Effect of stacking layers, disc size, twist angle and vertical electric field on the band gap of multilayer graphene quantum dots

First-principles calculations are used to study the joint modulation of the number of stacking layers, disc size, twist angle and vertical electric field on the band gap of multilayer graphene quantum dots. The structure and properties of multi-layer graphene quantum dots have many degrees of freedom in modulation. In addition to the usual quantum confinement effect, multi-layer assembly, interlayer twist, and external vertical electric field are all effective modulation methods. The above-mentioned complex operational elements lead to a lot of complexity, and the physicochemical mechanism therein remains unclear. In this work, single-layer graphene quantum dots with different diameters are used as the building block to construct the twisted multilayer graphene (TMG_N, N is the number of stacked layers) quantum dot structures. Density functional theory calculations are used to study the variation of quantum dot band gap with stacking thickness, interlayer twist angle and vertical electric field. Studies have shown that the band gap of TMG_N varies with θ. For a specific θ, the band gap of TMG_N continuously decreases with increasing N, and reaches a stable value when N = 6. The band gap of TMG_N reduces with the increasing field strength. Under the applied vertical electric field, the band gap change caused by the electric field increases significantly with N. Our research proposes a method to realize the quasi-continuously controllable band gap of multilayer graphene quantum dots by synergistically controlling the number of layers, size, interlayer twist angle of the quantum dots and electric field strength.