bluuebunny/crossref_metadata_2025 huggingface dataset:
Stability coefficients for the multianode microchannel array detector
Authors: Joseph Charles L. , Bybee Richard , Argabright Vic
Published: July 2002

We conducted a study to estimate the impact that thermal variations and electronic drifts would have on the photometric stability of the multianode microchannel array (MAMA) detectors that are currently flying aboard the space telescope imaging spectrograph (STIS). Included in the present analysis is the expected impact of preferential aging of the microchannel plate due to prolonged concentrations of light in the same location. These data and analyses were used to examine the suitability of specified electronic tolerances to achieve a photometric accuracy of ±1% over a period of 1 week, but may be also useful should the spacecraft environment begin to vary. The original parameter tolerances were found to be adequate in most cases, although a few voltages did require somewhat better tolerance specifications. The present analysis indicates the sensitivity of the STIS MAMA detectors are reproducible over long periods of time to an accuracy of 0.62% (0.33% rms and 0.29% systematic uncertainties) at an arbitrary location in the detector format. This result indicates the detectors are capable of obtaining data with a signal-to-noise ratio (S/N)≳200 in a STIS 2×2 pixel optical resolution element, consistent with observed departures found in high-signal laboratory data. Even higher S/N levels have been demonstrated on orbit using techniques that move the spectral image around on the detector.
A simple ultraviolet radiation-triggered switch with an electric field distortion gap for long-lifetime electrodes
Authors: Niedbalski Jorge
Published: July 2002

A simple high-voltage gaseous switch designed to minimize the erosion of the discharge electrodes is described. The switch is triggered by ultraviolet radiation produced by a corona pulsed discharge. A pin-shaped auxiliary electrode, centered within an orifice made on the discharge surface of a hollow anode and connected to this electrode in series with an inductor, is used to promote the contraction of the discharge channel allowing it to penetrate the orifice. The switch has been tested by discharging capacitors of 5 and 40 nF at voltages and peak currents up to 16 kV and 8 kA, respectively. Negligible erosion of the electrodes was obtained.
A two-inch dc/rf circular magnetron sputtering gun for a miniature chamber for an in situ experiment
Authors: Rue Gi-Hong , Kim Hyung-Kook
Published: July 2002

Many experiments have been made in an in situ miniature chamber for x-ray experiments using synchrotron radiation beam during sputtering. We have designed and fabricated a 2 in. circular magnetron sputtering gun for an in situ reflectivity experiment. The head diameter of the gun is 6.4 cm, the height is 4.5 cm, and the length of the vacuum tight neck is 11 cm. The permanent magnet is isolated from water for prevention of corrosion. Only one O-ring is used for both insulation and vacuum seal. Therefore, its frame is simple and lightweight, with a volume about 1/5 compared to commercial units. The target holder is not fixed so it can be adjusted for the target thickness. In multi-target sputtering, the distance between target and substrate is closer than commercial equipment so deposition rate and uniformity of the deposited film can be increased. In order to check the performance of the newly sputtering gun, SnO2 film on sapphire(0001) is grown, which turns out to be of the epitaxial single domain.
Plasma potential profile determination by a new diagnostic based on neutral particle beam injection and laser induced fluorescence
Authors: Gonçalves B. M. S. , Varandas C. A. F. , Malaquias A. , Mendonça J. T. , Cabral J. A. C.
Published: July 2002

A new method for the determination of the plasma potential radial profile based on the combination of a heavy neutral beam diagnostic, equipped with a light transparent multiple cell array detector, with a laser induced fluorescence system is presented. This profile is retrieved from the light intensities associated with decay processes following Doppler-shifted resonance excitation by the laser outside the plasma volume. Numerical studies were made for the tokamak ISTTOK assuming different sets of beam, laser, and plasma parameters. Results have shown that good spatial and temporal resolutions could be achieved with a 4 keV barium neutral beam and a 20 kW laser tuned at 4553 Å.
Diagnostics for exploding wires (abstract)
Authors: Moosman B. , Bystritskii Vitaly , Wessel F. J. , Van Drie A.
Published: July 2002

Two diagnostics, capable of imaging fast, high temperature, plasmas were used on exploding wire experiments at UC Irvine. An atmospheric pressure nitrogen laser (λ=337.1 nm) was used to generate simultaneous shadow and shearing interferogram images with a temporal resolution of ∼1 ns and a spatial resolution of 10 μm. An x-ray backlighter imaged the exploding wire 90° with respect to the laser and at approximately the same instant in time. The backlighter spatial resolution as determined by geometry and film resolution was 25 μm. Copper wires of diameters (25, 50, and 100 μm) and steel wire d=25 μm were exploded in vacuum (10−5 Torr) at a maximum current level of 12 kA, by a rectified marx bank at a voltage of 50 kV and a current rise time (quarter period) of 900 ns. Copper wires which were cleaned and then resistively heated under vacuum to incandescence for several hours prior to high current initiation, exhibited greater expansion velocities at peak current than wires which had not been heated prior to discharge. Axial variations on the surface of the wire observed with the laser were found to correlate with bulk axial mass differences from x-ray backlighting. High electron density, measured near the opaque surface of the exploding wire, suggests that much of the current is shunted outward away from the bulk of the wire.
Polarized laser-induced fluorescence spectroscopy for measuring electric field distribution in plasmas
Authors: Watanabe M. , Takiyama K. , Oda T.
Published: July 2002

