bluuebunny/crossref_metadata_2025 huggingface dataset:
Improvement of catastrophic optical damage level of AlGaInP visible laser diodes by sulfur treatment
Authors: Kamiyama Satoshi , Mori Yoshihiro , Takahashi Yasuhito , Ohnaka Kiyoshi
Published: July 2002

An increase of 70% in the catastrophic optical damage (COD) level of AlGaInP visible laser diodes is achieved by sulfur treatment. From transmission electron microscope and energy dispersive microanalysis, we have confirmed that most of the oxide at the mirror facets is replaced by sulfur after this treatment. It is thought that oxide at the facets introduces surface states which cause the COD, and removal of the oxide by sulfur treatment results in the higher COD level.
High mobility hydrogenated and oxygenated microcrystalline silicon as a photosensitive material in photovoltaic applications
Authors: Faraji M. , Gokhale Sunil , Choudhari S. M. , Takwale M. G. , Ghaisas S. V.
Published: July 2002

Hydrogenated and oxygenated microcrystalline silicon (mc-Si:O:H) is prepared by rf glow discharge method with a mixture of silane, hydrogen, and oxygen. It is observed that the Hall mobility for the films can be ∼35 cm2 V−1 s−1 under optimal oxygen contents. When used as i layer in a p-i-n solar cell configuration, the corresponding solar cell exhibited a 7.8% efficiency with a fill factor of 0.53 over 1-mm-diam spots. Further improvements are indicated from the solar cell characteristics.
AlGaAs/GaAs-based triangular-shaped ring ridge lasers
Authors: Behfar-Rad A. , Ballantyne J. M. , Wong S. S.
Published: July 2002

Triangular-shaped ring ridge lasers (ridge trilasers) have been fabricated using quantum-well semiconductor laser material. The spectra of these ridge trilasers show single-wavelength operation above threshold confirming traveling-wave behavior in these lasers. Unidirectional operation is reported based on asymmetry between the clockwise and counterclockwise directions, in contrast to conventional unidirectional operation in ring lasers based on magnetic techniques.
Diode array-pumped Er, Yb: Phosphate glass laser
Authors: Hutchinson J. Andrew , Allik Toomas H.
Published: July 2002

A diode-array side-pumped Er, Yb: phosphate glass laser has been constructed. Pumped with two 970 nm, InGaAs strained-layer diode arrays, a long pulse slope efficiency of 14% was obtained, with thresholds of 60 mJ input, a maximum output pulse energy of 20 mJ, and with output wavelengths at 1545±12 nm. When Q-switched, the laser generated 0.3 mJ, 50 ns FWHM pulses at an output wavelength of 1533±1 nm. Visible upconversion emission in the laser rod was observed.
Injection locking of antiguided resonant optical waveguide arrays
Authors: Jansen M. , Botez D. , Mawst L. J. , Roth T. J. , Yang J. J. , Hayashida P. , Dozal L. , Rozenbergs J.
Published: July 2002

We report on the first demonstration of injection locking of strong index-guided large-aperture devices [20-element resonant-optical-waveguide (ROW) antiguided arrays] under pulsed operation. Full locking was achieved far above the threshold level (2.6×Ith) by injecting light from a master oscillator in a direction normal to the diode facet and only in one element of the 20-element ROW array. Single-frequency tuning is achieved over a ≥30 Å spectral range for emission in the 8500 Å region, while the beam pattern remains spatially stable and diffraction limited. For devices operating nearly resonant (i.e., beam width 2 to 3× the diffraction limit) injection locking accomplishes both single-frequency as well as diffraction-limited-beam operation.
Free-standing microstructures of YBa2Cu3O7−δ: A high-temperature superconducting air bridge
Authors: Lee L. P. , Burns M. J. , Char K.
Published: July 2002

We describe the fabrication of a free-standing YBa2Cu3C7−δ air bridge for useful applications of microstructures and microcircuits integration. We have used a sacrificial dielectric layer, which was subsequently etched, to produce the air gap between top and bottom layers. We have used conventional photolithographic processing, ion-beam dry etching, and selective wet etching with HF to create the novel microstructures. Step coverage of epitaxial bridge layers have been achieved without significant degradation of the superconducting properties of YBa2Cu3O7−δ layers.
Ultrafast local field dynamics in photoconductive THz antennas
Authors: Pedersen J. E. , Lyssenko V. G. , Hvam J. M. , Jepsen P. Uhd , Keiding S. R. , So/rensen C. B. , Lindelof P. E.
Published: July 2002

We demonstrate a new ultrafast pump-probe technique using terahertz pulses to investigate carrier transport and screening in semiconductors. As an example we have studied the temporal evolution of the local electric field in a dipole antenna, used for generation of ultrafast terahertz pulses. Ultrafast screening effects are shown to be important for both carrier transport and the emission of THz radiation. At high carrier densities the external bias field is screened on a time scale comparable to the duration of the THz pulse, giving rise to changes in the shape and bandwidth of the radiated pulses.
Coherent 1 W continuous wave operation of large-aperture resonant arrays of antiguided diode lasers
Authors: Zmudzinski C. , Botez D. , Mawst L. J. , Tu C. , Frantz L.
Published: July 2002

