bluuebunny/crossref_metadata_2025 huggingface dataset:
CdS induced homojunction formation in crystalline p-CuInSe2
Authors: Matson R. J. , Noufi R. , Bachmann K. J. , Cahen D.
Published: July 2002

The deposition of CdS onto single-crystal p-CuInSe2 (at a substrate temperature of 200 °C) results in a CuInSe2 homojunction rather than the expected heterojunction. Junction depths, varying from 1 to 9 μm, correlated well with the free-carrier concentration of the sample crystals. The junction depths were measured by electron-beam-induced current line scans of cleaved junctions and were corroborated by quantum efficiency measurements. All the materials deposited to date (CdS, Cd, Au, and Mo) have resulted in type conversion of the CuInSe2. The experimental evidence for this type conversion is presented and possible defect chemical origins identified.
Order-disorder transformation in ternary tetrahedral semiconductors
Authors: Zunger Alex
Published: July 2002

The recently discovered order-disorder transformations in pseudobinary semiconductor alloys AxB1−xC are shown to belong to a broader class of such transformations in AnB4−nC4 semiconducting compounds (e.g., chalcopyrites, for n=2). Strain energy, set up by the atomic size mismatch between the A–C and B–C bonds, is shown to control the nature of the state of order in chalcopyrites and pseudobinary alloys alike. These considerations lead to a classification of all bulk tetrahedral semiconductors into four classes of order-disorder characteristics.
High-performance thin-film transistors from optimized polycrystalline silicon films
Authors: Meakin D. B. , Coxon P. A. , Migliorato P. , Stoemenos J. , Economou N. A.
Published: July 2002

The performance of thin-film transistors fabricated in unrecrystallized (small-grain) polcrystalline silicon is shown to be greatly improved by depositing the films at much lower pressures than normally used in the low-pressure chemical vapor deposition process. Electronic measurements on completed devices are presented and related to the film structure by transmission electron microscopy examination.
cw surface-emitting grating-coupled GaAs/AlGaAs distributed feedback laser with very narrow beam divergence
Authors: Mitsunaga Kazumasa , Kameya Masaaki , Kojima Keisuke , Noda Susumu , Kyuma Kazuo , Hamanaka Koichi , Nakayama Takashi
Published: July 2002

Room-temperature cw operation of a GaAs/AlGaAs surface-emitting grating-coupled distributed feedback laser is reported. By using a transverse junction stripe scheme which provides a window structure for the surface-emitted light, cw surface emission having a very narrow beam divergence angle of 0.13° and an output power of more than 3 mW was observed.
Electron spin resonance observation of defects in device oxides damaged by soft x rays
Authors: Triplett B. B. , Takahashi T. , Sugano T.
Published: July 2002

We report the use of vacuum soft x-ray (VXR) exposure to efficiently generate paramagnetic defects in thin oxide layers. The VXR technique allows the observation of an E′ related defect called the 74-G doublet in quantities as large as the E′. This defect is the first paramagnetic defect observed in thin oxides at room temperature to involve hydrogen.
NbN/BN granular films—a sensitive, high-speed detector for pulsed far-infrared radiation
Authors: Leung M. , Strom U. , Culbertson J. C. , Claassen J. H. , Wolf S. A. , Simon R. W.
Published: July 2002

Thin superconducting, granular films of NbN/BN are investigated as photodetectors for pulsed, far-infrared radiation. These films may be thought of as a random network of Josephson junctions. The absorption of photons causes the film resistance to increase. This is thought to occur by destroying the phase coherence of the Cooper pair wave function among the junctions. This resistance change can be used as a basis for a photodetector. It is found that the NbN/BN thin-film detectors have response times faster than 1 ns, and sensitivities of about 0.7 V/W when terminated to 50 Ω, at wavelengths of about 0.50 mm.
High-power extended-cavity laser at 1.3 μm with a single-mode fiber output port
Authors: Eisenstein G. , Koren U. , Tucker R. S. , Raybon G. , Dentai A. G. , Stulz L. W. , Miller B. I.
Published: July 2002

We describe a high-power extended-cavity laser which uses a multiple transverse mode laser as the gain medium and an intracavity single-mode fiber for mode stabilization. The laser delivers up to 30 mW to a single-mode fiber.
Reduction of relative intensity noise in 1.3 μm InGaAsP semiconductor lasers
Authors: Hill P. , Olshansky R. , Schlafer J. , Powazinik W.
Published: July 2002

Relative intensity noise (RIN) from 1.3 μm InGaAsP vapor phase regrown buried heterostructure diode lasers with cavity lengths of 100–300 μm and resonant frequencies exceeding 15 GHz is measured for the first time over the 2.5–18 GHz frequency range. We show that the RIN decreases by nearly 8 dB as the cavity length increases from 100 to 300 μm, and that the RIN is also reduced by lowering the active p-doping concentration. The measured RIN is in excellent agreement with the expression derived from the laser rate equations.
Ferroelectric domain inversion caused in LiNbO3 plates by heat treatment
Authors: Nakamura Kiyoshi , Ando Haruyasu , Shimizu Hiroshi
Published: July 2002

It is demonstrated that heat treatment of a LiNbO3 plate at temperatures somewhat lower than the Curie point causes a ferroelectric domain inversion, thereby yielding an inversion layer useful for various piezoelectric devices. The dependences of the inversion layer thickness on the heat treatment conditions, such as temperature, time, and atmosphere, are experimentally examined. The results show that the domain boundary appears to stop at the median plane of the plate finally. The possible mechanism of the domain inversion is also discussed.
Nonlocal electrical properties in mesoscopic devices
Authors: Umbach C. P. , Santhanam P. , van Haesendonck C. , Webb R. A.
Published: July 2002

