Topography and Electronic Contours

Equation (3) indicates that the STM tip does probe the density of electronic contours rather than the surface topography in terms of a hard-sphere model [47]. Electronic contours generally coincide with atoms on metals. With semiconductors the interpretation of images is not trivial because electrons are located in bound states (dangling bonds on clean surfaces in UHV, chemical bonds between surface atoms and ligands in liquids) whose density and occupation can vary from one atom to another. 

The structure of semiconductor surfaces under bulk solution can generally not be extrapolated from adsorption studies in UHV. For instance, Si(lOO) oxidizes in pure water with time and the surface is not simply saturated by Si-H and Si-OH 

On metals and in the liquid environment, Magnussen et al. [60] have also found an electronic effect when imaging ordered layers of hydrogensulfate ions on Au(l 11). 

---