CNR-Istituto per lo Studio dei Materiali Nanostrutturati (ISMN), Department of Chemistry, Sapienza University, P.le Aldo Moro 5, 00185, Roma, Italy.
Nanoscale. 2018 Apr 19;10(15):7085-7094. doi: 10.1039/c8nr00648b.
The adsorption of Si atoms on a metal surface might proceed through complex surface processes, whose rate is determined differently by factors such as temperature, Si coverage, and metal cohesive energy. Among other transition metals, iridium is a special case since the Ir(111) surface was reported first, in addition to Ag(111), as being suitable for the epitaxy of silicene monolayers. In this study we followed the adsorption of Si on the Ir(111) surface via high resolution core level photoelectron spectroscopy, starting from the clean metal surface up to a coverage exceeding one monolayer, in a temperature range between 300 and 670 K. Density functional theory calculations were carried out in order to evaluate the stability of the different Si adsorption configurations as a function of the coverage. Results indicate that, at low coverage, the Si adatoms tend to occupy the hollow Ir sites, although a small fraction of them penetrates the first Ir layer. Si penetration of the Ir surface can take place if the energy gained upon Si adsorption is used to displace the Ir surface atoms, rather then being dissipated differently. At a Si coverage of ∼1 monolayer, the Ir 4f spectrum indicates that not only the metal surface but also the layers underneath are perturbed. Our results point out that the Si/Ir(111) interface is unstable towards Si-Ir intermixing, in agreement with the silicide phase formation reported in the literature for the reverted interface.
硅原子在金属表面的吸附可能通过复杂的表面过程进行，其速率由温度、硅覆盖率和金属内聚能等因素决定。在其他过渡金属中，铱是一个特殊的例子，因为铱(111)表面首先被报道，除了 Ag(111)，它还适合硅烯单层的外延生长。在这项研究中，我们通过高分辨率核心层光电子能谱跟踪硅在 Ir(111)表面的吸附，从清洁的金属表面开始，直到覆盖超过单层，温度范围在 300 到 670 K 之间。为了评估不同 Si 吸附构型随覆盖率的稳定性，我们进行了密度泛函理论计算。结果表明，在低覆盖率下，Si 原子倾向于占据空心 Ir 位，尽管它们中的一小部分会穿透第一层 Ir。如果 Si 吸附所获得的能量用于取代 Ir 表面原子，而不是以不同的方式耗散，那么 Si 就可以穿透 Ir 表面。在 Si 覆盖率约为 1 单层时，Ir 4f 谱表明，不仅金属表面，而且下面的层都受到了干扰。我们的结果表明，Si/Ir(111)界面在 Si-Ir 混合方面不稳定，这与文献中报道的反向界面上形成硅化物相的情况一致。
