First-principles study on physical properties of a single ZnO monolayer with graphene-like structure

TL;DR

This study uses first-principles calculations to explore the elastic, piezoelectric, electronic, and optical properties of a single ZnO monolayer with a graphene-like structure, revealing its phonon behavior, mechanical softness, piezoelectricity, and wide band gap.

Contribution

It provides a comprehensive first-principles analysis of the physical properties of ZnO monolayer with a graphene-like structure, including phonon dispersion, elastic, piezoelectric, and optical characteristics, which were not previously detailed.

Findings

SZOML is much softer than graphene.

It exhibits piezoelectric properties.

The electronic band gap is 3.576 eV.

Abstract

The elastic, piezoelectric, electronic, and optical properties of a single ZnO monolayer (SZOML) with graphene-like structure are investigated from the first-principles calculations. The phonon dispersion curves contain three acoustic and three optical branches. At $\Gamma$ point, the out-of-plane acoustic mode has an asymptotic behavior $\omega (q)=Bq^2$ with $B=1.385 \times 10^{-7}$ m$^2$/s, while two in-plane acoustic modes have sound velocities $2.801$ km/s and $8.095$ km/s; the other three optical modes have frequencies 250 cm$^{-1}$, 566 cm$^{-1}$, and 631 cm$^{-1}$. The elastic and piezoelectric constants are obtained from the relaxed ion model. It is found that the SZOML is much softer than graphene, while it is a piezoelectric material. The electronic band gap is 3.576 eV, which implies that the SZOML is a wide band gap semiconductor. Many peaks exist in the linear optical spectra, where the first peak at 3.58 eV corresponds to the band gap of SZOML.