Theoretical Investigation of W(CO)6 and CO Selenization Process

Detailed atomic-level insight into the mechanism of $W(CO)_6$ and CO selenization is essential for the fabrication of cheap and environmentally benign transition metal chalcogenides such as $MoS_2$ and $WSe_2$. Earlier discussions in literature have focused mainly on the CO methanation by sulfur and its derivatives but $H_2Se$ mediated CO methanation at the atomic level is yet to be explored. First-principles calculations and ReaxFF-based molecular dynamics simulations are conducted here to explore the relative stabilities of intermediates formed during the gas-phase interactions of $W(CO)_6$ and $H_2Se$, determined associated reaction energies and kinetic barriers. The methanation of CO, which is released from the organometal, by H2Se is further investigated. The results indicate that the chain reactions of $W(CO)_6$ and H2Se lead to the formation of a thermodynamically stable end product of $W(SeH)_2Se_2$. Depending on the temperature, $W(HSe)_2Se_2$ is expected to go through a last uphill reaction by releasing H2Se into the environment and evolving into a $WSe_3$ molecule. Additionally, the dehydrogenation of organometallic molecules is thermodynamically feasible but kinetically controlled, requiring a significant activation energy. When all CO groups are released from the W atom, the H2 release from W-compund becomes nearly barrierless. Since CO radical groups are dominant byproducts formed during the MOCVD chain reactions but in a chalcogen rich environment, this work also shed light into the CO selenization during the growth of transition metal diselenides $(e.g., WSe_2, MoSe_2, CrSe_2)$ and discusses the formation of potential products such as $CSe_2, CH_4, H_2Se, CO, H_2O, Se_2.$

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