Environmental Stability and Electronic Properties of Individual Flakes of Ti2CTx MXene

ABSTRACT We present a synthetic procedure for large Ti2CTx MXene monolayers with the majority of flakes having sizes of 10–15 µm and the largest ones reaching 40 µm, which are used for device fabrication and electrical measurements on a single‐flake level. We demonstrate that if exposed to ambient conditions, Ti2CTx monolayers oxidize in an aqueous solution or on a substrate on a time scale of hours, but multilayer flakes are more resistant to environmental degradation. The partially oxidized monolayer Ti2CTx flakes exhibit low electrical conductivity and electron mobility, as well as the semiconducting‐like temperature dependence of resistance with dR/dT < 0. However, the more degradation‐resistant multilayer flakes show electrical conductivity of about 3700 S cm−1 and electron mobility of about 1.6 cm2 V−1 s−1, which are among the highest values reported for MXene materials, as well as the metallic temperature dependence of resistance with dR/dT > 0, which is expected for Ti2CTx with mixed surface terminations (Tx = ─F, ─OH, = O) based on prior theoretical calculations. These results correlate with the electrical measurements of Ti2CTx films, which showed that the thicker films exhibit better environmental stability. The characteristics of multilayer flakes suggest high intrinsic electrical conductivity of Ti2CTx and justify its potential for electronic applications.