Sulfur isotope engineering in heterostructures of transition metal dichalcogenides

Heterostructuring of two-dimensional materials offers a robust platform to precisely tune optoelectronic properties through interlayer interactions. Here we achieved a strong interlayer coupling in a double-layered heterostructure of sulfur isotope-modified adjacent MoS₂ monolayers via two-step chemical vapor deposition growth. The strong interlayer coupling in the MoS₂(³⁴S)/MoS₂(³²S) was affirmed by low-frequency shear and breathing modes in the Raman spectra. The photoluminescence emission spectra showed that isotope-induced changes in the electronic structure and strong interlayer coupling led to the suppression of intralayer excitons, resulting in dominant emission from the MoS₂(³²S) layer. Time-resolved photoluminescence experiments indicated faster lifetimes in the MoS₂(³⁴S)/MoS₂(³²S) heterostructure compared to the conventional bilayers with the natural isotopic abundance, highlighting nuanced interlayer exciton dynamics due to the isotopic modification. This study underscores the great potential of isotope engineering in van der Waals heterostructures, as it enables tailoring the band structure and exciton dynamics at the nuclear level without the need of chemical modification.