Origin of the enhanced edge optical transition in transition metal dichalcogenide flakes

Abstract

Various edge configurations for transition metal dichalcogenide (TMD) flakes are inevitable during the material preparation. Such edge configurations with different local motifs play an important role in the optical transition. It is found in experiments that enhanced photoluminescence appears at the edge with a cation-terminated zigzag pattern but not at other edge configurations [Nat. Nanotechnol., 2020, 15, 29–34; Nano Lett., 2013, 13, 3447–3454]. We systematically studied the edge states of the feasible MoS₂ flakes, and identified the edge modes at the S-passivated cation-terminated zigzag edge that endow strong optical transition. The identified edge states consist of the non-uniform edge mode of s–p-hybridized states within edge atoms, which can be preserved by the interior oxygens but destroyed by edge oxygens. The enhanced optical transition can be effectively tuned by in-plane and out-of-plane strains. Our study suggests the long-sought origin of the enhanced optical transition at the edge of TMD flakes, and provides a route to precisely manipulate the transition eigenstates for abundant functional edge structures with potential applications in transition-controlled electronic and optoelectronic devices.