Near-diffraction-limited cw operation at 1 W power level is demonstrated, for the first time, from all-monolithic, phase-locked diode-laser arrays. In pulsed operation purely diffraction-limited beams (0.4° lobewidth) are obtained from relatively large-aperture (120 μm) devices to power levels of 1 W, with 70%–75% of the energy in the central lobe at low drives. These record-high coherent powers are achieved from 20-element resonant-optical-waveguide arrays of antiguided diode lasers by significantly increasing the aperture width while maintaining strong discrimination against high-order array modes via Talbot-type spatial filters.
Correlation of refractive index profiles with substitutional hydrogen concentrations in annealed proton-exchanged LiNbO3 waveguides
Authors: Zavada J. M. , Casey H. C. , Chen Chang-Ho , Loni A.
Published: July 2002

We have studied the behavior of the extraordinary refractive index in a set of annealed z-cut proton-exchanged lithium niobate (LiNbO3) substrates by means of optical prism-coupling measurements and numerical simulations. Values of the index as a function of depth have been determined and fitted with a single Gaussian diffusion expression. At 400 °C, the effective index diffusivity Dn of 4.6×10−12 cm−2/s is nearly identical to the diffusivity of substitutional H in these samples. Furthermore, we find a linear relationship between the increase in the extraordinary refractive index and the substitutional H concentration. At a wavelength of 0.6238 μm, the coefficient for this relationship is ∼1.5×10−23 (H cm−3)−1.
Coherent photon seeding of actively mode locked laser diodes
Authors: Kawaguchi Hitoshi , Sarwar Abedin Kazi
Published: July 2002

We have applied a coherent photon seeding technique to actively mode locked laser diodes for the first time and successfully achieved a single longitudinal laser diode mode operation with a side mode suppression ratio of −20 dB. We have also proposed a new kind of pulse compressor consisting of a grating and a plane mirror, which gives positive group velocity dispersion. We obtained 11 ps pulses with spectral width of 0.32 nm. This gives us a time bandwidth product of 0.63, which is approximately twice the transform limited value for a sech2 pulse.
Field emission from an elliptical boss: Exact versus approximate treatments
Authors: Jensen K. L. , Zaidman E. G.
Published: July 2002

Field emission from tips, in comparison to planar surfaces, is complicated by current enhancement effects and changes in the image charge. We show that the approximations typically used for the calculation of the transmission coefficient are inappropriate for small spherical surfaces but adequate for elliptical surfaces. A simple analytical formula for the average emitting area may be derived based on the Fowler–Nordheim equation under conditions of field emission. By use of the elliptical approximation, a simple scale factor is sufficient to deal with spherical and pointed tips.
Intensity dependent absorption/transparency of a reducing BaTiO3
Authors: Chang J. Y. , Garrett M. H. , Jenssen H. P. , Warde C.
Published: July 2002

We report intensity dependent absorption and transparency as a function of wavelength for barium titanate. The BaTiO3 crystal examined has an as-grown, light-blue color due to an absorption centered at 690 nm, and when reduced in a partial pressure of 10−15 atm of oxygen it has a yellow-orange color due to an absorption centered at 470 nm. Both energy levels are active in the reduced sample as revealed in the spectrum of the intensity dependent changes in absorption.
Nonuniform distribution of oxygen hole centers in silica optical fibers
Authors: Kannan S. , Fineman M. E. , Li J. , Sigel G. H.
Published: July 2002

This letter reports spatially variant distributions of nonbridging oxygen hole centers (NBOHCs) in pure synthetic silica core optical fibers with fluorine doped silica claddings. Results of low-temperature x-band electron spin resonance (ESR) etchback measurements have established the presence of NBOHCs in increased concentration at the core-clad interfacial region. The observations on a low-OH content silica core fiber are contrasted with that on a high-OH fiber. The correlation between the ESR results and the spatially variant luminescent patterns observed in these fibers during excimer laser irradiation is also discussed.
Energy-resolving superconducting x-ray detectors with charge amplification due to multiple quasiparticle tunneling
Authors: Mears C. A. , Labov Simon E. , Barfknecht A. T.
Published: July 2002

Superconducting tunnel junctions coupled to superconducting absorbers may be used as high-resolution, high-efficiency x-ray spectrometers. We have tested devices with niobium x-ray absorbing layers coupled to aluminum layers that serve as quasiparticle traps. The energy resolution at 6 keV was 49 eV full width at half-maximum. We estimate that each quasiparticle tunnels an average of 19 times before recombining, increasing the total charge transferred and therefore decreasing the effects of electronic noise.
Hot carrier and hot phonon effects on high-speed quantum well lasers
Authors: Tsai C. Y. , Eastman L. F. , Lo Y. H.
Published: July 2002

We present a theoretical model to analyze the hot carrier and hot phonon effect on the modulation response of semiconductor quantum well lasers. We find that the carrier heating strongly depends on the energy relaxation time of carriers and the lifetime of longitudinal-optic (LO) phonons. Furthermore, the carrier heating will significantly decrease the differential gain and increase the nonlinear gain coefficient and thus reduce the modulation bandwidth. From the numerical result, we demonstrate the bottleneck effect of the hot LO phonons on the modulation response of quantum well lasers. This implies that reducing the lifetime of LO phonons, for example, by doping in the quantum well, will most effectively decrease the carrier temperature and thus improve the modulation bandwidth.
Observation of nonhexagonal laser-beam patterning in a thin liquid crystal cell in front of a single feedback mirror
Authors: Ciaramella E. , Tamburrini M. , Santamato E.
Published: July 2002

We present here the first experimental evidence of spontaneous laser filamentation with patterns other than hexagons, in a thin Kerr medium placed in front of a single backreflecting mirror. In particular, we observed hexagons-to-rolls transition and, by proper external seeding, generation of square-like patterns.
Optical mixing in a patterned YBa2Cu3O7−δ thin film
Authors: Lindgren M. , Zorin M. A. , Trifonov V. , Danerud M. , Winkler D. , Karasik B. S. , Gol’tsman G. N. , Gershenzon E. M.
Published: July 2002

