Edge-state signature in optical absorption of nanographenes: Tight-binding method and time-dependent density functional theory calculations

Abstract

The optical absorption of triangular nanographenes with well-defined edge structure, that is, zigzag-and armchair-type edges, is studied using the tight-binding method within the Hückel approximation. The absorption spectra of zigzag triangular nanographenes exhibit rich peak structures originating from the excitations associated with the edge states, while those of armchair ones do not. The main feature in the absorption spectra is reproduced by time-dependent density functional theory calculations within a real-time scheme. By varying the size of the nanographenes, we elucidate the role of the edge states in the optical absorption, which becomes conspicuous when the graphene size is on a nanometer scale. Our finding in this paper provides a way to capture the edge-state signature by optical experiments with visible light.

Electro-absorption of silicene and bilayer graphene quantum dots

“…3(a). The results are in good agreement with those of Yamamoto et al 39 Figure 3(b) presents the corresponding rð Þ=n tot for silicene QDs. The low-energy zoom at the inset to this figure reveals the shift of the 0.85 eV graphene peak toward 0.45 eV in silicene as a result of the decrease in the hopping energy.…”

“…1(c) and 1(d), edge atom pairs are counted. 39 The lattice parameter a 0 is the distance between the nearest atoms, or their projections onto a horizontal plane as depicted in Figs. 2(d) and 2(b) for a flat and low-buckled structure, respectively.…”

Effects of long-range disorder and electronic interactions on the optical properties of graphene quantum dots

“…In particular, armchair and zigzag edges are the most stable edge structures [16,23,24] while GQDs with zigzag edges are found to exhibit unusual magnetic [25][26][27] and optical [28][29][30][31][32] properties due to the presence of a degenerate band of states at the Fermi level. On the other hand, armchair edges do not lead to degenerate band of states at the Fermi level, hence, can be used as small model of bulk graphene which does not have edge states [33].…”

Zero-energy states of graphene triangular quantum dots in a magnetic field

“…5,33,[36][37][38][39][40][41][42][43][44][45][46] These edge states have significant effects on low-energy electronic properties such as a decrease of the energy gap compared to structures with armchair termination or, when combined with broken sublattice symmetry, a creation of the degenerate shell of zero-energy states in the middle of the energy gap. 33,[40][41][42][43][44][45][46][47][48][49] It was shown that the degenerate shell survives when various types of disorder are present in the system. [44][45][46][47] The influence of an external magnetic field on the electronic properties of the graphene quantum dots was also studied.…”