Dislocation propagation in GaN films formed by epitaxial lateral overgrowth

We have investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) the relationship between surface morphological evolution and dislocation propagation in GaN films formed by epitaxial lateral overgrowth (ELO) in hydride vapour phase epitaxy. The SEM observations revealed that step and terrace structures were formed on (0001) surfaces of the films both in the earlier and the later stages of growth, suggesting the occurrence of step-flow growth during ELO. Bending dislocations with laterally propagated segments were frequently observed in the ELO films and their morphology led to a reduction in threading dislocation density in the film surface regions. Systematic TEM observations were performed to reveal the detailed structure of the bending dislocations. Comparison between the SEM and the TEM results showed that the lateral propagation of the dislocation was closely related to the appearance of the [1101) facets. A mechanism for dislocation propagation is discussed that explains the observed dislocation structure and surface step morphology.     

C60 thin-film transistors with high field-effect mobility,fabricated by molecular beam deposition

We report performance of C₆₀ thin-film field-effect transistors and characterizations of C₆₀ thin-films on SiO₂ substrates fabricated by molecular beam deposition. Devices, fabricated and characterized under high vacuum without exposing to air, routinely showed current on/off ratios >10⁸ and field-effect mobility in the range of 0.5–0.3 cm²/V s. The obtained mobility is comparable to the highest value among n-type organic thin-film transistors and close to that derived from the photocurrent measurements on C₆₀ thin-films.The grain size of C₆₀ thin-film, condensed in an fcc solid, increases with the substrate temperature, while themobility did not exhibit a clear relation with substrate temperature.

© 2003 Elsevier Ltd. All rights reserved.     

Current Issues of Intercalation and Superconductivity in Solid State Fullerenes

Abstract

Co-intercalation of alkali metals and neutral molecules into C₆₀ have been investigated. Successful synthesis of this class of materials provides us a new insight into superconductivity and other physical properties; such as criterion for the occurrence of superconductivity and metal-insulator transitions. Based on the recently synthesized ammoniated fullerides, we discuss on the relation between the structure, and electronic properties.     

Imaging polarimetry and retinal blood vessel quantification at the epiretinal membrane

We evaluated a polarimetry method to enhance retinal blood vessels masked by the epiretinal membrane. Depolarized light images were computed by removing the polarization retaining light reaching the instrument and were compared with parallel polarized light images, average reflectance images, and the corresponding images at 514 nm. Contrasts were computed for retinal vessel profiles for arteries and veins. Contrasts were higher in the 514 nm images in normal eyes but higher in the depolarized light image in the eyes with epiretinal membranes. Depolarized light images were useful for examining the retinal vasculature in the presence of retinal disease.     

Anisotropic lattice coherency of GaAs nanocrystals deposited on Si(100) surface by molecular beam epitaxy

Lattice coherency and morphology of GaAs nanocrystals grown on Si(100) substrate have been studied by transmission electron microscope in order to see growth mechanism of the nanocrystals. GaAs nanocrystals consisting of four {111} facet planes and a rectangular basal plane with four sides along [01 ] and [011] directions have grown on the Si surface. Either (011) or (01) lattice planes along the minor axis on the rectangular basal plane in the GaAs nanocrystal are completely-coherent with {011} lattice planes in the Si substrate. On the other hand, another (01) or (011) lattice planes along the major axis are partially-coherent with those in the Si substrate. When the lattice planes of the either (011) or (01), which is randomly determined by local atomic structures, become partially-coherent with those in the Si substrate to relax accumulated lattice strain, the growth rate of nanocrystal is remarkably increased along the direction parallel to unstrained (011) or (01) planes which prevents from each area of the strained {011} planes in the nanocrystals increasing. The anisotropic lattice coherency between the GaAs nanocrystals and the Si substrate causes the anisotropic morphology of the GaAs nanocrystals which is elongated the directions parallel to the strained {011} planes.     

A cytoplasmic xylanase (XynX) of Aeromonas caviae ME-1 is released from the cytoplasm to the periplasm by osmotic downshock

Aeromonas caviae ME-1 is a multiple xylanase-producing gram-negative bacterium which was isolated from the gut contents of a wild silkworm, Samia cynthia pryeri. One of the xylanases produced by A. caviae ME-1, XynX (38 kDa, family 10 xylanase), hydrolyzes xylan to xylobiose and xylotetraose as final degradation products. Generally, xylanases are extracellular or cell surface enzymes. However, XynX is not exported to the extracellular fluid by A. caviae ME-1 and an Escherichia coli transformant harboring the xynX gene. In this study, we investigated the intracellular localization of XynX in A. caviae ME-1 and an E. coli transformant. XynX was found in the cytoplasm when the cells were grown under normal culture conditions. However, XynX was released from the cytoplasm to the periplasm during osmotic downshock. This release of XynX in the E. coli transformant was blocked in the presence of gadolinium chloride, which has been reported to be an inhibitor of bacterial mechanosensitive channels.     

Effect of electrode ice layer on prebreakdown current in liquidnitrogen

The effect of ice on dc prebreakdown events was investigated using a needle-to-plane electrode system in liquid nitrogen at 77.3 K. It was found that H₂O ice has marked effects on prebreakdown current, corona onset voltage and breakdown voltage. The breakdown voltage at atmospheric pressure depends on microscopic cracks in H₂ O ice     

Synthesis and Electron Paramagnetic Resonance Studies of Oligodeoxynucleotides Containing 2‐N‐tert‐Butylaminoxyl‐2′‐deoxyadenosines

Oligodeoxynucleotides (ODNs) containing 2‐N‐tert‐butylaminoxyl‐2′‐deoxyadenosine ( A* ) residues were synthesized to allow accurate monitoring of adenine motion by EPR spectroscopy through the agency of direct linkage of the acyclic aminoxyl group to the nucleobase, and EPR studies of the ODNs in single‐ and double‐stranded forms were performed. Upon duplex formation, peak broadening and decreases in peak height were observed in EPR spectra, and the synthesized ODNs were shown to be excellent monitors of hybridization. Comparison of peak height and the h₁/h₀ signal ratio provided information on the relative mobility of A* in duplexes with different stability. A second set of ODNs each containing two A* residues at different intervals and four dA residues were also synthesized. For these ODNs, correlations were observed between the EPR spectral shapes of the duplexes and the number of dA residues between A* residues, thus demonstrating the potential of A* residues in monitoring of the structures of nucleic acids.     

Room Temperature Ambient Pressure (RTAP)‐Hydroformylation in Water Using a Self‐Assembling Ligand

We herein demonstrate a hydroformylation at room temperature and ambient pressure (RTAP) using our Rh/6‐DPPon ( 1 ) system in aqueous media. The hydrogen bonding network of the ligand backbone stays intact, exemplified by the excellent regioselectivity for the linear aldehyde. Various substrates with different functional groups (with some prone to hydrolysis) are stable under the applied conditions and can undergo hydroformylation resulting in good yields.