Enhancement of the WS 2 A 1g Raman Mode in MoS 2 /WS 2
Annika Bergmann‐Iwe, Tomasz Woźniak, Mustafa Hemaid, Oisín Garrity, Patryk Kusch, Rico Schwartz, Ziyang Gan, Antony George, Ludger Wirtz, Stephanie Reich, Andrey Turchanin, Tobias KornWhen combined into heterostructures, transition metal dichalcogenide monolayers enable the exploration of novel physics beyond their individual properties. However, for interesting phenomena such as interlayer charge transfer and interlayer excitons to occur, control of the interface and high‐quality interlayer contact are crucial. Here, we investigate heterostructures fabricated by combining chemical‐vapor‐deposition‐grown MoS 2 and exfoliated WS 2 monolayers, allowing us to form several heterostructures with various twist angles within one preparation step. Under good interfacial contact—evaluated by photoluminescence quenching—we observe a twist‐angle‐dependent enhancement of the WS 2 A 1 g Raman mode. In contrast, other Raman modes do not show an enhancement under the same conditions. The experimental study is complemented with ab‐initio and ball‐and‐spring model calculations of Raman spectra. We find that the selective enhancement of the WS 2 A 1 g mode exhibits a strong dependence on interlayer distance. We show that this selectivity is related to the A 1g eigenvectors: these are predominantly localized on one of the two layers; yet, the intensity of the MoS 2 mode is attenuated because the WS 2 layer is vibrating out of phase, while the WS 2 mode is amplified because the atoms on the MoS 2 layer are vibrating in phase.