bluuebunny/crossref_metadata_2025 huggingface dataset:
50 nm linewidth platinum sidewall lithography by effusive-source metal precursor chemical deposition and ion-assisted etching
Authors: Hsu David S. Y.
Published: July 2002

Vertical platinum sidewall structures 50 nm thick and 700 nm tall have been fabricated by Pt deposition from the thermal decomposition of tetrakis-(trifluorophosphine)-platinum using an effusive gas source followed by ion-assisted etching. Scanning electron microscope micrographs show that the sidewalls have high uniformity, very fine grains, and very sharp contours, demonstrating a high degree of conformal deposition. Scanning Auger microscopy confirms the presence of platinum only in the sidewalls. X-ray photoelectron spectroscopy analysis of the as-deposited platinum film reveals no detectable impurity and Scotch tape test shows good bonding of the film. The method is suitable to large-scale processing.
In situ pulsed laser deposition of superconducting Ba1−xKxBiO3 thin films
Authors: Moon B. M. , Platt C. E. , Schweinfurth R. A. , Van Harlingen D. J.
Published: July 2002

We have grown superconducting thin films of Ba1−xKxBiO3 by in situ pulsed laser deposition from a stoichiometric (x=0.4) target. The best films exhibit an onset transition temperature of 28 K and have zero resistance as high as 26 K. Films are single phase and highly oriented in the (100) or (110) direction on MgO, SrTiO3, LaAlO3, and Al2O3 substrates. We have observed high-quality normal-insulator-superconductor and superconductor-insulator-superconductor quasiparticle tunneling characteristics with the films.
Superconducting properties and normal-state resistivity of single-crystal NbN films prepared by a reactive rf-magnetron sputtering method
Authors: Shoji A. , Kiryu S. , Kohjiro S.
Published: July 2002

In this letter, we report some superconducting properties and normal-state resistivities of single-crystal NbN films prepared by a reactive rf-magnetron sputtering method. It was found that the prepared single-crystal NbN films have Tc’s above 16 K, normal-state resistivities in the range from 12.2 to 14.3 μΩ cm (at 20 K), and magnetic penetration depths in the range from 93 to 100 nm (at 4.2 K). From a temperature dependence of the upper critical magnetic field for a single-crystal NbN film, the zero-temperature Ginzburg–Landau coherence length ξGL(0) for the film was calculated to be 6.9 nm.
YBa2Cu3O7−δ films on Si with Y-stabilized ZrO2 and Y2O3 buffer layers: High-resolution electron microscopy of the interfaces
Authors: Bardal A. , Zwerger M. , Eibl O. , Wecker J. , Matthée Th.
Published: July 2002

The interfaces of YBa2Cu3O7−δ (YBCO) thin films grown on Si substrates with Y-stabilized ZrO2 (YSZ) and Y2O3 buffer layers have been studied by high-resolution electron microscopy. At the Si-YSZ interfaces a 4-nm-thick amorphous silica layer is found, bridged by 10-nm-wide crystalline YSZ regions. Close to these regions the Si substrate contains planar {111} faults. At the YSZ-Y2O3 interfaces perfect misfit dislocations are present, with Burgers vector 1/2〈110〉. They occur either as separated single dislocations or as separated groups of closely spaced dislocations. The atomic coordination at the planar and atomically sharp Y2O3-YBCO interface could be revealed. The first atomic layer of the YBCO is found to be a Ba layer.
Surface production of H− ions by hyperthermal hydrogen atoms
Authors: Lee Brian S. , Seidl M.
Published: July 2002

Hyperthermal atomic hydrogen of energy in the range of 1–10 eV has been produced by electron impact dissociation in a cw 2.45 GHz microwave electron cyclotron resonance (ECR) discharge using a Lisitano-Coil. The flux and the energy of the hydrogen atoms have been measured by negative surface ionization of the atoms backscattered from pure and cesiated metal surfaces. A hyperthermal atomic hydrogen flux density equivalent to more than 0.5 A/cm2 and a temperature of about 5 eV has been produced for 420 W discharge power under cw condition. These hydrogen atoms can be directed onto an external converter located outside the discharge. This opens up new possibilities for H− ion source design.
Epitaxial growth of Ba1−xKxBiO3 thin films by pulsed-laser deposition
Authors: Norton D. P. , Budai J. D. , Chakoumakos B. C. , Feenstra R.
Published: July 2002

Epitaxial Ba1−xKxBiO3 thin films have been grown by pulsed-laser deposition at temperatures as low as 400 °C. Films have been grown on (100) MgO and SrTiO3 with Tc(R=0)=19.5 K and transition widths less than 1 K. Four circle x-ray diffraction shows that these epitaxial films are mostly (00l) oriented with good in-plane epitaxy. We find that, especially for growth on (100) MgO, an initial epitaxial layer of BaBiO3 grown at 600 °C significantly improves the properties of the Ba1−xKxBiO3 films.
Photoabsorption in n-type Si-SiGe quantum-well infrared photodetectors
Authors: Shadrin V. D. , Coon V. T. , Serzhenko F. L.
Published: July 2002

The calculation of the photoabsorption spectra and quantum efficiency of Si-SiGe quantum-well (QW) detectors are presented, with the effects of depolarization and electron-electron exchange interaction taken into consideration. We show that the Si-SiGe QW detectors possess lower dark current, lower tunneling rates, and better photoabsorption characteristics when compared to GaAs-AlGaAs photodetectors. These imply that Si-SiGe QW detector performance characteristics are superior to GaAs-AlGaAs QW infrared photodetectors in addition to its advantage of compatibility with Si-readout circuity.
Hydrophobic silicon wafer bonding
Authors: Tong Q.-Y. , Schmidt E. , Gösele U. , Reiche M.
Published: July 2002

