利用XAS探討氧化釩薄膜(VOx)的氣致色變現象與機制

近年來氣致色變開關設備已被廣泛的研究，在氣體感測器領域中具有優秀的應用前景。氧化釩(Vanadium Oxide)是個眾所皆知的變色材料，然而此類型的智慧材料在氣致色變相關機制與微觀影響的研究已知之甚少。所以本篇論文利用溶膠凝膠法(Sol-gel)製作出一系列不同薄膜厚度與不同退火環境下的新氧化釩薄膜(VOx)，此製程方法具有低成本且可塗佈於大面積底材的優勢。實驗結果得知，不同薄膜厚度不僅僅有著不同的顏色深淺效果，也改變了其光學與電子特性。藉由X光吸收光譜(XAS)的調查結果得知，氧化釩薄膜(VOx)於氣致色變的現象與其原子區域結構和電子結構有著密切關係。薄膜厚度於X光吸收光譜(XAS)分析顯示，氫擴散至薄膜內的深度與其著色過程有著相對關係。隨著通氫著色後在V K-edge中發現有化學位移現象產生，整體釩原子價態改變，由混價的V4.8+下降至V4.1+，且價態變化伴隨著晶體結構扭曲，這些結果是氫氣薄膜於氣致色變特性的關鍵。此外，在In situ XAS實驗中調整氫與氮的比例，發現這些薄膜甚至可降低至V3.5+。吸收光譜顯示退火造成p-d軌道雜交明顯改變，將氧化釩薄膜(VOx)後退火處理進行討論其電子特性與結構扭曲。所以在此提出電子和結構上的修改決定了氧化釩薄膜(VOx)於氣致色變的特性效果。

關鍵字

氣致色變；氧化釩； X光吸收光譜；溶膠凝膠法；氫氣

並列摘要

Gasochromic switching device has been widely studied because of its promising application in the gas-sensing field. Vanadium Oxide is a well-known gasochromic materials. However, the gasochromic mechanism and microscopic effects of these types of smart materials are poorly understood to date. In this study, the new Vanadium Oxide films (VOx) with different layer thickness and post-annealing treatments were fabricated by sol-gel method, which possesses great advantages of low cost and large area substrate coating. Varying film thickness not only results in different gasochromic color but also changes the optical and electronic properties. The investigation of x-ray absorption spectroscopy (XAS) reveals that gasochromic effect of these VOx films is closely related to their local atomic and electronic structure. The analysis of thickness dependent XAS suggests that the coloration processes are correlated with depth of the hydrogen diffusion in the film. The change of vanadium valence during the coloration, obtained by the chemical shifting of V K-edge, is form V4.8+ to V4.1+. The valence variation accompanied by lattice structural distortion is observed and these facts are crucial for gasochromic properties in these hydric films. Furthermore, In situ XAS measurement with adjustable H2/N2 ratio indicates the saturated adsorption of H2 in these films can even reduce the vanadium valence to V3.5+. The significant changes in the p-d hybridization arose from the annealing effect were revealed in XAS spectra. The effects of post-annealing treatments on the electronic properties and structural distortion are also discussed. It is suggested that the electronic and structural modification determines the gasochromic properties of these vanadium oxides films.

並列關鍵字

Gasochromic ； Vanadium Oxide ； XAS ； Sol-gel ； Hydrogen

參考文獻

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國際替代計量

利用XAS探討氧化釩薄膜(VOx)的氣致色變現象與機制

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