Multivalency-Induced Band Gap Opening at MoS<sub>2</sub> Edges
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Abstract
Zigzag
edges of monolayer MoS<sub>2</sub> and other transition-metal
(TM) dichalcogenides are experimentally shown to exhibit strong photoluminescence.
Atomic models that have been proposed for these edges, however, are
all metallic. Here, we address this puzzle by using first-principles
calculations. We found that a more generic electron counting model
(ECM) can be developed, which, when coupled with the ability of TM
atoms at edges to change their valency from 4+ to 5+, can quantitatively
account for the band gap opening at the zigzag edges. Due to the ECM,
a 3× periodicity along the zigzag edge is necessary to open the
band gap. Moreover, consistent with experiment, oxygen adsorption
is shown to open even larger band gaps than intrinsic edges