Gap Opening in Double-Sided Highly Hydrogenated Free-Standing Graphene
Maria Grazia Betti, E. Placidi, Chiara Izzo, Elena Blundo, A. Polimeni, Marco Sbroscia, J. Ávila, Pavel Dudin, Kailong Hu, Yoshikazu Ito, Deborah Prezzi, Miki Bonacci, Elisa Molinari, Carlo Mariani
Abstract
Conversion of free-standing graphene into pure graphane─where each C atom is sp3 bound to a hydrogen atom─has not been achieved so far, in spite of numerous experimental attempts. Here, we obtain an unprecedented level of hydrogenation (≈90% of sp3 bonds) by exposing fully free-standing nanoporous samples─constituted by a single to a few veils of smoothly rippled graphene─to atomic hydrogen in ultrahigh vacuum. Such a controlled hydrogenation of high-quality and high-specific-area samples converts the original conductive graphene into a wide gap semiconductor, with the valence band maximum (VBM) ∼ 3.5 eV below the Fermi level, as monitored by photoemission spectromicroscopy and confirmed by theoretical predictions. In fact, the calculated band structure unequivocally identifies the achievement of a stable, double-sided fully hydrogenated configuration, with gap opening and no trace of π states, in excellent agreement with the experimental results.