TiO2@Ti3C2Tx heterostructure as an environmentally stable saturable absorber for ultrafast photonics

MXenes, one of the largest families of two-dimensional (2D) materials, provide great potential in photonics, electronics and energy. Especially, MXenes are recently discovered as alternatives to conventional saturable absorbers (SAs). However, the inevitable exposure of metal atoms on surface is likely to react with oxygen or oxygen-containing groups, leading to the severe problem of environmental instability. Here, we developed a partially-controlled oxidation strategy to prepare TiO2@Ti3C2Tx heterostructures. The dense nanosized TiO2 on the surface of heterostructures prevent the further oxidation of the Ti3C2Tx inside, enabling a stable performance in ultrafast photonics. The saturable absorption property of TiO2@Ti3C2Tx heterostructures is verified using the balanced twin-detector measurement system. The modulation depth and saturation intensity were determined to be 14.4% and 2.929 GW/cm2 at 1550 nm, respectively. The Erbium-doped fiber laser (EDFL) with the use of TiO2@Ti3C2Tx SAs exhibits pulse width of 552 fs. More importantly, there is no obvious degradation in saturable absorption property of the TiO2@Ti3C2Tx based EDFL after an exposure in air for more than thirteen months, indicating the excellent environmental stability of the TiO2@Ti3C2Tx heterostructures. This work provides an alternative approach to enhance the long-term performance of Ti3C2Tx optoelectronic devices, which may shed light on the material synthesis and device design of MXenes.