Two-dimensional (2D) MT2 (M = Ba, Hf, Si, Sr and T = F, O) monolayers for possible electronic and optoelectronic applications

The present work shed light on the structural, electronic, dielectric, and optical properties of MT2 (M = Ba, Hf, Si, Sr and T = F, O) two-dimensional (2D) monolayers using density functional theory. The investigated electronic properties indicate that these 2D monolayer materials exhibit insulating properties. The complex dielectric function is calculated to investigate the optical functions of these monolayer materials. The dielectric and optical calculations are performed for the electric field vectors' orientation parallel (E||x, i.e., in-plane direction) and perpendicular (E||z, i.e., out-of-plane direction) to the plane of these 2D monolayer materials in the energy range 0-60 eV. It is noticed that the dielectric and optical responses of BaF2, HfO2, and SrF2 are shifted toward the lower energy in the ultraviolet (UV) region compared to SiO2. It may be attributed to their larger ionic radii. Due to a similar chemical environment, the studied properties show similar behavior in BaF2 and SrF2. These 2D materials offer high absorption of incident light in a wide energy range of UV region, hence the higher extinction coefficient. The obtained reflection and transmission coefficients in the vacuum ultraviolet (VUV) wavelength region suggest the potential candidature of these materials for VUV optical coatings, such as reflection, bandpass, absorption edge filters, and avoiding solar heating. BaF2 and SrF2 can combine to make low-high refractive index pair material with high refractive index HfO2. The present results indicate that these 2D monolayer materials may be potential candidates for designing optical, photonic, and optoelectronic devices.