bluuebunny/crossref_metadata_2025 huggingface dataset:
Fabrication and evaluation of a dimension-reduction fiberoptic system for chemical imaging applications
Authors: Nelson Matthew P. , Myrick M. L.
Published: July 2002

A novel system for rapid chemical imaging is described and evaluated. The system operates via single-frame spectroscopic chemical imaging with high spectroscopic resolution using a second-generation dimension-reduction fiberoptic array. Images are focused onto a rectangular array of square close-packed 25 μm cross-sectional f/2 optical fibers that are drawn into a linear distal array with serpentine ordering. The distal end is then imaged with an f/2 spectrograph equipped with a holographic grating and a gated intensified charge-coupled device (ICCD) camera for analysis. Software is used to extract the spatial/spectral information contained in a single ICCD image and deconvolute it into wavelength-specific univariate reconstructed images or position-specific spectra that span an 86 nm wavelength space using our present grating. A description of the fabrication of the dimension-reduction array is given as well as a zero-order reconstruction of a binary target and single-wavelength image reconstructions of a laser-induced plasma. The system is evaluated for spatial and spectral resolution, throughput, image brightness, resolving power, depth of focus, and channel cross talk. Treatment of the spectroscopic data obtained from the ICCD images for use in potential chemical imaging applications is discussed.
Diamond epitaxy on (001) silicon: An interface investigation
Authors: Jiang X. , Jia C. L.
Published: July 2002

In combination with scanning electron microscopy and x-ray pole-figure analysis high resolution electron microscope (HREM) observation of the diamond-silicon cross section in a 〈001〉 epitaxially oriented diamond film was carried out to investigate the atomic interfacial microstructure. The films were prepared by microwave plasma chemical vapor deposition using a bias-enhanced nucleation technique. Due to the multiple fit of diamond and silicon lattices, there is a periodic 3-to-2 registry of {111} atom planes of the epitaxial diamond-silicon interface. Planar defects on diamond {111} planes and interface misfit dislocations are shown for epitaxially oriented and for slightly misoriented diamond crystallites. A cubic silicon carbide ‘‘transition’’ is found to be unnecessary for the epitaxy. The misorientation of the grown crystallites is also studied and found to be probably due to interface imperfection.
High-efficiency spin-resolved and spin-integrated electron detection: Parallel mounting on a hemispherical analyzer
Authors: Ghiringhelli G. , Larsson K. , Brookes N. B.
Published: July 2002

We have mounted a compact 25 kV mini-Mott spin polarimeter on a commercial high-throughput hemispherical electron analyzer with a double purpose: to maximize the polarization detection and to preserve the original efficiency of the spectrometer in the spin-integrated measurements. We have thus replaced the 16-anode microchannel-plate detector with a 12-anode microsphere-plate detector in parallel with a Rice University retarding Mott spin polarimeter. Passing from one detection mode to the other is quick and easy. The transfer optics from the analyzer exit slit to the scattering target of the polarimeter allows the full potential of both the electron analyzer and the spin detector to be exploited. The expected effective Sherman function (Seff=0.17) and figure of merit (η0≅1.4×10−4) are found in the spin-resolved mode, and only 25% of the original efficiency is lost in the spin-integrated acquisitions.
The polarizer-analyzer correction problem in neutron polarization analysis experiments
Authors: Wildes A. R.
Published: July 2002

The equations for correcting the instrumental depolarization effects in neutron polarization analysis experiments are presented in matrix form. It is proved that, when no approximations are made, it is always possible to solve for individual flipper efficiencies but is only sometimes possible to solve for polarizer and analyzer efficiencies. For certain experiments it is necessary to know these quantities to correctly analyze data. This is not a serious problem when the elements are very efficient, but has important ramifications when the efficiency is poor and/or time dependent, as is often the case with the helium-3 neutron polarizing method. Methods of solving for the polarizer and analyzer efficiencies are presented.
An electrostatic probe with end plugs for measurements in a magnetized plasma
Authors: Demidov V. I. , Ratynskaia S. V. , Rypdal K.
Published: July 2002

An electrostatic probe for measurements in a magnetized plasma is proposed. It consists of a cylindrical rod with insulating end plugs, and is operated by obtaining the current-voltage characteristic and its first derivative for different orientations of the rod with respect to the magnetic field. The probe provides a simple estimate of ion temperature and ion density and an improved measurement of the electron energy distribution function.
A method for determining orifice loss coefficients in strongly transient compressible liquid flows
Authors: Moss E. A. , Skews B. W.
Published: July 2002

The aim of the current work was to devise a method of establishing orifice loss coefficients in highly transient liquid flows. This was motivated by the fact that (i) many physical systems involve liquid transfer through narrow channels between cavities under unsteady conditions, and (ii) such data does not exist in the literature. A test facility was constructed, consisting of a drop-weight tester which operates in conjunction with a test cell comprising a vertically mounted thick-walled cylinder blanked off at the bottom, and containing upper and lower water-filled cavities separated by a plate with a small, sharp-edged orifice (thickness to diameter ratio of four). The upper cavity is enclosed at its top surface by a piston which protrudes beyond the upper section of the cylinder. When a weight is dropped onto the piston, a variation of pressure (p1) occurs in the upper cavity, approximating the shape of a half sinusoid with time, and with a typical half cycle (T) in the range 1.34–2.73 ms. Mass transfer takes place from the upper to the lower cavity, with a commensurate increase of pressure (p2) in the latter. At a certain time p1 and p2 become equal, at which the latter is at its maximum and the former is close to the end of its sinusoidal half cycle. Thereafter, p1 rapidly diminishes to ambient pressure and p2 approaches ambient pressure over a period of about 5T. During this latter phase, p2 exceeds p1, which is consistent with flow reversal. A comprehensive analysis of the system, in conjunction with pressure measurement, enabled experimental loss coefficients to be determined during that time when mass transfer was taking place between the upper and lower cavities (with p1>p2). Values of cd obtained were in the range 0.85–1.2, increasing for the smaller values of T. These data are viewed in the context of the expected steady flow value of 0.79 for this configuration of orifice, and confirm the hypothesis that flow unsteadiness of a sufficiently small time scale has a significant effect on loss coefficients.
Simple apparatus for contact angle measurements by the heavy drop method
Authors: Viallet A. , Rousset E. , Baudin G.
Published: July 2002

