Si(100) dosed with NO and thermally nitrided with ammonia was investigated by X-ray photoelectron spectroscopy (XPS) and high-resolution electron energy loss spectroscopy (HREELS) fura wide range of temperatures. A 410-eV peak was observed in the N Is XPS spectrum region. It is proposed to be an enhanced shake-up satellite of the N Is photoelectrons. The temperature dependence of both this peak and HREELS data suggests that precursor silicon nitrides such as planar and pyramidal Si3N species as well as Si3N4 can form at different temperatures.