A sensitive and reliable spectroscopic system measuring simultaneously polarized components of time-resolved laser induced fluorescence (LIF) is being developed for determining electric field distribution in transient plasmas under strong magnetic field. In this LIF method which we have already proposed, only the polarization has to be observed of a LIF due to a laser-excited forbidden transition caused by both the Stark effect and the electric quadrupole (QDP) moment in the plasmas. Temporal evolution of both the polarized LIF components is simultaneously observed using a Glan–Thompson polarizing beamsplitter with extinction ratio of 10−5 and a pair of photomultipliers with fast rise time. The polarization components observed in a hollow cathode discharge He plasma under magnetic field of 2.5 kG were successfully analyzed and electric field distribution in the sheath region was accurately estimated using this procedure. It was also shown that electric field strength was determined from the intensity ratio of the Stark and QDP components separated in the strong magnetic field. We briefly discuss the applicability of this spectroscopic system to diagnostic in the edge region of tokamak plasmas.
Prototype tests of a combined CO2 laser interferometer/polarimeter for ITER (abstract)
Authors: Carlstrom T. N. , Snider R. T.
Published: July 2002

Line density measurements on ITER are expected to be provided by a conventional vibration-compensated CO2 laser interferometer. This type of interferometer relies on maintaining an accurate measurement of hundreds of vibration fringes during the entire time history of the plasma. Because of the very long pulse lengths (1000 s) and the possibility of fringe counting errors, a second method that measures the Faraday rotation of a laser beam with a tangential laser beam path through the plasma will be used to provide a history-independent measurement of the line density with somewhat reduced accuracy. These two measurements can be accomplished in a combined interferometer/polarimeter system that uses a single CO2 laser and detector. We have constructed a prototype of this type of system, which uses two acousto-optic modulators to generate two beams, shifted from the laser frequency by 40 and 45 MHz. These probe beams are converted to left- and right-hand circular polarization and combined into a single probe beam. Vibrations are simulated by moving a mirror in the reference beam path, and the Faraday rotation is simulated by rotating the linear polarized probe beam. Frequency analysis of the interference signal from a single detector is used to separate the phase of the interferometer and the phase of the polarization rotation. Limits on the phase resolution of the two methods and possible sources of error will be presented.
Neutral beam spectroscopy for equilibrium and stability measurements for the PEGASUS toroidal experiment (abstract)
Authors: Thorson T. , Fonck R. , Lewicki B.
Published: July 2002

An optical neutral beam spectroscopy system is being designed to provide equilibrium and stability measurements for the PEGASUS toroidal experiment. Spatially localized measurements of the electron temperature and plasma density are possible by observing the intensity of the collisionally induced neutral beam fluorescence. In a helium beam, the population of the singlet levels are relatively independent of the plasma temperature compared to the triplet levels. Therefore, the ratio of intensities of a triplet transition (e.g., 33S→23P, λ=706.5 nm) to a singlet transition (e.g., 31P→21S, λ=501.6 nm) provides a measure of the local plasma temperature for the range 10 eV<Te<1.0 keV. The plasma density profile can be inferred from the attenuation of the beam fluorescence signal as the beam passes through the plasma. Additionally in a deuterium beam, the local plasma density can be directly inferred from the local radial gradient in the observed beam fluorescence signal. Plasma stability will be studied with localized magnetohydrodynamics measurements via beam emission spectroscopy, which otherwise is problematic for low-field spherical plasmas.
Apparatus for statistical studies of heterogeneous nucleation
Authors: Seeley L. H. , Seidler G. T. , Dash J. G.
Published: July 2002

We report a new instrument for studies of heterogeneous nucleation rates for materials with nucleation temperatures in the range between −30 °C and room temperature. This device is particularly well suited for studies of heterogeneous nucleation of ice from liquid water for a diverse selection of nucleation agents. This instrument allows rapid, automated sampling of nucleation temperatures for a single sample following a specified temperature profile. A complete data set that characterizes the temperature dependence of heterogeneous nucleation rates by a specific substrate can be obtained in a few days. In this article we describe initial studies of ice nucleation on borosilicate glass with two different surface treatments.
A new electro-optic hybrid current-sensing scheme for current measurement at high voltage
Authors: Zhang Gang , Li Shaohui , Qin Yi , Zhang Zhipeng
Published: July 2002

A new electro-optic hybrid current sensor is presented here. The sensor consists of three parts: first is a Rogowski coil and integrator whose output voltage is proportional to the current flowing in the power line. Second is a combination voltage to frequency converter and electro-optic converter. The combination converter transforms the integrated Rogowski coil voltage into a FM optical signal. The optical signal can then be transmitted to a low voltage region via an optical fiber for subsequent demodulation processing. Third is an intrinsic power supply in which a small conventional current transformer is used to draw power from the power line. A current sensor based on this design was developed, having a diameter of 15 cm, length of 30 cm, and weight of 2 kg, and has been working well at a 110 kV substation for two years. This sensor features small size, light weight, high accuracy, low cost, and reduced hazard.
Commissioning and initial operation of a radioactive beam ion source at ISAC
Authors: Dombsky M. , Bishop D. , Bricault P. , Dale D. , Hurst A. , Jayamanna K. , Keitel R. , Olivo M. , Schmor P. , Stanford G.
Published: July 2002

