Studies on local electronic structures in the vicinity of graphene edges by means of scanning tunneling microscopy

Abstract

The present thesis focused on the local electronic structure of graphene edges, which is characterized by two distinct edge geometry (zigzag and armchair edges), investigated by scanning tunneling microscopy (STM) at low temperature and ultra high vacuum condition. In Part 1, fabrication of graphene edges and their thermal stability are discussed. Graphene edges formed by oxidation reaction on graphite substrate tended align parallel to armchair direction. It is figured out that the armchair edge is thermally favorable than zigzag edge due to the energy gain coming from the delocalization of π-electrons. In Part 2, STM study about electron wave interference in the vicinity of armchair edges is described. In this study three-symmetric fine structure was discovered on individual bright site in honeycomb superlattice. Through the theoretical calculation it was revealed that the K–K′ intervalley scattering specific to a presence of an armchair edge is responsible for the generation of honeycomb superlattice. Furthermore, STM simulation result was in excellent agreement with the fine structure experimentally observed. Fine structure was appeared due to the antiphase coupling of wave function between nearest neighbor bright sites mediated by STM tip. In Part 3, direct observation of graphene edges in presence and absence of magnetic fields was summarized. Short zigzag edges embedded in armchair edge contributed to the enhancement of electron density distribution, as the generation of edge states. STM observation under applied magnetic field indicated that the strong electron density near both zigzag and armchair edges could be ascribed to Landau levels on the Fermi energy. In summary, the present thesis clarified the correlation between local geometric structure and electronic structure at the graphene edges by means of STM.