Optical Properties of Tetracene Evaporated Films

The optical properties of tetracene films evaporated onto the fused quartz plates have been measured. They are markedly dependent on the film thickness as well as the substrate temperature. Their absorption spectra and X-ray diffraction patterns suggest that the two kinds of layers with different structure exist in a film. One of them, being in contact with substrate, has an unusual crystal structure and the other has a normal crystal structure. The unusual structure seems to be caused by the difference of the thermal expansions between tetracene crystals and the fused quartz plates. The temperature dependence of fluorescence spectra of the films, which were prepared at a low temperature, is different from that of the single crystal. The difference is interpreted in terms of tetracene dimerization in a film.