bluuebunny/crossref_metadata_2025 huggingface dataset:
Controlled fundamental supermode operation of phase-locked arrays of gain-guided diode lasers
Authors: Kapon E. , Katz J. , Margalit S. , Yariv A.
Published: February 2003

Uniform semiconductor laser arrays tend to oscillate in a superposition of their supermodes, thus leading to large beam divergence and spectral spread. Discrimination among the supermodes in phase-locked arrays is discussed theoretically. It is shown that supermode discrimination in gain-guided arrays, in favor of the fundamental supermode, is made possible by the near-field interference patterns which result from the complex optical fields of the gain-guided lasers. A fundamental supermode operation is demonstrated, for the first time, in GaAlAs/GaAs gain-guided laser arrays. This is achieved by control of the current (gain) profile across the array by means of individual laser contacts.
Drawing-induced hydrogen-associated defect centers at the silica optical fiber surface
Authors: Hibino Yoshinori , Hanafusa Hiroaki
Published: February 2003

Defect centers in optical fibers induced by drawing were investigated using the electron spin resonance technique. The hydrogen hyperfine (hf) doublet with splitting of 119 G was observed for both GeO2-doped and pure silica optical fibers, which contain few hydroxyl ions. The hf peak intensity was directly proportional to specific surface area of optical fibers. These results indicate that the hf doublet arises from the hydrogen interaction with a drawing-induced germanium defect center at or near the optical fiber surface.
Comparison of laser-initiated and thermal chemical vapor deposition of tungsten films
Authors: Deutsch T. F. , Rathman D. D.
Published: February 2003

ArF excimer laser radiation has been used to deposit W films on silicon and on SiO2 by initiating the gas phase reaction of WF6 with H2. Deposition rates >100 nm/min and film resistivities as low as two times the bulk value have been obtained at deposition temperatures of 440 °C. The properties of the laser-deposited films are compared with those of fims obtained using conventional thermal deposition techniques. Film resistivity correlates with the microstructure which in turn depends on the deposition temperature; above 350 °C the low-resistivity α-W phase dominates.
Suppression of lateral diffusion in the Cr-Si system by ion irradiation
Authors: Zheng L. R. , Mayer J. W.
Published: February 2003

Effects of ion irradiation on lateral diffusion have been studied in device geometry structures prepared by deposition of Cr films on patterned Si substrates with scanning electron microscopy and transmission electron microscopy. Lateral diffusion can be greatly reduced, and even completely suppressed by using arsenic ion implantation, but not by using silicon irradiation. In Cr/Si planar structures the dopant atoms accumulate near the Si-CrSi2 interface or redistribute into the unreacted Cr films. The presence of 1–2 at. % arsenic substantially slows down the CrSi2 formation. We attribute the suppression of lateral diffusion in device geometry structures to interactions of impurities with the matrix atoms.
New mode of IR detection using quantum wells
Authors: Coon D. D. , Karunasiri R. P. G.
Published: February 2003

A new mode of IR detection using photoemission from a single quantum well is proposed and optimization of the device performance by the proper choice of parameters is discussed. Despite the very thin device structures, theoretical calculations show large absorption at wavelengths near cutoff. The largest photoemissive response is found by adjusting the well parameters so that an excited virtual state lies just above threshold.
Picosecond measurement of Auger recombination rates in InGaAs
Authors: Prise M. E. , Taghizadeh M. R. , Smith S. D. , Wherrett B. S.
Published: February 2003

The picosecond decay of carriers in InGaAs, following photo excitation at photon energies just above the band edge, has been measured. A mode-locked neodymium:yttrium aluminum garnet pumped optical parametric amplifier provided the tunable, 35-ps pulses for excite-probe measurements. At carrier densities in excess of 1018 cm−3 Auger processes are found to dominate the carrier recombination. We determine an Auger rate of 2.5±0.5×10−28 cm6 s−1.
Is the intrinsic conductivity of AlGaSb grown at low temperatures n or p type?
Authors: Takeda Y. , Noda S. , Sasaki A.
Published: February 2003

In liquid phase epitaxial GaSb and AlGaSb grown at low temperatures some papers reported p-type conductivity and others observed the conversion to n-type conductivity. In this paper, it is shown that p-type conductivity is intrinsic at growth temperatures down to 350 °C and that the extrinsic impurities influence the concentration at lower growth temperatures than 350 °C.
Phosphorus gettering and intrinsic gettering of nickel in silicon
Authors: Ourmazd A. , Schröter W.
Published: February 2003

High resolution electron microscopy has been used to study the microstructural changes brought about by phoshorus gettering and intrinsic gettering of Ni in Si. Phosphorus gettering proceeds by the formation of SiP particles at the Si/phosphosilicate glass interface, which emit a large concentration of Si interstitials and result in the gettering of Ni to produce NiSi2 particles at the interface. Intrinsic gettering, under the conditions studied, also proceeds by the emission of Si interstitials due to oxygen precipitiation, with no dislocation generation, and results in the production of NiSi2 at the Si/SiO2 interface. It is suggested that the supersaturation of Si interstitials may be responsible for gettering in both cases.
cw operation of 1.57-μm GaxIn1−xAsyP1−yInP distributed feedback lasers grown by low-pressure metalorganic chemical vapor deposition
Authors: Razeghi M. , Blondeau R. , Kazmierski K. , Krakowski M. , de Cremoux B. , Duchemin J. P. , Bouley J. C.
Published: February 2003

