Electrochemistry has been used to deposit zinc oxide in track etched polymer membranes and to monitor the composition of the reaction solution during hydrothermal growth of zinc oxide nanostructures on seeded substrates. This presentation will consider the advantages and disadvantages of the two techniques.

Electrodeposition in a track etched polymer membrane involves two steps; (i) electroreduction of either hydrogen peroxide or nitrate ions to alter the local pH within the pores, (ii) precipitation of the metal oxide within the pores. Synthesis at 25⁰C via the reduction of hydrogen peroxide yielded polycrystalline zinc oxide nanorods. When deposition was performed at 90⁰C, using the reduction of nitrate to control the local pH, zinc oxide nanorods which displayed the same growth direction along their entire length were obtained. The length of all as-grown rods increased with the integrated charge passed. The growth direction of the ZnO rods obtained at the higher temperature was unusual, being perpendicular to the (1,0,1(bar), 1) plane.

The immersion of a material, seeded with ZnO nanoparticles, in an aqueous solution of Zn(NO₃)₂ and hexamethylenetetramine (HMT) at 90⁰C yielded an extended array of one-dimensional ZnO on the substrate surface. The structure of the ZnO evolves with reaction time. Initially nanorods are formed. At longer times the rods are tipped with nanotubes. Here we report a series of experiments in which both the composition of the reaction solution; concentrations of H⁺, Zn²⁺ and HMT; and the structure of ZnO deposited on the substrate are monitored as a function of reaction time. It is shown that the change from ZnO rod to tube growth arises when the solution composition is such that it is no longer thermodynamically favorable to precipitate Zn(OH)₂.

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