Highly-charged ion induced surface nano-modification

Nano-modification of highly-oriented pyrolytic graphite (HOPG) surfaces using slow highly-charged ion (HCI) beam irradiation has been demonstrated. Single HCI impact creates nanoscale protrusions in which the electronic structure is different from that formed by singly-charged ion impact. By combining slow HCI irradiation with electron injection onto the impact region, a transition of sp2 to sp3 hybridization is obtained, resulting in I–V characteristics of the impact region showing non-conductive properties with ∼ 6 eV band gap. The size of the features created by Ar8+-impact on HOPG are about ∼ 1 nm in diameter at 400 eV kinetic energy, which corresponds with a region where electron emission occurs by the Coulomb potential of the HCI. Assuming that 20 carbon atoms are contained in the structure formed, we discuss plausible sp3 carbon structures by means of Raman spectroscopic measurements and DV-Xα molecular orbital calculations. The energy level structure of the non-spherically symmetric sp3 structure of 20 carbon atoms shows values of energy gap corresponding to those obtained in the experiment. The results presented suggest that single impact of HCI on solid surfaces creates new nanostructure features, and HCI would be a good tool for collective material-modification-processing with nanoscale controllability.