bluuebunny/crossref_metadata_2025 huggingface dataset:
A femtojoule calorimeter using micromechanical sensors
Authors: Barnes J. R. , Stephenson R. J. , Woodburn C. N. , O’Shea S. J. , Welland M. E. , Rayment T. , Gimzewski J. K. , Gerber Ch.
Published: July 2002

We describe a highly sensitive new type of calorimeter based on the deflection of a ‘‘bimetallic’’ micromechanical sensor as a function of temperature. The temperature changes can be due to ambient changes, giving a temperature sensor or, more importantly, due to the heat absorbed by a coating on the sensor, giving a heat sensor. As an example we show the results of using the sensor as a photothermal spectrometer. The small dimensions and low thermal mass of the sensor make it highly sensitive and we demonstrate a sensitivity of roughly 100 pW. By applying a simple model of the system the ultimate sensitivity is expected to be of the order of 10 pW. The thermal response time of the cantilever can also be determined, giving an estimate of the minimum detectable energy of the sensor. This we find to be 150 fJ and again from our model, expect a minimum value of the order of 20 fJ.
An application of induction heating for fast thermal nondestructive evaluation
Authors: Lehtiniemi R. , Hartikainen J.
Published: July 2002

The application of induction heating as a selective heat source in a thermal nondestructive evaluation system is described. The conductive parts of the sample are heated with a scanning induction coil. Defects such as broken fibers or delaminations affect the heat flow in the sample and thus can be detected by monitoring the infrared radiation from the sample surface. In addition to thermal irregularities, the altered electrical characteristics of the flaws also contribute to the signal. Therefore, the detectability of the defects can be enhanced compared to that of defects investigated using the traditional nonselective heating methods. The functionality of the system is demonstrated with carbon fiber reinforced composites.
Micro x-ray diffraction technique for analysis of the local layer structure in the ferroelectric liquid crystal
Authors: Iida A. , Noma T. , Miyata H. , Hirano K.
Published: July 2002

A hard x-ray microprobe has been developed for small-angle x-ray diffraction studies. The x-ray microprobe system consists of a multilayer monochromator in combination with x-ray focusing mirrors (Kirkpatrick–Baez type) and achieves both high spatial resolution (5×5 μm at the sample) and high angular resolution (about 0.6 and 0.2 mrad in horizontal and vertical directions, respectively). The local layer structure of the surface stabilized ferroelectric liquid crystals was determined, for the first time, directly with this arrangement. Advantages of x-ray microbeam topography are also discussed.
A simple method to fabricate lenses for in situ Fourier transform infrared spectroscopy
Authors: Treffman Lia M. , Morrison Philip W.
Published: July 2002

A process has been developed to hand grind and polish infrared KBr lenses with a wide choice of focal lengths. These lenses are designed for coupling the infrared (IR) beam from a Fourier transform infrared spectrometer into a hot filament chemical vapor deposition reactor. These IR lenses are ground using a glass lens as a mold; the mold lens is a commercial glass lens used for spectacles and is available in a wide range of focal lengths. Rough grinding begins with ♯100 sandpaper and followed by a sequence of fine grinding steps under ethanol: ♯400 SiC powder, ♯600 SiC powder, and emery powder. Polishing is done with a CeO slurry in water followed by a chamois cloth moistened with ethanol. As an indication of the surface finish of the lenses, a flat KBr window that is hand ground and polished in the above manner has a transmission of ≳89% at 8000 cm−1 and ≳91% at 500 cm−1; the commercially polished KBr window has a transmittance of 92% throughout this spectral range.
Apparatus for detecting the homogeneity of large area high-T
c superconducting thin films
Authors: Ma L. P. , Li H. C. , Wang R. L. , Li L.
Published: July 2002

A new apparatus using the inductance method has been built to test the homogeneity of large area high-Tc superconducting thin films. The apparatus has an X–Y scanning probe that can be moved at liquid nitrogen temperature to test the different regions of the films. The sample chamber of the apparatus can provide large area with high temperature homogeneity. The maximum sample size that can be measured is 50×50 mm2. A small size of high-Tc superconducting thin film is applied to test the temperature homogeneity of the testing system and the sameness of the gap distance between the surface of the film and probe. A method for testing the apparatus is illustrated, and some experiments for the test of the apparatus have been performed. Experimental results find that the maximum temperature difference is 0.05 K at the surface of the sample mounter, and the drive field remains constant within the error of 5% in the process of X–Y scanning. The apparatus can test the homogeneity of high-Tc superconducting films not only by the superconducting transition temperature Tc, but also by the critical sheet current density Kc.
2π spectrometer: A new apparatus for the investigation of ion surface interaction
Authors: Morosov V A. , Kalinin A. , Szilagyi Z. , Barat M. , Roncin P.
Published: July 2002

A new spectrometer for studying ion surface interaction is described. This apparatus is built around a secondary electron and ion detector with a very large acceptance angle and made of 16 individual microchannel plate detectors located on a half sphere. A simultaneous detection of the scattered projectiles with an additional position sensitive detector allows measurements of the correlation between all these particles using a multicoincidence technique. With this spectrometer, a large variety of measurements are possible such as the energy spectra of the secondary electrons as well as the statistics of the number of ejected electrons, the scattering pattern of the reflected projectiles and their charge-state distribution, the analysis of the sputtered ions. Some examples are given concerning the impact of multiply charged ions on a LiF single crystal. The dependence of the secondary electron multiplicity as a function of the charge state, of the surface channeling condition, and of the scattering angle of the reflected ion, is given as a type of information provided by the analysis of the correlation.
Mechanical design of a plane grating monochromator for the new undulator at Aladdin
Authors: Fisher Mike V. , Kubala Tim , Severson Mary , Reininger Ruben
Published: July 2002

