The transformation of the stripe domain structure of spontaneously-formed
epitaxial silicene on ZrB$_2$ thin film into a single-domain driven by the
adsorption of a fraction of a monolayer of silicon was used to investigate how
dislocations react and eventually annihilate in a two-dimensional honeycomb
structure. The in-situ real time STM monitoring of the evolution of the domain
structure after Si deposition revealed the mechanisms leading to the nucleation
of a single-domain into a domain structure through a stepwise reaction of
partial dislocations. After its nucleation, the single-domain extends by the
propagation of edge dislocations at its frontiers. The identification of this
particular nucleation-propagation formation of dislocation-free silicene sheet
provides insights into how crystallographic defects can be healed in
two-dimensional materials.