Study on the fabrication and application of core shell nanostructure by nanoimprint lithography and electrodeposition

Abstract

Direct application of nanostructures into devices and systems has been limited because of low func-tional efficiency, poor mechanical and chemical reliability, and low manufacturability. In this work, we introduce new nanomanufacturing methods that combine top-down nanofabrication (nanoimprint lithography) and bottom-up nanofabrication (local electrodeposition of nanostructures) processes to address these issues. Various novel nanostructures are proposed as high performance photocatalysts, piezoelectric nano-generators and anti-oxidation transparent electrodes by using nanoimprint lithography and electrodeposition processes. First, periodic arrays of silver/titanium dioxide ($Ag/TiO_2$) open core-shell nanowires have been developed as flexible and strong plasmonic photocatalysts. Nanoimprint lithography, oblique thermal evaporation of Ag thin film and selective electrodeposition of $TiO_2$ thin film are used to fabricate a uniform and periodic array of $Ag/TiO_2$ core-shell nanowires with a dramatic enhancement in the plasmonic behavior. The improved photocatalysis functionality is investigated by numerical simulation and photocatalytic measurement. Moreover, the mechanical bendability and repeatable photocatalytic activity due to the mechanical robustness of $Ag/TiO_2$ core-shell nanowire array are verified. Second, strongly adhesive metal electrodes have been fabricated by the metal deposition on the nanoimprinted polymer substrate, followed by a selective electrodeposition of piezoelectric ZnO nanowires on the nanostructured metal electrodes. The nano-textured surface of metal electrodes enhances the adhesion with ZnO nanowires. The adhesion properties of nanoimprinted metal electrode are investigated by bending and accelerated test. Pull-off forces of various patterned interfaces have been simulated to study the effect of geometries on the adhesion characteristics. Furthermore, the piezoelectricity of ZnO nanowires electrodeposited on the surface of nano-textured metal electrodes has been investigated. Lastly, an anti-corrosion method for the Ag nanowire based transparent electrode by Ni electrodeposition is introduced for the chemical-resistive and durable electronic applications. We have verified that the formation of Ag/Ni core-shell nanostructures can dramatically improve the anti-oxidation and anti-sulfurization performance of Ag nanowire-based transparent electrodes. Also, anti-corrosion mechanisms of Ni coated Ag nanowires are analyzed by the surface characterization techniques for the samples after exposure to harsh environment.