bluuebunny/crossref_metadata_2025 huggingface dataset:
Necessity of Ga prelayers in GaAs/Ge growth using gas-source molecular beam epitaxy
Authors: Fitzgerald E. A. , Kuo J. M. , Xie Y. H. , Silverman P. J.
Published: July 2002

We have investigated the gas-source molecular beam epitaxy growth of GaAs on a (001) Ge surface, off-cut 6° towards the [110]. Initiation of GaAs on Ge with the typical procedure of using a self-terminating As layer invariably produces poor GaAs surface morphology and generates a plethora of antiphase boundaries, despite the large miscut of the (001) surface. However, initiation of GaAs growth with approximately 1 ML (monolayer) of Ga results in single-domain films with excellent surface morphology. We conclude that the Ga monolayer prevents the Ge surface from forming a high step density surface which is established when Ge is exposed to As2.
Effect of surface composition on the radiation pattern from a photonic-crystal planar-dipole antenna
Authors: Brown E. R. , Parker C. D. , McMahon O. B.
Published: July 2002

Radiation patterns are measured from a planar-dipole antenna mounted on two {111}-oriented surfaces of a face-centered-cubic photonic-crystal substrate. The photonic crystal consists of nonspherical air atoms in a dielectric matrix having a permittivity of 12. The measurements are made at a frequency of 14.5 GHz in the middle of the photonic band gap. We find that the antenna pattern depends strongly on the fraction of the crystal surface occupied by dielectric material. A surface having a low dielectric fraction yields much narrower patterns in polar angle than one having a high fraction. We attribute this difference to the strong excitation of a TE mode by the dipole on the surface having a high dielectric fraction.
High temperature pulsed and continuous-wave operation and thermally stable threshold characteristics of vertical-cavity surface-emitting lasers grown by metalorganic chemical vapor deposition
Authors: Lu Bo , Zhou P. , Cheng Julian , Malloy K. J. , Zolper J. C.
Published: July 2002

A systematic and comparative study of the temperature performance of vertical-cavity surface-emitting lasers (VCSELs) is presented to discuss how thermal effects govern their temperature range for cw operation. These include the temperature-induced detuning of the lasing mode from the gain peak, thermal self-heating, and thermal runaway. The power dissipation of the VCSELs and the resultant rise in junction temperature have been measured as a function of the mode detuning. It is shown that low power dissipation is achieved by aligning the cavity mode to the gain peak and introducing continuously graded heterointerfaces throughout the VCSEL structure. By selecting the optimal mode detuning, VCSELs have achieved excellent operating characteristics over a broad range of temperatures, including thermally stable threshold voltage and current, and a very wide temperature range for both pulsed (100–580 K) and continuous-wave (100–400 K) operations.
Metalorganic chemical vapor deposition technique for growing c-axis oriented ZnO thin films in atmospheric pressure air
Authors: Kumar N. Deepak , Kamalasanan M. N. , Chandra Subhas
Published: July 2002

ZnO thin films have been grown in atmospheric pressure and ambient atmospheric air using zinc 2-ethyl hexanoate as zinc source by metalorganic chemical vapor deposition technique. The films grown on glass above 350 °C showed c-axis orientation as seen from x-ray diffraction studies. The films were highly transparent and free from any visual defects. The growth rate and morphology of the film was found to depend on the substrate temperature. Auger electron spectroscopy shows the presence of carbon as an impurity.
Giant magnetoresistance in La1−xSrxMnOz films near room temperature
Authors: Ju H. L. , Kwon C. , Li Qi , Greene R. L. , Venkatesan T.
Published: July 2002

We report the observation of giant magnetoresistance near room temperature in ferromagnetic films of La1−xSrxMnOz for 0.16≤x≤0.33. For B=5 T, the maximum magnetoresistance ratio [R(0)−R(B)]/R(0) of an annealed film is 60% at 260 K for x=0.2, and 35% at 330 K for x=0.33. Annealed films have higher Curie temperature (Tc), a larger saturation moment and a larger magnetoresistance effect near Tc than do as-grown films. The temperature dependence of resistivity for all the samples investigated is unusual, activated above Tc and metallic below Tc. This and the giant magnetoresistance are possibly explained by scattering from magnetic polarons which dominate the transport near Tc.
Preparation of ultrathin microcrystalline silicon layers by atomic hydrogen etching of amorphous silicon and end-point detection by real time spectroellipsometry
Authors: Nguyen H. V. , An Ilsin , Collins R. W. , Lu Yiwei , Wakagi M. , Wronski C. R.
Published: July 2002

The etching of hydrogenated amorphous silicon (a-Si:H) in thermally generated atomic hydrogen has been investigated in detail, utilizing real time spectroellipsometry for characterization and end-point detection. When properly controlled, etching can yield ultrathin microcrystalline Si (μc-Si:H) films of relatively high density on virtually any substrate material. These films are unique in that their microstructure is established by the crystallization of the near-surface a-Si:H, rather than by the nucleation of crystallites on the substrate, as occurs for plasma-enhanced chemical vapor-deposited μc-Si:H films.
Two-dimensional, remote micropositioner for a scanning tunneling microscope
Authors: Mamin H. Jonathon , Abraham David W. , Ganz Eric , Clarke John
Published: July 2002

