Thermoelectric Transport in Noble Metals Monolayers: A First Principles Study

In this study, we have carried out a first principles calculation of thermoelectric transport in freestanding monolayers of noble metals (viz. Au, Ag, Cu, and Pt). The electrical conductance, the thermal conductance (electronic as well as phononic), and the thermopower are calculated to assess the thermoelectric efficiency. While the electronic transport is determined by using the non-equilibrium Greens function (NEGF) approach based on the density functional theory (DFT) as implemented in the TranSIESTA module of SIESTA package, the phononic contribution is obtained using the Phonons module of ASE python package with ATOMISTICA as a calculator, together with the NEGF utility code, Phtrans. Our study predicts that the electronic thermal conductance rises in a non-linear fashion with temperature, while its phonon counterpart saturates to a characteristic constant after exhibiting an initial steep rise. Interestingly, the heat transport is found to be more in the zigzag direction. At room temperature, the relative phononic contribution to thermal conductance is seen to be the least for the Pt monolayer. The considered monolayers show only a small thermopower in the zero-biasing condition. However, it can be tuned by applying an external bias to achieve a value as large as about 1.05 mV/K in the Pt monolayer. Likewise, the Pt monolayer exhibits a maximum (about unity) thermoelectric figure of merit. As an interesting result, the predicted figure of merit is of the same order as for the noble metal atomic chains.