bluuebunny/crossref_metadata_2025 huggingface dataset:
Early stages of void formation in Al-Cu lines studied using positron annihilation
Authors: Simpson P. J. , Umlor M. T. , Lynn K. G. , Rodbell K. P.
Published: July 2002

We have applied positron annihilation spectroscopy to examine the formation of voids in SiO2-passivated 1 μm×1 μm Al-0.5 wt. % Cu lines. Samples were heat-treated both ex situ and in the positron beam to monitor void formation as a function of time and temperature. By measuring the fraction of 3-γ annihilations (a sensitive indicator of large open volume defects) we have established that voids are present at the interface between the Al alloy lines and the SiO2 passivation before heat treatment. The 3-γ fraction then grows to a maximum in less than 1 h at a temperature of 300 °C. Changes in the Doppler-broadening S parameter are also observed. Studies are underway to apply the same methodology to investigate electromigration.
Characterization of polycrystalline Al and Cu metal films sputtered on SiO2/Si substrate using the Laue method with synchrotron x radiation
Authors: Yasuami S. , Takase T. , Ohsumi K.
Published: July 2002

Reflection spots from granular aluminum and copper films were recorded on imaging plates. By comparing the reflection spots with the overall illuminated area, it was estimated that the aluminum granules were several microns in dimensions. The copper granules were much smaller. The spots spread and exhibited contrast, proving that stress was present in the aluminum granules. Assuming constant lattice parameters, the orientation shift between specific points in a single granule was determined to be around half a degree. It is highly likely that the granules have suffered plastic deformation.
Frequency doubled diode-pumped pulse compressed additive-pulse mode-locked N
d
3+ doped lithium yttrium fluoride laser producing 250 fs duration pulses
Authors: Robertson A. , Langford N. , Ferguson A. I.
Published: July 2002

The frequency doubling and subsequent pulse compression of pulses from an additive-pulse mode-locked Nd:YLF laser have been reported. Pulses as short as 245 fs with an average power of 140 mW corresponding to a peak power of 4 kW at 523.5 nm are generated using a simple fiber-grating pulse compressor.
Contrast reversal of antiparallel domains in Cu-doped (Ba0.25Sr0.75)0.9(K0.5Na0.5)0.2Nb2O6 single crystal with synchrotron topography
Authors: Huang X. R. , Jiang S. S. , Zeng W. , Hu X. B. , Liu W. J. , Feng D. , Chen H. C. , Jiang Q. Z. , Jiang J. H. , Wang Z. G.
Published: July 2002

Synchrotron-radiation topographic observations have shown that the Cu-doped (Ba0.25Sr0.75)0.9(K0.5Na0.5)0.2Nb2O6 crystal has a strong ferroelectric x-ray anomalous-scattering effect at the wavelength near the absorption edge of Ba atoms. The reversal of anomalous contrast of antiparallel domains in the crystal was directly revealed in the topographs of hkl and hkl̄ reflections. It was found that the domain walls are all polar and are formed to compensate the charges resulting from the inhomogeneous distributions of the metal atoms in the bulk crystal.
Low-temperature electron cyclotron resonance chemical vapor deposition of very low resistivity TiN for InP metallization using metalorganic precursors
Authors: Boumerzoug Mohamed , Mascher Peter , Simmons John G.
Published: July 2002

Titanium nitride (TiN) thin films were deposited onto Si and InP using the electron cyclotron resonance chemical vapor deposition technique. Tetrakis(dimethylamido)titanium (TDMATi) was used as a precursor. Depositions onto unheated substrates were carried out downstream of a nitrogen plasma. Stoichiometric (Ti:N≊1) and very low resistivity (43 μΩ cm) films were obtained at a deposition rate of 13 Å/min. The carbon and oxygen contaminants in the films were below the detectability limits of Rutherford backscattering and Auger electron spectroscopy. The Auger depth profile shows that the TiN/InP structure is stable for rapid thermal annealing up to 800 °C.
Normal incidence intersubband absorption in vertical quantum wells
Authors: Berger V. , Vermeire G. , Demeester P. , Weisbuch C.
Published: July 2002

N-doped vertical AlGaAs quantum wells have been fabricated by metalorganic vapor phase epitaxial growth of a single-doped AlGaAs layer on a submicron grating. Intersubband absorption at normal incidence is demonstrated in those quantum wells. This opens new possibilities for infrared quantum well devices using intersubband transitions.
Thermogravimetric analysis to determine the lithium to manganese atomic ratio in Li1+xMn2−xO4
Authors: Gao Yuan , Dahn J. R.
Published: July 2002

Li1+xMn2−xO4 samples show reversible oxygen intercalation and deintercalation upon heating in the temperature range between 700 and 950 °C which can be monitored using thermal gravimetric analysis. There are two kinks, due to phase transitions, in the weight-temperature curve observed on heating. The temperature of the low-temperature kink depends linearly on x and therefore can be used to infer the sample stoichiometry. This provides a simple and straightforward quality control check on Li1+xMn2−xO4 samples for the lithium battery industry.
Liquid phase epitaxial growth of high quality GaAs on InP using Se-doped GaAs buffer layer and grating-patterned substrates
Authors: Kim Dong-Keun , Ahn Ju-Heon , Lee Byung-Teak , Lee H. J. , Cha S. S. , Lim K. Y. , Kim J. B. , Lee J.-L. , Jang S. J. , Park I.-S.
Published: July 2002

