Unveiling the Stable Semiconducting 1T′-HfCl$_2$ Monolayer: A New 2D Material

Designing novel 2D materials is crucial for advancing next-generation optoelectronic technologies. This work introduces and analyzes the 1T′-HfCl$_2$ monolayer, a novel low-symmetry variant within the 2D transition metal dichloride family. Phonon dispersion calculations reveal no imaginary frequencies, suggesting its dynamical stability. 1T′-HfCl$_2$ exhibits semiconducting behavior with a direct band gap of 1.52 eV, promising for optoelectronics. Strong excitonic effects with a binding energy of 525 meV highlight significant electron–hole interactions typical of 2D systems. Furthermore, the monolayer achieves total reflection of linearly polarized light along the ŷ direction at photon energies above 2.5 eV, showcasing its potential as an optical polarizing filter. Raman spectra calculations also reveal distinct peaks between 96.72 and 270.38 cm$^{–1}$. The tunable excitonic and optical properties of 1T′-HfCl$_2$ highlight its potential in future functional devices, paving the way for its integration into semiconducting and optoelectronic applications.