LEED, Auger and work function study of iodine adsorbed on W(110)

Abstract

The adsorption of iodine on a W(110) surface has been studied by LEED, Auger and work function changes. LEED has revealed several phases which desorb in different temperature regimes and are accordingly designated γ, α, β 1, β 2, and β 3. The γ and α phases exhibited p(2 × 2) and p(2 × 1) surface nets respectively with coherently positioned antiphase boundaries which produced a splitting of selected LEED beams. The separation between the antiphase boundaries of the α phase increased with decreasing coverage. Both the γ and α phases were associated with molecularly absorbed iodine. The three β phases were associated with dissociatively adsorbed iodine which formed chain structures on the surface with the arrangement of iodine atoms within each chain being unique to the particular phase. Continuous changes in coverage then occurred by sheets of these chains shearing to produce packing faults at the resulting shear lines. This shearing process occurred coherently in the β 1 and β 3 phases and incoherently in the β 2 phases. In the former cases, the effect was seen by the continuous movement of coherent LEED beams with changing coverage. A phase diagram was constructed to describe the relative coverages and thermal stability of the phases. The characteristic Auger electron emission of iodine was observed at 495 eV and used to estimate the surface coverage. The work function was found to decrease by 0.4 eV with the adsorption of the first half monolayer and remained unchanged with further adsorption.