bluuebunny/crossref_metadata_2025 huggingface dataset:
Functional preference of the constituent amino acid residues in a phage‐library‐based nonphosphorylated inhibitor of the Grb2‐SH2 domain
Authors: Lung F.‐D. T. , Long Y.‐Q. , Roller Peter P. , King C. R. , Varady J. , Wu X.‐W. , Wang S.
Published: July 2002

Abstract: A nonphosphorylated disulfide‐bridged peptide, cyclo(Cys‐Glu1‐Leu‐Tyr‐Glu‐Asn‐Val‐Gly‐Met‐Tyr9‐Cys)‐amide (termed G1) has been identified, by phage library, that binds to the Grb2‐SH2 domain but not the src SH2 domain. Synthetic G1 blocks the Grb2‐SH2 domain association (IC50 of 15.5 µm) with natural phosphopeptide ligands. As a new structural motif that binds to the Grb2‐SH2 domain in a pTyr‐independent manner, the binding affinity of G1 is contributed by the highly favored interactions of its structural elements interacting with the binding pocket of the protein. These interactions involve side‐chains of amino acids Glu1, Tyr3, Glu4, Asn5, and Met8. Also a specific conformation is required for the cyclic peptide when bound to the protein. Ala scanning within G1 and molecular modeling analysis suggest a promising model in which G1 peptide binds in the phosphotyrosine binding site of the Grb2‐SH2 domain in a β‐turn‐like conformation. Replacement of Tyr3 or Asn5 with Ala abrogates the inhibitory activity of the peptide, indicating that G1 requires a Y‐X‐N consensus sequence similar to that found in natural pTyr‐containing ligands, but without Tyr phosphorylation. Significantly, the Ala mutant of Glu1, i.e. the amino acid N‐terminal to Y3, remarkably reduces the binding affinity. The position of the Glu1 side‐chain is confirmed to provide a complementary role for pTyr3, as demonstrated by the low micromolar inhibitory activity (IC50 = 1.02 µm) of the nonphosphorylated peptide 11, G1(Gla1), in which Glu1 was replaced by γ‐carboxy‐glutamic acid (Gla).
Anticipation in familial chronic lymphocytic leukaemia
Authors: Wiernik Peter H. , Ashwin Murigeppa , Hu Xiao‐Ping , Paietta Elisabeth , Brown Kelly
Published: July 2002

Anticipation, a phenomenon in which an inherited disease is diagnosed at an earlier age in each successive generation of a family, has been demonstrated in certain heritable neurological disorders and in multiple myeloma, non‐Hodgkin's lymphoma and other haematological neoplasms. The present study was conducted to determine whether anticipation occurs in familial chronic lymphocytic leukaemia (CLL). Fourteen published reports of multigenerational familial CLL were analysed for anticipation, together with 10 previously unreported families with familial CLL, and the difference in disease‐free survival between generations was determined. The difference between age at onset for each affected parent–child pair was tested against the null hypothesis that there was no difference in age at onset. The age at onset of the studied cases was also compared with that of the Surveillance Epidemiology and End Results (SEER) Program of the U.S. National Cancer Institute. The median ages at onset in the child and parent generations of all families (51·0 and 72·0 years respectively) were significantly different (P < 0·000001), and the null hypothesis was rejected (P < 0·000001). A significant difference was observed between the ages of onset of the child generation and the SEER population (P < 0·00001), but not between the parent generation and the SEER population. Anticipation characterizes familial CLL.
Interobserver variability of sonographically determined second‐trimester nuchal skinfold thickness measurements
Authors: Donnenfeld A. E. , Meister D. , Allison J. , Brennan K. , Ludomirsky A. , Rightmire D.
Published: July 2002

Twenty physicians experienced in fetal sonographic evaluation obtained fetal nuchal skinfold thickness measurements in each of five pregnant women between 16 and 18 weeks' gestation. A random effects analysis of variance model was used to explore the sources of variation in the set of measurements, to determine the interobserver variability of sonographically measured second‐ trimester nuchal skinfold thickness. It was possible to obtain 96 measurements. Four measurements (all in the same patient) were deemed unobtainable due to fetal position. All recorded measurements were between 1.7 and 4.5 mm. The means (and ranges) for the five patients were 2.7 (1.7–3.6), 2.9 (2.0–4.5), 2.7 (2.0–4.0), 3.3 (2.2–4.0), and 2.7 (1.8–4.0) mm. The standard deviation for interobserver variability, caused by the combined effect of physician and machine imprecision, was 0.56 mm and the overall coefficient of variation was 19.8%. Inter patient differences were statistically significant (p = 0.004). Interphysician differences were not (p = 0.11). We conclude that experienced physician sonographers using high‐resolution ultrasound equipment are able to obtain second‐trimester nuchal skinfold thickness measurements within 1.1 mm of the estimated true value with 95% probability. Copyright © 1995 International Society of Ultrasound in Obstetrics and Gynecology
Deregulation of Light‐Induced Plastidogenesis in Etiolated Euglena gracilis Klebs Treated with DNA Hypermethylating 3′‐Azido‐3′‐deoxythymidine
Authors: Pancaldi S. , Bonora A. , Baldisserotto C. , Gualandri R. , Neri L. M. , Fasulo M. P.
Published: July 2002

