Transmission electron microscopy study of the nitridated sapphire under a mixed gas flow of nitrogen and methane

Delta-alumina (δ-Al2O3) nanopowders and c-plane sapphires (α-Al2O3) were nitridated under a mixed gas flow of nitrogen and methane. The δ-Al2O3 nanopowders began to be converted to aluminum nitride (AlN) at 1300°C with phase transformation to α-Al2O3 but were not completely converted to AlN even after 10 h at 1600°C. The X-ray diffraction pattern and cross-sectional high-resolution transmission electron microscopy image of the nitridated sapphire showed the orientation relationship of AlN[0001]||Al2O3[0001] in the growth and the formation of an amorphous AlOxNy interlayer between the AlN layer and the sapphire substrate. This formation strongly supported the reaction mechanism in which Al2O3 converts to AlN through solid-state intermediates in the carbothermal reduction and nitridation reaction.