Growth and electronic properties of Rh and Au nanoclusters supported on CuO/Cu(110)

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题名:	Growth and electronic properties of Rh and Au nanoclusters supported on CuO/Cu(110)
作者:	李易暽;Li, Yi-Lin
贡献者:	物理學系
关键词:	銠;金;氧化銅;高能電子繞射儀;掃描穿隧式顯微鏡;X光光電子能譜儀;Rh;Au;CuO;RHEED;STM;XPS
日期:	2023-07-10
上传时间:	2024-09-19 15:55:14 (UTC+8)
出版者:	國立中央大學
摘要:	本研究透過掃描穿隧電子顯微術(STM)、高能電子繞射儀(RHEED)及位於新竹同步輻射中心的X光光源與能譜儀研究銠及金在氧化銅/銅(110)上的生長形貌及電子特性。STM顯示銠在室溫下在氧化銅/銅(110)上便透過自組裝形成三維結構，即便是在很小的鍍量下(0.09 ML)。此三維結構也被RHEED監測到，呼應STM的結果。銠奈米團簇的平均直徑隨著鍍量上升，並在達到0.62 ML以上時，達到1.50奈米左右並趨於飽和。然而平均高度並未隨著鍍量上升，並保持在0.22奈米左右。銠奈米團簇於表面的密度在鍍量達到0.62 ML以上時也達到飽和。綜合團簇密度及粒徑大小的不變性來看，下層的銠奈米團簇可能已經結合形成薄膜。銠奈米團簇的電子特性透過XPS量測。在小鍍量時(0.02到0.12 ML)，銠〖3d〗_(5/2) 軌域的束縛能坐落在306.3 eV，比塊材銠小0.7 eV。隨著鍍量上升，銠〖3d〗_(5/2) 軌域的束縛能逐漸往高束縛能移動且接近塊材值。並在達到1.44 ML時，坐落於306.8 eV。銠3d雙峰的束縛能在小鍍量時比塊材值還小許多，此結果與一般認知及其他研究的實驗結果不同，可能與電荷從基板或擔體轉移至銠奈米粒子有關。金在鍍量小於1 ML時以二維團簇的形式存在於表面，並由STM鑑定。當鍍量增加超過1 ML時，金薄膜便成形，被STM及RHEED所確認。金團簇與薄膜的電子結構也由XPS所鑑定，在小鍍量時(≤ 0.23 ML)，金〖4f〗_(7/2) 軌域的束縛能坐落於84.1 eV，高於塊材0.1 eV。隨著鍍量上升後增加至84.2 eV。金4f雙峰隨鍍量上升的移動方向與一般認知不同，代表金表面的化學環境有所改變，可能與底層氧原子浮出至表面有關。 ;By utilizing the reflection high energy diffraction (RHEED), scanning tunneling microscopy (STM), and X-ray photoelectron spectroscopy (XPS), we have investigated the growth and electronic properties of Rh and Au nanoclusters grown on CuO/Cu(110). Rh atoms that are deposited on CuO/Cu(110) at 300 K self-assemble into nanoclusters in a 3D (three-dimensional) fashion even at small coverage (0.09 ML), indicated by STM. RHEED patterns also reflect the 3D structure of Rh nanoclusters, and are consistent with STM results. The averaged diameter of these nanoclusters increases with Rh coverage, and saturates at around 1.50 nm when above 0.62 ML. However, the averaged height does not increase with coverage but maintains at around 0.22 nm. The cluster density also saturates when above 0.62 ML, together with the unchanged size of Rh nanoclusters, the clusters at the lower position may merge into a Rh film. Electronic structure of Rh nanoclusters evolves with coverage. At small coverages (0.02 to 0.12 ML), Rh 〖3d〗_(5/2) centers at 306.3 eV which is 0.7 eV smaller than the bulk value (307.0 eV). On increasing the Rh coverage, Rh 〖3d〗_(5/2) shifts toward it bulk value, and finally locates at 306.8 eV when at 1.44 ML. This unusual shift of Rh 3d doublet may indicate a charge transfer from substrate or support to Rh nanoclusters. The Au nanoclusters grow in a 2D fashion at sub-monolayer level, indicated by STM. Au films form on the surface when increasing the coverage, identified by the STM images and RHEED patterns. The electronic structure of Au nanoclusters also evolves with coverage. At the low coverages (≤ 0.23 ML), Au 〖4f〗_(7/2) centers at 84.1 eV which is 0.1 eV higher than its bulk value (84.0 eV), and increases to 84.2 eV at higher coverage. The abnormal shift of the Au 4f doublet may indicate that the chemical enviroment on the Au surface is modified by an extra element, such as the oxygen atoms floating to the CuO surface.
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