Two-dimensional materials draw further attention because of their superior properties applicable in novel technologies. We have calculated the optical properties of α and β allotropes of antimonene monolayers. The dielectric matrix has been calculated within the random phase approximation (RPA) using density functional theory. We have calculated dielectric function, absorption coefficient, refractive index, electronic energy loss spectroscopy and optical reflectivity in the energy range between 0 and 21 eV. Our simulations predict that absorption process starts in the infrared, but peaks in the ultraviolet. Refractive indices are 2.3 (α-Sb) and 1.5 (β-Sb) at the zero energy limit and scale up to 3.6 in the ultraviolet. Reflection rises up to 86% at the UV energies, where antimonene behaves like a metal regarding the incident electromagnetic radiation. Our calculations show that antimonene is appropriate as a material for the microelectronic and optoelectronics nanodevices and solar cell applications, as well as new optical applications using various light emission, detection, modulation and manipulation functions.

In the present work, Janus monolayers WSSe and WSTe are investigated by combining first-principles calculations and semiclassical Boltzmann transport theory. Janus WSSe and WSTe monolayers show a direct band gap of 1.72 and 1.84 eV at K-points, respectively. These layered materials have an extraordinary Seebeck coefficient and electrical conductivity. This combination of high Seebeck coefficient and high electrical conductivity leads to a significantly large power factor. In addition, the lattice thermal conductivity in the Janus monolayer is found to be relatively very low as compared to the WS 2 monolayer. This leads to a high figure of merit (ZT) value of 2.56 at higher temperatures for the Janus WSTe monolayer. We propose that the Janus WSTe monolayer could be used as a potential thermoelectric material due to its high thermoelectric performance. The result suggests that the Janus monolayer is a better candidate for excellent thermoelectric conversion.

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Two dimensional monolayer nanostructures for water splitting solar photocatalyst are drawing more attention due to their extraordinary properties. Using the first principles calculations we have systematically investigate the structural, electronic and vibrational properties of the corresponding HfS 2 monolayer in both phases of hexagonal (1H) and trigonal (1T). The most stable adsorption configurations and adsorption energies are calculated. The adsorption energy of H 2 O on the substrate is 646.53 kJ/mol for 1H-phase and 621.65 kJ/mol for 1T-phase of HfS 2 . It shows that H 2 O molecule has higher interaction with the HfS 2 substrate. The calculated redox potentials of H 2 O splitting are properly astride by the valence and conduction bands suggesting monolayer of 1H and 1T-HfS 2 shows same characteristic as a photocatalyst for water splitting.Further we have also calculated obtained optical band gap for 1H and 1T phases of HfS 2 is 2.60 eV and 3.10 eV, respectively. We have also calculated Raman spectrum signatures of the monolayer 1H and 1T-phase of in -plane vibrational mode of the Hf and S atoms (E 1g ) and the out-of-plane vibrational mode of S atoms (A 1g and A 2u ). Our works suggest a lot more research and attention in this field needed for their practical application as a visible light active photocatalysts.

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