Abstract
The intrinsic atomic mechanisms responsible for electronic doping of epitaxial graphene Moirés on transition metal surfaces is still an open issue. To better understand this process we have carried out a first-principles full characterization of the most representative Moiré superstructures observed on the Gr/Pt(111) system and confronted the results with atomically resolved scanning tunneling microscopy experiments. We find that for all reported Moirés the system relaxes inducing a non-negligible atomic corrugation both, at the graphene and at the outermost platinum layer. Interestingly, a mirror “anti-Moiré” reconstruction appears at the substrate, giving rise to the appearance of pinning-points. We show that these points are responsible for the development of the superstructure, while charge from the Pt substrate is injected into the graphene, inducing a local n-doping, mostly localized at these specific pinning-point positions.
Highlights
We have performed a quantitative theoretical characterization of five of the most stable and representative Moiré superstructures predicted by our aforementioned geometrical model[19], by using, as explained, two different atomistic simulation packages: the plane-wave code PWSCF25 used for the structural optimization of the atomic configurations accounting van der Waals forces; and the localized basis set code FIREBALL26 for the theoretical Keldish-Green scanning tunneling microscopy (STM) imaging calculations
Our group has proposed a simple model to study Gr/transition metal (TM)(111) systems[19]. This phenomenological model describes the stability of a Moirés on TM(111) surfaces taking only into account the lattice parameters of substrate and graphene, and yielding, as an example, a large number of different Moiré patterns (22) for the Gr/ Pt(111) system. Comparing these predictions with the structures observed in our scanning tunneling microscopy (STM) sessions we find a rather surprising agreement
We have reported on the effect of the tip geometry in the theoretical STM images within the Keldysh—Green formalism[40]
Summary
We have performed a quantitative theoretical characterization of five of the most stable and representative Moiré superstructures predicted by our aforementioned geometrical model[19], by using, as explained, two different atomistic simulation packages: the plane-wave code PWSCF25 used for the structural optimization of the atomic configurations accounting van der Waals forces; and the localized basis set code FIREBALL26 for the theoretical Keldish-Green STM imaging calculations. The charge transfers obtained are 0.0057, 0.0067, 0.0073, 0.0106 and 0.0114 e− per C atom for the βR19 , εR8.9 , μR0.8 , ζR7.2 , and ζR25 Moirés, respectively, always occurring from the Pt substrate towards the graphene, which manifests the n-doped character of the graphene layer in all the superstructures, as reported previously[44].
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