Instability of dewetting fronts in thin solid films

Anisotropy has an important effect in the dewetting dynamics of thin solid films.
Instabilities in the dewetting front morphology have been experimentally observed~$[1,2]$,
for instance in films of $Si$ and $Ge$ on $SiO_2$ substrates.
When an initial hole is produced in a thin film, its edges can be unstable,
and void fingers may develop. In the case of $Si$ films,
these fingers grow along diagonal directions with respect to the main axes of
the film lattice, whereas in the case of $Ge$ films, the fingers grow along axial directions.
To investigate the effect of anisotropy in dewetting, we employ kinetic Monte Carlo simulations to implement the dynamics, using a 2D
solid-on-solid model. In this model, epilayer atoms can hop to nearest neighbor sites and
an atom needs to break all its bonds to hop,
therefore the hopping barrier is given by the binding energy of the atom.
The hopping rates also depend if the atom is in contact with
the substrate or not. The model parameters are the adsorbate-substrate excess
energy $E_S$,the temperature $T$ and the thickness $h$ of the film.

$[1]$ F. Leroy, F. Cheynis, T. Passanante, P. Muller, Phys. Rev. B {\bf 88}, 035306 (2013).
$[2]$ C.V. Thomson, Annu. Rev. Matter. Res. {\bf 42} 399 (2012).