Universal Aspects of Brittle Fracture, Adhesion, and Atomic Force Microscopy

Abstract

AbstractThe universal relation between binding energy and interatomic separation was originally discovered for adhesion at bimetallic interfaces involving the simple metals Al, Zn, Mg, and Na. We show here that the same universal relation extends to adhesion at transition metal interfaces. Adhesive energies have been computed for the low index interfaces of Al, Ni, Cu, Ag, Fe, and W using the Equivalent Crystal Theory (ECT) and keeping the atoms in each semi-infinite slab fixed rigidly in their equilibrium positions. These adhesive energy curves can be scaled onto each other and onto the universal adhesion curve. We have also investigated the effect of tip shape on the adhesive forces in the Atomic Force Microscope (AFM) by computing energies and forces using the ECT. While the details of the energy-distance and force-distance curves are sensitive to tip shape, all of these curves can be scaled onto the universal adhesion curve. This means that although absolute magnitudes of adhesive forces in the AFM cannot be determined without knowing the geometry of the tip, the shape of the force-distance curve is universal, at least for distances changing normal to the substrate.