Size effects in thermoelectric Na x CoO2 thin films are studied, focusing on the electrical resisitivity and Seebeck coefficient. For very thin films below 10 nm, we have observed an increase in resistivity, which is in agreement with theoretical models. In contrast to a predicted simultaneous suppression of the Seebeck coefficient for ultrathin films, we observe a constant Seebeck coefficient as a function of layer thickness due to changes in the structural properties as well as the presence of strong electron correlations. This preserved high Seebeck coefficient opens up new directions for Na xCoO2 ultrathin films as basic building blocks in thermoelectric superlattices with enhanced phonon scattering.
Brinks, P., Rijnders, A. J. H. M., & Huijben, M. (2014). Size effects on thermoelectric behavior of ultrathin NaxCoO2 films. Applied physics letters, 105(193), -. . https://doi.org/10.1063/1.4901447