Taking graphene materials toward applications – Chemistry at the nano-surface

Abstract

Graphene is an allotrope of carbon that consists of a single layer of carbon atoms arranged in a covalently-bonded hexagonal lattice. It is the basic structural element of many other allotropes of carbon, such as graphite, charcoal, carbon nanotubes and fullerenes. Graphene has been reported to have many intrinsically interesting properties, including its potential to replace silicon in electronic devices and act as the core of next generation of logic circuits. However there are still significant technological barriers to overcome in order to permit the large-scale application of this relatively newly 'discovered' material. The most fundamental barrier is the lack of appropriate methods to synthesize graphene efficiently. Indeed, several methods have been used to date to produce graphene as a film or powder, these can generally be separated into two groups – “Top-down” and “Bottom-up” methods, with each approach having its own advantages and disadvantages. We have sought to combine these two different approaches (top-down Hummers’ method and bottom-up chemical vapour deposition) and this thesis focuses on a novel production method of graphene films based on seeded-growth from graphene and graphene oxide (GO) flakes, performed directly on silicon wafers with a 200 nm SiO2 layer. The results show that this approach can lead to a uniform “graphene film” that is continuous and of relativity high quality (about 2 layers), having the potential to be used to in technological applications. A significant advantage is the fact that additional film transfer processes can be avoided, with good control over selective growth (shape or size) to achieve specific properties. This approach has been used to deliver working devices such as PN junctions and the ability to pattern film growth has also been investigated. A clear outcome of the initial seeded-growth studies was that higher quality graphene seeds are required in order to further optimise film growth, with a simple annealing process developed to remove additional graphene layers from the flakes produced by Hummers’ or detonation methods.