氧化亚氮和二己二硫醚分子自组装的NEXAFS研究

【作者】 吴太权；

【导师】 唐景昌； 李海洋；

【作者基本信息】 浙江大学 ， 凝聚态物理， 2005， 博士

【摘要】 近边X射线吸收精细结构(Near-edge X-rays Absorption Fine Structure, NEXAFS)是研究凝聚态物质原子结构和电子结构的可靠方法,特别对于无序体系NEXAFS已成为局域结构研究中的“指纹分析”法(fingerprint analysis),具有很高的精确度。这种方法非常适合于研究分子自组装系统的局域结构。本文我们利用多重散射团簇理论(MSC)和离散变分DV-Xa方法研究了氧化亚氮(N2O)分子多层膜以及其在过渡金属Cu(100)和Ag(110)表面吸附和反应的NEXAFS谱,求得这些系统的原子结构和电子结构信息。研究发现N20分子多层膜是一个分子自组装系统：N2O分子通过电荷和共价作用组成一条条平行错位的分子链,分子链相互耦合形成一个稳定的单层,最后N2O单层膜通过电荷和共价作用一层一层堆积成多层膜。优化计算求得相邻单层的间距(0.240 nm)和分子链中相邻N2O分子的间距(0.238 nm)很接近,这说明同一链间的作用和相邻层之间的作用的性质是一样的；但是相邻两条分子链相距0.478 nm,比上述层间距大得多,说明链与链之间为弱范德华力作用。MSC和DV-Xa揭示了实验谱中各共振峰的物理起源,其中两个强峰为π共振峰；高能区可区分5个弱结构,分别命名为s1,σ,s2,w1和w2,研究判定其中的弱结构σ和w2是σ型共振,都与特定的σ*空轨道相对应,其它弱结构没有特定空分子轨道与之对应,因此我们判定它们都是N2O分子N 1s NEXAFS谱中1峰和2峰的卫星峰。此外,研究揭示了N2O分子自组装形成的离子型势场严重的遏制了σ共振,使之成为一个弱结构。对于N2O/Cu(100)和N2O/Ag(110)吸附系统的研究,我们发现这两个吸附系统都属于弱分子吸附系统,他们的吸附模型是相似的,即N2O分子通过NT倾斜吸附在金属表面。这个结论和Ceballos等人的观点不同。对二己二硫醚(C12H26S2)分子自组装的研究,我们发现这些线性的二己二硫醚分子作平行有序排列,其截面为正方形,如同(100)面,相邻二直线分子之间达到0.47 nm,它们之间的弱范德华力保证了二己二硫醚多层膜成为一种稳定的分子自组装系统。更多还原

【Abstract】 NEXAFS (Near-edge X-rays Absorption Fine Structure) is a reliable method in studying the atomic and electronic structure of the condensed matter, especially for the disorder system, in which it has been identified as the "fingerprint analysis" of the local structure, and exhibits itself a high precision. The method is suitable for studying the local structure of the molecular self-assembly system. In this paper, we mainly utilize the multiple-scattering cluster (MSC) and DV-Xa methods to approach the NEXAFS spectra for the N2O multilayer and the N2O adsorbed on the Cu(100) and Ag(110) surfaces, and obtain their atomic structures and electronic states information. As for the N2O multilayer, the MSC calculation shows that it is a self-assembly system. Due to the electric and covalent interaction the N2O molecules make up a parallel dislocation chain. The molecular chains form a stable single layer by the coupling each other. At last the molecular layers stack one by one, thereupon become into a N2O multilayer by the electric and covalent interaction. Optimizetion calculation shows that the distance between the neighbor molecular layers (0.240 nm) is close to the distance between the neighbor molecules (0.238 nm) in the same molecular chain. They display the same characteristics. But the distance between the neighbor molecular chains is 0.478 nm, which is much bigger than the distance between the molecular layers, and this fact implies that the molecular chains in the same layer are coupling by the weak Van de Waals force. The MSC and DV-Xa methods have been employed to analyze the physical origin of all resonances in N 1 s NEXAFS spectrum of the N2O multilayer, in which the two intense peaks are both theπresonances, after these there are five weak features, named as s1,σ, s2, w1 and w2, in which the weak featuresσand w2 are both theσ-resonances, while the other weak features don’t correspond to the LUMOs, which are all the satellites of the peaks 1 and 2 due to the shake up effect of the N nuclei in the N2O molecules. Furthermore, the ionic potential of the N2O molecular self-assembly layer seriously weakens theσresonance, and makes it to be a weak feature. As to the N2O/Cu(100) and N2O/Ag(110) systems, we find that they are both the weak molecule adsorbption systems. The adsorption model of them are the same each other, that is, the NT atom of the N2O molecule attachs the surface. The conclusion is different from that of mentioned by Ceballos et al.As to dihexyldisulfide multilayer, we find that the linear dihexyldisulfide molecules are arranged in parallel each other, and show the cross section just like the (100) face. The distance between the neighbor molecules is 0.47 nm, so the interaction between them is only the weak Van de Waals force, which makes the dihexyldisulfide multilayer to be a stable molecular self-assembly system.更多还原