A theoretical investigation of structural, electronic, and optical properties of Pentagonal PtX\(_2\) (X=S, Se, Te) monolayers under applied electric field and biaxial strain

Pentagonal two-dimensional (2D) materials, distinguished by their unique pentagonal atomic configurations, have emerged as a new class of materials with remarkable physical and chemical properties. In this work, we investigate the effect of an external electric field and biaxial strain on the electronic and optical properties of two-dimensional Pentagonal PtX \(_2\) ${}_2$ (X= S, Se, Te) monolayers denoted by Penta-PtX \(_2\) ${}_2$ using the first-principles calculations. We found that Penta-PtX \(_2\) ${}_2$ monolayers are semiconductors with an indirect band gap of 1.92 eV, 1.51 eV, and 1.4 eV for Penta-PtS \(_2\) ${}_2$ , Penta-PtSe \(_2\) ${}_2$ , and Penta-PtTe \(_2\) ${}_2$ , respectively, that is larger than the 1T phase. External electric fields cause a slight decrease in the band gap of Penta-PtX \(_2\) ${}_2$ monolayers without changing the main feature of the electronic band structures. Tensile biaxial strain causes a continuous decrease in the band gap up to 12 \(\%\) $\%$ while compressive biaxial strain increases the band gap at first then it starts to decrease. However, phonon dispersion calculations showed that Penta-Ptx \(_2\) ${}_2$ are stable under tensile strain up to 12 \(\%\) $\%$ while they are unstable under compressive strain. The investigation of the optical properties revealed that monolayers Penta-PtX \(_2\) ${}_2$ have in-plane anisotropic optical properties with higher absorption spectra occurring along the y-direction for strained and unstrained structures. The maximum absorption occurs in the Ultraviolet (UV) region, therefore, they can harvest UV and visible photons more effectively. In contrast, the reflectivity is higher along the x-direction for both strained and unstrained monolayers where the maximum reflectivity occurs in the Infrared (IR) region. The combination of anisotropic properties and the unique characteristics of Pentagonal symmetry make Penta-PtX \(_2\) ${}_2$ monolayers attractive for fundamental scientific studies to better understand their behavior. They hold great promise for developing new technologies in the fields of optoelectronics and nanotechnology, potentially leading to innovative devices and applications.