In November of 1998, the ISAC radioactive beam facility at TRIUMF started delivering on-line isotope separated radioactive beams to experiments. A surface ionization source developed for ISAC has been used to commission the mass separator and beam transport systems and is providing radioactive beams to the first generation of ISAC experiments. The ion source is integral with the radioactive beam production target and is designed to be simple, radiation hard, inexpensive, and easily exchanged by remote-handling techniques. The ion source and its extraction column are suspended at the bottom of ∼2 m of steel shielding incorporated in the target module. The module is suspended in a vacuum tank with primary and secondary vacuum systems. All services for the target/ion source and beam extraction system are ducted through the module shielding. The first sets of beam transport elements and beam diagnostic devices are similarly suspended in vacuum at the bottom of two additional shielded modules. Ion beam characteristics can be routinely monitored during on-line operation by a system of Faraday cups, wire scanners, “harp” monitors, and a novel emittance measurement apparatus that can measure beam emittance in both horizontal and vertical planes. The diagnostics devices are capable of resolving beam signals down to the 10 pA range.
A novel intensity interferometer for synchrotron radiation in the vacuum ultraviolet and soft x-ray regions
Authors: Tai RenZhong , Takayama Yasuhiro , Takaya Noriko , Miyahara Tsuneaki , Yamamoto Shigeru , Sugiyama Hiroshi , Urakawa Junji , Hayano Hitoshi , Ando Masami
Published: July 2002

Based upon a method of Hanbury-Brown and Twiss, while considering the nonstationary characteristics of synchrotron radiation (SR), a novel optical intensity interferometer was constructed to extract the true two-photon correlation of soft x-ray SR. This intensity interferometer consists of an optical vacuum chamber, which includes a wire scanner, a beam divider, and a grating monochromator with a coherence time modulator, and of an electric correlator which completes the multiplication of two broadband electric currents. The technique of coherence time modulation, together with the two bandpass filters in the correlator, play an essential role to cancel a huge trivial correlation, which arises from the accidental coincidence between a pair of divided pulses being largely enhanced by the finite slow time response of the detection system compared to the coherence time of the photon. A preliminary performance test was conducted, and the results exhibit satisfactory functions of this interferometer.
Measurement of mechanical vibrations excited in aluminum resonators by 0.6 GeV electrons
Authors: van Albada G. D. , Coccia E. , Fafone V. , van der Graaf H. , Heijboer G. , van Holten J. W. , Kasdorp W. J. , van der Laan J. B. , Lapikás L. , Mazzitelli G. , Nooren G. J. L. , Noteboom C. W. J. , Oberski J. E. J. , Pallottino G. , Peek H. Z. , Ronga F. , Schimmel A. , Sluijk T. G. B. W. , Steman P. , Venema J. , de Witt Huberts P. K. A.
Published: July 2002

We present measurements of mechanical vibrations induced by 0.6 GeV electrons impinging on cylindrical and spherical aluminum resonators. To monitor the amplitude of the resonator’s vibrational modes we used piezoelectric ceramic sensors calibrated by standard accelerometers. Calculations using the thermo-acoustic conversion model agree well with the experimental data, as demonstrated by specific variations of the excitation strengths with the absorbed energy, and with the traversing particles’ track positions. For the first longitudinal mode of the cylindrical resonator we measured a conversion factor of 7.4±1.4 nm/J, confirming the model value of 10 nm/J. Also, for the spherical resonator, we found the model values for the L=2 and L=1 mode amplitudes to be consistent with our measurement. We thus have confirmed the applicability of the model, and we note that calculations based on the model have shown that next generation resonant mass gravitational wave detectors can only be expected to reach their intended ultrahigh sensitivity if they are shielded by an appreciable amount of rock, where a veto detector can reduce the background of remaining impinging cosmic rays effectively.
Plasma and ion barrier for electron beam spot stability
Authors: Kwan Thomas J. T. , Snell Charles M.
Published: July 2002

High-current electron beams of small spot size are used for high-resolution x-ray radiography of dense objects. Intense energy deposition in the bremsstrahlung target causes generation of ions which can propagate upstream and disrupt the electron beam. We have investigated the use of a thin beryllium foil placed 1–2 cm in front of the target, which serves as a barrier for the ions but is essentially transparent to the incoming electron beam. Analysis and computer simulations confirm that this confinement method will halt ion propagation and preserve the spot size stability of the electron beam.
Microsphere plate detectors used with a compact Mott polarimeter for time-of-flight studies
Authors: Snell G. , Viefhaus J. , Dunning F. B. , Berrah N.
Published: July 2002

A compact retarding-potential Mott polarimeter combined with microsphere plates (MSP) as electron detectors was built to perform spin-resolved time-of-flight electron spectroscopy. The comparison of the performance of MSP and channeltron detectors shows that the MSP detector has a better time resolution but a lower efficiency. The overall time resolution of the system was determined to be 350 ps using synchrotron radiation pulses.
A sensitive dispersion interferometer with high temporal resolution for electron density measurements
Authors: Licht Valentin , Bluhm Hansjoachim
Published: July 2002

