STM study on one-dimensional cluster formation processes of Y@C-82 and C-60 molecules

Using scanning tunneling microscopy (STM), we have studied cluster formation processes of fullerene molecules adsorbed on the Cu(111) 1 x 1 surface. We used two endohedral metallofullerenes; Y@C-82 and Gd@C-82, and pristine C-60. All adsorbed molecules are observed at step edges of the surface, and thus their processes can be treated with a model of one-dimensional cluster formation. When small amounts of molecules are deposited on the surface, we found that the dimer is most abundant among the clusters of Y@C-82 while monomers are dominant in the cases of Gd@C-82 and C-80. Since Y@C-82 has an electronic spin while the others do not, we speculated that the preferred dimer formation of Y@C-82 is owing to an interaction of the spin. Interaction energies among fullerene molecules were estimated based on a statistical analysis of the STM data.