The magnetoconductance of nominally identical, 2-μm-long, Au lines has been measured. A 0.7-μm-diam loop was attached to the end of one of the lines outside the probes in such a way that classically no current would flow through it. As expected, the line by itself showed only aperiodic conductance fluctuations. In contrast, the line with the attached loop also exhibited h/e periodic oscillations. The periodic oscillations are due to the quantum interference of electrons diffusing around the loop. These results clearly demonstrate that the voltage measured between contact probes separated by a distance on the order of an electron phase coherence length is strongly influenced by regions outside the contact probes.
Exceptionally pronounced redistribution of silver in oxygen bombarded silicon
Authors: Wittmaack K. , Menzel N.
Published: July 2002

Silicon samples covered with thin layers of silver were bombarded with normally incident 10 keV O+2 ions. Using high-resolution (∼2 nm) Rutherford backscattering spectrometry the following stages of beam induced Ag relocation could be identified: (1) rapid incorporation of surface atoms into the bulk of the sample, (2) strong bombardment induced mixing, (3) pronounced profile broadening at high levels of oxygen implantation, and (4) very effective segregation of Ag atoms at the SiO2/Si interface. Upon completion of beam induced oxide formation about 40% of the initial Ag coverage is still retained in the sample. At higher bombardment fluences the backscattering data and secondary ion mass spectrometry measurements reveal a vanishingly small partial sputtering yield for Ag atoms.
Direct and accurate measurement of etch rate of polymer films under far-UV irradiation
Authors: Lazare Sylvain , Soulignac Jean Claude , Fragnaud Pascal
Published: July 2002

We have developed a new technique for measuring the etch rate of polymer films under ablative photodecomposition condition obtained by absorption of the far-UV radiation of the excimer laser. The technique is based on the use of a quartz crystal microbalance interfaced with a microcomputer. It has good accuracy and thus provides precise evidence of a new feature of the etch curve for laser intensity right above the ablation threshold value. Further applications are proposed.
Fast burning of persistent spectral holes in small laser spots using photon-gated materials
Authors: Moerner W. E. , Carter T. P. , Bräuchle C.
Published: July 2002

We report extremely fast (30 ns) burning of detectable persistent spectral holes in 200-μm-diam laser spots using a new photon-gated donor-acceptor material: a derivative of zinc-tetrabenzoporphyrin as a donor with chloroform acceptors in a poly(methylmethacrylate) thin film. The fast burning pulse near 630 nm was accompanied by a 200-ms gating pulse at 488 nm to produce the ≂1% deep spectral holes in transmission. This result illustrates one crucial advantage of photon-gated materials over single-photon materials: greatly increased reading fluences can be tolerated, allowing fast burning in small laser spots to be easily detected.
Plasma oxidation of the high T
c superconducting perovskites
Authors: Bagley B. G. , Greene L. H. , Tarascon J.-M. , Hull G. W.
Published: July 2002

A near room-temperature plasma oxidation process is shown to restore superconductivity and metalliclike behavior in oxygen deficient La2−x Srx CuO4−y and YBa2Cu3O7−x compounds. In the YBa2Cu3O7−x compound the conversion from an oxygen deficient n-type tetragonal to the p-type orthorhombic phase with a concomitant factor of 5×105 increase in room-temperature conductivity is also accomplished. This process is of technological importance because oxygen can be restored in these materials at temperatures compatible with device processing. Of scientific interest, the process allows us to carefully control the oxidation state and thereby systematically study the 90 and 55 K superconducting transitions in YBa2Cu3O7−x.
Power-dependent switching in a coherent nonlinear directional coupler in the presence of saturation
Authors: Caglioti E. , Trillo S. , Wabnitz S. , Daino B. , Stegeman G. I.
Published: July 2002

The fundamental limitations for all-optical switching in a nonlinear directional coupler due to the saturation of the nonlinearity have been obtained by solving analytically the nonlinear coupled-mode equations. We found that there is a minimum value required for the saturation index change to obtain efficient switching, and that the number of powers at which switching occurs at one beat length can double.
Bright white-light electroluminescence based on nonradiative energy transfer in Ce- and Eu-doped SrS thin films
Authors: Tanaka Shosaku , Yoshiyama Hideki , Nishiura Junichi , Ohshio Shozo , Kawakami Hiroyuki , Kobayashi Hiroshi
Published: July 2002

A bright white-light electroluminescence (EL) is obtained in a thin-film EL device with Ce- and Eu-doped SrS phosphors. The device shows a luminance level of 1500 cd/m2 with 5 kHz drive (500 cd/m2 at 1 kHz). The dominant excitation process of the Eu2+ centers is found to be due to an efficient nonradiative energy transfer from the Ce3+ to the Eu2+ centers.
Maximum thickness of amorphous NiZr interlayers formed by a solid-state reaction technique
Authors: Meng W. J. , Nieh C. W. , Johnson W. L.
Published: July 2002

Formation of the equilibrium intermetallic compound NiZr in sputter deposited Ni/Zr diffusion couples is suppressed by the formation of a metastable amorphous NiZr alloy until a critical thickness of the amorphous NiZr interlayer is reached. The temperature dependence of this critical thickness is studied experimentally. A phenomenological model based on the premise of interfacial heterogeneous nucleation is proposed to understand the evolution of Ni/Zr diffusion couples.
Effect of substrate surface structure on nucleation of GaAs on Si(100)
Authors: Hull R. , Fischer-Colbrie A. , Rosner S. J. , Koch S. M. , Harris J. S.
Published: July 2002

