Dependence of Optical Band Gap on Crystallite Size of TiO2 Thin Films Prepared Using Sol Gel Process (Published)
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 Doctor-blade method. The films had been annealed at rates of 1oC/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 , , , and was measured on the as-deposited, 1-Step, 2oC/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 , and , for 1-step annealed, 2oC/Min and 1oC/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.
Optical Properties of Titanium Substituted Manganese -Zinc Ferrite System- Mn0.8+X Zn0.2tixfe2-2xo4 with X=0.10 (Published)
Titanium substituted Manganese-Zinc ferrite (Mn0.8+x Zn0.2TixFe2-2xO4 with x=0.10) was synthesized thermo chemically by solid state method at different treating temperatures. Basically, the substitution cause a rearrangement of Fe+3 ions into the two preexisting octahedral and tetrahedral sites. The X-ray analysis confirms the formation of single phase cubic spinel structure. The lattice constant decreases slightly and porosity increases with increase in sintering temperature. They can be disrupted into smaller particles by shear forces generating mechanical stress gradients. A characteristic feature of all solid-state reactions is that they involve the formation of product phase(s) at the interfaces of the reactants. UV-VIS analysis of the sample was carried out. Tunable band gaps can be obtained by varying annealing temperatures. The optical constants of refractive index, extinction coefficient, normal-incidence reflectivity, and absorption coefficient showed systematic variation with temperature. The dispersion of refractive index was analyzed by the Wemple-DiDomenico single-oscillator model.
This study presents the effects of Radioclimatic variables on signal propagation in Nsukka, Nigeria. The primary Radioclimatic data used in the study include temperature, pressure and humidity or water vapour pressure, while secondary radioclimatic data includes refractivity (N), refractive index (n) and effective earth’s radius (k-factor). The measurements of the primary variables were made at time interval of 30 minutes daily from August 2013 to July 2014. The results obtained show seasonal variation of the temperature and relative humidity. This leads to the increase in the values of radio refractivity and refractive index. The results also, show that the k-factor values for those months were at the range 1.555 – 1.653. This high values of k-factor is an indicator to the possible causes of signal interference in the study area.