Inelastic multiphonon helium scattering from a stepped Ni„977... surface

The multiphonon energy exchange between a neutral He atom and a stepped Ni~977! surface has been measured in order to examine how the presence of a regular array of atomic-scale steps on a surface modifies energy exchange in the classical multiphonon scattering regime. At elevated substrate temperatures, we compare the multiphonon scattering with the predictions of a classical theory that has previously been used by others for assessing energy exchange involving a smooth surface. There is a significant discrepancy between the theoretical predictions and our experimental data, which we attribute to differences between a smooth and stepped surface. Specifically, changes in the vibrational modes and associated surface density of states due to the presence of extended surface defects have a fundamental impact on the details of the energy exchange mechanism. © 1998 American Institute of Physics. @S0021-9606~98!70640-3#