Strain-doping tailoring of MoS2 on Au substrate under controlled environment conditions

Two-dimensional materials, in particular transition metal dichalcogenides, represent the new edge of materials research thanks to their tunable optical and charge transport properties. Among all of the materials in this category, molybdenum disulfide (MoS2) is one of the most studied1. Its bulk structure is made of layers kept together by weak van der Waals interactions that make it easy to exfoliate the material down to few layers or even monolayers. MoS2 monolayers, in particular, show a characteristic photoluminescence peaked around 1.8-1.9 eV, which is related to a transition across a direct band gap; this photoluminescence reduces its intensity when increasing the number of layers and is not observed in the relative bulk structure2. However, the interaction of this 2D material with the different substrates used for electronic applications or with molecules intersperse between the substrate and the monolayers, can produce various doping and strain effects that change its optical and conduction characteristics3,4. These modifications, often occurring due to aging processes, frequently worsen the material properties; on the other hand, being able to revert and control these processes could allow advantages such as obtaining specific doping. For all these reasons, in this work, we present a study of the interactions of MoS2 with a gold substrate under controlled thermal and gas conditions and we follow the induced strain and doping effects. We show that these changes can be removed or applied permanently using thermal treatments in controlled atmosphere conditions. To control the modifications occurring on the material, MoS2 monolayer flakes are exposed to temperatures ranging from 150 to 300 °C in three different gases, respectively Ar, O2 and N2. The Raman analysis of the monolayer flakes shows that it is possible to induce changes in the tensile strain and negative doping in such conditions. Our results allow us to find the threshold above which tensile strain or/and n-doping effects are induced and to propose a practical way to select and control these changes on MoS2. Generally, MoS2 monolayers on a gold substrate present a quenching of the normal luminescence5. Microluminescence measurements allow us to recognize an enhancement of the photoluminescence on the gold substrate, never seen before, after the thermal treatment under controlled conditions. These modifications in the material could be used to control and tailor the properties of MoS2 and adapt it to the specific needs of optoelectronic devices or light-emitting diodes. 1. Iqbal et al., Microelectron Eng 219, 111152 (2020). 2. Wang, T. et al., Journal of Physical Chemistry C 122, (2018). 3. Serron, J. et al., ACS Appl Mater Interfaces 15, 26175–26189 (2023). 4. Yu, Y. et al., Adv Funct Mater 26, 4733–4739 (2016). 5. Panasci, S. E. et al., Appl Phys Lett 119, (2021).