bluuebunny/crossref_metadata_2025 huggingface dataset:
Optical free piston cell with constant diameter for use under high pressure
Authors: Ishihara Koji , Takagi Masahiro
Published: July 2002

An optical free piston cell (a modified le Noble and Schlott type optical cell) is described for use in spectrophotometric study under high pressure. The cell consists of a disk, a cylinder, and a free piston, which are made of quartz and are mounted within a stainless-steel holder. A small amount of sample solution (∼0.6 cm3), which only contacts with quartz, is required for measurements. The path length is fixed (1.2 cm) at ambient pressure, but is self-adjusting at elevated pressure so that no compressibility corrections are necessary.
Grazing angle x-ray photoemission system for depth-dependent analysis
Authors: Jach Terrence , Chester M. J. , Thurgate S. M.
Published: July 2002

We have developed an x-ray photoelectron spectrometer system which combines an adjustable grazing incidence angle source with reflected beam detection. When operated about the critical angle, this combination permits a variation of the x-ray penetration depth which can be monitored by means of the reflectivity. At angles of incidence less than the critical angle, the sampling depth of the photoemission is diminished, but the photoemission from the surface is enhanced due to the constructive interference of the incident and reflected x-ray beams. When used with Mg Kα radiation (Eγ=1253.6 eV), the spectrometry system obtains useful distributions of chemical species in surface layers of 10–40 Å thickness. We present data showing the depth dependence obtained with the spectrometer of different oxides in a sulfide-treated, oxidized GaAs (100) surface.
PVDF hydrophone and hydrophone array with side-looking elements
Authors: Chan H. L. W. , Whitnall D. F. , Dencher P. R.
Published: July 2002

Two single element hydrophones and an eight-element hydrophone array with side-looking polyvinylidene fluoride (PVDF) sensing elements are described. They were designed for measurements in which the ultrasonic beam insonifies the hydrophone from a direction perpendicular to the hydrophone axis. These hydrophones and the array have found various industrial and medical applications, especially for determining the ultrasound exposure of a patient in vivo. The construction and characterization of the hydrophones and the hydrophone array are reported and the directivities of the elements are compared with modeling results.
Short intense hydrogen gas pulses for transport studies in fusion plasmas produced by laser thermal desorption from titanium hydride
Authors: Fischer R. , Nolte R. , Steuer K.-H.
Published: July 2002

The suitability of laser thermal desorption (LTD) from titanium hydride targets for the production of short intense hydrogen gas pulses for diagnostic applications in fusion devices was investigated. A hydrogen yield of 2.2×1018 H2 molecules was achieved with a pulse energy of 11 J on a target spot diameter of 4.5 mm. The duration of the gas puff is closely coupled to the laser pulse length of 1 ms. The production of gas pulses by LTD close to the plasma creates the requirements for investigating very fast transport processes, especially at the high-field side. The hydrogen pulses were contaminated by 2×10−3 Ti atoms/H2 molecule, primarily as a result of evaporation on overheated surface inhomogeneities. Conditioning the surface with giant laser pulses allowed the contamination to be reduced by a factor of 2.
Feasibility of ultratrace detection of CO in cryogenic liquids using infrared excitation
Authors: Turnidge M. L. , Simpson C. J. S. M.
Published: July 2002

CO has been detected down to 500 parts per trillion by volume using infrared excitation of CO dissolved in liquid Ar solution with laser induced fluorescence detection. The feasibility of the in situ detection of trace concentrations of atmospheric and industrial pollutants dissolved in liquid air is discussed.
A multifunctional scanning force microscope for biological applications
Authors: Wiegräbe W. , Knapp H. F. , Eberhart H. , Gatz R. , Hartmann T. , Heim M. , Lorek Ch. , Guckenberger R.
Published: July 2002

Many questions to be tackled by scanning force microscopy (SFM) require the comparison of several nontopographic signals, like electrical conductance, friction, and elasticity. Especially in biology, which is our main field of interest, most of these signals are superimposed. To disentangle them, it is advantageous to measure them simultaneously. Because all known SFMs; home-built or commercial, allow either no or only very few such signals to be measured simultaneously, we developed the new multimode SFM. Moreover, we have applied new modes which measure breakdown voltages of thin insulators and static friction. The presented SFM is designed to investigate such properties of biological material, simultaneously. In addition, the instrument uses some new features, not used elsewhere: The elasticity signal is utilized for a reverse feedback during contact loss which makes imaging with very small forces practicable. The elasticity signal is further used to perform a very smooth approach, to prevent damage to tip and sample. Features like a movable sample stage, light microscopic access, and enhanced computer control using a Macintosh IIfx are described. The liquid cell is designed such that no seal is necessary which would disturb the scanner movement. As an application requiring these features, results obtained on a DPPC Langmuir–Blodgett film in the two phase coexistence region on a partly conductive support are shown. One can distinguish areas in the liquid expanded phase from areas in the liquid condensed phase using the information contained in the topographic, elastic, frictional, and conductivity signals. Correct interpretation was only possible using the simultaneously collected different signals.
Complex-coupled distributed feedback laser with negative differential coupling
Authors: Kruschwitz Brian E. , Brown T. G.
Published: July 2002

