Reconstruction of Vacancy Defects in Graphene and Carbon Nanotube

Recently, various structures of vacancy defects in graphene layers and carbon nanotubes have been reported by high resolution transmission electron microscope (HR-TEM) and those arouse an interest of reconstruction processes of vacancy defects. In this talk, we present reconstruction processes of vacancy defects in a graphene and a carbon nanotube by tight- binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. We~found that a structure of a dislocation defect with two pentagon-heptagon (5-7) pairs in grapheme becomes more stable than other structures when the number of vacancy units is ten and over. The simulation study of scanning tunneling microscopy reveals that the pentagon-heptagon pair defects perturb the wavefunction of electrons near Fermi level to produce the $\surd 3 \times \surd$3 superlattice pattern, which is good agreement with experiment. It is also observed in our tight- binding molecular dynamics simulation that 5-7 pair defects play a very important role in vacancy reconstruction in a graphene layer and carbon nanotubes.