Two-dimensional Graphitic Metal Carbides: A New Class of Atomically Thin Carbon-based Crystals

The recent prediction of several single-atom thin two-dimensional (2D) graphitic metal carbides (g-MCs) with honeycomb-in-honeycomb (HIH) structures is the first instance of designing 2D metal-carbon-only crystals from porous carbon allotropes via lattice reconstruction and these 2D g-MCs represent a new class of 2D carbon-based crystals. Here by extensive first-principles calculations, we show that this class of carbon-based crystals can be expanded to include 33 different members in total. These materials exhibit a myriad of properties, which can be useful in many different applications such as catalysis, spintronics, thermoelectrics, optoelectronics, etc. We reveal the chemical bonding in 2D g-MCs in terms of natural bonding orbitals to shed light on the origin of their unique electronic properties. In addition, these crystals show interesting but puzzling magnetic properties. A unified model to understand the origin of the magnetic properties of 2D g-MCs is hence proposed.