Mixing of 1.56 μm infrared radiation from two lasers in a high quality YBa2Cu3O7−δ thin film, patterned to parallel strips, was demonstrated. A mixer bandwidth of 18 GHz, limited by the measurement system, was obtained. A model based on nonequilibrium electron heating gives a good fit to the data and predicts an intrinsic mixer bandwidth in excess of 100 GHz, operating in the whole infrared spectrum. Reduction of bolometric effects and ways to decrease the conversion loss of the mixer is discussed. The minimum conversion loss is expected to be ∼10 dB.
Variable delay dual wavelength picosecond optical pulse generation using an actively mode-locked multichannel grating cavity laser
Authors: Zhu B. , White I. H.
Published: July 2002

Two optical pulse trains are generated at different wavelengths with a programmable delay between them, using active mode-locking of a multichannel grating cavity laser. For a channel separation of 2.2 nm, pulses with a duration of 60 ps and with a spectral width of 11.6 GHz have been obtained at a repetition rate of 1.78 GHz. The pulse width and power are stable to within 6%, irrespective of delay for a relatively wide range of dc bias conditions.
Local Ga implantation with focused ion beam and ambipolar lateral carrier transport in strained Si1−xGex /Si quantum wells
Authors: Okubo A. , Fukatsu S. , Shiraki Y.
Published: July 2002

Lateral carrier diffusion in a strained Si1−xGex/Si quantum well (QW) is reported using a periodic two-dimensional grating geometry defined by focused ion beam local-Ga-implantation. With systematically changing the grating period, we observed a clear dominance switch of steady-state photoluminescence (PL) intensity between defect-related luminescence from Ga-implanted grating stripes and PL emanating from the centered QW region. Fitting to a simple diffusion model, the lateral diffusion length was found to extend to several microns at low temperatures, whereas it increases with temperature up to 58 K.
Reproducibility studies of lattice matched GaInAsP on (100) InP grown by molecular beam epitaxy using solid phosphorus
Authors: Baillargeon J. N. , Cho A. Y. , Thiel F. A. , Fischer R. J. , Pearah P. J. , Cheng K. Y.
Published: July 2002

Growth of lattice matched GaInAsP on (100) InP was achieved using all solid source molecular beam epitaxy (MBE). Two valved cracking cells, one for phosphorus and the other for arsenic, were employed to supply the column V fluxes. The ability to obtain lattice matched conditions to InP was found to be highly reproducible and readily achievable using two valved cracking cells. X-ray diffraction and photoluminescence measurements showed run-to-run variations in the arsenic/phosphorus mole fractions of less than 1%. Lattice matched Ga0.30In0.70As0.68P0.32 layers displayed 300 K luminescence full width at half maximums as low as 40.6 meV at λ∼1.43 μm. The results suggest all solid source MBE offers a viable alternative to existing heterojunction growth technologies.
Seam line defects in silicon-on-insulator by merged epitaxial lateral overgrowth
Authors: Shih Yang-Chin , Lou Jen-Chung , Oldham William G.
Published: July 2002

Selective epitaxial growth of silicon through windows in SiO2 in a hot wall low-pressure chemical vapor deposition system has been used to fabricate silicon-on-insulator structures by epitaxial lateral overgrowth. Under suitable conditions this process yields a continuous epitaxial film over buried oxides. However, a unique ‘‘seam-like’’ defect was observed at the interfaces where two lateral growth fronts meet each other. A series of threading dislocations along the merging interface were identified as the structure of the seam defect. Epitaxial lattice mismatch at certain juncture points of two opposing growth fronts could have initiated the dislocations. Accumulated strain in the epitaxial film from oxide surface perturbation or interfacial stress are possible sources of the juncture point mismatch.
Two-photon intersubband transitions in quantum well infrared photoconductors
Authors: Dupont E. , Corkum P. , Liu H. C. , Wilson P. H. , Buchanan M. , Wasilewski Z. R.
Published: July 2002

We demonstrate that a symmetric GaAs/GaAlAs quantum well photodetector with a peak responsivity centered at 8.1 μm shows a significant quadratic power response at 10.6 μm. This is due to intersubband two-photon transitions from the ground level to continuum states. The two-photon responsivity agrees with a theoretical prediction based on a perturbative approach and photoconductive gain estimations.
Kinetic routes to the growth of monodisperse islands
Authors: Ngo Tue T. , Williams R. Stanley
Published: July 2002

Strictly kinetic processes can lead to the formation of monodisperse colloidal particles in solution [H. Reiss, J. Chem. Phys. 19, 482 (1951)]. We demonstrate that the narrow size distribution of Ni islands grown on a Si (100) surface by chemical vapor deposition can be modeled very well by a simple kinetic theory, which indicates that monodisperse nanoparticles can be grown on surfaces by proper control of island nucleation and growth kinetics.
Gated Hall effect measurements in high-mobility n-type Si/SiGe modulation-doped heterostructures
Authors: Ismail K. , Arafa M. , Stern Frank , Chu J. O. , Meyerson B. S.
Published: July 2002

