bluuebunny/crossref_metadata_2025 huggingface dataset:
Saturation broadening of laser-induced fluorescence from plasma ions
Authors: Goeckner M. J. , Goree J. , Sheridan T. E.
Published: July 2002

Saturation broadening is an obstacle in using laser-induced fluorescence as a plasma diagnostic. The Doppler-broadened line shape ideally yields the ion velocity distribution function, but at high laser power, saturation of the optical transition leads to additional undesirable line broadening. We test three different prescriptions for plasma experimentalists to avoid saturation broadening while maintaining a strong signal. Based on experiments in an argon plasma, and a semiclassical atomic physics simulation, we have identified the prescription that is the easiest to use and the least sensitive to the spatial profile of the laser beam. This procedure is to measure the laser intensity that leads to saturation on the peak of the spectral line, and then to reduce the intensity to 20% of the saturation level.
New experimental technique for the fabrication of ion diffused optical glass waveguides
Authors: Sundaram K. B.
Published: July 2002

A new electric-field-assisted ion diffusion technique has been used for the fabrication of optical waveguides in glass. The construction of the setup is discussed in detail. Ion exchange in standard glass slide can be performed very efficiently and the setup can be conveniently used for double diffusions which are required for the fabrication of buried waveguides. Silver ions of various mole fractions were diffused in glass by this technique. Diffusion depth measurements were made both for the fabricated planar and channel waveguides.
A high-voltage pulser circuit with subnanosecond rise time
Authors: Rai V. N. , Shukla M.
Published: July 2002

A fast (≤1 ns rise time) high-voltage pulser circuit was developed using 2N5551/2N5550 transistors in avalanche mode as switching elements. This circuit has transistors in series stack configuration and provides ∼2 kV amplitude and ≤1 ns rise time into 50 Ω with a 13 ns delay and <500 ps jitter. A simple arrangement to generate two symmetrical opposite polarity pulses from single pulse of either polarity is also presented.
A one-dimensional time-resolved pinhole camera for intense pulsed bremsstrahlung sources
Authors: Fehl D. L. , Leeper R. J. , Lee J. R. , Hedemann M. A. , Stygar W. A. , Sujka B. R. , Hebron D. E. , Robischon S. J. , Peyton B. P.
Published: July 2002

A time-resolved pinhole camera has been constructed to diagnose flash x-ray bremsstrahlung sources with end-point energies of ∼2 MeV. The detector is a 20-channel linear array of noncontinguous plastic scintillators with a sampling distance of 6.4 mm. Optical signals from the scintillators are conducted by fiber-optic links to a remote bank of photomultiplier tubes. Nominally, the absolute sensitivity of the channels is ∼18 nC/R at 1.1 MeV. The temporal resolution is ∼5 ns, and the spatial resolution in the source plane is ∼38 mm for a 3-mm pinhole and magnification of 1/3. The spectral response of the scintillator channels, the relative channel-to-channel sensitivities, cross talk between channels, backgrounds, and noise limitations have also been studied. Experiments with this camera on the Saturn simulator have yielded information on the simultaneity and duration of the x-ray emission from individual source rings. This camera complements time-integrated and time-gated cameras, as well as spatially integrated, but time-resolved, PIN diode and scintillator/photodiode detectors.
Thin film microcalorimeter for heat capacity measurements from 1.5 to 800 K
Authors: Denlinger D. W. , Abarra E. N. , Allen Kimberly , Rooney P. W. , Messer M. T. , Watson S. K. , Hellman F.
Published: July 2002

A new microcalorimeter for measuring heat capacity of thin films in the range 1.5–800 K is described. Semiconductor processing techniques are used to create a device with an amorphous silicon nitride membrane as the sample substrate, a Pt thin film resistor for temperatures greater than 40 K, and either a thin film amorphous Nb–Si or a novel boron-doped polycrystalline silicon thermometer for lower temperatures. The addenda of the device, including substrate, is 4×10−6 J/K at room temperature and 2×10−9 J/K at 4.3 K, approximately two orders of magnitude less than any existing calorimeter used for measuring thin films. The device is capable of measuring the heat capacity of thin film samples as small as a few micrograms.
Efficient high-homogeneous wide-aperture excimer discharge using a stabilizing low-current predischarge
Authors: Bychkov Yu. , Kostyrya I. , Makarov M. , Suslov A. , Yastremsky A.
Published: July 2002

A technique of initiation of a self-sustained electrical discharge for pumping excimer lasers, based on the use of a stabilizing predischarge with an electron density Ne∼1012–1013 cm−3, has been developed. It has been demonstrated that such an auxiliary discharge is stable for random disturbances of the plasma parameters. An efficient, stable, and highly homogeneous pumping discharge of duration up to 800 ns with an aperture of 6×12 cm2 and current density of ∼300 A/cm2 has been realized in Ne(He,Ar)/Xe(Kr)/HCl mixtures. The proposed technique can be used in developing wide-aperture excimer lasers and shows promise for creating high-repetition-rate systems of kilowatt average power.
Pressure-tuning flotation method for measurement of specific volume of solid organic compounds under high pressures
Authors: Yokoyama Chiaki , Ebina Takeo , Takahashi Shinji
Published: July 2002

