Understanding the Microscopic Structure of SAMs/SiO2 Interfaces in the Presence of Water Using First-Principles Modeling

Atomic scale modeling has been carried out on the grafting of chain organosilane compounds on SiO2 hydroxylated solid surfaces in the presence of water. The solvent is introduced explicitly from one to six water molecules in different positions of the grafting complex. The presence of water molecules has no effect on the arrangement of the chain with respect to the substrate, that is, the single chain does not lie perpendicular to the surface. However, the presence of one water molecule in the case of dimerized chains grafted on the surface allows a nice organization by decreasing the steric repulsion between the chains. This result demonstrates that the presence of water is primordial, even at low concentrations, to form a nice organization of SAMs on the surface. Energetic and geometrical properties obtained for each grafting system in the presence of water are discussed in detail and provide new insights on the understanding of the formation of self-assembled homogeneous organic films on microelectronics-type substrates.