Fabrication of 3D Nanoshell Structured ZnO Thermoelectric Material via Proximity Field Nanopatterning

Abstract

Recently, many researchers have focused on realizing 3D nanostructured materials for enhanced functionality with high specific surface area and low relative density. Especially, 3D nanostructures can be applied to thermoelectric materials due to their low thermal conductivity. ZnO is a potential thermoelectric material because of its non-toxicity, high thermal stability, and relatively high Seebeck coefficient (S) of metal oxides. However, the extremely low figure of merit (zT), which comes from a high thermal conductivity (κ) over 40 W/mK, limits the thermoelectric application of ZnO. Here, we propose a new strategy for achieving a reduced κ and a correspondingly increased zT of pure ZnO over a wide temperature range from 333 K to 723 K by forming an ~72 nm thick, 3D nanoshell structure. The suppressed κ of the 3D ZnO film is ~3.6 W/mK at 333 K, which is ~38 times lower than that of the blanket ZnO film (3.2 μm thick), which was set as a reference. The experimental zT of the 3D ZnO film is ~0.017 at 333 K, which is the highest value among ZnO reported to date and is estimated to increase by ~0.072 at 693 K according to the Debye-Callaway approach. Largearea(~1 in2) fabrication of the 3D ZnO film with high structural uniformity allows the realization of an integrated thermoelectric device,which generates ~60 mV at a temperature difference of 40 K along the in-plane direction.