Effect of salicylic acid on Fe2O3 films properties, obtained from the film-forming solution, based on iron chloride(III)

Relevance of the work was caused by absence of information in the literature about effect of organic ligand in composition of film-forming solution (precursor of synthesis) onto the properties of obtained Fe ₂O ₃ films. Nowadays these films are widely used in the production of coatings for many optical applications (interference filters, solar energy conversion and etc.), due to high thermodynamic stability at high temperatures, electrochemical stability, high refractive index; band gap's value (~ 2.2-2.4 eV), which allows utilization of a big fraction of the solar spectrum. The main aim of the study was to determine effect of salicylic acid in the composition of film-forming solution onto the optical properties of Fe ₂O ₃ films. In present work the composition of alcoholic film-forming solutions based on ferric chloride(III) with and without salicylic acid and theirs film-forming ability were investigated by viscosimetry (VPZh-2 viscometer), IR-spectroscopy (Thermo Nicollet NEXUS FT IR spectrophotometer), and UV-spectroscopy (ПЭ-5400UV spectrophotometer). Temperature of destruction of film-forming solutions was determined by thermal analysis on STA 449 C Jupiter analyzer. The phase of the prepared films were characterized by X-ray diffraction (Rigaku MiniFlex 600diffractometer). Films of iron oxide(III) were prepared by dip-coating and spin-coating techniques with the silicon and glass as the substrates. The surface morphology, thickness, refractive index and transmittance in the visible range of Fe ₂O ₃ films were investigated by spectrophotometry (ПЭ-5400UV spectrophotometer), ellipsometry (SE400 advanced ellipsometer) and scanning electron microscopy (Hitachi TM-3000 microscope). The results indicate that organic ligand in composition of film-forming solution influences the properties of Fe ₂O ₃ films. Addition of salicylic acid to the film-forming solutions based on ferric chloride (III) inhibits salt hydrolysis, causes to formation a complex of iron(III) salicylate in solution, promotes viscosity increase and has no effect on the time during which solutions achieve stable ability of film-forming (9 days). According to X-ray powder diffraction and thermal analysis, annealing of film-forming solutions at 600°С results in formation of a single phase of a-Fe ₂O ₃. The Fe ₂O ₃ films produced from FFS film-forming solution based on ferric chloride(III) have thicknesses (d) of 57 nm, refractive indices (n) of 2,2 and value of the transmittance - 98%. In comparison, the Fe ₂O ₃ films produced from film-forming solution based on ferric chloride(III) with salicylic acid are thinner (49 nm) and have refractive index of 2.6. The surface morphology of these films are not uniform, and it is the reason why theirs value of transmittance is less than 92%.

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