Dissociated and faceted large-angle coincident-site-lattice boundaries in silicon

The interaction of three large-angle near-coincident-site-lattice grain boundaries ([Sgrave]3, [Sgrave]9 and [Sgrave]27) in a polycrystal of silicon, has been observed both optically and by transmission electron microscopy (TEM). [Sgrave]3 boundaries were found to be formed on {111} and {112} planes, [Sgrave]9 on {122}, {411} and {111}/{115} planes, and [Sgrave]27 on {255} planes. On a macroscopic scale, [Sgrave]9 {122} dissociated repeatedly into two coherent [Sgrave]3 boundaries which, when contacted with a third non-coherent [Sgrave]3 boundary, formed a triangular twin grain with an average size of 0·3 mm. Further TEM observations showed the [Sgrave]27 boundary to dissociate into a series of 100nm triangular grains, consisting of a coherent [Sgrave]3, a {122} [Sgrave]9 and a {111}/{115} [Sgrave]9 boundary. The [Sgrave]9 boundary {111}/{115} dissociated further to form still smaller 10nm twin grains consisting of two coherent and one noncoherent [Sgrave]3 boundaries. The dissociation reactions at each point have been analysed, and the driving forces for the reactions are discussed.