Ultrafast Photoexcitations in 2D MXenes

MXenes are 2D transition metal carbides and nitrides with electronic properties that can be tuned by their chemistry and structure. Metallic-like conductivity, flexibility, high optical damage threshold and ease of processing owing to their hydrophilicity, make MXenes candidates for a host of electronic and optical applications. We use ultrafast optical and THz spectroscopic techniques to investigate the nature and behavior of photoexcitations in MXenes of different chemistries. We show that electronic and optical properties of MXenes can be engineered by choices of the transition metals and their order as well as by controlling the intercalants in the interlayer gaps [1,2]. Furthermore, we demonstrate that MXenes with high free carrier density show promise as polarizers and tunable electromagnetic interference shields in the THz range [3,4].<br/>[1] G. Li, V. Natu, T. Shi, M.W. Barsoum, L.V. Titova, “Two-Dimensional Mxenes Mo₂Ti₂C₃T_z and Mo₂TiC₂T_z: Microscopic Conductivity and Dynamics of Photoexcited Carriers,” <i>ACS Applied Energy Materials </i>3, 1530-1539 (2020).<br/>[2] E. Colin Ulloa, A. Fitzgerald, K. Montazeri, J. Mann, V. Natu, K. Ngo, J. Uzarski, M.W. Barsoum, L.V. Titova, “Ultrafast Spectroscopy of Plasmons and Free Carriers in 2D MXenes,” <i>Adv. Materials</i> 35, 2208659 (2023).<br/>[3] G. Li, N. Amer, H.A. Hafez, S. Huang, D. Turchinovich, V.N. Mochalin, F.A. Hegmann, L.V. Titova, “Dynamical Control over Terahertz Electromagnetic Interference Shielding with 2D Ti₃C₂T_y MXene by Ultrafast Optical Pulses,” <i>Nano Lett</i>. 20, 636-643 (2020).<br/>[4] G. Li, K. Montazeri, M.K. Ismail, M.W. Barsoum, B. Nabet, L.V. Titova, "Terahertz Polarizers Based on 2D Ti3C2Tz MXene: Spin Cast from Aqueous Suspensions," <i>Adv. Photonics Research</i>, 2000084 (2020).