An apparatus for measuring contact angles by the heavy drop method is proposed. After a few introductory considerations, the article reviews some experimental methods and shows their main advantages and drawbacks. In the heavy drop method, the mean contact angle of a liquid on a solid is calculated from a measurement of the height in the central zone of a large pancake-like drop. This measurement is based in turn on partial occultation of a parallel light beam, detected by a photodiode. Connected to a microcomputer for data storage and processing, the device allows investigations to be made of either static or dynamic phenomena by contact angle and/or contact angle hysteresis measurements; it is simple and well suited to various problems of surface characterization.
Transparent, conducting, metallic thin films
Authors: Avrekh M. , Thibadeau B. M. , Monteiro O. R. , Brown I. G.
Published: July 2002

Metallic films that are sufficiently thin compared to the wavelength of light can be optically transparent, and if the film is continuous and without too many disconnected regions (islands), then the electrical resistivity of the film can remain usefully low as well. That is, surface films that are both electrically conducting and optically transparent can be formed if the film is continuous on the nanoscale over macroscopic distances. We have used a filtered vacuum arc plasma deposition technique to form high quality platinum thin films of thickness of the order of several hundred angstroms, on glass substrates, with optical transparency of order 50%, and with sheet resistance of order 10 Ω per square. The films could have application to a number of fields of research and technology.
A 4 g, battery-powered, data logger accelerometer for free-flying birds
Authors: Tucker Vance A.
Published: July 2002

This computer-controlled instrument has a battery life in excess of 16 h and fits on a circuit board that is 11.9 mm wide and 27.8 mm long. A programmable microcontroller digitizes the output of a single-axis accelerometer and stores up to 4096 acceleration values in memory. A personal computer can connect to the instrument and retrieve the data through a parallel port. The instrument can be calibrated on a small centrifuge, and the data have a linear relation to acceleration between 1 and 22 g (expandable to 50 g) with a resolution of 0.3 g.
Increasing the frequency of surface acoustic waves generated by phase velocity scanning of laser interference fringes
Authors: Sato Harumichi , Ogiso Hisato , Yabe Akira , Yamanaka Kazushi
Published: July 2002

To nondestructively detect surface defects that reduce the strength of ceramics and structural materials of micromachines, we previously developed the phase velocity scanning method. By using scanning interference fringes generated by two laser beams whose frequencies are shifted, the method can generate a 110 MHz surface acoustic wave (SAW). However, the frequency of the SAW depends on the frequency of the Bragg cell used, thus making the upper-limit frequency about 110 MHz. In this study, we propose multiple use of Bragg cells in series, and successfully generated a 200 MHz SAW.
Apparatus for measuring thermodynamic properties at low temperatures
Authors: Allen J. E. , Nelson R. N. , Harris B. C.
Published: July 2002

An apparatus has been constructed to provide thermodynamic data for models of planetary atmospheres. Often these data are needed at low temperatures, especially for the outer planets and their satellites, but are not readily available in the literature. The vapor pressure of propane was measured from 85 to 240 K to demonstrate one application of the apparatus for the acquisition of these types of data and to assess the performance of the system. This molecule was chosen because it is available in high purity, it has a well-established vapor-pressure curve, and it exhibits only one phase change over this temperature range. Our results compare favorably with the values available in the literature. The major components of the system include several types of pressure measuring instruments (1000 and 1 Torr capacitance manometers, spinning-rotor gauge), a residual gas analyzer to monitor sample purity in situ, and a helium closed-cycle refrigerator for cooling. The gas-handling manifold was constructed using materials and techniques adapted from the semiconductor production industry to minimize sample impurities which constitute a significant source of error in these types of measurements. Several unique design features were also incorporated in the construction of the sample cell to facilitate proper correction for thermal transpiration—an important factor for pressure measurements at low temperatures—and to ensure that the temperature sensor accurately reflected the sample temperature. The operational temperature and pressure limits are 62–240 K and 3×10−6–103 Torr, respectively. The lowest achievable temperature is governed by the no-load temperature of the first stage of the refrigerator and vertical thermal gradients along the sample cell walls, while the minimum obtainable pressure is set by the base pressure of the manifold and a slight outgassing rate.
Promising blue sensitive photodetectors using thallium bromide crystals
Authors: Hitomi K. , Muroi O. , Shoji T. , Hiratate Y.
Published: July 2002

