Atomic corrugation in scanning tunneling microscopy images of the Fe (001 ) -p (1×1 )O surface

We have investigated the formation of scanning tunneling microscopy (STM) atomically resolved images of the Fe (001) -p (1×1) O surface. The latter is characterized by a high in-plane symmetry for both oxygen and iron atoms, thus representing a very appealing template for understanding how to distinguish between oxygen and metal atoms in STM images of an oxidized metal surface. We report on the occurrence of a corrugation reversal as a function of the tip-sample distance, and we use the conclusions of such an investigation for interpreting the experimental images of an oxygen vacancy created on the surface. Our experimental work, supported by ab initio density-functional theory calculations, allows us to assess the fundamental role of the local potential barrier in determining the STM image formation.