Study of structure and lattice dynamics of the Sr$_2$CuO$_2$Cl$_2$(001) surface by helium-atom scattering

Structure and lattice dynamics of the (001) surface of Sr$_2$CuO$_2$Cl$_2$ have been studied by helium atom scattering (HAS). Analysis of diffraction patterns obtained by elastic HAS revealed a surface periodicity consistent with bulk termination, and confirms that the surface is non-polar and stable which favors a SrCl surface termination. Bulk and surface lattice dynamical calculations based on the shell-model were carried out to characterize the experimental phonon dispersions obtained by inelastic HAS. No experimental surface mode was observed above 200 cm$^{-1}$. Comparison between the experimental data and theoretical results for two different slabs with SrCl and CuO$_2$ terminations showed that the experimental data conforms exclusively with the SrCl surface modes.