A nearly stigmatic plane grating monochromator under construction for the new undulator beamline at Aladdin will provide a resolving power ≳10000 as it scans from 8 to 240 eV with a single grating. Scanning requires the precise, simultaneous movements of both a plane mirror and a plane grating in close proximity to one another inside a UHV chamber. The mirror, which absorbs up to 16.5 watts, is internally water cooled to minimize thermally induced slope errors. The radiatively cooled grating absorbs less than a watt. Careful examination of the focusing requirements revealed that the monochromator could be scanned either in the conventional mode of rotating-translating the mirror and rotating the grating or in a modified mode of rotating the mirror and rotating-translating the grating. The latter mode was chosen for simplicity of design. The mirror and grating rotate nearly 30 and 40 degrees, respectively, with subarcsec resolution. Both utilize a stepping-motor lead-screw piezoelectric actuator scan drive that is controlled with a feedback loop using a laser interferometer to measure the actual rotation of the optics. The grating mechanism translates nearly 200 mm along a granite surface plate with a positional accuracy and vertical stability of a few micrometers.
Installation and initial operation of the Suss Advanced Lithography Model 4 X-ray Stepper (abstract)
Authors: Wells Gregory M. , Wallace J. P. , Brodsky E. L. , Leonard Q. J. , Reilly M. T. , Anderson P. D. , Lee W. K. , Cerrina F. , Simon Klaus
Published: July 2002

A Suss Advanced Lithography X-ray Stepper designed as a production tool for high throughput in the sub-quarter-micron device range has been installed and is being commissioned at the University of Wisconsin’s Center for X-ray Lithography (CXrL). Illumination for the stepper is provided by a scanning beamline designed and constructed at CXrL. The beamline optical components are a gold-coated plane mirror, a 1-micron-thick silicon carbide window, and a 25-micron-thick beryllium exit window. Beamline features include synchronized scanning of the mirror and exit window, variable scan velocity to compensate for reflectivity changes as a function of incident angle, and a horizontal oscillation of the beryllium window during vertical scanning to average the effects of nonuniform beryllium window transmission. A helium purged snout transports the x-rays from the beamline exit window, to the exposure plane in the stepper. This snout is retractable to allow for the loading and unloading of masks into the stepper. The motions of the mirror, exit window, and snout are computer controlled by a LABVIEW program that communicates with the stepper control software. The design of the beamline and initial operating experiences with the beamline and stepper will be discussed.
Phase-contrast computed microtomography with 50 keV synchrotron x-rays
Authors: Raven C. , Snigirev A. , Snigireva I. , Spanne P. , Suvorov A.
Published: July 2002

The possibilities to determine the internal structure of low density materials by a simple microtomography setup with high energy synchrotron x-rays are demonstrated experimentally. The coherent properties of a 50 keV x-ray beam at the ESRF wiggler beamline are used to observe phase-contrast images of a boron fiber, which has negligible absorption in this energy range. Images of the boron fiber are recorded with a high-resolution x-ray film at various distances up to 2 m. For microtomography studies, 61 images are taken over an angular range of 180 degrees. In the reconstructed cross sections, the hollow, 15-mm-diameter core of the fiber is clearly visible.
High-resolution multielement solid-state detectors (invited)
Authors: Pullia Alberto , Furenlid L. , Kraner H.W. , Pietraski P.J. , Siddons D.P.
Published: July 2002

Recent advances in multielement solid-state detector systems for high rate, high resolution x-ray spectroscopy at noncryogenic temperatures will be described in this paper. A 16-channel silicon detector system, designed and built at BNL, has been recently operated in the NSLS machine beam ♯X19A, showing an average energy resolution of less than 250 eV FWHM, which is adequate to discriminate the fluorescence trace element against the background of elastically scattered photons in a typical EXAFS application. A larger, 128 channel system, will soon permit a higher overall count rate: ≳106 counts per second. It is shown that, in order to achieve high resolution with a solid-state detector, special care must be spent in the detector-preamplifier assembly. A low noise detectorpreamplifier may be obtained integrating the front-end devices (an FET and/or a feedback capacitor) with the detector itself.
Position sensitive x-ray detector OD-3
Authors: Aulchenko V.M. , Velikzhanin Yu.S. , Titov V.M. , Ponomarev S.A. , Usov Yu.V. , Dubrovin M.S. , Tolochko B.P. , Gaponov Yu.A. , Ancharov A.I. , Evdokov O. , Besserguenev A.V.
Published: July 2002

A fast one-coordinate x-ray detector of a new design aimed for angular measurements in diffraction experiments was developed in BINP. The detector is based on a multiwire proportional chamber with x-ray absorption drift volume. It allows acceptance of photons in the energy range from 6 keV to 20 keV with a maximum rate of 10 MHz/detector and coordinate resolution about 0.1 mm (rms) in linear scale. The first OD-3 chamber has a 0.4-mm-thick Be inlet window 200 mm x 10 mm, a photoabsorbtion length of 50 mm, and a parallax-free cathode structure for angles up to ±15 degrees at variable focal length (from 300 mm to 450 mm without any modification and to infinite at cathode plane replacement). The first tests of the detector at synchrotron radiation beamline 5-b VEPP-3 and with a x-ray tube show a good performance. The detector construction specifics and test results will be discussed in the report.
Advantages of using a mirror as the first optical component for APS undulator beamlines
Authors: Yun W. , Khounsary A. M. , Lai B. , Randall K. J. , McNulty I. , Gluskin E. , Shu D.
Published: July 2002

