A Comprehensive Study of the Bridge Site and Substrate Relaxation Asymmetry for Methanethiol Adsorption on Au(111) at Low Coverage
A Comprehensive Study of the Bridge Site and Substrate Relaxation Asymmetry for Methanethiol Adsorption on Au(111) at Low Coverage
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DOI：
10.1021/acsomega.0c02328
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发表时间：
2020-08
期刊：
影响因子：
4.1
通讯作者：
S. Bhattacharya;G. Speyer;D. Ferry;L. A. Bumm
中科院分区：
文献类型：
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作者：
S. Bhattacharya;G. Speyer;D. Ferry;L. A. Bumm
我们使用色散校正密度泛函理论来探索吸附在具有两种不同 S-C 键方向的 Au(111) 上的甲硫醇的桥位不对称性。我们将这种不对称性归因于 Au(111) 表面的内在特征，而不是吸附物。桥式 fcc 与桥式 hcp SCH3 吸附位点的偏好由 S-C 键方向控制。在未松弛的 Au(111) 表面上，系统能量差有利于桥面催化裂化位点 8.1 meV。松弛 Au 基底可将能量差增加至 26.1 meV。这种不对称性也反映在松弛金表面的原子位移上。尽管在这两种情况下，桥位Au原子都从fcc 3重中空位点移开，但桥-fcc的运动更大，从而为硫原子与桥接原子键合提供了更有利的几何形状。我们确认吸附能强烈依赖于 S-C 键的方向和位置，这可以用简单的配位几何模型来理解。这项工作对于烷硫醇表面扩散及其自组装单层结构具有重要意义。
We use dispersion-corrected density functional theory to explore the bridge-site asymmetry for methanethiol adsorbed on Au(111) with two different S–C bond orientations. We attribute the asymmetry to the intrinsic character of the Au(111) surface rather than the adsorbate. The preference for bridge-fcc versus bridge-hcp SCH3 adsorption sites is controlled by the S–C bond orientation. The system energy difference favors the bridge-fcc site by 8.1 meV on the unrelaxed Au(111) surface. Relaxing the Au substrate increased this energy difference to 26.1 meV. This asymmetry is also reflected in the atomic displacement of the relaxed Au surface. Although in both cases, the bridge-site Au atoms shift away from the fcc 3-fold hollow site, the motion is greater for the bridge-fcc allowing a more favorable geometry for the sulfur atom to bond to the bridging atoms. We confirm that the adsorption energy is strongly dependent on the S–C bond orientation and position, which can be understood in terms of a simple coordination geometry model. This work has important implications for alkanethiol surface diffusion and the structure of their self-assembled monolayers.