Atom-surface scattering: a comparative study considering real and complex absorbing potentials

In this paper a low density atomic gas colliding on a solid surface was modelled using the quantum scattering theory. The surface has discrete trapping/scattering centers in its lattice. In the model, a harmonic potential for the surface atoms interaction and a constant effective mean field for the gas atoms interactions were considered. The projectile atoms were assumed to be interacted with a solid surface atoms by two different potential models: (i) the Morse potential model, which is a real absorbing potential; and (ii) the Scarf II potential, which is a complex absorbing potential. The scattering probability densities for both models were calculated analytically via the first Born approximation. The effect of the incident atom energies as well as the distance of gas atoms from the surface on the probability densities were studied for both real and complex absorbing potentials. Comparisons have been made between these two types of potentials using the Lippmann-Schwinger quantum scattering equation. It was found that in addition to the competition between repulsive and attractive parts of the potentials, the imaginary part of the complex Scarf II potential has a significant effect on the distance of gas atoms from the surface. The adsorption probabilities of incident atoms on the surface considering the Morse model as well as Scarf II potential were obtained analytically as a function of distance from surface and kinetic energy of projectiles. Comparison our calculated adsorption coefficient with the simulation data of isothermal density distribution for nitrogen and argon adsorbed on the graphite surface shows that the maximum adsorption positions for both potential models provide a good agreement with simulation results.