First-principles calculations to investigate stability, electronic and optical properties of fluorinated MoSi2N4 monolayer

Based on first-principles calculations, variations in the stability as well as the electronic and optical properties of fluorinated MoSi2N4 (MoSi2N4-F-x, x = 0-16) were investigated. Analyses of the adsorption energy and phonon band dispersions proved that the fluorinated MoSi2N4 formed a stable structure. The band gap of MoSi2N4 was 1.92 eV. When the F number increased to x = 16, the band gap of MoSi2N4-F-16 decreased to 0 eV, indicating that the fully fluorinated monolayer showed a metallic nature. At the same time, the work function of MoSi2N4-F-x increased from 4.72 (x = 0) to 6.17 eV (x = 16). Based on dielectric function spectra, MoSi2N4-F-x (x = 0-16) showed significant optical anisotropy. The light absorption range and intensity in the visible-light range were obviously enhanced after the fluorination process. The transmittance of the 10-nm-thick MoSi2N4 film (10 layers of MoSi2N4) was larger than 80%, indicating that this material had a good optical transmission ability. After the fluorination process, the optical transmittance of MoSi2N4 showed a significant decrease. Therefore, the properties of MoSi2N4 could be adjusted through the facile fluorination process, which could largely expand the applications of MoSi2N4 in electronic/optoelectronic devices and photocatalysts.