Optical properties of amorphous polyazomethine thin films

Optical transmission and fundamental reflectivity spectra of amorphous thin films of the basic aromatic polyazomethine, i.e., 1,4-phenylene-methylenenitrilo-1,4-phenylenenitrilomethylene (PPI), prepared by chemical vapor deposition (CVD) method via the polycondensation process have been investigated. The absorption coefficient of PPI films reveals a significant broad band at 2.9 eV and the others, much weaker at 4.0 and 4.9 eV. The absorption edge follows the Tauc relation typical for amorphous semiconductors yielding the energy gap in the range 2.28–2.42 eV. The electronic structure of films and possible optical transitions, depending on changes in planarization of the PPI backbone under different deposition conditions, are discussed.