A dispersion interferometer with a sensitivity of up to 10−4 fringe shifts and a time resolution of about 1 ns was developed. This time resolution exceeds previous systems by three orders. The operation of the dispersion interferometer and its characteristic properties are discussed and the experimental setup of the installation is explained in detail. The stability of the interferometer was tested and it was shown that its operation point drifts less than 0.25 rad/h. The interferometer was used to investigate the high power ion diodes at the pulse generator KALIF, where focused proton beams with power densities of up to 1 TW/cm2 are generated. For the very first time the electron line density inside the diode gap, where the protons are accelerated, could be directly measured. The line density was on the order of several 1013 cm−2. A straightforward estimation of the line density using a simplified diode model proved to be in excellent agreement with the results. The dispersion interferometer can be used for sensitive electron density measurements on nanosecond time scales. Further developments to improve the sensitivity are discussed.
High Tc superconducting asymmetric gradiometer for biomagnetic applications
Authors: Kouznetsov K. A. , Borgmann J. , Clarke John
Published: July 2002

We describe a high transition temperature superconducting, first-order gradiometer intended for biomagnetic measurements in an unshielded environment. The gradiometer involves a single-layer, planar flux transformer with two loops of unequal size, the smaller of which is inductively coupled to the pickup loop of a directly coupled magnetometer. In this configuration, the presence of the flux transformer reduces the sensitivity of the magnetometer by only about 5%. The flux transformer is patterned in a thin film of YBa2Cu3O7−δ deposited on a 100 mm diam wafer, and has a baseline of 48 mm. The flux transformer and magnetometer substrates are permanently bonded together in a flipchip arrangement. The common mode rejection of uniform magnetic field fluctuations in any direction is better than 1 part per 100. The outputs of two such gradiometers are subtracted to form a second-order gradiometer, which rejects first-order gradient fluctuations to about 1 part in 100. With the aid of three orthogonally mounted magnetometers, one can reduce the response of the gradiometers to uniform field fluctuations to below 100 ppm. This system is used to detect magnetic signals from the human heart in an unshielded environment.
Enhancement of radiative recombination in Si-based quantum wells with neighboring confinement structure
Authors: Usami N. , Issiki F. , Nayak D. K. , Shiraki Y. , Fukatsu S.
Published: July 2002

Intense photoluminescence (PL) was observed from a new class of Si-based quantum well structures (QWs), that is, neighboring confinement structure (NCS). NCS consists of a single pair of tensile-strained-Si layer and a compressive-strained Si1−yGey layer sandwiched by completely relaxed Si1−xGex ( layers. In spite of the indirect band structure in real and k spaces, radiative recombination was enhanced compared with not only type-II strained-Si/relaxed-Si1−xGex QWs but also type-I strained-Si1−yGey/relaxed-Si1−xGex QWs. PL without phonon participation was found to dominate the spectrum possibly due to the effective carrier confinement for both electrons and holes. Quantum confinement effect was clearly observed by varying the well width, showing that the expected band alignment is realized.
Transport properties of two-dimensional electron gas in AlGaAs/GaAs selectively doped heterojunctions with embedded InAs quantum dots
Authors: Sakaki H. , Yusa G. , Someya T. , Ohno Y. , Noda T. , Akiyama H. , Kadoya Y. , Noge H.
Published: July 2002

Transport properties of two-dimensional electron gas (2DEG) are studied in selectively doped GaAs/n-AlGaAs heterojunctions, in which nanometer-scale InAs dots are embedded in the vicinity of the GaAs channel. When the distance Wd between the InAs dot layer and the channel is reduced from 80 to 15 nm, the mobility μ of electrons at 77 K decreases drastically from 1.1×105 to 1.1 ×103 cm2/V s, while the carrier concentration increases from 1.1×1011 to 5.3×1011 cm−2. Such a reduction of mobility is found only when the average thickness of InAs layer is above the onset level (∼1.5 monolayer) for the dot formation. Origins of these changes in μ and Ns are discussed in connection with dot-induced modulations of the electronic potential V(r) in the channel.
Transport characteristics of polycrystalline-silicon wire influenced by single-electron charging at room temperature
Authors: Yano Kazuo , Ishii Tomoyuki , Hashimoto Takashi , Kobayashi Takashi , Murai Fumio , Seki Koichi
Published: July 2002

Conductance of ultrathin polycrystalline silicon wire was measured and periodic plateaus, which provide evidence of the Coulomb staircase at room temperature, are observed. This shows that single-electron charging effects are important to transport in a semiconductor system at room temperature. The very small (∼10-nm diam) silicon-grain structure is presumably playing a key role in creating the observed effects. From the temperature dependence, the electron transport is clearly dominated by the thermal emission, whose activation energy is more than 400 meV. This reveals that the treatment beyond well-established single-electron tunneling, including thermal-emission transfer, is essential to understand such high-temperature charging effects in semiconductor systems.
Interface of iron metal/aluminum nitride multilayered composite film
Authors: Kikkawa Shinichi , Fujiki Mitsushi , Takahashi Masao , Kanamaru Fumikazu , Yoshioka Hideki , Hinomura Tohru , Nasu Saburo , Watanabe Iwao
Published: July 2002

Several kinds of multilayer films were sputter deposited between iron metal and AlN at room temperature up to a total film thickness of about 1 μm. The formation of iron nitride at the interface was explicitly observed on the film with a single-layer thickness of about 6 nm by He ion yield x-ray absorption spectroscopy and conversation electron Mössbauer spectroscopy. The partial reduction of AlN to aluminum metal at the interface was also observed by x-ray photoelectron spectroscopy depth profile. Metal substitution between Fe and AlN occurred even at room temperature at the Fe/AlN interface.
Laser induced impact ionization in semiconductors: A Monte Carlo study for silicon
Authors: Kochman Boaz , Yeom Keesoo , Singh Jasprit
Published: July 2002

