Abstract
The knowledge of the phonon coherence length is of great importance for
two-dimensional-based materials since phonons can limit the lifetime of
charge carriers and heat dissipation. Here we use tip-enhanced Raman
spectroscopy (TERS) to measure the spatial correlation length L-c of the
A(1g)(1) and A(1g)(2) phonons of monolayer and few-layer gallium sulfide
(GaS). The differences in L-c values are responsible for different
enhancements of the A(1g) modes, with A(1g)(1) always enhancing more
than the A(1g)(2), independently of the number of GaS layers. For five
layers, the results show an L-c of 64 and 47 nm for A(1g)(1) and
A(1g)(2), respectively, and the coherence lengths decrease when
decreasing the number of layers, indicating that scattering with the
surface roughness plays an important role.
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