Film Structure of Epitaxial Graphene Oxide on SiC: Insight on the Relationship Between Interlayer Spacing, Water Content, and Intralayer Structure

Abstract

International audienceChemical 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 Å. 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 fi lm 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

Elastic coupling between layers in two-dimensional materials

“…We also find that 10-layer EGO is much softer than 10-layer EG; this result can be explained by the increase of the interlayer distance d, in EGO compared with EG, precisely from d = 3.4 Å to d = 9.3 Å (ref. 48) as also observed in X-ray diffraction spectroscopy measurements 49 . The more surprising result is the difference in the perpendicular elasticity between EGO films and GO films produced with the conventional exfoliation/filtration/deposition method (see Methods).…”

“…Owing to this explanation, it is now possible to understand the different values of E ⊥ in EGO compared with conventional GO. EGO is not a porous structure, and water intercalation is minimal 49 and independent of humidity. For this reason we find that E ⊥ in EGO remains constant and ∼22 GPa for all RHs.…”

“…To prepare EGO samples, the 10-layer EG samples on SiC chips are then directly oxidized shortly after preparation by using a milder Hummers' method 49 , which avoids graphene exfoliation and dispersion in solution. Once the reactions are terminated, EGO films on the SiC chips are picked up from the solution and rinsed with deionized water for 1 min.…”

Signatures of different carbon bonds in graphene oxide from soft x-ray reflectometry

“…[18,22] This and the other conclusions based on the x-ray reflectometry may, however, be compared with those that can be drawn from Fourier transform infrared (FT-IR) spectra of the same samples that are shown in Fig. 6.…”

“…[17] A recent report, however, proposes that the large interlayer spacing of graphene oxide is mostly due to hydroxyl groups decorating the graphene oxide, regardless of the content of water molecules between layers. [18] Soft x-ray reflection spectroscopy Soft x-ray reflection spectroscopy was performed on the graphene oxide samples at beamline 11 originating at the U55 undulator of the 1.5 GeV DELTA synchrotron in Dortmund, Germany. [19] This permanent magnet undulator delivers linearly polarized light over an energy range of 55-1500 eV with a horizontal linear polarization plane.…”