Dynamic phonon scattering rates of nanosurfaces with gas particles

The scattering rate of a nanosurface lattice interfaced with a gaseous boundary is derived and characterized. Gas particle collisions with crystal lattice atoms are found to exhibit dynamic behavior under varying gas flow speeds, accommodation coefficients and gas atomic/molecular masses. Numerical results of SiO 2 in a stationary N 2 atmosphere predict scattering rates ranging from 7.6 ps at 0.1 accommodation to 0.69 ps at full accommodation. Varying the inert gas masses was found to induce shorter carrier lifetimes of 0.23 ps for Xe/SiO 2 compared to 1.2 ps for He/SiO 2 . Additional results show longer phonon lifetimes for Ar and Ne compared to He, which is attributed to a greater He collision rate that exceeds the effects of heavier Ar and Ne perturbations. Comparison of the lattice-gas scattering rates to the scattering rates of adsorbed gas particles at 50% surface coverage show a 44% contribution to the total nanosurface-gas scattering component. The lattice-gas scattering effects on transport coefficients are investigated through thermal conductivity. Numerical predictions of thermal conductivity for a SiO 2 thin-film structure are first correlated to experimental data then characterized in both a stationary and flowing N 2 atmospheres. Decreases of 12% and 18% are predicted for stationary and Mach 0.9 flow velocity respectively, indicating that nanosurface-gas interactions can substantially impact transport coefficients when interfaced with gaseous boundaries. In order to gauge the magnitude of gaseous scattering effects, a dimensionless scattering number for nanosurface-gas systems is introduced as a ratio of the nanostructure characteristic dimension and gas particle surface interaction distance.