Abstract: The effect of the DNA hypermethylating 3′‐azido‐3′‐deoxythymidine (AZT) on plastidogenesis was investigated on asynchronous, etiolated Euglena gracilis exposed to continuous light for 72 h. Based on (i) fluorescence and electron microscope aspects of the plastids, (ii) cytochemical localizations of functional PSI and PSII, (iii) immunolocalization of LHCII apoproteins, and (iv) spectrophotometric and HPLC analyses of the photosynthetic pigments, it was found that AZT, at a dose of 5 μM, which does not encroach on cell viability and only slightly interferes with cell proliferation, causes profound alterations of plastids in 10 ‐ 15 % of the cells, without apparently affecting the rest of the cell population. Proplastid‐to‐chloroplast transformation slowed in this cell sub‐population and occurred without the normal co‐regulation that characterizes the process in wild type Euglena. In particular, thylakoid assembly was partially prevented while building materials continued to be synthesized and accumulated in the stroma. Chlorophylls were over‐synthesized, while carotenoids, phaeophytin and phylloquinone dramatically diminished. The assemblage of PSI and PSII was inhibited. The external envelopes and thylakoid membranes were frequently damaged. Plastids, whose total volume increased with respect to the controls, were often malformed and interconnected. Their fluorescence under UV light declined quickly. The fact that AZT acts specifically at the plastid level, causing effects that are greatly opposed to those previously observed in the alga treated with the DNA demethylating 5‐azacytidine, points to a relationship between DNA methylation and plastid differentiation in Euglena.
First room-temperature cw operation of a GaInAsP/InP light-emitting diode on a silicon substrate
Authors: Razeghi M. , Blondeau R. , Defour M. , Omnes F. , Maurel P. , Brillouet F.
Published: July 2002

We report in this letter the first successful fabrication of an InP-GaInAsP light-emitting diode, emitting at 1.15 μm grown by low-pressure metalorganic chemical vapor deposition on a silicon substrate. The device has been operated under continuous wave operation at room temperature for 24 h (with an injection current of 200 mA), and showed no degradation.
Effect of oxygen precipitation on phosphorus diffusion in Czochralski silicon
Authors: Ahn S. T. , Kennel H. W. , Plummer J. D. , Tiller W. A. , Rek Z. U. , Stock S. R.
Published: July 2002

The effects of oxygen precipitation and surface films (SiO2 vs Si3N4) on P diffusion at 1100 °C in Czochralski silicon have been studied. With a fast precipitation rate, P diffusion under both kinds of films is enhanced because of the supersaturation of Si interstitials caused by oxygen precipitation. The larger enhancement in P diffusion under Si3N4 than that under SiO2 covered with Si3N4 is attributed to the slower recombination velocity of interstitials at the Si3N4/Si interface. P diffusion in a denuded zone behaves like that in float-zone Si until the interstitials generated under that zone arrive at the interface.
Observation of carbon incorporation during gallium arsenide growth by molecular beam epitaxy
Authors: Joseph David M. , Balagopal Rajappan , Hicks Robert F. , Sadwick Laurence P. , Wang Kang L.
Published: July 2002

Carbon incorporation has been observed by infrared spectroscopy during the growth of a gallium arsenide film at 200 °C by molecular beam epitaxy. Infrared absorbances are observed at 2925 and 2855 cm−1 with a shoulder at 2950 cm−1. These frequencies are characteristic of the symmetric and asymmetric stretches of CH3 and/or CH2 groups.
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u thermal oxidation for surface cleaning and mask generation prior to selective area epitaxy
Authors: Jones Stephen H. , Lau Kei May
Published: July 2002

Dry thermal oxidation of GaAs and AlAs has been carried out in an organometallic chemical vapor deposition system. This in situ process performed either before or after an epitaxial growth serves the purposes of surface cleaning and mask generation for selective area epitaxy of various III-V semiconductors. AlAs oxidized immediately after growth and patterned for the next regrowth provides better oxide-semiconductor interfaces and minimizes wafer handling. Pre-epitaxy oxidation at 435 °C on a patterned wafer with AlAs/GaAs areas resulted in a selective oxide mask. Since thermal oxides of GaAs sublime at temperatures >600 °C, a 700 °C pregrowth annealing thus thermally cleans the oxidized GaAs areas while the oxides of AlAs remain as a mask for the following regrowth. Photoluminescence results indicate that high quality regrown interfaces have been obtained.
Ensemble Monte Carlo simulation of Te-induced intermixing of AlGaAs-based interfaces
Authors: Kahen K. B.
Published: July 2002

An ensemble Monte Carlo simulation has been used to model the enhanced disordering of AlGaAs-based interfaces in the presence of high concentrations of Te atoms. The model is based on the experimental finding that the thermal interdiffusion process is similar to the self-diffusion of Ga in GaAs. The model agrees well with the experimental data for both the Ga self-diffusion and intermixing. The intermixing is found to be caused by the enhanced solubility of the Ga vacancy acceptors in the presence of the donor Te atoms, and not as a result of the diffusion of the Te atoms. The activation energy of the process is found to be approximately 2.7 eV.
Narrow conducting channels defined by helium ion beam damage
Authors: Cheeks T. L. , Roukes M. L. , Scherer A. , Craighead H. G.
Published: July 2002

We have developed a new technique for patterning narrow conducting channels in GaAs-AlGaAs two-dimensional electron gas (2DEG) materials. A low-energy He ion beam successfully patterned narrow wires with little or no etching of the thin GaAs cap. The damage propagation of the He ion even at low energies was sufficient to decrease the mobility of the 2DEG located deep within the structure. The damage can be removed by a low-temperature anneal but remains stable at room temperature. Conducting channels as narrow as 300 nm have been fabricated and measured using low-temperature magnetoresistance.
Spatial and frequency dependence of four-wave mixing in broad-area diode lasers
Authors: Lucente M. , Fujimoto J. G. , Carter G. M.
Published: July 2002

