The system of C-60 layer on Si(1 1 1)root 7 x root 7-Co surface has a negligible lattice mismatch and with the designed two-step procedure which allows formation of the highly ordered Si(1 1 1)root 7 x root 7-Co surface with domain size of similar to 100nm, one could expect to achieve a perfect epitaxial growth of C-60 molecular layer. However, using scanning tunneling microscopy observations we have found that regular C-60 arrays grown on such a promising surface typically do not exceed the size of similar to 10 nm. It has been recognized that the main reason for lacking the long-range ordering in the C-60 layer is occurrence of several adsorption sites within the root 7 x root 7 unit cell. (C) 2013 Elsevier B.V. All rights reserved.