An accurate and simple method for the measurement of specific volumes of solid organic compounds under high pressures was proposed. The principle of this method was based on the flotation methods, in which pressure was adjusted to find the floating equilibrium point at isothermal condition. One of the advantages of the proposed method is that the specific volume of solid organic compounds under high pressures can be determined with almost the same accuracy as that of immersion liquids. The specific volumes of naphthalene were measured at 293.15 K and at pressures up to 440 MPa. The immersion liquid used consisted of aqueous NaNO3 solutions. The specific volumes of the aqueous NaNO3 solutions under high pressures were measured with the glass piezometer method proposed in our previous study. Experimental results of the specific volume and also the isothermal compressibility were compared with the literature data. It was found that good agreement was obtained between the present results and the literature data for the volume compressibility.
A technique for the investigation of organic reactions driven by shock waves in liquids
Authors: Davis Lloyd L. , Brower Kay R. , Libersky Larry D.
Published: July 2002

A method has been developed for investigating the chemical reactions of organic compounds under the dynamic shock loading conditions of detonation. Sealed capsules are placed along the axis of a cylindrical charge which is initiated at one end. As the detonation wave progresses along the charge, a major part of the sample inside each capsule is subjected to a well-balanced annular compression with peak pressure approximately equal to the Chapman–Jouguet pressure of the explosive used. The geometry of the system ensures both minimal structural deformation and low residual velocity of the capsules; consequently high survival rates have been obtained. The temperature and pressure distribution within the sample space has been calculated as a function of time by a computer simulation using MAGI, a three-dimensional Smooth Particle Hydrodynamics code. The temperature has also been measured experimentally with a variety of organic reactions known to be insensitive to pressure, whose Arrhenius parameters are obtained from the literature and measurements in our laboratory.
Tunable, long-wavelength PtSi/SiGe/Si Schottky diode infrared detectors
Authors: Jimenez J. R. , Xiao X. , Sturm J. C. , Pellegrini P. W.
Published: July 2002

We have fabricated p-type PtSi/SiGe/Si Schottky diodes with barrier heights (from photoresponse) that are lowered (relative to PtSi/Si) and highly dependent on the applied bias. The variability in the barrier height is obtained by using the SiGe/Si valence band offset as an additional barrier. When placed in close proximity to the PtSi/SiGe Schottky barrier, the total effective barrier can be altered dramatically by adjusting the applied reverse bias. The voltage sensitivity of the total barrier height can be controlled by the SiGe layer thickness. The voltage-variable barrier heights range, for example, from 0.30 eV at zero bias to 0.12 eV at 2.4 V reverse bias for a 20%, 450 Å thick SiGe layer. This lowest barrier height corresponds to a cutoff wavelength of 10 μm, extending the detection range of PtSi infrared detectors to the long-wavelength range. The quantum efficiency coefficients C1 are normal at this long-wavelength end, but reduced over the rest of the tunable range, because hot carriers have to traverse the entire SiGe thickness in order to be detected. The hot carriers’ energy losses from quasielastic scattering in the SiGe are taken into account in a theoretical model that gives good agreement with data.
An elliptical wiggler for SPring-8
Authors: Maréchal X. M. , Tanaka T. , Kitamura H.
Published: July 2002

This paper presents a study for the realization of an elliptical multipole wiggler to be installed on the pilot beamline dedicated to material science at SPring-8. Such a wiggler should meet the requirements of third generation synchrotron sources (e.g., large horizontal aperture), as it uses a planar structure (two jaws above and below the vacuum chamber). Compared to the APPLE concept proposed by Sasaki, this new wiggler exhibits similar performances: 65% (85%/90%) circular polarization rate can be obtained up to 300 keV (200/150 keV) with high brilliance (≳1015photons/s/0.1%/mr2/mm2). Moreover this new design is easier to characterize than APPLE, since the sources of vertical and horizontal magnetic fields are independent. The effects of the magnet interactions (e.g., demagnetization in magnets and the consecutive loss of field) are not considered in the following but should be addressed in a future paper.
Height calibration of optical lever atomic force microscopes by simple laser interferometry
Authors: Jaschke Manfred , Butt Hans-Jürgen
Published: July 2002

A new and simple interferometric method for height calibration of AFM piezo scanners is presented. Except for a small mirror no additional equipment is required since the fixed wavelength of the laser diode is used as a calibration standard. The calibration is appliable in the range between several ten nm and several μm. Besides vertical calibration many problems of piezo elements like hysteresis, nonlinearity, creep, derating, etc. and their dependence on scan parameters or temperature can be investigated.
Ferromagnetic resonance and magnetic disaccommodation of Ti-doped single crystal lithium ferrites
Authors: Flores A. G. , Torres L. , Zazo M. , Raposo V. , Iñiguez J.
Published: July 2002

Disaccommodation and ferromagnetic resonance measurements for single crystal titanium-doped lithium ferrites are presented. Magnetic disaccommodation is performed at 1 kHz from 77 to 400 K while ferromagnetic resonance is carried out at 11 GHz from 77 to 300 K. Ferromagnetic resonance line shape asymmetry and anisotropy field data are also shown. A relationship between the asymmetry and the disaccommodation spectra is suggested.
Microstructure of GaN epitaxy on SiC using AlN buffer layers
Authors: Ponce F. A. , Krusor B. S. , Major J. S. , Plano W. E. , Welch D. F.
Published: July 2002

The crystalline structure of GaN epilayers on (0001) SiC substrates has been studied using x-ray diffraction and transmission microscopy. The films were grown by metalorganic chemical vapor deposition, using AlN buffer layers. X-ray diffraction measurements show negligible strain in the epilayer, and a long-range variation in orientation. Transmission electron lattice images show that the AlN buffer layer consists of small crystallites. The nature of the buffer layer and its interfaces with the substrate and the GaN film is discussed. The defect structure of the GaN film away from the substrate consists mostly of threading dislocations with a density of ∼109 cm−2.
Optical cell for the study of biological systems under high gas pressures
Authors: Somasundaram Thayumanasamy , Makowski Lee
Published: July 2002

