扫描探针显微镜研究CeO₂(100)表面重构的原子尺度反应性
Reconstruction-Dependent Imaging, Reactivity and Local Reduction of the CeO$_2$(100) surface
浏览论文内容
中文总结 AI 辅助
该研究结合扫描探针显微实验与第一性原理建模，揭示CeO₂(100)两种表面重构的原子尺度反应性，明确STM对不同重构表面还原状态的敏感性差异，建立了相关实验-理论框架。
中文摘要 AI 辅助
CeO₂(100)表面的原子尺度结构与反应性仍未被充分理解，因为其固有极性和低稳定性会引发复杂的表面重构。本文结合扫描隧道显微镜（STM）实验、采用氧终止探针的原子力显微镜（AFM）实验以及第一性原理建模，对CeO₂(100)薄膜开展原子尺度研究。STM揭示了与CeO₄金字塔终止的(2×2)重构、氧终止的c(2×2)重构相关的图案，其中氧终止的c(2×2)重构在台阶边缘形成小区域。AFM成像和力谱直接识别出暴露的表面原子物种，并显示出与吸附质相关扰动相符的特征。密度泛函理论和AFM模拟重现了主要实验观察结果，表明氧终止表面与探针的相互作用由短程泡利排斥主导，而CeO₄终止表面的相互作用则受静电贡献显著影响，凸显了简单探针模型在描述强波纹极性氧化物表面的铜氧化物探针时的局限性。对于CeO₄终止表面，仅靠STM无法可靠表征局部还原状态，因为氧化与还原表面的STM模拟会因局部态密度的真空衰减与高度波纹表面几何结构的相互作用产生相似的表观衬度。相比之下，对于氧终止重构，STM对还原状态敏感，可提供第一Ce层中Ce³⁺与Ce⁴⁺离子分布的信息。这些结果建立了连接复杂氧化物表面的重构、原子位点归属、局部力响应及吸附质敏感性的实验-理论框架。
英文摘要
The possibility of mapping the local reactivity and reduction state to the atomic structure of chemically active oxide surfaces opens new avenues for further understanding of catalysis. Here, we combine scanning tunnelling (STM) and atomic force microscopy (AFM) with first-principles modelling to explore this possibility on the CeO2(100) surface. While STM reveals the periodicity of cerium-terminated and oxygen-terminated CeO$_2$(100) reconstructions coexisting on the same surface, AFM imaging and force spectroscopy provide direct identification of the exposed atomic species and their reactivity as the chemical interaction with the probe. Density functional theory based STM and AFM simulations reproduce the main experimental observations and show that STM contrast cannot be in general assigned to the atomic positions of certain chemical species, as traditionally assumed from previous studies. Simulated STM contrast of the two reconstructions across different reduction states associated with the removal of oxygen atoms in deeper layers, evidence that STM alone does not offer a robust fingerprint of the local reduction state for the cerium-terminated reconstruction, but it is sensitive to the reduced state in the case of the oxygen-terminated one, being able to provide information on a mixed distribution of Ce$^{3+}$ and Ce$^{4+}$ ions on the first sub-surface Ce layer.
