  We report a direct observation of dramatic mass transport due to 1.5 MeV Au2+
ion impact on isolated Au nanostructures of an average size 7.6 nm and a height
6.9 nm that are deposited on Si (111) substrate under high flux (3.2x10^10 to
6.3x10^12 ions cm-2 s-1) conditions. The mass transport from nanostructures
found to extend up to a distance of about 60 nm into the substrate, much beyond
their size. This forward mass transport is compared with the recoil
implantation profiles using SRIM simulation. The observed anomalies with theory
and simulations are discussed. At a given energy, the incident flux plays a
major role in mass transport and its re-distribution. The mass transport is
explained on the basis of thermal effects and creation of rapid diffusion paths
at nano-scale regime during the course of ion irradiation. The unusual mass
transport is found to be associated with the formation of gold silicide
nanoalloys at sub-surfaces. The complexity of the ion-nanostructure interaction
process has been discussed with a direct observation of melting (in the form of
spherical fragments on the surface) phenomena. The transmission electron
microscopy, scanning transmission electron microscopy and Rutherford
backscattering spectroscopy methods have been used.
