Template-electrodeposited nanowires: synthesis, manipulation and application
Prof. Dr. Ing. D.H.A. Blank
Dr. Ir. J.E. ten Elshof
Nanotechnologies will not be incorporated into products and devices without the development of scalable, cost-effective manufacturing techniques that retain and preserve the properties of the nanoscalar material in the final product. Because nanowires and nanotubes can be the actual building blocks to construct future nanotechnological products and devices, the properties of the nanoscalar material are retained by default. Here, templated electrodeposition was used as a scalable and cost-effective manufacturing technique for nanowires and nanotubes. As a template, a polycarbonate track-etched (PCTE) membrane was used with different pore sizes: 50 nm and 200 nm. During templated electrodeposition, zinc hydroxide and iron(III) hydroxide formation, decomposition and the following growth processes of zinc oxide nanowires and iron(III) oxide nanotubes were investigated by chronoamperometry. Diffusion limited growth in the template was responsible for zinc oxide nanowires at 70°C. An electrochemically induced sol-gel process in the template and subsequent drying were responsible for iron(III) oxide nanotube formation. Also, steps were taken towards a low-cost and effective incorporation of nanowires and nanotubes on electrodes by dielectrophoresis. The working principle of dielectrophoresis is based on an alternating electric field between (two) electrodes trapping nanowires from a medium in that electric field. To increase reproducibility a set of boundary conditions were used to derive a set of parameters (including frequency, voltage) fit for incorporating nanowires on electrodes regardless of composition. Furthermore, the functionality of nanowires has been engineered to demonstrate hydrogen evolution by photocatalytic nanowires from a methanol/water solution: A segmented nanowire -containing a silver segment and a n-type zinc oxide segment- creates a space charge layer at the silver/zinc oxide interface. The space charge layer creates an electron/hole pair under UV-irradiation. The electron moves towards the silver segment to initiate a reduction reaction. The hole in the zinc oxide is scavenged by the methanol for an oxidative reaction. The overall reaction creates hydrogen and carbon dioxide. Lastly, nanowires were synthesized of the rather unknown silver oxysalt (Ag7NO11). Because of the little attention, no nanowires existed previously of this material.