nc-AFM Imaging and Manipulation of a Triphenylene Derivative on KBr(001)

The adsorption of single hexamethoxyltriphenylene molecules on KBr(001) at low temperature (T < 10 K) was studied by low-temperature (T = 5 K) noncontact atomic force microscopy in ultrahigh vacuum. Images of the frequency shift, measured at constant height, show intramolecular features that are interpreted on the basis of molecular force-field calculations. The main conclusion is that the experimental contrast originates from the electrostatic interaction between a negatively terminated ionic tip and the atomic charges of the molecule. The main trends of the experimental observations of lateral manipulations could also be reproduced by the same method, giving some insight into the manipulation mechanisms. In particular, it is shown that the strong interaction of the oxygen atoms of the molecule with positive ions of the tip plays a major role by facilitating the partial lifting of the molecule from the substrate during the intermediate stages of these manipulation processes.