  Here we report a scanning tunneling microscopy (STM) and spectroscopy (STS)
study in the superconducting state of 2H-NbS2. We directly visualize the
existence of incommensurate charge density wave (CDW) that is pinned by atomic
impurities. In strong tunneling conditions, the incommensurate CDW is de-pinned
from impurities by the electric field from STM tip. We perform STM-based
inelastic tunneling spectroscopy (IETS) to detect phonon excitations in 2H-NbS2
and measure the influence of atomic impurities on local phonon excitations. In
comparison with the calculated vibrational density of states in 2H-NbS2, we
find two branches of phonon excitations which correspond to the vibrations of
Nb ions and S ions, and the strength of the local phonon excitations is
insensitive to the atomic impurities. Our results demonstrate the coexistence
of incommensurate CDW and superconductivity in 2H-NbS2, and open the way of
detecting atomic-scale phonon excitations in transition metal dichalcogenides
with STM-based IETS.

Mesoscale and Nanoscale Physics;Materials Science