By injecting two external optical beams into a broad-area laser diode, four-wave mixing is generated via gain nonlinearities in the device. The nonlinear signals are observed by spectrally analyzing the transverse far-field profile of the emission from the device. By varying the injection angle and oscillation wavelength of one of the injected beams, the spatial and frequency dependence of this nonlinear process is measured. The results support a spatially dependent dynamic carrier concentration model which includes the effects of carrier diffusion. These measurements provide a direct determination of the ambipolar diffusion constant in the device D=9.5 cm2/s.
Individual oxide traps as probes into submicron devices
Authors: Restle Phillip
Published: July 2002

In field-effect transistors with gate areas less than 0.5 μm2 the effect of a single electron trapped in the gate oxide on the device resistance is easily observable. In about 10% of these devices a single thermally activated two-state trap produces most of the low-frequency resistance fluctuations in a wide bandwidth near room temperature. Detailed information about this single oxide interface trap can be extracted from the temperature and bias dependence of the trapping kinetics. In this work we extend this technique to locating the trap between the source and drain. With this information these traps become unique local 5–50 Å probes into submicron devices to study the local surface potential and the sensitivity to localized trapped charges under different bias conditions.
Superconducting glass-ceramic rods in BiCaSrCu2Ox prepared by crystallization under a temperature gradient
Authors: Abe Yoshihiro , Hosono Hideo , Hosoe Masahiro , Iwase Jiro , Kubo Yukio
Published: July 2002

Superconducting BiCaSrCu2Ox glass rods and coils were successfully prepared by pumping up the melt at 1150 °C into SiO2 or Pyrex glass tubes. After the outer glass tubes were removed, the resultant glass rods up to 30 cm long were crystallized under a temperature gradient of 30 °C/mm without deforming and cracking. The Tc (onset) and Tc (zero) of the resulting glass-ceramic rods were ∼80 and 62 K, respectively.
AlGaInP/GaAs red edge-emitting diodes for polymer optical fiber applications
Authors: Dutt B. V. , Racette J. H. , Anderson S. J. , Scholl F. W. , Shealy J. R.
Published: July 2002

Pulsed and cw operation of AlGaInP/GaAs graded refractive index separate confinement heterostructure edge light-emitting diodes fabricated from epitaxial structures grown by organometallic vapor phase epitaxy is reported. The device consists of an active region of a single 100 Å quantum well of ternary Ga0.5In0.5P and 1600-Å-thick lattice-matched confining layers of quaternary (AlxGa1−x)0.5In0.5P. A coupled power of −10 dBm at 100 mA into a 500 μm polymer optical fiber of 0.48 NA is realized in a package consisting of a graded refractive index lens with uncoated facets from a 60×300 μm mesa-shaped stripe geometry diode. The 10–90% rise and fall times at 100 mA with a 5 mA prebias were measured to be 5 ns. Higher launched powers are expected to result from improvements in the materials growth, facet coatings, and packaging techniques.
Correlation of superconductivity with ‘‘oxygen dimer’’ peak in photoelectron spectra from YBa2Cu3−xCoxO7−y
Authors: Chang C. C. , Hegde M. S. , Tarascon J. M. , Venkatesan T. , Inam A. , Wu X. D. , McLean W. L.
Published: July 2002

X-ray photoelectron spectroscopy of YBa2Cu3−xCoxO7−y (0<x<0.4) shows a systematic change in the O 1s and Cu 2p3/2 regions as a function of x. Three peaks in the O 1s spectra at 528.5, 531, and 532.7 eV are seen for x=0 which are assigned to O2−, O1−, and O2−2 ions, respectively. As x is increased, the relative intensity of the O2−2 or O1− to the O2− peak decreases and the Cu2+ fraction increases showing a correlation with the decrease in the superconducting transition temperature. The result is interpreted in terms of Co ions substituting for the Cu ions in the chain with the Co ion in octahedral coordination.
New modulated structure in a Pb-doped Bi-Ca-Sr-Cu-O superconductor
Authors: Ramesh R. , van Tendeloo G. , Thomas G. , Green S. M. , Luo H. L.
Published: July 2002

A new modulated structure has been observed in a Pb-doped Bi-Ca-Sr-Cu-O superconductor (Tc,0=105 K) in addition to the incommensurate modulated structure reported by several researchers. This new modulation occurs in the b* direction and shows up as satellite spots to each of the original diffracted spots. Upon cooling to 88 K the diffraction spots due to the original modulation disappear, while the spots due to the new modulation remain. In the case of the undoped samples, the modulation does not disappear upon cooling to 30 K, which is below the Tc,0 of the sample (∼75 K).
Magnetic suspension of superconductors at 4.2 K
Authors: Adler Ronald J. , Anderson W. W.
Published: July 2002

We have observed the stable suspension of superconductors at 4.2 K below a permanent magnet; the superconductors were the type II material Nb3Sn and the high transition temperature material YBa2Cu3Ox. Suspension below a magnet is to be distinguished from levitation above a magnet, which is the classic demonstration of the Meissner effect. Suspension at 4.2 K can be quantitatively explained as due to complete flux trapping in the superconductor. Suspension has previously been observed only at high temperatures in high transition temperature materials, in which the flux trapping is not complete.
60–90 K superconducting phase transition in YBa2Cu3O7−δ
Authors: Shi Donglu , Capone D. W.
Published: July 2002

The kinetic process between the 60 and 90 K superconducting phase transition has been explored to study the oxygen ordering mechanisms. An abrupt change in Tc from 60 to 90 K is observed as the sample’s oxygen content is rapidly varied from around 6.6 to 6.9. No intermediate Tc values are obtained, which suggests an oxygen ordering instability, leading to a phase transition between the 60 and 90 K superconducting phases.
Superconducting thin films of Bi-Sr-Ca-Cu-O obtained by laser ablation processing
Authors: Kim B. F. , Bohandy J. , Phillips T. E. , Green W. J. , Agostinelli E. , Adrian F. J. , Moorjani K. , Swartzendruber L. J. , Shull R. D. , Bennett L. H. , Wallace J. S.
Published: July 2002

