The (111) surface structure of non-stoichiometric material was studied by means of scanning tunnelling microscopy. By using extremely low tunnelling currents, it was possible to obtain the first reported atomically resolved images of this oxide. Scanning tunnelling microscopic imaging was possible at a sample bias voltage of between -2 and -3.5V. Upon comparing this with the band-structure of ceria, it was claimed that the main contribution to image contrast resulted from O in the uppermost layer. The predominant defect type on the surface at room temperature was triangular, and comprised three O vacancies. Scanning tunnelling microscopy, at a substrate temperature of 500C, revealed an alignment of O vacancies on the surface. The defect shapes were in qualitative agreement with previous energy calculations.

H.Nörenberg, G.A.D.Briggs: Physical Review Letters, 1997, 79[21], 4222-5