bluuebunny/crossref_metadata_2025 huggingface dataset:
The Growth Form of Croton pullei (Euphorbiaceae) ‐ Functional Morphology and Biomechanics of a Neotropical Liana
Authors: Gallenmüller F. , Müller U. , Rowe N. , Speck T.
Published: July 2002

Abstract: Croton pullei (Euphorbiaceae) is a woody climber of the lowland rainforest in French Guyana and Surinam. During ontogeny, a shift from a juvenile free‐standing growth phase to an older supported growth phase is observed. The following biomechanical parameters were studied: structural Young's modulus, structural torsional modulus, flexural stiffness and bend to twist ratios. Changes in anatomical development were also analysed for different stages of development of C. pullei which differ significantly in their mechanical properties. Free‐standing plants show a nearly constant structural Young's modulus and structural torsional modulus during ontogeny, with flexural stiffness increasing proportionally with the axial second moment of area. These patterns are typical for ?semi‐self‐supporting plants”. In contrast, supported plants show a significant decrease in structural Young's modulus in older stem parts, as well as a decrease in structural torsional modulus. Due to the decrease in structural Young's modulus, flexural stiffness does not increase proportionally with the axial second moment of area. These patterns are typical for non‐self‐supporting lianas. In all supported plants, a sudden transition occurs from early dense wood to a wood type with a much higher proportion of large diameter vessels. In contrast, only the dense wood type is present in all tested free‐standing plants. The data are compared with results from other climbing species of the same study area and discussed with reference to observed features characterizing the growth form and life history of C. pullei.
Disordering, intermixing, and thermal stability of GaInP/AlInP superlattices and alloys
Authors: O’Brien S. , Bour D. P. , Shealy J. R.
Published: July 2002

The disordering of an ordered state of Ga0.5In0.5P and the partial intermixing of Ga0.5In0.5P/Al0.5In0.5P superlattices has been demonstrated at temperatures between 650 and 975 °C. The localized disordering or intermixing was accomplished by the deposition of SiO2 followed by rapid thermal annealing. Regions with no SiO2 showed minimal intermixing over this temperature range while the capped areas exhibited superlattice energy shifts up to 47 meV. Bulk Ga0.5In0.5P disordered at 900–925 °C for these samples with SiO2 while remaining ordered for samples with no SiO2. The degree of disordering or intermixing was measured using room-temperature and low-temperature photoluminescence and Raman spectroscopy.
New shallow donors in high-purity silicon single crystal
Authors: Yu Zhiyi , Huang Y. X. , Shen S. C.
Published: July 2002

High-resolution photothermal ionization spectroscopy has been performed on n-type high-purity silicon crystals. Two new shallow donors with binding energies of 36.61 and 36.97 meV, respectively, are observed for the first time, in addition to lithium (Li), lithium-oxygen complex [D(Li,O)], phosphorus (P), and arsenic (As) donors. These new shallow donors show similar spectral features to Li, D(Li,O), P, and As, which implies that they are also hydrogenic shallow donors. These new complex centers are probably generated during crystal growth. In addition, previously unresolved transitions related to very high excited states of phosphorus as well as the above-mentioned new shallow donors, have also been observed.
Semiconducting silicide-silicon heterojunction elaboration by solid phase epitaxy
Authors: Cherief N. , D’Anterroches C. , Cinti R. C. , Nguyen Tan T. A. , Derrien J.
Published: July 2002

Semiconducting βFeSi2 has been successfully grown on a Si (111) substrate. It has been proven that under ultrahigh vacuum conditions, the solid phase epitaxy temperature can be lowered to ∼800 K, where only the βFeSi2 phase is stabilized. The disilicide formation was monitored in situ by various surface-sensitive techniques such as low-energy electron diffraction, Auger electron spectroscopy, and ultraviolet photoelectron spectroscopy. The epitaxial relationships were ascertained by transmission electron diffraction and microscopy including high-resolution cross-sectional image. The results show the epitaxy of βFeSi2 (110) and (101) planes parallel to the Si (111) plane. The disilicide-silicon heterojunction displays an atomically abrupt interface.
Drastic reduction of series resistance in doped semiconductor distributed Bragg reflectors for surface-emitting lasers
Authors: Tai K. , Yang L. , Wang Y. H. , Wynn J. D. , Cho A. Y.
Published: July 2002

Modifications to reduce the series resistance in p-type semiconductor distributed Bragg reflectors (DBR) consisting of ten pairs of quarter-wavelength GaAs (high refractive index)/Al0.7Ga0.3As (low index) layers were made by inserting an intermediate Al0.35Ga0.65As layer or a 200 Å superlattice of GaAs(10 Å)/Al0.7Ga0.3As (10 Å) at the GaAs/Al0.7Ga0.3As heterointerfaces. The specific DBR series resistance was reduced by two orders of magnitude to about 6.2×10−5 Ω cm2. These modifications did not alter the optical reflectivity and nearly identical reflection spectra were measured.
Fabrication of minority-carrier-limited n-Si/insulator/metal diodes
Authors: Kumar Amit , Rosenblum Mark D. , Gilmore Delwyn L. , Tufts Bruce J. , Rosenbluth Mary L. , Lewis Nathan S.
Published: July 2002

