bluuebunny/crossref_metadata_2025 huggingface dataset:
The role of sulphonylurea in combination therapy assessed in a trial of sulphonylurea withdrawal
Authors: Landstedt‐Hallin L. , Arner P. , Lins P. ‐E. , Bolinder J. , Olsen H. , Groop L. , Team The Scandinavian Insulin–sulphonylurea Study Group Research
Published: July 2002

Aims To evaluate the effect of adding insulin to sulphonylurea (SU) and the effect of SU withdrawal on glycaemic control in Type 2 diabetic patients who failed on treatment with SU alone.

Method One hundred and seventy‐five patients were included in a placebo‐controlled multicentre study. During phase I (4 months), premixed insulin was added to glibenclamide therapy; during phase II (1–4 months, depending on response) the insulin dose was fixed, while placebo or glibenclamide replaced the open SU therapy. Insulin sensitivity (KITT), beta‐cell function (C‐peptide) and metabolic control (HbA1c) were monitored.

Results HbA1c improved from 9.65% to 7.23% (P < 0.0001) during phase I. A high HbA1c value (P < 0.0001) and a high KITT‐value (P = 0.045) at baseline were associated with a beneficial response to combination treatment. During phase II, glycaemic control was unchanged in the control (glibenclamide) group. In the placebo group, after SU withdrawal, fasting blood glucose (FBG) increased by 10% or more within 4 weeks in 79% of the patients. Patients (67 of 112) with an FBG increase ≥40% during phase II were defined as ‘SU responders’ by protocol. In a multivariate analysis only a long duration of diabetes was associated with SU response. There were more GAD‐antibody‐positive patients among non‐responders (18% vs. 4%, P = 0.0263).

Conclusions Poor glycaemic control in combination with preserved insulin sensitivity and lack of GAD antibodies predicts a beneficial response to combination therapy, which can be achieved in 75% of patients with SU failure.
Two eyes are better than one: binocular enhancement in the contrast domain
Authors: Rabin Jeff
Published: July 2002

The purpose of this study was to compare the improvement in visual acuity (VA) with the improvement in contrast sensitivity (CS) with two eyes as compared with one. Computer generated letter charts were used to measure VA and small letter CS (20/25 Snellen equivalent) in 13 emmetropic subjects. Letter size (for VA) and contrast (for CS) were varied in equal log steps making the task comparable for the two types of measurement. VA improved by an average of 10% (2–3 letters), while CS improved by an average of 40% (1 1/2 lines) when tested with two eyes as compared with one. Greater sensitivity in the contrast domain prevailed even when expressed relative to variability. Using this approach, binocular enhancement was identified in 8/13 subjects with CS, but in only 4/13 subjects with VA. Binocular enhancement of letter recognition occurs in both size and contrast domains. However, the effect is 4 × greater when small letters are varied in contrast rather than size. Potential applications are considered.
Evaluation of the Effectiveness of Tai Chi for Improving Balance and Preventing Falls in the Older Population—A Review
Authors: Wu Ge
Published: July 2002

One of the challenges faced by people with advancing age is decreased postural stability and increased risks for falls. There has been an increased interest over the last decade in using Tai Chi as an intervention exercise for improving postural balance and preventing falls in older people. Despite the increased number of studies in recent years relating Tai Chi to balance and fall prevention, results are scattered and inconsistent. There is wide variation in the use of balance measures, subject population, type and duration of Tai Chi exercise, and type of study. This paper provides a systematic review/analysis of currently available study reports. The goal of the review is to address the following concerns: how the effect of Tai Chi on balance or fall prevention has been evaluated to date, what level of evidence exists supporting Tai Chi as an effective exercise for improving balance or preventing falls, and what factors could possibly affect the benefit of Tai Chi on balance or falls. This review also helps identify directions for future research.
Low-temperature deposition of zirconium and hafnium boride films by thermal decomposition of the metal borohydrides (M[BH4]4)
Authors: Wayda A. L. , Schneemeyer L. F. , Opila R. L.
Published: July 2002

Conductive (150 μΩ cm), adherent films of zirconium and hafnium borides have been deposited on various substrates by the low-temperature (100–270 °C) thermal decomposition of Zr[BH4]4 and Hf[BH4]4. Auger electron spectroscopy of these films shows that their composition is ZrB2 and HfB2. The film surfaces are oxidized and slightly carbon contaminated. However, the bulk contains less than 1 at. % C or O. This synthesis is by far the lowest temperature preparation of these materials (plasma-enhanced chemical vapor deposition of TiB2 requires 480–600 °C) and holds great promise for the use of these materials in electronics applications.
Electron tunneling time measured by photoluminescence excitation correlation spectroscopy
Authors: Jackson M. K. , Johnson M. B. , Chow D. H. , McGill T. C. , Nieh C. W.
Published: July 2002

The tunneling time for electrons to escape from the lowest quasibound state in the quantum wells of GaAs/AlAs/GaAs/AlAs/GaAs double-barrier heterostructures with barriers between 16 and 62 Å has been measured at 80 K using photoluminescence excitation correlation spectroscopy. The decay time for samples with barrier thicknesses from 16 Å (≊12 ps) to 34 Å(≊800 ps) depends exponentially on barrier thickness, in good agreement with calculations of electron tunneling time derived from the energy width of the resonance. Electron and heavy hole carrier densities are observed to decay at the same rate, indicating a coupling between the two decay processes.
Anharmonic oscillator model of a quantum dot nanostructure
Authors: Luban Marshall , Luscombe James H. , Reed Mark A. , Pursey D. L.
Published: July 2002

