Stacking structures of few-layer graphene revealed by phase-sensitive infrared nanoscopy

The stacking orders in few-layer graphene (FLG) strongly influences the electronic properties of the material. To explore the stacking-specific properties of FLG in detail, one needs powerful microscopy techniques that visualize stacking domains with sufficient spatial resolution. We demonstrate that infrared (IR) scattering scanning near-field optical microscopy (sSNOM) directly maps out the stacking domains of FLG with a nanometric resolution, based on the stacking-specific IR conductivities of FLG. The intensity and phase contrasts of sSNOM are compared with the sSNOM contrast model, which is based on the dipolar tip-sample coupling and the theoretical conductivity spectra of FLG, allowing a clear assignment of each FLG domain as Bernal, rhombohedral, or intermediate stacks for tri-, tetra-, and pentalayer graphene. The method offers 10-100 times better spatial resolution than the far-field Raman and infrared spectroscopic methods, yet it allows far more experimental flexibility than the scanning tunneling microscopy and electron microscopy.The work is supported by the SNU grant (Research Resettlement Fund for the new faculty of SNU, for D.S.K., H.K, and Z.H.K.), NRF Grant No. 2014001871 (for D.S.K., H.K., and Z.H.K.), by NRF Grant No. 2012R1A1A1013963 (for S.A. and H.M.), by NRF Grant No 2014M3A6A5060934 (for S.R.), by EU Graphene Flagship contract no. 604391 (for L.M.- M.), and by the Spanish Ministerio de Economia y Competitividad within project MAT2011-28581-C02 (for A.Y.N., L.M.-.M, and F.J. G.-V.).Peer Reviewe