Effects of static charging and exfoliation of layered crystals

Using first-principle plane wave method we investigate the effects of static charging on structural, elastic, electronic and magnetic properties of suspended, single layer graphene, graphane, fluorographene, BN and MoS2 in honeycomb structures. The limitations of periodic boundary conditions in the treatment of charged layers are clarified. Upon positive charging the band gaps between the conduction and valence bands increase, but the single layer materials become metallic owing to the Fermi level dipping below the maximum of valence band. Moreover, their bond lengths increase and their in-plane stiffness decreases. As a result, phonons are softened and frequencies of Raman active modes are lowered. High level of charging leads to instability. We showed that wide band gap BN and MoS2 slabs are metallized as a result of electron removal and their outermost layers are exfoliated once the charging exceeds a threshold value.