In-plane alignment of para-sexiphenyl films grown on KCl(0 0 1)

The three-dimensional growth of para-sexiphenyl (p-6P) on KCl(0 0 1) is characterized by a large polymorphism. Using grazing-incidence diffraction, we have found that two of the known five orientational phases feature preferential in-plane alignments along the [1 1 0] in-plane direction of the substrate: p-6P(1 1 −1) ∥ KCl(0 0 1) with [1 −1 0] ∥ KCl[1 1 0] as well as p-6P(0 0 1) ∥ KCl(0 0 1) with [1 −1 0] ∥ KCl[1 1 0]. The latter structure is a peculiar low-symmetry configuration, which can be understood by analysis of the molecular crystal lattice and the substrate symmetry.