of hydrogenic ions and measurements of dielectronic recombination cross sections, in order to test current understanding of simple highly charged ions.
Photothermal dielectric spectroscopic microscope
Authors: Cho Yasuo , Kumamaru Tomoyuki
Published: July 2002

A new photothermal technique is proposed. It is based on the temperature characteristic of the dielectric constant of light-irradiated material. When chopped light is absorbed in a dielectric material, an alternating variation of capacitance is caused by the heat produced due to light absorption and is detected by using a frequency demodulation technique. A quantitative derivation is presented for the alternating capacitance variation in terms of the optical, thermal, dielectric, and geometric parameters of the system. The experimental results for lead zirconate titanate ceramics, barium titanate single-crystal, TiO2–Bi2Ti4O11 ceramics, and ethyl alcohol are shown, where the observed signals agree with theoretical ones very well.
Computer controlled high-voltage injector
Authors: Constantin F. , Dumitru M. , Korschinek G.
Published: July 2002

This paper reports the results of the operation, under active computer control, of a high-voltage (400 kV) injector. The automation system uses a microcomputer placed on the high-voltage deck of the ion source, which takes over some of the process control decisions, and a master IBM-PC at ground potential. Various ion beams (p, H+2, H+3, d, He+, He2+) have been produced, proving the reliability of the system. A maximum value of 460 kV accelerating potential has been reached during the tests. The beam fulfills the requirements for the operation of a room-temperature IH linac. By using a modular expandable computer system the acceleration voltage is continuously adjusted keeping its standard error within 0.1%. A future enlargement of the injector has been taken into account and the upgrading of the control system for an electron cyclotron resonance ion source would be very simple.
The baffle system for the gas space instrument
Authors: Hl/ond M.
Published: July 2002

The construction of the baffle system for the GAS instrument (neutral hydrogen analyzer) prepared for the RELICT-2 space mission is presented. The method and the equipment used for the direct measurements of the baffle’s suppression factor of the ultraviolet photons flux (Ly-α spectral line) are described and the main physical parameters of the device are given.
Cold-cathode, pulsed-power plasma discharge switch
Authors: Goebel Dan M.
Published: July 2002

CROSSATRONTMmodulator switches are cold-cathode, grid-controlled, plasma-discharge devices that are used for thyratron and hard-tube replacement in high-voltage, pulsed-power applications. CROSSATRON modulator switches have been used to produce square pulses of up to 100 kV and 1000 A, and CROSSATRON laser-discharge switches have switched peak discharge currents of up to 10 kA at 40 kV. The major advantage that CROSSATRON switches offer over other plasma switches is a rapid deionization time that permits high pulse-repetition frequencies (103 to 106 pulses per second depending on the application), and a long life associated with the cold-cathode plasma production mechanism. Compared to hard tubes, CROSSATRON switches have a relatively low forward voltage drop (500 V), the ability to close and open up to 1 kA of peak current, and lower grid-drive power requirements. In this article, we describe the physical mechanisms for how the switch works based on simple models and experimental data. The design of CROSSATRON switches is explained, and characteristic performance in closing and opening applications is described and explained.
Orthogonal superposition measurements using a rheometer equipped with a force rebalanced transducer
Authors: Vermant J. , Moldenaers P. , Mewis J. , Ellis M. , Garritano R.
Published: July 2002

The design of a device for rheological orthogonal superposition measurements on fluids is discussed. Superposing a small amplitude oscillatory motion on a steady or transient shear flow provides a technique to probe flow-induced microstructural changes in situ by means of mechanical spectroscopy. Oscillations perpendicular to the main shear flow possess intrinsic advantages over the parallel case. It is shown that the closed loop system of a force rebalanced transducer of an existing rheometer can be modified to drive an orthogonal oscillatory motion and to measure the material response. Nonhomogeneous flow, annular pumping or cavitation can occur and have to be avoided by means of a suitable flow cell. A double walled Couette cell, open at the bottom is suggested for that purpose. The device is evaluated with Newtonian fluids and with a viscoelastic polymer solution. The apparatus has two major advantages. First the forces associated with the main shear flow can be measured simultaneously with the orthogonal moduli. Second, the present design is implemented on an instrument already capable of performing parallel superposition measurements, hence the two superposition modes are available on a single instrument. The relative simplicity of the proposed modification could boost the use of orthogonal superposition measurements and facilitate the development of new applications, e.g., to probe the time evolution of the flow-induced anisotropy in complex systems.