Trans-scale metal nanostructure synthesis using electrochemical deposition and its applications

Abstract

In this thesis, a combinational way of top-down lithography and bottom-up electrochemical deposition was presented to implement novel nanostructures and various applications were studied from biosensor to transistor. As a primary study, patterned arrays of flower-like gold nanostructure (Au nanoflower) with various features were fabricated over large areas by photolithography with electrochemical synthesis. This combined top-down and bottom-up approach eliminated the significant drawbacks encountered with conventional bottom up techniques. The effects of the applied voltage, the concentration of the $HAuCl_4$ solution, and the initial Au pattern size on a nanoflower array were investigated. The results showed that the Au nanoflower array can be constructed according to different requirements. Electrochemical experiments clearly implied that the Au nanoflower array electrode exhibits excellent electrochemical sensitivity and capacitance. In a second phase, the Au nanoflower was investigated as a template of surface-enhanced Raman spectroscopy (SERS). The correlation of the length of the electrodeposition time in the fabrication of the Au nanostructure with the SERS enhancement was analyzed. High-quality SERS spectra were obtained for various molecules. This work showed that Au nanoflower array and its strong SERS enhancement can be implemented onto a lab-on-a-chip-based total analysis system for label-free chemical and biomolecular detection processes. The unique 3-dimensional geometry of the Au nanoflower was also applied to neuroscience for neural electrode engineering. The nanoflake-modified electrodes were fabricated by combining conventional lithography and electrochemical deposition to implement a microelectrode array (MEA) on a glass substrate. The unique geometrical properties of nanoflake sharp tips and valleys were studied by optical, electrochemical, and electrical methods in order to verify the advantages of using nanoflakes for neural recording devi...