Fabrication Of Nanoporous Metals Films And Their Surface Enhanced Raman Scattering Performance

Nanoporous metal films with three dimensional and bicontinuous structure which are fabricated through dealloying is a special kind of porous materials.They are used in catalysis,optics,sensing,energy storage and medical areas due to their high specific areas,uniform porous structure,superior electric conductivity and thermal conductivity.A number of nanoporous metals such as nanoporous gold,nanoporous silver,nanoporous copper and nanoporous nickel have been successfully prepared through dealloying.The fabrication methods and compositions of precursors,and dealloying conditions will significantly influence the morphology of these nanoporous metals.The mostly used fabrication methods for precursors have limited command on elements,and it is hard to get large area and thickness controllable nanoporous films.So it is of grate importance for nanoporous metals to develop new methods to meet specific application requirements.Surface enhanced Raman scattering(SERS)has been applied in chemical and biochemical analysis because it has high sensitivity and can provide vibrational and quantification information of analytes.Enhancement factor is a result of chemical enhancement and electromagnetic enhancement,relying on the interaction of molecules and substrates,and the nanostructures of noble metals' surface.The latter one plays a more important role.Therefore more efforts are devoted to design metal surface structures.Although sensitivity is important for SERS substrates,other properties like reproducibility,stability,uniformity and steps of fabrication methods will influence the application.Nanoporous metal films from dealloying which have been studied for SERS can solve these problems to some degree.But more efforts need to be made to improve sensitivity and stability.And to develop low cost methods for uniformity nanoporous metal film is an important issue for application.In this dissertation,nanoporous copper film integrated on copper foil and freestanding nanoporous silver film were fabricated by choosing metal compositions,adjusting sputtering power and time,changing dealloying conditions.Electron microscopes and electrochemical analysis were used to characterize their nanostructures and surface morphology.SERS properties including sensitivity,reproducibility,stability and uniformity were tested.Finally two kinds of nanoporous metal films with good SERS properties and uniform porous structures were prepared.Detailed contents are as follows.1.Three precursors with atom ratios 75:25,65:35 ? 48:52 were fabricated through controlling Cu and Ti co-sputtering power.The thickness of precursor has a linear relationship with depositing time with an average co-sputtering rate of 11.3 ± 0.2 nm/min.Dealloying was performed in 0.03 M HF solutions.Longer dealloying time leads to larger pore size and smoother surface.The enhancement factor reaches 4.71 ×107,and it can detect R6G molecules with a concentration of 10-9 M.It is the pore size and rough ligaments that have a great influence on SERS performance.2.AgxCu100-x precursors which consisted Ag and Cu nanoparticles on A1 foil were fabricated by Ag and Cu co-sputtering.HCl solution and HNO3 solution were used to corrode Al foil and Cu nanoparticles in precursor films,respectively.And freestanding nanoporous silver films were prepared.The integrity,surface imperfection,flexibility,thickness and pore size control,and morphology of ligaments were all studied here.Besides this,this kind freestanding nanoporous film can detect 10-7 M R6G molecules,with an enhancement factor reaches 5.10×105.Experiments show that the nanoporous silver film has good uniformity and stability.