bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-gated photon counting method for two-photon spectroscopy using synchrotron radiation and laser
Authors: Asaka Shuji , Nakanishi Shunsuke , Itoh Hiroshi , Kamada Masao , Watanabe Masayuki , Arimoto Osamu , Fujiwara Shigeki , Tsujibayashi Toru , Itoh Minoru
Published: July 2002

A new measurement system has been developed for two-photon spectroscopy in solids with a combination of synchrotron radiation and laser. This system is based on a time-gated photon counting technique to observe luminescence signals induced by two-photon excitation. It is demonstrated that this technique enables us to achieve a high sensitivity and a good signal-to-noise ratio because it is a kind of zero method.
A high energy phase retarder for the simultaneous production of right- and left-handed circularly polarized x rays
Authors: Venkataraman C. T. , Lang J. C. , Nelson C. S. , Srajer G. , Haeffner D. R. , Shastri S. D.
Published: July 2002

We have fabricated and characterized the performance of a monolithic Ge Bragg–Laue phase retarder capable of simultaneously producing both right- and left-handed circularly polarized x rays. The energy range of operation of the phase retarder is between 50 and 100 keV making it well suited to the measurement of spin-dependent Compton profiles within the impulse approximation, primarily because of the increased momentum resolution and larger Compton scattering cross section available at these higher incident energies. Although the phase retarder was optimized for operation at 86 keV, it can produce highly circularly polarized x rays over a substantial energy range. The performance of the phase retarder was tested via magnetic Compton scattering measurements on an Fe sample at the undulator A of the Advanced Photon Source. It was found to perform well in terms of flux and degree of circular polarization thereby greatly reducing the data collection times required for this inherently weak scattering process.
A crossed beam double trochoidal electron spectrometer
Authors: Vićić M. , Poparić G. , Belić D. S.
Published: July 2002

A crossed-beam collision geometry has been successfully applied to a double trochoidal electron spectrometer. In order to improve the efficiency of the instrument, an original design of the sample gas inlet system has been developed. The instrument has been tested by measuring low energy vibrational excitation of the nitrogen molecule. A high energy resolution and a high sensitivity have been achieved. Obtained spectra exhibit some new structure, not previously recorded in a similar measurements.
Real-time phase-selective data acquisition system for measurement of wave phenomena in pulsed plasma discharges
Authors: Sanders S. J. , Stern R. A. , Bellan P. M.
Published: July 2002

A novel data acquisition system and methodology have been developed for the study of wave phenomena in pulsed plasma discharges. The method effectively reduces experimental uncertainty due to shot-to-shot fluctuations in high repetition rate experiments. Real-time analysis of each wave form allows classification of discharges by wave amplitude, phase, or other features. Measurements can then be constructed from subsets of discharges having similar wave properties. The method clarifies the trade-offs between experimental uncertainty reduction and increased demand for data storage capacity and acquisition time. Finally, this data acquisition system is simple to implement and requires relatively little equipment: only a wave form digitizer and a moderately fast computer.
Hot-dome anemometry
Authors: Thompson Brian E.
Published: July 2002

Hot-dome anemometry obtains three components of flow velocity using an array of sensors, specifically five hot films in the present contribution, which are mounted around the hemispherical tip of a cylindrical support. Calibration for speed and angle resembles that of hot wires and split films except that the procedures accommodate heat transfer dominated by forced convection from the surface of a sphere rather than single or multiple cylinders. Measurements are obtained with hot domes, conventional hot wires, and impact probes in the wake of a wing to quantify measurement uncertainties.
MEPHISTO: Performance tests of a novel synchrotron imaging photoelectron spectromicroscope
Authors: De Stasio Gelsomina , Capozi M. , Lorusso G. F. , Baudat P. A. , Droubay T. C. , Perfetti P. , Margaritondo G. , Tonner B. P.
Published: July 2002

We discuss the scheme and test performances of this recently commissioned system in its final configuration. The tests show that the improvements in the electron optics system with respect to other instruments in the same class made it possible to reach lateral resolutions in the 50 nm range. They also demonstrate rather good spectromicroscopy and spectroscopy performances, reliability and flexibility of operation.
A thermal microprobe fabricated with wafer-stage processing
Authors: Zhang Yongxia , Zhang Yanwei , Blaser Juliana , Sriram T. S. , Enver Ahsan , Marcus R. B.
Published: July 2002

A thermal microprobe has been designed and built for high resolution temperature sensing. The thermal sensor is a thin-film thermocouple junction at the tip of an atomic force microprobe (AFM) silicon probe needle. Only wafer-stage processing steps are used for the fabrication. For high resolution temperature sensing it is essential that the junction be confined to a short distance at the AFM tip. This confinement is achieved by a controlled photoresist coating process. Experiment prototypes have been made with an Au/Pd junction confined to within 0.5 μm of the tip, with the two metals separated elsewhere by a thin insulating oxide layer. Processing begins with double-polished, n-type, 4 in. diameter, 300-μm-thick silicon wafers. Atomically sharp probe tips are formed by a combination of dry and wet chemical etching, and oxidation sharpening. The metal layers are sputtering deposited and the cantilevers are released by a combination of KOH and dry etching. A resistively heated calibration device was made for temperature calibration of the thermal microprobe over the temperature range 25–110 °C. Over this range the thermal outputs of two microprobes are 4.5 and 5.6 μV/K and is linear. Thermal and topographical images are also obtained from a heated tungsten thin film fuse.
A low-energy ion implanter for surface and materials science
Authors: Habenicht Sönke , Bolse Wolfgang , Lieb Klaus-Peter
Published: July 2002

