bluuebunny/crossref_metadata_2025 huggingface dataset:
In-plane scattering in titanium-diffused LiNbO3 optical waveguides
Authors: Armenise M. N. , De Sario M. , Canali C. , Franzosi P. , Singh J. , Hutchins R. H. , De La Rue R. M.
Published: February 2003

In-plane scattering in Ti-indiffused LiNbO3 optical waveguides arises from several possible sources. The importance of the different sources changes as a function of the total diffusion time used in waveguide fabrication. This letter describes detailed observations of different sources and shows that at long diffusion times the in-plane scattering is dominated by an increasing density of misfit dislocations growing in the waveguiding layer.
Second harmonic generation of 2-methyl-4-nitroaniline by a neodymium: yttrium aluminum garnet laser with a tapered slab-type optical waveguide
Authors: Sasaki K. , Kinoshita T. , Karasawa N.
Published: February 2003

A thin single crystal of 2-methyl-4-nitroaniline for second harmonic generation experiment is prepared by vapor phase growth. The crystal is used as a high-index top layer on a tapered slab-type waveguide. A Nd:yttrium aluminum garnet laser (1.064 μm) is guided as a fundamental wave. The phase match condition between the fundamental wave (the TE first wave) and the second harmonic wave (the TE second wave) is realized by coincidence of both propagation constants with translational adjustment of the thickness of the waveguide.
Spectral linewidth of gain- and index-guided InGaAsP semiconductor lasers
Authors: Elsässer W. , Göbel E. O.
Published: February 2003

We report measurements of the spectral linewidth of InGaAsP lasers emitting at 1.3 μm as a function of the optical mode power. The spectral linewidth is of the order of 0.1–2.0 GHz for both gain- and index-guided lasers. The linewidth can be described by a modified Schawlow–Townes formula taking into account a power-independent contribution to the linewidth. This power-independent contribution is attributed to mode intensity fluctuations due to mode coupling.
CO2-laser radiation absorption by metal gratings
Authors: Ursu I. , Mihǎilescu I. N. , Popa Al. , Prokhorov A. M. , Konov V. I. , Ageev V. P. , Tokarev V. N.
Published: February 2003

It is shown that CO2-laser radiation-induced periodic structures on the surface of metallic targets result in a dramatic increase (by up to one order of magnitude) in the sample absorptivity. This behavior has made it possible to gain new insight into the thermal coupling of powerful CO2-laser radiation with the initially highly reflectant metallic surfaces.
Deep-ultraviolet induced wet etching of GaAs
Authors: Podlesnik D. V. , Gilgen H. H. , Osgood R. M.
Published: February 2003

We report on deep-ultraviolet (UV), light-assisted wet etching of GaAs. The etching chemistry differs from that using visible wavelengths and all doping types of GaAs can be efficiently etched. The UV processing offers rapid etching at low, nonthermal laser intensities and permits very deep, vertical features to be made.
Contact resistance improvements by implantation through an Al mask
Authors: Faith T. J. , O’Neill J. J. , Hicinbothem W. A.
Published: February 2003

Comparisons were made between (Al-1% Si)/n+Si contacts in which the phosphorus dopant had been implanted through native-oxide or grown-oxide layers, and similar contacts in which the phosphorus dopant had been implanted through a ∼300-Å Al layer. The Al layer was flash evaporated immediately after in situ plasma cleaning to remove the native oxide from the silicon, thereby minimizing the incidence of oxygen ‘‘knock-on’’ during implantation. Pre-alloy and post-alloy contact resistance measurements showed the contacts implanted through Al to be more responsive to the metal alloying process and to have significantly lower post-alloy contact resistances than contacts implanted through either native-oxide or grown-oxide layers.
Origin of nonsymmetric dielectric relaxation in dipolar materials
Authors: Shimakawa Koichi
Published: February 2003

A model for the origin of asymmetric dielectric relaxation in dipolar materials is proposed through a Monte Carlo study. The principal shortcomings of the Debye approach with a distribution of relaxation times can be overcome.
Uniformity characterization of semi-insulating GaAs by cathodoluminescence imaging
Authors: Chin A. K. , Caruso R. , Young M. S. S. , Von Neida A. R.
Published: February 2003

Miyazawa et al. [Appl. Phys. Lett. 43, 853 (1983)] have recently established a spatial correlation between variations in field-effect transistor performance and nonuniformities in the cathodoluminescence (CL) efficiency of semi-insulating (SI) GaAs substrates. In this study, we compare the CL uniformity of both Cr-doped and undoped SI GaAs crystals grown by the liquid-encapsulated Czochralski (LEC) technique with undoped SI crystals grown by the horizontal gradient freeze (HGF) technique. In contrast to the LEC crystals, HGF GaAs has extremely uniform CL characteristics which should result in uniform device performance.
Thickness variations in x-ray filters and laser targets
Authors: Whitlock R. R. , Sprague J. A.
Published: February 2003

Thickness variation of visually opaque foils used as x-ray and ultraviolet (XUV) photon filters and photocathodes can introduce anomalies in recorded intensities, images, and spectral line profiles. In laser fusion studies, mass thickness variations of laser-accelerated foils can hydrodynamically disrupt their motion. We have used transmitted electrons to obtain quantitative local (area ≤1 μm2) measurements of mass thickness as well as qualitative images of mass thickness variations in free-standing Be, C, and Al foils presently in use in the above areas of investigation. Substantial mass thickness variations, up to a factor of 4 for Al and 1.3 for Be, were found which can produce considerable modulations in transmitted XUV photon intensity.
Laser cathode ray tube operation at room temperature
Authors: Levy U. , Logan R. A. , Niv Y.
Published: February 2003

