Crystallographic studies on hexaphenyl thin films - a review

Thin films of hexaphenyl show interesting crystallographic features, which are of great importance for technological applications. The textures and the sizes of the crystallites have large influence on the electronic and optical properties of the thin films. Hexaphenyl thin films are prepared by physical vapour deposition on various types of substrates: isotropic and mechanical pretreated substrates or single crystalline surfaces. Polymorphism, several types of pronounced textures with characteristic sizes of the crystallites but also epitaxial growth of hexaphenyl thin films are found. Recent results of different experimental methods-mainly X-ray diffraction pole figure technique, X-ray line profile analysis and transmission electron diffraction are summarised. The growth of the hexaphenyl thin films is analysed using the current knowledge of thin film formation of crystalline conjugated molecules. The observations on hexaphenyl thin films are compared with the thin film properties of other aromatic and heterocyclic molecules like oligoacene, PTCDA, sexithiophene and metal-phthalocyanines. (C) 2003 Elsevier Science B.V. All rights reserved.