Combinatorial synthesis and high throughput evaluation of doped TiO₂ thin films for the development of photocatalysts

TiO₂ thin films doped with various transition metals were systematically fabricated by combinatorial laser MBE technique. Alternating KrF excimer laser (λ = 248 nm) ablation of TiO₂ and Ti_1-x M_xO₂ (M = transition metal) was employed to deposit combinatorial library of 18 samples for each dopant with different concentrations. Anatase films with c-axis orientation were grown epitaxially on SrTiO₃(001) substrate while the rutile phase films with a-axis orientation were on Al₂O₃(0001) substrate. Solid solubility of transition metals in both the phases was determined by X-ray diffraction. The anatase phase was found to dissolve the transition metals in higher concentrations than rutile phase. The parallel evaluation of the photocatalytic activity of the doped TiO₂ in combinatorial libraries was performed with respect to photodecomposition of water in presence of a small amount of oxidizing or reducing agent which induced pH changes on the pixels. The high throughput evaluation of combinatorially deposited photocatalytic thin films was realized by adopting a potentiometric pH field effect transistor for sensing such pH changes.