| AVS 60th International Symposium and Exhibition | |
| Graphene and Other 2D Materials Focus Topic | Wednesday Sessions |
| Session GR+AS+EM+NS+SS-WeA |
| Session: | Dopants, Defects and Interfaces in 2D Materials |
| Presenter: | X. Feng, Lawrence Berkeley National Laboratory |
| Authors: | X. Feng, Lawrence Berkeley National Laboratory M.B. Salmeron, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
Epitaxial graphene on metal substrates has been demonstrated to be a promising route for graphene synthesis. The produced graphene is however typically polycrystalline, with defects that can affect its properties. The impact of defects might be critical when graphene interacts with gas molecules due to their enhanced reactivity, so there is a need to understand the adsorption of environmentally abundant molecules (such as water and oxygen). Here we report a study of water adsorption on epitaxial graphene on Ru and Cu substrates using scanning tunneling microscopy (STM). We found that on Ru(0001), graphene line defects are extremely fragile towards chemical attack by water, which splits the graphene into numerous fragments at temperatures as low as 90 K, followed by water intercalation under the graphene [1]. On Cu(111) water can also split graphene but far less effectively, indicating that the chemical nature of the substrate strongly affects the reactivity of C-C bonds in epitaxial graphene.
The graphene splitting produced many graphene flakes that were displaced onto the first graphene layer on Ru. These flakes show very facile translational and rotational motions between commensurate initial and final states at temperatures as low as 5 K. The motion is initiated by a transition of the flakes from a commensurate to an incommensurate registry with the underlying graphene (the superlubric state), followed by a rapid sliding until another commensurate position is reached [2]. We also studied the electronic screening effects in stacked graphene flakes on Ru. The screening affects the apparent STM height of each flake in successive layers reflecting the density of states near the Fermi level and thus the doping level. It is revealed in this way that the strong doping of the first graphene layer on Ru(0001) is attenuated in the second one, and almost eliminated in the third and fourth layer [3].
References:
[1] X. Feng, S. Maier and M. Salmeron. J. Am. Chem. Soc.134, 5662–5668 (2012).
[2] X. Feng, S. Kwon, J. Y. Park and M. Salmeron. ACS Nano7, 1718–1724 (2013).
[3] X. Feng and M. Salmeron. Appl. Phys. Lett.102, 053116 (2013).