A novel mechanism for creating a periodic gain is presented which can be used in the design of complex-coupled distributed feedback semiconductor lasers. A one-dimensional longitudinal analysis shows that this gain-coupling mechanism is characterized by negative differential coupling, which earlier reports have shown can offer the most significant reduction in the linewidth enhancement factor. A linewidth analysis predicts that the linewidth enhancement factor can be reduced by about a factor of 2 because of the negative differential coupling.
Transition matrix approach for Monte Carlo simulation of coupled electron/phonon/photon dynamics
Authors: Alam Muhammad A. , Lundstrom Mark S.
Published: July 2002

A new approach for simulating the dynamics of electrons, phonons, and photons is described. The technique provides a Monte Carlo simulation of particle dynamics without the statistical noise associated with direct Monte Carlo simulation, treats physical phenomena with a wide range of time scales, and has a good computational efficiency. A transition matrix is first precomputed by direct Monte Carlo simulation. Particle populations are then updated at regular time steps by simple matrix multiplication while correcting for nonlinear effects such as carrier–carrier scattering, band filling, hot phonons, etc. The technique is well suited to studies of quantum well laser devices and pump-probe experiments where direct Monte Carlo simulation is exceedingly difficult.
A new absorption spectroscopy setup for the sensitive monitoring of atomic and molecular densities
Authors: Buuron A. J. M. , Otorbaev D. K. , van de Sanden M. C. M. , Schram D. C.
Published: July 2002

This paper deals with the specifications and the possibilities of a novel highly sensitive optical absorption spectroscopy method. It consists of a cascaded arc as an extremely bright broadband light source with a high resolution spectrometer as a detector. Its interest for a continuous quantitative monitoring of the densities of waste atoms and molecules in the atmosphere is investigated. To this end, theoretical considerations are given with respect to the detection limits and the resolution necessary for selective spectrochemical analysis. In the first measurements with the setup, on a laboratory argon-hydrogen plasma, the versatility and sensitivity of the technique for measuring low species densities is demonstrated. Densities of the sublevels of the argon first excited state, the four Ar(3p54s) metastable and resonant substates, were measured simultaneously in one measuring sequence. The data were analyzed using an efficient line of sight integration technique. The densities of these substates are of the order of 1017 m−3 in a plasma with a pressure of 40 Pa. For the atomic hydrogen H(n=2) state, densities of the order of 1014 m−3 over a length of about 2 cm could be measured, representing a detection limit of approximately 2×1012 m−2.
A digital system for ‘‘optimum’’ resolution in x-ray spectroscopy
Authors: Sampietro M. , Bertuccio G. , Geraci A. , Fazzi A.
Published: July 2002

This paper describes an experimental setup for spectroscopy measurements based on the digital processing of samples obtained by digitizing the signal pulse as it appears at the output of a proper conditioning circuit. The system shares with conventional pulse-height analysis systems the connection to the detector and the preamplifier, but differs from them as it uses an antialiasing filter and a digitizer instead of a shaper and a multichannel analyzer. The implemented algorithm maximizes the signal-to-noise ratio in the estimate of the amplitude of the signal pulse and represents the digital counterpart of the optimum analog processor stated by the theory of the optimum filtering. The system is able to synthesize the best possible filter through the on line measurement of the noises actually present in the experiment, thus leading to the best resolution and allowing a total flexibility in adapting to changeable noise conditions. The performance of the digital system in terms of resolution is investigated and its count rate capability is mentioned. In particular, an improvement in energy resolution of more than 10% has been experimentally achieved with respect to conventional systems based on analog circuitry. All the components of the system are described and, as an example of application, the energy spectrum of 241Am is acquired and reported.
X-ray microscopy using the photoexcitation to unoccupied π*-character molecular orbits
Authors: Iketaki Yoshinori , Watanabe Tsutomu
Published: July 2002

We studied the possibility of soft x-ray microscopy using unoccupied π*-character molecular orbits of bases in DNA and RNA. We estimated the photoabsorption cross section of benzene molecule using the atomic base model. Discussion is extended to the case of nuclear acid bases caused by excitation of the 1s electron to the π* orbit under assumption of the similar electronic transition with the benzene case and found that for the photon energy used in this study it is three times larger than that for the photoionization of the 1s electron at the water window region. We concluded that an image of DNA or RNA in wet biological cells may be observed with good contrast using this proposed method.
A dual line multicell ionization chamber for transvenous coronary angiography with synchrotron radiation
Authors: Menk R. H. , Dix W.-R. , Graeff W. , Illing G. , Reime B. , Schildwächter L. , Tafelmeier U. , Besch H. J. , Grossmann U. , Langer R. , Lohmann M. , Schenk H. W. , Wagener M. , Walenta A. H. , Kupper W. , Hamm C. , Rust C.
Published: July 2002

A position sensitive one-dimensional x-ray detector with a large dynamic range (≳214:1) for high photon fluxes with fast image recording sequence (300 ms per frame) has been developed for transvenous coronary angiography with synchrotron radiation. A position resolution of 1 LP/mm and a detection quantum efficiency (DQE) of at least 58% (for 11 000 photons per pixel) has been achieved for 33 keV photons in a Xe-CO2 gas mixture at 20 bars. The use of Kr-CO2 as conversion gas provides a better contrast of the weak iodine signal than Xe-CO2 or Si, respectively, for a fraction of 2% of the second harmonics of the synchrotron beam used.
Absolute calibration of a photodiode array with the use of the synchrotron radiation in the range of 1–10 keV
Authors: Beck L. , Bizeuil C. , Soullie G.
Published: July 2002

