bluuebunny/crossref_metadata_2025 huggingface dataset:
Bacterial endocarditis in neonatal intensive care
Authors: Drew GF OPIE, SH FRASER, JH , Drew S
Published: July 2002

Objectives: To ascertain the incidence of bacterial endocarditis in a level III neonatal nursery. To document the clinical features, assess survival, and evaluate the role of central venous catheters in neonates with bacterial endocarditis.

Methodology: Index cases were identified by retrospective review of the echocardiographic records of infants admitted to the neonatal nursery from 1983 to 1995. Data obtained by review of the clinical records of these infants, and case‐matched controls.

Results: From January 1983 to December 1995, 12 249 infants were admitted to the Special Care Nursery. Eight infants with endocarditis were identified, an incidence of 0.07%. Presenting symptoms and signs were often vague and nonspecific. Gestation less than 32 weeks, birthweight less than 1500 g, thrombocytopenia and neutropenia or neutrophilia were common features. Infants with endocarditis had a significantly higher Clinical Risk Index for Babies score than those without endocarditis. The tricuspid valve was involved in seven infants, six of whom had a percutaneous central venous catheter in situ before diagnosis. Mitral valve involvement occurred in two infants, neither of whom had central lines inserted. However, compared to infants without endocarditis, the placement of a central venous line was not of statistical significance. Seven of the eight infants survived following prolonged antibiotic therapy.

Conclusions: Bacterial endocarditis is a rare but serious condition, which is usually not fatal. In the premature newborn infant, presenting signs and symptoms are often nonspecific. Endocarditis should therefore be considered in the unwell very low birthweight infant.
Gene expression of prothrombin in the human kidney and its potential relevance to kidney stone disease
Authors: Stapleton  , Timme  , Ryall
Published: July 2002

Objective

 To determine whether urinary prothrombin fragment 1 (UPTF1), which shows considerable promise as a critical determinant of calcium oxalate (CaOx) stone formation, is manufactured by the human kidney.

Materials and methods

 Ribonucleic acid was isolated from eight kidneys, two spleens and one liver. Using reverse transcriptase‐polymerase chain reaction, mRNA corresponding to the UPTF1 portion of prothrombin was analysed by agarose‐gel electrophoresis and Southern blotting.

Results

 Six kidney specimens showed clear evidence of prothrombin gene expression; expression in the kidney was less than that in the liver.

Conclusion

 This is the first demonstration of prothrombin gene expression within the human kidney, a finding that not only has implications for CaOx stone disease but also potentially for blood coagulation.
Fixation disparity and near visual acuity
Authors: Jenkins T. C. A. , Abd‐Manan F. , Pardhan S.
Published: July 2002

Twenty patients having associated heterophoria values of 2 Δ and greater, as recorded with a Mallett unit, had their near monocular and binocular visual acuities measured. In the latter case, measurements were taken both with the associated heterophoria corrected by prisms and without prism correction. Bradford Near Vision charts, specially designed to measure visual acuity at near in seconds of arc, were used in the acuity measurement. The improvement of binocular acuity compared with monocular acuity was less than would occur in normal subjects without associated heterophorias. When the associated heterophorias were corrected with prisms the improvement in binocular over monocular acuity was similar to that found in normal subjects, with zero associated heterophoria readings.
An Auxin Transport Inhibitor Interferes With Unicellular Gravitropism in Protonemata of the Moss Ceratodon purpureus
Authors: Schwuchow J. , Michalke W. , Hertel R.
Published: July 2002

Abstract: Gravitropism of the protonemata of the moss Ceratodon purpureus (Hedw.) Brid. was studied after treatment with auxin transport inhibitors and auxin‐related substances. The phytotropins NPA (naphthylphthalamic acid) and PBA (pyrenoylbenzoic acid), known to block auxin efflux in higher plants, strongly inhibited gravitropic curvature of the apical protonemal cell. At 3 μM NPA or PBA, approximately 60 % inhibition of curvature was observed; growth rates were less affected. Tyrphostin A47, a known antagonist of NPA effects in higher plants, released the inhibition of moss protonemal gravitropism and restored the full curvature response. Exogenous IAA, even at high concentrations (40 μM), did not interfere with protonemal gravitropism. To account for the results, modified hypotheses for auxin transport and action are discussed.
Growth of high T
c superconducting Bi4(Ca,Sr)6Cu4O16+x crystals
Authors: Morris P. A. , Bonner W. A. , Bagley B. G. , Hull G. W. , Stoffel N. G. , Greene L. H. , Meagher B. , Giroud M.
Published: July 2002

To determine intrinsic properties of the newly discovered Bi-Ca-Sr-Cu-O high Tc superconductors, single crystals are necessary. Compositions in this system have been heat treated to survey the melting temperatures and phase field in which superconductivity is detected. The nucleation and growth of the 85 K phase from the melted composition Bi4Ca3Sr3Cu4O16+x is observed to be a kinetically slow process which can be precluded by a sufficiently rapid quench, but post-anneals produce the 85 and 110 K phases in the quenched material. The melted composition (23% Bi2O3-46% CaO,SrO-31% CuO), after subsequent slow cooling, results in large discrete crystals of the 85 K superconducting phase and a residual flux.
Carbon diffusion in undoped, n-type, and p-type GaAs
Authors: Cunningham B. T. , Guido L. J. , Baker J. E. , Major J. S. , Holonyak N. , Stillman G. E.
Published: July 2002