The energy level spacings observed recently in resonant tunneling through an axially symmetric double-barrier quantum dot structure are reproduced by an isotropic two-dimensional anharmonic oscillator model. We propose that the extent of the depletion region in such a device effectively controls the possible angular momentum states of those electrons contributing to the current-voltage curve.
Electrical properties and band offsets of InAs/AlSb n-N isotype heterojunctions grown on GaAs
Authors: Nakagawa Atsushi , Kroemer Herbert , English John H.
Published: July 2002

The MBE growth and selected properties of InAs/AlSb n-N isotype heterojunctions on n+-GaAs substrates are described. Because of a large conduction-band offset (1.35 eV), these junctions behave like Schottky barriers, with excellent rectification characteristics, despite the presence of a very high density (>107 cm−2) of threading dislocations resulting from the large lattice mismatch (7%) between AlSb and the GaAs substrate. The forward I-V characteristics, corrected for series resistance, exhibit a large nonideality factor of about 1.8, suggesting that the main current flow is along a defect path, presumably related to the misfit dislocations. Reverse C-V characteristics exhibit a perfectly linear 1/C2 vs V plot, from which a conduction-band offset of 1.35±0.05 eV is deduced. This value is in excellent agreement with the value predicted from the known band offsets in InAs/GaSb and GaSb/AlSb.
Buffer layer effects on residual stress in InP on Si substrates
Authors: Sugo Mitsuru , Yamaguchi Masafumi
Published: July 2002

Heteroepitaxial growth of InP on Si(100) substrates using InP direct growth, and with a GaAs or GaP buffer layer has been grown by organometallic vapor phase epitaxy (OMVPE). The effects of buffer layers on residual stress in InP films are examined. For InP/(GaP buffer layer)/Si, stress (∼6×108 dyn/cm2) is almost independent on buffer layer thickness and somewhat higher than that (∼4×108dyn/cm2) in InP grown directly on Si. For InP/(GaAs buffer layer)/Si, stress is as low as 2×108 dyn/cm2 with buffer layer thicknesses ≳1 μm. The GaAs buffer layer effect on reduction of stress in InP film is found to be attributed to compressive strains thermally induced by the InP/GaAs interface.
Use of surface charging in x-ray photoelectron spectroscopic studies of ultrathin dielectric films on semiconductors
Authors: Lau W. M.
Published: July 2002

The use of surface charging of a thin dielectric film on a semiconductor during x-ray photoelectron spectroscopic analysis has been investigated. The binding energy shifts measured from 1.5 nm SiO2/p-Si and 4 nm Si3N4/n-InP indicate that a positive surface potential can be induced by the loss of photoelectrons in the dielectric, whereas a controllable negative potential can be applied by flooding the sample with low-energy electrons. The measurements of the resultant depth-dependent potentials in the oxide and in the semiconductor give useful information on the dielectric/semiconductor structure. For example, the results obtained using this technique show that in the case of SiO2/p-Si, the Fermi level of the semiconductor at the interface was not pinned but in the case of Si3N4/n-InP, it was pinned at 0.3 eV from the conduction-band minimum. Moreover, the charging potential associated with a local impurity in the sample structure can be used to estimate the depth location of the impurity. Finally, the measurement of the degree of charging also gives information on the insulating properties of the dielectric.
Analysis for dislocation density reduction in selective area grown GaAs films on Si substrates
Authors: Yamaguchi Masafumi , Tachikawa Masami , Sugo Mitsuru , Kondo Susumu , Itoh Yoshio
Published: July 2002

High quality GaAs films with dislocation densities of less than 1×106 cm−2 on (100) Si substrates have been obtained by selective area growth using the metalorganic chemical vapor deposition method. Remarkable reduction of residual stress and dislocation density in the GaAs layers due to selective area growth have been analyzed using a simple model, in which the assumptions are that the generation of dislocations is caused by thermal stress in the films and dislocation density reduction in GaAs films on Si due to selective growth is caused by stress relief.
On the feasibility of growing dilute CxSi1−x epitaxial alloys
Authors: Posthill J. B. , Rudder R. A. , Hattangady S. V. , Fountain G. G. , Markunas R. J.
Published: July 2002

Dilute CxSi1−x epitaxial films have been grown on Si(100) by remote plasma-enhanced chemical vapor deposition. Carbon concentrations of ∼3 at.% have been achieved at a growth temperature of 725 °C. No evidence for the formation or precipitation of SiC was found using x-ray diffraction and transmission electron microscopy.
Defect states of amorphous Si probed by the diffusion and solubility of Cu
Authors: Polman A. , Jacobson D. C. , Coffa S. , Poate J. M. , Roorda S. , Sinke W. C.
Published: July 2002

The diffusivity and solubility of Cu impurities have been measured in different structural states of amorphous Si (a-Si) formed by MeV Si implantation. The 2.2-μm-thick a-Si layers were first annealed (structurally relaxed) at 500 °C and then implanted with 200 keV Cu ions, returning a 300-nm-thick surface layer to the as-implanted state. After diffusion at temperatures in the range 150–270 °C, we observe solute partitioning at a sharp phase boundary between the annealed and Cu-implanted layers, the partition coefficient being as large as 8.2±1.3. The diffusion coefficient in annealed a-Si is 2–5 times larger than in as-implanted a-Si, with activation energies of 1.39±0.15 and 1.25±0.04 eV, respectively. The data show quite strikingly the role which defects can play in the a-Si structure.
Double quantum well resonant tunnel diodes
Authors: Day D. J. , Chung Y. , Webb C. , Eckstein J. N. , Xu J. M. , Sweeny M.
Published: July 2002

