bluuebunny/crossref_metadata_2025 huggingface dataset:
Extension of long wavelength response by modulation doping in extrinsic germanium infrared detectors
Authors: Hadek V. , Farhoomand J. , Beichman C. A. , Watson D. M. , Jack M. D.
Published: July 2002

We have investigated a new concept for infrared detectors based on multilayer epitaxy and modulation doping. This permits a high doping concentration and lower excitation energy in the photodetecting layer as is necessary for longer wavelength response, without incurring the detrimental effects of increased dark current and noise as would be the case with conventional detector designs. Germanium photodetectors using conventional materials and designs have a long wavelength cutoff in the infrared at 138 μm, which can only be extended through the inconvenient application of mechanical stress or magnetic fields. As a result of this approach which we arrived at from theoretical considerations and subsequently demonstrated experimentally, the long wavelength cutoff for germanium extrinsic detectors was extended beyond 200 μm, as determined by direct infrared optical measurements.
Optical bistability in bulk ZnSe due to increasing absorption and self-focusing
Authors: Taghizadeh M. R. , Janossy I. , Smith S. D.
Published: July 2002

We report the first observation of cavityless optical bistability in ZnSe. A shift in the band edge and self-focusing occurs due to the temperature rise of the material as the laser irradiance is increased. These two mechanisms are believed to provide the feedback necessary for bistable operation.
Heavy ion beam probe measurement of local electron heating in the Elmo Bumpy Torus
Authors: Bieniosek F. M. , Connor K. A.
Published: July 2002

Measurements of the abundance of multiply charged ionization products from a heavy ion beam probing beam have been used as a spatially resolved plasma diagnostic on Elmo Bumpy Torus. Radial profile measurements demonstrate that two classes of electrons are present: those that communicate toroidally to form the core plasma and those that are mirror trapped and depend on local heating (particularly ω=2Ωce) for their existence. Both types show a systematic dependence on resonant heating locations.
Channeling of ions near the silicon 〈001〉 axis
Authors: Ziegler J. F. , Lever R. F.
Published: July 2002

The first experimental mapping of ion beam channels near the Si 〈001〉 axis is reported. All features are identified by theoretical plots of silicon planar channels and axial channels.
Gamma ray detectors with HgCdTe contact layers
Authors: Ryan F. J. , Shin S. H. , Edwall D. D. , Pasko J. G. , Khoshnevisan M. , Westmark C. I. , Fuller C.
Published: July 2002

A new device structure for room-temperature gamma ray spectrometry has been developed and demonstrated. The device is a heterojunction p-i-n, HgCdTe/CdTe/HgCdTe structure. The p layer is Au doped with NA=1.9×1016 cm−3, μp=35 cm2/Vs, and a Cd composition xCd=0.6. The n layer is In doped with ND=2×1017 cm−3, μn=1880 cm2/Vs, and xCd=0.31. Ohmic contacts were achieved using electron beam evaporated Au (p layer contact) and In (n-layer contact). Devices (with approximately 2-mm2 area, 2-mm thickness) exhibited reverse leakage currents of 50 pA–4 nA, good photovoltaic response with visible light, and voltage breakdowns in excess of 1000 V. At 250-V reverse bias, the energy resolutions at the principal photopeaks of Am-241 (60 keV) and Co-57 (122 keV) were 12.5% and 8.4%, respectively.
UV laser photodeposition of patterned catalyst films from adsorbate mixtures
Authors: Ehrlich D. J. , Tsao J. Y.
Published: July 2002

Efficient catalysts for hydrocarbon polymerization have been prepared photochemically by reaction of mixed TiCl4 and Al2(CH3)6 adsorbate layers, in the scanned focus of a 257.2-nm laser beam. Monolayer coverages of the photodeposited catalyst have been shown effective for in situ patterned polymerization of ethylene and acetylene at room temperature from the vapor phase organic monomers. Three-micrometer spatial resolution has been obtained in selected-area polymer growth. The chemical kinetics of the mixed-adsorbate reactions and the effects of compositional changes on the catalytic activity of the laser-photodepostied films have been studied.
Nitrification of zirconium by cw CO2 laser irradiation in ambient atmosphere
Authors: Ursu I. , Mihailescu I. N. , Nanu L. , Prokhorov A. M. , Konov V. I. , Ralchenko V. G.
Published: July 2002

The preferential nitrification of zirconium can be obtained as a result of cw CO2 laser heating in air in some specific conditions, followed by rapid cooling in a jet of high purity argon.
Shallow beryllium implantation in GaAs annealed by rapid thermal annealing
Authors: Chambon P. , Berth M. , Prévot B.
Published: July 2002

Very shallow (40 nm) ion implants of Be in GaAs have been annealed with no noticeable redistribution using rapid thermal annealing (RTA). Differential Hall effect measurements, Raman Scattering, and spectroscopic ellipsometry have shown that a peak concentration of 3×1019 cm−3 is achieved, with an electrical activation of 80% and crystalline quality similar to unimplanted material. These results are interpreted in terms of diffusing (interstitial) atoms gettered by defects not yet annealed when electrical activation occurs in the RTA process.
GaAs/Ga0.47In0.53As lattice-mismatched Schottky barrier gates: Influence of misfit dislocations on reverse leakage currents
Authors: Chen C. Y. , Chu S. N. G. , Cho A. Y.
Published: July 2002

