CNRS-Sorbonne Université, UMR 7588, INSP, F-75005 Paris, France.
Carl von Ossietzky Universität, Institut für Physik, D-26111 Oldenburg, Germany.
J Phys Condens Matter. 2023 Jul 14;35(41). doi: 10.1088/1361-648X/ace01d.
Cation mixing is a well-recognized means to obtain oxides of desired functionality with predetermined structure and stoichiometry, which yet has been only little analyzed at the nanoscale. In this context, we present a comparative analysis of the stability and mixing properties of O-poor and O-rich two-dimensional V-Fe oxides grown on Pt(111) and Ru(0001) surfaces, with the aim of gaining an insight into the role of substrate and oxygen conditions on the accessible Fe contents. We find that due to the high oxygen affinity of the Ru substrate, the mixed O-rich layers are highly stable while the stability of O-poor layers is limited to inaccessibly oxygen-poor environments. In contrast, on the Pt surface, O-poor and O-rich layers coexist with, however, a much lower Fe content in the O-rich phase. We show that cationic mixing (formation of mixed V-Fe pairs) is favored in all considered systems. It results from local cation-cation interactions, reinforced by a site effect in O-rich layers on the Ru substrate. In O-rich layers on Pt, Fe-Fe repulsion is so large that it precludes the possibility of substantial Fe content. These findings highlight the subtle interplay between structural effects, oxygen chemical potential, and substrate characteristics (work function and affinity towards oxygen), which governs the mixing of complex 2D oxide phases on metallic substrates.
阳离子混合是一种获得具有预定结构和化学计量比的所需功能氧化物的常用方法，但在纳米尺度上，这种方法的分析还很少。在这方面，我们对在 Pt(111)和 Ru(0001)表面生长的贫氧和富氧二维 V-Fe 氧化物的稳定性和混合特性进行了比较分析，旨在深入了解衬底和氧条件对可获得的 Fe 含量的作用。我们发现，由于 Ru 衬底的高氧亲和力，混合富氧层非常稳定，而贫氧层的稳定性仅限于难以获得的贫氧环境。相比之下，在 Pt 表面，贫氧和富氧层共存，但富氧相中 Fe 的含量要低得多。我们表明，阳离子混合（形成混合 V-Fe 对）在所有考虑的系统中都是有利的。它是由局部阳离子-阳离子相互作用以及 Ru 衬底上富氧层中的位错效应共同导致的。在 Pt 上的富氧层中，Fe-Fe 排斥力非常大，以至于不可能有大量的 Fe 含量。这些发现强调了结构效应、氧化学势和衬底特性（功函数和对氧的亲和力）之间的微妙相互作用，这种相互作用控制着复杂二维氧化物相在金属衬底上的混合。