A photoelectrochemical anodization technique has been used to fabricate n-Si/insulator/metal (MIS) diodes with improved electrical properties. MIS structures fabricated with Au have provided the first experimental observation of a solid-state n-Si surface barrier device whose open circuit voltage Voc is controlled by minority-carrier bulk diffusion/recombination processes. For these diodes, variation of the minority-carrier diffusion length and majority-carrier dopant density produced changes in Voc that were in accord with bulk diffusion/recombination theory. Additionally, the variation in Voc in response to changes in the work function of the metal overlayer indicated that these MIS devices were not subject to the Fermi level pinning restrictions observed for n-Si Schottky structures. X-ray photoelectron spectroscopic characterization of the anodically grown insulator indicated 8.2±0.9 Å of a strained SiO2 layer as the interfacial insulator resulting from the photoanodization process.
Unusual properties of photoluminescence from partially ordered Ga0.5In0.5P
Authors: Fouquet J. E. , Robbins V. M. , Rosner S. J. , Blum O.
Published: July 2002

Ga0.5In0.5P grown lattice matched to GaAs by metalorganic chemical vapor deposition (MOCVD) exhibited domains of varying degrees of column III sublattice ordering. Continuous-wave photoluminescence spectra were single peaked and relatively narrow, but the peak wavelengths from samples grown at low (630–670 °C) temperatures varied strongly with excitation density at low measurement temperatures, while peak wavelength did not vary for high (775 °C) temperature growth. The half width was 6.5 meV in the latter case, the narrowest reported from MOCVD-grown Ga0.5In0.5P. Time-resolved photoluminescence of partially ordered GaInP at liquid-helium temperatures is reported for the first time. For samples grown at low temperatures, the spectral peak displayed a slow (τ≳1 μs) decay at low excitation density. The decay was more rapid (τ=1.8 ns) at higher excitations and at higher photon emission energies. Possible explanations discussed include spatial separation of carriers and trapping.
Thermally stimulated hot-electron spectroscopy
Authors: Choi K. K. , Fotiadis L. , Newman P. G. , Iafrate G. J.
Published: July 2002

We introduce and utilize a novel method to characterize the energy levels of quantum well structures. In this method, thermal stimulation is utilized to excite conduction electrons from the lowest subband to the higher subbands of the structure while the structure is subjected to an applied voltage. The energy distribution of the electrons injected from this structure is then analyzed by a quantum barrier placed adjacent to the structure. This spectroscopic method results in the identification of the energy levels and the electron transport mechanisms of the structure in question. In this letter, excitation spectra from three different quantum well structures are presented to demonstrate the utility of this technique.
Quantized resistance in in-plane gated narrow constriction fabricated by wet etching
Authors: Takagaki Y. , Gamo K. , Namba S. , Takaoka S. , Murase K.
Published: July 2002

A narrow in-plane gated constriction is defined by technique employing electron beam lithography and wet chemical etching. Two-dimensional electron gas beside the narrow channel is used to control the number of occupied subbands in the constriction. A ballistic transport through the point contact is manifested by the observation of successive resistance steps when the subbands are depopulated.
Structure, chemistry, and band bending at Se-passivated GaAs(001) surfaces
Authors: Chambers S. A. , Sundaram V. S.
Published: July 2002

Se-passivated n-GaAs(001) surfaces prepared in a metalorganic chemical vapor desposition reactor have been investigated by means of x-ray photoelectron spectroscopy, low-energy electron diffraction, and x-ray photoelectron diffraction. The band bending of these free surfaces was as low as ∼0.1 eV, indicating excellent passivation. It was found that Se undergoes an anion exchange reaction with As to depths of at least five atomic layers. This result suggests that the reduction of surface states is brought about by the formation of a GaAsxSe1−x/GaAs heterojunction interface of very high structural quality.
Model for dislocation locking by oxygen gettering in silicon crystals
Authors: Maroudas Dimitris , Brown Robert A.
Published: July 2002

Oxygen gettering to dislocations slows and stops dislocation motion caused by applied stress in silicon crystals. A model is presented that quantitatively describes the inhibition of dislocation motion by accounting for the drag caused by the oxygen atmosphere in the crystal around the dislocation and for oxygen aggregates inside the dislocation core. The oxygen distribution is computed by analysis of diffusion and stress-assisted migration in the crystalline lattice. The predictions of the model agree quantitatively with the experimental data of Imai and Sumino. Hysteresis is predicted in the dependence of the dislocation velocity on applied stress and explains the difference in the unlocking and locking stresses for dislocation motion.
Thermodynamics of facet damage in cleaved AlGaAs lasers
Authors: Moser A.
Published: July 2002

The time dependence of catastrophic optical mirror damage (COMD) is investigated for the cw operation of AlGaAs quantum well lasers with cleaved unprotected and protected mirrors. Based on the rate equation for a COMD failure it is found that facet heating leading to COMD depends on the quantum wells and on the reflectivity modification of the protected mirrors. The investigations show that control of damage in the mirror region of the AlGaAs lasers is feasible and leads to very reliable devices.
Correlations between stress-induced positive charges and time-dependent dielectric breakdown in ultrathin silicon oxide films
Authors: Yamada Hiroshi , Makino Takahiro
Published: July 2002

With attention to total energy loss of injected electrons through Fowler–Nordheim (F–N) tunneling, time-dependent dielectric breakdown (TDDB) of 5-nm-thick silicon oxide films was investigated. Metal-oxide-semiconductor (MOS) diodes with four combinations of gate electrode and substrate type were fabricated. This produced different energy losses of injected electrons at a constant F–N tunneling current stress in spite of the same oxide thickness. TDDB lifetime was strongly affected by this energy loss difference. Since other electrical changes caused by trapping of stress-induced positive charges in oxide also exhibited the similar energy loss dependence to the lifetime, TDDB for ultrathin oxide films is probably dominated by the trapping of positive charges, which are mainly generated near anode-side oxide interfaces through the surface plasmon mechanism.
Effects of secondary laser illumination during the transient measurement in optical and electrical deep level transient spectroscopy
Authors: Chen Zhuohui , Mandelis Andreas
Published: July 2002

