Nanostructures based on graphene and functionalized carbon nanotubes | Grafén és szén nanocső alapú nanoszerkezetek előállítása és jellemzése

Abstract

In this thesis I have explored the preparation of graphene nanostructures, having crystallographically well defined edges and the scanning probe measurements of graphene and functionalized carbon nanotubes. The results of my research can be summarized in three main parts. I have developed a sample preparation technique, based on a carbon nanotube – few layer graphite composite that provides a simple and effective solution to sample stability issues encountered when measuring functionalized carbon nanotubes with STM. Such a composite has enabled for the first time to measure functionalized carbon nanotubes in atomic resolution, as well as to acquire energy resolved STM images of the tubes. Functionalized and pristine regions of the nanotube surface were made visible and the positions of the functional groups could be correlated with crystal lattice directions. The ease of the sample preparation allows the use of my method to study the properties of other types of functionalized carbon nanotubes. This adds STM to the toolbox of functionalized carbon nanotube characterization techniques, complementing optical spectroscopic methods. I have investigated the source of anomalous thickness measurements of graphene and few layer graphite, obtained by tapping mode AFM. The physical origin of these artefacts was elucidated by measurements and theoretical modeling of the AFM tip oscillation and tip – sample interaction. Numerical calculations and experiments have been used to show the correct experimental parameters needed to image the true thickness of graphene layers on a supporting substrate. The conclusions are general enough so that they can be applied to the measurements of other nanosized objects by AFM. I have demonstrated the existence of a chemical etching procedure that discriminates between the armchair and zigzag type edge termination of graphene layers. Coupled with AFM patterning, I have used this chemical process to pattern graphene sheets into nanostructures having zigzag edges. Raman measurements show that the edge roughness of these nanostructures is low enough that inelastic light scattering processes specific to the zigzag edge could be measured. This is the first study which shows that zigzag edged graphene nanostructures can be prepared in the laboratory in a controlled manner, which have a low enough edge disorder to enable the experimental observation of zigzag edge specific physical processes