A simple walker is described that is suitable as the coarse positioner in a scanning tunneling microscope. The walker is fabricated from a single piece of piezoelectric ceramic and has feet coated with thin metal and insulating films. The walker can move in either of two orthogonal, horizontal directions on an insulated, metallized quartz substrate in steps that can be varied from 25 to 400 nm.
Metal vapor vacuum arc ion source
Authors: Brown I. G. , Galvin J. E. , Gavin B. F. , MacGill R. A.
Published: July 2002

A high-current ion source is described in which a metal vapor vacuum arc is used to create the plasma from which the ion beam is extracted. An ion beam current of up to about 1 A has been measured at an extraction voltage of 25 kV for a range of metallic species spanning the periodic table from lithium to uranium. Multiply ionized charge states are seen up to as high as Q=6+ in the case of uranium. In the metal vapor vacuum arc, regions of intense current concentration are formed at the cathode, and it is at these regions, the cathode spots, that the cathode material is vaporized and ionized to form a dense, quasi-neutral plasma which plumes away from the cathode surface. The plasma plume is caused to impinge upon a set of extractor grids, and the ion beam is extracted from the streaming metal plasma. A preliminary survey of the performance of the source has been made. We describe here the principle of operation of the source, the source design, and the results of those measurements that we have made to date.
Fano interference of the Raman phonon in heavily boron-doped diamond films grown by chemical vapor deposition
Authors: Ager Joel W. , Walukiewicz W. , McCluskey Matthew , Plano Mary Anne , Landstrass Maurice I.
Published: July 2002

A series of boron-doped polycrystalline diamond films grown by direct current and microwave plasma deposition was studied with Raman and infrared (IR) absorption spectroscopy. A Fano line shape is observed in the Raman spectra for films with a boron concentration in a narrow range near 1021 cm−3. The appearance of the Fano line shape is correlated with the disappearance of discrete electronic transitions of the boron acceptor observed in the IR spectrum and the shift of the broadened peak to lower energy. The Fano interaction is attributed to a quantum mechanical interference between the Raman phonon (0.165 eV) and transitions from the broadened impurity band to continuum states composed of excited acceptor and valence band states.
Image reconstructions of ECE and x-ray signals for high β plasmas on TFTR
Authors: Nagayama Y. , Büchse R. , Cavallo A. , Fredrickson E. D. , Janos A. , McGuire K. M. , Petravic G. Kuo , Sule C. , Taylor G.
Published: July 2002

Reconstruction techniques have been developed to obtain 2-D images of high β plasmas by taking advantage of the large toroidal rotation rate on TFTR. The Shafranov shift, which is large in high β plasmas, is taken into account in the reconstructions. A 2-D image of the electron temperature is reconstructed from the electron cyclotron emission with the assumption of rigid poloidal rotation. The soft x-ray tomography is performed using the Fourier–Bessel expansion technique from two x-ray cameras. The reconstruction techniques are tested numerically through the use of model islands. The image is reproduced from the source function with these techniques; however, the x-ray tomography without rotation using the two cameras gives unacceptable results.
Improvement of photodetection quantum efficiency by noiseless optical preamplification
Authors: Bencheikh K. , Lopez O. , Abram I. , Levenson J. A.
Published: July 2002

We demonstrate experimentally that a phase-sensitive optical parametric amplifier used to amplify the incoming optical signal on a lossy photodiode improves the noise figure of detection. At high parametric gains this noise figure tends to 0 dB corresponding to a detection quantum efficiency approaching 100%. This result contrasts with the performance of preamplification by a classical laserlike amplifier in which the noise figure tends to 3 dB giving a saturation of the detection quantum efficiency at 50%.
Proposal for a novel method of precisely determining the atomic mass unit by the accumulation of ions
Authors: Gläser Michael
Published: July 2002

An experiment for direct measurement of the atomic mass unit is proposed. A mononuclidic ion flux is collected and accumulated to an amount that can be weighed with high accuracy. Simultaneously, the ion current is measured and integrated. By means of voltage and resistance references based on the Josephson and the quantum Hall effect, the mass is then related to atomic mass by frequency counting over a certain time interval. This experiment may enable a new, physical definition of the kilogram.
Multiframe x-ray imaging system for temporally and spatially resolved measurements of imploding inertial confinement fusion targets
Authors: Katayama M. , Nakai M. , Yamanaka T. , Izawa Y. , Nakai S.
Published: July 2002

A compact and simple multiframe x-ray imaging system was developed in order to monitor the implosion of spherical targets in inertial confinement fusion research. Time intervals between consecutive frames can be adjusted flexibly, and the maximum number of adjacent frames is 20 for an overall duration of 1.4 ns. Each frame is recorded with a temporal resolution of 83±20 ps, a spatial resolution of 10 lp/mm at a modulation transfer function of 20%, and an intensity dynamic range of 103. A proximity focused image intensifier with two microchannel plates allows to obtain a gain of 105. Measured temporal response and gain characteristics could be reproduced by a simple Monte Carlo calculation.
A new method to do time-resolved, x-ray diffraction studies: The rotating crystal Laue method
Authors: Knapp G. S. , Beno M. A.
Published: July 2002