Laser cathode ray tube operation has been demonstrated at room temperature with GaAs/GaAlAs double heterostructure targets. An external efficiency of 2.7% was achieved with a 20-A/cm2 beam of 30-keV electrons. Reasonable uniform emission over a 2 mm×2 mm area was observed.
Reconstruction of electrodes and pole pieces from optimized axial field distributions of electron and ion optical systems
Authors: Szilagyi M.
Published: February 2003

The solution of the electrode and pole piece reconstruction problem is given. The axial potential or flux density distribution is sought in the form of a simple curve with a continuous second derivative. The reconstruction procedure then is extremely simple and quite accurate. As an example the electrode system for an optimized electrostatic lens is shown.
Direct polarization switching in semiconductor lasers
Authors: Chen Y. C. , Liu J. M.
Published: February 2003

Direct polarization switching controlled by the level of the injection current is achieved in InGaAsP lasers operating near the polarization transition temperature. The laser output can be switched from a pure TM00 mode at low injection currents to a TE00 mode at high currents with high extinction ratios and nanosecond response time. Conditions for polarization switching in InGaAsP and AlGaAs lasers at room temperature are also discussed.
Channeled-substrate GaAs/AlGaAs multiple quantum well lasers grown by molecular beam epitaxy
Authors: Wu Yao-Hwa , Werner Michael , Wang Shyh
Published: February 2003

(GaAl)As/GaAs multiple quantum well channeled-substrate lasers with lateral index guiding have been made by molecular beam epitaxy. They operate stably in a single longitudinal mode.
Mutual phase locking of a coupled laser diode-Gunn diode pair
Authors: Izadpanah S. H. , Rav-Noy Z. , Mukai S. , Margalit S. , Yariv Amnon
Published: February 2003

Mutual phase locking has been achieved through series connection of a semiconductor laser and a Gunn diode oscillator. Experimental results obtained demonstrate a mutual interaction between the two oscillators which results in a short term Gunn diode oscillator stability and improved spectral purity of its output. We also observe a narrowing of laser pulses and an improvement in regularity.
Spatially resolved electric field measurements in the cathode fall using optogalvanic detection of Rydberg atoms
Authors: Doughty D. K. , Lawler J. E.
Published: February 2003

Spatially resolved electric field measurements in the cathode fall region of a glow discharge are performed using optogalvanic detection of He Rydberg atoms. The large linear Stark effect of Rydberg levels provides an accurate, sensitive measure of discharge electric fields.
Formation of bulk metallic glass by fluxing
Authors: Kui H. W. , Greer A. L. , Turnbull D.
Published: February 2003

Bulk specimens (0.4–4 g mass) of the alloy Pd40Ni40P20 have been undercooled consistently to the glass state, with no detectable superficial crystallinity, in a molten flux of dehydrated boron oxide. The minimum dimension of the most massive glass specimen, so formed, was 1.0 cm. The absence of crystallinity in the specimens was confirmed by x-ray diffraction, scanning electron microscopy, and calorimetry.
Patterned photonucleation of chemical vapor deposition of Al by UV-laser photodeposition
Authors: Tsao J. Y. , Ehrlich D. J.
Published: February 2003

UV-laser photodeposition has been used to predispose surfaces to pyrolytic chemical vapor deposition (CVD) of Al from triisobutylaluminum. Two laser beam (UV and IR) experiments indicate that the predisposition is due to the formation of a catalytic surface for heterogeneous chemistry. Time-resolved transmission measurements indicate that a few photodeposited monolayers are sufficient to nucleate CVD growth. The technique may be generally useful for maskless patterned growth by CVD processes with large nucleation barriers.
Silica at ultrahigh temperature and expanded volume
Authors: Holmes N. C. , Radousky H. B. , Moss M. J. , Nellis W. J. , Henning S.
Published: February 2003

Shock compression experiments were performed on samples of 0.13 g/cm3 density silica aerogel. The aerogel is a transparent, homogeneous, open cell, SiO2, glass structure with a pore size of 10 nm. A shock velocity of 11.4 km/s was measured at 14.6 GPa (146 kbar) and over sevenfold compression of the specimen, which is threefold expanded relative to the density of crystalline α-quartz. A shock temperature of nearly 1 eV was measured at 6.7 GPa. These experiments access a new regime for accurate laboratory measurements on high-temperature, expanded-volume states of glass.
Hydrogenated amorphous silicon for archival storage
Authors: McLeod R. D. , Pries W. , Card H. C. , Kao K. C.
Published: February 2003

Changes in optical reflectivity of hydrogenated amorphous silicon films of up to 90% have been induced by Ar laser processing, and are correlated with hydrogen evolution from the material. Accompanying changes greater than three orders of magnitude in resistivity also provide a mechanism for interrogation of the stored data by an electron beam. Storage densities as high as 109 bits/in2 for optical recording and 1011 bits/in2 for recording with electron beams are predicted on the basis of these results.
Spatially resolved electrical and spectroscopic studies around dislocations in GaAs single crystals
Authors: Watanabe K. , Nakanishi H. , Yamada K. , Hoshikawa K.
Published: February 2003

