Nanostructured TiO2 membranes by atomic layer deposition

Conformal TiO2 films have been deposited on track-etched polycarbonate membranes by means of atomic layer deposition. Membranes with pore aspect ratios of 25 : 1 and 50 : 1 were selected for initial study. A suite of complementary characterisation techniques was used to probe the nanostructure, stoichiometry and uniformity of the TiO2 coatings. These established that both the surfaces and pores of the membranes were completely covered with an amorphous film. Further, the stoichiometry of the films was close to that of TiO2 though they were found to contain similar to 6 atom% chlorine. While the internal walls of the membrane pores were covered with film over their full length, the coating thickness decreased in the direction of gas flow. This was attributed to a variation in reactant concentrations along the pores due to the process conditions. Gas conductance measurements were performed on several coated membranes. These showed that membrane conductance could be controlled by varying the coating thickness.