Thin films of Bi-Sr-Ca-Cu-O, deposited on (100) cubic zirconia by laser ablation from a bulk superconducting target of nominal composition BiSrCaCu2 Ox , have been investigated by dc resistance and magnetically modulated microwave absorption measurements. The latter technique reveals important features regarding the phase purity of superconducting samples that are masked in the dc resistance measurements. The superconducting behavior of the films, as a function of the substrate temperature during deposition and the post-deposition annealing conditions, is discussed.
Isotropic and anisotropic Nd-Fe-B-type magnets by mechanical alloying and hot pressing
Authors: Heisz W. , Schultz L.
Published: July 2002

Mechanically alloyed Nd-Fe-B powder has been formed to compacted isotropic and anisotropic magnets by hot pressing and die upsetting. The coercivity and its composition dependence of hot-pressed samples are similar to those obtained for resin-bonded samples of the reacted powder. A ratio of up to 2.6 was obtained for the remanences measured parallel and perpendicular to the press direction during die upsetting in preliminary experiments.
Improvement of the stability of hydrogenated amorphous silicon films and solar cells by light pulse treatment
Authors: Nevin W. A. , Yamagishi H. , Tawada Y.
Published: July 2002

The effect of exposure to high-intensity Xe light pulses at moderate temperatures on the electrical properties and light-induced degradation of intrinsic a-Si:H films and a-Si two-stacked tandem solar cells is described. Little change is observed in the dark electrical properties of the films and in the efficiency of the solar cells, while the photoconductivity of the films is lowered. The light stability of both the films and solar cells is considerably improved, such that the degradation of a light pulse treated solar cell is almost 30% smaller than its dark reference after 23 h under AM1.
Inhomogeneous defect activation by rapid thermal processes in silicon
Authors: Thuong-Quat Vu , Eichhammer W. , Siffert P.
Published: July 2002

In silicon, rapid thermal processes are observed to induce recombination centers whose distribution as a function of the depth below the surfaces shows an extremum towards the middle of 1000-μm-thick samples. This nonhomogeneous defect activation is correlated to a surface effect. Impurity-related complexes are believed to be the origin of these recombination centers.
Dense Bi-Sr-Ca-Cu-O superconducting films prepared by spray pyrolysis
Authors: Hsu H. M. , Yee I. , DeLuca J. , Hilbert C. , Miracky R. F. , Smith L. N.
Published: July 2002

Dense oriented superconducting Bi-Sr-Ca-Cu-O films having zero resistance as high as 100 K have been made using a technique in which spray deposited and pyrolyzed films are densified by either melt quenching or flux sintering. The highest Tc films were those prepared with PbO as a dopant/flux on MgO substrates. Films without lead doping prepared on both BeO and MgO substrates yielded resistive transitions of 81–83 K. For these latter films, it was demonstrated that a subsequent anneal in argon enhanced the Tc to 87 K. The films were characterized by x-ray diffraction, scanning electron microscopy, and four-point probe resistance measurements. The critical current density of a film having a Tc of 81 K was 4000 A/cm2 at 78 K and 14 000 A/cm2 at 55K.
Laser-assisted photochemical etching of Hg0.8Cd0.2Te
Authors: Bienstock Rachelle J.
Published: July 2002

A laser-assisted photochemically driven etching process has been developed for Hg0.8Cd0.2Te (12 μm material). It is an etch which does not melt the surface of the material or induce mercury migration. Small geometry features (vias less than 10 μm in diameter) with straight-edged sidewalls have been produced. The etching mechanism is a photoenhanced rapid oxidation with subsequent solvation of the oxides.
New mechanism for diffusion of ion-implanted boron in Si at high concentration
Authors: Holland O. W.
Published: July 2002

Modeling of the diffusion of high-concentration implanted B in Si is done. The normally accepted model, which assumes that diffusivity of boron is controlled by the singly charged donor vacancy, is shown to be inadequate in describing the boron profiles. Rather, a two-stream model, in which boron movement is dominated by a dissociative process involving both interstitial and substitutional diffusion, is found to be in good agreement with the data.
Tertiary butylarsine grown GaAs solar cell
Authors: Sundaram V. S. , Arau B. A. , Avery J. E. , Bailey A. L. , Girard G. R. , Hager H. E. , Thompson A. G. , Fraas L. M.
Published: July 2002

High quality, intentionally doped (both p and n type) gallium arsenide layers have been grown using trimethylgallium and tertiary butylarsine in a low-pressure metalorganic chemical vapor deposition reactor. Using an alternate arsenic source, namely, tertiary butylarsine, a concentrator GaAs solar cell has been fabricated. Under 37 sun, air mass 1.5 illumination, the cell had an open-circuit voltage of 1.095 V, a fill factor of 83%, and an overall efficiency of 18.5%.
Infrared absorption of Ir and IrSi thin films on Si substrates
Authors: Chen C. K. , Tsaur B-Y. , Finn M. C.
Published: July 2002

