Theoretical study of the mechanical and electronic properties of [111]-Si nanowires with interstitial lithium

Abstract

In this work, we present a density functional study of the Young’s modulus and electronic properties of hydrogen passivated silicon nanowires (H-SiNWs) grown along [111] crystallographic direction as function of concentration of interstitial lithium (Li) atoms. The study is performed using the supercell scheme, within the local density approximation implemented in the SIESTA code. The results show that the presence of Li closes the known semiconductor band gap of the H-SiNWs showing a like metallic behavior even when just one Li atom is placed in the nanowire structure. The participation of the Li atoms in the electronic density of states is almost constant in the valence and conduction bands. The formation energy analysis show how the system loses energetic stability when the concentration of Li grows, while the binding energy per Li atom suggests the formation of Si–Li bonds. On the other hand, the Young’s modulus of the silicon nanowires (SiNWs) is higher than that of the H-SiNW and lower than the bulk value. Moreover, the Young’s modulus is almost constant independently of the Li concentration. This result indicates that the H-SiNWs support the internal stress due to the addition of Li atoms and could offer a better useful life as electrodes in Li-ion batteries. The results of this work help to understand how the electronic and mechanical properties of H-SiNWs change during the charge/discharge process and the possibility to incorporate them as electrodes in Li batteries.