Modelling of non-contact atomic force microscopy imaging of individual molecules on oxide surfaces

We have modelled NC-AFM imaging of organic molecules adsorbed on the MgO(100) and TiO2(110) surfaces, to study whether molecules adsorbed at well determined surface sites could serve as markers for chemical resolution of surface species and possible mechanisms of adsorption and manipulation of such molecules with NC-AFM tips. We calculated images of perfect MgO and TiO2 surfaces and considered the adsorption of the formate ion and 3-{4-[ Tris-(3,5-di-tert-butyl-phenyl)-methyl]-phenoxy}-propionic acid (C52H72O3) at the MgO(100) and TiO2(110) surfaces, respectively, using several types of oxide tip models. The results demonstrate that using adsorption of even small molecules, such as formate, for identifying surface chemical species in NC-AFM images may not be practical. The interaction of hydrocarbon molecules with perfect oxide surfaces is weak and their adsorption should be aided by attaching special anchoring groups. Flat molecules can be identified by their shape, but simultaneous atomic resolution inside the molecule and on the substrate under the same imaging conditions is not feasible.