In order to achieve the ultimate time resolution of a synchrotron source we propose a new experimental technique by which time-dependent structural changes can be monitored on the time scale of synchrotron pulse widths. Samples will be studied by a rotating crystal Laue diffraction technique where we rapidly spin the sample and observe the diffraction pattern from a broadband of incident x rays. A computer simulation is presented of the diffraction pattern time evolution using the parameters for an APS undulator of a phase change in the YBa2Cu3O7−x superconductor. We will discuss the application of this and closely related techniques at other synchrotron sources including bending magnets and insertion devices at NSLS and CHESS.
Phase-locked detection of fluorescence lifetime
Authors: Zhang Zhiyi , Grattan Kenneth T. V. , Palmer Andrew W.
Published: July 2002

A newly developed category of signal processing scheme for the detection of fluorescence lifetime is discussed, with application to a number of inexpensive, compact, and reliable fluorescence lifetime-based fiber optic sensors. With phase-sensitive detectors being used to achieve a high noise-suppression ability, the schemes discussed here include some of the features of existing phase and modulation techniques for lifetime measurement. However, they differ from them in several aspects, especially in that they operate in a way rather similar to that of a phase-locked loop. Based on such schemes, the measured lifetime is converted to a repetitive signal whose period is directly proportional to it, and thus a high measurement resolution can be achieved. Such schemes can be operated over a wide consecutive measurement range of fluorescence lifetime, and they are particularly useful for temperature sensor applications using long lifetime (≳1 μs) fluorescent media. Illustrations of the applications of these schemes in lifetime-based fiber optic thermometers are presented showing their promising potential for both biomedical and industrial uses.
An improvement in the VIRGO Super Attenuator for interferometric detection of gravitational waves: The use of a magnetic antispring
Authors: Braccini S. , Bradaschia C. , Cobal M. , Del Fabbro R. , Di Virgilio A. , Flaminio R. , Giazotto A. , Kautzky H. , Morganti M. , Passuello D. , Calloni E. , Di Fiore L. , Holloway L. E. , Montelatici V.
Published: July 2002

We present a method of lowering below 2.5 Hz the vertical normal mode frequencies of the Pisa Super Attenuator by using permanent magnets which provide an antispring force. This method allows a more efficient suppression of the seismic noise decreasing the lower limit of the frequency region devoted to gravitational wave detection.
An isothermal scanning calorimeter controlled by linear pressure variations from 0.1 to 400 MPa. Calibration and comparison with the piezothermal technique
Authors: Randzio Stanislaw L. , Grolier Jean-Pierre E. , Quint Jacques R.
Published: July 2002

An isothermal scanning calorimeter controlled by linear pressure variations is described for the pressure range 0.1–400 MPa at temperatures from 303 to 573 K. The rate of pressure variations can be as low as 0.002 MPa/s over the whole pressure range. The functioning of the instrument was tested by measuring the coefficient of thermal expansivity of liquid n-hexane, with calibration performed with gaseous nitrogen and by measuring the coefficient of thermal expansivity of benzene with calibration performed with liquid n-hexane. The results are compared with literature results obtained by the piezothermal technique and with results obtained in the present instrument by the use of a pressure stepwise scanning mode. An example of an investigation of an isothermal solid-to-liquid transition in benzene is also given.
Optical detection of ultrasound using a microchip laser
Authors: Duggal A. R. , Yakymyshyn C. P.
Published: July 2002

A novel ultrasound detector is presented which uses a microchip laser as the sensing element. An incident acoustic field modulates the optical cavity length of a microchip laser operating in continuous wave mode. The single longitudinal mode laser output wavelength is frequency modulated by the acoustic field. An optical slope filter is used to demodulate the FM signal and generate an intensity modulated optical signal which mimics the acoustic field present in the microchip laser. Parameters are derived for designing the microchip laser for maximum sensitivity and frequency bandwidth. An Nd:YAG microchip laser detecting 5 MHz ultrasound is predicted to have a shot noise limited nonresonantly enhanced sensitivity of 10−4 Pa*(mW/Hz)0.5, a linear dynamic range of 109, and a nearly flat frequency response from dc to slightly below the first acoustic resonance peak. Experimental verification of the sensor operation is presented and compares well with theory. The sensor had a monotonically increasing frequency response from 1 to 7 MHz, with a FM sensitivity of 1–2 MHz/kPa. A large sensitivity enhancement was observed at an acoustic resonance of 8 MHz.
Measurement and dynamic simulation of particle trajectories in an electrodynamic balance: Characterization of particle drag force coefficient/mass ratios
Authors: Maloney D. J. , Lawson L. O. , Fasching G. E. , Monazam E. R.
Published: July 2002

Complementary measurement and simulation methods are described that enable rapid characterization of drag force coefficient/mass (Cd/m) ratios of individual particles in the 20 to 200 μm size range. Individual particles are suspended in a charge trap known as an electro-dynamic balance (EDB). A step change is applied to the EDB end cap voltage to stimulate a dynamic response of the particle from an initial steady state. The resulting transient response is measured by means of a high speed, two-dimensional diode array and imaging system which provides an analog output indicating particle position along the EDB center axis at frame rates of 6200 per second. A particle dynamic model (PDM) is developed to simulate trajectories of particles in the EDB. The PDM is a force balance simulation which accounts for field forces, gravitational forces, and drag forces acting on a particle. Simulations are performed using particle Cd/m ratio as a fit parameter to match model outputs with measurements. Data are presented for polystyrene and glass spheres showing that Cd/m ratios can be determined with an uncertainty less than ±5 percent. When applied to characterize spheres, particle densities, diameters, and mass can be accurately determined. The methods described are an integral part of a powerful new system that enables detailed characterization of mass, density, external surface area, and volume of irregular shaped particles in the 20 to 200 μm size range.
Insertion devices for third-generation light sources (invited)
Authors: Kitamura Hideo
Published: July 2002