Continuous wave operation of 1.57-μm distributed feedback lasers fabricated on material grown by two-step low-pressure metalorganic chemical vapor deposition growth process is reported for the first time. Room-temperature continuous wave threshold currents as low as 60 mA have been measured for devices with cavity length of 300 μm and stripe width of 5 μm. Single longitudinal mode operation at fixed mode was obtained under the continuous wave condition, in the temperature range 9–90 °C, with the wavelength shift of 0.9 Å/°C. A stop band of 25 Å in which no resonance mode emission existed, was observed in the output spectrum of the distributed feedback laser.
Doping of phosphorus in hydrogenated amorphous silicon by a neutron transmutation doping technique
Authors: Hamanaka H. , Kuriyama K. , Yahagi M. , Satoh M. , Iwamura K. , Kim C. , Kim Y. , Shiraishi F. , Tsuji K. , Minomura S.
Published: February 2003

Doping of phosphorus in hydrogenated amorphous silicon (a-Si:H) produced by rf glow discharge has been achieved by a neutron transmutation doping technique. Electrical and electron spin resonance measurements showed that the neutron irradiation damages have been recovered by the thermal annealing near the growth temperature of a-Si:H films. After thermal annealing at 220 °C, the activation energies of 0.57 and 0.50 eV were obtained for transmuted phosphorus concentrations of 3.1×1012 and 1.6×1013/cm3, corresponding to neutron doses of 1.8×1016 and 9.0×1016 n/cm2, respectively.
Ion implantation into Nb/Nb oxide/PbAuIn Josephson tunnel junctions
Authors: Raider S. I. , Clark G. J.
Published: February 2003

Boron ions have been implanted into complete planar and edge Nb/Nb oxide/PbAuIn Josephson tunnel junctions to directly trim the Josephson current I0. Implantation caused reproducible increases in I0 and in the junction subgap conductance and decreases in the junction energy gap voltage Vg. The variations in junction properties were monotonic with 11B implant dose. Trimming of I0 was optimized when the 11B ions were implanted with the depth distribution peaked near the tunnel barrier.
Stimulated emission on copper I and gold I at room temperature
Authors: Perry N. D. , Tobin R. C.
Published: February 2003

Stimulated emission has been observed on the copper 510.6-, 570.0-, and 578.2-nm, and the gold 627.8-nm transitions at room temperature. Separate discharges are used to produce the metal vapor by sputtering in the presence of a supersonic gas flow, and to excite the metal atoms.
Temperature-dependent polarization behavior of semiconductor lasers
Authors: Chen Y. C. , Liu J. M.
Published: February 2003

InGaAsP lasers are found to operate in a pure TM mode or in a mixture of TE and TM modes at low temperatures. The polarization change at low temperatures is attributed to a thermal-stress effect in the InGaAsP active layer. However, none of the AlGaAs/GaAs lasers tested exhibits such behavior because the thermal stress in the active layer is significantly offset by the GaAs substrate.
Residence time before sodium migration in proton irradiated glasses
Authors: Battaglin G. , Della Mea G. , De Marchi G. , Mazzoldi P.
Published: February 2003

Measurements of residence time prior to Na migration resulting from 600-keV proton irradiation of glasses are reported. The residence time was a function of the beam current (rather than current density), sample temperature, and glass composition. The residence time decreased exponentially with increasing current and increasing temperature.
n-ZrS3/p-WSe2 heterojunctions
Authors: Späh R. , Lux-Steiner M. , Bucher E. , Wagner S.
Published: February 2003

We report the first heterojunction with WSe2 (Eg=1.16 eV) which also introduces the semiconductor ZrS3 (Eg=2.05 eV) to device use. The junctions were prepared in sealed ampoules by iodine vapor transport of presynthesized zirconium trisulfide onto substrates of tungsten diselenide. Diodes exhibited a rectification ratio of up to 20 at 1 V. The photocurrent saturated at 0.5–4 V of reverse bias. The highest quantum efficiency for HeNe laser light (λ=632.8 nm) was 0.5 at 4-V reverse bias.
Thermionic emission in silicon at temperatures below 30 K
Authors: Yang Y. N. , Coon D. D. , Shepard P. F.
Published: February 2003

Experimental results on the injection of carriers into the i region of silicon p-i-n diodes at temperatures below 30 K are described and a simple model is presented to explain the observed I-V characteristics. A range of temperatures is identified in which it is argued that thermionic emission into the i region can be observed unmasked by other effects. The model generalizes the Richardson–Dushman equation to include the effect of impurity bands and a finite transition region between heavily doped and lightly doped regions. As an application, a fast nondestructive means of determining the abruptness of doping profiles is suggested.
Optimization of excitation channels in the discharge-excited Sr+ recombination laser
Authors: Butler M. S. , Piper J. A.
Published: February 2003

We report efficient operation of a longitudinal discharge-excited Sr+ recombination laser operating at λ=430.5 nm in a ‘‘long pulse’’ (∼1 μs full width at half-maximum) mode which utilizes Sr++ ions produced in the afterglow by heavy body processes. Optimum operating conditions have been established and compared with those for the ‘‘short pulse’’ (∼200 ns full width at half-maximum) mode of operation observed previously. Single pulse energies at 180 and 250 μJ have been obtained in the short and long pulse modes respectively corresponding to extraction energy densities of 6 and 8 μJ/cm3.
Donor and acceptor behavior of gold in silicon
Authors: Utzig J. , Schröter W.
Published: February 2003

We have investigated by capacitance transient spectroscopy concentration profiles of gold produced by electrotransport and concentration variations by pairing of gold with iron in p-type silicon. We have found that the line amplitude of the gold donor and that of the gold acceptor have a constant radio independent of gold concentration, diffusion temperature, and of gold-iron-pair concentration. From this result we conclude that the two levels are associated with one gold species in silicon.
Backgating in GaAs/(Al,Ga)As modulation-doped field-effect transistors and its reduction with a superlattice
Authors: Arnold D. , Klem J. , Henderson T. , Morkoç H. , Erickson L. P.
Published: February 2003

