In the quest for new heterogeneous catalysis materials, structures based on atomically thin carbon nanosheets are of a promising class. Here, by means of scanning tunneling microscopy (STM) and density functional theory (DFT) we investigate chemical functionalization of graphene supported on Ru(0001) with atomic oxygen (AO). The local differences in the periodic Moiré structure of graphene on the metal offer three types of distinct adsorption sites: bright regions with largest distances from the metal substrate (TOP), dark regions closest to the metal (HCP), and medium-bright regions slightly further than the dark ones (FCC). AO is mainly observed within the medium-bright regions and starts to diffuse above 400 K. By analyzing the AO diffusion paths we show that AO is located on top of carbon atoms, forming enolate groups. In agreement with experiments, our DFT calculations show that the stability of atomic oxygen is strongly region-dependent, and increases from TOP, to HCP and FCC, as clearly evidenced by the calculated adsorption energy of +0.18, -1.28, -1.67 eV, respectively. In the HCP and FCC regions, the enolate structure is the most stable while the bridge site adsorption is unstable. We have also found that in the TOP region the stable AO binding configuration is in the bridge position. This is because in the TOP region, graphene is much less affected by the Ru support, while in the HCP and FCC regions the adsorption of AO is stabilized by the formation of C-Ru bonds. Computationally, the maximum diffusion barrier of AO in all regions is about 1.1 eV, consistent with the onset temperature for AO diffusion of 400 K. The methods developed in this manuscript can be easily transferred to any supported graphene systems to determine adsorption structures of different ad-atoms.

Identifying the adsorption sites of atomic oxygen on Ru(0001)-supported graphene

254th National Meeting (2017)

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