The influence of crystallinity on the properties of carbon nanotubes

Sammanfattning: Carbon nanotubes have been advertised as a material with quite extraordinary properties, both mechanically and electrically. The truth is that carbon nanotubes is not one material, but several different. Depending on the method used to produce them, and consequently the quality of the atomic structure within their walls, their physical properties can also differ drastically. In this doctoral thesis a method was developed for quantifying the degree of order within the tubes' walls, namely their crystallinity, by using transmission electron microscopy. The method enables the characterization of the inherent properties of the tubes such as electrical conductivity and bending stiffness, alongside the determination of crystallinity, making it possible to quantify the influence of tube crystallinity on these critical properties. Furthermore, a model for electrical conduction in the outermost wall of multi-walled carbon nanotubes is suggested, enabling the determination of intrinsic quantities like the sheet resistance of individual crystallite grains within the walls and the boundaries in-between them. The studies reveal a profound shift in both mechanical and electrical behavior at a critical crystallite size, with large differences connected to production method, and even between individual tubes from the same production batch. These findings successfully explain previously seen differences and highlight the need for well-defined characterization techniques with protocols and classification systems, in order to successfully exploit the promising properties of carbon nanotubes in the future.