bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrahigh finesse microcavity with distributed Bragg reflectors
Authors: Stanley R. P. , Houdré R. , Oesterle U. , Gailhanou M. , Ilegems M.
Published: July 2002

We have grown a very high finesse microcavity using distributed Bragg reflectors of AlxGa1−xAs and AlAs. The measured Fabry–Pérot mode has a linewidth of 0.84 Å at 930 nm. This implies a finesse in excess of 5500 and an effective (mirror corrected) finesse greater than 1450. Comparison with theoretical calculations for such a structure shows that (i) the growth rates are stable to 0.25% over 14 h and (ii) the internal losses are less than 1 cm−1.
Single-asperity friction in friction force microscopy: The composite-tip model
Authors: Putman Constant A. J. , Igarashi Masaru , Kaneko Reizo
Published: July 2002

Friction measurements on muscovite mica and glass have been performed with a friction force microscope using Si3N4 tips. The environment was changed from ambient conditions to N2- or Ar-gas conditions. In ambient conditions, the friction-versus-load curves showed a nonlinear behavior closely following the Hertzian contact mechanics of a single-asperity contact: friction force ∼load2/3. For the same tip under gaseous conditions the friction force increased linearly with the load, indicating multi-asperity contact. A new model is proposed to explain this change in the nature of the friction behavior. In this composite-tip model, the tip is formed by the actual Si3N4 tip and ‘‘solidlike’’ contaminants present in enclosed cavities between tip and sample surface.
TFTR Michelson interferometer electron cyclotron emission diagnostic
Authors: Stauffer F. J. , Boyd D. A. , Cutler R. C. , McCarthy M. P.
Published: July 2002

In July 1984, a Fourier transform spectrometer employing a fast-scanning Michelson interferometer began operating on TFTR. This diagnostic system can measure the electron cyclotron emission spectrum 72 times per s with a time resolution of 11 ms and a spectral resolution of 3.6 GHz. The initial operating spectral range is 75–540 GHz, which is adequate for measuring the first three cyclotron harmonics at present TFTR magnetic field levels. The range can be extended easily to 75–1080 GHz in order to accommodate increases in toroidal magnetic field or to study superthermal ECE. The measured spectra are absolutely calibrated using a liquid nitrogen cooled blackbody reference source. The second harmonic feature of each spectrum is used to calculate the absolute electron temperature profile.
High-frequency response heat-flux gauge
Authors: Epstein A. H. , Guenette G. R. , Norton R. J. G. , Yuzhang Cao
Published: July 2002

A double-sided, high-frequency response heat-flux gauge has been developed which allows measurement of heat flux from dc to 100 kHz. The instrument is designed for heat-flux magnitudes ranging from one to several hundred kW/m2 at temperatures up to 400 °C and is independent of the test article material. The gauges consist of a metal film (1500 Å) resistance thermometers sputtered on both sides of a thin (25 μm) polyimide sheet. The sheet, which can contain many gauges, is then adhesively bonded to a test article. The temperature difference across the polyimide is a direct measure of the heat flux at low frequencies, while a quasi-1D analysis is used to infer the high-frequency heat flux from the upper surface temperature history. The design criteria, construction and application techniques, and a novel, ratiometric calibration procedure are discussed in detail.
Theories of the feedback and vibration isolation systems for the scanning tunneling microscope
Authors: Park Sang-il , Quate C. F.
Published: July 2002

The theories of the feedback and vibration isolation systems have been developed to illuminate the essential points in the design and operation of the scanning tunneling microscope (STM). By analyzing a delay differential equation, we can understand the behavior of feedback and estimate the necessary gain and time constant for the best performance of the STM. Design considerations for a vibration isolation system consisting of spring suspension and magnetic damping are discussed with theoretical optimization.
Optical fiber refractometer
Authors: Meyer Martin S. , Eesley Gary L.
Published: July 2002

We report on the use of an optical fiber to measure the refractive index of liquid materials. With a relatively simple detection system, indices can be determined with an average accuracy of ±0.2%.
Magnetic bottle electron spectrometer using permanent magnets
Authors: Tsuboi Toshio , Xu Emily Y. , Bae Young K. , Gillen Keith T.
Published: July 2002

Design principles and initial results are presented for a magnetic bottle electron spectrometer of high collection efficiency (2π sr) and good energy resolution. The instrument duplicates the carefully shaped axially decreasing magnetic field configuration of Kruit and Read [J. Phys. E 16, 313 (1983)], but replaces the high-field electromagnet central to the Kruit–Read design with two simple pole pieces energized by permanent magnets. The use of permanent magnets requires modifications of the transition region (between the high-field electron production zone and the low-field drift tube analyzer) to avoid axial field reversals associated with fringing fields.
Ruby decay-time fluorescence thermometer in a fiber-optic configuration
Authors: Grattan K. T. V. , Selli R. K. , Palmer A. W.
Published: July 2002

In this article, a fluorescence decay-time thermometer using ruby crystal as the transducer material and carefully designed signal processing, with a light-emitting diode source and solid-state optical detection is reported. Results over a range to 170 °C are discussed with a standard deviation in the measurement, at best, corresponding to ±0.04 K, in laboratory tests.
Automatic kelvin probe compatible with ultrahigh vacuum
Authors: Baikie I. D. , van der Werf K. O. , Oerbekke H. , Broeze J. , van Silfhout A.
Published: July 2002