Blue sensitive photodetectors have been fabricated from thallium bromide (TlBr) crystals for scintillation detection. Lu2SiO5 (LSO)/TlBr detectors consisting of 3 mm×4 mm TlBr photodetectors coupled to 2 mm×2 mm×4 mm long LSO scintillators have demonstrated energy resolutions of 34.5% and 25.5% full width at half maximum for 511 keV and 662 keV γ rays, respectively.
Single-frequency external-cavity tapered diode laser in a double-ended cavity configuration
Authors: Wakita Akinori , Sugiyama Kazuhiko
Published: July 2002

We achieved stable single-frequency oscillation in an external-cavity tapered diode laser. The external cavity was constructed from a diffraction grating and an output mirror, which were placed, respectively, in the narrow-area side and the broad-area side of the tapered-stripe chip, with collimator lenses on both sides. The best position for the output mirror was a focal point of the output beam along the axis parallel to the diode junction plane, while the beam along the axis perpendicular to the junction plane was collimated by the collimator lens. Continuous frequency tuning of 900 MHz and a linewidth below 1 MHz were obtained. A bistability was observed in the output power around the threshold current after the output mirror was installed.
A laser beam analyzer for resonance ionization mass spectrometry studies
Authors: Thattey S. S. , Suri B. M. , Bajaj P. N. , Dev Vas
Published: July 2002

We have developed a laser beam analyzer for quantitative studies in resonance ionization experiments. The laser beam profiles, which can be represented as images or as graphs, were used to compute the overlap of a number of laser beams interacting with an atom beam. In our experimental setup, resonance ionization signal was monitored as a function of overlap of laser beams employing the laser beam analyzer developed. The dependence of resonance ionization signal was explained with the help of an interaction model that includes the effects of geometry of the atom beam.
An imaging spectrometer with a convex crystal for pulsed x rays in plasma experiments
Authors: Yanagidaira Takeshi , Shimoda Katsuji , Ono Yasushi , Hirano Katsumi
Published: July 2002

An imaging spectrometer with a convex rubidium acid phthalate (RbAP) crystal is designed and examined. Using the ray tracing technique based on the kinematical theory of diffraction, resolution power, dispersion, linearity, spatial resolution and dynamic range of the monochromatic image are discussed. Broadening by a rocking curve is also taken into account. Performance of the spectrometer is successfully examined using the so-called hot spots as the soft x-ray source which are generated in the pinched plasma by the plasma focus facility with an additional gas puff.
Optical beam deflection noncontact atomic force microscope optimized with three-dimensional beam adjustment mechanism
Authors: Yokoyama Kousuke , Ochi Taketoshi , Uchihashi Takayuki , Ashino Makoto , Sugawara Yasuhiro , Suehira Nobuhito , Morita Seizo
Published: July 2002

We present a design and performance of an optical beam deflection noncontact atomic force microscope (nc–AFM). The optical deflection detection system can be optimized by the three-dimensional beam position adjustment mechanism (the slider which mounts laser diode module, the spherical rotors with mirror and the cylinder which mounts quadrant photodiode) using inertial stepping motors in an ultrahigh vacuum (UHV). The samples and cantilevers are easily exchanged in UHV. The performance of the instrument is demonstrated with the atomically resolved nc-AFM images for various surfaces such as Si(111)7×7, Cu(111), TiO2(110), and thymine/highly oriented pyrolytic graphite.
Development of a new instrument for performing microwave thermal analysis
Authors: Parkes G. M. B. , Bond G. , Barnes P. A. , Charsley E. L.
Published: July 2002

This article describes the design and operation of a new thermal analysis instrument which uses microwaves to simultaneously heat and detect thermally induced transformations in samples with masses in the range of 50 mg to 0.5 g. The data acquisition and control software developed for the instrument support a range of experimental techniques including constant power, linearly ramped power, linearly ramped temperature, and various modulated methods. Microwave thermal analysis utilizes the fact that physical or chemical alterations in a material, caused by processes such as melting, decomposition, or solid-solid phase changes, cause variations in its dielectric properties. These can be revealed by a variety of means including changes in the sample temperature, the differential temperature, or the shape of the power profile during linear heating experiments. The scope of the instrument is demonstrated with the decomposition of basic copper carbonate. The large temperature increase (∼100 °C) observed on the formation of the strongly coupling oxide indicates the potential sensitivity of using the thermal effects of dielectric changes as a means of detection. Further fine detail can be revealed by the use of derivative plots of either the applied power or the temperature.
DESCARTES: A novel lightweight balloon-borne instrument for measurement of halocarbons
Authors: Danis François , Harris Neil R. P. , Taylor William H. , McIntyre John D. , Simmonds Peter G. , Pyle John A.
Published: July 2002

A new, lightweight balloon-borne instrument (DESCARTES) has been developed to make measurements of long-lived trace gases in the stratosphere. DESCARTES is designed to be simple to operate and to fly on small balloons or to “piggyback” on larger payloads. To collect samples, a measured volume of air is passed through a sample tube containing a Carboxen adsorbent. Atmospheric halocarbons are adsorbed and the sample tube is then isolated under an inert nitrogen atmosphere. A number of sample tubes are filled at different altitudes during the flight. After recovery of the instrument the halocarbons are thermally desorbed and quantified using a gas chromatograph with an electron capture detector. In this article we present the design, test, and operation of the instrument with particular emphasis on CFC-11 (CFCl3), the gas for which operation has been optimized.
Cryostat insert with gas loading capabilities for use in neutron diffraction studies
Authors: Koehler C. F. , Larese J. Z.
Published: July 2002

