Impact of random nanoscale roughness on gas scattering dynamics

In this work, we develop a scattering kernel for surfaces having nanoscale roughness that distinctly characterises the two major types of interactions between gas molecules and rough surfaces, namely (a) the weak perturbations arising from the thermal motion of wall atoms, essentially gas–phonon collisions, which are captured by the well-established Cercignani–Lampis model, and (b) the hard collisions owing to the irregularities of the rough, static potential energy surface, which are generally described by the fully diffuse model. Drawing an analogy between wave–surface and gas–surface scattering, a pseudo Debye–Waller factor is incorporated into modelling as a weighting coefficient to allow the transition between smooth and rough surface conditions. The proposed scattering kernel is validated through high-fidelity molecular dynamics simulations that are performed for systems with varying roughness, temperature, and gas-surface combinations. The results indicate that the model well captures the scattering dynamics of gas molecular beams impinging on surfaces at different velocities, specifically for the accommodation coefficients and reflection patterns. Additionally, it accurately predicts macroscopic quantities such as velocity slip and temperature jumps across the range of tested conditions. The dataset contains molecular dynamics LAMMPS files and post-processing scripts to reproduce results from this work.