  Chemical oxidation of multilayer graphene grown on silicon carbide yields
films exhibiting reproducible characteristics, lateral uniformity, smoothness
over large areas, and manageable chemical complexity, thereby opening
opportunities to accelerate both fundamental understanding and technological
applications of this form of graphene oxide films. Here, we investigate the
vertical inter-layer structure of these ultra-thin oxide films. X-ray
diffraction, atomic force microscopy, and IR experiments show that the
multilayer films exhibit excellent inter-layer registry, little amount (<10%)
of intercalated water, and unexpectedly large interlayer separations of about
9.35 {\AA}. Density functional theory calculations show that the apparent
contradiction of "little water but large interlayer spacing in the graphene
oxide films" can be explained by considering a multilayer film formed by carbon
layers presenting, at the nanoscale, a non-homogenous oxidation, where
non-oxidized and highly oxidized nano-domains coexist and where a few water
molecules trapped between oxidized regions of the stacked layers are sufficient
to account for the observed large inter-layer separations. This work sheds
light on both the vertical and intra-layer structure of graphene oxide films
grown on silicon carbide, and more in general, it provides novel insight on the
relationship between inter-layer spacing, water content, and structure of
graphene/graphite oxide materials.
