Control of spintronic and electronic properties of bimetallic and vacancy-ordered vanadium carbide MXenes via surface functionalization

Abstract

MXenes are 2D transition metal carbides with high potential for overcoming limitations of conventional two-dimensional electronics. In this context, various MXenes have shown magnetic properties suitable for applications in spintronics, yet the number of MXenes reported so far is far smaller than their parental MAX phases. Therefore, we have studied the structural, electronic and magnetic properties of bimetallic and vacancy-ordered MXenes derived from a new (V_2/3Zr_1/3)₂AlC MAX phase to assess whether MXene exfoliation would return stable magnetic materials. In particular, we have investigated the properties of pristine and surface-functionalized (V_2/3Zr_1/3)₂CX₂ bimetallic and (V_2/3□_1/3)₂CX₂ (where □ denotes the vacancies) vacancy-ordered MXenes (X = O, F and OH). Our density functional theory (DFT) calculations showed that modifying the MXene stoichiometry and/or MXene surface functionalization changes MXene properties. After testing all possible combinations of metallic motifs and functionalization, we identified (V_2/3Zr_1/3)₂CX₂, (V_2/3□_1/3)₂CF₂ and (V_2/3□_1/3)₂C(OH)₂ as stable structures. Among them, (V_2/3Zr_1/3)₂CO₂ MXene is predicted to be an FM intrinsic half-semiconductor with a remarkably high Curie temperature (T_C) of 270 K. The (V_2/3Zr_1/3)₂C(OH)₂ MXene exhibits a rather low work function (WF) (1.37 eV) and is thus a promising candidate for ultra-low work function electron emitters. Conversely, the (V_2/3□_1/3)₂CF₂ MXene has a rather high WF and hence can be used as a hole injector for Schottky-barrier-free contact applications. Overall, our proof-of-concept study shows that theoretical predictions of MXene exfoliation and properties support further experimental research towards developing spintronics devices.