Atomic layer deposition of SnOx onto mesoporous, nanocrsytalline TiO2 and SnO2 thin films

Abstract

The atomic layer deposition of tetrakisdimethylamidotin(IV) and water on mesoporous thin films of nanocrystalline anatase TiO2, rutile SnO2, and rutile TiO2 was investigated. For all deposition conditions tested, highly oxygen deficient coatings were created; purge time and temperature were found to be the factors most affecting the stoichiometry. Long purge times and a 180 °C deposition temperature produced the least oxygen-deficient coatings. Under these conditions, crystalline rutile SnO2 deposited epitaxially on rutile SnO2 substrates. As-deposited SnOx coatings on anatase TiO2 and rutile TiO2 substrates were mostly smooth and amorphous, but contained various SnOx nanocrystals along the surface of the substrate nanocrystals. Post-deposition annealing at 450–500 °C results in the delamination of the SnOx shells from the nanocrystalline cores concomitant with the formation of SnO2 nanocrystals that are speckled along the periphery of the substrate nanocrystals. On anatase substrates the SnOx coatings form the rare orthorhombic phase of SnO2 after annealing, while rutile SnO2 nanocrystals are formed on rutile TiO2 substrates. The emergence of orthorhombic SnO2 on anatase TiO2 substrates and rutile SnO2 on rutile TiO2 substrates is rationalized by interfacial lattice mismatch and strain between the core and shell materials.