電漿子光學(Plasmonics)是探討表面等離子共振（Surface plasmon resonance, SPR）相關的科學技術，表面電漿子(Surface plasmon polaritons, SPPs)吸引人的特性是可利用次波長結構(subwavelength structure)設計，引導SPPs產生奈米聚焦效應。其奈米聚焦產生高侷限高增益電場，可應用於操控光與物質的相互作用或增強非線性光學現象。在此論文中，我們引入Plasmonics的概念來創建具有高解析度、高增益和高訊雜比的納米光源，通過SPR結構設計，產生打破繞射極限的奈米光源，以期解決現代光學顯微鏡的問題。
近場掃描光學顯微鏡（NSOM）為一種超出繞射極限的光學成像技術，可應用於光譜分析和化學鑑定，但是現代NSOM技術遇到一些基本限制，例如，孔隙型探針(aperture tip, a-tip)的奈米光源特性，為低通量(約為激發光的10-6倍)，空間解析度至(60-100 nm)受到限制；另一種光學探針，無孔隙型探針(scattering tip, s-tip)的奈米光源，壟罩在激發光的照射下，其信噪比（Signal to noise ratio, SNR）下幾乎為零，需利用麥克干涉儀及鎖相放大器等技術，取得近場訊號。我們提出的電漿子探針(plasmonic tip, p-tip)利用SPPs奈米聚焦效應及Fabry-Pérot共振效應，產生無背景光的奈米光源。在實驗上證明光學分辨率為10 nm，空間分辨率為10 nm，通量為3.28％，SNR高達18.2（近乎無背景光源），證明p-tip優於目前的NSOM探針。
接下來，我們擴展尖端增強拉曼光譜（TERS）的應用，該技術是一種新興探測技術，不僅揭示了高分辨率的結構信息，並提供了超出光學繞射極限的光譜影像分析。先前技術是基於間隙模式機制(gap mode configuration)激發並增強拉曼訊號，通過在貴金屬單晶基板和金屬針尖（例如Au和Ag）之間的間隙，產生的強侷限電漿子電場，有效地增強了分子物質的拉曼光譜信號。但是，其侷限電場會因間隙變大以及基板的金屬損耗迅速下降，因此，此間隙模式TERS檢測會受到薄樣品（數個納米以下）以及單晶貴金屬基板的限制。在此論文中，我們展示電漿子探針激發的拉曼訊號(p-TERS)，具有23.4 nm光學空間分辨率和約60000 a.u. 增強訊號，並消除了樣品和基材限制等問題，p-TERS適用於分析原位化學分析以及結構分析，也適用於分析較厚的樣品和非導電性基板。在未來，P-TERS影像應用於研究分子結構或檢測生物系統的詳細化學等信息方面具有巨大潛力。

The field of plasmonics has given rise to surface plasmon resonance (SPR)-related science and technology. The attractive properties of surface plasmon polaritons (SPPs) are the ability to concentrate and channel light in a very small volume using subwavelength structures. Concentrating light in this way leads to an electric field enhancement that can be used to manipulate light-matter interactions and boost nonlinear phenomena. In this dissertation, we employ plasmonics to create a nanosource with concentrated SPs and solve an issue in optical microscopy. We demonstrate a plasmonic tip design with super-resolution, high throughput and a high signal-to-noise ratio. With the plasmonic structure design, the SPs can shrink the nanovolume beyond the diffraction limit.
Near-field scanning optical microscopy (NSOM) is a powerful technique that simultaneously enables optical imaging, spectroscopic analysis and chemical identification beyond the diffraction limit. However, the modern NSOM technique encounters a few fundamental restrictions. For example, for an aperture tip (a-tip), the throughput is extremely low, the lateral resolution is poor, and both are limited by the aperture size; for a scattering tip (s-tip), the signal-to-noise ratio (SNR) of the 0th optical signal is almost zero, so one should use the techniques of Michelson interferometer and locking amplifier to get near field signal. We show that a p-tip supports a radial symmetric SPP excitation and a Fabry-Pérot resonance and experimentally demonstrate an optical resolution of 10 nm, a topographic resolution of 10 nm, a throughput of 3.28%, and an outstanding SNR of up to 18.2 (near-free background). The demonstrated p-tip outperforms state-of-the-art NSOM tips.
Next, we further extend an application in tip-enhanced Raman spectroscopy (TERS), a burgeoning probing technique that not only reveals structural information with high resolution but also provides in situ chemical information of a sample beyond the optical diffraction limit. Based on the gap-mode configuration, TERS efficiently enhances the spectral signals of molecular species via the strong localized plasmonic field produced in the gap between the noble metal substrate and the tip, e.g., Au and Ag. However, the local field rapidly decreases with a large gap and a high-plasmonic-loss substrate. As a result, gap-mode TERS detection is limited to a thin sample (a few nanometers) and a crystal noble metal substrate. Here, we demonstrate plasmonic TERS (p-TERS) with an optical spatial resolution of 23.4 nm and an enhancement of ~60000 a.u. and eliminate the sample and substrate issues. p-TERS is a powerful method for analyzing local chemistry and is also suitable for analyzing thicker samples and nonconductive substrates. P-TERS has great potential for visually characterizing biomolecular structures and detecting detailed chemical information of biological systems.