The advantages of using a mirror as the first optical component for an Advanced Photon Source (APS) undulator beamline for thermal management, radiation shielding mitigation, and harmonic rejection are presented.
A monolithic, integrally cooled CVD SiC mirror substrate for high heat load applications
Authors: Lunt D. L. J. , Lunt A. G.
Published: July 2002

The thermal loading on the optical components of third-generation synchrotron systems is putting severe restrictions on the design and materials of these components to ensure that they maintain their pointing and beam-forming characteristics. Recent advances in the properties and reliability of CVD silicon carbide, coupled with newly developed techniques in optical fabrication, have resulted in a monolithic, integrally cooled SiC mirror substrate model that can be manufactured at a cost that makes it viable. Two examples have been fabricated, and we report on their construction and characteristics, together with an assessment of the potential for extrapolating the design and the process to larger sizes.
IMCA-CAT BM first monochromator crystal optimization (abstract)
Authors: Ivanov Ivan Neschev , Cimpoes Sorinel , Chrzas John
Published: July 2002

The high heat load at the surfaces of the first x-ray optical elements at the APS requires special measures to be taken to more completely utilize the beam. A conceptually new design for such an element, proposed, realized, and tested by M. Hart and conveniently called ‘‘matchbox,’’ is to be implemented at the IMCA-CAT BM beamline as the first monochromator crystal. The requirements of the IMCA-CAT companies for the BM beamline dictate that an optimization of the design is made for a given x-ray energy range E=13 keV ±1 keV. A modification of the original design to improve the vacuum compatibility of the device was made in collaboration with M. Hart. A FEA optimization of the geometry is made using the ALGOR and ABAQUS programs. Determination of the resulting slopes and the useful crystal surface after the best compensation of the thermal distortions are also made. The surface profile obtained by the FEA study was used to perform a ray-tracing analysis of the IMCA-CAT BM beamline. The results of the ray-tracing study will be presented.
Design and analysis of a high heat load pin-post monochromator crystal with an integral water manifold (abstract)
Authors: Schildkamp W. , Tonnessen T.
Published: July 2002

Conventional minichannel water cooling geometry will not perform satisfactorily for x-radiation from a wiggler source at the Advanced Photon Source. For closed-gap wiggler operation, cryogenic silicon appears to be the only option for crystals in Bragg-Bragg geometry. For operation of the wiggler at more modest critical energies (<17 keV), the first crystal can be cooled by a pin-post cooling scheme, using water at room temperature as a coolant. In order to limit the water consumption to 4 gpm and hence the risk of introducing vibrations to the crystal, the intensely cooled area of the crystal was matched to the footprint of the beam, leaving a less cooled area of the crystal subject to survival in a missteered beam but not to perform as a monochromator. The manifold design avoids large areas of high water pressure that would bow the crystal. We present here the design of a pin-post monochromator consisting of a four-layer silicon manifold system and an integrally bonded 39% nickel-iron alloy base plate. A transparent prototype of the design will be exhibited. Fabrication techniques and design advantages will be discussed.
Measurement of thermal diffusivity parallel to the surface of platelike specimen by the laser pulse heating method
Authors: Yamane Tsuneyuki , Katayama Shin-ichiro , Todoki Minoru
Published: July 2002

A new method has been developed to measure the thermal diffusivity parallel to the surface of a platelike specimen using laser pulse heating. A pulsed laser beam which has a circular cross section is irradiated onto the front surface of the specimen. The time dependence of the temperature response of a circular area on the back surface at a certain distance from the irradiated area is determined using a radiation detector for which the spatial distribution of sensitivity is experimentally determined. The geometry of the apparatus is determined using standard specimens the thermal diffusivity of which is known. For isotropic samples, the values parallel to the surface obtained by the present method agree within 10% with those perpendicular to the surface obtained by the conventional pulse heating method.
Incorporation of nitrogen in chemical vapor deposition diamond
Authors: Samlenski R. , Haug C. , Brenn R. , Wild C. , Locher R. , Koidl P.
Published: July 2002

To study the incorporation of nitrogen, diamond films were prepared by chemical vapor deposition homoepitaxially on {100} and {111} oriented diamond substrates. 50 ppm of isotopic 15N2 was added to the process gas. Nuclear reaction analysis was applied to determine quantitatively the concentration of incorporated 15N. The analysis is based on the detection of the 4.44 MeV γ-radiation of the 15N(p,α1γ)12C reaction. By a proper suppression of the γ-background, a sensitivity of better than 0.5 ppm can be achieved. The measurements reveal a preferred incorporation of nitrogen into {111} growth sectors, the 15N concentration in {111} growth sectors is by a factor of 3–4 larger than in the {100} growth sectors. The N/C ratios in the films were found to be in the ppm regime and four orders of magnitude below the N/C ratios in the gas phase.
Thrust stand for pulsed plasma thrusters
Authors: Haag Thomas W.
Published: July 2002

