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

The electrodeposition of Ge, Si and, for the first time, of SixGe1-x from the air- and water-stable ionic liquid 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl) amide ([Py1,4] Tf2N) containing GeCl4 and/or SiCl4 as precursors is investigated by cyclic voltammetry and high-resolution scanning electron microscopy. GeCl2 in [Py1,4] 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 SixGe1-x can be deposited reproducibly and easily in this ionic liquid. Interestingly, the SixGe1-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 SixGe1-x electrodeposition is demonstrated.