Surface modification of titanium carbide MXene monolayers (Ti₂C and Ti₃C₂)viachalcogenide and halogenide atoms

Inspired by the recent successful growth of Ti₂C and Ti₃C₂monolayers, here, we investigate the structural, electronic, and mechanical properties of functionalized Ti₂C and Ti₃C₂monolayers by means of density functional theory calculations. The results reveal that monolayers of Ti₂C and Ti₃C₂are dynamically stable metals. Phonon band dispersion calculations demonstrate that two-surface functionalization of Ti₂C and Ti₃C₂viachalcogenides (S, Se, and Te), halides (F, Cl, Br, and I), and oxygen atoms results in dynamically stable novel functionalized monolayer materials. Electronic band dispersions and density of states calculations reveal that all functionalized monolayer structures preserve the metallic nature of both Ti₂C and Ti₃C₂except Ti₂C-O₂, which possesses the behavior of an indirect semiconductorviafull-surface oxygen passivation. In addition, it is shown that although halide passivated Ti₃C₂structures are still metallic, there exist multiple Dirac-like cones around the Fermi energy level, which indicates that semi-metallic behavior can be obtained upon external effects by tuning the energy of the Dirac cones. In addition, the computed linear-elastic parameters prove that functionalization is a powerful tool in tuning the mechanical properties of stiff monolayers of bare Ti₂C and Ti₃C₂. Our study discloses that the electronic and structural properties of Ti₂C and Ti₃C₂MXene monolayers are suitable for surface modification, which is highly desirable for material property engineering and device integration.