Shortwave infrared surface plasmons in multilayered two-dimensional Ti₃C₂T_x MXenes

MXene, an ultra-thin two-dimensional conductive material, has attracted considerable interest in various fields due to its exceptional material properties. In particular, Ti₃C₂T_x MXene exhibits distinct optical properties, enabling it to support surface plasmons in the shortwave infrared (SWIR) region. However, it is challenging to enhance the field confinement of MXene surface plasmons in a single-interface structure due to the substantial intrinsic absorption of Ti₃C₂T_x MXene. Herein, we explore various multilayer structures capable of supporting high field confinement of Ti₃C₂T_x MXene plasmons, including insulator-MXene-insulator (IMI), MXene-insulator-MXene (MIM), and insulator-MXene-insulator-MXene (IMIM) configurations. We observe that the field confinement of MXene plasmons improves as the thickness of either the MXene or insulator layers decreases, which is attributed to the strong coupling between plasmons at the multilayer interfaces. Furthermore, the IMIM structure demonstrates the most substantial enhancement in field confinement. In an IMIM structure with a 1.3 nm-thick MXene monolayer and a 1.0 nm thick SiO₂ layer, the wavelength and effective field size of the plasmon at a frequency of 150 THz (λ ₀ = 2.0 μm) are calculated to be 24.61 nm and 1.50 nm, respectively. These values demonstrate a reduction by factors of 55 and 596, respectively, compared to those obtained in a single SiO₂-MXene interface structure. Multilayer-based MXene plasmons provide a solution for enhancing the field confinement of MXene plasmons in the SWIR region, and we expect them to play a crucial role in a variety of 2D material-based SWIR plasmonic applications.