02275nas a2200289   4500008004100000022001400041245007000055210006900125260000800194490000700202520140500209653001801614653001101632653002301643653001301666653002701679100002301706700002301729700002101752700001701773700001601790700001301806700002001819700002401839700002301863856009901886       2023                        eng d  a0935-964800aUltrafast spectroscopy of plasmons and free carriers in 2D MXenes0 aUltrafast spectroscopy of plasmons and free carriers in 2D MXene  cFEB0 v353 a<p>
	2D MXenes have diverse and chemically tunable optical properties that arise from an interplay between free carriers, interband transitions, and plasmon resonances. The nature of photoexcitations and their dynamics in three different members of the MXene family, Ti3C2, Mo2Ti2C3, and Nb2C, are investigated using two complementary pump-probe techniques, transient optical absorption, and time-resolved terahertz (THz) spectroscopy. Measurements reveal pronounced plasmonic effects in the visible and near-IR in all three. Optical excitation, with either 400 or 800 nm pulses, results in a rapid increase in lattice temperature, evidenced by a pronounced broadening of the plasmon mode that presents as a plasmon bleach in transient absorption measurements. Observed kinetics of plasmon bleach recovery provide a means to monitor lattice cooling. Remarkably slow cooling, proceeding over hundreds of picoseconds to nanoseconds time scales, implies MXenes have low thermal conductivities. The slowest recovery kinetics are observed in the MXene with the highest free carrier density, viz. Ti3C2, that supports phonon scattering by free carriers as a possible mechanism limiting thermal conductivity. These new insights into photoexcitation dynamics can facilitate their applications in photothermal solar energy conversion, plasmonic devices, and even photothermal therapy and drug delivery.</p>
10a2D properties10aMXenes10aOptical properties10aplasmons10aultrafast spectroscopy1 aColin-Ulloa, Erika1 aFitzgerald, Andrew1 aMontazeri, Kiana1 aMann, Javery1 aNatu, Varun1 aNgo, Ken1 aUzarski, Joshua1 aBarsoum, Michel, W.1 aTitova, Lyubov, V.  uhttps://library.ncl.res.in/content/ultrafast-spectroscopy-plasmons-and-free-carriers-2d-mxenes