High quality GaAs layers with excellent crystal quality and surface morphology were grown on InP substrates (GaAs/InP) using liquid phase epitaxy. Thin GaAs buffer layers heavily doped with Se were utilized to prevent the substrate meltback and the InP substrates patterned with gratings to reduce the dislocation density. Double crystal x-ray diffraction showed about 230 arcsec full width at half maximum of the (400) reflection, which represents significant improvement compared to the previously reported 350 arcsec of the GaAs/InP layer grown by chemical beam epitaxy using strained superlattice buffer layers.
Molecular beam epitaxy regrowth using a thin In layer for surface passivation
Authors: Peng C. K. , Tu S. L. , Chen S. S. , Lin C. C.
Published: July 2002

We report a molecular beam epitaxy regrowth technique using a thin In layer for surface passivation. X-ray photoemission spectroscopy measurements show that an In layer as thin as a few tenths of an angstrom is adequate for the effective protection of the underlying III-V epilayers from carbon and oxygen contamination, while still providing exposure to the atmosphere. C–V depth profilings of the regrown pseudomorphic high electron mobility transistors (PHEMTs) reveal no significant residual charge carriers near the regrowth interface. The regrown PHEMTs with 1 μm gate length have a transconductance as high as 330 mS/mm and ft over 23 GHz.
Semi-insulating InP grown by chemical beam epitaxy with pentacarbonyliron doping
Authors: Walker J. D. , Tsang W. T.
Published: July 2002

We present semi-insulating iron-doped InP grown by chemical beam epitaxy using the gaseous source pentacarbonyliron, Fe(CO)5. Analysis by secondary ion mass spectroscopy shows that iron incorporation is proportional to the Fe(CO)5 flow rate over the 5×1017–5×1019 cm−3 range studied. Use of Fe(CO)5 as an iron source also leads to high ∼1018 cm−3 carbon incorporation in the material, but this does not interfere with semi-insulating behavior. The material shows 30 MΩ cm resistivity for a broad range of Fe(CO)5 flow rates. No oxygen incorporation was observed
Crystallization upon thermal annealing of a glass-forming liquid crystal in the nematic regime
Authors: Mastrangelo John C. , Blanton Thomas N. , Chen Shaw H.
Published: July 2002

As an example of a novel class of glass-forming liquid crystals, compound (I) was synthesized and characterized to possess a nematic mesophase between Tg and Tc as the pristine crystal was heated beyond its Tm followed by quenching to below room temperature. Differential scanning calorimetry (DSC) and x-ray diffraction techniques were employed to investigate its morphological stability. It was found that the nematic mesophase persists upon annealing for a period of up to 22 h without the appearance of new phases. However, after annealing in the nematic regime over a longer period of time, thermally activated phase transformations were observed, resulting in a new crystalline phase plus the pristine crystalline phase based on DSC thermal transition data and x-ray diffraction patterns.
Strained Si1−xGex multi-quantum well waveguide structures on (110) Si
Authors: Bernhard-Höfer K. , Zrenner A. , Brunner J. , Abstreiter G. , Wittmann F. , Eisele I.
Published: July 2002

Pseudomorphic Si1−xGex/Si multi-quantum well structures for waveguide applications have been grown on (110) Si by molecular beam epitaxy. In a series of samples the Ge fraction x has been varied from x=0.25 to x=0.37 and x=0.50, respectively. We have used photocurrent spectroscopy on mesa diodes to demonstrate that the absorption edge of the strained Si1−xGex quantum wells can be tuned from 1.3 to 1.55 μm by the Ge fraction x. Realization and characterization of single-mode (110) Si1−xGex rib waveguides with end facets of high optical quality, prepared by cleaving, is reported.
Influence of DX centers in the AlxGa1−xAs barrier on the low-temperature density and mobility of the two-dimensional electron gas in GaAs/AlGaAs modulation-doped heterostructure
Authors: Yang Bin , Wang Zhan-guo , Cheng Yong-hai , Liang Ji-ben , Lin Lan-ying , Zhu Zhan-ping , Xu Bo , Li Wei
Published: July 2002

In GaAs/AlGaAs modulation-doped heterostructure, adopting triangular quantum well approximation and including the seven major scattering mechanisms, we considered the existence of the DX centers in the AlxGa1−xAs barrier and calculated the dependence of low-temperature two-dimensional electron gas (2DEG) density and mobility on spacer layer thickness, Al composition and Si-doping concentration of the AlxGa1−xAs barrier. The calculated results explained the experimental results that cannot be explained by the previous studies. Our calculations demonstrate that DX centers in the AlxGa1−xAs barrier play an important role in determining low-temperature 2DEG density and mobility.
Nonlinear absorption of a carbocyanine dye 1,1′,3,3,3′,3′-hexamethylindotricarbocyanine iodide using a z-scan technique
Authors: Swatton S. N. R. , Welford K. R. , Till S. J. , Sambles J. R.
Published: July 2002

Experimental and theoretical data are presented for the nonlinear absorption of the organic laser dye 1,1′,3,3,3′,3′-hexamethylindotricarbocyanine iodide (HITCI) using a z-scan technique. Experimental data show an induced absorption above laser fluences of 10 mJ/cm2 and a saturation of the nonlinear absorption above fluences of 0.5 J/cm2. A self-consistent theoretical analysis, based on rate equations, is used to predict accurately the results of z scans taken at different pulse energies. Photophysical parameters, including the excited state lifetimes and absorption cross sections are derived for HITCI.
Pulse width reduction in single mode diode lasers via external injection of optical pulses
Authors: Mirasso Claudio R.
Published: July 2002

