Date of Completion

8-2-2011

Embargo Period

8-1-2011

Advisors

Yu Lei; Puxian Gao

Field of Study

Chemical Engineering

Degree

Master of Science

Open Access

Open Access

Abstract

Electrodeposition is an efficient and economical approach for template synthesis of one-dimensional (1D) nanostructured materials. Based on the porous membranes as templates during electrodeposition, metallic nanowires, nanorods, and nanotubes can overcome the geometrical restrictions to be inserted into the nanometric recesses with both diameter and length well controlled by tuning the size and thickness of the templates.

In this work, the morphology, growth rate and texture of copper nanowires prepared with templates were investigated by the controlled parameters in various experiments. Cu nanowire arrays with preferential orientations can be successfully synthesized into the Anodic Aluminum Oxide (AAO) templates with optimized electrodepositing conditions at room temperature. The nanowires embedded in AAO were released and dispersed on Si/SiO2 wafer for further observation and analysis in the preliminary studies. The morphology of the copper nanowires has been characterized by scanning electron microscopy (SEM), demonstrating the high density of nanowires grown into the pores of AAO. The chemical composition and crystalline structures of copper nanowires were analyzed by Energy-dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and Transmission Electron Microscopy (TEM).

Both potential and current were used as controlled variables during electrodeposition. Also, the influences of deposition time, concentration of CuSO4.5H2O in the electrolyte and pH value on morphology and crystalline structure of copper nanowires were investigated. Results show that the diameters of nanowires are 200 nm, same as the pore size of the templates. The lengths of nanowires are positively correlated with the deposition time and the growth rate of nanowires is strongly affected by the applied potential and concentration of the electrolyte. Characterizations of XRD and TEM proved that (220) is the preferential orientation of copper nanowires when lower current density was selected for electrodeposition with a galvanostatic experiment. The orientation obtained was the same as the preferential orientation of nanowires prepared in an electrolyte with higher pH using a potentiostatic technique. Moreover, a different preferred growth direction of [200] was identified when a less negative applied potential was employed, as well as increasing the current density in a certain range. The nucleation-growth mechanism of nanowires during electrodeposition was systematically investigated and results concerning preferred orientations were compared with previous studies. Overall, we demonstrated how growth rate and preferred orientations could be controlled using electrodeposition to prepare copper nanowires. Extension of the methods for synthesizing other nanowires is also discussed. This approach may contribute to applications that require single-crystal metallic nanowires along a cubic axis direction, e.g. electronic tunneling devices.

Major Advisor

Brian G. Willis

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