Bond strengthening in lateral heterostructures of transition metal dichalcogenides

The adhesion strength of lateral heterostructures composed of transition metal dichalcogenides ($\mathrm{Mo}{\mathrm{S}}₂, \mathrm{Mo}{\mathrm{Se}}₂, {\mathrm{WS}}₂$, and $\mathrm{W}{\mathrm{Se}}₂$) monolayers is investigated with first-principles electronic structure calculations. Our density functional theory calculations demonstrate that the adhesion strength, which is gauged by the ideal work of separation (${W}_{\mathrm{sep}}$), strongly depends on the local atomic configuration, and that ${W}_{\mathrm{sep}}$ becomes enhanced (diminished) at the interface where a chalcogen atom forms bonds with one (two) W and two (one) Mo atoms compared to those of the homogeneous cases. It is further shown that the increase (decrease) in ${W}_{\mathrm{sep}}$ from the homogeneous value is caused by the charge redistribution among the interfacial bonds, which is determined by the differences in the electronegativity of the transition metal species at the interface. Such geometrically controlled interfacial strength presents a route to control the materials' mechanical characteristics through structural engineering.