Novel 2D Silica Monolayers with Tetrahedral and Octahedral Configurations

Free-standing and well-ordered two-dimensional (2D) silica monolayers with tetrahedral (T-silica) and octahedral (O-silica) building blocks are found to be stable by first principles calculations; T-silica is formed by corner-sharing SiO4 tetrahedrons in a rectangular network and O-silica consists of edge-sharing SiO6 octahedrons. Moreover, the insulating O-silica is the strongest silica monolayer, and can therefore act as a supporting substrate for nanostructures in sensing and catalytic applications. Nanoribbons of T-silica are metallic while those of O-silica have band gaps regardless of the chirality. We find the interaction of O-silica with graphene to be weak suggesting the possibility of its use as a monolayer dielectric material for graphene-based devices. Considering that the six-fold coordinated silica exists at high pressure in the bulk phase, the prediction of a small energy difference of O-silica with the synthesized silica bilayer together with the thermal stability at 1000 K suggest that synthesis of O-silica can be achieved in experiments.