The silicon photodiode array Hamamatsu S3901 series (1024, 25 μm pixel) were primarily developed for the visible-UV spectral range, mainly for photon wavelengths between 200 and 1100 nm. By utilizing it without a quartz window, it is demonstrated that this sensor can be used for x rays, especially in the 1–10 keV range. Experimental measurements of the absolute detection efficiency of the photodiode array between 1.5 and 12 keV are presented. The experiments were performed on an x-ray tube-excited secondary targets and on the SB3 beamline at the Super ACO storage ring (LURE-Orsay). The measured spectral efficiency is compared with the results of a simple model calculation based on the data given in the Hamamatsu note. The simulation is in good agreement with the experimental data for a silicon active depth of 6 μm and a silicon dioxide passivation layer of 5 μm. The linearity is better than 1% and the spatial resolution is estimated to be 120 μm.
The present status of SRL-ISSP
Authors: Ishii Takehiko
Published: July 2002

The present status of SOR-RING and its beam lines owned by the Synchrotron Radiation Laboratory of the Institute for Solid State Physics of the University of Tokyo are described. Experimental facilities in the Tsukuba Branch Laboratory built in the Photon Factory are also described.
Determination of pinning strength of YBa2Cu3O7−δ from magnetic stiffness measurements
Authors: Lehndorff Beate , Kürschner Hans-Gerd , Lücke Bernhard
Published: July 2002

A method is presented to determine the Labusch parameter α from the measurement of magnetic stiffness η. Quantitative results on various YBa2Cu3O7−δ samples are reported. For all samples η is a function of the external magnetic field and does not depend on magnetic history. For small magnetic fields η obeys a B1.5 behavior. At fields above 120 mT the melt grown material and the thin film turn over to a B2 dependence. The results can be understood in terms of a crossover from nearly single vortex characteristics to the elastic interaction of vortices in the flux line lattice.
Design of a multislit, variable width collimator for microplanar beam radiotherapy
Authors: Slatkin D. N. , Dilmanian F. A. , Nawrocky M. M. , Spanne P. , Gebbers J.-O. , Archer D. W. , Laissue J. A.
Published: July 2002

Microbeam radiation therapy of the intracerebral 9L gliosarcoma in rats, an experimental surrogate for human malignant gliomas, using mainly 30–130 keV wiggler-generated x rays, extended the residual lifespans of some rats ten or more times over those of untreated, similar gliosarcoma-bearing rats. The rats were exposed 300 or 600 times to an upright, 25-μm-wide, 4-mm-high x-ray beam. A multislit collimator has been designed to shorten the time required for the therapy.
Intracavity, frequency-doubled, miniaturized Nd:YAlO3 blue laser at 465 nm
Authors: Zarrabi Joseph H. , Gavrilovic Paul , Singh Shobha
Published: July 2002

A blue laser at 465 nm has been demonstrated by intracavity frequency doubling of the 930 nm transition in neodymium-doped crystal of yttrium orthoaluminate (Nd:YAlO3). The compact plano–plano laser cavity comprising a 1.2-mm-thick Nd:YAlO3 crystal and a 1.3 mm potassium niobate (KNbO3) crystal generated more than 15 mW of blue power when pumped by a Ti:sapphire laser. The blue output is linearly polarized with a TEM00 spatial profile.
Cross-correlation measurement of ultrafast switching in a symmetric Mach–Zehnder all-optical switch
Authors: Nakamura Shigeru , Tajima Kazuhito , Sugimoto Yoshimasa
Published: July 2002

We present cross-correlation measurement of ultrafast switching in a symmetric Mach–Zehnder all-optical switch. A full width at half-maximum of 2 ps has been achieved in the cross-correlation trace, corresponding to the estimated switching time of 1.5 ps. Both the switch-on and switch-off time of the measured traces are limited only by the control pulse duration of 1.1 ps. These results indicate that the effects of group velocity dispersion and intraband carrier relaxation are negligible within the present time scale.
Effects of Sb doping on Si(001) surface roughening and epitaxial thickness at low growth temperatures (100–300 °C)
Authors: Lee N.-E. , Greene J. E.
Published: July 2002

The Sb incorporation probability in homoepitaxial Si(001) films grown by ultrahigh vacuum ion-beam sputter deposition at temperatures Ts between 100 and 300 °C was found, using quantitative secondary ion mass spectrometry, to be unity with no evidence of surface segregation. Surface roughnesses and epitaxial thicknesses te were measured by atomic force microscopy and cross-sectional transmission electron microscopy, respectively, for both undoped and Sb-doped Si layers. Sb doping was found to dramatically increase the rate of surface roughening and to decrease te by a factor of ≳2 at growth temperatures between 250 and 300 °C while having no measurable effect at lower temperatures.
Implantation-induced dopant diffusion in the framework of the droplet model of structural disorder
Authors: Konstantinov A. O.
Published: July 2002