Backgating in GaAs/(Al, Ga)As modulation-doped field-effect transistors was investigated experimentally and theoretically. The backgating transconductance varied linearly with buffer layer thickness for thicknesses of 1–3 μm. Incoporation of a thin superlattice at the substrate-epi interface reduced the backgating by about 20%. A model consistent with these findings was developed by treating the substrate potential and buffer layer background doping as a perturbation which raises or lowers the subband energies in the potential well containing the two-dimension electron gas.
High photoconductivity in dual magnetron sputtered amorphous hydrogenated silicon and germanium alloy films
Authors: Rudder R. A. , Cook J. W. , Lucovsky G.
Published: February 2003

Thin-film alloys of amorphous hydrogenated silicon and germanium have been grown by dual magnetron sputtering in a chamber with an ultrahigh vacuum base pressure. Photoconductivities greater than 10−7 (Ω cm)−1 with a light flux of 1015 photons/(cm2 s) were obtained for approximately equal concentrations of Si and Ge in near-intrinsic films with optical gaps near 1.4 eV. The intrinsic nature of these films is established by an activation energy of approximately 0.63 eV. Infrared measurements indicate that the maximum photoconductivity is obtained when sufficient hydrogen has been incorporated to result in a small amount of dihydride bonding on both the Si and Ge alloy constitituents.
Magnesium doping of efficient GaAs and Ga0.75In0.25As solar cells grown by metalorganic chemical vapor deposition
Authors: Lewis C. R. , Ford C. W. , Werthen J. G.
Published: February 2003

Magnesium has been substituted for zinc in GaAs and Ga0.75In0.25As solar cells grown by metalorganic chemical vapor deposition (MOCVD). Bis(cyclopentadienyl)magnesium (Cp2Mg) is used as the MOCVD transport agent for Mg. Full retention of excellent material quality and efficient cell performance results. The substitution of Mg for Zn would enhance the abruptness and reproducibility of doping profiles and facilitate high-temperature processing and operation, due to the much lower diffusion coefficient of Mg, relative to Zn, in these materials.
Modulated transmittance and reflectance in crystalline electrochromic WO3 films: Theoretical limits
Authors: Svensson J. S. E. M. , Granqvist C. G.
Published: February 2003

A quantitative theory for the optical properties of crystalline electrochromic materials is introduced. It is based on the double injection model and includes ionized impurity scattering of free electrons. Solar and luminous properties are evaluated versus electron density for doped WO3 films. Our results point to the possibility of creating efficient ‘‘smart windows’’ with dynamic control of the inflow of radiant energy.
Demonstration of optical bistability with intensity-coupled high gain lasers
Authors: Oudar J. L. , Kuszelewicz R.
Published: February 2003

Competition between external beam amplification and normal laser action is shown to result in a new type of optical bistability in high gain lasers. With one dye laser in a delayed self-extinction configuration, periodic pulsations are observed, showing the alternation of two quasi-stable states. With a twin dye laser configuration, only one laser at a time could be above threshold due to their mutual coupling. Switching with subnanosecond rise time has been obtained in a purely optical way.
Carrier induced refractive index change in AlGaAs quantum well lasers
Authors: Dutta N. K. , Olsson N. A. , Tsang W. T.
Published: February 2003

Measurements of the carrier induced refractive index change in AlGaAs quantum well lasers are presented which show that the guided mode in single quantum well lasers exhibits a small (Δn/ΔN∼−3×10−22 cm3) carrier induced change in refractive index. This is more than an order of magnitude smaller than the corresponding value for conventional active layer lasers. The measured ΔnA/ΔN ∼−7×10−21 cm3 in the active layers of AlGaAs multiquantum well structures. The measured index changes of the guided mode at threshold (Δnth) are −5.6×10−3 and −7.6×10−3 for the single quantum well and multiquantum well lasers, respectively. This should be compared with a value of ∼1.2×10−2 for conventional active layer lasers. These results suggest that single frequency sources fabricated using real index guided single quantum well active layers may have improved frequency stability under direct current modulation.
Improved mode extinction modulator using a Ti in-diffused LiNbO3 channel waveguide
Authors: Ashley P. R. , Chang W. S. C.
Published: February 2003

An efficient, linear mode extinction modulator has been demonstrated using a weakly guided, near cutoff, channel waveguide. Modulation slopes as high as 16% per volt have been measured. Deviation from a linear voltage-intensity relationship of less than 1% has been observed over a 77% modulation range. Over 97% modulation has been achieved with ±4 V applied. An optical bias is also demonstrated. A coupled mode analysis for the modulator is reported which includes propagation loss effects.
Buried ion-exchanged optical waveguides with refractive index profiles controlled by rediffusion
Authors: Baba Kazutaka , Shiraishi Kazuo , Hanaizumi Osamu , Kawakami Shojiro
Published: February 2003

New buried optical waveguides whose refractive index profiles can be controlled by rediffusion are formed by the ion exchange and rf sputtering technique. A buried waveguide with a nearly symmetric refractive index distribution and a new slowly tapered structure are fabricated.
High-power operation of index-guided visible GaAs/GaAlAs multiquantum well lasers
Authors: Uomi K. , Nakatsuka S. , Ohtoshi T. , Ono Y. , Chinone N. , Kajimura T.
Published: February 2003

