Combined fast X-ray photoelectron spectroscopy and density functional theory
calculations reveal the presence of two types of hydrogen adsorbate structures at the graphene/
Ir(111) interface, namely, graphane-like islands and hydrogen dimer structures. While the former
give rise to a periodic pattern, dimers tend to destroy the periodicity. Our data reveal distinctive
growth rates and stability of both types of structures, thereby allowing one to obtain well-defined
patterns of hydrogen clusters. The ability to control and manipulate the formation and size of
hydrogen structures on graphene facilitates tailoring of its properties for a wide range of
applications by means of covalent functionalization.