Thickness-dependent molecular arrangement and topography of ultrathin ionic liquid films on a silica surface.

The molecular arrangement and topography of ultrathin ionic liquids (ILs) on a silicon wafer have been studied by AFM and ARXPS, respectively. The results indicate a transition from an "anion-cation" layered (smooth) structure to a "drop-on-layer"/"sponge" (rough) structure when the film gets thicker, which can be attributed to the competition between solid/IL attraction and anion-cation cohesion.