We report gated Hall effect measurements and the study of electron mobility versus density in high-mobility modulation-doped Si/SiGe heterostructures. Front and back gates have been used to control the electron density and the shape of the electron wave function in the strained Si channel. The gate control on the electron density is modeled using a self-consistent Schrödinger and Poisson equation solution. We find that the electron mobility μ increases with electron density n as μ∝nα, where α is 1.2–1.8 at low n, and 0.7–1.0 at high n. A peak mobility of 5.2×105 cm2/V s at 0.4 K, considerably higher than the value in comparable ungated structures, is achieved when the electron wave function is moved away from the top heterointerface towards the center of the Si channel.
Phase stable automatic gain control for heterodyne holographic interferometry
Authors: Wagner James W. , Gardner Douglas J.
Published: July 2002

A simple circuit is described which provides a fixed output amplitude for an input variation of 20 dB and with a relative phase shift variation (output versus input) of only 0.12° over the same range. The circuit was developed for use in a heterodyne holographic interferometry system where relative phase measurements to an accuracy of 0.36° are required of signals whose amplitudes may vary by as much as an order of magnitude during a single experiment.
Glove-box-based fabrication system for inelastic electron tunneling junctions
Authors: Gajda G. J. , Weinberg W. H.
Published: July 2002

The design and the utility of a glove-box-based fabrication system for inelastic electron tunneling junctions are described. The system consists of a stainless-steel, turbomolecularly pumped ultrahigh-vacuum fabrication system, mounted to the evacuable entrance chamber (vacuum box) of the glove box. The glove box is a recirculating, catalytically purified, argon-based system, with a reactive impurity concentration below 2 ppm. In particular, there is ≲1-ppm water vapor. To demonstrate the advantages of the system, junctions prepared with m-cresol (3-methylphenol) chemisorbed from both the vapor and the liquid phases are compared, as well as junctions prepared with ethanolamine (2-aminoethanol) chemisorbed from the liquid phase both inside the glove box and externally in the laboratory atmosphere. Junctions prepared from the liquid phase with m-cresol exhibit significantly greater intensities (higher surface concentration) compared to the vapor-phase adsorption. The junctions prepared with ethanolamine exhibit spectral changes characteristic of different surface structures depending upon whether the adsorption is done in an inert atmosphere or in the laboratory atmosphere.
Magnetic shielding in ultrahigh vacuum systems: Using a computer code to design a shield for an electron energy loss spectrometer
Authors: Dobscha S. , Siekhaus W.
Published: July 2002

Using a computer code, a magnetic shield has been designed for an electron energy loss spectrometer. Two methods are used to approximate the effect of pumpout holes on the internal magnetic field. These approximations show that the ambient magnetic field can be attenuated by a factor of approximately 1000 in the sample region of the spectrometer. Actual tests of the constructed shield confirm the approximations.
Resonant modulation of single contact monolithic semiconductor lasers at millimeter wave frequencies
Authors: Cutrer David M. , Georges John B. , Wu Ta-Chung , Wu Bin , Lau Kam Y.
Published: July 2002

Resonant modulation of a single contact semiconductor laser at the cavity roundtrip frequency of 40 GHz is demonstrated. Efficient mode coupling is obtained with a single contact device by utilizing the high attenuation of the millimeter-wave modulation signal along the laser stripe. The properties and limitations of this technique are analyzed using a distributed circuit model of the laser.
Optical absorption at high pressure using a system response corrector
Authors: Roubi Larbi , Beliveau Alain , Carlone Cosmo
Published: July 2002

We describe how the optical absorption of solids at high pressures can be obtained through the combined use of a diamond-anvil cell and an absorption system using a response corrector.
Accurate measurement of the temperature coefficient of the ultrasonic velocity of fused quartz near room temperature
Authors: Chen S. E. , Meeks Steven W. , Johnson George C. , Tam Andrew C.
Published: July 2002

A technique has been adapted to measure the relative change in the acoustic velocity of materials at frequencies up to 500 MHz with a maximum sensitivity of one part in 107. This technique is applied to the measurement of the temperature coefficient of the longitudinal-acoustic velocity of fused quartz over the temperature range 28–47 °C. The longitudinal velocity is observed to increase linearly over this temperature range. The temperature coefficient of the fractional longitudinal velocity increase of fused quartz is determined to be (1.075±0.025)×10−4 °C−1. This number is in agreement with the results of previous investigators and is the most accurate measurement available at room temperature.
Temperature compensated high-temperature/high-pressure Merrill–Bassett diamond anvil cell
Authors: Schiferl D.
Published: July 2002

A Merrill–Bassett diamond anvil cell for high-temperature/high-pressure studies up to 5 GPa at 1000 K and 13 GPa at 725 K is described. To maintain uniform, well-characterized temperatures, and to protect the diamond anvils from oxidation and graphitization, the entire cell is heated in a vacuum oven. The materials are chosen so that the pressure remains constant to within ±10% over the entire temperature range.
Ruby fluorescence wavelength division fiber-optic temperature sensor
Authors: Grattan K. T. V. , Selli R. K. , Palmer A. W.
Published: July 2002

A LED-based fiber-optic temperature sensor is developed which uses the change in the wavelength distribution of emission of fluorescence from a small sample of pink ruby as the means of sensing temperature. An all fiber-optic system is described using simple electronics to measure temperature in the range from 293 to 433 K, with an accuracy of ±3 K.
Technique for bonding ultrasound transducers to recalcitrant materials
Authors: Bishop D. J. , Paalanen M. A.
Published: July 2002

A technique is described for bonding ultrasound transducers to materials with values of thermal expansion such that ordinary bonding methods become unusable. The technique has been developed in particular to allow measurements at dilution refrigerator temperatures of the ultrasonic attenuation and sound velocity of heavily doped silicon near its metal-insulator transition.
Minicomputer interface for magneto-optic spatial light modulator
Authors: Knoesen A. , Hartman N. F. , Gaylord T. K. , Guest C. C.
Published: July 2002

