Tuning the electronic and optical properties of Ti₂X (X = C, N)-based MXenes through surface termination with oxygen and fluorine functional groups

MXenes, a new class of layered materials with favorable characteristics, have attracted considerable attention owing to their extensive applications. This study reports the effect of surface functionalization on the behavior of Ti₂XT_x(X = C, N; T_x = O₂, F₂)-based MXenes monolayers using the “density functional theory (DFT)-based full-potential linearized augmented-plane-wave (FP-LAPW)” method. Variation in the physical properties of the designed MXene systems is governed and analyzed by the M elements replacement and the surface termination with F and O functional groups. The O-terminated Ti₂CO₂ demonstrated semiconducting behavior with an indirect bandgap of 0.61 eV, while Ti₂CF₂, Ti₂NO₂, and Ti₂NF₂ exhibited metallic behavior with energy bands over the Fermi level. Notably, the highest recorded absorption occurs at different energy levels for each MXene, with Ti₂CO₂ absorbing ultraviolet (UV) light at 5.25 eV, Ti₂CF₂ at 5.48 eV, Ti₂NO₂ at 7.60 eV, and Ti₂NF₂ at 6.87 eV. Furthermore, the highest optical absorption coefficients are measured as 73.61 × 10⁴ cm⁻¹ for Ti₂CO₂, 89.80 × 10⁴ cm⁻¹ for Ti₂CF₂, 78.85 × 10⁴ cm⁻¹ for Ti₂NO₂, and 81.69 × 10⁴ cm⁻¹ for Ti₂NF₂. Our findings offer valuable perspectives into the electronic and optical properties of Ti₂XT_x-based MXenes for potential applications in various optoelectronic devices.