We describe a versatile insert for use with the “Standard Orange cryostat” commonly found at neutron scattering facilities worldwide. Its design permits condensable gases to be introduced into a low-temperature sample cell through a vacuum-insulated, fill-line capillary. It also allows the top-flange-to-sample-cell distance to be easily adjusted and provides for auxillary heating of the fill-line capillary.
Metastability and persistent photoconductivity in Mg-doped p-type GaN
Authors: Johnson C. , Lin J. Y. , Jiang H. X. , Khan M. Asif , Sun C. J.
Published: July 2002

Electrical properties of Mg-doped p-type GaN grown by metalorganic chemical vapor deposition have been investigated by Hall effect and conductivity measurements. Metastability and persistent photoconductivity effects have been observed in GaN. It was found that at low temperatures, it takes several hours for the free hole concentration to reach its equilibrium value in the dark as well as in the photoexcited state, implying a bistable nature of impurities in p-type GaN. Temperature dependence of these behaviors have been studied, from which the energy barrier for free hole capture by ionized impurities as well as between the metastable and the stable states of neutral impurities have been obtained.
Chemical surface modification on polytetrafluoroethylene films by vacuum ultraviolet excimer lamp irradiation in ammonia gas atmosphere
Authors: Heitz J. , Niino H. , Yabe A.
Published: July 2002

Irradiation of polytetrafluoroethylene films with vacuum UV light in an ammonia gas atmosphere resulted in a hydrophilic surface, where abstraction of fluorine atoms, and introduction of nitrogen, oxygen, and hydrogen atoms occurred. We used Kr2* and Xe2* excimer lamps at wavelength of 146 and 172 nm, respectively. The reaction mechanism for chemical surface modification is discussed on the basis of x-ray photoelectron spectroscopy, secondary ion mass spectroscopy, and attenuated total reflection Fourier transform infrared spectroscopy analyses.
Low-voltage varistors based on zinc antimony spinel Zn7Sb2O12
Authors: Ezhilvalavan S. , Kutty T. R. N.
Published: July 2002

It is possible to prepare low-voltage varistors from the zinc antimony spinel Zn7Sb2O12 with breakdown voltages in the range of 3–20 V and nonlinearity coefficient α=7–15. The varistor property is due to the formation of high ohmic potential barriers at the grain boundary regions on low-ohmic n-type grain interiors of the polycrystalline samples. The method of preparation of the spinel, synthesized by coprecipitation followed by annealing under restricted partial pressures of oxygen, controls the mixed valence states for antimony, namely, Sb3+ and Sb5+. This is critical in attaining high nonlinearity and lower breakdown voltages.
Near-edge x-ray absorption fine structure study of bonding modifications in BN thin films by ion implantation
Authors: Jiménez I. , Jankowski A. , Terminello L. J. , Carlisle J. A. , Sutherland D. G. J. , Doll G. L. , Mantese J. V. , Tong W. M. , Shuh D. K. , Himpsel F. J.
Published: July 2002

Near-edge x-ray absorption fine structure (NEXAFS) has been used to study the defect content and the bonding modifications induced in BN thin films by ion implantation. The initial films were hexagonal-like BN grown on Si(100) by pulsed laser deposition. Subsequent ion implantation with N2+ at 180 keV induces the formation of a significant proportion of sp3 bonding (cubic-like), and the formation of nitrogen void defects in the remaining sp2 BN. These modifications in the bonding of a film lacking long range order can only be distinguished with a local order technique like NEXAFS.
Local barrier heights on quantum wires determined by ballistic electron emission microscopy
Authors: Eder C. , Smoliner J. , Strasser G.
Published: July 2002

In this letter, ballistic electron emission microscopy (BEEM) studies on quantum wire structures are reported. GaAs/AlGaAs heterostructures were laterally patterned with a period of 800 nm by laser holography and wet chemical etching. After evaporation of a 70 Å Au film, wires are directly observed both in sample topography and BEEM current image. The BEEM current is found to be enhanced if the ballistic electrons are injected directly into the wire region. Measurements of local effective barrier heights yield increased values between the wires. In this case, the effective threshold for BEEM current detection is determined by the underlying AlGaAs layer. Thus, the quantum wires are also resolved in a barrier height profile.
Micromachined ultrasonic transducers: 11.4 MHz transmission in air and more
Authors: Ladabaum Igal , Khuri-Yakub B. T. , Spoliansky Dimitri
Published: July 2002

The fabrication and modeling of novel, capacitive, ultrasonic air transducers is reported. Transmission experiments in air at 11.4, 9.2, and 3.1 MHz are shown to correspond with theory. The transducers are made using surface micromachining techniques, which enable the realization of center frequencies ranging from 1.8 to 11.6 MHz. The bandwidth of the transducers ranges from 5% to 20%, depending on processing parameters. Custom circuitry is able to detect 10 MHz capacitance fluctuations as small as 10−18 F, which correspond to displacements on the order of 10−3 Å, in a bandwidth of 2 MHz with a signal to noise ratio of 20 dB. Such detection sensitivity is shown to yield air transducer systems capable of withstanding over 100 dB of signal attenuation, a figure of merit that has significant implications for ultrasonic imaging, nondestructive evaluation, gas flow and composition measurements, and range sensing.
Noninvasive measurement of charging in plasmas using microelectromechanical charge sensing devices
Authors: Pangal Kiran , Firebaugh Samara L. , Sturm James C.
Published: July 2002