Epitaxial GaAs has been grown on Ga0.47In0.53As by molecular beam epitaxy to form a lattice-mismatched Schottky barrier gate for field-effect transistor applications. The study of cross-sectional transmission electron microscopy shows that the misfit dislocations accommodating the 3.7% lattice mismatch between these two materials are confined in a GaAs interfacial layer of 300–400-Å thickness. As a result of significant reduction in dislocation densities, Schottky barrier gates made on a sample having a 960-Å-thick GaAs layer exhibit reverse leakage currents two orders of magnitude lower than those made on a sample with a 580-Å-thick GaAs layer. This approach looks promising for fabricating Ga0.47In0.53As field-effect transistors for optoelectronic integration as well as high-speed logic applications.
Thermal profiles during recrystallization of silicon on insulator with scanning incoherent light line sources
Authors: Kubota Katsuhiko , Hunt Charles E. , Frey Jeffrey
Published: July 2002

The classical heat equation is solved in one and two dimensions to obtain temperature profiles during recrystallization of silicon thin films on insulators with scanning incoherent light sources. The extent of the Si molten region in multilayered structures is predicted using a macroscopic approach. The enthalpy method incorporates the latent heat of fusion into the temperature-enthalpy relation for Si; the Kirchhoff transformation takes the temperature dependence of the thermal conductivities for the materials into account. The calculations yield the Si melt depths and temperatures and are intended to establish proper experimental conditions.
Controlled low barrier height n+-InGaAs/n-GaAs pseudomorphic heterojunction Schottky diodes
Authors: Kleinsasser A. W. , Woodall J. M. , Pettit G. D. , Jackson T. N. , Tang J. Y.-F. , Kirchner P. D.
Published: July 2002

Heterojunction Schottky barrier diodes, in which a pseudomorphic layer of n+-InGaAs played the role of a metal contacting n-GaAs, were grown by molecular beam epitaxy. The junctions had low barrier heights (30–150 meV) which could be controlled by composition and doping of the n+ layer. I-V measurements of the devices confirmed that the devices behaved as Schottky diodes, in accordance with the theory of tunneling and thermally assisted tunneling in the temperature range 4–200 K. An exponential increase in conductance with decreasing In concentration indicates a decrease in barrier height which is at least qualitatively consistent with simulations of the barriers based on earlier experiments, which showed that the band-gap discontinuity appears predominately in the conduction band.
Stability of (100)GaAs surfaces in aqueous solutions
Authors: Aspnes D. E. , Studna A. A.
Published: July 2002

Abrupt (100) GaAs surfaces are observed to be stable against the development of pervasive microscopic roughness in strongly basic (pH 14) solutions but not in NH4OH and neutral H2O. Strong acids (pH 0) produce deep microroughness. The stability can be understood from the free energy of Ga ions in solution and the action of electrophilic bifunctional etching groups on the Ga–As bond.
Optical phase conjugation with frequency up-conversion via high-order, nondegenerate multiwave mixing
Authors: Ducloy Martial
Published: July 2002

One proposes a new way of getting optical phase conjugation, associated to frequency conversion (namely, frequency doubling, frequency multiplication or mixing), within a broad angular field of view. This technique is based on nondegenerate, higher order multiwave mixing in a phase-matched backward configuration. Applications to wave front reversal, spatial or temporal information processing with frequency up-conversion are outlined.
Laser frequency stabilization by a polarization-sensitive optical system using a reflecting reference cavity
Authors: Cha Sung Do , Lee Sang Soo
Published: July 2002

A simple polarization-sensitive optical system with no polarizing element inside a reference cavity is developed for locking the laser frequency to a high finesse reference cavity. The dispersion-shaped error signal suitable for the laser frequency stabilization is obtained experimentally by analyzing the change in the polarization of the output obtained by superposing two orthogonal, linearly polarized beams which are the reference beam and the beam reflected off a high finesse reference cavity.
Proposed model for stress relaxation at low temperatures
Authors: Raza S. M. , Abidi S. B. H. , Farooqui N.
Published: July 2002

A model for stress relaxation is outlined in which the movement of dislocations over a volume dispersion of obstacles requires dislocation/dislocation interactions. The relation for the creep rate is modified for low temperatures which suggests that the behavior of stress relaxation rate is ‘‘athermal’’ and logarithmic in character.
Highly photoconductive and photosensitive hydrogenated amorphous silicon carbon alloy films prepared by magnetron sputtering
Authors: Saito Nobuo
Published: July 2002

Undoped hydrogenated amorphous silicon carbon alloy thin films were prepared by the magnetron sputtering of silicon in a gas mixture of methane argon. It is found that the photoconductivities of the films with carbon concentration above 15% are one order of magnitude or more larger than the films prepared by the glow discharge decomposition of silane-methane gas mixture reported by other groups before now. Moreover, the photosensitivities of these films are larger than those of the glow discharge films, as a result of small dark conductivities of the former compared with those of the latter.
Conductive layer formation by high-dose Si ion implantation into SiO2
Authors: Miyake Masayasu , Kiuchi Kazuhide
Published: July 2002

It is found that a conductive layer in SiO2 is formed by high-dose Si ion implantation followed by As ion implantation into SiO2. Sheet resistance of the Si-implanted SiO2 layer changes from 1010 to 103 Ω/⧠ according to ion implantation conditions and annealing temperature. Auger electron spectroscopy analysis and reflecting electron diffraction show that the Si-implanted layer consists of both polycrystalline Si and amorphous Si.
A semiconductor laser with a converging output beam
Authors: Mukai S. , Yajima H. , Watanabe M. , Itoh H. , Takabe Y. , Tsunekawa Y.
Published: July 2002

