Atomically resolved edges and kinks of NaCl islands on Cu(111) : experiment and theory

Atomically resolved dynamic force microscopy (DFM) images of step and kink sites of NaCl films grown on the Cu(111) surface are presented. Combining experimental results with an atomistic modeling of DFM imaging, we study the mechanism of contrast formation and extract more information about the tip and NaCl film structure. The experimental results and theoretical modeling systematically demonstrate the enhanced interaction of step and kink sites of one kind with the tip. This is explained by the enhanced gradient of the electrostatic potential at low-coordinated surface sites, and considerable displacements of the step edge and kink atoms from their sites due to the interaction with the tip upon approach. The theoretical analysis predicts that the silicon tip is effectively an insulator, and that the NaCl island cannot be thicker than two monolayers. We discuss the shape and chemical structure of the tip and the mechanism of damping during DFM imaging.