Nitrogen doping of nanoporous WO₃ layers by NH₃ treatment for increased visible light photoresponse

Nanoporous WO₃ layers were grown by electrochemical anodization of W in a fluoride containing electrolyte. These layers were exposed to a thermal treatment in NH₃ to achieve nitrogen doping of the material. The morphology, crystal structure, composition and photoresponse of pure and nitrogen doped WO₃ were compared using scanning electron microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and photoelectrochemical measurements. The results clearly show that successful nitrogen doping into WO₃ layers can be achieved by controlling the temperature and time during the NH₃ treatment. Most importantly, it is demonstrated that for the nitrogen doped WO₃ layers the photocurrent is significantly enhanced in the visible light region.