Spatially resolved electrical and spectroscopic behavior around isolated grown-in dislocation in p-type undoped GaAs crystals grown by liquid-encapsulated Czochralski technique is investigated. Surface spreading resistance is found to remarkably increase at about 100 μm in diameter around dislocations. In a corresponding area, photoluminescence intensity of the 1.49-eV and 1.44-eV acceptor level peaks decreases. However, that of 0.8-eV deep level peak does not vary. These results demonstrate that dislocations should give rise to carrier density variation due to the relative concentration change of levels around them.
Electron and hole ionization coefficients in (100) oriented Ga0.18In0.82As0.39P0.61
Authors: Osaka Fukunobu , Mikawa Takashi , Kaneda Takao
Published: February 2003

The impact ionization coefficients for electrons and holes in (100) oriented Ga0.18In0.82As0.39P0.61 whose band gap is 1.11 eV have been obtained from photomultiplication measurements on a Cd diffused p+n abrupt junction having a donor concentration of 2.5×1016 cm−3. The electron-to-hole ionization coefficient ratio has been found to be about 1.1 in the electric field range 4.0×105–5.0×105 V/cm.
Growth of CdTe on InSb by organometallic vapor phase epitaxy
Authors: Ghandhi S. K. , Bhat I.
Published: February 2003

Organometallic vapor phase epitaxy of CdTe on InSb substrates is described in this letter. It is shown that high quality CdTe layers can be grown on InSb substrates by this process. Growths under various temperatures and reactant partial pressures are described. Growth under excess diethyltelluride pressure is shown to result in material with improved electrical and photoluminescence properties over that produced under excess dimethylcadmium pressure.
Photovoltaic investigations of GaAs/AlAs heterostructures
Authors: Schlesinger T. E. , Collins R. T. , McGill T. C. , Burnham R. D.
Published: February 2003

We present the results of the application of photoresponse techniques to the study of the transport of electrons past an energy barrier. In this study, the barrier was provided by a thin layer of AlAs sandwiched between GaAs layers. The experiment measured the voltage resulting from the migration of optically excited electrons from one side of the barrier to the other. The voltage is measured as a function of the wavelength of the incident light. We also present the results of calculations which explain the nature of the observed spectra and how they change when the thickness of the top layer (the illuminated side) of GaAs is changed.
Indium incorporation during the growth of (100)Si by molecular beam epitaxy: Surface segregation and reconstruction
Authors: Knall J. , Sundgren J.-E. , Greene J. E. , Rockett A. , Barnett S. A.
Published: February 2003

The In incorporation probability σIn in (100) Si grown by molecular beam epitaxy was found, using secondary ion mass spectrometry (SIMS), to decrease from essentially unity at film growth temperatures Ts of ∼500 °C to <10−4 at 840 °C. SIMS depth profiles of both uniformly doped and modulation-doped samples showed evidence of strong surface segregation with the amount of profile broadening directly related to σIn(Ts). A combination of in situ electron diffraction and Auger electron spectroscopy was used to show that the surface segregation rate was sufficient over a wide range in Ts and In to Si flux ratios to cause the initial (2×1)-(100) Si surface reconstruction to transform to (3×4) due to the formation of an ordered In surface layer. The In surface coverage in the (3×4) state was ∼0.05–0.1 monolayer even though the bulk In concentration was ≤2×1017 cm3. The (2×1) to (3×4) surface phase transition was reversible by either terminating film growth and reevaporating the excess surface In or terminating the In flux while continuing Si film growth.
cw operation of an AlGaInP double heterostructure laser diode at 77 K grown by atmospheric metalorganic chemical vapor deposition
Authors: Ikeda M. , Mori Y. , Takiguchi M. , Kaneko K. , Watanabe N.
Published: February 2003

Continuous wave operation of an Al0.21Ga0.31In0.48P /Ga0.52In0.48P /Al0.21Ga0.31In0.48P double heterostructure (DH) laser diode was achieved for the first time at 77 K. The device was made from a DH wafer grown by atmospheric metalorganic chemical vapor deposition using triethyl metals and phosphine as source materials. At 77 K, the lasing wavelength was 0.653 μm and the threshold current was 55 mA for a diode with a nitride-insulated, 8-μm-wide and 250-μm-long stripe geometry.
A mechanism for i
n s
i
t
u monitoring of hydrogen incorporation into amorphous silicon
Authors: Pries W. , McLeod R. D. , Card H. C. , Kao K. C.
Published: February 2003

An optical mechanism based on temporal changes in reflectivity during the growth of hydrogenated amorphous silicon films is shown to provide for an accurate determination of the degree of hydrogen incorporation, as well as the growth rate of the growing film. This mechanism is described experimentally and modeled phenomenologically, and is expected to provide a basis for in situ correlation of hydrogen incorporation with process parameters.
Preheated cw laser annealed transistors in silicon on sapphire
Authors: Holmén G. , Peterström S. , Alestig G.
Published: February 2003

p-channel metal-oxide-semiconductor transistors have been fabricated in silicon on sapphire. The electrical properties of cw laser annealed transistors which had been subjected to a low-temperature annealing before the laser annealing treatment, were found to be superior to laser annealed transistors and to furnace annealed transistors. The new annealing processes prevent the formation of the defect centers which normally after laser annealing have a degrading influence on the carrier mobility of the material. The defect concentration was measured by deep level transient spectroscopy.
Quantum size effects in GaAs/GaAsxP1−x strained-layer superlattices
Authors: Gourley P. L. , Biefeld R. M.
Published: February 2003

