Abstract:
We report on a simple and robust analysis of the energy band gap and crystal size
of anatase TiO2 thin films on doped Fluorine Tin Oxide (SnO2:F) prepared using sol-gel Doctorblade method. The films had been annealed at rates of 1
oC/Min, 2oC/Min, 1-step and referenced
with as-deposited film, and the optical and structural properties characterized using UV-VIS
spectrophotometer and X-ray diffraction (XRD), respectively. The films had a refractive index
which was noted to depend on the annealing rate consistent with Cauchy’s relation. An optical
band gap of
3.88eV , 3.72eV , 3.33eV
, and
3.13eV
was measured on the as-deposited, 1-Step,
2
oC/Min and 1oC/Min annealing, respectively. Optical conductivity was highest in the UV region
and diminished sharply in the visible region in all the annealed samples. The as-deposited film
exhibited a diminished optical conductivity in the visible electromagnetic field due to high density
of charge trapping sites resulting to negligible interaction of the film molecules with the applied
electric field. The XRD spectra revealed thermal enhancement in crystallinity, with the crystallite
sizes of
21.8382nm, 24.3087nm
and
24.9633nm, for 1-step annealed, 2oC/Min and 1
oC/Min,
respectively. The broadened XRD spectrum of the as-deposited film is attributed to the presence
of dangling bonds that act as trapping sites. Comparison of the measured values of the optical
band gap with simulation from SCOUT at low annealing rates (2oC/min and 1oC/min) was found
to decrease with enhancement in crystallite size, indicating a reduction in porosity and
improvement in both densification and crystallinity of the films.
