Theory of helium diffraction from copper surfaces

There has been a variety of theoretical potentials proposed for the diffraction of low-energy helium atoms from metal surfaces. In this paper we shall consider a number of these potentials and test their predictions against the experimental results. An ideal system in which to carry out this comparison is provided by the set of copper surfaces Cu(110), Cu(100), Cu(113), Cu(115), and Cu(117), which provide a wide range of surface corrugations varying from very smooth to highly stepped. The comparison of theory and experiment is carried out by both calculation of the leading corrugation amplitudes and by coupled-channels calculations of the diffraction intensities. Good agreement of theory with experiment is found only if the hybridization energy of the helium with unoccupied metal states is included in the potential.