The plasma induced charging of surfaces in a plasma during semiconductor processing has been measured noninvasively using microelectromechanical devices. We have designed, modeled, and fabricated microcantilevers to act as charge sensing probes. The devices exhibit a mechanical deformation when charged, which is probed in situ by optical techniques, or measured by optical inspection after removal from plasma. Charging voltage measurements in a parallel-plate reactive-ion-etching reactor show that more charging is evident at the electrode edge, and that the charging is a strong function of input rf power, chamber pressure, and flow rate of gases.
Effects of thermally grown native oxides on the luminescence properties of compound semiconductors
Authors: Islam M. R. , Dupuis R. D. , Curtis A. P. , Stillman G. E.
Published: July 2002

Data are presented on the luminescence characteristics of GaAs layers adjacent to native-oxide regions derived from epitaxial AlGaAs and InAlP films. The native-oxide ‘‘window’’ layers capping the epitaxial structures are formed by the oxidation of the exposed Al0.9Ga0.1As and In0.48Al0.52P cladding layers. Extensive photoluminescence and time-resolved photoluminescence studies performed at 300 K show that both the luminescence intensity and lifetime from GaAs ‘‘active regions’’ drop dramatically when the adjacent AlGaAs window layer is oxidized completely. However, there is a marked increase in the efficiency and decay time of the luminescence with the oxidation of InAlP window layers which are grown immediately above the GaAs layer.
Crystalline phases at the p- to n-type transition in Cu-ternary semiconducting films
Authors: Morell G. , Katiyar R. S. , Weisz S. Z. , Walter T. , Schock H. W. , Balberg I.
Published: July 2002

We report here a study of the Raman spectra of ternary Cu–In–S and Cu–In–Se polycrystalline film compounds as a function of the x=[In]/{Cu]+[In]} ratio. Using these spectra we were able to identify, with high resolution in x, the phases present in the films. We found that the single phase of chalcopyrite CnInSe2 exists over the fairly wide composition range of 0.48⩽x⩽0.55, and that the lattice disorder increases with the increase of In content. No such single phase range was found for the Cu–In–S films. Considering the electrical properties of these materials around x=0.5, it is concluded that the native defect model accounts for the electrical properties of the Cu–In–Se films but does not account simply for the electrical properties of the Cu–In–S films.
Phase transformations during microcutting tests on silicon
Authors: Tanikella B. V. , Somasekhar A. H. , Sowers A. T. , Nemanich R. J. , Scattergood R. O.
Published: July 2002

Controlled slow-speed microcutting tests were made on single crystal silicon. Micro-Raman spectroscopy confirmed the presence of amorphous silicon within the microcutting grooves as well as in the debris particles removed from the grooves. These results indicate that pressure-induced transformation to metallic silicon can occur during microcutting and the ductile metallic phase will facilitate the cutting process. Raman spectroscopy further indicated the presence of large residual tensile strains in some areas of the microcutting grooves.
The effect of annealing on the structure and dielectric properties of BaxSr1−xTiO3 ferroelectric thin films
Authors: Knauss L. A. , Pond J. M. , Horwitz J. S. , Chrisey D. B. , Mueller C. H. , Treece Randolph
Published: July 2002

The effect of a postdeposition anneal on the structure and dielectric properties of epitaxial BaxSr1−xTiO3 (BST) thin films (x=0.35–0.65) have been measured. The films were grown by pulsed laser deposition on LaAlO3 (001) substrates. The films were single phase and (001) oriented with a lattice parameter larger than the bulk. The dielectric properties of the x=0.35 film exhibited a broad temperature dependence and a peak at 168 K, which is 36 K below the peak observed in bulk BST (x=0.35). Annealing films for 8 h in flowing oxygen at 900 °C caused the lattice parameter to decrease and dielectric properties to become more like the bulk. Annealing also resulted in an increased electric field dependent dielectric tuning without increased dielectric loss.
Controlling polarization of vertical-cavity surface-emitting lasers using amorphous silicon subwavelength transmission gratings
Authors: Schablitsky Steven J. , Zhuang Lei , Shi Rick C. , Chou Stephen Y.
Published: July 2002

Control of the polarization of vertical-cavity surface-emitting lasers (VCSELs) using a 240-nm-thick amorphous silicon subwavelength transmission grating (SWTG) is demonstrated. The grating, which has a strong polarization dependent reflectance and transmittance, was placed in front of the output window of a VCSEL. It was found that the SWTG can fix the VCSEL’s polarization in the direction perpendicular to the grating fingers, switch polarization directions, enhance the polarization ratio from 20:1 to over 200:1, and decrease the threshold current. Integration of these gratings into the VCSEL structure is discussed.
Nonaxial sites for Er in LiNbO3
Authors: Rebouta L. , da Silva M. F. , Soares J. C. , Serrano D. , Diéguez E. , Agulló-López F. , Tornero J.
Published: July 2002

Off-axis sites for Er have been identified and investigated in congruent LiNbO3 by ion-beam/channeling techniques. They do not constitute a different crystalline phase and appear to be associated to clusters or amorphous precipitates. The axial Er ions lie at the Li octahedron but shifted about 0.2 Å from the regular lattice site. Their concentration increases with total Er doping up to saturation level of about 2%.
Optical gain in optically pumped cubic GaN at room temperature
Authors: Klann R. , Brandt O. , Yang H. , Grahn H. T. , Ploog K. H.
Published: July 2002