Stable transverse mode operation has been realized for the first time in visible (780 nm) multiquantum well lasers composed of seven 3-nm-thick GaAs wells separated by six 5-nm-thick Ga0.8Al0.2As barriers grown by metalorganic chemical vapor deposition. A self-aligned structure with a built-in optical waveguide to stabilize the transverse mode is fabricated by a two-step epitaxial technique. Low threshold current (35 mA), high output power (up to 40 mW) in the fundamental transverse mode, and a very low degradation rate at 70 °C have been confirmed.
Ion-enhanced gas-surface kinetics: The Si-Cl2-Ar+ system
Authors: Rossen Rebecca A. , Sawin Herbert H.
Published: February 2003

The mechanisms of ion-enhanced gas-surface etching reactions have been investigated by the simultaneous exposure of 300-K silicon to coincident beams of Cl2 and modulated 1-keV Ar+ ions. The transient emission at low modulation frequencies suggests that a chlorinated film several atomic layers in depth is formed. SiClx emission products are thought to be formed on and within the film by sequential chlorination and are released in subsequent sputtering events. SiCl, which is believed to be emitted from surface of this film, exhibits a lower emission energy (≊0.03 eV) than SiCl4, which is emitted from within the film (≊4.0 eV).
cw laser induced low-temperature decomposition of CdTe crystals
Authors: Uzan C. , Legros R. , Marfaing Y. , Triboulet R.
Published: February 2003

A cw argon ion laser was used to study the thermal behavior of CdTe under laser irradiation. The temperature time profile was calculated from a theoretical model. It turns out that surface decomposition occurs at temperatures well below the melting point (∼850 K), for pulse duration above 100 μs. The sputtering depth plotted against the temperature reached at the end of the pulse reveals a thermally activated process with an energy of 0.49 eV; by contrast, for a purely thermal sublimation, the activation energy is 1.93 eV. The difference of 1.44 eV, close to the band-gap energy, suggests the intervention of a recombination enhanced surface reaction.
Bulk photovoltaic effect in polyvinylidene fluoride
Authors: Ogden T. R. , Gookin D. M.
Published: February 2003

A bulk photovoltaic effect has been observed in a ferroelectric polymer, polyvinylidene fluoride. Permanent photocurrents and photovoltages are generated by incident light in the visible region without application of any external electric field. The results are interpreted according to theory developed for similar effects found in ferroelectric and pyroelectric single crystals and ceramics.
Contaminant and defect analysis of optical surfaces by infrared laser induced desorption
Authors: Allen S. D. , Porteus J. O. , Faith W. N. , Franck J. B.
Published: February 2003

Infrared laser induced desorption (LID) has been demonstrated for water and other contaminants on nominally transparent substrates. For the samples measured to date, the LID is defect dominated for both small (120 μm) and large (380 μm) spot sizes. For the larger spot sizes, the data for multiple irradiations of the same site (N/1) can be explained using a simple defect model. The surface damage threshold of these materials correlates with the measured LID fluence, i.e., samples and sites with high contaminant fluences damage at low thresholds. Laser cleaned surfaces of CaF2, BaF2, and NaCl which were dosed with H2O at approximately −100 °C showed no evidence of readsorbed water on subsequent LID testing, indicating a passivation of the surface.
High-power gain-guided InGaAsP laser array
Authors: Dutta N. K. , Napholtz S. G. , Wilson R. B. , Brown R. L. , Cella T. , Craft D. C.
Published: February 2003

We have fabricated InGaAsP gain-guided laser arrays emitting at 1.3 μm. These devices have threshold currents in the range 300–400 mA at 30 °C and have been operated to pulsed output powers as high as 400 mW. More than 100 mW of output power has been obtained up to an ambient temperature of 60 °C. The lasers emit in multilongitudinal modes with a far-field divergence of 20°×35°. A gain-guided InGaAsP laser array of the type described here can be used in some applications requiring high-power lasers emitting at 1.3 μm.
Mode locking a Ti:LiNbO3-InGaAsP/InP composite cavity laser with an integrated high-speed directional coupler switch
Authors: Alferness R. C. , Eisenstein G. , Korotky S. K. , Tucker R. S. , Buhl L. L. , Kaminow I. P. , Burrus C. A. , Veselka J. J.
Published: February 2003

We propose and demonstrate the first Ti:LiNbO3 waveguide-InGaAsP/InP composite cavity laser. Mode locked optical pulses shorter than 22 ps have been generated at repetition rates up to 7.2 GHz by sinusoidally driving the integrated traveling-wave directional coupler switch.
Synthesis of rare gas-halide mixtures resulting in efficient XeF(C→A) laser oscillation
Authors: Nighan W. L. , Tittel F. K. , Wilson W. L. , Nishida N. , Zhu Y. , Sauerbrey R.
Published: February 2003

Significantly improved XeF(C→A) laser performance has been achieved using electron beam excitation of complex, multicomponent gas mixtures specifically tailored so as to reduce medium transient absorption in the blue-green region. Use of Ar and Kr together as the effective rare gas buffer-energy transfer species, along with a combination of NF3 and F2 to produce the desired F-donor molecule characteristics, has permitted synthesis of near optimum medium properties for which XeF(C) is produced efficiently while transient absorption is minimized. With this technique we have achieved laser pulse energy density and intrinsic efficiency of 2.2±0.3 J/l and ∼1.5%, respectively, values that are comparable to those of the B→X rare gas-halide lasers.
Infrared absorption and low-temperature photoluminescence spectra of GaAs grown by molecular beam epitaxy
Authors: Akimoto K. , Dohsen M. , Arai M. , Watanabe N.
Published: February 2003