By the introduction of the concepts of short-period undulators or minipole undulators, we can raise the upper limit of the fundamental photon energy of undulator radiation up to 300 keV region without any unreasonable heat load, so that the utilization of synchrotron radiation without any wiggler may be possible. Furthermore, we can bring down the lower limit of the fundamental without either unreasonable heat load or unnecessary higher harmonics by adopting helical undulators.
Characterization, modeling, and design of an electrostatic chuck with improved wafer temperature uniformity
Authors: Olson Kurt A. , Kotecki David E. , Ricci Anthony J. , Lassig Stephan E. , Husain Anwar
Published: July 2002

The resulting temperature distribution of a silicon wafer held by an electrostatic chuck (ESC) in an electron-cyclotron-resonance chemical vapor deposition (ECR-CVD) reactor is characterized and modeled. The effects of the clamping voltage VESC, pressure between the ESC and wafer PHe, and the surface finish and pattern on the ESC are investigated. Heat transfer coefficients between the wafer and various ESCs are determined experimentally. A model is developed to predict the temperature distribution at the surface of the wafer, and used to explain the experimentally observed temperature variations both within wafer and between different chucks. The model is then used to aid in the design of an ESC which provides improved temperature uniformity at the wafer surface. The results of this study indicate: (a) the thermal resistances across the interface between the wafer and ESC control both the absolute wafer temperature and the wafer temperature uniformity; (b) the surface roughness of the ESC and the size of the ‘‘contact’’ regions are major design factors controlling the absolute temperature of the wafer—the temperature can be adjusted by varying the value of VESC and fine tuned by adjusting the value of PHe; (c) the nonuniform temperature distribution across the wafer surface is dictated by the surface pattern on the ESC, the variation in surface roughness, and the size of the ESC relative to the wafer; (d) wafer temperature variations from chuck to chuck are reduced by controlling the surface finish of the ESC and by ensuring that PHe is a dominant heat transfer mechanism; and (e) maximum uniformity in the temperature of the wafer is obtained when the radius of the ESC is matched as closely as possible to that of the wafer. We have shown that numerical heat transfer models can be used to optimize the geometry of the ESC to provide a uniform distribution of temperature across the surface of the wafer.
Uniaxial stress method for delicate crystals: Application to Shubnikov–de Haas and superconductivity studies in organic conductors
Authors: Campos C. E. , Brooks J. S. , van Bentum P. J. M. , Perenboom J. A. A. J. , Rook J. , Klepper S. J. , Tokumoto M.
Published: July 2002

A method to measure the resistance of fragile single crystals under high uniaxial stress is reported. To compensate for its natural brittleness, the crystal is embedded in epoxy, whose shape is optimized to sustain the stress. This method was used to study the magnetoresistance of (BEDT-TTF)2KHg(SCN)4 at low temperatures and high magnetic fields and the superconducting transition temperature of (BEDT-TTF)2Cu(NCS)2 under uniaxial stress perpendicular to the planes of BEDT-TTF molecules. The results obtained indicate a high degree of homogeneity of the stress in the crystal and comparison with previous hydrostatic pressure measurements reveal the true uniaxial nature of the stress applied.
Thermal-wave resonator cavity
Authors: Shen Jun , Mandelis Andreas
Published: July 2002

A thermal-wave resonant cavity was constructed using a thin aluminum foil wall as the intensity-modulated-laser-beam induced oscillator source opposite a pyroelectric polyvilidene fluoride wall acting as a signal transducer and cavity standing-wave-equivalent generator. It was shown that scanning the frequency of oscillation produces the fundamental and higher overtone resonant extrema albeit with increasingly attenuated amplitude—a characteristic of thermal-wave behavior. Experimentally, scanning the cavity length produced a sharp lock-in in-phase resonance with simple linewidth dependencies on oscillation (chopping) frequency and intracavity gas thermal diffusivity. The thermal diffusivity of air at 294 K was measured with three significant figure accuracy: 0.211±0.004 cm2/s. The novel resonator can be used as a high-resolution thermophysical property sensor of gaseous ambients.
Effects of limited spatial resolution on fluctuation measurements (invited)
Authors: Bravenec R. V. , Wootton A. J.
Published: July 2002

The finite sample volumes of fluctuation diagnostics distort the measurements not only by averaging the gross fluctuation parameters over the sample volumes, but more importantly (except for collective scattering), by attenuating the shorter wavelength components. In this work, the response of various sample volume sizes and orientations to a model fluctuation power spectrum S(k,ω) are examined. The model spectrum is fashioned after observations by far-infrared scattering on TEXT. The sample-volume extent in the direction of propagation of the turbulence is shown to be the most critical—not only does it reduce the measured fluctuation amplitude and increase the correlation length (as does an extent perpendicular to the propagation direction), but it also reduces the measured mean frequency and increases the apparent average phase velocity of the fluctuations. The differing sizes, shapes, and orientations of the sample volumes among fluctuation diagnostics, as well as deliberate variations within a single diagnostic, provide information on the form of the underlying turbulence and can be exploited to refine the model.
Modeling of magnetostrictive sensors
Authors: Kleinke Darrell K. , Uras H. Mehmet
Published: July 2002

