A First-Principles Study of Adsorption of an Au Atom and Dimer on a θ-Al2O3/NiAl(100) Surface

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題名:	A First-Principles Study of Adsorption of an Au Atom and Dimer on a θ-Al2O3/NiAl(100) Surface
作者:	夏敬倫;Hsia,Ching-Lun
貢獻者:	物理學系
關鍵詞:	第一原理;氧化鋁;鎳鋁合金;密度泛函理論;金奈米粒子;first-principles;Al2O3;NiAl;DFT;Au nanocluster
日期:	2013-07-30
上傳時間:	2013-08-22 11:46:45 (UTC+8)
出版者:	國立中央大學
摘要:	我們使用第一原理方法計算一到兩顆金原子在不同厚度的θ型氧化鋁/鎳鋁合金(100)表面上的吸附特性。我們架構了具有不同氧化鋁厚度(一到五層)的θ型氧化鋁/鎳鋁合金(100)模型，並計算了單一金原子和金分子(兩顆金)在其表面不同位置及不同形貌上的吸附能。金原子趨向於吸附在氧化鋁表面平坦位置的中央，並與表面的鋁原子鍵結。金分子吸附於氧化鋁表面的最穩定形貌則分為兩類:對於二、四、五層厚度的θ型氧化鋁/鎳鋁合金(100)而言，金分子的其中一顆金原子會與表面的氧原子鍵結，而另外一顆則懸吊於空中；對於一、三層厚度的θ型氧化鋁/鎳鋁合金(100)而言，金分子則平躺於表面上[010]方向，並且兩顆金原子皆與表面的鋁原子鍵結。金原子在有鎳鋁合金作為基底的氧化鋁表面上的吸附能，大於在純氧化鋁表面上的吸附能。我們用了四種方法來討論，這種與氧化鋁層數相關的吸附現象: (1)結構馳豫、(2)功函數縮減、(3)電荷轉移、(4)態密度的移動。每一層的氧化鋁的結構馳豫皆會貢獻於吸附能，尤其是表面氧化鋁的結構馳豫。結構馳豫在吸附能中扮演了重要的角色，但無法解釋其整體的吸附特性。鎳鋁合金基底所造成的功函數縮減，將會增加從氧化鋁基底轉移到金原子或分子的電荷，而電荷轉移的增加將會增強θ型氧化鋁/鎳鋁合金(100)和金吸附物之間的交互作用。金吸附物的能隙縮減和態密度向低能量方向的移動則是另一個造成吸附能提升的原因。 We constructed θ-Al2O3/NiAl(100) models with varied thickness (1 – 5 layers) of Al2O3 slabs on NiAl(100) slabs. We calculated the adsorption and cohesive energies for Aun clusters (n = 1 or 2) in various initial configurations and at various sites on the oxide surface. The most stable configuration for a single Au atom adsorbed on θ-Al2O3/NiAl(100) surface is the Au atom bound to the Al atom at the middle of the flat area. For an Au dimers adsorbed on θ-Al2O3/NiAl(100) surface, two kinds of stable configurations are indicated: on 2-layer, 4-layer and 5-layer θ-Al2O3 on NiAl(100), the dimer adsorbs preferentially with one Au bonded to a surface O and the other dangling, whereas on 1-layer and 3-layer θ-Al2O3 slabs, the dimer lies on the surfaces with the Au-Au bond along [010] direction and with the two Au atoms bound to the Al atoms. The adsorption energies of Au atom on NiAl-supported alumina surfaces are greater than that on pure alumina surface. These thickness-dependent adsorption properties of Au adsorbed on θ-Al2O3/NiAl(100) are discussed in four origins: (1) structural relaxation, (2) work function reduction, (3) charge transfer, and (4) density of state (DOS) shift. The structural relaxation of every layer of alumina slabs all contribute to adsorption energy. The most significant contribution is from the relaxation of the surface layer. The structural relaxation plays an important role in the adsorption energy but cannot account for all the adsorption properties. The reduction of work function of NiAl-supported alumina surface enhances the charge transfer from substrate to Au atom and dimer, and the charge transfer increases the interaction between substrate and the Aun adsorbate. The reduction of the band gap and the left-shift of DOS of Au adsorbate is another reason to cause the enhancement of adsorption energy.
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