Probing Bilayer Grain Boundaries in Large Area Graphene with Tip-Enhanced Raman Spectroscopy
By: Kyoung-Duck Park, Markus B. Raschke, Joanna M. Atkin, Young Hee Lee, and Mun Seok Jeong
Advanced Materials 29, 1603601 (2017)
As contrasted with small graphene flakes, relatively little is known about the lattice and electronic structures of grain boundaries in large area graphene sheets, and their optical and Raman properties, despite their increasing significance for technological applications. Here we identify that grain boundaries in chemical vapor deposition grown large area graphene possess a twisted bilayer structure, as determined from correlated analyser of topography, near-field scattering, and multispectral tip-enhanced Raman spectroscopy (TERS) imaging with ~18 nm spatial resolution. In addition, we determine the misorientation angle of the bilayer grain boundaries from a detailed quantitative analysis of the phonon scattering properties associated with the modified electronic structure at the K-point of the Brillouin zone. We also investigate the distinct Raman characteristics of other defects such as wrinkles and nucleation sites, which are strongly correlated with nanoscopic structural curvature effects and atomic scale carbon hybridization. This work not only reveals the detailed properties of the defects in large area graphene at the nanoscale regime, but also demonstrates the potential of correlated analysis of multispectral TERS imaging as generally applicable to a wide range of two-dimensional materials beyond graphene.