Wafers prepared by an HF dip without a subsequent water rinse were bonded at room temperature and annealed at temperatures up to 1100 °C. Based on substantial differences between bonded hydrophilic and hydrophobic Si wafer pairs in the changes of the interface energy with respect to temperature, secondary ion mass spectrometry (SIMS) and transmission electron microscopy (TEM), we suggest that hydrogen bonding between Si-F and H-Si across two mating wafers is responsible for room temperature bonding of hydrophobic Si wafers. The interface energy of the bonded hydrophobic Si wafer pairs does not change appreciably with time up to 150 °C. This stability of the bonding interface makes reversible room-temperature hydrophobic wafer bonding attractive for the protection of silicon wafer surfaces.
Low voltage electron beam lithography in self-assembled ultrathin films with the scanning tunneling microscope
Authors: Marrian C. R. K. , Perkins F. K. , Brandow S. L. , Koloski T. S. , Dobisz E. A. , Calvert J. M.
Published: July 2002

With a scanning tunneling microscope (STM) operating in vacuum, we have studied the lithographic patterning of self-assembling organosilane monolayer resist films. Where the organic group is benzyl chloride, the resist layer can be patterned with electrons down to 4 eV in energy. The patterned films have been used as templates for the electroless plating of thin Ni films. Linewidths down to ∼20 nm have been observed in scanning electron micrographs of the plated films. Still smaller features are observed in STM images of the exposed organosilane films.
Diffusion barrier effects of transition metals for Cu/M/Si multilayers (M=Cr, Ti, Nb, Mo, Ta, W)
Authors: Ono H. , Nakano T. , Ohta T.
Published: July 2002

In order to find appropriate diffusion barrier materials for Cu, the diffusion of Cu into Si through various barrier metals M (M=Cr, Ti, Nb, Mo, Ta, W) was investigated. The behavior of Cu in Cu/M/Si multilayers was measured after annealing using x-ray diffraction analysis, secondary ion mass spectroscopy, Rutherford backscattering spectroscopy, and electric resistance change. Only Cu/Ta/Si and Cu/W/Si multilayers retained their multilayer structures after annealing at 600 °C×1 h in H2 without resistivity increases. Multilayers of the other metals did not retain their structures after the same annealing condition. This difference in the barrier properties of the transition metals appeared to be related to the metal-Cu binary phase diagrams and their self-diffusion coefficients.
Low-loss microwave cavity using layered-dielectric materials
Authors: Maggiore C. J. , Clogston A. M. , Spalek G. , Sailor W. C. , Mueller F. M.
Published: July 2002

Loss measurements have been carried out on a cylindrical pillbox cavity whose metallic flat end walls have been replaced by an ordered sequence of high purity sapphire and air dielectric layers. The loss of the TE01 mode at 18.99 GHz was substantially lowered. An improvement in cavity Q for this mode from 8.30×103 to 531×103 was observed. These experimental results closely reproduce two independent theoretical simulations. All measurements were taken at 30 °C.
Uniform and delta doping of carbon in GaAs by solid-source molecular beam epitaxy using electron beam evaporation: Evidence for atomic pairing
Authors: Sato D. L. , Szalkowski F. J. , Lee H. P.
Published: July 2002

Uniform and delta-doped GaAs:C layers were grown by solid source molecular beam epitaxy (MBE) using electron-beam evaporation of the dopant. Uniform doping concentrations of up to 6×1019 cm−3 were measured and degradation of optical properties was noted when the hole concentration exceeded the mid-1018 cm−3 range. Delta-doping studies were carried out under various deposition conditions and an extremely high sheet carrier concentration of 9.6×1012 cm−2 was obtained under modulated beam condition. In contrast to carbon doping by resistively heated filament sources, all doping results were obtained with C1/C3 isomer ratios greater than unity. These findings show strong evidence for the identification of atomic carbon pairing as the dominant defect formation mechanism in heavily doped GaAs:C films prepared by solid source MBE.
Current–voltage characteristics of dc voltage biased high temperature superconducting microbridges
Authors: Poulin G. Darcy , Lachapelle Jean , Moffat Steven H. , Hegmann Frank A. , Preston John S.
Published: July 2002

We have investigated the dc current–voltage characteristic of high temperature superconducting microbridges. When a dc voltage is applied to a microbridge, it switches to a lossy state due to the formation of a hotspot in the bridge. We have measured the length and temperature of the hotspot as a function of the applied voltage, and have developed a thermal model to explain its steady state behavior. The hotspot has a flat-topped temperature profile, with the maximum temperature independent of the applied voltage. The length of the hotspot, and hence the bridge resistance, increases linearly with the applied bias, so the current is independent of the applied voltage once switching has occurred.
Scaling of terahertz radiation via optical rectification in electro-optic crystals
Authors: Carrig Timothy J. , Rodriguez G. , Clement Tracy Sharp , Taylor A. J. , Stewart Kevin R.
Published: July 2002

