Model of scanning force microscopy on ionic surfaces

Abstract

We present a theoretical model of the scanning force microscope using an atomistic simulation technique for the interaction between a crystalline sample and a tip nanoasperity combined with a semi- empirical treatment of the mesoscopic van der Waals attraction between tip and surface, and the macroscopic parameter of cantilever deflection. For the nanoasperity at the end of the tip, we used a neutral and a protonated (MgO${)}_{32}$ cube, which model a hard tip made of oxide material. Static calculations based on total-energy minimization were used to determine the surface and tip geometries and total energy as a function of tip position. Scan lines of the perfect (001) surfaces of NaCl and LiF and of a monatomic step edge on the surface of NaCl were calculated at different constant vertical forces exerted on the tip with and without jump to contact. Ion transfers between sample and tip, together with their effects on the simulated scan trajectories, are illustrated.