Metal Nanostructures And Nanoscale ZnO Film Enhanced Emission

During the past several years, the interactions of fluorophores with metallic particles or surfaces have attracted considerable attention in the bio-research and physics optical research fileds. We will refer to conducting metallic structures as metals. A sub-wavelength metallic particle can enhance the local field near its surface. The local fields are increased because the optical cross sections of silver and gold colloids are many-fold larger than their physical cross-sections. These local fields result in increased rates of excitation of nearby fluorophores. As a result the cross-sections for fluorophore excitation can become larger than the possible with far-field illumination. A more important effect occurs for excited state fluorophores which are close to metal surfaces. Interaction of these fluorophores with plasmons on the particle surfaces result in increased rates of emission. A number of important spectral changes, including increases in intensity and photostability, decreased lifetimes due to increased the rate of the radiative decay, and increased distances for Fluorescence Resonance Energy Transfer were found. Published results suggest that by using fluorophore-metal interactions it will be possible to control the migration of electromagnetic energy across and through metal surfaces, and to control when and where the energy is converted back into light.By using the interactions of fluorophores with metallic particles or surfaces, it offers the potential for developing new types of photonic device (such as high efficiency LED) and ultra bright bio-probes. In this paper, on the basic of interactions between fluorophores and metallic particles or surfaces, we will design new structures which include both metal and fluorescence materials, and try to enhanced the emission efficiency of these structures.In chapter1, we reviewed interactions of fluorophores with metallic particles or surfaces, and provided an overview for their mathematical calculation. There are three Classes ofmetal-enhanced fluorescence:metal enhanced fluorescence (MEF), surface Plasmon coupled emission (SPCE) and Plasmon control fluorescence (PCF). It is easier to understand the diverse experiments and the goals of the experiments by using the terms MEF, SPCE and PCF. We also outlined the research content and significance of this thesis.In chapter2, ZnO and ZnO/Ag films are grown on Si (111) substrates by rf magnetron sputtering at room temperature. After annealing, it is found that the ultraviolet (UV) emission of ZnO/Ag films strongly depends on thickness of the initial internal Ag layer. During the annealing process, Ag nanoparticles are formed and diffused into up the ZnO film. The resonant coupling between localized surface plasmons (LSPs) of Ag nanoparticles and ZnO enhances the UV emission. The largest UV enhancement over12times was obtained when the initial internal Ag layer is10nm. It is also observed that the diffusion of Ag nanoparticles destroy the ZnO crystal quality in different grades, depending on sizes of the Ag nanoparticles.The poor crystal quality induces bad UV emission. It is concludes that the UV emission is the result of the competition between the LSP enhancement and the thermal diffusion destroying effect from Ag nanoparticles.In chapter3, the ability of nanoscaled ZnO films to enhance fluorescence was studied. We found that the fluorescence intensity of dyes such as Cy5, Rhodamine6G and Fluorescein can be enhanced about10fold on nanoscaled ZnO films as compare to glass substrates. Lifetimes of all the samples were measured, but no obvious changes in lifetimes were observed for dyes on different substrates. The mechanism for nanoscaled ZnO films enhanced fluorescence is appears to be different from the mechanism for metal-fluorophore systems. Even though the exact mechanism for ZnO enhanced fluorescence was still unknown, what we’ve done can promote the use of ZnO nanostructures as enhanced substrate for fluorescence detection and expand the applications of ZnO nanostructures in biotechnologyIn chaper4, we develop a new class of probes which contain organic fluorophores and metal shells designed to increase the process of both excitation and emission. We are proposing a unique geometry which can position multiple fluorophores between two closely spaced concentric metal shells. The calculations predict over100-fold increases in the rates of excitation and emission for these fluorophores, and thus a10,000-fold increase theoretically in the brightness of a single fluorophore. This research is focused on the central limitations of fluorescence detection, namely the signals available from single probe molecules. The proposed plasmon-fluorophore probes (PFPs) will be useful in most applications of fluorescence including cell imaging and clinical testing. The PFPs will be non-toxic and thus useful for in-vivo animal and possibly human experiments. However, it is sad that we did not get enhanced fluorescence for PFP in real experiment at last. In the last chapter, we provided an overview for the full text and the vision for future.