ABSTRACT
Understanding how the electronic state of transition metal atoms can influence molecular adsorption on a substrate is of great importance for many applications. Choosing NH3 as a model molecule, its adsorption behavior on defected SnS2 monolayers is investigated. The number of valence electrons n is controlled by decorating the monolayer with different transition metal atoms, ranging from Sc to Zn. Density-Functional Theory based calculations show that the adsorption energy of NH3 molecules oscillates with n and shows a clear odd-even pattern. There is also a mirror symmetry of the adsorption energies for large and low electron numbers. This unique behavior is mainly governed by the oxidation state of the TM ions. We trace back the observed trends of the adsorption energy to the orbital symmetries and ligand effects which affect the interaction between the 3σ orbitals (NH3) and the 3d orbitals of the transition metals. This result unravels the role which the spin state of TM ions plays in different crystal fields for the adsorption behavior of molecules. This new understanding of the role of the electronic structure on molecular adsorption can be useful for the design of high efficiency nanodevices in areas such as sensing and photocatalysis.
ABSTRACT
Two-dimensional Janus MXY materials have been successfully synthesized from their parent species by CVD, SEAR, or PLD techniques. However, their detailed evolution process and underlying atomistic mechanism are far from understood conclusively, which are prompts for further research. Here, taking Janus MoSSe as a representation, the evolution process from MoS2 is systematically investigated by first-principles calculation. The simulation shows that the lowest formation energy of MoS(2-δ)Seδ increases with selenylation ratio δ. Unexpectedly, Se atoms prefer to form a pair in next-nearest neighboring state (Se-NN-Se), eventually transferred into a growth rule of (6n + 1) during the evolution process. Particularly, it is demonstrated that the stability of the intermediate is mainly governed by the Mo 4d orbitals in different distorted triangular crystal fields, rendering a different degree of orbital splitting. Both the occupied and unoccupied Mo 4d orbitals of Se-NN-Se are farther from the Fermi level than other cases, which is clearly illustrated by d-band center theory. These findings will be helpful to understand the evolution process and the underlying atomistic mechanism of Janus MXY.
