Effect of Hydrogen concentration on the structural, electronic and optical properties of 2D monolayer MXenes: DFT study

Abstract

After the discovery of graphene and its unique optical properties, the investigation and discovery of 2D materials expanded. Electrons and phonons of 2D materials react differently to light compared to their bulk state, which will cause unique optical properties. Compared to graphene, 2D monolayer MXenes have non-zero gap energy, which increases their application in optical industries. In this article the density-functional-theory (DFT) approach is employed to investigate the electronic, structural and optical properties of (M2CO2, M = Zr, Sc, Mo and Hf) 2D monolayer MXenes. On the other hand, with the addition of Hydrogen to MXenes (M2C(OH)2), their structural and optical properties change significantly. The electronic band structure results showed that Zr2CO2, Sc2CO2 and Hf2CO2 monolayers are semiconductors with indirect band gaps and Mo2CO2 is a conductor. By adding hydrogen to the layers, Sc2CO2 monolayers changed from an indirect band gap semiconductor to a direct band gap semiconductor. The optical results showed that the highest static refractive index belongs to Zr2CO2 monolayers and the lowest to Sc2CO2. By adding hydrogen to the system, the refractive index of Sc2C(OH)2 increases. According to the imaginary part of the dielectric function, the optical gap of Sc2CO2 has the highest value. Also, Mo2CO2 monolayers does not have an optical gap. These results are in agreement with the electronic band structure results.