IN SITU PROCESSING OF InP BY FLASH LPCVD FOR SURFACE PREPARATION AND GATE OXIDE DEPOSITION

Des films de silice sont réalisés dans un réacteur CVD opérant à basse pression, refroidi par air et eau et commandé par chauffage optique rapide. Des vitesses de dépôt allant jusqu'à 100 Å/sec sont obtenues sous un flash thermique de 700°C. Ces dépôts sont effectués sur InP sans que sa surface soit endommagée. Les structures InP/SiO2 ainsi formées ont d'excellentes propriétés électriques adaptées aux exigences du MISET. L'amélioration des propriétés d'interface de cette structure est obtenue par exposition de la surface d'InP au silane avant le dépôt d'oxide. Une étude de surface indique que le silane réduit les oxydes natifs d'InP.Silicon dioxide films deposited on InP substrates are obtained in a reduced pressure, air and water cooled CVD reactor, with a rapid thermal heating. It is shown that a 700°C temperature flash results in SiO2 deposition rates close to 100 Å/sec. High temperature deposition (700°C) is thus obtained in few seconds on InP substrates without any surface damage. These layers display excellent electrical properties well suited for MISFET applications. Improvement of the interface properties of this structure is obtained by flowing silane on the InP substrate prior to oxide deposition. Interface studies show that silane reduces the InP native oxides

SURFACE MECHANISMS IN THE UVCVD OF SiO2 FILMS

Surface-sensitive multiple internal reflection absorption infrared spectroscopy has been applied to the study of the growth of SiO2 films under far ultraviolet illumination. Spectra provide evidence for a previously unreported Si-H absorption peak occurring at 2208 cm-1. It is shown that this line characterizes the molecular structure of the photochemisorption site of silane and that this phenomenon occurs on sites including hydroxyl groups which are also produced in a photochemical gas-solid process. In the first step of silane photochemisorption, photoexcitation occurs on the surface while in the oxidization step, photoexcitation of oxygen molecules is an active process in the gas phase

Spéciation et flux des métaux-trace dans une station d'épuration importante : impact des traitements successifs

International audienceSeven metals (Cd, Co, Cr, Cu, Fe, Ni and Pb) were monitored at the Seine-Aval wastewater treatment plant during 6 sampling campaigns in April 2004. Particulate and dissolved metals have been measured in 24 h composite samples at each treatment stage (primary settling, secondary activated sludge and tertiary flocculation by FeCl3). In addition, the diffusive gradient in thin film technique (DGT) was used to determine the dissolved inert and labile metal fraction. Although all treatment stages were able to decrease particulate metals concentrations in wastewater, most dissolved metals concentrations were mainly affected during primary settling. This unexpected result was attributed to tertiary sludge filtrate recirculation. Metals added via the FeCl3 reagent at the tertiary treatment were shown to lower the overall Cr removal from wastewater and to enrich Ni in effluents. The plant operating conditions (recirculation and reagent addition) appear therefore as important as treatment processes for the metals removal. Total metal fluxes were highly decreased by the whole treatment plant for Cd, Cr, Cu and Pb and to a lesser extend for Co and Ni. However, the labile metal fluxes were poorly decreased for Cu (18%), not significantly decreased for Ni and increased for Fe. The labile fraction of Cd, Co and Cr was not detectable at any stage of the plant. Discharged labile fluxes, at least for Ni, were potentially significant compared to the labile metal fluxes in the river measured downstream the plant. Treated urban wastewater discharges should be carefully considered as a possible source of bioavailable trace metals

MOCVD InP/AlGaInAs distributed Bragg reflector for 1.55 [micro sign]m VCSELs

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Experimental observation of double-walled peptide nanotubes and monodispersity modeling of the number of walls

