Extended Data Fig. 5: Reversibility of hydrogenation of graphene.

a, In-plane electronic conductance in graphene as a function of gate voltage V_t for V_b = 0. The electronic system undergoes a reversible conducting-insulating transition as V_t is swept along the loop marked with red arrows. Blue arrows mark the points at which the system undergoes the reversible insulating (hydrogenation) and conductive (dehydrogenation) transitions. The neutrality point is indicated with a black arrow. Drain-source bias, 0.5 mV. b, Raman spectra show that the conducting-insulation transition is accompanied by a sharp D band, consistent with hydrogenation of the lattice. The devices can be hydrogenated and dehydrogenated multiple times. Dashed lines mark the position of the D, G and 2D bands. c, Raman spectra as a function of V_t show that the D band appears suddenly for gate voltages between 1.2 V–1.5 V. The background signal from the electrolyte was subtracted and the spectra of hydrogenated graphene in panels b and c were divided by a factor of 5 for clarity.