An Exploration in Nano-Carbons: Bulk Graphene, Ultrafast Physics, Carbon-Nanotubes
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Carbon nanomaterials encompass the newly discovered allotropes of carbon with at least one of its spatial dimensions on the order of a few nanometers. The physical properties of these nanomaterials differ substantially from the bulk carbon allotropes such as graphite and diamond. Of these nanomaterials, single-walled carbon nanotubes (SWNTs) and graphene have illicited much of the attention owing to their unique and attractive electronic, optical, thermal, and mechanical properties which have found numerous applications in emerging technologies. Raman spectroscopy is an invaluable technique in the characterisation of these materials as it allows for both a rapid and non-destructive analysis of these nanomaterials. We examined a number of methodologies for the synthesis of “bulk” quantities of graphene, and using Raman spectroscopy, analysed these samples to critically assess their crystalline quality, finding that many of the bulk methods produce material which could be considered as amorphous, rather than crystalline, having crystalline domain sizes less than a few nanometers. An important finding, as many of graphene’s unique properties are severely attenuated with increasing defects. Using these findings, we utilised the non-linear optical properties of graphene, namely its property of saturable absorption (wherby its light absorption decreases with increasing light intensitiy), to create saturable absorber mirrors (SAMs) which are used in the mode-locking of lasers creating pulses of light on the order femtoseconds with very high peak power. We developed graphene SAMs from the bulk synthetic methods which we found to have good crystalline quality and attempted to use them to passively mode-lock an Er:fiber laser operating at t 1560 nm. We successfully mode-locked the laser with graphene produced from the ultrasound induced exfoliation of graphite generating pules of sub-200 fs duration with low nonsaturable loss, and large modulation depths allowing use in low-gain lasers.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Biomolecular and Physical Sciences
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In order to comply with copyright some images have been removed. Appendix A "Humidity chamber maual' , and Appendix B "Authored publications" have not been published here.
Single-walled carbon nanotubes (SWNTs)
Saturable absorber mirrors (SAMs)