Self-assembled nanoarchitectures based on biological molecules are attractive because of the simplicity and versatility of the building blocks. However, size control is still a challenge. This control is only possible when a given system is deeply understood. Such is the case with the lanreotide acetate, an octapeptide salt that spontaneously forms monodisperse nanotubes when dissolved into pure water. Following a structural approach, we have in the past demonstrated the possibility to tune the diameter of these nanotubes while keeping a strict monodispersity, either by chemical modification of one precise amino acid on the peptide sequence or by changing the size of the counterions. On the basis of these previous studies, we replaced monovalent counterions by divalent ones to vary the number of walls. Indeed, in the present work, we show that lanreotide associated with a divalent counterion forms double-walled nanotubes while keeping the average diameter constant. However, the strict monodispersity of the number of walls was unexpected. We propose that the divalent counterions create an adhesion force that can drive the wall packing. This adhesion force is counterbalanced by a mechanical one that is related to the stiffness of the peptide wall. By taking into account these two opposite forces, we have built a general model that fully explains why the lanreotide nanotubes formed with divalent counterions possess two walls and not more

Tailoring the photoelectrochemistry of catalytic metal-insulator-semiconductor (MIS) photoanodes by a dissolution method

International audienceApart from being key structures of modern microelectronics, metal-insulator-semiconductor (MIS) junctions are highly promising electrodes for artificial leaves, i.e. photoelectrochemical cells that can convert sunlight into energy-rich fuels. Here, we demonstrate that homogeneous Si/SiO x /Ni MIS junctions, employed as photoanodes, can be functionalized with a redox-active species and simultaneously converted into high-photovoltage inhomogeneous MIS junctions by electrochemical dissolution. We also report on the considerable enhancement of performance towards urea oxidation, induced by this process. Finally, we demonstrate that both phenomena can be employed synergistically to design highly-efficient Si-based photoanodes. These findings open doors for the manufacturing of artificial leaves that can generate H 2 under solar illumination using contaminated water

Structural role of counterions adsorbed on self-assembled peptide nanotubes

Among noncovalent forces, electrostatic ones are the strongest and possess a rather long-range action. For these reasons, charges and counterions play a prominent role in self-assembly processes in water and therefore in many biological systems. However, the complexity of the biological media often hinders a detailed understanding of all the electrostatic-related events. In this context, we have studied the role of charges and counterions in the self-assembly of lanreotide, a cationic octapeptide. This peptide spontaneously forms monodisperse nanotubes (NTs) above a critical concentration when solubilized in pure water. Free from any screening buffer, we assessed the interactions between the different peptide oligomers and counterions in solutions, above and below the critical assembly concentration. Our results provide explanations for the selection of a dimeric building block instead of a monomeric one. Indeed, the apparent charge of the dimers is lower than that of the monomers because of strong chemisorption. This phenomenon has two consequences: (i) the dimer-dimer interaction is less repulsive than the monomer-monomer one and (ii) the lowered charge of the dimeric building block weakens the electrostatic repulsion from the positively charged NT walls. Moreover, additional counterion condensation (physisorption) occurs on the NT wall. We furthermore show that the counterions interacting with the NTs play a structural role as they tune the NTs diameter. We demonstrate by a simple model that counterions adsorption sites located on the inner face of the NT walls are responsible for this size control

Atomic view of the histidine environment stabilizing higher-pH conformations of pH-dependent proteins

External stimuli are powerful tools that naturally control protein assemblies and functions. For example, during viral entry and exit changes in pH are known to trigger large protein conformational changes. However, the molecular features stabilizing the higher pH structures remain unclear. Here we elucidate the conformational change of a self-assembling peptide that forms either small or large nanotubes dependent on the pH. The sub-angstrom high-pH peptide structure reveals a globular conformation stabilized through a strong histidine-serine H-bond and a tight histidine-aromatic packing. Lowering the pH induces histidine protonation, disrupts these interactions and triggers a large change to an extended β-sheet-based conformation. Re-visiting available structures of proteins with pH-dependent conformations reveals both histidine-containing aromatic pockets and histidine-serine proximity as key motifs in higher pH structures. The mechanism discovered in this study may thus be generally used by pH-dependent proteins and opens new prospects in the field of nanomaterials