High-Quality Reduced Graphene Oxide by CVD-Assisted Annealing

Abstract

Graphene oxide is a promising solution-processable precursor for the mass production of graphene thin films. However, during the wet chemical oxidation and reduction process toward reduced graphene oxide (rGO) a large number of defects are created. Although it is possible to synthesize rGO with an average defect distance of 3–4 nm, the performance is still limited. Here we demonstrate the partial restoration of the graphene basal plane of rGO by annealing in Ar/H2/isopropanol flow. Detailed statistical Raman analysis over large areas corroborates that the mean defect distance increases from initially 2–3 to 10–12 nm after CVD annealing. Some areas even reach defect distances of up to 18 nm. However, residual manganese impurities from the oxidation process lead to undesired carbon nanotube growth on the substrate under these conditions and had to be removed before the deposition of graphene oxide flakes on the substrate. The observed defect reduction during CVD annealing indicates that the lattice defects in rGO are mostly decorated vacancies that can be healed by addition of carbon under suitable conditions.

Defects in Graphene Oxide as Structural Motifs

“…However, under these harsh reaction conditions, over‐oxidation is very likely leading to the rupture of the graphene lattice via formation of CO 2 ,. The loss of carbon atoms from the lattice represents an in‐plane lattice defect that cannot be repaired and must therefore be considered as permanent . Thus, in‐plane defects in graphene oxide must be avoided at the synthesis step, as we introduced in 2013 …”

“…Vacancy defects and hole defects, respectively, must both be considered as permanent defects, since a carbon source is necessary for their healing. Recently, we demonstrated that some defects, such as presumably few‐atom vacancies can be healed by a carbon source treatment at 700 °C . However, healing out a hole also requires a catalytically active metal surface to restore the hexagonal lattice.…”

Influence of addition of selective metallic species on mechanical properties of graphene/acrylonitrile‐butadiene‐styrene composites

“…This shows poor networking in rGO sheets obtained from the solvent‐based exfoliation. The key reason behind this incompetence may be the vacancies created either during thermal reduction or during the ultrasonication processes . The reflection of such defects can be easily realized through poor mechanical and electrical properties of such composites.…”

Bioelectronics and Interfaces Using Monolayer Graphene

“…In addition to the high conductivity, graphene is also transparent and hence can be utilized efficiently for photoactive electrodes and devices. It is important to emphasize that the understanding of structural and interfacial properties of monolayer graphene depends mostly on the fabrication approach used, with due consideration of chemically adsorbed/bound species and defects in the structure . Among numerous methods which employ oxidative/reductive chemical environment for obtaining graphene flakes with superior conductivity for application in single layer devices, the two most important methods are the mechanical cleavage of highly‐oriented pyrolytic graphite and chemical vapor deposition method (CVD) .…”