The effects of background doping, surface encapsulation, and As4 overpressure on carbon diffusion have been studied by annealing samples with 1000 Å p-type carbon doping spikes grown within 1 μm layers of undoped (n−), Se-doped (n+), and Mg-doped (p+) GaAs. The layers were grown by low-pressure metalorganic chemical vapor deposition using CCl4 as the carbon doping source. Two different As4 overpressure conditions were investigated: (1) the equilibrium pAs4 over GaAs (no excess As), and (2) pAs4 ∼2.5 atm. For each As4 overpressure condition, both capless and Si3N4-capped samples of the n−-, n+-, and p+-GaAs crystals were annealed simultaneously (825 °C, 24 h). Secondary-ion mass spectroscopy was used to measure the atomic carbon depth profiles. The carbon diffusion coefficient is always low, but depends on the background doping, being highest in Mg-doped (p+) GaAs and lowest in Se-doped (n+) GaAs. The influence of surface encapsulation (Si3N4) and pAs4 on carbon diffusion is minimal.
Effect of two-photon absorption on all-optical guided-wave devices
Authors: DeLong K. W. , Rochford K. B. , Stegeman G. I.
Published: July 2002

We show that two-photon absorption can lead to serious deterioration in the all-optical switching characteristics of nonlinear directional couplers and distributed feedback gratings.
Passive mode locking of a two-section multiple quantum well laser at harmonics of the cavity round-trip frequency
Authors: Sanders Steve , Yariv Amnon , Paslaski Joel , Ungar Jeffrey E. , Zarem Hal A.
Published: July 2002

A multiple quantum well GaAs/AlGaAs laser with two electrically isolated contacts is passively mode locked in an external cavity at the first through sixth harmonics of the pulse round-trip frequency of 1.17 GHz to produce pulses shorter than 10 ps. The repetition rate is switched between harmonics by adjusting the gain section current, and large hysteresis between the different repetition rates is observed, with up to four different repetition rates for the same gain current. The results are compared with small and large signal passive mode-locking theories by considering modifications to the saturated gain recovery between pulses when the laser operates at different harmonics.
Director-polarization reorientation via solitary waves in ferroelectric liquid crystals
Authors: Abdulhalim I. , Moddel G. , Clark N. A.
Published: July 2002

The spatial nonuniformity of the director field in ferroelectric liquid crystals during switching is demonstrated using the electro-optic response to a bipolar field and explained by director solitary wave motion.
Charged dangling bonds in undoped amorphous silicon
Authors: Schumm G. , Lotter E. , Bauer G. H.
Published: July 2002

We report a basic disproportionality between light-induced changes in the defect density of undoped hydrogenated amorphous silicon (a-Si:H) determined from optical absorption and determined from spin density measurements. The results yield a lower limit for the ratio of charged to neutral dangling bonds in annealed a-Si:H of around 2–2.5, and in degraded material this ratio is reduced. The derived minimum ratio holds if charged dangling bonds are caused by unintentional impurity doping, a ratio approximately twice as large is obtained if the charged dangling bonds are formed according to thermodynamical equilibration models. The observed Fermi level shifts and optical absorption spectra during light soaking and annealing favor the thermodynamical equilibration model.
Comparison of magnetic and electric field induced switching in polymer dispersed liquid crystal films
Authors: Li Zili , Kelly J. R. , Palffy-Muhoray P. , Rosenblatt C.
Published: July 2002

We report, for the first time, the switching of a polymer dispersed liquid crystal film by a magnetic field. We have measured the optical transmittance of such samples as a function of magnetic and electric field strength. The response to these fields is similar. The observed behavior is in good agreement with theoretical predictions. The magnetic field results give information about the origin of the observed hysteresis.
Fragmentation process induced by microsecond laser pulses during lithotripsy
Authors: Rink K. , Delacrétaz G. , Salathé R. P.
Published: July 2002

A fiber optic stress sensing technique is applied to evaluate the fragmentation mechanism for pulsed dye-laser lithotripsy. We demonstrate for the first time that the fragmentation process with microsecond laser pulses originates from the shock wave induced by the cavitation bubble collapse. This shock occurs some hundreds of microseconds after the laser pulse. The shock induced by the plasma expansion, which occurs during laser irradiation, has a minor effect.
In situ solid phase epitaxial growth of C49-TiSi2 on Si (111)-7×7 substrate
Authors: Choi Chi Kyu , Yang Soo Jeong , Ryu Jai Yon , Lee Jeong Yong , Park Hyung-Ho , Kwon Oh Joon , Lee Yong Pak , Kim Kun Ho
Published: July 2002

C49-TiSi2 film was grown epitaxially on Si(111) substrate by depositing Ti film on Si(111)- 7×7 surface followed by in situ annealing in ultrahigh vacuum. The deposition was monitored by means of reflection high energy electron diffraction as a function of the thickness of Ti film. The best result for the growth of epitaxial C49-TiSi2 was obtained from the Ti(30 ML)/Si(111)-7×7 sample which was annealed at 650 °C for 20 min. Images of cross-sectional high resolution transmission electron microscopy shows that the silicide/silicon interface is shown to be clear and flat. The orientation relationships are TiSi2[2̄11]∥Si[011̄], TiSi2 (120)∥Si(111) without misorientation angle. Almost the whole area of the TiSi2 layer is revealed as an epitaxial C49 structure.
Transverse mode emission characteristics of gain-guided surface emitting lasers
Authors: Tai K. , Lai Y. , Huang K. F. , Huang T. C. , Lee T. D. , Wu C. C.
Published: July 2002

