Structural and Optical Evolution of SnO₂ Thin Films with Precursor Concentration Variation via Thermochemical Decomposition

Abstract

This paper presents a study on the synthesis of nanostructured tin dioxide (SnO₂) thin films via thermochemical decomposition of SnCl₂.2H₂O (0.01 M, 0.02 M, and 0.03 M). The systematic influence of precursor concentration on morphological and optical properties of the films was studied by a combination of scanning electron microscopy (SEM), atomic force microscopy (AFM), and UV-Vis spectroscopy. SEM and AFM studies confirmed that with the increase in concentration, there is a gradual increment in grain size and surface roughness. The grain size mean was changed by increasing the average grain size overall 29.81 nm to 51.84 nm and the mean surface roughness varied between 24.70 nm and 43.38 nm. Optical absorption measurements showed that it is strongly absorbed in the UV region with absorption coefficients greater than 10⁴ cm^-1. Analysis of Tauc plots indicates a direct allowed transition where the optical bandgap decreased systematically as quantum confinement descended and crystallinity increased (3.80 eV, 0.01 M to 3.68 eV, 0.03 M). There was further enhancement in refractive index at a higher concentration indicating enhanced film density and compactness in the structure. These findings demonstrate that the precursor concentration is a central factor in controlling the structure and optical properties of SnO₂ thin films and a scalable approach to material optimization in optoelectronic, sensing, and energy devices.