Optical anisotropy in a two-dimensional C₆₀ network

The buckyball (C 60 ) is generally considered an isotropic identity. However, when forming a two-dimensional (2D) network, these identical C 60 balls covalently bound with each other could have two kinds of choices of orientations. In this paper, we have studied quasiparticle electronic structure, electron-hole excitation, and optical properties in these 2D C 60 networks. For such a mixed-dimensional system consisting of C 60 molecules embedded in a 2D graphene-like network, the optical response is dominated by bound excitons where the binding energy is much larger than that in atomically thin 2D materials of similar band gap. Furthermore, the optical absorption exhibits an obvious contrast between incident lights linearly polarized along the in-plane two orthogonal directions and, consequently, significant optical anisotropy. In accordance with a typical and realistic experimental setup, we find that the rotation angle of transmitted light could be close to 1 ∘ for incident near-ultraviolet light. In the meantime, by modifying the microstructures of 2D C 60 networks, we could further modify the absorption edge by about 0.2 eV and even double the rotation angle. Our study provides a deep understanding of the optical responses in 2D C 60 networks and shows the microstructure-dependent optical anisotropy for applications of 2D optoelectronics and optics.