Metal-insulator transition in quasi-two-dimensional Mo-C films

We have studied the insulator-to-metal transition in Mo-C films by tuning the thickness from 2.6 to 20. The temperature dependence of the conductivity evolves from hopping transport, for the thin insulating films, to a lnT dependence for the thicker metallic films. In the insulating regime we find a variable range Mott hopping law at high temperatures crossing over to Efros-Shklovskii hopping at lower temperatures with the opening of a soft Coulomb gap. We also obtain the dependence of the characteristic parameters on the film thickness.