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Page 10 of 15 Shang et al. J. Mater. Inf. 2025, 5, 52 https://dx.doi.org/10.20517/jmi.2025.36

Figure 6. Work function comparison under different surface conditions for various compounds. (A) Hf compounds; (B) Mo compounds;
(C) Nb compounds; (D) Sc compounds; (E) Ta compounds; and (F) W compounds. Each panel shows the work function for bare
surfaces as well as for surfaces terminated by OH, O, and F groups.

N) as shown in Figure 7. In the figure, the yellow-orange and pink bars represent carbides and nitrides,
respectively, with the overlapping orange area indicating their common range. The red lines further
highlight that the absolute differences in work function between the two types are generally small, typically
around 1 eV. As shown in Figure 7, bare MXenes or those with OH as the functional group exhibit
essentially negligible differences in work function between carbide and nitride forms. MXenes with F or O
as the functional group show certain variations in work function between carbide and nitride forms, but
these differences are relatively small, approximately around 1 eV. Based on the above analysis, it can be
concluded that the work function of MXenes is primarily determined by the surface functional groups, with
a relatively minor dependence on whether their chemical compositions are carbides or nitrides. This
research also offers valuable guidance for practical applications, enabling materials to be tailored to specific
requirements. For applications requiring high work functions, such as advanced sensors that rely on stable
surface potential for accurate detection or photodetectors benefiting from efficient charge separation with
minimal recombination, O-terminated MXenes are preferable. Conversely, in scenarios demanding low
work functions, including vacuum ion plating processes that depend on facile electron emission for uniform
coating or field emission displays requiring low-threshold electron sources for high-brightness imaging,
OH-terminated MXenes are preferred.

To further elucidate this rule, we refer to the Langmuir-Gettys theorem, which defines the work function
(Φ) of a material as the energy difference between its vacuum level (E ) and Fermi level (E ). In the context
Vac
F
of 2D materials such as MXenes, the work function is determined not only by the material’s Fermi level but
also by surface effects, predominantly variations in the vacuum level (E ) induced by surface dipole
Vac
moments (representative stable configurations shown in Supplementary Figure 6). As given in
Supplementary Equation (3), when MXene surfaces undergo functionalization, the charge density
distribution ρ(z) is altered, resulting in a shift in the E , which directly impacts the Φ.
Vac