We study the effect of surface structure upon the nucleation of GaAs in molecular beam epitaxy growth on vicinal Si(100) surfaces. In general, cross-sectional transmission electron microscopy reveals that nucleation of GaAs islands is associated with surface steps produced by the deliberate substrate misorientation. Furthermore, it is found that standard in situ cleaning of the Si surface prior to deposition can result in steps grouping together, producing local surface facets. GaAs nucleation then occurs on these facets, the nucleation sites being correspondingly further apart than for an equilibrium distribution of monolayer steps.
Novel photochemical vapor deposition reactor for amorphous silicon solar cell deposition
Authors: Rocheleau Richard E. , Hegedus Steven S. , Buchanan Wayne A. , Jackson Scott C.
Published: July 2002

A novel photochemical vapor deposition (photo-CVD) reactor having a flexible ultraviolet-transparent Teflon curtain and a secondary gas flow to eliminate deposition on the window has been used to deposit amorphous silicon films and p-i-n solar cells. The background levels of atmospheric contaminants (H2O, CO2, N2) depend strongly on the vacuum procedures but not on the presence of a Teflon curtain in the reactor. Intrinsic films with a midgap density of states of 3×1015 eV−1 cm−3 and all-photo-CVD pin solar cells with efficiencies of 8.5% have been deposited.
Buried heterostructure lasers by silicon implanted, impurity induced disordering
Authors: Welch D. F. , Scifres D. R. , Cross P. S. , Streifer W.
Published: July 2002

Buried heterostructure lasers have been fabricated using impurity induced disordering from an implanted Si diffusion source. The diffused Si extends over 1 μm deep through the active region where the quantum wells are partially homogenized with the barrier and cladding layers to produce a lower refractive index and higher band-gap material. The resulting real refractive index waveguide exhibits single longitudinal and transverse mode behavior to greater than 20 mW for a 4-μm-wide waveguide.
Imaging of deep level domains in semi-insulating GaAs by voltage contrast
Authors: Johnson D. A. , Myhajlenko S. , Edwards J. L. , Maracas G. N. , Roedel R. J. , Goronkin H.
Published: July 2002

We have used the voltage contrast effect to image deep level domains in semi-insulating (SI) GaAs n-i-n resistor structures. Our samples consisted of SI, undoped, liquid encapsulated Czochralski material with alloyed AuGe/Ni contacts at spacings from 1.3 to 2.27 mm. By viewing the contact side of the samples with a scanning electron microscope while the devices were biased in the oscillation region, we observed domain formation and motion from cathode to anode in real time. Long range potentials in the GaAs were observed by viewing the polished back surface of the samples. That is, the domains which are launched from the front contacts were clearly evident in voltage contrast measurements on the back of the sample. Also, because of the nonuniform charging of the semiconductor surface by the electron beam, we observed interactions between the propagating domains and the cellular dislocation structure in the SI GaAs.
Critical current densities and transport in superconducting YBa2Cu3O7−δ films made by electron beam coevaporation
Authors: Oh B. , Naito M. , Arnason S. , Rosenthal P. , Barton R. , Beasley M. R. , Geballe T. H. , Hammond R. H. , Kapitulnik A.
Published: July 2002

Thin films of the high Tc superconductor YBa2Cu3O7−δ were prepared and characterized. The films made on SrTiO3 showed epitaxial growth and high critical current densities in excess of 9×104 at 78 K and 2×106 at 4.2 K. Also, surface pinning in the parallel direction was found to be very high. The measurements put a lower limit on the depairing critical current density of 5×107 A/cm2.
Activation energy for thermal donor formation in silicon
Authors: Claybourn M. , Newman R. C.
Published: July 2002

Czochralski silicon samples have been heated for increasing periods of time at temperatures of 395, 415, 450, 475, and 490 °C. At each stage infrared spectra of the electronic absorption of thermal donors TD2–TD9 were obtained with the samples at 4.2 K. The data for all the thermal donor centers can be presented on one universal plot, provided the concentration and time axes are simply scaled by factors that depend only on the temperature of heating. It is implied that the rate of formation of each center is limited by the same mechanism. An activation energy of 1.7±0.1 eV is determined for these processes.
Grown-facet-dependent characteristics of silicon-on-insulator by lateral solid phase epitaxy
Authors: Kusukawa K. , Moniwa M. , Murakami E. , Warabisako T. , Miyao M.
Published: July 2002

Electrical characteristics of Si layers on SiO2 formed by seeded lateral solid phase epitaxy are evaluated using metal-oxide-semiconductor field-effect transistors (MOSFET’s) fabricated in the layer. To evaluate the {110} and {111} facet grown areas separately, the locations of the MOSFET’s are varied as a function of distance from the seeding region. Significant differences in electrical characteristics of the MOSFET’s are observed depending on the single-crystal growth mode. A field-effect (electron) mobility of about 700 cm2/(V s) was obtained for n-channel MOSFET’s fabricated in the {110} facet grown region. That for the {111} facet growth region was inadequate. The results indicate the possibility of applying the method for future three-dimensional device structures using a {110} facet grown region.
X-ray double-crystal characterization of molecular beam epitaxially grown Si/Si1−xGex strained-layer superlattices
Authors: Baribeau J.-M.
Published: July 2002

