Van
der Waals (vdW) α-MoO3 has a strong anisotropic
phonon polariton effect in the middle- and far-infrared up to terahertz
band. This can be of a great importance for developing new nanophotonics
and optoelectronic devices. The anisotropic phonon polaritons originate
from the anisotropic lattice vibrational properties. Therefore, the
phonon modes of α-MoO3, especially the in-plane anisotropic
phonon modes, should be systematically studied. To the best of our
knowledge, there are no correlative theoretical and experimental studies
on the phonon behaviors in vdW α-MoO3 thin films
(∼100 nm). Here, the lattice vibrational properties of α-MoO3 were investigated using density functional theory and polarization-resolved
Raman spectroscopy. Several Ag modes, whose polarization-resolved
Raman spectra could be used for identifying the orientation of the
α-MoO3 crystal, were observed. Furthermore, it was
demonstrated that modes with higher frequency have longer lifetimes,
and the phonon modes in bulk α-MoO3 have longer lifetimes
than those in monolayer α-MoO3. The group velocity
of each mode was also obtained. These results can help understand
the physical origin of the highly anisotropic phonon polaritons in
α-MoO3 and other types of vdW crystals.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.