The variation in the intensity of the excitonlike luminescence lying 5–10 meV below the free-exciton energy value specific to molecular beam epitaxially grown GaAs was studied under various growth conditions. The intensity of the luminescence increases with increasing CO in the background and/or decreasing As4/Ga flux ratio. Fourier transform infrared spectra indicated the existence of polynuclear carbonyls in the GaAs. The excitonlike luminescence may be caused by radiative recombination of excitons bound to CO incorporated from the ambient on an As site.
Optical bistability due to induced absorption: Propagation dynamics of excitation profiles
Authors: Koch S. W. , Schmidt H. E. , Haug H.
Published: February 2003

For an optically bistable system with induced absorption the transport equations for the light intensity and the excitation density are solved. Under pulse operation a kink in the excitation density is found, which moves discontinuously in the beam direction and causes a sawtooth variation in the transmitted intensity.
Impact ionization rates for electrons and holes in Al0.48In0.52As
Authors: Capasso F. , Mohammed K. , Alavi K. , Cho A. Y. , Foy P. W.
Published: February 2003

The first measurement of the impact ionization rates for electrons and holes in Al0.48In0.52As is reported. Photomultiplication measurements in pin avalanche photodiodes give α/β≊2.5–3.0 in the electric field range 3.3×105 V/cm≤F≤4.3×105 V/cm. This material can therefore be used to implement a potentially high-performance, long-wavelength avalanche photodiode, with separate absorption and multiplication regions and a high-low electric field profile (HI-LO SAM APD).
Raman scattering from molecular beam epitaxially grown superlattices of diluted magnetic semiconductors
Authors: Venugopalan S. , Kolodziejski L. A. , Gunshor R. L. , Ramdas A. K.
Published: February 2003

We report the first Raman scattering study of Cd1−xMnxTe superlattices. The films are grown by molecular beam epitaxy. Brillouin zone-folding effects on LA phonons, resonant scattering by LO phonons, and the magnetic field-induced shift of the photoluminescence peak are reported. The latter yields an effective electronic g factor of ∼100, comparable to that of Cd1−xMnxTe bulk crystals. No collective magnetic excitation was detected at zero field even at 5 K in the superlattices studied. However, the Raman paramagnetic resonance of Mn2+ ions could be excited in an applied field. The implications of this result for magnetic phase transitions within superlattice layers are briefly mentioned.
Complementary metal-oxide-silicon field-effect transistors fabricated in 4-MeV boron-implanted silicon
Authors: Terrill K. W. , Byrne P. F. , Hu C. , Cheung N. W.
Published: February 2003

Boron was implanted into p-type (100) silicon at an energy of 4 MeV to create a layer of heavily doped silicon centered at a depth of 5.2 μm below the surface. Both n-channel and p-channel metal-oxide-silicon, field-effect transistors (MOSFET’s) and various diode structures were fabricated over this implanted region by using a 3-μm complementary MOSFET (CMOS) technology. The results show that the implanted silicon is recrystallized to a device quality state. No increase in diode leakage or degradation in MOSFET device characteristics is observed. Experimental results show that this subdevice buried layer leads to a reduction of CMOS latch-up susceptibility.
Effect of surface irradiation, substrate temperature, and annealing on laser deposited silicon dioxide
Authors: Boyer P. K. , Emery K. A. , Zarnani H. , Collins G. J.
Published: February 2003

A pulsed ArF laser is used to photochemically deposit thin films of silicon dioxide on silicon substrates. As the substrate temperature was increased during film deposition, the etch rate, dielectric constant, flatband voltage shift, and hydrogen bonding of the SiO2 film decreased while the refractive index, resistivity, and breakdown voltage increased. The etch rate and infrared absorbance of bonded hydrogen incorporated in the SiO2 film also decreased when surface photons impinged on the growing films or when a post-deposition anneal was performed.
Tin phosphide as a phosphorus beam source for molecular beam epitaxy
Authors: Chai Young G.
Published: February 2003

The use of Sn-P is proposed as a new method of generating phosphorus beams for molecular beam epitaxy. This method generates almost pure P2 beams with negligible by-product. Theoretical predictions and experimental data are presented.
Reflectivity spectra of epitaxial GaAs-rich GaAs1−xSbx
Authors: Radojewska E. Beata , Bryśkiewicz Tadeusz , Jȩdral Lech , Brzeziński Janusz , Lewandowski Wojciech
Published: February 2003

Epitaxial single-crystalline GaAs-rich GaAs1−xSbx layers have been examined at room and liquid nitrogen temperatures by means of reflectivity measurements in the fundamental absorption region. The energies of observed interband transitions have been linearly correlated with the composition.
An improved design of high order superconducting gradiometer coils for magnetic monopole detection
Authors: Donaldson G. B. , Bain R. J. P.
Published: February 2003

A family of planar superconducting magnetic gradiometers for use as magnetic monopole detectors has recently been proposed. We describe an alternative system which reduces the number of loop crossovers for a two-dimensional Nth order gradiometer from approximately 22N to N2. This system permits much higher order gradiometers to be used, for a given detector area and superconducting quantum interference device input inductance, resulting in improved signal to noise performance. The simplification of design should also minimize the practical difficulties of fabricating high order gradiometers.
Sequence Analysis of a 282-Kilobase Region Surrounding the Citrus Tristeza Virus Resistance Gene (Ctv) Locus inPoncirus trifoliata L. Raf.
Authors: Yang Zhong-Nan , Ye Xin-Rong , Molina Joe , Roose Mikeal L. , Mirkov T. Erik
Published: February 2003

