Yamamoto Hideaki, Watanabe Takanobu, Ohdomari Iwao
Faculty of Science and Engineering, Waseda University, 3-4-1 Ohkubo, Shinjuku-ku, Tokyo 169-8555, Japan.
J Chem Phys. 2008 Apr 28;128(16):164710. doi: 10.1063/1.2895052.
The bonding network of an alkylsilane self-assembled monolayer (SAM)SiO(2) substrate interface is investigated by means of canonical Monte Carlo (MC) simulations. SAMSiO(2) systems with different interfacial bonding topologies are sampled by the Metropolis MC method, and the AMBER potential with a newly developed organosilicon parameters are used to obtain an optimized structure with a given bonding topology. The underlying substrates are modeled as hydroxy-terminated (100) or (111) cristobalites. The SAMSiO(2) interface is characterized by a polysiloxane bonding network which comprises anchoring bonds and cross-linking bonds, namely, molecule-substrate and molecule-molecule Si-O-Si bonds, respectively. We show that at thermal equilibrium, the ratio of the number of anchoring bonds to cross-linking bonds decreases as a total Si-O-Si bond density increases, and that nevertheless, number of anchoring bonds always dominate over that of cross-linking bonds. Moreover we show that the total Si-O-Si bond density strongly affects the lateral ordering of the alkylsilane molecules, and that increase in the Si-O-Si bond density disorders the molecular packing. Our results imply that a lab-to-lab variation in the experimentally prepared SAMs can be attributed to different Si-O-Si bond densities at the SAMSiO(2) interface.
通过规范蒙特卡罗（MC）模拟研究了烷基硅烷自组装单分子层（SAM）与SiO₂衬底界面的键合网络。采用Metropolis MC方法对具有不同界面键合拓扑结构的SAM-SiO₂系统进行采样，并使用具有新开发的有机硅参数的AMBER势来获得具有给定键合拓扑结构的优化结构。底层衬底被建模为羟基封端的（100）或（111）方石英。SAM-SiO₂界面的特征是一个聚硅氧烷键合网络，它包括锚定键和交联键，即分别为分子-衬底和分子-分子的Si-O-Si键。我们表明，在热平衡时，随着总Si-O-Si键密度的增加，锚定键与交联键的数量比降低，然而，锚定键的数量始终超过交联键的数量。此外，我们表明总Si-O-Si键密度强烈影响烷基硅烷分子的横向有序性，并且Si-O-Si键密度的增加会使分子堆积无序。我们的结果表明，实验制备的SAM在不同实验室之间的差异可归因于SAM-SiO₂界面处不同的Si-O-Si键密度。
