Scanning Tunneling Microscopy Study of Fluorinated Graphene on Copper

We probe by ultrahigh vacuum scanning tunneling microscopy (UHV-STM) the structural and electronic properties of monolayer fluorinated graphene (C$_{x}$F, x$\approx $4) synthesized by chemical vapor deposition on copper substrates and fluorinated by xenon difluoride gas [1]. The chemical composition and structure of the resulting film is probed by x-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and scanning tunneling spectroscopy (STS). In contrast to metallic graphene, this material exhibits a large ($>$3 eV) band gap with a muted gap state corresponding to a copper surface state near -0.4 eV. We further investigate by STM alignment between the fluorographenic surface layer and copper substrate, uniformity of fluorination, and stability of fluorinated graphene under electron bombardment and thermal annealing.\\[4pt] [1] J.T. Robinson, et al., Nano Lett. 10, 3001-2005 (2010)