Effect of growth temperature on the electrodeposition of zinc oxide layers on diamond surfaces

• The cathodic electrodeposition of ZnO, with dissolved O2 as a precursor, has been tested, for the first time, on boron doped diamond films with bath temperature ranging from 20 °C to 80 °C.
• X-Ray Diffraction, XPS analysis and Scanning Electron Microscopy analysis, have been performed to study composition, crystallinity and morphology of zinc oxide deposits.
• At 20 °C, a thin layer constituted of Zn(OH)2 is evidenced while at T ≥ 40 °C, the diamond electrodes are covered by μm thick ZnO layers, whose morphology and crystallinity depend on bath temperature.
• The formation of a dense and smooth ZnO layer is shown at T = 40 °C while the growth of well crystallized ZnO nanorod-like structures is evidenced for electrochemical process made at T ≥ 60 °C.
• This work demonstrates the opportunity to prepare various ranges of ZnO/BDD heterostructures from a solution route based on the molecular reduction of molecular oxygen in presence of zinc chloride.

The electrochemical deposition of ZnO layers from an oxygenated zinc chloride bath has been realized on Boron Doped Diamond films as substrate for the first time. The influence of the bath temperature has been investigated from 20 °C to 80 °C. Scanning Electron Microscopy, X-Ray Diffraction and X-Ray Photoelectron Spectroscopy, performed on the treated surfaces, show the influence of the bath temperature on the composition, the structure and the morphology of the resulting deposits. For experiments made at 20 °C, a thin and non-covering amorphous layer constituted of Zn(OH)2 is evidenced at the diamond surface. For deposits performed at bath temperatures equal or above 40 °C, the diamond electrodes are covered with a few μm thick ZnO layer. However, X-Ray Photoelectron Spectroscopy analysis suggests the additional presence of Zn(OH)2 at the top surface of the zinc oxide deposits. The morphology and the crystallinity of these 2-D layers depend on the bath temperature. At 40 °C, the film is constituted of big and smooth micrometric grains, while at 60 °C the electrode is covered with closely packed and well crystallized ZnO micrometric rods. Finally, for the bath temperature of 80 °C, the formation of nanorod-like and nanotube-like structures is observed. The main effects of increasing the bath temperature are the improvement of the crystallinity of the deposits, the texturation of the films along the direction perpendicular to the substrate surface and the increase of the deposited quantities.

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