Enhancement of thermoelectric power factor in NaxCoO2/Au multilayers

Abstract

Na_xCoO₂/Au thin film multilayers, with a thickness of the Au layer of 0.5–12 nm, have been fabricated on c-Al₂O₃ by post annealing of the CoO/Au thin film multilayers in Na vapor at high temperature in air. X-ray diffraction measurements revealed that the resulting Na_xCoO₂ layer was c-axis oriented with perfect ab-plane alignment and there was no reaction between Au and Na_xCoO₂. The resistivity of the Na_xCoO₂/Au multilayers decreased significantly with increasing the volume fraction of the Au layer without obvious deterioration of the Seebeck coefficient. Consequently, a considerable enhancement of the power factor was achieved in Na_xCoO₂/Au multilayers with the right Au volume fraction, which was about 2.2 times larger than that of the single Na_xCoO₂ layer with the same thickness.