Photoelectron spectroscopy study of the surface of the ionic liquid BmImPF6 before and after Ar+ sputtering

This study investigates the effects of Ar+ sputtering on an ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate (BmImPF6) with the use of x-ray photoelectron spectroscopy (XPS) and nuclear magnetic resonance (NMR). XPS analysis showed spectral changes in the C 1s and O 1s peaks, with surface contaminants nearly disappearing after Ar+ sputtering. Complementary 1H NMR spectroscopy indicated no bulk structural modification. These results suggest that impurities undergo preferential removal during sputtering by both desorption into the vacuum and segregation of nonvolatile species into the bulk, behavior that reflects the inherent fluidity of ionic liquids. This behavior differs from that of solid samples, where impurities are more restricted in mobility. This study contributes to the methodology for surface characterization of ionic liquids under vacuum conditions, with implications for research in materials science and electrochemistry.