Electronic properties of hydrogenated quasi-free-standing graphene

Tailoring the electronic properties of graphene is of fundamental interest regarding its application in electronic devices. One of the key strategies is chemical functionalization which modifies the p-electron system and thus can induce band gaps. However, in order to control the degree of functionalization it is crucial to know the exact amount of the chemisorbed species. We show with angle-resolved photoemission spectroscopy (ARPES) the formation of a band gap in graphene and estimate the hydrogen coverage from the scattering rate. Using X-ray photoemission spectroscopy (XPS) we identify the chemical environments in hydrogenated graphene and determine the total hydrogen to carbon (H/C)-ratio directly from the spectra. We then compare ARPES and XPS as tools for determining the H/C-ratio and discuss the results from molecular dynamics (MD) simulations. Angle-resolved photoemission spectra of (left panel) pristine graphene intercalated with Au and (right panel) hydrogenated graphene on Au with an estimated H-coverage of 5.8%. Besides the formation of a band gap, a broadening is observable which can be used to determine the H amount. Both spectra show the π-band at the K-point.