Rh(111)-supported graphene: Size-selective carbon nano-clusters as growth precursors, and the unusual C-Rh epitaxy

When?

Thursday 8 March 2012, 13:00 to 14:00

Where?

ATI seminar room - 02ATI02

Open to:

Staff, Students

Speaker:

Renald Schaub, University of St Andrews, School of Chemistry

I will discuss two recent studies focussing on epitaxial graphene supported on transition metal surfaces. In a first part, the nucleation and growth mechanisms of graphene on a Rh(111) surface will be discussed. STM and DFT calculations show that carbon nano-islands form in the initial stages of graphene growth using ethylene as the carbon source, possessing an exclusive size of 7 honeycomb carbon units (hereafter labeled as 7C6). These magic-sized clusters adopt a dome-like hexagonal shape indicating that bonding to the substrate is localized on the peripheral C atoms. Smoluchowski ripening is identified as the dominant mechanism leading to the formation of graphene, with the size-selective carbon islands as precursors. Control experiments and calculations, whereby coronene molecules, the hydrogenated analogues of 7C6, are deposited on Rh(111), provide an unambiguous structural and chemical identification of the 7C6 building blocks.

In a second part, Resonance Tunneling Spectroscopy and DFT calculations will be presented, which explore local variations in the electronic surface potential of a single graphene layer grown on Rh(111). A work function modulation of 220 meV is experimentally measured, indicating that the chemical bonding strength varies significantly across the supercell of the Moiré pattern formed when graphene is bonded to Rh(111). In combination with high-resolution images, which provide precise knowledge of the local atomic registry at the carbon-metal interface, the atomic configuration of maximum chemical bonding to the substrate is identified experimentally, and confirmed theoretically. These observations are at odds with reported trends for other transition metal substrates. I will explain why this is the case by considering the various factors that contribute to the bonding at the graphene/metal interface.