  We investigate the effects of lattice disorders on the low frequency Raman
spectra of bilayer MoS2. The bilayer MoS2 was subjected to defect engineering
by irradiation with a 30 keV He+ ion beam and the induced morphology change was
characterized by transmission electron microscopy. With increasing ion dose the
shear mode is observed to redshift and it is also suppressed sharply compared
to other Raman peaks. We use the linear chain model to describe the changes to
the Raman spectra. Our observations suggest that crystallite size and
orientation are the dominant factors behind the changes to the Raman spectra.
