STM observation of HOPG surfaces irradiated with Ar cluster ions

Cluster ion beams offer new surface modification processes because of their unique interaction between cluster atoms and solid surfaces, For example, surface smoothing and shallow implantation by cluster ion beam have been demonstrated. Ln order to reveal such cluster-surface interaction, a single trace formed by a cluster ion impact on a solid surface has been investigated using Scanning Tunneling Microscopy (STM). STM images of Highly Oriented Pyrolitic Graphite (HOPG) surfaces, were obtained after irradiation with 150 keV Ar cluster or 1.5 keV monomer ions. The 150 keV cluster ions, with a size of about 100 atoms, were used in comparison with 1.5 keV monomer ion. The velocity of an atom in each case was the same. In spite of these equal velocities, large craters with diameter of about 180 Angstrom were observed in the STM image of cluster-irradiated HOPG surface, while only small hills were observed in monomer-irradiated surface.