Effect of a SiO2 layer on the thermal transport properties of <100> Si nanowires: A molecular dynamics study

The presence of a SiO2 layer on Si nanowires (SiNWs) has been found through molecular dynamics simulation to reduce their thermal conductivity (κ), with κ approaching the amorphous limit of Si as the oxide layer thickness is increased. Through analysis of the phonon energy dispersion and vibrational density of states (VDOS) spectrum, this decrease in κ was attributed to dispersionless vibrational states that appear in the low energy range below 4 THz as a result of the lattice vibration of Si atoms near the SiO2/Si interface. The SiO2 layer also induced a low-frequency tail in the VDOS spectrum, the length of which was more closely correlated to the reduction in κ than the frequency-integrated value of the VDOS spectrum. These findings provide a more refined explanation for the decrease in κ than has been previously observed, and contribute to providing a greater understanding of the anomalistic vibration near the interface that is critical to determining the heat conductivity in nanoscale materials.