  Transition metal dichalcogenides (TMDs) are layered materials which show
excellent potential for nanoelectronic and optoelectronic applications.
However, as many of the exciting features of these materials are controlled by
the anharmonic effects, a proper understanding of the phonon properties and
anharmonicity associated with these materials is essential for the proposed
applications to be realized. We present here a comprehensive study on the
phonon properties of two different TMDs; viz., MoS2 and MoTe2, as a function of
temperature, laser excitations, and polarization, as well as flake-thickness.
Our study includes the measurement of anharmonicity in the first-order and
higher order Raman scattering processes. The variations in anharmonicity with
the thickness of MoS2 and MoTe2 have been explained in terms of their phonon
symmetries, electron-phonon coupling, and phonon-phonon interactions. Further,
the effect of the underlying substrate on the anharmonic properties of the
in-plane and out-of-plane phonons has also been estimated from the Raman
measurements, thus elucidating the intrinsic phonon properties of the 2D
layered materials.