We report on the scalability of generating terahertz radiation by optical rectification with the electro-optic materials LiNbO3, LiTaO3, and dimethyl amino 4-N-methylstilbazolium tosylate (DAST). A Ti:sapphire laser system, producing 215 fs, 20 mJ pulses at 810 nm, was used for the experiment. Using LiNbO3 and LiTaO3, the peak of the generated terahertz electric field was found to scale linearly with increasing optical fluence for fluences up to 60 mJ/cm2, while with DAST the peak field scaled sublinearly in this fluence range.
Two-channel, elliptical analyzer spectrograph for absolute, time-resolving time-integrating spectrometry of pulsed x-ray sources in the 100–10 000-eV region
Authors: Henke B. L. , Jaanimagi P. A.
Published: July 2002

A new spectrographic system has been developed and calibrated in this laboratory for the absolute spectrometry of high-intensity pulsed x-ray sources in the 100–10 000-eV region. This spectral region is analyzed with fixed elliptically curved crystals and molecular or sputtered-or-evaporated multilayers of 2d values in the 3–160-A range. Twin channels are utilized for simultaneous time-integrated photographic recording and for time-resolved x-ray streak camera recording. Absolute calibrations of the elliptical analyzers, of the photographic film, and of the gold and CsI transmission photocathodes have been made using monoenergetic, cw laboratory x-ray sources. The overall transmission characteristics of the spectrograph have also been determined. The instrument has been designed for mounting through a pneumatically controlled high-vacuum valve onto a 4-in. port of a 1-m-diameter source chamber and includes an appendage, high-vacuum, sputter-ion prepumping station. The initial dynamic testing and application of this new spectrographic system has been on the University of Rochester’s LLE 24 laser beam OMEGA source facility.
Simultaneous measurement of the thermal conductivity and thermal diffusivity of unconsolidated materials by the transient hot wire method
Authors: Glatzmaier Greg C. , Ramirez W. Fred
Published: July 2002

This paper describes a new design for the transient hot wire method that can obtain the thermal conductivity and thermal diffusivity of unconsolidated materials. In this method, the thermal conductivity is determined from the slope of the temperature rise versus time of an electrically heated wire. The temperature rise is detected as the unbalanced voltage of a precision Wheatstone bridge. This voltage is read by a microcomputer via a high-speed analog-to-digital converter. The instrument was designed so that measurements can be taken over a temperature range of 20–200 °C and a pressure range of atmospheric down to 10 mTorr. Tests using glycerin indicate an accuracy of 1% for the conductivity and 6% for the diffusivity and a precision of 0.4% for the conductivity and 4.5% for the diffusivity. Measurements have also been made on materials such as 50-μ glass beads and unconsolidated spent oil shale.
High-temperature and -pressure system for laser Raman spectroscopy of aqueous solutions
Authors: Marley N. A. , Ott M. , Fearey B. L. , Benjamin T. M. , Rogers P. S. Z. , Gaffney J. S.
Published: July 2002

A high-temperature, high-pressure experimental system is presented that is compatible with a state-of-the-art laser Raman spectrometer. The apparatus and associate electronics and valving, which allow Raman spectra acquisition from ambient conditions to 500 °C and 1-kbar pressure in corrosive aqueous solutions, are described. Diamond windows and a titanium bodied optical design are used to obtain these conditions. Automatically controlled heating jackets have been built that allow ±0.4 °C temperature stability over this range. Raman spectra are presented that demonstrate the capabilities of this experimental apparatus for aqueous studies as a function of temperature and pressures.
Superconducting microwave undulator
Authors: Boni R. , Savoia A. , Spataro B. , Tazzioli F. , Fabbricatore P. , Parodi R. , Fernandes P.
Published: July 2002

We have studied the possibility of using a superconducting microwave cavity resonator as an undulator. A small cavity, made from bulk niobium, has been built and tested. The cavity has an elliptical cross section in order to force a linearly polarized oscillation mode. The TE118 mode has been chosen as the most suitable. Fields of about 300 G have been obtained with 10 W of microwave power. Fields up to 1 kG are reachable with niobium of higher thermal conductivity and better surface treatment. A circular cross-section cavity, where left- or right-handed helical fields can be excited, is also briefly studied. If used as an undulator this cavity produces circularly polarized radiation which can be switched in short times from left- to right-handed polarization.
High-resolution time-of-flight mass spectrometer
Authors: Bergmann T. , Martin T. P. , Schaber H.
Published: July 2002

To perform experiments with clusters, a time-of-flight mass spectrometer with a mass resolution of 35 000 (m/Δm, 50% definition) has been constructed. The main design features of the instrument are presented.
Magnetic alignment and the Poisson alignment reference system
Authors: Griffith L. V. , Schenz R. F. , Sommargren G. E.
Published: July 2002

Three distinct metrological operations are necessary to align a free-electron laser (FEL): the magnetic axis must be located, a straight line reference (SLR) must be generated, and the magnetic axis must be related to the SLR. This article begins with a review of the motivation for developing an alignment system that will assure better than 100-μm accuracy in the alignment of the magnetic axis throughout an FEL. The 100-μm accuracy is an error circle about an ideal axis for 300 m or more. The article describes techniques for identifying the magnetic axes of solenoids, quadrupoles, and wiggler poles. Propagation of a laser beam is described to the extent of revealing sources of nonlinearity in the beam. Development of a straight-line reference based on the Poisson line, a diffraction effect, is described in detail. Spheres in a large-diameter laser beam create Poisson lines and thus provide a necessary mechanism for gauging between the magnetic axis and the SLR. Procedures for installing FEL components and calibrating alignment fiducials to the magnetic axes of the components are also described. The Poisson alignment reference system should be accurate to 25 μm over 300 m, which is believed to be a factor-of-4 improvement over earlier techniques. An error budget shows that only 25% of the total budgeted tolerance is used for the alignment reference system, so the remaining tolerances should fall within the allowable range for FEL alignment.
Demonstration of reduced source size broadening with a Johann focusing elliptical spectrograph and theory of the second-order source broadening
Authors: Hammel B. A. , Phillion D. W. , Ruggles L. E.
Published: July 2002

