Effect of Co2+ concentration on the crystal structure of electrodeposited Co nanowires

Abstract

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 in 1.06M 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 −1.6V 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 0.71 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 0.71 and 1.067M.