Imaging and simulation of surface plasmon polaritons on layered 2D MXenes

Two-dimensional (2D) transition metal carbides and nitrides, commonly known as MXenes, are a class of 2D materials with high free carrier densities, making them highly attractive candidates for plasmonic 2D materials. In this study, we use multiphoton photoemission electron microscopy (nP-PEEM) to directly image the plasmonic near fields of multilayers of the prototypical MXene, Ti₃C₂T_x, with mixed surface terminations (T_x = F, O, and OH). Photon-energy dependent nP-PEEM reveals a dispersive surface plasmon polariton between 1.4 and 1.9 electron volts on MXene flakes thicker than 30 nanometers and waveguide modes above 1.9 electron volts. Combining experiments with finite-difference time-domain simulations, we reveal the emergence of a visible surface plasmon polariton in MXenes, opening avenues for exploration of polaritonic phenomena in MXenes in the visible portion of the electromagnetic spectrum.