Synthesis, characterization and applications of carbon nanowalls

Abstract

Both fullerenes and carbon nanotubes represent unusual forms of carbons in the nanometer regime. Their unique crystalline structures and dimensionality bring about carbons with new mechanical, chemical, and electronic properties. In some senses, the fullerenes can be thought of as zero-dimensional (0D) carbons, while the nanotubes apparently exhibit a quasi-one-dimensional (1D) structure. Recently, Wu et al. have succeeded in growing well-aligned two-dimensional (2D) carbons (dubbed carbon nanowalls) on various substrates using microwave plasma enhanced chemical vapor deposition. As a new form of nanostructured carbon, in particular its 2D dimensionality, carbon nanowalls may have potential applications in areas which required high surface areas materials, e.g. batteries, gas sensors, catalysts, flat panel display and data storage. Carbon nanowall may provide an excellent opportunity for physicists to explore new physics of carbon nanostructures with open boundaries. In this thesis, carbon nanowalls were grown under different conditions including substrates, catalysts, gas ratios and growth time. Selective growth of carbon nanowalls was also carried out with the help of deep trenches. Moreover, it was found that carbon nanowalls can be grown without the catalysts. In order to understand the mechanism of nanowall growth, the effect of electric field on nanowall growth were also studied. It is found that the existence of a strong localized electric field is the key to growing carbon nanowalls in our case. A Class of nanostructured materials have also been synthesized on carbon nanowall templates using plasma enhanced chemical vapor deposition (PECVD), molecular beam epitaxy (MBE), evaporator and electrodeposition. These materials included ZnO, TiO2, SiO2, Fe3O4, AlOx and SnO2. In addition, a series of experiments have been carried out to study the field emission characteristics of this novel type of carbon nanostructure with different conditions, e.g. different anode areas, temperatures and background gases. The filed-emission characteristics obtained with different anode areas demonstrate that the field emission is fairly uniform over the sample surfaces. It was also found that the carbon nanowalls exhibited a low turn-on field and a large field enhancement factor using carbon nanowalls as the emitter.