A low-energy ion-beam facility for surface and materials science has been built which allows ion beam treatments of solid surfaces via single-ion impacts up to high-fluence implantations. The system offers mass-separated ion beams of 0.5–10 keV by a normal acceleration, and of 5–2000 eV by an acceleration/deceleration lens combination. Its energy spread is estimated to be as small as 2 eV in the whole range. Ion current densities are available in the range between 0.1 nA/cm2 and up to 50 μA/cm2, corresponding to a particle flux of 109–1014 ions/cm2 s. Homogeneous implantation profiles are achieved using an electrostatic x-y deflection system. First applications for ion induced defect production on highly oriented pyrolytic graphite surfaces detected via scanning tunneling microscopy are presented. Hillock shaped defect formations were detected and attributed to protusions of the atomic surface structure, which were induced by interstitials and interstitial clusters between the first atomic planes originated from recoil atoms of the collision cascade.
ASTRAL, a hyperspectral imaging DNA sequencer
Authors: O’Brien Kevin M. , Wren Jonathan , Davé Varshal K. , Bai Diane , Anderson Richard D. , Rayner Simon , Evans Glen A. , Dabiri Ali E. , Garner Harold R.
Published: July 2002

We are developing a prototype automatic DNA sequencer which utilizes polyacrylamide slab gels imaged through a novel optical detection system. The design of this prototype sequencer allows the ability to perform direct optical coupling over the entire read area of the gel and hyperspectrographic separation and detection of the fluorescence emission. The machine has no moving parts. All the major components incorporated in this prototype are all currently available “off the shelf,” thus reducing equipment development time and decreasing costs. Software developed for data acquisition, analysis, and conversion to other standard formats facilitates compatibility.
An instrument for time resolved monitoring of fast chemical transitions: Application to the kinetics of refolding of a globular protein
Authors: Ratner Vladimir , Haas Elisha
Published: July 2002

The dynamics of kinetic intermediates of protein folding can be studied by time resolved measurements of nonradiative excitation energy transfer, in site-specific labeled protein derivatives, combined with fast mixing experiments. A new device based on the single pulse approach was developed. This experiment is performed over two time scales: the “chemical time scale” of the conformational changes (milliseconds), defined by the rates of changes of conformations in the sample, and the “spectroscopic time scale” (nanoseconds) defined by the lifetimes of the excited states of the fluorescent probes. The chemical process was synchronized by means of a fast mixing stopped flow device. The low cost laser used here is suitable for use with dyes with excitation wavelengths of 337 nm and higher. Up to 20 fluorescence decay curves per second, can be measured within a single stopped flow run. Each fluorescence decay curve is recorded within 250 ns or more. The time resolution (of the spectroscopic time scale) was 0.5 ns. The noise level is low enough to estimate distance distributions from energy transfer experiments, provided that the shortest changeable lifetime component of the fluorescence decay of the donor probes would not be lower than ∼4 ns. The amount of double labeled protein which should be used for each experiment in order to obtain a full data set, with time resolution of 10 ms during protein transition, is only fourfold more than the amount needed for a stopped flow study with steady state fluorescence monitoring. The results obtained for refolding of α-lactalbumin in the presence of 1,8-anilino-naphthalene sulfonic acid from the GuHCl induced denatured state, support the model in which the probe has two states. The first state, is characterized by a fluorescence lifetime of 14.2±0.5 ns and the second by a fluorescence lifetime of 0.5±0.4 ns or less. During refolding the dye is transferred from the first state to the second, at a rate that coincides with the rate of the steady state fluorescence change. Refolding from the acid-induced molten globule state shows a more complex change in the parameters of the fluorescence decay, probably due to partial aggregation of the protein during refolding.
Spot-welding of fine thermocouple wires for use in ac calorimetry
Authors: Garfield N. J. , Patel M.
Published: July 2002

A simple method is described for forming reliable spot welded cruciform hot junctions with thermocouple wires of diameter 12 μm for use in ac calorimeters. By following this method the mounting of small, thin samples onto thermocouples for measurements of thermal conductivity, diffusivity, and specific heat is facilitated, producing a low thermal contact resistance between sample and thermocouple junction.
Characterization of an x-ray framing camera utilizing a charge coupled device or film as recording media
Authors: Logory L. M. , Farley D. R. , Conder A. D. , Belli E. A. , Bell P. M. , Miller P. L.
Published: July 2002

A compact charge coupled device (CCD) camera system has been designed and characterized for use in the six inch manipulator (SIM) at the Nova laser facility. The camera system has been designed to directly replace the 35 mm film packages currently used in SIM-based x-ray imaging diagnostics. The unit’s electronic package has been constructed for small size and high thermal conductivity which reduces the overall camera size and improves its performance when operated within the vacuum environment of the Nova target chamber. Measurements of the x-ray imager’s contrast transfer function (CTF) were made under a variety of operating conditions on a static x-ray Manson source using both the CCD and Kodak T-Max 3200 film as recording media. The CTF data were converted to an equivalent modulation transfer function (MTF). The MTF plots show that the microchannel plate has a uniform response within our measurement accuracy along its strips. In a direction normal to the strip, however, the MTF is reduced due to the slant angle of the pores in the MCP. The measurements show that the CCD camera has a lower MTF response than T-MAX film for all spatial frequencies and configurations measured. However, data obtained from the film exhibited reciprocity failure and border effects that are not observed in the CCD data. Measurements indicate that the signal-to-noise ratio for the CCD data is four to six times larger than that obtained with film and higher photon flux levels were recorded. The CCD-based diagnostic offers immediate access to the data, improved dynamic range, and reduced turnaround time, while eliminating the need for film development, digitization, equipment, and personnel.
Noncryogenic pellet injector for diagnostic purposes on the RFX reversed field pinch
Authors: Garzotti L. , Innocente P. , Martini S. , Reggiori A. , Daminelli G. B.
Published: July 2002

