Atomic Structure of Low-Index CeO_2 Surfaces

摘要

We have shown the structure of low-index surfaces of CeO_2 with atomic resolution. STM at elevated temperatures and/or very low tunnelling currents are crucial to obtain this resolution. The reduction of CeO_2 as it may happen in a catalytic converter was illustrated on the (111) surface of a single crystal of CeO_2. Starting from a (1x1) terminated surface, agglomerations of oxygen vacancies in triangular arrangement could be observed after annealing the crystal under extremely oxygen lean conditions (UHV). Upon further annealing more oxygen vacancies are introduced forming lines in different, equivalent crystallographic directions. The CeO_2 (001) surface shows a strong tendency for reconstruction. Calculations showed that it is able to maintain the same surface symmetry for oxygen coverage between 0.25 and 0.5.