We investigate the transient surface emission and the optical gain of cubic GaN on GaAs(001) upon pulsed optical pumping at room temperature. The initial decay time of the transient surface emission drastically decreases with increasing excitation density, reaching a value as short as 20 ps at a fluence of 50 μJ cm−2. This rapid decay suggests the presence of laterally amplified spontaneous emission. In fact, gain-stripe measurements of the edge emission reveal an optical gain exceeding 100 cm−1 at a fluence of 20 μJ cm−2.
4 W quasi-continuous-wave output power from 2 μm AlGaAsSb/InGaAsSb single-quantum-well broadened waveguide laser diodes
Authors: Garbuzov D. Z. , Martinelli R. U. , Lee H. , Menna R. J. , York P. K. , DiMarco L. A. , Harvey M. G. , Matarese R. J. , Narayan S. Y. , Connolly J. C.
Published: July 2002

AlGaAsSb/InGaAsSb single-quantum-well (SQW) laser diodes emitting at 2 μm were fabricated and tested. At 10–15 °C, the uncoated SQW lasers with 2–3 mm cavity lengths exhibit a threshold current density of 115 A/cm2, a continuous-wave output power of 1.9 W, a differential efficiency of 53%, and a quasi-continuous-wave output power of 4 W. Their performance deteriorates rapidly as output losses increase beyond 10 cm−1.
Bandstructure effect on high-field transport in GaN and GaAlN
Authors: Krishnamurthy Srinivasan , van Schilfgaarde Mark , Sher A. , Chen A.-B.
Published: July 2002

The velocity-field characteristics in zinc-blende GaN are calculated from the Boltzmann equation, using realistic energy bands taken from ab initio theory. The drift velocity and the high-field negative differential resistance are shown to be largely determined by the inflection point in the bands centered around the Γ valley, instead of the usual intervalley scattering. We analyze the relative importance of these competing mechanisms for GaN and Al0.5Ga0.5N. The importance of this anomaly to device properties is also discussed.
Chemical erosion of amorphous hydrogenated boron films
Authors: Annen A. , Jacob W.
Published: July 2002

Amorphous-hydrogenated boron (a-B:H) and carbon (a-C:H) thin films were prepared by radio-frequency plasma deposition using (B2H6+H2) or CH4 as a precursor gas. The film composition and density were investigated by ion-beam analysis. The films were eroded by hydrogen electron cyclotron resonance plasmas at floating potential and by atomic hydrogen dissociated by a hot filament. The temperature of the substrates was increased during the erosion process from 330 to 680 K. Erosion rates were measured in situ by ellipsometry. a-B:H films are shown to be much more resistant to erosion by hydrogen ions (H+) and atomic hydrogen (H0) than a-C:H films. In contrast to a-C:H films, no chemical erosion of a-B:H films by H0 was observed at temperatures below 600 K. Ion energies lower than the threshold energy for physical sputtering cause measurable erosion rates for a-B:H films. It is concluded that this is a synergistic effect of simultaneous H0 and H+ bombardment and it is designated as ion-induced chemical erosion.
Stable 1 volt programmable voltage standard
Authors: Benz S. P. , Hamilton C. A. , Burroughs C. J. , Harvey T. E. , Christian L. A.
Published: July 2002

Several fully functional programmable voltage standard chips, each having a total of 32 768 Nb–PdAu–Nb Josephson junctions, have been fabricated and tested. The chips are based on a new design that provides fast programmability (1 μs) between voltages and stable voltage operation from −1 to +1 V. A comparison of the new standard with a conventional Josephson voltage standard is in agreement to 0.5±1.1 parts in 109. We demonstrate the utility of this standard by measuring the linearity of a digital voltmeter.
Imaging and identification of atomic planes of cleaved Bi2Sr2CaCu2O8+δ by high resolution scanning tunneling microscopy
Authors: Pan S. H. , Hudson E. W. , Ma J. , Davis J. C.
Published: July 2002

Imaging of the surface of a cleaved Bi2Sr2CaCu2O8+δ (BSCCO) single crystal with a scanning tunneling microscope reveals a series of repeating terraces, whose separations are then used to identify the atomic planes which are exposed. On each of the exposed planes, the incommensurate modulation is also clearly resolved with atomic resolution. The measured separations between the terraces lead to the deduction that any atomic layer can be exposed by mechanical cleavage of BSCCO. We, therefore, suggest that the identity of atomic planes, and the direction of tunneling, should always be taken into consideration when interpreting tunneling spectra obtained on such cleaved BSCCO crystals.
Uniaxial magnetic anisotropy of submicron MnAs ferromagnets in GaAs semiconductors
Authors: Ando K. , Chiba A. , Tanoue H.
Published: July 2002

Submicron (100–500 nm) room-temperature ferromagnets of MnAs have been successfully incorporated into GaAs semiconductor substrates by Mn+ ion implantation and subsequent heat treatment at 920 °C for 1 s in a nitrogen gas. Atomic force microscopy indicates an epitaxial relation of [0001] oriented hexagonal MnAs crystallites on (001) GaAs substrates: [11 2̄0]MnAs∥[110]GaAs. A stronger shape anisotropy along [110]GaAs is observed for the smaller crystallites. Magnetic characterizations by superconducting quantum interference device reveal uniaxial in-plane magnetic anisotropy of the sample. Magnetic force microscopy imaging shows that the uniaxial magnetic anisotropy comes from the alignment of magnetic dipoles along the magnetic easy [11 2̄0] axis of MnAs, which is parallel to [110]GaAs.
Design of one-dimensional band-limited uniform diffusers of light
Authors: Leskova T. A. , Maradudin A. A. , Novikov I. V. , Shchegrov A. V. , Méndez E. R.
Published: July 2002