An impurity pellet injector is being developed for the RFX reversed field pinch (RFP) with three aims: measurement of the pitch of the magnetic field lines, transport studies, and first wall conditioning. The injector uses pneumatically accelerated metal sabots to launch the pellets. In this way the same barrel can be used for pellets of different sizes, speeds and materials. With drive pressures of 1–10 bars, velocities of 50–400 m/s can be obtained, which, based on code simulations, are adequate for core ablation. The measurement of the internal magnetic field will be done by diagnosing the direction of elongation of the pellet plasmoid using a masked charge coupled device camera capable of acquiring 28 images 40 lines×1024 pixels each with a maximum sampling rate of 50 kHz.
Investigation of quantum efficiencies in multilayered photocathodes for microchannel plate applications
Authors: Ze Frederic , Landen Otto L. , Bell Perry M. , Turner Robert E. , Tutt Teresa , Alvarez Sharon S. , Costa Robert L.
Published: July 2002

Microchannel plates (MCPs) are used in many diagnostic systems to study laser-plasma interactions. Typically the front surface of a MCP is coated with some photocathode (PC) material to convert x ray to electron. This is followed by electron multiplication along the microchannels. Materials such as CsI, Al, and Au have been identified as good PC materials, but the overall quantum efficiencies of these materials are low, so that electron multiplication along the channel has been the only path to signal amplification. This approach is known to have some problems (J. D. Wiedwald, University of California UCRL-JC-110906, August 1992). We investigated the effect of pairing transmission PC to standard MC’s and found that CsI and Au foils used in multilayered configuration, significantly enhance the overall quantum efficiency of the combination. The findings could lead to better MCP design and fabrication.
Nature of defect centers in B- and P-doped SiO2 thin films
Authors: Warren W. L. , Shaneyfelt M. R. , Fleetwood D. M. , Winokur P. S.
Published: July 2002

An electron paramagnetic resonance study has been carried out on B- and P-doped oxide films on Si. The principal defects are the boron-oxygen-hole-center (BOHC) and phosphorus- oxygen-hole-center (POHC), which are unpaired electrons on oxygen atoms with B or P in the near vicinity. Our results demonstrate that the centers are activated by hole capture. We find that holes are trapped very efficiently in both B- and P-doped dielectrics; however, electrons are more efficiently trapped in the B-doped dielectrics. We find that the electrical data can be explained by assuming that the precursor to the BOHC is negatively charged and the precursor to the POHC is electrically neutral.
Experimental artifacts in the surface pressure measurement for lignin monolayers in Langmuir troughs
Authors: Constantino C. J. L. , Dhanabalan A. , Oliveira O. N.
Published: July 2002

The surface pressure measured with the Wilhelmy method may vary considerably with the experimental conditions adopted for isotherms of nonamphiphilic, macromolecular substances, in contrast to the majority of traditional amphiphilic compounds such as fatty acids. This is demonstrated here by analyzing monolayer characteristics of lignins, for which a variety of conditions were employed, including change in the mode of compression, positioning of the Wilhelmy plate, and compression speeds. A minimum in the decompression leg of a hysteresis experiment was found to arise from experimental artifacts, which are explained in terms of the various forces experienced by the Wilhelmy plate.
Setup for in situ x-ray diffraction and ion-channeling studies of ion-implantation effects in thin films
Authors: Grigull S. , Foltyn S. , Hollander M. G. , Evans C. R. , Nastasi M.
Published: July 2002

A novel setup is introduced that combines energy-dispersive x-ray diffraction and ion-channeling capabilities for damage studies on single-crystalline thin films irradiated with 100–720 keV heavy ions. Channeling measurements using 2 MeV He ions provide depth-resolved information on the damage buildup. The x-ray diffraction tool is used to measure damage-related lattice strain, and can provide information on bombardment-induced disorder complementary to the channeling technique. Data obtained during the implantation of 360 keV Ar2+ ions into a zirconia thin film illustrate the potential of the instrument.
A method for “on-line” determination of beam-jet overlaps; application to cluster fragmentation studies
Authors: Wohrer K. , Chabot M. , Fossé R. , Gardès D.
Published: July 2002

We present a method for determination of beam-jet overlaps in crossed-beam experiments (particle beam–molecular beam). This quantity, necessary for extracting absolute values of collisional cross sections, is difficult to determine and most of the experimentalists use normalization procedures or rely on calculations. In the present method, essentially experimental, there is no need to know precisely either the beam or local jet characteristics, the only requirement being to have a beam smaller than the jet’s dimensions. It is an “on-line” method, then allowing beam-jet overlaps under the exact conditions of the experiments to be determined; in that respect, it may be a useful tool for all accelerator-based experiments. We have shown, through detailed experiments, that the theoretical part entering in the determination could be confidently predicted. The method was applied mostly to the determination of beam-jet overlaps in cluster-atom collision studies and in the particular conditions of a beam passing very near the jet’s capillary exit. In this special situation, we could prove the applicability of the method as well.
Characterization of phosphosilicate thin films using confocal Raman microscopy
Authors: Matthews Manyalibo J. , Harris Alexander L. , Bruce Allan J. , Cardillo Mark J.
Published: July 2002

