Molecular layering and local order in thin films of 1-alkyl-3-methylimidazolium ionic liquids using X-ray reflectivity

X-ray reflectivity measurements in air of thin films of 1-alkyl-3-methylimi dazolium salts in the liquid, liquid crystalline and solid states supported on Si( 111) are described. The films show Bragg features in both liquid cr ystalline and solid phases, but only after an initial annealing cycle. Kies sig fringes are observed only for the 1-octadecyl-3-methyl-imidazolium hexa fluorophosphate films and, following analysis using Parratt32, a bi-layer m odel is proposed whereby the molecules are orientated with ionic groups at both salt-air and salt-silicon interfaces.