INRS-EMT, Université du Québec, Varennes, Québec, Canada.
Phys Chem Chem Phys. 2013 Aug 14;15(30):12488-94. doi: 10.1039/c3cp50793a.
We have characterized the structural properties of submonolayer amounts of Zn on Pd(111) using scanning tunneling microscopy (STM) and spot-profile analysis low energy electron diffraction (SPA-LEED). Following room temperature deposition of ≈0.06 monolayers (ML) Zn onto Pd(111), we observe the substitution of Zn for Pd in the surface layer. At ≈0.20 ML of deposited Zn, STM reveals a locally ordered phase with a (2/√3 × 2/√3)R30° unit cell located near Zn substitutions; SPA-LEED patterns reveal the same periodicity. We attribute this phase to the metastable bonding of atoms or clusters predominantly in hollow sites surrounding Zn substitutions in the surface layer. At ≈0.4 ML, STM images reveal local (√3 × √3)R30° and (2 × 1) ordering on surfaces annealed to 350 K. At coverages near 0.5 ML, both STM and SPA-LEED show the onset of the formation of the (2 × 1) ordering associated with the Zn : Pd 1 : 1 alloy phase. At all coverages, the surface is dominated by island growth; the islands' size and density is shown to depend critically on annealing at temperatures as low as 350 K. These results provide insight into the structural features of a Zn/Pd(111) coverage regime that has been much debated in recent years.
我们使用扫描隧道显微镜（STM）和点-剖面分析低能电子衍射（SPA-LEED）对 Pd(111)上亚单层量的 Zn 的结构性质进行了表征。在室温下沉积 ≈0.06 单层（ML）Zn 到 Pd(111)上后，我们观察到 Zn 取代了表面层中的 Pd。在 ≈0.20 ML 的沉积 Zn 时，STM 揭示了一个局部有序的相，其具有位于 Zn 取代物附近的 (2/√3 × 2/√3)R30° 单元胞；SPA-LEED 图案揭示了相同的周期性。我们将此相归因于原子或簇的亚稳键合，主要位于表面层中 Zn 取代物周围的中空位置。在 ≈0.4 ML 时，STM 图像揭示了在 350 K 退火的表面上局部的 (√3 × √3)R30° 和 (2 × 1) 有序。在接近 0.5 ML 的覆盖范围内，STM 和 SPA-LEED 都显示出与 Zn : Pd 1 : 1 合金相相关的 (2 × 1) 有序形成的开始。在所有覆盖范围内，表面主要由岛状生长主导；岛的大小和密度被证明严重依赖于低至 350 K 的退火温度。这些结果提供了对 Zn/Pd(111)覆盖范围的结构特征的深入了解，近年来该范围一直存在争议。
