MODEL OF SCANNING FORCE MICROSCOPY ON IONIC SURFACES

We present a theoretical model of the scanning force microscope using an atomistic simulation technique for the interaction between a crysta lline sample and a tip nanoasperity combined with a semiempirical trea tment of the mesoscopic van der Waals attraction between tip and surfa ce, and the macroscopic parameter of cantilever deflection. For the na noasperity 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 c alculations based on total-energy minimization were used to determine the surface and tip geometries and total energy as a function of tip p osition. 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 dif ferent constant vertical forces exerted on the tip with and without ju mp to contact. Ion transfers between sample and tip, together with the ir effects on the simulated scan trajectories, are illustrated.