Samsung Advanced Institute of Technology

Graphene-based two-dimensional heterostructures are of substantial interest both for
fundamental studies and their various potential applications. Particularly interesting are
atomically-thin semiconducting oxides on graphene, which uniquely combine a wide band gap
and optical transparency. Here, we report the atomic-scale investigation of a novel selfformation
of a ZnO monolayer from Zn metal on a graphene oxide substrate. The spontaneous
oxidation of ultra-thin Zn metal occurs by reaction with oxygen supplied from the graphene
oxide substrate and graphene oxide is deoxygenated by a transfer of oxygen from O-containing
functional groups to zinc metal. The ZnO monolayer formed by this spontaneous redox reaction
shows a graphene-like structure and band gap of about 4 eV. This study demonstrates a unique
and straightforward synthetic route to atomically-thin two-dimensional heterostructures made
from a two-dimensional metal oxide and graphene, formed by the spontaneous redox reaction
of a very thin metal layer directly deposited on graphene oxide.