A model for the annealing of implantation-induced structural disorder is proposed. The phenomenon is treated on the basis of a physical analogy between point defect cluster formation/dissolution in a crystal and droplet condensation/evaporation in a saturated vapor. Explicit relationships are obtained for diffusion broadening and drift of the dopant profile upon disorder annealing. The predictions of the droplet model are compared with experimental data on boron in silicon and are found to be accurate better than within a factor of 2 in the temperature range 800–1050 °C.
Observation of x-ray sheet beam from radioisotopes embedded in thin-film waveguide
Authors: Sasaki Y. C. , Tomioka Y. , Satoh I.
Published: July 2002

A specific angular distribution of x rays from 111In embedded in a thin-film waveguide (Au film/Langmuir–Blodgett film/Au substrate) is observed by a non-energy-dispersive two-dimensional detector (imaging plate). The angular distribution for the thickness of the upper Au layer of 90 Å can be explained by normal calculation of the optical electromagnetic wave solution of Maxwell’s equations for each interface and reciprocity. However, the angular pattern in the upper 400 Å Au thickness layer cannot be accounted for by the normal approach without considering the intensity of the x-ray sheet beam emerging from the end of the multilayer.
New synthesis method of fullerenes using microwave-induced naphthalene-nitrogen plasma at atmospheric pressure
Authors: Ikeda Tetsuya , Kamo Toshihiro , Danno Minoru
Published: July 2002

A new synthesis method of fullerenes has been investigated for microwave induced naphthalene-nitrogen plasma at atmospheric pressure using a cylindrical coaxial cavity. The toluene extract solution of soot obtained after discharges showed HPLC peaks with retention times corresponding well to those of C60 and C70. The production of fullerenes was also confirmed by mass-spectrometric analysis. Gas temperature of nitrogen plasma determined from radiative transitions of N2+ was 3800–5700 K. From a comparison of the gas temperature and the incident microwave power, it was found that the reaction efficiency for fullerenes decreases with the increase in the gas temperature of the plasma and shows a maximum at about 4500 K.
Ultrasonic measurement of convective heat transfer coefficients on a nonuniform melt layer
Authors: Bhansali Anil P. , Black W. Z. , Jarzynski J.
Published: July 2002

This article describes a new ultrasonic measurement technique that evaluates local convective heat transfer coefficients on a curved, melting layer of ice based on measured time-of-flight data. A 2.25 MHz dual element transducer was used to measure the time-dependent thickness of a nonuniform layer of ice that was rapidly melting. The instantaneous thickness data were used to determine the velocity and slope of the ice/water interface and this information was converted into local, instantaneous heat transfer rates at the melt surface. The application of an ultrasonic technique to the measurement of heat transfer rates is unique because it is the first time that thickness measurements on a curved surface that is continually varying in shape have been used to determine local convective heat transfer coefficients.
Far-infrared emission from hot quasi-one-dimensional quantum wires in GaAs
Authors: Grayson M. , Tsui D. C. , Shayegan M. , Hirakawa K. , Ghanbari R. A. , Smith Henry I.
Published: July 2002

We have observed far-infrared radiation from an array of hot quasi-one-dimensional wires in GaAs. The wires have 6000 Å period with 3000 Å lithographic width. Spectroscopy of the infrared emission with a bolometer detector filtered by a magnetic field-tunable InSb cyclotron resonance wedge reveals: an intersubband plasmon resonance at 45 cm−1, and a measure of the resonance linewidth and electron temperature as a function of pulse current. The total intensity of the infrared signal yields a confirming measure of the temperature of the electrons, ranging from 6.0 to 12.1 K for currents of 40 nA to 2 μA per wire.
Manipulation of ion channeling patterns using magnetic quadrupole lenses
Authors: Breese M. B. H. , King P. J. C. , Grime G. W. , Seiberling L. E. , Boshart M. A.
Published: July 2002

This letter demonstrates that ion channeling patterns, produced by the passage of 3 MeV protons through a 0.5 μm thick [001] silicon crystal, can be transported and manipulated to produce enlarged or reduced area patterns using magnetic quadrupole lenses. The different effects on the ion channeling patterns obtained by using single quadrupole lenses and quadrupole multiplets are shown. The maximum attainable magnification under present conditions is investigated and a fundamental limitation to this process is identified as being the energy spread gained by the proton beam as it passes through the crystal.
Fluorescence spectrophotometer for the real time detection of cytosolic free calcium from cell suspensions during exposure to extremely low frequency magnetic fields
Authors: Carson Jeffrey J. L. , Prato Frank S.
Published: July 2002

