Chemical interaction between nitrogen and iron in silica glasses via sequential ion-implantation

Silica glass plates (Corning 7940 excimer grade) were implanted sequentially with N⁺ at 52 keV to different doses, ranging from 0 to 1.2 × 10¹⁷ ions cm^-2, and then with Fe⁺ at 160 keV to 6 × 10¹⁶ ions cm^-2 at room temperature and 4 μA cm^-2. The intensity of ferromagnetic magnetic resonance (FMR) absorption and the magnetization calculated by the angular dependence of the FMR field reach maxima at an N/Fe atomic ratio ∼0.2. Two peaks due to Fe 2p_3/2 electron are observed at 707.2 ± 0.2 and 710.9 ± 0.2 eV in the x-ray photoelectron spectra. The intensity of the former relative to the latter decreases with increasing the N dose. The conversion electron Mössbauer spectrum reveals the formation of superparamagnetic iron nitride as well as the existence of Fe²⁺ and Fe³⁺ in silica when implanting N⁺ to 7.5 × 10¹⁵ ions cm^-2 and then ⁵⁷Fe+ to 6 X 10¹⁶ ions cm^-2 at N/Fe = 0.125. These results suggest that sequential ion-implantation of N⁺ and Fe⁺ produces iron nitride in silica glasses.