Enhanced thermoelectric efficiency in armchair silicene nanoribbons decorated by Mn

Abstract

In this study, we use density functional theory to investigate the structural stability as well as the magnetic and thermoelectric properties of Mn-passivated armchair silicene nanoribbons (Mn-ASiNRs). All structures considered in this study were thermodynamically stable, and existed in ferromagnetic ground states with a Curie temperature greater than 400 K. The Mn-ASiNRs showed spin-polarized electronic properties that were tunable with respect to their width (N). Mn-ASiNRs with N = 4, 5, and 7 (4-, 5- and 7-Mn-ASiNRs) were semiconducting, while 6-Mn-ASiNR was half-metallic and 8-Mn-ASiNR was metallic. We simulated N-Mn-ASiNR-based devices to evaluate their thermoelectric properties, and observed a high-spin Seebeck coefficient (SS) of 1800 μV/K at μ=0 and a charge Seebeck coefficient (SC) of 1350 μV/K at μ=−0.17 eV for 4-Mn-ASiNRs. We obtained significantly enhanced charge and spin thermoelectric figures of merit (ZCT and ZST) compared with those of pristine nanoribbons (H-ASiNRs) that had maximum values of 25 and 18 at room temperature for 4- and 7-Mn-ASiNRs, respectively. ZCT and ZST further improved to values of 150 and 190, respectively, at temperatures lower than 100 K owing to a rapid increase in SC and SS, and exhibited decreased thermal conductance (Kt). Moreover, we showed that a thermally driven spin current with a negligibly small charge current can be generated by our devices. The results of this theoretical study indicate that Mn-ASiNR can be used to develop effective thermoelectric energy conversion devices.