Chemical Vapor Deposition of silicon nanodots on TiO2 submicronic powders in vibrated fluidized bed
Résumé
Silicon nanodots have been deposited on TiO2 submicronic powders in a vibrated Fluidized Bed Chemical Vapor Deposition (FBCVD) reactor from silane SiH4. Deposition conditions involving very low deposition rates have been studied. After treatment, powders are under the form of micronic agglomerates. In the operating range tested, this agglomerates formation mainly depends on the fluidization conditions and not on the CVD parameters. The best results have been obtained for anatase TiO2 powders for which the conditions of fluidization have been the most optimized. For these anatase powders, agglomerates are porous. SEM and TEM imaging prove that silicon nanodots (8-10 nm in size) have been deposited on the surface of particles and that this deposition is uniform on the whole powders and conformal around each grain, even if not fully continuous. Raman spectroscopy shows that the TiO2 powders have been partially reduced into TiO2-x during deposition. The TiO2 stoichiometry can be recovered by annealing under air, and IR spectroscopy indicates that the deposited silicon nanodots have been at least partly oxidized into SiO2 after this annealing.