**2. Experimental evidence of microstructure changes induced by ion beam irradiation**

In order to explain the changes induced by irradiation on a complex surface formed by the presence of two regions with different chemical compositions, the Ni-22%at.Si (Ni-22Si) concentrated alloy was selected. The Ni-22Si alloy is of the hypereutectic type, consisting of two regions, the dendritic and the interdendritic, the dendritic region is constituted by the Ni3Si-monoclinic phase, and in the interdendritic region there is a regular eutectic formed by the regular alternation of the Ni(Si) and Ni3Si-monoclinic phases lamellae (**Figure 1**), it was determinate by optical microscopy that 70% of the surface is occupied by the Ni3Si-monoclinic phase. The terminal Ni(Si) phase has a maximum solubility of 12 atomic % of Silicon at the irradiation temperature, on the other hand, the Ni3Si-monoclinic phase is an intermetallic phase with a Silicon concentration of 25 atomic %.

In summary, the main characteristics of the hypereutectic microstructure are the presence of two crystalline phases with different chemical compositions and crystalline structures, as well as the high density of grain boundaries.

Before being irradiated, the surface was mirror-polished to eliminate protrusions or surface defects that could locally modify the sputtering yield. The surface was analyzed using atomic force microscopy (AFM) to establish the surface topography parameters, an AFM image of the Ni-22Si alloy surface before being irradiated is shown in **Figure 2**.

As a result of the MFA images analysis of the surface before being irradiated, the protrusions' existence with heights of angstroms has been detected, as well as the presence of a step between the dendritic and interdendritic regions, the dendritic

*Surface Microstructure Changes Induced by Ion Beam Irradiation DOI: http://dx.doi.org/10.5772/intechopen.112015*

**Figure 2.** *Atomic force microscopy image of the Ni-22Si alloy surface before to be irradiated.*

region is located on the upper right side of **Figure 2**, the interdendritic region occupies the rest of the surface shown in **Figure 2**.
