Nanoscale structural damage due to focused ion beam milling of silicon with Ga ions

•We used Synchrotron X-ray Reflectivity to characterise the amorphous layer generated by Gallium Focused Ion Beam irradiation.•The amorphous layer thickness was found to be 25 nm thick.•High material density gradient was found in correspondence at the transition amorphous-crystalline region. The exposure of sample to Focused Ion Beam leads to Ga-ion implantation, damage, material amorphisation, and the introduction of sources of residual stress; namely eigenstrain. In this study we employ synchrotron X-ray Reflectivity technique to characterise the amorphous layer generated in a single crystal Silicon sample by exposure to Ga-ion beam. The thickness, density and interface roughness of the amorphous layer were extracted from the analysis of the reflectivity curve. The outcome is compared with the eigenstrain profile evaluated from residual stress analysis by Molecular Dynamics and TEM imaging reported in the literature.