Environmental Stability and Electronic Properties of Individual Flakes of Ti ₂ CT <i> _x </i> MXene

ABSTRACT We present a synthetic procedure for large Ti 2 CT x 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, Ti 2 CT x 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 Ti 2 CT x flakes exhibit low electrical conductivity and electron mobility, as well as the semiconducting‐like temperature dependence of resistance with d R /d T &lt; 0. However, the more degradation‐resistant multilayer flakes show electrical conductivity of about 3700 S cm −1 and electron mobility of about 1.6 cm 2 V −1 s −1 , which are among the highest values reported for MXene materials, as well as the metallic temperature dependence of resistance with d R /d T &gt; 0, which is expected for Ti 2 CT x with mixed surface terminations (T x = ─F, ─OH, = O) based on prior theoretical calculations. These results correlate with the electrical measurements of Ti 2 CT x films, which showed that the thicker films exhibit better environmental stability. The characteristics of multilayer flakes suggest high intrinsic electrical conductivity of Ti 2 CT x and justify its potential for electronic applications.