| AVS 56th International Symposium & Exhibition | |
| Graphene Topical Conference | Tuesday Sessions |
| Session GR+TF-TuA |
| Session: | Graphene: Characterization, Properties, and Applications |
| Presenter: | B. Borca, Universidad Autónoma de Madrid, Spain |
| Authors: | S. Barja, Universidad Autónoma de Madrid, Spain B. Borca, Universidad Autónoma de Madrid, Spain M. Garnica, IMDEA Nanociencia, Spain F. Hermanns, Universidad Autónoma de Madrid, Spain J.J. Hinarejos, Universidad Autónoma de Madrid, Spain A.L. Vazquez de Parga, UAM & IMDEA Nanociencia, Spain R. Miranda, UAM & IMDEA Nanociencia, Spain |
| Correspondent: | Click to Email |
Moiré patterns are generated by the superposition of two periodic structures with a lattice mismatch. They have been observed by means of Scanning Tunneling Microscopy (STM) on different systems and their interpretation, in some cases, is not straightforward. The influence, at the atomic scale, of these patterns in the local density of states of the overlayer is not clear and can be studied by STM.
The growth of graphene on metallic substrates allow us not only control the periodicity of the Moiré pattern but also tailor the interaction strength between the carbon atoms and the metallic substrate [1]. In this work we compare the results obtained on graphene overlayers grown on two different metallic substrates. We studied graphene/Ir(111) and graphene/Ru(0001) in the former there is a weak interaction between the graphene overlayer and the substrate and in the later the strength of the chemical interaction is modulated by the Moiré pattern.
Field Emission Resonances (FERs), which are detected by STM when applying voltages larger than the work function, can be used to explore with nanometer resolution, the inhomogeneities in the local surface potential landscape. Operating the STM in constant current mode implies a constant electric field between tip and sample and the expected energy position for the FERs is given by the expression founded by Gundlach some time ago [2]. From that expression it is possible to determine experimentally the local work function of the surface. We applied this method to the Moiré pattern formed by graphene grown on Ir(111) and Ru(0001). For graphene on Ir(111) we did not find any modulation in the work function due to the Moiré pattern. On the contrary for graphene on Ru(0001) we have found a difference of 0.25 eV in the work function values depending on the position on the Moiré pattern. For graphene on Ru(0001) we also found that the energy position of the first FER presents strong spatial variations that can be measured by scanning tunneling spectroscopy. In fact, for the grahene/Ru(0001) system, the energy position of the first FER is not easily related with the local work function and is modified by the interaction between graphene and the Ruthenium underneath. The energy position of the higher FERs is only influenced by the variations in the local work function.
[1] A.B. Preobrajenski et al., Phys. Rev. B 78, 073401 (2008)
[2] K.H. Gundlach, Solid State Electron. 9, 949 (1966)