Electrodeposition of Ge, Si and SixGe1−x from an air- and water-stable ionic liquid

Abstract

The electrodeposition of Ge, Si and, for the first time, of Si_xGe_1−x from the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py_1,4]Tf₂N) containing GeCl₄ and/or SiCl₄ as precursors is investigated by cyclic voltammetry and high-resolution scanning electron microscopy. GeCl₂ in [Py_1,4]Tf₂N is electrochemically prepared in a two-compartment cell to be used as Ge precursor instead of GeCl₄ in order to avoid the chemical attack of Ge(IV) on deposited Ge. Silicon, germanium and Si_xGe_1−x can be deposited reproducibly and easily in this ionic liquid. Interestingly, the Si_xGe_1−x deposit showed a strong colour change (from red to blue) at room temperature during electrodeposition, which is likely to be due to a quantum size effect. The observed colours are indicative of band gaps between at least 1.5 and 3.2 eV. The potential of ionic liquids in Si_xGe_1−xelectrodeposition is demonstrated.