A mathematical model of a generic single branch magnetostrictive sensor is presented in this article. The model is based on an equivalent magnetic circuit which accounts for all significant reluctance elements. Predictions of the model are compared to the experimental data obtained from a noncontacting magnetostrictive strain sensor and a force sensor. The model predicts the behavior of both sensors with reasonably good accuracy, despite the differences in their configurations.
Fluorescence microscopy in superfluid helium: Single molecule imaging
Authors: Jasny Jan , Sepiol Jerzy , Irngartinger Thomas , Traber Markus , Renn Alois , Wild Urs P.
Published: July 2002

A fluorescence microscope for the detection of spatially resolved single molecules at low temperature has been developed. The main part consists of a microscope objective which is inserted in superfluid helium. Two versions of the optical system are described. Both setups have a high numerical aperture and thus high collection efficiency. A video camera with an image intensifier is used to detect the fluorescence images. Detection of single molecule fluorescence has been achieved. It was even possible to visualize individual fluorescing molecules on a video monitor in real time. Spectroscopic applications of this parallel detection scheme are discussed.
A technique for quantitative determination of the profile of the residual stress along the depth of p+ silicon films
Authors: Yang E. H. , Yang S. S. , Yoo S. H.
Published: July 2002

A quantitative method to determine the profile of the residual stress along the depth of a highly boron doped silicon film is reported. First, the stress profile relative to the stress at the neutral surface of the film is obtained by measuring deflection of p+ silicon cantilevers with different etch depths. Second, the average of the residual stress is obtained by using a rotating beam structure. The stress profile is determined completely from these two calculations. One example of application by this method illustrates that most of the p+ region is subjected to the tensile stress except for the region near the front surface.
Dual optical monitoring of axisymmetric thin aqueous film drainage
Authors: Chuang Tsung-Kai , Flumerfelt Raymond W.
Published: July 2002

Dual optical devices (a charge coupled device camera and a photometer) were attached to a modified microscope for the observation of axisymmetric thin aqueous film drainage. Light intensities were recorded through both devices. The film thickness distribution around the film area was calculated using a light interference method. An adjustable horizontal platform was used to support the main drainage cell so that the horizontal axisymmetric thin aqueous film drainage was secured. Results showed that dimple film structures could persist at the center of the aqueous film for longer than 150 s during the drainage process, which was long enough to support the theoretical model.
A CdS photoconductivity gas sensor as an analytical tool for detection and analysis of hazardous gases in the environment
Authors: Miremadi Bijan K. , Colbow Konrad , Harima Yutaka
Published: July 2002

A highly sensitive gas sensor for detection and analytical identification of hazardous gases was developed, by depositing partially crystalline powder from an aqueous suspension of CdS powder on an alumina substrate. When the deposited layers were promoted with catalysts from Pt-group metals, they exhibited high sensitivity to different gas molecules upon modulation with light of certain frequency, depending on catalyst and impurity concentration. Dark resistance and photosensitivity of the sensors were monitored against gas concentration, sensor temperature, and frequency of the modulating light. Depending on the gas and its concentration, a change of up to 100% in sensor response was observed. Variation of photosensitivity with dark resistance showed different slopes for different molecules. Variation of the low frequency phase angle with photosensitivity at different concentrations also produced different slopes, depending on the type of molecule. This differentiation likely comes about by different interactions of gas molecules with surface recombination centers, depending on the nature of physisorption and/or chemisorption on the surface. Thus, in addition to detecting the gas, it can be identified from their slopes of variation with light frequency, and the sensor can be used as an analytical tool.
Large area electron beam pumped krypton fluoride laser amplifier
Authors: Sethian J. D. , Obenschain S. P. , Gerber K. A. , Pawley C. J. , Serlin V. , Sullivan C. A. , Webster W. , Deniz A. V. , Lehecka T. , McGeoch M. W. , Altes R. A. , Corcoran P. A. , Smith I. D. , Barr O. C.
Published: July 2002

Nike is a recently completed multi-kilojoule krypton fluoride (KrF) laser that has been built to study the physics of direct drive inertial confinement fusion. This paper describes in detail both the pulsed power and optical performance of the largest amplifier in the Nike laser, the 60 cm amplifier. This is a double pass, double sided, electron beam-pumped system that amplifies the laser beam from an input of 50 J to an output of up to 5 kJ. It has an optical aperture of 60 cm × 60 cm and a gain length of 200 cm. The two electron beams are 60 cm high × 200 cm wide, have a voltage of 640 kV, a current of 540 kA, and a flat top power pulse duration of 250 ns. A 2 kG magnetic field is used to guide the beams and prevent self-pinching. Each electron beam is produced by its own Marx/pulse forming line system. The amplifier has been fully integrated into the Nike system and is used on a daily basis for laser-target experiments.
Potential for temperature sensor applications of highly neodymium-doped crystals and fiber at up to approximately 1000 °C
Authors: Zhang Z. Y. , Grattan K. T. V. , Palmer A. W. , Meggitt B. T.
Published: July 2002

This work reports on the thermographic characteristics and their potential for use, in fiber optic temperature sensors, of a range of neodymium-doped materials. Their comparative value for low-cost, simple sensors is discussed, using both crystalline materials in the bulk form and a specimen of highly doped, multimode neodymium fiber. The effects of annealing of the bulk materials are discussed in light of their suitability for such sensor applications.
A high resolution dual mass gate for ion separation in laser desorption/ionization time of flight mass spectrometry
Authors: Stoermer Carsten W. , Gilb Stefan , Friedrich Jochen , Schooss Detlef , Kappes Manfred M.
Published: July 2002