Transverse mode emission characteristics of gain-guided surface emitting lasers at 0.85 μm were investigated. Up to six nondegenerate circularly symmetrical modes were observed with detunings between the adjacent modes around 2.5 Å. Numerical simulations were performed. The calculated beam sizes, difference of modal gains to account for the side mode suppression ratio when operated with one dominant mode, and wavelength detunings agreed with experiments. Numerical simulations also predict that the mirror loss due to Gaussian beam diffraction is nonnegligible for the 1.3–1.55 μm devices.
Record low SiO2/Si interface state density for low temperature oxides prepared by direct plasma-enhanced chemical vapor deposition
Authors: Chen Z. , Yasutake K. , Doolittle A. , Rohatgi A.
Published: July 2002

A new process has been developed to achieve a very low SiO2/Si interface state density for low temperature deposited oxides on silicon substrates. The technique involves direct plasma-enhanced chemical vapor deposition (PECVD), with appropriate growth conditions, followed by a photo-assisted anneal. Approximately 500-Å-thick SiO2 layers, deposited on Si by PECVD at 250 °C with 0.02 W/cm−2 rf power, then covered with an evaporated thin aluminum layer, and finally subjected to a photo-assisted anneal in forming gas ambient at 350 °C, resulted in interface state density, (Dit), in the range of 1–4×1010 cm−2 eV−1 near midgap of silicon. The best Dit value achieved in this study was 1.1×1010 cm−2 eV−1, which sets a new record for the lowest Dit for the PECVD oxides fabricated to date. Detailed analysis showed that the PECVD deposition conditions, photo-assisted anneal, forming gas ambient, and the presence of an aluminum layer on top of the oxides during the anneal, all contributed to this extremely low value of Dit.
New method to improve thermal stability in the interface of silicon and tungsten by the interposition of plasma deposited tungsten nitride thin film
Authors: Lee Chang Woo , Kim Yong Tae , Lee Jeong Yong
Published: July 2002

Thermally stable tungsten nitride/tungsten bilayer has been proposed for the application of metallization. This bilayer is sequentially formed by plasma enhanced chemical vapor deposition without breaking vacuum. The Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy reveal that the interaction between the W and Si substrate can be prevented by interposing a 800-Å-thick W67N33 layer. The W67N33/W bilayer maintains the integrity of the interface during annealing at 850 °C for 30 min without the formation of Si2W and interdiffusion phenomena. Sheet resistivity of the W67N33/W bilayer is gradually decreased from 17 to 12 μΩ cm at annealing temperatures up to 850 °C.
On the nature of cross-hatch patterns on compositionally graded Si1−xGex alloy layers
Authors: Shiryaev Sergey Yu. , Jensen Flemming , Petersen Jon Wulff
Published: July 2002

The effect of strain relaxation on the surface morphology of compositionally graded Si1−xGex layers grown at 550 °C has been investigated by a combination of transmission electron and atomic force microscopy. By annealing unrelaxed graded layers, we have found that shear displacements caused by dislocation glide roughen the surface dramatically. This effect is attributed to the formation of a network of dislocation clusters which give rise to the pronounced slip-band pattern on the surface of the graded layers. It is shown that the surface plastic displacements produced by such a network during growth of the graded layer contribute significantly to the formation of the cross-hatch patterns.
Direct measurement of the Hall factor for holes in relaxed Si1−xGex (0<x<1)
Authors: Chen Y. C. , Li S. H. , Bhattacharya P. K. , Singh J. , Hinckley J. M.
Published: July 2002

The Hall factor for holes in relaxed p-type Si1−xGex alloys has been determined from mobility measurements at magnetic fields up to 7 T at 290 K. Our data together with previously published values for Si and Ge suggest that r for holes in SiGe varies between 0.73 and 1.7 with a possible strong bowing.
Artificially engineered pyroelectric Sr1−xBaxTiO3 superstructure films
Authors: Wiener-Avnear E.
Published: July 2002

Artificially engineered superstructure films of SrTiO3/BaTiO3 were deposited layer by layer via pulsed laser deposition onto substrates of sapphire with and without Pt/Ti electrodes. Secondary-ion-mass-spectroscopy and x-ray diffraction measurements were performed to explore the nature of the multilayered structure. Dielectric measurements versus temperature revealed a broad peak near the extrapolated Curie temperature.
Effect of chiral dopant on the performance of polymer dispersed liquid crystal light valve
Authors: Lu Z.-J. , Yang D.-K.
Published: July 2002

We have experimentally studied the effect of chiral dopant on the electro-optical performance of a polymer-dispersed liquid crystal (PDLC) light valve. Adding a small amount of chiral dopant decreases the turn-OFF time significantly but increases the drive voltage only slightly. A phenomenological theory is presented to explain the experimental results.
Arsenic segregation and passivation in the heteroepitaxy of Ge/GaAs
Authors: Leycuras André
Published: July 2002

