  We investigate the thermal properties of these Zirconium based materials
using confocal Raman spectroscopy. We observed 2 different and distinctive
Raman signatures for exfoliated ZrX2 (where X = S or Se). These Raman modes
generally depend on the shape of the exfoliated nanosheets, regardless of the
incident laser polarization. These 2 shapes are divided into 2D- ZrX2 and quasi
1D- ZrX2. For 2D- ZrX2, Raman modes are in alignment with those reported in
literature. However, for quasi 1D-ZrX2, we show that Raman modes are identical
to exfoliated ZrX3 nanosheets, indicating a major lattice transformation from
2D to quasi-1D. We also measure thermal properties of each resonant Raman mode
for each ZrX2 shape. Based on our measurements, most Raman modes exhibit a
linear downshift dependence with temperature. However, for ZrS2, we see an
upshift (blueshift) with temperature for A1g mode, which is attributed to
non-harmonic effects caused by dipolar coupling with IR-active modes. Moreover,
the observed temperature dependence coefficient for some phonon modes of quasi
1D-ZrX2 differ dramatically, which can be caused by the quasi 1D lattice.
Finally, we measure phonon dynamics under optical heating for each of 2D-ZrX2
and quasi 1D-ZrX2 and show phonon confinement in quasi 1D-ZrX2 nanosheets. We
extract the thermal conductivity and the interfacial thermal conductance for
each of 2D-ZrX2 and quasi 1D-ZrX2 nanosheets. Our calculations indicate lower
interfacial thermal conductance for quasi 1D-ZrX2 compared to 2D-ZrX2, which
can be attributed to the phonon confinement in 1D. Based on our model, we show
low thermal conductivity for all ZrX2 nanosheets. Our results demonstrate
exceptional thermal properties for ZrX2 materials, making them ideal for future
thermal management strategies and thermoelectric device applications.
