Structures of Na and Cs layers adsorbed on Pt(111)

Abstract

The atomic structures of Na and Cs layers adsorbed on the Pt(111) face have been studied at 85 K and room temperature by LEED. At room temperature, Na layers are fully disordered while Cs overlayers exhibit ordered structures. At low temperature, (2×2) and ( 3 × 3 ) R30° phases are observed at Na coverage below 0.33. At higher coverages, the Na layer is formed by a mosaic of domains with incommensurate hexagonal structures which are either aligned or rotated relative to the substrate. The rotation angle of the rotated domains depends on the interatomic spacing in the layer. For Cs layers at low temperature the (2×2) structure is observed but the ( 3 × 3 ) structure is rotationally disordered. For Cs coverage beyond 0.33, a mosaic of domains with incommensurate structures which are either aligned or angularly disordered is formed at 85 K while at room temperature only the aligned structure is observed. The origin of the incommensurate aligned phases observed for both alkali layers is discussed and may be attributed to the influence of steps during the overlayer growth.