Electronic excitation induced structural modification of FeCo nanoparticles embedded in silica matrix

Electronic excitation mediated energy loss by 120 MeV Au9+ swift heavy ions (SHIs) results in significant structural modifications of FeCo nanoparticles embedded in thin SiO2 matrix. The variations in local atomic structure and particle size/shape at different irradiation fluences are probed by extended x-ray absorption fine structure spectroscopy (EXAFS) and grazing incidence small angle x-ray scattering (GISAXS). The crystallinity and ordering of the films are found to first decrease and then increase with fluence. The observed alterations in co-ordination number of Fe/Co from EXAFS are correlated primarily with particle size modifications due to a transient thermal spike generated in the embedded nanoparticles by SHIs. The role of hydrogen desorption from nanoparticles is also highlighted.