Dresden 2014 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 9: Surface Chemical Reactions and Heterogeneous Catalysis I

O 9.2: Vortrag

Montag, 31. März 2014, 10:45–11:00, PHY C 213

Etching of Graphene on Ir(111) with Molecular Oxygen — •Ulrike A. Schröder1, Elin Grånäs2, Timm Gerber1, Mohammad A. Arman2, Karina Schulte3, Jan Knudsen2,3, Jesper N. Andersen2,3, and Thomas Michely11Universität zu Köln, II. Physikalisches Institut, Germany — 2Lund University, Division of Synchrotron Radiation Research, Sweden — 3Lund University, MAX IV Laboratory, Sweden

Although oxidation of carbon has been studied for decades, it remains unclear how oxygen attacks and oxidizes closed and submonolayer graphene on the atomic scale level. We provide new insights by using the well-defined system graphene on Ir(111) and exposing it to molecular oxygen.

Using scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and thermal desorption spectroscopy (TDS), we find that etching is a thermally activated process and depends on temperature and Gr morphology. For submonolayer Gr films, etching sets in at 550 K. The molecular oxygen dissociates on the free Ir(111) surface. Real time STM measurements reveal that oxygen then attacks Gr via the edges. Free edges are preferentially etched, compared to Gr bound to Ir steps. Perfectly closed Gr films are remarkably stable against oxygen etching, which only starts above 700 K. At this temperature, 5-7 defects stemming from the Gr growth process act as dissociation sites for the O2 molecules. At higher etching temperatures, large hexagonal etch holes are visible in the STM: Zigzag edges are more stable against etching than armchair edges.

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