The infrared absorption of Ir and IrSi thin films on Si substrates has been determined by transmission and reflection measurements over the wavelength range 2.5–25 μm. Detailed analysis of the dependence of absorption at 4 μm on film thickness indicates that a thin boundary layer with lower absorption than Ir is present at the Ir/Si interface and that such a layer with lower absorption than IrSi is present at the IrSi/Si interface. The existence of the boundary layers has been confirmed by the detection of oxygen at the interfaces by Auger analysis. Absorption and Auger measurements give no evidence of boundary layer formation at Pt/Si or PtSi/Si interfaces.
Electrical and optical time-of-flight experiments in GaAs/AlAs superlattices
Authors: Schneider H. , Rühle W. W. , Klitzing K. v. , Ploog K.
Published: July 2002

The dynamics of electron transport by sequential resonant and nonresonant tunneling along the growth direction of tight-binding GaAs/AlAs superlattices is studied by electrical time-of-flight experiments and by time-resolved photoluminescence. In the limit where the decay time of the photoluminescence is determined by transport (and not by recombination), we observe structures in the field dependences of both the optical and electrical response times which are related to resonances between different electronic subbands of adjacent wells. Here the time-resolved photoluminescence and the electrical time-of-flight experiment provide independent tools to investigate the dynamics of the conduction processes.
Is intrinsic bistability really intrinsic tristability?
Authors: Coon D. D. , Bandara K. M. S. V. , Zhao H.
Published: July 2002

The issue of intrinsic bistability in resonant tunneling devices is examined analytically and quantitatively. The results indicate that the putative argument for intrinsic bistability is actually an argument for intrinsic tristability. If a third stable configuration really exists, it might be hard to access experimentally although its existence could have consequences for high-speed device applications. If an intrinsic bistable regime is ipso facto a tristable regime, then an experimental search for a third stable configuration could provide persuasive evidence for the physical mechanism commonly advocated as the basis for intrinsic bistability.
High quality GaAs quantum well lasers grown on InP substrates by organometallic chemical vapor deposition
Authors: Chang-Hasnain C. J. , Lo Y. H. , Bhat R. , Stoffel N. G. , Lee T. P.
Published: July 2002

High quality GaAs quantum well lasers grown on (100) and 3°-off (100)InP substrates by organometallic chemical vapor deposition were investigated for the first time. 50-μm-wide broad-area gain-guided lasers were fabricated using preferential proton implantation. Low threshold densities, 800 and 1080 A/cm2, were obtained at room temperature for lasers with 1.25-mm-long cavities grown on 3°-off (100) and (100) oriented InP substrates, respectively. High quantum efficiency of 36% and nearly single longitudinal mode emission were also achieved from these lasers.
High-field perpendicular conduction in GaAs/AlAs superlattices
Authors: Sibille A. , Palmier J. F. , Minot C. , Mollot F.
Published: July 2002

Miniband conduction in undoped GaAs/AlAs superlattices (SLs) has been investigated through current-voltage measurements on n+-SL-n+ structures. From the comparison with simulations based on an effective medium approximation for the conduction through the superlattice, we directly obtain the field dependence of the electron velocity perpendicular to the layers. Our data show strong evidence of negative differential velocity in a 35.5/20 Å (well/barrier width) SL.
Application of organometallic vapor phase epitaxy on patterned substrates for a new monolithic laser waveguide butt coupling technique
Authors: Azoulay R. , Remiens D. , Menigaux L. , Dugrand L.
Published: July 2002

An important issue in the realization of monolithic optical circuits is the coupling of laser to optical waveguides. To obtain these structures, we have studied the epitaxial growth of GaAs/GaAlAs superlattices by organometallic vapor phase epitaxy on patterned substrates, with mesa along the [011] and the [011̄] directions. By careful adjustments of the mesa profile and on the layer thicknesses, we have grown in a single step structures containing a waveguide and a laser in such a way that the active layer and the transparent optical waveguides are directly butt jointed. Broad-area lasers exhibit typical threshold current of 1.5 kA/cm2. Coupling efficiency up to 70% has been measured on some devices.
Elimination of microtwins in silicon grown on sapphire by molecular beam epitaxy
Authors: Twigg M. E. , Richmond E. D. , Pellegrino J. G.
Published: July 2002

Using transmission electron microscopy, we have examined a number of (001) silicon thin films grown on (1̄012) sapphire substrates by molecular beam epitaxy (MBE). We have found that for silicon films less than 0.55 μm thick, microtwins are very much in evidence. For silicon films greater than 700 nm thick, however, dislocations, rather than microtwins, are the predominant defect. It is our conjecture that dislocation extension, and the associated disappearance of microtwins in thicker MBE-grown SOS films, is analogous to the generation of misfit dislocations in silicon-germanium films grown on silicon or germanium substrates by MBE; furthermore, these observations can be understood via the concept of excess stress that has been recently formulated by Tsao, Dodson, and others. The persistence of microtwins in SOS grown by chemical vapor deposition, as opposed to MBE-grown SOS, can be understood in terms of Dodson and Tsao’s formulation of plastic deformation kinetics in thin films.
Silicon epitaxial growth by rapid thermal processing chemical vapor deposition
Authors: Lee S. K. , Ku Y. H. , Kwong D. L.
Published: July 2002

High quality thin silicon epitaxial films have been grown on heavily doped p+ substrates using rapid thermal processing chemical vapor deposition with superior thickness and dopant profile control. The epitaxial growth kinetics have been studied by examining the dependence of growth rate on the deposition temperature, the volume percentage of SiH2Cl2, and the total gas flow rate. Submicron epitaxial layers with hyperabrupt dopant transition (<200 Å/decade) and excellent crystalline perfection with low defect density have been obtained.
Electroabsorption in single quantum well GaAs laser structures
Authors: Swanson P. D. , Tang T. K. , Givens M. E. , Miller L. M. , DeTemple T. A. , Coleman J. J.
Published: July 2002