A Johann focusing elliptical spectrograph has been developed for the measurement of high-resolution x-ray spectra from a spatially extended source. The instrument was designed for the study of high-density, high-temperature plasmas produced by z-pinch implosion or ion-beam bombardment on pulsed-power accelerators. We have constructed and tested this instrument, and have demonstrated an improvement in resolution over what we obtain with a standard circular detector when viewing an extended source. Analytic results for the second-order source broadening due to a finite source size have been obtained and verified by ray tracing. Also given is a simple parametric equation for the Johann crossover curve in terms of either the ellipse sweep angle λ or the Bragg angle θB.
EXAFS at grazing incidence: Data collection and analysis
Authors: Heald S. M.
Published: July 2002

Extended x-ray absorption fine structure (EXAFS) at grazing incidence can be applied to a large variety of surface and interface problems. This paper discusses in detail the collection and analysis of such data using interface EXAFS from metal/Al bilayers as an example. A comparison of the fluorescence and reflectivity detection channels is given, along with a discussion of the methods for correction of anomalous dispersion distortions. In addition, data from a Ni-Ti multilayer is used to demonstrate the potential of enhancing the sensitivity of the EXAFS signal to selected regions using standing wave effects.
Density and temperature diagnostic based on the Ar He β line and associated Li-like satellites
Authors: Mancini R. C. , Hooper C. F. , Delamater N. D. , Hauer A. , Keane C. J. , Hammel B. A. , Nash J. K.
Published: July 2002

We have modeled the temperature and density dependence of the Li-like satellites of the Ar He β line by performing NLTE kinetic modeling of level populations in conjunction with Stark broadening calculations. Composite line profiles are computed including resonance and satellite line transitions that have built-in the temperature and density dependence characteristic of the level populations and Stark broadening of these transitions. These synthetic spectra can be used to analyze experimental data, providing a simultaneous diagnostic of temperature and density.
Measurement of volume flow through a microporous membrane by a NTC thermistor miniature bead
Authors: Molina C. , Victoria L. , Ibáñez J. A.
Published: July 2002

We propose an application for the NTC (negative temperature coefficient) thermistor miniature bead as a sensor to measure the volume flowing through a microporous membrane over a 0–15 cm3/min range. Only one thermistor is used and small temperature changes that can occur during the experiment can be ignored. No compensation or linearity circuitry is used [C. Yang, M. Kümmel, and H. Soeberg, Sensors and Actuators 15, 51 (1988)]. Assembly is easy and it can be adapted to automatic control, for example, to control the flow of a peristaltic pump by connection to an A/D D/A board and computer. When the experimental data was fitted to a potential type curve (y=axb), a sensitivity between 5% and 8% and a correlation coefficient of 0.99 were obtained. The response of the sensor when the flow changes is immediate, although the time taken for the measurement to stabilize is dependent on the size of the variation (between 4 and 7 s). The fitting curve is used to determine the volume flow that is caused by a pressure gradient applied to the membrane placed between two bulks with the same fluid.
Decomposition and primary crystallization in undercooled Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 melts
Authors: Busch R. , Schneider S. , Peker A. , Johnson W. L.
Published: July 2002

Zr41.2Ti13.8Cu12.5Ni10.0Be22.5 bulk metallic glasses were prepared by cooling the melt with a rate of about 10 K/s and investigated with respect to their chemical and structural homogeneity by atom probe field ion microscopy and transmission electron microscopy. The measurements on these slowly cooled samples reveal that the alloy exhibits phase separation in the undercooled liquid state. Significant composition fluctuations are found in the Be and Zr concentration but not in the Ti, Cu, and Ni concentration. The decomposed microstructure is compared with the microstructure obtained upon primary crystallization, suggesting that the nucleation during primary crystallization of this bulk glass former is triggered by the preceding diffusion controlled decomposition in the undercooled liquid state.
Cryogenic, all-sapphire, Fabry–Perot optical frequency reference
Authors: Taylor C. T. , Notcutt M. , Blair D. G.
Published: July 2002

This paper presents a design for a Fabry–Perot optical frequency reference resonator which utilizes the high dimensional stability of cryogenically cooled sapphire. We show that cryogenic sapphire cavities can achieve substantial improvements in frequency stability compared with room-temperature cavities. The design of a laser stabilization system based on such a resonator is discussed. Estimates of fundamental and practical limitations on the frequency stability of such a system suggest that a fractional frequency stability of 10−16 over integration times from 10 to 104 s is possible. The fundamental limits to stability from quantum shot noise, radiation pressure fluctuations, and thermal noise are overwhelmed by practical limits which arise due to mechanical, thermal, and optical effects.
A high-flux 3-M normal incidence monochromator at beamline 20A of the Photon Factory
Authors: Ito Kenji , Morioka Yumio , Ukai Masatoshi , Kouchi Noriyuki , Hatano Yoshihiko , Hayaishi Tatsuji
Published: July 2002

