Tip Surface Interactions in STM and AFM

The interaction between tip and flat surface in the STM and AFM is reviewed and a new, AC method to determine the absolute value of area of contact and interaction is presented. Evidence that the tip-surface interaction can be purely elastic down to the near single atom scale is obtained, and has been confirmed by TEM on Al 2 O 3 . Strengths close to that of an ideal lattice are observed. Applied to the Atomic Force Microscope this AC method will give operation at a controlled, drift free level of interaction. The effects of attractive (surface energy) forces in the STM geometry are discussed, and the equilibrium configurations and extent of inelastic processes for tip and flat are described. A new imaging mechanism in STM is proposed for the cases (e.g., graphite, point contact microscope) where significant tip-surface contact occurs.