A molecular dynamics study on mass transport characteristics in the vicinity of SiO₂-water/IPA interfaces

Mass transport in the vicinity of solid-liquid interfaces exhibits anomalous characteristics that differ from those in bulk liquids. These anomalous transport properties play a crucial role in recent nanoscale applications such as wet processing in semiconductor fabrication, surface modification by chemical treatment, and dynamic coating. In the present study, interfaces between solid SiO₂ and liquid water or isopropyl alcohol (IPA), which are typically used in the semiconductor industry, were investigated using molecular dynamics (MD) simulations. The molecular-scale structures of the adsorption layers of water or IPA molecules were examined, and self-diffusion coefficients of these liquids related to migration of molecules in the direction parallel to the interfaces were calculated. Both H- and OH-terminated SiO₂ surfaces were investigated in this study. It was found that layered structures of water and IPA molecules form near the interfaces, and were influenced by the crystal plane orientation. To examine the influences of these structures on molecular transport, local self-diffusion coefficients of water and IPA were derived via MD simulation using two methods based on the mean square displacement and on the velocity auto correlation function. The present study focused on a system of two solid walls with a spacing on the order of 10 nm with the liquids confined in between. It was found that the self-diffusion coefficients of water and IPA are reduced in the vicinity of the interfaces. The self-diffusion coefficient of water approaches its bulk value when separated from the solid wall by approximately 2-3 nm, while in the case of IPA, the solid wall influences the liquid properties more deeply into the liquid phase.