Microstructural analysis of liquid and amorphous SiO2 nanoparticles

Microstructural properties of liquid and amorphous SiO2 nanoparticles have been investigated via molecular dynamics (MD) simulations with the interatomic potentials that have weak Coulomb interaction and Morse-type short-range interaction under non-periodic boundary conditions. Structural properties of spherical nanoparticles with different sizes of 2, 4 and 6 nm obtained at 3500 K have been studied through partial radial distribution functions (PRDFs), coordination number and bond-angle distributions, and compared with those observed in the bulk. The core and surface structures of liquid SiO2 nanoparticles have been studied in detail. We found significant size effects on structure of nanoparticles. Calculations also show that if the size is larger than 4 nm, liquid SiO2 nanoparticles at the temperature of 3500 K have a lightly distorted tetrahedral network structure with the mean coordination number ZSi-O≈4.0 and ZO-Si≈2.0 like those observed in the bulk. Moreover, temperature dependence of structural defects and SiOx stoichiometry in nanoparticles on cooling from the melt has been found and presented.