Semiconductor lasers with converging output beams are reported for the first time. The lasers have a low-gain region on the center of the mesa stripe near one cleaved facet. The low-gain region distorts the phase front of the guided light and beam convergence results. The width of the laser beam in the direction parallel to the junction plane decreases with distance from 30 μm at the facet down to 7 μm at 111 μm off the facet. Moreover, the one-dimensional optical power density increases with distance in accordance with the decrease in beam width.
Room-temperature optical bistability in InGaAsP/InP amplifiers and implications for passive devices
Authors: Sharfin W. F. , Dagenais M.
Published: July 2002

Optical bistability has been observed for the first time in a room-temperature InGaAsP/InP amplifier. Switching occurred at an optical input power of about 3 μW, corresponding to a change in the refractive index of 5×10−4. The results are discussed in terms of a light-induced change in carrier concentration. Implications for bistability in passive devices are also discussed.
Contribution of knock-on processes in ion-induced interface reactions
Authors: Horino Yuji , Matsunami Noriaki , Itoh Noriaki , Yamamura Yasumichi
Published: July 2002

CrSi2 formation at the Cr-Si interface induced by irradiation with ions having a wide range of linear nuclear energy deposition density has been investigated in the temperature range where the ion-induced reaction rate is temperature dependent. It is found that the yield is not proportional to the energy deposition density for low-energy light ions but proportional to number of knock ons. The result indicates that the interface reaction that governs the CrSi2 formation is induced by atomic displacements.
Microwave generation from picosecond demodulation sources
Authors: De Lucia Frank C. , Guenther B. D. , Anderson Todd
Published: July 2002

A mode-locked picosecond laser has been used to prebunch electron beams at a photocathode. These electrons are subsequently accelerated through coupling structures and microwaves radiated. The relation between the microwave output and the properties of the picosecond pulse train and the electron beam output coupling process are reported and related to theory. Among the important attributes of these devices are their ability to generate almost arbitrary microwave waveforms, to operate in the 100–200 kV region with very simple power supplies and excellent spectral purity, and to generate substantially more microwave power than contained in the optical drive.
Attainment of transparent boron-implanted layers for silicon solar cell applications
Authors: Spitzer M. B. , Keavney C. J.
Published: July 2002

The formation of boron-doped p+ layers that are transparent to minority-carrier transport is reported. Ion implantation is used to limit the peak dopant concentration to 5×1018 cm−3 so as to avoid deleterious heavy doping effects. Solar cell open circuit voltage of 657 mV has been obtained in this way. The importance of surface passivation is indicated.
Broadband laser diode emitting at 1.28 μm wavelength
Authors: Takada K. , Noda J.
Published: July 2002

This letter presents a broadband laser diode (LD) emitting at the 1.28 μm wavelength fabricated by introducing an absorption region (300 μm long) into a conventional 600-μm-long InGaAsP laser diode. The LD operates by the pulsed modulation of a high peak current whose repetition rate and duty cycle are respectively 200 kHz and 5%. The typical output power and the spectral width of the LD are 3.8 mW and 58 Å, and the measured coherence length is 210 μm.
Energy partitioning between the equilibrated A and X states of the CN radical formed in the C+N2O reaction
Authors: Torchin L. , Bordas M. C. , Robert J. C.
Published: July 2002

Similar populations have been observed between the A and X states of the CN radical, formed in the C+N2O chemical reaction. Relative vibrational populations were measured by laser-induced fluorescence (X state) and chemiluminescence (A state). The electronic branching ratio was then obtained by assuming a Boltzmann equilibrium between the v″=4–6 and v′=1–4 levels of the X and A states. This assumption was checked by absolute calibration of the number densities of both states. About 1/3 of the radicals were found in the A state.
Anodic oxidation of tantalum silicide
Authors: Martínez-Duart J. M. , Fernández M. , Paule E. , Climent A. , Albella J. M. , Perriere J. , Siejka J.
Published: July 2002

Oxide films on cosputtered tantalum silicide have been formed by anodic oxidation. The films were characterized by Rutherford backscattering and nuclear microanalysis measurements yielding a composition consisting in a mixture of Ta2O5 and SiO2. The films show good quality insulating properties as determined by capacitance, electrical conductivity, and dielectric strength measurements. The results of this work are compared with those obtained by the thermal oxidation of tantalum silicide.
Thin-sheet sensor for particle beams
Authors: Stoner John O.
Published: July 2002

A charged-particle beam passing through a dielectric sheet releases carriers whose collection serves to detect the beam. A simple device to demonstrate this effect has been constructed and tested. By applying sufficient bias to electrodes on the faces of the dielectric sheet, the device can be operated at gains of 1000 or more. The device shows promise of applicability to position-sensitive and single-particle detection.
Compensation of p-type cast polycrystalline silicon by hydrogen ion implantation at 300 °C
Authors: Martinuzzi S. , Sebbar M. A. , Gervais J.
Published: July 2002

Hydrogen ion implantation used to passivate grain boundaries and intragrain defects can also compensate p-type polycrystalline silicon within the implanted surface, when the implantation is done at 300 °C. This compensation may be explained by means of shallow acceptor neutralization.
Low-temperature SiO2 growth using fluorine-enhanced thermal oxidation
Authors: Morita M. , Aritome S. , Tsukude M. , Murakawa T. , Hirose M.
Published: July 2002