To separate the majority and minority carriers in the deep level transient spectroscopy (DLTS), the transient is usually measured in the dark. However, under some circumstances, the transient measurement should be performed under illumination. In these cases, the effects introduced by the illumination become a concern. In this letter, effects of secondary laser illumination on samples of hydrogenated amorphous silicon (a-Si:H) during the transient measurement in optical and electrical DLTS are reported. The experimental results show that background illumination decreases the time constant of the transient but it is unlikely to create new gap states during the short time period.
A novel preparation technique for preparing hydrogenated amorphous silicon with a more rigid and stable Si network
Authors: Shirai Hajime , Das Debajyoti , Hanna Jun-ichi , Shimizu Isamu
Published: July 2002

A novel preparation technique, termed ‘‘chemical annealing,’’ was developed with the aim of making a stable and rigid Si network structure. The hydrogen content (CH) in the films and the optical gap could be reduced gradually without any change in substrate temperature by alternating deposition of a hydrogenated amorphous silicon layer several tens of Å thick and treatment with atomic hydrogen. These films showed CH of 1.5–10 at. %, and exhibited high photoconductivities in the level of 10−5–10−4 S/cm. In the films with CH of 3 at. % or less, in particular, improvement was observed in stability against illumination with light. Their photoconductivity remained at about 65% of the initial value even after illumination with white light (AM1, 100 mW) for 60 h. In addition, time-of-flight experiments revealed a significant enhancement in hole drift mobility to a value of 0.2 cm2/V s at 300 K.
Evolution of quasi-epitaxial growth of a crystalline organic semiconductor on graphite
Authors: Haskal Eliav I. , So Franky F. , Burrows Paul E. , Forrest Stephen R.
Published: July 2002

We have studied the evolution of the growth of a crystalline organic semiconductor thin film using reflection high energy electron diffraction (RHEED). Our results indicate that highly ordered crystalline films of an organic compound; namely 3, 4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA), can be grown on graphite by the ultrahigh vacuum process of organic molecular beam deposition even though the crystal structures of the two materials are highly mismatched. The RHEED patterns show the evolution of planar crystal growth from 2 monolayer (∼6 Å) coverage until at least 50 Å as the films are deposited onto substrates cooled to 100 K. At larger film thicknesses, somewhat nonplanar but still crystalline growth occurs. Furthermore, crystalline thin films were obtained independent of growth rate, which was as high as 3.0 Å/s. To our knowledge, this is the first direct experimental evidence of the evolution of growth from monolayer to bulk film coverage into an ordered, quasi-epitaxial structure.
Donor level of interstitial hydrogen in GaP
Authors: Clerjaud B. , Côte D. , Hahn W. -S. , Wasik D. , Ulrici W.
Published: July 2002

The nitrogen-hydrogen complex in GaP is evidenced by its stretching local vibrational mode. H+ is probed through the formation of the C-H complex and H0 through the formation of the N-H complex. The corresponding donor level H0/H+ is shown to be located around 0.3 eV above the valence band maximum.
New approach to the preparation of ultrathin silicon dioxide films at low temperatures
Authors: Xu Xueping , Goodman D. W.
Published: July 2002

Ultrathin silicon dioxide films have been prepared on a Mo(110) substrate at a relatively low temperature (<100 °C) by evaporating silicon in an oxygen background. The SiO2 films were characterized by Auger electron, electron energy loss, and IR reflection absorption spectroscopies. At low substrate temperatures, the SiO2 films are amorphous, consisting of networks of [SiO4] tetrahedra units with limited size. Upon post-annealing, the small networks of [SiO4] fuse together, and become more ordered. In turn, the electronic properties of the SiO2 films approach those of vitreous silica.
Time-dependence of the interface trap build-up in deuterium-annealed oxides after irradiation
Authors: Saks N. S. , Rendell R. W.
Published: July 2002

The rate of interface trap Nit build-up after irradiation has been studied in metal-oxide semiconductor oxides which were annealed in either deuterium or hydrogen. The build-up rate is found to be substantially retarded in the deuterium-annealed oxide. This result demonstrates conclusively that the Nit build-up rate is determined by the rate of H+ (D+) drift through the oxide to the Si-SiO2 interface.
Measurement of CO2 laser small angle Thomson scattering on a magnetically confined plasma
Authors: Richards R. K. , Hutchinson D. P. , Bennett C. A. , Hunter H. T. , Ma C. H.
Published: July 2002

We report the first successful small-angle (less than 1°) Thomson scattering measurement of 10 μm radiation from a magnetically confined toroidal plasma. This represents a proof-of-principle demonstration of a new diagnostic technique for confined deuterium-tritium fusion-product alpha particles in future fusion reactors. This result was achieved by detecting scattered CO2 laser light from the plasma of the ATF torsatron at an angle of 0.86° using a novel heterodyne receiver scheme. A predicted resonance in the scattered power as a function of plasma electron density is clearly resolved in the measurements.
Direct observation of the defect structure of polycrystalline diamond by scanning electron microscopy
Authors: Harker A. B. , DeNatale J. F. , Flintoff J. F. , Breen J. J.
Published: July 2002

