Structural, vibrational, elastic, and electronic properties of MgO cluster-assembled monolayers

Abstract

Atomic-thin two-dimensional (2D) cluster-assembled metal oxide monolayers have been pursued as a rapidly emerging class of 2D materials with unprecedented properties and potential for versatile applications. Using stable Mg₆O₆ clusters as building blocks, here, we established two new MgO monolayers (namely g-MgO and r-MgO) that completely differ from the known phases, and explored their growth pattern based on cluster assemblies, structural, vibrational, elastic, and electronic properties by exploiting density functional theory (DFT) calculations. Phonon dispersion calculations reveal both monolayers are dynamically stable. The g-MgO and r-MgO monolayers retain structural integrity at 1200 and 1000 K, respectively. Both monolayers have completely different Raman spectra with unique characters, enabling them to be easily identified them in experiments. The calculated in-plane stiffness and Poisson ratio of g-MgO are 75.69 N/m and 0.40, while that of r-MgO are 62.34 (33.87) N/m and 0.97 (0.53), respectively, revealing the isotropic and anisotropic mechanical response for g-MgO and r-MgO monolayers. The g-MgO (r-MgO) monolayer has direct (indirect) semiconducting properties with a wide bandgap of 4.53 (4.64) eV from HSE06 functional and possesses outstandingly high carrier mobilities (all >2.40 × 10³ cm² V⁻¹ s⁻¹), offering promising potential in advanced electronic and photoelectronic applications.