Surface diffusion and dynamics on Dirac materials. (Please notice the unusual time!)

DIPC Seminars

Dr. Anton Tamtögl, Institute of Experimental Physics, Graz University of Technology, Graz, Austria
Donostia International Physics Center
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Surface diffusion and dynamics on Dirac materials. (Please notice the unusual time!) We have studied the diffusion of water on the surfaces of Dirac materials (graphene and the topological insulator Bi2Te3) using helium-3 spin-echo spectroscopy[1]. While water is ubiquitous in everyday life, the simplest mechanisms controlling its molecular motion at a surface have yet to be revealed by experiment[2-4]. Our experimental results provide a detailed insight into the behaviour of H2O molecules on the surfaces of Dirac materials. Diffusion occurs by an activated hopping motion where in particular in the case of graphene a strong signature for cooperative behaviour due to repulsive forces between the molecules appears. The diffusion of water on Bi2Te3 is governed by a large atomic-scale friction between the adsorbate and the substrate. I will also present some details on the surface dynamics of pristine topological insulator surfaces. The atom-surface scattering probabilities can be used to extract the electron-phonon coupling of topological insulator surfaces[5] and inelastic helium atom scattering measurements are able to resolve the acoustic surface phonon modes of Bi2Te3. Here the low energy region of the lattice vibrations is mainly dominated by the Rayleigh mode which has been claimed to be absent in previous experimental studies. [1] A. Jardine _et al._ , Prog. Surf. Sci. 84, 323 (2009). [2] A. Hodgson _et al._ , Surf. Sci. Rep. 64, 381 (2009). [3] S.-C. Heidorn _et al._ ACS Nano 9, 3572 (2015). [4] J. Carrasco _et al._ , Nat. Mater. 11, 667 (2012). [5] A. Tamtögl _et al._ , Phys. Rev. B. 95. 195401 (2017).