A method has been demonstrated to directly observe the surface crystallography and defect structures in diamond films by scanning electron microscopy. Individual diamond crystals in the polycrystalline films are polished to a rms smoothness of less than 2 nm using iron metal at temperatures in excess of 725 °C. In the absence of topography, the detailed microstructure of the films can be characterized by secondary electron imaging in a scanning electron microscope by charge-induced electron contrast which shows strong beam voltage dependence. It is hypothesized that defects and grain boundaries form a connected pathway in the film which has greater conductivity than the generally insulating diamond and creates the charge-induced contrast.
Observation of arsenic precipitates in GaInAs grown at low temperature on InP
Authors: Ibbetson J. P. , Speck J. S. , Gossard A. C. , Mishra U. K.
Published: July 2002

Single-crystal Ga1−xInxAs (x=0.4) grown on InP by molecular-beam epitaxy at low substrate temperatures (250–150 °C) has been examined by transmission electron microscopy. Arsenic precipitates were observed following an ex situ anneal at 550 °C. The precipitates coarsen during higher-temperature anneals at 600 and 700 °C. Microstructure dependence on the growth temperature was similar to that observed in low-temperature grown GaAs. Arsenic precipitate volume fraction increased with decreasing growth temperature, with a measured maximum value of ∼0.4%.
Experimental study of volume holographic interconnects using random patterns
Authors: Lee Hyuk , Jin Sang Kyu
Published: July 2002

An optical interconnecting scheme utilizing volume holograms of random patterns instead of plane waves is described. The new method is analyzed by using a perturbative integral expansion technique. Experimental results demonstrating the new scheme are also presented.
Fabrication conditions and superconducting properties of Ag-sheathed Bi-Sr-Ca-Cu-O tapes prepared by partial melting and slow cooling process
Authors: Nomura K. , Seido M. , Kitaguchi H. , Kumakura H. , Togano K. , Maeda H.
Published: July 2002

Ag-sheathed Bi2Sr2Ca1Cu2Ox(Bi-2212) tapes with various oxide superconductor core (SC-core) thicknesses, SC-core ratios (SC-core area to overall cross-sectional area), and tape configurations were prepared by a partial melting and slow cooling process. For single-core tapes the critical current density, Jc(core), for SC-core, increases with decreasing SC-core thickness, due to the highly aligned Bi-2212 grains, and the highest Jc(core) of 1.4×105 A/cm2 at 4.2 K in 10 T is achieved at a core thickness of 15 μm. Furthermore, the Jc(core) increases with increasing SC-core ratio (i.e., with decreasing Ag-sheath thickness). From the practical point of view, high Jc(overall) as well as high critical current (Ic) is more important than Jc(core). This requirement is attained by the double-tube method, which shows the highest Jc(overall) value of 3.0×104 A/cm2 at 4.2 K in 10 T. In the tape fabrication process, the slow heating rate just below the partial melting becomes important, because oxygen released from the SC-core during heating makes void swelling in the Ag sheath and leads to the degradation of Jc.
Piezoelectric constant of InP
Authors: Rottner K. , Helbig R. , Müller G.
Published: July 2002

The piezoelectric modulus d14 of InP was not determined experimentally up to now. By doping InP with Fe now high compensated bulk material is available by liquid-encapsulated Czochralski crystals with a conductivity lower than 10−8 (Ω cm)−1. Excitation of vibration modes leads to a set of closely spaced resonance lines. These data were used to calculate a set of parameters for an electrical equivalent circuit with which the impedance behavior can be described successfully. From this the piezoelectric modulus of InP was derived to be −1.8 pC/N at room temperature. The sign of the constant was determined by qualitative static measurements of the piezovoltage by compressing the crystal.
Extension of infrared-laser interferometric thermometry to silicon wafers polished on only one side
Authors: Donnelly V. M.
Published: July 2002

Interferometric thermometry, a noncontact method of measuring the temperature of semiconductor substrates, has been extended to standard Si wafers that are polished on only one side. These substrates make up the majority of wafers used in manufacturing. This is the first application of this technique to substrates that are not polished to an optical finish on both sides. Contrasts between constructive and destructive interference were typically 19% and as high as 39% when the 1.5 μm laser beam was incident on the rough surface and the reflected beam was monitored. While considerably lower than the near-100% contrast with Si wafers that are polished on both sides, this level of contrast is nonetheless sufficient for correctly counting interference cycles and therefore determining temperature in real time. Temperature measurements were successfully made on both bare substrates and processed Si wafers covered with transparent films and photoresist patterns.
Evaluation of niobium transmission lines up to the superconducting gap frequency
Authors: Dierichs M. M. T. M. , Feenstra B. J. , Skalare A. , Honingh C. E. , Mees J. , Stadt H.v.d. , Graauw Th. de
Published: July 2002

The frequency dependence of the coupling of niobium superconducting transmission lines is measured for frequencies up to and above the superconducting gap frequency. For this purpose superconducting microstrips are integrated in log-periodic planar antennas and the spectral response is measured by means of a Fourier transform spectrometer with 1 μm2 Nb/Al2O3/Nb SIS junctions as detectors. Resonances of microstrips are observed up to 650 GHz, the superconducting gap frequency of niobium, but above that frequency no resonances have been detected. The measured resonance frequencies are in good agreement with a dispersive model for superconducting transmission lines based on the Mattis–Bardeen theory. The radiation coupling is lower than calculated, indicating significant dielectric losses.
Fabrication and properties of epitaxial ferroelectric heterostructures with (SrRuO3) isotropic metallic oxide electrodes
Authors: Eom C. B. , Van Dover R. B. , Phillips Julia M. , Werder D. J. , Marshall J. H. , Chen C. H. , Cava R. J. , Fleming R. M. , Fork D. K.
Published: July 2002

