Scanning tunneling microscopy and X-ray photoelectron spectroscopy studies of graphene films prepared by sonication-assisted dispersion.

We describe scanning tunneling microscopy and X-ray photoelectron spectroscopy studies of graphene films produced by sonication-assisted dispersion. Defects in these samples are not randomly distributed, and the graphene films exhibit a "patchwork" structure where unperturbed graphene areas are adjacent to heavily functionalized ones. Adjacent graphene layers are likely in poor mechanical contact due to adventitious species trapped between the carbon sheets of the sample.