摘要 I
Abstract II
Acknowledgments III
Table of contents IV
List of Figures VII
List of Tables XVII
Chapter 1 Introduction 1
1.1 Overview of this thesis 1
1.2 Optical measurement 3
1.3 Elastic scattering and inelastic scattering optical measurement 7
1.4 Surface plasmon polariton 10
1.4.1 Nanofocusing of electromagnetic radiation 14
Chapter 2 Principles and Experimental instruments 16
2.1 Imaging quality 16
2.2 Confocal microscopy 18
2.2.1 Diffraction limit 19
2.3 Scanning probe microscopy (SPM) 22
2.4 Scanning near field microscopy (SNOM) 24
2.4.1 Aperture-type NSOM 24
2.4.2 Scattering-type NSOM 26
Chapter 3 Excitation of the Superfocusing SPP mode 29
3.1 Literature review 29
3.2 Design of the optimal plasmonic tip 31
3.3 Theoretical calculation of Lagurra-Gaussian modes in plasmonic tip 33
3.4 Simulation of optimal plasmonic tip 42
3.4.1 Tip shape 42
3.4.2 2D FDTD optimization procedure 42
3.4.3 3D FDTD simulation of the plasmonic tip 44
3.5 Characteristic of the Plasmonic tip 47
3.5.1 The enhancement of the optimal annular structure 47
3.5.2 The optical resolution is defined by tip apex size 48
Chapter 4 Near-Field Plasmonic Probe with Super Resolution, High Throughput and Great Signal-to-Noise Ratio 51
4.1 Tip preparation and experimental procedure 51
4.2 Characteristics of nanosource at the plasmonic tip 55
4.2.1 Throughput measurement 57
4.2.2 Optical resolution 59
4.2.3 Near field contrast of a-tip and p-tip 62
4.2.4 Signal to noise ratio 66
4.2.5 Analysis of near field measurement with plasmonic tip 68
4.3 Conclusion 73
Chapter 5 Plasmonic Tip Enhanced Inelastic Scattering Spectroscopy 75
5.1 Motivation 75
5.1.1 STM-based TERS 76
5.1.2 AFM-based TERS system 77
5.2 Gap-mode-free and background-near-free Plasmonic-Tip design 79
5.3 Comparison among the optimized plasmonic TERS and gap mode TERS 81
5.4 Demonstration of superfocusing on plasmonic tip 86
5.5 Plasmonic tip enhanced inelastic signal imaging 88
5.6 Plasmonic tip enhanced Raman signal imaging 93
5.6.1 Raman enhancement 94
5.6.2 Raman mapping 96
5.7 Conclusion 100
Chapter 6 Summary and Future work 101
Appendix 102
AI.1 Academic publication & patent 102
AI.1.1 Journal Paper 102
AI.1.2 Conference Paper 103
AI.1.3 Patent 105
AI.2 Au Fischer pattern fabrication 107
AI.3 Alignment steps for Witec system alpha 300s 113
Reference 115

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