Vibrational Spectrum of ``Crystalline Graphane''

Since the discovery of graphene, a flat monolayer of carbon atoms, a great interest was attracted to synthesis of chemically modified carbon sheets. In particular, it was proposed that graphane, representing a graphene sheet saturated by hydrogen adsorbed from both sides, would be stable [1], and this prediction was confirmed by TEM [2]. Recently, hydrogenated graphite with a composition close to CH has been synthesized by exposing the graphite to gaseous hydrogen at P=2 to 7 GPa and T=350 to 450$^{o}$C [3]. The formation of hydrographite is accompanied by a 40{\%} increase in the $c$-parameter of the unit cell. The IR spectrum shows a strong band near 2850 cm$^{-1}$ due to stretching vibrations of the C-H covalent bonds. In the present work, we studied the vibrational spectrum of hydrographite by inelastic neutron scattering. The obtained spectrum is very similar to that calculated for a single graphane plane [4]. This suggests a weak interaction between the graphane layers in hydrographite, so it could be considered as a ``crystalline graphane'' material. 1. J.O. Sofo et al., PRB \textbf{75}, 153401 (2007). 2. D.C. Elias et al., Sci. \textbf{323}, 610 (2009). 3. I.O. Bashkin et al., Int. Symp. Metal-Hydr. Syst., Reykjavik, Iceland, 2008. 4. G. Savini et al., PRL \textbf{105}, 037002 (2010).