A new low-temperature oxidation technique of silicon to obtain high quality Si-SiO2 interface and bulk SiO2 layer is presented. A few tens-nanometer-thick oxide layers are grown within 30 min at temperatures between 600 and 800 °C by fluorine-enhanced thermal oxidation using an O2+NF3 gas mixture. Fluorine atoms incorporated in the oxide layer are substituted by oxygen atoms through post-annealing in pure oxygen gas at the same temperature as oxidation. An interface state density as low as 2×1010 cm−2 eV−1 near midgap is achieved for oxides grown at 800 °C and 8×1010 cm−2 eV−1 even for oxides at 600 °C. The dielectric breakdown strength of the oxide is improved by the post-annealing in O2.
Time-resolved photoluminescence study of molecular beam epitaxial growth induced defect lines in GaAs
Authors: Steiner T. , Thewalt M. L. W. , Koteles E. S. , Salerno J. P.
Published: July 2002

A time-resolved photoluminescence study of the ‘‘damage’’ lines often observed in molecular beam epitaxial GaAs shows two recent models of the origin of these lines to be incorrect. Our results show that the p through v lines have identical transient behavior which is significantly different from that of the g line. These measurements support the general conclusion of a recent excitation spectroscopy study that the g line is due to an acceptor bound exciton, but call for a reinterpretation of several of the lines related to g which leads to a new value for the g-acceptor binding energy.
Wavelength-selective voltage-tunable photodetector made from multiple quantum wells
Authors: Wood T. H. , Burrus C. A. , Gnauck A. H. , Wiesenfeld J. M. , Miller D. A. B. , Chemla D. S. , Damen T. C.
Published: July 2002

We show that a pin-doped multiple quantum well (MQW) diode can be used as a photodetector whose voltage of maximum photocurrent is wavelength dependent. The voltage of maximum photocurrent can be located accurately and related to the wavelength of the incident light, allowing measurements of the wavelength with a precision of 0.03 Å=1.2 GHz. This provides a simple, compact, solid-state device that can be simultaneously used to measure the intensity and wavelength of an optical beam. Furthermore, the device shows high responsivity, low dark current, and fast response.
Evidence of mode splitting in a single mode, homogeneously broadened Raman laser
Authors: Biswas Dhruba J. , Harrison Robert G.
Published: July 2002

Self-pulsating instabilities in a detuned single mode, homogeneously broadened Raman laser are shown here to provide evidence of spontaneous mode splitting in this system.
Spot size dependence of switching power for an optically bistable InSb element
Authors: Hagan D. J. , MacKenzie H. A. , Reid J. J. E. , Walker A. C. , Tooley F. A. P.
Published: July 2002

The dependence of switching power upon input beam spot radius for an optically bistable InSb étalon has been measured. The results show that the irradiance required for switching increases as the spot radius is reduced. There is no evidence of any lower limit to the switching power, even for spot radii much less than the ambipolar diffusion length. Studies of the transmitted beam intensity profile in the near-field demonstrate the role of diffusion in our observations. The implications of our results for digital optical processing are briefly discussed.
Effects of As impurities on the solidification velocity of Si during pulsed laser annealing
Authors: Peercy P. S. , Thompson Michael O. , Tsao J. Y.
Published: July 2002

The effect of As dopants on the solidification velocity during pulsed laser annealing of Si was measured using the transient conductance technique. At high concentrations, As is found to decrease the solidification velocity; for 7 at. % As, the velocity decreases ∼20% as the interface approaches the peak of the As distribution, followed by a velocity increase when the interface exits the region of maximum As concentration. The measurements are interpreted in terms of a decrease in the melting temperature. The observation of surface nucleation to produce buried molten layers and internal nucleation of melt at higher As concentrations supports this interpretation.
Luminescence in ion-implanted In0.53Ga0.47As
Authors: Shah Jagdeep , Tell B. , Bridges T. J. , Burkhardt E. G. , DiGiovanni A. E. , Brown-Goebeler K.
Published: July 2002

We report luminescence studies of In0.53Ga0.47As implanted with Ar, Be, Se, and Si at doses ranging from 5×1010 to 2.5×1012 cm−2. A new feature in the luminescence spectrum, identified as emission from an exciton-neutral acceptor complex, appears at Be doses in excess of 5×1011 cm−2. We employ a rapid thermal annealing procedure, which produces no degradation in the luminescence properties of unimplanted samples but is very effective in removing the damage introduced by ion implantation of light and medium mass species (Be, Ar, and Si). Implantation of donors and of electrically inactive Ar introduces no new features in the observed spectra.
Effects of GaAs/AlAs superlattice buffer layers on selective area regrowth for GaAs/AlGaAs self-aligned structure lasers
Authors: Noda Susumu , Fujiwara Kenzo , Nakayama Takashi
Published: July 2002

The effects of GaAs/AlAs superlattice buffer layers on selective area regrowth by molecular beam epitaxy were investigated for self-aligned structure lasers. It is demonstrated that the superlattice buffer layer is an effective means to obtain a smoother interface with reduced alloy clustering, from which the threshold current was reduced and stable single transverse mode operation was obtained.
Electrical conductivity of p-type CuInSe2 thin films
Authors: Datta T. , Noufi R. , Deb S. K.
Published: July 2002

The dark ohmic conductivity σ(T) of several p-type CuInSe2 thin films of different compositions was measured in vacuum in the temperature range 100–350 K. The room-temperature resistivity of Cu-rich, highly conducting films and the Cu-poor, highly resistive films varied by seven orders of magnitude. For the most conducting films (Cu:In>1, ρ∼0.1 Ω cm), σ(T) was pseudometallic, i.e., dσ/dT≲0. The Cu-poor films exhibited a thermally activated conductivity, i.e., σ(T)=σ0 exp(−E/kT), over a considerable temperature range. The data of post-deposition anneal in air and subsequently in hydrogen are in excellent agreement with Meyer–Neldel type of conduction, i.e., σ(T)=σ00 exp(−E/kT0)exp(E/kT). We attribute this behavior to the compensation of the films by oxygen.
Current induced periodic ferroelectric domain structures in LiNbO3 applied for efficient nonlinear optical frequency mixing
Authors: Feisst A. , Koidl P.
Published: July 2002

