1. For a survey see;Ehrlich;Surf Sci,1995
2. der;Meyer;Phys Rev,1995
3. Some early observations have been reported by Armin Gölzhäuser and Gert;Gölzhäuser;Phys Rev Lett Surf Sei,1996
4. Procedures are discussed by;Wang;Surf Sci,1988
5. about the technique see in Handbook of Surface Imaging and Visualization edited by Boca;Ehrlich;Chap,1994