Sorbonne Universités, UPMC Univ Paris 06, CNRS-UMR 7588, Institut des NanoSciences de Paris, F-75005, Paris, France.
Nanoscale. 2018 Feb 1;10(5):2291-2300. doi: 10.1039/c7nr06833f.
Using real-time in situ scanning tunneling microscopy and density functional theory simulations, we have studied the growth of Si films on Ag(111) beyond the silicene monolayer, evidencing the existence of metastable phases and an original growth mechanism. Above monolayer Si coverage, an initial structure forms, which is identified as an Ag-free Si bilayer with additional Si adatoms. With further deposition, this structure is replaced by a distinct bilayer structure covered by Si trimers and Ag atoms. The formation of these bilayers follows counterintuitive dynamics: they are partially inserted within the Ag substrate and form by expelling, from the underlying substrate, the atoms that reinsert below the adjacent silicene layer. The growth is therefore characterized by an unexpected "surfactant competition" between Ag and silicene: while silicene is a metastable surfactant for the Ag(111) surface, Ag plays the role of a surfactant for thicker diamond-like Si islands. In spite of being thermodynamically unfavoured, the silicene monolayer is, thus, a remarkably stable structure because of the high kinetic barrier for the growth of thicker layers.
利用实时原位扫描隧道显微镜和密度泛函理论模拟，我们研究了 Si 薄膜在 Ag(111)上的生长，超出了硅烯单层，证明了亚稳相和原始生长机制的存在。在单层 Si 覆盖层之上，形成了初始结构，该结构被鉴定为具有额外 Si adatoms 的无 Ag 双层 Si。随着进一步的沉积，这种结构被一个独特的双层结构所取代，该结构由 Si 三聚体和 Ag 原子覆盖。这些双层的形成遵循违背直觉的动力学：它们部分插入 Ag 衬底中，并通过从底层衬底中逐出重新插入到相邻硅烯层下方的原子来形成。因此，生长的特点是 Ag 和硅烯之间的意想不到的“表面活性剂竞争”：虽然硅烯是 Ag(111)表面的亚稳表面活性剂，但 Ag 对于更厚的类金刚石 Si 岛起到了表面活性剂的作用。尽管从热力学上看是不利的，但硅烯单层是一种非常稳定的结构，因为形成更厚层的动力学障碍很高。
