Raman Spectroscopic Studies on Silicon Electrodeposition in a Room-Temperature Ionic Liquid

Abstract

The electrochemical reduction of SiCl₄ to Si in a room-temperature ionic liquid, trimethyl-n-hexylammonium bis(trifluoromethylsulfonyl)amide (TMHATFSA) has been investigated by Raman spectroscopy. For the electrolyte solution itself, most of silicon chloride species exist as SiCl₄ molecules in TMHATFSA. It is considered that the SiCl₄ molecules are stabilized by the induced dipole-induced dipole interaction with the hexyl group in TMHA⁺ cations. In situ Raman spectroscopy revealed that SiCl₄ is electrochemically reduced to form amorphous Si (a-Si) as well as silicon chloride species containing Si networks as represented by Si _m Cl _n (n/m < 4). The amount of the formed a-Si increases as the electrolysis proceeds. Besides, there seems to be an incubation period in which Si _m Cl _n are generated, followed by the intensive production of a-Si. This information implies that a-Si may be produced by further reduction of Si _m Cl _n to form larger Si networks or by disproportionation reactions of Si _m Cl _n .