Twinning effects in polycrystalline hexaphenyl thin films

A new type of preferred orientation is observed within polycrystalline film s of hexaphenyl molecules (C36H26) The thin films are prepared by physical vapour deposition in ultra-high vacuum on highly cleaned glass and Al subst rates. The preferred orientation is characterised by X-ray diffraction usin g pole figure and rocking curve measurements. The fibre texture is observed with the (21 (1) over bar) crystallographic planes of the hexaphenyl cryst allites parallel to the substrate surface. This unusual type of preferred o rientation is explained by reflection twinning of the crystallites.