Characterisation of iron oxide thin films prepared from spray pyrolysis of iron trichloride-based aqueous solution

Abstract This work concerns growth and characterization of iron oxide (mainly α-Fe 2 O 3 ) thin films with a non-toxic and easy to manipulate technique. The latter consists of spraying FeCl 3 ·6H 2 O (0.03 M)-based aqueous solution during 30 min onto glass substrates heated at 350 °C with a spray flow of 5 ml/min. These conditions led to the formation of rust red amorphous films. Well crystallized Fe 2 O 3 films were obtained after annealing in vacuum-sealed tube (~ 10 − 4 Pa) for 5 h at different temperatures ranging from 250 °C to 400 °C. The structure of the crystallized films was investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microprobe analyses. Two phases corresponding to α-Fe 2 O 3 and Fe(OOH) were evidenced. The major phase was found to be related to the α-Fe 2 O 3 compound, which appears at low annealing temperature, while the best growth of the Fe(OOH) minor phase was obtained after annealing at about 350 °C; beyond this temperature the Fe(OOH) minor phase tends to disappear and completely transforms into α-Fe 2 O 3 . The average crystallite size dimension of the α-Fe 2 O 3 phase, determined from XRD patterns, changes from 45 nm to 85 nm as the annealing temperature increases from 250 °C to 400 °C. SEM images show compact and granular films, while microprobe analyses show rather stoichiometric Fe 2 O 3 films at an annealing temperature of about 350 °C. Optical analyses enabled to point out direct band-gap energy of about 2.1 eV.