| 摘要: | 二維材料（Two-dimensional, 2D materials）因其獨特的電子與結構特性，在電子、能源與感測等領域具有廣泛應用潛力，並因此受到廣泛關注。二維過渡金屬碳化物與氮化物 (MXenes) 是一類由過渡金屬與碳或氮元素組成的層狀材料家族，具備優異的機械強度與超導行為，因而在眾多2D材料中脫穎而出。先前研究指出，提升未成對電子數可增強材料的磁性，例如在 Cr2C MXene 中，透過不對稱官能基修飾即可使其從金屬態轉變為半金屬態。另一方面，Co2C MXene 本身具有本徵鐵磁性，且獨特地穩定於1H型結構，相較之下多數MXene傾向於穩定於1T型態。基於上述特性，本研究藉由密度泛函理論（Density Functional Theory, DFT）探討不同官能基（A/B = F、OH、Cl、Br、S）修飾下的 Janus 型 Co2CAB MXene，評估其作為自旋電子元件材料的應用潛力。
本研究系統性地探討了表面非對稱修飾下 Co_2CAB Janus MXene 的電子與磁性質。計算結果顯示，雖然未修飾的1T與1H相皆呈現金屬性，在引入F、OH或Cl官能基後，這些結構轉變為半導體，顯示出透過不對稱修飾可實現能隙的有效調控。在所有探討的系統中，Co_2CFOH 於自旋向上通道表現出最大的能隙（1.65 eV），顯示其具備優異的自旋過濾應用潛力。此外，應變分析顯示，1H-Co_2CClS 與 1H-Co_2CBrS 在特定壓縮應變條件下會出現磁矩的劇烈變化。上述結果不僅揭示了表面官能基修飾與機械調控對 MXene 自旋電子特性的影響，亦為未來非對稱修飾的二維鈷基碳化物材料的進一步研究奠定了重要基礎。;Two-dimensional (2D) materials have attracted widespread interest for their applications in electronics, energy, and sensing, owing to their distinctive electronic and structural properties. MXenes, a family of layered transition metal carbides and nitrides, are particularly notable for their mechanical robustness and superconducting behavior. Prior studies have shown that increasing the number of unpaired electrons can enhance magnetic properties. For instance, asymmetric functionalization of Cr2C MXenes can induce a transition from metallic to half-metallic states. In parallel, Co2C MXene is intrinsically ferromagnetic and uniquely stabilizes in a 1H-type configuration, unlike most MXenes that favor the 1T phase. Building on these findings, this study investigates Janus Co2CAB MXenes with various functional groups (A/B = F, OH, Cl, Br, S) using density functional theory (DFT), aiming to evaluate their potential for spintronic applications.
In this study, the electronic and magnetic properties of Co2CAB Janus MXenes with asymmetrically functionalized surfaces have been explored. The results show that while both 1T and 1H phases are metallic in their pristine state, they become semiconducting upon functionalization with F, OH, or Cl groups. The band gap is sensitive to the choice of surface terminations, demonstrating the tunability enabled by asymmetric modifications. Among the examined systems, Co2CFOH displays the widest band gap of 1.65 eV in the spin-up channel, indicating strong potential for spin-filtering applications. Furthermore, strain analysis reveals that 1H-Co2CClS and 1H-Co2CBrS exhibit abrupt magnetic moment transitions under specific compressive strain levels. This work offers valuable insights into how surface functionalization and mechanical tuning impact the spintronic potential of MXene materials and lays a solid foundation for further studies of related systems. |
