Modelling the effect of changes in defect geometry on chemically active surfaces by the boundary element technique

The boundary element (BE) technique is used to analyze the effect of defect structures upon desorption processes on two-dimensional chemically active surfaces. The standard BE algorithm for diffusion is modified to incorporate the effects of bulk desorption, and an explicit scheme is proposed for the treatment of the non-linear equations associated with localized defect structures. The BE algorithm proposed here provides an elegant representation of the effects of localized non-linear reactions which allows arbitrarily oriented defect structures to be modelled without having to perform mesh deformation. A class of trapping reactions is assumed to occur along defect structures, and the effect of changes in defect geometry on the balance between the desorptive processes is explored. A number of interesting competitive/cooperative phenomena are observed to occur for the various shapes of defect geometry, including strong intrinsic competition in circular defect structures that form islands of nearly constant concentration, a redistribution of material along V-shaped defect structures in a way that reflects relative competitiveness of defects on opposite sides of the defect structure, and a reduction of competitiveness for defect distributions that are less regular in shape. The proposed BE algorithm is shown to provide a useful technique for modelling the effect of defect structures on chemically active surfaces.