We have previously observed that cytosolic free calcium ([Ca2+]i) is increased in HL-60 cells after exposure to an extremely low frequency (ELF) magnetic field. To facilitate the investigation of the time dependence of this effect, we built a magnetic field exposure system in which four samples of cells could be kept at constant temperature and maintained in suspension with constant mixing. Fluorimetric measurements of [Ca2+]i from these samples were made in real time using a periscopic optical system attached to a fluorescence spectrophotometer. This design feature eliminated possible confounding influences of the applied magnetic field on the light detection electronics, and isolated the cell samples against stray magnetic fields from electronic equipment. The operation of the instrument was computerized. This permitted the precise definition and replication of experimental conditions such as the properties of the applied magnetic field, the rate of sample mixing, and the instant at which an agonist was added to the cells. It also provided a time-resolved record of sample temperature and fluorescence for each experiment. Characterization of the instrument enabled us to rule out potential confounding influences on fluorimetric [Ca2+]i measurements, such as temperature and mechanical vibration, and to have confidence in the accuracy and precision of the applied ELF and static magnetic fields. Experiments with HL-60 and Jurkat cells verified that the instrument could measure [Ca2+]i in live cells and follow large rapid changes in [Ca2+]i after activation with an agonist. This instrument will provide an ideal tool with which to investigate in greater detail the effect of ELF magnetic fields on [Ca2+]i in HL-60 cells.
Dielectric Fabry–Pérot interferometer for temperature dependent far-infrared reflectivity measurements of heavy-fermion metals in high magnetic fields
Authors: Kohnen T. , Koning J. J. , Burghoorn J. , Wyder P. , Lejay P.
Published: July 2002

A far-infrared reflectivity set up has been developed for spectroscopy on highly reflective materials in a 20 T-class resistive Bitter magnet. As a first application, far-infrared reflectivity measurements on the heavy-fermion compound URu2Si2 have been performed using a silicon reflection Fabry–Pérot interferometer as a multiple reflection device. In a resonance, this Fabry–Pérot technique is one order of magnitude more sensitive than a single reflection measurement. Changes in the reflectivity as a function of magnetic field are resolved with an accuracy of 0.2% and the absolute value of the reflectivity can be obtained with an accuracy of 0.5%. With this interferometer, an excitation at about 40 cm−1 in the heavy-fermion system URu2Si2 is investigated at temperatures between 2 and 20 Kelvin and in magnetic fields up to 20 T. The excitation appears to extend to lower energies under influence of a large magnetic field.
Inversion of the Poisson transform using proportionally spaced cubic B-splines
Authors: Earnshaw J. C. , Haughey D.
Published: July 2002

A simple but effective approach to inversion of the Poisson transform is described. The use of cubic splines to approximate the inverse function automatically provides a degree of regularization which helps to overcome the ill-conditioned nature of the problem. Representative tests of the method are presented.
A scanning force microscope designed for fluid cell measurements
Authors: Wigren Roger , Olsson Lars , Erlandsson Ragnar
Published: July 2002

We present a scanning force microscope working in the repulsive force mode designed for fluid–cell measurements and tip–sample interaction studies. The instrument uses the optical beam deflection principle to measure cantilever motion and is compatible with commercially available microfabricated cantilevers. The instrument is designed to accommodate tube scanners with lengths up to 2 in. In order to minimize memory effects in the piezoelectric scanner, we have introduced a technique of pre- and postscanning to get reproducible force versus distance curves. Different linearizing algorithms to decrease the unlinearities of the scanner motions are demonstrated. As examples of the performance, we present an image of a mica surface obtained in air showing atomic scale stick–slip features, and a force measurement using the fluid cell with NaCl electrolyte showing the double layer interaction between a glass sphere and a mica surface.
Background reduction in experiments with x-ray glass capillary optics
Authors: Engström P. , Riekel C.
Published: July 2002

An analysis of the background at the exit of tapered borosilicate glass capillaries in synchrotron radiation scattering experiments suggests scattering due to short-range order at larger angles while low-angle scattering is attributed to phase separation in the glass. Background scattering can be largely suppressed by introducing a pinhole aperture at the exit of the capillary. The lowest background was obtained for a pinhole approaching the size of the exit beam. Background reduction is particularly important for wide- and small-angle scattering experiments on weakly scattering samples like thin polymeric fibers.
Laser-micromachined millimeter-wave photonic band-gap cavity structures
Authors: Özbay E. , Tuttle G. , McCalmont J. S. , Sigalas M. , Biswas R. , Soukoulis C. M. , Ho K. M.
Published: July 2002

We have used laser-micromachined alumina substrates to build a three-dimensional photonic band-gap crystal. The rod-based structure has a three-dimensional full photonic band gap between 90 and 100 GHz. The high resistivity of alumina results in a typical attenuation rate of 15 dB per unit cell within the band gap. By removing material, we have built defects which can be used as millimeter-wave cavity structures. The resulting quality (Q) factors of the millimeter-wave cavity structures were as high as 1000 with a peak transmission of 10 dB below the incident signal.
Thermal conductivity and diffusivity measurements in the sub-μm and sub-μs scale on centimeter area samples using a microthermocouple
Authors: Forster R. , Gmelin E.
Published: July 2002

A micro-thermocouple, made of tungsten versus gold-0.07% Fe, is used in a scanning tunnel microscopelike setup to measure temperature profiles with submicrometer (100 nm) and submicrosecond (50 ns) resolution on centimeter (cm) area thin film surfaces. The installation is equipped with a new type of three-directional piezoelectric inertia drive and enables measurements in the temperature range from 4 to 300 K. The thermal conductivity of a 10 μm gold foil and a silicon wafer (260 μm) has been measured from 8 to 300 K and the thermal boundary resistances of GE-7031 varnish and In-foil, used to mount the samples, were determined. The measured temperature profiles, as a function of time and tip location on the sample, were modeled and fitted by the finite element method. The installation has been designed for mesoscopic temperature profiling to investigate thermal conductivity and diffusivity of thin films, multilayers, and thermal boundary resistances. The results for gold films agree with data reported in the literature. The importance of the boundary resistance (and boundary conditions) in heat flow experiments is emphasized.
Electronic states in GaAs v-groove quantum wire structures with superlattice barriers
Authors: Kiener C. , Rota L. , Freyland J. M. , Turner K. , Maciel A. C. , Ryan J. F. , Marti U. , Martin D. , Morier-Gemoud F. , Reinhart F. K.
Published: July 2002