A high-flux 3-m normal incidence monochromator (3-m NIM) has been installed at beam line 20A of the Photon Factory. The 3-m NIM can supply a high photon flux in the wavelength region 30–200 nm, primarily because of a large horizontal acceptance angle of 28 mrad for the synchrotron radiation (SR) beam from bending magnet 20. The photon flux of the 3-m NIM was estimated to be ≊1012 photons/s with Δλ≊0.1 nm at ≊50 nm by measuring the photoemission current from a gold-coated surface. The resolving power with a 2400 grooves/mm grating was found to be greater than 25 000 at 90 nm from the autoionization profile of the Xe nd′ states converging to Xe+ 2P1/2.
Laboratory-scale setup for anionic polymerization under inert atmosphere
Authors: Ndoni Sokol , Papadakis Christine M. , Bates Frank S. , Almdal Kristoffer
Published: July 2002

‘‘Living’’ anionic polymerization offers a readily feasible preparation of very well-controlled homo- or copolymers in a wide range of molar masses and chemical structures. Such samples are vital in experimental polymer physics and the technique presented here offers self-sufficiency with such samples. The technique of anionic polymerization performed under inert atmosphere is presented here. The components of the setup are described in detail. Purification procedures for glassware and chemicals for specific polymerizations are given. Illustrative examples and results are presented.
Design and performance of a new ophthalmic instrument for dynamic light-scattering measurements in the human eye
Authors: Rovati L. , Fankhauser F. , Ricka J.
Published: July 2002

A new optical instrument for in vivo dynamic light-scattering measurements in the human eye is described. The instrument is based on the well-known dynamic light-scattering technique. Results can be obtained from the anterior as well as the posterior segment with high spatial resolution and sensitivity. This instrument allows, to our knowledge for the first time, in vivo measurements of dynamic light scattering to be performed in the vitreous. Interesting performance is obtained using single-mode optical fibers to guide the excitation and the scattered light resulting in a modular, compact system with high-beam quality and electrical insulation of the patient. The instrument demonstrates good safety characteristics (the optical power impinging the patient’s eye is 36 times below the maximum laser power at the cornea, recommended for intrapupil exposure by ANSI standard). To demonstrate the possible clinical use of this technique, in vivo measurements were made and the results compared with the known eye pathologies.
Principles and characteristics of a new generation plasma immersion ion implanter
Authors: Chu P. K. , Tang B. Y. , Cheng Y. C. , Ko P. K.
Published: July 2002

A new generation multipurpose plasma immersion ion implanter (PIII) was custom designed, constructed, and installed in the City University of Hong Kong. The system is designed for general R&D applications in metallurgy, tribology, surface modification, and fabrication of novel materials. Using the new rf ion source in conjunction with the internal antenna system, the plasma density achieves excellent uniformity both laterally and axially. The system also incorporates two metal sources, including four metal arc sources and a sputtering electrode, so that multiple metal deposition and implantation steps can be performed in succession in the same equipment without exposing the samples to air. This capability can be critical to the study of surface properties and corrosion resistance. This article describes the design objectives, the novel features, and the characteristics of this new generation PIII equipment.
Dual toroidal photoelectron spectrometer for investigating photodouble ionization in atoms and molecules
Authors: Reddish T. J. , Richmond G. , Bagley G. W. , Wightman J. P. , Cvejanović S.
Published: July 2002

A photoelectron-photoelectron coincidence spectrometer, incorporating two independent toroidal analyzers, has been developed to study photodouble ionization of gas targets using synchrotron radiation. The energy-resolved and angle-dispersed electron images are recorded using two-dimensional position-sensitive detectors. The design and performance of the spectrometer is described, with particular emphasis on the electron optical properties of toroidal deflectors and their associated electrostatic lenses. The operation and calibration of the spectrometer are discussed and sample (γ,2e) results of helium are presented.
A new rotating spark gap design
Authors: Haddad A. , Abdul-Malek Z.
Published: July 2002

Standard spark gaps have lower time limits of gap recovery when testing with high repetition rate impulses and in high-current high-voltage multiple impulse testing. More important, they are not suitable for the generation of opposite-polarity successive impulses using conventional capacitive-type generation techniques. In this article, an improved design incorporating two rotating spark gaps is described. The new spark gap was used to test ZnO surge arresters with two successive impulses of currents up to 5 kA and voltages up to 50 kV. Time intervals as low as 10 ms were achieved between the two impulses. Both similar and opposite polarity tests were carried out successfully.
Instrumentation for the joint European torus motional Stark effect diagnostic
Authors: Stratton B. C. , Long D. , Palladino R. , Hawkes N. C.
Published: July 2002

A motional Stark effect magnetic field pitch angle diagnostic has been implemented on the joint European torus (JET) tokamak. The instrumentation designed following the study by Hawkes et al. (these proceedings) is described. Dα emission from the Octant 4 neutral beams is collected by optics which transport the plasma image outside the vacuum vessel and through a pair of photoelastic modulators (PEMs) and a linear polarizer. The light is fiber-optically coupled to interference filter spectrometers, which incorporate a remotely controlled filter tilting mechanism. This allows the center wavelength of the filter bandpass to be tuned over a range sufficient for observation of the σ and π lines of the Stark spectrum emitted by the full- and half-energy components of the beam, providing flexibility to make measurements with a variety of beam configurations. The detectors are low-noise avalanche photodiode modules. Fast digital signal processing techniques are used to extract the Fourier components of the signal at the PEM first and second harmonic frequencies. Analysis of these signals will yield the magnetic field pitch angle, which will be used as a constraint on EFIT equilibrium reconstruction modeling to obtain the q(r) profile. The system has 25 spatial channels covering the outer-half of a JET plasma with spatial resolution of 0.03–0.07 m per channel with ∼0.05 m channel-to-channel separation. Time resolution is expected to be 1–10 ms.
Longitudinal impedance tuner using new material FINEMET
Authors: Koba K. , Arakawa D. , Fujieda M. , Ikegami K. , Ishi Y. , Kanai Y. , Kubota C. , Machida S. , Mori Y. , Ohmori C. , Shinto K. , Shibuya S. , Takagi A. , Toyama T. , Uesugi T. , Watanabe T. , Yamamoto M. , Yokoi T. , Yoshii M.
Published: July 2002

