Study of Self-Assembling Mechanims of Thiol-Self-Assembled Monolayers

本研究计划旨在了解分子自组装的微观机制。利用STM和XAFS研究了硫醇及相关分子自组装单层的形成过程。特别是，我们一直在关注分子-底物相互作用对自组装的影响。研究了不同底物（Au、Ag、Cu、O/Cu、Si）自组装过程中的分子取向和界面结构。通过对这些基质的系统比较，我们发现了形成有序结构的三个重要因素；(1)足够的分子密度，(2)表面扩散，(3)层内和界面结构之间的一致性。它需要实现一个良好的有序结构来满足所有这三个因素。我们还发现，如果因子(1)相对重要，吸附过程是限速步骤；如果因子(2)相对重要，扩散过程是限速步骤。另一个重点是在烷硫醇分子末端引入官能团时分子间相互作用变化的影响。特别是，我们已经研究了噻吩和卟啉引入的烷硫醇在金底物上的自组装。在引入噻吩的情况下，由于因子(3)提到的结构一致性随着分子密度的变化而变化，因此发现自组装仅在一定的覆盖范围内发生。在引入卟啉的分子中，除非巯基在空间上通过通道与卟啉部分分离，否则它们不会表现出自组装。插入长烷基链，因为由于空间位阻，大的卟啉部分阻止巯基接近底物，从而导致较低的分子密度。此外，我们还研究了与硫醇结构完全不同的硫代酚烯的自组装，发现硒代酚（C_4H_4Se）形成了一个高度有序的结构。少

The purpose of this research proposal is to understand microscopic mechanism of molecular self-assembly via. investigating formation process of self-assembled monolayers of thiol and related molecules by the use of STM and XAFS.In particular, we have been focusing on effects of molecule-substrate interactions on the self-assembly. The molecular orientation and the interface structure during self-assembling process have been investigated for different substrates (Au, Ag, Cu, O/Cu, Si). From systematic comparison for these substrates, we found three important factors to form well-ordered structures ; (1) sufficient molecular density, (2) surface diffusion and (3) consistency between intralayer and interface structures. It needs for achieving a well-ordered structure to satisfy all the three factors. We also found that the adsorption process is the rate-limiting step if the factor (1) is relatively important compared to the other factors while the diffusion process is the rate-limiting on … More e if the factor (2) is crucial. Another focusing point is effects of change in intermolecular interactions when introducing functional groups to the end of the alkanethiol molecules. Particularly, we have investigated self-assembly of thiophene- and porphyrin-introduced alkanethiols on gold substrates. In case of thiophene-introduced one, since the structure consistency as mentioned as factor (3) changes depending on molecular density, the self-assembly was found to take place only for a certain coverage range. In case of porphyrin-introduced molecules they exhibit no self-assembly unless the thiol group is spatially separated from the porphyrin moiety via.inserting long alkyl chains, because the large porphyrin moiety prevents the thiol group from having access to the substrate due to steric hindrance, which results in lower molecular density. Furthermore, we have investigated self-assembly of chalcogenophenes, of which structures are totally different from thiol, and found that selenophene (C_4H_4Se) forms a highly-ordered structure. Less