We present a joint theoretical and experimental investigation of GaAs v-groove quantum wires confined in GaAs/AlAs superlattice barriers. We have computed the electronic states for both the quantum wire and the barriers. The intrinsic bending of the superlattice layers, together with systematic spatial variations of their thickness, create localized states in the barriers that are separated from the wire. This effect has a strong impact on the overall luminescence efficiency of the wires. The results are in excellent agreement with photoluminescence and photoluminescence excitation spectra.
A shear force feedback control system for near-field scanning optical microscopes without lock-in detection
Authors: Hsu J. W. P. , McDaniel A. A. , Hallen H. D.
Published: July 2002

An improvement to the currently used ac impedance detection method for tip-sample distance control in near-field scanning optical microscopes is described and demonstrated. The output signal of the electronic bridge is increased by a factor of 5000 so that a root-mean-square chip can be used in place of sensitive lock-in detection. It is shown that the signal-to-noise ratio of this new method is high enough to detect 0.07 nm changes in topography. In addition, this modification makes the electronics for the shear force feedback compact and inexpensive.
GaInAs/GaAs/GaInP strained quantum well lasers (λ∼0.98 μm) grown by molecular beam epitaxy using solid phosphorus and arsenic valved cracking cells
Authors: Baillargeon J. N. , Cheng K. Y. , Cho A. Y.
Published: July 2002

Aluminum-free GaInAs/GaInP strained quantum well (QW) laser diodes grown on GaAs were prepared by molecular beam epitaxy (MBE) employing solid phosphorus and arsenic valved cracking cells for the first time. The separate confinement heterojunction laser structure utilized Ga0.51In0.49P cladding layers, a GaAs waveguide region, and a single 100 Å Ga0.18In0.82As QW. Stimulated emission from this structure was observed at λ∼0.98 μm (1.265 eV). The threshold current density of broad area devices with 100×500 μm2 dimensions were measured as low as 290 A/cm2 and had power slope efficiencies between 0.35 and 0.40 W/A. The estimated transparency current density for the structure is 50 A/cm2. The data show all solid source MBE is a growth technology capable of producing laser diode structures of comparable quality to that of the other growth processes requiring hydrides.
Interaction of laser ablation plasma plume with grid screens
Authors: Anisimov V. N. , Baranov V. Yu. , Grishina V. G. , Derkach O. N. , Sebrant A. Yu. , Stepanova M. A.
Published: July 2002

Optical emission spectroscopy and charge collector time-of-flight measurements have been used to study interaction of laser ablation carbon plasma with grid screens in vacuum under conditions typical for pulsed laser deposition of thin diamondlike films. The effect of velocity distribution transformation of the ion flow has been observed and studied in a variety of experimental conditions. Our results indicate that the observed phenomenon is due to interaction of two plasma flows, the initial expanding one and the fraction of that flow scattered by the substrate or the screen. Three typical modes of velocity distribution function transformation have been observed depending on the plasma density: linear attenuation of the flow density, nonlinear attenuation of the slow ‘‘tail’’ of the velocity distribution function, and nonlinear transformation of the entire velocity spectrum. The latter regime occurs when plasma is throttling through the fine mesh screen. Our observations show that the reported phenomenon may substantially affect deposited film properties.
Electron-beam extraction system for the Frankfurt 14 GHz electron cyclotron resonance ion source
Authors: Runkel S. , Hohn O. , Schmidt L. , Stiebing K. E. , Schmidt-Böcking H. , Schempp A. , Becker R.
Published: July 2002

A new concept to assist in the extraction of ion beams from an electron cyclotron resonance ion source (ECRIS) by the injection of an electron beam from the extraction side into the ion-source plasma is proposed. In this article, the construction of a test setup is described and first results of experiments with this setup at the 14 GHz ECRIS of the Frankfurt ECRIS-(ve)RFQ facility are reported.
Fast metal diffusers in Si in the presence of Si self-interstitial traps
Authors: Gossmann H.-J. , Stolk P. A. , Eaglesham D. J. , Rafferty C. S. , Poate J. M.
Published: July 2002

The diffusion of Au, Pt, and Zn in Si yield Si self-interstitial diffusivities, DI, that exceed those obtained from dopant marker experiments by 6 orders of magnitude at 800 °C. Both types of experiments can be reconciled by assuming the existence of a nonannihilating interstitial trap, related to carbon. In this context, selected metal diffusion data are reanalyzed. Nonannihilating immobile traps and a second-order reaction involving interstitial carbon and carbon–carbon pairs are considered. Quantitative point-defect parameters are extracted at 1115 °C for an assumed trap concentration of Ctt=5×1016 cm−3. In all cases and independent of the value of Ctt, excellent fits to concentration versus depth profiles of Zn are obtained; the extracted equilibrium concentration of Si self-interstitials, CI*, varies inversely with Ctt, while DICI* remains approximately constant. Hence agreement, or disagreement, of metal diffusion results with the Si self-diffusion coefficient cannot be used to exclude or prove trap-limited diffusion. Literature values of point-defect parameters obtained by neglecting traps represent lower bounds on DI and upper bounds on CI*. The time evolution of the Zn profile in the presence of traps is discussed. Proper inclusion of traps in the analysis of metal diffusion data leads to a decrease in the extracted activation energy of DI.
Observation of very efficient hybrid mode locking in an InGaAs/InGaAsP multiple quantum well distributed Bragg reflector laser diode
Authors: Kim Dug Y. , Seo Dong-Sun , Liu Hai-Feng
Published: July 2002

