Electrochemically structured tantalum surfaces via anodization for core-shell nanostructures: Optimization and characterization of Zn-ZnO nanoparticle deposition using magnetron sputtering

This study explores the electrochemical anodization of tantalum surfaces to create nanostructured substrates for the deposition of Zn-ZnO nanoparticles (NPs) through magnetron sputtering. The anodization process, conducted at different potentials (25 V and 50 V), resulted in tantalum surfaces with distinct dimple structures. The formation of these nano-level dimples is attributed to the dynamic equilibrium between the continuous formation and dissolution of the anodic TaOx layer. The dimple diameter is observed to increase with applied potential, correlating with the dissolution rate of the anodic oxide. The NP deposition parameters were studied in two steps. First, the effect of the deposition conditions on the nanoparticle size and distribution was evaluated and optimized on silicon substrates. Second, the conditions that resulted in the optimum size and distribution of the nanoparticles were utilized in tantalum substrates and evaluated to which extent these conditions were reproduced onto the anodized Ta substrate. Comparisons of Zn-ZnO nanoparticle depositions on silicon and tantalum substrates reveal similar island growth trends, with differences in nanoparticle size and distribution attributed to substrate properties. Further investigation involves anodized tantalum substrates with varying dimple sizes, and deposition conditions are adjusted with bias voltage, pressure, and deposition time to control nanoparticle characteristics. Characterization of the Zn-ZnO nanoparticles deposited on anodized tantalum surfaces is performed using scanning electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, and energy-dispersive x-ray spectroscopy. The resulting core-shell structures are confirmed through structural analysis, revealing a core of hexagonal close-packed Zn and a shell of ZnO. The study demonstrates the influence of substrate properties and deposition conditions on the morphology and composition of Zn-ZnO nanoparticles, providing insights for applications in nanoelectronics and catalysis.