The Influence of Subwavelength Grating Profiles to Surface Plasmon Resonance: Development of Nanowriter Optical Head and Related Applications

光柵耦合為激發表面電漿共振的一種主要方法，本論文基於Ebbesen等人所提出由表面電漿共振引發之異常穿透現象，針對不同材質及表面輪廓形狀的光柵進行研究，以了解其改變對於產生表面電漿共振之影響。並且利用在此研究的發現，期盼能對於奈米直寫儀光學頭的設計及其他相關應用上作出貢獻。 本論文在模擬方面，以嚴格耦合波分析及有限時域差分法計算光柵耦合表面電漿時的反射頻譜及電磁場模態，並且求出不同表面輪廓光柵下的表面電漿色散曲線及耦合效率，我們認為非金屬表面光柵可以視為一等效介質層來處理，而對於金屬表面光柵，我們發現漸變式光柵的表面電漿共振條件異於二維光柵，故在不同光柵深度下，光柵的耦合效率及能隙寬度會有所不同，且在不同波長的入射光之下，電磁場強度的分佈會有所不同，經由以上模擬我們順利得到設計奈米直寫儀光學頭或相關光電元件時的參考資訊。 在實驗方面，則使用電子束微影法製作漸變式光柵，並且配合相關製程可製作金屬及非金屬表面光柵，進而討論奈米直寫儀光學頭之製程。並且配合溼蝕刻方式製造三角形奈米壓印母模，以增加使用奈米壓印技術來製造奈米直寫儀光學頭或其他相關應用之可能性。Grating coupling is a major method to excite surface plasmon resonance; this thesis took the extraordinary transmission phenomenon first proposed by Ebbesen et al. as the starting point to study gratings of different materials and various profiles in order to understand the influence of these changes on surface plasmon resonance. It is anticipated to utilize parameters learned during the course of this research to facilitate the design of nanowriter optical head and other related applications. In simulations, we use rigorous coupled wave analysis (RCWA) and finite difference time domain (FDTD) to calculate the reflection spectrum and electromagnetic mode of surface plasmons, both of which is coupled by using gratings. The surface plasmon dispersion curve and coupling efficiency under different grating profiles were successfully calculated. We consider the non-metal surface gratings as a homogeneous dielectric layer by using effective medium theory. For metal surface gratings, we found the surface plasmon resonance condition of gradient gratings is different to binary gratings, thus the coupling efficiency and band gap width of gratings under different grating depths will be different. The distribution of electromagnetic field under different wavelength of light will be different. More specifically, the coupling efficiencies and band gap width under different grating depth were found to be different. We can obtain the design criterion of optical head and other optical devices through the above simulations. In experiments, we use electron beam lithography to make the gradient gratings, and produce metal and non-metal surface gratings with proper fabrication process. The fabrication process of nanowriter optical head was then detailed. We also take advantage of wet etching to manufacture the triangular nanoimprint mold with an attempt to reach the mass production goal of nanowriter optical head and other applications by using nanoimprint techniques.Table of Contents 謝誌 I 摘要 V Abstract VI Table of Contents VIII List of Figures XI List of Tables XVI CHAPTER 1 Introduction -1- 1.1 Preface -1- 1.2 Research Background -1- 1.3 Motivation -5- 1.4 Thesis Organization -6- Chapter 2 Literature Review -9- 2.1 The Limit of Traditional Optics -9- 2.1.1 The limitation of diffraction limit -9- 2.1.2 Development and restrictions of near field optics -12- 2.2 Related Paper Review -14- 2.2.1 Extraordinary transmission phenomenon -14- 2.2.2 Directional beaming effect -18- 2.2.3 Debates of the physical mechanism -20- 2.3 Physical Mechanism of Extraordinary Transmission -23- 2.3.1 New explanation of Ebbesen group -23- 2.4 Nanoimprint Lithography -26- 2.4.1 Introduction of nanoimprint -26- 2.4.2 Triangular imprint molds -27- 2.4.3 Nanoimprint and the development of nanowriter -28- 2.5 Photonic Crystal -30- 2.5.1 Introduction of photonic crystal -30- 2.5.2 The beaming effect of photonic crystal waveguide -30- Chap 3 Theory -32- 3.1 Surface Plasmons -32- 3.1.1 From plasmons to surface plasmons -32- 3.1.2 The theory of surface plasmons -33- 3.1.3 The method to excite surface plasmons -35- 3.2 Introduction of gratings -39- 3.2.1 Reflection gratings -39- 3.2.2 The influence of grating profiles to diffraction efficiency -40- 3.2.3 Surface plasmons on gratings -40- 3.2.4 Energy gap of surface plasmons -41- 3.3 Subwavelength Gratings -44- 3.3.1 Analysis of subwavelength structures -44- 3.3.2 Brief introduction of RCWA -47- Ch.4 Simulation -49- 4.1 Optical Properties Simulated by RCWA -50- 4.2 Simulation Results of RCWA -52- 4.2.1 Simulation results of non-metal surface relief gratings -52- 4.2.2 Simulation results of metal surface relief gratings -53- 4.3 Simulations of Surface Plasmon Mode by FDTD -67- Chap 5 Experiments -73- 5.1 Experiment Purpose -73- 5.2 Fabrication of Gradient Gratings -73- 5.2.1 Experimental procedures of e-beam lithography -73- 5.2.2 Fabrication of gradient surface grating by e-beam lithography -77- 5.2.3 Fabrication by holographic lithography -83- 5.3 Fabrication Methods of Optical Head -86- 5.3.1 Double-sided metal optical head -86- 5.3.2 Single-sided non-metal optical head -88- 5.3.3 Fabrication of non-metal optical head by nanoimprint -90- 5.4 Experiment Results -93- 5.4.1 Fabrication of double-sided metal optical head -93- 5.4.2 Fabrication of single-sided non-metal optical head -97- 5.4.3 Fabrication of nanoimprint mold by wet etching -100- 5.5 Verifications of Simulation -104- 5.5.1 Experiment of reflectance spectrum -104- 5.5.2 Experiment of beaming angle -106- Chapter 6 Conclusion and Future Works -110- 6.1 Conclusion -110- 6.2 Future Works -113- References -114