In the recent years the increase in nano-scale applications has creat-
ed signi
fi
cant interest in self assembled pattern formation due to ion
beam irradiation. Nano-patterning and modi
fi
cations require nuclear
collision between ions and substrate atoms in less than 100 eV energy
range. Compared to monomer ion beams the cluster ion interactions
with the surface produces unique structural alterations because of
their capability to deliver a very low particle energy beam (a few eV's)
with high current density. Upon impact the cluster ions
[15]
simulta-
neously arrive at the same location and transfer their high total energy
to a small impact volume (of the order of a tens of angstroms). Due to
high energy density collisions, extreme pressure and temperature con-
ditions are generated. Consequently, dissociations close to the surface
create synergetic reactions that produces a high sputtering yield and
strong enhancement in chemical reactivity and diffusion.
Gas cluster ion beam forms nano-ripple structures on a thin metal
surface at oblique angle incidences
[16]
. When thousands of very low
energy atoms simultaneously bombard the surface of a target at an in-
clined angle to the normal, a nano-ripple pattern is formed because of
thelateralsputteringofthesurfaceatoms.Clusterformationisacompli-
cated process and the theoretical descriptions of this process are limit-
ed. First model explaining ripple formation and mechanism was
derivedbyBradleyandHarper
[17]
onsolidmaterials.Itpredictsthelin-
ear growth of ripples, but does not predict ripple saturation. The
Makeev, Cuerno and Barabási (MCB) model
[18]
modi
fi
ed the Bradley
and Harper model and included the non-linear terms that depend on
the random ion
fl
ux and the slope of the surface and considered