Spectroscopic Fingerprints of Carbon Monomers and Dimers on Ir(111): Experiment and Theory

By combining high-resolution photoelectron spectroscopy and ab initio calculations, we show that different carbon clusters can be formed on Ir(111) upon low temperature molecular beam epitaxy using a solid state carbon source. Besides carbon monomers, also dimers, trimers, and larger clusters are detected through C 1s core level measurements. The spectroscopic signal of carbon monomers is then used as a fingerprint to detect their presence during the early stages of graphene growth by ethylene chemical vapor deposition at high temperature. We demonstrate that our spectroscopic approach can be employed to investigate the role of carbon monomers and dimers in the nucleation and growth of graphene on different metal surfaces.