Effect of Synthesis on Quality, Electronic Properties and Environmental Stability of Individual Monolayer Ti₃C₂ MXene Flakes

2D transition metal carbide Ti₃C₂T_x (T stands for surface termination), the most widely studied MXene, has shown outstanding electrochemical properties and promise for a number of bulk applications. However, electronic properties of individual MXene flakes, which are important for understanding the potential of these materials, remain largely unexplored. Herein, a modified synthetic method is reported for producing high-quality monolayer Ti₃C₂T_x flakes. Field-effect transistors (FETs) based on monolayer Ti₃C₂T_x flakes are fabricated and their electronic properties are measured. Individual Ti₃C₂T_x flakes exhibit a high conductivity of 4600 ± 1100 S cm⁻¹ and field-effect electron mobility of 2.6 ± 0.7 cm² V⁻¹ s⁻¹. The resistivity of multilayer Ti₃C₂T_x films is only one order of magnitude higher than the resistivity of individual flakes, which indicates a surprisingly good electron transport through the surface terminations of different flakes, unlike in many other 2D materials. Finally, the fabricated FETs are used to investigate the environmental stability and kinetics of oxidation of Ti₃C₂T_x flakes in humid air. The high-quality Ti₃C₂T_x flakes are reasonably stable and remain highly conductive even after their exposure to air for more than 24 h. It is demonstrated that after the initial exponential decay the conductivity of Ti₃C₂T_x flakes linearly decreases with time, which is consistent with their edge oxidation.