CAPILLARY INSTABILITIES OF A CATENOIDAL HOLE IN A SOLID FILM

Holes formed in a solid film during annealing can grow and lead to the formation of many isolated islands. The morphological evolution of ho les is thus of primary importance in the production of planar films. T his work studies the linear instability of a stationary axisymmetric h ole in a film with zero surface mean curvature. At the hole, the film forms a contact angle alpha with the substrate at a circular contact l ine of radius a(0). The film is bounded by an outer wall at a distance a(0)L from the center. An infinitesimal disturbance in the form of a normal mode is applied and its stability analyzed for 0 less than or e qual to alpha less than or equal to 180 degrees and 1 less than or equ al to L < infinity. Capillarity-driven surface diffusion is taken to d ominate the mass transport. As L --> 1, the film is a ring that is uns table to periodic disturbances along the ring. For an unbounded film w ith L --> infinity, only axisymmetric disturbances can grow, and the g rowth rates become independent of L or the boundary conditions at the outer wall. This instability persists even when the film is ''flat'' i n the limit alpha --> 0, in contrast to the stability results of a uni form film without a hole. The growth rates agree qualitatively with th ose observed in experiments. (C) 1997 American Institute of Physics.