Citrus tristeza virus (CTV) is the major virus pathogen causing significant economic damage to citrus worldwide, and a single dominant gene, Ctv, provides broad spectrum resistance to CTV inPoncirus trifoliata L. Raf. Ctv was physically mapped to a 282-kb region using a P. trifoliata bacterial artificial chromosome library. This region was completely sequenced to about 8× coverage using a shotgun sequencing strategy and primer walking for gap closure. Sequence analysis predicts 22 putative genes, two mutator-like transposons and eight retrotransposons. This sequence analysis also revealed some interesting features of this region of the P. trifoliata genome: a disease resistance gene cluster with seven members and eight retrotransposons clustered in a 125-kb gene-poor region. Comparative sequence analysis suggests that six genes in theCtv region have significant sequence similarity with their orthologs in bacterial artificial chromosome clones F7H2 and F21T11 from Arabidopsis chromosome I. However, the analysis of gene colinearity between P. trifoliata and Arabidopsis indicates that Arabidopsis genome sequence information may be of limited use for positional gene cloning in P. trifoliataand citrus. Analysis of candidate genes for Ctv is also discussed.
Xylem Ray Parenchyma Cells in Boreal Hardwood Species Respond to Subfreezing Temperatures by Deep Supercooling That Is Accompanied by Incomplete Desiccation
Authors: Kuroda Katsushi , Kasuga Jun , Arakawa Keita , Fujikawa Seizo
Published: February 2003

It has been accepted that xylem ray parenchyma cells (XRPCs) in hardwood species respond to subfreezing temperatures either by deep supercooling or by extracellular freezing. Present study by cryo-scanning electron microscopy examined the freezing responses of XRPCs in five boreal hardwoods: Salix sachalinensis Fr. Schmit, Populus sieboldii Miq., Betula platyphylla Sukat. var japonica Hara,Betula pubescens Ehrh., and red osier dogwood (Cornus sericea), in which XRPCs have been reported to respond by extracellular freezing. Cryo-scanning electron microscopy observations revealed that slow cooling of xylem to −80°C resulted in intracellular freezing in the majority of XRPCs in S. sachalinensis, an indication that these XRPCs had been deep supercooled. In contrast, in the majority of XRPCs in P. sieboldii, B. platyphylla, B. pubescens, and red osier dogwood, slow cooling to −80°C produced slight cytorrhysis without clear evidence of intracellular freezing, suggesting that these XRPCs might respond by extracellular freezing. In these XRPCs exhibited putative extracellular freezing; however, deep etching revealed the apparent formation of intracellular ice crystals in restricted local areas. To confirm the occurrence of intracellular freezing, we rewarmed these XRPCs after cooling and observed very large intracellular ice crystals as a result of the recrystallization. Thus, the XRPCs in all the boreal hardwoods that we examined responded by deep supercooling that was accompanied with incomplete desiccation. From these results, it seems possible that limitations to the deep-supercooling ability of XRPCs might be a limiting factor for adaptation of hardwoods to cold climates.
Differences in Whole-Cell and Single-Channel Ion Currents across the Plasma Membrane of Mesophyll Cells from Two Closely RelatedThlaspi Species
Authors: Piñeros Miguel A. , Kochian Leon V.
Published: February 2003

The patch clamp technique was used to study the physiology of ion transport in mesophyll cells from two Thlaspispp. that differ significantly in their physiology. In comparison withThlaspi arvense, Thlaspi caerulescens (a heavy metal accumulator) can grow in, tolerate, and accumulate very high levels of certain heavy metals (primarily zinc [Zn] and cadmium) in their leaf cells. The membrane conductance of every T. arvense leaf cell was dominated by a slowly activating, time-dependent outward rectifying current (SKOR). In contrast, only 23% of T. caerulescens cells showed SKOR activity, whereas the remaining 77% exhibit a rapidly developing instantaneous K+ outward rectifier (RKOR) current. In contrast to RKOR, the channels underlying the SKOR current were sensitive to changes in the extracellular ion activity. Single-channel recordings indicated the existence of K+ channel populations with similar unitary conductances, but distinct channel kinetics and regulation. The correlation between these recordings and the whole-cell data indicated that although one type of channel kinetics is preferentially activated in each Thlaspi spp., both species have the capability to switch between either type of current. Ion substitution in whole-cell and single-channel experiments indicated that although the SKOR and RKOR channels mediate a net outward K+ current, they can also allow a significant Zn2+ permeation (i.e. influx). In addition, single-channel recordings allowed us to identify an infrequent type of plasma membrane divalent cation channel that also can mediate Zn2+ influx. We propose that the different K+ channel types or channel states may result from and are likely to reflect differences in the cytoplasmic and apoplastic ionic environment in each species. Thus, the ability to interchangeably switch between different channel states allows each species to constantly adjust to changes in their apoplastic ionic environment.
Characterization of a Plant Homolog of Hop, a Cochaperone of Hsp90
Authors: Zhang Zhongming , Quick Michelle K. , Kanelakis Kimon C. , Gijzen Mark , Krishna Priti
Published: February 2003