The electric field dependent spectral properties of a GaAs graded barrier quantum well heterostructure laser are measured for the first time. Data are presented which show that the electroabsorption below the band gap is due to states in the confinement layers which are perturbed by the quantum well under high field conditions. This effect, which is intermediary between the quantum confined Stark effect and bulk Franz–Keldysh effect, should be present in all quantum well systems with shallow wells in short, high field depletion regions.
Isolation of the 110 K superconducting phase of Bi-Pb-Sr-Ca-Cu-O compounds
Authors: Escudero R. , Chavira E. , Rios-Jara D.
Published: July 2002

We have prepared 90% single-phase bulk samples of the 110 K superconducting phase of the Bi-Sr-Ca-Cu-O compounds with different Pb amounts. Critical superconducting temperatures (zero resistance) of up to 109 K were measured in the bulk samples. X-ray powder diffraction patterns of the almost isolated 110 K phase are presented. Computer-simulated diffractograms were obtained, which are in general agreement with the measured ones. A discussion of the role of Pb in the stability of the 110 K phase in this compound is presented.
Design of guided-wave components using growth of GaAs/AlGaAs superlattices on patterned substrates by organometallic chemical vapor deposition
Authors: Colas E. , Yi-Yan A. , Bhat R. , Seto M. , Deri R. J.
Published: July 2002

We demonstrate how an adequate choice of growth conditions and GaAs/AlGaAs superlattice series leads to a desired refractive index profile and to confinement of light at the cusp of a planarized structure over a previously photolithographically etched groove. Waveguiding at 1.52 μm wavelength with measured propagation losses of 1.5 dB/cm was obtained in these structures. The effect of growth parameters is discussed and potential applications of this concept to other structures suitable for guided-wave devices are proposed.
Plastic flow during thermal oxidation of silicon
Authors: Rafferty C. S. , Borucki L. , Dutton R. W.
Published: July 2002

Is silicon dioxide a viscous liquid or an elastic solid at silicon processing temperatures? Simple calculations using either assumption lead to gross discrepancies with experimental observations. This letter shows that a plastic flow model resolves these discrepancies. Flow develops much sooner than predicted by a linear viscoelastic model. Large deformations (<5%) are accommodated almost entirely by plastic flow. Small deformations are accommodated either elastically or by plastic flow depending on temperature.
Generation of acoustic phase conjugate waves using nonlinear electroacoustic interaction in LiNbO3
Authors: Ohno Masahiro
Published: July 2002

Acoustic phase conjugate waves were generated at 60 MHz using nonlinear electroacoustic interaction in LiNbO3. The phase conjugate reflectivity was measured as a function of the incident pulse duration. The amplitude reflectivity was of the order of 10−3 for a 1.8×104 V m−1 pump electric field and was proportional to the incident pulse duration, showing agreement with the theory.
Reduced reactivity to air on HF-treated YBa2Cu3O7−x surfaces
Authors: Vasquez R. P. , Hunt B. D. , Foote M. C.
Published: July 2002

Treatment of YBa2Cu3O7−x films with a nonaqueous solution of HF in absolute ethanol results in the formation of an oxyfluoride with relative Y:Ba:Cu concentrations of 1:4:3 on the surface, as determined by x-ray photoelectron spectroscopy. The passivation properties of chemically treated films were tested by monitoring the growth of the high binding energy O 1s peak, associated with nonsuperconducting surface species, as a function of air exposure time, for both HF-treated and untreated films. The native oxyfluoride is shown to reduce the reactivity of the superconductor to air.
Preparation of Y-Ba-Cu-O superconducting thin films using BaF2 as a buffer layer
Authors: Radpour F. , Singh R. , Sinha S. , Tulpule A. M. , Chou P. , Thakur R. P. S. , Rahmati M. , Hsu N. J. , Kumar A.
Published: July 2002

Thin films of barium fluoride (BaF2 ), used as a buffer layer between the substrate and the superconducting films, dramatically improve the properties of Y-Ba-Cu-O (YBCO) superconducting films deposited by metalorganic chemical vapor deposition on yttrium-stabilized zirconia (YSZ) substrates. For the as-deposited films at a substrate temperature of 780 °C, the observed transition temperature Tc of 80 K on the BaF2 /YSZ structure represents the highest value reported to date. By using BaF2 buffer layers, superconducting films formed by using a paste of the YBCO powder and a binder, on BaF2 /Si provided a Tc of 80 K.
Superconducting (Nd,Ce)2CuO4 thin films grown by rf magnetron sputtering
Authors: Adachi Hideaki , Hayashi Shigenori , Setsune Kentaro , Hatta Shin-ichiro , Mitsuyu Tsuneo , Wasa Kiyotaka
Published: July 2002

Thin films of an electron-doped-type (Nd,Ce)2CuO4 system have been prepared by rf magnetron sputtering and subsequent annealing. The films showed a highly oriented structure with the c axis normal to the film plane. They exhibited superconductivity after the reducing treatment by heating at 800–900 °C in vacuum. The resistivity of the films was fairly low with metallic characteristics, and the sign of the Hall coefficient was negative in the normal state. The sharp superconducting transition with zero resistivity at 22 K was observed for the film of Nd/Ce/Cu:1.855/0.145/1.2.
Origin of enhanced growth of the 110 K superconducting phase by Pb doping in the Bi-Sr-Ca-Cu-O system
Authors: Shi Donglu , Boley Mark S. , Chen J. G. , Xu Ming , Vandervoort K. , Liao Y. X. , Zangvil A. , Akujieze Justin , Segre Carlo
Published: July 2002

