以基於表面電漿子共振與靜電感應的限制擴散聚集現象來形成銀奈米網絡結構

Abstract

在本篇論文中，我們發展可進一步改善基於熱電子限制擴散聚集現象而形成銀奈米網絡的透明度及導電性之技術。與以前的銀奈米網絡研究相比，我們改變的製程條件如下：（1）使用可見光發光二極體代替紫外光發光二極體來照射氮化鎵基板上的銀奈米顆粒；（2）激發銀奈米顆粒的局域表面電漿子共振以產生熱電子；（3）將濕度提高到接近100％；（4）將銀沉積厚度增加到3-5奈米來形成銀奈米顆粒。與以前的結果相比，新的銀奈米網絡有較低的片電阻，可降低到約140歐姆。而可見光範圍內的漫透射率可高於80％。此外，我們也有一些發現。首先，靜電感應效應在限制擴散聚集現象過程中扮演重要角色。第二，在銀奈米網絡中發現氧成分，因此銀奈米網絡的成分包括銀和氧化銀。氧化銀的形成乃由於周圍的高濕度，這可能使得進一步降低片電阻變得困難。第三，電子穿隧現象可能是熱電子從銀奈米顆粒遷移到氮化鎵基板的重要機制。最後，銀奈米網絡的結構及其透明度和導電性可以通過照明條件來控制。

In this study, we further develop the techniques for improving the transparent conducting behavior of an Ag nano-network (NNW), which is formed based on the concept of hot electron regulated diffusion-limited aggregation (DLA). Compared with the previous NNW fabrication studies, our improved fabrication conditions include the following changes: (1) using visible light-emitting diodes (LEDs), instead of ultraviolet LEDs, for illuminating Ag nanoparticles (NPs) on GaN templates; (2) exciting the localized surface plasmon resonances of Ag NPs for generating hot electrons; (3) increasing the ambient humidity up to a level close to 100 %; and (4) increasing the Ag deposition thickness to 3-5 nm for forming Ag NPs. Compared to the previous results, new NNWs show reduced sheet resistance down to the level of ~140 /square while the diffused transmittance in the visible range is maintained to be higher than or close to 80 %. We also make a few discoveries. First, the electrostatic induction effect plays an important role in the DLA process. Second, the material compositions of an NNW include both Ag and AgO with a varied O content. The AgO forms because of the ambient high humidity. It may make the further reduction of sheet resistance difficult. Third, electron tunneling can be an important mechanism for hot electron migration from an Ag NP into a GaN template. Finally, the structure of an NNW and its transparent conducting behavior can be controlled by the illumination condition. A post-treatment of thermal annealing at a temperature lower than 406 oC does not change the morphology, transparency, and conductivity behavior of an NNW structure. However, when the annealing temperature exceeded 412 oC, the AgO portion in the NNW is evaporated and the conductivity is degraded. The NNW is formed by connecting existing Ag NPs with AgO for becoming a conductive network.