Pentagons and Heptagons on Edges of Graphene Nanoflakes Analyzed by X-ray Photoelectron and Raman Spectroscopy.

Identifying pentagons and heptagons in graphene nanoflake (GNF) structures at the atomic scale is important to completely understand the chemical and physical properties of these materials. Herein, we used X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy to analyze the spectral features of GNFs according to the position of pentagons and heptagons introduced onto their zigzag and armchair edges. The XPS peak maxima were shifted to higher binding energies by introducing the pentagons or heptagons on armchair rather than zigzag edges, and the structures could be distinguished depending on the positions of the introduced pentagons or heptagons. Raman spectroscopic analyses also revealed that the position of edges with introduced pentagons or heptagons could also be identified using Raman spectroscopy, with characteristic bands appearing at 800-1200 cm-1, following the introduction of either pentagons or heptagons on armchair edges. This precise spectroscopic identification of pentagons and heptagons in GNFs provides the groundwork for the analysis of graphene-related materials.