Controlled laser-induced dehydrogenation of free-standing graphane probed by pump–probe X-ray photoemission

Abstract

The effects of optical excitation on fully hydrogenated free-standing nanoporous graphene have been characterized by pump–probe X-ray photoemission spectroscopy. Hydrogenated graphene, known as graphane, is characterized by a sp3 hybridization, which induces a sp3 component in the C 1s core level whose intensity can be used to monitor the hydrogen content. Under optical excitation we observe a partial dehydrogenation of graphane, which we attribute to local laser-induced heating; such result allows us to estimate the thermal conductivity of the material, for which we found an upper limit of 0.2 W/(m K), four orders of magnitude smaller than that of graphene. Such stark difference, combined with the possibility of dehydrogenating the graphane substrate via laser exposure, may be exploited to engineer nanostructured heat conduction channels in organic and hybrid organic–inorganic devices. We then explored the sub-nanosecond dynamics of the C 1s core level, which displays a kinetic energy shift and a peak broadening with two different decay constants, 210 ps and 130 ps, respectively. We assign the former to surface photovoltage, and the latter to transient lattice heating.