The 90-kD molecular chaperone hsp90 is the key component of a multiprotein chaperone complex that facilitates folding, stabilization, and functional modulation of a number of signaling proteins. The components of the animal chaperone complex include hsp90, hsp70, hsp40, Hop, and p23. The animal Hop functions to link hsp90 and hsp70, and it can also inhibit the ATPase activity of hsp90. We have demonstrated the presence of an hsp90 chaperone complex in plant cells, but not all components of the complex have been identified. Here, we report the isolation and characterization of soybean (Glycine max) GmHop-1, a soybean homolog of mammalian Hop. An analysis of soybean expressed sequence tags, combined with preexisting data in literature, suggested the presence of at least three related genes encoding Hop-like proteins in soybean. Transcripts corresponding to Hop-like proteins in soybean were detected under normal growth conditions, and their levels increased further in response to stress. A recombinant GmHop-1 bound hsp90 and its binding to hsp90 could be blocked by the tetratricopeptide repeat (TPR) domain of rat (Rattus norvegicus) protein phosphatase 5. Deletion of amino acids 325 to 395, adjacent to the TPR2A domain in GmHop-1, resulted in loss of hsp90 binding. In a minimal assembly system, GmHop-1 was able to stimulate mammalian steroid receptor folding. These data show that plant and animal Hop homologs are conserved in their general characteristics, and suggest that a Hop-like protein in plants is an important cochaperone of plant hsp90.
Arabidopsis ICX1 Is a Negative Regulator of Several Pathways Regulating Flavonoid Biosynthesis Genes
Authors: Wade Helena K. , Sohal Awinder K. , Jenkins Gareth I.
Published: February 2003

Flavonoid biosynthesis gene expression is controlled by a range of endogenous and environmental signals. The Arabidopsisicx1 (increased chalcone synthase expression 1) mutant has elevated induction of CHS(CHALCONE SYNTHASE) and other flavonoid biosynthesis genes in response to several stimuli. We show thatICX1 is a negative regulator of the cryptochrome 1, phytochrome A, ultraviolet (UV)-B, low temperature, sucrose, and cytokinin induction of CHS expression and/or anthocyanin accumulation, demonstrating that these pathways are regulated either directly or indirectly by at least one common component. Expression analysis of CHS and other genes (LTP,CAB, and rbcS) indicates thatICX1 functions in both seedlings and mature leaf tissue and acts principally in the epidermis, consistent with the alterations in epidermal development seen in icx1. The mutant was unaltered in the synergistic interactions between UV-B, blue, and UV-A light that regulate CHS and we propose a model of action of ICX1 in these responses.
A Sequence-Based Map of Arabidopsis Genes with Mutant Phenotypes,
Authors: Meinke David W. , Meinke Laura K. , Showalter Thomas C. , Schissel Anna M. , Mueller Lukas A. , Tzafrir Iris
Published: February 2003

The classical genetic map of Arabidopsis contains 462 genes with mutant phenotypes. Chromosomal locations of these genes have been determined over the past 25 years based on recombination frequencies with visible and molecular markers. The most recent update of the classical map was published in a special genome issue ofScience that dealt with Arabidopsis (D.W. Meinke, J.M. Cherry, C. Dean, S.D. Rounsley, M. Koornneef [1998] Science 282: 662–682). We present here a comprehensive list and sequence-based map of 620 cloned genes with mutant phenotypes. This map documents for the first time the exact locations of large numbers of Arabidopsis genes that give a phenotype when disrupted by mutation. Such a community-based physical map should have broad applications in Arabidopsis research and should serve as a replacement for the classical genetic map in the future. Assembling a comprehensive list of genes with a loss-of-function phenotype will also focus attention on essential genes that are not functionally redundant and ultimately contribute to the identification of the minimal gene set required to make a flowering plant.
The Arabidopsis STICHEL Gene Is a Regulator of Trichome Branch Number and Encodes a Novel Protein
Authors: Ilgenfritz Hilmar , Bouyer Daniel , Schnittger Arp , Mathur Jaideep , Kirik Victor , Schwab Birgit , Chua Nam-Hai , Jürgens Gerd , Hülskamp Martin
Published: February 2003

Here, we analyze the STICHEL(STI) gene, which plays an important role in the regulation of branch number of the unicellular trichomes in Arabidopsis. We have isolated the STI locus by positional cloning and confirmed the identity by sequencing seven independent sti alleles. The STI gene encodes a protein of 1,218 amino acid residues containing a domain with sequence similarity to the ATP-binding eubacterial DNA-polymerase III γ-subunits. Because endoreduplication was found to be normal insti mutants the molecular function of STIin cell morphogenesis is not linked to DNA replication and, therefore, postulated to represent a novel pathway. Northern-blot analysis shows that STI is expressed in all organs suggesting thatSTI function is not trichome specific. The analysis ofsti alleles and transgenic lines overexpressingSTI suggests that STI regulates branching in a dosage-dependent manner.
The Maize Low-Phytic Acid Mutant lpa2 Is Caused by Mutation in an Inositol Phosphate Kinase Gene
Authors: Shi Jinrui , Wang Hongyu , Wu Yunsheng , Hazebroek Jan , Meeley Robert B. , Ertl David S.
Published: February 2003

Reduced phytic acid content in seeds is a desired goal for genetic improvement in several crops. Low-phytic acid mutants have been used in genetic breeding, but it is not known what genes are responsible for the low-phytic acid phenotype. Using a reverse genetics approach, we found that the maize (Zea mays) low-phytic acidlpa2 mutant is caused by mutation in an inositol phosphate kinase gene. The maize inositol phosphate kinase (ZmIpk) gene was identified through sequence comparison with human and Arabidopsis Ins(1,3,4)P3 5/6-kinase genes. The purified recombinant ZmIpk protein has kinase activity on several inositol polyphosphates, including Ins(1,3,4)P3, Ins(3,5,6)P3, Ins(3,4,5,6)P4, and Ins(1,2,5,6)P4. The ZmIpk mRNA is expressed in the embryo, the organ where phytic acid accumulates in maize seeds. The ZmIpk Mutator insertion mutants were identified from a Mutator F2family. In the ZmIpk Mu insertion mutants, seed phytic acid content is reduced approximately 30%, and inorganic phosphate is increased about 3-fold. The mutants also accumulatemyo-inositol and inositol phosphates as in thelpa2 mutant. Allelic tests showed that the ZmIpkMu insertion mutants are allelic to thelpa2. Southern-blot analysis, cloning, and sequencing of the ZmIpk gene from lpa2 revealed that thelpa2-1 allele is caused by the genomic sequence rearrangement in the ZmIpk locus and the lpa2-2 allele has a nucleotide mutation that generated a stop codon in the N-terminal region of the ZmIpk open reading frame. These results provide evidence that ZmIpk is one of the kinases responsible for phytic acid biosynthesis in developing maize seeds.
cor Gene Expression in Barley Mutants Affected in Chloroplast Development and Photosynthetic Electron Transport
Authors: Dal Bosco Cristina , Busconi Marco , Govoni Chiara , Baldi Paolo , Stanca A. Michele , Crosatti Cristina , Bassi Roberto , Cattivelli Luigi
Published: February 2003

