GROWTH AND PREFERRED CRYSTALLOGRAPHIC ORIENTATION OF HEXAPHENYL THIN-FILMS

Vacuum-evaporated hexaphenyl grows in a crystalline stale showing stro ng fibre texture. The fibre axis of this texture is perpendicular to t he surface of the substrate. Dependent on the sample preparation condi tions, these types of texture (or preferred growth) could be detected: (i) at high substrate temperatures and low deposition rates (DR), the (001) plane of the crystallites develop perpendicular to the fibre ax is; (ii) at low substrate temperatures and high DR, the (11-2) and/or (20-3) planes are aligned perpendicular to the fibre axis. Small influ ences on the preferred growth are observed by different substrate mate rials like glass, amorphous Indium Tin Oxide (ITO)-coated glass and ep iready GaAs. The first hexaphenyl layers on the surface of the substra tes are formed by dendritic growth of islands. Molecules perpendicular to the surface of the substrate are observed up to the third monolaye r. Strongly structured surfaces and cracks in the films are found for films produced at high substrate temperatures and low DR on epiready G aAs substrates. Smooth surfaces are obtained at low substrate temperat ures and high deposition rates on GaAs and TTO substrates. The size of the crystallites is strongly dependent on the substrate temperature, whereas big crystallites are found at high substrate temperatures. (C) 1997 Elsevier Science S.A.