Results of X-ray and ellipsometric studies on self-assembled monolayer films of three fluorinated chlorosilanes are presented. By inferring an index of refraction, the monolayer thicknesses obtained from both these types of studies are self-consistent. The tilt of the molecules with respect to the layer normal is found to be strongly dependent on the functionality of (i.e. the number of chlorine atoms attached to) the terminal Si atom of the molecule.