Geometrical effects on the thermoelectric properties of ballistic graphene antidot lattices

Abstract

The thermoelectric properties of graphene-based antidot lattices are theoretically investigated. A third nearest-neighbor tight-binding model and a fourth nearest-neighbor force constant model are employed to study the electronic and phononic band structures of graphene antidot lattices with circular, rectangular, hexagonal, and triangular antidot shapes. Ballistic transport models are used to evaluate transport coefficients. Methods to reduce the thermal conductance and to increase the thermoelectric power factor of such structures are studied. Our results indicate that triangular antidot lattices have the smallest thermal conductance due to longer boundaries and the smallest distance between the neighboring antidots. Among them, iso-triangular antidot lattices have also a large power factor and as a result a large figure of merit. V

Enhanced thermoelectric figure of merit in vertical graphene junctions

“…A Seebeck coefficient higher than 1 mV/K can be easily achieved in these systems, compared to values of a few tens µV/K in pristine graphene [16]. To suppress the thermal conductance, nano-structuring techniques such as edge roughness [17,18], defect engineering [19,20], isotope engineering [21,22], nano-hole lattices [11,13], hybrid heterostructures of graphene and boron nitride [12], or complex geometries as in [14,15] have been investigated. It has been shown that the thermoelectric efficiency is significantly improved in these structures and ZT values higher than 1 can be achieved.…”

“…In particular, it has been shown that the Seebeck effect can be significantly enhanced in graphene nanostructures having finite energy gaps such as graphene armchair nanoribbons (GNRs) [10], graphene nano-hole (nanomesh, i.e. GNM) lattices [11], hybrid graphene/boron nitride structures [12], graphene nanoribbons with a nanopore array [13], graphene nanoribbons consisting of alternate zigzag and armchair sections [14], and graphene nanoribbons with a chevron-type geometry [15]. A Seebeck coefficient higher than 1 mV/K can be easily achieved in these systems, compared to values of a few tens µV/K in pristine graphene [16].…”

“…In the complex systems as studied in [12,14,15], the well-controlled fabrication of nanostructures may be an issue. The use of nano-hole lattices can improve the thermoelectric performance of GNRs [13] but the improvement is still limited in 2D systems [11].It is well known that the thermal properties of graphite and graphene are highly anisotropic [23,24]. While the thermal conductance along the in-plane direction is high, it is hundreds of times weaker in the cross-plane direction (for graphite) [25], limited by weak van-der Waals interactions between layers.…”

“…In the complex systems as studied in [12,14,15], the well-controlled fabrication of nanostructures may be an issue. The use of nano-hole lattices can improve the thermoelectric performance of GNRs [13] but the improvement is still limited in 2D systems [11].…”

“…The relaxation of armchair edges [27] was also taken into account in the cases of armchair GNR. For the in-plane transport of phonons, a force constant model including four nearest neighbors [11] was used. To describe the coupling between graphene layers, we employed the spherically symmetric interatomic potential and hence the force constant matrix elements are given by Φ ij pq = −α exp (−βr) r p r q /r 2 with α = 573.76 N/m and β = 20 nm −1 [28].…”