We have demonstrated a characterization tool based on confocal Raman microscopy capable of studying the vibrational spectrum of silica-on-silicon-based thin films within a confined, ∼1 μm3-size volume beneath the sample surface. The Raman spectra of a set of phosphosilicate thin film samples have been quantitatively analyzed and correlated with both phosphorus concentration CP and refractive index n, as determined by conventional methods. The normalized intensity of the P=O vibration scaled linearly with CP and n, and allowed for the calibration of the Raman measurements to a precision of ∼0.2 wt. %P and ∼10−4 in index. The capability of this technique for studying index and dopant profiles in arbitrary systems is also discussed.
Investigation of integrated diffractive/refractive microlens microfabricated by focused ion beam
Authors: Fu Yongqi , Bryan Ngoi Kok Ann
Published: July 2002

Integrated diffractive/refractive microlens with dual focus point is introduced in detail in the view of design, microfabrication, and testing. Two manufacturing methods—milling and deposition directly by focused ion beam technology is discussed and compared. It was shown by testing results that the deposition method is more suitable to form the refractive spherical/aspherical lens and milling is suitable for microfabrication of diffractive optical elements. Focusing spot size (full width at half maximum) are 0.55 and 0.87 μm (λ=638 nm) for refractive and diffractive lens, respectively, with NA 0.35 and 0.5.
Extended frequency range dielectric measurements of thin films
Authors: Mopsik Frederick I.
Published: July 2002

A method is described to measure the dielectric constant and loss of thin films. It employs a sample holder based on precision 50 Ω air line and can be used from audio frequencies to 1 GHz with a single sample. It is shown to maximize the precision available from commercial instrumentation with minimal data correction. This is confirmed by regions in which the different instruments overlap their frequency coverage.
Monolithic sapphire parametric transducer operation at cryogenic temperatures
Authors: Locke C. R. , Tobar M. E. , Ivanov E. N.
Published: July 2002

The operation of a novel monolithic sapphire transducer from room temperature to cryogenic temperature is presented. The transducer is a microwave sapphire resonator that senses the motion of internal acoustic resonances through the interaction between electric and acoustic fields. The system is noncontacting and has low mechanical and electrical losses. Also, the microwave characteristics of sapphire are used as an inherent temperature sensor. High mechanical quality factors of 108 and 4.5×108 were attained at 300 and 4 K, respectively.
Epitaxial growth of metal phthalocyanines on hydrogen terminated vicinal surfaces of Si(111)
Authors: Shimada Toshihiro , Suzuki Akira , Sakurada Takafumi , Koma Atsushi
Published: July 2002

Hydrogen-terminated vicinal Si(111) surfaces provide quasi-van der Waals substrates with regularly spaced atomic height steps for the epitaxy of organic material films. Molecular beam epitaxy of vanadyl and copper phthalocyanines (VOPc and CuPc) was attempted on just-cut and 7°-miscut surfaces in order to investigate the effect of the steps on the epitaxial growth feature. The molecular arrangement of the films was characterized by a new technique using multiple-azimuth reflection high energy electron diffraction. Growth on misoriented substrates producted VOPc monolayer films consisting of one-dimensional chains nearly aligned to the steps and multilayer CuPc films with controlled domain orientations.
Hybrid organic/inorganic complementary circuits
Authors: Dodabalapur A. , Baumbach J. , Baldwin K. , Katz H. E.
Published: July 2002

The transfer characteristics of hybrid complementary inverters with n-channel a-Si transistors and p-channel organic transistors are described. These inverters can operate at supply voltages as low as 7 V. Such circuit schemes may be useful in low-cost, low-power applications.
Metalorganic vapor phase epitaxy and characterization of Zn1−xFexSe films
Authors: Mountziaris T. J. , Peck J. , Stoltz S. , Yu W. Y. , Petrou A. , Mattocks P. G.
Published: July 2002

The epitaxial growth of the diluted magnetic semiconductor (DMS) Zn1−xFexSe (0<x≤0.22) by metalorganic vapor phase epitaxy (MOVPE) is reported. The films were grown on (100) GaAs substrates in a vertical stagnation flow reactor with a specially designed inlet to minimize prereactions between the groups II and VI precursors. The precursors used in this study were (CH3)2Zn:N(CH2H5)3, Fe(CO)5, and H2Se diluted in H2 carrier gas. The epilayers were characterized by x-ray diffraction (XRD), Raman, absorption, and x-ray photoelectron spectroscopies (XPS). Typical growth rates were from 3–4 μm/h, which are significantly higher than those obtained by molecular beam epitaxy. Thus, in addition to the growth of DMS multilayer structures, MOVPE appears to be very promising for efficient growth of thick DMS films for Faraday magneto-optical applications.
1/f noise as an early indicator of electromigration damage in thin metal films
Authors: Dagge K. , Frank W. , Seeger A. , Stoll H.
Published: July 2002

Electromigration in thin films of aluminium and aluminium alloys is shown to lead to stepwise increases of the electrical 1/f noise. These are attributed to the generation of highly mobile defect configurations by a nucleation-and-growth process. It is conjectured that among them may be the defects that are responsible for the eventual failure of VLSI electronic devices by electromigration damage. 1/f noise promises to be an early indicator of this damage.
Mass spectroscopic investigations of a hydrocarbon arcjet plasma operating under diamond deposition conditions
Authors: Stalder K. R. , Homsi W.
Published: July 2002

