The mechanism of high-resolution STM/AFM imaging with functionalized tips

摘要

High resolution Atomic Force Microscopy (AFM) and Scanning TunnellingMicroscopy (STM) imaging with functionalized tips is well established, but adetailed understanding of the imaging mechanism is still missing. We present anumerical STM/AFM model, which takes into account the relaxation of the probedue to the tip-sample interaction. We demonstrate that the model is able toreproduce very well not only the experimental intra- and intermolecularcontrasts, but also their evolution upon tip approach. At close distances, thesimulations unveil a significant probe particle relaxation towards local minimaof the interaction potential. This effect is responsible for the sharpsub-molecular resolution observed in AFM/STM experiments. In addition, wedemonstrate that sharp apparent intermolecular bonds should not be interpretedas true hydrogen bonds, in the sense of representing areas of increasedelectron density. Instead they represent the ridge between two minima of thepotential energy landscape due to neighbouring atoms.