Epitaxial ferroelectric SrRuO3/Pb(Zr0.52Ti0.48)O3/SrRuO3 heterostructures have been fabricated employing isotropic metallic oxide electrodes on (100) SrTiO3 and (100) Si with an yttria stabilized zirconia buffer layer. The structures have been grown in situ by 90° off-axis sputtering, which allows the growth of uniform stoichiometric films over large areas with excellent step coverage. X-ray diffraction, Rutherford backscattering spectroscopy, and cross-sectional transmission electron microscopy reveal high crystalline quality and coherent interfaces. They exhibit superior fatigue characteristics over those made with metal electrodes, showing little degradation over 1010 cycles, with a large remnant polarization.
IIA-III2-S4 ternary compounds: New host matrices for full color thin film electroluminescence displays
Authors: Benalloul P. , Barthou C. , Benoit J. , Eichenauer L. , Zeinert A.
Published: July 2002

Strontium thiogallate (SrGa2S4) thin films have been prepared by rf reactive magnetron sputtering. This sulfur matrix permits the acceleration of charge carriers to optical energies under high electric field and provides green electroluminescence when doped with europium. The color coordinates are better than those achieved by other known green thin film electroluminescent phosphors. Strontium thiogallates as other ternary IIA-III2-(S,Se)4 compounds doped with Eu2+ or Ce3+ are good candidates for thin film electroluminescence phosphors of full color displays.
Z-contrast investigation of the ordered atomic interface of CoSi2/Si(001) layers
Authors: Chisholm M. F. , Browning N. D. , Pennycook S. J. , Jebasinski R. , Mantl S.
Published: July 2002

The atomic structure of mesotaxial CoSi2/Si(001) interfaces has been investigated by Z-contrast scanning transmission electron microscopy. The directly interpretable images reveal a 2×1 ordered structure at the interface, which is clearly seen to involve a doubling of the periodicity of the interfacial Co atoms. From these high-resolution images, we deduce a new structure model for the CoSi2/Si(001) interface.
(Pt/Co/Pt)/X multilayer films with high Kerr rotations and large perpendicular magnetic anisotropies
Authors: Bertero G. A. , Sinclair R.
Published: July 2002

We have sputter-deposited a series of (Pt/Co/Pt)/X multilayer structures with X=Pd,Ag,Cu displaying large Kerr rotations with improved perpendicular anisotropy and magnetic coercivity compared to the corresponding Co/X multilayers. In particular, Ar-sputtered (Pt/Co/Pt)/Pd multilayers, with the Pt layer thicknesses corresponding to one atomic monolayer, present Kerr rotations of the order of 0.26°, perpendicular anisotropy energies of 33×106 ergs/cc (Co) or better, and magnetic coercivities as high as 8 kOe.
Heteroepitaxial growth of tin-doped indium oxide films on single crystalline yttria stabilized zirconia substrates
Authors: Kamei Masayuki , Yagami Teruyuki , Takaki Satoru , Shigesato Yuzo
Published: July 2002

Heteroepitaxial growth of tin-doped indium oxide (ITO) film was achieved for the first time by using single crystalline yttria stabilized zirconia (YSZ) as substrates. The epitaxial relationship between ITO film and YSZ substrate was ITO[100]∥YSZ[100]. By comparing the electrical properties of this epitaxial ITO film with that of a randomly oriented polycrystalline ITO film grown on a glass substrate, neither the large angle grain boundaries nor the crystalline orientation were revealed to be dominant in determining the carrier mobility in ITO films.
Surface-induced ordering: A model for vapor-deposition growth of amorphous materials
Authors: Hellman F.
Published: July 2002

During vapor deposition growth of amorphous materials, we propose that adatom clusters align such as to minimize surface energy. This alignment, a thermally activated process, causes the as-grown structure of the amorphous thin film to be anisotropic and stabilizes the structure against subsequent relaxation, presumably by reducing free volume. A two-level-systems analysis describes the effect of deposition temperature, deposition rate, and subsequent annealing. The model is used to describe the growth-induced magnetic anisotropy of amorphous Tb-Fe.
Scanned electrostatic force microscope for noninvasive high frequency potential measurement
Authors: Said Ra’a A. , Bridges Greg E. , Thomson Doug J.
Published: July 2002

This letter presents a technique for performing localized noncontact measurements of high frequency signals on integrated circuits using a scanned force microscope. The technique extracts the amplitude and phase of the signal voltage at a point on the circuit by nulling the electrostatic force interaction between a small driven probe and the test point. A heterodyne approach is used to enable the measurement of high frequency signals, including frequencies which are much greater than the mechanical resonance of the probe mechanism. Accurate measurements can be performed without complex calibration requirements and are not sensitive to dc offset effects.
Patterning of self-assembled alkanethiol monolayers on silver by microfocus ion and electron beam bombardment
Authors: Gillen Greg , Wight Scott , Bennett Joe , Tarlov Michael J.
Published: July 2002

Decanethiol [CH3(CH2)9SH] self-assembled monolayer films on silver substrates have been irradiated in selected areas by focused ion or electron bombardment. Subsequent immersion of the irradiated sample in a solution of a fluoromercaptan [CF3(CF2)2(CH2)2SH] results in attachment of this molecule to the silver surface in the ion or electron-exposed regions, producing a micrometer spatial-scale pattern of two chemically distinct alkanethiol monolayers. The coverage of the fluoromercaptan on the bombarded areas was found to reach maximum levels of 70% at ion doses of 6×1013 ions/cm2 and 50% at electron doses of 2×1017 electrons/cm2 as determined by secondary ion mass spectrometry. These methods of maskless patterning may be useful for semiconductor or biosensor device fabrication.
Electrospray organometallic chemical vapor deposition—A novel technique for preparation of II–VI quantum dot composites
Authors: Danek M. , Jensen K. F. , Murray C. B. , Bawendi M. G.
Published: July 2002

