Electron energy-loss spectra of functionalized titanium and zirconium MXene monolayers, including excitonic effects

Using the full-potential linearized augmented plane wave (FP-LAPW)-based energy-loss near-edge structure (ELNES), the present study deals with the electronic properties of titanium and zirconium MXene monolayers. Specifically, the carbon and nitrogen K-edges of M2CT2 and M2NT2 (M = Ti, Zr; T = F, O, OH) MXene monolayers have been calculated and compared with those of the existing experimental spectra. On going from the bulk systems to MXene monolayers, the main spectral features occur at higher energies as a result of the shorter M-X bond lengths in the monolayers. As fingerprints of the terminal groups, in the C K- and N K-edges of Ti- and Zrbased terminated MXenes, the oscillator strengths and overall spectral shapes are changed, and in comparison to bare MXenes, the main spectral features are red-shifted. Moreover, on going from O termination to OH and then to F, one can observe a slight red-shift in the K-edge spectra of Ti2C(N) and Zr2C(N). While the peaks originating from the px + py states are modified through the appending of terminal elements, showing an obvious red-shift, the terminal substituent has no significant effect on features engendered by pz character. In addition, including excitonic effects on the K-edge absorption spectra considerably changes the response of MXene semiconductors, resulting in red-shifts of the ELNES spectral features.

Automated summary

In this study, the electronic properties of titanium and zirconium MXene monolayers were investigated using the FP-LAPW and ELNES methods. The results show that the main spectral features occur at higher energies in the monolayers due to the shorter M-X bond lengths. The terminal groups affect the oscillator strengths and overall spectral shapes, as well as causing a red-shift in the main spectral features. The terminal substituents have a significant effect on the px + py states but do not affect the features caused by the pz character.