Periodic laminar ferroelectric domain superstructures in chromium-doped LiNbO3 have been grown by modulating the bias current during Czochralski growth. Periodic domain patterns stacked along the y axis with domain thicknesses as low as 8 μm have been prepared. The alternating sign of the effective nonlinear optical (nlo) coefficient enables efficient frequency mixing independent of the constraints of birefringence. This is demonstrated by realizing frequency doubling of 1.06-μm YAG : Nd laser radiation using the largest nlo coefficient, d33. For domain thicknesses equal to an odd multiple of the coherence length, d=(2m+1)lc, the second harmonic intensity varies as the square of the domain number. For the optimum case, d=lc, an improvement of the nlo efficiency, as compared to the 90° phase-matched process, by the factor [(2/π)d33/d31]2=15 is inferred.
Enhanced modulation bandwidth of GaAlAs double heterostructure lasers in high magnetic fields: Dynamic response with quantum wire effects
Authors: Arakawa Y. , Vahala K. , Yariv A. , Lau K.
Published: July 2002

The modulation bandwidth of GaAlAs double heterostructure (DH) lasers in high magnetic fields is measured. We found that the modulation bandwidth is enhanced by 1.4× with a magnetic field of 20 T. This improvement is believed to result from the increase of the differential gain due to two-dimensional carrier confinement effects in the high magnetic field (quantum wire effects). A comparison of the experimental results with a theoretical analysis indicates that the intraband relaxation time τin of the measured DH laser in the range of 0.1 to 0.2 ps.
cw recombination laser in a flowing negative glow plasma
Authors: Rocca Jorge J.
Published: July 2002

cw laser oscillation has been obtained in the 1.43-μm line of Cd I populated by electron-ion recombination in the flowing afterglow of a negative glow plasma. The metal vapor in the recombining plasma is produced at room temperature by cathode sputtering. Negative glow plasmas having an electron energy distribution in which energetic beam electrons and supercooled secondary electrons coexist under steady-state conditions are shown to be an attractive medium for the excitation of cw recombination lasers.
1.54-μm phase-adjusted InGaAsP/InP distributed feedback lasers with mass-transported windows
Authors: Broberg Björn , Koentjoro Sekartedjo , Furuya Kazuhito , Suematsu Yasuharu
Published: July 2002

1.54-μm wavelength phase-adjusted InGaAsP/InP distributed feedback lasers with low threshold and almost symmetrical subthreshold spectra are demonstrated. Antireflecting window structures were formed by a novel mass transport technique over a length of 25 μm. The phase adjustment was accomplished by a groove in the substrate. Asymmetric output characteristics due to displacement of the groove from the cavity center were observed in agreement with theory.
Morphology of hydrogenated amorphous silicon films by photochemical vapor deposition
Authors: Mutsukura Nobuki , Machi Yoshio
Published: July 2002

The microstructure of hydrogenated amorphous silicon films deposited by the photochemical vapor deposition method was investigated using transmission electron microscopy. The circular structures on the top surface of the amorphous silicon film corresponded to both columnar crystalline structures and the amorphous-microcrystalline mixed structures. The growth of a single crystalline grain as large as 0.3 μm at a mere 150 °C through the photochemical vapor deposition process was also demonstrated.
Laser etching of 0.4 μm structures in CdTe by dynamic light guiding
Authors: Arnone C. , Rothschild M. , Ehrlich D. J.
Published: July 2002

CdTe single crystals have been etched by photosublimation with a cw visible laser. Structures with lateral widths comparable to the laser wavelength (∼0.5 μm) and depths exceeding 10 μm were obtained using a moderately focused beam. The formation of these structures is highly nonlinear with respect to laser power and is analyzed in terms of the dynamic interaction of the beam with the induced microstructure. Once initiated, deep structures are formed via laser-induced tellurium enrichment of CdTe surface layers and the consequent enhanced waveguiding properties of these surfaces. The mechanism of etching has been studied by mass spectrometer and light scattering experiments.
Nb3Sn(Ti) powder metallurgy processed high field superconductors
Authors: Pourrahimi S. , Thieme C. L. H. , Foner S. , Suenaga M.
Published: July 2002

Powder metallurgy processed Nb3Sn(Ti) superconducting wires were fabricated with Sn x wt. % Ti cores for 0≤x≤3, 16 or 22 vol % cores, and a Cu 45 wt. % Nb composite. The processing used swaging, cold hydrostatic extrusions, wire drawing and heat treatments of 750 °C for two to four days. Nominal areal reductions of 104 were used. Hydride-dehydride Nb and rotating electrode processed Nb powders gave the same performance. Overall critical current densities Jc were measured between 4.2 and 1.8 K for applied fields up to 23 T. Jc increased with increased Ti and/or Sn content. The Nb3Sn(Ti) wires using a Sn 3 wt. % Ti, 22 vol % core gave Jc >104 A/cm2 at 20 T and 4.2 K and Jc =104 A/cm2 at 23 T at 1.8 K. Removal of the precompression of the matrix increased Jc by about a factor of 2 at 20 T and 4.2 K.
Fowler–Nordheim tunneling and conduction-band discontinuity in GaAs/GaAlAs high electron mobility transistor structures
Authors: Smoliner J. , Christanell R. , Hauser M. , Gornik E. , Weimann G. , Ploog K.
Published: July 2002