A novel technique combining electrospray and organometallic chemical vapor deposition (OMCVD) has been developed for the synthesis of new II–VI quantum dot composites. CdSe nanocrystals (quantum dots) of selected size are dispersed in a pyridine/acetonitrile mixture. The nanocrystals are transferred by electrospray into the growth zone of an OMCVD reactor and codeposited on a ZnSe matrix grown from hydrogen selenide and diethyl zinc. Composites consisting of CdSe nanocrystals and an amorphous or polycrystalline ZnSe matrix have been deposited on glass substrates at temperatures of 150–250 °C. Room-temperature absorption and photoluminescence spectra show optical transitions characteristic of the initial nanocrystal dispersions. The emission wavelength may be tuned in a broad spectral region by incorporating nanocrystals of varying sizes. The composites have been characterized by Auger electron spectroscopy, high resolution transmission electron microscopy, and scanning transmission electron microscopy.
Photoactivated birefringence in antiferroelectric thin films via a structural transition
Authors: Wang Feiling , Li Kewen K. , Haertling Gene H.
Published: July 2002

A photoactivated birefringence has been observed in an antiferroelectric lead zirconate titanate (PZT) thin film material bounded by an indium-tin oxide (ITO) electrode. This phenomenon stemmed from the ultraviolet (UV) assistance to an antiferroelectric-to-ferroelectric structural transition which otherwise was inhibited by an effect of the lead zirconate titanate (PZT)-ITO interface. The UV-assisted structural transition was accompanied by a significant change in the birefringence of the PZT thin films. Using this phenomenon, an UV-addressed visible-light modulation was demonstrated with an ITO/PZT/Pt thin film structure on silicon substrates.
N depth profiles in thin SiO2 grown or processed in N2O: The role of atomic oxygen
Authors: Carr E. C. , Ellis K. A. , Buhrman R. A.
Published: July 2002

Atomic oxygen, which can be liberated as an intermediate product in the decomposition of N2, is shown to be effective in removing N previously incorporated in SiO2 layers grown in N2O. This removal results in a N distribution that is sharply peaked at the Si–SiO2 interface for oxides grown in N2O by rapid thermal oxidation, but in a flat N distribution for N2O oxides grown in a furnace where the concentration of atomic oxygen is generally not substantial at the wafer position. This effect provides a means of tuning N profiles in a manner that may be useful for optimizing oxide quality.
Efficient and compact discharge XeCl laser with automatic UV preionization
Authors: Miyazaki Kenzo , Toda Yuzo , Hasama Toshifumi , Sato Takuzo
Published: July 2002

Considerable improvements in overall efficiency of a compact UV-preionized discharge XeCl laser have been achieved by possible operation at relatively low charging voltages V for high pressure P HCl/Xe/Ne mixtures. A peak overall efficiency of 2.9% has been obtained with the output energy of 280 mJ at V=18 kV and P=4 atm. A maximum output energy of 680 mJ has been extracted with the overall efficiency of 1.8% in 20-ns (FWHM) pulses at P=6 atm and V=36 kV, corresponding to an energy density of 5.8 J/1. The efficient performance and simple design of the discharge XeCl laser with automatic preionization are described.
High-speed multichannel photon counter for time-resolved laser spectroscopy
Authors: Baba Hiroshi , Hoshina Satoshi , Sakurai Katsumi , Takeuchi Nobuo
Published: July 2002

A versatile, high-speed multichannel counter, which has maximum temporal resolution Δt=30 ns and channel length up to 4095, has been developed for various kinds of time-resolved laser spectroscopic measurements. High speed, large counting capacity, low cost for fabrication, and ease of circuit assembly have been accomplished by introducing both parallel and pipe-line processing. The performance of this system has been verified in the applications to cw laser radar, time-of-flight measurement of molecular beam, and radiative lifetime measurement.
Battery driven field data logger with static random-access memory storage
Authors: Ohsumi Takashi
Published: July 2002

A data logger using static CMOS-type nonvolatile random-access memory (RAM) is described. Its compactness and low requirement of electric power allows outdoor use with battery operation for a period of more than 1 year. The device provides a low-cost strategy for field monitoring of the surface manifestation of volcanic activity or earthquake precursors.
Fluorescence spectroscopy of organic reaction intermediates in solution using a commercial spectrofluorimeter
Authors: Casal H. L. , Scaiano J. C. , Charette G. M. , Sugamori S. E.
Published: July 2002

The fluorescence spectra of excited free radicals have been recorded using a pulsed laser to generate these reaction intermediates in the modified cell compartment of a commercial gated spectrofluorimeter. The technique, illustrated with data for the diphenylmethyl and diphenylhydroxymethyl radicals can also be applied to the study of the kinetics of free radical reactions.
Theoretical signal-to-noise ratio and resolution for the stochastic excitation technique in radio frequency spectroscopy
Authors: Amano C. , Katakura H.
Published: July 2002

Analytical expressions are derived for the signal-to-noise ratio and resolution in the stochastic excitation technique applied to radio frequency spectroscopy such as ion cyclotron resonance and nuclear-magnetic resonance. The expressions reduce to particularly simple forms under two limiting cases. Under intermediate cases, numerical calculations have been performed for them. Their results and the inspection of the limiting forms confirm the following properties: (1) noise on the spectrum is mainly due to that employed for the excitation; (2) the signal-to-noise ratio is independent of the observation period and it is always unity; (3) resolution is given by the observation period and, in consequence, it increases linearly with the observation period. Finally, a comparison is made of some features for the present technique with three other techniques, namely, the pulsed Fourier transform, the rapid scan, and the conventional continuous-wave techniques.
Molecular flux distribution in the detector plane of an effusive source molecular-beam apparatus
Authors: Steckelmacher W. , Man K. F.
Published: July 2002

