  We explore the occurrence of low-energy and low-temperature transient cluster
burrowing leading to intact cluster inclusions. In particular, the anomalously
fast (ballistic) Pt nanocluster implantation into Al and Ti substrates has been
found by molecular dynamics simulations using a tight-binding many-body
potential with the 1-5 eV/atom low impact energy. Similar behavior has also
been found for many other cluster/substrate couples such as Cu/Al and Ni/Ti,
Co/Ti, etc. In particular, in Ni/Ti at already $\sim 0.5$ eV/atom impact energy
burrowing takes place. At this few eV/atom low impact energy regime instead of
the expected stopping at the surface we find the propagation of the cluster
through a thin Al slab as thick as $\sim 50$ $\hbox{\AA}$ with a nearly
constant speed ($\propto 1$ eV/atom). Hence the cluster moves far beyond the
range of the impact energy which suggests that the mechanism of cluster
burrowing can not be explained simply by collisional cascade effects. In the
couples with reversed succession (e.g. Ti/Pt, Al/Pt) no burrowing has been
found, the clusters remain on the surface (the asymmetry of burrowing). We
argue that cluster penetration occurs at few eV/atom impact energy when the
cluster/substrate interaction is size-mismatched and mass anisotropic
atomically.
