The adsorption and molecular orientation of Dy@Cs2 isomer I on Au（111） has been investigated using ultrahigh-vacuum scanning tunneling microscopy at 80 K. At low coverages, the Dy@Cs2 molecules tend to grow along the step edges of Au（111）, forming small clusters and molecular chains. Adsorption of Dy@Cs2 on the edges is dominated by the fullerene-substrate interaction and presents various molecular orientations. At higher coverages, the Dy@Cs2 is found to form ordered islands consisting of small domains of equally oriented molecules. The Dy@Cs2 molecules in the islands prefer the adsorption configurations with the major C2 axis being approximately parallel to the surface of the substrate. Three preferable orientations of the Dy@Cs2 molecules are found in a two-dimensional hexagonal close packed overlayer. These observations are attributed to the interplay of the fullerene-substrate interaction and dipole-dipole interaction between the metallofullerenes.
