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

Abstract

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.2

Electronic properties and applications of MXenes: a theoretical review

“…It is indeed shown theoretically that the surfaces are fully functionalized at particular chemical potentials in some of the MXene systems [39,105]. Phonon frequency analyses have proved that many of these MXenes with full surface functionalization are locally stable [39,68,72,106,107]. Therefore, various fully functionalized MXenes can be realized experimentally in appropriate conditions although there are still some challenges.…”

“…Second, during the synthesis of MXenes, their surfaces are functionalized naturally, which changes the electrostatic potential near the surfaces and affects the electronic structures, especially, giving rise to the shift of the Fermi level. These two features have significant effects on the work function [72].…”

“…This is in remarkable contrast with the systems functionalizated with F or O, in which the work functions increase or decrease depending on the type of transition metal. Interestingly, M 2 C(OH) 2 , M 10 C 9 (OH) 2 , M ′ 2 N(OH) 2 and M ′ 10 N 9 (OH) 2 all exhibit ultralow work functions, as compared with the corresponding bare and the functionalized ones with F and O [72]. The thickness dependences of the work function for Ti n+1 C n (n=1-9) functionalized with F, OH and O has been systematically studied, and shown that, regardless of the thickness, a family of Ti n+1 C n (OH) 2 exhibits ultralow work function [72].…”

“…From the work function calculations of M 2 C and M 10 C 9 (M= Sc, Ti, Zr, Hf, V, Nb, Ta) as well as M [72]. It is also shown that work functions always decrease by the functionalization with OH.…”

“…Some of MXenes are predicted to be topological insulators with large band gaps involving only d orbitals [67][68][69][70][71]. MXenes are also expected to be used as ultralow work function materials [72] and Schottky barrier junctions [73][74][75][76].…”