Direct atomic-resolution Z-contrast imaging was applied to As impurities which segregated in specific atomic columns in grain boundaries. By using a combination of image intensity analysis, first-principles calculations and statistical mechanics, it was established that segregation occurred in the form of isolated dimers. The formation of As dimers in the boundary was shown to be preferred, to ordered chains, due to entropy considerations and kinetic constraints.

Atomic configurations and energetics of As impurities in a silicon grain boundary M.F.Chisholm, A.Maiti, S.J.Pennycook, S.T.Pantelides: Physical Review Letters, 1998, 81[1], 132-5