Hexagonal moiré superlattices, twist-angle disorder and rhombohedral-stacking in a commercially available grafoil-film

Abstract

We report an advanced investigation on the structural properties of graphitic interfaces within a commercially available film of grafoil, by employing a combination of high-resolution transmission electron microscopy (HRTEM), selective area electron diffraction (SAED) and Raman mapping and point spectroscopy. We identify large-area hexagonal moiré superlattices with dimensions in the order of 2 μm ∗ 2 μm, with a periodicity ranging from D ∼ 12 nm to D ∼ 22 nm, which correspond to a variable twist angle parameter θtwist from 0.65° to 1.15°. These sample regions identified with HRTEM evidence the presence of local structural disorder (twist-angle moiré disorder). By employing SAED we identify the possible presence of a disordered A|ABAB|BCBC|CACA|A stacking sequence, which corresponds to a disordered rhombohedral phase, previously identified in nitrates-intercalated graphitic systems. The structural components and parameters associated to this phase were analysed by employing a combination of techniques, including HRTEM, SAED, Raman point and mapping spectroscopy, X-ray diffraction (XRD) and Rietveld refinements. In particular, XRD, Rietveld refinements and calculated diffractograms evidence the presence of coexisting disordered and crystalline rhombohedral phases in the analysed film.