Program

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Tuesday June 23

Tu3: Chemistry and growth of graphene

Chair: H. Hedgeland, London, UK

Contributed talk

Helium diffraction from graphene grown by chemical vapor deposition on copper catalysts

A. Al Taleb¹, H. Ki Yu^2,3, G. Anemone¹, A. M. Wodtke^2,3, and D. Farías^1,4,5

¹Departamento de Física de la Materia Condensada, Universidad Autónoma de Madrid, Spain

²Institute for Physical Chemistry, University of Göttingen, 37077 Göttingen, Germany

³Max Planck Institute for Biophysical Chemistry, 37077 Göttingen, Germany

⁴Instituto "Nicolás Cabrera", Universidad Autónoma de Madrid, Spain

⁵Condensed Matter Physics Center (IFIMAC), Universidad Autónoma de Madrid, Spain

In this work we use Helium atom scattering (HAS) as a sensitive probe of the crystallinity of graphene grown by chemical vapor deposition (CVD) on Cu, and as a probe of its interactions with its substrate. The high sensitivity of HAS to surface defects [1] precluded its use with current available graphene/Cu foils. Our current results have been obtained using graphene/Cu(111) grown on sapphire samples and graphene grown on a peeled-off epitaxial Cu(111) foil using a recently developed scheme [2]. We have measured the structure and the acoustic phonon modes of CVD graphene grown on these two samples. The observation of high reflectivities and clear diffraction peaks demonstrates the presence of high-quality graphene, with both long-range order and a very low density of defects over a surface area of the order of 1mm². The shape of elastic and quasi-elastic scattering features proves that, surprisingly, graphene grown on a peeled-off epitaxial Cu(111) foil exhibits a much higher crystallinity than the one grown on Cu(111)/Al₂O₃ samples. The graphene lattice parameter was found to remain constant in the temperature range between 110-500 K, which proves that graphene is decoupled from the Cu substrate. A parabolic dispersion phonon branch has been measured along ΓM, as expected for the acoustic ZA mode in free-standing graphene.

[1] B. Poelsema and G. Comsa, Scattering of Thermal Energy Atoms from Disordered Surfaces. Springer Tracts in Modern Physics 115. Springer, Berlin, (1989)

[2] H. K. Yu, K. Balasubramanian, K. Kim, J.-L. Lee, M. Maiti, C. Ropers, J. Krieg, K. Kern, and A. M. Wodtke, ACS Nano 8, 8636 (2014)