Monte Carlo computer simulations are carried out to study impact ionization due to a sinusoidal field present in high-power laser pulses. As an application we study the impact ionization coefficient, α, for electrons in silicon as a function of the field frequency, pulse width, and the rms value of the field. In all cases we stay below the frequency values where band-to-band absorption would create electron-hole pairs. As is the case for constant (dc) fields, log α is found to be linear with field strength. For fields oscillating at frequencies much below the inverse of the carrier scattering rate, the impact ionization coefficient is found to have the same value as in the constant field case with the rms field replacing the dc value. At higher frequencies the impact ionization rate decreases. The dependence of α on field frequency and pulse width is studied.
Resonant tunneling properties of single electron transistors with a novel double-gate geometry
Authors: Fujisawa Toshimasa , Tarucha Seigo
Published: July 2002

We describe the operation of single electron transistors with a double-gate geometry defined by Ga focused ion beam implanted in-plane gates and line Schottky gates. The in-plane gates are used to squeeze the channel and to increase the charging energy. The Schottky gates are placed on the channel to form the tunnel junctions. Independent control of these gates is useful to define the geometry of single electron transistors. We found strong resonances exhibiting negative differential resistance in the small devices, which is attributed to tunneling through zero-dimensional states when the barrier has a parabolic-shaped potential.
Scanning microdeformation microscopy in reflection mode
Authors: Vairac P. , Cretin B.
Published: July 2002

A scanning microdeformation microscope based on a vibrating tip with piezoelectric detection in a transmission operating mode is upgraded to operate in reflection mode. Images which reveal subsurface inhomogeneities in silicon and metallic samples are presented. As in the first configuration the lateral resolution and the apparent penetration depth is related to the tip diameter.
Effect of texture on grain boundary misorientation distributions in polycrystalline high temperature superconductors
Authors: Goyal A. , Specht E. D. , Kroeger D. M. , Mason T. A.
Published: July 2002

Computer simulations were performed to determine the most probable grain boundary misorientation distribution (GBMD) in model polycrystalline superconductors. GBMDs in polycrystalline superconductors can be expected to dictate the macroscopic transport critical current density, Jc. Calculations were performed by simulating model polycrystals and then determining the GBMD. Such distributions were calculated for random materials having cubic, tetragonal, and orthorhombic crystal symmetry. In addition, since most high temperature superconductors are tetragonal or pseudotetragonal, the effect of macroscopic uniaxial and biaxial grain orientation texture on the GBMD was determined for tetragonal materials. It is found that macroscopic texture drastically alters the grain boundary misorientation distribution. The fraction of low angle boundaries increases significantly with uniaxial and biaxial texture. The results of this study are important in correlating the macroscopic transport Jc with the measured grain orientation texture as determined by x-ray diffraction
Upconversion dye-doped polymer fiber laser
Authors: He Guang S. , Bhawalkar Jayant D. , Zhao Chan F. , Park Chi K. , Prasad Paras N.
Published: July 2002

Two-photon pumped frequency upconversion cavity lasing at ∼610 nm is accomplished in a dye-doped polymer fiber system, pumped with ∼12 ns and 1.06 μm IR laser pulses. The dopant is a novel dye, trans-4-[p-(N-hydroxyethyl-N-methylamino)styryl]-N-methylpyridinium iodide, abbreviated as ASPI, which possesses a greater two-photon absorption cross section and stronger upconversion fluorescence emission compared to common commercial dyes (such as rhodamine 6G). Using a Q-switched Nd:YAG pulse laser as the pump source, cavity lasing could be achieved in a 3-cm-long ASPI-doped poly(2-hydroxyethyl methacrylate) solid fiber of 100 μm diameter. The experimental results of spectral, temporal, spatial, and input–output characteristics of the cavity lasing are presented. The slope efficiency of upconversion lasing was 0.9%.
Elasto-optic anisotropy and polarization orientation of vertical-cavity surface-emitting semiconductor lasers
Authors: Jansen van Doorn A. K. , van Exter M. P. , Woerdman J. P.
Published: July 2002

We report a new technique to apply strain to a vertical-cavity surface-emitting semiconductor laser. This has allowed us to study the relation between strain and birefringence. We have found that the corresponding tensor is anisotropic, with a measured anisotropy 2p44/(p11−p12)=4.7±0.6. This anisotropy explains the natural preference of the polarization for the [110]/[11̄0] axes.
Shunted bicrystal Josephson junctions arrays for voltage standards
Authors: Klushin A. M. , Prusseit W. , Sodtke E. , Borovitskii S. I. , Amatuni L. E. , Kohlstedt H.
Published: July 2002

Series arrays of 365 shunted YBa2Cu3O7−x Josephson junctions on yttria-stabilized zirconia bicrystals were investigated under microwave irradiation in the K-band. Sub-arrays of up to 39 junctions were synchronized to the external microwave power at a temperature of 15 K. Although there was a considerable spread in the critical currents of the junctions and in the microwave bias current distribution, a first Shapiro step with a height of 30% of the total critical current of the sub-array was obtained by using an external shunt resistor, thus reducing the spread in normal resistances to 5%. Such high-Tc cryoelectronic circuits are applicable for voltage standards and precision digital-analog converters.
Spectra investigation on Hall–Petch relationship in nanocrystalline Fe78Si9B13 alloy
Authors: Li Jian-Min , Quan Ming-Xiu , Hu Zhuang-Qi
Published: July 2002

