Molecular Modeling Of MPS SAMs On Si(100) Surface

In the recent decades, alkylsilanes self-assembled monolayers (SAMs) had been intensively studied because of their excellent physical and chemical properties and wide applications. But there are few studies to the short chain alkylsilane SAMs, especially for the SAMs mechanism. With the rapid development of computer technology, it becomes possible to study the structures and the properties of this material using molecular modeling. In this dissertation, molecular mechanical (MM) simulations, quantum mechanical (QM) density functional theory (DFT) calculations, together with molecular dynamic (MD) method have been used to study the self-assembled monolayer (SAMs) formed from 3-mercaptopropyltrimethoxysilane (MPS) on hydroxylated Si wafer.Firstly, the model of MPS self-assembled monolayer on the hydroxylated Si wafer was built, and then the quantum mechanical DFT method was used to correct the validations of the COMPASS force field which we chose in this simulation. The optical surface coverage and the packing pattern were obtained by comparing the average energy per chain in different simulation cells. The optical packing structure is zigzag substituted pattern with about 50% surface coverage. The thickness of the monolayer is about 0.8nm.The dynamic simulations at different temperature showed that the temperature have little effect to the SAMs monolayer structure, as the monolayer structure at 500 K is approximate to the one at 298 K. We also carried out the solvent dynamic simulation to find how the solvent affects the monolayer structure. The results showed that all of the solvent molecules stayed on the surface of the monolayer film not in the middle of it, which indicated that the SAMs monolayer is a highly compacted film.