Electrical and optical properties of (PPh₄)₂[Fe(CN)₅NO] non-crystalline thin films prepared with the vacuum thermal evaporation technique

Molecular-material thin films of (PPh₄)₂[Fe(CN)₅NO] and a double potassium salt from 1,8-dihydroxyanthraquinone have been prepared by vacuum thermal evaporation on Corning glass substrates and crystalline silicon wafers. The surface morphology, thickness and structure of the deposited films were studied by scanning electron microscopy (SEM), atomic force microscopy (AFM), ellipsometric measurements, ultraviolet-visible (UV-vis) and Fourier-transform infrared (FT-IR) spectroscopies. The amorphous films show the same intra-molecular bonds as the IR spectroscopic studies, which suggests that the thermal evaporation process did not alter the initial chemical structures. The conductivity and the electrical-conduction mechanism in the thin films were also investigated. Finally, the optical band gap (E_g) of these molecular complexes was evaluated from optical absorption measurements.