Department of Physics and Astronomy, Tufts University, Medford, Massachusetts 02155, USA.
J Chem Phys. 2018 Jun 14;148(22):224702. doi: 10.1063/1.5030862.
The adsorption behavior of CO on Ni islands grown on Au(111) was studied with a combination of temperature programmed desorption, Fourier transform infrared spectroscopy, and surface resistivity measurements. The Au(111) herringbone reconstruction provides a template for the growth of ordered Ni islands, with evidence for the presence of strain and Au atoms within the islands. The islands grow radially until θ ≈ 0.3 ML, after which subsequent Ni atoms contribute primarily to a second layer. We study saturated CO adsorption at 227 K over a range of Ni island sizes and find layer-dependent adsorption properties. For single-layer islands at low Ni coverage, CO adsorbs primarily in the atop position and desorbs at lower temperatures than on pure Ni, with a saturation CO coverage of about 0.5 CO/Ni. As second layer Ni grows, saturated CO coverages on the Ni approach unity, with higher desorption temperatures, but still with primarily atop CO. Based on previous studies, we propose that in the first Ni layer, ligand effects from the Au substrate and possibly Au in the islands and strain due to the Ni/Au lattice mismatch affect the Ni-CO bonds. CO adsorption behavior on the two-layer islands is qualitatively explained by a decrease in Au nearest neighbors and the presence of a more expanded/corrugated structure.
我们采用程序升温脱附、傅里叶变换红外光谱和表面电阻测量相结合的方法研究了 CO 在 Au(111) 上生长的 Ni 岛的吸附行为。Au(111) 之字形重构为有序 Ni 岛的生长提供了模板，其中存在应变和岛内的 Au 原子。这些岛径向生长，直到θ≈0.3 ML，之后，随后的 Ni 原子主要贡献给第二层。我们研究了在 Ni 岛尺寸范围内的 227 K 下饱和 CO 的吸附，发现了依赖于层的吸附性质。对于低 Ni 覆盖度的单层岛，CO 主要在顶位吸附，并在低于纯 Ni 的温度下解吸，CO 的饱和覆盖率约为 0.5 CO/Ni。随着第二层 Ni 的生长，Ni 上的饱和 CO 覆盖率接近 1，解吸温度更高，但仍主要是顶位 CO。基于先前的研究，我们提出在第一层 Ni 中，Au 衬底和可能的岛内的 Au 以及由于 Ni/Au 晶格失配引起的应变对 Ni-CO 键产生配体效应。通过减少最近的 Au 邻居和存在更扩展/起伏的结构，可以定性地解释双层岛上的 CO 吸附行为。