This article describes a new type of in situ ultrahigh-vacuum compatible kelvin probe based on a voice-coil driving mechanism. This design exhibits several advantages over conventional mechanical feed-through and (in situ) piezoelectric devices in regard to the possibility of multiple probe geometry, flexibility of probe geometry, amplitude of oscillation, and pure parallel vibration. Automatic setup and constant spacing features are achieved using a digital-to-analog converter (DAC) steered offset potential. The combination of very low driver noise pick-up and data-acquisition system (DAS) signal processing techniques results in a work function (wf ) resolution, under optimal conditions, of <0.1 meV. Due to its high surface sensitivity and compatibility with standard sample cleaning and analysis techniques this design has numerous applications in surface studies, e.g., adsorption kinetics, sample topography and homogeneity, sputter profiles, etc. For semiconductor specimens the high wf resolution makes it eminently suitable for surface photovoltage (SPV) spectroscopy.
Growth of heteroepitaxial Si1−x−yGexCy alloys on silicon using novel deposition chemistry
Authors: Todd Michael , Matsunaga Philip , Kouvetakis John , Chandrasekhar D. , Smith David J.
Published: July 2002

We report heteroepitaxial growth of diamond-structured Si1−x−yGexCy alloys on (100)Si substrates. Introduction of C into the diamond lattice is kinetically favored by low-temperature (470 °C) interactions of C(SiH3)4, a novel C–H free carbon precursor, with mixtures of SiH4 and GeH4 using ultrahigh-vacuum chemical vapor deposition techniques. Film thicknesses of 100 to 110 nm with 4–6 at. % C as indicated by Rutherford backscattering carbon resonance spectroscopy were obtained. Cross-sectional transmission electron microscopy and Fourier transform infrared spectroscopy showed crystalline alloy phase formation with no detectable SiC precipitation. Secondary ion mass spectrometry revealed pure and highly homogeneous films. In situ annealing at 675 °C resulted in heteroepitaxial films with relatively few defects.
Study of chemically assisted ion beam etching of GaN using HCl gas
Authors: Ping A. T. , Adesida I. , Asif Khan M.
Published: July 2002

The use of an Ar ion beam and hydrogen chloride gas in the chemically assisted ion beam etching of GaN grown by metalorganic chemical vapor deposition is reported. Etch rates were investigated as a function of ion beam energy and substrate temperature. Hydrogen chloride gas was found to produce higher etch rates at lower ion beam energies (300 eV) and lower rates at higher energies (600 eV) in comparison to Cl2. Highly anisotropic etch profiles are demonstrated that indicate that the process may be suitable for the fabrication of laser facets and mirrors. Changes in surface stoichiometry resulting from the etching process were also investigated using Auger electron spectroscopy.
The use of silver tips in scanning tunneling microscopy
Authors: Gorbunov A. A. , Wolf B. , Edelmann J.
Published: July 2002

We propose to use silver tips for scanning tunneling microscopy (STM). Silver is the cheapest noble metal that is practically chemically inactive in the air environment. A simple reliable procedure of the tip preparation and resharpening is presented. The procedure is based on two-step electrochemical processing resulting in final tip curvature of less than 200 nm in radius as seen by an electron microscope. The tips show durability for at least a week of daily operation in an air STM.
Characterization of tips for conducting atomic force microscopy
Authors: O’Shea S. J. , Atta R. M. , Welland M. E.
Published: July 2002

The conductivity of a variety of atomic force microscopy tips was investigated by measuring both current-voltage characteristics and force profile data for the tip in contact with graphite. This allows the conductivity to be studied as a function of tip-sample distance. It was found that etched gold wires or levers coated with a conducting diamond film were the best tips to use for experimentation on hard (SiO2) surfaces. Metal-coated levers, particularly gold, were found to wear rapidly such that the very end of the tip became insulating.
One- and two-dimensional x-ray detector systems at NSLS beam line X12B, for time-resolved and static x-ray-diffraction studies
Authors: Capel M. S. , Smith G. C. , Yu B.
Published: July 2002

Some important characteristics are described of one- and two-dimensional gas proportional detectors with delay line position readout which are currently in use at beam line X12B of the National Synchrotron Light Source. The importance of careful choice of geometric design parameters is emphasized with respect to position linearity and electrical stability; position resolution of 100 μm FWHM and counting rates up to several times 105 s−1 are obtained in calibration studies. Results from some recent beam-line experiments further illustrate the excellent position resolution and linearity, and demonstrate the usefulness of these detector systems for small-angle scattering, particularly in dynamic studies.
Construction of constant-deviation constant-length spherical grating monochromator at UVSOR
Authors: Hiraya Atsunari , Nakamura Eiken , Hasumoto Masami , Kinoshita Toshio , Sakai Kusuo , Ishiguro Eiji , Watanabe Makoto
Published: July 2002

A constant-deviation constant-length spherical grating monochromator was constructed at the bending-magnet beamline 8B1 of the UVSOR. The monochromator has a simple scanning mechanism with a fixed position of the entrance and exit slits, as well as fixed directions of incident and exit photon beams. The monochromator was designed to cover the photon energy of 31–620 eV with three interchangeable laminar gratings (1080 lines/mm: R=15 m, 540 lines/mm: R=15 m, 360 lines/mm: R=7.5 m). All gratings are original gratings fabricated on synthetic quartz substrates and coated with Au. The resolving power evaluated by ray tracing at the lowest energy of each grating with 10 μm slit width is ∼4400 for two high energy gratings and ∼7000 for a low energy grating. In the preliminary performance check, it was found that the output spectrum of the monochromator with G1 grating extends up to 870 eV with resolving power of ∼4000 at 400 eV with 10 μm slits.
Phosphorescence quenching and the microcirculation: An automated, multipoint oxygen tension measuring instrument
Authors: Shonat Ross D. , Richmond Keith N. , Johnson Paul C.
Published: July 2002

