Nature of bonding forces between two hydrogen-passivated silicon wafers

The nature and strength of the bonding forces between two II-passivated Si surfaces are studied with the density-functional theory, using an approach based on recent theoretical advances in understanding of van der Waals forc es between two surfaces. Contrary to previous suggestions of van der Waals attraction between H overlayers, we find that the attraction is mainly due to long-range van der Waals interactions between the Si substrates, while t he equilibrium separation is determined by short-range repulsion between oc cupied Si-H orbitals. Estimated bonding energies and Si-H frequency shifts are in qualitative agreement with experiment. [S0163-1829(98)06448-0].