We propose and numerically study a simple scheme to obtain large pulse-width reduction of optical pulses generated by semiconductor lasers. The scheme consists of modulating two single-mode semiconductor lasers coupled through a normal dispersion fiber. The optimal pulse compression is obtained for a particular range of phase delay between the two modulated electrical injection currents. In addition, the optical pulses so obtained have a larger output power and are very close to transform-limited as required for soliton communication systems.
Enhancement of photoelectric emission sensitivity of tungsten by potassium ion implantation
Authors: Girardeau-Montaut J. P. , Girardeau-Montaut C. , Afif M. , Perez A. , Moustaïzis S. D.
Published: July 2002

Measurements of single-photon photoelectric emission sensitivity of ion implanted polycrystalline tungsten surface by 3×1016 K+ ions/cm2 are reported. They are compared to the data previously obtained for pure tungsten tested under the same conditions. The enhancement of the photoelectric sensitivity up to a factor of 50 was measured as a consequence of the change in the electronic properties of the tungsten surface, induced by the implanted alkali metal ions. Compared with other techniques used to reduce the work function of pure tungsten, the implanted surface exhibits a lower work function than the pure metal, and is capable of supporting high laser intensity for a long time. For these reasons it seems possible to consider the ion-implantation technique as a suitable new method to significantly improve the photoelectric performances of usual metals, under high laser intensity illuminations.
Technique to suppress dislocation formation during high-dose oxygen implantation of Si
Authors: Holland O. W. , Thomas D. K. , Zhou D. S.
Published: July 2002

Damage accumulation during high-dose oxygen implantation of Si to form a silicon-on-insulator material can deleteriously affect the quality of the material. In particular, dislocations formed in the superficial silicon layer are difficult to anneal, requiring temperatures near the melting point of Si to reduce their density to acceptable levels. A technique to suppress the formation of these dislocations during irradiation is presented. The success of this technique lies in its ability to interact with vacancy-type defects within the superficial layer whose accumulation precedes dislocation formation. A Si+ self-ion beam is used as a spatially specific tool to introduce Si atoms into the vicinity of these precursor defects prior to the onset of dislocation growth. The interaction of this beam with the precursor defects is shown to be effective in suppressing dislocation formation during subsequent O+ implantation.
Effect of PH3 on the dissociative chemisorption of SiH4 and Si2H6 on Si(100): Implications on the growth of in situ doped Si thin films
Authors: Maity N. , Xia L.-Q. , Engstrom J. R.
Published: July 2002

The effect of PH3on the dissociative chemisorption of SiH4 and Si2H6 on the Si(100) surface has been investigated with supersonic molecular beam techniques. Adsorbed phosphorus atoms, formed as a result of the reaction of PH3on the Si surface, inhibit the dissociative chemisorption of both SiH4 and Si2H6 through a short-range steric mechanism. The probability of dissociative adsorption of both silicon hydrides is found to be proportional to the quantity 1-θP2, where θP is the fractional coverage of adsorbed phosphorous atoms. These results have been employed to formulate a predictive model for the kinetics of Si thin-film growth in the presence of PH3(g).
Superlattice-equivalent (In,Ga)As/(In,Al)As quantum wells with large Stark shifts in the 1.3-μm spectral region
Authors: Leavitt R. P. , Bradshaw J. L. , Pham J. T.
Published: July 2002

We have measured room-temperature photocurrent spectra of p-i-n diode structures containing multiple superlattice-equivalent quantum wells wherein each quantum well consists of a few periods of a fine-period (In,Ga)As/(In,Al)As superlattice. Both the absolute exciton absorption energies and the Stark shifts are in excellent agreement with calculations, which predict a larger Stark shift for this structure than for a quaternary quantum well with the same width and absorption edge. Calculated electric-field-induced changes in the real and imaginary parts of the refractive index show that these structures are promising candidates for semiconductor intensity and phase modulators for wavelengths around 1.3 μm.
Genetic algorithms: A new approach to energy balance equations
Authors: Jakumeit J.
Published: July 2002

The observation of nonclassical conductivity in n-Hg0.8Cd0.2Te gives the possibility to investigate the hot electron transport in the absence of magnetic fields at temperatures around 4.2 K. Based on calculations of the electron phonon scattering rates, a comparison of the predictions of the standard electron temperature model with the experimental data revealed a large discrepancy. By means of a genetic algorithm energy distribution functions have been calculated which describe the experimental results correctly. This application of genetic algorithms to solve a energy balance equation demonstrates that genetic algorthims are a promising tool to compare general theoretical methods with experimental data, without further theoretical assumptions or simplifications.
Early dynamics of laser-ablated YBa2Cu3O7 plasmas from their vacuum ultraviolet radiation time history
Authors: Mehlman G. , Chrisey D. B. , Horwitz J. S.
Published: July 2002

Simultaneous time and space resolution of the monochromatic vacuum ultraviolet emission from an excimer laser-ablated plasma has yielded quantitative information on the plasma generation and velocity. From the time-resolved spectral data, plasma velocities were measured and found to be ∼2.5×106 cm/s. The observed radiation time profile at the target surface reflects essentially the dynamics of the laser pulse absorption. Material continues to be ejected from the target for more than 100 ns after the end of the laser pulse.
Effects of quantum well subband structure on the temperature stability of vertical-cavity semiconductor lasers
Authors: Chow Weng W. , Choquette Kent D. , Gourley Paul L.
Published: July 2002

