Application of Bu2Sn(acac)2 for the deposition of nanocrystallite SnO2 films: Nucleation, growth and physical properties

High-quality uniform SnO₂ thin films were successfully prepared by pulsed-spray evaporation chemical vapor deposition (PSE-CVD) method, using a cost-efficient precursor of ⁿBu₂Sn(acac)₂. The volatility and stability of ⁿBu₂Sn(acac)₂ were studied through thermogravimetric-differential thermal (TG-DTA) analysis and mass spectrometry, indicating the good adaptability for the CVD process. Deposition of SnO₂ films was made in the range of 250-450 °C to investigate the effect of substrate temperature on their structural and physical properties. The film growth activation energy changes from 66.5 kJ/mol in the range of 250-330 °C to 0 kJ/mol at 330-450 °C, suggesting the change of the rate-limiting step from surface kinetics to diffusion control. All films possess the rutile-type tetragonal structure, while a change of preferred orientation from (1 1 0) to (1 0 1) plane is observed upon the increase of the deposition temperature. The different variation of the nucleation and growth rates with the deposition temperature is proposed to explain the observed unusual change of crystallite size. A significant deterioration of the electrical conductivity was observed upon the increase of the deposition temperature, which was tentatively attributed to the non-specific decomposition of the precursor at high temperature leading to carbon contamination. Optical measurements show transparencies above 80% in the visible spectral range for all films, while band gap energy increases from 4.02 eV to 4.08 eV when the deposition temperature was raised from 250 °C to 450 °C.