The effects of silver nanoring gaps on surface plasmons.

• Main Authors: Kuo, Meng-Wei, 郭孟偉
• Other Authors: Chen, Sheng-Chung
• Format: Others
• Language: zh-TW
• Published: 2011
• Online Access: http://ndltd.ncl.edu.tw/handle/32421154917023277853

碩士 === 遠東科技大學 === 電機工程研究所 === 99 === We use parallelized Three-Dimensional Finite-Difference Time-Domain Method to analyze the interaction of polarized visible light with a gapped silver nanoring, try to establish a mechanism to control the intensity of surface plasmon. The gapped silver nanoring is constructed from a toroid of which size is 20nm in diameter and the radius of the cross section is 5 nm. The gap is created by removing an arc of 60-degree angle. The double-gapped nanoring has two gaps at opposite positions. Under the polarized-fixed visible light, we turn around the gapped nanoring and calculate the absorption variation with different gap positions. Based on the symmetry of Maxwell’s equations, it is expected that the absorption of the single gapped nanoring should be the same as the gap is at 2, 4, 8 and 10 o’clock. However, under 600nm wavelength, there are only two absorption maxima occurred when the gap is at 2 and 10 o’clock respectively. It might be explained as the excitation of higher order of multipoles, say, toroid multipoles. If the wavelength is changed to 400nm, the absorption is normal except that it has a less absorption when the gap is at 6 o’clock. For a double-gapped nanoring, the results conform to the symmetry of expectation, but the situations of maximal absorptions are quite different with wavelengths. Under 400nm wavelength, the maxima are happened when the gaps are at 3 and 9 o’clock, but it is changed to 6 and 12 o’clock if the wavelength is tuned to 600nm. The reason why the maxima have a 90-degree transformation is because of the coupling effects between two separated arcs. Overall, polarization and wavelength of incident light both have influences on the absorption of gapped silver nanorings, however, the generation of surface plasmon is more sensitive to the direction of polarization.