This letter investigates the effects of band-structure, band-filling, and many-body interactions on the temperature behavior of a vertical-cavity surface-emitting laser. Significant improvement in temperature stability of the laser output is predicted in the presence of gain arising from high lying quantum well subbands.
Low power electronic optical bistability in single quantum well InP/InGaAsP Fabry–Perot waveguide resonators
Authors: Hübner B. , Zengerle R. , Forchel A.
Published: July 2002

Optical bistability in a single quantum well waveguide resonator in the InP/InGaAsP material system is demonstrated. High contrast ratio (≳3:1) and switching at low power (≊1.5 mW) was obtained by using a single quantum well at a wavelength near the maximum nonlinear refractive index change and by depositing a reflective coating on the rear end of the waveguide. Clear optical bistability is observed in a wide wavelength range of 1480–1525 nm. Due to the low input power, cw operation of the device was possible at room temperature.
Excimer laser assisted chemical machining of SiC ceramic
Authors: Hibi Yuko , Enomoto Yuji , Kikuchi Kaoru , Shikata Nobuo , Ogiso Hisato
Published: July 2002

A highly effective method of machining ceramic has been newly developed using a krypton fluoride (KrF) excimer laser with a 248 nm wavelength. The laser was irradiated on SiC in water to form a soft hydrous oxide layer by photochemical reaction. The softened layer was then cut with a diamond tool to form a mirror surface finish. The optimum conditions were found for both high machining rate and better surface integrity of SiC.
Composition profiles in electrodeposited ceramic superlattices
Authors: Switzer Jay A. , Phillips Richard J. , Golden Teresa D.
Published: July 2002

Superlattices in the Pb–Tl–O system with layer thicknesses in the 4–6 nm range were electrodeposited from a single aqueous solution by pulsing the applied potential during deposition. The current-time transients that resulted from the potential steps were monitored to both calculate and tailor the composition profiles of the superlattices during growth. The Cottrell method was used to determine that Tl(l) oxidation was diffusion limited at high potentials. The diffusion limitation resulted in a composition profile that was graded throughout the layer with a t−1/2 dependence. Superlattices grown at lower potentials in which both reactants were under kinetic control had square composition profiles.
Ultrahigh nucleation density for growth of smooth diamond films
Authors: Yang G. S. , Aslam M.
Published: July 2002

An ultrahigh density seeding process of diamond thin-film deposition is demonstrated. Diamond powders with average grain sizes of 0.038 and 0.101 μm were used to study the surface roughness as a function of deposition time, film thickness, and nucleation density. The diamond films, prepared by hot filament chemical vapor deposition, were characterized by atomic force microscopy, scanning electron microscopy, and Raman spectroscopy. An extremely high nucleation density on the order of 1011 cm−2 was achieved by coating 0.038 μm diamond powder on the surface of the Si substrate. One micron thick films were obtained with the mean surface roughness of 30 nm.
Efficiency enhancement in a Smith–Purcell free-electron laser
Authors: Shiozawa T. , Sata M.
Published: July 2002

A systematic method to enhance the efficiency of energy transfer in a Smith–Purcell free-electron laser composed of a metallic grating and a relativistic electron beam is proposed. To maintain the synchronism between an electron beam and a slow electromagnetic wave propagated along a metallic grating, either one of the three grating parameters is adiabatically changed in the direction of wave propagation in accordance with the decrease in the drift velocity of the electron beam. The numerical simulation, which takes into account the reflection or scattering due to discontinuities in the grating parameters, demonstrates sufficient efficiency enhancement in energy transfer.
Gain in pulsed x-ray irradiated Cr,Nd:GdScGa-garnet
Authors: Brannon P. J.
Published: July 2002

The transmission properties of gadolinium scandium gallium garnet doped with chromium and neodymium have been studied during and after a 20 ns high-energy x-ray pulse. Gain is observed in the transmission which indicates a small signal gain of 0.175/cm. About 5% of the absorbed dose is converted to inversion, which is comparable to flash-lamp-pumped inversion. The small signal gain scales with dose.
Novel second-order nonlinear optical, aromatic, and aliphatic polyimides exhibiting high-temperature stability
Authors: Yu Dong , Gharavi Ali , Yu Luping
Published: July 2002

Novel aromatic and aliphatic polyimides exhibiting sizable second-order nonlinear optical properties and long term thermal and temporal stability were synthesized. Detailed physical characterization revealed that the polymers are stable up to 300 °C with high glass transition temperatures (≳200 °C). Exceptional thermal stabilities at elevated temperatures were observed even at 150 °C.
Picosecond cross-polarization beam coupling in semi-insulating Ga-doped CdTe at high fluences
Authors: Tomita Yasuo , Enami Eiji
Published: July 2002

We demonstrate the high-contrast polarization-rotation switching in semi-insulating CdTe:Ga using a 30-ps pump and probe pulses at a wavelength of 1.064 μm. It is found that the maximum switching contrast in the photorefractive cross-polarization beam coupling configuration is about eight times higher for CdTe:Ga compared to undoped GaAs at fluences above 10 mJ/cm2.
Ordered, quasiepitaxial growth of an organic thin film on Se-passivated GaAs(100)
Authors: Hirose Y. , Forrest S. R. , Kahn A.
Published: July 2002