We report the first observations of quantum size effects in GaAs/GaAs0.5P0.5 strained-layer superlattices (SLS’s). Using excitation and photoluminescence spectroscopies, we have observed optical transitions between excited states of the electron and hole quantum wells. These observations provide a measure of the biaxial compressive strain in the GaAs layers, interfacial roughness, and valence-band offset for the GaAs/GaP heterojunction.
Junction leakage studies in rapid thermal annealed diodes
Authors: Kamgar Avid , Fichtner W. , Sheng T. T. , Jacobson D. C.
Published: February 2003

A detailed and comprehensive study of As-implanted Si annealed using incoherent tungsten radiation has been perfomed. The study emphasized the leakage currrent results, correlating them with the junction depths obtained from Rutherford backscattering measurements, and the residual damage observed in transmission electron microscopy (TEM). Sheet resistance measurements, as well as comparisons with wafers annealed in conventional furnaces, were also made. It was found that higher temperatures and shorter times resulted in lower leakage currents for given junction depths. We also found that the absence of residual dislocations in TE studies of annealed wafers was not a sufficient indication of low junction leakage.
High-speed photoconductivity and infrared to visible up-conversion in GaP light-emitting diodes
Authors: Moser K. , Eisfeld W. , Werling U. , Wahl S. , Prettl W.
Published: February 2003

In GaP:N (Zn,Te) light-emitting diodes extrinsic photoconductivity and infrared to visible up-conversion have been investigated by short laser pulses at 10-μm wavelength. A time constant of the order of 1 ns was observed indicating that free infrared excited hole to bound donor recombination yields the fast response.
Bistable optical electrical/microwave switching using optically coupled monolithically integrated GaAlAs translasers
Authors: Lau K. Y. , Yariv A.
Published: February 2003

A novel switching device consisting of optically coupled laser and field-effect transistor monolithically integrated on a semi-insulating substrate is demonstrated. The physical origin of the bistable behavior is illustrated. The input and output to this device can take the form of optical and/or electrical signals. Applications of this device in optical, electrical, microwave switching, and pulse-position/pulse frequency demodulation are illustrated.
Production of single phase chalcopyrite CuInSe2 by spray pyrolysis
Authors: Abernathy Cammy R. , Bates Clayton W. , Anani Anaba A. , Haba Belgacem , Smestad Greg
Published: February 2003

Thin films (0.5–2 μ) of CuInSe2 were prepared by spray pyrolysis from solutions with various pH levels and initial Cu:In ratios, and in which the Cu source was either CuCl or CuCl2. The substrate temperature was varied between 225 and 300 °C. All films prepared with CuCl2 were chalcopyrite, while only Cu-rich CuCl based films exhibited this phase. The appearance of Cu2−xSe and/or Cu2/Se as a second phase was found to depend strongly on solution stoichiometry, pH, temperature, and substrate. Two layer structures consisting of a Cu-deficient layer on top of a Cu-rich layer were produced without the presence of any second phases on both glass and Mo-coated glass. This is the first time single phase chalcopyrite Cu-deficient layers have been fabricated by spray pyrolysis. A CuInSe2/CdS photovoltaic cell made from a single phase double layer filme on glass gave a Voc of 0.558 V after heat treatment. This Voc is higher than any reported to date. Absorption spectra have also been measured, and are found to improve when CuCl2 is used instead of CuCl.
Orientation dependent reactive ion etching of GaAs in SiCl4
Authors: Li J. Z. , Adesida I. , Wolf E. D.
Published: February 2003

The reactive ion etching characteristics of (100) GaAs in SiCl4 have been investigated. It was found that pronounced orientation dependent etching could be obtained under plasma conditions of low power density and moderate pressures (around 20 m Torr). At very low pressures, structures with vertical sidewalls were obtained. The structures obtained in the orientation dependent etching mode are similar to those obtained by wet etching and those observed in bromine plasma etching. Etch profiles were different along the [011] and [01̄1] orientations and the relation of etch rates in the different planes follows the relation R〈100〉>R〈111〉>R〈100〉.
Two-step Al/Ti metallization to PtSi/Si structures
Authors: Eizenberg M. , Tu K. N. , Palmstro/m C. J. , Mayer J. W.
Published: February 2003

A two-step Al metallization procedure to prevent Al degradation of PtSi/Si Schottky barrier characteristics has been evaluated using Al3Ti as the kinetic barrier to the consumption of Ti. In the first step a thin Al layer is deposited on a Ti layer on PtSi/Si and is heated to the standard metallization process temperature of 450–500 °C. The Al and Ti thicknesses are chosen so that the Al is consumed to form Al3Ti with Ti remaining between the aluminide and silicide. In the second step a thick layer of Al, compatible with interconnect requirements, is deposited and annealed at temperatures around 350 °C. The formation rate of Al3Ti at this temperature is sufficiently low that consumption of Ti is minimal and the electrical characteristic of the PtSi/Si contact is preserved.
Thermionic emission in bulk unipolar camel diodes
Authors: Woodcock J. M. , Shannon J. M.
Published: February 2003

An analysis of the current-voltage characteristics of bulk unipolar camel diodes in GaAs with a high doping concentration in the barrier region has concluded that current transport is close to the thermionic limit.
Nonlinear mode coupling in birefringent fiber: Application to optical pulse reshaping
Authors: Kitayama Ken-ichi , Kimura Yasuo , Seikai Shigeyuki
Published: February 2003

