The growth of thin fluoride films on Si(111) was studied by means of  in situ  low-energy electron microscopy and transmission electron microscopy. As the strained epitaxial film passed through the critical thickness, the initial dislocations formed triplets (so-called trigons). These acted as sources for full edge dislocations which subsequently formed a dense network. The unusual dislocation structure provided a natural explanation for a so-called 2-dimensional structural modulation of the Si(111)/CaF2 interface.

R.M.Tromp, F.K.LeGoues, M.C.Reuter: Physical Review Letters, 1995, 74[14], 2706-9