Velocity-dependent surface corrugation in gas-surface scattering

Abstract

Gas-surface scattering transitions from the thermal to the structure scattering regime as incident energy increases, with the dominant mechanism shifting from surface thermal motion to surface corrugation. Conventional models such as the Maxwell and Cercignani-Lampis-Lord (CLL) models incorporate thermal motion but neglect explicit corrugation effects, while the washboard model accounts for corrugation yet violates reciprocity. To overcome these limitations, the washboard-CLL hybrid approach has been proposed. In this approach, the surface is represented using a washboard model with random local tilts, while velocity updates are performed via the CLL model to ensure reciprocity. However, this approach assumes an energy-independent distribution of surface tilts, while in reality high-energy incident particles penetrate deeper into the surface and experience enhanced corrugation. To address this, this study proposes a corrugated CLL model incorporating a velocity-dependent corrugation factor. Building on the washboard-CLL hybrid approach, the model represents surface corrugation as a function of incident velocity and employs a Metropolis-Hastings acceptance to preserve reciprocity. Validation against molecular beam scattering experiments demonstrates that the model successfully reproduces the nonmonotonic angular distribution, which narrows in the thermal regime and broadens in the structural regime with increasing incident energy. Additionally, it captures the gradual inversion of the energy distribution slope from negative to positive as incident energy increases. Overall, the corrugated CLL model provides a unified and physically consistent description of gas-surface scattering over a wide range of incident energies and scattering angles.