Surface and sub-surface O vacancies on the slightly reduced (111) surface were studied by means of atomic-resolution dynamic force microscopy at 80K. Both types of defect were clearly identified by comparison of the observed topographic features with the corresponding structures predicted by first-principles calculations. By combining 2 simultaneously acquired signals (topography, and energy dissipated from the cantilever oscillation), it was possible unambiguously to locate sub-surface O vacancies buried at the third surface atomic layer. A local ordering of the sub-surface defects was reported which suggested the existence of a delicate balance between subtle interactions among adjacent sub-surface O-vacancy structures.

Evidence of Subsurface Oxygen Vacancy Ordering on Reduced CeO2(111). S.Torbrügge, M.Reichling, A.Ishiyama, S.Morita, Ó.Custance: Physical Review Letters, 2007, 99[5], 056101 (3pp)