Figure 4.

In addition to morphological changes under high-vacuum conditions, the MgO cubes embedded in the as-received indium foil after (a) 1 h and (b) 4 days in the HIM chamber (chamber pressure p < 3·10⁻⁷ mbar) exhibit contrast changes, which are attributed to the surface chemistry. MgO cubes that are not in contact with the indium foil (marked by arrows) do not exhibit any changes. (c,d) MgO cubes in areas I–IV at higher magnification illustrating both morphological and contrast changes. (HIM SE images recorded at 30 kV acceleration voltage and (a,b) 0.3 pA beam current, 5·10¹⁴ cm⁻² ion dose, (c,d) 0.3 pA beam current, 2·10¹⁵ cm⁻² ion dose.)