A torsional-type thrust stand has been designed and built to test pulsed plasma thrusters in both single shot and repetitive operating modes. Using this stand, momentum per pulse is determined strictly as a function of thrust stand deflection, spring stiffness, and natural frequency. No empirical corrections are required. The accuracy of the method was verified using a swinging impact pendulum. Momentum transfer data between the thrust stand and the pendulum were consistent to within 1%. Following initial calibrations, the stand was used to test a Lincoln experimental satellite (LES-8/9) thruster. The LES-8/9 system had a mass of approximately 7.5 kg, with a nominal thrust to weight ratio of 8.0×10−6. A total of 34 single shot thruster pulses was individually measured. The average impulse bit per pulse was 266 μN s, which was slightly less than the value of 300 μN s published in previous reports on this device. Repetitive pulse measurements were performed similar to ordinary steady-state thrust measurements. The thruster was operated for 30 min at a repetition rate of 132 pulses/min and yielded an average thrust of 573 μN. Using average thrust, the average impulse bit per pulse was estimated to be 260 μN s, which was in agreement with the single shot data. Zero drift during the repetitive pulse test was found to be approximately 1% of the measured thrust.
Tailoring the heavy-hole and light-hole quantum-confined Stark effect using multistrain-stepped quantum wells
Authors: Silver M. , Greene P. D. , Adams A. R.
Published: July 2002

We show theoretically how the quantum-confined Stark effect (QCSE) shifts of the E1–HH1 and E1–LH1 energy transitions can be engineered to be closely matched over the entire range of applied fields up to ±100 kV/cm using structures containing more than one strained-layer composition within each well. In contrast, conventional quantum wells that contain a single uniform composition within each well can at best have the energy levels for the HH1 and LH1 states matched at only one field value. Furthermore, we show how the TE and TM absorption spectra are modified using multistrain-stepped structures leading to improved polarization-insensitive QCSE modulators.
Study on the temperature sensing capability of a light-emitting diode
Authors: Acharya Y. B. , Vyavahare P. D.
Published: July 2002

A study on the temperature sensing capability of a light-emitting diode (LED) has been made. Dependence of I–V characteristics as a function of temperature is used as a temperature sensing mechanism. It is found that the temperature voltage characteristics of a GaP LED are quite linear from 77 to 533 K. The measured sensitivity of the diode is 5.31 mV/K at 1 pA and is 2.34 mV/K at 0.1 mA. Since the reverse saturation current of LED is less than fempto-ampere range, it is possible to operate the thermometer at low currents, as compared to silicon or germanium diode thermometers, which reduce power dissipation in the device. It has been possible to extend the temperature range to higher value due to large value of band gap for LEDs.
Piezoelectrically actuated droplet ejector
Authors: Perçin Gökhan , Levin Laurent , Khuri-Yakub Butrus T.
Published: July 2002

This article presents a novel piezoelectric fluid ejector that is based on a variation of the design of a flextensional transducer that excites axisymmetric resonant modes in a clamped circular membrane. The transducer is made by bonding a thin piezoelectric ring to a thin, fully supported, circular membrane. The transducer design is optimized for maximum flexure at the lowest order resonant frequency using finite element modeling. The fluid ejector is formed by placing a fluid, at atmospheric pressure, behind one face of the membrane and an orifice in its center. We achieve continuous or drop-on-demand ejection of the fluid by applying the appropriate voltage to the piezoelectric transducer. We present results of ejection of water, ink, powder, and photoresist. The application of photoresist with minimum waste on silicon wafers is one of the motivations for developing this device. In present applications, over 95% of the photoresist is wasted and has to be disposed as a toxic material, thus making this one of the more expensive steps in integrated circuit manufacturing. The ejector is harmless to sensitive fluids and can also be used to eject fuels, chemical and biological samples. The ejector configuration is unique in that it can be implemented using silicon micromachining as a microelectromechanical system, thus allowing the manufacture of true two-dimensional arrays of ejectors.
Contact and distributed effects in quantum well infrared photodetectors
Authors: Ershov M. , Ryzhii V. , Hamaguchi C.
Published: July 2002

We propose a simple distributed model for intersubband quantum well infrared photodetectors (QWIPs), which explicitly takes into account the injecting properties of the contacts. We show that the QWIP operation with multiple QWs involves the formation of a high-field domain near the emitter, caused by the modulation of the bound electron density in the QWs by applied voltage and infrared radiation. The external characteristics of the QWIP (total current, differential resistance, and quasistatic capacitance) are strong functions of the voltage and radiation intensity.
Portable autocollimators using the laser diode and the position sensitive detector
Authors: Sohn Yeung J. , Kwon Jin H. , Choe Ok S. , Eom Tae B.
Published: July 2002

We were able to simplify the structure of the autocollimators and enhance the performance by using one- and two-axis PSDs (position-sensitive detectors) which have spatial resolution of 0.1 and 2.5 μm, respectively, with little dependence on the spot size of incident beam and the visible laser diodes as the light source. Two kinds of portable autocollimators which can measure angles with resolutions 0.01″ and 0.1″, respectively, were made. They were calibrated by the reference angle generator which employed the laser interferometer. The characteristics of temporal stability were evaluated and the profile of a test surface was measured.
Imaging of laser produced plasma at 1.43 keV using Fresnel zone plate and Bragg–Fresnel lens
Authors: Cauchon Gilles , Pichet-Thomasset Muriel , Sauneuf Richard , Dhez Pierre , Idir Mourad , Ollivier Marc , Troussel Philippe , Boutin Jean-Yves , Le Breton Jean-Pierre
Published: July 2002

