Nanometer-Thin Stacks of MXenes (Ti₃C₂T_x and Ta₄C₃T_x) for Applications as Nonlinear Photonic Devices

Two-dimensional (2D) carbides of transition metals, so called “MXenes”, maintain excellent optical properties and unique layer stacking form via hydrogen bonds in contrast to other low-dimensional materials. These promising features have attracted increasingly research interest in the field of ultrafast photonics. In this work, titanium carbide (Ti₃C₂T_x) and tantalum carbide (Ta₄C₃T_x), as two promising MXene materials for photonic applications, are experimentally synthesized by the ultrasound-assisted liquid phase exfoliation technique. The morphology of prepared few-layer Ti₃C₂T_x and Ta₄C₃T_x has been systematically characterized by transmission electron microscopy and X-ray diffraction analysis. Density functional theory is performed to obtain their electronic band structures, demonstrating metallic properties and verifying their optical absorption at 1 μm. Their tempting optical modulation properties for multi-gigahertz pulsed laser emission are demonstrated by using them as saturable absorbers in a waveguide laser cavity. Particularly, high-performance Q-switched mode-locked lasers with/without laser mirrors are realized based on the hybrid waveguide laser configuration, delivering 1 μm laser pulses with durations as short as 30 ps. The results presented in this work show the great potential of metallic MXenes and waveguide structures for applications in functional photonic devices.