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(Color online) Cross-section SEM images of bare ZnO:Cl nanowires (a) and ZnO:Cl/ZnO homojunction nanowires with a 15 nm shell thickness (b). (c) Histograms of the thickness distribution of the ZnO:Cl/ZnO (up) and the bare ZnO:Cl (down) nanowires. (d) Chlorine region of the XPS spectra of ZnO:Cl and ZnO:Cl/ZnO nanowires with increasingly thicker shell thicknesses as noted in the graph. The fitting of the chlorine 2P band with two peaks, corresponding to 2P3/2 and 2P1/2 is also shown.
(Color online) Absorbance spectra of ZnO:Cl nanowires and ZnO:Cl/ZnO homojunction nanowires with increasingly thicker shell thicknesses. The inset shows the dependence of vs. and the lineal fit used to point the shift of the optical band gap.
(Color online) Room temperature photoluminescence spectra of ZnO:Cl nanowires and ZnO:Cl/ZnO homojunction nanowires with increasingly thicker shell thicknesses obtained using 325 nm excitation wavelength. Insets show the evolution of the photoluminescence peak area corresponding to the band-to-band transition and to the visible emission, as noted.
(Color online) (a) Photocurrent density vs. applied potential (V vs. Ag/AgCl) for ZnO:Cl nanowires and ZnO:Cl/ZnO homojunction nanowires with increasingly thicker shell, measured under chopped UV illumination (100 mW/cm2) in 0.1 M Na2SO4 aqueous solution. (b) Photocurrent as a function of the shell thickness for a second set of ZnO:Cl and ZnO:Cl/ZnO nanowires. (c) Schematic illustration of the photoelectrochemical reaction taking place at the ZnO:Cl/ZnO nanowire surface. Photogenerated carriers are separated at the depletion region. Holes are driven to the surface where the water oxidation reaction takes place. Electrons are swept to the nanowire core and funnelled inside there towards the platinum electrode where the reduction reaction takes place. (d) Band diagrams of the ZnO:Cl and ZnO:Cl/ZnO nanowires illustrating the increase of the surface depletion region with the growth of the ZnO shell.
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