A complicated behavior was indicated in nanocrystalline Fe78Si9B13 alloy with grain size lower than 65 nm. No sign of dislocations after deformation has been found in nanocrystalline material, suggesting that it is unlikely that the dislocation pileup is involved. The reduction of the mean hyperfine field is attributed to a decrease in the number of nearest neighbor atoms on the grain boundaries, which may be responsible for the softening behavior in nanocrystalline material with an average crystallite size of 65 nm. An increasing peak of the phonon mode near 900 cm−1, reflecting strong electron–atom coupling in grain boundary of nanocrystalline material, was observed.
Electronic diffusivity measurement in silicon by photothermal microscopy
Authors: Forget Benoît C. , Barbereau Isabelle , Fournier Danièle , Tuli Suneet , Battacharyya Amalendu B.
Published: July 2002

In this letter we demonstrate that a photothermal microscopy experiment can be used to determine the electronic diffusivity (or carrier mobility) in the same way it is now widely used to measure locally thermal diffusivity of various nonsemiconductor materials. The main difficulty lies in the fact that in order to separate thermal and carrier diffusion, the experiment must be performed for a relatively large distance between the pump and probe beams. Photothermal signals are therefore rather weak and great experimental care must be taken. We present and discuss experimental results on Si.
Hole traps in oxide layers thermally grown on SiC
Authors: Afanas’ev V. V. , Stesmans A.
Published: July 2002

Hole trapping in the oxides thermally grown on different polytypes of SiC (3C, 4H, 6H) was studied using photogeneration of charge carriers in SiO2 and electron-spin-resonance spectroscopy. Oxygen vacancy defects were found to be the dominant hole traps in the oxide. Generation of thermally unstable SiC/SiO2 interface states is observed during hole injection, which resembles creation of hydrogen-related states at the Si/SiO2 interface.
In vivo laser computed tomographic imaging of human fingers by coherent detection imaging method using different wavelengths in near infrared region
Authors: Devaraj B. , Takeda M. , Kobayashi M. , Usa M. , Chan K. P. , Watanabe Y. , Yuasa T. , Akatsuka T. , Yamada M. , Inaba H.
Published: July 2002

We report in vivo laser computed tomographic images of the proximal interphalangeal joint region of a healthy human volunteer’s index finger. The laser computed tomographic (CT) images were obtained with a highly sensitive coherent detection imaging method that is based on the optical heterodyne detection method. These laser CT images are compared at the wavelengths of 715 nm and 1.064 μm and with images obtained by conventional imaging methods such as x-ray CT and magnetic resonance imaging. Internal structures of the proximal interphalangeal joint region could be clearly identified in the laser CT images.
Time-resolved cathodoluminescence study of carrier relaxation in strained (InP)2/(GaP)2 quantum wires
Authors: Rich D. H. , Tang Y.
Published: July 2002

The carrier relaxation kinetics and nonlinear optical properties of strain-induced laterally ordered (InP)2/(GaP)2 quantum wire (QWR) samples were examined with time-resolved cathodoluminescence. A temperature dependence of the QWR luminescence decay time reveals that thermal activation of carriers in the QWR and transfer to and from In0.49Ga0.51P barriers plays an important role in determining the measured lifetimes. The presence of disorder in the QWRs was found to induce inhomogeneous regions which exhibit large variations in carrier capture and band filling.
Differential reflectance spectroscopy of GaAs/GaAlAs at elevated temperatures
Authors: Kraisingdecha P. , Gal M.
Published: July 2002

Differential reflectance (DR), a contactless optical modulation technique, has been used to study GaAs/AlGaAs quantum wells and bulk GaAs, over a wide temperature range (77<T<600 K). The objective of this study was to demonstrate that DR, unlike most optical modulation spectroscopies, can be effectively and effortlessly used at elevated temperatures, and, thus, provide considerable potential for in situ monitoring. We have used DR to measure the temperature dependence of several critical points of GaAs and AlxGa1−xAs (x=0.31).
Optical and magneto-optical properties of Co(001)/Ge/Co sandwiches
Authors: Kang S. S. , Jin G. J. , Xu X. N. , Hu A. , Zhai H. R. , Jiang S. S. , Chen Y. , Zhu W. R. , Dong G. S. , Zhou S. M. , Jin X. , Feng J. W.
Published: July 2002

A series of bcc-Co(001)/Ge/Co trilayers was grown on a GaAs(001) substrate by the molecular beam epitaxy technique. The optical and magneto-optical properties of the samples were studied. An oscillatory variation of the magneto-optical Kerr effect (MOKE) with the thickness of the Ge spacers was observed. We conclude that the effective optical constants as well as the real and imaginary off-diagonal element of the dielectric tensor should be considered in explanation of the MOKE activities since both have a large influence on the MOKE oscillations. Moreover, the coercivity and magnetization also oscillate with the Ge layer thickness.
Electric field dependent EL2 capture coefficient in semi-insulating GaAs obtained from propagating high field domains
Authors: Piazza F. , Christianen P. C. M. , Maan J. C.
Published: July 2002

We have determined the electric field dependence of the carrier capture coefficient of the EL2 traps in semi-insulating GaAs up to 7 kV/cm by means of the quantitative analysis of propagating high electric field domains. The experimental data show a trapping coefficient which is proportional to the electron drift velocity, supporting the microscopic model of electric field enhanced trapping of carriers over a configurational barrier.
Room-temperature electroluminescence from Si/Ge/Si1−xGex quantum-well diodes grown by molecular-beam epitaxy
Authors: Presting H. , Zinke T. , Splett A. , Kibbel H. , Jaros M.
Published: July 2002

