Tomography of molecular nanographene double layers using scanning tunneling microscopy

Abstract

Double layers of a nanographene with defined molecular structure have been self-assembled at the interface between a molecular solution and the basal plane of graphite. Bias-dependent scanning tunnel microscopy allowed nondestructive imaging of the first or the second or both layers. While the first molecular layer can be well recognized at low negative or high positive sample biases, it is the other way around---at high negative or low positive sample biases---for the second molecular layer. This is attributed to the dependence of the resonant tunneling conditions for the molecules in the first and second layers on the position of the molecules within the tip-substrate gap. The effect may be used for a nanotomography of molecular multilayers.