Influence of pH and Surface Orientation on the Photochemical Reactivity of SrTiO₃

The photochemical reactivity of the SrTiO₃ surface is affected by the pH of the surrounding aqueous solution. Scanning electron microscopy and atomic force microscopy have been used to quantify the amount of silver that is photochemically reduced on the surfaces of (100), (110), and (111) oriented crystals as a function of pH. For all orientations, the reactivity increases from pH 3, reaches a maximum, and then decreases at higher pH. The pH associated with the maximum reactivity depends on the crystallographic orientation of the surface. The results indicate that the solution pH influences the charge on the SrTiO₃ surface. The amount of surface charge influences band bending within SrTiO₃, and the maximum reactivity is achieved at a surface charge where neither the photocathodic nor the photoanodic reaction limit the overall reaction rate.