Photoelectrochemical imaging and microscopic reactivity of oxidised Ti

To clarify the correlation between photoelectrochemical images and surface reactivity, investigations of ellipsometry (d(ox), structure), coulometry (d), capacitance (N-D) and i(ph) were carried out on single grains (hkl) of passive titanium. The results prove that only the oxide layers on (xxx0) planes grow homogeneously up to 10 V. The observed strong decrease of i(ph) with increasing d(ox) is in clear contrast to the Butler-Gaertner model, This is explained by the large recombination rate which can be diminished by an electric field. On more closely packed planes, N-D, structure and thickness change simultaneously. Hence, a quantitative interpretation is not possible, but qualitatively it is the same as on (xxx0). Thus, in photoelectrochemical images, an increasing i(ph) indicates a high field strength and a corresponding high electrochemical reactivity expressed by rate of etr, eg Fe2+ oxidation or oxygen evolution. Since ionic motions are hindered in tightly packed oxide films, itr changes in the opposite direction. (C) 1997 Published by Elsevier Science Ltd.