We report on mass spectroscopic measurements of species originating near the stagnation point of an arcjet plasma impinging on a tantalum surface. The plasma is produced in a 1-kW arc through which flows a gas mixture of ∼1% methane in hydrogen. This plasma is near thermal equilibrium, except that a few species such as C2 are slow to equilibrate internally due to the large exothermicity of the reactions that form them. A polycrystalline diamond film grows on the substrate as the measurements are taken. A small gas sampling hole in the deposition substrate samples molecules as they diffuse to the surface. Two stages of differential pumping are used to form a molecular beam which is detected by a quadrupole mass spectrometer. Significant conversion of methane to acetylene (C2H2) and ethylene (C2H4) is observed, as are radicals such as CH3 and C 2H5.
Far infrared video detection and difference frequency mixing with tilted c-axis epitaxial YBa2Cu3O7−δ thin films
Authors: Huber W. M. , Berr M. , Kalbeck A. , Prettl W. , Huggard P. G.
Published: July 2002

Epitaxial YBa2Cu3O7−δ thin films, grown with a controllable misalignment between c-axis and surface normal, exhibit a sensitive photoresponse to far infrared laser radiation at temperatures below Tc. While no photoresponse was observed in c-axis normal films, a sensitivity of 0.2 V/W was measured at a wavelength of 432 μm for a film with a 20° c-axis tilt. Difference frequency mixing of two laser modes has also been demonstrated at intermediate frequencies between 200 kHz and 6 MHz. Both mixing and video detection are believed to originate in the ac Josephson effect: the effect of the tilted growth is to allow a component of the radiation field to be applied along the c-axis, thus modulating the relatively weak Josephson coupling in this direction.
Chemical beam epitaxial growth of Si-doped GaAs and InP by using silicon tetraiodide
Authors: Izumi Shigekazu , Hayafuji Norio , Ito Kazuhiko , Sato Kazuhiko , Otsubo Mutsuyuki
Published: July 2002

Silicon tetraiodide (SiI4), which has a very weak Si–I bond strength (70 kcal/mol), is successfully employed as a novel Si dopant in the chemical beam epitaxy of GaAs and InP. No precracking is necessary before supplying SiI4 with He carrier gas. High electrical quality is ascertained for both GaAs and InP with linear Si doping controllability in the range from 2×1016 to 6×1018 cm−3 with a uniformity of less than 2% within a 3-in.-diam area. The electron mobility in a GaAs with a carrier concentration of 1×1017 cm−3 is 4400 cm2/V s and that in InP with a carrier concentration of 4×1017 cm−3 is 2400 cm2/V s, respectively. Abrupt interfaces and precise on-off controllability without any memory effect is also confirmed by secondary-ion-mass, spectroscopy measurements. The electrical activation ratio of Si in SiI4 for both GaAs and InP is almost 100% in the range studied here. These versatile features suggest that SiI4 is a promising candidate as a Si dopant source for chemical beam epitaxy growth.
Nucleation and evolution of misfit dislocations in ZnSe/GaAs (001) heterostructures grown by low-pressure organometallic vapor phase epitaxy
Authors: Ruvimov Sergei , Bourret Edith D. , Washburn Jack , Liliental-Weber Zuzanna
Published: July 2002

Transmission electron microscopy and x-ray diffraction were used to study strain relaxation and the evolution of the dislocation structure in ZnSe epilayers grown by low-pressure organometallic vapor phase epitaxy on a (001) surface of semi-insulating GaAs. Before the ZnSe growth, the substrate surface was exposed to a flow of tertiarybutylarsine to promote an As-terminated surface. This surface treatment results in a low density of stacking faults; 60° misfit dislocations were observed at a layer thickness as low as 0.05 μm. This agrees well with the theoretical critical value for misfit dislocation formation in the ZnSe/GaAs system, but is much lower than experimental critical thicknesses reported earlier. Various mechanisms of misfit dislocation generation were observed at different growth stages. The evolution of the dislocation structure is discussed in relation with the morphology of the ZnSe layers.
Optical degradation of InGaN/AlGaN light-emitting diode on sapphire substrate grown by metalorganic chemical vapor deposition
Authors: Egawa T. , Ishikawa H. , Jimbo T. , Umeno M.
Published: July 2002

We report an optical degradation of an InGaN/AlGaN double-heterostructure light-emitting diode (LED) on a sapphire substrate grown by metalorgonic chemical vapor deposition. Electroluminescence, electron-beam induced current, and cathodoluminescence observations have shown that the degraded InGaN/AlGaN LED exhibits formation and propagation of dark spots and a crescent-shaped dark patch, which act as nonradiative recombination centers. The values of degradation rate under injected current density of 0.1 kA/cm2 were determined to be 1.1×10−3, 1.9×10−3, and 3.9×10−3h−1 at ambient temperatures of 30, 50, and 80°C, respectively. The activation energy of degradation was also determined to be 0.23 eV.
Controlling and tuning strong optical field gradients at a local probe microscope tip apex
Authors: Martin Olivier J. F. , Girard Christian
Published: July 2002

