The effect of calcination heating rate and the number of deposition cycles on the structural and optical properties of tin dioxide nanostructures

This study explores a facile approach to tailor the structural and optical properties of tin dioxide (SnO 2 ) nanostructures by controlling the calcination heating rate and the number of coating layers. Nanoparticles and thin films were synthesized via a sol-gel method under different thermal and deposition conditions. The findings reveal that moderate calcination rates and increased coating repetitions significantly reduce the band gap and modify the morphology of SnO 2 nanostructures. Notably, the smallest band gap of 4.32 eV was achieved in thin films with multiple coating layers, indicating enhanced optical absorption. This tunability in nanoscale structure and band gap opens promising avenues for optimizing SnO 2 -based materials in transparent conducting oxides, UV photodetectors, and gas sensing applications. The study demonstrates a cost-effective and scalable route for engineering SnO 2 nanomaterials with application-specific functionalities. • Novelty of the Study:Unlike previous studies that primarily focused on calcination temperature , this research investigates the calcination heating rate and its impact on the structural, morphological, and optical properties of SnO 2 nanostructures. The simultaneous examination of this parameter along with the number of deposition steps represents the main novelty of this study. • •Nanopowders Crystalline Structure (XRD): • Calcination heating rate of 5°C/min → Increased crystallite growth and improved crystalline order , with the largest crystallite size observed under these conditions. • Calcination heating rate of 10°C/min → Reduction in crystallite size due to a higher nucleation rate and limited growth time. Morphology (SEM): • The mean nanoparticle size decreased with an increase in the calcination heating rate up to an optimal value. • At higher heating rates, the nanoparticle size increased again , which may be attributed to enhanced growth and particle agglomeration.Optical Properties (UV-Vis & Bandgap): • The absorption peak of all samples appeared at approximately 250 nm. • Smaller and denser nanoparticles → Higher optical absorption , attributed to increased active surface area and reduced light scattering. • Samples calcined under optimized conditions exhibited the highest bandgap values , indicating the significant influence of the calcination heating rate on the electronic structure of SnO 2 nanoparticles. • •Thin Films Morphology (SEM): • Increasing the number of deposition steps resulted in larger nanoparticles. • This growth trend indicates better control over particle formation and prevention of excessive agglomeration.Optical Properties (UV-Vis & Bandgap): • More deposition steps → Increased mean nanoparticle size , reduced light transmission , and higher reflectance due to greater thickness and density. • More deposition steps → Decreased bandgap , attributed to improved crystallinity, increased nanoparticle size, quantum confinement effects, and reduced structural defects.