Simultaneous Ultrafast Transmission and Reflection of Nanometer-Thick Ti3C2T x MXene Films in the Visible and Near-Infrared: Implications for Energy Storage, Electromagnetic Shielding, and Laser Systems

Unambiguous determination of the optical dynamics in MXenes is necessary for their reliable development into applications such as EMI shielding, energy storage, and laser systems. Here, simultaneous ultrafast transmission and reflection (SUTR) is used to determine the temporal change in refractory index (n) and extinction coefficient (k) of Ti3C2T x from 450 to 1300 nm which is dominated by intraflake mechanisms. We assign the dynamics for wavelengths below 600 nm with interband transitions, while those at 800 nm are assigned to a plasmon resonance. The response from 1000 to 1300 nm shows changes in index of refraction with no changes in extinction coefficient, consistent with free carriers.