We report the first study of Si/Si1−xGex strained-layer superlattices using x-ray double-crystal diffractometry. Symmetric rocking curves (400) were used to determine the structural parameters and strain distribution. All the superlattices were found to have excellent crystalline quality and uniformity both in thickness and alloy composition. Kinematical simulations of rocking curves revealed that most of the misfit between Si and Si1−xGex is accommodated by lattice deformation of the alloy layers. A small tensile strain (∼0.05%) in the growth direction was also found in Si and was attributed to the difference in thermal expansion coefficients of Si and Si1−xGex.
Effect of bias on the response of metal-oxide-semiconductor devices to low-energy x-ray and cobalt-60 irradiation
Authors: Fleetwood D. M. , Winokur P. S. , Dozier C. M. , Brown D. B.
Published: July 2002

The response of metal-oxide-semiconductor (MOS) transistors and capacitors to high-energy Co-60 gamma and low-energy x-ray irradiation is evaluated as a function of gate bias during exposure. It is demonstrated that, in contrast to previous expectations, the relative response of MOS devices to Co-60 gamma and 10 keV x-ray irradiation cannot be explained simply in terms of electron-hole recombination and dose enhancement effects.
Growth of high quality indium phosphide from metalorganic sources by molecular beam epitaxy
Authors: Andrews D. A. , Davey S. T. , Tuppen C. G. , Wakefield B. , Davies G. J.
Published: July 2002

We report the growth of nominally undoped InP by molecular beam epitaxy (MBE) from metallic indium, trimethylindium, or triethylindium and phosphine. We find significantly reduced acceptor incorporation when metalorganic sources are used, with exciton-dominated photoluminescence at 4.2 K and electron mobilities up to 47 500 cm2 V−1 s−1 at 77 K. The 4.2 K photoluminescence indicates that the residual shallow acceptors are either Ca, Mg, or Be. The carbon incorporation appears to be minimal. Interestingly, there is also little difference in electrical and optical properties of InP grown by metalorganic molecular beam epitaxy (MOMBE) using trimethyl or triethylindium, in marked contrast to the situation for GaAs MOMBE growth using trimethyl or triethylgallium.
‘‘Coreless defects’’ and the continuity of epitaxial NiSi2/Si(100) thin films
Authors: Batstone J. L. , Gibson J. M. , Tung R. T. , Levi A. F. J.
Published: July 2002

Epitaxial thin films of NiSi2 on Si(100) have been grown by room-temperature deposition of Ni followed by a high-temperature reaction. Initial stages of epitaxy revealed by transmission electron microscopy show nucleation of crystallographically equivalent islands related by a translation vector a/4〈111〉 via the underlying silicon substrate. Coalescence of islands thus requires the generation of a/4〈111〉 dislocations, which is energetically unfavorable. We find that very thin films (∼60 Å) do not coalesce, but choose to remain as islands leaving trenches of exposed substrate 15±1.5 Å in width between them. We propose that the trench left between islands can be described as a coreless defect in the silicide.
Preparation of thin-film YBaCuO quantum interference devices with a lift-off technique
Authors: Häuser B. , Diegel M. , Rogalla H.
Published: July 2002

Highly textured and polycrystalline YBaCuO thin films were sputtered on cold MgO single-crystal substrates. After annealing in oxygen for 1 h at 920 °C, the films show critical temperatures Tc,end up to 74.5 K. Superconducting quantum interference devices (dc SQUID’s) structured in ≊1-μm-thick polycrystalline films with a lift-off technique exhibit a critical current of 2 mA at 5.5 K and 35 μA at 72 K. Voltage modulation can be observed at temperatures up to 63 K.
High-power gain-guided coupled-stripe quantum well laser array by hydrogenation
Authors: Jackson G. S. , Hall D. C. , Guido L. J. , Plano W. E. , Pan N. , Holonyak N. , Stillman G. E.
Published: July 2002

High-power coupled-stripe (ten-stripe) AlxGa1−xAs-GaAs quantum well lasers that are fabricated by hydrogenation are described. Continuous (cw) room-temperature thresholds as low as Ith=90 mA and internal quantum efficiency as high as 85% are demonstrated. Continuous 300 K laser operation generating 2×375 mW (0.75 W) at 910 mA (10Ith) or 57% efficiency is described (8-μm-wide stripes on 12 μm centers). Minimal heating effects are observed up to the point of catastrophic failure.
Characterization of planar crystal lattice defects in the high-temperature superconductor YBa2Cu3O7
Authors: Tafto J. , Suenaga M. , Sabatini R. L.
Published: July 2002

Transmission electron microscopy shows that sintered YBa2Cu3O7 contains many planar defects in the a-b plane. They range from stacking faults to 10–100 nm thick sheets of disordered material that extend through the entire crystal grains. The stacking faults may be precursors for the thick layers of disordered material. In this letter we characterize the stacking faults and find that the displacement vector switches from (a/2,0,c/6) to (b/2,0,c/6) as the faults cross the twin boundaries.
Anomalous reduction of lattice parameter by residual impurity boron in undoped Czochralski-grown GaAs
Authors: Okada Yasumasa , Orito Fumio
Published: July 2002

An anomalous reduction of lattice parameter is observed for undoped semi-insulating liquid encapsulated Czochralski-grown GaAs by precision lattice parameter measurements with the use of the bond method. The anomalous reduction is though to be due to the incorporation of residual boron from the B2O3 encapsulant. The reduction rate is about 2 times larger than the predicted rate for the boron concentration derived from Vegard’s law. Possible defect models for this phenomenon are discussed.
Direct control and characterization of a Schottky barrier by scanning tunneling microscopy
Authors: Bell L. D. , Kaiser W. J. , Hecht M. H. , Grunthaner F. J.
Published: July 2002