Kinetics of the 110 K superconducting phase formation has been studied in the Bi-Sr-Ca-Cu-O system with and without the addition of small amounts of lead. The kinetics of the phase transformation has been greatly affected by lead doping. The time required for the maximum formation of the 110 K phase is substantially reduced by the addition of lead. This phenomenon has been shown to be associated with the lead enhancing the nucleation and growth process of the 110 K phase and the diffusivity of calcium and copper.
New class of unstable orbits of the equilibrium electrons in free-electron lasers
Authors: Zhang Shi-Chang , Zhang Zhong
Published: July 2002

We present a theoretical prediction of a new class of unstable orbits of the equilibrium electrons in free-electron lasers, which is entirely associated with the radial self-electric field and azimuthal self-magnetic field. It is also pointed out that these self-fields may deteriorate the beam quality and thus decrease the growth rate of the free-electron laser mode.
Band offsets and deep defect distribution in hydrogenated amorphous silicon-crystalline silicon heterostructures
Authors: Essick John M. , Cohen J. David
Published: July 2002

Voltage filling pulse measurements taken on a-Si:H/c-Si heterostructure Schottky diode samples are used to examine the capture of electrons from the c-Si substrate into a-Si:H defect states. These measurements, along with the capacitance versus temperature spectra of these diodes, indicate a nearly zero conduction-band offset (50±50 meV). In addition, we have observed trapping of holes at the valence-band discontinuity ΔEv. A clear threshold for the subsequent optical release of these holes yields a value of ΔEv =0.58±0.02 eV. Our measurements also provide the energy and spatial distribution of deep defects within the a-Si:H layer and indicate a region of anomalously large defect density (1018 cm−3) within roughly 350 Å of the a-Si:H/c-Si interface.
Development of a cone-geometry positron moderator
Authors: Lynn K. G. , Gramsch E. , Usmar S. G. , Sferlazzo P.
Published: July 2002

Results are presented on a new cone-shaped positron moderator which shows a high moderator efficiency (i.e., conversion of beta decay to emitted slow positrons). The moderator efficiencies for the cone moderators studied were found to be up to 0.14% compared to thin-foil measurements of 0.06% in the same experimental system including identical source and holder. These moderators are rugged and easily fabricated, however, they have a lower brightness than single-crystal foil moderators. Comparison of various geometries is presented as well as suggestions for further improvements to increase the total efficiencies.
Correlation of thermally stimulated luminescence with radio frequency surface resistance of high-temperature superconductors
Authors: Cooke D. W. , Bennett B. , Gray E. R. , Houlton R. J. , Hults W. L. , Maez M. A. , Mayer A. , Smith J. L. , Jahan M. S.
Published: July 2002

We recently demonstrated that insulating surface impurity phases in high-temperature superconductors can be detected by thermally stimulated luminescence. Moreover, we suggested that the intensity of luminescence is related to the magnitude of the rf surface resistance. In this work we show that a quantitative correlation exists between these two quantities, and that luminescence can be a very useful technique for estimating rf surface resistance.
Reduction of Be diffusion in GaAs by migration-enhanced epitaxy
Authors: Tadayon Bijan , Tadayon Saied , Schaff W. J. , Spencer M. G. , Harris G. L. , Tasker P. J. , Wood C. E. C. , Eastman L. F.
Published: July 2002

Be-doped GaAs layers were grown by the migration-enhanced epitaxy (MEE) method at 300 °C. The MEE layers showed practically no electrical activation. Rapid thermal annealing on the MEE layers resulted in mobility and hole concentration comparable to those of conventional molecular beam epitaxy (MBE) layers grown at 600 °C. Secondary-ion mass spectroscopy showed that the Be diffusion in annealed MEE layers was much smaller than that in conventional MBE layers, especially for highly doped layers. Raman spectroscopy and 4 K photoluminescence were also performed. The MEE method can replace the conventional MBE method for device applications which require high hole concentration with small diffusion.
Crystallization kinetics for quenched Bi-Ca-Sr-Cu-O glasses
Authors: Tatsumisago M. , Angell C. A. , Akamatsu Y. , Tsuboi S. , Tohge N. , Minami T.
Published: July 2002

The kinetics of crystallization in the BixCaSrCu2Ow (x=1.5, 2.7) glasses prepared by twin-roller and metal-plate quenching methods have been studied by a nonisothermal method using differential scanning calorimetry. Scanning electron microscopy studies suggest surface crystallization as the dominant mechanism. The activation energy for crystal growth calculated from modified Kissinger plots assuming surface nucleation decreased with an increase in the Bi content. Such a composition dependence is consistent with that of the activation energy for viscous flow in the glass transformation range.
Optical blue shift in a double quantum well structure under an electric field
Authors: Campi Domenico , Alibert Claude
Published: July 2002

A calculation for an effective mass model of a double quantum well structure subjected to a moderate electric field is presented. The behavior of the transitions between energy levels is investigated, allowing prediction of an effective blue shift in the optical spectrum of this simple system. It is suggested that the optimum strategy for obtaining a rapid effect is to reduce the coupling between the heavy hole states.
Comment on ‘‘Ion mixing of metal/Al bilayers near 77 K’’ [Appl. Phys. Lett. 5
4, 413 (1989)]
Authors: Vasconcellos M. A. Z. , Borges da Costa J. A. T. , Schreiner W. H. , Baumvol I. J. R.
Published: July 2002

The correct mixing efficiency for the Fe/Al bilayer (900 keV Xe +3 , 77K) is presented in the context of the recent analysis by Ma, IE.E., Work man, W.L>, Johnson, W.L., and Nicolet, M.A. (AIP)
Timing synchronization of a passively mode-locked dye laser using a pulsed optical phase lock loop
Authors: Dijaili S. P. , Smith J. S. , Dienes A.
Published: July 2002

