奈米天線為在光波段工作、因表面電漿共振所形成的奈米尺度振盪體。而奈米粒子-薄膜為其中一種具有穩定的光學特性以及具有侷域性增強場的奈米天線結構。在奈米粒子-薄膜的結構中，其低階的模態偶極態(dipole mode)為主要表現的模態，具有穩定且區域極小的增強場效應，現今也被應用於近場下與分子的強交互作用。然而，當奈米粒子與薄膜的間距只有幾個奈米的情況下，其高階模態也開始變得較明顯1。在本論文的第一部份工作中，我們探討金奈米粒子-金薄膜奈米天線結構的高階模態。實驗上利用不同偏振態的入射光激發奈米天線以得到奈米天線的散射光譜和在不同波段下的散射影像。經由與實驗室先前的理論結果對照，證實了高階模態的存在並且瞭解奈米天線的模態對於激發光的偏振性是有高度相關性的。此外，藉由理論計算探討改變奈米粒子的粒徑和改變奈米粒子與薄膜的間距，其結果顯示低階模態相較高階模態對於結構尺寸的變化具有較高的敏感性，因此在第二部份工作之中我們探討調變低階模態。
在過去調變的研究中，較常見的改變材料以及改變結構尺寸的方式通常會提高製程所需的流程和時間2，而加入電路來調變奈米天線方式具有較簡易調控且電路可製作於微小尺寸的優點。在本研究中的第二階段，我們探討了不同電路結合奈米粒子-薄膜奈米天線結構後，奈米天線在加入電流或偏壓後對其光學特性的影響。在所有的電路架設中，使用電容的電路使奈米天線受到外部平行電場的影響，在其散射光譜的低階模態散射峰值上出現了6 %的強度變化。我們也藉由有限元素法和實驗探討奈米粒子與薄膜之間的間隔層導電性對其光學特性的影響，導電性越高可能使散射波長更加紅移但散射強度較弱。藉由了解奈米天線的本質特性和電可調性，奈米天線有機會被應用於奈米級的寬頻調變器。

For different kinds of nanoantennas based on surface plasmon resonance, a nanoparticle above a thin film is a structure of nanoantennas with stable and localized enhanced field. The well-known gap dipole mode of the nanoparticle-film structure dominates the optical behavior with stable and localized field enhancement in ultra-small region and has been utilized for the strong interaction with molecular1. However, as the distance between the nanoparticle and the thin film is below a few nanometers, the induced gap dipole mode shifts to the red region of the spectra and the high order (HO) modes become significant 3. In the first topic of this thesis, the HO modes of a gold nanoparticle above a gold thin film with a nanometer scale spacer was investigated. The scattering spectra and scattering patterns at several wavelengths were obtained by far-field optical measurement under different polarized excitations. By comparing the results from experiments with the results from simulations done by previous work, the existence of HO modes is proved. Also, the scattering behavior of HO modes highly depends on the polarization of the excitation. Moreover, through the simulations by changing the nanoparticle size and the spacer thickness, it is found that the gap dipole mode was more sensitive than the HO modes Therefore, the modulation of nanoantennas were also investigated. For previous research in the modulation of nanoantennas, the common methods such as altering the metal material and changing the size of the morphology often take more efforts on the fabrications. Instead, the electrical modulation of nanoantennas is more easily controllable and can be integrated to nano-scale devices. In the second topic of this thesis, the nanoparticle-film were connected with several kinds of circuits to investigate the optical effect on the nanoantenna with a flux of current or external electric field. There was 6 % variation of scattering intensity observed when the nanoantenna was between the electric pads of a capacitor. In addition, the analysis of the finite element method (FEM) and the experimental results of the spacer between nanoparticle-film showed the more red-shift and lower scattering intensity of the conductive spacer. Through the revealing of HO modes and the electro-controllable potential of nanoantenns, it has a potential to be applied to the wide band nano-scale modulator.

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