During the epitaxy of Ge, the arsenic introduced for doping is known to be partially incorporated into the layer and partially segregated at the Ge free surface. Arsenic at the (001) surface can saturate the Ge dangling bonds and the growth rate should decrease accordingly. An in situ monitoring of the chemical vapor deposition of Ge by laser reflectometry, and its theoretical simulation, give the morphology and the growth rate as a function of time (and thickness) and hence the segregation rate of As. The variation of the growth rate versus the AsH3/GeH4 flow rate ratio shows the formation of As2 dimers. Under constant temperature and constant AsH3/GeH4 flow rates, the growth rate first decreases, showing the segregation of As at the Ge(001) surface, then remains stable and finally increases, due to a change in the surface morphology exhibiting high order crystallographic planes on which no As2 dimers can stay.
High-power mode-locked semiconductor lasers using flared waveguides
Authors: Mar Alan , Helkey Roger , Zou W. X. , Young D. Bruce , Bowers John E.
Published: July 2002

We describe the use of flared waveguide diode lasers for obtaining increased output power under mode-locked operation. The flared waveguide expands the optical mode from a narrow region which gives a single lateral optical mode, to a wider multimode region for higher pulse saturation energy. Flared gain and flared absorber section geometry devices are compared to devices with conventional uniform waveguides. Using flared gain section devices, improvements in both pulse energy (6.8 pJ) and pulsewidth (3.3 ps) were measured compared to uniform waveguide devices. Peak powers of over 2 W are obtained, which, to our knowledge, is the highest peak power obtained directly from mode-locked single stripe diode lasers.
Polarization modulation ellipsometry: A compact and easy handling instrument
Authors: Huber E. , Baltzer N. , von Allmen M.
Published: July 2002

A polarization modulation ellipsometer for measurements of the complex dielectric function of opaque and reflecting materials in the wavelength range 230–920 nm is presented. The instrument can be built at relatively moderate cost but offers reasonable accuracy. It is suitable for routine measurements in a general solid-state laboratory because of its easy handling and maintenance.
Design of a rocket-borne radiometer for stratospheric ozone measurements
Authors: Barnes Robert A. , Simeth Peter G.
Published: July 2002

A four-filter ultraviolet radiometer for measuring stratospheric ozone is described. The payload is launched aboard a Super-Loki rocket to an apogee of 70 km. The instrument measures the solar ultraviolet irradiance over its filter wavelengths as it descends on a parachute. The amount of ozone in the path between the radiometer and the sun is calculated from the attenuation of solar flux using the Beer–Lambert law. Radar at the launch site measures the height of the instrument throughout its flight. The fundamental ozone value measured by the ROCOZ-A radiometer is the vertical ozone overburden as a function of geometric altitude. Ozone measurements are obtained for altitudes from 55 to 20 km, extending well above the altitude range of balloon-borne ozone-measuring instruments. The optics and electronics in the radiometer have been designed within relatively severe size and weight limitations imposed by the launch vehicle. The electronics in the improved rocket ozonesonde (ROCOZ-A) provide essentially drift-free outputs throughout 40-min ozone soundings at stratospheric temperatures. The modest cost of the payload precludes recovery and makes the instrument a versatile tool compared to larger ozonesondes.
X-ray sensing pickup tube
Authors: Suzuki Yoshio , Hayakawa Kazunobu , Usami Katsuhisa , Hirano Tatsumi , Endoh Tooru , Okamura Yoshinori
Published: July 2002

An x-ray sensing pickup tube free of white defects in the scanning area has been developed, and its characteristics have been evaluated. This pickup tube functions in a wide x-ray energy range from 7 to 40 keV. The maximum spectral sensitivity observed at 20 keV photon energy is 6×10−17 A/(photon/s). The limiting resolution is about 8 μm. The observation of a focused x-ray beam has been carried out.
Photodegradation of CdxZn1−xSe quantum wells
Authors: Haugen G. M. , Guha S. , Cheng H. , DePuydt J. M. , Haase M. A. , Höfler G. E. , Qiu J. , Wu B. J.
Published: July 2002

Photoluminescence imaging was used to study photodegradation in CdZnSe quantum wells, important to II-VI based blue-green light emitter technology. The observed degradation microstructure evolves similarly to features observed during CdZnSe based LED and laser operation. Degradation is shown to emanate from pre-existing defects to form dark line defects along the 〈100〉 directions. We report an observation of a mobile defect in II-VI materials that is the precursor to the 〈100〉 dark line defects.
A fast 35-GHz time-resolved EPR apparatus
Authors: Forbes Malcolm D. E.
Published: July 2002

A time-resolved Q-band (35-GHz) electron paramagnetic resonance (EPR) apparatus with a 25-ns rise time and 10-ns time resolution is described. Built around the Varian E110 microwave bridge, a detailed description of the resonator, flow system, optical alignment, and preamplifier electronics is given. The resonator is a TE103 rectangular cavity with front and back cutoff flanges attached to allow maximum laser light access. An adjustable Gordon coupler was constructed to achieve critical coupling to the cavity. Two separate designs of quartz sample flow cell are described, one for low dielectric organic solvents and one for aqueous samples. The standard diode detection system as shipped by Varian was used, but the signal from the detector diode was branched into two separate amplifiers, one the standard preamplifier for automatic frequency control lock-in operation, the other based on a Comlinear op-amp which gave fast rise times (9 ns) before the signal was trapped by a boxcar signal averager. Test systems clearly showed that the instrument response is no longer limited by the quality factor of the cavity but by the laser pulse width and jitter. Strong, spin-polarized EPR signals from the photolysis of dimethoxyphenylacetophenone, which were well separated due to their large g-factor difference, were distinguished at sampling delay times as early as 10 ns after the laser flash producing the radicals. A sensitivity comparison to X-band is made using the acetone/2-propanol system.
Skin friction measurement with partially exposed polymer dispersed liquid crystals
Authors: Parmar D. S. , Holmes H. K.
Published: July 2002

