Nonstoichiometric Phases of Two-Dimensional Transition-Metal Dichalcogenides: From Chalcogen Vacancies to Pure Metal Membranes

Abstract

membranes consisting of a single layer of Mo atoms were recently manufactured [Adv. Mater. 2018, 30, 1707281] from MoSe 2 sheets by sputtering Se atoms using an electron beam in a transmission electron microscope. This is an unexpected result as formation of Mo clusters should energetically be more favorable. To get microscopic insights into the energetics of realistic Mo membranes and nonstoichiometric phases of transition-metal dichalcogenides (TMDs) M a X b , where M = Mo and W and X = S, Se, and Te, we carry out first-principles calculations and demonstrate that the membranes, which can be referred to as metallic quantum dots embedded into a semiconducting matrix, can be stabilized by charge transfer. We also show that an ideal neutral 2D Mo or W sheet is not flat but a corrugated structure, with a square lattice being the lowest-energy configuration. We further demonstrate that several intermediate nonstoichiometric phases of TMDs are possible as they have lower formation energies than pure metal membranes. Among them, the orthorhombic metallic 2D M 4 X 4 phase is particularly stable. Finally, we study the properties of this phase in detail and discuss how it can be manufactured by the top-down approaches.

Spatially Controlled Fabrication and Mechanisms of Atomically Thin Nanowell Patterns in Bilayer WS2 Using in Situ High Temperature Electron Microscopy

“…This spread W membrane with nonstoichiometry was recently predicted to be the most energetically favorable monolayer pure metal phase, which exhibits squared lattice from the projection view and corrugated side view. 62 The simulated ADF-STEM image via a multislice method accords well with the experimental image (Figure 5h).…”

“…This exposed edge provides abundant defective sites for adsorb excessive W atoms along it, and the positions of the stacked W atom membrane (shown by the purple atom model) is relative to the WS 2 lattice beneath, as illustrated by the overlaid atomic model in Figure f,g. This spread W membrane with nonstoichiometry was recently predicted to be the most energetically favorable monolayer pure metal phase, which exhibits squared lattice from the projection view and corrugated side view . The simulated ADF-STEM image via a multislice method accords well with the experimental image (Figure h).…”

“…This localized phase change is a result of S depletion, electron stimulation, thermal energy, as well as the templating of supported WS 2 layer. According to the previous calculation, the formed metallic 2D metal membrane could be stabilized by charge transfer . Besides, the good match between the d -spacing of {002} W with that of {110} WS2 may also contribute to the stabilization of the heteroepitaxial structure.…”

Computational Design of Gas Sensors Based on V3S4 Monolayer

“…; X = S, Se, Te, etc. ), new two-dimensional and non-stoichiometric structures can be formed [ 28 ]. There are several studies devoted to vanadium sulfide crystals such as VS 4 [ 29 , 30 ], V 3 S 4 [ 31 , 32 ], V 5 S 4 [ 33 ], V 5 S 8 [ 34 ], and V 3 S [ 35 ] structures in different applications.…”

Insights into the regularity of the formation of 2D 3d transition metal monocarbides

“…Intercalation of a lithium into bilayered graphene uncovered ultrathin and superdense 2D Li phase. 10 Monoatomic Au 11 and Mo-based 12,13 films were fabricated under electronic beam. As for 3d transition metal (TM) based films, in one of the pioneering works, the formation of 2D square Fe cluster inside graphene pore was reported.…”