Tunable room-temperature electroluminescence, photocurrent, and photoluminescence in the near infrared (λ∼1.3 μm) has been observed from Ge/Si/Ge/Si1−xGex quantum-well (QW) diodes grown by molecular-beam epitaxy. The QWs are grown on a p+-doped 〈100〉-Si substrate and consist of two thin Ge wells separated by a thicker Si middle layer, and the whole structure is embedded by two Si0.85Ge0.15 alloy layers. Our theoretical analysis of the data suggests that the strength of the spectra is linked to states localized at the interface.
Infrared spectroscopy study of the Si–SiO2 interface
Authors: Okuno Yasutoshi , Park Kyung-ho
Published: July 2002

The thermally oxidized vicinal Si(001)– SiO2 interface was studied by using polarized beam Fourier transform infrared spectroscopy and cross-sectional transmission electron microscopy. We observed an anisotropic absorption of the Si–O–Si stretching mode at the vicinal interface, which is explained with a proposed Si–SiO2 interface model; a single-layer/double-layer stepped structure. We also show that the interface of the Si–SiO2 formed at 1000 °C consists mostly of a double-layer stepped structure with a single domain terrace, while that formed at 850 °C has a single-layer stepped structure.
Molecular dynamics calculation of the Zr(Ni) enthalpy of mixing
Authors: Cleri Fabrizio , Mazzone Giorgio , Rosato Vittorio
Published: July 2002

The Zr-terminal portion of the Ni–Zr phase diagram was studied by means of molecular dynamics simulations. The internal energy and the enthalpy of mixing at 300 K of the α- and β-Zr(Ni) solid solutions and of the Zr–Ni amorphous phase were calculated for Ni concentrations ≤10 at. %. The values of the enthalpy of mixing obtained are positive for the terminal solid solutions, and negative for the amorphous phase. This behavior is attributed to the differences in strain energy generated in the Zr lattice or in the amorphous phase by Ni atoms. Implications of these results relevant to the problem of amorphization in metallic systems by solid-state reactions are discussed.
Microstructure of laterally oxidized AlxGa1−xAs layers in vertical-cavity lasers
Authors: Twesten R. D. , Follstaedt D. M. , Choquette K. D. , Schneider R. P.
Published: July 2002

We have studied the lateral oxidation of AlxGa1−xAs (x=0.98 and 0.92) layers contained in vertical-cavity lasers using cross-sectional transmission electron microscopy. We find a fine-grained (∼4 nm) cubic spinel phase of Al2O3 in both the 2% Ga- and 8% Ga-oxidized layers. The 8% Ga-oxidized layers contract vertically by 6.7% and not the expected 20% for a fully dense Al2O3 layer, with the 2% Ga-oxidized layers showing a similar contraction. We observe a ∼17-nm-thick amorphous interface between the oxidized and unoxidized AlxGa1−xAs layers, which may account for the excellent electrical properties of these devices. We also observe metastable amorphous cavities associated with the moving reaction front. We infer the reaction proceeds from an initial amorphous phase that then transforms to a porous γ-Al 2O3 layer.
Optical detection of charge carriers in organic light-emitting diodes
Authors: Redecker M. , Bässler H.
Published: July 2002

A modulation technique is described to measure the optical absorption due to majority carriers (holes) in single layer and bilayer organic light-emitting diodes. It allows determination of the space-charge density inside the device at a given current, the time response of the system and the charge carrier mobility.
Low-threshold picosecond optical parametric oscillation in quasi-phase-matched lithium niobate
Authors: Pruneri V. , Butterworth S. D. , Hanna D. C.
Published: July 2002

We report a singly resonant optical parametric oscillator in periodically poled lithium niobate, synchronously pumped by the second harmonic of an amplified 10 μs pulse train from a continuous wave mode-locked Nd:YLF laser. Pulses of ∼2 ps duration have been generated over the tuning range from 883 to 1285 nm with a typical threshold of 200 mW average power within the 10 μs envelope. The M2 beam quality factor for the generated signal was ∼1.1, indicating absence of any significant photorefractive damage.
Carrier transport in ordered and disordered In0.53Ga0.47As
Authors: Ahrenkiel R. K. , Ahrenkiel S. P. , Arent D. J. , Olson J. M.
Published: July 2002

Room temperature recombination dynamics have been studied in partially ordered and disordered ternary alloys of In0.53Ga0.47As by correlated measurements of transmission electron diffraction and photoconductive decay. Ultrahigh frequency photoconductive decay measurements show that pulsed yttrium-aluminum-garnet laser-induced excess carriers in disordered films decay by conventional mechanisms such as the Shockley–Read–Hall effect. In highly ordered ternaries, recombination of excess carriers is retarded by some mechanisms such as charge separation. Excess carrier lifetimes exceeding several hundred microseconds have been observed.
Self-organized CdSe quantum dots onto cleaved GaAs (110) originating from Stranski–Krastanow growth mode
Authors: Ko Hyun-Chul , Park Doo-Cheol , Kawakami Yoichi , Fujita Shizuo , Fujita Shigeo
Published: July 2002