Scanning tunneling microscopy (STM) methods are used to directly control the barrier height of a metal tunnel tip-semiconductor tunnel junction. Barrier behavior is measured by tunnel current-voltage spectroscopy and compared to theory. A unique surface preparation method is used to prepare a low surface state density Si surface. Control of band bending with this method enables STM investigation of semiconductor subsurface properties.
Optical investigations of the band structure of strained InAs/AlInAs quantum wells
Authors: Meynadier M.-H. , de Miguel J.-L. , Tamargo M. C. , Nahory R. E.
Published: July 2002

We report photoluminescence and photoconductivity measurements on single InAs quantum wells under a 3.4% biaxial compression. The photoluminescence line, which is in the 1.2–1.6 μm wavelength range depending on well thickness, is interpreted as recombination between electrons and holes distributed over a range of confined energy states associated with quantum well width fluctuations. Photoconductivity is found to provide spectroscopic measurements of the optical transitions even for single, extremely thin quantum wells. We find excellent agreement between the measured transition energies and the result of an envelope function calculation taking into account the effect of both strain and quantum confinement.
Efficient narrow-band direct modulation of semiconductor injection lasers at millimeter wave frequencies of 100 GHz and beyond
Authors: Lau K. Y.
Published: July 2002

It has been demonstrated both theoretically and experimentally that it is possible to mode lock semiconductor lasers at millimeter wave frequencies approaching and beyond 100 GHz. The mode-locked output usually takes the form of sinusoidal modulation, and can be regarded for practical purposes as a highly efficient means of directly modulating an optical carrier in a narrow band at millimeter wave frequencies. In active mode locking, the external signal efficiently creates the optical modulation, while in passive mode locking a small external signal imposes its information on the optical carrier by injection locking the passive mode-locked output. Experimentally, we have demonstrated passive mode locking at 70 GHz using a tandem contact GaAs laser.
Anisotropy of thermal expansion of GaAs on Si(001)
Authors: Lucas N. , Zabel H. , Morkoç H. , Unlu H.
Published: July 2002

We have measured the thermal expansion between 20 and 450 °C of epitaxially grown GaAs thin films on Si(001) as well as of the Si substrate by means of high-resolution x-ray scattering. Our results show that the thermal expansion of GaAs in the direction parallel to the film plane follows the thermal expansion of the silicon substrate and is therefore smaller than in bulk GaAs. Furthermore, the thermal expansion perpendicular to the film plane (parallel to the growth direction) exceeds the bulk GaAs value by the Poisson contribution as a result of the in-plane constraint. The thermal expansion coefficients for GaAs films on Si(001) substrates in the directions parallel and perpendicular to the film plane are αT∥(GaAs) =3.46×10−6/K and αT⊥(GaAs) =8.91×10−6/K, respectively.
Surface, interface, and bulk properties of amorphous carbon films characterized by i
n s
i
t
u ellipsometry
Authors: Collins R. W.
Published: July 2002

Hydrogenated amorphous carbon film growth in diamond-like and polymer-like forms has been studied by in situ ellipsometry. The experiments provide accurate values of the optical functions, thickness, and deposition rate in real time. Reactions between the substrate and the gas phase species or film in the initial stages of growth, inaccessible to ex situ probes, have been detected with monolayer resolution. Monolayer changes in near-surface bonding have also been detected.
Atomic steps at GaInAs/InP interfaces grown by organometallic vapor phase epitaxy
Authors: Wang T. Y. , Fry K. L. , Persson A. , Reihlen E. H. , Stringfellow G. B.
Published: July 2002

InP/GaInAs/InP quantum well structures have been grown using atmospheric pressure organometallic vapor phase epitaxy (OMVPE). For thin wells the 10 K photoluminescence spectra show a clearly resolved doublet (or in some cases a triplet). The energy separation of the two peaks increase with decreasing well width down to a nominal width of approximately two to three atomic monolayers. For thinner wells the energy separation decreases with decreasing well width. The doublet is interpreted as being due to the photoluminescence from two wells differing in thickness by a single monolayer. A simple calculation for a finite quantum well describes the general features of the energy splitting versus well width. The half-widths of the two photoluminescence peaks for the thin wells, where the two peaks are resolved, are extremely narrow. The value of <15 meV for the thinnest well is much better than observed previously for low-pressure or atmospheric-pressure OMVPE and matches the results obtained by chemical beam epitaxy.
Control of epitaxial orientation of Si on CoSi2(111)
Authors: Tung R. T. , Batstone J. L.
Published: July 2002

Template techniques for Si epitaxy are designed based on the two structures, CoSi2-C and CoSi2-S, of the CoSi2 surface. The different stacking sequences of the two CoSi2 surfaces have led to the growth of single-crystal epitaxial Si layers with either type A or type B orientation on CoSi2(111). The crystalline quality of these Si/CoSi2/Si structures far exceeds that of those reported previously. The orientation of the epitaxial Si overlayer is also found to depend on the strain in the epitaxial CoSi2 thin films.
Ozone-UV irradiation effects on Ba2YCu3O7−x thin films
Authors: Tamura H. , Yoshida A. , Morohashi S. , Hasuo S.
Published: July 2002

We studied the effects of ultraviolet (UV) irradiation in an ozone atmosphere on the electrical properties of Ba2 YCu3 O7−x thin films. The ozone-UV treatment had effects similar to plasma oxidation; it decreased the room-temperature resistivity and increased the zero resistance temperature of 460 nm Ba-Y-Cu-O thin films. Film resistivity decreased by about 25% in 100 min during ozone-UV treatment. This decreasing rate is one order of magnitude lower than plasma treatment. The ozone-UV treatment, however, resulted in a more stable film than the plasma treatment. The rate at which the room-temperature resistivity increased, measured 35 days after the ozone-UV treatment, was 0.06%/day, or about 1/6 that of the plasma treatment.
Extremely sharp erbium-related intra-4f-shell photoluminescence of erbium-doped GaAs grown by metalorganic chemical vapor deposition
Authors: Nakagome Hiroshi , Uwai Kunihiko , Takahei Kenichiro
Published: July 2002

