International tourism : identity and change

x, 246 p. ; 24 cm

A thorough FT-IR spectroscopy study on micrometric silicon oxide films deposited by atmospheric pressure microwave plasma torch

International audienceSiOxHyCz micrometer thick films are deposited from an argon/hexamethyldisiloxane mixture on Si (100) substrate by plasma enhanced chemical vapour deposition process using an axial injection torch at atmospheric pressure. Results highlight a similar effect of low and high substrate temperatures both on the deposition process and on the microstructure of the deposited films. Mesoscopically, scanning electron microscopy analyses reveal that particles are promptly produced in the gas phase and incorporated to the film. Microscopically, a detailed infrared analysis in transmission mode demonstrates a high carbon contamination in the low and high temperature intervals resulting in a lower stoichiometry. This work allows to define an optimum growth window for the substrate temperature, leading to smooth, particle-free and carbon-free films: [60 ◦ C; 90 ◦ C]

Elaboration of Nano-SiC / Carbon Nanotubes Composites: Mechanical, Thermal and Electric Properties

International audienceCeramic carbides materials such as SiC, due to their refractory nature and their low neutron absorption are believed to be promising candidates for high temperature nuclear or aerospace applications. However, SiC brittleness has limited its structural application. In order to overcome this drawback, a reduction of grain size below 100 nm is expected to enhance mechanical properties. On the other hand, the grain downsizing should result in a strong decrease of the thermal conductivity because of the enhanced phonon scattering at the grain boundaries. In order to counteract this effect, multiwall carbon nanotubes (MWCNTs) could be of great interest because of their interesting thermal properties. Moreover, MWCNTs show a strong toughness which should also help to enhance the mechanical properties as reviewed by several authors. We report here the study of the elaboration of such nanoSiC / MWCNTs composites using gas-phase synthesized nano-objects together with the related thermal, electric and mechanical properties. For this study, the starting nanoscale building blocks (nanoparticles and nanotubes) were synthesized by gas phases processes. β-SiC nanopowders with a mean particle smaller than 20 nm were obtained by a laser assisted CVD flow process, namely laser pyrolysis, using a CO2 laser to decompose the gaseous precursors (silane and acetylene). MWCNTs several hundred microns in length were grownas carpets on substratesby continuous catalytic CVDusing an aerosol oftoluene and ferrocene used as carbon and catalytic iron precursors, respectively. Dispersion of SiC nanopowders was obtained in an aqueous medium under magnetic stirring with dedicated dispersing agent. Several samples were prepared, differing in surface composition (C or Si excess) and sintering additives content (from 0 to few wt%). MWCNTs were dispersed by means of an ultrasonic probe and subsequently mixed with SiC slurries with different concentrations. Green bodies were then prepared by slip-casting.In order to avoid grain growth while keeping satisfying densification, spark plasma sintering(SPS)was used for this study. Thanks to this fast sintering process, SiC matrix grain size was kept under 100 nm while final densities were higher than 96%. Finally, samples with different chemical (Si, O, C) compositions and MWCNTs contents were subjected to mechanical characterization (hardness, toughness), resistivity,and thermal conductivity measurements with the aim of correlating the final microstructures to the mechanical, electricand thermal behavior

Ordering of SiOxHyCz islands deposited by atmospheric pressure microwave plasma torch on Si(100) substrates patterned by nanoindentation

International audienceSiOxHyCz nanometric layers are deposited from hexamethyldisiloxane by atmospheric pressure microwave plasma torch on Si(100) substrates submitted to temperatures varying on the range [0 ◦ C; 120 ◦C]. Atomic force microscopy (AFM) characterizations of samples grown at intermediate substrate temperatures (∼30 ◦C) demonstrate a layer-by-layer growth (Frank van der Merwe growth) leading to smooth flat and compact films while films deposited at lower and higher substrates temperatures show an island-like growth (Volmer-Weber growth) generating a high surface roughness. Concomitantly, a detailed infrared spectroscopy analysis of the growing films evidences structural modifications due to changes in the bond types, Si-O-Si conformation and stoichiometry correlated with scanning electron microscopy and AFM characterizations. Then, deposition conditions and specific microstructure are selected with the aim of generating 3-dimensional SiOxHyCz nanostructure arrays on nanoindented Si (100) templates. The first results are discussed

Depositon of nanometric SiOxHyCz films at different substrate temperatures by an atmospheric pressure microwave plasma torch (TIA) : first steps towards self-assembled 3-dimensional nano-sensors

International audienc

Nano-SiC / Carbon Nanotubes Composites : Elaboration and Thermomechanical Properties.

International audienc