**3. Analysis of the surface microstructure changes induced by the ion irradiation**

**Figure 3** shows, an optical microscopy image of the irradiated and non-irradiated regions of the Ni-22Si alloy, two regions are observed, one in bright contrast and the other one in dark contrast, the dark contrast region corresponds to the irradiated region. This change from bright to dark contrast is generated by the surface topography modification induced by irradiation, as a consequence, the reflective power of the irradiated surface is reduced. The surface topographic change is generated by the preferential sputtering of boundaries between the dendritic lobes and the interdendritic region, as well as by the crater's formation, dark spots, both changes are surface damage induced by irradiation [12].

As a result of several reported works on irradiation-induced damage in metallic alloys, it has been established that preferential sputtering of grain boundaries occurs because the atoms located in that region have lower binding energy with their neighbors [13].

**Figure 3.** *Optical microscopy image of the irradiated and non-irradiated region.*
