Electrodeposition of tin oxide thin film from nitric acid solution: the role of pH

Tin oxide (SnO₂) thin films were synthesized by electrodeposition method from nitric acid medium with SnCl₂ precursor and NaNO₃ supporting electrolyte at 70 °C. The effect of pH electrolyte in the properties of SnO₂ thin films was investigated. Cyclic voltammetry (CV) was utilized for the determination of the selective potential for electrodeposition of pure SnO₂. Mott–Schottky (M–S) plots and electrochemical impedance spectroscopy (EIS) techniques were carried out to estimate the electrical characteristics of the SnO₂ thin films deposited at different pH electrolytes. These latter techniques show n-type conductivity for all the samples with optimal carrier density of 8.41 × 10²⁰/cm³ and high value of conductivity for the films electrodeposited at pH ~ 1.10. Atomic force microscopy (AFM) observations showed that the SnO₂ thin films obtained at different pH are more homogenous in appearance and present lower surface roughnesses at lower pH value. Structural analysis of the SnO₂ thin films was performed by X-ray diffraction (XRD) which exhibit a polycrystalline structure for pH ~ 1.25 and amorphous one for another pH values. From the optical study, the transmittance and the gap energy were founded to be depending to the pH of electrolyte.