A new, phosphorescence-based optical instrument for making oxygen tension (PO2) measurements in individual vessels of microvascular preparations is described. Palladium–porphyrin compounds injected into the systemic vasculature are excited by light and the measured phosphorescence emission lifetime used to calculate intravascular PO2. Because this technique is relatively new, we have undertaken a rigorous examination of its usefulness and inherent limitations for microvascular studies.
A compact hot-nozzle Fourier-transform microwave spectrometer
Authors: Harmony Marlin D. , Beran Kyle A. , Angst Deanna M. , Ratzlaff Kenneth L.
Published: July 2002

A newly constructed pulsed nozzle, Fourier-transform microwave spectrometer utilizes a Fabry–Perot cavity consisting of spherical resonators having diameters of only 10 cm. Tests of this very compact-cavity system show that its sensitivity is only slightly lower than that of a comparably configured system of the Balle–Flygare design having resonators with diameters of 36 cm. With a volume 50 times smaller than in conventional systems, the compact cavity also requires a much smaller vacuum chamber which can be pumped by a relatively small 6 in. diffusion pump. The system includes an integral ceramic nozzle which can be heated to temperatures above 1000 °C. Spectrometer characteristics have been demonstrated by means of experiments on OCS isotopomers in ground and excited vibrational states, ArOCS complexes, and chloroketene, a reactive intermediate formed by pyrolysis of chloroacetylchloride.
Silicone fluid as a high-pressure medium in diamond anvil cells
Authors: Ragan Deirdre D. , Clarke David R. , Schiferl David
Published: July 2002

The usefulness of a silicone oil, Dow Corning 200, as a pressure medium in diamond anvil cells has been investigated. Common indicators of deviatoric stresses on ruby, such as changes in the R-line widths and the R2-R1 peak separation, show that this fluid does not deviate from hydrostaticity up to ∼15 GPa (150 kbar). The behavior of silicone is found to be very similar to the commonly used 4:1 methanol:ethanol mixture, while being much easier to use because of its higher viscosity. This ease of use and excellent performance makes silicone fluid a superior pressure medium.
A high resolution autogain ranging linear electrometer amplifier
Authors: Rajput S. S. , Garg S. C.
Published: July 2002

A current electrometer, capable of operating over a wide range of temperatures is presented. It measures bipolar currents from 3.16 pA to 50 μA in ten sensitivity ranges on a linear scale with a current resolution of 0.2%. The electrometer range depends upon the magnitude of the input current. The measurement accuracy is better than ±1% at 25 °C for currents between 100 pA and 50 μA and remains within ±3% in the temperature range of −15 to 55 °C.
Characterization of arsenide/phosphide heterostructure interfaces grown by gas-source molecular beam epitaxy
Authors: Lew A. Y. , Yan C. H. , Tu C. W. , Yu E. T.
Published: July 2002

We have used cross-sectional scanning tunneling microscopy to study interface structure in arsenide/phosphide heterostructures grown by gas-source molecular beam epitaxy. High-resolution images of a sample grown at 550 °C by interrupting the growth of GaAs at 200 Å intervals with a 40 s P2 flux reveal phosphide interlayers of widths as large as 30 Å with lateral variations in structure over <100 Å length scales. Images of a similar sample grown at 450 °C exhibit narrower interlayers and a lower level of phosphorus incorporation. These samples have also been characterized by high-resolution x-ray diffraction and reflection high-energy electron diffraction. Together, these studies provide direct information about nanometer-scale grading and lateral nonuniformity of interfaces that can occur under these growth conditions.
〈111〉 oriented and twin-free single crystals of Terfenol-D grown by Czochralski method with cold crucible
Authors: Wu Guang-heng , Zhao Xue-gen , Wang Jing-hua , Li Jing-yuan , Jia Ke-chang , Zhan Wen-shan
Published: July 2002

The growth of twin-free single crystals of Tb0.3Dy0.7Fe2 with 〈111〉 orientation by the Czochralski method with cold crucible is reported. Various characterizations demonstrated the twin-free and single-crystalline quality of the crystals. The optimized growth parameters have been experimentally found to avoid constitutional supercooling. Decanting method was used to provide direct evidence that the unstable growth is the origin of the dendrite growth in this material and made the previous growth of 〈111〉 single crystal a failure.
Large area deposition of YBa2Cu3O7−x films by pulsed laser ablation
Authors: Schey B. , Bollmeier T. , Kuhn M. , Biegel W. , Stritzker B.
Published: July 2002

A special patented design is built up to produce homogeneous YBa2Cu3O7−x (YBCO) films by pulsed laser deposition (PLD) over areas as large as 7×20 cm2. The use of a line focus (8 cm) reduces the substrate movement to one dimension. The demands on plasma homogenization, substrate scanning and film temperature during the deposition process for large area PLD are discussed and their technical realization is presented. First results of 1×1 cm2 YBCO films at different positions on the substrate holder (11×28 cm2) show homogeneous deposition conditions. The transition temperatures of the deposited YBCO thin films on 1×1 cm2 SrTiO3 substrates are TC=89 K with critical currents of 4×106 A/cm2 at T=77 K. The structural properties of these films (χmin=4.5%) indicate also their high crystalline quality. The variation of film thickness perpendicular to the scanning direction is less than ±9% and along the scanning direction ±7%.
Blue-violet electroluminescence and photocurrent spectra from polycrystalline chemical vapor deposited diamond film
Authors: Manfredotti C. , Wang F. , Polesello P. , Vittone E. , Fizzotti F. , Scacco A.
Published: July 2002

