Analysis of surface state and stability during storage of AIN powders by X-ray photoelectron spectroscopy

The surface state of as-prepared AlN powders produced by direct nitridation and carbothermal methods was characterized by X-ray photoelectron spectroscopy (XPS) and X-ray excited Auger electron spectroscopy (XAES). In the as-prepared AlN powders, small peaks assigned to imide and amide groups were detected in the N1s XPS spectra of directly nitrided powders but not in those of the carbothermally treated powders. Both an oxidized surface phase and a parent AlN phase could be distinguished in the A12p XPS and Al (KLL) XAES spectra of all the samples. The structural state of the oxidized surface phase was found to be similar to γ-Al₂O₃. The average thickness of the oxidized surface phase was determined to be about 0.5-0.6 nm in directly nitrided AlN powders whereas it was 1.1 nm in carbothermally treated AlN powders. The thickness of the oxidized surface phase increased with increasing storage times of the AlN powders in a container under ambient atmosphere. The increase of thickness with storage time of the oxidized surface phase in directly nitrided AlN powder was faster than in the carbothermally treated AlN powder. The oxidized surface phase changed from X-Al₂O₃ in the as-prepared AlN powders to a hydroxide phase during storage.