The use of EXAFS spectroscopy to show the structural modifications in metals implanted with N⁺ ions

Tantalum and titanium were implanted with different doses of N⁺ ions at 70 keV, and the structural modifications of the targets were analysed by X-ray absorption spectroscopy (XAS) (EXAFS and XANES). The analysis requires the use of total yield detection and the correct calibration of the extraction depth of the XAS signal by means of MO/M standards (i.e. a metal oxide layer of known thickness grown on a metal). In the implanted samples of Ta, EXAFS spectroscopy shows the formation of Ta-N bonds at approximately 2.90 Å and the amorphization of the structure for a dose of 3.46 × 10¹⁷ ions cm^-2. A reordering of the network occurs for higher doses, as revealed by the increase in intensity of the EXAFS oscillations and the appearance of new Ta-Ta and Ta-N distances of second and higher shells. In Ti, a metal whose coordination number with neighbouring metal atoms does not change on implantation of nitrogen, only small differences at the second and higher shells were detected by EXAFS spectroscopy. The possibility of the use of XAS to study the implantation of metals with highly energetic ions is discussed.