Nanoindentation of nanocolumnar TiO2 thin films with single and stacked zig-zag layers

This paper reports a systematic analysis of the mechanical properties of nanocolumnar TiO2 thin films prepared by evaporation at a glancing geometry. A systematic study of the mechanical properties is carried out by comparing the hardness and the Young's modulus determined by nanoindentation for thin films prepared at different deposition angles and characterized by a tilted nanocolumnar structure and others where the nanocolumns are perpendicular to the substrate or are arranged as zig-zag stacked layers. A correlation between mechanical properties and glazing angle geometry is proposed. Differences in the results are discussed in view of the cross section images obtained by focused ion beam and of the deformed areas. Zig-zagged layers present lower values of hardness and Young's modulus due to the collapse of the angles of the columns, but at the same time this configuration impedes the appearance of fracture or delamination, as observed for tilted columns.