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

TL;DR

This study uses density functional theory to explore how surface functionalization and stoichiometry modifications of bimetallic and vacancy-ordered MXenes derived from a new MAX phase influence their electronic and magnetic properties, identifying stable structures with potential spintronics applications.

Contribution

The paper provides the first theoretical analysis of bimetallic and vacancy-ordered MXenes from a novel MAX phase, predicting stable structures and their magnetic and electronic properties relevant for spintronics.

Findings

V2/3Zr1/3)2CO2 MXene is an intrinsic half-semiconductor with a high Curie temperature of 270 K.

(V2/3Zr1/3)2C(OH)2 MXene has a low work function of 1.37 eV, suitable for electron emission.

(V2/3)2C(F)2 MXene has a high work function, suitable as a hole injector.

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_{2/3}Zr_{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 $(V_{2/3}Zr_{1/3})_2CX_2$ bimetallic and $(V_{2/3} \square_{1/3})_2CX2$ vacancy-ordered MXenes with 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 $V_{2/3}Zr_{1/3})_2CX_2$, $(V_{2/3}\square_{1/3})_2CF_2$ and $(V_{2/3}\square_{1/3})_2C(OH)_2$ as stable structures. Among them, $(V_{2/3}Zr_{1/3})_2CO_2$ MXene is predicted to be an FM intrinsic half-semiconductor with a remarkably high Curie temperature ($T_C$)) of 270 K. The $(V_{2/3}Zr_{1/3})_2C(OH)_2$ 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 $(V_{2/3}\square_{1/3})_2CF_2$ 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.