三維高分子奈米陣列結構之光學性質研究

Abstract

在現代光學系統中如何降低元件表面光線反射並增進光學效率之相關製程技術，始終為研發上重要課題；近年來一種採用3D次波長結構製作抗反射層，以增進材料表面光線穿透並降低反射率之研究頗受重視。本論文採用時域有限差分(finite difference time domain, FDTD)之數值方法分析模擬可見光波段3D次波長結構之抗反射光學特性。繼之於塑膠基材表面以奈米壓印方式製作兩種不同形態之3D次波長結構，並檢驗其光學性質。最後於次波長結構表面鍍製金屬薄膜，製作完成一種具備可見光低反射率及紅外光低穿透率效果之隔熱膜片。於奈米光學模擬研究中發現，結構採尖錐或蛾眼圓錐形狀，當高寬比≧0.8時，在波長250nm~800nm範圍內其反射率均小於1%。實際之結構製作係於PMMA、PC及PET等塑膠材料表面以熱壓印及紫外光固化成型結構。經驗證實作結構之光學性質與FDTD數值模擬結果相當一致。在此類次波長結構表面鍍製金、銀兩種具備3D次波長形狀之金屬薄膜，展現了與一般平面金屬薄膜的不同光學性質。以25nm厚度之銀薄膜為例，3D銀薄膜其反射率由平面薄膜之47.6%大幅降低為10.6%(於入射光波長550nm時)，此結果得以實際對應於隔熱膜產品需求。

The development of coating technique to lower the reflected light and increase the optical efficiency of an optical system is a very important topic for modern optical elements. Recently, the use of anti-reflection (AR) structured surface has been proposed as an applicable alternative based on both the theoretical and the experimental study. In this article, antireflection structured surface was analyzed by the finite difference time domain (FDTD) method in the visible light spectrum and has been successfully fabricated on plastic substrate by nano-imprint process. The optical properties, include transmittance and reflectance were inspected. In addition, two kinds of metal thin films (gold and silver) were coated on the 3-D subwavelength nanostructure surface to examine their optical properties. It was found that the metal-coated AR structures perform well with very low reflectance in visible range and low transmittance in infrared range. This special optical property can be applied in window film to reduce the heat caused by IR absorption. The FDTD numerical calculation was used to analyze the AR structured surface by the designed profile 3-D pyramid and conical structure. Both of the structures showed the antireflection (AR) effect (reflectance<1%) when the aspect ratio of the 3D structure was larger than 0.8. In the nano-imprint process, hot embossing and UV curing process were applied to generate 3D nano-structure on plastic substrate as PMMA,PC and PET. The optical property of the fabricated polymer film showed good agreement with the simulation result. In addition, the metal thin films on 3D nano-structure showed much better optical reflection performance compared with the films coating on the flat PET substrate. It also showed that the reflectance of 25 nm-thick silver film on the moth-eye structure can be decreased from 47.6% ( the reflectance of flat silver film with 25nm-thick ) to 10.6% at the entrance wave length equal to 550 nm. The results are very useful for the commercial application of window film product.