Digital optical data storage and processing are rapidly increasing in technological importance. The magneto-optic spatial light modulator (MOSLM) is a relatively low-cost, small pixel optical parallel input device that is capable of binary amplitude or binary phase modulation of each pixel. Thus, it is well matched to digital optical coherent storage and processing technology. However, potential problems associated with its use include: lack of a design for a general minicomputer interface, lack of interactive data-page file generation software, lack of ability to switch single pixels in some cases, lack of remote-from-computer operation capability, spurious pixel switching, and catastrophic failure due to thermal effects. The hardware and software components of a versatile minicomputer interface that has been successful in overcoming all of these problems are described. This interface allows easy data entry of entire data pages or single pixels and minimizes cross talk and noise developed over long cable lengths. In tests, the designed interface has produced highly stable operating characteristics.
Automatic measurement of laser diode thermal impedance
Authors: Chinn S. R. , Whitman T. L.
Published: July 2002

An automated procedure has been developed for data acquisition and analysis in the measurement of laser diode thermal impedance. This method is an extension of previous optical measurement techniques, and has the advantage of obtaining many data points in a short time interval. Standard commercial instrumentation is widely used, with many variants of the technique being possible.
Sensitive gas-phase photoacoustic spectrometer with provision for simultaneous recording of absorption spectrum
Authors: Chakrapani G. , Venkateswarlu Putcha , Rao Yerneni V. , George M. C.
Published: July 2002

The design of a sensitive pulsed photoacoustic spectrometer system for studying media in gaseous phase in the visible and ultraviolet regions is described. The system provides for simultaneous recording of the laser absorption spectrum of the sample by measuring the radiation transmitted through the sample cell. A highly sensitive optogalvanic detection subassembly for recording the calibration spectrum and analog signal processing/averaging electronics including gated integrators also form part of the system. Typical sensitivities of detection are a few tens of picobar acoustic pressure disturbances induced through two-photon absorption in iodine vapor in the sample cell and 0.1 pC charge fluctuation induced in the neon/uranium hollow cathode discharge through optogalvanic effect. Typical recordings of the photoacoustic, laser absorption, and two-photon photoacoustic spectra of the saturated vapor of iodine at room temperature in the presence of air at atmospheric pressure are presented together with the optogalvanic calibration spectra.
Fabrication of lateral npn-phototransistors with high gain and sub-μm spatial resolution
Authors: Baumgartner P. , Engel C. , Abstreiter G. , Böhm G. , Weimann G.
Published: July 2002

A novel kind of phototransistor with high gain and sub-μm spatial resolution is fabricated by focused laser beam-induced Zn doping of an n-modulation doped GaAs/Al0.4Ga0.6As quantum well structure. To produce this lateral npn-structure, p-doped lines are directly written over a mesa without degrading the quality of the sample. The local Zn doping causes an effective potential barrier for electrons. Photogenerated holes reduce this barrier and amplify the thermionic electron current. Spatially resolved photocurrent measurements show typical responsivities above 103 A/W and linewidths as small as 605 nm.
Construction of insertion devices for elliptically polarized synchrotron radiation
Authors: Yamamoto Shigeru , Shioya Tatsuro , Sasaki Shigeki , Kitamura Hideo
Published: July 2002

Two new insertion devices for the generation of elliptically polarized synchrotron radiation have been constructed to be installed in two electron storage rings, the Accumulation Ring for the TRISTAN project and the Photon Factory ring at KEK, National Laboratory for High Energy Physics. These new light sources are designed to produce (1) intense radiation with a degree of circular polarization (Pc) between 0.5 and 0.9 in hard x-ray region, and (2) quasimonochromatic radiation with Pc>0.7 in vacuum ultraviolet region.
Ultrahigh vacuum picosecond laser-driven electron diffraction system
Authors: Elsayed-Ali H. E. , Herman J. W.
Published: July 2002

A laser-driven picosecond time-resolved electron diffraction system operating in ultrahigh vacuum is described. A picosecond laser pulse is split into two beams. The first interacts with the sample under study. The second activates the cathode of an electron gun creating a collimated and focused electron pulse that is well synchronized with the heating laser pulse. By spatially delaying the part of the laser pulse that photoactivates the cathode from that which irradiates the sample, the electron pulse can be set to arrive at the sample at a specific time after sample irradiation. When a flat smooth sample is aligned such that the electrons are in grazing incidence on its surface, a reflection high-energy electron diffraction pattern of its first few atomic layers is generated. Analysis of the diffraction pattern provides information on the surface structure and temperature at a set time lapse between the arrival of the laser and the electron pulse to the sample. Design, characterization, and operation of this system along with an example of its application to monitor the transient surface temperature using the surface Debye–Waller effect are discussed.
Low-loss broadband multimode corrugated waveguide performance
Authors: Cavallo A. , Doane J. , Cutler R.
Published: July 2002

A 30-m-long waveguide run using circular corrugated waveguide (i.d.=6.35 cm) with a corrugated period and depth of 254 μm (0.01 in.) has been fabricated and installed on TFTR (Tokamak Fusion Test Reactor) for use in electron cyclotron emission measurements, and is the first large scale application of this type of waveguide. It is designed for low-loss (<0.01 dB/m) multimode operation between 75 and 575 GHz, and includes three E-plane and four H-plane miter bends. Single-mode measurements at 140 GHz and multimode measurements at 250 GHz indicate that both ohmic losses as well as loss due to mode conversion are negligible with this type of transmission line.
A compact, high temperature nuclear magnetic resonance probe for use in a narrow-bore superconducting magnet
Authors: Adler Stuart B. , Michaels James N. , Reimer Jeffrey A.
Published: July 2002

