Diffraction of helium from a stepped surface: Cu(117) — An experimental study

The scattering of an helium nozzle beam (incident energy 21 and 63 meV) from a copper (117) stepped surface has been studied for crystal temperature ranging from 70 to 773 K. The diffraction pattern from the step array is readily seen. The influence of residual impurity on the surface is carefully discussed. Special attention has been paid to the influence of experimental factors upon peak shapes. True peak amplitudes are deduced. The peak intensities versus temperature and versus incidence angle has been measured. Extrapolation of the intensities to 0 K allows a direct comparison of the data with the prediction of a hard corrugated wall model. A corrugation profile is given which fits quite well the data. Clear evidence for resonances with bound states has been found. Three energy levels of the potential well are thus determined (5.9,4.0, 2.1 meV) which agrees with a Morse or a 3–9 potential.