A high-pressure system incorporating an optical cell and suitable for the study of aqueous biological systems is described. The high-pressure system can be assembled from commercially available components. Using the system gas pressures up to 70 MPa of various gases can be generated from pressures available in the laboratory and maintained over samples for extended periods of time. Preliminary optical measurements on aqueous solutions incubated with nitrogen or methane gas pressures have indicated that there is a gas-specific interaction between the solution and the gas. Biological membranes and their components are modified by the aqueous solutions incubated against high-pressure methane whereas nitrogen incubated solutions do not show comparable effects. Some of the observed modifications are irreversible whereas others are reversible when pressure is reduced.
High sensitivity sensor for moderate pressures
Authors: Rosenbaum T. F. , Carter S. A. , Honig J. M.
Published: July 2002

The metal–insulator transition of (V0.99Ti0.01)2O3 is marked by dramatic changes in the electrical resistivity and the magnetic susceptibility, with a linear pressure variation of −6.06 K/kbar for P≤15 kbar. We propose its use as the sensing element of a manometer in applications where the superconducting transition of soft metals has been traditional.
Short cantilevers for atomic force microscopy
Authors: Walters D. A. , Cleveland J. P. , Thomson N. H. , Hansma P. K. , Wendman M. A. , Gurley G. , Elings V.
Published: July 2002

We have designed and tested a family of silicon nitride cantilevers ranging in length from 23 to 203 μm. For each, we measured the frequency spectrum of thermal motion in air and water. Spring constants derived from thermal motion data agreed fairly well with the added mass method; these and the resonant frequencies showed the expected increase with decreasing cantilever length. The effective cantilever density (calculated from the resonant frequencies) was 5.0 g/cm3, substantially affected by the mass of the reflective gold coating. In water, resonant frequencies were 2 to 5 times lower and damping was 9 to 24 times higher than in air. Thermal motion at the resonant frequency, a measure of noise in tapping mode atomic force microscopy, decreased about two orders of magnitude from the longest to the shortest cantilever. The advantages of the high resonant frequency and low noise of a short (30 μm) cantilever were demonstrated in tapping mode imaging of a protein sample in buffer. Low-noise images were taken with feedback at a rate of about 0.5 frames/s. Given proper setpoint adjustment, the sample was not damaged, despite this cantilever’s high spring constant of 1.3 N/m. Without feedback, images were taken at 1.5 frames/s.
Effects of macroscopic inhomogeneities on resistive and Hall measurements on crosses, cloverleafs, and bars
Authors: Koon D. W. , Knickerbocker C. J.
Published: July 2002

The effect of macroscopic inhomogeneities on resistivity and Hall angle measurements is studied by calculating weighting functions (the relative effect of perturbations in a local transport property on the measured global average for the object) for cross, cloverleaf, and bar-shaped geometries. The ‘‘sweet spot,’’ the region in the center of the object that the measurement effectively samples, is smaller for crosses and cloverleafs than for the circles and squares already studied, and smaller for the cloverleaf than for the corresponding cross. Resistivity measurements for crosses and cloverleafs suffer from singularities and negative weighting, which can be eliminated by averaging two independent resistance measurements, as done in the van der Pauw technique. Resistivity and Hall measurements made on sufficiently narrow bars are shown to effectively sample only the region directly between the voltage probes.
Magnetic field induced broadening of the resistive transition in epitaxial c-axis-oriented HgBa2CaCu2O6+δ films
Authors: Rupp M. , Gupta A. , Tsuei C. C.
Published: July 2002

The resistive transition in epitaxial c-axis-oriented HgBa2CaCu2O6+δ (Hg-1212) thin films Tc∼122 K) in magnetic fields up to 9 T have been investigated. A considerably larger broadening of the resistive transition is observed for magnetic fields perpendicular to the ab plane than for fields parallel to the ab plane. Over the measured range of magnetic fields, the resistivity exponentially approaches zero as a function of decreasing temperature, suggesting a thermally activated flux creep behavior. The anisotropic characteristics of Hg-1212 are compared with other high-temperature cuprate superconductors and found to be less than for the Bi or Tl two-layer systems, but still considerably larger than for YBa2Cu3O7−δ. This can be qualitatively explained on the basis of the differences in the insulator spacing layer thickness between the adjacent CuO2 layers in these cuprates.
A fiber optic frequency shifter
Authors: Xu Renliang , Schmitz Brian , Lynch Martin
Published: July 2002

A fiber optic frequency shifter capable of shifting the frequency of light traveling through the fiber has been designed, constructed, and tested. The frequency of the transmitted light is shifted by stretching and contracting the optical fiber that is wound around two piezoelectric ceramic tubes. The frequency of the light is shifted by linearly changing the path length along which the light must travel. The diameters of two piezoelectric ceramic tubes are changed when a linearly increasing electric field is applied to the tubes. A servo control system is used to correct and compensate for nonlinearity of the piezoelectric material and assembly. A frequency shift of up to 305 Hz for up to 2.5 s with a linewidth of less than 1 Hz is achieved with the present setup. This frequency shifter has been successfully applied to a laser light scattering apparatus for which heterodyne experiments are made for particle electrophoretic mobility and zeta potential measurements.
Conceptual design for a time resolved x-ray imaging system useable in a strong hard x-ray background
Authors: Masugata K. , Chishiro E. , Nakahama N. , Yatsui K. , Tazima T.
Published: July 2002

