Structural transitions of chemisorbed iodine on Cu(1 0 0)

The adsorption of molecular iodine on Cu(1 0 0) was studied by low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) in conditions of ultrahigh vacuum. Chemisorbed iodine exhibits several structural phase transformations with increasing coverage. At the coverage θ=0.25 a simple p(2×2) structure with one iodine atom per unit mesh forms. The coverage θ is determined as the ratio of adsorbate species to surface substrate atoms. Further iodine dosing leads to the disappearance of the p(2×2) phase and the formation of a disordered (liquid) phase characterised by a diffuse LEED pattern. For this phase, no modulations at the atomic scale were observed by STM. At a coverage of θ=0.33 the iodine layer solidifies into a new well-ordered phase with a c(6×2) periodicity. At θ>0.33 a new c(14×2) phase was detected on the surface coexisting with the c(6×2). After the complete covering of the surface with the c(14×2) structure (θ=0.36) it continuously transforms into the more dense c(5×2) structure at saturation.