Center for Functional Nanomaterials Seminar

Epitaxial graphene on Ru (0001) surface has led to recent scientific activities [1-2 and a lot more],
since it is thought to be a smart way to obtain large-scale graphene.
In the last two years, we have investigated epitaxial graphene on Ru(0001) by means of large-scale
DFT calculations and STM-based imaging and spectroscopy simulations. In contrast to similar studies
of graphene on Ir(111) [3], we show that the graphene layer displays a large geometric buckling of 1.5
Ǻ over the 30 Ǻ periodic moire structure [4]. The buckling arises from strong chemical contact when
one of the two carbon atoms of the graphene unit cell sits atop on Ru surface atoms. This perfect
matching occurs in very localized regions of the moire unit cell, where atop C atoms gain electrons
from Ru, while the neighboring hollow C atoms loose electrons. This gives rise to a 2 eV band gap
opening of the graphene electronic states, which has been verified in an ARUPS measurement [5].
STM simulations of the buckled model agree well with the STM images unravelling 3-fold symmetry in the low (dark) regions of the moire. STS simulations [6] also reproduce the asymmetry found in the measurements [7] between low and high-lying C electronic states.
More recently we tackle other issues like the Moire periodicity and the work fonction variation upon
the graphene covering. We propose that the 11 Ru periodicity structure is an absolute minimum among smaller (10-fold) and larger commensurabilities (12-fold). We thus confirm the stability of the SXRD-detected 23x23 structure [8] consisting of four 11.5-fold-quasi periodicity. Secondly, we unveil that the reduced work function originates from the charge depletion in the graphene skeleton states at the bonded carbon atoms, despite the n-doping of the π states. [9]
Finally, we explore the adsorption properties of this template with respect to metals by comparing adsorption of Au and Pt single atoms.