We designed an impedance tuner consisting of an inductive material, FINEMET, to cancel the space charge impedance in the longitudinal direction. It was installed in the KEK Proton Synchrotron (PS) main ring. We observed the frequency shift of the coherent quadrupole oscillations and inferred the shift of the incoherent synchrotron oscillation. The total reactive impedance can be estimated as the coefficient between the shift and the beam intensity. The measured impedance is reduced from −j2475Ω to −j1182Ω by the impedance tuner which consists of 12 pieces of FINEMET cores. We demonstrated that the space charge impedance is compensated by the impedance tuner. This is the first time for FINEMET to be equipped with an accelerator component. One may think that the characteristics of FINEMET deteriorate under an environment with strong radiation generated by unavoidable beam loss. We have proved that the radiation dose not affect FINEMET even with a total neutron dose of 1.83×1012(n cm−2), which is considered to be the highest dose of the main ring.
Mechanism of yellow luminescence in GaN
Authors: Suski T. , Perlin P. , Teisseyre H. , Leszczyński M. , Grzegory I. , Jun J. , Boćkowski M. , Porowski S. , Moustakas T. D.
Published: July 2002

We investigated the pressure behavior of yellow luminescence in bulk crystals and epitaxial layers of GaN. This photoluminescence band exhibits a blueshift of 30±2 meV/GPa for pressures up to about 20 GPa. For higher pressure we observe the saturation of the position of this luminescence. Both effects are consistent with the mechanism of yellow luminescence caused by electron recombination between the shallow donor (or conduction band) and a deep gap state of donor or acceptor character.
Improved AlGaInP-based red (670–690 nm) surface-emitting lasers with novel C-doped short-cavity epitaxial design
Authors: Schneider R. P. , Hagerott Crawford M. , Choquette K. D. , Lear K. L. , Kilcoyne S. P. , Figiel J. J.
Published: July 2002

A modified epitaxial design leads to straightforward implementation of short (1λ) optical cavities and the use of C as the sole p-type dopant in AlGaInP/AlGaAs red vertical-cavity surface-emitting lasers (VCSELs). Red VCSELs fabricated into simple etched air posts operate continuous wave at room temperature at wavelengths between 670 and 690 nm, with a peak output power as high as 2.4 mW at 690 nm, threshold voltage of 2.2 V, and peak wallplug efficiency of 9%. These values are all significant improvements over previous results achieved in the same geometry with an extended optical cavity epitaxial design. The improved performance is due primarily to reduced optical losses and improved current constriction and dopant stability.
Electroless nickel plated contacts on porous silicon
Authors: Dhar S. , Chakrabarti S.
Published: July 2002

We have presented the electroless nickel plating technique as a preferred method for making ohmic or rectifying contacts on porous silicon. Nickel, plated by this technique, penetrates the pores and forms contact on an effective area, about 4.5 times the actual area of the sample. High-temperature annealing of the plated metal produced excellent ohmic contacts with porous silicon formed on n-type silicon. The properties of this contact are shown to be much superior to that of conventional evaporated and alloyed ohmic contacts made on p-type porous silicon of identical characteristics. Contacts made under similar conditions by electroless nickel plating on p-type porous silicon, on the other hand, showed good rectifying diode characteristics. The observed electrical properties of electroless nickel contacts are believed to be due to the presence of minute amounts of phosphorous with the plated metal.
Extraction of real-space correlation function of a rough surface by light scattering using diode array detectors
Authors: Zhao Y. P. , Yang H.-N. , Wang G.-C. , Lu T.-M.
Published: July 2002

Based on an inverse transform method originally developed by Chandley and modified by us in the present work, we show that the height-height correlation function of a rough Si surface can be obtained directly from a single intensity distribution profile of light scattering. A novel diode array detectors arrangement was used to obtain the intensity profile. The roughness parameters, including the interface width, lateral correlation length, and roughness exponent were extracted from the height-height correlation function and were compared with that obtained by an atomic force microscope.
Atomic force microscopy and photoluminescence study of Ge layers and self-organized Ge quantum dots on Si(100)
Authors: Palange E. , Capellini G. , Di Gaspare L. , Evangelisti F.
Published: July 2002

In this letter we present an atomic force microscopy and photoluminescence investigation of two- and three-dimensional Ge structures deposited on Si(100) substrates. The photoluminescence spectra demonstrated the presence of quantum confinement effects in flat and uncapped Ge layers and in Ge islands even for the relatively large size of the structures. Moreover, a correlation between the sample morphology and the features of the photoluminescence is demonstrated.
Absorption enhancement in silicon-on-insulator waveguides using metal island films
Authors: Stuart Howard R. , Hall Dennis G.
Published: July 2002

