Daniel Ramírez

New insights on the doping of ZnO films with elements from group IIIA through electrochemical deposition

This study was focused in the electrodeposition of both compact and nanostructured extrinsic n-type doped ZnO films, which was achieved with aluminum, gallium, and indium. These elements were directly added into a Zn(II) rich electrolyte with molecular oxygen acting as an oxide precursor in aqueous perchlorate media. This way, the use of nitrate ions, whose by-products are accumulated in the aqueous electrolyte, and chloride ions, an electrically active element in ZnO, was therefore avoided. Speciation diagrams, conditional solubility diagrams and a potentiodynamic study were used to explain the way in which extrinsic n-type ZnO can be prepared by electrochemical deposition. Relatively compact films with a highly preferred orientation along the c-axis were suitable for impedance measurements, thus allowing the measurement of their doping levels. Al- and Ga-doped lamellar nanostructures were successfully prepared when the nature of the anion was changed from perchlorate to sulfate. Under specific conditions, the structure of these films changed from opened and isolated nanosheets to interconnected ones. Morphological, optical, and crystallographic properties of these films were also analyzed. Results and discussion presented here should provide a better understanding toward the study of alternative materials in fields such as photovoltaics and photocatalysis.

Electrodeposition of ZnO from DMSO solution: influence of anion nature and its concentration in the nucleation and growth mechanisms

The influence of the anion nature and its concentration in the electrodeposition of ZnO onto a gold electrode from dimethylsulfoxide (DMSO) solutions was studied. Voltammetric experiments revealed important changes in the zinc oxide electrodeposition process depending on the employed anion as electrolyte. From chronoamperometric experiments, the corresponding current-time curves were fitted with different nucleation and growth mechanism models. The analysis of these results showed changes from an instantaneous to a progressive growth when the solution composition was changed from ZnCl2 to ZnCl2 + LiCl. The change of the mechanism is associated to the adsorption of chloride ion on the active sites of the electrode surface when LiCl is present in the solution.