多層奈米結構表面對表面電漿子耦合之影響： 奈米直寫儀光學頭耦合能量增強之設計與研製

Abstract

本論文以Ebbesen於金屬薄膜表面次波長週期性孔洞陣列上所發現的能量異常穿透現象與指向性現象作為研究基礎，嘗試在玻璃基材表面製作出具有雙面結構的金屬光學頭。藉由光學頭入射面結構激發之表面電漿子，增加入射光與光學頭間的能量耦合效率，以提升光學頭之穿透能量強度；並將傳遞於金屬表面之表面電漿子能量利用射出面結構重新耦合回光波，以特定之指向角度向外射出。以期在遠離光學頭一個波長之外的距離，仍能保有次波長光點之聚焦能力。 論文中首先以嚴格耦合波理論，建立出一套光學頭結構參數之設計流程，並利用有限時域差分法模擬表面電漿子於次波長結構表面產生能量耦合時，電磁場在幾何結構上的共振現象，進而與嚴格耦合波理論作相互之驗證。最後並設計出符合實際情況，具有玻璃基材之最佳化金屬光學頭。 於實驗上，則提出兩種使用電子束曝光技術製作光學頭的步驟程序，嘗試以簡化的製程，製作出兼具高能量耦合效率與指向性的雙面結構金屬光學頭。並於論文最後，實際觀察雙面結構金屬光學頭的穿透光行為，作為理論與模擬結果之最佳驗證。

This dissertation exploits the extraordinary transmission and directional beaming phenomena of periodic subwavelength hole array on a thin metal film first observed by T.W. Ebbesen and tries to fabricate a metallic optical head with periodic subwavelength structures on both sides to maintain a subwavelength spot size in the far field. Structures on the incident surface exciting surface plasmon on the interface between metal and dielectric enable us to improve energy coupling from incident light and enhance transmission of optical head. Structures on the exit surface recouple the surface plasmon propagated on metal surface back to free space while propagating the exit light beam at a specific angle. Using RCWA (rigorous roupled wave analysis method), a parameter design flow of optical head has been established. Using FDTD (finite different time domain method), analysis of geometry resonance on the structures has also been proposed. Follow the parameter design flow developed, structure configurations of a metallic optical head with glass substrate were decided for fabrication. For experimental needs, two E-beam lithography processes were developed to fabricate the double sides structures metallic optical head with an attempt to achieve both enhanced transmission and directionality. Last, observation of actually transmission behavior was obtained to verify the validity and agreement between simulation and experiment.