Fabrication Of Ordered Microstructures Templated From Porous Polymer Films

Functional nanomaterials have attracted a great deal of interests due to their unique properties and potential applications in optical devices, microelectronics and biosensors, and so forth. A variety of methods have been developed for fabrication of ordered microstructures of different materials including traditional photolithography, scanning e-beam lithography, scanning probe lithography, etc. Each of these methods has their own advantages and shortages in preparing ordered microstructures with respect to the precision, repetition, productivity and cost, etc. Template-assistant strategies have attracted more and more attention as it is simple, productive, and low-cost. Many kinds of periodical structures have been used as templates commonly, such as, the porous anodic aluminum oxide (AAO), colloidal crystals self-assembled from monodispersed colloidal microspheres, and microstructures obtained by microphase-separated of block copolymer, etc. The combination of these periodical structures as masks and deposition, etching, a series of ordered patterns could be fabricated on the substrate. In this paper, we prepared porous polymer films by microcontact printing technique, and investigated the effect of thermal degradation of polymer on pattern morphology. Then, utilizing the porous polymer films as structure-directing template, many ordered microstructures of metal and oxides were fabricated.In chapter 2, we prepared PVA porous films with circular openings by microcontact printing technique, and then the as-prepared PVA porous films were annealed at different temperatures. When the temperature is higher than the starting thermal degradation temperature of PVA, the pore morphology changed obviously from circular to noncircular, and finally polymer films with polygonal pore shape were achieved. The pore pattern transformation from circular to noncircular is driven by thermal degradation of PVA. According to the experimental results, we supposed an explanation that when treated at temperatures higher than the initial thermal degradation of PVA, diminishing of polymer content together with volume shrinkage result in the diameter of openings increased, extrusion of the adjacent pores should cause shape transformation from circular to polygonal. By tuning the geometry lattice of the original PVA porous films, square or hexagonal pore shape was achieved. Furthermore, inorganic network structures of functional materials were fabricated using pattern transformation process driven by thermal degradation of PVA. By mixing different decomposable functional precursors with PVA and using polymer matrix as structure-directing agent in the following pyrolysis process. The organic components of hybrid film were removed by calcinations and finally inorganic polygonal networks were left on the substrate.In chapter 3, hybrid polymer porous films were prepared by microcontact printing technique by adding HAuCl4 to PVA. The as-prepared hybrid porous polymer films were treated with O2 plasma for several minutes to make the pore throughout to the substrate prior to annealing. This makes the HAuCl4 in the bottom of the pore etched away. Polymer matrix was removed by calcinations and finally gold nanoring arrays were formed on the silicon substrate. Increasing the time of O2 plasma etching, gold network structures were formed. According to the experimental results, ring or network structures depending on the spacing between the adjacent pores of polymer porous films formed. We supposed an explanation to these results, during the process of pyrolysis, decompose of HAuCl4 results in the metal gold generated together with HC1 and Cl2 gase. The phase separate between gold nanoparticles and polymer promote the metal gold nanoparticles acces to the interface between porous films and atmosphere and enrich in there, which make the pore deformation become difficult. With degradating of polymer content, the diameter of pore increased. When the spacing between the adjacent pores larger than the pore expanding, ring structures formed, while the spacing is smaller, the adjacent wall of ring encountered with each other and melted into one, then network structures formed. According to this explaination, we could selectively fabricate the ring structures arrays of different functional materials on the substrate.In chapter 4, we prepared porous PVA films by microcontact printing technique and then the porous films were annealed at 325℃for 3 h. Ulitilizing the annealed porous polymer films as masks, gold thin films were evaporated on them and polymer/gold bilayer films formed. Polymer templates were removed via a calcinations process, and finally gold particle arrays were fabricated on the silicon substrate. Decreasing the thickness of gold thin film evaporated, binary particle arrays were obtained, while increasing the thickness of gold thin film evaporated, circular aperture structures in gold films formed. By tuning the titled angle of evaporation of gold, crescent-shaped aperture structures could also be prepared. Due to the localized surface plasmonic resonance, these gold microstructures will find application in the fields of enhanced spectroscopy and biosensors, etc.