Electrochemical Synthesis of Magnetic Nanostructures for Mutifunctionalization
Compared to the traditional physical vapor deposition or chemical synthesis methods, electrochemical deposition has the advantages of low cost, high yield, low processing temperature and is easy to scale-up. In this study, we aim to reveal the nanoscale electrochemical growth mechanism and develop efficient electrochemical based approaches to produce multifunctional nanomaterials and structures that are difficult to obtain by other synthesis methods. This study focuses on developing electrochemical based nanomanufacturing techniques to synthesize magnetic nanostructures with controllable size, morphology, composition and structure with cost efficiency and scalability. The dissertation includes two research themes: 1) Electrodeposition mechanism study of metallic nanostructure on carbon micro- nano-structure surfaces; and 2) Electrochemical synthesis of non-spherical magnetic nanostructures for bio-medical applications. By combining synchrotron x-ray diffraction/fluorescence and special electrochemical experimental setup design, we demonstrated real time, non-contact and high resolution composition and structure characterization capabilities for electrochemical processes. As an example, we systematically studied the solution concentration, pH value and deposition potential effects on the Ni nucleation, growth, stability and dissolution on the surfaces of carbon micro- and nano-materials. When acidic electroplating solutions are used, the deposited Ni nuclei are found to have strong size dependent instability and can dissolve chemically. This stability also depends on deposition potential; a passivation layer can form under more negative deposition potential which can prevent chemical dissolution and even electrochemical dissolution. At the micron and below dimensions, the substrate surface curvature also shows significant impact on the deposition rate and efficiency when compared to conventional flat substrates. To explore the unique synthesis capability of electrochemical synthesis and application potential of non-spherical nanomaterials, we have fabricated high aspect ratio Fe nanowires with sizes suitable for bio-medical applications. In situ synchrotron diffraction has again been used to provide real time compositional and crystallographic information during electrodeposition. The composition of nanowires with iron at the core and iron oxide at the surface can also be confirmed by TEM-EDS and XPS study. The biocompatibility of the Fe nanowires has been evaluated by using rat-2 fibroblast cells. In summary, through the study of nanoscale nucleation, growth and micro-structure evolution, this research helps to quantify the nanoscale electrochemical process, establish structure-properties correlation and develop novel magnetic materials applications.