We present two methods for generating numerically a one-dimensional random surface, defined by the equation x3=ζ(x1), that has a prescribed probability density function of slopes. This problem arises in the design of a diffuser that scatters light uniformly within a range of scattering angles and produces no scattering outside this range. Numerical calculations of the scattering of light from random surfaces generated by these approaches show that the scattered intensity, indeed, has a rectangular distribution as a function of the scattering angle.
Josephson junctions defined by a nanoplough
Authors: Irmer B. , Blick R. H. , Simmel F. , Gödel W. , Lorenz H. , Kotthaus J. P.
Published: July 2002

We define superconducting constrictions by ploughing a deposited Aluminum film with a scanning probe microscope. The microscope tip is modified by electron-beam deposition to form a nanoplough of diamond-like hardness which allows the definition of highly transparent Josephson junctions. Additionally, a dc superconducting quantum interference device is fabricated in order to verify the junction’s behavior. The devices are easily integrated in mesoscopic devices as local radiation sources and can be used as tunable on-chip millimeter-wave sources.
Coherent, broadband midinfrared terahertz beam sensors
Authors: Han P. Y. , Zhang X.-C.
Published: July 2002

With proper selection of the electro-optic terahertz (THz) wave emitter and sensor crystals, we demonstrate the coherent measurement of free-space broadband radiation spanning 100 GHz to over 30 THz. This effort supports the feasibility of midinfrared time-domain spectroscopy.
Cubic C3N4 particles prepared in an induction thermal plasma
Authors: Peng Yingguo , Ishigaki Takamasa , Horiuchi Shigeo
Published: July 2002

Carbon nitride particles of nm size were prepared in an induction thermal plasma treatment of carbon powder including a small amount of nitrogen. Relatively large ones of about 5 nm in diameter are mostly in a dodecahedral shape. The structure was analyzed by high-resolution transmission electron microscopy and electron energy-loss spectroscopy to be a cubic C3N4, which had been predicted by a first-principles calculation as a substance with the highest bulk modulus. The lattice parameter is, however, rather large (a=0.582 nm) as compared to the prediction. N-deficient planar defects are included in some of the particles.
Silicon nanowhiskers grown on a hydrogen-terminated silicon {111} surface
Authors: Ozaki N. , Ohno Y. , Takeda S.
Published: July 2002

Using a hydrogen-terminated Si {111} surface as a substrate, we have grown Si nanowhiskers along the 〈112〉 direction by the vapor–liquid–solid mechanism. The minimum silicon core diameter was 3 nm and the maximum length was about 2 μm. The minimum silicon core diameter is close to the critical value for visible light emission due to the quantum confinement effect. In contrast to an oxidized Si surface, the hydrogen-terminated surface facilitates the formation of small molten Au–Si catalysts at a lower temperature (500 °C) which is slightly above the eutectic temperature. The formation of catalysts and the subsequent growth at the low temperature yield thin Si nanowhiskers on a Si substrate.
Surface conditioning of chemical vapor deposited hexagonal boron nitride film for negative electron affinity
Authors: Loh Kian Ping , Sakaguchi Isao , Gamo Mikka Nishitani , Tagawa Shigeru , Sugino Takashi , Ando Toshihiro
Published: July 2002

The surface conditions favoring a negative electron affinity (NEA) on hexagonal boron nitride (h-BN) grown by radio-frequency plasma-assisted chemical vapor deposition (CVD) have been investigated by ultraviolet photoelectron spectroscopy. The NEA condition on the h-BN film appears to be resistant to oxygen-plasma or in-vacuo atomic oxygen treatment. It is not certain whether the segregation of bulk hydrogen onto the surface helps to promote the NEA; the depth profile of the deposited film reveals about 0.01%–0.1% atomic concentration of hydrogen. High temperature annealing at 1100 °C results in a positive electron affinity surface (PEA). Reexposure of PEA surface to atomic hydrogen at room temperature regenerates the NEA condition. This is evident of the role of superficial hydrogen in promoting NEA on the h-BN film.
Defect generation and diffusion mechanisms in Al and Al–Cu
Authors: Liu C.-L. , Liu X.-Y. , Borucki L. J.
Published: July 2002

A defect generation mechanism, namely, the grain-boundary Frenkel pair model, and corresponding diffusion mechanisms during electromigration are developed using atomic simulation techniques in Al and Al–Cu. We contend that large numbers of interstitials and vacancies exist at grain boundaries and both contribute to mass transport. Cu preferentially segregates to the interstitial sites at grain boundaries via a Frenkel pair generation process and reduces the overall grain-boundary diffusivity due to the stronger Al–Cu binding. Predictions from our models are in excellent agreement with available experimental data and observations.
Optical investigations of AlGaN on GaN epitaxial films
Authors: Steude G. , Meyer B. K. , Göldner A. , Hoffmann A. , Bertram F. , Christen J. , Amano H. , Akasaki I.
Published: July 2002

We investigated coherently strained AlxGa1−xN/GaN heterostructures (0<x<0.22) grown by metalorganic vapor phase epitaxy on sapphire with photoluminescence (PL), reflexion and cathodoluminescence experiments. The energetic positions of the free A exciton as a function of the alloy compositions are deduced from temperature dependent PL and from reflexion measurements. We obtain a small bowing parameter and no evidence for a Stokes shift between absorption and emission. Compositional inhomogeneities are present, but the fluctuations are too small to be important for carrier localization. The broadening of the luminescence linewidth in the alloys can be described by statistical disorder of a random alloy.
Electron energy distribution function and plasma potential in a planar inductive argon discharge without electrostatic screen
Authors: Seo Sang-Hun , Hong Jung-In , Chang Hong-Young
Published: July 2002