Partially exposed polymer dispersed liquid crystal thin film (10–25 μm) deposited on a flat glass substrate has been used for the first time to measure skin friction. Utilizing the shear stress induced director reorientation in the partially exposed liquid crystal droplets, optical transmission under crossed polarization has been measured as a function of the air flow differential pressure. Direct measurement of the skin friction with a skin friction drag balance, under the same aerodynamic conditions, lets us correlate the skin friction with optical transmission. This provides a unique technique for the direct measurement of skin friction from the transmitted light intensity. The results are in excellent agreement with the model suggested in this paper.
In situ measurement of the deuterium (hydrogen) charging of a palladium electrode during electrolysis by energy dispersive x-ray diffraction
Authors: Felici R. , Bertalot L. , DeNinno A. , LaBarbera A. , Violante V.
Published: July 2002

A method to determine the concentration of deuterium inside a palladium cathode during the electrolysis of LiOD–heavy water solution is described. This method is based on the measurement of the host metal lattice parameter which is linearly related to the concentration in a wide range. A hard-x-ray beam which is able to cross two glass walls and few centimeters of water solutions without suffering a strong attenuation has been used. The measurement of the lattice parameter is performed in situ, during the electrolysis, by using energy dispersive x-ray diffraction. The sample volume illuminated by the x-ray beam is limited to a small region close to the surface and depends on the incident photon energy. In principle, this allows one to study the dynamics of the charging process and to determine the concentration profile in the range from few up to tens of micrometers. The deuterium concentration, determined by this method, was then checked by degassing the cathode in a known volume and was always found in a very good agreement, showing that the charging was uniform for the whole sample.
A system to measure complex permittivity of low loss ceramics at microwave frequencies and over large temperature ranges
Authors: Meng Binshen , Booske John , Cooper Reid
Published: July 2002

A system has been developed for measuring the complex permittivities of low loss ceramic materials at frequencies from 2 to 20 GHz and over a temperature range 20–1000 °C. The measurement technique involves a modified version of the conventional cavity perturbation method. Details of the design and fabrication of the circular cylindrical cavity and the input and output coupling transmission lines are discussed. Particular features related to high-temperature operation and temperature cycling are described. Data are presented for an illustrative measurement of the complex microwave dielectric properties of NaCl single crystals between 20 and 400 °C. The experimental results are in excellent agreement with theoretical models.
Time-domain photoacoustic measurements of absolute optical absorption coefficient using three-chamber cell
Authors: Egerev S. V. , Fokin A. V. , Pashin A. E.
Published: July 2002

Pulsed photoacoustic spectroscopy (PAS) technique for immediate measuring absolute optical absorption coefficient is presented. It is based on determination of amplitude-time characteristics of photoacoustic (PA) signal generated in air surrounding the sample under investigation. The PA signal is excited by a short laser pulse. The sample is placed in the lateral chamber of a three-chamber PA cell. The difference of PA signals excited in two other chambers is recorded. Time dependence of PA signal for each PA cell chamber is derived. The theoretical predictions are experimentally verified. The pulsed PAS technique presented was tested experimentally by measuring water absorption coefficient at an infrared wavelength.
Conceptual development and characterization of a diamond-based ultraviolet detector
Authors: Jiang Wei , Ahn Jaeshine , Chuen Chan Yuen , Loy Lam Yee
Published: July 2002

A metal–semiconductor–metal (MSM) structure ultraviolet (UV) photodetector has been designed and fabricated on chemical vapor deposition grown diamond and its performance has been characterized. A concept was envisioned of creating a new process by which 1 μm small gap spacing was achieved. This kind of detector can be operated at a lower bias voltage with a higher photoresponsivity in the UV range. The success of this device depended on the bilayer metal electrodes, good Ohmic contact, image reversal technique, direct writing process, and sacrificial layer technology. Current–voltage and capacitance–voltage characteristics, photoresponsivity, and quantum efficiency of planar MSM structures with Au/Ti–diamond contacts are presented.
An active telescope secondary mirror control system
Authors: Bortoletto Favio , Bonoli Carlotta , Fantinel Daniela , Gardiol Daniele , Pernechele Claudio
Published: July 2002

One of the main constraints for a modern astronomical telescope is the active control of the secondary mirror, mainly for the correction of the decentering coma and defocus induced by thermomechanical distortions. The mirror movements should be smooth, as precise as the optical design requires, and restricted to within predefined limits. It should be possible to perform mirror alignment and focus corrections without pausing the exposure (online control). The Galileo telescope achieves all this by using a support structure driven via six actuator bars (a hexapod system or Stewart platform) and a real-time control system based on a transputer network that allows parallel control of each actuator. Both the hexapod secondary support and the control system have been built and tested at the telescope. The results show that the errors introduced during mirror positioning lead to optical aberrations well below the diffraction figure of the telescope, and the systems work smoothly enough to allow online control.
A tunable focusing beamline for desktop x-ray microtomography
Authors: Gurker N. , Nell R. , Seiler G. , Wallner J.
Published: July 2002