Films of the organic semiconductor 3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) are deposited at room temperature in ultrahigh vacuum on the (2×4)-c-(2×8) As-terminated, and the (2×1) Se-passivated (100) GaAs surfaces. The PTCDA deposition on the (2×4)-c(2×8) surface produces domains randomly oriented in the plane parallel to the interface, giving rise to diffuse ringlike low energy electron diffraction (LEED) patterns. A marked improvement in the PTCDA molecular order is observed for the growth on the Se-passivated substrate. The resulting LEED patterns are sharp, and indicate that the interface molecular unit cells are azimuthally oriented with respect to the Se-dimers. The improvement in the crystallinity of the PTCDA layer is attributed to the termination of the chemically active sites by Se and to the smoothness of the Se-passivated surface. This work provides information as to the conditions under which the quasiepitaxial growth of a lattice mismatched van der Waals film oriented to the substrate can be achieved.
X-ray reciprocal space mapping of GaAs/AlAs quantum wires and quantum dots
Authors: Darhuber A. A. , Koppensteiner E. , Bauer G. , Wang P. D. , Song Y. P. , Sotomayor Torres C. M. , Holland M. C.
Published: July 2002

Periodic arrays of 150 and 175 nm-wide GaAs–AlAs quantum wires and quantum dots were investigated, fabricated by electron beam lithography, and SiCl4/O2 reactive ion etching, by means of reciprocal space mapping using triple axis x-ray diffractometry. From the x-ray data the lateral periodicity of wires and dots, and the etch depth are extracted. The reciprocal space maps reveal that after the fabrication process the lattice constant along the growth direction slightly increases for the wires and even more so for the dots.
Fracture strength of free-standing chemically vapor-deposited diamond films
Authors: Steyer Todd E. , Faber K. T. , Drory Michael D.
Published: July 2002

The fracture strength of free-standing chemically vapor-deposited diamond films was assessed by four-point bending. A two-parameter Weibull analysis was performed on 130 μm thick films resulting in a Weibull modulus of 4.3 and a statistical scaling stress of 626 MPa. The residual stress in films was measured from the free-standing film curvature to be 384±10 MPa. The fracture surface chemistry was examined using scanning Auger spectroscopy. The fracture did not occur preferentially along grain boundaries.
Evidence for enhanced zinc interstitial concentration in strain-relaxed heteroepitaxial indium phosphide
Authors: Sieg R. M. , Chatterjee B. , Ringel S. A.
Published: July 2002

Heteroepitaxial InP films grown on GaAs substrates by metalorganic chemical vapor deposition are demonstrated to have a higher concentration of zinc occupying interstitial sites than do equivalent homoepitaxial InP layers. A zinc interstitial-related donor-to-acceptor photoluminescence peak is observed in heteroepitaxial InP films which is absent in the homoepitaxial sample spectra. Capacitance–voltage measurements yield a lower hole concentration in the heteroepitaxial layers versus the homoepitaxial layers, which is attributable to a higher fraction of zinc in interstitial sites within the heteroepitaxial layers. Additionally, the hole concentration of the heteroepitaxial layers is found to be lower near the heterojunction as compared with the film surface region, correlating with a higher dislocation density near the heterojunction as seen by transmission electron microscopy. We conclude that the increased zinc interstitial concentration and the reduced hole concentration are due to dislocation-zinc solute interactions.
Estimation of the configurational entropy of fusion
Authors: Ohsaka K. , Trinh E. H.
Published: July 2002

The entropy of fusion of a metal consists of the configurational and vibrational entropies. A formula is presented to evaluate the configurational entropy by assuming an amorphous phase to be a frozen liquid that has lost the configurational entropy but still maintains the vibrational entropy of the corresponding liquid. The magnitude of the configurational entropy may provide information on the nature of liquid structures. The evaluation requires the enthalpy of the amorphous phase in addition to those of the liquid and crystalline phases. The illustrative evaluation on the Ni24Zr76 alloy shows that ΔSconf is approximately 1k per atom, where k is the Boltzmann constant, which suggests some degree of clustering of atoms in the liquid.
Critical influence of reactant pressure on the evolution of single phase CuInSe2 during selenization at low temperatures
Authors: Lakshmikumar S. T. , Rastogi A. C.
Published: July 2002

Single phase chalcopyrite CuInSe2 (CIS) phase formation at low temperatures (≊260 °C) is demonstrated by Se vapor selenization of evaporated metal precursors at a pressure of ≊0.3 mbar. The low pressure changes the relative kinetics of selenization of Cu and In due to the modification of the availability of Se reacting species. Consequently, the thermodynamically favorable reaction CuSe+In(1)+Se→CIS proceeds to completion at lower temperatures. This is confirmed by the absence of In2Se3 at intermediate pressures (0.5–1.0 mbar). At higher pressures (≊7–10 mbar) and Se flux, simultaneous formation of the equilibrium binaries, CuSe and In2Se3 at low temperatures, leads to the formation of CIS through a diffusion limited reaction of the binaries at higher (≥400 °C) temperatures.
Alternating-current losses in Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox multifilamentary tapes
Authors: Oota A. , Fukunaga T. , Abe T. , Yuhya S. , Hiraoka M.
Published: July 2002

The alternating-current (ac) losses in the Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox multifilamentary tapes with the filament number equal to 7, 19, 37, and 61 are investigated through an inductive method at 77 K under ac magnetic fields with the frequency 50 Hz≤f ≤700 Hz and the field amplitude 2 mT≤B0≤50 mT, and the results are compared with those for a monofilamentary tape. The subdivision of superconductor into multifilaments suppresses the hysteresis loss within the filaments, which is the main contribution to the ac losses in the monofilamentary tape. However, the enhancement of the eddy current loss in the multifilamentary tapes makes the ac losses comparable to those in the monofilamentary tapes.
Large and stable second harmonic generation in a crystalline phase of a ferroelectric liquid crystal
Authors: Sprunt S. , Naciri J. , Ratna B. R. , Shashidhar R. , Bihari B. , Kumar J. , Tripathy S. K.
Published: July 2002

