  We experimentally discovered that Al2O3 and MgO exhibit well-pronounced
nanometric modifications on the surfaces when irradiated under grazing
incidence with 23 MeV I beam, in contrast to normal incidence irradiation with
the same ion beam when no damage was found. Moreover, ions in these two
materials produce notably different structures: grooves surrounded with
nanohillocks on MgO surfaces vs. smoother, roll-like discontinuous structures
on the surfaces of Al2O3. To explain these results, detailed numerical
simulations were performed. We identified that a presence of the surface
inhibits recrystallization process, thereby preventing transient tracks from
recovery, and thus forming observable nanopatterns. Furthermore, a difference
in the viscosities in molten states in Al2O3 vs. MgO explains the differences
in the created nanostructures. Our results thus provide a deeper understanding
of the fundamental processes of surface nanostructuring, potentially allowing
for controlled production of periodic surface nanopatterns.
