**3.1 Preferential erosion**

**Figure 4** shows an optical microscopy image of the boundary formed between the dendritic lobes and the interdendritic region, this image shows in detail the preferential sputtering suffered by the border between the two regions, the sputtering yield suffered by the border is greater than the erosion suffered by the dendritic region or the interdendritic region. In the image in **Figure 4**, it can also be seen that the sputtering of the boundary is not homogeneous, the alternation of protrusions and hollows is clearly observed, for this reason, atomic force microscopy was used to analyze in greater detail the sputtering process of grain frontier.

Atomic force microscopy images (**Figure 5**) of the irradiated region provide experimental evidence of sputtering process inhomogeneity, in **Figure 5(a)**, on the left side, a dendrite nodule (monophasic region) and on the right side of the same figure, the inter-dendritic region (biphasic region), and the border formed between the two regions can be seen. In **Figure 5(a)**, it is clearly seen that some specific regions of the boundary had suffered a greater sputtering giving rise to the bridges formation with a regular alternation, **Figure 5(b)** shows the same boundary at higher resolution, this last image allows us to establish that the sputtering process is indeed a non-homogeneous process since certain portions of the boundary were totally eliminated.

**Figure 4.** *Optical microscopy image of irradiated región.*

## **Figure 5.**

*Atomic force microscopy images of the boundary between dendritic and interdendritic regions.*
