Ni在ZrO2(111)薄膜表面的生长、电子结构及热稳定性

利用X射线光电子能谱、紫外光电子能谱和低能电子衍射研究了Ni纳米颗粒在ZrO₂(111)薄膜表面的生长模式、电子结构及热稳定性. ZrO₂(111)薄膜外延生长于Pt(111)单晶表面,厚度约为3 nm.结果表明,当Ni气相沉积到ZrO₂(111)薄膜表面上时,遵循Stranski-Krastanov生长模式,即先二维生长至0.5 ML(monolayer),然后呈三维岛状生长.随着覆盖度的减小, Ni 2p_3/2峰逐渐向高结合能位移.利用俄歇参数法分析发现,引起该峰向高结合能位移的主要原因来源于终态效应的贡献,但在低的Ni覆盖度时,也有部分初态效应的贡献,说明Ni在ZrO₂表面初始生长时,两者存在较强的界面相互作用, Ni向ZrO₂衬底传递电荷,形成带部分正电荷的Ni_δ+.两种不同覆盖度(0.05和0.5 ML)的Ni/ZrO₂(111)模型催化剂热稳定性研究表明,当温度升高时, Ni逐渐被氧化成Ni₂₊,并伴随着向ZrO₂衬底的扩散.本文从原子水平上认识了Ni与ZrO₂表面的相互作用和界面结构,为理解实际ZrO₂担载的Ni催化剂结构提供了重要的依据.

Growth,Electronic Structure and Thermal Stability of Ni on ZrO2(111) Thin Film Surfaces

The growth mode, electronic structure, and thermal stability of Ni nanoparticles on thin ZrO₂(111) film surfaces were investigated using X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and low-energy electron diffraction. Stoichiometric ZrO₂(111) thin films with thickness of 3 nm were epitaxially grown on a Pt(111) single-crystal surface. The results indicate that the growth of Ni vapor deposited on thin ZrO₂(111) films follows two-dimensional growth up to 0.5 ML (monolayer), followed by threedimensional growth (i.e., the Stranski-Krastanov growth mode). The Ni 2p_3/2 binding energy (BE) increases with decreasing Ni coverage. We used the Auger parameter method to differentiate the contributions to this BE shift from the initial-state and final-state effects. The main contribution to the Ni 2p core level BE shift is made by the final-state effect. However, at low Ni coverages, the initial-state effect also contributes. This suggests that at the initial stage of Ni growth on the ZrO₂(111) surface, Ni and ZrO₂ interact strongly, leading to charge transfer from Ni to the ZrO₂ substrate, with the appearance of partially positively charged Ni_δ+. Thermal stability studies of Ni/ZrO₂(111) model catalysts with two different coverages (0.05 and 0.5 ML) indicate further oxidation of Ni to Ni₂₊ and concurrent diffusion of Ni into the ZrO₂ substrate at elevated temperatures. These findings provide an atomic-level fundamental understanding of the interactions between Ni with ZrO₂, which is essential for identifying the structures of real ZrO₂-supported Ni catalysts.