Fig. 1

Evolution of MXene electronic properties with in situ vacuum annealing. Resistance versus temperature measurements are shown for Ti₃C₂T_x (a), Ti₃CNT_x (b), and Mo₂TiC₂T_x (c). The measurements were conducted during various vacuum annealing steps performed in the TEM. Each vacuum annealing step is represented with a different color and symbol. For each annealing step, both the heating and cooling curves are shown. In all cases, the resistance decreased during annealing, hence, the cooling curve is always beneath the heating curve. The atomic structures of the various MXenes are shown as insets. The initial state schematics (top schematics) show Ti₃C₂T_x and Ti₃CNT_x with intercalated water molecules on their surfaces, and Mo₂TiC₂T_x is shown with water and TBA⁺ molecules. With annealing, the MXene sample resistance is affected by the loss of adsorbed species, intercalants, and terminating species. Some of these processes are shown schematically. The resistance data in this figure are also shown in Supplementary Figures 13-15, where the resistance is plotted as a function of annealing time