Timing sychronization between a colliding-pulse mode-locked dye laser and a gain-switched Fabry–Perot-type AlGaAs laser diode has been achieved with less than 40 fs of relative timing jitter by using a pulsed optical phase lock loop. The relative timing jitter was measured using the error voltage of the feedback loop which has a 5 kHz bandwidth. This technique of measuring the relative timing jitter is accurate since the frequencies of all the timing fluctuations fall within the loop bandwidth. The novel element in the implementation of the pulsed optical phase lock loop is the time delay discriminator which is based on a cross correlation between the two pulse trains. Under locked conditions, the output of the cross correlator operates quiescently about a point of nonzero temporal slope.
Photorefractive characterization of deep level compensation in semi-insulating GaAs
Authors: Partovi Afshin , Garmire Elsa M. , Valley George C. , Klein Marvin B.
Published: July 2002

We show that photorefractive beam coupling can be used for deep level spectroscopy in semi-insulating GaAs. In four samples cut from different locations in a single boule of GaAs, we find the same degree of compensation as determined from absorption spectra, Hall measurements, and the photorefractive effect. In the most compensated of our samples, the sign of the photorefractive beam coupling changes from electron to hole dominated as the optical wavelength is changed from 1.06 to 1.15 μm. Furthermore, we show that absorption spectra for semi-insulating GaAs can be used to choose samples for optimal photorefractive behavior at wavelengths of 0.9–1.5 μm.
Capture of photoexcited carriers by a laser structure
Authors: Deveaud B. , Clérot F. , Regreny A. , Fujiwara K. , Mitsunaga K. , Ohta J.
Published: July 2002

The capture of photoexcited carriers in different laser structures is investigated by subpicosecond luminescence spectroscopy. The capture time at 20 and 80 K is monitored by the decay of the luminescence of the confinement layers. It is found to range between 2 and 3 ps for both linear and parabolic grading, and to be much longer in nongraded structures. The improvement of the capture in the case of graded structures is due to the quasi-electric field experienced by the carriers, and might allow the devices to run at much higher frequencies.
Au-Ag ion mixing rate—disagreement with theory resolved
Authors: Bo/rgesen P. , Lilienfeld D. A. , Johnson H. H.
Published: July 2002

Measurements of the low-temperature mixing of several 5d–4d bilayers by 600 keV Xe ions have strongly supported the assumption of a thermal spike mechanism. Quite disturbingly, however, the Au-Ag mixing rate appeared to exceed theoretical predictions by about a factor of 3. A closer examination of this system shows the discrepancy to be caused by the formation of a strongly nonuniform Au surface structure during irradiation. An improved value for the mixing rate is in reasonable agreement with predictions.
Critical steps in the molecular beam epitaxy of high quality Ag/Fe superlattices on (001) GaAs
Authors: Etienne P. , Massies J. , Nguyen-Van-Dau F. , Barthélémy A. , Fert A.
Published: July 2002

It is shown that high quality Ag/Fe superlattices can be grown on (001) GaAs by molecular beam epitaxy, provided that adequate intermediate layers are interposed between the GaAs substrate and the superlattice structure. In addition to the growth of a GaAs buffer layer, a sufficiently thick Fe nucleation layer is necessary for the further growth of a high quality Ag buffer layer showing clear reflection high-energy electron diffraction intensity oscillations. This growth sequence ensures the obtention of single-crystal Ag/Fe superlattices with well-defined interfaces.
Magneto-optics of a quasi-zero-dimensional electron gas
Authors: Liu C. T. , Nakamura K. , Tsui D. C. , Ismail K. , Antoniadis D. A. , Smith Henry I.
Published: July 2002

We have investigated theoretically and experimentally the energy levels and allowed optical transitions with energies ΔE of a quasi-zero-dimensional (Q0D) electron gas in a magnetic field B. Using a two-dimensional harmonic confining potential with oscillator frequency ω0, the theory predicts two values for ΔE. The resonance position in the magnetotransmission spectra from the Q0D system realized on a grid-gate GaAs/AlGaAs heterostructure, depends strongly on the 2D confining potential induced by the gate voltage Vg and, when Vg=−0.5 and −1.5 V, agrees with ΔE calculated with ℏω0=1.5 and 2.8 meV, respectively.
Thermal stability of Si/GexSi1−x/Si heterostructures
Authors: Hull R. , Bean J. C.
Published: July 2002

The thermal stability of Si/GexSi1−x/Si (100) heterostructures is studied by in situ electron microscope observations of the thermal relaxation process. Structures are observed to relax by misfit dislocation propagation at both strained interfaces, and are stable to significantly higher temperatures than equivalent strained GexSi1−x layers at a free surface. This observed difference in thermal stability between double and single interface structures is due at least in part to much lower dislocation velocities in the double interface structures, with a measured glide activation energy approximately twice as high as single interface structures. It is argued that this difference in glide activation energies may be due to a smaller kink nucleation activation energy in the single interface structure.
Spectroscopic determination of the electrostatic potential profile in a plasma-prefilled ion diode
Authors: Coleman M. D. , Hammer D. A.
Published: July 2002

The electrostatic potential profile in the accelerating gap in a plasma-prefilled magnetically insulated intense pulsed ion beam diode has been determined using laser-induced fluorescence spectroscopy. Results for a 300–400 kV planar diode are presented, both with and without an electron emitting vane protruding from the cathode. In both cases, a 5–6 mm accelerating gap forms in the 1012–1013/cm3 plasma in a few nanoseconds. The experimental potential profiles are not consistent with electrons confined to a sheath near the cathode. Rather, electrons are required throughout the gap to explain the observations.