From MAX to MXene: A case study of Sc2TlC MAX phase, Sc2C pristine MXene, and surface-functionalized Sc2CT2 (T=O, F) MXenes

The MXenes-based two-dimensional (2D) materials have become a hotspot of recent research due to their exciting physical behavior. In this first-principles study, we investigate the Sc₂TlC MAX phase and its 2D derivatives, focusing on the transformation of Sc₂TlC into a Sc₂C 2D sheet and the subsequent surface functionalization of Sc₂C with oxygen (O) and fluorine (F). Investigations of the electronic structures reveal that the Sc₂TlC MAX phase is metallic and nonmagnetic, while the conversion to the Sc₂C pristine monolayer and surface functionalized Sc₂CO₂ induces significant changes in its electronic structure but retains its metallic behavior. On the other hand, functionalization of the Sc₂C monolayer with F₂ (such as Sc₂CF₂) evolves semiconductor-like behavior with an energy gap of magnitude 1.325 eV for the up-spin state and 1.227 eV for the down-spin state. The optimal optical absorption of ultraviolet (UV) for Sc₂TlC MAX phase and Sc₂C, Sc₂CO₂, and Sc₂CF₂ MXenes have been found as 13.8 × 10⁵ cm⁻¹, 49.17 × 10⁴ cm⁻¹, 81.39 × 10⁴ cm⁻¹, and 69. ×10⁴ cm⁻¹, respectively. Investigations of the optical properties reveal considerable reflection and absorption capabilities, particularly upon exposure to low-energy light photons, suggesting their potential for optoelectronic and energy harvesting applications.