Double quantum well resonant tunnel diodes are demonstrated in InAlAs/InGaAs for the first time. Peak-to-valley ratios of greater than 70:1 at room temperature and 125:1 below 200 K are observed.
Ultralow chirping short optical pulse (16 ps) generation in gain-coupled distributed feedback semiconductor lasers
Authors: Luo Y. , Takahashi R. , Nakano Y. , Tada K. , Kamiya T. , Hosomatsu H. , Iwaoka H.
Published: July 2002

We describe optical short pulse generation in novel gain-coupled distributed feedback (GC-DFB) semiconductor lasers by using a simple electrically pumped gain switching method. An optical pulse as short as 16 ps has been obtained from a 130 ps current pulse. The most exciting result is that the lasers keep single longitudinal mode oscillation with very low wavelength chirping (∼0.12 nm) during the gain switching operation. From the optical pulse width and the amount of the wavelength chirping, we have estimated the α parameter of the GC-DFB laser to be less than 1.6.
High-transport current density up to 30 T in bulk YBa2Cu3O7 and the critical angle effect
Authors: Ekin J. W. , Salama K. , Selvamanickam V.
Published: July 2002

Measurements of the dc transport critical current of oriented-grained YBa2Cu3O7 have been made using high quality Ag contacts and a high-current sample mount. The critical- current density Jc at 77 K for mutually perpendicular current and magnetic field B in the a,b plane is 8 kA/cm2 at 8 T, decreasing gradually to 3.7 kA/cm2 at 20 T, and remaining over 1 kA/cm2 out to 30 T. High magnetic field measurements of Jc as a function of the angle θ of B with respect to the c axis are also reported. In contrast to earlier results at lower fields (<3 T) the measurements reported here in high fields reveal a Jc vs θ curve with a head-and-shoulders shape, consisting of a sharp peak (‘‘head’’) <5° wide for B parallel to the CuO2 planes, and a wide (30° at 9 T, for example) shoulder region on either side of B⊥c, where the transport Jc remains high and constant. Beyond the shoulder region, however, the transport Jc decreases sharply, giving rise to the concept of a critical field angle for application design, defined by the minima in d2Jc/dθ2 at the edge of the shoulders.
Intuitive model to include the effect of free-carrier absorption in calculating the two-photon absorption coefficient
Authors: Laughton Frances R. , Marsh John H. , Roberts John S.
Published: July 2002

We report a simple model to include the effect of free-carrier absorption (FCA) in calculating the two-photon absorption (TPA) coefficient, β, and demonstrate its use in evaluating β from nonlinear transmission experiments. When only linear absorption and TPA are considered and the experimental analysis is carried out in the usual way, β is calculated to be 2.0 and 2.7×10−10 m W−1 for TM and TE polarizations, respectively. Including the effect of FCA in the waveguide, the model predicts β to be 1.5 and 2.0×10−10 m W−1 for TM and TE polarizations, respectively.
Electroluminescence in Li-codoped ZnS: TmF3 thin-film devices
Authors: Sohn S. H. , Hyun D. G. , Yamada A. , Hamakawa Y.
Published: July 2002

The effects of Li codoping in ZnS:TmF3 thin-film electroluminescent devices are reported. ZnS:Tm, Li thin films are prepared at several Li concentrations and substrate temperatures. The electroluminescent characteristics of ZnS:Tm,Li devices depend on Li concentrations, substrate temperatures, the annealing, and drive voltages.
Photo-optical liquid crystal cells driven by molecular rotors
Authors: Ichimura Kunihiro , Hayashi Yuko , Akiyama Haruhisa , Ikeda Tomiki , Ishizuki Norio
Published: July 2002

Photochemical regulation of in-plane alignment of a nematic liquid crystal is presented. A quartz plate surface was modified with 4-hexyl-4′-hexyloxyazobenzene substituted with triethoxysilyl group through a spacer at the 2′ position to introduce the side-on type azobenzene unit of the surface. A liquid crystal hybrid cell fabricated with the azo-modified plate was irradiated with linearly polarized visible light for the n-π* transition. This resulted in the in-plane reorientation of the liquid crystal molecules to afford homogeneous alignment. Discussion is made on the mechanism of the in-plane alignment regulation, and the concept of a molecular rotor is proposed.
Ultrafast all-optical switching in GaAlAs directional couplers at 1.55 μm without multiphoton absorption
Authors: Al-hemyari K. , Villeneuve A. , Kang J. U. , Aitchison J. S. , Ironside C. N. , Stegeman G. I.
Published: July 2002

We demonstrate ultrafast, high throughput, all-optical switching in optimized, 2-cm-long, half- and full-beat-length nonlinear directional couplers operated at 1.55 μm, below half the band gap of Ga0.82Al0.18As. The long device length allowed the elimination of nonlinear loss and resulted in a switching peak power and energy of 85 W and 65 pJ, respectively.
Polarity of small {111}GaAs domains on (100)Sc0.32Er0.68As formed during molecular-beam epitaxial growth
Authors: Hugsted B. , Tafto/ J. , Finstad T. G. , Palmstro/m C. J.
Published: July 2002

