Nano and composite structure control of two-dimensional MXene material and its high performance gas sensor applications

Abstract

Two-dimensional (2D) materials are widely used in gas sensing application due to their special intrinsic property, which are high surface to volume ratio, easy chip fabrication, room temperature operation, and adjustable band gap to more sensitive from bulk to atomic thin layer. In addition, they have special active sites such as vacancy, defect and edges structure and their functional groups can be changed to show different sensing behavior. Especially, MXene, emerging new 2d material shows outstanding gas sensing performance with high signal to noise ratio than other 2d materials. We controlled the interface of Ti$_3$C$_2$ MXene and semiconductor TiO$_2$ inducing the inter-flake Schottky barrier which affects sensitivity to toxic oxidizing gas. We achieved 13.7 times enhanced gas sensing performance for Ti$_3$C$_2$/TiO$_2$ composite gas sensor than pristine Ti$_3$C$_2$ MXene. And also, the fabrication of ultrathin film is important to increase gas sensing performance, however, it is not easy to make sub 10 nm film with simple steps. The spin coating method is suitable for ultrathin film fabrication, but high concentration solution is needed. MXene unlike other 2d materials, as following by synthetic protocol, we can obtain high concentration over 2 mg/mL which utilize sensor chip fabrication by spin coating method. We managed the thickness of Mo$_2$C MXene from 5 nm to 700 nm and organic intercalant molecule existence demonstrating the variety of gas sensing performance form n-type, p-type, and conductor in a single channel. Our results provide new approaches for enhancing gas sensing performance in sensitivity and selectivity dramatically