N-doped titanium oxide photocatalyst is found to be activated by visible light irradiation as well as ultraviolet irradiation. We evaluated its crystal structure, N states in the lattice, composition, and surface morphology using X-ray diffiraction (XRD), X-ray photoemission spectroscopy (XPS), and scanning probe microscopy (SPM). As a result, it is found that the materials have rutile or anatase crystal structure with nitrogen doped into substitutional sites of oxygen in TiO2, which contributes band gap narrowing. It is also confirmed that XPS measurement was influenced by surface treatment such as Ar ion bombardment.
