Surface Functionalization of Single-Layered Ti3C2Tx MXene and Its Application in Multilevel Resistive Memory.

MXenes are a new type of two-dimensional material, and they have attracted extensive attention because of their outstanding conductivity and rich surface functional groups that make surface engineering easy and possible for adapting to diverse applications. However, there are scarce studies on surface engineering of MXene. Herein, we demonstrate for the first time that octylphosphonic acid-modified Ti3C2Tx MXene can be used as an active layer for memory devices and exhibits stable ternary memory behavior. Low threshold voltage, steady retention time, clearly distinguishable resistance states, high ON/OFF rate, OFF/ON1/ON2 = 1:102.7:104.1, and considerable ternary yield (58%) were obtained. In the proof of the mechanism, in situ conductive atomic force microscopy was conducted and the electrode-area relationship was analyzed to demonstrate that charge trapping and filament conduction are more suitable in the nonvolatile information memory of Ti3C2Tx-OP MXene devices. In addition, a polyethylene-terephthalate-based flexible Ti3C2Tx-OP memory device can maintain its stable ternary memory performance after being bent 5000 times. This work provides an easy method for surface modification of MXene and broadens the field of MXene.