A new type of time resolved soft x-ray pinhole camera has been conceptually designed for the measurement of the size of pinched electron beam of sub-mm size in the strong x-ray background. In the camera an x-ray image is converted to an optical image and transferred by an image guide of 1 m length to the place where hard x-ray background is weak. The optical image is intensified and gated by a multichannel plate image intensifier (MCP-II) and recorded on a film. In the test operation, an x-ray image of a flash x-ray source was successfully observed in an open shutter mode operation. The minimum exposure time of the MCP-II was estimated to be 6.5 ns from measurement with a short pulsed laser diode.
Application to optical components of dielectric porous silicon multilayers
Authors: Mazzoleni C. , Pavesi L.
Published: July 2002

Narrow-band color filters have been integrated on porous silicon layers. Distributed Bragg reflectors and Fabry–Pérot interference filters based on layered porous silicon samples are demonstrated. The effects of narrowing and tuning the porous silicon emission band are shown in structures composed by Fabry–Pérot filters integrated on top of thick porous silicon layers.
A 36 cm2 large monolythic pn-charge coupled device x-ray detector for the European XMM satellite mission
Authors: Strüder L. , Bräuninger H. , Briel U. , Hartmann R. , Hartner G. , Hauff D. , Krause N. , Maier B. , Meidinger N. , Pfeffermann E. , Popp M. , Reppin C. , Richter R. , Stötter D. , Trümper J. , Weber U. , Holl P. , Kemmer J. , Soltau H. , Viehl A. , Zanthier C.v.
Published: July 2002

Monolythic arrays of 12 pn-charge coupled devices 3×1 cm2 each, have been developed and produced for the focal plane instrumentation of the high throughput European Photon Imaging Camera on XMM and the German ABRIXAS x-ray satellite mission. The design parameters have been optimized to match the properties of the x-ray imaging optics as well as the x-ray intensity, energy bandwidth, and characteristic time constants of objects to be observed. The pixel size is 150×150 μm2; read-out is performed in parallel with 64 channels in each subunit, resulting in a total of 768 channels; low noise, spectroscopic performance is realized by on-chip integrated JFET electronics; high ohmic, ultrapure bulk material allows full depletion and enhances the efficiency for higher energy x-ray detection. The fabrication process, the layout topology, and the operating conditions guarantee ten years operation in space without performance degradation.
Design of a film balance for optical investigations at the oil–water interface
Authors: Teppner R. , Harke M. , Motschmann H.
Published: July 2002

A film balance for the investigation of insoluble monolayers at the macroscopic oil–water interface is described. The design of the balance enables simultaneous surface tension and optical reflection measurements under well defined conditions. The oil-phase is contained within a quartz housing whose dimensions are optimized for imaging purposes. The performance of the apparatus is illustrated by the π, A-isotherm of a phospholipid and ellipsometric images of the morphology of the phospholipid dipolmitoyl-phosphatidyl-ethanolamine at the hexadecane–water interface.
Imaging system to monitor the pendulum mode of a vibrationally driven torsion balance
Authors: Winkler L. I. , Stevenson B. A.
Published: July 2002

A digital-imaging system based on a personal computer was tested for its ability to track in real time periodic motion with a frequency near 1 Hz. When imaging a vibrationally isolated stationary target, the system displayed a limitation in positional measurement of 0.3×10−6 m. Further tests indicate that this limitation arises from environmental vibrations driving the target, even though it is mounted on a vibration-isolation table. This work demonstrates the feasibility of using digital imaging to measure motions other than the (usually very low frequency) torsion motion of a torsion balance, where the ultimate goal is to remove the effects of these motions from the torsion signal of interest.
Electron paramagnetic resonance detection by time-locked subsampling
Authors: Hyde James S. , Mchaourab Hassane S. , Camenisch Theodore G. , Ratke Joseph J. , Cox Robert W. , Froncisz W.
Published: July 2002

A detection method for electron paramagnetic resonance spectroscopy is described that permits simultaneous acquisition of multiple in- and out-of-phase harmonics of the response to magnetic-field modulation for both dispersion and absorption: (i) conversion of the microwave carrier to an intermediate frequency (IF) carrier; (ii) subsampling of the IF carrier by an analog-to-digital converter four times in K IF cycles where K is an odd integer; (iii) dividing the digital words into two streams, odd indexes in one and even in the other, followed by sign inversion of every other word in each stream; and (iv) feeding the two streams to a computer for the digital equivalent of phase-sensitive detection (PSD). The system is broadbanded, in the frequency domain, with narrow banding for improved signal-to-noise ratio occurring only at the PSD step. All gains and phases are internally consistent. The method is demonstrated for a nitroxide spin label. A fundamental improvement is achieved by collecting more information than is possible using a single analog PSD.
High accuracy magnetic field measurements with a Hall probe
Authors: Schott C. , Popovic R. S. , Alberti S. , Tran M. Q.
Published: July 2002

A silicon-based temperature stabilized axial Hall probe with an absolute accuracy of ±40 ppm in the full range between 0 and 6 T is presented. The absolute calibration of the probe is performed against a nuclear magnetic resonance (NMR) probe. The application of the probe to a magnetic field profile of a 5 T superconducting magnet system, with field gradients as high as 30 T/m, reaching an overall accuracy of better than ±100 ppm, is demonstrated. In addition to the high absolute accuracy, this Hall probe allows high spatial resolution measurements of inhomogeneous fields in configurations where present NMR probes are not usable.
New optical probe of GHz polarization dynamics in ferroelectric thin films
Authors: Hubert Charles , Levy Jeremy
Published: July 2002

