• MXene exhibits significant electric conductive variation relying on surface states. • Complete elimination of surface termination boosts up MXene’s electric conductance. • Surface termination coverage predictably determines MXene’s conductive degree. • The largest electric resistance is obtained at ∼ 50 % of surface termination coverage. Two-dimensional (2D) transition metal carbides (MXenes) are promising electron conducting materials. Noticeably, they intrinsically have surface functionality and the control of surface termination has proven robust and efficient for modulating MXenes’ mechanical and optical properties. However, its effects to MXenes’ electronic conduction have rarely been studied. Using nonequilibrium quantum mechanical simulations, here we showed that surface termination engineering can be powerful means of regulating the electric conductance of Ti 3 C 2 T x MXenes. Two extreme fully oxygen-terminated (Ti 3 C 2 O 2 ) and bare (Ti 3 C 2 ) surfaces were considered since oxygen is one of dominant surface terminations of MXenes. We revealed that Ti 3 C 2 are superior electric conductors compared to Ti 3 C 2 O 2 , showing five-times high performance in our system. We further explored this issue by gradually increasing the surface oxygen-terminated degree of the scattering region of Ti 3 C 2 . The conductance underwent an S-like variation, representing significant 7.5-times tunability showing minimum at the oxygen-termination portion of 50%. Ti 3 C 2 O 2 with various surface bareness also exhibited significant and dynamic conduction variation with minimum around 40%, but in a quantitatively different manner due to the use of oxygen-terminated electrodes.

Abstract Large optical nonlinearity at short‐wavelength‐infrared (SWIR) has enabled 2D MXene to be used explosively in ultrafast nonlinear photonics and optoelectronics. Despite the high technological interest in V 4 C 3 MXene in electrochemistry, investigations from a nonlinear photonics perspective have yet to be conducted. Here, the nonlinear optical characteristics of V 4 C 3 MXene at SWIR wavelengths are systemically investigated. First, Z‐scan measurements are performed and the saturated absorption and self‐defocusing properties of V 4 C 3 MXene at both wavelengths of 1560 and 1910 nm are observed. Density functional theory calculation shows metallic characteristics of V 4 C 3 MXene. Based on the saturable absorption properties of V 4 C 3 MXene, a single saturable absorber (SA) operating at both wavelengths of 1560 and 1910 nm is experimentally implemented. Stable mode‐locked pulses of 638 fs pulse duration at 1559.9 nm are produced instantaneously from an erbium‐doped fiber ring cavity using SA. The same SA generates 1.08 ps mode‐locked pulses at 1911.9 nm from the thulium holmium co‐doped fiber ring cavity. This indicates that the operating bandwidth of this realized V 4 C 3 MXene‐based SA could be at least 350 nm. This work strongly suggests that V 4 C 3 MXene can serve as an ultra‐broadband and high‐performance nonlinear optical material platform in the SWIR regions.