Influence of square wave anodization on the electronic properties and structures of the passive films on Ti in sulfuric acid solution

Abstract Two types of square wave anodization (type 1 and type 2) were employed in this work to form a passive film on Ti in a 0.5 M H 2 SO 4 solution. The influences of the anodization potential and duration on the electronic properties and structures of the passive films were studied by Mott-Schottky plots, auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS). The results showed that the donor density, N D , of the passive film decreased and the flat band potential, E FB , shifted to the positive direction with the increase of the anodization duration and high anodization potential irrespective of whether type 1 or type 2 was used. Moreover, the passive film that formed on Ti using type 1 had a lower donor density and a more positive flat band potential than that on Ti using type 2 at one fixed anodization duration (only exchanging the anodization order of 1 V and the high potential). XPS analysis revealed that the outmost passive film was only composed of TiO 2 , the inner passive film was mainly composed of TiO 2 with some amount of TiO and Ti 2 O 3 , and the TiO 2 concentration in the outermost passive film increased with the increase of the anodization duration and the high potential in the case of using type 1 or type 2, implying an increased degree of crystallinity. The AES results showed that the O/Ti atomic ratio of the passive film obviously increased with the increasing anodization duration and high potential, demonstrating the increased homogeneous characteristic of the passive film; this was in agreement with the Mott-Schottky and XPS results.