So far, the design of new multifunctional devices based on the combination of different materials has been a real challenge in materials science. One way to develop multifunctional materials is the design of a surface at the nanometer scale. However, modifying the surface of materials by organizing nanoparticles of controlled size, morphology and amount of coverage into a uniform shell has proven to be a considerable hurdle. Numerous approaches are being developed for the synthesis of these materials using organic or inorganic coatings. French researchers used a coating process called supercritical fluid chemical deposition for nanomaterial surface design.
Conventional methods for surface modifications such as chemical vapor deposition, atomic layer deposition or various solution-based approaches are not convenient for modifying surfaces of particles with different materials at the nanoscale. Rather, processes using supercritical fluids are an interesting alternative here.
Dr. Cyril Aymonier from the Bordeaux Institute of Condensed Matter Chemistry explained the process to Nanowerk: "Supercritical fluid deposition (SFCD) is the most convenient of the supercritical fluid processes for the design of surfaces with inorganic nanoparticles. It consists of dissolving metallic precursors in a supercritical medium, generally CO2 (environmentally friendly, cheap, low critical coordinates...), in which the particles to be coated are suspended. Metallic precursors with fluorous ligands such as hexafluoroacetylacetonates (M(hfac)x ) are mostly used owing to their high solubility in scCO2. These metallic precursors are chemically transformed to give the subsequent metal that deposits onto the surface of particles."
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By Michael Berger, Copyright 2006 Nanowerk LLC