The effect of temperature and excitation energy on Raman scattering in bulk HfS$_2$

TL;DR

This study investigates how temperature and excitation energy influence Raman scattering in bulk HfS$_2$, revealing unexpected temperature-dependent shifts, mode quenching, and optical anisotropy linked to resonant interactions and intercalated molecules.

Contribution

It provides new insights into the temperature and excitation energy dependence of Raman modes in HfS$_2$, including mode quenching, emergence of new modes, and anisotropy effects, considering intercalation influences.

Findings

Unexpected blueshift of Raman modes at low temperatures.

Quenching of specific Raman modes at certain temperatures.

Optical anisotropy highly dependent on excitation energy.

Abstract

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$_{\textrm{1g}}$ and E$_{\textrm{g}}$) modes with the temperature-induced blueshift in the low-temperature limit is observed. The low-temperature quenching of a mode $\omega_1$ (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$_{\textrm{1g}}$ mode at $T$=5 K and of the E$_{\textrm{g}}$ 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.