The Atomic-scale Characterization of Defects on Cleaved Vanadium and Molybdenum Oxide Surfaces Using Stm

Scanning tunneling microscopy (STM) was used to determine the structure of cleaved, single crystal surfaces of V20 5, V60 13, Mo 180 52, and Mo80 23. Constant current images were recorded in ultrahigh vacuum and in air. By imaging well-defined surfaces that exhibit structural and chemical similarities, and comparing the observations to the known bulk structures, it is possible to establish a reliable interpretation for the contrast in the STM images. A comparison of images from the V60 13(001) and the V20 5(001) surfaces clearly shows that the surface V coordination polyhedra that are capped by vanadyl 0 can be distinguished from those that are not. This allows vacancies in the vanadyl 0 position to be identified on cleaved V20 5(001) surfaces. Mo 180 52(100) and Mo 80 23(010) provide models for two different characteristic types of surface/crystallographic shear (CS) plane intersections. The shear in Mo 80 23 lies in the (010) surface plane and creates dark contrast along the [001]. The CS planes in Mo 180 52 , on the other hand, have components of shear both in and normal to the (100) surface plane and create white contrast parallel to [010]. These standards for contrast identification can be used to identify defects on inhomogeneous surfaces.