We describe a method for measuring the response of ferroelectric thin films to microwave-frequency electric fields. A mode-locked Ti:sapphire laser is used to generate a microwave drive signal that is phase locked to an optical probe pulse. The induced polarization change in the ferroelectric film is measured stroboscopically via the electro-optic effect. Images are acquired by scanning the laser beam across the sample in a confocal geometry. Time resolution is achieved by changing the delay between the electrical pump and the optical probe. Initial results show large local phase shifts in the ferroelectric response of closely separated (1 μm) regions of a Ba0.5Sr0.5TiO3 thin film. This new experimental technique may help to understand the physical mechanisms of dielectric loss in these materials.
A new instrument for measuring both the magnitude and angle of low level linear birefringence
Authors: Wang Baoliang , Oakberg Theodore C.
Published: July 2002

This article describes a sensitive method for measuring both the magnitude and the angle of the fast axis of low level linear birefringence in optical materials. Several different approaches have been investigated and one of them has been chosen as the basis for a linear birefringence measurement instrument. The instrument employs a low birefringence photoelastic modulator for modulating the polarization states of a He–Ne laser beam. After the modulated laser beam passes through the sample, two detecting channels analyze the polarization change caused by the sample. An algorithm has been developed to calculate the magnitude and angle of the retardance in a sample. A computer program implements the algorithm and displays the calculated values. Using this instrument, selected samples with different levels of linear birefringence have been studied. The resulting instrument achieves high precision and sensitivity for the final measurements. The sensitivity of the magnitude of linear birefringence is better than 0.005 nm (∼0.003 ° with a He–Ne laser at 632.8 nm), and the sensitivity of the fast axis angle of the sample is <1 ° (for retardance ⩾0.5 nm).
The L3A facility at the Vinča Institute: Surface modification of materials, by heavy ion beams from an electron cyclotron resonance ion source
Authors: Dobrosavljević A. , Milosavljević M. , Bibić N. , Efremov A.
Published: July 2002

This article describes the L3A experimental facility for surface modification of materials at the Vinča Institute of Nuclear Sciences, in Belgrade. This facility was completed and put into operation in May 1998. It is connected to the mVINIS ion source, an electron cyclotron resonance ion source capable of producing a wide range of multiply charged ions from gaseous and solid substances. The heavy ion beams obtained from mVINIS are separated by charge to mass ratio (q/m) and transported to the target chamber for sample irradiation and modification. The target chamber is equipped with a multipurpose target holder, an electron-beam evaporation source for thin layer deposition, a residual gas analyzer, and other auxiliary equipment. There is also an additional low energy argon ion source for target preparation/sputtering and for ion beam assisted deposition. In this article we describe the layout and performances of the L3A facility, the experience gained during 1 yr of operation, and the requirements imposed by the current and future experimental programs. Currently, there are 24 experimental programs competing for the ion beam time at the L3A facility.
Study of the effect of hydrogen on transport properties in chemical vapor deposited diamond films by Hall measurements
Authors: Hayashi Kazushi , Yamanaka Sadanori , Okushi Hideyo , Kajimura Koji
Published: July 2002

Using Hall effect measurements, we have investigated carrier transport in a high-conductivity layer formed in the surface region of as-deposited homoepitaxial diamond films prepared by chemical vapor deposition. The results of undoped and B-doped films were compared to those obtained from an oxidized B-doped film. It is found that (1) the carrier (hole) density per unit area of both as-deposited films is 4–5 orders of magnitude larger than that of the oxidized B-doped film at 297 K and is nearly constant in the temperature range of 150–400 K, while that of the oxidized B-doped film shows a strong temperature dependence with an activation energy of 0.38 eV, and (2) the Hall mobility of both as-deposited films is 1–2 orders of magnitude smaller than that of the oxidized B-doped film at 297 K and increases with increasing temperature, while that of the oxidized B-doped film decreases. These results and the secondary ion mass spectroscopy analysis suggest that the high-conductivity layer formed in the as-deposited films originates from the incorporated hydrogen in the subsurface region.
Flexible giant magnetoresistance sensors
Authors: Parkin S. S. P.
Published: July 2002

Exchange-biased magnetic sandwiches are shown to exhibit ‘‘giant’’ magnetoresistive properties when deposited on free-standing organic films. This allows for the possibility of preparing flexible magnetoresistance heads or head arrays for tape or floppy-disk drive and hard-disk drive applications. Similar structures deposited on thin organic layers spin coated onto silicon substrates also exhibit giant magnetoresistive behavior.
Real-time scanning Hall probe microscopy
Authors: Oral A. , Bending S. J. , Henini M.
Published: July 2002

We describe a low-noise scanning Hall probe microscope having unprecedented magnetic field sensitivity (∼2.9×10−8 T/√Hz at 77 K), high spatial resolution, (∼0.85 μm), and operating in real-time (∼1 frame/s) for studying flux profiles at surfaces. A submicron Hall probe manufactured in a GaAs/AlGaAs two-dimensional electron gas (2DEG) is scanned over the sample to measure the surface magnetic fields using conventional scanning tunneling microscopy positioning techniques. Flux penetration into a high Tc YBa2Cu3O7−δ thin film has been observed in real time at 85 K with single vortex resolution. Flux is seen to enter the film in the form of vortex bundles as well as single flux quanta, Φ0.
Hydrogen ion motion in amorphous silicon solar cells at elevated temperatures
Authors: Carlson D. E. , Rajan K.
Published: July 2002

