Chemical Kinetics of Photoinduced Chemical Vapor Deposition: Silica Coating of Gas-Phase Nanoparticles

Experimental studies of gas-phase nanoparticle coating by photoinduced chemical vapor deposition (photoCVD) have shown that silica coatings can be produced with controllable thicknesses on different nanoparticle cores for a variety of applications. This study presents a chemical reaction sequence for the photo-CVD process to describe the production of silica coatings from the decomposition of tetraethyl orthosilicate (TEOS). The model incorporates photochemical reactions into known thermal reaction sequences involving gas-phase and surface reactions to describe the nanoparticle coating process. Modeled results of the photo-CVDprocess indicate that the dominant reactions for the production of silica coatings on the surface of the nanoparticles are the photodecomposition of TEOS and the removal of surface ethyl groups from adsorbed TEOS species. Relative concentrations of gas-phase and surface species are compared for different model configurations and system parameters. Modeled coating thicknesses agree well with experimental findings and demonstrate that coating thickness increases with increasing TEOS concentration and increased residence time within the reaction chamber.