Polyoxoniobates as molecular building blocks in thin films

Niobium oxide thin films have been prepared by spin-coating aqueous solutions of tetramethylammonium salts of the isostructural polyoxometalate clusters [Nb₁₀O₂₈]^6-, [TiNb₉O₂₈]^7- and [Ti₂Nb₈O₂₈]^8- onto silicon wafers, and annealing them. The [Nb₁₀O₂₈]^6- cluster yields films of Nb₂O₅ in the orthorhombic and monoclinic crystal phases when annealed at 800 °C and 1000 °C, respectively, whereas the [TiNb₉O₂₈]^7- and [Ti₂Nb₈O₂₈]^8- clusters yield the monoclinic crystal phases of Ti₂Nb₁₂O₂₉ and TiNb₂O₇ (titanium-niobium oxides) in different ratios. We also demonstrate a protocol for depositing successive layers of metal oxide films. Finally, we explore factors affecting the roughness of the films.