Interlayer coupling in isotopic heterobilayers of MoS2

Heterostructure engineering of two-dimensional materials overlapped with isotope engineering provides a comprehensive platform to distinctly tune optoelectronic properties driven by interlayer interaction. A strong interlayer coupling is reported in a double-layered HS of two different sulfur isotope-modified adjacent MoS2 monolayers (MLs) grown via 2-step chemical vapor deposition (CVD). The growth propagation reveal that the top layer of MoS2 grew at separate nucleation centers on the underlying crystal, forming distinct triangular domains and resulting in heterogeneity in the stacking arrangement. Raman analysis of layered HS depicts the merging of fingerprint Raman spectra of individual isotope-modified MoS2 ML implying a coupling factor. The interlayer coupling in double-layered HS is affirmed by low-frequency shear and breathing modes and the variability in shear to breathing intensity ratio across different positions in HS indicates the potential for tuning interlayer coupling through stacking in a heterogeneous manner. The hefty decrement of A exciton intensity in layered HS as well as the relative enhancement of B exciton in the photoluminescence spectra provide corroborative evidence for interlayer interaction. This is further ascertained by the observation of an additional slower decay channel in time-resolved photoluminescence measurements due to interlayer crossing recombination of the carriers in layered HS.