Atomic Scale Study on Growth and Heteroepitaxy of ZnO Monolayer on Graphene

Abstract

Atomically thin semiconducting oxide on graphene carries a unique combination of wide band gap, high charge carrier mobility, and optical transparency, which can be widely applied for optoelectronics. However, study on the epitaxial formation and properties of oxide monolayer on graphene remains unexplored due to hydrophobic graphene surface and limits of conventional bulk deposition technique. Here, we report atomic scale study of heteroepitaxial growth and relationship of a single-atom-thick ZnO layer on graphene using atomic layer deposition. We demonstrate atom-by-atom growth of zinc and oxygen at the preferential zigzag edge of a ZnO monolayer on graphene through in situ observation. We experimentally determine that the thinnest ZnO monolayer has a wide band gap (up to 4.0 eV), due to quantum confinement and graphene-like structure, and high optical transparency. This study can lead to a new class of atomically thin two-dimensional heterostructures of semiconducting oxides formed by highly controlled epitaxial growth.

Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage

“…We first optimize the lattice parameters of the nondefective and defective ZnO monolayer and the results are shown in Table I. The lattice constant of the nondefective ZnO monolayer is 3.29Å, which agrees pretty well with experimental values of ∼3.29-3.30Å [10,16,18], superior to the previous theories (∼3.20-3.28Å) [12,13,23]. While the lattice constant of the nondefective ZnO remains almost unchanged in the presence of a Zn-vacancy, it is reduced by ∼1% when an O-vacancy is introduced (in a 4×4 unit cell of ZnO monolayer).…”

Electronic properties of two-dimensional zinc oxide in hexagonal, (4,4)-tetragonal, and (4,8)-tetragonal structures by using Hybrid Functional calculation

“…Up to recent experiments, few were successful but it shows some possibilities. For instance, the epitaxial growth of ZnO monolayer in hexagonal structure on graphene substrate was recently achieved and reported to have band gap up to 4 eV [4]. In addition, sub 100-nm-sized ZnO nanosheet in hexagonal wurtzite was also found to successfully grow in the solution synthesis using surfactant molecules as a facet at the water-air interface [5].…”

Epitaxial Growth of ZnO Monolayer on Graphene: The Thinnest Metal Oxide Semiconductor

“…For example, a ZnO grown with 10 ALD cycles displays a band gap of 4.0 eV, whereas a ZnO grown with 200 ALD cycles exhibits a band gap of 3.25 eV, which is close to the bulk ZnO value. The observed gradual spectral shift in the band edge with the ALD cycles can be attributed to the expected quantum confinement effect [6].We demonstrate the formation of ZnO monolayer on graphene, which is the thinnest heteroepitaxial layer of semiconducting oxide on graphene. The optimized UV/ozone treatment enhances the 1434…”

“…In addition, we demonstrate the presence of 2-3 nm quantum dots of the epitaxial ZnO monolayer grown by atomic layer deposition (ALD). Unlike conventional bulk ZnO, ZnO quantum dots have potential applications in nanoscale devices, such as photonic and electronic devices, due to the quantum confinement effect [6]. Figure 1 shows a ZnO monolayer grown on pristine graphene and the UV/ozone-treated graphene after 20 ALD cycles.…”