It is theoretically shown that intensity dependent mode coupling is induced by nonlinear birefringence between two orthogonally polarized modes in optical fibers in such way that the weak light field polarized along the slow axis of the birefringent fiber couples more strongly to the other mode having the perpendicular polarization than to the strong light field. By utilizing the mode coupling property it is possible in a birefringent single-mode fiber to isolate the optical pulse launched, say, in the LPx01 mode from the precursor and tailing edges or weak background by coupling them to the LPy01 mode. This will readily lead to the application of birefringent fibers to optical pulse compression. In this scheme of pulse reshaping, the loss of the LPy01 mode is required to be much larger than that of the LPx01 mode in order to avoid the unnecessary coupling back to the main mode.
Growth of amorphous Ti2O3 layers by laser-induced oxidation
Authors: Merlin R. , Perry T. A.
Published: February 2003

Amorphous Ti2O3 films with thicknesses ≳103 Å have been obtained by cw laser irradiation of Ti50Zr10Be40 exposed to low oxygen pressures. In contrast, thermal oxidation of (nonirradiated) samples reveals scales composed of crystalline oxides. Raman scattering, x-ray, and electron microscopy data on the layers are reported. It is suggested that irradiation leads to an enhanced oxidation rate preventing crystallization. Possible mechanisms of enhancement are discussed.
15-mJ pulses from a 4.3-μm CO2 laser
Authors: Brimacombe R. K. , Reid J.
Published: February 2003

Output energies of 15 mJ/pulse and peak powers of 100 kW/pulse are obtained from a 4.3-μm CO2 laser which is optically pumped by a 10-μm sequence-band CO2 laser. The dominant operating characteristics of the laser and their effect on output energy, line tunability, and scalability are discussed.
Residual photocurrent decay in hydrogenated amorphous silicon
Authors: Shimakawa K. , Yano Y.
Published: February 2003

The residual photocurrent decay following the steady photoexcitation was measured in hydrogenated amorphous silicon as a function of temperature. The data were analyzed by the Fermi level analysis first outlined by Rose [RCA Rev. 12, 362 (1951)]. By introducing a time-dependent recombination rate (∼t−(1−α)), we obtained a good agreement between density of states values obtained from the photoconductivity decay and from space-charge-limited current measurements.
Amorphous silicon solar cells fabricated by photochemical vapor deposition
Authors: Tanaka Tatsuya , Kim Woo Yeol , Konagai Makoto , Takahashi Kiyoshi
Published: February 2003

Hydrogenated amorphous silicon solar cells were fabricated by photochemical vapor deposition. Wide optical band-gap (∼2.0 eV) hydrogenated amorphous silicon carbide was employed for the p layer. Acetylene (C2H2) or dimethylsilane (Si(CH3)2H2) was used as a carbon source instead of methane which is usually used in a glow discharge process. Although p, i, and n layers were deposited in a single reaction chamber, the solar cell showed high-energy conversion efficiency of 8.29% under AM1, 100-mW/cm2 insolation. The distribution of boron atoms in the solar cell was analyzed by secondary ion mass spectroscopy. The boron content in the i layer was of the order of 1016 cm−3. This is comparable to that in the i layer of the solar cell fabricated by the glow discharge system with separated three reaction chambers.
Perpendicular magnetic anisotropy of Tb-Co amorphous films sputtered in H2-added Ar gas
Authors: Niihara T. , Takayama S. , Kaneko K. , Sugita Y.
Published: February 2003

Very large perpendicular magnetic anisotropy has been observed in Tb-Co amorphous films deposited by nonbiased rf sputtering using H2-added Ar gas. As the hydrogen partial pressure of the gas increases, the perpendicular anisotropy constant Ku increases remarkably and rectangular Kerr hysteresis loop appears. For 10% H2, Ku reaches near 105 J/m3, which is sufficient to direct the magnetization perpendicular to the film plane. These films can be used as magneto-optical recording media because of the relatively large Kerr rotation angle and coercive force. The mechanism of increasing Ku remains to be clarified.
Solid phase epitaxy of evaporated amorphous silicon films
Authors: Milosavljević M. , Jeynes C. , Wilson I. H.
Published: February 2003

Amorphous silicon films were deposited in an electron beam evaporator. Substrates of silicon (100) wafers with predeposited epitaxial films were held at 380 °C to avoid porosity. Processing of the films before annealing may include implantation. Solid state epitaxy is then achieved by annealing at 600 °C for 30 min.
A new photoelectrochemical profiling technique for recombination centers in GaAs
Authors: Chiang C.-L. , Wagner S. , Shieh C.-L.
Published: February 2003

A new profiling technique for shallow damage in semiconductors is described. The technique combines successive anodizations with in situ surface photovoltage measurements. Profiles of recombination centers in Ar+ beam (400–600 eV) milled GaAs were determined. The density of recombination centers near the surface is ≳105 times the bulk value. The density drops to the bulk value within ∼300 Å from the surface.
Subpicosecond time-resolved luminescence spectroscopy of highly excited CuCl
Authors: Hulin D. , Etchepare J. , Antonetti A. , Chase L. L. , Grillon G. , Migus A. , Mysyrowicz A.
Published: February 2003

An apparatus for the detection of luminescence spectra with subpicosecond resolution is described. It is applied to the measurement of the formation time of excitonic particles in CuCl.
A new class of instabilities in a diode laser with an external cavity
Authors: Kawaguchi Hitoshi , Otsuka Kenju
Published: February 2003

