Lousada Cláudio M, Johansson Adam Johannes, Korzhavyi Pavel A
Department of Materials Science and Engineering, KTH Royal Institute of Technology SE-, 100 44, Stockholm, Sweden.
Swedish Nuclear Fuel and Waste Management Co. (SKB), Evenemangsgatan 13, Box 3091, 169 03, Solna, Sweden.
Chemphyschem. 2018 Sep 5;19(17):2159-2168. doi: 10.1002/cphc.201800246. Epub 2018 Jun 19.
Understanding the surface site preference for single adsorbates, the interactions between adsorbates, how these interactions affect surface site specificity in adsorption and perturb the electronic states of surfaces is important for rationalizing the structure of interfaces and the growth of surface products. Herein, using density functional theory (DFT) calculations, we investigated the adsorption of H S, HS and, S onto Cu(110). The surface site specificity observed for single adsorbates can be largely affected by the presence of other adsorbates, especially S that can affect the adsorption of other species even at distances of 13 Å. The large supercell employed with a surface periodicity of (6×6) allowed us to safely use the Helmholtz method for the determination of the dipole of the surface-adsorbate complex at low adsorbate coverages. We found that the surface perturbation induced by S can be explained by the charge transfer model, H S leads to a perturbation of the surface that arises mostly from Pauli exclusion effects, whereas HS shows a mix of charge transfer and Pauli exclusion effects. These effects have a large contribution to the long range adsorbate-adsorbate interactions observed. Further support for the long range adsorbate-adsorbate interactions are the values of the adsorption energies of adsorbate pairs that are larger than the sum of the adsorption energies of the single adsorbates that constitute the pair. This happens even for large distances and thus goes beyond the H-bond contribution for the H-bond capable adsorbate pairs. Exploiting this knowledge we investigated two models for describing the first stages of growth of a layer of S-atoms at the surface: the formation of islands versus the formation of more homogeneous surface distributions of S-atoms. We found that for coverages lower than 0.5 ML the S-atoms prefer to cluster as islands that evolve to stripes along the [1 0] direction with increasing coverage. At 0.5 ML a homogeneous distribution of S-atoms becomes more stable than the formation of stripes. For the coverage equivalent to 1 ML, the formation of two half-monolayers of S-atoms that disrupt the Cu-Cu bonds between the first and second layer is more favorable than the formation of 1 ML homogeneous coverage of S-atoms. Here the S-Cu bond distances and geometries are reminiscent of pyrite, covellite, and to some extent chalcocite. The small energy difference of ≈0.1 eV that exists between this structure and the formation of 1 ML suggests that in a real system at finite temperature both structures may coexist leading to a structure with even lower symmetry.
理解单个吸附质的表面位点偏好、吸附质之间的相互作用、这些相互作用如何影响吸附中的表面位点特异性以及如何扰动表面的电子态，对于阐明界面结构和表面产物的生长具有重要意义。在此，我们使用密度泛函理论（DFT）计算研究了H₂S、HS⁻和S在Cu(110)上的吸附。单个吸附质所观察到的表面位点特异性会受到其他吸附质的显著影响，尤其是S，即使在距离为13 Å时，它也能影响其他物种的吸附。采用具有(6×6)表面周期性的大超胞，使我们能够在低吸附质覆盖度下安全地使用亥姆霍兹方法来确定表面 - 吸附质复合物的偶极。我们发现，S引起的表面扰动可以用电荷转移模型来解释，H₂S导致的表面扰动主要源于泡利不相容效应，而HS⁻则表现出电荷转移和泡利不相容效应的混合。这些效应在观察到的长程吸附质 - 吸附质相互作用中起了很大作用。吸附质对的吸附能值大于构成该对的单个吸附质吸附能之和，这进一步支持了长程吸附质 - 吸附质相互作用。即使对于较大距离也是如此，因此超出了能形成氢键的吸附质对的氢键贡献。利用这一知识，我们研究了两种描述表面S原子层生长第一阶段的模型：岛状形成与S原子更均匀表面分布的形成。我们发现，对于覆盖度低于0.5 ML的情况，S原子倾向于聚集成岛状，随着覆盖度增加，这些岛状会沿[1 0]方向演变成条纹。在0.5 ML时，S原子的均匀分布比条纹的形成更稳定。对于相当于1 ML的覆盖度，形成破坏第一层和第二层之间Cu - Cu键的两个半单层S原子比形成1 ML均匀覆盖的S原子更有利。这里S - Cu键的距离和几何形状让人联想到黄铁矿、铜蓝，在一定程度上还有辉铜矿。这种结构与形成1 ML之间存在约0.1 eV的小能量差，这表明在有限温度的实际系统中，这两种结构可能共存，导致对称性更低的结构。