We have measured current–voltage characteristic, blue-violet electroluminescence (EL) and subgap photocurrent spectra of free standing polycrystalline chemical vapor deposited diamond film. The current increases as a power law function of the voltage with an exponent of about 5.5. The EL spectra show a main luminescence band peaked at 3.0 eV, whose intensity increases linearly with the electric current. The photocurrent increases rapidly with the photon energy in the range from 2.0 to 3.5 eV and then tends to saturate. It is found that all these results can be consistently explained in relation to gap states centered at 3.0 eV above the valence band.
Photodetector designs for low-noise, broadband, and high-power applications
Authors: Gray Malcolm B. , Shaddock Daniel A. , Harb Charles C. , Bachor Hans-A.
Published: July 2002

We present design and performance details of three photodetector circuits that have been developed in the authors laboratory over the past eight years. These detectors have been optimized to meet the unique demands of experiments such as high power, high sensitivity interferometry, nonlinear optics, and laser noise measurements. The circuits are: a low-noise dc coupled (dc 20 MHz) general purpose detector, a low-noise broadband (15–1100 MHz) detector capable of detecting 10 mW of light, and a high-power large dynamic range detector (30 kHz–60 MHz) capable of detecting up to 100 mW of light. We present bandwidth dynamic range and noise performance details for all three designs. In addition, we present detailed circuit schematics along with design and construction guidelines to enable assembly and use of these designs.
Thermally actuated interferometric sensors based on the thermal expansion of transparent elastomeric media
Authors: Grzybowski Bartosz A. , Brittain Scott T. , Whitesides George M.
Published: July 2002

In this article the fabrication and characterization of two thermally actuated optical devices for the measurement of temperature and power are described. A transparent polymer having a high coefficient of thermal expansion—poly(dimethylsiloxane) (PDMS)—was used as the temperature-sensitive medium. Changes in the dimensions of the polymer on heating caused the observed optical responses of both devices. The temperature sensor based on the Fabry–Pérot cavity measures temperature differences to a precision of 0.005 °C within the linear working ranges of the device. The power sensor uses the architecture of a Mach–Zender interferometer; it is suitable for measurements of powers in the mW/cm2 range, delivered optically to the surface of the device in the visible wavelength region. The devices are inexpensive, easy to fabricate, and mechanically rugged. They offer alternatives to other sensors for measuring temperature and power.
A dusty double plasma device
Authors: Nakamura Y. , Bailung H.
Published: July 2002

A novel dusty plasma device to create spatially and temporally uniform steady state dusty plasma is described. An ultrasonic vibrator is used to vibrate a dust dispenser which disperses the dust uniformly through a fine mesh. A dusty plasma of large dimension with controllable dust density is produced. Measured dusty plasma parameters are compared with existing theories. Some experimental results related to propagation characteristics of dust-ion-acoustic waves in a dusty plasma column are presented.
Nd
3+
-doped optical fiber temperature sensor using the fluorescence intensity ratio technique
Authors: Wade S. A. , Muscat J. C. , Collins S. F. , Baxter G. W.
Published: July 2002

An optical fiber temperature sensor employing the fluorescence intensity ratio using Nd3+-doped silica fiber and exhibiting high sensitivity is presented. The development and construction of the sensor, which requires relatively simple electronics and data analysis, is described together with its calibration over the −50 to +500 °C temperature range.
Formation of multi-charged ions and plasma stability at quasigasdynamic plasma confinement in a mirror magnetic trap
Authors: Golubev S. V. , Razin S. V. , Semenov V. E. , Smirnov A. N. , Vodopyanov A. V. , Zorin V. G.
Published: July 2002

It is known that an increase in plasma density in sources of multicharged ions leads to a substantial increase of ion current and slightly improves the ion distribution over charge states. The validity of this statement was verified in experiments with plasma densities not exceeding several units of 1012 cm−3. In the present work it is demonstrated experimentally that, for the electron densities exceeding 1013 cm−3, the regime of plasma confinement in a trap changes significantly and the quasigasdynamic regime of plasma confinement is realized. Comparison of numerical simulations and experimental data showed the essential influence of the anisotropy of electron velocity distribution in a plasma on the ion charge state distribution. This allows looking for the optimal conditions for the creation of highly charged ions in plasma. In this article we also address problems of plasma stability in an axisymmetric mirror trap under powerful microwave pumping. First experiments on ion extraction from a dense plasma pumped by millimeter wave radiation are described.
3.2 μm infrared resonant cavity light emitting diode
Authors: Hadji E. , Bleuse J. , Magnea N. , Pautrat J. L.
Published: July 2002

A CdHgTe resonant cavity light emitting diode is proposed as a new infrared emitter. The device consists of a bottom Bragg reflector of 86% reflectivity, a half-wavelength cavity, n doped at the beginning (1018 cm−3) and p doped at the end (1018 cm−3), containing an active layer at the antinode position, and a top gold mirror of 95% reflectivity which also serves as an Ohmic contact. The emission spectrum shows a narrow peak of 8 meV full width at half-maximum (FWHM) at 300 K, which is much less than the inhomogeneous linewidth of CdHgTe quantum wells (QWs). This electroluminescent peak matches very well the cavity resonance wavelength and FWHM, as given by transmission measurements of the unbiased cavity. The directivity is also improved by the cavity effect. Thus, we have demonstrated that even a relatively low Q microcavity can greatly enhance the characteristics of an infrared emitter in the 2–5 μm range.
Magneto-impedance effect in NiFe plated wire
Authors: Beach R. S. , Smith N. , Platt C. L. , Jeffers F. , Berkowitz A. E.
Published: July 2002