Second harmonic generation (SHG) has been studied in a nitro-substituted ferroelectric liquid crystal cooled from the smectic-C* into a three-dimensional crystalline (K) phase in an applied electric field. The SHG efficiency in the K phase is found to be deff≳4.5 pm/V, about 25 times the value in the SmC* phase, and, unlike the SmC* case, remains constant in zero field for ≳25 h. A quantitative analysis of the polarization dependence of the SHG reveals that the dominant d coefficients contributing to the measured signal differ for the two phases, and that the orientation of the liquid-crystal director in the K phase is modulated in one dimension.
Novel high-power and coherent semiconductor laser with a shaped unstable resonator
Authors: Guel-Sandoval Salvador , Paxton Alan H. , Srinivasan Swaminathan T. , Sun Shang-Zhu , Hersee Stephen D. , Allen Michael S. , Moeller Charles E. , Gallant David J. , Dente Gregory C. , McInerney John G.
Published: July 2002

We describe a novel high power semiconductor laser that employs a shaped unstable resonator waveguide to maintain fundamental spatial mode operation at high power levels. We call this device the SHUR (shaped unstable resonator) laser. By photoetching and regrowth we locate a secondary, nonplanar antiguide, beneath the main part of the waveguide. The lasing mode couples to this secondary guide and experiences lateral antiguiding, which is the basis of the unstable resonator action. Prototype versions of the SHUR laser show a maximum pulsed output power of 770 mW per facet. The focused beam is dominated by a single lobe that contains 47% of the output power.
Effect of terahertz irradiation on ballistic transport through one-dimensional quantum point contacts
Authors: Arnone D. D. , Frost J. E. F. , Smith C. G. , Ritchie D. A. , Jones G. A. C. , Butcher R. J. , Pepper M.
Published: July 2002

A one-dimensional ballistic constriction has been fabricated from a two-dimensional electron gas formed at the interface of a GaAs/AlGaAs heterostructure. The constriction was induced via a pair of front gates which also served as a broadband far-infrared (FIR) antenna. The photocurrent through the constriction was recorded as a function of source-drain bias at various FIR frequencies, one-dimensional subband spacings, and for orthogonal FIR polarizations. The photocurrent was compared to the derivative of dc conductance with respect to source-drain bias. While dc rectification is shown to dominate the photocurrent, deviations from this model occur at frequencies above ∼1 THz, yielding an estimate of the upper limit of the electron scattering time in the constriction region.
Observation of electronic correlation effect in C60 adsorbed on an (0001) surface of 2H–MoS2 by scanning tunneling microscopy
Authors: Zhao D. , Chen T. , Wang L.
Published: July 2002

Scanning tunneling microscopy (STM) studies of monolayer coverage of C60 molecules on a 2H–MoS2 (0001) surface reveal electronic features on the molecules that are rather different from those observed on metal and other semiconductor surfaces. The STM current contrast of the adsorbed C60 is dominated by that of the underlying crystalline lattice at low bias voltages. The observations can be understood by considering (1) a weak adsorption of C60 and (2) an electronic correlation effect between the substrate surface and the molecule. All essential aspects of the experimental STM results are quantitatively reproduced by our calculation.
Pulsed x-ray induced damage to metal and multilayer mirrors
Authors: Kohler D. , Guttman J. L. , Watson B. A. , Gerassimenko Michael
Published: July 2002

The effects of intense pulses of laser-produced x rays upon the reflective and diffractive properties of metal mirrors and layered synthetic microstructure mirrors (artificial crystals) have been investigated. Laser pulses from a Nd–glass pulsed laser system of 25-ns pulse width and 50-J energy were focused onto a copper target to generate x-ray pulses. A polished planar nickel mirror reflected 0.98- to 1.3-keV x rays onto photographic film. The x-ray flux onto the mirror (at grazing incidence angles near 3.5°) was split into two adjacent fields with a beryllium filter over one field and with an equal thickness beryllium filter placed over the film holder covering the adjacent field. Thin pieces of Kimfol were used as debris shields ahead of the mirror sample. This technique provided an in situ normalization since both a low- and high-intensity irradiation can be simultaneously achieved on adjacent portions of the mirror. A similar technique was used to study reflection by a multilayer mirror of carbon–tungsten carbide layering with a 2d spacing of 3.92 nm. Experimental details and the results obtained are presented.
Simple circuit to passively synchronize the predischarge and main discharge in a UV preionized TEA CO2 laser
Authors: Shikarkhane N. S. , Nundy U. , Chatterjee U. K.
Published: July 2002

A simple, inexpensive circuit for synchronizing the preionizer and the main discharge in an UV preionized TEA CO2 laser is described. The circuit uses only two coupling capacitors of value 1.35 nF, between the two discharge circuits to achieve the synchronization. For a delay of 1 μs, the jitter is ±50 ns.
High-accuracy optical attenuator continuously variable in the range of 1:20
Authors: Yamashita Mikio , Kawada Yasushi , Takeuchi Satoshi
Published: July 2002

A continuously variable optical attenuator is described that uses optical fiber light guides and high-accuracy dial micrometers mounted on mechanical stages. The attenuation factors thereby obtained have proved reproducible to ∼0.1% over a dynamic range of 1:20. It should, therefore, be particularly useful in testing the linearity of the response of various photodetectors.
Microvibration sample magnetometer: A force-type measurement
Authors: Morais P. C. , Köche N. M. L. , Tronconi A. L. , Skeff Neto K.
Published: July 2002

