MXenes comprise a new class of 2D transition metal carbides, nitrides, and carbonitrides that exhibit unique light–matter interactions. Recently, 2D Ti₃CNT_x (T_x represents functional groups such as OH and F) was found to exhibit nonlinear saturable absorption (SA) or increased transmittance at higher light fluences, which is useful for mode locking in fiber‐based femtosecond lasers. However, the fundamental origin and thickness dependence of SA behavior in MXenes remain to be understood. 2D Ti₃C₂T_x thin films of different thicknesses are fabricated using an interfacial film formation technique to systematically study their nonlinear optical properties. Using the open aperture Z‐scan method, it is found that the SA behavior in Ti₃C₂T_x MXene arises from plasmon‐induced increase in the ground state absorption at photon energies above the threshold for free carrier oscillations. The saturation fluence and modulation depth of Ti₃C₂T_x MXene is observed to be dependent on the film thickness. Unlike other 2D materials, Ti₃C₂T_x is found to show higher threshold for light‐induced damage with up to 50% increase in nonlinear transmittance. Lastly, building on the SA behavior of Ti₃C₂T_x MXenes, a Ti₃C₂T_x MXene‐based photonic diode that breaks time‐reversal symmetry to achieve nonreciprocal transmission of nanosecond laser pulses is demonstrated.

中文翻译：

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二维Ti3C2 MXene薄膜中用于无源光子二极管的饱和吸收

MXene包括一类新型的2D过渡金属碳化物，氮化物和碳氮化物，它们表现出独特的光-物质相互作用。最近，2D的Ti ₃ CNT _X（T _X表示的官能团如 OH和 F）被发现表现出非线性饱和吸收（SA）或在较高的光能量密度增大的透射率，其是用于在基于光纤的飞秒锁模有用激光。然而，MXenes中SA行为的基本起源和厚度依赖性尚待了解。2D钛₃ C ₂ T _x使用界面成膜技术制造了不同厚度的薄膜，以系统地研究它们的非线性光学特性。使用开孔Z扫描方法，发现Ti ₃ C ₂ T _x MXene中的SA行为是由等离子激元引起的，在光子能量高于自由载流子振荡阈值时，基态吸收的基态吸收增加。观察到Ti ₃ C ₂ T _x MXene的饱和通量和调制深度取决于薄膜厚度。与其他2D材料不同，Ti ₃ C ₂ T _x被发现对光致损伤具有更高的阈值，非线性透射率最多可增加50％。最后，以Ti ₃ C ₂ T _x MXenes的SA行为为基础，展示了一种基于Ti ₃ C ₂ T _x MXene的光子二极管，该二极管打破了时间反转对称性，实现了纳秒级激光脉冲的不可逆传输。