The structural, mechanical, electronic, and optical properties of Janus Hf2CXY (X, Y = O, S, Se or Te, X ≠ Y) MXenes

Janus functionalized MXenes have attracted growing interest due to their exceptional properties. In this work, the structural, mechanical, electronic, and optical properties of Janus Hf2CXY (X, Y = O, S, Se or Te, X Y) MXenes are investigated using density functional theory. The results of the formation energy, phonon spectrum analysis, and elastic properties validate their structural stability. The Young's modulus (Y), shear modulus (G), and Poisson's ratio (v) of Janus Hf2CXY MXenes can be modulated by the different surface functional groups. It is found that the Janus Hf2COS is a semiconductor with an indirect band gap, while other Hf2CXY MXenes exhibit metallic character. Furthermore, we also explore the effect of strain on the electronic and optical properties of Hf2COS. The results show that the semiconductor to metal transition can occur under compressive strain, and the dielectric spectrum and static dielectric constant can be altered by the tensile strain. These results demonstrate Janus Hf2CXY MXenes' potential applications in electronic and optical nanodevices.