Electrodeposition of Silicon Thin Films from Ionic Liquids

The possibility of obtaining Si thin films by electrodeposition from the oxygen and water stable N-butyl-N-methyl-pyrrolidinium bis(trifluoromethyl-sulfonyl) amide ionic liquid at room temperature was investigated. The results obtained using SiCl4 and SiBr4 as precursors and aluminium and nickel as substrates were compared. Cyclic voltammetry, square wave voltammetry and chronoamperometry were used to characterize the electroreduction step of the silicon species. The results showed that the growth of the silicon layer is very slow, yielding only clusters of silicon at low cathodic potentials and short electrolysis times. At higher electrodeposition potentials and/or longer deposition times, the films became rougher and cracks appeared in the layers. This was mainly due to the accumulation of tensile strains during growth. The layers were very reactive to air and humidity, probably due to the high porosity of the film. In some cases, contamination of the layers by S and F was also observed.