A simple microvibrating sample magnetometer (MVSM), particularly inexpensive, sensitive, and versatile has been developed. An alternating magnetic field superposed to a steady uniform magnetic field is applied to the sample. The sample undergoes a periodic motion around an equilibrium position, causing a pressure fluctuation within a closed gas cell which is detected as an acoustic signal by a microphone.
Thermocouple probe for surface-temperature measurement
Authors: Hager N. E.
Published: July 2002

A portable thermocouple probe is designed with physical and geometric properties such that its principal performance characteristics can be predicted from relatively uncomplicated mathematical models. Theory and experiment show that usual thermocouple errors and surface-temperature perturbations can be kept unimportant in a variety of practical applications. Techniques are described for using the probe to measure temperature of stationary and moving materials, including thermal insulating materials and thin sheets where temperature is normally severely perturbed during contact measurements. It is convenient to use the device in combination with a battery-operated digital readout device, permitting temperatures within a few hundred degrees of ambient to be measured with an accuracy of ±2° and a response speed of about 2 s. The probe is found well suited for use in the heat-transfer laboratory, in the factory, and in energy-conservaton field work.
Irradiation cell for electron pulse radiolysis in liquid anhydrous hydrogen fluoride and other corrosive fluoride solvents
Authors: Martin-Rovet D. , Hickel B. , Guitton R. , Potier J.
Published: July 2002

An irradiation cell for electron pulse radiolysis experiments in reactive liquid fluoride media, such as anhydrous hydrogen fluoride, is described. The construction material is Kel-F, the irradiation window being a part of the body of the cell. The optical windows for the analytical light are made from sapphire. The cell has been tested with reactive solutions which have been added and removed on a vacuum line, and has been shown to be suitable for electron beam radiolysis studies.
Far-infrared radiation-induced thermopower in a quantum point contact
Authors: Wyss Rolf A. , Eugster C. C. , del Alamo J. A. , Hu Qing , Rooks M. J. , Melloch M. R.
Published: July 2002

We have observed a far-infrared (0.3–2.5 THz) radiation-induced photovoltaic signal in an antenna-coupled quantum point contract, which oscillates with the gate voltage and peaks at the onset of each subband. The polarity of this photovoltaic signal can be reversed by shifting the far-infrared beam from the drain to the source, or vice versa. This signal has been unambiguously attributed to thermopower generated by asymmetric heating of the drain and the source by the far-infrared radiation. Quantitative agreement has been obtained between measurements and calculations based on ballistic transport in one-dimensional electron systems and the electrical and thermal circuit elements in our experimental system.
Irradiation system based on dodecahedron for inertial confinement fusion
Authors: Murakami M.
Published: July 2002

Two different types of irradiation systems based on dodecahedral configuration are proposed for 60, 72, 80, and 92 beams. By optimizing the system, it is expected that enough uniformity (≤1% rms) is provided. Furthermore, it is quantitatively discussed that the number of beams, power imbalance, and the beam pattern must be improved synchronously for a high illumination uniformity.
Modular instrument for organic secondary ion mass spectrometry and direct chromatographic analysis
Authors: Fiola John W. , DiDonato Gerald C. , Busch Kenneth L.
Published: July 2002

A secondary ion mass spectrometer has been constructed for the analysis of organic samples introduced via a direct insertion probe and for the direct analysis of chromatographic samples. For discrete organic samples, a level of performance commensurate with commercial instruments has been established. Novel spatially resolved spectra for organic samples are presented, as well as the results of the direct sputtering of samples from a chromatographic matrix. The use of a matrix cycled through the solid/liquid phase transition for the in situ extraction of material is also described.
Ultrasonic level sensor for liquids under high pressure
Authors: Zuckerwar Allan J. , Mazel David S. , Hodges Donald Y.
Published: July 2002

An ultrasonic level sensor of novel design continuously measures the level of a liquid subjected to a high pressure (up to 6000 psi or ∼4×107 Pa), as is sometimes required for the effective transfer of the liquid. The sensor operates as a composite resonator, fabricated from a standard high-pressure plug. A flat-bottom hole is machined into the plug along its center line. An ultrasonic transducer is bonded rigidly to the interior surface of the bottom wall, while the exterior surface is in contact with the liquid. Although the bottom wall is designed to satisfy the pressure code, it is still sufficiently thin to permit ready excitation of the axisymmetric plate modes of vibration. The liquid level is measured by a conventional pulse-echo technique. A prototype sensor was tested successfully in a 600-gal (∼2300-l) water vessel at pressures up to 5500 psi. A spectral analysis of the transmitted pulse reveals that the flexural, extensional, thickness-shear, and radial plate modes are excited into vibration, but none of these appears to be significantly affected by pressurization of the liquid.
Noncontacting detection in ultrasonic nondestructive evaluation of materials: Simple optical sensor and fiber-optic interferometric application
Authors: Sarrafzadeh-Khoee A. , Duke J. C.
Published: July 2002

An optical displacement sensor based on the two-beam interferometry of coherent light using two principal diffracted orders of a fine reflection blazed grating is constructed. The inherent capability of the interferometer for absolute calibration, its maximum sensitivity adjustment, and the simplicity of the configuration of its components are explained. Utilization of a single-mode optical fiber in the test arm of the interferometer to enhance the geometric flexibility of the optical system is demonstrated. The sensor’s application in the noncontacting detection of stimulated ultrasonic stress waves for nondestructive evaluation of advanced composite materials is emphasized. The detected signal is digitized and recorded using an IBM PC with a plug-in data-acquisition board. The combination of high sampling rate capability of the device and optical detection has facilitated the signal processing of ultrasonic waves in order to achieve interpretation and quantification of the physical parameter of interest (i.e., displacement).
Hydrogen effusion from evaporated Si1−xSnx:H (0≤x≤0.2) amorphous semiconductors
Authors: Vergnat M. , Zoubir N. Hadj , Houssaïni S. , Marchal G.
Published: July 2002

