Structural modifications which were induced by equilibrium S segregation to pure tilt Ge {710}<001>, Σ = 25 (θ = 16.26°) and {551}<011>, Σ = 51 (θ = 16.10°) grain boundaries

 were investigated by using high-resolution electron microscopy and electron energy-loss spectroscopy, supported by modelling and image simulations. The results showed that the as-grown Σ = 25 grain boundary was composed of 2 parts: a stable structural region and a variable perturbed core. On the basis of the simulations, it was shown that this boundary could be formed only by a multiplicity of configurations which were energetically close to each other but configured differently along the boundary plane. When sulphurized, marked changes were observed in the structure of the grain boundary. Energy-filtered electron microscopic imaging revealed S-enrichment in the perturbed part of the boundary. Although S segregation at the boundary was detected, no information could be extracted concerning segregation sites and bonding configurations because of the complexity of the boundary. A simpler grain boundary (Σ = 51) was studied instead. The structure of such a boundary involved a well-known configuration: a Lomer dislocation which was basically a 5-fold ring adjacent to a 7-fold ring. After S-treatment, high-resolution electron microscopic imaging also revealed significant contrast modifications which were apparently concentrated at the dislocation core. Chemical imaging also indicated the presence of S-enrichment along the boundary plane. This strongly suggested that equilibrium S segregation into the grain boundary occurred in this system, and confirmed previous results on the Σ = 25 grain boundary. It could be argued that it was the presence of odd-membered rings at the boundary, coupled with the electronic properties of S, which were responsible for the preferential segregation into the boundary.

Structural Change Induced on an Atomic Scale by Equilibrium Sulphur Segregation in Tilt Germanium Grain Boundaries. A.Charaï, M.Benaissa, C.Alfonso, L.Fares, O.B.M.Hardouin Duparc, J.L.Rouvière, J.Thibault: Philosophical Magazine B, 2001, 81[11], 1821-32