We show that strong optical field gradients can be created at the tip apex of a local probe microscope illuminated by an external light source. We demonstrate that these confined fields can be easily, precisely and continuously tuned by changing the polarization and the incidence of the external field. We also investigate the topology of the field intensity in the tip–surface junction.
Optical gain for wurtzite GaN with anisotropic strain in c plane
Authors: Domen K. , Horino K. , Kuramata A. , Tanahashi T.
Published: July 2002

We calculated band structures of (11̄00)-oriented GaN with various strains. We found that introducing anisotropic strain in the c plane separates heavy- and light-hole bands. We also found that a tensile strain in the (11̄00) plane makes the light-hole band topmost. These two effects result in a reduction in the density of states at the valence-band edge. In this way we can significantly reduce the transparent carrier density to generate gain.
Evaluation of strained InGaAs/GaAs quantum wells by atomic force microscopy
Authors: Sato M. , Zeimer U. , Bugge F. , Gramlich S. , Weyers M.
Published: July 2002

Atomic force microscopy (AFM) is adopted for evaluation of strained InGaAs/GaAs quantum well structures grown by metalorganic vapor phase epitaxy. InAs-rich clusters are formed at the upper interface when the structure is grown with excessive supply of the In precursor. The defects arising from the clusters are clearly observed as convex domains from the irregularity of monolayer steps. The density of the convex domains coincides with the dark spot density measured by cathodoluminescence. Photoluminescence intensity is drastically reduced at high density of this type of defects. Thus, AFM measurements are able not only to give information on the structural quality but also to provide an estimation of the optical quality of such InGaAs/GaAs structures.
Effects of V/III ratio on ordering and antiphase boundaries in GaInP layers
Authors: Seong Tae-Yeon , Kim Joon Hyung , Chun Y. S. , Stringfellow G. B.
Published: July 2002

Transmission electron microscope (TEM) and transmission electron diffraction (TED) studies have been performed to investigate the effects of V/III ratio on ordering and antiphase boundaries (APBs) in organometallic vapor phase epitaxial Ga0.5In0.5P layers grown onto (001) GaAs vicinal substrates at 670 °C. TED and TEM examination showed that the degree of order is higher in the layer grown using a V/III ratio of 160 than in the layer grown using a V/III ratio of 40. TEM results showed that the higher V/III ratio could be used to suppress APBs. In addition, the growth of order-induced heterostructures, where the V/III ratio is increased abruptly during growth, could be used to block the propagation of APBs. Mechanisms are proposed to explain these phenomena.
Ferroelectric-semiconductor heterostructures obtained by direct wafer bonding
Authors: Alexe Marin , Kästner Gerhard , Hesse Dietrich , Gösele Ulrich
Published: July 2002

A novel fabrication process of ferroelectric-semiconductor heterostructures based on direct wafer bonding has been demonstrated. Polycrystalline Bi4Ti3O12 ferroelectric thin films were deposited on 3 in. silicon wafers using chemical solution deposition. The films were polished and then directly bonded to silicon wafers in a micro-cleanroom. After thermal annealing in air at 500 °C for 12 h, the bonding energy increases up to 1.5 J/m2. High resolution transmission electron microscopy shows the difference between the bonded and reacted interfaces. Obtaining a metal-ferroelectric-silicon (MFS) structure containing the ferroelectric-Si bonded interface was achieved by polishing down and etching the handling wafer. The Bi4Ti3O12 film kept its ferroelectric properties as shown by C–V measurement.
Reflectance spectroscopy on GaN films under uniaxial stress
Authors: Yamaguchi A. A. , Mochizuki Y. , Sasaoka C. , Kimura A. , Nido M. , Usui A.
Published: July 2002

The uniaxial stress effects on valence band structures in GaN are investigated by reflectance spectroscopy. It is observed that the energy separation between A and B valence bands increases with the application of uniaxial stress in the c plane. The experimental results are analyzed on the basis of the k⋅p theory, and deformation potential D5 is determined as −3.3 eV. It is indicated that the uniaxial strain effect could be utilized for improving GaN-based laser performance.
Transmission ellipsometry of a thin-film helicoidal bianisotropic medium
Authors: Rovira P. I. , Yarussi R. A. , Collins R. W. , Messier R. , Venugopal V. C. , Lakhtakia A. , Robbie K. , Brett M. J.
Published: July 2002

Experimental evidence is introduced for circularly birefringent and dichroic behavior in a MgF2 thin-film helicoidal bianisotropic medium (TFHBM), which is a rotationally inhomogeneous and anisotropic material. Optical rotation (OR) of an incident linearly polarized monochromatic plane wave is observed upon transmission through the MgF2/glass TFHBM/substrate system, and it is accompanied by an ellipticity in the polarization of the transmitted plane wave. Both OR and ellipticity spectra have remarkable features within a narrow wavelength zone not unlike the Cotton effect in isotropic chiral media. The features in the experimental spectra are in accord with theoretical predictions.
Chromium-containing metallic fibers confined within carbon nanotubes: Possibility of template-mediated crystal growth
Authors: Okuyama Fumio , Ogasawara Isao
Published: July 2002

So-called “anode activation” is shown to entail the growth of metallic fibers with nanometric dimensions. These fibers grow from dendritic deposits comprised of carbon and chromium, and thus chromium is a major component. They are confined inside thin-wall carbon nanotubes, with their diameter defined by the inner diameter of the host nanotube. This growth behavior reflects a template-mediated type of fiber growth.
Role of extraordinary waves in uniform electron cyclotron resonance plasmas
Authors: Ueda Yoko , Kawai Yoshinobu
Published: July 2002

