本論文探討奈米結構電致色變(Electrochromic)材料的基礎性質與其應用性。電致色變現象泛指當材料被施加不同直流電壓或電流時，該材料會可逆地改變對光線的吸收度進而呈現不同的顏色變化。本研究首次提出以真空物理氣相沈積方法製備氧化鎢(鉬)奈米線於透明導電基板上，探討氧化鎢奈米線的成長機制並且分析其成分、結構及電致色變性質。

實驗中以依據需求而設計組裝的高真空加熱爐做為成長氧化鎢奈米線的設備，三氧化鎢粉末做為蒸發源，適當地控制製程參數，如工作壓力、加熱溫度及成長時間等，於透明導電ITO基板上成長出均勻分佈的氧化鎢奈米線。接著利用掃描式電子顯微鏡、穿透式電子顯微鏡、XRD、X光能譜分析儀對氧化鎢奈米線進行分析。氧化鎢奈米線為結晶態，其屬於W18O49之斜方(monoclinic)晶體結構，其成長方向為<010>，成長機制為氣相-固相成長，首先在基板表面沈積一層很薄的奈米多晶氧化鎢薄膜，隨後在其突起處藉由氧化鎢氣體分子沈積成長出氧化鎢奈米線。

以循環伏安法、紫外光-可見光光譜儀對氧化鎢奈米線電極進行分析；在1.0M LiClO4/PC電解液中，氧化鎢奈米線在-1.0V(vs. Ag/AgCl)還原為藍色，1.0V(vs. Ag/AgCl)氧化為透明無色，在700 nm下的穿透度變化(□T)為42.6%。施加正負一伏特階梯電位於氧化鎢奈米線電極，同時量測其穿透度變化，計算氧化鎢奈米線的著/去色反應時間分別為1.5 s和0.5s。對氧化鎢米線電極施加-1.0V電位使其著色，隨後切斷電位量測其著色記憶效應，測試時間達五小時候，氧化鎢奈米線電極仍維持一半以上的著色深度。

接著對氧化鎢奈米線在大氣環境下分別施加不同的溫度200℃、300℃、400℃、500℃、600℃進行熱處理一小時，探討熱處理對氧化鎢奈米的結構與光電化學性質的影響。氧化鎢奈米線加熱至500℃並沒有改變其奈米線外觀，但是600℃熱處理將使奈米線結晶遭受破壞。隨著增加熱處理溫度可以提升氧化鎢奈米線電極的電致色變性質，500℃熱處理試片在700 nm的穿透度變化高達65%以上，著色效率為61.3 cm2/C。但是600℃熱處理試片的所有電致色變性質皆下降，歸因於結構產生巨大的變化。次外，對氧化鎢奈米線以著、去色電壓操作，連續10000次，氧化鎢奈米線的著色反應電量仍然維持80％以上，說明氧化鎢奈米線的結構相當穩定。

除了二元氧化鎢奈米線以外，本論文以共同熱蒸發的方式製備三元氧化鎢鉬奈米線於透明導電ITO基板上。利用TEM和XRD分析氧化鎢鉬奈米線，結果顯示每根奈米線均為單晶結構，且為W0.4Mo0.6O3之正交(orthorhombic)晶體結構，其成長方向為<110>。利用EDX-map來觀察W、Mo及O在奈米線中分佈的情況，鉬元素整體是均勻分佈在氧化鎢奈米線中而沒有特別聚集的現象。以循環伏安法、紫外光-可見光光譜儀對氧化鎢鉬奈米線電極進行分析。實驗結果顯示，添加鉬元素於氧化鎢奈米線中，可使奈米線電極的吸收波峰移往高能量的位置，接近人類眼睛對光線最敏感的波長，使得奈米線電極在著、去色狀態有更好的顏色對比

