2D silica

Two-dimensional silica (2D silica) is a layered polymorph of silicon dioxide. Two varieties of 2D silica, both of hexagonal crystal symmetry, have been grown so far on various metal substrates. One is based on SiO₄ tetrahedra, which are covalently bonded to the substrate. The second comprises graphene-like fully saturated sheets, which interact with the substrate via weak van der Waals bonds. One sheet of the second 2D silica variety is also called hexagonal bilayer silica (HBS); it can have either ordered or disordered (amorphous) structure.^[1]

Top and side views of graphene (left) and HBS structures (right). Red atoms are oxygens.^[1]

Models and TEM images of defects in HBS (middle) and graphene (bottom row): Stone-Wales (a), flower (b), divacancy (c) and a more complex, interstitial defect (d).^[1]

TEM images of amorphous HBS

2D silica has potential applications in electronics as the thinnest gate dielectric. It can also be used for isolation of graphene sheets from the substrate.^[1] 2D silica is a wide band gap semiconductor, whose band gap and geometry can be engineered by external electric field. It was shown to be a member of the auxetics materials family with a negative Poisson's ratio.^[2]