Dresden 2011 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 98: Graphene VI

O 98.1: Vortrag

Freitag, 18. März 2011, 11:15–11:30, WIL A317

Tuning the Kohn Anomaly in the Phonon Dispersion of Graphene by Interaction with the Substrate — •Ludger Wirtz and Adrien Allard — Institute for Electronics, Microelectronics, and Nanotechnology (IEMN), CNRS, Lille, France

The phonon dispersion of graphene displays two strong Kohn Anomalies (kinks) in the highest optical branch (HOB) at the high-symmetry points G and K. The slope of the HOB around K is a measure of the electron-phonon coupling (EPC) and determines the dispersion of the Raman D and 2D lines as a function of the laser energy [1]. We show that the EPC can be strongly modified both due to interaction with the substrate [2] (in particular, if the substrate is metallic) and due to doping [3]. For graphene grown on a Ni(111) surface, a total suppression of the Kohn anomaly occurs: the HOB around K becomes completely flat. This is due to the strong hybridization of the graphene pi-bands with the Nickel d-bands which lifts the linear crossing of the pi-bands at K. For other metallic substrates, where the distance between the graphene sheet and the substrate is larger, hybridization is much less pronounced and the Kohn anomaly is only weakly perturbed. From experimental phonon dispersions one can therefore draw conclusions about the interaction strength between graphene and its different substrates .

[1] S. Piscanec, M. Lazzeri, F. Mauri, A.C. Ferrari, and J. Robertson, PRL 93, 185503 (2004). [2] C. Attaccalite, L. Wirtz, M. Lazzeri, F. Mauri, and A. Rubio, Nano Lett. 10, 1172 (2010). [3] A. Allard and L. Wirtz, Nano Lett. 10, 4335 (2010)