The extraordinary wave (X wave) was found to contribute to the uniformity of an electron cyclotron resonance (ECR) plasma whose electron density is about 1–2×1017 m−3. The X wave propagated radially in the plasma both before and after the ECR point. The electron density jump occurred when the electron density was equal to the cutoff density of the X wave at the ECR point. Upon increasing the electron density, only the whistler wave propagated in a high density plasma of about 1018 m−3.
Observation of the single electron charging effect in nanocrystalline silicon at room temperature using atomic force microscopy
Authors: Otobe Masanori , Yajima Hiroshi , Oda Shunri
Published: July 2002

We have measured current–voltage (I–V) characteristics of individual surface oxidized nanocrystalline silicon (nc-Si) particles, which were grown in the gas phase of a plasma and which had well-defined grain sizes of less than 10 nm and a regular octahedron shape. The I–V characteristics were measured at room temperature using atomic force microscopy with conductive tips, which allows the grain size of nc-Si particles to also be measured directly. The measured I–V characteristics show staircaselike features. The period of the staircase increases with decreasing grain size, which is consistent with the single electron charging effect in nc-Si.
Equation of state of wurtzitic boron nitride to 66 GPa
Authors: Solozhenko Vladimir L. , Häusermann Daniel , Mezouar Mohamed , Kunz Martin
Published: July 2002

The compressibility of wurtzitic boron nitride (wBN) taken in mixture with cubic BN has been measured at room temperature up to 66 GPa, using a diamond anvil cell and powder diffraction of synchrotron radiation. From the obtained pressure-volume relation for wBN the isothermal bulk modulus of B0=375±9 GPa and its first pressure derivative of dB0/dp=4.9±0.7 have been calculated indicating that this phase has nearly the same compressibility as cBN (B0=377±4 GPa and dB0/dp=4.1±0.2). Thermodynamic calculations using our findings on wBN equation of state have shown that wurtzitic boron nitride is metastable over the whole ranges of pressures and temperatures.
Laser purification of Ag using a time-division collection method
Authors: Mori Hiroshi
Published: July 2002

In laser purification of Ag from an Ag-In alloy based on multistep photoexcitation for ionization, we demonstrated that a time-division collection method employing a high-speed rotation disk is effective in suppressing an impurity level. High purity Ag film of 0.11% In impurity concentration was obtained from a starting Ag-In alloy of 6.08% In. This impurity reduction was much higher than the case without the new method, in which only half reduction was obtained. This work also showed that the contamination is mainly due to neutral atoms that failed to be irradiated by pulsed-mode lasers.
Giant acoustoelectric effect in GaAs/LiNbO3 hybrids
Authors: Rotter M. , Wixforth A. , Ruile W. , Bernklau D. , Riechert H.
Published: July 2002

The acoustoelectric effect in a hybrid of a strong piezoelectric material and a semiconductor layer containing a two-dimensional electron system is investigated. Caused by the very strong interaction between a surface acoustic wave and the mobile carriers in the semiconductor, the acoustoelectric effect is very large as compared to other materials, which might be interesting for device applications. Moreover, the tunability of the sheet conductivity of the electron system enables us to tune the magnitude of the acoustoelectric effect over a wide range. We present experimental results for a GaAs/LiNbO3 layered hybrid system at room temperature and describe our experimental findings quantitatively using a recently developed model calculation.
Easy axis distribution in interacting fine-particle systems
Authors: Iglesias R. , Rubio H. , Suárez S.
Published: July 2002

A general method applicable to interacting fine-particle systems in the mean-field approximation is developed. When the external applied field is decreased, interaction and disorder give rise to a rotation of the integration domain that must be considered for the determination of the average values. This model provides useful expressions for obtaining the magnetic easy axis distribution, and reproducing the results of the preceding noninteracting theories when interaction between particles is not taken into account.
1.3 μm room-temperature GaAs-based quantum-dot laser
Authors: Huffaker D. L. , Park G. , Zou Z. , Shchekin O. B. , Deppe D. G.
Published: July 2002

Room-temperature lasing at the wavelength of 1.31 μm is achieved from the ground state of an InGaAs/GaAs quantum-dot ensemble. At 79 K, a very low threshold current density of 11.5 A/cm2 is obtained at a wavelength of 1.23 μm. The room-temperature lasing at 1.31 μm is obtained with a threshold current density of 270 A/cm2 using high-reflectivity facet coatings. The temperature-dependent threshold with and without high-reflectivity end mirrors is studied, and ground-state lasing is obtained up to the highest temperature investigated of 324 K.
Arsenic-doped Si(001) gas-source molecular-beam epitaxy: Growth kinetics and transport properties
Authors: Soares J. A. N. T. , Kim H. , Glass G. , Desjardins P. , Greene J. E.
Published: July 2002

