Electrochemical Characterisation of Oxide Layers on Single Grains of a Polycrystalline Ti‐Sample

AbstractElectronic properties of passive films (d≤20 nm) on single grains of polycrystalline Titanium were investigated by micro‐ellipsometry and electrochemical methods using photoresist microelectrodes with defined areas. A number of experimental improvements are reported here: i) The minimisation of the electrochemical active area down to 3×10−6 cm2, ii) the determination of the crystallographic orientation of single grains by anisotropy microellipsometry, as well as iii) the determination of local film thicknesses under potentiostatic control by in‐situ micro‐ellipsometry. iv) The capacity C of the microelectrodes was measured applying a new droplet technique. Anodisation of Ti single grains up to the same potential U yields different oxide thicknesses, anodic charges, donor densities and oxygen evolution. Thin passive layers need less anodic charge qOx for the oxide formation and have a higher donor density Nd. The great extent of oxygen evolution at these grains can be explained by an increased tunnel probability for the transition to the conduction band. The properties vary with the substrate orientation in a systematic manner, indicating a change of the properties at the (0111) orientation.