Electric field-enhanced degradation has been observed in amorphous silicon solar cells exposed to intense illumination (45–60 suns) at elevated temperatures (≳160 °C). The front tin oxide contacts of both p–i–n and n–i–p cells darken significantly when a strong reverse bias is applied at elevated temperatures and under intense illumination. Compositional profiles of the cells show that a strong reverse bias causes a depletion of hydrogen near the contacts. These results are interpreted in terms of proton motion near the p/i interface of p–i–n cells and negative hydrogen ion motion near the i/n interface.
Local crystallographic texture and voiding in passivated copper interconnects
Authors: Nucci J. A. , Keller R. R. , Sanchez J. E. , Shacham-Diamand Y.
Published: July 2002

A correlation between local crystallographic texture and stress-induced void formation in tantalum-encapsulated, copper interconnects was revealed by electron backscattering diffraction studies in a scanning electron microscope. Lines exhibiting an overall stronger 〈111〉 texture showed better resistance to void formation. Furthermore, grains adjacent to voids exhibited weaker 〈111〉 texture than grains in unvoided regions of the same line. The locally weaker 〈111〉 texture at voided locations suggests the presence of higher diffusivity, twist boundaries. This work, which represents the first characterization of local texture in stress voided, copper lines, helps to elucidate the relative importance of the thermodynamic and kinetic factors which govern void formation and growth.
Electron spin relaxation in InGaAs/InP multiple-quantum wells
Authors: Tackeuchi Atsushi , Wada Osamu , Nishikawa Yuji
Published: July 2002

The electron spin relaxation of InGaAs/InP multiple-quantum wells (MQW) is investigated using time-resolved polarization-dependent absorption measurement. The MQW has an excitonic absorption at 1.54 μm which is suitable for application in optical communications. A theoretical prediction assuming the D’yakonov-Perel’ interaction as the main relaxation mechanism gives a spin relaxation rate for the InGaAs quantum well over twice as high as that for the GaAs quantum well. The spin relaxation time measured at room temperature is 5.2 ps and found to be an order of magnitude faster than that of a GaAs quantum well.
Measurement and manipulation of Mn clusters on clean and fullerene terminated Si(111)-7×7
Authors: Upward M. D. , Moriarty P. , Beton P. H. , Baker S. H. , Binns C. , Edmonds K.
Published: July 2002

We have investigated the properties of Mn clusters deposited on clean semiconductor surfaces using an ultrahigh vacuum scanning tunnelling microscope. The clusters were formed using a gas aggregation source and were deposited on Si(111)-7×7 and Si(111)-7×7 terminated by a C60 monolayer. A distribution of cluster widths was observed with a most frequent value of 2.6 nm. There was no evidence of either cluster coalescence or preferential bonding sites. The clusters had an irregular shape, but did not appear to be grossly deformed upon adsorption onto the surface. The clusters could be selectively removed from the C60 terminated surface during scanning at negative sample bias.
Giant magneto-impedance and its relaxation in Co–Fe–Si–B amorphous ribbons
Authors: Sartorelli M. L. , Knobel M. , Schoenmaker J. , Gutierrez J. , Barandiarán J. M.
Published: July 2002

Systematic measurements of giant magneto-impedance (GMI) and its relaxation (magneto-impedance aftereffect) have been carried out in a series of Co-rich amorphous ribbons ranging in magnetostriction values from −3.5 to +3.5 ppm. The value of GMI is a maximum for the alloy with the lowest value of magnetostriction, corresponding to a maximum of the transverse permeability. The impedance relaxation between two fixed times depends on the magnetostriction constant (λs) of the samples, and the observed trend is consistent with the theories which predict a direct relationship of the conventional permeability aftereffect (MAE) with the square of λs. Furthermore, the variation of the impedance aftereffect with the driving current resembles the behavior of MAE, and a connection between both effects can be established.
Minority-carrier characteristics of SiNx/GaAs metal–insulator–semiconductor structures with Si/Ge interlayers
Authors: Park Dae-Gyu , Reed J. C. , Morkoç Hadis
Published: July 2002

Minority-carrier response and conductance loss characteristics of SiNx/Si/Ge/n-GaAs(001) metal–insulator–semiconductor (MIS) structures are presented. The response time of minority carriers with Si(⩽10 Å)/Ge (20 Å) interlayers, as determined by the capacitance–voltage (C–V) method, is several orders of magnitude smaller than those with Si interlayers only. The minority carriers in n-type Si/Ge/GaAs layers respond to even a small ac signal of 1 kHz at room temperature, which is ascribed to the smaller band gap and thus a higher intrinsic carrier concentration of Ge. The minority carriers in the SiNx/Si/Ge/n-GaAs MIS structures respond to a 1 MHz signal at a sample temperature of 230 °C. Temperature-dependent C–V measurements on the GaAs MIS structure with Si/Ge, interlayers revealed the activation energy (Ea) of the minority-carrier recombination to be about 0.58 eV. The conductance loss characteristics of SiNx/Si/Ge/GaAs structures indicate a contribution by interface traps responding to slow states, while the fast states are a result of interface defects of the SiNx/Si/GaAs MIS system.
Effects of Ga addition to CuInSe2 on its electronic, structural, and defect properties
Authors: Wei Su-Huai , Zhang S. B. , Zunger Alex
Published: July 2002

