Stable single-layer honeycomb like structure of silica

TL;DR

This paper predicts a stable, single-layer honeycomb structure of silica with unique electromechanical properties, derived from first-principles calculations, expanding the understanding of silica's possible 2D allotropes.

Contribution

It introduces a novel stable single-layer honeycomb silica structure, hα-silica, with unique properties and potential for functionalization, derived from theoretical analysis and numerical calculations.

Findings

hα-silica is a wide band gap semiconductor

It exhibits negative Poisson's ratio and high piezoelectricity

Can form stable multilayer structures and functionalized derivatives

Abstract

Silica or SiO$_2$, the main constituent of earth's rocks has several 3D complex crystalline and amorphous phases, but it does not have a graphite like layered structure in 3D. Our theoretical analysis and numerical calculations from the first-principles predict a single-layer honeycomb like allotrope, h$\alpha$-silica, which can be viewed to be derived from the oxidation of silicene and it has intriguing atomic structure with re-entrant bond angles in hexagons. It is a wide band gap semiconductor, which attains remarkable electromechanical properties showing geometrical changes under external electric field. In particular, it is an auxetic metamaterial with negative Poisson's ratio and has a high piezoelectric coefficient. While it can form stable bilayer and multilayer structures, its nanoribbons can show metallic or semiconducting behavior depending on their chirality. Coverage of dangling Si orbitals by foreign adatoms can attribute new functionalities to h$\alpha$-silica. In particular, Si$_2$O$_5$, where Si atoms are saturated by oxygen atoms from top and bottom sides alternatingly can undergo a structural transformation to make silicatene, another stable, single layer structure of silica.