title: Probing the intrinsic properties of exfoliated graphene: Raman spectroscopy of free-standing monolayers.
abstract: The properties of pristine, free-standing graphene monolayers prepared by mechanical exfoliation of graphite are investigated. The graphene monolayers, suspended over open trenches, are examined by means of spatially resolved Raman spectroscopy of the G-, D-, and 2D-phonon modes. The G-mode phonons exhibit reduced energies (1580 cm(-1)) and increased widths (14 cm(-1)) compared to the response of graphene monolayers supported on the SiO(2)-covered substrate. From analysis of the G-mode Raman spectra, we deduce that the free-standing graphene monolayers are essentially undoped, with an upper bound of 2 x 10(11) cm(-2) for the residual carrier concentration. On the supported regions, significantly higher and spatially inhomogeneous doping is observed. The free-standing graphene monolayers show little local disorder, based on the very weak Raman D-mode response. The two-phonon 2D mode of the free-standing graphene monolayers is downshifted in frequency compared to that of the supported region of the samples and exhibits a narrowed, positively skewed line shape.
authors.affiliation: Departments of Physics and Electrical Engineering and Department of Chemistry, Columbia University, New York, New York 10027, USA.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Berciaud
authors.forename: Sunmin
authors.initials: S
authors.lastname: Ryu
authors.forename: Louis E
authors.initials: LE
authors.lastname: Brus
authors.forename: Tony F
authors.initials: TF
authors.lastname: Heinz
mesh_terms: D003460:Crystallization / Q000379:methods*; D006108:Graphite / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008422:Materials Testing; D008968:Molecular Conformation; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure*; D036103:Nanotechnology / Q000379:methods*; D010316:Particle Size; D013059:Spectrum Analysis, Raman / Q000379:methods*; D013499:Surface Properties
chemical_list: D046911:Macromolecular Substances; D006108:Graphite