We deal with the formation of thin aluminum oxynitride (AlON) layers after adsorption of nitric oxide (or coadsorption of oxygen and ammonia) on NiAl(001) at 75 K and subsequent annealing at 1200 K. The adsorption of NO and formation of the AlON films are investigated by means of high‐resolution electron energy loss spectroscopy (HREELS), low‐energy electron diffraction (LEED), and Auger electron spectroscopy (AES). The AlON film shows a distinct (2×1) LEED pattern and the HREEL spectrum exhibits five loss peaks. An oxygen to nitrogen atomic ratio of &bartil;2 has been estimated from the AES analysis. The energy gap is determined to beEg=6.6±0.2 eV. The structure of &thgr;‐AlON is derived from that of &thgr;‐Al2O3. ©1996 American Institute of Physics.