  Through the positive role of alkali halides in realizing large area growth of
transition metal-di-chalcogenide layers has been validated, the film-growth
kinematics has not yet been fully established. This work presents a systematic
analysis of the MoS$_2$ morphology for films grown under various pre-treatment
conditions of the substrate with sodium chloride (NaCl). At an optimum NaCl
concentration, the domain size of the monolayer increased by almost two orders
of magnitude compared to alkali-free growth of MoS$_2$. The results show an
inverse relationship between fractal dimension and areal coverage of the
substrate with monolayers and multi-layers, respectively. Using the Fact-Sage
software, the role of NaCl in determining the partial pressures of Mo- and
S-based compounds in gaseous phase at the growth temperature is elucidated. The
presence of alkali salts is shown to affect the domain size and film morphology
by affecting the Mo and S partial pressures. Compared to alkali-free synthesis
under the same growth conditions, MoS$_2$ film growth assisted by NaCl results
in $\approx$ 81$\%$ of the substrate covered by monolayers. Under ideal growth
conditions, at an optimum NaCl concentration, nucleation was suppressed, and
domains enlarged, resulting in large area growth of MoS$_2$ monolayers. The
monolayers were found to be free of unintentional doping with alkali metal and
halogen atoms and exhibit high crystallinity and excellent opto-electronic
quality.
