The surface of sapphire most widely used as a substrate for III-V nitride growth was modified by N-2(+) ion irradiation with ion-beam energies from 100 to 1000 eV. As the ion-beam energy increased from 100 to 500 eV, the root-mean-square roughness of the surface morphology decreased. However no significant change in surface roughness at energy higher-than 500 eV was observed. From the N Is x-ray photoelectron spectroscopy core-level spectra, no peak related to a nitrogen bond could be found in the samples irradiated with;ion energy below 500 eV. An AlON peak began to appear in the samples irradiated with 600-900 eV N-2(+) ions, and two peaks corresponding to AlON and AlN were distinctively observed in the sample irradiated at 1 keV.