ADHESIVE AVALANCHE IN COVALENTLY BONDED MATERIALS

When two strongly interacting materials approach each other, a critical separation can be reached, perhaps several angstroms greater than the bulk separation, when they snap together. This process is known as adhesive avalanche, and is characterized by a structural phase transition from a system possessing two surfaces, to a state in tensile strain with no identifiable surfaces. In this paper, we use the self-consistent pseudopotential method to study the adhesive avalanche between two flat Si(111) surfaces. A detailed description of the evolution of charge densities, total energies, and relaxed structures for five initial separations of the Si(111) surfaces are given. The calculations show that the avalanche event in Si is due to the initiation of covalent-bond formation at a separation of about 2 angstrom greater than the bulk interplanar spacing, and is driven by localized stresses in the first few surface planes.