Oscillatory structure is observed in the dI/dV and d2I/dV2 characteristics of conventional GaAs/GaAlAs high electron mobility transistor samples at liquid-helium temperature, which can be explained using a Fowler–Nordheim tunneling theory. The position of the oscillations allows a determination of the conduction-band discontinuity, and the depth of the deep donor levels in the GaAlAs for high aluminum concentrations. The fit of the data gives a value of ΔEc/ΔEg=0.61±0.04 for aluminum concentration 30, 36, and 40%. The deep donor level in the GaAlAs was determined to be 130 meV below the conduction band.
Phosphorus doping for hydrogenated amorphous silicon films by a low-energy ion doping technique
Authors: Yoshida A. , Setsune K. , Hirao T.
Published: July 2002

A heated film of hydrogenated amorphous silicon was doped with phosphorus and hydrogen by a 6.0-kV diffused and accelerated beam of ions from rf discharge in a magnetic field, which produced a plasma from phosphine gas containing hydrogen. This doping technique achieved a dark conductivity of 8.7×10−4 (Ω cm−1) at room temperature. The conductivity activation energy was 0.17 eV.
Fe acceptor level in In1−xGaxAsyP1−y/InP
Authors: Sugawara M. , Kondo M. , Takanohashi T. , Nakajima K.
Published: July 2002

The Fe acceptor level in In1−xGaxAsyP1−y lattice matched to InP (x=0.47y) is investigated employing current-voltage characteristics and deep level transient spectroscopy. The activation energy decreases as the proportion of arsenic, y, increases. However, considering the band-edge discontinuity in this material, it was found that the Fe acceptor level is aligned at a constant energy. This is in excellent agreement with the vacuum referred binding energy model.
Long minority hole diffusion length and evidence for bulk radiative recombination limited lifetime in InP/InGaAs/InP double heterostructures
Authors: Gallant M. , Zemel A.
Published: July 2002

Minority hole diffusion length, lifetime, and mobility for undoped InGaAs were measured at 297 and 77 K in metalorganic chemical vapor deposited InP/InGaAs/InP double heterostructures using continuous-wave and pulsed optical beam induced current techniques. A hole diffusion length Lp=140 μm, a lifetime τp=18.5 μs, and a mobility μp=425 cm2/(V s) were obtained at room temperature. To the best of our knowledge, these properties are the highest reported values for InGaAs. The measured carrier lifetime and its temperature dependence are consistent with bulk radiative recombination in undoped InGaAs.
Role of a locus control region in the mutually exclusive expression of human red and green cone pigment genes
Authors: Smallwood Philip M. , Wang Yanshu , Nathans Jeremy
Published: July 2002

Trichromacy in humans and other Old World primates evolved from a dichromatic color vision system ≈30–40 million years ago. One essential part of this evolution was the duplication and divergence of sequences on the X chromosome to create the present-day red and green cone pigment genes. Earlier work demonstrated that a locus control region (LCR) located upstream of these genes is essential for their expression. In the present work, we have generated a variety of modified human red and green pigment gene arrays that direct the expression of distinguishable histochemical reporters from each gene promoter. Transgenic mice carrying a single copy of each modified array were studied to define the role of three variables in producing mutually exclusive expression of red and green pigment transgenes: the distance between the promoter and the LCR, the identity of the visual pigment promoter, and LCR copy number. The results support a model in which the mutually exclusive expression of these genes in their respective cone types is controlled by competition between visual pigment promoters for pairing with the LCR, and they suggest a facile mechanism for the evolution of trichromacy after visual pigment gene duplication.
The neural basis of intermittent motor control in humans
Authors: Gross J. , Timmermann L. , Kujala J. , Dirks M. , Schmitz F. , Salmelin R. , Schnitzler A.
Published: July 2002

The basic question of whether the human brain controls continuous movements intermittently is still under debate. Here we show that 6- to 9-Hz pulsatile velocity changes of slow finger movements are directly correlated to oscillatory activity in the motor cortex, which is sustained by cerebellar drive through thalamus and premotor cortex. Our findings suggest that coupling of 6- to 9-Hz oscillatory activity in the cerebello–thalamo–cortical loop represents the neural mechanism for the intermittent control of continuous movements.
A mitochondrial-like aconitase in the bacterium
Bacteroides fragilis
: Implications for the evolution of the mitochondrial Krebs cycle
Authors: Baughn Anthony D. , Malamy Michael H.
Published: July 2002

Aconitase and isocitrate dehydrogenase (IDH) enzyme activities were detected in anaerobically prepared cell extracts of the obligate anaerobe
Bacteroides fragilis
. The aconitase gene was located upstream of the genes encoding the other two components of the oxidative branch of the Krebs cycle, IDH and citrate synthase. Mutational analysis indicates that these genes are cotranscribed. A nonpolar in-frame deletion of the
acnA
gene that encodes the aconitase prevented growth in glucose minimal medium unless heme or succinate was added to the medium. These results imply that
B. fragilis
has two pathways for α-ketoglutarate biosynthesis—one from isocitrate and the other from succinate. Homology searches indicated that the
B. fragilis
aconitase is most closely related to aconitases of two other
Cytophaga–Flavobacterium–Bacteroides
(CFB) group bacteria,
Cytophaga hutchinsonii
and
Fibrobacter succinogenes
. Phylogenetic analysis indicates that the CFB group aconitases are most closely related to mitochondrial aconitases. In addition, the IDH of
C. hutchinsonii
was found to be most closely related to the mitochondrial/cytosolic IDH-2 group of eukaryotic organisms. These data suggest a common origin for these Krebs cycle enzymes in mitochondria and CFB group bacteria.
Conformation and anion binding properties of cyclic hexapeptides containing
l
-4-hydroxyproline and 6-aminopicolinic acid subunits
Authors: Kubik Stefan , Goddard Richard
Published: July 2002

