Intrinsic setting of the exciton state in MoS ₂ monolayers via tailoring the Moiré correlation with a sapphire substrate

This study aims to elucidate the specific Moiré correlation and associated exciton properties within MoS₂ monolayers grown randomly oriented on a c-cut single-crystalline sapphire (Al₂O₃) substrate, which facilitates a distinct Moiré correlation. Notably, the exciton state in MoS₂ monolayers appeared periodically linked to the stacking geometry with the sapphire substrate. Specifically, the observed stacking configuration of MoS₂[112̄0]/Al₂O₃[112̄0] induced a redshifted exciton state, while a 30-degree-misaligned stacking, such as MoS₂[112̄0]/Al₂O₃[011̄0], increased the exciton energy. The variation in the exciton state due to changes in the stacking geometry between MoS₂ and sapphire thus exhibited a 6-fold periodicity, reflecting the combination of hexagonal MoS₂ and the trigonal sapphire substrate. This transition in the exciton state of the MoS₂ monolayer was attributed to stacking-induced strain: the MoS₂[112̄0]/Al₂O₃[112̄0] stack resulted in a closely packed nature with induced tensile strain in the film plane, whereas the MoS₂[112̄0]/Al₂O₃[011̄0] stack appeared lightly packed, thus rendering the MoS₂ structurally relaxed. These findings regarding the stacking-induced strain issues are consistent with the results of Raman spectra. This work underscores the potential for manipulating the crystallographic stacking between single-crystalline MoS₂ monolayers and sapphire substrates to serve as a versatile platform for investigating photonics in MoS₂-based heterostructures.