A new class of instabilities is reported in a semiconductor laser which is coupled to an external optical cavity with an intracavity Fabry–Perot etalon. Power spectra of the laser suggest periodic oscillation and its subharmonic modulations. The calculated results, using the van der Pol equation which includes a carrier density-dependent refractive index, are outlined to explain the observed subharmonic modulation phenomena.
Optical recording by reducing a metal salt complexed to a polymer host
Authors: Auerbach A.
Published: February 2003

An alternative approach which makes use of a laser to reduce a polymer/complexed metal ion matrix to generate small reflective surfaces is described. The thermal energy provided by the laser promotes an electron transfer from the polymer to the metal ion to form metal. Since the reduction occurs within the thermal profile of the focused laser beam, the reflective area has a diameter close to that of the beam waist. We have formed ∼l-μm-diam reflective areas using a pulsed diode laser. Application of this method to optical disk recording is discussed.
Analysis of diffusion in polymers by forward recoil spectrometry
Authors: Mills Peter J. , Green Peter F. , Palmstro/m Christopher J. , Mayer James W. , Kramer Edward J.
Published: February 2003

We demonstrate that an ion beam analysis method that detects the energies of forward recoiling deuterons can be used to measure concentration profiles and tracer diffusion coefficients D* of a deuterated polymer (d-polystyrene) diffusing into its hydrogenated analog. The D*’s decrease as M−2 as predicted by the reptation theory of polymer diffusion and agree in magnitude with both the theory and marker displacement measurements of D* in the same system.
Expression of a Bifunctional Fusion of the Escherichia coli Genes for Trehalose-6-Phosphate Synthase and Trehalose-6-Phosphate Phosphatase in Transgenic Rice Plants Increases Trehalose Accumulation and Abiotic Stress Tolerance without Stunting Growth
Authors: Jang In-Cheol , Oh Se-Jun , Seo Ju-Seok , Choi Won-Bin , Song Sang Ik , Kim Chung Ho , Kim Youn Shic , Seo Hak-Soo , Choi Yang Do , Nahm Baek Hie , Kim Ju-Kon
Published: February 2003

Trehalose plays an important role in stress tolerance in plants. Trehalose-producing, transgenic rice (Oryza sativa) plants were generated by the introduction of a gene encoding a bifunctional fusion (TPSP) of the trehalose-6-phosphate (T-6-P) synthase (TPS) and T-6-P phosphatase (TPP) ofEscherichia coli, under the control of the maize (Zea mays) ubiquitin promoter (Ubi1). The high catalytic efficiency (Seo et al., 2000) of the fusion enzyme and the single-gene engineering strategy make this an attractive candidate for high-level production of trehalose; it has the added advantage of reducing the accumulation of potentially deleterious T-6-P. The trehalose levels in leaf and seed extracts from Ubi1::TPSP plants were increased up to 1.076 mg g fresh weight−1. This level was 200-fold higher than that of transgenic tobacco (Nicotiana tabacum) plants transformed independently with eitherTPS or TPP expression cassettes. The carbohydrate profiles were significantly altered in the seeds, but not in the leaves, of Ubi1::TPSP plants. It has been reported that transgenic plants with E. coli TPSand/or TPP were severely stunted and root morphology was altered. Interestingly, our Ubi1::TPSP plants showed no growth inhibition or visible phenotypic alterations despite the high-level production of trehalose. Moreover, trehalose accumulation in Ubi1::TPSP plants resulted in increased tolerance to drought, salt, and cold, as shown by chlorophyll fluorescence and growth inhibition analyses. Thus, our results suggest that trehalose acts as a global protectant against abiotic stress, and that rice is more tolerant to trehalose synthesis than dicots.
Subcellular Targeting of Methylmercury Lyase Enhances Its Specific Activity for Organic Mercury Detoxification in Plants
Authors: Bizily Scott P. , Kim Tehryung , Kandasamy Muthugapatti K. , Meagher Richard B.
Published: February 2003

Methylmercury is an environmental pollutant that biomagnifies in the aquatic food chain with severe consequences for humans and other animals. In an effort to remove this toxin in situ, we have been engineering plants that express the bacterial mercury resistance enzymes organomercurial lyase MerB and mercuric ion reductase MerA. In vivo kinetics experiments suggest that the diffusion of hydrophobic organic mercury to MerB limits the rate of the coupled reaction with MerA (Bizily et al., 2000). To optimize reaction kinetics for organic mercury compounds, themerB gene was engineered to target MerB for accumulation in the endoplasmic reticulum and for secretion to the cell wall. Plants expressing the targeted MerB proteins and cytoplasmic MerA are highly resistant to organic mercury and degrade organic mercury at 10 to 70 times higher specific activity than plants with the cytoplasmically distributed wild-type MerB enzyme. MerB protein in endoplasmic reticulum-targeted plants appears to accumulate in large vesicular structures that can be visualized in immunolabeled plant cells. These results suggest that the toxic effects of organic mercury are focused in microenvironments of the secretory pathway, that these hydrophobic compartments provide more favorable reaction conditions for MerB activity, and that moderate increases in targeted MerB expression will lead to significant gains in detoxification. In summary, to maximize phytoremediation efficiency of hydrophobic pollutants in plants, it may be beneficial to target enzymes to specific subcellular environments.
A New Type of a Multifunctional β-Oxidation Enzyme in Euglena
Authors: Winkler Uwe , Säftel Werner , Stabenau Helmut
Published: February 2003

