Enhanced and tunable surface plasmons in two-dimensionalTi3C2stacks: Electronic structure versus boundary effects

The dielectric response of two-dimensional (2D) ${\mathrm{Ti}}_{3}{\mathrm{C}}_{2}$ stacked sheets was investigated by high-resolution transmission electron energy-loss spectroscopy and ab initio calculations in the 0.2--30-eV energy range. Intense surface plasmons (SPs), evidenced at the nanometer scale at energies as low as 0.3 eV, are shown to be the dominant screening process up to at least 45-nm-thick stacks. This domination results from a combination of efficient free-electron dynamics, begrenzungs effect, and reduced interband damping. It is shown that, in principle, the SPs energies can be tuned in the mid-infrared, from 0.2 to 0.7 eV, by controlling the sheets' functionalization and/or thickness. This point evidences a new attribute of this new class of 2D materials.