Ion probe measurement of Fe species ejected by KrF laser ablation of Fe in ambient nitrogen gas

Time-resolved ion current measurements for laser ablation of Fe in nitrogen gas were performed. The current due to electrons, N₂⁺, Fe ion and Fe neutral was observed at the substrate. At nitrogen pressures between 1×10^-3 Torr and 1×10^-1 Torr, the amount and the velocity of the Fe ion arriving at the substrate increased as the nitrogen pressure was increased. The velocity of the Fe ion was approximately 60 km/s and the maximum amount of it was estimated to be not more than 0.3 percent of the ejected Fe species. The Fe-N thin films prepared in this nitrogen pressure region showed the highest (200) orientation and increase of the crystallite size. It is considered that the Fe ion arriving at the substrate has the effect of enhancing the mobility of deposited species, resulting in the generation of the highest oriented Fe-N thin film composed of the largest crystallites.