Inelastic Scattering Dynamics of Argon and Oxygen Atoms on Roughened Kapton H Surfaces: Experiments and Modeling

Abstract The relationship between surface roughness and gas-surface scattering dynamics is important for several applications. However, there is a lack of detailed experimental data on hyperthermal gas-surface scattering dynamics on well-characterized rough surfaces. In this work, the link between surface roughness and gas-surface scattering dynamics was studied with experimental and computational tools. Molecular beam-surface scattering experiments were performed to evaluate the scattering dynamics of hyperthermal atomic beams of argon (at 7.1 and 5.3 eV) and oxygen (at 5.4 eV) on six different polyimide polymer (Kapton H) surfaces with root-mean-squared roughnesses spanning 2 orders of magnitude. Low-roughness surfaces produced quasi-specular angular flux distributions dominated by impulsive scattering, whereas rough surfaces exhibited broad angular distributions, enhanced thermal desorption, and greater out-of-plane scattering. Energy transfer depended on the incident atom and its energy but was largely independent of the roughness at a fixed deflection angle. Both energy accommodation and thermal desorption probability increased with decreasing incident angle and increasing surface roughness, approaching unity on the roughest surfaces. To model these results, we extended a Gaussian washboard roughness model using gamma-distributed surfaces. The gamma model improved predictions over Gaussian descriptions, accurately reproducing experimental trends in angular flux and energy transfer as well as accommodation coefficients estimated from experimental data. The fitted roughness parameters correlated positively with the topographical parameters measured by atomic force microscopy, although they did not match these parameters directly. A single set of roughness parameters captured scattering dynamics across different energies and incident atoms when coupled with gas-specific local gas-surface scattering models. These results establish the practical value of the model to simulate gas-surface scattering dynamics in the rarefied regime, as found in satellite interactions with the residual atmosphere in a very low Earth orbit.