Single-particle energy – and optical absorption – spectra of multilayer graphene quantum dots

Abstract

The energy spectra of quantum dots formed by stacked disks of graphene are calculated as a function of the disk shape and size, the number of disk layers and the edge type (zigzag /armchair) within a tight-binding approach in the single-particle picture. Stacks formed by up to seven disks of hexagonal, rhombic and triangular shape are considered. For both edge types, we find a monotonously decreasing energy gap as the number of stacked disks or the disk size is increased, with the exception of triangular dots with zigzag edges, which have a metallic character. In some cases, simple scaling relations for the energy gaps can be formulated. Furthermore, the optical absorption spectra within the dipole approximation are calculated. The results are interpreted with the help of selected HOMO wave functions that form inside the stacks. • The densities of states of multilayer graphene quantum dots of different shapes (GQDs) are calculated. • Graphene quantum dots with up to seven layers are considered. • The corresponding optical absorption spectra are computed. • Zigzag and armchair multilayer dots show strong differences in the energy gaps. • The limit of infinitely many layers is computed for both types of edges.