title: Spectroscopic investigation of functionalized single-walled carbon nanotubes and graphene nanoribbons
Creators: name: Meingast, Laura Madeleine
Publisher: name: Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU)
Year: 2025

description: Single-walled carbon nanotubes - hollow cylinders of seamless rolled graphene sheets – and graphene nanoribbons - narrow strips of graphene - are in the focus of this dissertation. Based on new functionalization and synthesis strategies, three unexplored nanotube and nanoribbon systems have been created and are investigated here for the first time. The thesis is divided into three main parts, one for each material system: In the first part, a new covalent click-functionalization of single-walled carbon nanotubes is studied, which combines the two strategies cycloaddition and silanization. The new approach allows for a modular nanotube modification with a large variety of interchangeable functional groups, molecules or nanostructures. Here nanotubes were studied, which were attached to gold nanoparticles, after stepwise connection of silane molecules and azide groups. The Raman investigation presented here confirms a mild behavior of the new functionalization approach, direct evidence for the attached molecules/nanostructures in form of Raman fingerprints were not identified. The stepwise attached molecules and nanostructures were however found to affect the nanotube’s properties, observed by increasing charge transfer with every step of the functionalization. This observed impact on the nanotube’s characteristics needs to be considered for the use of the new approach as modular functionalization strategy. It might even be beneficial to realize for example adjustable nanotube doping. The second part of this thesis is devoted to mechanically interlocked carbon nanotubes (MINTs). The encapsulation of tubes with ring-shaped molecules has proven as attractive strategy for non-covalent functionalization. Here a new MINT system, based on positively charged macrocycles, is investigated. The Raman and tip-enhanced Raman spectroscopy (TERS) studies presented in this work contributed significantly to the discovery of an unexpected and unknown twofold functionalization effect: while the nanotubes are enclosed by positively charged macrocycles, negatively charged triiodide and polyiodide ions (I−3 ,I−n) fill the nanotubes’ cavities. All components of this unique material were found to interact with other, forming a three-compound-system of high complexity. A characteristic Raman fingerprint was only observed for the iodide chains, the macrocycles remained "invisible" in my experiments. The investigations performed via Raman and photoluminescence spectroscopy confirmed the non-covalent bonding between all components of the system and demonstrated a non-diameter-selective behavior of the ring enclosure. To gain deeper insight, thin, isolated bundles of the MINT material were further analyzed via Raman spectroscopy and first TERS studies. Due to the rather strong signal of the iodide chains in both methods, inhomogeneous functionalization of the nanotubes was identified down to the nanometer scale. This demonstrates a significant influence of local conditions on the functionalization result, whose exploration needs further work. My spectroscopic studies provide therefore a first insight into this unique double-functionalized nanotube material, paving the way for its further and deeper investigation. In the third part, we focus on a new class of cove-edged graphene nanoribbons. They incorporate chirality as new, additional parameter to tune their properties. Two representative members of the nanoribbon family were created via a new bottom-up synthesis. They differed in their chiral indices and the arrangement of functional groups along their edges. Here, we present a first investigation via Raman spectroscopy and compare the results to density functional theory simulations of the vibrational modes. No clear impact of chirality and functional group arrangement was observed for the investigated samples. We expect therefore similar Raman responses for all cove-edged nanoribbons with chiral indices of the form (n, 2). Due to the low symmetry of the nanoribbon structures, a large number of vibrational modes with overlapping frequency ranges is predicted by density functional theory. To further study the impact of the chirality, TERS might therefore be preferable, as it might offer deeper insight into the local influence of the chiral nanoribbon shape.