We report the design of a nuclear magnetic resonance (NMR) probe that can be used in narrow-bore superconducting solenoids for the observation of nuclear induction at high temperatures. The probe is compact, highly sensitive, and stable in continuous operation at temperatures up to 1050 °C. The essential feature of the probe is a water-cooled NMR coil that contains the sample-furnace; this design maximizes sensitivity and circuit stability by maintaining the probe electronics at ambient temperature. We demonstrate the design by showing high temperature 17O NMR spectra and relaxation measurements in solid barium bismuth oxide and yttria-stabilized zirconia.
A new light scattering technique for a wide-band ripplon spectroscopy at the MHz region
Authors: Sakai K. , Choi P.-K. , Tanaka Hajime , Takagi K.
Published: July 2002

A new light scattering system was developed to investigate the propagation of liquid surface waves over a wide wave-number range 4×104–3×106 m−1 (or 10 kHz–6 MHz in frequency). Thermal fluctuation of liquid surface displacement excites a surface tension wave called a ‘‘ripplon’’ whose behavior yields information on the dynamics of the liquid surface. The transmission diffraction method and some optical and electrical improvements are successfully applied to the light scattering system and the upper limit of the frequency measured was extended about two orders higher than the conventional one. The wave-number dependence of the ripplon frequency and damping constant was measured for several kinds of liquids and the results agreed well with the classical hydrodynamic theory.
A flat flame burner as calibration source for combustion research: Temperatures and species concentrations of premixed H2/air flames
Authors: Prucker S. , Meier W. , Stricker W.
Published: July 2002

A commercially available flat flame burner with a sintered porous bronze disk was used to stabilize premixed H2/air flames at atmospheric pressure. Temperatures for various stoichiometries, flow rates, and heights above the burner disk have been measured by coherent anti-Stokes Raman scattering with an accuracy of ≊2.5%. The corresponding exhaust gas compositions have been derived from equilibrium calculations. This burner together with the data presented in this article can be used for the verification or calibration of a variety of measuring techniques in combustion research.
Energetics of microvoid formation in Si from supersaturated vacancies
Authors: Cuendet Nicolas , Halicioglu Timur , Tiller William A.
Published: July 2002

Using a Tersoff-type empirical potential energy function, the free energy of formation for microvoids in silicon containing from 1 to 57 vacancies was calculated as a function of temperature and vacancy supersaturation. The results apply equally well to microvoid nucleation during crystal growth or, at low temperatures, as a consequence of ion implantation. The results indicate that homogeneous nucleation is an unlikely process for the crystal growth case where heterogeneous nucleation via adsorbate attachment to the microvoid surface is a very likely process.
Phase intergrowth in Bi2Sr2Ca2Cu3Ox superconducting thin films prepared by single cylindrical-sputtering gun
Authors: Ohkubo M. , Geerk J. , Linker G. , Meyer O.
Published: July 2002

Bi2Sr2Can−1CunOx thin films have been prepared in situ on MgO(100) by dc-sputtering employing a single cylindrical target. The thin films are of almost pure Bi2Sr2Ca2Cu3Ox (2223) or intergrowth phases known as random stacking-fault structures of two phases having adjacent n. Deviations from the sputtering conditions for the 2223 growth induce the phase intergrowth of 2212, 2223, and 2234. The phase intergrowth occurs in connection with film compositions.
Asymmetrically cut crystals as optical elements for highly collimated x-ray beams
Authors: Brauer S. , Stephenson G. B. , Sutton M. , Mochrie S. G. J. , Dierker S. B. , Fleming R. M. , Pindak R. , Robinson I. K. , Grübel G. , Als-Nielsen J. , Abernathy D. L.
Published: July 2002

Asymmetrically cut perfect crystals, in both the Laue and Bragg geometries, are examined as single crystal monochromators for x-ray beams that are collimated to a small fraction of the Darwin width, as is typical in experiments with coherent x rays. Both the Laue and asymmetric Bragg geometries are plagued by an inherent chromatic aberration that increases the beam divergence much beyond that of the symmetric Bragg geometry. Measurements from a recent experiment at the ESRF are presented to compare Si(220) (symmetric Bragg), diamond(111) (asymmetric Laue), and diamond(111) (symmetric Bragg inclined) geometries.
Evaluation of a simple method for chopping Penning surface-plasma source H− beams
Authors: Smith H. Vernon , Allison Paul , Schneider J. David , Stelzer James E. , Stevens Ralph R.
Published: July 2002

Accumulator rings proposed for use in high-intensity spallation-neutron sources require a chopped beam with ∼100-ns-wide particle-free gaps at 1–2 MHz rates, with fall and rise times ≤20 ns. Chopping the beam directly in the ion source may be an attractive way to provide the desired beam structure. Previous measurements showed that placing a grounded collar in the drift region just before the emission aperture lowers the e−/H− ratio in the Penning surface-plasma source H− beam. We electrically isolated the collar and biased it to modulate the extracted H− current. Positive collar bias decreases the H− beam by up to 90%. The fastest H− current fall and rise times achieved to date are 400 ns and 2 μs, respectively. The current fall time is close to the 300-ns pulser rise time. The current rise time is considerably longer than the 500-ns pulser fall time. Negative collar bias lowers the H− beam by up to 50%. Simulations indicate that the beam time structure will be preserved in transport from the ion source to the radio-frequency quadrupole entrance.
Ultrathin SrTiO3 films prepared by chemical vapor deposition on Nb-doped SrTiO3 substrates
Authors: Kiyotoshi Masahiro , Eguchi Kazuhiro
Published: July 2002