In this article a desktop x-ray microtomography (μXCT) instrument is presented, which utilizes conventional diffraction tubes and tunable focusing optics. The beamline is based on an elastically bent cylindrical multilayer mirror, given by a coated and rhombic shaped Si wafer, which is placed on bearings with two of its tips and is actuated by a single transverse center force to a desired curvature and herewith focal length. This optical element is used in a grazing incidence reflection geometry, demagnifying the tube focal spot into an image line with width (w) and position following from a classical imaging equation (magnification ratio M). While the tube and the image (“focal”) position are kept fixed, the curvature and axial position of the mirror are adaptively controlled for different M values and Bragg angles θ̄ (i.e., pass-energies Ē), which results in a one-dimensional zoom-optical system. The specimen is placed in the high-depth focal region of the condensed beam for the CT-scanning procedure with the slice orientation given by the focusing direction. Minor modifications of the fundamental rhombic mirror shape also enable the establishment of imaging geometries with elliptical and parabolic cylindrical-type optical figures. Multilayer reflection inherently results in a small bandpass of photon energies (ΔE/Ē). Pass-energy Ē is preferably tuned to characteristic lines of the tubes in use (Cr, Cu, Mo target) with the option of also using the white x-ray spectrum. Numerical values of beamline specifications are characterized by: 0.1⩽M⩽1.0, 10⩽w⩽100 μm, 0.5⩽θ̄⩽2°, 5⩽Ē⩽30 keV, ΔE/Ē≲0.1. Photon intensity along the focal line is given by 106<N<2×107 (s mm)−1, depending on the type of tube, mirror reflectivity and M setting. The fundamental principles, the experimental setup and major components of the beamline are described and the theoretical and experimental performance in terms of photon flux, pass-energy bandwidth and beam geometry are evaluated. Examples of μXCT scanning are also given. In the current configuration, a fast scintillation counter behind an object slice collimator is used for photon detection, although the sheet-like geometry of the focused x-ray beam can be further used for parallel projection data acquisition along the nonfocusing direction of the optical system (i.e., for different object slices) by application of a suitable charge coupled device-type detector.
Lock-in common-mode rejection demodulation: Measurement technique and applications to thermal-wave detection. Experimental
Authors: Paoloni Stefano , Nicolaides Lena , Mandelis Andreas
Published: July 2002

A new signal generation methodology based on lock-in amplifier common mode rejection demodulation for materials nondestructive evaluation has been implemented experimentally with thermal waves in a photothermal radiometric apparatus. A procedure to calibrate the experiment is described in order to take into account instrumental time delay phase shifts between the reference and the optical excitation wave form. Some preliminary results obtained on Zr–2.5Nb shot peened samples are presented and compared to those obtained by temporally modulating the pump intensity as a 50% duty cycle square wave. The comparison shows the new measurement methodology to be a very promising technique for nondestructive evaluation and depth profiling applications, featuring high detectivity for low-dynamic-range and poor-signal to noise ratio signals, such as those obtained with thermal-wave diagnostics.
Effects of interfacial chemistry on the formation of interfacial layers and faulted defects in ZnSe/GaAs
Authors: Kuo L. H. , Kimura K. , Yasuda T. , Miwa S. , Jin C. G. , Tanaka K. , Yao T.
Published: July 2002

Existence of Zn-As and Ga-Se interfacial layers were suggested by transmission electron microscopy in Zn treated and Se treated or reacted ZnSe/GaAs interfaces, respectively. High densities of As precipitates and Shockley partials were introduced in films with Zn treatment on a c(4×4) As-rich GaAs surface. In addition, high densities of vacancies and Shockley partials were obtained in samples with a Se-reacted ZnSe/GaAs interface. Formation of the Shockley partials may originate from the stacking errors induced by disordering of Zn- or Ga-interstitials on the GaAs surface.
Evanescent-field amplification in Nd3+-doped fluoride planar waveguide
Authors: Ohtsuki T. , Honkanen S. , Peyghambarian N. , Takahashi M. , Kawamoto Y. , Ingenhoff J. , Tervonen A. , Kadono K.
Published: July 2002

Planar channel waveguides of rare-earth doped fluoride glass are demonstrated with single mode excitation and propagation losses below 3 dB/cm. The waveguide core was fabricated by Ag+–Na+ molten salt ion exchange process in a borosilicate glass (BGG31), and a Nd3+-doped ZBLAN glass was used as a cladding. A 0.45 dB signal amplification at 1.064 μm was observed in the fabricated 1 cm long waveguide, and a 0.9 dB amplification is expected at the emission peak (1.049 μm). Modeling results show 2.5 dB/cm potential gain with the improvement in surface flatness of ZBLAN glass.
Anomalous temperature dependence of persistent photoconductivity in C60 single crystal
Authors: Chiu K. C. , Wang J. S. , Dai Y. T. , Chen Y. F.
Published: July 2002

The temperature dependence of persistent photoconductivity (PPC) has been investigated in high-quality C60 single crystals. We found that the rotational order and disorder phase transition (Tc≊260 K) can significantly change the PPC behavior. At temperatures above Tc, the PPC relaxation rate increases as temperature increases. Quite surprisingly, in the region T<Tc, the PPC relaxation rate decreases with increasing temperature. Our result clearly indicates that the underlying mechanism of the PPC effect involves the motion of the C60 molecule.
Effects of a series resistor on electron emission from a field emitter
Authors: Luginsland J. W. , Valfells A. , Lau Y. Y.
Published: July 2002

Universal curves are constructed that provide an immediate determination of the effect of a series resistor on the electron emission from a field emitter. These curves are applicable to both the low current and high current regime. The effects of space charge and of the series resistor are apparent from these curves, which are applicable to a large class of materials. An example is given to illustrate their use.
Influence of surface treatment and dopant concentration on field emission characteristics of boron-doped diamond thin films
Authors: Nagao M. , Kondo T. , Gotoh Y. , Tsuji H. , Ishikawa J. , Miyata K. , Kobashi K.
Published: July 2002

