Surface chemical studies of the influence of In and Al on the decomposition of TEG on GaAs(100)

The interaction of triethylgallium (TEG) with the Ga-stabilized GaAs(100) surface in the presence of In and Al has been investigated using AES (Auger electron spectroscopy), HREELS (high resolution electron energy loss spectroscopy) and TDS (thermal desorption spectroscopy) techniques. Al is shown to greatly increase the saturation surface coverage of TEG on the surface and to suppress the desorption of TEG and diethylgallium (DEG). Etching of the surface Al by TEG is observed, resulting in the formation of gas phase Al organic species. Alkyl migration from GA to Al centres occurs, and the presence of Al substantially enhances the irreversible deposition of C. In is found to enhance DEG desorption and to lower the temperature at which absorbed ethyl groups decompose to gas phase ethene. Computer modelling has been carried out to extract kinetic parameters from measured thermal desorption spectra. These parameters are then used to calculate expected partial growth rates of GaAs during the growth of Ga_xAl_1−xAs and Ga_xIn_1−xAs using TEG. The data provide a molecular level understanding of the GaAs pa rtial growth rate variations arising during the deposition of III–V ternary materials.     

An aqueous route to organically functionalized silica diatom skeletons

Diatomaceous earth was functionalized by grafting organotrialkoxysilane precursors onto the surface of the porous silica cell walls of this biomineral. Vinyl- and mercapto-containing structures were prepared in aqueous media without disruption of the diatomic architecture. Successful grafting of the organic moieties was confirmed using solid state ²⁹Si MAS NMR spectroscopy, and the presence of the intact diatom framework by scanning electron microscopy. The sorption properties of mercaptopropyl-functionalized diatoms towards heavy metals was studied by measuring the accessibility and diffusion rates of mercury(II) species to the binding sites (-SH) by the means of electrochemical methods.     

Selected-area growth of carbon nanotubes by the combination of focused ion beam and chemical vapor deposition techniques.

In this article, we report a technique for growing carbon nanotubes in a more controllable fashion, which enables us to synthesize nanotubes directly in various forms of designed patterns. This nanofabrication process is based on a combination of focused ion beam (FIB) and chemical vapor deposition (CVD) techniques. In this process, arrays of conductive patterns were first deposited on silicon substrates by directing a gaseous compound (C(9)H(16)Pt) via the capillary needle-sized nozzles within a FIB system. The substrates were then coated with catalyst and further modified by the FIB to localize the position of the catalyst. Finally, the growth of carbon nanotubes on the designed substrates was carried out by CVD of hydrocarbon gases. This fabrication technique has the advantage of positioning carbon nanotubes in selected locations. This may open up opportunities for the direct synthesis of carbon nanotubes onto almost any substrate material, thus allowing fabrication of carbon nanotube-based devices.     

Uniqueness and continuous dependence on the initial data for a class of non-linear shallow shell problems

This note is concerned with the non-linear shallow shell model introduced in 1966 by W.T. Koiter, and later studied by M. Bernadou and J.T. Oden. We show the uniqueness of the solution to the dynamical model and that this solution is continuous with respect to the initial data. To cite this article: J. Cagnol et al., C. R. Acad. Sci. Paris, Ser. I 342 (2006).     

Efficient synthesis of an imidazole-substituted delta-amino acid by the integration of chiral technologies

Two methods to produce (2S)-5-amino-2-(1-n-propyl-1H-imidazol-4-ylmethyl)-pentanoic acid were investigated. Diastereoisomeric salt resolution, using the quinidine salt, gave the desired intermediate in 98% ee and 33% yield. Asymmetric hydrogenation of various substrates gave high conversions, with up to 83% ee. Integration of these two approaches via asymmetric hydrogenation of a quinidine salt substrate followed by crystallization provided the desired intermediate in 94% ee and 76% yield.     

Lamellar Organo-Bridged Silicones

The acid-hydrolysis of an organo-bridged bisdiethoxysilylated molecular precursor bearing urea groups, (EtO)₂MeSi(CH₂)₃NHCONH(CH₂)₁₂NHCONH(CH₂)₃SiMe(OEt)₂, has been performed in pure aqueous medium. Scanning electron microscopy (SEM) analysis of the resulting insoluble solid revealed plate-like forms with a lamellar structure as determined by powder X-ray diffraction (PXRD) studies with a sharp peak at 28.5 Å. The solid state ²⁹Si MAS-NMR spectrum of this bridged siloxane hybrid is consistent with a moderately condensed material with complete preservation of the Si–C bonds throughout the hybrid network. In comparison, the classical sol–gel hydrolysis-condensation of the molecular precursor in ethanol with stoichiometric amount of water and fluoride anion as catalyst produced an amorphous featureless solid.     

Syntheses of Two Potential Ligands for Tc-99m Labeling as Diagnosis Agents of Alzheimer''''s Disease

Two types of ligands-biphenyl and stilbene derivatives, whichcan be labeled with Tc-99m for the diagnosis of Alzheimer'sdisease (AD) have been synthesized successfully. The key stepsin these two syntheses involved Suzuki reaction and Wittig reac-tion respectively. The new discovered debromination reactionmay be expanded to the compounds with double or triple bondadjacent to the carbon atom bearing the bromine atoms. Thesetypes of syntheses provide a route to a series of biphenyl andstilbene derivatives that will benefit the search of new imagingagents for AD.