Improved Photoactivity Of NiO/ZnO Nanorods Heterostructured Films Relying On Scaffold Surface Cleaning And NiO Deposition Time Optimization

Herein, a surface cleaning procedure involving vacuum annealing under oxygen was applied for cleaning the zinc oxide nanorod (ZNR) scaffold film's surface before nickel oxide (NiO) deposition for heterostructure formation. The scaffold properties (surface stoichiometry, defects fluctuation, Fermi level shift, carrier concentration) were studied as a function of the vacuum level and the NiO deposition time and correlated to the NiO/ZNR interface (charge transfer resistance, band bending) and photo-response properties. The surface cleaning under a higher vacuum enabled the adsorbate and surface oxygen vacancy passivation but also influenced the surface doping. Our best performing NiO/ZNR interface in terms of photocatalytic efficiency was composed of a high-vacuum-cleaned (0.5 Pa) ZNR scaffold and 40 s sputter deposited NiO layer which was post-annealed. The high photocatalytic efficiency could be correlated with a maximized near-band edge emission, effective band bending, low charge transfer resistance (as proven by photoelectrochemical impedance measurements), and optimum light harvesting (maximized photocurrent density). The optimized NiO/ZNR showed about 1.5 times increase in photo-response and improved photodegradation efficiency compared to the ZNR scaffold.