Analysis of FIB-induced damage by electron channelling contrast imaging in the SEM

We have investigated the Ga+ ion-damage effect induced by focused ion beam (FIB) milling in a [001] single crystal of a 316 L stainless steel by the electron channelling contrast imaging (ECCI) technique. The influence of FIB milling on the characteristic electron channelling contrast of surface dislocations was analysed. The ECCI approach provides sound estimation of the damage depth produced by FIB milling. For comparison purposes, we have also studied the same milled surface by a conventional electron backscatter diffraction (EBSD) approach. We observe that the ECCI approach provides further insight into the Ga+ ion-damage phenomenon than the EBSD technique by direct imaging of FIB artefacts in the scanning electron microscope. We envisage that the ECCI technique may be a convenient tool to optimize the FIB milling settings in applications where the surface crystal defect content is relevant. Lay description Focused ion beam (FIB) has become a powerful tool to assist the characterization of bulk materials from micro- to nanoscale in the scanning electron microscope (SEM). FIB allows the milling of large amounts of material yielding the fabrication of microsamples of different geometries and the serial sectioning of microslices of few nanometres thick that are subsequently characterized in the SEM. Nevertheless, FIB milling may induce a radiation-damage layer created by the impact of highly accelerated Ga+ ions over the metal surface. The characterization of such damage layer has been commonly performed by transmission electron microscopy (TEM). However, this approach requires the fabrication of thin TEM lamellae by FIB milling, which is a time-consuming process that can also alter the initial crystal defect content. In this work, we have investigated the Ga+ ion-damage effect induced by FIB milling in a [001] single crystal of a 316 L stainless steel by electron channelling contrast imaging (ECCI). We analyse the influence of FIB milling on the characteristic electron channelling contrast of surface dislocations. We find that the ECCI approach provides sound estimation of the damage depth produced by FIB milling. For comparison purposes, we have also studied the same milled surface by a conventional electron backscatter diffraction (EBSD) approach. We observe that the ECCI approach provides further insight into the Ga+ ion-damage phenomenon than the EBSD technique by direct imaging of FIB artefacts in the SEM. We envisage that the ECCI technique may be a convenient tool to optimize the FIB milling settings in applications where the surface crystal defect content is relevant.