ADHESION BETWEEN ATOMICALLY FLAT METALLIC SURFACES

The study of adhesive interactions between atomically flat surfaces in close proximity requires that their separation be controlled and known to within a tenth of an angstrom. In some instances, however, two solids will display a structural instability of their surface layers as their separation approaches the bulk value. When this occurs, an abrupt transition, termed "adhesive avalanche," from a geometry with two spatially distinct surfaces to a single homogeneous structure takes place as the surfaces are brought to within 1-2 angstrom of their equilibrium bulk separation. The avalanche event is the result of a critical growth in the adhesive force gradient at each surface as their separation is reduced to a critical value. We have applied the embedded-atom method to examine this phenomenon for (001)- and (111)-oriented Ni, Cu, and Au surfaces. Both statics and dynamics of adhesion are considered, revealing that tensile stress waves are generated upon avalanche and eventually decay into heat due to the effects of dispersion and dissipation. These tensile waves are associated with a wavelike transmission of the adhesive force, caused by the occurrence of the avalanche event. The presence of avalanche events will cause difficulties in the interpretation of experimental studies of interfacial forces.