The release of hydrogen from Si1−xSnx:H (0≤x≤0.2) amorphous semiconductors prepared by reactive evaporation on substrates maintained at 77 K is monitored by effusion experiments. The effusion peaks are associated with desorption from voids. The deconvolution of these peaks allows one to deduce the different atomic configurations containing hydrogen and to determine their stability and their Gibbs free energy of desorption.
Continuous operated H−-surface plasma ion source
Authors: Piosczyk B. , Dammertz G.
Published: July 2002

A H−-surface plasma source with a cesiated converter electrode has been operated continuously. Out of a single extraction aperture of a diameter of 13 mm, a H− current of 50 mA has been extracted with reasonable beam properties. The current was limited by the extraction voltage of 30 kV. The dependence of the generated H− current on different parameters has been examined. In addition, the profile and the emittance of the extracted ion beam has been measured. At optimum conditions, the beam divergence was found to be ±22 mrad. The normalized rms emittance was measured to be 0.4×10−6 π mrad. The emittance of the beam is mainly determined by the geometrical arrangement of the converter electrode with respect to the extraction aperture.
Dopant incorporation during epitaxial growth of a multicomponent oxide thin film from vapor phase: A case study of Fe/YBa2Cu3O7−δ system
Authors: Ogale S. B. , Takeuchi I. , Rajeswari M. , Greene R. L. , Venkatesan T. , Choughule D. D.
Published: July 2002

Incorporation of Fe in YBa2Cu3O7−δ matrix during its epitaxial growth on (001) LaAlO3 by pulsed excimer laser ablation is examined. It is shown that oxygen pressure during deposition plays a critical role in the incorporation process and that a low-temperature postsynthesis annealing is essential for complete substitution. Clustering of iron atoms and its control via the anion controlled reactions are identified as the key features in this context. It is also shown by using atomic force microscopy that Fe incorporation influences the surface morphology. These issues are of importance in the formation of cationic defects in multicomponent thin films.
Microwave noise in high-T
c Josephson junctions
Authors: Grossman Erich N. , Vale Leila R. , Rudman D. A.
Published: July 2002

We have measured the noise of YBa2Cu3O7−δ superconductor-normal-superconductor (SNS) junctions whose high normal-state resistances and characteristic frequencies make them suitable for THz frequency mixers. By directly measuring the 1 GHz power spectral density delivered to a low-noise 50 Ω radiometer system, the noise could be measured over a wide range of dc voltage and temperature, without complications due to 1/f noise, and without invoking any specific model. At a physical temperature of 4 K, the lowest noise junction had an available noise temperature of 31±2 K, corresponding to an effective noise temperature of the normal resistance of 9 K. The effective noise temperature of the normal resistance is approximately equal to the physical temperature at high temperatures, but approaches a limiting value at low temperatures, implying an excess current noise of unknown origin.
Dependence of the nematic liquid crystal pretilt angle on the thickness of the orientation layer
Authors: Alexe-Ionescu A. L. , Barberi R. , Giocondo M. , Cnossen G. , van der Donk T. H.
Published: July 2002

The influence of an isotropic substrate on the anchoring properties of a nematic liquid crystal has been investigated by varying the thickness of a polyimide orientation layer. By invoking the screening effect of the polymer film on the anisotropic van der Waals interactions between the nematic and the solid substrate, the dependence of the pretilt angle on the thickness of the film has been theoretically evaluated. The agreement of the proposed theory with the experimental data is fairly good.
Specific capacitance of Nb/AlOx/Nb Josephson junctions with critical current densities in the range of 0.1–18 kA/cm2
Authors: Maezawa M. , Aoyagi M. , Nakagawa H. , Kurosawa I. , Takada S.
Published: July 2002

The specific capacitance Cs of Nb/AlOx/Nb Josephson tunnel junction has been measured by means of the superconducting quantum interference device (SQUID) resonance technique. We have investigated the junctions with critical current densities Jc in the range of 0.1–18 kA/cm2 and found that 1/Cs linearly depends on a logarithm of Jc. This suggests that the barrier thickness is moderately uniform in the junction area and increases continuously during growth. The results also show that increasing Jc reduces time constants of the junction.
Measurement of charge-to-mass ratio (Q/m) distribution of an ionized cluster beam by a special type of quadrupole mass analyzer
Authors: Nayak Deepak , Pourrezaei Kambiz , Francois Michel , Bahasadri Ali
Published: July 2002

Quadrupole mass analyzers (QMA) are the most common type of instruments for the measurement of partial pressures of residual gases in semiconductor industry. The maximum range of this instrument available today is 1–1000 amu, which is equivalent to charge-to-mass ratios (Q/m) of 108–105 C/kg. Here, we report in detail the design, construction, and testing of a QMA capable of measuring (Q/m) ratios down to 5 C/kg. This instrument has been used to measure the Q/m distribution of ions, clusters, and microdroplets emitted from a needle-tip type liquid metal ion source (LMIS). The Q/m distribution of clusters and microdroplets has been found to form a broad peak, and is concentrated mainly between 105 and 103 C/kg. The variation of this distribution as a function of total beam current and beam emission angle has been studied.