Molecular-beam epitaxial growth of GaAs on (100)ScxEr1−xAs can result in domains of various orientations. Most of the GaAs domains are of the epitaxial (100) or the twin related (221) orientation. A {111} orientation is also common. We have studied the orientational relationships of these domains by transmission electron microscopy. The polarity of small {111}GaAs domains on (100)ScErAs have been determined by electron channeling. We observe that the polarity is such that the GaAs [1̄1̄1̄] direction (as opposed to the [111] one) points outward from the original ScxEr1−xAs(100) surface. We use this observation in discussing possible models of the interface between ScErAs and GaAs.
Electron stimulated polymerization of solid C60
Authors: Zhao Y. B. , Poirier D. M. , Pechman R. J. , Weaver J. H.
Published: July 2002

Electron-stimulated modifications to pure C60 films grown on GaAs(110) have been induced by ∼3 eV electrons from a scanning tunneling microscope (STM) and from 1500 eV electrons from an electron gun. In the STM-modified area, a variety of apparent molecular sizes and shapes were observed with intramolecular contrast and a blurring of intermolecular distinction. Surfaces bombarded by 1500 eV electrons showed modifications over larger areas and these results suggested a growth mode for polymerization. Annealing of such modified surfaces restored the ordered fcc structure.
Low-field hole mobility of strained Si on (100) Si1−xGex substrate
Authors: Nayak Deepak K. , Chun Sang Kook
Published: July 2002

Strain Hamiltonian and k⋅p theory are employed to calculate low-field hole mobility of strained Si layers on (100)Si1−xGex substrate. Nonparabolicity and the warped nature of the valence bands are included. At room temperature, in-plane hole mobilities of strained Si are found to be 1103 and 2747 cm 2 V−1 s−1 for x equal to 0.1 and 0.2, respectively. These hole mobilities are, respectively, 2.4 and 6 times higher than that of bulk Si. This improvement in the mobility results is mainly due to the large splitting energy between the occupied light-hole band and the empty heavy-hole band and smaller effective mass. The effect of p-type doping on mobility is also presented.
Microstructural characterization of α-GaN films grown on sapphire by organometallic vapor phase epitaxy
Authors: Qian W. , Skowronski M. , De Graef M. , Doverspike K. , Rowland L. B. , Gaskill D. K.
Published: July 2002

Microstructure of α-GaN films grown by organometallic vapor phase epitaxy on sapphire substrates using low temperature AlN (or GaN) buffer layers has been studied by transmission electron microscopy. The defects which penetrate the GaN films are predominantly perfect edge dislocations with Burgers vectors of the 1/3〈112̄0〉 type, lying along the [0001] growth direction. The main sources of threading dislocations are the low angle grain boundaries, formed during coalescence of islands at the initial stages of GaN growth. The grain sizes range from 50 to 500 nm, with in-plane misorientations of less than 3°. The nature of these threading dislocations suggests that the defect density would not likely decrease appreciably at increasing film thickness, and the suppression of these dislocations could be more difficult.
A lidar system for measuring atmospheric pressure and temperature profiles
Authors: Schwemmer Geary K. , Dombrowski Mark , Korb C. Laurence , Milrod Jeffry , Walden Harvey , Kagann Robert H.
Published: July 2002

The design and operation of a differential absorption lidar (LIght Detection And Ranging) system capable of remotely measuring the vertical structure of tropospheric pressure and temperature are described. The measurements are based on the absorption by atmospheric oxygen of the spectrally narrowband output of two pulsed alexandrite lasers. Detailed laser output spectral characteristics, which are critical to successful lidar measurements, are presented. Spectral linewidths of 0.026 and 0.018 cm−1 for the lasers were measured with over 99.99% of the energy contained in three longitudinal modes.
Dispersion and resolution of a Moellenstedt energy analyzer
Authors: Tian Renhe , Fink Manfred
Published: July 2002

The equipotential lines and the trajectories of electrons in a Moellenstedt analyzer are computed. The effects of relativity and the self-magnetic field of the moving electrons are taken into account. The dispersion, resolution, and caustic position are defined and calculated. The sensitivity of the dispersion and resolution to not only the voltage V applied to the electrode rods, the electron energy E, the incident angle φ, or the geometrical construction of the analyzer, but also the distance L between the analyzer and detector has been investigated. The caustic position varies strongly with the incident angle and the geometrical construction of the analyzer. The dependencies of resolution on the incident angle and the geometrical construction are significantly reduced in the vicinity of the caustic with the angular spread of the incident electrons remaining the major contributor to the finite resolution.
Photoelectron microscopy with synchrotron radiation
Authors: Tonner B. P. , Harp G. R.
Published: July 2002

Real-time images produced by photoelectrons from metal and semiconductor samples have been generated using synchrotron radiation. A single electrostatic objective lens coupled to a two-stage image intensifier has been used to evaluate the feasibility of combined imaging and spectroscopy with photoelectrons in the ultraviolet and soft x-ray regions. Images were generated using photon energies ranging from 9 to 160 eV. The use of monochromatic synchrotron radiation provides a unique capability for generating image contrast by digital subtraction of images formed with photon energies above and below a core-level binding energy. A simple electron-optical objective lens produces images with a few microns resolution, and adequate sensitivity to image 45-eV kinetic energy electrons using bending magnet radiation. Calculations based on these experiments show that comparable resolutions are possible for combined microscopy and spectroscopy with electrons of order 100-eV kinetic energy using currently available bending magnet synchrotron radiation. Calculations for expected performance from undulator sources are presented.
A low-cost high power fast response voltage probe
Authors: Saw S. H. , Wong C. S. , Lee S.
Published: July 2002

