| AVS 59th Annual International Symposium and Exhibition | |
| Graphene and Related Materials Focus Topic | Tuesday Sessions |
| Session GR+AS+NS+SP+SS-TuA |
| Session: | Graphene Characterization Including Microscopy and Spectroscopy |
| Presenter: | E. Grånäs, Lund University, Sweden |
| Authors: | E. Grånäs, Lund University, Sweden J. Knudsen, Lund University, Sweden U. Schröder, Universität zu Köln, Germany T. Gerber, Universität zu Köln, Germany C. Busse, Universität zu Köln, Germany M.A. Arman, Lund University, Sweden K. Schulte, Lund University, Sweden J.N. Andersen, Lund University, Sweden T.W. Michely, Universität zu Köln, Germany |
| Correspondent: | Click to Email |
Intercalation of gases between epitaxial graphene and its substrate has become a topic of interest for studies due to, for example, the unique opportunities to modify the graphene-substrate interaction and the possibilities to perform chemistry under the graphene layer. Further, a profound knowledge about graphenes stability in gases at elevated temperatures and pressures is essential for, among other things, the correct interpretation of gas adsorption studies on graphene supported metal cluster arrays.
We have studied intercalation and etching of Ir(111) supported graphene upon gas exposure to common gasses such as O2 and CO in the entire pressure interval from 10-8 to 0.1 mbar. Comparing perfect graphene layers without holes with graphene films, that only covers a fraction of the Ir(111) surface, we reveal that the holes - or more specific the graphene edges - are essential for intercalation.
For oxygen exposed graphene we develop a coherent picture of temperature dependent oxygen etching and intercalation. Using X-ray photoemission spectroscopy (XPS) and scanning tunnelling microscopy (STM) we show that a perfect graphene layer is stable against etching and intercalation up to 700 K, whereas at higher temperatures etching, but no intercalation, takes place. In contrast, a partial graphene coverage on Ir(111) enables dissociative oxygen adsorption on the bare Ir and subsequent intercalation underneath graphene flakes at 355 K and above. Intercalated oxygen remains stable up to a temperature of 600 K, above this temperature it desorbs in the form of CO or CO2. We have determined XPS and STM fingerprints for the intercalated oxygen structure and we unambiguous assign it to a p(2x1)-O structure similar to the one observed on clean Ir(111). The decoupling of the intercalated graphene film from the metal substrate is directly visualized through the inability to form well-ordered Pt cluster arrays on the O-intercalated areas of graphene on Ir(111). Further, we have identified the rate limiting step for oxygen intercalation to be unlocking of the graphene edge and propose that this takes place through bond breaking between graphene edge bonds and the Ir substrate.
Using a combination of high pressure X-ray photoemission spectroscopy (HP-XPS) and STM we also show that CO intercalation takes place at room temperature and pressures in the 1 mbar range. The adsorption structure of intercalated CO is determined to be (3√3 × 3√3)R30o, identical to the structure observed on clean Ir(111) upon high pressure CO exposure.