A dual mass gate is described which allows for high resolution separation of ions under realistic laser desorption/ionization and matrix assisted laser desorption/ionization time of flight mass spectrometry conditions at 10 kV kinetic energy. The device consists of two interleaved comb units sequentially positioned in the ion beam path. This allows significant improvement in resolution relative to one unit by separation of “low pass” and “high pass” functions. Principal limits as given by mechanical dimensions of the device and electrical properties of the switches are also discussed.
Characterization of erbium-doped intrinsic optical fiber sensor probes at high temperatures
Authors: Zhang Z. Y. , Grattan K. T. V. , Palmer A. W. , Meggitt B. T. , Sun T.
Published: July 2002

The use of rare-earth-doped fibers for high temperature measurement has shown considerable promise. In this work, studies of the key characteristics of the performance of Er-doped fiber-based thermometer probes using the fluorescence decay time technique were carried out. Results showed the effects of fluorescence intensity as a function of doped fiber length and temporal and dopant concentration features of the probes. Annealing effects were seen to occur, and a satisfactory stable performance at up to 1100 °C was reported from this material, yielding improvement on results obtained with Nd-based systems.
5–20 keV laser-induced x-ray generation at 1 kHz from a liquid-jet target
Authors: Tompkins R. J. , Mercer I. P. , Fettweis M. , Barnett C. J. , Klug D. R. , Porter Lord G. , Clark I. , Jackson S. , Matousek P. , Parker A. W. , Towrie M.
Published: July 2002

We report ultrashort pulse, 1 kHz repetition rate x-ray generation in the 5–20 keV spectral region, induced by the interaction of laser radiation with copper nitrate solution and ethylene glycol liquid-jet targets. The characteristics of the copper nitrate source are relevant for application to time-resolved x-ray diffraction studies as well as for spectroscopic x-ray absorption studies. The x-ray sources were operated uninterrupted for in excess of 5 h with no detectable buildup of debris on the associated optics. The x-ray flux generated by both sources is estimated to be of the order of 106 photons s−1 sr−1 in the 5–20 keV region. The spectra have been measured with both a PIN photodiode, and with transmission measurements taken using aluminum filters. We find that the plasma emission has a broadband component attributed to bremsstrahlung emission, with the bulk of the x-ray emission emitted from the chamber lying between 5 and 20 keV for both sources. The copper nitrate emission, however, delivers a dominant emission peak at 9 keV, attributed to the characteristic K emission of copper.
A portable, pulsed-molecular-beam, Fourier-transform microwave spectrometer designed for chemical analysis
Authors: Suenram R. D. , Grabow Jens Uwe , Zuban Andrei , Leonov Igor
Published: July 2002

M. D. Harmony, K. A. Beran, D. M. Angst, and K. L. Ratzlaff [Rev. Sci. Instrum. 66, 5196 (1995)] recently published some design specifications for a smaller version of a Fourier transform microwave (FTMW) spectrometer. In that work they used a nozzle arrangement which pulsed the molecular beam perpendicular to the axis of the Fabry–Pérot cavity. They found that even though the size of the vacuum chamber and Fabry–Pérot cavity mirrors had been reduced, the overall sensitivity of the instrument was nearly the same as one with a conventional sized resonator. In an effort to establish FTMW spectroscopy as a viable new technique for analytical chemists, we have constructed a miniaturized version of our laboratory instrument for use as an analytical instrument. The vacuum chamber of the instrument is based on a commercially available, multiport 30 cm (12 in.) sphere. An integral end-flange mirror permits a coaxial nozzle injection of the molecular beam which greatly improves the sensitivity of the instrument. The movable cavity mirror rides on a fast motorized stage which allows tuning to any frequency within the range of the spectrometer in 1–2 s. The entire spectrometer is mounted on a mobile cart, allowing it to be easily transported to other laboratories or remote locations. The per-pulse sensitivity of this smaller instrument is slightly less than the larger laboratory instruments, however the smaller vacuum chamber allows the nozzle to be pulsed much faster without overloading the vacuum pumps. The new miniaturized FTMW spectrometer is only a factor of 2 less sensitive than the larger laboratory instrument. This instrument provides analytical chemists with a new tool that can unambiguously identify trace amounts of large organic compounds in gas streams. The instrument also permits real-time analysis which should be useful for monitoring and optimization of process gas streams. Lower detection limits are typically in the nanomol/mol regime.
Low temperature ultrahigh vacuum cross-sectional scanning tunneling microscope for luminescence measurements
Authors: Khang Yoonho , Park Yeonjoon , Salmeron Miquel , Weber Eicke R.
Published: July 2002

We have constructed a scanning tunneling microscope with simultaneous light collection capabilities in order to investigate the opto-electronic properties of semiconductors. The microscope has in situ sample cleavage mechanism for cross-sectional sample. In order to reach low temperature (4 K), we used a specially designed cryostat. The efficiency of light collection generated in the tip-surface junction was greatly improved by use of a small parabolic mirror with the tip located at its focal point.
A He3 refrigerated scanning tunneling microscope in high magnetic fields and ultrahigh vacuum
Authors: Kugler M. , Renner Ch. , Fischer O/. , Mikheev V. , Batey G.
Published: July 2002

