Lattice Dynamics of van der Waals Layered Rhodium Chalcochlorides: Janus RhSeCl and 1.5-Dimensional RhTeCl.

van der Waals layered rhodium chalcochlorides demonstrate a unique interplay between the structure of the layers and the size of the anions. While RhSeCl has a 2D Janus structure with Se and Cl on opposite sides of the layers, RhTeCl forms a non-Janus structure with alternating stripes of Cl and Te. Here, we study the lattice dynamics of these semiconductors by a combination of far-infrared and Raman spectroscopy and DFT phonon calculations. Polarization-dependent measurements enabled the complete assignment of all Raman-active modes of both compounds. The resonance effects in Raman scattering were addressed by using multiple excitation wavelengths and a tunable dye laser between 457 and 785 nm. Raman excitation profiles appeared to be more sensitive to optical excitations than direct measurements of excitation spectra by diffuse reflectance spectroscopy. Finally, variable-temperature Raman measurements between 10 and 300 K revealed that the optical phonons of RhSeCl are weakly susceptible to temperature variations, whereas the temperature dependence of RhTeCl is more pronounced.