Photoelectron spectroscopy study on alkyl chain restructuring at the surface of ionic liquid BmImPF6 induced by Argon ion sputtering

This study explores the impact of argon ion (Ar⁺) sputtering on the surface structure of the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF₆) using XPS. The analysis focused on the alkyl chains of the cation, examining changes in the Carbon 1s peaks before and after sputtering. Results show a significant decrease in the alkyl chain component after Ar⁺ sputtering, suggesting migration into the bulk or decomposition of these chains. This change is irreversible, as the C1s line shape remains stable 24 hours post-sputtering. Quantitative surface analysis revealed a reduction in carbon and an increase in fluorine, nitrogen, and phosphorus, attributed to the migration of alkyl chains and the attraction of anions to the surface. These findings demonstrate that Ar⁺ sputtering can selectively modify the outermost surface composition of ionic liquids, offering a method to engineer surface polarity and reactivity for advanced applications.