Intact-sheet double-layer ablation induced by femtosecond-laser excitation of graphite

Structural changes of graphite surfaces induced by femtosecond (fs) laser excitation at a fluence regime above 75 mJ/cm2 are reported. Direct imagings of excited surfaces by means of scanning tunneling microscopy have revealed that fs-excitations induce nanometer-scaled craters, together with sp3-type interlayer-bonded domains. The nano-craters are characterized by atomically-flat bottom and two atomic-steps in depth, indicating the exfoliation of fragmentary intact-sheets of double-layer of graphite. The theoretical simulation has shown that the required energy for the double-layer ablation is much lowered by the help of interlayer-bond formation, compared to the sequential removal of individual graphene layers. Based on the experimental and theoretical results, the exfoliation of double graphite layers, that is a novel mode of laser-ablation observed first, indicates clearly that the formation of strong interlayer bonds between the two atomic layers is a crucial step in the ablation process.