Applied Surface Science, Vol.432, 163-169, 2018
A study on selective surface nitridation of TiO2 nanocrystals in the afterglows of N-2 and N-2-O-2 microwave plasmas
Surface-selective chemical modification of anatase TiO2 nanocrystals is performed in the post-discharge region of N-2 microwave plasma and the chemical bonding states of surface nitrogen species are carefully evaluated using X-ray photoemission spectroscopy (XPS). It is found that the surface treatments in the afterglows induce the formation of stable nitrogen species at or near the surface of TiO2. Interestingly, the detailed bonding structure varies strongly depending on the afterglow condition. In pure N-2 afterglows, various N species with a direct Ti-N bond are formed on the surface, while the use of N-2-O-2 mixtures induces the formation of additional oxidized species of NO3- on the surface. This is attributed to the high concentrations of O or NO in the afterglows of N-2-O-2 plasmas. The incorporation of substitutional N species in the subsurface is also achieved after a prolonged exposure in the early afterglow with a high density of N-2(+) species. Our results show that the exposure condition can be controlled for a selective chemical modification of TiO2 surface for the control of surface properties in various applications. (C) 2017 Elsevier B.V. All rights reserved.