分子束系統架設;The Building of the Molecular Beam System

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题名:	分子束系統架設;The Building of the Molecular Beam System
作者:	廖庭偉;Ting-Wei Liao
贡献者:	物理研究所
关键词:	分子束;表面形貌探測;金奈米粒子;molecular beam;morphology;gold nano-clusters
日期:	2012-01-05
上传时间:	2012-06-15 20:27:16 (UTC+8)
摘要:	我們建立一套超高真空分子束系統，其中包含樣品製備設備、脈衝分子束源及其腔體、散射及反應腔體(主腔體)、氣態偵測器及其腔體。本系統引入差壓抽氣系統，藉此使主腔體之氣壓不會因脈衝閥作用而影響。除了系統之架設外，我們同時將本系統之分子束最佳化及樣品位置最佳化，以得到最佳之分子束訊號。此分子束系統可被應用在觀測奈米觸媒催化之過程的物理機制以及奈米團簇之形貌隨溫度或其他參數之變化。最後我們利用此系統進行金奈米團簇在氧化鋁表面上之形貌隨溫度變化之實驗。我們利用氦氣分子束的反射率而得知表面的粗糙程度。金奈米團簇在低覆蓋率時，其殘留於氧化鋁表面之數量會隨樣品溫度的增加而減少；當樣品溫度達到1000 K時，金幾乎不再殘留於氧化鋁表面上，而使得氧化鋁表面裸露在外。然而大量的金奈米團簇覆蓋於氧化鋁表面上時，雖然其殘留數量同樣會隨樣品溫度的增加而減少，但是當樣品溫度達到1000 K後依然有一定量之金奈米團簇殘留於表面上，此殘留於表面的金奈米團簇其形貌隨溫度不同而產生變化。由300 K變化到900 K之間，被金奈米團簇覆蓋的氧化鋁表面會形成平整的結構；在溫度上升到1000 K後，被金奈米團簇覆蓋的氧化鋁表面會再次變為粗糙。We have built up a new ultrahigh vacuum molecular beam system. This system contains a molecular beam source chamber, a main chamber and a QMS chamber. Between any two of them, there is an aperture. These apertures are utilized for differential pumping, which prevents the pressure of the main chamber increase too much, when the pulsed valve operates. In order to obtain the optimized specular molecular beam, we found out the optimal conditions of the molecular beam and the optimal position for the scattering experiments. We also utilized this system to demonstrate the morphological evolution of gold nano-clusters supported by θ-Al2O3/NiAl(100) with the sample temperature. At low coverages of Au, such as 1 ML and 4 ML, the Au on the θ-Al2O3/NiAl(100) diffuses into the oxide film, as temperature varies from 300 K to 1000 K, and that makes the bare oxide surface exposed. At high coverage of Au, such as 8 ML, there are some Au nano-clusters remained on the θ-Al2O3/NiAl(100) after annealing to 1000 K and the morphology of these Au clusters is a function of the temperature: as the temperature increased from 300 K to 900 K, it is more likely the Au covered-surface became more smooth. As the temperature of the sample further increased to 1000 K, the surface became relatively rough, resulting in drop of the reflectivity.
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