THE INFLUENCE OF MASS FORCES ON THE CRITICAL THICKNESS OF PRESTRESSEDHE-4 AND SOLID EPITAXIAL-FILMS

We investigate the influence of mass forces (in particular, of gravita tion and van der Waals forces) on the critical film thickness of thin films attached to solid substrates. It is assumed that the film's part icles are able to rearrange their relative positions in the lattices, and the equilibrium rearrangement is determined my minimizing the tota l static energy. Recently, it was demonstrated that morphological stab ility of interfaces in crystalline solids with the rearrangement is ex tremely sensitive to the presence of shear stresses. Equilibrium theor y of elasticity of pre-stressed solids with the rearrangement of their material particles has already allowed to predict the appearance of c orrugations in He-4 films and to shed light on the dislocation-free St ranski-Krastanov pattern of epitaxial growth of thin solid films. We e stablish the corrections of the earlier published formula H(crit) = si gmamu/tau2 (where sigma is the surface energy, mu the shear modulus, a nd tau the mismatch stress) relating to rigid substrates and announce a novel formula of the critical thickness for deformable substrates.