Two cyclic hexapeptides containing alternating all
R
and all
S
configured
l
-(4
R
/
S
)-hydroxyproline and 6-aminopicolinic acid subunits are presented, and the influence of the hydroxyl groups on the solubility, conformation, and receptor properties is investigated. Cyclopeptide 2, containing the natural 4
R
configured hydroxyproline, adopts a conformation similar to that of the unsubstituted peptide 1, which is able to bind anions such as halides and sulfate in aqueous solution. 2 also interacts with these anions, but whereas 1 forms sandwich type 2:1 complexes, in which the anion is bound by two cyclopeptide moieties, 2 forms 1:1 complexes. The stabilities of the halide and sulfate complexes of 2 range between 10
0
and 10
2
M
−1
in 80% D
2
O/CD
3
OD. Complex formation is detectable even in water, but with slightly smaller stability constants. Using this information a quantitative evaluation of the stability of the 2:1 complexes of 1, for which overall stability constants in the order 10
4
to 10
5
M
−2
in 80% D
2
O/CD
3
OD were observed, was made. In contrast to 2, the conformation of 3, containing the non-natural 4
S
configured hydroxyproline, is strongly affected by the presence of the hydroxyl groups. In
d

6

-DMSO and methanol/water mixtures a slow conformational equilibrium between two
C

3

-symmetrical conformers is observed, and 3 is thus much less preorganized for anion binding than either 1 or 2.
Insulin inhibits transcription of IRS-2 gene in rat liver through an insulin response element (IRE) that resembles IREs of other insulin-repressed genes
Authors: Zhang Jiandi , Ou Jiafu , Bashmakov Yuriy , Horton Jay D. , Brown Michael S. , Goldstein Joseph L.
Published: July 2002

Recent data indicate that sustained elevations in plasma insulin
suppress the mRNA for IRS-2, a component of the insulin signaling
pathway in liver, and that this deficiency contributes to hepatic
insulin resistance and inappropriate gluconeogenesis. Here, we use
nuclear run-on assays to show that insulin inhibits transcription of
the IRS-2 gene in the livers of intact rats. Insulin also inhibited
transcription of a reporter gene driven by the human IRS-2 promoter
that was transfected into freshly isolated rat hepatocytes. The human
promoter contains a heptanucleotide sequence, TGTTTTG, that is
identical to the insulin response element (IRE) identified previously
in the promoters of insulin-repressed genes. Single base pair
substitutions in this IRE decreased transcription of the IRS-2-driven
reporter in the absence of insulin and abolished insulin-mediated
repression. We conclude that insulin represses transcription of the
IRS-2 gene by blocking the action of a positive factor that binds to
the IRE. Sustained repression of IRS-2, as occurs in chronic
hyperinsulinemia, contributes to hepatic insulin resistance and
accelerates the development of the diabetic state.
Complete genome sequence of an M1 strain of
Streptococcus pyogenes
Authors: Ferretti Joseph J. , McShan William M. , Ajdic Dragana , Savic Dragutin J. , Savic Gorana , Lyon Kevin , Primeaux Charles , Sezate Steven , Suvorov Alexander N. , Kenton Steve , Lai Hong Shing , Lin Shao Ping , Qian Yudong , Jia Hong Gui , Najar Fares Z. , Ren Qun , Zhu Hua , Song Lin , White Jim , Yuan Xiling , Clifton Sandra W. , Roe Bruce A. , McLaughlin Robert
Published: July 2002

The 1,852,442-bp sequence of an M1 strain of
Streptococcus
pyogenes
, a Gram-positive pathogen, has been determined and
contains 1,752 predicted protein-encoding genes. Approximately
one-third of these genes have no identifiable function, with the
remainder falling into previously characterized categories of known
microbial function. Consistent with the observation that
S.
pyogenes
is responsible for a wider variety of human disease
than any other bacterial species, more than 40 putative
virulence-associated genes have been identified. Additional genes have
been identified that encode proteins likely associated with microbial
“molecular mimicry” of host characteristics and involved in
rheumatic fever or acute glomerulonephritis. The complete or partial
sequence of four different bacteriophage genomes is also present, with
each containing genes for one or more previously undiscovered
superantigen-like proteins. These prophage-associated genes encode at
least six potential virulence factors, emphasizing the importance of
bacteriophages in horizontal gene transfer and a possible mechanism for
generating new strains with increased pathogenic potential.
Identification of progenitor cells in long-term spleen stromal cultures that produce immature dendritic cells
Authors: Wilson Heather L. , Ni Keping , O'Neill Helen C.
Published: July 2002

Dendritic cells (DC) are produced continuously by a unique, long-term culture (LTC) system in which hemopoiesis is supported by a splenic stromal cell layer in the absence of added growth factors. Flow cytometric analysis reveals the production of two distinct cell subsets. The more predominant large-cell subset resembles highly endocytic DC that are large, granular, and possess membrane extensions. They also express high levels of the DC markers CD11c, CD11b, DEC-205, and CD80 on their cell surface. They do not resemble mature DC because they express low levels of MHC type II and CD86 molecules, as well as c-kit and Fc receptor (FcR). These are known characteristics of immature DC. Small cells are smaller and less granular than large cells, with negative to low expression of CD11c, DEC-205, and CD86. A majority of small cells express varying levels of CD11b and CD80. Subpopulations of small cells express low levels of c-kit, FcR, and MHC type II, and only a 20% subpopulation is weakly endocytic. Upon transfer to an irradiated stromal layer, cells within the small subset proliferate and differentiate to resemble the large cells in size, complexity, membrane extensions, and CD11c and CD86 expression. The two cell subsets produced in LTC are developmentally linked, with the heterogeneous small-cell subset containing progenitors of the larger homogeneous, immature DC subset. LTC represent a valuable model system for studying DC development from hemopoietic progenitors.
RNA tertiary interactions in the large ribosomal subunit: The A-minor motif
Authors: Nissen Poul , Ippolito Joseph A. , Ban Nenad , Moore Peter B. , Steitz Thomas A.
Published: July 2002