We report the degree to which the resonances associated with metal island films can be used to enhance the sensitivity of very thin semiconductor photodetectors. The island films can couple incident light into the waveguide modes of the detector, resulting in increased absorption. To characterize the coupling, silver-, gold-, and copper-island layers were formed on the surface of a thin-film photodetector fabricated in the 0.16 μm thick silicon layer of a silicon-on-insulator (SOI) wafer. The copper islands gave the best result, producing more than an order of magnitude enhancement in the photocurrent for light of wavelength 800 nm. The enhancements appear to be due primarily to coupling between the metal island resonances and the waveguide modes supported by the SOI structure.
Enhanced quantum efficiency in polymer electroluminescence devices by inserting a tunneling barrier formed by Langmuir–Blodgett films
Authors: Kim Young-Eun , Park Heuk , Kim Jang-Joo
Published: July 2002

Quantum efficiency in a polymer electroluminescence device is significantly improved by inserting a thin insulating layer with the thickness of tunneling range. Four times higher quantum efficiency was obtained without the increase of the threshold voltage. Poly(methyl methacrylate) Langmuir–Blodgett films were used as the thin tunneling barrier. The enhancement may result from the lowering of the effective barrier height for electron injection while increasing the effective barrier for hole injection. The effects improve the balanced injection of electrons and holes into the light-emitting devices.
Ferroelectric field effect in ultrathin SrRuO3 films
Authors: Ahn C. H. , Hammond R. H. , Geballe T. H. , Beasley M. R. , Triscone J.-M. , Decroux M. , Fischer O/. , Antognazza L. , Char K.
Published: July 2002

We report the observation of a ferroelectric field effect in the conducting oxide SrRuO3 using Pb(Zr0.52Ti0.48)O3/SrRuO3 epitaxial heterostructures. Upon reversing the polarization of the ferroelectric Pb(Zr0.52Ti0.48)O3 layer, we measured a 9% change in the resistance of a nominally 30 Å SrRuO3 film at room temperature. This change was nonvolatile for a period of several days. Conductivity measurements taken between 4.2 and 300 K are consistent with n-type conduction throughout this temperature range. Hall effect measurements also yield n-type conduction, with n≈2×1022 electrons/cm3, and furthermore allow us to understand quantitatively the magnitude of the observed resistivity change.
X-ray photoelectron spectroscopic evaluation of valence band offsets for strained Si1−xGex, Si1−yCy, and Si1−x−yGexCy on Si(001)
Authors: Kim Myeongcheol , Osten H. J.
Published: July 2002

The crucial parameters which determine the electrical and optical behavior of a heterojunction are the valence and conduction band offsets. We demonstrate that carefully performed in situ x-ray photoelectron spectroscopic measurements allow the evaluation of valence band offsets in strained heteroepitaxial systems on Si(001). The result obtained for a Si0.75Ge0.25 alloy layer agrees very well with the known value, indicating the reliability of the used method. For Si0.977C0.023 alloy layers tensily strained on Si(001), we could not find any significant valence band offset to Si. The observed band gap narrowing is mainly dominated by a conduction band offset. Ternary strained Si0.727Ge0.25C0.023 alloy layers show the same valence band offset to Si as the appropriate binary Si0.75Ge0.25 alloy layers, that is, the valence band offset is dominated by Ge effects.
Comparison of high field electron transport in GaN and GaAs
Authors: Foutz B. E. , Eastman L. F. , Bhapkar U. V. , Shur M. S.
Published: July 2002

An ensemble Monte Carlo simulation is used to compare high field electron transport in bulk GaN and GaAs. In particular, velocity overshoot and electron transit times are examined. In GaN, we find the steady state velocity of the electrons is the most important factor determining transit time over distances longer than 0.2 μm. Over shorter distances velocity overshoot effects in GaN at high fields are comparable to those in GaAs. We estimate the minimum transit time across a 1 μm GaN sample to be about 3.0 ps. Similar calculations for GaAs yield 5.4 ps.
Highly textured and conductive undoped ZnO film using hydrogen post-treatment
Authors: Baik Seung Jae , Jang Jae Hoon , Lee Chang Hyun , Cho Woo Yeong , Lim Koeng Su
Published: July 2002

We proposed a method to enhance the characteristics of undoped ZnO films by H2 post-treatment using photochemical vapor deposition. The resistivity of a H2-treated film decreased from 1×10−2 to 2×10−3 Ω cm, the haze ratio increased from 37% to 48%, and no degradation of total transmittance was observed. There are two possible explanations for these phenomena. First, hydrogen atoms assist the desorption of oxygen atoms from the film, resulting in decreased resistivity. Second, hydrogen atoms etch small grains growing among large ones on the surface of the film, resulting in a rough surface.
Laser emission of a flash-lamp pumped Rhodamine 6 G solid copolymer solution
Authors: Calderón Oscar G. , Guerra J. M. , Costela A. , Garcı́a-Moreno I. , Sastre R.
Published: July 2002

A Rhodamine 6 G solid solution in a copolymer of 2 hydroxyethyl methacrylate and methyl methacrylate have been flash-lamp pumped in an untuned laser cavity. The pumping energy threshold to obtain laser emission is 20 percent higher than in equivalent methanol solutions. With a flash-lamp electrical excitation average energy of 150 joules per pulse, no photodegradation was observed in the laser emission after more than 30 pumping pulses. There was an absence of local irregular fluctuations found typically in high Fresnel number dye lasers. An interpretation based on the assumption of stereospecificity in the lodging cavity of dye molecules, is consistent with the high photostability and the absence of local fluctuations obtained with this polymeric solid-state laser.
Wideband optical modulation via the magneto–optic interaction in a bismuth-lutetium-iron garnet film
Authors: Prabhakar A. , Stancil D. D.
Published: July 2002

