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    Considerations about the determination of optical bandgap from diffuse reflectance spectroscopy using the tauc plot
    (Springer India, 2024) Jubu, Peverga R.; Obaseki, O. S.; Ajayi, D. I.; Danladi, E.; Chahrour, Khaled M.; Muhammad, A.; Landi Jr, S.
    The optical diffuse reflectance data of a semiconductor material is usually converted into the Kubelka-Munk function before proceeding to process the conventional Tauc's plot from which optical bandgap energy can be determined. Firstly, it is conventional/ customary to convert the percentage reflectance (R-infinity(%)) data, which is obtained from UV-vis measurement into an equivalent reflectance (R-infinity) that range between 0 and 1 before processing the Tauc's plot. Secondly, the Kubelka-Munk function is usually multiplied by the incident photon energy, h nu, to produce an all-elements/ comprehensive Tauc's plot. Literature is scarce to convincingly demonstrate that a correct bandgap value can, alternatively be obtained from the Tauc's plot that is derived directly from the (R-infinity(%) data without having to convert to R-infinity. Also, publication is rarely available to demonstrate that a proper bandgap value can be determined without having to multiply the Kubelka-Munk function by the term h nu. The present investigation shows diminutive differences in the bandgap values estimated from the R-infinity(%)-based Tauc's plots and the equivalent R-infinity-based Tauc's plots. This suggests that either of the methods can be employed for a precise bandgap estimate. A comparison between the magnitudes of the bandgap energies determined from the comprehensive Tauc's plot and when the Kubelka-Munk function is not multiplied by h nu reveals insignificant differences in the estimated values. This suggests that either of the two methods can be employed to obtain a reliable bandgap for direct and indirect optical gap semiconductors.
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    Enhanced photoelectrochemical transient photoresponse properties of molybdenum oxide film deposited on black silicon
    (Elsevier, 2023) Jubu, Peverga R.; Yusuf, Bashir; Abdulkadir, Auwal; Obaseki, O. S.; Chahrour, Khaled M.; Yusof, Yushamdan; Dehiin, Hile D.
    Nanostructured black silicon (b-Si) is widely deployed for different solar applications due to its novel light-harvesting characteristics, and large surface area-to-volume ratio. The present research work applies a novel approach via the chemical vapour deposition method to prepare molybdenum oxide (MoO3) film on a b-Si substrate for photoelectrochemical application. X-ray diffraction revealed alpha-MoO3 phase, with the MoO3/b-Si film exhibiting a relatively large crystallite size and improved crystalline quality. Optical reflectance measure-ments showed a relatively low reflectance and reduced optical bandgap energy for the MoO3/b-Si film. Chro-noamperometric measurements showed an enhanced photocurrent density of 656.34 mu A/cm2 at 1 V bias for the MoO3/b-Si photoanode measured in a 0.5 M H2SO4 solution. The enhanced photoelectrochemical activity could be attributed to an increase in light absorption, the relatively small bandgap energy, improved crystalline quality, and improved charge carrier separation and transfer at the interface.