Monolayers of MoS2 and WS2 as oxidation protective nanocoating materials

First-principles simulation techniques are employed to analyse the interaction of oxygen with MoS$_2$ and WS$_2$ monolayers. Our calculations show that while oxygen atoms are strongly bound on top of sulphur atoms, oxygen molecule only weakly interact with the system. The penetration of oxygen atom and molecule through MoS$_2$ monolayer require a very high energy barrier indicating that MoS$_2$ can serve as protective layer from oxidation. Not only ideal structures but also possible defect formations are considered and penetration/diffusion barriers of oxygen are calculated for each case. The study is extended for WS$_2$ as well, and obtained results are compared. Our predictions indicate that ideal and/or defected MoS$_2$ and WS$_2$ monolayers can improve the oxidation and corrosion-resistance of the covered surface and can be used as an efficient nanocoating material.