Gitonga M. John^1,, Simon W. Mugo¹, James M. Ngaruiya¹, Nelson Mugambi¹, Geoffrey G. Riungu¹

We report on the correlation between bond energy and optical band energy of TiO₂ thin films prepared through sol gel doctor-blade technique. The TiO₂ films were deposited on doped fluorine tin IV oxide (SnO₂:F) layer on glass substrates. UV-Vis-NIR spectroscopy was carried out on as-deposited and subsequent annealed films at different rates from room temperature up to 450°C. The average optical transmittance within the visible region was 73.5%, 73.4%, 70.5% and 69.9% for the as-deposited, 1-step annealed, 2°C/min, and 1°C/min films, respectively. FTIR spectroscopy confirmed presence of functional elements of Ti = O with a peak at 587.7 cm^-1. Bond energy for the films was calculated using Madelung equation with inclusion of the second coordination sphere for crystalline state. The values of bond energies were found to be 3.99 eV, 4.02 eV, 4.12 eV and 4.16 eV for the as-deposited, 1-step annealed, 2°C/min, and 1°C/min films respectively. The analysis of the band gap was done using Tauc’s relation. Band gap energy ranged from 4.02 eV to 5.04 eV. A statistical correlation between bond energy and optical band energy was established. Films annealed at 1°C/min recorded the highest bond energy and lowest band gap energy. This is attributed to the process of nucleation and crystal growth which are governed by thermodynamic properties. Prolonged exposure to higher temperatures through low annealing rates led to formation of films with high bond energy and low band gap.

bonding energy, optical band energy, annealing rate, TiO₂