Structure organization of sexithiophene vapour deposited onto HOPG and SiH/Si(111)

We hale studied the morphology and structure of thin films of sexithiophene (GT), vacuum deposited onto Highly Oriented Pyrolytic Graphite (HOPG) and SiH/Si(lll) substrates, using UV-Vis and Infrared absorption spectroscopy, Transmission Electron Microscopy and Electron Diffraction. The evaporated f ilms on HOPG show a monocrystalline structure, which is retained even over several hundred Angstrom ngstroms thickness (1000 Angstrom). On SiH/Si(111) evaporated films have a different structure from the bulk. This latter is lost for thicknesses larger than 500-1000 Angstrom, owing to the generation of high densities of defects which leads to an apparently random polycryst alline film.