Optical modulation with a bandwidth of about 3 GHz centered at 5.75 GHz was observed in a thin film of [BiLu]3Fe5O12 using the magneto-optical interaction. A microstrip transducer was placed in contact with the film and TM polarized optical guided modes were excited beneath and parallel to the transducer. The TM→TE mode conversion was measured as a function of the angle between an in-plane field, of up to 100 Oe, and the optical beam. The bandwidth of the modulation was limited by the microwave components used in the external circuit. The experiments qualitatively agree with a simple model that describes a modulation of the optical beam by a nonresonant precession of the magnetization about an equilibrium.
Controlling charge injection in organic electronic devices using self-assembled monolayers
Authors: Campbell I. H. , Kress J. D. , Martin R. L. , Smith D. L. , Barashkov N. N. , Ferraris J. P.
Published: July 2002

We demonstrate control and improvement of charge injection in organic electronic devices by utilizing self-assembled monolayers (SAMs) to manipulate the Schottky energy barrier between a metal electrode and the organic electronic material. Hole injection from Cu electrodes into the electroluminescent conjugated polymer poly[2-methoxy,5-(2′-ethyl-hexyloxy)-1,4-phenylene vinylene] was varied by using two conjugated-thiol based SAMs. The chemically modified electrodes were incorporated in organic diode structures and changes in the metal/polymer Schottky energy barriers and current–voltage characteristics were measured. Decreasing (increasing) the Schottky energy barrier improves (degrades) charge injection into the polymer.
Formation of Sn nanocrystals in thin SiO2 film using low-energy ion implantation
Authors: Nakajima Anri , Futatsugi Toshiro , Horiguchi Naoto , Yokoyama Naoki
Published: July 2002

This letter reports on a simple technique for fabricating Sn nanocrystals in thin SiO2 film using low-energy ion implantation followed by thermal annealing. These Sn nanocrystals have excellent size uniformity and position controllability. Their average diameter is 4.8 nm with a standard deviation of 1.0 nm. Most of the Sn nanocrystals reside at the same depth. The lateral edge-to-edge spacing between neighboring Sn nanocrystals is fairly constant: about 3 nm. A narrow as-implanted ion distribution profile and the effect of the SiO2–Si interface are considered to contribute to the size uniformity and position controllability. The features of these nanocrystals will open up new possibilities for novel devices.
Large third-order optical nonlinearity in Au:TiO2 composite films measured on a femtosecond time scale
Authors: Liao H. B. , Xiao R. F. , Wang H. , Wong K. S. , Wong G. K. L.
Published: July 2002

The wavelength dependence of the third-order nonlinear optical susceptibilities, χ(3), of the Au:TiO2 composite films with Au concentration varying from 15% to 60% (volume fraction), was measured by a degenerate four-wave mixing (DFWM) technique using a probe laser with a pulse width of 200 fs. It was found that, with the wavelength of the probe laser close to the surface plasmon resonance (∼680 nm), both the χ(3) and the figure of merit, χ(3)/α (α is optical absorption coefficient) were significantly enhanced. The maximum value of the χ(3) was 6×10−7 esu and occurred at an Au concentration of about 38%. Femtosecond time-resolved DFWM measurements revealed that the response time of the optical nonlinearity in the Au:TiO2 films is extremely fast. The time-resolved DFWM results suggest that the main physical mechanism involved in the optical nonlinearity in Au:TiO2 films on the femtoseconds time scale is the interband electric–dipole transition, and the hot electron excitation only partially contributes to the χ(3) on the femtosecond time scale and it becomes dominant only in the picosecond region.
Generation of Q-switched Er:YAG laser pulses using evanescent wave absorption in ethanol
Authors: Vodopyanov K. L. , Shori R. , Stafsudd O. M.
Published: July 2002

We report on a technique of passively Q switching an Er:YAG laser operating at 2.94 μm. The Q switch consists of a high refractive index prism having one total internal reflection surface in contact with an absorbing liquid. The initial losses were achieved via attenuated total reflection. Using the above Q switch, pulses with up to 85 mJ having 130–140 ns pulse width were generated. The output was linearly polarized and the spacial beam profile was near TEM00. The laser was operated at 2 Hz repetition rate.
Microstructure of GaN laterally overgrown by metalorganic chemical vapor deposition
Authors: Marchand H. , Wu X. H. , Ibbetson J. P. , Fini P. T. , Kozodoy P. , Keller S. , Speck J. S. , DenBaars S. P. , Mishra U. K.
Published: July 2002

Extended defect reduction in GaN grown by lateral epitaxial overgrowth (LEO) on large-area SiO2/GaN/Al2O3 wafers by low pressure metalorganic chemical vapor deposition is characterized using transmission electron microscopy and atomic force microscopy. The laterally overgrown GaN (LEO GaN) has a rectangular cross section with smooth (0001) and {112̄0} facets. The density of mixed-character and pure edge threading dislocations in the LEO GaN (<5×106 cm−2) is reduced by at least 3–4 orders of magnitude from that of bulk GaN (∼1010 cm−2). A small number of edge dislocations with line directions parallel to the basal plane are generated between the bulk-like overgrown GaN and the LEO GaN regions as well as at the intersection of adjacent merging LEO GaN stripes. The edge dislocations are most likely generated to accommodate the small misorientation between bulk-like GaN and LEO GaN regions as well as between adjacent single-crystal LEO GaN stripes.