A high power resistive divider-type high voltage probe with the response tested to better than 40 ns is designed to measure the high voltage of 150 kV output from a 3-stage Marx. The probe consists of two sections, the high power resistive divider near the source, and the low power in-line attenuators at the measuring end.
An automated, high precision unit for low-pressure physisorption
Authors: Borghard W. S. , Sheppard E. W. , Schoennagel H. J.
Published: July 2002

A physisorption apparatus with very high sensitivity has been constructed. It is capable of accurately measuring adsorption and desorption isotherms of gases on solids in the pressure range of 10−5–1000 Torr. This is particularly useful for investigating argon sorption on catalysts and catalyst supports, e.g., FCC, reforming and hydroprocessing catalysts; zeolites; and pillared layered materials. The isotherms contain information about micropore and mesopore size distribution, BET surface area, etc. The operation of the unit and the analysis of isotherm data are both fully automated. Details of the equipment and the software are described.
An electrostatic microscope for synchrotron radiation x-ray absorption microspectroscopy (invited)
Authors: Tonner B. P. , Harp G. R. , Koranda S. F. , Zhang J.
Published: July 2002

An x-ray photoemission microscope is described that is designed for x-ray absorption imaging and spectroscopy with 1-μm spatial resolution. The energy resolution of x-ray absorption near-edge structures microspectroscopy is determined only by the bandpass of the monochromator, and not by the photoemission microscope detector.
Afterpulse measurement and correction
Authors: Campbell L.
Published: July 2002

A pulse of electrons in a photomultiplier sometimes generates succeeding spurious pulses, called afterpulses. These are detrimental to statistical analysis of the distribution of photocounts. A method is outlined to determine the probability of occurrence of afterpulses, by analysis of the frequency distribution of output pulses produced by constant light. A related method is outlined to correct for the effect of afterpulsing, so that the original distribution of photocounts can be determined, even if the light is fluctuating. This correction technique is tested by application to measurements of twinkling starlight and shown to work very well. The method to deduce afterpulse probabilities is developed further to produce values in a form which allows comparison with previous measurements. For one tube the results agree with expectations, but not for another. A plausible reason is given for the discrepancy, illustrating the potential of the method to give information about the operation of photomultipliers.
Evaluation of a squirrel-cage photomultiplier base for time-resolved spectroscopy with low-repetition rate pulses
Authors: Naqvi K. Razi , Haggquist G. W. , Burkhart R. D. , Sharma D. K.
Published: July 2002

A wiring diagram is presented which permits using a squirrel-cage photomultiplier tube as a versatile, low duty-cycle detector in a kinetic spectrometer. The performance of the circuit is illustrated and some crucial tests are described.
An infrared pyrolyzer for analysis of solid samples by gas chromatography/mass spectrometry
Authors: Wiezorek Bernd , Schiller Anatoly , Baykut Gökhan , Wanczek Karl-Peter
Published: July 2002

A pyrolysis instrument operating with an infrared radiation source in an optical focusing system has been developed to obtain volatile products from solid samples for gas chromatographic/mass spectrometric analysis. The device spatially separates heating source and heated material, avoiding severe contaminations. Solid materials like soil samples or polymeric compounds can be pyrolyzed in the reactor tube of the instrument. Gases formed during the pyrolysis are collected in a sorbent-filled preconcentration tube. The analysis is performed after desorbing the collected gases by gas chromatography/mass spectrometry. Analysis results of the pyrolysis products are then correlated to the compounds in the solid samples.
Apparatus for the measurement of the optical constants and thermal radiative properties of pure liquid metals from 0.4 to 10 μm
Authors: Havstad M. A. , McLean W. , Self S. A.
Published: July 2002

Measurements of the optical constants and thermal radiative properties of high-temperature solid tungsten and molten aluminum have been made using a new instrument that includes two independent optical systems and surface control and analysis capability. The two optical systems, one for measuring the complex index of refraction by ellipsometry, the other for measuring the normal spectral emissivity by direct comparison to an integral blackbody cavity, operate over the wavelength range 0.4–10 μm with sample temperatures between 940 and 1630 K. The surface science capabilities of the instrument permit the preparation of high-purity samples of known composition in situ. The apparatus includes two 5-keV argon-ion sputter guns, an ultrahigh vacuum pumping system, and an Auger spectrometer. The two sputter guns allow surface cleaning to occur while optical measurements are being made, or while Auger spectroscopy is determining the surface composition of solid or liquid samples. The ellipsometric optical system uses a novel radiation source (a carbon composite element), refractive optics (calcium fluoride), interference filters for spectral selection, and both calcite and wire grid polarizers to cover the extended wavelength range. The system for measuring the normal spectral emissivity uses reflective optics and an integral blackbody cavity that is located in the wall of the crucible holding the liquid sample. The use of two measurement techniques gives independent determinations of the normal spectral emissivity and thus allows reliable estimation of experimental errors.
Four-wave mixing efficiency in traveling wave semiconductor optical amplifiers at high saturation
Authors: D’Ottavi A. , Mecozzi A. , Scotti S. , Romeo F. Cara , Martelli F. , Spano P. , Dall’Ara R. , Eckner J. , Guekos G.
Published: July 2002

