Phenomenological Modeling of Confined Phonon States in TMD Quantum Dots

Several reports have shown band-gap tuning in TMDs, from indirect band gap in the bulk material to a direct gap in single layer due to the absence of interlayer coupling. This unique property stems from the modified electronic states. The phononic properties are extremely modified as well, due to layered effect and quantum size effect. There are several reports on layered effect; however, reports on the confined phonon states in these structures are limited. Thus, we present a preliminary studies of the confined phonon states in TMDs (WS2 and MoS2) quantum dots, and elucidate on the evolution of the phonon lineshape with diameter using a phenomenological model with an envelop function that truncates the phonon wave at the surface of the quantum dot. Furthermore, we delineate the layered effect from the quantum size effect in the phonon lineshape of WS2 and MoS2.