| AVS 59th Annual International Symposium and Exhibition | |
| Late Breaking Session | Wednesday Sessions |
| Session LB+EM+GR+MN+TR-WeA |
| Session: | Select Topics in Surface and Interface Science |
| Presenter: | S. Lizzit, ELETTRA Sincrotrone Trieste, Italy |
| Authors: | S. Lizzit, ELETTRA Sincrotrone Trieste, Italy R. Larciprete, CNR , Institute of Complex Systems, Italy P. Lacovig, ELETTRA Sincrotrone Trieste, Italy K. Kostov, Bulgarian Academy of Sciences, Bulgaria D. Menzel, Technische Universität München and Fritz Haber Institute, Germany |
| Correspondent: | Click to Email |
The importance and scientific appeal of graphene monolayers (Gr) are out of question, and investigations of its electronic properties abound. Most of these center on the most spectacular region, that around the Dirac cone, which is also the most relevant region for possible devices. But regions outside of this region are also important, since their correct representation requires basic understanding, and since they may relate to applications in photonics, photochemistry, and contact formation. Also, static investigations are more frequent than those of dynamics.
We present here the first investigation of electron dynamics at energies above the Fermi (and Dirac) energy but below the vacuum level [1]. To this purpose we used the core hole clock (CHC) method with adsorbed argon and measured the transfer rate of a localized electron (the 4s electron on core-excited Ar) to the surface of Gr monolayers with variable substrate coupling: strong but graded coupling for Gr on Ru(0001) ("valleys" and "hills"), and decoupled Gr ML on SiO2. We obtained the latter system by using the recently developed transfer-free approach [2] based on the synthesis of SiO2 layers directly below Gr epitaxially grown on Ru(0001), through a stepwise reaction between intercalated silicon and oxygen. This method provides the optimal system to study the electronic properties of Gr using spectroscopic approaches, such as the CHC method.
We find strong variations of CT time between ~3 fs (Gr ML strongly coupled to substrate on Ru(0001) “valleys”) and ~ 16 fs (decoupled Gr on SiO2). A ratio of 1.7 is found between the “hills” and “valleys” of the corrugated Gr/Ru. The very fast CT on Gr/Ru valleys is interpreted as due to hybridized Ru orbitals "reaching through" the Gr layer which change with the relative Gr/Ru alignment and distance. On the decoupled Gr layers the intrinsic coupling to the Gr empty π* states determines the CT time. The intermediate CT time for the Gr hills on Ru shows that these regions are far from the "decoupled" condition. The results contribute new information on the still controversial states of Gr/Ru, and shed light on the empty density of states above Gr surfaces and the coupling to them in an energy range possibly important for photonic applications of Gr, such as solar energy conversion.
[1] S. Lizzit, R. Larciprete, P. Lacovig, K.L.Kostov, D. Menzel, in preparation
[2] S. Lizzit et al. Nanoletters (2012) DOI: 10.1021/nl301614j