We report an experimental investigation of the conversion efficiency of a frequency converter based on four-wave mixing in semiconductor optical amplifiers. We find that the maximum of conversion efficiency has a nonlinear dependence on the unsaturated gain of the device. The observed features are explained by the presence of the Auger and bimolecular recombination.
Variable exit beam height double-crystal monochromator for high-power insertion devices
Authors: Oyanagi H. , Haga K. , Kuwahara Y.
Published: July 2002

A variable exit beam height double-crystal monochromator for high-power insertion devices was built and tested at the Photon Factory. The second crystal is mounted on a high-precision XY translational stage and its position in the parallel and perpendicular direction to the reflecting plane (x,y) is computer controlled. In this design, the exit beam height (y) and geometrically required positioning of the second crystal (x) are separately controlled. Either a fixed or variable exit beam height is obtained over the Bragg angle (θ) range from 6° to 25°. A systematic noise caused by degraded parallelity between the two crystals is observed in extended x-ray absorption fine structure spectra when x and y are simultaneously controlled. This noise is significantly reduced by a versatile control of (x,y): for a typical scan (∼1 keV) only y is allowed to vary while both coordinates are controlled when a monochromator is tuned over a wider energy range.
Prony’s method for exponential lifetime estimations in fluorescence-based thermometers
Authors: Zhang Zhiyi , Grattan K. T. V. , Hu Youlin , Palmer A. W. , Meggitt B. T.
Published: July 2002

Noniterative algorithms using Prony’s method are proposed for the estimation of the exponential lifetime in fluorescence-based fiber-optic sensor systems. The uses of a variety of Prony’s algorithms are evaluated using Monte Carlo simulations. It is shown that the performance of Prony’s algorithms is quite close to that of Marquardt algorithms and they are the better alternatives to their Marquardt counterparts, when illustrated for real-time applications in temperature sensors with a 98% decrease in running time.
Plateau tank apparatus for the study of liquid bridges
Authors: Resnick A. , Alexander J. I. D.
Published: July 2002

An apparatus has been constructed and used to study the equilibrium and dynamical behavior of liquid bridges under reduced effective gravity. Liquid bridges are created and manipulated using six independent computer controlled stepper motors which drive linear motion tables. The bridges are visualized with a high magnification coherent Fourier optical system and in an orthogonal view using incoherent white light. By calibrating a density hydrometer and measuring the interfacial energy between the bridge and bath, reliable Bond numbers as low as 10−4 can be created and held stable for extended periods of time. Dimensional control of the liquid bridges approaches one part in 10−4 for the aspect ratio and volume. The apparatus has been tested by measuring the static stability limits of axisymmetric bridges and comparing the results with previous theoretical predictions. Experimental error for the apparatus is δBo/Bo=0.03, δΛ/Λ=0.001 and δV/V =0.001, where Bo is the Bond number, Λ is the aspect ratio of the bridge, and V is the dimensionless (relative) volume of the bridge.
Distance control in near-field optical microscopy with piezoelectrical shear-force detection suitable for imaging in liquids
Authors: Brunner R. , Bietsch A. , Hollricher O. , Marti O.
Published: July 2002

We introduce an improved piezoelectric shear-force feedback system for tip-sample distance control in a scanning near-field optical microscope. A tapered glass fiber is glued into a metal tube and both are integrated in a mounting, sandwiched between two piezosegments. One of the piezoelements excites the fiber tip at mechanical resonance while the other one is used for detection. During surface approach the fiber resonance is damped by shear forces, which is registered by the second piezoelement and used for distance control. The main attractions of this setup are its simplicity, its compactness, and the lack of disturbing light sources. The fiber is easy accessible and tip exchange is simple. With an acceptable fiber amplitude of 5–10 nm (peak to peak) we obtained a topographical resolution of 5 pm/Hz. The geometry also allows the measurement of samples covered with a few millimeters of liquid, which is important for applications in biology and medicine.
Instrument for high resolution magnetization measurements at high pressures, high magnetic fields and low temperatures
Authors: Koyama K. , Hane S. , Kamishima K. , Goto T.
Published: July 2002

An instrument has been developed for the first time that makes high resolution magnetization measurements at high pressures, high magnetic fields and low temperatures. The instrument consists of an extraction-type magnetometer, a nonmagnetic high pressure clamp cell and a 20 T superconducting magnet with a 3He refrigerator and is able to precisely measure the magnetization of weakly magnetic materials. TiCu alloy with 3 wt % Ti is employed as a nonmagnetic material with high mechanical strength for the high pressure clamp cell. This apparatus can be used in the pressure range 0⩽P⩽13 kbar, the field range 0⩽H⩽200 kOe and the temperature range 0.5⩽T⩽4.2 K. The resolution of the instrument is estimated to be ±0.002 emu. For demonstrating the ability of the instrument, the experimental results on a heavy fermion antiferromagnet Ce7Ni3 is presented.
Spectroscopy in the extreme ultraviolet on an electron beam ion trap
Authors: Beiersdorfer P. , López-Urrutia J. R. Crespo , Springer P. , Utter S. B. , Wong K. L.
Published: July 2002

