Nanoscale plasmonic phenomena in CVD-grown MoS2 monolayer revealed by ultra-
broadband synchrotron radiation based nano-FTIR spectroscopy and near-field
microscopy
Nanoscale plasmonic phenomena observed in single and bi-layers of molybdenum
disulfide (MoS2) on silicon dioxide (SiO2) are reported. A scattering type
scanning near-field optical microscope (s-SNOM) with a broadband synchrotron
radiation (SR) infrared source was used. We also present complementary optical
mapping using tunable CO2-laser radiation. Specifically, there is a
correlation of the topography of well-defined MoS2 islands grown by chemical
vapor deposition, as determined by atomic force microscopy, with the infrared
(IR) signature of MoS2. The influence of MoS2 islands on the SiO2 phonon
resonance is discussed. The results reveal the plasmonic character of the MoS2
structures and their interaction with the SiO2 phonons leading to an
enhancement of the hybridized surface plasmon-phonon mode. A theoretical
analysis shows that, in the case of monolayer islands, the coupling of the
MoS2 optical plasmon mode to the SiO2 surface phonons does not affect the
infrared spectrum significantly. For two-layer MoS2, the coupling of the extra
inter-plane acoustic plasmon mode with the SiO2 surface transverse phonon
leads to a remarkable increase of the surface phonon peak at 794 cm−1. This is
in agreement with the experimental data. These results show the capability of
the s-SNOM technique to study local multiple excitations in complex non-
homogeneous structures