The SrTiO3 ultrathin film capacitors were realized on Nb-doped single-crystal SrTiO3 substrates by chemical vapor deposition. The leakage current density of 10.4 nm thick SrTiO3 thin-film capacitor was below 1×10−8 A/cm2 in the applied voltage range of −1.8 to +0.45 V, and its SiO2 equivalent thickness was 0.48 nm. The relative dielectric constant was over 160 for SrTiO3 thickness above 20 nm, but it decreased for SrTiO3 thickness below 20 nm. Dependence of leakage current on SrTiO3 film thickness was slight. These results could be explained by the existence of applied electric field concentration near the SrTiO3/electrode interface.
A scanning force microscope for simultaneous force and patch-clamp measurements on living cell tissues
Authors: Langer M. G. , Öffner W. , Wittmann H. , Flösser H. , Schaar H. , Häberle W. , Pralle A. , Ruppersberg J. P. , Hörber J. K. H.
Published: July 2002

For the investigation of mechanosensitive ion channels of living cells it is of great interest to apply very local forces in the piconewton range and to measure, simultaneously, ion currents down to 1 pA. Scanning force microscopy (SFM) is a suitable technique, that allows the application of such small forces with a lateral resolution in the range of 10 nm. We developed a novel type of experimental setup, because no existing SFM, home built or commercial, allows a simultaneous investigation of ion currents and mechanical properties of living cells. The construction consists of a SFM that is combined with an upright infrared differential interference contrast (DIC) video microscope and a conventional patch-clamp setup. Instead of the object, the force sensor is scanned to prevent relative movements between the patch pipette and the patched cell. The deflection of the SFM cantilever is detected with the so-called optical deflection method through the objective of the optical microscope. In opposite to common optical setups the laser beam was not focused on the force sensor. The presented optic creates a parallel laser beam between the objective and the SFM cantilever, which allows a vertical displacement of the sensor without any changes of the detector signal. For the three-dimensional positioning of the specimen chamber a two-axis translation stage including a vertical piezoelectric translation device was developed. The SFM tip is fixed on a combined lateral and vertical translation stage including a piezoelectric tube scanner for three-dimensional fine positioning. Thus the instrument enables an easy approach of the SFM tip to any optically identified cell structure. The head stage of the patch-clamp electronics and the patch pipette are directly fixed on the specimen stage. This prevents relative movements between patched cells and patch pipette during the approach to the SFM tip. The three-axis positioning of the patch pipette is done by a compact hydraulic manipulator. With this combined setup, subcellular structures can be identified on living cells with the video microscope and simultaneously investigated with the SFM and the patch-clamp pipette. The features of the instrument are demonstrated with preparations of cultivated neuronal cells. Simultaneous measurements of ion current and force in organotypic cultures of mechanosensitive hair cells of the inner ear are proposed, as investigations of cell tissue preparations of up to 400 μm thickness are possible with this instrument.
Phosphor thermometry at cryogenic temperatures
Authors: Cates Michael R. , Beshears David L. , Allison Stephen W. , Simmons Cathy M.
Published: July 2002

The temperature dependence of the lifetimes of two phosphors, La2O2S:Eu and Mg4FGeO6:Mn, is presented from 300 to 11 and 140 to 8 K, respectively. Emission from the D35 state of La2O2S:Eu reveals a strong temperature dependence from 11 to about 130 K, where the signal becomes too weak to measure accurately. Emission from the F24 state of Mg4FGeO6:Mn changes throughout the temperature range measured. Both of these materials are used for higher temperature thermometry applications. This work illustrates their utility down to liquid helium temperatures.
Reactive ion etching of GaN using CHF3/Ar and C2ClF5/Ar plasmas
Authors: Lee Heon , Oberman David B. , Harris James S.
Published: July 2002

III–V nitride semiconductors have great potential for optoelectronic and electronic devices due to their wide direct band gaps. Because GaN is chemically very stable, dry etching techniques must be established in order to fabricate devices. In this work, we report the reactive ion etching (RIE) of GaN using CHF3/Ar and C2ClF5/Ar plasmas. GaN films on (001) GaAs were grown by electron cyclotron resonance (ECR) plasma associated molecular beam epitaxy (MBE) and the films showed (0001)hex orientation along the surface normal. We used a Drytek DRIE-184 rf plasma discharge RIE system with no ECR discharge or high energy Ar ion beam. The effects of rf plasma power, pressure, and gas flow rates on the etch rate were investigated and the surface contamination due to RIE was examined by XPS. The etch rate varied between 60 and 470 Å/min. The conditions for etching were 100–500 W of rf plasma power, 60–300 mTorr of pressure, a CHF3 or C2ClF5 flow rate of 5–50 sccm and an Ar flow rate of 0–50 sccm. The highest etch rates were obtained with high rf plasma power and low pressure.
InAlP/InGaP strain-modulated aperiodic superlattice heterobarrier for enhanced electron confinement in visible (λ∼650 nm) light-emitting devices
Authors: Islam M. R. , Chelakara R. V. , Dupuis R. D.
Published: July 2002

