SEIRAS of functionalised graphene nanomaterials : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Nanoscience at Massey University, Manawatū, New Zealand
Graphene exhibits many excellent properties, but many next-generation devices require post chemical treatment to introduce structural confirmations, defects or a particular impurity to obtain functionality. The understanding of these defects and the manifestation of desirable properties using chemical modification is a fundamental problem with low defect graphene as the small number of functional groups provides insufficient signal intensity for many characterisation techniques. Metallic nanoparticles are at the centre of plasmonics for enhancing optical signals. This work is a unique undertaking for the examination of novel Steglich esterification chemistry that is performable on graphene as well as providing insight into the native edge structure of as-produced graphene flakes using surface enhanced infrared reflection absorption spectroscopy (SEIRAS) to characterise covalently functionalised graphene materials.
Two methods of producing graphene flakes that are relatively low or high in defects have been developed to contrast the effect that inherent defects have on the macroscopic physical and spectroscopic properties. Ultraviolet-visible spectroscopy in conjunction with Raman, electron and atomic force microscopy was used to elucidate the origins and density of defects to draw conclusions on how graphene’s macroscopic properties manifest from atomic level defects.
Discussions of infrared vibrational spectroscopy are carried out before an extension to SEIRAS where the use of near-field plasmon and phonon modes are attributed to observed optical enhancements. The experimental preparation is focused towards understanding the role nanoparticles play in SEIRAS of graphene and is discussed such that other graphene researchers can recreate SEIRAS for their graphene research. TEM is used to characterise the variety of nanoparticle shapes and geometries as well as provide topological insights on nanoparticles adsorbed to flakes of graphene.
SEIRAS probes the defects native to graphene which confirms the presence of oxygen functionality. Steglich esterification reactions were utilised to successfully prepare a range of graphene materials with novel covalently bound functional groups as confirmed by SEIRAS. Covalent chemistry was extended to introduce a redox-active ferrocene derivative where SEIRAS was used to observe in real-time, the effect of interconversion of ferrocene to the ferrocenium cation.
The foundations for the development of graphene-based solid state solar cells was the final focus of this work. Development and production of a potential photo-active layer was explored with Cl-BODIPY as the basis chromophore. Production of a flexible, electrically conductive substrate from graphene flakes was carried out, and tunnelling electron microscopy (TEM) was used to characterise topological and morphological surface features. The focus here was on covalent and physical absorption to graphene flakes. SEIRAS was used to confirm nucleophilic substitution (covalent) modification while STEM was used to confirm the uniformity of BODIPY on the substrate and chlorine atomic mapping to confirm physisorption.