Helium-atom scattering investigation of facetting of the Al stepped (332) surface

Helium-atom scattering has been used to study the facetting of an aluminum crystal that was cut at an angle of 10.0° from the (111) face to produce a (332) periodically stepped surface. After initial surface preparation of repeated sputtering and annealing cycles, the diffraction peak structures indicated strong facetting. Data collected for a wide range of initial He-atom wave vectors between 4.3 A${\mathrm{̊}}^{\mathrm{-}1}$ (9.7 meV) and 12.5 A${\mathrm{̊}}^{\mathrm{-}1}$ (81.8 meV) along the [1¯ 1¯3] azimuth reveal well-formed (111), disordered (221), and a small proportion of (113) facets. The identification of facets is made relatively easy with He-atom scattering due to the large form factors for individual steps. From studies of the temperature dependence, three temperature ranges were identified. At the highest investigated surface temperatures (${\mathit{T}}_{\mathrm{Al}}$>650 K), (111) and (221) facets build up and predominate. For intermediate temperatures (650 K>${\mathit{T}}_{\mathrm{Al}}$>500 K) the macroscopic (332) face begins to form. At lower temperatures the surface is sufficiently immobile to inhibit a redistribution between facets. However, (221) facets do show a temperature-dependent roughness down to 300 K. The instantaneous long-range step distribution freezes in at ${\mathit{T}}_{\mathrm{Al}}$≤500 K.