Cluster shapes in STM images of isolate clusters and cluster materials

The formation of cluster images in a scanning tunneling microscope (STM) has been modeled using isolate C60 molecules deposited on top of crystalline monolayers of C60 on Ge(100) and Si(100) containing vacancies. C60 molecules occupy positions above vacancies and depending on the dimensions of the latter protrude to a different height above the surface. A simple model of the image formation is suggested and the variation of the shape of C60 molecules in STM images as a function of their apparent height is explained by the convolution of their images with that of the tip and by scattering of tunneling electrons on vacancies below C60 molecules.