X-ray imaging of plasmas with a resolution on the order of 1 μm could not be achieved with pinholes because the light flux on the detector would be too low. We tested two different types of diffractive lenses derived from the circular grating based on the Fresnel zones. Compared to pinholes, they can have an equivalent diameter of about 100 μm with a resolution of about 1 μm. The two kinds of devices tested were: (1) a transmission phase Fresnel zone lens (PFZL) associated with a multilayer mirror; (2) a reflective Bragg–Fresnel lens (BFL) which combines a multilayer mirror and the grating. The PFZL works at normal incidence by transmission; an additional mirror is used to reflect only a small bandwidth within the spectrum; the angle of reflection of the multilayer of the imaging beam on the mirror is set as to adjust the center of the useful bandwidth. The BFL works at fixed grazing incidence and we only use an off-axis part of the BFL in order to avoid the illumination of the detector by zeroth order diffracted light. We computed the spatial response of both devices and found that the aberrations were very low within an object field of 100 μm for the BFL device and 1 mm for the PFZL device. Their theoretical resolution is given by the width of their last zone: below 0.1 μm for the BFL device and 0.4 μm for the PFZL device. We also made images of plasma with both devices and using back-lighted grids, we obtained a resolution on the order of 4–5 μm. In the discussion, we try to explain the difference between the theoretical and experimental results.
Progress in multipass tandem Fabry–Perot interferometry: I. A fully automated, easy to use, self-aligning spectrometer with increased stability and flexibility
Authors: Hillebrands Burkard
Published: July 2002

A computer control for a Sandercock-type multipath tandem Fabry–Perot interferometer is described, which offers many advantages over conventionally used analog control: The range of stability is increased due to active control of the laser light intensity and the mirror dither amplitude. The alignment is fully automated enabling start of a measurement within a minute after start of align, including optionally finding the optimum focus on the sample. The software control enables a programmable series of measurements with control of, e.g., the position and rotation of the sample, the angle of light incidence, the sample temperature, or the strength and direction of an applied magnetic field. Built-in fitting routines allow for a precise determination of frequency positions of excitation peaks combined with increased frequency accuracy due to a correction of a residual nonlinearity of the mirror stage drive.
Toroidal crystal spectrometer for time-resolved x-ray absorption diagnostic in dense plasmas
Authors: Pisani Francesca , Koenig Michel , Batani Dimitri , Hall Tom , Desenne Denis , Bruneau Jean , Reverdin Charles
Published: July 2002

A toroidal crystal spectrometer was designed with the purpose of measuring the aluminum K-absorption edge shift, in the wavelength range around 7.9 Å, in strongly compressed matter. The expected shift is about 100 mÅ (∼20 eV). The x rays reflected from the crystal are focused onto a streak camera slit of 16 mm high and 100 μm width, to obtain a time-resolved spectrum. High resolution and dispersion of about 1–16 Å/mm on the detection window are obtained. A crystal with a toroidal surface is used to enhance the focusing power in the spatial dimension as in the spectral one. Numerical simulations are performed by means of one- and two-dimensional codes for the determination of the crystal characteristics like the dimension and the curvature radius with respect to the geometric constraints. Some experimental results are presented concerning the obtained spectra.
Operation of a separated-type x-ray interferometer for phase-contrast x-ray imaging
Authors: Yoneyama Akio , Momose Atsushi , Seya Eiichi , Hirano Keiichi , Takeda Tohoru , Itai Yuji
Published: July 2002

Aiming at large-area phase-contrast x-ray imaging, a separated-type x-ray interferometer system was designed and developed to produce 25×20 mm interference patterns. The skew-symmetric optical system was adopted because of the feasibility of alignment. The rotation between the separated crystal blocks was controlled within a drift of 0.06 nrad using a feedback positioning system. This interferometer generated a 25×15 mm interference pattern with 0.07 nm synchrotron x-rays. A slice of a rabbit’s kidney was observed, and its tubular structure could be revealed in a measured phase map.
Remote query pressure measurement using magnetoelastic sensors
Authors: Grimes C. A. , Stoyanov P. G. , Kouzoudis D. , Ong K. G.
Published: July 2002

Two magnetostriction-based methods for measuring atmospheric pressure are presented. Each technique correlates changes in pressure with the characteristic resonant frequency of a magnetoelastic magnetostrictive thick-film sensor. In each case the sensor is monitored remotely, using an adjacently located pickup coil, without the use of physical connections to the sensor.
High current, low pressure plasma cathode electron gun
Authors: Goebel Dan M. , Watkins Ron M.
Published: July 2002

A plasma-cathode electron gun based on a moderate pressure (>5 mTorr) cold-cathode discharge and a high perveance, multiaperture accelerator was previously developed at Hughes Research Laboratories and produced electron beam currents of up to 1 kA at voltages of over 200 kV for pulse lengths of 100 μs. This gun was limited in pulse repetition frequency and duty by the gas-puff system that provided adequate gas pressure in the hollow cathode to operate the glow discharge while keeping the pressure in the beam transport region sufficiently low. We describe a new plasma cathode electron gun (PCE gun) that eliminates this problem by replacing the glow-discharge plasma generator in the electron gun by a low-pressure thermionic discharge in a magnetic multipole confinement chamber. Proper design of the plasma generator and electrical circuit provides high electron-current densities to the accelerator structure at very low gas pressure (<10−4 Torr). The static gas pressure permits the pulse repetition frequency to be very high (>1.5 kHz demonstrated) with electron beam currents up to 200 A at voltages up to 120 kV demonstrated. The design and performance of the PCE gun, along with several models used to predict and scale the performance, are discussed.
High quality InP on Si by conformal growth
Authors: Parillaud O. , Gil-Lafon E. , Gérard B. , Etienne P. , Pribat D.
Published: July 2002

