Program

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Tuesday June 23

Tu4: Electron-phonon coupling in graphene

Chair: W. Widdra, Halle, Germany

Contributed talk

Nanostructured phonons in epitaxial graphene on ruthenium surfaces

D. Stradi¹, C. Diaz², P. Ordejon³, F. Martin^2,4, T. Frederiksen^5,6, M. Brandbyge¹

¹Center for Nanostructured Graphene (CNG), Department for Micro- and Nanotechnology (DTU Nanotech), Technical University of Denmark, 2800 Kgs. Lyngby, Denmark

²Department of Chemistry, Autonomous University of Madrid, 28049 Madrid, Spain

³CSIC and ICN2 – Institut Català de Nanociència i Nanotecnologia, 08193 Barcelona, Spain

⁴IMDEA Nanoscience – Madrid Institute for Advanced Studies in Nanoscience, 28049 Madrid, Spain

⁵Donostia International Physics Center (DIPC), 20018 Donostia-San Sebastian, Spain

⁶IKERBASQUE, Basque Foundation for Science, 48013 Bilbao, Spain

The growth of epitaxial graphene on lattice-mismatched metallic substrates has emerged as a well-established method to achieve high quality and ultra-perfect nanostructured graphene samples [1]. By varying the nature of the metallic substrate, atomic-scale control can be exerted on the graphene-metal interaction and on the resulting properties of the supported graphene layer, as demonstrated by the observation of periodic deformations in the graphene morphology [2] as well as of highly confined electronic states appearing in the proximity of the Fermi level and well above it [3,4]. Nevertheless, the impact of such modulations on the vibrational properties of these systems has been explored to a much lesser extent [5,6]. Here, we characterize the phonons of the moiré superstructure formed by epitaxial monolayer graphene on Ru(0001) by large-scale frozen phonons density functional theory simulations to evaluate the lattice vibrations and the associated electron-phonon couplings [7,8]. We find that, as a consequence of the adsorption on the Ru(0001) surface, the vibrational properties of the graphene layer are strongly modified with respect to the freestanding counterpart, due to the appearance of, e.g., highly confined phonons appearing in the regions of the graphene/Ru(0001) moiré in which the graphene is more detached from the metallic substrate, as shown in Figure 1.

Figure 1: Highly confined phonon in epitaxial graphene on Ru(0001).

[1] J. Wintterlin and M.L. Boquet, Surf. Sci. 603, 1841 (2009)

[2] B. Wang et al., Phys. Chem. Chem. Phys. 10, 3530 (2008)

[3] B. Borca et al., Phys. Rev. Lett. 105, 036804 (2010)

[4] D. Stradi et al., Phys. Rev. B 85, 121404 (2012)

[5] S. Koch et al., ACS Nano 7, 2927 (2013)

[6] A. Castellanos-Gomez et al., Appl. Phys. Lett. 102, 063114 (2013)

[7] J. M. Soler et al., J. Phys.: Cond. Matter 14, 2745 (2002)

[8] T. Frederiksen et al., Phys. Rev. B 75, 205413 (2007)