Functionalized Ti₃C₂T_x MXene with layer-dependent band gap for flexible NIR photodetectors

Ti3C2Tx MXene as a representative material in the emerging two-dimensional (2D) MXene family with high conductivity, abundant functional surface terminals, and large layer spacing is supposed to show specific semiconducting properties like other 2D graphene or transition metal dichalcogenides, thus extending Moore's law beyond silicon. However, despite extensive efforts, the design of Ti3C2Tx MXene based semiconductor materials often depends on the availability of traditional semiconductors to form heterojunctions, where Ti3C2Tx MXene is still in metallic characters and is not in dominant status in the heterojunctions. Here, we demonstrate semiconducting Ti3C2Tx MXene modified with dodecyl (-C12H26) groups, as functionalized Ti3C2Tx MXene possesses opened and typical layer-dependent bandgap. The new arising characteristics, red-shift of characteristic peaks, and intensity ratio of the A1g(C)/A1g(Ti, C, Tx) in Raman spectroscopy suggested the successful grafting of the -C12H26 groups on the Ti3C2Tx MXenes. In addition, the theoretical calculations by density functional theory, photoluminescence spectrum, together with photoelectric measurements of Ti3C2Tx-C12H26 MXene on different layers, show a tunable bandgap of 0.49-2.15 eV and superior photoresponse properties in fabricating near infrared photodetectors.