Temperature- and Phase-Dependent Phonon Renormalization in 1T'-MoS2

Abstract

Polymorph engineering of 2H-MoS2, which can be achieved by alkali metal intercalation to obtain either the mixed 2H/1T′ phases or a homogeneous 1T′ phase, has received wide interest recently, since this serves as an effective route to tune the electrical and catalytic properties of MoS2. As opposed to an idealized single crystal-to-single crystal phase conversion, the 2H to 1T′ phase conversion results in crystal domain size reduction as well as strained lattices, although how these develop with composition is not well understood. Herein, the evolution of the phonon modes in Li-intercalated 1T′-MoS2 (LixMoS2) are investigated as a function of different 1T′-2H compositions. We observed that the strain evolution in the mixed phases is revealed by the softening of four Raman modes, Bg (J1), Ag (J3), E12g, and A1g, with increasing 1T′ phase composition. Additionally, the first-order temperature coefficients of the 1T′ phonon mode vary linearly with increasing 1T′ composition, which is explained by increased electron–phonon and strain–phonon coupling.