Point defects with a 3-fold symmetrical electronic perturbation were observed at the surface. Such a perturbation had been predicted by simulation studies. Due to the covalent nature of the material, the propagation length of the perturbation was equal to only one tenth of that in the free electron system. Its symmetry reflected the crystallographic symmetry. The perturbation was taken to be the initial formation stage of a (3 x 3)R30 superlattice, which was often found in the neighborhood of larger defects.

S.Kondo, M.Lutwyche, Y.Wada: Japanese Journal of Applied Physics 2, 1994, 33[9B], L1342-4