Al2C monolayer: the planar tetracoordinate carbon global minimum†
Inspired by our theoretical finding that C2Al62− has a planar D2h minimum with two planar tetracoordinate carbons (ptCs), we computationally designed a new two-dimensional (2D) inorganic material, an Al2C monolayer. All carbons in this monolayer are ptC's, stabilized inductively by binding to four electropositive Al atoms in the same plane. The Al2C monolayer is semiconducting with an indirect minimum band gap and a slightly larger direct band gap. Good persistence of the Al2C monolayer is indicated by its moderate cohesive energy, the absence of imaginary modes in its phonon spectrum, and the high melting point predicted by molecular dynamics (MD) simulations. Moreover, a particle-swarm optimization (PSO) global minimum search found the Al2C monolayer to be the lowest-energy 2D structure compared to other Al2C alternatives. Dividing the Al2C monolayer results in one-dimensional (1D) Al2C nanoribbons, which are computed to have quite rich characteristics such as direct or indirect band gaps with various values, depending on the direction of the division and the resulting edge configuration.