Defect Structure of Nonstoichiometric CeO₂(111) Surfaces Studied by Scanning Tunneling Microscopy

The surface structure of nonstoichiometric CeO₂(111) has been studied by scanning tunneling microscopy (STM). By using extremely small tunneling currents it was possible to obtain the first ever reported atomically resolved images of this oxide. STM imaging was possible at a sample bias voltage between -2 and -3.5V. Comparing this with the band structure of ceria we claim that the main contribution to the image contrast results from oxygen in the topmost layer. The dominant defect type on the surface at RT is of triangular shape and contains three oxygen vacancies. Elevated temperature STM at a substrate temperature of 500 °C revealed an alignment of oxygen vacancies on the surface. The defect shapes are in qualitative agreement with previous energy calculations.