Abstract
"Graphene has had significant attention since it was successfully isolated in 2004 by Geim and Novosolov, who were later awarded the Nobel Prize in Physics for their outstanding work. The discovery uncovered a whole new area of research into 2D materials with numerous applications. 16 years later, graphene is now transitioning into industry. However, for the transition to be successful, the supply chain needs internationally agreed measurement standards in place and methods for comparing different types of graphene.
There are many variations of what is commonly referred to as “graphene”, with differences in size, chemistry and bulk form. This thesis includes the structural characterisation of graphene, describing the research on which the NPL Good Practice Guide (No. 145) was based. This GPG will form the basis of two international ISO standards, one for flakes (ISO TS 21356-1), and another for CVD-grown sheets (ISO NWI 21356-2). ISO standards are important in industry for maintaining consistency across different institutions and companies, and ensuring repeatable and reliable measurements.
The chemical characterisation of graphene requires a more thorough investigation, and additional measurement techniques. This thesis explores the physicochemical characterisation of three different types of material (graphene oxide, a graphitic powder containing few-layer graphene flakes, and graphene sheets), and the suitability of their modified forms (reduced graphene oxide, functionalised flakes, and functionalised sheets) for use in several applications (conductive thin films, nanocomposites, and biosensors).
The work in this thesis has improved our understanding of functionalised graphene and in turn aided in its optimisation for industrial products. Graphene oxide (GO) has been significantly reduced at low temperatures (150°C), resulting in competitive sheet resistances (~1.3 kΩ□-1). For the first time, tip-enhanced Raman spectroscopy (TERS) measurements have been performed on a commercially available product containing few-layer graphene and show differences between the location of functionalisation (edge vs basal plane), and the effect on the final nanocomposite. Finally, functionalised sheets of graphene have been investigated for their use as biosensors, by combining Raman spectroscopy and atomic force microscopy measurements, enhancing our understanding of the bonding mechanisms and observing changes that have not been recorded previously for single layer graphene sheets in atmospheric conditions."