Ag Nanoparticles on Reducible CeO2(111) Thin Films: Effect of Thickness and Stoichiometry of Ceria

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• 作者：Shanwei Hu ; Yan Wang ; Weijia Wang ; Yong Han ; Qitang Fan ; Xuefei Feng ; Qian Xu ; Junfa Zhu
• 刊名：Journal of Physical Chemistry C
• 出版年：2015
• 出版时间：February 19, 2015
• 年：2015
• 卷：119
• 期：7
• 页码：3579-3588
• 全文大小：706K
• ISSN：1932-7455

文摘

The growth and structures of Ag nanoparticles on CeO_2鈥?i>x(111) thin films with different thicknesses, morphologies, and reduction degrees have been systematically studied by scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and low energy electron diffraction (LEED). The CeO_2鈥?i>x(111) thin films were epitaxially grown on Cu(111). With increasing the ceria thin film thickness, the size of the terraces decreases along with the increase of the number of open monolayers and defects. In most cases, Ag exhibits three-dimensional (3D) growth with constant particle densities on the CeO_2鈥?i>x(111) surfaces at 300 K. Ag mainly populates the sites at the ceria鈥揷eria step edges instead of ceria terraces, independent of the thicknesses but influenced by the reduction degree of the ceria films. On the fully oxidized ceria films, the particle density is directly proportional to the number of step edges of ceria, which is related to its thickness on Cu(111). On the slightly reduced ceria films which were prepared by annealing the fully oxidized ceria films in ultrahigh vacuum, single surface oxygen vacancies and their linear agglomerates are observed, but they do not anchor Ag particles during Ag deposition. While on the strongly reduced ceria films produced by decreasing the oxygen pressure during ceria film growth, large defect sites related to surface and subsurface oxygen vacancies are found; they can anchor the Ag nanoparticles, leading to the random distribution of Ag nanoparticles on ceria terraces upon deposition. Upon heating, the Ag nanoparticles undergo serious sintering before desorption at 800 K on the fully oxidized CeO₂ films. While on the reduced ceria films, the sintering and desorption processes are slowed down at the same annealing temperatures as those on CeO₂. This result suggests that the defects on reduced ceria surfaces can enhance the thermal stability of Ag nanoparticles during annealing.