A STM Study of Growth of Rh and Pt Nanoclusters Supported by Graphene on Pt(111)

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題名:	A STM Study of Growth of Rh and Pt Nanoclusters Supported by Graphene on Pt(111)
作者:	黃彥文;HUANG,YAN-WEN
貢獻者:	物理學系
關鍵詞:	掃描穿隧式顯微鏡;奈米團簇;銠;鉑;石墨烯;STM;nanocluster;Rh;Pt;graphene
日期:	2016-08-23
上傳時間:	2016-10-13 13:29:39 (UTC+8)
出版者:	國立中央大學
摘要:	我們以掃描穿隧式顯微鏡顯微鏡(Scanning Tunneling Microscope, STM)探測Pt及Rh金屬奈米團簇生長在以Pt(111)為基底的石墨烯(graphene)上的形貌，主要研究奈米團簇在室溫下的成長模式以及加熱對團簇造成的影響。從實驗中觀察到Pt及Rh團簇在石墨烯上有三種偏好生長的位置，分別為台階邊上、台階上及領域邊緣。生長在台階邊上及領域邊緣的團簇會有較小的尺寸，但是擁有較高的分布密度。我們還觀察到在某些鍍量下，石墨烯表面上的團簇會有兩種不同的分布密度。從Gao et al.的實驗中可知，石墨烯薄膜可以根據生長方向大小的不同區分為兩類，進而推論出在不同的石墨烯上生長出來的金屬奈米團簇會擁有不同的生長特性。　　在室溫下形成的Pt團簇於低鍍量時(<0.7ML)，團簇的密度及尺寸會隨著鍍量的增長而有所增加，但在高鍍量時(>0.7ML)，尺寸的增加速度會趨於緩和。將其加熱到450K之後，石墨烯表面上的Pt金屬原子數量並沒有太大的改變，而團簇尺寸會縮小進而形成能量較為穩定的結構，同時團簇密度會增大；加熱到700K後，石墨烯表面上的Pt金屬原子數量縮減至原來的一半，而由於燒結的效應，團簇尺寸會增大，且團簇密度會大幅減少。　　在室溫下生長於石墨烯上的Rh團簇隨著鍍量的增加，團簇密度也會跟著增加，但Rh團簇的尺寸將維持不變直到鍍量到達0.65ML。而在高鍍量時(>0.65ML)，團簇尺寸會因為密度達到飽和而開始增長。將Rh團簇加熱之後，團簇尺寸會有所增大且趨於統一，但其密度會減少。加熱Rh團簇會使Rh原子聚集，而使表面上的團簇密度會開始有不均勻的分布現象。 ;Pt and Rh nanoclusters formed through vapor deposition on the graphene/Pt(111) are studied by scanning tunneling microscopy (STM). We investigate the growth behaviors of Pt and Rh clusters at 300 K and the effect of thermal treatments. We observe that there are three kinds of positions where Pt and Rh clusters formed preferentially on the graphene/Pt(111): step edge, terrace and domain boundary. The size of clusters on the step edge and domain boundary is smaller than that on terrace site, but their cluster density is greater. We observe two kinds of cluster density of Pt and Rh nanoclusters on the graphene surface at several coverages. The graphene films can be classified into two types large and small rotation angle of graphene with respect to Pt(111) substrate. It is reasonable to assume that these two domains could have different properties for the growth of nanoclusters. The studies of Pt clusters formed at 300 K show that at coverage < 0.7 ML, the cluster density and size of Pt clusters increase with the coverage increasing; at coverage > 0.7 ML, the increase rate of size become slowly. After annealing to 450 K, the coverage is almost the same as the original. However, after annealing to 700 K, only 50 % of Pt remained on the graphene. Because of getting thermal energy during annealing, the cluster sizes become smaller and uniform, and density increases obviously. The studies of Rh clusters formed at 300 K show that when the coverage increases, the cluster density increases, but the Rh clusters remain the same size until the coverage is increased to about 0.65 ML. The Rh cluster sizes start to increase when the cluster density become saturated (4.76×1012 cm-2) at coverage > 0.65 ML. After annealing, the Rh clusters become bigger and more uniform in size, but the clustery density decreases.
顯示於類別:	[物理研究所] 博碩士論文

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