奈米結構氧化鎢之電致色變特性研究

Electrochromic property of nanostructured tungsten oxide

廖家慶(Jie-Qing Liao)

指導教授 ： 開執中 ； 陳福榮

國立清華大學/原子科學院/工程與系統科學系/博士(2007年)

摘要

無資料

關鍵字

電致色變 ； 氧化鎢奈米線 ； 氧化鎢鉬奈米線 ； 熱處理 ； 氣相-固相成長 ； 記憶效應 ； 奈米複合薄膜 ； 噴塗技術 ； 電鍍方法 ； ITO奈米顆粒

並列摘要

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.

並列關鍵字

electrochromism ； tungsten oxide nanowires ； tungsten-molybdenum oxide nanowires ； annealing ； vapor-solid growth ； memory ； nanocomposite WO3 films ； spray ； electroplating ； ITO nanoparticles

參考文獻

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