Self-organized CdSe/ZnSe quantum dots (QDs) have been fabricated on GaAs (110) crystal surfaces, which were obtained by cleaving GaAs (100) wafers in ultrahigh vacuum. CdSe showed a conventional Stranski–Krastanow growth mode on the ZnSe (110) lower cladding layer, whose surfaces are atomically flat. The wetting layers, which are compose of quantum wells with well widths of 1, 2, and 3 monomolecular layers, showed sharp photoluminescence (PL). The fabricated CdSe QDs showed intense green PL spectra, whose peak is located at 2.192 eV, with a linewidth of 0.24 eV. The state filling effect in CdSe QDs was also observed by employing excitation power dependence of the PL intensity.
Micron-sized control of molecular orientation: Thin film deposition of liquid crystalline polymer on polyimide layer exposed with a linearly polarized laser
Authors: Itadani Toshiaki , Saito Koichi , Niino Hiroyuki , Yabe Akira
Published: July 2002

Linearly polarized laser chemical vapor deposition of liquid crystalline polymer was carried out on the polyimide layer which was exposed with a linearly polarized laser. We used 4[ω(2-methylpropenoyloxy)hexyloxy]-4′-cyanobiphenyl as a source of polymer film and a KrF excimer laser as an UV laser light source. Before deposition, exposure to a polyimide layer on a substrate was performed through a photomask. In both exposed and nonexposed areas, the film was deposited during laser irradiation. The molecular orientation of the film in the exposed area was perpendicular to the polarization of the exposed laser beam while that in the nonexposed area was parallel to the polarization of a deposition laser beam.
Diffuse reflectance spectroscopy measurement of substrate temperature and temperature transient during molecular beam epitaxy and implications for low-temperature III–V epitaxy
Authors: Thompson P. , Li Y. , Zhou J. J. , Sato D. L. , Flanders L. , Lee H. P.
Published: July 2002

We report diffuse reflectance spectroscopy (DRS) measurement of Knudsen cell induced radiative heating of the sample during molecular beam epitaxy of GaAs at substrate temperatures between 200 and 600 °C. The temperature rises, as large as 12 °C, were observed for In-bonded samples at a substrate temperature of 200 °C. As-grown GaAs layers deposited between 200 and 300 °C are characterized using double crystal x-ray diffraction. The onset of a distinct x-ray peak associated with the low-temperature grown GaAs layer is identified, at a DRS measured temperature between 260 and 270 °C.
Local identification and mapping of the C49 and C54 titanium phases in submicron structures by micro-Raman spectroscopy
Authors: De Wolf I. , Howard D. J. , Lauwers A. , Maex K. , Maes H. E.
Published: July 2002

In this letter, it is shown that micro-Raman spectroscopy allows easy, nondestructive determination of the C49 and C54 phase of titanium silicide with μm resolution within single structures with area dimensions down to 1×1 μm2 and along isolated line structures with widths down to 0.25 μm. The micro-Raman spectroscopy technique is used to study isolated 0.25–5-μm-wide TiSi2 lines with thicknesses as small as 16 nm that are formed in both crystalline Si and polycrystalline Si. The phase mapping ability of the technique is demonstrated on several 80-μm-long, 0.35-μm-wide TiSi2 lines that are part of four-terminal line resistance devices created using complementary metal–oxide–semiconductor processing.
Onionlike structures and small nested fullerenes formation under electron irradiation of turbostratic BC2N
Authors: Stephan O. , Bando Y. , Dussarrat C. , Kurashima K. , Sasaki T. , Tamiya T. , Akaishi M.
Published: July 2002

Turbostratic BC2N samples were exposed to intense irradiation regimes in a high resolution electron microscope equipped with a field emission gun. Electron energy loss spectroscopy (EELS) analysis was used to check the sp2-bonding type and the composition of the starting materials. In highly crystalline areas, we observed a tendency for the basal planes to curl and form large “open” onionlike features. According to EELS quantification, no change of the composition occurs during their formation. Very occasionally, small nested fullerenes of less than 10 shells each with dimensions of the very internal shell close to that of a C60 were observed. These onions are thought to arise from the bending of a few basal planes of the planar starting material.
Observation of bistability in GaAs/AlAs superlattices
Authors: Zhang Yaohui , Klann Robert , Ploog Klaus H. , Grahn Holger T.
Published: July 2002

We have experimentally observed a new kind of current bistability in the time-averaged current-voltage (I-V) characteristic of doped, weakly coupled GaAs/AlAs superlattices, in which the transport is dominated by sequential resonant tunneling between adjacent quantum wells. Time-resolved current measurements show that in some cases the bistability is correlated with a subcritical Hopf bifurcation, while in other cases a discontinuous change of the current oscillation frequency is observed in the bistable region. The origin of this new bistability is attributed to a change of the space charge layer in the superlattice involving charging and discharging effects, which creates a feedback to the external bias.
Real space transfer in a velocity modulated transistor structure
Authors: Cohen E. B. , Webb K. J. , Janes D. B. , Melloch M. R.
Published: July 2002

We report experimental, room temperature data showing real space transfer in a heterostructure which can support the movement of electrons over a barrier in both directions between two channels. Real space transfer occurs between two channels connected in parallel in a three-gate transistor, which has been developed to interrogate the channel populations. Results are presented that demonstrate real space transfer in a heterostructure which features a 2.5:1 mobility ratio between channels. This heterostructure is designed for use in a velocity modulation transistor, which requires reciprocal, gate-assisted transfer between two channels of differing mobilities.