The voltage V(t) induced by a sinusoidal drive current traversing a 125-μm-diameter BeCu wire plated with 1 μm NiFe is observed to be a very strong function of axial dc magnetic field. The basic physics of this phenomenon is explained classically in terms of Faraday’s law of induction and Stoner–Wohlfarth magnetization reversal, which yield theoretical predictions that are in good agreement with experiment. For drive current amplitudes of the order of 100 mA, and frequencies of the order of 5 MHz, the field sensitivity dV/dH can be as large as 1 V/Oe (per cm of wire), which offers the potential for application in relatively simple, very high sensitivity magnetic field sensors.
Structures and dielectric properties of thin polyimide films with nano-foam morphology
Authors: Cha H. J. , Hedrick J. , DiPietro R. A. , Blume T. , Beyers R. , Yoon D. Y.
Published: July 2002

Thin polyimide films with dispersed nano-foam morphology have been prepared for the purpose of obtaining low dielectric polymer insulators for microelectronic applications. They were obtained by utilizing micro phase-separated triblock copolymers where the thermally stable polyimide matrix component was derived from pyromellitic dianhydride (PMDA) with 1,1-bis(4-aminophenyl)-1-phenyl-2,2,2-trifluoroethane (3F) and a thermally labile poly(propylene oxide)(PO) component comprised the outside block of the ABA triblock architecture. TEM studies show that the initial irregular nanoscale phase-separated morphology of polyimide triblock copolymers are mostly maintained in the final nano-foam films upon thermal decomposition of the dispersed PO component. The nano-foam polyimide films exhibit significantly lower dielectric constants ε′ (e.g., 2.3 at 19% porosity) as compared with ε′≊2.9 for the homopolymer, as predicted by Maxwell–Garnett theory, with the nano-pore structures remaining stable at 350 °C.
Nitrogen doped fluorinated amorphous carbon thin films grown by plasma enhanced chemical vapor deposition for low dielectric constant interlayer dielectrics
Authors: Endo Kazuhiko , Tatsumi Toru
Published: July 2002

Nitrogen doped fluorinated amorphous carbon thin films for low dielectric constant interlayer dielectrics have been investigated. The films were deposited with a parallel-plate plasma enhanced chemical vapor deposition. Source gases were CH4, CF4, and N2. The thermal stability of the films can be improved by the addition of N2. X-ray photoelectron spectroscopy (XPS) measurement revealed that the C-N bonds were formed in the films with the addition of N2. The dielectric constant of the films was increased from 2.1 to 2.4 at the nitrogen concentration of 10%.
Electroluminescence of erbium–oxygen-doped silicon diodes grown by molecular beam epitaxy
Authors: Stimmer J. , Reittinger A. , Nützel J. F. , Abstreiter G. , Holzbrecher H. , Buchal Ch.
Published: July 2002

We have fabricated erbium–oxygen-doped silicon light emitting diodes with molecular beam epitaxy by simultaneously evaporating erbium and silicon and providing a suitable background pressure of oxygen. In reverse bias, the diodes show intense room-temperature electroluminescence at λ=1.54 μm, originating from the intra-4f transition of erbium. This luminescence does not show temperature quenching between 4 and 300 K. In forward bias the erbium peak intensity is reduced by a factor of 30 at low temperatures and shows temperature quenching.
Fabrication of arrays of large step-free regions on Si(001)
Authors: Tanaka So , Umbach C. C. , Blakely Jack M. , Tromp Ruud M. , Mankos M.
Published: July 2002

In this letter we describe a method for producing large areas of Si(001) surfaces which are (i) free of atomic steps and (ii) arranged in regular patterns on the wafer. The first step is the fabrication of a two-dimensional grating structure using e-beam lithography and reactive ion etching. This grating is then annealed within the appropriate temperature window in ultrahigh vacuum to produce the desired array of (001) step-free regions. We illustrate the success of the method through the use of low-energy electron microscopy for a few repeat spacings on test structures each extending over a 3×3 mm2 area. Alternative processing steps are discussed as well as application to submicron device technology.
Phase coupling of two optically pumped vertical-cavity surface-emitting lasers
Authors: Hendriks R. F. M. , van Exter M. P. , Woerdman J. P. , van der Poel C. J.
Published: July 2002

We have studied the interaction between two optically pumped vertical-cavity surface-emitting lasers (VCSELs) on a wafer as a function of their separation d. The VCSELs are strongly coupled for d⩽13 μm, leading to the appearance of higher-order lateral modes. For d⩾13 μm the VCSELs are weakly coupled, leading to phase locking of the individual emitters.
Room temperature 1.54 μm light emission of erbium doped Si Schottky diodes prepared by molecular beam epitaxy
Authors: Du Chun-Xia , Ni Wei-Xin , Joelsson Kenneth B. , Hansson Göran V.
Published: July 2002

Schottky-type light emitting devices have been fabricated on Er-oxide doped Si layers grown by molecular beam epitaxy, in order to study the light emission process of Er-doped Si structures. By applying a reverse bias on the Schottky junction, Er ions incorporated within the depletion layer can be electrically excited via a hot electron impact process. Rather intense electroluminescence (EL) at a wavelength of 1.54 μm has been observed at room temperature. The optoelectronic properties of the devices have been characterized by both input-power dependent and temperature dependent EL measurements. An activation energy value of ∼160 meV responsible for luminescence thermal quenching has been obtained.
Antenna-coupled polycrystalline silicon air-bridge thermal detector for mid-infrared radiation
Authors: Chong N. , Ahmed H.
Published: July 2002

