Controlled morphology evolution of ZnO nanostructures in the electrochemical deposition: From the point of view of chloride ions

A systematic study of the influence and mechanism of chloride ions on the morphology of ZnO nanostruc-tures in nitrate electrolyte by electrochemical deposition was performed. The concentration of Zn(NO₃) ₂remained constant, and the additional KNO3and KCl were added to modulate the effect of chloride ions.Scanning electron microscopy graphs revealed that the effect of chloride ions on ZnO nanostructuremorphology was not only dependent on the concentration of chloride ions, but also relied on the concen-tration of hydroxide ions. When the concentration of hydroxide ions was low, the adsorption of chlorideions on the ZnO (0 0 0 1) surface played a dominant role and promoted two dimensional growth of ZnO.When the concentration of hydroxide was increased to high level, enough hydroxide ions gave rise tothe faster deposition rate of ZnO under the same concentration of chloride ions, especially growth ratealong c-axis due to polar nature of ZnO. The high density one dimensional nanostructure was achieved. Inthis case, the adsorption of chloride ions caused flat top surface of nanorods. Morphology evolution fromdense film to nanorods or nanotowers would be achieved by altering the concentration KCl and addi-tional KNO₃, which is a simple method to control the morphology of ZnO nanostructures for abundantapplication.