Why Phonon Behaviors in Transition Metal Dichalcogenides Matter

Phonons are critical in understanding the electronic, optical and optoelectronic properties of transition metal dichalcogenides (TMDs). The interpretation of lineshapes is important for understanding the effect of specific physical processes on the electronic, optical and optoelectronic properties of TMDs. We employ an analytical approach to investigate the influence of the layered effect, the quantum size effect, the Breit-Wigner-Fano effect, and the inhomogeneous heating effect on the phonon lineshape of TMDs, using WS2 and MoS2 as prototypes. We demonstrate the similarities and differences in how individual processes affect the lineshapes and also the effect of combining processes. Such an approach is useful in guiding the interpretation of the phonon lineshapes of TMDs in particular, and nanostructures in general.