Polycrystalline silicon (polysilicon) airbridges coupled to log-periodic and bow-tie planar antennas have been fabricated for mid-infrared radiation detection. The detectors in thermocouple and bolometer modes exhibit a higher electrical responsivity than previously reported metal based antenna-coupled thermal detectors. Measurements made at 10.2 μm wavelength indicate that the linearly polarized antennas have an on-axis cross-polarization ratio of about −4.5 dB and the pattern in the free-space side has a directivity of approximately 5–9 dB. The coupling efficiency is about 15%. Frequency responses for modulated optical signals agree with thermal transport models.
Thermal stability of amorphous hard carbon films produced by cathodic arc deposition
Authors: Anders Simone , Dı́az Javier , Ager Joel W. , Yu Lo Roger , Bogy David B.
Published: July 2002

The thermal stability of amorphous hard carbon films produced by cathodic arc deposition was studied by near edge x-ray absorption fine structure (NEXAFS) spectroscopy, Raman spectroscopy, and nanoindentation evaluation. Pure carbon films of up to 85% sp3 content were deposited using a pulsed biasing technique and annealed in ultrahigh vacuum up to 850 °C. NEXAFS spectra show no change in the film properties up to 700 °C, and a modification of the spectra for 800 and 850 °C, which indicate graphitization. Raman spectra show only a very slight change up to 850 °C. The nanoindentation data show no change in hardness and elastic modulus with annealing up to 850 °C. The study demonstrates the high thermal stability of the films. The difference in the NEXAFS and the Raman and nanoindentation results can be attributed to the surface sensitivity of NEXAFS in comparison to the more bulk sensitivity of Raman spectroscopy and nanoindentation.
Analysis of a thin AlN interfacial layer in Ti/Al and Pd/Al ohmic contacts to n-type GaN
Authors: Luther B. P. , DeLucca J. M. , Mohney S. E. , Karlicek R. F.
Published: July 2002

Using high resolution transmission electron microscopy, a thin pseudomorphic AlN layer (2–3 nm) has been observed at the metal/GaN interfaces of Ti/Al (35/115 nm) and Pd/Al (25/125 nm) ohmic contacts to n-type GaN annealed in Ar at 600 °C for 15 and 30 s, respectively. The interfacial layer has a c-plane (002) lattice spacing of 2.48±.03 Å and an a-plane (100) spacing matching that of GaN (2.76 Å), and the identification of this layer as AlN is consistent with chemical analysis by energy dispersive x-ray spectroscopy. The formation of this interfacial AlN layer coincides with the onset of ohmic behavior in Ti/Al and Pd/Al contacts annealed at 600 °C and may be the cause.
Deep ultraviolet enhanced wet chemical etching of gallium nitride
Authors: Peng L.-H. , Chuang C.-W. , Ho J.-K. , Huang C.-N. , Chen C.-Y.
Published: July 2002

We report a study of the ultraviolet (UV) irradiation effects on the wet chemical etching of unintentionally doped n-type gallium nitride (GaN) layers grown on sapphire substrates. When illuminated with a 253.7 nm mercury line source, etching of GaN is found to take place in aqueous phosphorus acid (H3PO4) and potassium hydroxide (KOH) solutions of pH values ranging from −1 to 2 and 11 to 15, respectively. Formation of gallium oxide is observed on GaN when illuminated in dilute H3PO4 and KOH solutions. These results are attributed to a two-step reaction process upon which the UV irradiation is shown to enhance the oxidative dissolution of GaN.
Secondary ion yield changes on rippled interfaces
Authors: Makeev Maxim A. , Barabási Albert-László
Published: July 2002

Sputter erosion often leads to the development of surface ripples. Here we investigate the effect of the ripples on the secondary ion yield, by calculating the yield as a function of the microscopic parameters characterizing the ion cascade (such as penetration depth, widths of the deposited energy distribution) and the ripples (ripple amplitude, wavelength). We find that ripples can strongly enhance the yield, with the magnitude of the effect depending on the interplay between the ion and ripple characteristics. Furthermore, we compare our predictions with existing experimental results.
Characterization of high-quality InGaN/GaN multiquantum wells with time-resolved photoluminescence
Authors: Minsky M. S. , Fleischer S. B. , Abare A. C. , Bowers J. E. , Hu E. L. , Keller S. , Denbaars S. P.
Published: July 2002

Recombination in single quantum well and multiquantum well InGaN/GaN structures is studied using time-resolved photoluminescence and pulsed photoluminescence measurements. Room-temperature measurements show a rapid lifetime (0.06 ns) for a single quantum well structure, while an increasingly long decay lifetime is measured for multiquantum wells as more quantum wells are incorporated into the structure. Temperature-dependent lifetime measurements show that a nonradiative recombination mechanism activates above 45 K in the single quantum well but is less important in the multiquantum wells.
Effects of inhomogeneous oxygen content in (La,Gd)0.7Ca0.3MnO3+δ perovskites
Authors: Sun J. R. , Rao G. H. , Zhang Y. Z.
Published: July 2002

Magnetoresistance properties of compounds with the same formula La0.7−xGdxCa0.3MnO3+δ (x=0, 0.04) but synthesized by the solid-state reaction method from different starting materials are studied. Nearly stoichiometric compounds are obtained when La(OH)3 is used for sample preparation. However, under the same condition, La2O3 causes considerable oxygen deficiency in resulting samples, characterized by a broad metal–semiconductor transition far below the magnetic transition. Inhomogeneous distribution of the oxygen content in compounds (an inhomogeneity beyond the detection of powder x-ray diffraction) can occur when both La2O3 and La(OH)3 coexist in the starting materials, leading to two metal–semiconductor transitions which are obviously developments of those in compounds prepared respectively from La2O3 and La(OH)3, and one magnetic transition corresponding to the upper resistive transition.
Strain compensated InGaAs/InGaP quantum well infrared detector for midwavelength band detection
Authors: Maimon S. , Cohen G. M. , Finkman E. , Bahir G. , Ritter D. , Schacham S. E.
Published: July 2002