Field emission characteristics of B-doped diamond thin films terminated with oxygen and hydrogen were investigated. The diamond thin films were prepared by microwave plasma chemical vapor deposition. The dependence of emission characteristics on the surface treatment and on the B concentration was investigated. The turn-on voltage required to extract a current of 0.1 nA depended on these preparation parameters. The emitters with lower B concentration emitted electrons at a lower turn-on voltage, and the H-terminated emitters had a lower turn-on voltage than O-terminated emitters. The analysis of the slope and the intercept of Fowler–Nordheim plot revealed that the dependence of turn-on voltage on the surface treatment is due to the difference of emission barrier height, and that the dependence on B concentration is due not to the emission barrier height but to the surface morphology.
Mechanism of the photochemically induced reaction between Ga(CH3)3 and HN3 and the deposition of GaN films
Authors: Linnen C. J. , Coombe R. D.
Published: July 2002

Gaseous HN3 reacts with surface-bound Ga(CH3)x species slowly at 300 K to produce thin films containing azide-substituted gallium compounds. When mixtures of HN3 and Ga(CH3)3 over the surface are irradiated at 253.7 nm, the reaction is dramatically accelerated, and films containing GaN and complexed N2 are produced. Heating of these films to 400 K drives off the N2 leaving GaN. The mechanism of the reaction is thought to involve photodissociation of HN3 to produce excited NH(a1Δ) and N2, followed by insertion of the NH(a1Δ) into the Ga–C bond of surface-bound Ga(CH3)x molecules. The insertion product eliminates CH4 to leave GaN.
Boundary condition effects on field-induced deformation modes in polymer dispersed liquid crystals
Authors: Yamaguchi Takeshi , Kawata Yasushi , Mori Yasushi
Published: July 2002

Electric field-induced deformation modes, which are considered one of the causes of the hysteresis in the V-T response of polymer dispersed liquid crystal (PDLC), were investigated. We constructed model PDLC cells with varied alignment treatments at the interface of the liquid crystal droplets. The electric field-induced deformation modes of the liquid crystals in the model cells were analyzed by polarized microscope observations. Our results suggested a possible way to hysteresis-free PDLC devices.
Nonlinearity and scaling behavior in donor-doped lead zirconate titanate piezoceramic
Authors: Mueller Volkmar , Zhang Q. M.
Published: July 2002

Two different effective thresholds for the onset of nonlinearity in the dielectric and piezoelectric coefficients of donor-doped lead zirconate titanate (soft PZT) piezoceramics at electric ac fields Ec1≈100 V/cm and Ec2≈1 V/cm are found. Both are characterized by a scaling behavior x=x0+A[E−Ec)/Ec]φ above the respective threshold, where x is the dielectric or piezoelectric coefficient. The values of the effective exponent φ are apparently independent of the particular ceramic system which suggests a universal behavior in soft PZT. We suggest that the nonlinearity is dominated by the dynamics of domain walls in a randomly pinned medium.
Phase transitions in planar magnetic nanostructures
Authors: Cowburn R. P. , Welland M. E.
Published: July 2002

Using numerical micromagnetics we have studied the ground state magnetization distribution of square planar ferromagnetic elements (“nanostructures”). As the element size is reduced from 250 to 2 nm at constant thickness (2–35 nm), we find that the magnetization distribution undergoes up to three phase transitions involving as many as three different near single domain states. One of these phase transitions is analogous to the reorientation phase transition observed in continuous ultrathin magnetic films.
Exchange bias and spin-valve structures using amorphous ferromagnetic Co65Mo2B33 layers
Authors: Wu X. W. , Ambrose T. , Chien C. L.
Published: July 2002

Exchange biasing has been observed in bilayers of amorphous ferromagnetic Co65Mo2B33 and antiferromagnetic CoO indicating new latitude in materials for exploring exchange-coupled structures. Angular dependence measurements show that the exchange field in such structures displays a simple cos θ dependence. Spin-valve structures based on a-Co65Mo2B33 and Co0.5Ni0.5O have also been made, and the expected switching and magnetoresistance characteristics have been illustrated.
Single-pass thin-film electro-optic modulator based on an organic molecular salt
Authors: Thakur M. , Xu Jianjun , Bhowmik A. , Zhou Ligui
Published: July 2002

Single crystal films of 4′-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) with excellent optical quality have been prepared by modified shear method. Electro-optic modulation for light propagating perpendicular to the film surface was measured at a wavelength (720 nm) where absorption is small. Very large electro-optic modulation (20%) was demonstrated in a 3 μm thick film at a low ac field (1 V/μm, at 4 kHz). Electro-optic modulation in such thin films is suitable for a wide range of applications in free-space interconnects and various modulator structures with light propagating perpendicular to the film. The magnitude of the electro-optic coefficient at 720 nm, r11∼530 pm/V, is significantly larger than that of bulk crystals.
Lateral ordering of coherent Ge islands on Si(001) studied by triple-crystal grazing incidence diffraction
Authors: Kegel I. , Metzger T. H. , Peisl J. , Schittenhelm P. , Abstreiter G.
Published: July 2002

