Mixing of mode symmetries in top gated bilayer and multilayer graphene field effect devices

Abstract

We report Raman study to investigate the influence of stacking on the inversion symmetry breaking in top gated bi- and multi-layer (~10 layers) graphene field effect transistors. The G phonon mode splits into a low frequency (G_low) and a high frequency (G_high) mode in bi- and multi-layer graphene and the two modes show different dependence on doping. The mode splitting is explained in terms of mixing of zone-center in-plane optical phonons representing in-phase and out-of-phase inter-layer atomic motions. Unlike in bilayer graphene, there is no transfer of intensity from G_low to G_high in multilayer graphene. A comparison is made for the bilayer graphene data with the recent theory of Gava et al.