Conformal growth is a confined epitaxial lateral overgrowth technique previously used to achieve low dislocation density GaAs films on Si. Conformal growth was used here to obtain high quality InP films on silicon, starting from GaAs seeds. Detailed characterization of the InP films (chemical etching of dislocations, photoluminescence at 300 K, cross-section transmission electron microscopy) proved the high defect filtering power of this technique. Dislocations initially present in the GaAs seeds and dislocations generated at the InP/GaAs interface were blocked and did not propagate through the growing films. Dislocations densities below 5×105 cm−2 have been obtained in submicrometer-thick conformal InP films on Si.
Role of threading dislocation structure on the x-ray diffraction peak widths in epitaxial GaN films
Authors: Heying B. , Wu X. H. , Keller S. , Li Y. , Kapolnek D. , Keller B. P. , DenBaars S. P. , Speck J. S.
Published: July 2002

In this letter we demonstrate that the anomalously low (002) x-ray rocking curve widths for epitaxial hexagonal GaN films on (001) sapphire are a result of a specific threading dislocation (TD) geometry. Epitaxial GaN films were grown on c-plane sapphire by atmospheric pressure metalorganic chemical vapor deposition (MOCVD) in a horizontal flow reactor. Films were grown with (002) rocking curves (ω-scans) widths as low as 40 arcsec and threading dislocation densities of ∼2×1010 cm−2. The threading dislocations in this film lie parallel to the [001] direction and within the limit of imaging statistics, all are pure edge with Burgers vectors parallel to the film/substrate interface. These TDs will not distort the (002) planes. However, distortion of asymmetric planes, such as (102), is predicted and confirmed in (102) rocking curve widths of 740 arcsec. These results are compared with films with (002) rocking curves of ∼270 arcsec and threading dislocation densities of ∼7×108 cm−2.
Real time control of plasma deposited multilayers by multiwavelength ellipsometry
Authors: Kildemo M. , Bulkin P. , Deniau S. , Drévillon B.
Published: July 2002

A robust direct method for real time control, by multiwavelength phase modulated ellipsometry (PME), of the growth of plasma deposited structures is presented here. Transparent multilayers consisting of SiO2 and SiNx alloys are investigated. This feedback control method is based on the comparison between the real time PME measurements and precomputed target trajectories. It can provide the high precision required to deposit high performance optical coatings. In particular an overall accuracy better than 1% is obtained on a fifteen layer quarter-wave filter, designed at 670 nm. This real time procedure, which is not limited to transparent materials nor plasma processes, appears to be a useful tool for process control.
c-axis oriented ferroelectric thin films of PbTiO3 on Si by pulsed laser ablation
Authors: Palkar V. R. , Purandare S. C. , Pai S. P. , Chattopadhyay S. , Apte P. R. , Pinto R. , Multani M. S.
Published: July 2002

We have deposited single phase c-axis oriented ferroelectric thin films of PbTiO3 on Si(100) by pulsed laser ablation technique in situ. It has been shown that the formation of a nonferroelectric, Pb2Ti2O6 pyrochlore phase at the interface could be avoided by raising the substrate temperature.
NiMn-pinned spin valves with high pinning field made by ion beam sputtering
Authors: Mao S. , Gangopadhyay S. , Amin N. , Murdock E.
Published: July 2002

Spin valves of film layer structure, Ta/NiMn/NiFe/Co/Cu/Co/NiFe/Ta/Substrate were fabricated by ion beam sputtering. Optimization of the processes of deposition and posthermal treatment yields highly (111) oriented spin valve films with a giant-magnetoresistance ratio of above 4% and pinning field of 650 Oe. This is the strongest pinning field ever observed. It stays constant up to 180 °C, then decreases to zero at a blocking temperature of 380 °C. These spin valves are highly thermally stable and, thus, suitable for the application of high density recording heads.
Variable range hopping conduction in LaC2, CeC2, or GdC2 crystals encapsulated carbon nanocages
Authors: Yosida Yositaka , Oguro Isamu
Published: July 2002

An experimental study of electrical transport phenomena in magnetic fields H up to 15 T in pressed samples of three porous systems composed of carbon nanocages in which LaC2, CeC2, or GdC2 crystals are encapsulated is reported. The exp[(T0/T)1/3] temperature dependence in the zero-field dc electrical resistance R(0) is found at low temperatures. Below 50, 50, and 35 K for the LaC2, CeC2, and GdC2 system, respectively, transverse magnetoresistance (MR), [R(H)–R(0)]/R(0), is negative. In the weak field region (H<0.15 T), the negative MR is quadratic in H, and becomes linear in the field range 0.15–0.5 T. The linear and negative MR shows T−1.04±0.10 temperature dependence. The temperature dependence of R(0) is described in terms of Mott’s law for two-dimensional variable range hopping (2D VRH) conduction. The low field magnetotransport features support a predicted quantum interference effect on 2D VRH conduction.
SiCN alloys deposited by electron cyclotron resonance plasma chemical vapor deposition
Authors: Gómez F. J. , Prieto P. , Elizalde E. , Piqueras J.
Published: July 2002

