Molecular dynamics simulation of amorphous SiO2 thin films

Amorphous SiO2 thin films have been studied via molecular dynamics (MD) simulations. Thin film models (with two free surfaces) have been obtained by cooling from the melt with reactive force field (ReaxFF) potential. Structural and dynamic properties of the thin films are analyzed via radial pair distribution functions (RPDFs), coordination number distributions, ring statistics and bond-angle distributions. Fraction and role of structural defects have been analyzed and discussed. We also show temperature dependence of various thermodynamic quantities of the system. We found that structure of interior of thin films is close to that of the bulk while surface region contains a large amount of structural defects including dangling bonds, undercoordinated sites, small membered rings. Small and large membered rings concentrate mainly in the surface region and their fraction has a tendency to decrease with decreasing temperature.