發展平行化三維有限差分時域數值模型以研究金屬鍍膜週期奈米結構

Developing Parallel 3D FDTD Numerical Models for Studying Metal-Coated Periodic Nanostructures

陳薏卉(Yi-Hui Chen)

指導教授 ： 張宏鈞

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2010年)

https://doi.org/10.6342/NTU.2010.01104

摘要

本篇論文發展建立平行化三維有限差分時域法數值模型，並以之模擬研究兩種次波長週期結構其近場光學與反射穿透頻譜。本研究引入Drude-Lorentz模型模擬金屬色散材料，並在計算空間的邊界上以單軸完美匹配層作為散射波的吸收邊界。本研究應用平行標準協定工具OpenMP及MPI(包含阻塞型及非阻塞型通信樣態)，建立平行化的三維有限差分時域法的計算程式碼，以克服計算過程中所需之大量計算時間與記憶體空間問題。利用此程式，本研究計算探討的第一個結構為以表面增強拉曼散射機制作用的生化感測器AgFON結構。為得到較好的表面增強拉曼散射信號，調整結構參數使其反射的相對極小值發生在激發光波長位置。在此情況下，其表面上的電場增強效果較其它結構參數的結果為大。第二個結構為鍍銀次波長抗反射結構的隔熱膜，計算其在正向入射光的情況下的穿透與反射頻譜，發現其金屬表面附近的強電場會使得在穿透頻譜有一相對低點出現，將頻譜分為兩部分：在短波長區有高穿透性，而在長波長區有低穿透性。透過調整結構參數可使這一個低點移至700 nm波長位置，並提高兩頻譜區域的穿透比例以獲得較佳的隔熱膜設計。兩個結構利用有限差分時域法計算的結果均與實驗結果做比對，觀察到不錯的一致性。

關鍵字

三維 ； 有限差分時域法 ； 平行化 ； 金屬鍍膜 ； 週期結構 ； 表面增強拉曼散射 ； 隔熱膜

並列摘要

In this thesis, a three dimensional (3D) finite-difference time-domain (FDTD) numerical model is developed with parallel codes and applied to study the near-field enhancement and the reflectance and transmittance spectra of two subwavelength periodic structures. The Drude-Lorentz model is implemented for a metallic dispersive material into the FDTD algorithm and the uniaxial perfectly matched layer (UPML) is employed as a absorber for truncating the computational domain. For the large computational time and memory in the 3D FDTD method, we make use of different parallel computation methods, which are the Open Multi-Processing (OpenMP), and the blocking and nonblocking message passing interface (MPI) libraries. The first structure studied is the AgFON substrate with silver film deposited over nanospheres, which is applied as a chemical or biological sensor by the surface-enhanced Raman scattering (SERS) mechanism. The optimal structural parameters of the AgFON substrate for SERS application can be identified as the wavelength of the reflectance minimum coincides with that of the given excitation. In that situation, the AgFON substrate possesses greater electric-field enhancement on the surface compared to others with different parameters. The second structure is the periodic antireflection subwavelength structure (ASS) deposited with a silver layer forming a thermal-insulation film. The reflectance and transmittance spectra under normally incident wave condition are calculated. The strong electric fields around the metal surface are found to correspond to a relatively large dip in the transmittance spectrum separating the spectral regions into two parts: high transmittance in the shorter wavelength region and low transmittance in the longer wavelength region. Through varying the structural parameters, including adjusting the wavelength of the dip to 700 nm and enhancing the transmittance ratio of the two parts in the spectrum, the better design for thermal-insulation application is obtained. The FDTD calculated results for both structures are compared with respective measurement results with good agreement observed.

並列關鍵字

3D ； FDTD ； parallel ； metal-coated ； periodic structure ； SERS ； thermal-insulation film

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