Ionic Liquid-Assisted Vacuum Deposition of Organic Ionic Plastic Crystal Thin Films

We report the preparation of thin films of 1-ethyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([C₂mpyr][TFSA]), which is among organic ionic plastic crystals, using an ionic liquid (IL) -assisted vacuum deposition method. 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C₂mim][TFSA]), a well-known IL, was used as a solvent to assist the crystal growth. The effect of the IL on the growth morphology and crystal orientation of the thin films was investigated. It was found that the IL-assisted growth resulted in the preferential growth of (100)-oriented [C₂mpyr][TFSA] crystallites, whose morphology depended on the deposition temperature and the presence of IL. Growth models for [C₂mpyr][TFSA] thin films under different growth conditions are proposed and discussed.