V₂C and Nb₂C MXenes: An Emerging Tunable Platform for Nanophotonics

MXenes, or transitional metal carbides, carbon nitrides, and nitrides, have recently emerged as a fascinating class of two-dimensional nanomaterials. These materials follow the chemical formula Mn+1XnTx. A prototypical MXene, Ti₃C₂Tx has been studied extensively over the past two decades demonstrating remarkable electrical and optical properties and utilized for linear optical devices such as broadband absorbers, and nonlinear devices like saturable absorbers in lasing cavities. Here, we expand upon our groups’ previous work with Ti₃C₂Tx to new members in the MXene family, specifically V₂C and Nb₂C. By employing ellipsometry, we investigate the optical response of V₂C and Nb₂C. Our findings reveal a metallic transition for V₂C at longer wavelengths, while Nb₂C retains its dielectric nature due to the higher carrier concentration in V₂C. This transition from dielectric to metallic behavior is marked by the permittivity ε crossing zero in a region known as epsilon-near-zero (ENZ), which holds significant implications for optical technology. Furthermore, our research demonstrates that the ENZ point can be manipulated by adjusting the film thickness of V₂C, thereby affecting both its linear and nonlinear properties. These findings lay the foundation for future device development utilizing various members of the MXene family, including the creation of layered metamaterials.