Subsurface Space-Charge Dopant Segregation to Compensate Surface Excess Charge in a Perovskite Oxide.

Since the first prediction by Frenkel, many follow-up studies have been carried out to show the presence of subsurface space-charge layers having the opposite sign to that of the excess charge at the surface, producing overall neutrality in ionic crystals. However, no precise experimental evidence demonstrating how the aliovalent solutes segregate in the space-charge region beneath the surface has been provided over the past several decades. By utilizing atomic-scale imaging and chemical probing in a perovskite oxide, the origin of the surface excess charge at the topmost surface and the position of segregated dopants in the space-charge region is precisely determined. The impact of the space-charge contribution to the dopant distribution near the surface in oxide crystals is explored.