An analysis of the molecular effusive flow pattern through a narrow rectangular slit orifice is given in terms of the arrival flux on a parallel detector plane. It is shown that the advantage of having an orifice in the form of a long narrow slit in terms of a pronounced peaked incident beam at the detector plane is only achieved at detector plane separations less than the length of the orifice slit. At separations of the detector plane larger than twice the slit length the arrival flux distribution asymptotically approaches that of an infinitesimal orifice source of arbitrary shape. This is in contrast to recent calculations of flux density versus off-axis detector position reported by Perram and Dorko in Rev. Sci. Instrum. 54, 275 (1983).
Radiochemistry and secondary reactions for the diagnostics of laser-driven fusion plasmas
Authors: Miyanaga N. , Azechi H. , Stapf R. O. , Itoga K. , Nakaishi H. , Shiraga H. , Yamanaka M. , Yamanaka T. , Tsuji R. , Ido S. , Sakurai K. , Nishihara K. , Yabe T. , Takagi M. , Nakatsuka M. , Izawa Y. , Nakai S. , Yamanaka C. , Kobayashi K. , Kimura I. , Morinobu S.
Published: July 2002

Radiochemical measurements have been developed for the diagnostics of laser-driven implosion plasmas. The excellent calibration for neutron-yield measurement has been done using β-γ coincidence technique. The multiactivable tracer method has been examined for measuring the pusher areal density by means of a high-purity germanium detector. The first experimental success of the secondary nuclear fusion reaction method is also demonstrated for the direct measurement of the fuel ρR.
Low-noise Hall probe preamplifier
Authors: Smith Steven W.
Published: July 2002

A low-noise preamplifier circuit for use with Halltron HR-66 Hall effect probes in the frequency range dc to 100 kHz, shows a wideband noise of 6- and 2-mG rms for bandwidths of dc to 100 kHz and dc to 100 Hz, respectively. Below 100 Hz the noise is due to the 1/f noise from the Hall probe, while white preamplifier noise dominates above 100 Hz. Above 1 kHz, preamplifier noise exceeds the noise of the Hall probe alone by a factor of five. dc drift of the system is approximately 10 mG in 24 h.
Solid-state radio frequency oscillator for optogalvanic spectroscopy: Detection of nitric oxide using the 2-0 overtone transition
Authors: May Randy D. , May Paul H.
Published: July 2002

A compact, solid-state radio frequency oscillator of low-power consumption is described which allows quantitative measurement of the optogalvanic effect in low-pressure gas discharges. The oscillator has been used to record a portion of the 2-0 overtone band of nitric oxide at a pressure of ∼1 Torr using a tunable color-center laser operating at 2.65 μm.
High-energy resolution electron spectrometer for 1-nm spatial analysis
Authors: Batson P. E.
Published: July 2002

A Wien Filter electron spectrometer has been successfully combined with a dedicated scanning transmission electron microscope (STEM) to obtain an energy resolution of 140 meV with a specimen collection semiangle of 25 mR at 100 keV. A cold-field emission electron source is used to produce a 0.35–10-nm-size electron beam which has a spread in energy of about 0.25 eV. Because this energy spread is much larger than the spectrometer energy resolution, deconvolution techniques may be applied under appropriate conditions to yield a spectroscopic energy resolution of about 70 meV at a 12.5-mR collection semiangle. The Wien Filter is a conventional design, but is immersed in a high-voltage electrode of asymmetric design to facilitate control of prespectrometer electron trajectories. A doublet quadrupole lens is used to match the spectrometer angular acceptance range with that of scattered electrons at the specimen. A weak sextupole lens is used to reduce the second-order angular aberrations.
Theoretical signal-to-noise ratio for correlators with linear averaging
Authors: Dmowski K. , Pióro Z.
Published: July 2002

Detailed calculations of the output signal-to-noise ratio for correlators with a linear averaging and an arbitrarily chosen weighting function are presented. Analytical relationships are derived for three mathematical models of white noise. Finally, a comparison of obtained results is made.
Multiphoton optical rotary dispersion
Authors: Gedanken A. , Tamir M.
Published: July 2002

An experimental setup for the measurements of multiphoton optical rotary dispersion is described. It is demonstrated that the effect is measurable and amenable to experimental observation. The experiments were carried out on 10% aqueous solutions of (+)−, (−)−, and racemic camphorsulfonic acid.
Plasma data acquisition with a Macintosh
Authors: Tai Kim , Lim Wee Beng , Seyhoonzadeh Amir , Cooney Jamie , Tao Jin , Bailey Mark , Forsling Peter , Andersen David R. , Lonngren Karl E.
Published: July 2002

This note demonstrates that with relatively inexpensive external hardware, the Macintosh series of computers with their closed architecture (Mac Plus and Mac SE) can be used in the laboratory for data acquisition and data interpretation. The measurement and interpretation of data acquired from a Langmuir probe inserted in a plasma are described.
Pressure cell for magnetostrictive measurements
Authors: Ostenson J. E. , Finnemore D. K. , Jiles D. C.
Published: July 2002