A compact grazing-incidence spectrometer was implemented on the Livermore electron beam ion trap facility for spectral measurements in the extreme ultraviolet spectral region. The spectrometer employed a 1200 ℓ/mm grating designed for flat-field focusing and a charge coupled device camera for readout. The instrument was used to measure line emission in the range from 25 to 220 Å with a resolving power as high as 600. The performance and calibration of the instrument is described and spectra from highly charged nitrogen and iron ions are presented. Measurements of the K-shell spectrum of He-like N5+ are presented that confirm earlier wavelength determinations and illustrate the accuracy achievable with the instrument. Our measurement suggests a change in the line identifications of the forbidden He-like N5+ transition 1s2s 3S1→1s2 1S0 and of the Li-like N4+ collisional satellite transition 1s2s2p 2P3/2→1s22s 2S1/2 observed on the Alcator C-Mod tokamak.
Microstructure of heteroepitaxial CdTe grown on misoriented Si(001) substrates
Authors: Smith David J. , Tsen S.-C. Y. , Chen Y. P. , Faurie J.-P. , Sivananthan S.
Published: July 2002

Transmission electron microscopy has been used to characterize the microstructure of heteroepitaxial CdTe (111) layers grown by molecular beam epitaxy directly on nominal and misoriented Si(001) substrates. High-resolution electron micrographs showing atomic-scale details of the CdTe (111)/Si(001) interface have been recorded. Layer quality depended on the substrate tilt parameters, including the offcut orientation angle θ, and the azimuthal angle φ relative to [110]. Small φ values (4° and 10°) gave high densities of stacking fault twins throughout the epilayer whereas larger misorientation angles led to a rapid falloff away from the substrate. Under optimized growth conditions, the occurrence of twins effectively dropped to zero within a distance of less than 2.5 μm from the substrate surface.
Space charge measurement in a dielectric material after irradiation with a 30 kV electron beam: Application to single-crystals oxide trapping properties
Authors: Vallayer B. , Blaise G. , Treheux D.
Published: July 2002

When an insulating material is subjected to electron irradiation, it produces a secondary emission the yield of which varies from a few percent to very high values (up to 24 per incoming electron) depending on the material and the experimental conditions. If the secondary electron emission yield is less than one, a net negative charge remains trapped in the sample. In this case, the study of the electric charges trapping properties of the material becomes possible. This article describes how it is possible to use a secondary electron microscope (SEM) as a device to perform such a study. In Sec. II, the effect of a net negative trapped charge resulting (from the injection of typically 50 pC) on the imaging process of the SEM has been described. It has been shown that when the trapped charge is high enough, it acts as a mirror reflecting the incoming electron beam which is deflected somewhere in the vacuum chamber of the microscope. A global qualitative description of the image displayed on the screen is first presented. Then electron trajectories are quantitatively studied by using the Rutherford scattering cross section in the case of a point charge. When the charge is extended, a numeric simulation has been done in order to predict the validity range of the previous model. Once the trajectories have been calculated, the connection between the remarkable elements of the image and the quantity of trapped charges has been established. Moreover, this technique allows one to study the lateral dimension of the trapped charge zone and to measure the surface potential. In Sec. III, the discussion is first focused on some precautions to be taken concerning the sample preparation before the experiment is performed. It has been shown that surface defects due either to contamination layers or machining change the trapping properties of single-crystals ceramics such as MgO and Al2O3. A cleaning procedure is proposed that consists of annealing the sample at 1500 °C for 4 h in order to heal the crystalline defects and a heating at 400 °C in the vacuum chamber of the SEM to remove the contamination layers. Finally, the effect of the temperature on the trapping properties of pure and chromium doped sapphire has been studied in relation with the chromium concentration. It is shown that temperature behavior of trapping is in relation with the chromium concentration. In the pure sapphire trapping is activated below −16 °C, in 500 ppm rubis it is below −9.5 °C due to isolated chromium atoms, and in the 8000 ppm rubis the critical trapping temperature rises to 3.7 °C due to Cr3+ pairs. The interpretation of the role played by chromium on trapping is based on the experimental study of the fluorescence of chromium atoms and pairs as a function of concentration.
Characterization of geometrical detection-system properties for two-dimensional tomography
Authors: Ingesson L. C. , Maggi C. F. , Reichle R.
Published: July 2002

Quantities that characterize the three-dimensional geometrical properties of detection systems for two-dimensional tomography are reviewed and compared. It is discussed how the quantities can be calculated and how they can be measured, including a measuring technique that uses a parallel laser beam. In many detection systems the finite detector size and the finite sizes of bounding apertures are not negligible, and these result in instrument functions with finite widths. Line-integral measurements are referred to as ideal measurements, whereas measurements by systems with instrument functions with finite width are nonideal. The quantities discussed make it possible to take into account these finite sizes in several tomography algorithms. If the spacing between adjacent lines of sight is much smaller than the widths of the instrument functions, the ideal measurements can be approximately reconstructed from the nonideal measurements. Such a reconstruction has been applied to bolometer measurements in a high plasma-density discharge in the Joint European Torus tokamak by sweeping the plasma in front of the bolometer detectors. The sweeping creates many extra virtual lines of sight and thus increases the resolution of the measurements close to the X point, where in high-density plasmas a peak in the radiation is found.
Extraordinary anisotropic magnetoresistance effect under 35 Oe field at room temperature in Co/Ni multilayers
Authors: Prados C. , García D. , Lesmes F. , Freijo J. J. , Hernando A.
Published: July 2002