A drastic change is observed in the 1.5 μm Er-related photoluminescence spectra for GaAs:Er grown by metalorganic chemical vapor deposition, when the growth temperature and arsine partial pressure are reduced. An optically efficient Er-emitting center which shows a photoluminescence spectrum with narrow linewidth (less than 0.03 nm at 2 K) and high peak intensity is preferentially photoexcited in the crystal grown at 550 °C with a V/III ratio of 3. The linewidth of the luminescence is comparable to rare-earth-related luminescence of rare-earth-doped insulators such as YAG:Nd.
High-power, diffraction-limited-beam operation from phase-locked diode-laser arrays of closely spaced ‘‘leaky’’ waveguides (antiguides)
Authors: Botez D. , Mawst L. , Hayashida P. , Peterson G. , Roth T. J.
Published: July 2002

A novel type of phase-locked diode-laser array is demonstrated: an array of closely spaced index depressions (antiguides). The arrays are ten-element AlGaAs/GaAs devices fabricated by metalorganic chemical vapor deposition and liquid phase epitaxy over a patterned substrate. The fundamental and highest-order modes of the array of antiguides have negligible radiation loss: 20–30 times less than that for a single antiguide. The modal-gain differentials between adjacent array modes are at least an order of magnitude larger than those for evanescently coupled arrays of positive-index guides. Fundamental-array-mode operation in a virtually diffraction-limited-beam (1.4°) pattern is obtained to 200 mW. Out-of-phase-mode operation in a virtually diffraction-limited-beam (1.2°) pattern is achieved to 110 mW/uncoated facet. The inherent array-mode stability of antiguided arrays is discussed.
Preparation of oriented Bi-Ca-Sr-Cu-O thin films using pulsed laser deposition
Authors: Fork D. K. , Boyce J. B. , Ponce F. A. , Johnson R. I. , Anderson G. B. , Connell G. A. N. , Eom C. B. , Geballe T. H.
Published: July 2002

Oriented c-axis thin films of Bi-Ca-Sr-Cu-O on [100] SrTiO3 substrates have been fabricated using the pulsed excimer laser evaporation technique. Deposition at room temperature in 1 mTorr oxygen followed by an 875 °C anneal in oxygen yields superconducting films with zero resistance at 80 K and a resistivity drop near 110 K, hinting at the presence of another superconducting phase. Transmission electron microscopy shows that the films are epitaxial with the substrate, with an abrupt and planar interface boundary. The observed crystal structure is consistent with diffraction results on bulk materials.
New fluid filter structure in silicon fabricated using a self-aligning technique
Authors: Stemme Göran , Kittilsland Gjermund
Published: July 2002

A new fluid filter structure in silicon has been designed and fabricated. The structure consists of two hole membranes of silicon displaced laterally relative to each other. The size of the largest particles which can pass through the structure is determined by the thickness of the silicon dioxide spacers separating the two hole membranes. One single-hole pattern is used in combination with a special two-step self-aligning technique involving heavy boron diffusion, anisotropic silicon etching, and silicon dioxide undercut etching. Structures with membrane separation distances of 50 and 200 nm have been made. Since the structure electrically is a capacitor, other applications are possible.
Inhibitory pathways and the inhibition of luteinizing hormone-releasing hormone release by alcohol
Authors: Lomniczi Alejandro , Mastronardi Claudio A. , Faletti Alicia G. , Seilicovich Adriana , De Laurentiis Andrea , McCann Samuel M. , Rettori Valeria
Published: July 2002

In this research we examined the mechanisms by which ethanol (EtOH) inhibits luteinizing hormone-releasing hormone (LHRH) release from incubated medial basal hypothalamic explants. EtOH (100 mM) stimulated the release of two inhibitory neurotransmitters: γ-aminobutyric acid (GABA) and β-endorphin. EtOH also inhibited NO production, indicative of a suppression of nitric oxide synthase (NOS) activity. This inhibition was reversed by naltroxone (10
−8
M), a μ-opioid receptor blocker, indicating that the inhibition of NOS by EtOH is mediated by β-endorphin. EtOH also blocked
N-
methyl-
d
-aspartic acid-induced LHRH release, but the blockade could not be reversed by either the GABA receptor blocker, bicuculline (10
−5
M), naltroxone (10
−8
M), or both inhibitors added together. However, increasing the concentration of naltrexone (10
−6
M) but not bicuculline (10
−4
M) reversed the inhibition. When we lowered the concentration of EtOH (50 mM), the EtOH-induced blockade of LHRH release could be reversed by either bicuculline (10
−5
M), naltroxone (10
−8
M), or the combination of the two blockers. Therefore, GABA is partially responsible for the blockade of
N-
methyl-
d
-aspartic acid-induced LHRH release. The block by GABA was exerted by inhibiting the activation of cyclooxygenase by NO, because it was reversed by prostaglandin E
2
, the product of activation of cyclooxygenase. Because the inhibition caused by the higher concentration of EtOH could not be reduced by bicuculline (10
−4
M) but was blocked by naltroxone (10
−6
M), the action of alcohol can be accounted for by stimulation of β-endorphin neurons that inhibit LHRH release by inhibition of activation of NOS and stimulation of GABA release.
Invariant chain induces B cell maturation in a process that is independent of its chaperonic activity
Authors: Matza Didi , Lantner Frida , Bogoch Yoel , Flaishon Liat , Hershkoviz Rami , Shachar Idit
Published: July 2002

