Investigation of hexagonal 2D super structures by dynamic force spectroscopy : boron nitride and graphene on transition metals

Investigation of hexagonal 2D super structures by dynamic force spectroscopy
-Boron nitride and graphene on transition metals-
Inauguraldissertation zur Erlangung der Wuerde eines Doktors der Philosophie
The 2D hexagonal superstructures of h-BN on Rh(111) and graphene on
Ru(0001) were prepared. By Dynamic Force Microscopy(DFM) as well as
spectroscopy methods, these superstructures, which are due to specific lattice
mismatches between the overlayer and atomic lattice were highly resoluted
partly using bimodal DFM and verifying former investigations done by
scanning tunneling microscopy and photo electron spectroscopy. On both
samples, a contrast inversion of the superstructure was observed, so that
the former elevations appeared depressed. Further, 2D force spectroscopy
maps for the first time pointed out that a probably elastic deformation of
the elevated sites of the superstructure is the reason for the observed contrast
switching. Additionally, Kelvin Probe Force Microscopy measurements
(KPFM) were complemented by 2D KPFM maps. The results showed, that
the substrate bonded sites of the 2D monolayers are areas of lower work
function, which is supported by former PES measurements as well as calculations.
Finally the influence of a elastic deformation or rather contrast
inversion on the workfunction was determined, showing an increasing of work
function for the elevated sites pushed towards the transition metal substrate.