Twinning effects in polycrystalline hexaphenyl thin films

A new type of preferred orientation is observed within polycrystalline films of hexaphenyl molecules (C 36 H 26 ). The thin films are prepared by physical vapour deposition in ultra-high vacuum on highly cleaned glass and Al substrates. The preferred orientation is characterised by X-ray diffraction using pole figure and rocking curve measurements. The fibre texture is observed with the (211) crystallographic planes of the hexaphenyl crystallites parallel to the substrate surface. This unusual type of preferred orientation is explained by reflection twinning of the crystallites.