Surface potential of a polar oxide film: FeO on Pt(111)

Abstract

We have studied a thin FeO film on Pt(111) using scanning tunneling microscopy. The corrugation of the Moir\'e pattern, that arises due to a lattice mismatch between the oxide film and the substrate, is found to increase dramatically when the microscope is operated in the field-emission regime. This contrast enhancement can be attributed to variations in the energy at which field-emission resonances are observed. We assign this effect to variations of the surface potential within the Moir\'e unit cell. Using a simple electrostatic model we show that in this oxide film with polar termination, such variations can be induced by very subtle differences in geometry.