Study On Multiphoton Photoreduction For The Fabrication Of Metallic Micro/nano Structures

Metallic micro/nano structures are formed through successive chemical and physical reactions of metal nanoparticles or atoms/ions, which finally achieve a shape with the geometry in micro/nano scales. These structures have attracted much attention due to their unique surface Plasmon resonance (SPR) characteristics and their SPR-related applications. Great efforts have been made concerning the fabrication of metallic micro/nano structures, due to the strong dependence of the resonance frequency and strength of the SPR on their geometry, size and surface morphology. However, most approaches are just suitable for the fabrication of simply two-dimensional (2D) structures. The lack of methods for the fabrication of three dimensional (3D) structures has greatly inhibited the new experimental finding in the research of metallic nanostructures, which also limit the potentials of 3D nano-devices applications. Therefore, it is critical important to develop the fabrication techniques for the 3D metallic nanostructures.In this work, we focused on the fabrication of metallic nanostructure. We introduced surfactants into multiphoton induced photoreduction (MPR) process to inhibit the growth of metal particles, which led to nanometer scale fabrication exceeding the light diffraction limit. Furthermore, we investigate the dependence of surface morphologies and continuities of metallic structures on fabrication conditions. We found many unexpected effects in MPR, such as the optical tweezer, thermal and laser ablation effects, which also greatly influence morphologies of metallic structures. These researches may open the way for both the exploration of the optical/electronical properties of 3D metallic structures and the fabrication of micro/nano device in future.The thesis contains six chapters and main points of each chapter are listed as follows:Chapter 1: This chapter covered the background of the research. It reviewed applications and properties of metallic micro/nano structures, microfabrication methods and the principle, characteristics and applications of multiphoton microfabrication. The purpose, significance and contents were addressed in the last part.Chapter 2: Silver microstructures were fabricated in aqueous solution by MPR. Surface morphologies and size dependence of silver structures on the laser power and exposure time was investigated. Moreover, the size and morphologies dependence of silver particles produced in MPR was also explored.Chapter 3: Silver microstructures were fabricated in aqueous solution mixed with fatty salts by MPR. Surface morphologies and size dependence of silver structures on the chain length of fatty salts was investigated. Not only the feature size of the silver structure was reduced but also the surface smoothness was improved by increasing the chain length of the fatty salts. The threshold for the fabrication of silver structures was found by changing the laser irradiation condition. The size of silver structures can exceed the diffraction limit by optimizing the fabrication condition. Furthermore, the mechanism for surfactant assisted MPR was discussed. The dependence of the size of silver dots on the exposure time was simulated by using ions diffusion model.Chapter 4: 1D/2D/3D silver micro/nano structures were fabricated by using n-decanoylsarcosine sodium in MPR. The smallest feature size of silver structures was in nanometer scale. The morphologies and shapes dependence of silver structures on the fabrication condition was investigated. The high temperature and solvent annealing process was also used to modify morphologies of the silver structures. In addition, the electrical conductivity of silver line was estimated by fabricating silver electrodes and silver gratings, which open the way for the investigation of the optical/electronical properties of silver micro/nano structures. Chapter 5: Silver microstructures were fabricated in agarose gel. The morphologies and size dependence of silver structures on the ratio of reagent contents and fabrication condition was explored. The factors for improving the continuity and reducing the size of silver lines was found, which may provided the base for improving the fabrication resolution in gels.Chapter 6: Conclusions of main research results and corresponding future researches were provided in this chapter.