We present a scanning tunneling microscope (STM) designed to operate between 275 mK and room temperature, in magnetic fields up to 14 T and in ultrahigh vacuum (UHV). The system features a compact STM connected to an UHV compatible He3 refrigerator fitting into a bottom loading cryostat with a superconducting magnet. In this configuration, the cryostat is sitting on top of the UHV chamber, resulting in a very short distance between the STM access and the experimental position. It further enables proper thermal anchoring of the entire STM setup, allowing millikelvin temperatures to be reached in true UHV conditions. We achieve a hold time of about 40 h at 275 mK and a turnaround time of 10 h between room and base temperature. We demonstrate atomic resolution and present tunneling spectra obtained at 275 mK on the high-Tc superconductors Bi2Sr2CaCu2O8+δ and YBa2Cu3O7−δ.
Design and characterization of a research electrohydraulic lithotripter patterned after the Dornier HM3
Authors: Cleveland Robin O. , Bailey Michael R. , Fineberg Naomi , Hartenbaum Bruce , Lokhandwalla Murtuza , McAteer James A. , Sturtevant Bradford
Published: July 2002

An electrohydraulic lithotripter has been designed that mimics the behavior of the Dornier HM3 extracorporeal shock wave lithotripter. The key mechanical and electrical properties of a clinical HM3 were measured and a design implemented to replicate these parameters. Three research lithotripters have been constructed on this design and are being used in a multi-institutional, multidisciplinary research program to determine the physical mechanisms of stone fragmentation and tissue damage in shock wave lithotripsy. The acoustic fields of the three research lithotripters and of two clinical Dornier HM3 lithotripters were measured with a PVDF membrane hydrophone. The peak positive pressure, peak negative pressure, pulse duration, and shock rise time of the focal waveforms were compared. Peak positive pressures varied from 25 MPa at a voltage setting of 12 kV to 40 MPa at 24 kV. The magnitude of the peak negative pressure varied from −7 to −12 MPa over the same voltage range. The spatial variations of the peak positive pressure and peak negative pressure were also compared. The focal region, as defined by the full width half maximum of the peak positive pressure, was 60 mm long in the axial direction and 10 mm wide in the lateral direction. The performance of the research lithotripters was found to be consistent at clinical firing rates (up to 3 Hz). The results indicated that pressure fields in the research lithotripters are equivalent to those generated by a clinical HM3 lithotripter.
Measurements of characteristic transients of planar electrostatic probes in cold plasmas
Authors: Booth J. P. , Braithwaite N. St. J. , Goodyear A. , Barroy P.
Published: July 2002

This article describes how to extract accurate information about a plasma from a capacitively coupled planar probe that is biased using pulsed radio-frequency excitation. The conditions necessary to observe correct saturation of the probe current are investigated, particularly the use of correct geometry and biasing for the guard ring. With these precautions the probe is an effective diagnostic for electron tail temperature at energies beyond those probed by conventional cylindrical probes. The dynamic response of the probe is investigated using conventional sweep voltages and shows the onset of displacement current and inertial effects associated with ions and electrons. In addition the effect of insulating films on the probe surface is examined, showing how the probe continues to operate even when it is coated. Characteristic changes caused by the presence of an insulating film give information about its electrical properties and its thickness.
Calibration of the torsional spring constant and the lateral photodiode response of frictional force microscopes
Authors: Feiler Adam , Attard Phil , Larson Ian
Published: July 2002

We present a direct one-step technique to measure the torsional spring constant of cantilevers used for lateral or friction measurements with the atomic force microscope. The method simultaneously calibrates the photodiode response to the angular deflection of the cantilever. It does not rely upon any approximate theory for friction, nor upon any simplified model cantilever geometry or elasticity. The technique is verified by comparison with the calculated spring constant and with an independent measurement of the angle calibration. This nondestructive calibration may be performed with any type of cantilever, and the friction may subsequently be measured with any type of substrate or probe.
Diamond film orientation by ion bombardment during deposition
Authors: Jiang X. , Zhang W. J. , Paul M. , Klages C.-P.
Published: July 2002

The influence of ion bombardment during microwave plasma chemical vapor deposition (CVD) on diamond film orientation has been investigated. Two interesting findings were obtained: (1) The [001] axes of the grown diamond grains are always along the ion flow direction, perpendicular to the substrate and independent of the crystal orientation of the substrates and (2) for the crystallites which are homoepitaxially grown on the (001) diamond faces parallel to the substrate slight misorientations were found. These new findings confirm the role of ion impact in diamond CVD and can help us to understand the basic mechanism responsible for the crystal orientation in heteroepitaxial diamond films prepared using bias-enhanced nucleation.
Preparation of perovskite conductive LaNiO3 films by metalorganic decomposition
Authors: Li Aidong , Ge Chuanzhen , Lü Peng , Ming Naiben
Published: July 2002

Perovskite conductive LaNiO3 films, 250 nm thick, were prepared by metalorganic decomposition. Rutherford backscattering spectrometry was used to determine the film thickness and composition. The x-ray diffraction patterns of LaNiO3 films indicated that the lowest temperature for crystallization is about 530 °C. The measurement of resistivity as a function of annealing temperatures showed that the good metallic conductive LaNiO3 films could be obtained at 550 °C. The films with the lowest resistivity (4.0×10−4 Ω cm) were obtained on quartz by annealing in oxygen at 700 °C.
Visible photoluminescence from Ge nanocrystal embedded into a SiO2 matrix fabricated by atmospheric pressure chemical vapor deposition
Authors: Dutta Achyut Kumar
Published: July 2002

