Helium atom scattering experiments and molecular dynamics simulations of the structure and lattice dynamics of 15-layer acetylene films on KCl(001)

Abstract

The surface structure and lattice dynamics of thick films of 15 to 40 layers of acetylene adsorbed on a KCl(001) single crystal surface have been investigated at about 40 K by combining helium atom scattering (HAS) experiments with classical molecular dynamics simulations. As rarely occurs for physisorbates on ionic crystals layer-by-layer growth is observed by HAS up to at least 15 layers producing films with a (√2 × √2)R45° geometry. The simulations confirm the stability and structure of these layers up to about 100 K. The time-of-flight spectra reveal along the [110] direction at least four phonon modes, which are assigned by simulations based on the calculated power spectra of the velocity and angular autocorrelation functions.