[65] Piezoelectric enhancement by surface effect in hydrofluorinated graphene bilayer

We investigated the piezoelectricity of dipolar hydrofluorinated graphene (C₂HF)_n multilayers with first-principles calculations. Our results reveal that the dipole moment decreases as the number of layers increases, because electron and hole carriers are induced at the top and bottom layers due to the depolarization field. These carriers make (C₂HF)_n multilayers more stable by decreasing the depolarization field in the material. Through the calculation of the average layer piezoelectric stress constant e₃₁/ℓ in ℓ-layer chair (C₂HF)_n multilayers, we confirmed that the piezoelectricity of the bilayer is about three times larger than that of the monolayer and bulk material. Moreover, we found that the electron and hole carriers on the top and bottom layers played a significant role in the piezoelectric enhancement of the bilayer.