Helium reflectivity of the Si(111)-(1×1) H surface for use in atom optical elements

We investigate the reflectivity of Si(111)-(1×1) H for helium atoms with particular reference to atom optical applications, which require a high specular reflectivity. Quantum close-coupling calculations using an empirical potential are used to identify the optimum scattering conditions. We show that a diffraction probability >0.5 in the specular channel can be obtained in a kinematic window near 20 meV with near-normal incidence (polar angle <5°).