Unlike conventional hybrid mode-locking methods, a very low power (−1 dBm from a rf synthesizer) rf sinusoidal feeding signal is applied to the saturable absorber of the laser and ultrastable mode-locked pulse train at 34 GHz repetition rate is achieved. A new physical mechanism for the efficient hybrid mode locking is proposed.
Separation of beam and electrons in the spallation neutron source H− ion source
Authors: Whealton J. H. , Raridon R. J. , Leung K. N.
Published: July 2002

The spallation neutron source requires an ion source producing an H− beam with a peak current of 35 mA at a 6.2% duty factor. For the design of this ion source, extracted electrons must be transported and dumped without adversely affecting the H− beam optics. Two issues are considered: (1) electron containment transport and controlled removal; and (2) first-order H− beam steering. For electron containment, various magnetic, geometric, and electrode biasing configurations are analyzed. A kinetic description for the negative ions and electrons is employed with self-consistent fields obtained from a steady-state solution to Poisson’s equation. Guiding center electron trajectories are used when the gyroradius is sufficiently small. The magnetic fields used to control the transport of the electrons and the asymmetric sheath produced by the gyrating electrons steer the ion beam. Scenarios for correcting this steering by split acceleration and focusing electrodes will be considered in some detail.
Acoustic surface shape resonances of circularly symmetric defects on solid surfaces
Authors: Shchegrov A. V. , Maradudin A. A.
Published: July 2002

We present a formally exact Green’s tensor approach to the calculation of the frequencies of elastic vibrations localized in the vicinity of a circularly symmetric protuberance or indentation on an otherwise planar, stress-free surface of a semi-infinite, isotropic elastic medium–acoustic surface shape resonances. The method is illustrated by applying it to the determination of the frequencies of several of the lowest frequency acoustic surface shape resonances associated with protuberances or indentations of several different forms.
Laser-induced stresses versus mechanical stress power measurements during laser ablation of solids
Authors: Shannon Mark A. , Russo Richard E.
Published: July 2002

Laser-induced stresses resulting from high-power laser-material interactions have been studied extensively. However, the rate of change in mechanical energy, or stress power, due to laser-induced stresses has only recently been investigated. An unanswered question for monitoring laser-material interactions in the far-field is whether stress power differs from stresses measured, particularly with respect to laser-energy coupling to a solid target. This letter shows experimental acoustic data which demonstrate that stress power measured in the far field of the target shows changes in laser-energy coupling, whereas the stresses measured do not. For the ambient medium above the target, stress power and stress together reflect changes in laser-energy coupling.
Interdigital accelerating H structure in the multicharged ion linac
Authors: Bomko V. A. , Demchuk N. I. , Dyachenko A. F. , Kobets A. F. , Mazalov Yu. P. , Pipa A. V. , Rudyak B. I.
Published: July 2002

Two modifications of the interdigital accelerating H structure forming the basis for upgrading both the main and prestripper sections of the Kharkov multicharged ion linac (MILAC) are described. Possible application of this type of structure to heavy ion accelerator is discussed. It is shown that the use of the interdigital H structure in this particular case has enabled three major problems to be solved, namely: (i) to increase the operating wavelength from 2.1 m of the previously used Alvarez structure up to 6.3 m, (ii) to double the acceleration rate, and (iii) to increase the shunt impedance by 2–4 times. New methods and designs are described for tuning the cavities at an operating frequency and transforming the sinusoidal field distribution, peculiar to the H mode, into the homogeneously distributed field along the structure axis, with varying period lengths. Characteristics of the MILAC main and prestripper sections are given.
Nonintrusive rigid body tracking technique for dry particulate flows. Part I. Theoretical aspects
Authors: Dave Rajesh N. , Bukiet Bruce G.
Published: July 2002

A unique system to nonintrusively track a particle in three dimensions is presented. It is based on the principle of magnetic induction coupling and consists of small transmitters mounted inside the particle being tracked, and a set of receiving antennae surrounding the experimental apparatus. In Part I of the sequence of two papers, the focus is on the theoretical aspects, in particular, on developing a computational technique to solve the inverse problem, i.e., find the three-dimensional position as well as orientation of the particle from the voltages induced in the antennae. The computational technique is based on the Levenberg–Marquardt algorithm, along with a scheme for providing good initializations. Through simulated experiments that include various levels of added noise in the voltage readings, the success of this algorithm is demonstrated and the feasibility of the overall technique is established. It is also shown that a system with three mutually orthogonal transmitters provides accurate results even with the noise in the voltage data. Although this system is intended for use in experimental studies of dry granular flows, it has wide applicability due to its nonintrusive nature, and is particularly useful when optical tracking techniques are not feasible.
Apparatus for the detection and removal of vapor phase alkali species from coal-derived gases at high temperature and pressure
Authors: Griffin P. G. , Morrison R. J. S. , Campisi A. , Chadwick B. L.
Published: July 2002