Extraordinary magnetoresistance effect has been found in Ni/Co sputtered multilayers. Magnetoresistance values higher than 130% are achieved at room temperature with a saturation magnetic field of 35 Oe, using a particular arrangement of contacts. The large anisotropic magnetoresistance and the low coercivity of these samples are the origin of such an outstanding property. The results reported here seem to have promising applications in magnetoresistive devices.
Quantitative analysis of radiation induced Si/SiO2 interface defects by means of MeV He single ion irradiation
Authors: Koh Meishoku , Shigeta Bungo , Igarashi Kai , Matsukawa Takashi , Tanii Takashi , Mori Shigetaka , Ohdomari Iwao
Published: July 2002

Generation rates of Si/SiO2 interface defects, namely, the oxide trapped holes and the interface states, by MeV He single ion irradiation have been investigated quantitatively. From the analysis of threshold voltage shifts induced by single ions of 2 MeV He, the number of the oxide trapped holes and the interface states induced in an n-ch MOSFET in CMOS4007 by a single ion have been estimated to be about 28 and 9, respectively. The hole trapping efficiency is almost 100% at the ion dose below 1 ions/ μm2.
Naturally formed InxAl1−xAs/InyAl1−yAs vertical superlattices
Authors: Jun Sung Won , Seong Tae-Yeon , Lee J. H. , Lee Bun
Published: July 2002

InxAl1−xAs/InyAl1−yAs vertical superlattices (VS) were naturally formed by phase separation during the growth of InAlAs/InP layers at temperatures in the range 565–615 °C by metalorganic chemical vapor deposition. The VS lies perpendicular to the (001) growth plane. As the growth temperature increased from 565 to 615 °C, the VS decreased in thickness from ∼15 to ∼6 nm, and became less planar and uniform. Transmission electron diffraction results showed the occurrence of CuPt-type ordering in some of the layers. Band-gap reduction of ∼300 meV was observed in the InAlAs layers grown at temperatures ranging from 565 to 615 °C. Such a large reduction in band-gap energy was attributed to combined effects of the VS and CuPt-type ordering.
Large energy shifts in GaAs-AlGaAs quantum wells by proton irradiation-induced intermixing
Authors: Tan H. H. , Williams J. S. , Jagadish C. , Burke P. T. , Gal M.
Published: July 2002

Proton irradiation and subsequent rapid-thermal annealing are used to create intermixing in GaAs-Al0.54Ga0.46As quantum wells of various thicknesses. Very large energy shifts (up to 200 meV) with no apparent saturation have been observed even up to a dose of about 4×1016 cm−2. This effect is explained in terms of the dilute irradiation damage and the evolution of discrete (point) defects during annealing. In comparison to heavy ion irradiation effects, high point defect fraction in the case of light ions leads to efficient intermixing with large energy shifts. Although much of the proton energy loss occurs across the quantum wells, the generated defect density is dilute, and hence good recovery in photoluminescence intensities is achieved after rapid thermal annealing.
Surface modification of chemically vapor deposited diamond for producing adherent thick and thin film metallizations for electronic packaging
Authors: Menon E. S. K. , Dutta I.
Published: July 2002

In order to make chemically vapor deposited diamond (CVDD) substrates amenable to surface metallization without significant reduction in thermal conductivity, very thin alumina films were grown on diamond by vapor deposition of Al in oxygen atmosphere, followed by very low-temperature annealing in oxygen. A Cr interlayer initially deposited on CVDD prior to alumina deposition was found to lead to excellent adhesion between the substrate and the deposit. The alumina films were characterized by scanning and transmission electron microscopy as well as Auger electron spectroscopy.
Quantitative orientational analysis of a polymeric material (Kevlar® fibers) with x-ray microspectroscopy
Authors: Smith A. P. , Ade H.
Published: July 2002

It has previously been shown that x-ray linear dichroism microscopy can be utilized to image and determine orientation in a polymeric material at high spatial resolution. We have now expanded on this technique and extracted quantitative information about the orientation of specific functional groups in a polymeric system from submicron areas. This is accomplished by acquiring and analyzing spectral data sets rather than just images at specific energies. It has allowed us to compare the relative lateral orientation of various grades of Kevlar® fibers.
Interaction of threading and misfit dislocations in a strained epitaxial layer
Authors: Schwarz K. W. , Tersoff J.
Published: July 2002

The motion of a dislocation in a strained layer is calculated using continuum elastic theory. Blocking of the moving dislocation by a fixed misfit dislocation across its path is found to be weaker than previously believed. The calculation makes no approximation regarding the shape of the dislocation, and correctly includes the self-interaction of the moving dislocation.
Laser diodes based on beryllium-chalcogenides
Authors: Waag A. , Fischer F. , Schüll K. , Baron T. , Lugauer H.-J. , Litz Th. , Zehnder U. , Ossau W. , Gerhard T. , Keim M. , Reuscher G. , Landwehr G.
Published: July 2002

Beryllium chalcogenides have a much higher degree of covalency than other II–VI compounds. Be containing ZnSe based mixed crystals show a significant lattice hardening effect. In addition, they introduce substantial additional degrees of freedom for the design of wide gap II–VI heterostructures due to their band gaps, lattice constants, and doping behavior. Therefore, these compounds seem to be very interesting materials for short wavelength laser diodes. Here, we report on the first fabrication of laser diodes based on the wide band gap II–VI semiconductor compound BeMgZnSe. The laser diodes emit at a wavelength of 507 nm under pulsed current injection at 77 K, with a threshold current of 80 mA, corresponding to 240 A/cm2.