Ozonation of Group-IV Elemental Monolayers: A First-Principles Study

Environmental effect on the physical and chemical properties of two-dimensional monolayers is a fundamental issue for their practical applications in nanoscale devices operating under ambient conditions. In this paper, we focus on the effect of ozone exposure on group-IV elemental monolayers. Using density functional theory and the climbing image nudged elastic band approach, calculations are performed to find the minimum energy path of O₃-mediated oxidation of the group-IV monolayers, namely graphene, silicene, germanene, and stanene. Graphene and silicene are found to represent two end points of the ozonation process: the former showing resistance to oxidation with an energy barrier of 0.68 eV, while the latter exhibit a rapid, spontaneous dissociation of O₃ into atomic oxygens accompanied by the formation of epoxide like Si-O-Si bonds. Germanene and stanene also form oxides when exposed to O₃, but with a small energy barrier of about 0.3-0.4 eV. Analysis of the results via Bader's charge and density of states shows a higher degree of ionicity of the Si-O bond followed by Ge-O and Sn-O bonds relative to the C-O bond to be the primary factor leading to the distinct ozonation response of the studied group-IV monolayers. In summary, ozonation appears to open the band gap of the monolayers with semiconducting properties forming stable oxidized monolayers, which could likely affect group-IV monolayer-based electronic and photonic devices.