Abstract
Nanoscale thermoelectricity is an attractive target technology, because it can convert ambient heat into electricity for powering embedded devices in the internet of things. We demonstrate that the thermoelectric performance of graphene nanoconstrictions can be significantly enhanced by the presence of stable radical adsorbates, because radical molecules adsorbed on the graphene nanoconstrictions create singly-occupied orbitals in the vicinity of Fermi energy. This in turn leads to sharp features in their transmission functions close to Fermi energy, which increases the electrical conductance and Seebeck coefficient of the nanoconstrictions. This is a generic feature of radical adsorbates and can be employed in the design of new thermoelectric devices and materials.
Highlights
IntroductionGraphene has attracted huge interest for its extraordinary thermal, mechanical, electrical and spintronic properties.[1,2] It was recently demonstrated that stable electrode gaps below 5 nm can be formed using electroburning of graphene junctions.[3,4,5,6] Motivated by recent experimental progress in using such electrodes to probe transport through single molecules,[3,4,7,8,9,10,11,12,13,14] theoretical studies have focused on the electrical properties of graphene nanoconstrictions formed by incomplete electroburning of narrow graphene junctions.[3,14,15,16,17,18]
We demonstrate that the thermoelectric performance of graphene nanoconstrictions can be significantly enhanced by the presence of stable radical adsorbates, because radical molecules adsorbed on the graphene nanoconstrictions create singlyoccupied orbitals in the vicinity of Fermi energy
This in turn leads to sharp features in their transmission functions close to Fermi energy, which increases the electrical conductance and Seebeck coefficient of the nanoconstrictions
Summary
Graphene has attracted huge interest for its extraordinary thermal, mechanical, electrical and spintronic properties.[1,2] It was recently demonstrated that stable electrode gaps below 5 nm can be formed using electroburning of graphene junctions.[3,4,5,6] Motivated by recent experimental progress in using such electrodes to probe transport through single molecules,[3,4,7,8,9,10,11,12,13,14] theoretical studies have focused on the electrical properties of graphene nanoconstrictions formed by incomplete electroburning of narrow graphene junctions.[3,14,15,16,17,18]. Graphene nanoribbons with zigzag edges have been predicted to show half metallic and spin filtering properties,[19,20] with high densities of states near the graphene Fermi energy, which are attractive for thermoelectricity. These effects are not easy to isolate and control experimentally. We demonstrate that states close to the graphene Fermi energy could be created by doping graphene constrictions with radical adsorbates, leading to a significant improvement in their electrical and thermoelectric properties. As prototypes for different non-radical and radical molecules, we dope the nanoconstriction with four different molecules (see Fig. 1) namely a non-radical pyridine (C5H5N) 1, a pyridine radical (C5H4N) 2, a 4-picoline radical (C6H6N) 3, and a methyl radical (CH3) 4
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