除了一維奈米結構的氧化鎢電致色變材料以外，本研究亦發展一種新的奈米結構電致色變薄膜，即氧化鎢奈米複合薄膜。利用噴塗的技術在透明導電基板表面修飾一層ITO奈米顆粒薄膜，再以電鍍的方法將氧化鎢薄膜附著於修飾層的表面形成氧化鎢奈米複合材料。此種電致色變複合材料具有良好的著色對比及理想的光電調節時間。

本研究實驗結果提供了製備奈米線結構電致色變材料的製程，探討電致色變奈米線的成長機制，分析氧化鎢(鉬)奈米線電極的結構與電致色變性質，並成功證實了氧化鎢(鉬)奈米線商業化應用的競爭潛力。另外，本研究發展一種新的奈米結構電致色變薄膜，即氧化鎢奈米複合薄膜，此種薄膜亦具有良好的電致色變性質，同時其製程簡單，相當適合於工業上的應用。

In this thesis, the fundamental properties and the applications of the electrochromic nanostructured tungsten oxides are investigated. Electrochromism is a reversible phenomenon that some materials change their optical absorbance and exhibit visible color change in response to a dc voltage or current source. In this study, we firstly propose tungsten oxide nanowires, mixed oxide nanowires, and nanocomposite WO3 films fabricated on transparent conducting substrates by different methods, and study the electrochromic properties of these nanostructured WO3.

In experiments, the synthesis of tungsten oxide nanowires was based on thermal evaporation of tungsten trioxide powders under controlled conditions without the presence of catalyst. The structure, morphology, and composition of the WO3-x nanowires were characterized using SEM, TEM, XRD, Raman spectroscopy and XPS and the electrochromic properties of the nanowires layer under lithium intercalation was studied in detail by UV-VIS-NIR spectroscope and cyclic voltammeter. The tungsten oxide nanowire grows along the direction <010> and nearly perpendicular to the ITO substrate, and is W18O49 monoclinic structure. The growth mechanism is thought to be the VS mechanism (vapour-solid process) which tungsten oxide vapor was continuously generated from the source during the heating process, the vapour- solid phase transition took place as soon as the vapour reached to the ITO substrate. The electrochromic WO3-x nanowires shows cathodic coloration and considerable transmittance difference in the visible spectrum range, with a maximum value of T = 42.6 % at 700 nm. The coloration and bleaching time of the WO3-x nanowire film are 1.5 s and 0.5 s, respectively.

The effect of thermal annealing on the electrochromic properties of the tungsten oxide nanowires deposited on a transparent conducting substrate was investigated. The X-ray diffraction indicated that the structures of the nanowries annealed below 500 ℃ had no significant change. The X-ray photoelectron spectroscopy analysis suggested that the O/W ratio and the amount of W6+ ions in the annealed nanowire films could be increased as increasing annealing temperature. Increased annealing temperature could promote the coloration efficiency and contrast of the nanowire films; however, it could also affect the switching speed of the nanowire films. In addition, the cycle life of the annealed tungsten oxide nanowire is up to 10000 times with no significant decay.

The tungsten-molybdenum oxide nanowires were also synthesized on the ITO coated substrate by co-evaporation of tungsten oxide and molybdenum oxide powders. The TEM and XRD analysis indicate that the mixed oxide nanowires is the W0.4Mo0.6O3 orthorhombic structure with a preferred growth direction <110>。The absorption band of the mixed oxide nanowires shifts to near the maximum of the spectrum of human eye sensitivity. The higher coloration efficiency is obtained, due to increased electron transitions between the two kinds of metal sites with different valences (W6+, W5+, Mo6+, and Mo5+).

In addition to the tungsten oxide nanowires, a new nanostructured electrochromic material, nanocomposite WO3 (NWO) film, was also developed. The NWO films were fabricated by a spray and electroplating techniques in sequence. An ITO nanoparticle layer was employed as a permanent template to generate the particular nanostructure. The NWO films showed an improved contrast with compatible bleach-coloration transition time, owing to the larger reactive surface area.

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