SIMULATION OF THE SCANNING TUNNELING AND ATOMIC-FORCE MICROSCOPY IMAGES OF A XANTHINE MONOLAYER ON GRAPHITE

The atomic force microscopy (AFM) and scanning tunneling microscopy (S TM) images of a monolayer of xanthine molecules adsorbed on graphite w ere simulated by calculating total and partial electron density plots for a model bilayer of xanthine and graphite. Unlike the case of the t otal density plots, the partial electron density plots depend strongly on the registry of xanthine molecules on the graphite lattice. This r esult explains why the STM images show a superstructure modulation, wh ereas the AFM images do not. (C) 1998 Elsevier Science B.V. All rights reserved.