NATURE OF BONDING OF ALKALI-METALS TO SI(111)
NATURE OF BONDING OF ALKALI-METALS TO SI(111)
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DOI：
10.1103/physrevb.51.1581
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发表时间：
1995-01-15
影响因子：
3.7
通讯作者：
ILLAS, F
中科院分区：
文献类型：
--
作者：
CLOTET, A;RICART, JM;ILLAS, F
采用从头算Hartree-Fock簇模型方法研究了Si（111）表面碱金属Li与Cs之间的化学吸附键的性质。对模拟该表面高对称位置的各种簇模型进行了比较和系统的研究。在所有情况下，我们发现高离子键的共价效应对相互作用能的参与很小，其范围从化学吸附Li的20%到不同活性位点以上Rb和Cs的10%。这一结果与着重于相互作用能、最终Hartree-Fock波函数、偶极矩及其随吸附表面距离变化的分析相一致。我们发现化学吸附的碱金属的偶极矩比离子键的偶极矩要小，因为衬底极化。因此，我们认为，测量功函数的变化不足以提取有关给定相互作用的离子性的信息。这与先前考虑金属基板的工作一致。在这里，我们证明了同样的机制也适用于半导体表面。
The nature of the chemisorption bond between alkali metals, Li to Cs, on the Si (111) surface has been studied by means of the ab initio Hartree-Fock cluster-model approach. A comparative and systematic study has been carried out for a variety of cluster models simulating the high-symmetry sites of this surface. In all cases we found the bond highly ionic with a small participation of covalent effects to the interaction energy, which ranges from≊ 20% for chemisorbed Li to less than 10% for Rb and Cs above the different active sites. This result is consistent with several analyses of the interaction focused on the interaction energy, the final Hartree-Fock wave function, the analysis of the dipole moment, and of its variation with the adsorbate-surface distance. We show that the dipole moment for chemisorbed alkali metals is smaller than the one expected from an ionic bond because of the substrate polarization. Consequently we argue that changes in the measured work function are not adequate to extract information about the ionicity of a given interaction. This is in agreement with previous works considering a metal substrate. Here we show that the same mechanism holds for semiconductor surfaces as well.