Silicon–carbon–nitrogen alloys have been deposited by electron cyclotron resonance plasma chemical vapor deposition. Nitrogen, methane, and argon diluted silane have been used as precursor gases. The properties of the deposited films were studied by spectroscopic ellipsometry, Fourier transform infrared spectroscopy, X-ray photoelectron, and Auger electron spectroscopy. The structure and bond formation in the SiCN films is discussed in terms of the present results.
Giant acoustic stop bands in two-dimensional periodic arrays of liquid cylinders
Authors: Kushwaha M. S. , Halevi P.
Published: July 2002

Periodic binary systems can give rise to complete acoustic band gaps (i.e., stop bands) within which sound and vibrations are forbidden. We compute the band structure for two-dimensional (2D) periodic arrays of long water cylinders surrounded by mercury host. Complete acoustic stop bands are found for both square and hexagonal lattices. We emphasize that such a simple 2D inhomogeneous system of liquids exhibits the widest stop bands ever reported for elastic as well as dielectric composites. We find gap/midgap ratios as high as ∼1. For mercury cylinders surrounded by water the gaps obtained are much smaller.
Cathodoluminescence study of GaAs quantum wells and of submicron dots fabricated by magnetron reactive ion etching
Authors: Chao L.-L. , Cargill G. S. , Levy M. , Osgood R. M. , McLane G. F.
Published: July 2002

Cathodoluminescence has been employed to investigate the luminescence and lateral transport properties of excited carriers at 8 K in GaAs-AlGaAs quantum well material and in submicron features fabricated in this material by magnetron reactive ion etching. A carrier diffusion length of 0.85±0.04 μm in quantum wells and a surface recombination velocity (5.4±0.8)×103 m/s at etched sidewalls were measured. Also, the effect of feature size on luminescence efficiency was examined and compared with model calculations using the measured values of diffusion length and surface recombination velocity.
Metglas thin film with as-deposited domain alignment for smart sensor and actuator applications
Authors: Lu Yong , Nathan Arokia
Published: July 2002

We report on the deposition of in-situ domain aligned magnetostrictive Metglas2605S2 (Fe78Si9B13) thin films by dc magnetron sputtering. The as-deposited thin film has a well oriented magnetic domain structure. A saturation magnetostriction of 30×10−6 is observed, which is comparable to the data published on this material.
Attonewton force detection using ultrathin silicon cantilevers
Authors: Stowe T. D. , Yasumura K. , Kenny T. W. , Botkin D. , Wago K. , Rugar D.
Published: July 2002

A measured force resolution of 5.6×10−18 N/Hz at 4.8 K in vacuum using a single-crystal silicon cantilever only 600 Å thick is demonstrated. The spring constant of this cantilever was 6.5×10−6 N/m, or more than 1000 times smaller than that of typical atomic force microscope cantilevers. The cantilever fabrication includes the integration of in-line tips so that the cantilever can be oriented perpendicular to a sample surface. This orientation helps suppress cantilever snap-in so that high force sensitivity can be realized for tip-sample distances less than 100 Å.
Thermal conductivity and heat transfer in superlattices
Authors: Chen G. , Neagu M.
Published: July 2002

Understanding the thermal conductivity and heat transfer processes in superlattice structures is critical for the development of thermoelectric materials and optoelectronic devices based on quantum structures. This letter reports modeling of the heat transfer and thermal conductivity of superlattice structures based on solving the Boltzmann transport equation. Both diffuse and specular phonon scattering processes at interfaces are considered. The modeling results could explain recent experimental data on the cross-plane thermal conductivity of Si/Ge superlattices. Below the critical thickness, thermal conductivity is strongly influenced by diffuse interface scattering of phonons while above the critical thickness, dislocations are the dominant scattering centers in superlattices.
Optical study of GaAs/AlAs pillar microcavities with elliptical cross section
Authors: Gayral B. , Gérard J. M. , Legrand B. , Costard E. , Thierry-Mieg V.
Published: July 2002

GaAs/AlAs pillar microcavities with elliptical cross section have been fabricated by molecular beam epitaxy, electron-beam lithography, and reactive ion etching. We study their lowest energy confined photonic modes by photoluminescence, using a quantum box array placed inside the cavity as an internal broadband light source. Such an anisotropic cross section allows to split the twofold polarization degenerate fundamental mode of circular micropillars into a pair of orthogonal linearly polarized modes. Their energy splitting, which is well accounted for by a simple perturbative model, is studied experimentally and theoretically as a function of the eccentricity and average radius of the pillars. Splittings as large as 15 meV are observed, which is very encouraging for applications ranging from the improvement of the polarization locking in vertical cavity lasers to the fabrication of light emitting diodes with a better control of the spontaneous emission.
Structure and magnetic properties of exchange-spring Sm–Co/Co superlattices
Authors: Fullerton Eric E. , Jiang J. Samuel , Sowers C. H. , Pearson J. E. , Bader S. D.
Published: July 2002

We present structural and magnetic properties of epitaxial Sm–Co/Co superlattice films prepared via magnetron sputtering. X-ray diffraction and cross-sectional transmission electron microscopy show that the films are structurally coherent. The oriented nature of the interleaved ferromagnetically “hard” and “soft” layers comprising the superlattice provides a realization of the ideal nanostructure of exchange-spring magnets as well as a model system to study layer thickness dependences of the magnetic properties. The superlattice films have an effective fourfold, in-plane magnetic anisotropy. Room-temperature hysteresis loops are relatively square and the demagnetization of the Co is reversible, as expected of exchange-spring magnets with aligned hard magnet layers.
Sequential position readout from arrays of micromechanical cantilever sensors
Authors: Lang H. P. , Berger R. , Andreoli C. , Brugger J. , Despont M. , Vettiger P. , Gerber Ch. , Gimzewski J. K. , Ramseyer J. P. , Meyer E. , Güntherodt H.-J.
Published: July 2002