Early stages of B cell development take place in the bone marrow, resulting in formation of immature B cells, which migrate to the spleen for their final differentiation into mature cells. This final maturation step is essential for B cells to become responsive to antigens and to participate in the immune response. Previously, we showed that the MHC class II chaperone, invariant chain (Ii), controls the differentiation of B cells from the immature to the mature stage. In this study, by generating transgenic mice expressing truncated Ii lacking its luminal domain, we could dissect the chaperonin activity of Ii from its role in B cell maturation. We demonstratein vivothat Ii N-terminal domain is directly involved in the maturation of B cells and is sufficient to promote B cell differentiation.
Cell autonomous regulation of multiple Dishevelled-dependent pathways by mammalian Nkd
Authors: Yan Dong , Wallingford John B. , Sun Tian-Qiang , Nelson April M. , Sakanaka Chie , Reinhard Christoph , Harland Richard M. , Fantl Wendy J. , Williams Lewis T.
Published: July 2002

Genetic studies have identified
Drosophila
Naked
Cuticle (Nkd) as an antagonist of the canonical
Wnt/β-catenin signaling pathway, but its mechanism of
action remains obscure [Zeng, W., Wharton, K. A., Jr., Mack,
J. A., Wang, K., Gadbaw, M.,
et al.
(2000)
Nature (London)
403, 789–795]. Here we have cloned a
cDNA encoding a mammalian homolog of
Drosophila
Nkd,
mNkd, and demonstrated that mNkd interacts directly with Dishevelled.
Dishevelled is an intracellular mediator of both the canonical Wnt
pathway and planar cell polarity (PCP) pathway. Activation of the
c-Jun-N-terminal kinase has been implicated in the PCP pathway. We
showed that mNkd acts in a cell-autonomous manner not only to inhibit
the canonical Wnt pathway but also to stimulate c-Jun-N-terminal kinase
activity. Expression of mNkd disrupted convergent extension in
Xenopus
, consistent with a role for mNkd in the PCP
pathway. These data suggest that mNkd may act as a switch to direct
Dishevelled activity toward the PCP pathway, and away from the
canonical Wnt pathway.
Determining the role of patterned cell proliferation in the shape and size of the
Drosophila
wing
Authors: Resino Jaime , Salama-Cohen Patricia , García-Bellido Antonio
Published: July 2002

The present work is a detailed analysis of the numerical and positional parameters of cell proliferation in all of the derivatives of the wing disk. We have made use of twin clones resulting from mitotic recombination events at three different ages of development. The interfaces between twin clones indicate the relative position in the anlage of the mother cells. Interface types vary with age of clone initiation and with wing regions. They are indicative of the main allocation of postmitotic cells of the growing clones. Growth is exponential and intercalar, i.e., the progeny of ancestor cells becomes more and more separated. Clones are compact, indicating that daughter cells tend to remain side by side. The shape of the clones is wing region characteristic. Subpopulations of cells grow preferentially along veins and wing margins and show characteristic shapes in different pleural regions. The shape and size of the adult wing regions largely depend on the shape of clones and hence of the allocation of successive rounds of daughter cells. The role of mitogenic morphogens in wing size and shape is discussed.
What angle-resolved photoemission experiments tell about the microscopic theory for high-temperature superconductors
Authors: Abrahams Elihu , Varma C. M.
Published: July 2002

Recent angular-resolved photoemission experiments on high-temperature superconductors are consistent with a phenomenological description of the normal state of these materials as marginal Fermi liquids. The experiments also provide constraints on microscopic theories.
Origin of supposedly biogenic magnetite in the Martian meteorite Allan Hills 84001
Authors: Barber David J. , Scott Edward R. D.
Published: July 2002

Crystals of magnetite (Fe
3
O
4
) and periclase (MgO) in Fe-Mg-Ca carbonate in the Martian meteorite Allan Hills 84001 were studied by using transmission electron microscopy to understand their origin and evaluate claims that the magnetites were made by Martian microorganisms. In magnesian carbonate, periclase occurs as aggregates of crystals (grain size ≈3 nm) that are preferentially oriented with respect to the carbonate lattice. Larger periclase crystals ≈50 nm in size are commonly associated with voids of similar size. Periclase clearly formed by precipitation from carbonate as a result of partial decomposition and loss of CO
2
. Magnetite occurs in more ferroan carbonate, and, like periclase, it is associated with voids and microfractures and the two oxides may be intermixed. Magnetite nanocrystals that are commonly euhedral and entirely embedded in carbonate are topotactically oriented with respect to the carbonate lattice, showing that they formed as solid-state precipitates. Magnetites in Fe-rich carbonate rims are not well oriented. These magnetites are generally more irregular in shape and diverse in size than the euhedral variety. All occurrences of magnetite and periclase are entirely consistent with
in situ
growth by solid-state diffusion as a result of carbonate decomposition during impact heating. Biogenic sources should not be invoked for any magnetites.
Latitudinal difference in biodiversity caused by higher tropical rate of increase
Authors: Buzas Martin A. , Collins Laurel S. , Culver Stephen J.
Published: July 2002

