Controlling the microstructure of nanowires offers a very practical means of producing nanostructures that are amenable to the needs of technological applications. Here we report an interesting observation of structural transition of electrochemically deposited cobalt nanowires with change in aspect ratio of the nanowires. These nanowires were deposited in PCT polycarbonate template single side coated with silver from an optimized CoSO4.7H2O bath (50mM) and subsequently their crystal structure were studied using X-Ray Diffraction. At room temperature (303K) change in the aspect ratio (length to diameter) of the nanowires brought in a change in their crystal structure from hexagonal close packing (HCP) to face centered cubic (FCC) as we kept on increasing their aspect ratio by varying the deposition time from 200 to 1000 seconds. Rate of deposition for a fixed bath concentration was studied and using that a critical aspect ratio for the conversion was calculated which came out to be approximately 40. This interesting finding has useful bearing in designing the magnetic behavior and switching characteristics of the wires for device applications.
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