High resolution fast x-ray photoelectron spectroscopy study of ethylene interaction with Ir(111): from chemisorption to dissociation and graphene formation.

High-energy resolution fast X-ray photoelectron spectroscopy was used to study the thermal evolution of ethylene on Ir(111). Temperature programmed photoemission spectra of the C 1s and Ir 4f7/2 core levels were measured in 400 ms/spectrum while ramping the temperature from 170 to 1120 K. The C 1s spectra display a large variety of components, assigned to different carbon containing species present on the surface at increasing temperature, namely ethylene, ethylidene, ethylidyne, ethynyl, adsorbed carbon and finally graphene. Components due to the C–H stretch vibration excitation are clearly resolved for C2H4, CHCH3 and C2H3. The C 1s spectra of the last two species display also shifted components that belong to non-equivalent carbon atoms. At temperatures higher than 900K the narrowing of C 1s spectra is caused by graphene formation. Also the Ir 4f7/2 spectra are strongly affected by the presence of the different species. The clean surface component moves initially towards the bulk peak and shifts back and forth along the series, to recover the binding energy position corresponding to the clean surface when the graphene layer is completely formed. A comparison of ethylene interaction with Ir(111) and Pt(111) is presented.