Thermal conductivity and stability for ultrathin SiO₂ nanowires: Insight from molecular dynamics simulation

The thermal character of ultrathin silica (SiO₂) nanowires was studied by molecular dynamics simulation, whose structures have been predicted in our previous study. Eight structures including two-, three-, four-, five-membered ring structures (2MR, 2MR-2O, 3MR-3O, 4MR-4O, and 5MR-5O), 4MR-3facet, 4MR-4facet, 4MR-5facet (4MR-3f, 4MR-4f, and 4MR-5f) were considered for different nanowire sizes. Thermal conductivities of all nanowire structures were derived from the inverse ratio of thermal conductivity to the length of the simulated cell by non-equilibrium molecular dynamics simulation (NEMD). For the membered and faceted nanowires, the thermal conductivity considerably increases when the nanowire size decreases. For the membered nanowires, the thermal conductivities of 2MR and 5MR-5O were about 162 and 20.5 times higher than that of bulk silica, and for the faceted nanowires, the thermal conductivities of 4MR-3f and 4MR-5f were about 24.6 and 13.5 times higher than that of bulk silica. The thermal stability of these nanowires was also investigated during the heating process of 300 to 5000 K, and variations of Si-O-Si and O-Si-O angles with the increasing temperature were used to indicate their melting points. The simulation results show the structures of all SiO₂ nanowires are still stable at temperatures over 3000 K, which is much higher than the melting point of bulk silica about 1978 K. The simulation results have concluded that SiO₂ nanowires are potential materials with ultra-high thermal conductivities and can be safely used in an environment at the temperature higher than 3000 K.