Understanding the Effets of Dopants and Substrates on the Photoemission of Monolayer MoS₂ Flakes

Bidimensional transition metal dichalcogenides are a class of semiconducting nanomaterials presenting very interesting electronic and optical properties.[1] Monolayer molybdenum disulphide (1L-MoS₂) is particularly interesting for its high charge-carrier mobility and its strong light-absorption capabilities. Such properties, originating from the bidimensional structure of the material, are allowed by directtransitions occurring through its bandgap.[2] Visible-light photoexcitation allows 1LMoS₂ to generate an intense emission which has been shown to be caused by excitonic recombination and which, moreover, is strongly coupled to the strain and doping of the semiconductor’s crystalline flakes.[3] As such, it is possible to modify the bandgap's properties of 1L-MoS₂ by acting on its electronic and structural characteristics and, especially, to tune and control the shape and intensity of its peculiar emission in order to tailor it towards the development of optoelectronic nanodevices. Here we show how thermal treatments carried out on 1L-MoS₂ under a controlled gaseous atmosphere are able to alter the optical properties of such bidimensional material. We have compared the effects of different atmospheres and the influence of the substrate’s conductivity and roughness in order to try and shed light on the causes of such modifications, finally aiming to enhance the overall optical properties of 1L-MoS₂. Through the usage of a micro-photoluminescence setup developed inhouse and coupled to a tunable pulsed laser we are able to study single monolayer flakes under a wide variety of excitation conditions and its photoemission in both steady-state and time-resolved regimes. Our results are aimed at further understanding the optical properties of 1L-MoS₂ and the factors influencing them. By being able to control the light-emitting capabilities of such material we aim to tailor it for its usage in the field of optoelectronics and towards the development of devices in which the electronic and optical properties of 1L-MoS₂ are carefully coupled. [1] C. Ferrari, A. et al. Nanoscale 7, 4598–4810 (2015). [2] Splendiani, A. et al. Nano Lett. 10, 1271–1275 (2010). [3] Panasci, S. E. et al. ACS Appl. Mater. Interfaces 13, 31248–31259 (2021).