以飛秒雷射誘發氧化銦錫薄膜表面之週期奈米點及奈米線結構

Abstract

本研究以飛秒雷射(Femtosecond laser)，在不使用掃描平台及物鏡的情況下，製備大面積自我組裝奈米點陣列(self-organized nanodots)之表面週期結構於氧化銦錫薄膜(indium-tin-oxides, ITO)表面，並進行一連串的表面形貌和光電特性探討。這些週期微結構主要20-500 nm奈米點陣列和多重週期(~800 nm, ~400 nm和~200 nm)的間距所組成。此外，飛秒雷射處理之ITO薄膜具備局部較高的表面導電率，大約是初沉積薄膜之表面電流的30倍，可歸因於雷射照射後形成奈米點於表面。這些奈米點透過分析約為5 nm 高的類銦金屬的叢集(indium-like cluster)。此有效體積的增加歸因於該區域有較高的能量足以打斷ITO原先的In-O和Sn-O鍵結，而形成In-In的鍵結。 另外，透過精確的控制飛秒雷射的能量(fluence)和發數(shot)，可以更進一步的製備兩種不同的表面微結構於ITO薄膜，分別為奈米點陣列和奈米線(nanoline)。經由二維傅立葉轉換圖形(2D-Fourier transformation)的分析，可以確定這兩種結構分別是奈米點和奈米線的週期微結構，並同樣具備多重的週期(~800 nm 和~400 nm)。這兩種週期奈米結構皆在可見光波段具備光學異相性(anisotropic property)，推測該特性和雷射誘發的奈米結構之幾何形狀和銦金屬含量有很大的關聯性。

In this study, large-area surface ripple structures of indium-tin-oxide films, composed of self-organized nanodots, were induced by femtosecond laser pulses, without scanning and an objective lens. The multi-periodic spacing (~800 nm, ~400 nm and ~200 nm) was observed in the laser-induced ripple of ITO films. The local conductivity of ITO films is significantly higher, by approximately 30 times, than that of the as-deposited ITO films, due to the formation of these nanodots. Such a significant change can be ascribed to the formation of indium metal-like clusters, which appear as budges of ~5 nm height, due to an effective volume increase after breaking the In-O to form In-In bonding. Furthermore, two types of periodic nanostructures, self-organized nanodots and nanoline can be easily and reliably obtained by precisely controlling the fluences and numbers of femsecond laser pulses. The multiple periodicities (~800 nm and ~400 nm) were clearly observed on the ITO films with nanodot and nanoline structures and identified by 2D-Fourier transformation patterns. Both of them show the anisotropic characteristics in visible range, which is strongly correlated with the geometry and the metallic content in the laser-induced nanostructures.