We report the design, growth, and characterization of an InAlP/InGaP strain-modulated aperiodic superlattice heterobarrier (SMASH) for the enhancement of the performance of visible light-emitting devices. These InAlP/InGaP heterostructures are grown on GaAs substrates by low-pressure metalorganic chemical vapor deposition. Electron-wave reflectivity calculations show that the virtual confining potential energy for conduction-band electrons at the InAlP/InGaP interface can be increased by up to ∼660 meV by employing this novel barrier. Significant improvements in photoluminescence intensity at 300 and 4.2 K are observed from both InGaP quantum well and InGaP bulk-layer double heterostructures utilizing the SMASH structure.
Linear and nonlinear transmission of CuxS quantum dots
Authors: Klimov V. , Haring Bolivar P. , Kurz H. , Karavanskii V. , Krasovskii V. , Korkishko Yu.
Published: July 2002

CuxS nanocrystals (NC’s) are reported. The samples are prepared by a CdS-to-CuxS chemical conversion from the glasses originally containing CdS NC’s. A room-temperature linear absorption of the converted samples shows several well resolved peaks with spectral positions from red to blue. These spectral features are explained by size quantization within CuxS NC’s (∼4 nm radius) with different copper deficiency [x is in the range from 1.8 (digenite) to 2 (chalcosite)]. A strong bleaching of the samples with a 3-ns relaxation is observed in the pump–probe measurements. A high value of the third-order nonlinear susceptibility (∼10−7 esu) is derived from the nonlinear transmission spectra.
Fabrication of n- and p-channel in-plane-gate transistors from Si/SiGe/Ge heterostructures by focused laser beam writing
Authors: Holzmann M. , Baumgartner P. , Engel C. , Nützel J. F. , Abstreiter G. , Schäffler F.
Published: July 2002

Focused laser beam writing is applied for thermally activated diffusion of dopants into strained Si/Ge modulation-doped heterostructures. Lateral p- and n-type potential barriers of sub-μm width are achieved by local diffusion of boron and antimony into n- and p-type heterostructures, respectively. The potential modulation is determined from the temperature dependence of the thermionic current over the barrier. These npn and pnp structures can be used to fabricate in-plane-gate transistors which show transistor action up to room temperature.
Capillary waves in pulsed excimer laser crystallized amorphous silicon
Authors: Fork D. K. , Anderson G. B. , Boyce J. B. , Johnson R. I. , Mei P.
Published: July 2002

During short-pulse laser crystallization of amorphous silicon on quartz, surface roughening occurs via the freezing of capillary waves excited in the silicon melt. The velocity and viscous damping of these capillary waves is computed and discussed. Volume change of the silicon during solidification appears to drive liquid silicon toward the last areas of solidification. Film thickness variation observed by transmission electron microscopy and atomic force microscopy shows increased film thickness at grain boundaries, and vertices of single pulse irradiated films. This effect is most pronounced within a narrow laser fluence regime wherein large lateral grain growth occurs. For 100 nm thick amorphous silicon films on quartz, this regime extends from approximately 520 to 560 mJ/cm2; standard deviation roughness can be as large as 40 nm. These effects have important implications for large area thin film transistor manufacturing.
Micromachined room-temperature microbolometers for millimeter-wave detection
Authors: Rahman Arifur , de Lange Gert , Hu Qing
Published: July 2002

We have combined silicon micromachining technology with planar circuits to fabricate room-temperature niobium microbolometers for millimeter-wave detection. In this type of detector, a thin niobium film, with a dimension much smaller than the wavelength and fabricated on a 1 μm thick Si3N4 membrane, acts both as a radiation absorber and temperature sensor. Incident radiation is coupled into the microbolometer by a 0.37λ dipole antenna of center frequency 95 GHz with a 3 dB bandwidth of 15%, which is impedance matched with the Nb film. An electrical noise equivalent power (NEP) of 4.5×10−10 W/√Hz has been achieved. This is comparable to the best commercial room-temperature millimeter-wave detectors.
Large bandwidth and low noise in a diffusion-cooled hot-electron bolometer mixer
Authors: Skalare A. , McGrath W. R. , Bumble B. , LeDuc H. G. , Burke P. J. , Verheijen A. A. , Schoelkopf R. J. , Prober D. E.
Published: July 2002

Heterodyne measurements have been made at 533 GHz using a novel superconducting hot-electron bolometer in a waveguide mixer. The bolometer is a 0.3 μm long niobium microbridge with a superconducting transition temperature of 5 K. The short length ensures that electron diffusion dominates over electron-phonon interactions as the electron cooling mechanism, which should allow heterodyne detection with intermediate frequencies (if) of several GHz. A Y-factor response of 1.15 dB has been obtained at an if of 1.4 GHz with 77 and 295 K loads, indicating a receiver noise temperature of 650 K DSB. The −3 dB rolloff in the if response occurs at 1.7 GHz.
Millimeter-wave Hilbert-transform spectroscopy with high-T
c Josephson junctions
Authors: Divin Yu. Ya. , Schulz H. , Poppe U. , Klein N. , Urban K. , Pavlovskii V. V.
Published: July 2002

The application of Hilbert-transform spectroscopy for the measurement of high-harmonic content of the radiation from a frequency multiplier has been demonstrated in the spectral range from 60 to 450 GHz. YBa2Cu3O7−x grain-boundary Josephson junctions made on (110) NdGaO3 bicrystal substrates have been used in these experiments. The internal Josephson radiation of the junctions reveals a Lorentzian shape due to thermal noise broadening. The possibility to obtain a spectral resolution as low as 280 MHz (∼0.01 cm −1) has been shown with a Josephson junction operating at liquid-nitrogen temperature.