A pressure cell has been designed to study the magnetostrictive properties of a material as a function of both pressure and magnetic field. For changes in length on the order of 2000 ppm, it is necessary to have a substantial compliance in the pressure cell to retain a constant stress over the length of travel.
Magnetostatic surface wave dispersive line pulsed microwave frequency diagnostic
Authors: Treado Todd A. , Doggett Wesley O.
Published: July 2002

We report on a solid-state dispersive line frequency diagnostic circuit used in a short-pulse (50 ns), high-power microwave relativistic magnetron experiment. The dispersive element of the circuit consisted of an epitaxial yttrium iron garnett film upon which magnetostatic surface waves were launched transverse to the bias magnetic field. By varying the bias field from 200 to 1000 Oe, the circuit passband could be varied throughout the 2–5-GHz region of interest with an accompanying variation in the bandwidth from 1000 to 450 MHz, respectively. The nonlinear dispersion, which could also be varied by changing the bias field, was measured using both phase data and pulsed techniques. The results of magnetron frequency measurements at 3.1 and 4.3 GHz using both the dispersive line and a heterodyne circuit are compared. An agreement of 1% was achieved when the heterodyne output was Fourier analyzed and the dispersive line measurements were digitized and related to the pulsed calibration results.
Helium liquefaction by a Gifford–McMahon cycle cryogenic refrigerator
Authors: Yoshimura Hideto , Nagao Masashi , Inaguchi Takashi , Yamada Tadatoshi , Iwamoto Masatami
Published: July 2002

This article describes the principal design features and performance test results of a three-stage Gifford–McMahon cycle cryogenic refrigerator by which the authors have achieved a no-load temperature of 3.3 K and succeeded in helium liquefaction. The refrigeration capacity was 20 mW at 4.2 K and the helium liquefaction rate was 10 cm3/h. The key point of the success is the selection of GdxEr1−xRh compounds as a regenerator material. This is the first time that a Gifford–McMahon refrigerator has liquefied helium without the use of a Joule–Thomson stage.
Autotriggered crowbar switch for a compact 600-kV pulser
Authors: Humphries S. , Siergiej D. , Schamiloglu E.
Published: July 2002

We developed a shorting switch using commercial spark gaps triggered by a cable delay network. The combination of the switch and a Marx generator created a reproducible 600-kV, 80-ns voltage pulse for a 1-kA electron-beam gun.
A soft/hard x-ray beamline for surface EXAFS studies in the energy range 0.8–15 keV
Authors: MacDowell A. A. , Hashizume T. , Citrin P. H.
Published: July 2002

A new ultrahigh-vacuum x-ray beamline for surface EXAFS experiments has been constructed at the 2.5-GeV storage ring at Brookhaven National Laboratory, USA. Its design minimizes or eliminates a variety of problems inherent in other beamlines, providing state-of-the-art intensity, brightness, resolution, and beam stability over an extremely wide range of energy. Performance is discussed with initial results obtained after the recent x-ray ring shutdown.
SiC mirror development at the Photon Factory (invited)
Authors: Sato S. , Iijima A. , Takeda S. , Yanagihara M. , Miyahara T. , Yagashita A. , Koide T. , Maezawa H.
Published: July 2002

Several large-size mirrors coated with a thin layer of CVD-SiC for intense synchrotron radiation have been fabricated and commissioned at the Photon Factory. Substrates of these mirrors are high-purity graphite, recrystallized SiC and sintered SiC. Detailed properties of mirror-materials are described. First test of exposure of high-power mirrors to intense radiation from the 53-pole permanent-magnet wiggler are briefly reported.
Experimental techniques for the study of nuclear Bragg scattering in systems containing 57Fe (invited)
Authors: Siddons D. P. , Hastings J. B. , Faigel G. , Grover J. R. , Haustein P. E. , Berman L. E.
Published: July 2002

Resonant filtration of synchrotron radiation has been proposed as a method of obtaining x rays with extremely narrow bandwidths (or very long coherence lengths). Resonant scattering of x rays and neutrons is of general interest, and displays several phenomena, which require novel instrumentation in order to be properly observed. We describe here some of the techniques which we have developed for the specific purpose of studying dynamical diffraction by the Mössbauer resonance in 57Fe.
Coronary angiography using synchrotron radiation (invited)
Authors: Thompson A. C. , Rubenstein E. , Zeman H. D. , Hofstadter R. , Otis J. N. , Giacomini J. C. , Gordon H. J. , Brown G. S. , Thomlinson W. , Kernoff R. S.
Published: July 2002

Imaging of coronary arteries using a venous instead of an arterial injection of contrast agent could provide a much safer method to diagnose heart disease. The tunability, intensity, and collimation of synchrotron radiation x-ray beams makes possible imaging systems with greatly improved imaging sensitivity. A pair of fan x-ray beams, a movable patient chair, and a multielement x-ray detector are used to acquire a pair of x-ray images above and below the iodine K edge. The logarithmic subtraction of these two images produces an image with excellent sensitivity to contrast agent and minimal sensitivity to bone and tissue. High-quality images from a dog and preliminary images from five humans have been obtained. Improvements are being made to the system to increase the effective radiation flux and to measure the position of both x-ray beams.
Observation of x-ray undulator radiation on PEP (invited)
Authors: Lavender William , Brown George , Troxel Teresa , Coïsson Roberto
Published: July 2002

A 2-m undulator magnet and associated beamline have been installed on the electron-positron storage ring PEP. The undulator is designed to produce photons at 12 keV with high intensity when the storage ring is operated at its nominal energy of 14.5 GeV. We report measurements of the spectral and angular properties of the radiation when PEP is operated in a low-emittance (ε∼6×10−9 m rad) configuration. The spectral properties are in good agreement with theoretical predictions.