From MAX to MXene: A Case Study of Sc₂TlC MAX Phase, Sc₂C Pristine MXene, and Surface-Functionalized Sc₂CT₂ (T=O, F) MXenes

Recent research has shown a growing interest in the exciting physical properties exhibited by MXenes-based two-dimensional (2D) materials. In this study, which utilizes first-principles approaches, we explore the Sc₂TlC MAX phase and its 2D derivatives named MXene. The primary focus is transforming Sc₂TlC into a 2D Sc₂C sheet and the subsequent surface functionalization with oxygen (O) and fluorine (F). The investigation of the electronic structures of these materials, both in their original states and following surface modifications, reveals unique and distinctive characteristics. The Sc₂TlC MAX phase has been confirmed to be metallic and nonmagnetic. However, when it transforms into the Sc₂C monolayer, it undergoes significant changes in its electronic structure while still maintaining its metallic properties. We also discuss the influence of surface functionalization on electronic properties, observing that Sc₂CT_x (T_x=O₂, F₂) MXenes exhibit distinct electronic states based on their surface terminations. Specifically, Sc₂CO₂ remains metallic, whereas Sc₂CF₂ displays semiconductor-like behavior, with energy gaps of approximately 1.325 eV for the up-spin state and 1.227 eV for the down-spin state. The maximum optical absorption of ultraviolet (UV) light has been determined for various materials, including Sc₂TlC MAX phase, Sc₂C, Sc₂CO₂, and Sc₂CF₂ MXenes, with values of 13.8×10⁵ cm^-1, 49.17 ×10⁴ cm^-1, 81.39 ×10⁴ cm^-1, and 69.0 ×10⁴ cm^-1, respectively. Examination of their optical characteristics shows that these materials exhibit substantial reflectance and absorption capabilities, especially when exposed to low-energy photons of light. This suggests their potential suitability for applications in optoelectronics and energy harvesting devices.