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

Abstract

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 AlO_xN_y 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.