Thermoelectric Performance Study of Graphene Antidot Lattices on Different Substrates
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Thermoelectric Performance Study of Graphene Antidot Lattices on Different Substrates Qing Hao1, Dongchao Xu1, Ximena Ruden2, Brian LeRoy2, Xu Du3 1 Department of Aerospace & Mechanical Engineering, University of Arizona, 1130 N Mountain Avenue, Tucson, AZ 85721, U.S.A. 2 Department of Physics, University of Arizona, 1118 E. 4th Street, Tucson, AZ 85721, U.S.A. 3 Department of Physics, Stony Brook University, Stony Brook, NY 11794, U.S.A. ABSTRACT Pristine graphene has low thermoelectric performance due to its ultra-high thermal conductivity and a low Seebeck coefficient, the latter of which results from the zero-band gap of graphene. To improve the thermoelectric performance of graphene-based materials, various methods have been proposed to open a band gap in graphene. Graphene antidot lattices is one of the most effective methods to reach this goal by patterning periodic nano- or sub-1-nm pores (antidots) across graphene. In high-porosity graphene antidot lattices, charge carriers mainly flow through the narrow necks between pores, forming a comparable case as graphene nanoribbons. This will open a geometry-dependent band gap and dramatically increase the Seebeck coefficient. The antidots also strongly scatter phonons, leading to a dramatically reduced lattice thermal conductivity to further enhance the thermoelectric performance. In computations, the thermoelectric figure of merit of a graphene antidot lattices was predicted to be around 1.0 at 300 K but experimental validation is still required. The electrical conductivity and Seebeck coefficient of graphene antidot lattices on various substrates including SiO2, SiC and hexagonal boron nitride were measured. The antidots were drilled with a focused ion beam or reactive ion etching. INTRODUCTION Solid-state thermoelectric (TE) devices have the ability to directly convert heat into electricity for power generation [1]. In recent years, attractive features such as high reliability, environment friendliness, and the absence of moving parts have created a renewed interest in TE devices as sustainable energy source. In practice, TE power generators have been developed to generate electricity from the waste heat in car exhaust gas [2], and from solar-radiation heat as a cheap alternative to solar cells [3]. In physics, the effectiveness of a TE material is evaluated by its dimensionless figure of merit (ZT), defined as ZT=S2T/k, where S, , k and T represent Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. Here k can be further split into two parts: 1) the lattice (phonon) contribution kL; and 2) the electronic contribution kE. In principle, good TE materials should have a high PF S2 but a low k, which is challenging to be balanced within the same material. As the focus of this work, nanoporous graphene is investigated for TE applications. Since its discovery in 2004, graphene has attracted huge attention for its ultra-high thermal and electrical conductivities [4, 5]. In practice, however, graphene is a gapl
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