Electronic states in finite graphene nanoribbons: Effect of charging and defects

Abstract

Ijäs, M.; Ervasti, M.; Uppstu, Christer; Liljeroth, Peter; van der Lit, J.; Swart, I.; Harju, A. We study the electronic structure of finite armchair graphene nanoribbons using density-functional theory and the Hubbard model, concentrating on the states localized at the zigzag termini. We show that the energy gaps between end-localized states are sensitive to doping, and that in doped systems, the gap between the end-localized states decreases exponentially as a function of the ribbon length. Doping also quenches the antiferromagnetic coupling between the end-localized states leading to a spin-split gap in neutral ribbons. By comparing dI/dV maps calculated using the many-body Hubbard model, its mean-field approximation and density-functional theory, we show that the use of a single-particle description is justified for graphene π states in case spin properties are not the main interest. Furthermore, we study the effect of structural defects in the ribbons on their electronic structure. Defects at one ribbon terminus do not significantly modify the electronic states localized at the intact end. This provides further evidence for the interpretation of a multipeak structure in a recent scanning tunneling spectroscopy (STS) experiment resulting from inelastic tunneling processes [van der Lit et al., Nat. Commun. 4, 2023]. Finally, we show that the hydrogen termination at the flake edges leaves identifiable fingerprints on the positive bias side of STS measurements, thus possibly aiding the experimental identification of graphene structures. Electronic states in finite graphene nanoribbons: Effect of charging and defects

Tuning of the Electronic Properties of Armchair Graphene Nanoribbons through Functionalization: Theoretical Study of 1Δg O2 Border Addition

“…Models in set A are 0.98 nm wide (D) and up to 5.4 nm long (L), whereas models in set B are 1.35 nm wide (D) and up to 3.7 nm long (L). In contrast to previous studies,10, 13, 34, 35 our models are rhomboidal, therefore all their borders are genuine armchair s . As a consequence, they do not require any type of passivation, which can strongly affect their electronic properties 13.…”

Localized charge carriers in graphene nanodevices

“…[146][147][148][149] Under special conditions, hydrogenated zig-zag, armchair, and mixed edges were observed. 125,[149][150][151][152][153] Recently, also SFM scans of graphene edges were shown. 125 For multilayer graphene flakes, it is further possible that the edges of several layers fuse together and create so-called "closed edges."…”

“…125,[149][150][151][152][153] Recently, also SFM scans of graphene edges were shown. 125 For multilayer graphene flakes, it is further possible that the edges of several layers fuse together and create so-called "closed edges." 140,154,155…”

Identification of pristine and defective graphene nanoribbons by phonon signatures in the electron transport characteristics

“…In addition, there have been theoretical predictions [32,33] of the Raman spectrum, in good agreement with experiments [14,34]. For a finite AGNR the role of zigzag termini states have been studied theoretically, comparing DFT to the many-body Hubbard model [35].…”