Raman Spectra and Excitonic Effects of the Novel Ta₂Ni₃Te₅ Monolayer

We have investigated the Raman spectrum and excitonic effects of the novel 2D Ta₂Ni₃Te₅ structure. The monolayer is an indirect band gap semiconductor with an electronic band gap value of 0.09 and 0.38 eV, determined using GGA-PBE and HSE06 exchange-correlation functionals, respectively. Since this structure is energetically, dynamically, and mechanically stable, it could be synthesized as a free-standing material. We identify 10 Raman- and 10 infrared-active modes for various laser energies, including those commonly used in Raman spectroscopy experiments. It was also observed that the contribution of Ni atoms is minimal in most Raman vibrational modes. In contrast, most infrared vibrational modes do not involve the vibration of the Ta atoms. As far as the optical properties are concerned, this monolayer shows a robust linear anisotropy, an exciton binding energy of 287 meV, and a high reflectivity in the ultraviolet region, which is more intense for linear light polarization along the <i>x</i> direction.