Mechanism of $MoS_2$ growth and oxidation studied by density functional theory

Abstract

Recently, transition metals dichalcogenide materials (TMDCs) attracted considerable attention of scientific community due to intrinsic band gap, which first member of 2D family (i.e. graphene) lack. $MoS_2$ has been investigated widely among TMDCs, due to its stability as isolat-ed monolayer and indirect to direct band gap transition. Moreover, transition metal oxides has also been extensively studied for their promising facets in application of catalysis and solar cell applications. Many researchers are trying to oxidize $MoS_2$ into its corresponding oxidize. How-ever, understanding growth and oxidation mechanism, which is compulsory for large scale syn-thesis of $MoS_2$ and it oxides, is largely overlooked. Using first principles calculations based on density functional theory, we presented the insight study of $MoS_2$ growth and oxidation mech-anism in this thesis paper. This paper has two sections, first part will explain the science behind the different types of $MoS_2$ growth using organic ligand as precursor, whereas the second part includes fundamental insights into oxidation mechanism at edges and bulk region of single and multi-layer $MoS_2$. First, we calculated the energetics and stable geometry of precursor with S and Mo in vacuum as well as on $SiO_2$ substrate. We found energetically most favorable configu-ration of precursor on substrate, which was the result of mixture of solvents used in the syn-thesis process, will provide strong bases for homogenous single layer growth. Second, using energetically most promising $MoS_2$ nano-ribbon, we investigated the oxidation mechanism at edges as well as bulk region. Regardless to the number of layers in the system, edges are al-ways preferred to oxidized first, moreover kinetically restricted motion of oxygen atoms to the interstitial sulfur atoms will results in the top atom oxidation first. Once the top layer sulfur atoms oxidized, bending of ribbon has been observed which uncovers the bottom sulfur atoms for complete oxidization into $MoO_x$. The findings presented in this paper will help in better un-derstanding of growth and oxidation mechanism of transition metal dichalcogenide especially $MoS_2$.