STM studies of clean, CO- and O sub(2)-exposed Pt(100)-hex-R0.7 degree

• Published in: Surface science 1994-01, Vol.306 (1-2), p.10-20
• Main Authors: Borg, A, Hilmen, A-M, Bergene, E
• Format: Article
• Language: English
• ISSN: 0039-6028

The structure of the Pt(100)-hex-R0.7 degree reconstructed phase has been studied by scanning tunneling microscopy (STM). The hexagonal first layer superstructure of this surface, written in matrix notation as ( super(N) sub(-) sub(1) super(1) sub(5)), N identical with 12-14, was imaged with atomic resolution. The fivefold periodicity of this reconstruction was confirmed. The coexistence of differently oriented hexagonal domains on a single terrace was observed. Steps along the longer corrugation length of the surface reconstruction were found, on the average, to follow the [N 1] direction of the hexagonal Pt overlayer rather than any low-index direction of the square substrate. The transition from the ( super(N) sub(-) sub(1) super(1) sub(5)) reconstruction to the Pt(100)-(1 x 1) surface structure due to exposure to CO and O sub(2) was found to be initiated by heterogeneous nucleation, the nucleation centers being step edges and structural irregularities disrupting the hexagonal structure along a direction close to the hexagonal [1 5] direction. The growth of the (1 x 1) phase was highly anisotropic, i.e. the growth being much faster along the [01 1] direction (the substrate direction closer to the [N 1] direction of the hexagonal layer) than along the [011] direction. A higher density of atoms in the hexagonal than in the (1 x 1) surface layer causes islands, a single Pt(100) lattice spacing high, to form during the structural transformation. These islands were found to be a mixture of isotropic islands with diameter 10-15 angstrom and islands highly elongated along the faster growth direction of the (1 x 1) phase.