The biochemical and molecular properties of the β-oxidation enzymes from algae have not been investigated yet. The present study provides such data for the phylogenetically old alga Euglena (Euglena gracilis). A novel multifunctional β-oxidation complex was purified to homogeneity by ammonium sulfate precipitation, density gradient centrifugation, and ion-exchange chromatography. Monospecific antibodies used in immunocytochemical experiments revealed that the enzyme is located in mitochondria. The enzyme complex is composed of 3-hydroxyacyl-coenzyme A (-CoA) dehydrogenase, 2-enoyl-CoA hydratase, thiolase, and epimerase activities. The purified enzyme exhibits a native molecular mass of about 460 kD, consisting of 45.5-, 44.5-, 34-, and 32-kD subunits. Subunits dissociated from the complete complex revealed that the hydratase and the thiolase functions are located on the large subunits, whereas two dehydrogenase functions are located on the two smaller subunits. Epimerase activity was only measurable in the complete enzyme complex. From the use of stereoisomers and sequence data, it was concluded that the 2-enoyl-CoA hydratase catalyzes the formation ofl-hydroxyacyl CoA isomers and that both of the different 3-hydroxyacyl-CoA dehydrogenase functions on the 32- and 34-kD subunits are specific to l-isomers as substrates, respectively. All of these data suggest that the Euglena enzyme belongs to the family of β-oxidation enzymes that degrade acyl-CoAs via l-isomers and that it is composed of subunits comparable with subunits of monofunctional β-oxidation enzymes. It is concluded that the Euglena enzyme phylogenetically developed from monospecific enzymes in archeons by non-covalent combination of subunits and presents an additional line for the evolutionary development of multifunctional β-oxidation enzymes.
Functional Divergence of a Syntenic Invertase Gene Family in Tomato, Potato, and Arabidopsis
Authors: Fridman Eyal , Zamir Dani
Published: February 2003

Comparative analysis of complex developmental pathways depends on our ability to resolve the function of members of gene families across taxonomic groups. LIN5, which belongs to a small gene family of apoplastic invertases in tomato (Lycopersicon esculentum), is a quantitative trait locus that modifies fruit sugar composition. We have compared the genomic organization and expression of this gene family in the two distantly related species: tomato and Arabidopsis. Invertase family members reside on segmental duplications in the near-colinear genomes of tomato and potato (Solanum tuberosum). These chromosomal segments are syntenically duplicated in the model plant Arabidopsis. On the basis of phylogenetic analysis of genes in the microsyntenic region, we conclude that these segmental duplications arose independently after the separation of the tomato/potato clade from Arabidopsis. Rapid regulatory divergence is characteristic of the invertase family. Interestingly, although the processes of gene duplication and specialization of expression occurred separately in the two species, synteny-based orthologs from both clades acquired similar organ-specific expression. This similar expression pattern of the genes is evidence of comparable evolutionary constraints (parallel evolution) rather than of functional orthology. The observation that functional orthology cannot be identified through analysis of expression similarity highlights the caution that needs to be exercised in extrapolating developmental networks from a model organism.
AtCSLA7, a Cellulose Synthase-Like Putative Glycosyltransferase, Is Important for Pollen Tube Growth and Embryogenesis in Arabidopsis
Authors: Goubet Florence , Misrahi Audrey , Park Soon Ki , Zhang Zhinong , Twell David , Dupree Paul
Published: February 2003

The cellulose synthase-like proteins are a large family of proteins in plants thought to be processive polysaccharide β-glycosyltransferases. We have characterized an Arabidopsis mutant with a transposon insertion in the gene encoding AtCSLA7 of the CSLA subfamily. Analysis of the transmission efficiency of the insertion indicated that AtCSLA7 is important for pollen tube growth. Moreover, the homozygous insertion was embryo lethal. A detailed analysis of seed developmental progression revealed that mutant embryos developed more slowly than wild-type siblings. The mutant embryos also showed abnormal cell patterning and they arrested at a globular stage. The defective embryonic development was associated with reduced proliferation and failed cellularization of the endosperm. AtCSLA7 is widely expressed, and is likely to be required for synthesis of a cell wall polysaccharide found throughout the plant. Our results suggest that this polysaccharide is essential for cell wall structure or for signaling during plant embryo development.
Rewiring MAP Kinase Pathways Using Alternative Scaffold Assembly Mechanisms
Authors: Park Sang-Hyun , Zarrinpar Ali , Lim Wendell A.
Published: February 2003

How scaffold proteins control information flow in signaling pathways is poorly understood: Do they simply tether components, or do they precisely orient and activate them? We found that the yeast mitogen-activated protein (MAP) kinase scaffold Ste5 is tolerant to major stereochemical perturbations; heterologous protein interactions could functionally replace native kinase recruitment interactions, indicating that simple tethering is largely sufficient for scaffold-mediated signaling. Moreover, by engineering a scaffold that tethers a unique kinase set, we could create a synthetic MAP kinase pathway with non-natural input-output properties. These findings demonstrate that scaffolds are highly flexible organizing factors that can facilitate pathway evolution and engineering.
Control of Regulatory T Cell Development by the Transcription Factor
Foxp3
Authors: Hori Shohei , Nomura Takashi , Sakaguchi Shimon
Published: February 2003

