Synthesis of nanomaterials via anodic aluminium oxide templates

• Main Author: Gravani, Styliani
• Published: University of Surrey 2014
• Subjects: 620.5
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616919

This thesis is concerned with the synthesis of 1 D nanomaterials via a template-assisted route. Porous anodic aluminium oxide templates prepared electrochemically have been utilised with two intrinsically different deposition techniques, sol-gel and high power pulsed magnetron sputtering (HPPMS), to obtain ID metal and metal oxide nanowires and nanotubes. The resultant morphologies and crystal structures were examined via SEM, XPS, XRD, TEM and EELS. A number of porous template alumina structures have been grown via the anodisation of pure and sputtered aluminium. The effects of surface pre-treatments, etching treatments and anodisation conditions on the resultant morphologies were investigated. It has been found that pore growth is largely dependent on the surface roughness of the substrate as well as the anodisation conditions. The anodisation duration is critical in promoting and allowing self-ordering. Obtained templates, varied in thickness from a few hundred run to several tens of pu-m, with an average pore diameter of 70 nm, interpore distance of 100 nm and pore density of 4 x 1010 cm2. . The implementation of HPPMS led to the successful deposition of Ti inside the alumina template to depths of around 45-50 run. It was found that templates with highly parallel pores on a rigid substrate such as Si, are more suited if this deposition method is to be used. Control of the pressure and substrate biasing is critical in avoiding 'pinch-off and 'bridging' and leading to complete pore filling. The results have shown that HPPMS is a promising plasma technology for the synthesis of nanomaterials such as nanodots, nanopillars or nanowires, when used with porous alumina templates under appropriate conditions. The use of sol-gel deposition has led to the growth of a number of interesting materials and structures. Nanocrystalline Ce02 and Ce1-xZrx02 and Ce1-xSmx02 thin films and powders have been successfully obtained exhibiting novel micro- and nano-structures, likely to find useful applications in catalysis and gas sensing due to their redox properties and large surface to volume ratio. FUlihermore, the treatment of porous alumina templates via a sol-gel/hydrothermal method led to the formation of Ce-doped y-Ah03 nanowires. Hence, a simple, direct and cost effective method for producing large scale Ah03 (and doped Ah03) nanowires is repotied. Moreover, by annealing at temperatures above 600 DC, nanowires of different crystallographic forms such as 0-, e- and a-Ah03 can also be readily obtained. As the dopant Ce was successfully introduced through this method a wide range of doped-Ah03 nanowires (by other rare eatihs such as Y, La, Gd, Srn), at various concentrations (e.g. 1,3,5 at. %) can be readily obtained.