Dissertação de Mestrado #700 – Mirela Rodrigues Valentim – 21/07/2023

The exploration and investigation of two-dimensional (2D) materials have earned significant attention in recent years, primarily driven by the emergence of graphene, a compound of unique properties that allows for numerous applications. TMDs, MXenes, hexagonal boron nitride, silicene and phosphorene can be mentioned as examples of trending 2D materials. In this work, we propose and characterize a novel two-dimensional material with chemical composition B2N2O2, which can be regarded as an oxidized boron nitride layer. Employing a combination of theoretical
and computational techniques based on Density Functional Theory, we predict a number of low-energy geometries and assess their properties. Calculations performed with USPEX, a software for crystal structure prediction, show that the oxidation leads to a substantial restructuring. In the most stable configurations, the resulting lowest-energy compounds were found to be slabs featuring zigzag arrays of nitrogen atoms bonded to boron atoms which, in turn, are bridged by oxygen. We investigate their energetic, thermal and dynamic stability through formation energy and phonon
dispersion calculations and molecular dynamics simulations, from which we found that the structures are remarkably stable. To determine their electronic properties, we carried out band structure and mobility calculations for a phonon-mediated mechanism. The former revealed that the compound is a wide band-gap semiconductor with parabolic band edges, and the latter, performed within the deformation potential approach, indicated large electron and hole mobilities. We ascribe these result to the existence of electronic channels formed by the zigzag array of nitrogen bonds, which define the edges of both conduction and valence bands. Additionally, we propose a potential synthesis mechanism for the compound based on oxygen functionalization and application of pressure. Lastly, we demonstrate that the results obtained in this study can be extended to a broader family of two-dimensional compounds, that can be investigated in future works.