Tropical diversity has generally exceeded temperate diversity in the present and at points in the past, but whether measured differences have remained relatively constant through time has been unknown. Here we examine tropical vs. temperate diversities from the Neogene to Recent using the within-habitat diversity measure Fisher's alpha of Cenozoic benthic foraminifera from the temperate Central Atlantic Coastal Plain and the tropical Central American Isthmus. During the Neogene, the mean value of alpha at temperate latitudes increased 1.4 times or 40%, whereas in the tropics it increased 2.1 times or 106%. Thus, while both areas exhibit an increase of diversity with time, past differences in the rate of increase have generated a more pronounced gradient today (164%) than existed in the Miocene (80%). These data disagree with the suggestion that the world reached an equilibrium number of species during the Paleozoic and demonstrate the need to consider both temperate and tropical components in global diversity assessments.
Extreme morphological and ecological homoplasy in tropical salamanders
Authors: Parra-Olea Gabriela , Wake David B.
Published: July 2002

Fossorial salamanders typically have elongate and attenuated heads and bodies, diminutive limbs, hands and feet, and extremely elongate tails.
Batrachoseps
from California,
Lineatriton
from eastern México, and
Oedipina
from southern México to Ecuador, all members of the family Plethodontidae, tribe Bolitoglossini, resemble one another in external morphology, which has evolved independently. Whereas
Oedipina
and
Batrachoseps
are elongate because there are more trunk vertebrae, a widespread homoplasy (parallelism) in salamanders, the genus
Lineatriton
is unique in having evolved convergently by an alternate “giraffe-neck” developmental program.
Lineatriton
has the same number of trunk vertebrae as related, nonelongated taxa, but individual trunk vertebrae are elongated. A robust phylogenetic hypothesis, based on sequences of three mtDNA genes, finds
Lineatriton
to be deeply nested within a clade characterized by generalized ecology and morphology.
Lineatriton lineolus
, the only currently recognized taxon in the genus, shows unanticipated genetic diversity. Surprisingly, geographically separated populations of
L. lineolus
are not monophyletic, but are sister taxa of different species of the morphologically generalized genus
Pseudoeurycea. Lineatriton
, long thought to be a unique monospecific lineage, is polyphyletic. Accordingly, the specialized morphology of
Lineatriton
displays homoplasy at two hierarchical levels: (
i
) with respect to other elongate lineages in the family (convergence), and (
ii
) within what is currently recognized as a single taxon (parallelism). These evolutionary events are of adaptive significance because to invade the lowland tropics salamanders must be either arboreal or fossorial; the repeated evolution of elongation and attenuation has led to multiple lowland invasions.
Antagonistic forces generated by myosin II and cytoplasmic dynein regulate microtubule turnover, movement, and organization in interphase cells
Authors: Yvon Anne-Marie C. , Gross David J. , Wadsworth Patricia
Published: July 2002

Photoactivation of caged fluorescent tubulin was used mark the microtubule (MT) lattice and monitor MT behavior in interphase cells. A broadening of the photoactivated region occurred as MTs moved bidirectionally. MT movement was not inhibited when MT assembly was suppressed with nocodazole or Taxol; MT movement was suppressed by inhibition of myosin light chain kinase with ML7 or by a peptide inhibitor. Conversely, MT movement was increased after inhibition of cytoplasmic dynein with the antibody 70.1. In addition, the half-time for MT turnover was decreased in cells treated with ML7. These results demonstrate that myosin II and cytoplasmic dynein contribute to a balance of forces that regulates MT organization, movement, and turnover in interphase cells.
A cranium for the earliest Europeans: Phylogenetic position of the hominid from Ceprano, Italy
Authors: Manzi G. , Mallegni F. , Ascenzi A.
Published: July 2002

The human fossil evidence unequivocally pertaining to the first
inhabitants of Europe at present includes the sample from Atapuerca-TD6
(Spain) and the incomplete adult calvaria discovered near Ceprano, in
Southern Latium (Italy). On the basis of regional correlations and a
series of absolute dates, the age of the Ceprano hominid is estimated
to range between 800 and 900 kilo-annum (ka). In addition, the
association with archaic (Mode 1) Paleolithic findings from the same
area is suggested. After the completed reconstruction of the calvaria,
we present here a new study dealing with the general and more detailed
aspects of the morphology displayed by Ceprano, in comparison to fossil
samples ranging between Early and Middle Pleistocene. According to our
results, cranial features indicate that Ceprano represents a unique
morphological bridge between the clade
Homo
ergaster
/
erectus
and later Middle Pleistocene
specimens commonly referred to
Homo heidelbergensis
(and/or to
Homo rhodesiensis
), particularly those
belonging to the African fossil record that ultimately relates to the
origin of modern humans. In conclusion, given its geographical,
chronological, and phylogenetic position, an attribution to the species
Homo antecessor
is considered, although the sample from
Atapuerca-TD6 is not directly comparable to Ceprano. Alternatively, a
new species—ancestral to later European and African hominines—should
be named to accommodate such a unique fossil specimen.
Influenza virus inhibits amiloride-sensitive Na+channels in respiratory epithelia
Authors: Kunzelmann K. , Beesley A. H. , King N. J. , Karupiah G. , Young J. A. , Cook D. I.
Published: July 2002

Many pathogens causing diarrhea do so by modulating ion transport in the gut. Respiratory pathogens are similarly associated with disturbances of fluid balance in the respiratory tract, although it is not known whether they too act by altering epithelial ion transport. Here we show that influenza virus A/PR/8/34 inhibits the amiloride-sensitive Na+current across mouse tracheal epithelium with a half-time of about 60 min. We further show that the inhibitory effect of the influenza virus is caused by the binding of viral hemagglutinin to a cell-surface receptor, which then activates phospholipase C and protein kinase C. Given the importance of epithelial Na+channels in controlling the amount of fluid in the respiratory tract, we suggest that down-regulation of Na+channels induced by influenza virus may play a role in the fluid transport abnormalities that are associated with influenza infections.