| Summary: | 碩士 === 國立成功大學 === 光電科學與工程研究所 === 95 === In this dissertation, optical properties of metallic nanostructures are investigated using near-field scanning optical microscopy (NSOM). NSOM is consisted of a shear force atomic force microscope (AFM) with a metal-coated taper single mode fiber as the probe tip. Therefore, topography and optical images of the nanostructure with sub-wavelength resolution can be achieved at the same time.
The metallic nanostructures investigated in this study are fabricated by methods of chemical absorption and high temperature annealing. In the method of chemical adsorbing, the substrate surface was first functionalized with a self-assembled monolayer (SAM) of 3-aminopropyl-triethoxysilane (APTES). Au nanoparticles were subsequently absorbed on the substrate surface due to electrostatic attraction between the nanoparticles and the SAM. The Au absorption density reaches a maximum value after one hour of immersion, which is verified by both absorption measurements and secondary electron microscopy (SEM). The second method is high temperature annealing of a thin metal film. Nanoparticles with different particle size can be obtained by controlling the thickness of metallic thin film. Au nanoparticles with average size of 250、53、24nm and Ag nanoparticles with average size of 138、41、23nm can be obtained by annealing Au and Ag films of thickness of 10、5、3nm are annealed at 9000C for 30min and at 6000C for 30min, respectively.
Finally, transmission mode NSOM images of the metallic nanoparticles reveal that higher transmission occurs when illuminated with light that is on resonance with the localized surface plasmon mode of the metallic nanoparticles, which results in a brighter spot in the image. By contrary, off-resonance light results in a lower transmission intensity, which results in a dark spot in the NSOM image. Therefore, the results strongly support that localized surface plasmon from the metallic nanostructures enhance the conversion of near-field light into far-field light.
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