An investigation of interface interactions has been performed for the cerium/a-silicon nitride system by means of X-ray photoelectron spectroscopy (XPS). It is found that the nitrogen atoms can transfer from silicon nitride prepared by ion-beam implantation to a cerium him deposited on the surface, forming cerium nitride at room temperature (RT). The behavior of nitrogen migration exhibits a strong energy dependence of the nitrogen ion used in ion implantation. For a 1 keV-ion nitrided silicon substrate, a component of the N 1s spectrum grows with the thickness of Ce film at the binding energy of 1.8 eV lower than the N Is peak for silicon nitride. For a 3 keV-ion nitrided silicon substrate, however, nitrogen atoms migrate with great quantity from the substrate to a 15 ML, (monolayer)-thick Ce overlayer, giving a N Is spectrum with an abnormal broad peak width of 3.8 eV located at 396.0 eV. The possible causes for the great difference of nitrogen migration are mainly attributed to the different density of defects and interstitial nitrogen atoms as well as the different chemical states of silicon nitrides produced in the substrate during the ion implantation with different ion-beam energies.