A STM Study of Growth of Rh and Rh-Au Bimetallic Nanoclusters on the θ-Al2O3/NiAl(100)

Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/60726

Title:	A STM Study of Growth of Rh and Rh-Au Bimetallic Nanoclusters on the θ-Al2O3/NiAl(100)
Authors:	廖振和;Zhenhe,Liao
Contributors:	物理學系
Keywords:	掃描穿隧式顯微鏡;奈米團簇;銠;金;STM;nanocluster;Rh;Au
Date:	2013-07-26
Issue Date:	2013-08-22 11:46:53 (UTC+8)
Publisher:	國立中央大學
Abstract:	我們以掃描穿隧式顯微鏡顯微鏡(Scanning Tunneling Microscope, STM)探測Rh以及Rh-Au合金奈米金屬團簇在Al2O3/NiAl(100)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。在室溫下形成的純Rh團簇於低鍍量時(< 0.51 ML)，隨著鍍量的增加，團簇的尺寸會成長、同時團簇的數目會有顯著的增加；在較高鍍量時(> 0.51 ML)，隨著鍍量的增加，團簇的直徑會有顯著的成長、高度有些微成長，而團簇數目不會改變。在室溫下形成的Rh團簇傾向形成三維結構，並且在低鍍量(0.04 ML)及低溫(150 K)的條件下也有相同的結果。在室溫下形成的純Rh團簇的加熱實驗中，在高鍍量時(> 1.35 ML)，加熱到430 K後，Rh團簇的直徑會縮減、形成在430 K能量較穩定的結構，同時團簇數目會明顯增加；加熱到570 K後，由於燒結(sintering)的效應，團簇的尺寸增加、伴隨著團簇數目減少；加熱到800 K後，燒結的效應更加顯著，團簇尺寸的增加以及數目的縮減更為明顯。　　在Rh以及Rh-Au合金團簇的實驗中，Rh和Au依序在室溫下蒸鍍在Al2O3/NiAl(100)。在Rh後鍍的情況下，部分Rh會加入到Au的團簇、其餘Rh會形成額外的純Rh團簇；在Au後鍍的情況下，全部的Au都會加入到Rh的團簇形成合金團簇。在室溫下形成的Rh-Au合金團簇的加熱實驗中，Au的鍍量越高、加熱後Au-Rh團簇的鍍量減少越快。Rh以及Au團簇加熱過後的特性在Rh-Au合金團簇加熱過後都能被觀察到。當Rh的鍍量夠高時(> 1 ML)，從室溫加熱到430 K後，Rh-Au合金團簇會和純Rh團簇有相同的現象：合金團簇直徑會縮減、伴隨著團簇數目增加。當合金之中有高比例的Au時，加熱到700 K後，Rh-Au合金團簇會有類似純Au團簇的現象：團簇的尺寸分佈會變寬並出現類似雙峰分佈的情形。 Rh and Rh-Au bimetallic nanoclusters formed through vapor deposition on the thin film Al2O3/NiAl(100) are studied by scanning tunneling microscope (STM). We investigate the growth behaviors of Rh and Rh-Au bimetallic clusters at 300 K and the effect of thermal treatments. In the studies of pure Rh clusters formed at 300 K, at low coverage (< 0.51 ML), the cluster density increases with the coverage, more noticeable than the increase of average size at larger coverages (> 0.51 ML), the cluster density changes little while the diameter increases significantly, accompanied by a slightly increase of height. Rh clusters prefer to form 3D structures even at very low coverage (0.04 ML) and low temperature (150 K). In the studies of annealed Rh clusters formed at 300 K, for high coverages (> 1.35 ML), Rh clusters reduce to smaller ones to form an energetically more favored structure on annealing to 430 K, accompanied by increased cluster density, and then form larger clusters with lower density at 570 K the size increases and the density decreases further at 800 K. Oswald ripening is responsible for the increase of average size and the decrease of cluster density above 570 K. The Rh-Au bimetallic clusters are formed by sequential deposition of Au and Rh on the Al2O3/NiAl(100) at 300 K. For the deposition of Au and then Rh, the deposited Rh not only joins the existing Au clusters but also forms new Rh clusters on the oxide surface for the reverse order of deposition, all the deposited Au were incorporated in the existing Rh clusters. In the studies of thermal stability of the Rh-Au bimetallic clusters, more Au in the bimetallic clusters, more the coverage decreases (both Au and Rh) with the temperature. Both thermal-induced features of Au and Rh are exhibited. When initial amount of Rh is great (> 1 ML), the cluster density increase at 430 K, showing the feature of pure Rh clusters. For the sample with high Au-to-Rh ratio annealed above 700 K, the morphology of bimetallic clusters is similar to the pure Au clusters: broad and bimodal-like distributions of size are observed.
Appears in Collections:	[Graduate Institute of Physics] Electronic Thesis & Dissertation

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