Abstract
It was found that nitrogen-doped TiO2 revealed significant improvement in high photocatalytic reactivity under visible-light [Asahi et al, Science 293, 269-271 (2001)]. To investigate the optimal local concentration of doped nitrogen for visible-light response, N+-implanted TiO2 samples were examined by means of X-ray absorption near edge structure (XANES) and electron energy loss spectroscopy (EELS). Depth-resolved nitrogen K-edge EELS revealed two types of chemical state of nitrogen, depending on the concentration, consistent with the XANES results. We found that the local nitrogen concentration effective for visible-light response was approximately less than 1 at%. Further, we visualized the spatial distributions of the different chemical states of nitrogen by energy-filtering TEM (FETEM). It was also found that the photocatalytic activity was offset by the coexisting inactive state.
