Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
J Chem Phys. 2011 Oct 21;135(15):154701. doi: 10.1063/1.3635777.
Sulfur accelerates coarsening of Ag nanoislands on Ag(100) at 300 K, and this effect is enhanced with increasing sulfur coverage over a range spanning a few hundredths of a monolayer, to nearly 0.25 monolayers. We propose that acceleration of coarsening in this system is tied to the formation of AgS(2) clusters primarily at step edges. These clusters can transport Ag more efficiently than can Ag adatoms (due to a lower diffusion barrier and comparable formation energy). The mobility of isolated sulfur on Ag(100) is very low so that formation of the complex is kinetically limited at low sulfur coverages, and thus enhancement is minimal. However, higher sulfur coverages force the population of sites adjacent to step edges, so that formation of the cluster is no longer limited by diffusion of sulfur across terraces. Sulfur exerts a much weaker effect on the rate of coarsening on Ag(100) than it does on Ag(111). This is consistent with theory, which shows that the difference between the total energy barrier for coarsening with and without sulfur is also much smaller on Ag(100) than on Ag(111).
硫在 300K 下加速 Ag(100) 上 Ag 纳米岛的粗化，并且这种效果随着硫覆盖度在几百个单层到近 0.25 单层的范围内增加而增强。我们提出，在这个体系中，粗化的加速与主要在台阶边缘形成的 AgS2 簇的形成有关。这些簇可以比 Ag 吸附原子更有效地传输 Ag（由于扩散势垒较低且形成能相当）。Ag(100)上孤立硫的迁移率非常低，因此在低硫覆盖度下，复杂结构的形成受到动力学限制，因此增强作用最小。然而，较高的硫覆盖度迫使相邻台阶边缘的位置数量增加，从而使簇的形成不再受到硫在平台上扩散的限制。硫对 Ag(100)上粗化速率的影响远小于对 Ag(111)的影响。这与理论一致，理论表明，有硫和无硫时粗化的总能量势垒差在 Ag(100)上也比在 Ag(111)上小得多。