Arsenic-doped Si(001) layers with concentrations CAs up to 5×1018 cm−3 were grown on Si(001)2×1 at temperatures Ts=575–900 °C by gas-source molecular-beam epitaxy (GS-MBE) using Si2H6 and AsH3. This is almost an order of magnitude higher than the initially reported “maximum attainable” saturated CAs value for GS-MBE from hydride precursors. At constant JAsH3/JSi2H6, CAs decreases, while the film growth rate RSi increases, with Ts. Temperature programmed desorption measurements show that As segregates strongly to the growth surface and that the observed decrease in CAs at high film growth temperatures is primarily due to increasingly rapid arsenic desorption from the segregated layer. Decreasing Ts enhances As incorporation. However, it also results in lower film growth rates due to higher steady-state As surface coverages which, because of the lone-pair electrons associated with each As adatom, decrease the total dangling bond coverage and, hence, the Si2H6 adsorption rate. At constant Ts, CAs increases, while RSi decreases, with increasing JAsH3/JSi2H6. All incorporated As resides at substitutional electrically active sites for concentrations up to 3.8×1018 cm−3, the highest value yet reported for Si(001):As growth from hydride source gases, and temperature-dependent electron mobilities are equal to those of the best bulk Si:As.
ZnO quantum particle thin films fabricated by electrophoretic deposition
Authors: Wong Eva M. , Searson Peter C.
Published: July 2002

Thin films of quantum size ZnO particles were fabricated by electrophoretic deposition from stable colloidal suspensions. The average particle size and hence the optical properties can be tailored by controlling the aging time and temperature of the suspensions. Thin films prepared by electrophoretic deposition exhibit optical properties characteristic of the quantum size particles. Both the band-to-band and visible photoluminescence were progressively blue shifted with decreasing particle size in the film.
Spin-interference device
Authors: Nitta Junsaku , Meijer Frank E. , Takayanagi Hideaki
Published: July 2002

We propose a spin-interference device which works even without any ferromagnetic electrodes and any external magnetic field. The interference can be expected in the Aharonov–Bohm (AB) ring with a uniform spin-orbit interaction, which causes the phase difference between the spin wave functions traveling in the clockwise and anticlockwise direction. The gate electrode, which covers the whole area of the AB ring, can control the spin-orbit interaction, and therefore, the interference. A large conductance modulation effect can be expected due to the spin interference.
Raman imaging of stress in a SiGe/Si photoelastic optical channel waveguide structure
Authors: Rho H. , Jackson Howard E. , Weiss B. L.
Published: July 2002

We report Raman imaging of stress in a SiGe/Si optical channel waveguide structure. The difference in thermal expansion coefficients between a Si3N4 stripe and a SiGe layer creates a significant localized stress profile beneath the stripe, which can result in optical confinement suitable for optical waveguide fabrication. We image these areas utilizing Raman polarization selection rules for two transverse optical phonons, relate the Raman peak shifts to strain components, and then to refractive index changes via the photoelastic effect. These micro-Raman images provide spatially resolved two-dimensional refractive index information on the waveguiding region of a channel waveguide structure.
Measurement of internal spatial modes and local propagation properties in optical waveguides
Authors: Vander Rhodes G. H. , Goldberg B. B. , Ünlü M. S. , Chu S. T. , Pan W. , Kaneko T. , Kokobun Y. , Little B. E.
Published: July 2002

Internal spatial modes and local properties controlling optical wave propagation have been measured in glass/silica buried waveguides. The period of the observed standing modes provides a direct measure of the local effective index. The measured effective index and transverse model shape determines the values of all components of the wave vector. In addition, we describe a technique that can obtain detailed information about the locations of remote dielectric interfaces.
Improved ultraviolet quantum efficiency using a semitransparent recessed window AlGaN/GaN heterojunction p-i-n photodiode
Authors: Li T. , Beck A. L. , Collins C. , Dupuis R. D. , Campbell J. C. , Carrano J. C. , Schurman M. J. , Ferguson I. A.
Published: July 2002

We report on the improved quantum efficiency of GaN-based ultraviolet heterojunction photodiodes using a semitransparent recessed window device structure. At a reverse bias of −5 V the quantum efficiency was ∼57% at the band edge, and remained relatively flat down to ∼330 nm after which some absorption in the p-AlGaN layer became evident. The quantum efficiency only gradually declines after this point, remaining >20% at 280 nm. We attribute these results to avoidance of the optical dead space at the surface of GaN homojunction p-i-ns. The semitransparent p-AlGaN layer was comparatively resistive, causing an electric field crowding effect which resulted in a spatially nonuniform temporal behavior.
Measurement of photorefractive phase shift in mesogenic composites
Authors: Ono Hiroshi , Kawamura Tomomi , Frias Nazarene Mokam , Kitamura Keiko , Kawatsuki Nobuhiro , Norisada Hideki
Published: July 2002

Photorefractive phase shifts in high-performance photorefractive mesogenic composites were determined, and trap-limited space-charge fields were estimated. It is demonstrated that photorefractive mesogenic composites show high performance although the space-charge field is considerably low in comparison with other kinds of photorefractive materials which show no mesophase. This means that the high performance of photorefractive mesogenic composites originates in the easy reorientation of mesogen under a low electric field.
Two-element phased array of antiguided vertical-cavity lasers
Authors: Serkland Darwin K. , Choquette K. D. , Hadley G. R. , Geib K. M. , Allerman A. A.
Published: July 2002

We demonstrate antiguided coupling of two adjacent vertical-cavity surface-emitting lasers (VCSELs), obtaining a 1×2 phase-locked array at 869 nm. The lateral index modification required for antiguiding is achieved by a patterned 3 nm etch performed between two epitaxial growths. In contrast with prior coupled VCSELs, adjacent antiguided VCSELs can emit in phase and produce a single on-axis lobe in the far field. Greater than 2 mW of in-phase output power is demonstrated with two VCSELs separated by 8 μm. Moreover, phase locking of two VCSELs separated by 20 μm is observed, indicating the possibility of a promising class of optical circuits based upon VCSELs that interact horizontally and emit vertically.