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首页> 外文期刊>Physical review >Dissociative versus molecular adsorption of phenol on Si(100)2×1: A first-principles calculation
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Dissociative versus molecular adsorption of phenol on Si(100)2×1: A first-principles calculation

机译：Si（100）2×1上苯酚的解离与分子吸附：第一性原理计算

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摘要

We investigated the competitive adsorption of a bifunctional molecule, phenol, on Si(100)2 × 1 by ab initio calculations. We performed geometry optimizations of phenol adsorbed either molecularly or dissociatively, on five possible sites (top, bridge, valley bridge, cave, and pedestal), in the low coverage regime. We found that the dissociative adsorption of phenol on top of a silicon dimer is the most favorable adsorption configuration. In the group of dissociative adsorption the phenol initially placed on the bridge or the valley-bridge sites ends up as a toplike local minima. The pedestal and cave sites remain as low-adsorption energy "open" sites. In the group of molecular adsorption, a higher adsorption energy is associated to the adsorption through an addition reaction and loss of the aromatic character (bridge, valley-bridge, and pedestal sites). Standard butterfly or diagonal butterfly are the corresponding optimized geometries. Retention of aromatic character and lower adsorption energy are associated to the adsorption on the top and cave sites. The ordering of adsorption sites according to the adsorption energy shows a mixture of the dissociative and the molecular sites. In the case of adsorption on the top site, the adsorption energies after a rotation of the phenoxy fragment along the bonding axis and hydrogen migration on the surface are very similar. The bend of the phenoxy fragment on the surface, instead, is not favored (the adsorption energy is 1.004 eV lower compared to the vertical position). Different electron density maps were calculated for different adsorption sites and modes. Finally, we investigated the possibility that molecularly adsorbed phenol behaves as a precursor for the dissociative one by nudged elastic band calculations. We found a barrier of the same order of magnitude of the thermodynamic energy at room temperature for the conversion of the valley-bridge molecular into the top dissociative site.
机译：我们通过从头算算研究了双功能分子苯酚在Si（100）2×1上的竞争性吸附。在低覆盖范围内，我们在五个可能的位置（顶部，桥梁，山谷桥梁，洞穴和基座）上进行了分子吸附或解离吸附的苯酚的几何优化。我们发现苯酚在硅二聚体上的解离吸附是最有利的吸附构型。在解离吸附组中，最初放置在桥或谷桥位上的苯酚最终以顶部局部最小值的形式终止。基座和洞穴位置仍然是低吸附能量的“开放”位置。在分子吸附组中，较高的吸附能通过加成反应和芳族特性（桥，谷桥和基座位）的损失与吸附相关。标准蝶形或对角蝶形是相应的优化几何形状。保留芳香特性和较低的吸附能与顶部和洞穴位置的吸附有关。吸附位点根据吸附能的排序显示了离解位点和分子位点的混合。在顶部位置吸附的情况下，苯氧基片段沿键合轴旋转后的吸附能与表面上的氢迁移非常相似。相反，不希望苯氧基片段在表面上弯曲（吸附能量比垂直位置低1.004 eV）。针对不同的吸附位点和模式计算了不同的电子密度图。最后，我们通过推算弹性带计算了分子吸附的苯酚作为离解性苯酚的前体的可能性。我们发现了一个在室温下热力学能量数量级相同的屏障，可将谷桥分子转化为顶部离解位。

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