1. Sinha, S.K. (Ed.), Ordering in Two Dimensions (North Holland, Amsterdam, 1980 )
2. K. Kern and G. Comsa, in “Chemistry and Physics of Solid Surfaces VII”, ed. by R. Vanselow and R.F. Howe, ( Springer, Heidelberg, 1988 ), p. 65
3. R.J. Birgenau and P.M. Horn; Science 232, 329 (1986)
4. I. Estermann and 0. Stern; Z. Phys. 61, 95 (1930)
5. T. Engel, K.H. Rieder: Structural Studies of Surfaces with Atomic and Molecular Beam Diffraction, Springer Tracts Mod. Phys., Vol. 91 ( Springer, Berlin, Heidelberg 1982 )