Thickness-driven drastic transition in the electrical conductivity of ultrathin MoS2 films grown by pulsed laser deposition

Abstract

We report on the pulsed laser deposition of ultrathin MoS2 films and how their electrical conductivity is significantly sensitive to thickness variation. It is shown that the thickness of MoS2 ultrathin films can be fairly controlled over the (1.3–12.6) nm range by simply adjusting the number of incident laser ablation pulses (NLP). Noteworthy, the electrical conductivity of the MoS2 ultrathin films was found to change by more than 6 orders of magnitude, abruptly switching from semiconducting to conductive behavior, upon increasing the thickness in the nm range. Raman analyses revealed that our ultrathin films comprise both 2H and 1T phases with a clear tendency for the metallic 1T phase to increase at the expense of its 2H phase counterpart, as the film thickness is increased from 1.3 to ∼13 nm. Concomitantly, their density of defects also increases with N. Our results highlight the significant structural and electrical changes that occur in MoS2 ultrathin films as their thickness is barely increased from a few to only several layers. A direct relationship between the conductivity of the pulsed laser deposition (PLD)-MoS2 ultrathin films and their structural characteristics (both 1T-MoS2 phase content and density of defects) is established. Finally, this work paves the way for the PLD as an effective synthesis route for the controlled growth of hybrid 2H-/1T-MoS2 ultrathin films with the possibility of wafer scaling.