Epitaxial order of pentacene on Cu(110)–(2 × 1)O: One dimensional alignment induced by surface corrugation

The structure of a 30 nm thick pentacene film grown by molecular beam deposition on an oxygen passivated Cu(110) single crystal has been investigated ex-situ by X-ray diffraction methods. It is shown that pentacene crystallizes in two known bulk polymorphs with four unique crystal orientations. In all four cases, a principal pentacene direction is aligned along the surface corrugation provided by the Cu(110)–(2 × 1)O reconstruction. Since overlayer and substrate form incommensurate lattices, the results cannot be understood by classical criteria of organic epitaxy and the importance of one dimensional alignment is discussed.