Point defects in 1T'-MoS₂ from first principles

Monolayers of group VI Transition Metal Dichalcogenides (TMDs) exist in either the semiconducting 2H phase or semimetallic 1T’ phase. While the stable 2H phase has been extensively investigated due to prospective optoelectronic applications, the metastable 1T’ phase has appeared in the spotlight only recently, mainly due to its topological properties. In this talk, I will provide an overview on the formation of point defects in 1T’-MoS₂ within two experimentally-relevant situations, i.e. under thermodynamic equilibrium and under electron beam irradiation. First, I will address the stability of point defects, exploring several configurations of vacancy, adatom and antisite defects. All considered defects exhibit lower formation energies in the 1T’ phase compared to the 2H phase, suggesting that the 1T’ polymorph is more susceptible to lattice imperfections. Next, the response of 1T’-MoS₂ to the electron irradiation will be examined. The range of electron beam energies needed to carry out imaging without inducing any damages in the sample and some guidelines for the controlled creation of defects in the electron microscope are discussed. Throughout my talk, I will draw comparisons between local disorder in the two phases to portray a complete picture of the role of defects in TMDs.