C-AFM as a means to identify heterogeneities at the nanoscale in thin anodic TiO₂ films

The anodic oxidation of titanium allows the obtaining of an oxide layer with thickness. color, homogeneity and insulating properties that depend on the process parameters imposed. These thin films have been studied mostly to derive information on the oxidation kinetics of the metal. Still, a deeper understanding of oxide properties is vital to open the way to engineered applications of nanostructured Ti02 films, such as in the most recent field of memristive devices, where a precise control of oxide thickness and its electrical properties is required. In this work, titanium was anodized in diluted sulfuric acid, with cell voltage ranging from 0 to 20 V. Oxide thickness was estimated by coulometric and spectrophotometric measurements; these two techniques were then combined with C-AFM to gain a deeper understanding of the oxide coverage of the metal surface and of the presence of crystal nano-domains within amorphous oxide phase.