Au（111）表面甲基联二苯丙硫醇盐单层膜的原子结构∗

摘要

利用第一性原理研究了甲基联二苯丙硫醇盐(BP3S)单体、虚拟Au表面BP3S的分子链和单层膜及BP3S/Au(111)吸附系统的原子结构。计算表明BP3S单体呈对称结构，两苯环夹角为35◦±10◦。首先BP3S单体在虚拟Au(111)表面自组装成稳定的单一分子链。然后在虚拟Au(111)表面，分子链错位排列自组装成两种稳定的单层膜。在虚拟Au(111)-(√3×√7)和Au(111)-(√3×√13)表面，分子链与虚拟表面夹角分别为60◦和30◦。最后把两种稳定的单层膜吸附在Au(111)表面的四个吸附位，计算表明只有桥位和顶位稳定，且桥位的吸附能比顶位的吸附能低。比较吸附前后BP3S单层膜的结构变化，可知其变化不大，这说明吸附系统的结构参数主要取决于单层膜内的相互作用，衬底对其的影响不大。%The first-principle technique is employed to determine the structure of the BP3S monomer, the structures of the molecular chains and monolayers on virtual Au (111), and the atomic structure of BP3S/Au (111) adsorption system. The results show that the BP3S monomer presents a symmetric structure, and the angle between two benzene rings is 35◦± 10◦. At first, many BP3S monomers are assembled into one stable molecular chain in the virtual Au (111), the distance between the neighbor monmers is 0.516 nm, and the bind energy between the monmer and the molecular chain is 0.071 eV. It is a self-assembly system. Then many molecular chains are assembled into two stable monolayers in the virtual Au (111)-(√3 ×√7) and Au (111)-(√3 ×√13), and their coverages are 0.20 ML and 0.14 ML, respectively. In the virtual Au (111)-(√3 ×√7) and Au (111)-(√3 ×√13), the angles between the molecular chains and the virtual surface are 60◦ and 30◦, respectively, and the binding energies between the monmer and two monolayers are 0.101 eV and 0.125 eV, respectively. They are both the self-assembly systems. Finally, two monolayers are adsorbed on the Au (111)-(√3 ×√7) and Au (111)-(√3 ×√13) at four adsorption sites. The S atom is easy to obtain two electrons and turn into S2− ion, and the Au atom is easy to lose one electron and become Au+ ion, so the bridge site (two Au+ ions) is more stable than the top site (one Au+ ion), while the hcp and fcc hollow sites (three Au+ ions) are both unstable. In the Au (111)-(√3 ×√7), the chemisorption energy of the bridge site (−1.879 eV) is lower than that of the top site (−1.511 eV). And in the Au (111)-(√3×√13), the chemisorption energy of the bridge site (−1.691 eV) is lower than that of the top site (−1.492 eV). The results are confirmed in the other S-Au adsorption systems, such as the C6H13S/Au (111). A comparison between the structures of the BP3S monolayer before and after being adsorbed on Au (111) clearly shows that the structural parameters of the adsorption system depend mainly on the interaction in the monolayer, and that the contribution of Au (111) to the structure of the monolayer is weak. These results are confirmed in the other self-assembly adsorption systems.