Studies on electron heating are done during the power coupling change in the discharge mode transition (E–H mode transition) in a planar inductive argon discharge without electrostatic screen (Faraday shield). The electron energy distribution function (EEDF) evolution is measured by the alternating current superposition method with a radio frequency (rf) compensated Langmuir probe. The trend of its integrals, electron density and effective electron temperature, and especially the plasma potential against rf power are presented. It is demonstrated that the plasma potential is governed primarily by the high-energy electron tail in a plasma with bi-Maxwellian EEDF. The interdependence of the EEDF and the plasma potential is discussed. The experimental results show that the plasma potential against rf power reflects a change in the relative contribution of capacitive power coupling to electron heating.
Step-flow growth of SrTiO3 thin films with a dielectric constant exceeding 104
Authors: Lippmaa M. , Nakagawa N. , Kawasaki M. , Ohashi S. , Inaguma Y. , Itoh M. , Koinuma H.
Published: July 2002

The use of SrTiO3 films in cryogenic high-frequency applications has been limited by the low dielectric constant εr of thin films (≈103) when compared to the bulk value of over 104. We show that the extension of the pulsed laser deposition technique to temperatures well above 1000 °C, coupled with in situ reflection high energy electron diffraction monitoring, makes it possible to grow SrTiO3 films in the step-flow mode. Films grown in this mode showed at 4.2 K a maximum εr of 12 700, which could be tuned by 80% by applying a bias voltage of ±1 V.
Growth of SiC nanorods at low temperature
Authors: Lu Qingyi , Hu Junqing , Tang Kaibin , Qian Yitai , Zhou Guien , Liu Xianming , Zhu Jingsheng
Published: July 2002

Cubic-phase SiC (β-SiC) nanorods were synthesized through a one-step reaction under pressure at 400 °C by which the crystalline product can be obtained directly without annealing at high temperature. The reaction was carried out in an autoclave by using SiCl4 and CCl4 as reactants and metal Na as coreductant. The x-ray diffraction pattern indicates the formation of β-SiC and x-ray photoelectron spectra display the stoichiometric relation between Si and C. Transmission electron microscopy images reveal that the product consists of nanorods with diameters from 10 to 40 nm and lengths up to several micrometers.
Residual strain dependence of optical characteristics in GaN layers grown on (0001) sapphire substrates
Authors: Funato Kenji , Hashimoto Shigeki , Yanashima Katsunori , Nakamura Fumihiko , Ikeda Masao
Published: July 2002

GaN layers were grown on (0001) sapphire substrates by metalorganic chemical vapor deposition with various growth conditions. Some samples were grown with pressures higher than atmospheric. The residual strain in the epitaxial layer was estimated by measuring the lattice constants using x-ray diffraction. The optical quality was evaluated in terms of the threshold power density of stimulated emission. The residual strain perpendicular to C face, εzz, ranged from 0.058% to 0.125%. The strain ratio under biaxial stress (Δc/c)/(Δa/a), is estimated to be −0.46 from the relation between the lattice constants a and c. From the photoluminescence spectra with weak excitation, δEA/δεzz for undoped GaN is estimated to be 16.4 eV. The threshold power density decreased from 2.77 to 0.59 MW/cm2 as the strain increased, suggesting that the strain relaxation process is accompanied by a generation of defects which act as nonradiative recombination centers.
Patterning and switching of nanosize ferroelectric memory cells
Authors: Alexe M. , Harnagea C. , Hesse D. , Gösele U.
Published: July 2002

A fundamental limitation on the recent development of nonvolatile ferroelectric memories in 64 Mbit–4 Gbit densities has been the ability to scale ferroelectric capacitor cell sizes below 1 μm2. In the present work, ferroelectric memory cells with lateral sizes down to 100 nm were fabricated by electron-beam direct writing. Switching of single 100 nm cells was achieved and piezoelectric hysteresis loops were recorded using a scanning probe microscope working in piezoresponse mode.
Molecular beam epitaxy growth of ferromagnetic single crystal (001) Ni2MnGa on (001) GaAs
Authors: Dong J. W. , Chen L. C. , Palmstro/m C. J. , James R. D. , McKernan S.
Published: July 2002

The ferromagnetic shape memory alloy Ni2MnGa has been grown on GaAs by molecular beam epitaxy. In situ reflection high energy electron diffraction, ex situ x-ray diffraction, and transmission electron microscopy selective area electron diffraction indicate the single crystal growth of a pseudomorphic tetragonal phase of Ni2MnGa on (001) GaAs. Both vibrating sample magnetometry and superconducting quantum interference device magnetometry measurements show that the Ni2MnGa film is ferromagnetic with in-plane magnetization and has a Curie temperature of ∼320 K.
The effect of hydrogen on the network disorder in hydrogenated amorphous silicon
Authors: Gupta S. , Katiyar R. S. , Morell G. , Weisz S. Z. , Balberg I.
Published: July 2002

Previous Raman scattering studies of the effect of hydrogen on the atomic network disorder in various hydrogenated amorphous silicon (a-Si:H) materials resulted in contradicting conclusions. We resolve these contradictions by showing that the surface and the bulk of a-Si:H films can behave differently due to their different hydrogen contents. In particular, we establish that hydrogen has a relatively moderate effect in improving the short-range order but a profound effect in improving the intermediate-range order of the atomic network.