| AVS 60th International Symposium and Exhibition | |
| Graphene and Other 2D Materials Focus Topic | Wednesday Sessions |
| Session GR-WeM |
| Session: | 2D Materials on Metallic Substrates |
| Presenter: | D. Menzel, Technical University Muenchen, Germany |
| Authors: | D. Menzel, Technical University Muenchen, Germany P. Lacovig, Sincrotrone Trieste, Italy R. Larciprete, CNR Inst. for Complex Systems, Italy M. Dalmiglio, Sincrotrone Trieste, Italy K.L. Kostov, Bulgarian Academy of Sciences, Bulgaria S. Lizzit, Sincrotrone Trieste, Italy |
| Correspondent: | Click to Email |
The unique electronic properties of graphene (Gr) are being investigated vigorously with the entire arsenal of surface science. Nevertheless the dynamics of excited states remote from the Dirac cone range are still not well known, even though they should be important for photochemistry on Gr and for contact formation in electrochemistry. In a late breaking contribution at the AVS meeting last year we have reported our preliminary results on the investigation of ultrafast charge transfer at Gr monolayers on substrates with strongly varying coupling, using the well-established core-hole-clock method with adsorbed argon [1]. We have shown [2] that decoupled layers, irrespective of the way of decoupling, show the same rather slow charge transfer despite the high empty DOS at the relevant energies about 1.5 eV above the Dirac point. This slowdown has been tentatively explained by the local charge accumulation interfering with CT, similar to dynamical Coulomb blockade [3]. On Ru(0001) the much faster CT, graded depending on the location on the periodically buckled Gr layer, has been explained by the degree of hybridisation of Gr empty states with substrate states. The results on the Gr "hills" on Ru(0001) and on Pt(111), which are characterized by considerably faster CT than on the decoupled layers, show that these layers - often assumed to be essentially bound only by Van der Waals forces - must also exhibit considerable hybridisation. We have now extended our investigation to Gr on Ni(111) which, due to the good lattice match, is a flat layer and does not possess a Dirac cone, so that good coupling and fast CT should be expected. The results however, show CT much slower than on the Gr "valleys" on Ru, and about as fast as on the Gr "hills" on Ru. We will discuss this unexpected result in terms of hybridising states and the surface DOS. Another interesting finding is that oxygen intercalation acts very differently on Gr/Ni(111) from Gr/Ru(0001). While on Gr/Ru it fully decouples the Gr layer [2], for Gr/Ni much faster CT persists.
[1] See, e.g., D. Menzel, Chem. Soc. Rev. 37, 2212 (2008), and references therein.
[2] Lizzit et al., AVS-59, abstract #1538. S. Lizzit et al., ACS Nano (in press), DOI: 10.1021/nn4008862
[3] C. Brun et al., Phys. Rev. Lett. 108, 126802 (2012).