Enhanced thermoelectric figure of merit in assembled graphene nanoribbons

Abstract

Graphene nanowiggles (GNWs) are periodic repetitions of graphene nanoribbon (GNR) junctions resulting in quasi-one-dimensional wiggle-edged structures. They are synthesized using a surface-assisted bottom-up chemical approach and have been predicted to possess unusual electromagnetic properties. Here we show that GNWs also possess superior thermoelectric properties compared to their straight GNR counterparts. We employ a combination of density-functional theory and semiempirical approaches to demonstrate that the presence of wigglelike edges dramatically degrades thermal conductance due to phonons but preserves excellent electronic conduction, resulting in significant enhancement of the thermoelectric figure of merit $ZT$. We show that the resonant tunneling effect between alternate parallel and oblique sectors contributes to maintaining GNR electronic transport properties. We also present a systematic study for a large set of nanowiggle structures to establish how geometry and spin states influence $ZT$ at room temperature, thereby providing a road map for guiding the design and synthesis of specific GNWs for targeted thermoelectric applications.