利用PES探討吸附物對Au-Pt奈米團簇所引發表面發生重構的現象

我們利用同步輻射幅射光源激發電子能譜儀(PES)來研究吸附物引發金與白金所形成的合金奈米團簇在氧化鋁薄膜上的重構現象。在超高真空的環境下(小於 3 x 10-10) ，利用物理氣相沉積法將奈米團簇成長在完整且有序的氧化鋁薄膜 Al2O¬3/NiAl(100)上。從PES能譜圖中，當我們在120 K低溫下吸附甲醇、乙醇、環己烯時會引發金原子聚集在合金奈米團簇表面上。然而，我們發現從甲醇或是乙醇分解出來的CO會殘留在表面上並且會影響金原子的移動。當我們把樣品升高到 650 – 800 K的退火溫度時，合金的結構已經有所改變：白金奈米粒子已經形成氧化態的結構並且在合金奈米團簇表面上覆蓋了一層 PtxAlyOz 物質和部分些許的金。之後我們在120 K吸附甲醇、乙醇這些含有OH- 官能基的分子時，我們可以發現到經過退火過程的合金奈米團簇表面上的氧化白金還原成金屬性的白金，並且和存在於表面上的金再次形成合金。相反的，當我們吸附環己烯(只有(CHn-) group) 時，並沒有類似的情形發生。

關鍵字

奈米團簇；重構；吸附物；金；白金

並列摘要

We have studied the adsorbate-induced restructuring of Au-Pt bimetallic nanoclusters on the well-defined θ-Al2O3/NiAl(100) by using synchrotron-based high-resolution photoemission spectroscopy (PES). The Au-Pt bimetallic clusters were vapor deposited on ordered thin film Al2O3 at 300 K. Upon adsorption of adsorbates, such as methanol, ethanol and cyclohexene, the Au atoms aggregate at the surface of clusters. However, we find that the CO from methanol (and/or ethanol) decomposition remains on the surface and block the aggregation of Au atoms. After annealing to 650 - 800 K, the metallic Pt become oxidized Pt and the surface of clusters is coated with alumina materials; some Au are exposed at the surface. Adsorbing the hydroxyl group (-OH) such as CH3OH and C2H5OH, the annealed Au-Pt bimetallic undergo dramatic changes in chemical state—oxidized Pt is reduced to metallic Pt, and thus Pt alloys with Au again. In contrast, no substantial alternation was found in the oxidized bimetallic clusters exposed to C6H10 which had only (CHn-) group.

並列關鍵字

nanocluster ； restructuring ； Pt ； Adsorbate ； Au

參考文獻

Chapter 1

[2]. Johnston, R. L. Atomic and Molecular Clusters; Taylor and Francis: London, 2002.

[3]. Baletto, F.; Ferrando, R. ReV. Mod. Phys. 2005, 77, 371

[4]. Jortner, J. Z. Phys. D 1992, 24, 247.

[5]. Johnston, R. L. Philos. Trans. R. Soc. London A 1998, 356, 211.

國際替代計量

利用PES探討吸附物對Au-Pt奈米團簇所引發表面發生重構的現象

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