The effect of temperature and excitation energy on Raman scattering in bulk HfS 2 .

Raman scattering (RS) in bulk hafnium disulfide (HfS 2 ) is investigated as a function of temperature (5 K - 350 K) with polarization resolution and excitation of several laser energies. An unexpected temperature dependence of the energies of the main Raman-active (A 1g and E g ) modes with the temperature-induced blueshift in the low-temperature limit is observed. The low-temperature quenching of a mode ω 1 (134 cm -1 ) and the emergence of a new mode at approx. 184 cm -1 , labeled Z, is reported. The optical anisotropy of the RS in HfS 2 is also reported, which is highly susceptible to the excitation energy. The apparent quenching of the A 1g mode at T=5 K and of the E g mode at T=300 K in the RS spectrum excited with 3.06 eV excitation is also observed. We discuss the results in the context of possible resonant character of light-phonon interactions. Analyzed is also a possible effect of the iodine molecules intercalated in the van der Waals gaps between neighboring HfS 2 layers, which inevitably result from the growth procedure.