奈米尺度光與物質作用之增益和控制Part 1: 自組裝金奈米粒子表面增益拉曼效應之比較研究Part 2: 電漿奈米電路中模態之轉換

Abstract

Surface enhanced Raman spectroscopy (SERS) has ultrahigh sensitivity and is now wide used. SERS makes use of rough metal surfaces or metallic nanoparticles to enhance the Raman scattering of a specimen. However, the mechanism of the enhancement effect is still open to question. Thus, in the first part of the thesis, we try to study and compare the SERS signals from thiophenol molecules attached to self-assembled gold nanoparticles with distinct shape, size and facet. We also make an assumption to explain the experimental data from the aspect of electromagnetic theory by analyzing the near-field intensity of gold nanoparticles and chemical effect by calculating the surface area of gold nanoaprticles and binding energies of thiophenol molecules adsorbed on different crystal facets. We discovered that rhombic dodecahedron gold nanoparticles with facet have the largest Raman scattering intensity and the comparative SERS intensities predicted by theoretical calculations also consist with the experimental data. This research provides a criterion of choosing SERS-active substrates hereafter. Besides, for the sake of controlling the interaction between light with matter, we propose and design mode converters in a plasmonic nanocircuit by manipulating the phase of surface plasmon on TWTL to achieve passive or active control of the guided modes and then it is capable of controlling the impedance of the optical field. Hence, it offers the possibility to handle nanoscale light-matter interaction. The mode conversion transforms successfully at will between transverse magnetic (TM) mode and transverse electric (TE) mode by means of differing in the path length or cross section between two wires as well as the surrounding refractive index. To realize the mode converters and monitor the optical phenomena, I build up an optical system containing a home-made confocal laser scanning microscope and a near-field scanning microscope.