The inelastic scattering of He from Cu(001) at 20 K

The inelastic scattering of He atoms from a (001) surface of copper at 20 K has been studied. The energy analyzer consists of a LiF crystal situated close to the normal of the copper sample crystal. Incident energies of 23 and 64 meV have been used and evidence has been obtained of energy gain and energy loss events. The energy analyzer can be used in two modes: (1) to fix the analyzer crystal to receive atoms of a certain energy range while scanning the sample crystal or (2) to scan the analyzer crystal for a particular setting of the sample crystal. No evidence of phonons from a surface wave branch was found and most of the inelastic events occur very close to the forward direction.