Theoretical investigations of O- and F- surface functionalization of MXenes based on Cr₂M(M=C, N)

This study reports the effect of O- and F- based functional groups on the properties of Cr₂M(M = C, N) based MXenes that have emerged as promising two-dimensional (2D) materials in recent years. The physical properties of Cr₂MX₂ (X = O, F) are determined using the “Density Functional Theory (DFT)” based first-principles approach. The electronic structure calculations showed dramatic effects of surface functionalization on their electronic properties. The electronic structures of Cr₂CO₂, Cr₂NO₂, and Cr₂NF₂ showed half-metallic behavior, whereas Cr₂CF₂ exhibited metallic nature with energy states of Cr-d character observed above the Fermi level for both spin channels. Similarly, the surface functionalization has affected the magnetic behavior of Cr₂MX₂ that demonstrated magnetic moments of 3.409 μ_B, 4.623 μ_B, 5.004 μ_B, and 6.708 μ_B for Cr₂CO₂, Cr₂CF₂, Cr₂NO₂, and Cr₂NF₂, respectively. Investigations of their optical properties showed variations in optical performance across different energy ranges. In the ultraviolet (UV) range, Cr₂NO₂ exhibited the highest optical absorption at 52.45 × 10⁴ cm⁻¹, followed by Cr₂CO₂ at 48.80 × 10⁴ cm⁻¹, Cr₂CF₂ at 47.75 × 10⁴ cm⁻¹, and Cr₂NF₂ at 34.89 × 10⁴ cm⁻¹ below 6 eV. The optical refraction and reflection are recorded highest for infrared (IR light), which diminish significantly as the energy of the incident light increases. The interesting physical behavior of Cr₂MX₂ MXenes witnessed in the present study suggests them as potential 2D materials for next-generation technological applications.