INELASTIC MULTIPHONON HELIUM SCATTERING FROM A STEPPED NI(977) SURFACE

The multiphonon energy exchange between a neutral He atom and a steppe d Ni(977) surface has been measured in order to examine how the presen ce of a regular array of atomic-scale steps on a surface modifies ener gy exchange in the classical multiphonon scattering regime. At elevate d substrate temperatures, we compare the multiphonon scattering with t he 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 smo oth and stepped surface. Specifically, changes in the vibrational mode s and associated surface density of states due to the presence of exte nded surface defects have a fundamental impact on the details of the e nergy exchange mechanism. (C) 1998 American Institute of Physics. [S00 21-9606(98)70640-3].