Fingerprint Raman spectroscopy for two-dimensional MoSSealloys.

Two-dimensional transition metal dichalcogenides (TMDs) and alloys based on them, is a promising platform for creating opto- and nanoelectronic devices. For layered alloys, there is a strong need to theoretically determine the frequencies of vibrational modes and dependences of their energies on the stoichiometric composition. By comparing experimentally measured Raman modes with theoretical predictions, it becomes possible to determine the stoichiometric composition of the manufactured alloys. In this work, we investigated the vibrational properties of monolayer MoSSealloys utilizing density functional theory method and confirmed them experimentally by Raman spectroscopy. The dependence of A' and E'dactylographic' modes on the stoichiometric composition of alloys has been calculated. When in pure MoSestructure Se atoms are substituted by S atoms, the in-plane E(S-Mo), E(Se-Mo) and out-plane A' (S-Mo) modes shifted linearly into higher frequencies, while the out-plane A' (Se-Mo) mode did the same in nonlinear way. We also identified the E(Se-Mo-S) mode, which specific for the MoSSealloys and does not appear in pure two-component TMDs.