The role of hydrogen in the nitriding of anatase TiO2 films in the N2-H2 microwave afterglows

Abstract

Nitriding in the afterglows can be beneficial in the surface-selective nitridation of oxide materials for the control of surface defects or active sites in electronic devices or catalysts. Here we introduce our results on the nitriding of anatase TiO2 films in the afterglows of N2-H2 microwave plasmas at the substrate temperatures up to 300 °C. We employed optical emission spectroscopy (OES) and X-ray photoemission spectroscopy (XPS) to determine active species in the afterglows and the N species incorporated into the film, respectively. Adding a few percent of H2 into the N2 gas flow generates active species such as NH and H atoms in the afterglow region in addition to the N2-derived active species such as N atoms and excited N2 species. The XPS results revealed that such changes in the type and densities of active species in the afterglows can significantly enhance the surface nitriding performance. The origin for the enhanced surface nitriding is attributed to the efficient removal of surface oxygen atoms by reactive H atoms via the formation of H2O to result in an efficient surface uptake of nitrogen. Our results show that the N2-H2 afterglows can be effectively used for a selective surface nitriding of oxide films such as TiO2 at the relatively low temperature range.