We have used atomic force microscopy to investigate the response of NaCl and KCl surfaces exposed to 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF2) for 6-7 hours. As a first outcome, we observed the formation of molecular adlayers on KCl, but not on NaCl. This difference must be related to the significant misfit (11%) between the lattice constants a of the two alkali halide crystals, with only one value of a being favorable to the accommodation and sorption of the ionic liquid (IL) molecules. As the scanning process goes on, the surfaces are continuously worn off by the probing tip even with very low set points in the nanonewton range. In this way more and more terraces beneath the original cleavage surface are exposed to the IL, and possibly eroded by it, as attested by the jagged shape of the evolving step edges observed in the topography images. The lateral force images simultaneously acquired can provide quantitative information on the mechanical stability of the complex surfaces so formed, such as the interfacial shear strength of the IL adsorbates [1].

[1] C. Pimentel, C. M. Pina, and E. Gnecco, Cryst. Growth Des. 13 (2013) 2557–2563.