Design and Fabrication of the Catalyst Systems for the Control of Sintering of Metal Nanoparticles during the Growth of Carbon Nanotubes and ZnO nanorods
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis reports two distinct approaches towards controlled fabrication of catalyst systems for carbon nanotube (CNT) and ZnO nanorod growth. For CNT growth, a shallow porous anodic alumina (PAA) membrane was utilised to prevent the sintering of Co metal catalyst nanoparticles (NPs) during the growth of CNTs by chemical vapour deposition (CVD). This part of the work involved optimisation of PAA membrane fabrication (several key process parameters, such as pre-treatment, anodization and chemical etching), development of a new strategy for electrodeposition of Co (via control over voltage pulse sequence, pH and atmosphere) as well as optimisation of the CVD conditions (temperature used during the catalyst reduction and growth stage). Dense CNTs with diameters smaller than the PAA pores were successfully grown using optimised catalyst system under optimal growth conditions. For ZnO nanorod growth, the optimal catalyst system was fabricated by forming a sub-monolayer of Au nanocolloids adsorbed onto an APTMS-modified sapphire substrate. In order to optimize catalyst fabrication effects of various key catalyst fabrication parameters (drop- vs. dip-coating vs. sputtering, effect of the type of sapphire substrate surface, tether modification of substrate, colloid loading etc.) had been explored in the interactive fashion. Pulsed laser deposition (PLD) was utilised for the subsequent ZnO nanorod growth and effects of various key process parameters (use of eclipse configuration, oxidizing in situ during heating up stage, laser pulse frequency etc.) were explored in detail. By using the optimised catalyst system and the optimised PLD conditions which have been developed in this thesis, dense arrays of ZnO nanorods with highly uniform size and nanorods tip diameter similar to the diameter of the Au colloids used as catalysts were successfully fabricated.