We have applied triple-crystal grazing incidence diffraction to self-assembled islands on a Ge/Si(001) superlattice. Lateral ordering in the near-surface region is evaluated from reciprocal space mappings around different surface reflections. The observed intensities are explained by the short-range order strain modulation of the lattice parameter in the substrate induced by coherent Ge islands. We find the island-induced strain modulation to be arranged in a local square lattice. A nearest neighbor disorder parameter, the size distribution of the islands, and a correlation length are obtained from the presented model.
Electromechanical effect in freely suspended liquid crystal films
Authors: Yablonskii Serguei V. , Oue Toshiyasu , Nambu Hidetaka , Mikhailov Aleksey S. , Ozaki Masanori , Yoshino Katsumi
Published: July 2002

Electromechanical effect in a freely suspended film based on 4-n-octyl-4′-cyanobiphenyl has been detected by means of light scattering at both the first and second harmonics of the exciting electric field. Experimental studies on voltage and frequency dependencies of the optical response are carried out. Organic solvent vapor is shown to strongly affect the electromechanical response. A feasible mechanism for the electromechanical effect is discussed.
The equivalence of vacancy-type damage in ion-implanted Si seen by positron annihilation spectroscopy
Authors: Knights A. P. , Malik F. , Coleman P. G.
Published: July 2002

The response of the Doppler-broadened annihilation linewidth parameter S to ion dose has been measured using a controllable-energy positron beam for n-type Fz–Si(100) implanted with 120 keV Ge+, 400 keV O+, 200 keV He+, and 450 keV H+ ions. For all ions S increases with dose, indicating the presence of vacancy-type defects. It is found that the maximum S values for the Ge+, O+, and H+ implants can be normalized to one well-defined distribution using values of predicted vacancy concentration from the Monte Carlo code TRIM. This result implies that vacancy-type defects from these three implantations are similar in both structure and interstitial recombination rate. The He+ data do not lie perfectly on the universal distribution; it is suggested that this is a result of defect passivation by the implanted He.
Space–time digital holography: A three-dimensional microscopic imaging scheme with an arbitrary degree of spatial coherence
Authors: Indebetouw Guy , Klysubun Prapong
Published: July 2002

An on-line, spatiotemporal, digital holographic method is described and demonstrated experimentally. Using interferometric imaging, each scatterer of a three-dimensional object is encoded as a temporally modulated Fresnel pattern, and recorded on a charge-coupled device. Temporal heterodyning of the signal from each pixel results in a single-sideband, on-line holographic record in digital form. Reconstruction of an image focused on a chosen transverse plane in the object is done by digital correlation with a reconstruction function matched to that plane. The method circumvents most of the drawbacks of both coherent and incoherent holography, and may find applications in three-dimensional imaging and microscopy.
Design of composite InAsP/InGaAs quantum wells for a 1.55 μm polarization independent semiconductor optical amplifier
Authors: Haverkort J. E. M. , Dorren B. H. P. , Kemerink M. , Silov A. Yu. , Wolter J. H.
Published: July 2002

We investigate a composite InAsP/InGaAs quantum well in which an 8 nm tensile strained InGaAs well is surrounded by two compressively strained InAsP layers which feature a 70:30 conduction band offset ratio. The composite quantum well is found to provide a high TM differential gain. The InAsP layers provide strain compensation while simultaneously shifting the band gap to the relevant 1.55 μm wavelength region and increasing the electron confinement. Composite InAsP/InGaAs quantum wells are a promising candidate for realizing a polarization independent semiconductor optical amplifier at 1.55 μm.
Origin and perspectives of the 1.54 μm luminescence from ion-beam-synthesized β-FeSi2 precipitates in Si
Authors: Spinella C. , Coffa S. , Bongiorno C. , Pannitteri S. , Grimaldi M. G.
Published: July 2002

The structural and optical properties of β-FeSi2 precipitates in Si have been analyzed. Float zone Si samples were implanted at 250 °C with 350 keV Fe ions to fluences in the range 1–5×1015/cm2 and annealed in vacuum at 800 °C for times up to 24 h. Detailed morphological analyses of these samples, using transmission electron microscopy, reveal the presence of (i) a band of small (with a diameter <30 nm) highly strained β-FeSi2 precipitates centered at a depth of ∼150 nm, (ii) a band of large (>100 nm diameter) fully relaxed β-FeSi2 precipitates centered at a depth of ∼320 nm, and (iii) residual extended defects. A sharp photoluminescence peak at 1.54 μm is measured at 17 K. This peak remains unchanged when the region containing the small precipitates is removed, using Ar sputtering. On the other hand, it is also fully suppressed when the large precipitates region is removed and a high concentration of extended defects remains in the samples. This allowed us to identify the large unstrained precipitates as the main sources of the 1.54 μm luminescence. Finally, we found that carrier recombination within iron precipitates is characterized by a weak oscillator strength resulting in a long decay lifetime of the 1.54 μm signal at 17 K (∼60 μs) and in a strong temperature quenching of the luminescence yield.
Self-organized propagation of dislocations in GaN films during epitaxial lateral overgrowth
Authors: Sakai Akira , Sunakawa Haruo , Kimura Akitaka , Usui Akira
Published: July 2002

Dislocation propagation and defect evolution in GaN films formed by epitaxial lateral overgrowth (ELO) are examined by transmission electron microscopy. A novel effect that induces self-organized propagation of preexisting dislocations in ELO films is evaluated. This propagation forms dislocations into bundle structures along the stripes of masks used for ELO. The dislocation bundling gives rise to crystallographic tilting in the overgrown region on the mask and leads to a total reduction of threading dislocation density in the film.