Scattering of thermal helium beams from high Miller index (stepped) platinum crystal surfaces

Helium beams generated by a 300 K source were scattered from single crystal platinum surfaces. The angular distribution of the scattered beam was monitored as a function of azimuthal angle phi and incident angle theta/subi/. The effect of the presence of atomic steps on the angular distribution of scattered helium atoms was studied on a crystal surface composed of terraces on the average five atoms in width separated by steps of monatomic height. Rainbow scattering is observed when the steps are oriented perpendicular to the incident beam direction indicating strong modulation of the angular distribution by the periodic step potential. Only specular scattering is observed when the incident beam impinges on the crystal along the step edges which indicates minimal effects of the presence of steps on the scattering distribution. These results as well as the absence of diffraction are in good agreement with previous theoretical calculations