Using a first-principles band structure method we have theoretically studied the effects of Ga additions on the electronic and structural properties of CuInSe2. We find that (i) with increasing xGa, the valence band maximum of CuIn1−xGaxSe2 (CIGS) decreases slightly, while the conduction band minimum (and the band gap) of CIGS increases significantly, (ii) the acceptor formation energies are similar in both CuInSe2 (CIS) and CuGaSe2 (CGS), but the donor formation energy is larger in CGS than in CIS, (iii) the acceptor transition levels are shallower in CGS than in CIS, but the GaCu donor level in CGS is much deeper than the InCu donor level in CIS, and (iv) the stability domain of the chalcopyrite phase increases with respect to ordered defect compounds. Our results are compared with available experimental observations.
Contacting carbon nanotubes selectively with low-ohmic contacts for four-probe electric measurements
Authors: Bachtold A. , Henny M. , Terrier C. , Strunk C. , Schönenberger C. , Salvetat J.-P. , Bonard J.-M. , Forró L.
Published: July 2002

Contact resistances of multiwalled nanotubes deposited on gold contact fingers are very large. We show that the contact resistances decrease by orders of magnitudes when the contact areas are selectively exposed to the electron beam in a scanning electron microscope. The focused electron beam enables the selection of one particular nanotube for electrical measurement in a four-terminal configuration, even if a loose network of nanotubes is deposited on the gold electrodes. For all measured nanotubes, resistance values lie in a narrow range of 0.35–2.6 kΩ at room temperature.
Oxidation resistance of tantalum–ruthenium dioxide diffusion barrier for memory capacitor bottom electrodes
Authors: Yoon Dong-Soo , Baik Hong Koo , Lee Sung-Man , Park Chang-Soo , Lee Sang-In
Published: July 2002

The effect of the RuO2 addition into a Ta film on the oxidation resistance of a diffusion barrier for the Ta+RuO2/Si system was investigated. The Ta+RuO2/Si system was sustained up to 800 °C without an increase in resistivity, while the Ta/Si structure completely degraded after annealing at 450 °C. The Ta+RuO2 diffusion barrier showed an amorphous microstructure for an as-deposited state and formed a conductive RuO2 phase after annealing. Ta was sufficiently bound to oxygen of RuO2 for an as-deposited state, but RuO2 was divided into Ru and Ru–O binding states. Ta–O bonds showed a little change compared to the as-deposited state with increasing annealing temperature, whereas Ru–O bonds significantly increased. Therefore, the Ta layer deposited by the RuO2 addition effectively prevented the indiffusion of oxygen up to 800 °C and its oxidation resistance was superior to those of polycrystalline nitride (TiN, TaN) and ternary amorphous (TaSiN) barriers reported by others.
Influence of negative dc bias voltage on structural transformation of carbon nitride at 600 °C
Authors: Yap Y. K. , Kida S. , Aoyama T. , Mori Y. , Sasaki T.
Published: July 2002

Carbon nitride (CN) thin films were prepared at 600 °C by rf plasma pulsed laser deposition. As we increased the magnitude of the negative dc bias voltage, the CN bonds were transformed from a mixture of sp2 C–N and sp3 C–N states into a CN phase predominated by tetrahedral CN bonds. A biasing threshold of this transformation occurred due to the annihilation of the graphite microstructure, which coincided with a threshold of significant nitrogen incorporation. We found that suppression of graphite supersaturation appeared to be important for the formation of the tetrahedral sp3 C–N bonds. The nitrogen content of these films is stable upon annealing at 800 °C in vacuum.
The Meyer–Neldel rule in fullerenes
Authors: Wang J. C. , Chen Y. F.
Published: July 2002

We report that the thermally activated conductivity in several fullerene systems obeys the Meyer–Nelder (MN) rule, σ=σ00eΔE/kT0e−ΔE/kT. We found that the MN conductivity σ00 and the characteristic energy kT0 have a strong correlation, which is in good agreement with the prediction of the model proposed by Crandall [R. S. Crandall, Phys. Rev. B 43, 4057 (1991)] and Chen [Y. F. Chen and S. F. Huang, Phys. Rev. B 44, 13 775 (1991)]. In this model, the origin of the MN rule is attributed to the exponential energy distribution of the defect traps. A similar correlation between σ00 and kT0 is also found in chalcogenide glasses.
Femtosecond laser-induced three-dimensional bright and long-lasting phosphorescence inside calcium aluminosilicate glasses doped with rare earth ions
Authors: Qiu Jianrong , Miura K. , Inouye H. , Kondo Y. , Mitsuyu T. , Hirao K.
Published: July 2002

We report on a novel phenomenon in calcium aluminosilicate glasses doped with Ce3+, Tb3+, and Pr3+. After irradiation by an 800 nm femtosecond pulsed laser, the focused part of the laser in the glasses emits bright and long-lasting phosphorescence able to be clearly seen with the naked eye in the dark even one hour after the removal of the activating laser. Moreover, by selecting appropriate glass compositions and species of rare earth ions, optional three-dimensional image patterns emitting long-lasting phosphorescence in various colors, including blue, green, and red, can be formed within glass samples by moving the focal point of the laser. Based on absorption spectra, the long-lasting phosphorescence is considered to be due to the thermostimulated recombination of holes and electrons at traps induced by the laser irradiation, which leave holes or electrons in a metastable excited state at room temperature.
Polarization dependence of intraband absorption in self-organized quantum dots
Authors: Chua S. J. , Xu S. J. , Zhang X. H. , Wang X. C. , Mei T. , Fan W. J. , Wang C. H. , Jiang J. , Xie X. G.
Published: July 2002