A high-pressure, high-temperature apparatus has been developed for the analysis of sorbents capable of removing alkali compounds to the concentration levels required by advanced, coal-fired power generating systems. The reactor is capable of operating at temperatures up to 1200 °C and pressures up to 2.0 MPa. A laser-based technique—photofragment fluorescence—enables in situ analysis of the sodium content in a gas stream before and after a sorbent bed thereby determining the efficiency of the alkali removal by the various sorbents studied (typically alumino-silicate clays). The design and development of both the reactor and the laser-based analytical technique is described.
Automatic system for the direct and continuous measurement of the irreversibility line of high Tc superconductors
Authors: Flores L. E. , Noda C. , Abascal C. , González J. L.
Published: July 2002

A system for the direct and continuous determination of the irreversibility line in high Tc superconductors is described. The system, based on a standard ac susceptometer, operates by applying a controlled dc field to the sample that maximizes the imaginary (out-of-phase) component of the ac susceptibility. This control is achieved using a proportional-integral-derivative loop with the reference set to zero and with the magnetic field derivative of the imaginary component of the ac susceptibility taken as the feedback sample (error signal). To obtain a dc voltage proportional to this derivative a double lock-in detection scheme is used. This apparatus is able to carry out a continuous measurement of this line by sweeping the temperature in the range of interest while the sample is maintained, by the controller, at the irreversibility magnetic field at each temperature. Hence, the whole process is accomplished in the same time as a typical resistivity-versus-temperature measurement, which is faster than other methods.
Orientational relationship between cubic boron nitride and hexagonal boron nitride in a thin film synthesized by ion plating
Authors: Zhou Wei-Lie , Ikuhara Yuichi , Suzuki Tetsuya
Published: July 2002

Cubic boron nitride (c-BN) thin films synthesized by the ion-plating method were examined by high-resolution electron microscopy. It was found that the {0002} planes of hexagonal boron nitride (h-BN) at the boundaries of c-BN grains preferred to nucleate almost parallel to {111} planes of c-BN. Cross-sectional observation in the initial stage of growth showed that the c-BN can grow on top of the prismatic planes and the {0001} basal planes of h-BN, keeping the parallelism of the (111)c-BN to (0001)h-BN. A few degrees deviation (∼4°) between h-BN {0002} planes and c-BN {111} planes was frequently found in the film. The nucleation mechanism of c-BN was discussed analogous to that of diamond on graphite.
Change in sign of the photocurrent in a coherent asymmetric superlattice
Authors: Sumetskii Michael I. , Baranger Harold U.
Published: July 2002

We study the photocurrent induced in an asymmetric superlattice as a function of the frequency of applied radiation. In order to investigate the principal features, we consider the simplest finite-period structure: one containing an asymmetric unit formed of two narrow quantum wells. It is found that the main features of the photocurrent-frequency curve are insensitive to the number of periods. Considering a single-unit structure, we find simple equations for the photocurrent reversal points. The oscillations in sign of the photocurrent are shown to result from quantum interference of the electron waves reflected at the interfaces in the structure. Using our model, we approximate an experimental structure and explain the observed photocurrent reversal.
Effect of growth temperature on the electrical properties of CCl4-doped semi-insulating InP
Authors: Gardner Nathan F. , Hartmann Quesnell J. , Baker Judith E. , Stillman Gregory E.
Published: July 2002

The electrical properties of semi-insulating InP epitaxial layers grown by metalorganic chemical vapor deposition using CCl4 as a doping source have been studied as a function of the growth conditions of the material. Secondary ion mass spectrometry has been used to analyze the incorporation of impurity species in these layers. These measurements indicate that the resistivities of the CCl4-doped InP layers increase exponentially (exceeding 1012 Ω cm) with increasing growth temperature. The incorporation of C, H, and Cl decreases in these layers. In conjunction with the dependence of the resistivity on the flow rate of the diluted CCl4 dopant during growth, these results suggest that the semi-insulating nature of the InP layers is due to CCl4-mediated incorporation of one or more defects during growth. It is not likely that either a deep level created by Cl or hydrogen passivation of shallow donors and acceptors is responsible for the electrical properties of this material.
Controlling chaotic systems with occasional proportional feedback
Authors: Senesac Larry R. , Blass William E. , Chin Gordon , Hillman John J. , Lobell James V.
Published: July 2002

Utilizing the chaos control technique of occasional proportional feedback (OPF), we designed and constructed an inexpensive and easy to assemble electronic OPF controller. A number of built-in features provide ample versatility to enable the controller to be used with a wide variety of chaotic experimental systems. The controller has a standard OPF correction signal output, but also allows for the addition of a modulated signal to the correction. The rate and active duration of the correction pulse, the offset voltage, and the effective window width are variable. We present the basic principles of OPF control and discuss the individual component functions of the OPF controller. We have successfully used this controller to stabilize chaotic fluctuations in the frequency emission from a tunable lead–salt stripe geometry infrared diode laser.