Department of Chemistry, University of Utah, 315 S. 1400 E. RM 2020, Salt Lake City, Utah 84112-0850, USA.
J Chem Phys. 2009 Sep 21;131(11):114701. doi: 10.1063/1.3224119.
A series of planar model catalysts have been prepared via deposition of Ir(n) (+) on thermally grown amorphous SiO(2)/Si(100) and ion scattering spectroscopy was used to probe surface structure as a function of cluster size, impact energy, and surface temperature. Deposition of Ir(2) or Ir(10) at low energies and room temperature results in stable clusters forming one- or two-dimensional single layer islands on the oxide surface. Heating the samples to 750 K leads to agglomeration, forming multilayer structures on the surface. Ir(1) deposited under similar conditions sinters into large clusters at room temperature. Deposition at 110 K at least partially stabilizes the Ir atoms with respect to diffusion and sintering. At higher deposition energies, partial implantation into the surface is observed, but this appears to be insufficient to stabilize the clusters against sintering at elevated temperature. At low temperatures, substrate-mediated adsorption of CO is found to be highly efficient, leading to near saturation coverages of CO bound atop the Ir(n) clusters. The CO can be removed by careful He(+) sputtering. The deposition/binding behavior of Ir(n) on SiO(2) is quite different from Ir(n)/TiO(2)(110), for which the clusters bind in three-dimensional morphology, starting at Ir(5). That system also shows substrate-mediated adsorption of CO, but the CO preferentially binds at the periphery of the clusters rather than on top.
已经通过在热生长的无定形 SiO2/Si(100)上沉积 Ir(n)(+)制备了一系列平面模型催化剂，并使用离子散射光谱法探测了表面结构作为团簇尺寸、冲击能和表面温度的函数。在低能量和室温下沉积 Ir(2)或 Ir(10)导致稳定的团簇在氧化物表面形成一层或两层单层岛。将样品加热至 750 K 会导致团聚，在表面形成多层结构。在相似条件下沉积的 Ir(1)在室温下会烧结成大团簇。在 110 K 下沉积至少部分稳定了相对于扩散和烧结的 Ir 原子。在较高的沉积能下，观察到部分注入表面，但这似乎不足以稳定团簇，使其在高温下不烧结。在低温下，发现 CO 通过衬底介导的吸附非常有效，导致 CO 在 Ir(n)团簇顶部的吸附接近饱和。可以通过小心的 He(+)溅射去除 CO。Ir(n)在 SiO2 上的沉积/结合行为与 Ir(n)/TiO2(110)非常不同，在后者中，团簇以三维形态结合，从 Ir(5)开始。该系统还显示出 CO 通过衬底介导的吸附，但 CO 优先在团簇的外围结合，而不是在顶部结合。
