Structural features of CeO_2(111) revealed by dynamic SFM

摘要

Cerium dioxide is an insulating material that is important in various fields of catalysis and often used as an oxygen reservoir. The (111) surface of CeO_2 is catalytically active and we study this surface in its various oxidation states by dynamic force microscopy, an analysis that may eventually help to establish structure-function relationships for catalysis. We present highly resolved images and atomic details of surface features on CeO_2(l 11) like terrace structures, step edges, kinks and hexagonally shaped pits that are naturally formed during surface preparation by sputtering and annealing cycles. We find that such structures can be well imaged with atomic resolution and that they exhibit morphological characteristics that are significantly different in details from those of cleaved CaF_2(l 11), a surface with exactly the same crystallographic structure and very similar lattice constants and ionic radii. In this study, we continuously monitor the shape of the tip apex and demonstrate that high quality atomic resolution imaging is possible with one tip, although the tip apex is drastically changed by wear during 45 h of scanning.