Optical properties of 3,4,9,10-perylenetetracarboxylic dianhidride (PTCDA)

We have used spectroscopic ellipsometry (SE) to determine the optical functions of PTCDA. The samples have been prepared by thermal evaporation of PTCDA on quartz glass substrates. We have also investigated influence of the substrate temperature to the properties of PTCDA films. We have found that the surface roughness of the films, determined by atomic force microscopy, increases with the increase of substrate temperature. The lowest substrate temperature investigated here is the room temperature. At room temperature and higher substrate temperatures we have not observed ordering of the evaporated films (ordering would result in high anisotropy) which has been reported for PTCDA films grown by organic molecular beam deposition at very low temperatures (so called quasi-epitaxial growth). Therefore, the samples have been assumed to be isotropic. The obtained imaginary part of the dielectric function exhibits the expected features, i.e. low magnitude peak around 370 nm and higher magnitude two peak structure in 400-600 nm spectral region. The dielectric function spectra of the samples grown at room temperature and at 100#C have been compared and discussed.