Tuning the luminescence and structural properties of single layer MoS2 for optoelectronic devices under thermally controlled conditions

Nowadays, the increasing interest in the usage of bidimensional (2D) semiconductive materials towards the development of novel types of nano-optical devices raises the necessity to improve and tailor their conductive and optical properties. Molybdenum disulphide (MoS2) is a transition metal dichalcogenide (TMDC), a van der Waals material which is possible to reduce to a 2D structure composed of a single nanometric layer (1L-MoS2)1. In a 2D structure, MoS2 shows high charge-carrier mobility and strong light-absorption capabilities. Moreover, it shows a different energy band configuration, in comparison to its bulk form, that allows a direct excitonic transition useful for light generation or electron harvesting in the context of optoelectronic devices. Applying an excitation with visible light makes it possible to produce intense photoemission, which is at the same time extremely affected by strain and doping conditions. These properties are, consequently, strongly influenced by the interaction between MoS2 and the metallic, semiconductive or insulating nature of the substrate2 on which it is in contact. Here, we present the findings of our investigation into the impact of various substrate types on the conductivity, photoemission, and physical characteristics of 1L-MoS2, utilizing Micro-Raman spectroscopy, Atomic Force Microscopy, and Micro-photoluminescence steady-state and time-resolved techniques. We investigated the effects of different conductive and insulating substrates and we carried out thermal treatments in a controlled gaseous atmosphere (Ar, O2, N2 or CO2) to influence and tailor the strain-doping and luminescence properties of 1L-MoS2. The spot-by-spot analysis performed through these microscopy-coupled techniques has allowed us to obtain images and local information on the behaviour of single flakes after the treatment. By performing controlled thermal treatments, we aim to manipulate MoS2's doping and light emission in relation to how it interacts with its environment. In this way, we intend to obtain a multifunction material purposefully designed for its usage in nano-electronic devices. 1. Splendiani, A. et al., Nano Lett 10, (2010). 2. Yu, Y. et al., Adv Funct Mater 26, (2016). 3. Panasci, S. E. et a., Appl Phys Lett 119, 93103 (2021). 4. Esposito, F. et al., Appl Surf Sci 639, 158230 (2023).