Fig. 7: Mapping of the measured TiO₂ and ZnO energy bandgaps to the photon energies of the LEDs used for activation of the hydrophilic surface states.

a The electronic bandgaps of the MOx layers were measured using reflection electron energy loss spectroscopy (REELS) for both TiO₂ (I) and ZnO (II) layers. The results are shown in (b) for both TiO₂ and ZnO for different layer thicknesses. The average bandgap over all thicknesses for TiO₂ was thus determined to be 3.469(2) eV, and 3.159(5) eV for ZnO, where the outlier at \(d=\) 9 nm was discarded. Vertical error bars represent accumulated errors from the band gap determination shown in (a), where the energy loss values from three samples were used. Horizontal error bars were obtained from measured layer thickness variation (maximum–minimum) from five locations across each wafer (see Methods). The measured electronic- and optical energy gaps for the TiO₂ and ZnO layers are compared to the normalized Gaussian power output distributions on photon energies for the UV LEDs used in the experiments (c). The Gaussian distributions are obtained from the center frequencies and full-width-half-maxima (FWHM) values in the LED specifications sheets from the supplier.