Regulatory T cells engage in the maintenance of immunological self-tolerance by actively suppressing self-reactive lymphocytes. Little is known, however, about the molecular mechanism of their development. Here we show that
Foxp3
, which encodes a transcription factor that is genetically defective in an autoimmune and inflammatory syndrome in humans and mice, is specifically expressed in naturally arising CD4
+
regulatory T cells. Furthermore, retroviral gene transfer of
Foxp3
converts naïve T cells toward a regulatory T cell phenotype similar to that of naturally occurring CD4
+
regulatory T cells. Thus,
Foxp3
is a key regulatory gene for the development of regulatory T cells.
A Sublimation Model for Martian South Polar Ice Features
Authors: Byrne Shane , Ingersoll Andrew P.
Published: February 2003

In their pioneering work, Leighton and Murray argued that the Mars atmosphere, which at present is 95% carbon dioxide, is controlled by vapor equilibrium with a much larger polar reservoir of solid carbon dioxide. Here we argue that the polar reservoir is small and cannot function as a long-term buffer to the more massive atmosphere. Our work is based on modeling of the circular depressions commonly found on the south polar cap. We argue that a carbon dioxide ice layer about 8 meters thick is being etched away to reveal water ice underneath. This is consistent with thermal infrared data from the Mars Odyssey mission.
Exposed Water Ice Discovered near the South Pole of Mars
Authors: Titus Timothy N. , Kieffer Hugh H. , Christensen Phillip R.
Published: February 2003

The Mars Odyssey Thermal Emission Imaging System (THEMIS) has discovered water ice exposed near the edge of Mars' southern perennial polar cap. The surface H
2
O ice was first observed by THEMIS as a region that was cooler than expected for dry soil at that latitude during the summer season. Diurnal and seasonal temperature trends derived from Mars Global Surveyor Thermal Emission Spectrometer observations indicate that there is H
2
O ice at the surface. Viking observations, and the few other relevant THEMIS observations, indicate that surface H
2
O ice may be widespread around and under the perennial CO
2
cap.
A Methane Trigger for Rapid Warming?
Authors: Dickens Gerald R.
Published: February 2003

Methane Hydrates in Quaternary Climate Change
The Clathrate Gun Hypothesis. James P. Kennett, Kevin G. Cannariato, Ingrid L. Hendy, and Richard J. Behl. American Geophysical Union, Washington, DC, 2002. 224 pp. Paper, $42.00. ISBN 0-87590-296-0.

Using data from paleooceanography, climate dynamics, paleobotany, marine geology, and biogeochemistry, the authors argue that the remarkably abrupt global warmings during the ice ages (including that which terminated the last one) were caused by the destabilization of the reser-voir of methane hydrates frozen in ocean sediments.
BIMETRIC GRAVITY THEORY, VARYING SPEED OF LIGHT AND THE DIMMING OF SUPERNOVAE
Authors: MOFFAT J. W.
Published: February 2003

In the bimetric scalar–tensor gravitational theory there are two frames associated with the two metrics ĝμν and gμν, which are linked by the gradients of a scalar field ϕ. The choice of a comoving frame for the metric ĝμν or gμν has fundamental physical consequences for local observers in either metric spacetimes, while maintaining diffeomorphism invariance. If the metric gμν is chosen to be associated with comoving coordinates, then the speed of light varies in the frame with the metric ĝμν. Observers in this frame see the dimming of supernovae because of the increase of luminosity distance versus red shift, due to an increasing speed of light in the past universe. Moreover, in this frame the scalar field ϕ describes a dark energy component in the Friedmann equation for the cosmic scale without acceleration. If we choose ĝμν to be associated with comoving coordinates, then an observer in the gμν metric frame will observe the universe to be accelerating and the supernovae will appear to be farther away. The theory predicts that the gravitational constant G can vary in spacetime, while the fine-structure constant α = e2/ℏc does not vary. The problem of cosmological horizons as viewed in the two frames is discussed.
FAST LU FACTORIZATION ON THE HYPERSTAR INTERCONNECTION NETWORK
Authors: AL-AYYOUB ABDEL-ELAH , DAY KHALED
Published: February 2003

The hyperstar network has been recently proposed as an attractive product network that outperforms many popular topologies in various respects. In this paper we explore additional capabilities for the hyperstar network through an efficient parallel algorithm for solving the LU factorization problem on this network. The proposed parallel algorithm uses O(n) communication time on a hyperstar formed by the cross-product of two n-star graphs. This communication time improves the best known result for the hypercube-based LU factorization by a factor of log(n), and improves the best known result for the mesh-based LU factorization by a factor of (n - 1)!.
The Dynamic Neural Filter: A Binary Model of Spatiotemporal Coding
Authors: Quenet Brigitte , Horn David
Published: February 2003

We describe and discuss the properties of a binary neural network that can serve as a dynamic neural filter (DNF), which maps regions of input space into spatiotemporal sequences of neuronal activity. Both deterministic and stochastic dynamics are studied, allowing the investigation of the stability of spatiotemporal sequences under noisy conditions. We define a measure of the coding capacity of a DNF and develop an algorithm for constructing a DNF that can serve as a source of given codes. On the basis of this algorithm, we suggest using a minimal DNF capable of generating observed sequences as a measure of complexity of spatiotemporal data. This measure is applied to experimental observations in the locust olfactory system, whose reverberating local field potential provides a natural temporal scale allowing the use of a binary DNF. For random synaptic matrices, a DNF can generate very large cycles, thus becoming an efficient tool for producing spatiotemporal codes. The latter can be stabilized by applying to the parameters of the DNF a learning algorithm with suitable margins.