Molecular dynamics simulation of non-contact atomic force microscopy of self-assembledmonolayers on Au(111)

Abstract

We attempted molecular dynamics (MD) simulation of non-contact atomic forcemicroscopy (nc-AFM) of a self-assembled monolayer (SAM) on Au(111) by modifying apreviously developed MD simulation method. In the previous simulation, the interactionbetween a single gold atom tip and a SAM sample consisting of the united atoms(CH3) with amass (m0) and a continuum gold substrate was treated explicitly in terms of microscopicpotentials. On the other hand, the probe tip with an artificial reduced mass(msl) was bound to a cantilever spring in order to describe its macroscopic nc-AFM behaviour. Inthe present study, we treated explicitly the interaction between a gold probe tip (theradius = R) having a single gold atom at the apex and the same SAM on gold. By using this new MDmethod, we succeeded in interpreting our recent experimental nc-AFM observation.Namely, the local atom–atom interactions in terms of Lennard-Jones potentials togetherwith the long-range sphere–substrate interaction are responsible for inversion andmolecular-dependent imaging of van der Waals (i.e. chemically inert) molecules bound ongold substrates.