LATTICE DISORDER AND DENSITY-OF-STATES CHANGE OF GRAPHITE SURFACE BY SINGLE-ION IMPACT

We discuss changes in the electronic structure and the topography of t he graphite surface caused by a single ion impact. Both protrusion-lik e regions (PLR) and the lattice-disordered regions were found in scann ing tunneling microscope images. In atomic force images, however, no P LRs were found, even in when lattice-disordered regions were found. To determine the change in the density of states in PLRs, tunneling curr ent versus voltage characteristics were measured. It was found that th e density of states at the Fermi level of PLRs was greater than that o f the intact surface, which means that the semimetal to metal transiti on was caused by a single ion impact. These results indicate that PLRs may originate from the change in the density of states.