Analysis of the 2.4-Å resolution crystal structure of the large
ribosomal subunit from
Haloarcula marismortui
reveals
the existence of an abundant and ubiquitous structural motif that
stabilizes RNA tertiary and quaternary structures. This motif is termed
the A-minor motif, because it involves the insertion of the smooth,
minor groove edges of adenines into the minor groove of neighboring
helices, preferentially at C-G base pairs, where they form hydrogen
bonds with one or both of the 2′ OHs of those pairs. A-minor motifs
stabilize contacts between RNA helices, interactions between loops and
helices, and the conformations of junctions and tight turns. The
interactions between the 3′ terminal adenine of tRNAs bound in either
the A site or the P site with 23S rRNA are examples of functionally
significant A-minor interactions. The A-minor motif is by far the most
abundant tertiary structure interaction in the large ribosomal subunit;
186 adenines in 23S and 5S rRNA participate, 68 of which are conserved.
It may prove to be the universally most important long-range
interaction in large RNA structures.
Is the first hydration shell of lysozyme of higher density than bulk water?
Authors: Merzel Franci , Smith Jeremy C.
Published: July 2002

Characterization of the physical properties of protein surface hydration water is critical for understanding protein structure and folding. Here, using molecular dynamics simulation, we provide an explanation of recent x-ray and neutron solution scattering data that indicate that the density of water on the surface of lysozyme is significantly higher than that of bulk water. The simulation-derived scattering profiles are in excellent agreement with the experiment. In the simulation, the 3-Å-thick first hydration layer is 15% denser than bulk water. About two-thirds of this increase is the result of a geometric contribution that would also be present if the water was unperturbed from the bulk. The remaining third arises from modification of the water structure and dynamics, involving approximately equal contributions from shortening of the average water–water O–O distance and an increase in the coordination number. Variation in the first hydration shell density is shown to be determined by topographical and electrostatic properties of the protein surface. On average, denser water is found in depressions on the surface in which the water dipoles tend to be aligned parallel to each other by the electrostatic field generated by the protein atoms.
Changes in myosin S1 orientation and force induced by a temperature increase
Authors: Griffiths Peter J. , Bagni Maria A. , Colombini Barbara , Amenitsch Heinz , Bernstorff Sigrid , Ashley Christopher C. , Cecchi Giovanni
Published: July 2002

Force generation in myosin-based motile systems is thought to result from an angular displacement of the myosin subfragment 1 (S1) tail domain with respect to the actin filament axis. In muscle, raised temperature increases the force generated by S1, implying a greater change in tail domain angular displacement. We used time-resolved x-ray diffraction to investigate the structural corollary of this force increase by measuring M3 meridional reflection intensity during sinusoidal length oscillations. This technique allows definition of S1 orientation with respect to the myofilament axis. M3 intensity changes were approximately sinusoid at low temperatures but became increasingly distorted as temperature was elevated, with the formation of a double intensity peak at maximum shortening. This increased distortion could be accounted for by assuming a shift in orientation of the tail domain of actin-bound S1 toward the orientation at which M3 intensity is maximal, which is consistent with a tail domain rotation model of force generation in which the tail approaches a more perpendicular projection from the thin filament axis at higher temperatures. In power stroke simulations, the angle between S1 tail mean position during oscillations and the position at maximum intensity decreased by 4.7°, corresponding to a mean tail displacement toward the perpendicular of 0.73 nm for a temperature-induced force increase of 0.28
P
0
from 4 to 22°C. Our findings suggest that at least 62% of crossbridge compliance is associated with the tail domain.
Adenovirus-mediated gene transfer of endostatin
in vivo
results in high level of transgene expression and inhibition of tumor growth and metastases
Authors: Sauter Bernhard V. , Martinet Olivier , Zhang Wei-Jian , Mandeli John , Woo Savio L. C.
Published: July 2002

Inhibition of angiogenesis has been shown to be an effective strategy in cancer therapy in mice. However, its widespread application has been hampered by difficulties in the large-scale production of the antiangiogenic proteins. This limitation may be resolved by
in vivo
delivery and expression of the antiangiogenic genes. We have constructed a recombinant adenovirus that expresses murine endostatin that is biologically active both
in vitro
, as determined in endothelial cell proliferation assays, and
in vivo
, by suppression of angiogenesis induced by vascular endothelial growth factor 165. Persistent high serum levels of endostatin (605–1740 ng/ml; mean, 936 ng/ml) were achieved after systemic administration of the vector to nude mice, which resulted in significant reduction of the growth rates and the volumes of JC breast carcinoma and Lewis lung carcinoma (
P
< 0.001 and
P
< 0.05, respectively). In addition, the endostatin vector treatment completely prevented the formation of pulmonary micrometastases in Lewis lung carcinoma (
P
= 0.0001). Immunohistochemical staining of the tumors demonstrated a decreased number of blood vessels in the treatment group versus the controls. In conclusion, the present study clearly demonstrates the potential of vector-mediated antiangiogenic gene therapy as a component in cancer therapy.