Micro–nano behaviour of DMBI-PF₆ ionic liquid nanocrystals: large and small-scale interfaces

Microelectrical mechanical systems (MEMS) devices coated with a thin film of ionic liquid showed significant improvement in wear life. These promising tribological findings led to the current study of the micro–nano behaviour of an ionic liquid, 1,2-dimethyl–3-butyl imidazolium hexafluorophosphate (DMBI-PF₆), when applied as a thin film on a polished silicon surface. The films remain as microdroplets in ambient conditions but undergo drastic changes when agitated by an atomic force microscope (AFM) contact scan or touched with a biased AFM tip. The nanotribological characteristics including mobility, diffusion and scratch resistance are studied. In the case of DMBI-PF₆, it was observed that the imidazolium ion is a mobile phase while PF₆ is attached to the silicon surface. Crystallites are formed as a result of tip contact and depend on the tip bias and environmental conditions. Crystallization of DMBI-PF₆ from the liquid phase with no tip bias showed substantial variation in crystal shape compared to those formed under the influence of an electric bias.