A high detectivity multiquantum well midinfrared photodetector is reported. It is based on a strain compensated InGaAs/InGaP on InP structure, using bound-to-continuum intersubband absorption, with λP=4.9 μm and ∼0.5 μm full width at half maximum. This design is unique by enabling a large critical thickness, thus increasing the quantum efficiency. Photodetectors with background-limited performance (BLIP) with detectivity of Dλ*(BLIP)=3.2×1010 cmHz/W up to 110 K, with only ten quantum well periods were implemented. Arguments are given to predict an optimized background-limited performance for this design up to 135 K.
Vacancy ordering of Ga2Se3 at GaSe/GaAs(100) interface
Authors: Dai Z. R. , Ohuchi F. S.
Published: July 2002

Vacancy ordering was directly observed by high resolution transmission electron microscopy (HRTEM) at the heterointerface of GaSe/GaAs(100) grown by molecular beam epitaxy. Ga2Se3 crystalline film forms immediately to the GaAs (100) substrate, acting as an intermediate layer with thickness of 1.6–3.2 nm between the GaSe film and the GaAs substrate. Combining with fast Fourier transform analysis and simulations of HRTEM images and diffraction patterns, vacancy ordering in the Ga2Se3 was investigated. The vacancies preferably distribute on the (100) crystal planes of α-Ga2Se3 with a zinc-blende structure and the vacancy sheet appears on the planes of each three separated Ga sheets.
Nondispersive hole transport in an electroluminescent polyfluorene
Authors: Redecker M. , Bradley D. D. C. , Inbasekaran M. , Woo E. P.
Published: July 2002

Time-of-flight measurements have been used to study carrier transport in films of poly(9,9-dioctylfluorene). We find nondispersive hole transport with a room-temperature mobility, μp=4×10−4 cm2/V s at a field of 5×105 V/cm. The field dependence of the mobility is weak: μp=3×10−4 cm2/V s at 4×104 V/cm and increases only modestly to μp=4.2×10−4 cm2/V s at 8×105 V/cm. Both the relatively high mobility and weak field dependence point to a high degree of chemical regularity and purity that makes polyfluorene attractive for use as an electroluminescent polymer and for other device applications. We have not been able to measure clean electron current transients, suggesting highly dispersive transport with possible deep trapping, as found in many other conjugated polymers.
Band gap energy in nanocrystalline ZrO2:16%Y thin films
Authors: Kosacki Igor , Petrovsky Vladimir , Anderson Harlan U.
Published: July 2002

The results of optical absorption measurements on nanocrystalline ZrO2:16%Y thin films are presented. Dense 0.7 μm thick films with 1–300 nm grain size have been obtained on sapphire substrate using a polymeric precursor spin coating technique. The relationship between the energy gap and microstructure of ZrO2:16%Y has been determined and discussed. The quantum confinement effect was observed at the grain size lower than 100 nm with the band gap energy shift of 0.25 eV when the microstructure was changed up to 1 nm. Some limitation of the model has been observed and discussed. The band gap energy of 5.62±0.05 eV has been determined as microstructure independent value.
Magnetic and hardness properties of nanostructured Ni–Co films deposited by a nonaqueous electroless method
Authors: Chow G. M. , Ding J. , Zhang J. , Lee K. Y. , Surani D. , Lawrence S. H.
Published: July 2002

Nanostructured NixCo100−x films were deposited on Cu substrates by reducing the constituent metal salts in refluxing ethylene glycol at 194 °C. The average crystallite size increased with x, and reached a maximum of 64 nm when x=100. The coercivity Hc of the films measured in the direction perpendicular (⊥) to the plane of the film was higher than that in the parallel (∥) direction. For the sample of x=50, Hc⊥ was 379 Oe, which was six times that of Hc∥. Saturation magnetization Ms in the film plane was 1016 emu/cm3, and the remanent magnetization Mr 636 emu/cm3, giving a squareness ratio of 0.63. This film also had a Vickers hardness of 193.
Fracture behavior of a nanocrystallized Zr65Cu15Al10Pd10 metallic glass
Authors: Chen M. W. , Inoue A. , Fan C. , Sakai A. , Sakurai T.
Published: July 2002

Fracture surfaces of a nanocrystallized Zr65Cu15Al10Pd10 metallic glass were observed on an atomic scale with field ion microscopy. Based on geometrical and phase characteristics of the fracture morphologies, it can be determined that a crack propagates along the interfaces between nanocrystals and the amorphous matrix in the alloy with optimized microstructures. Combining with macromechanical properties, it is proposed that the strengthening effect of nanocrystals in the Zr-based metallic glass arises from a strong interaction between nanocrystals and local shear bands during deformation processes of the glassy matrix.
Oxygen-vacancy-related dielectric anomalies in La:SrTiO3
Authors: Yu Zhi , Ang Chen , Cross L. E.
Published: July 2002

The influence of post-sintering annealing on the dielectric relaxation behavior was studied in (Sr1−1.5xLax)TiO3 in the temperature range of 1.5–300 K. The results show that the dielectric permittivity peaks with frequency dispersion can be gradually and absolutely eliminated by annealing in an oxidizing atmosphere, and recovered by annealing in a reducing atmosphere; this implies that these anomalies are closely related to oxygen vacancies.
Stress analysis of selective epitaxial growth of GaN
Authors: Liu Q. K. K. , Hoffmann A. , Siegle H. , Kaschner A. , Thomsen C. , Christen J. , Bertram F.
Published: July 2002