Photoluminescence and intraband absorption were investigated in n-doped self-organized InAs and In0.35Ga0.65As quantum dots grown on a GaAs substrate. Intraband absorption of the dots is strongly polarized along the growth axis in the mid infrared spectral range. The absorption is maximum at around 120 meV for InAs dots and at 130 meV for In0.35Ga0.65As dots. The experimental results on InAs dots are in agreement with published theoretical calculations.
Blue-green organic light-emitting diodes based on fluorene-oxadiazole compounds
Authors: Antoniadis Homer , Inbasekaran Mike , Woo Edmund P.
Published: July 2002

We explore the electroluminescent properties of multilayer vapor-deposited organic light-emitting diodes based on a novel set of blue-green emitting-fluorene-oxadiazole compounds. The compounds were used both for the transport of electrons and for the emission of light; in all cases, arylamines were used for the transport of holes. Reducing the ionization potential of the fluorene-oxadiazole compound suppressed the exciplex formation between the hole-transporting layer (HTL) and the electron transport layer (ETL) and increased the corresponding photometric efficiency from 0.6 to 8.7 cd/A. High power efficiencies of 4.5 lm/W at a luminance of 200 cd/m2 were also achieved at low operating voltages. However, the device lifetime was very limited which was attributed mainly to the exciplex formation in the HTL/ETL interface and the instability of the oxadiazole moiety in the excited state.
Amphoteric behavior of arsenic in HgCdTe
Authors: Berding M. A. , Sher A.
Published: July 2002

The properties of arsenic in HgCdTe are predicted using ab initio calculations and a statistical theory. Predictions on the amphoteric nature of arsenic are in good agreement with experimental results on material growth both by liquid phase epitaxy and molecular beam epitaxy (MBE). The experimentally observed dependence of the arsenic diffusion on mercury partial pressure is also explained by our results. A microscopic model for activating the arsenic as an acceptor is suggested, and requirements of post-MBE-growth activation anneals are identified.
Pressure-induced energy level crossings and narrowing of photoluminescence linewidth in self-assembled InAlAs/AlGaAs quantum dots
Authors: Phillips J. , Bhattacharya P. , Venkateswaran U.
Published: July 2002

We present a study of the hydrostatic-pressure dependence of the photoluminescence from In0.5Al0.5As/Al0.25Ga0.75As self-assembled quantum dots. Three distinct regions of quantum-dot peak-energy shift with pressure are observed and are attributed to energy level crossings and band mixing effects. In addition, a large reduction in photoluminescence linewidth with applied pressure is noted.
Nanofabrication on Si oxide with scanning tunneling microscope: Mechanism of the low-energy electron-stimulated reaction
Authors: Li Nan , Yoshinobu Tatsuo , Iwasaki Hiroshi
Published: July 2002

Nanofabrication on Si oxide with a low-energy electron-beam-stimulated reaction has been demonstrated using scanning tunneling microscopy (STM) and the mechanism of the low-energy electron-induced etching is investigated further. Direct fabrication of a thin Ag film with this low-energy e-beam/STM method was also tested, which shows an additional capability of the nanofabrication technique. Nanometer-scale patterning of rings on a thin Si-oxide layer using this method shows that further progress nanolithography can be expected with the fabricated Si oxide as a mask.
Charge transfer in photovoltaics consisting of interpenetrating networks of conjugated polymer and TiO2 nanoparticles
Authors: Arango A. C. , Carter S. A. , Brock P. J.
Published: July 2002

We study the effect of blended and layered titanium dioxide (TiO2) nanoparticles on charge transfer processes in conjugated polymer photovoltaics. A two order of magnitude increase in photoconductivity and sharp saturation is observed for layered versus blended structures, independent of the cathode work function. Using electrodes with similar work functions, we observe low dark currents and open circuit voltages of 0.7 V when a TiO2 nanoparticle layer is self-assembled onto the indium–tin–oxide electrode. Our results for the layered morphologies are consistent with charge collection by exciton diffusion and dissociation at the TiO2 interface.
High-performance (Al,Ga)N-based solar-blind ultraviolet p–i–n detectors on laterally epitaxially overgrown GaN
Authors: Parish G. , Keller S. , Kozodoy P. , Ibbetson J. P. , Marchand H. , Fini P. T. , Fleischer S. B. , DenBaars S. P. , Mishra U. K. , Tarsa E. J.
Published: July 2002

Solar-blind ultraviolet photodiodes with a band-edge wavelength of 285 nm were fabricated on laterally epitaxially overgrown GaN grown by metalorganic chemical vapor deposition. Current–voltage measurements of the diodes exhibited dark current densities as low as 10 nA/cm2 at −5 V. Spectral response measurements revealed peak responsivities of up to 0.05 A/W. Response times for these diodes were measured to be as low as 4.5 ns for 90%-to-10% fall time. For comparison, diodes were fabricated using the same p–i–n structure deposited on dislocated GaN. These diodes had dark current densities many orders of magnitude higher, as well as a less sharp cutoff, and a significant slow tail under impulse excitation.
Experimental studies of rubidium absolute polarization at high temperatures
Authors: Appelt S. , Ünlü T. , Zilles K. , Shah N. J. , Baer-Lang S. , Halling H.
Published: July 2002

We report on measurements of the absolute rubidium (Rb) polarization, optically pumped by a high-power diode laser array, up to temperatures of 180 °C. The penetration of the pump laser light into a high-pressure cell has been studied experimentally and theoretically. The experimental results are compared to a model, which describes the local Rb polarization and optical pumping rate in the cell.