The expression of several barley (Hordeum vulgare) cold-regulated (cor) genes during cold acclimation was blocked in the albino mutanta  n, implying a chloroplast control on mRNAs accumulation. By using albino and xanthamutants ordered according to the step in chloroplast biogenesis affected, we show that the cold-dependent accumulation ofcor14b, tmc-ap3, andblt14 mRNAs depends on plastid developmental stage. Plants acquire the ability to fully express cor genes only after the development of primary thylakoid membranes in their chloroplasts. To investigate the chloroplast-dependent mechanism involved in cor gene expression, the activity of a 643-bp cor14b promoter fragment was assayed in wild-type and albino mutant a  n leaf explants using transient β-glucuronidase reporter expression assay. Deletion analysis identified a 27-bp region between nucleotides −274 and −247 with respect to the transcription start point, encompassing a boundary of some element that contributes to the cold-induced expression of cor14b. However, cor14bpromoter was equally active in green and in albinoa  n leaves, suggesting that chloroplast controls cor14b expression by posttranscriptional mechanisms. Barley mutants lacking either photosystem I or II reaction center complexes were then used to evaluate the effects of redox state of electron transport chain components on COR14b accumulation. In the mutants analyzed, the amount of COR14b protein, but not the steady-state level of the corresponding mRNA, was dependent on the redox state of the electron transport chain. Treatments of thevir-zb63 mutant with electron transport chain inhibitors showed that oxidized plastoquinone promotes COR14b accumulation, thus suggesting a molecular relationship between plastoquinone/plastoquinol pool and COR14b.
Chlamydomonas reinhardtii Genome Project. A Guide to the Generation and Use of the cDNA Information
Authors: Shrager Jeff , Hauser Charles , Chang Chiung-Wen , Harris Elizabeth H. , Davies John , McDermott Jeff , Tamse Raquel , Zhang Zhaodou , Grossman Arthur R.
Published: February 2003

The National Science Foundation-funded Chlamydomonas reinhardtii genome project involves (a) construction and sequencing of cDNAs isolated from cells exposed to various environmental conditions, (b) construction of a high-density cDNA microarray, (c) generation of genomic contigs that are nucleated around specific physical and genetic markers, (d) generation of a complete chloroplast genome sequence and analyses of chloroplast gene expression, and (e) the creation of a Web-based resource that allows for easy access of the information in a format that can be readily queried. Phases of the project performed by the groups at the Carnegie Institution and Duke University involve the generation of normalized cDNA libraries, sequencing of cDNAs, analysis and assembly of these sequences to generate contigs and a set of predicted unique genes, and the use of this information to construct a high-density DNA microarray. In this paper, we discuss techniques involved in obtaining cDNA end-sequence information and the ways in which this information is assembled and analyzed. Descriptions of protocols for preparing cDNA libraries, assembling cDNA sequences and annotating the sequence information are provided (the reader is directed to Web sites for more detailed descriptions of these methods). We also discuss preliminary results in which the different cDNA libraries are used to identify genes that are potentially differentially expressed.
The Role of Free Histidine in Xylem Loading of Nickel inAlyssum lesbiacum and Brassica juncea
Authors: Kerkeb Loubna , Krämer Ute
Published: February 2003

Exposure of the hyperaccumulator Alyssum lesbiacum to nickel (Ni) is known to result in a dose-dependent increase in xylem sap concentrations of Ni and the chelator free histidine (His). Addition of equimolar concentrations of exogenousl-His to an Ni-amended hydroponic rooting medium enhances Ni flux into the xylem in the nonaccumulator Alyssum montanum, and, as reported here, in Brassica juncea L. cv Vitasso. In B. juncea, reducing the entry of l-His into the root by supplying d-His instead of l-His, or l-His in the presence of a 10-fold excess of l-alanine, did not affect root Ni uptake, but reduced Ni release into the xylem. Compared with B. juncea, root His concentrations were constitutively about 4.4-fold higher in A. lesbiacum, and did not increase within 9 h of exposure to Ni. Cycloheximide did not affect root His or Ni concentrations, but strongly decreased the release of His and Ni from the root into the xylem of A. lesbiacum, whereas xylem sap concentrations of Ca and Mg remained unaffected. Near-quantitative chelation of Ni with nitrilotriacetate in the rooting medium did not enhance Ni flux into the xylem of A. lesbiacum and B. juncea, suggesting the absence of a significant apoplastic pathway for Ni entry into the xylem. The data suggest that in B. juncea roots, Ni2+uptake is independent of simultaneous uptake of His. In both species, enhanced release of Ni into the xylem is associated with concurrent release of His from an increased root free His pool.