Periodic trends in the structural, electronic, and transport properties of electrenes

Two-dimensional layered electrides are a class of atomically thin materials in which the anion is an excess electron rather than a negatively charged ion. These excess electrons form delocalized sheets of charge surrounding each layer of the material. A well-known example is Ca₂N; its identification and characterization has triggered an avalanche of studies aimed at broadening applications of electrides. Ca₂N is only one member of the M₂X family of materials, with M being an alkaline-earth metal and X belonging to the pnictogen group, which can be exfoliated to form single- or few-layer electrenes. The goal of this study is to systematically investigate the monolayer and bilayer properties for this family of materials. Density-functional calculations reveal linear relationships between surface and interstitial charges, work functions, exfoliation energies, and Ewald energies. Using the Landauer formalism, informed by rigorous electron-phonon scattering calculations, we also investigate the electronic transport characteristics of the monolayer and bilayer electrenes. Our findings indicate that the nitrogen-based electrenes (Ca₂N, Sr₂N, and Ba₂N) are more conductive than their counterparts involving heavier pnictogens. The results of this study highlight underlying periodic trends in electrene properties that can help identify which materials would be best suited for particular applications.