Stable blue photoluminescence (PL) at 580 nm visible to the naked eye has been observed for the samples consisting of Ge nanocrystals (nc-Ge) embedded in a silicon oxide (SiO2) solid matrix, fabricated by atmospheric pressure chemical vapor deposition techniques. Raman spectroscopy measurement strongly suggests the existence of Ge nanocrystal in the SiO2 matrices. The size of nc-Ge is dependent on aftergrowth thermal treatment under nitrogen ambient, and it is found that temperature above 700 °C for 1 h only exhibits the PL peak at the visible wavelength. The samples annealed for longer times at 700 °C do not exhibit any PL peak which is correlated with the change of the nanocrystal size.
A silicon nanocrystals based memory
Authors: Tiwari Sandip , Rana Farhan , Hanafi Hussein , Hartstein Allan , Crabbé Emmanuel F. , Chan Kevin
Published: July 2002

A new memory structure using threshold shifting from charge stored in nanocrystals of silicon (≊5nm in size) is described. The devices utilize direct tunneling and storage of electrons in the nanocrystals. The limited size and capacitance of the nanocrystals limit the numbers of stored electrons. Coulomb blockade effects may be important in these structures but are not necessary for their operation. The threshold shifts of 0.2–0.4 V with read and write times less than 100’s of a nanosecond at operating voltages below 2.5 V have been obtained experimentally. The retention times are measured in days and weeks, and the structures have been operated in an excess of 109 cycles without degradation in performance. This nanomemory exhibits characteristics necessary for high density and low power.
Persistent holographic absorption gratings in AlSb:Se
Authors: McKenna J. M. , Nolte D. D. , Walukiewicz W. , Becla P.
Published: July 2002

Photoquenching of DX-like defects in heavily doped AlSb:Se is used to write persistent volume absorption holograms. Read-out diffraction efficiencies of ∼0.5% were observed in samples 280 μm thick. The optical gratings are metastable, and semipermanent at liquid nitrogen temperatures, and are reversibly erased by heating the crystal above 140 K. The activation energy of regeneration of the stable DX state is obtained by measuring the decay times of the diffracted signal for temperatures between 100 and 116 K. We obtain a regeneration energy of 180 meV. Larger regeneration energies are important for eventual application of this material class to holographic optical memories.
Electrode interface effects on indium–tin–oxide polymer/metal light emitting diodes
Authors: Gautier Emmanuelle , Lorin André , Nunzi Jean-Michel , Schalchli Aude , Benattar Jean-Jacques , Vital Denis
Published: July 2002

A spin-coated doped-polymer light emitting diode is studied. Blue electroluminescence decays within 1 h. X-ray reflectivity analysis of the aged diode shows the formation of an interfacial layer made of the ITO semitransparent electrode indiffused into the polymer. X-ray reflectivity stands as a powerful tool for aging studies of organic semiconducting devices.
Narrow spectral bandwidths with grating waveguide structures
Authors: Sharon A. , Rosenblatt D. , Friesem A. A.
Published: July 2002

Under certain conditions grating/waveguide structures have a resonant behavior with narrow spectral bandwidths. Several such structures were designed, fabricated, and evaluated, demonstrating resonances with narrow spectral bandwidths ranging to as low as 0.035 nm at full width at half maximum. These can be exploited as compact spectral filters having high finesse.
Gettering of Fe to below 1010 cm−3 in MeV self-implanted Czochralski and float zone silicon
Authors: Kononchuk O. , Brown R. A. , Radzimski Z. , Rozgonyi G. A. , Gonzalez F.
Published: July 2002

The effects of Si ion fluence and oxygen concentration on secondary defect formation and gettering of metallic impurities in MeV self-implanted silicon have been studied for Czochralski (Cz) and float zone (FZ) silicon by means of deep level transient spectroscopy, secondary ion mass spectroscopy, transmission electron microscopy, and optical microscopy/chemical etching. We found that the density, depth distribution, and number of extended defects is strongly dependent upon both the Si ion fluence and the oxygen concentration. Effective gettering of iron to below 1010 cm−3 can be achieved in both FZ and Cz wafers at implantation doses of 1015 cm−2.
Enhanced emission from Eu2+ ions in sol-gel derived Al2O3–SiO2 glasses
Authors: Nogami Masayuki , Abe Yoshihiro
Published: July 2002

Eu2+ ions were incorporated in SiO2 and Al2O3–SiO2 glasses using a sol-gel process of Si(OC2H5)4, Al(OC4H9sec)3, and EuCl3 6H2O. Glasses incorporated with the Eu2+ ions showed the emission with peak at ∼22000 cm−1 due to 4f 6 5d→4f 7(8S7/2) transition of the Eu2+ ions. 1Al2O3⋅99SiO2 (mol %) glass had an intense emission, 250 times larger than that of 100SiO2 glass. The covalency of the Eu–O bonds is decreased by the Al3+ ions. We concluded that this weak covalency causes the offset of the excited 4f 6 5d level to be small, resulting in an increase in the probability of the radiative relaxation from the 4f 6 5d to 4f 7(8S7/2) level.