Characteristics of thin graphene sheets prepared by a laser ablation method

Graphenes are innovative carbon materials having a sheet-like structure; these materials are thought to have many applications in the fields of electrochemistry, biomedicine, and so on. In this study, we showed that thin graphene sheets (TGSs) prepared by a laser ablation method had a distinctive structure: even-number layered graphenes (2-, 4-, 6- and 8-layers) were preferentially grown (ca. 90{\%}), and their population decreased as the layer number increased. These phenomena have not been observed in graphenes prepared with other methods. Our results suggest a new growth mechanism in which single-layer graphene is unstable and bends to form bi-layers, and the bi-layers then go on to stack and form thicker TGSs. The inter-layer distances estimated by transmission electron microscope images were about 15{\%} larger than that of bulk graphite in the bi-layer TGSs, and they approached the bulk value as the layer number increased. Furthermore, we showed surface-selective functionalization of TGSs by mild oxidation with H$_{2}$O$_{2}$ at room temperature, indicating the possibility of multi-modal functionalization, which will make the graphene more attractive in various applications.