Optical and structural properties of FeSe2 thin films obtained by selenization of sprayed amorphous iron oxide films

We report in this work the optical and structural properties of iron diselenide films (FeSe2) obtained by selenization under vacuum of amorphous iron oxide films predeposited by spray pyrolysis. The structure of the FeSe2 films was investigated by scanning electron microscopy (SEM), microprobe analyses, atomic force microscopy (AFM) and X-ray diffraction (XRD). XRD and micro-probe analyses showed that FeSe2 as well as FeSe2−x phases begin to appear at a selenization temperature of 500 °C. As the selenization temperature rises, the iron diselenide films become more stoichiometric with a dominance of the FeSe2 phase. At 550 °C, a single FeSe2 phase having good crystallinity was obtained. At 600 °C, two phases were detected: the major one corresponds to Fe3O4, and the minor one to FeSe2. SEM surface views show that FeSe2 films have granular structure with small spherical crystallites. However, layered and clustered FeSe2 films were found, respectively, at 550 °C and 600 °C. Absorption measurements show that iron diselenide films have a direct and an indirect gaps of about 1.03 eV and 0.3 eV, which were suggested to be due to the stoichiometric FeSe2 phase and to a Fe-rich non-stoichiometric phase, respectively.