寬頻超穎材料吸收器:模擬與實驗

Abstract

近年來，高效能超材料寬頻吸收器被廣泛地研究並用於各種領域。透過超材料的設計，調整元件在各波段之參數，可使其最大之吸收能力，然而，寬頻高效能的吸收通常倚賴各種表面形狀的設計，然而在已提出之錐形結構中，其反覆的黃光及蝕刻製程十分曠日廢時，因此垂直側壁之結構相對受青睞，然而此情形下，寬頻的吸收範圍仰賴表面形貌的設計，不規則排列表面會是個可行的方案，但為了驗證某些結構是否可行，初步的模擬計算為一浩大工程，有鑑於此，本研究提出實驗型基因演算法用以直接求取最佳化表現之結構，此方法略過使用模型模擬的過程而直接用實驗求取結果，並透過人為選取直接產生下一個可能具有高效能之結構，從實驗中，此方法獲得22%的效率提升；同時，本研究亦提出另一個平面結構，此結構利用多層的金屬以及介電材料的交替沉積，使入射的光具有滲透及散射現象藉此達到高效率以及寬頻吸收的特性，由於黃光及蝕刻製程在此結構中皆不需要，因而省下了大量的時間；除此之外，此論文也嘗試利用碳米碳管作為吸收層材料，利用奈米碳管和共振腔結構的結合改善元件厚度過大的疑慮，構建出相對輕薄同時兼顧特性的元件。

Hyperbolic metamaterial (HMM) absorber is widely investigated recently. However, the proposed tapered structure needs repeated lithography and etching steps, which are very time-consuming. As a result, several methods are proposed to deal with this problem. Firstly, straight-sidewall structure is utilized whose performance mainly depends on pattern design. Random pattern is preferable to realize broadband and high absorption. Nevertheless, simulation on random pattern is time-consuming. Consequently, experiment genetic algorithm is proposed to conduct the optimization process directly in this study. Secondly, planar field-penetration structure can also be a potential solution method. Multiple metal-dielectric stacking is utilized to accomplish the high absorption and broadband absorption. The proposed structure is fabricated without any lithography and etching steps. Time and cost needed for fabrication is thus decrease. Thirdly, constructing a perfect absorption layer through electrophoretic deposited (EPD) carbon nanotubes (CNTs) are also demonstrated in this study. The combination of the CNT layer and a resonant cavity is proposed in this study. Experimental result confirms that the excessively large thickness issue, associated with past vertically aligned CNT ideal blackbodies, can be resolved while the broadband absorption is still maintained.