OH terminated two-dimensional transition metal carbides and nitrides (MXenes) as ultralow work function materials

TL;DR

This study uses first-principles calculations to show that OH-terminated MXenes have ultralow work functions, influenced by surface dipoles and intrinsic dipole moments, which is promising for electronic applications.

Contribution

It reveals the role of OH groups in achieving ultralow work functions in MXenes, expanding understanding of surface chemistry effects on electronic properties.

Findings

OH terminated MXenes have work functions between 1.6 and 2.8 eV.

Functionalization with F or O modulates work functions via surface dipole changes.

Intrinsic dipole moments of OH groups significantly influence work functions.

Abstract

MXenes are a set of two-dimensional transition metal carbides and nitrides that offer many potential applications in energy storage and electronic devices. As an important parameter to design new electronic devices, we investigate the work functions of bare MXenes and their functionalized ones with F, OH, and O chemical groups using first-principles calculations. From our calculations, it turns out that the OH terminated MXenes attain ultralow work functions between 1.6 and 2.8 eV. Moreover, depending on the type of the transition metal, the F or O functionalization affects increasing or decreasing the work functions. We show that the changes in the work functions upon functionalizations are linearly correlated with the changes in the surface dipole moments. It is shown that the work functions of the F or O terminated MXenes are controlled by two factors: the induced dipole moments by the charge transfers between F/O and the substrate, and the changes in the total surface dipole moments caused by surface relaxation upon the functionalization. However, in the cases of the OH terminated MXenes, in addition to these two factors, the intrinsic dipole moments of the OH groups play an important role in determining the total dipole moments and consequently justify their ultralow work functions.