Sequential position readout from a microfabricated array of eight cantilever-type sensors (silicon technology) is demonstrated. In comparison with single sensors we find that mechanical disturbances from noise, such as from vibrations, turbulent gas flow, or abrupt pressure changes, can be effectively removed in array sensors by recording difference signals with respect to reference cantilevers. We demonstrate that chemically specific responses can be extracted in a noisy environment using a sensor to detect specific chemical interactions and an uncoated cantilever as reference.
Magnesium induced changes in the selective growth of GaN by metalorganic vapor phase epitaxy
Authors: Beaumont B. , Haffouz S. , Gibart P.
Published: July 2002

Atmospheric pressure metalorganic vapor phase epitaxy is used to perform selective regrowth of GaN on a silicon nitride patterned mask, capping a GaN epitaxial layer deposited on (0001) sapphire substrate. The basic pattern is constituted by a 15 μm period hexagonal array of hexagonal openings in the mask, these openings being circumscribed into 10 μm diam circles. We investigate the effect of Mg incorporation on the growth anisotropy of the localized GaN islands by varying the ratio [Mg]/[Ga] of bis-methylcyclopentadienyl-magnesium and trimethylgallium partial pressures. Both undoped and Mg-doped GaN hexagonal pyramids, delimited by C (0001) and R (1 1̄01) facets, are achieved with a good selectivity. It is found that the GaN growth rates VR and VC, measured in the R〈11̄01〉 and C 〈0001〉 directions respectively, are drastically affected by the Mg incorporation. By adjusting the Mg partial pressure in the growth chamber, the VR/VC ratio can be increased so that the delimiting top C facet does not vanish as usually observed in undoped GaN localized growth, but by contrast expands.
Optical and electrical properties of aluminum oxide films deposited by spray pyrolysis
Authors: Aguilar-Frutis M. , Garcia M. , Falcony C.
Published: July 2002

The optical and electrical characteristics of spray pyrolysis deposited aluminum oxide films are reported. The films were deposited from a spraying solution of aluminum acetylacetonate in N,N-dimethylformamide using an ultrasonic mist generator on (100) Si substrates. The addition of water mist during the spraying deposition process resulted in an overall improvement of the films characteristics. The substrate temperature during deposition was in the 450–650 °C range. Deposition rates up to 90 Å/s were obtained depending on the spraying solution concentration and substrate temperature with an activation energy of the order of 31 kJ/mol. The optical energy band gap for these films was 5.63 eV and the refractive index at 630 nm up to 1.66 was measured by ellipsometry. The electrical characteristics of the films were determined from the capacitance and current versus voltage measurements of metal–oxide–semiconductor (MOS) structures incorporating them. A dielectric constant of 7.9, interface states density of the order of 1011×1/eV cm2 as well as breakdown fields higher than 5 MV/cm were determined in this way.
Deep centers in n-GaN grown by reactive molecular beam epitaxy
Authors: Fang Z-Q. , Look D. C. , Kim W. , Fan Z. , Botchkarev A. , Morkoç H.
Published: July 2002

Deep centers in Si-doped n-GaN layers grown by reactive molecular beam epitaxy have been studied by deep-level transient spectroscopy as a function of growth conditions. Si-doped GaN samples grown on a Si-doped n+-GaN contact layer at 800 °C show a dominant trap C1 with activation energy ET=0.44 eV and capture cross-section σT=1.3×10−15 cm−2, while samples grown at 750 °C on an undoped semi-insulating GaN buffer show prominent traps D1 and E1, with ET=0.20 eV and σT=8.4×10−17 cm2, and ET=0.21 eV and σT=1.6×10−14 cm2, respectively. Trap E1 is believed to be related to a N-vacancy defect, since the Arrhenius signature for E1 is very similar to the previously reported trap E, which is produced by 1-MeV electron irradiation in GaN materials grown by both metalorganic chemical-vapor deposition and hydride vapor-phase epitaxy.
A metal-free cathode for organic semiconductor devices
Authors: Parthasarathy G. , Burrows P. E. , Khalfin V. , Kozlov V. G. , Forrest S. R.
Published: July 2002

We introduce a class of low-reflectivity, high-transparency, nonmetallic cathodes useful for a wide range of electrically active, transparent organic devices. The metal-free cathode employs a thin film of copper phthalocyanine (CuPc) capped with a film of low-power, radio-frequency sputtered indium tin oxide (ITO). The CuPc prevents damage to the underlying organic layers during the ITO sputtering process. We present a model suggesting that damage-induced states at the cathode/organic film interface are responsible for the electron injection properties of the contact. Due to the low contact reflectivity, a non-antireflection-coated, metal-free transparent organic light-emitting device (MF-TOLED) is demonstrated with 85% transmission in the visible, emitting nearly identical amounts of light in the forward and backscattered directions. The MF-TOLED performance is found to be comparable to that of conventional TOLEDs employing a more reflective and absorptive cathode consisting of a semitransparent thin film of Mg:Ag capped with ITO.