Stress distributions in selectively overgrown self-organized GaN hexagonal pyramids have been analyzed by continuum elasticity theory. This has been carried out using the values for the moduli of elasticity found in the literature and an effective lattice mismatch between the GaN and the substrate that was determined from the Raman shift of the GaN buffer layer. The results of compressive stress in the buffer layer, tensile stress on the lower half of the pyramids’ facet surface, and full relaxation for approximately the upper 2/3 of the pyramids are in satisfactory agreement with the experimental observations that were deduced from cathodoluminescence microscopy and micro-Raman spectroscopy.
Large etch-selectivity enhancement in the epitaxial liftoff of single-crystal LiNbO3 films
Authors: Radojevic A. M. , Levy M. , Osgood R. M. , Kumar A. , Bakhru H. , Tian C. , Evans C.
Published: July 2002

We report on a large etch selectivity enhancement in the epitaxial liftoff of He+-implanted single-crystal lithium niobate (LiNbO3) films upon rapid thermal annealing. A buried sacrificial layer is formed by ion implantation. Heat treatment is found to reduce the time needed for film detachment by a factor as large as 100. Implant damage and postanneal stress-induced etch selectivity become nearly independent of implantation energy upon annealing. Large (0.5×1 cm2) 5–10-μm-thick single-crystal LiNbO3 films of excellent quality are detached in just a matter of a few hours.
Localization of Na impurities at the buried CdS/Cu(In, Ga)Se2 heterojunction
Authors: Heske C. , Eich D. , Fink R. , Umbach E. , Kakar S. , van Buuren T. , Bostedt C. , Terminello L. J. , Grush M. M. , Callcott T. A. , Himpsel F. J. , Ederer D. L. , Perera R. C. C. , Riedl W. , Karg F.
Published: July 2002

We demonstrate a general approach to identify and locate minority species at buried interfaces which are of fundamental interest in many fields of solid state research. The approach combines soft x-ray emission for bulk and photoelectron spectroscopy for surface sensitivity. In the present study, the interface between a thin CdS layer and a Cu(In, Ga)Se2 thin film solar cell absorber has been investigated, showing that Na impurities are localized at the buried CdS/Cu(In, Ga)Se2 heterojunction.
Observation of strong to Josephson-coupled crossover in 10° YBa2Cu3Ox bicrystal junctions
Authors: Redwing R. D. , Hinaus B. M. , Rzchowski M. S. , Heinig N. F. , Davidson B. A. , Nordman J. E.
Published: July 2002

A temperature-dependent strong to weak (Josephson) coupling crossover near 75 K is observed for 10° misorientation YBa2Cu3Ox grain boundaries. Below 75 K the current–voltage characteristic (IVC) shows strongly coupled, flux-flow behavior. Above 75 K, the IVC is Josephson coupled. The data are consistent with a network of microbridges at the grain boundary defined by dislocation strain fields. The data are compared to recent calculations by A. Gurevich and A. E. Pashitskii [Phys. Rev. B 57, 13878 (1998)]. The characteristic voltages for these low-angle grain boundaries are higher than high-angle boundaries at 77 K, and could lead to improved high-temperature superconducting device operation in this temperature range.
Semiclassical theory of terahertz multiple-harmonic generation in semiconductor superlattices
Authors: Feise M. W. , Citrin D. S.
Published: July 2002

A semiclassical theory is used to describe the emission of multiple electromagnetic harmonics in the terahertz (THz) regime due to coherent frequency-modulated Bloch oscillations in a superlattice driven by a strong THz field. A cutoff frequency to the harmonics linear in the applied THz field strength but independent of modulation frequency is predicted.
Thermal stability of supersaturated MgxZn1−xO alloy films and MgxZn1−xO/ZnO heterointerfaces
Authors: Ohtomo A. , Shiroki R. , Ohkubo I. , Koinuma H. , Kawasaki M.
Published: July 2002

We have examined the thermal stability of wurtzite-phase MgxZn1−xO alloy films and ZnO/MgxZn1−xO bilayer films with x exceeding the reported solubility limit of 0.04. When a Mg0.23Zn0.78O film was annealed, the segregation of MgO started at 850 °C and the band gap was reduced to the value of that for an x=0.15 film after annealing at 1000 °C. Mg0.15Zn0.85O films showed no change of the band gap even after annealing at 1000 °C. Therefore, we conclude that the thermodynamic solubility limit of MgO in MgxZn1−xO epitaxial film is about x=0.15. The thermal diffusion of Mg across the MgxZn1−xO/ZnO interface was observed only after annealing above 700 °C. Unlike other II–VI semiconductors, ZnO-based alloy films and heterointerfaces are stable enough for the fabrication of high-crystallinity heterostructures.
Synthesis of GaN–carbon composite nanotubes and GaN nanorods by arc discharge in nitrogen atmosphere
Authors: Han Weiqiang , Redlich Philipp , Ernst Frank , Rühle Manfred
Published: July 2002

A method using an arc discharge in a nitrogen atmosphere for synthesizing large quantities of gallium nitride (GaN)–Carbon composite nanotubes and GaN nanorods is reported. The reaction is achieved by a dc arc discharge between a graphite anode filled with a mixture of GaN, graphite, and nickel powders and a graphite cathode in a nitrogen atmosphere. The GaN are presented as rodlike fillings in the composite tubes and the isolated GaN nanorods have diameters in the range of 7–45 nanometers and a length of up to 40 μm. The outer graphitic shells of the composite carbon nanotubes have thicknesses ranging from 1 to 8 nm. It was found that the use of a nitrogen atmosphere plays a crucial role for the growth of the GaN nanorods fillings and the individual GaN nanorods.