| In this dissertation, we have studied the effect of Co ion concentration on the structure of Co nanowires as well as the effect of deposition potential on the structure and composition of Co-Ni alloy nanowires.The structure of Co nanowires deposited at the same potential depends on Co2+ concentration in solution. When depositing at -1.6V, the formed Co nanowire are hcp phase in 0.356M solution, a mixture of hcp and fcc phases in 0.53M solution, almost fcc phase in 0.71M solution and pure fcc phase in1.06M solution. The transient curves show two interesting observations. First, the imax increases with increasing concentration of Co2+ ions while the tm decreases with increasing concentration. Second, the imax and tm observed in depositing Co nanowires at -1.6 V in the 0.71M solution are close to those in depositing Co nanowires at -3.0V in the 0.356M solution. A higher imax and shorter tm can represent a larger Ns (saturation nucleus density). Therefore we believe that the deposition at -1.6V in higher concentrations such as 0.71M and 1.067M can lead to a larger Ns, indicating the formation of smaller critical nuclei. The structure of Co can be determined by the critical nucleus size and smaller critical nuclei favor the formation of fcc Co. Therefore the fcc Co nanowires were observed when depositing in the high concentration solution such as 0.71M and 1.067M.The effect of potential on the structure and composition of Co-Ni alloy nanowires is studied by XRD, FE-SEM and EDX. The alloy nanowires deposited at -3.0 V are metastable fcc phase Co84.45Ni15.55. The alloy nanowires deposited at-1.6 V are hep phase Co80.75Ni19.25. The formation of fee alloy nanowires can be attribute to smaller critical clusters formed at the high potential. A higher potential increases the content of Co inside nanowires. This can be understood by the observation that the slope of the linear polarization curve of depositing Co metal is larger than of depositing Ni. |
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