In order to shine further light on this issue, we have systematically investigated different types of epitaxial graphene/SiC(0001) samples using synchrotron-based grazing-incidence x-ray diffraction (GID). The GID analysis was complemented by Raman spectroscopy.
GID allowed us to measure the in-plane lattice parameters of single graphene layers, as well as of the BL (bare or covered by a monolayer graphene), with very high precision. Based on this, detailed information about the average strain level in each atomic layer could be obtained. We focused our attention on understanding the role played by the BL. We experimentally observed that its in-plane lattice parameter and corrugation changes when it is uncovered or beneath a monolayer of graphene. In the latter case, we made use of the GID results to unambiguously demonstrate that the BL is indeed the main responsible for the compressive strain generally measured in epitaxial monolayer graphene on SiC(0001).
By promoting its decoupling from the substrate via oxygen intercalation (thermal treatments in an O2-containing atmosphere leads to the oxidation of the SiC surface and breaking of the covalent bonds which connects the BL to SiC), the BL turns into a graphene monolayer.
Strikingly, this effect leads to a simultaneous relaxation of the uppermost monolayer graphene and formation of a strain-free graphene bilayer. The present results are of general relevance as they show that GID is a powerful tool for precise structural studies of purely two-dimensional (2D) atomic crystals.
|1||Author||T. Schumann , M. Dubslaff , M. H. Oliveira Jr. , M. Hanke , J. M. J. Lopes , H. Riechert|
The effect of the buffer layer coupling on the lattice parameter of epitaxial graphene on SiC(0001)
|Source||Phys. Rev. B , 90 , 041403(R) ( 2014 )|
: 10.1103/PhysRevB.90.041403 |
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