Variable range hopping and thermally activated transport in molybdenum-based MXenes

The magnetotransport of freestanding, vacuum filtered, thin films of Mo₂CTₙ, Mo₁. ₃₃CTₙ, Mo₂TiC₂Tₙ, and Mo₂Ti₂C₃Tₙ was measured in the 10--300-K temperature (T) range. Some of the films were annealed before measuring their transport properties. Analysis of the results suggest that---with the exception of the heavily defective Mo₁. ₃₃CTₙ composition---in the 10- to 200-K temperature regime, variable range hopping between individual MXene sheets is the operative conduction mechanism. For Mo₁. ₃₃CTₙ it is more likely that variable range hopping within individual flakes is rate limiting. At higher temperatures, a thermally activated process emerges in all cases. It follows that improved fabrication processes should lead to considerable improvements in the electrical transport of Mo-based MXenes.