Nanoscale modification of electronic states of HOPG by the single impact of HCI

Slow Ar8+ impact with 400 eV of kinetic energy upon graphite followed by subsequent electron injection induced the transition from sp2 to sp3 hybridization, resulting in the formation of a non-conductive region at the metallic graphite surface. From the I-V characteristics measured by scanning tunneling spectroscopy, it was confirmed that the Ar8+ impact region showed an energy gap with ∼6 eV. The impact region was found to work as an electron emitter similar to the CVD-grown poly-crystalline diamond film after the further treatment in hydrogen ambient at 600 °C. It was confirmed from the Raman spectroscopic measurements that vacancies were introduced into the sp2 region by the slow Ar8+ impact, and also found that the most presumable sp3 cluster model which can explain experimental results had a defective and more planar structure from DV-Xa molecular orbital calculations.