Effects of metallic electrodes on the thermoelectric properties of zigzag graphene nanoribbons with periodic vacancies

Abstract

We theoretically analyze the thermoelectric properties of graphene quantum dot arrays (GQDAs) with line- or surface-contacted metal electrodes. Such GQDAs are realized as zigzag graphene nanoribbons (ZGNRs) with periodic vacancies. Gaps and minibands are formed in these GQDAs, which can have metallic and semiconducting phases. The electronic states of the first conduction (valence) miniband with nonlinear dispersion may have long coherent lengths along the zigzag edge direction. With line-contacted metal electrodes, the GQDAs have the characteristics of serially coupled quantum dots (SCQDs) if the armchair edge atoms of the ZGNRs are coupled to the electrodes. By contrast, the GQDAs have the characteristics of parallel QDs if the zigzag edge atoms are coupled to the electrodes. The maximum thermoelectric power factors of SCQDs with line-contacted electrodes of Cu, Au, Pt, Pd, or Ti at room temperature were similar or greater than 0.186nW/K; their figures of merit were greater than three. GQDAs with line-contacted metal electrodes have much better thermoelectric performance than surface contacted metal electrodes.

Thermal rectification through the topological states of asymmetrical length armchair graphene nanoribbons heterostructures with vacancies

“…If one tunes Γ t to 1 meV, Σ outer,TSs will exhibit two peaks with a separated energy of |2t eff,x |. This suggests that the electron transport between the electrodes is considerably influenced by the coupling strengths between the AGNR heterostructures and the electrodes, which, in turn, are determined by the contact types of electrodes [51,52].…”

“…We investigate the transport properties of heterostructures composed of 9-7-9 AGNRs connected to electrodes, as shown in figure 1. To analyze this system, we employ a combination of the tight-binding model and the Green's function technique [50][51][52]. The Hamiltonian of the system consists of two parts:…”

“…Here, H 0 represents the Hamiltonian of the electrodes themselves, including the coupling between the electrodes and the 9-7-9 AGNR [51,52]. H AGNR corresponds to the Hamiltonian for the 9-7-9 AGNR heterostructures, which can be expressed as follows: In this equation, E ℓ,j represents the on-site energy for the p z orbital in the ℓth row and jth column.…”

“…For simplicity, we consider the wide band limit for the electrodes and an energy-independent approximation for Γ L (ε) and Γ R (ε). The retarded and advanced Green functions of the AGNR, G r (ε) and G a (ε), respectively, can be calculated using the system Hamiltonian (H = H 0 + H AGNR ) [51,52].…”

Effects of Coulomb Blockade on the Charge Transport through the Topological States of Finite Armchair Graphene Nanoribbons and Heterostructures

“…Here, Γ L (ε) and Γ R (ε) represent the tunneling rate (in energy units) at the left and right leads, respectively. Additionally, G r (ε) and G a (ε) correspond to the retarded and advanced Green functions of the AGNR, respectively [43][44][45].…”