Understanding the Three Phases of Iodine on Silver (111) Through Low-Temperature Imaging and Nearest Neighbor Networks.

We imaged the three phases ((√3×√3)R30 (R), triangular (T) and hexagonal (H)) of iodine on Ag (111) with low-temperature scanning tunneling microscopy and determined the relation of the surface atoms with observed superstructures and the underlying Ag (111) lattice in real space. Both the H and the T phase show a superstructure. For the H phase we found a charge-density-wave-like superstructure centered on iodine hollow sites. The superstructure lattice vectors vary between 4 and 5 lattice constants of the hexagonal iodine lattice leading to an uneven appearance. The structure of the T phase was surprising. A rosette like iodine monolayer is stabilized by adatoms sitting at the center of each rosette. Variations in the adatom distances match the Ag (111) lattice constant. Finally, measurements of mirror domains allow us to uniquely align the rosette structure to the Ag lattice. It has been known for some time from LEED observations that iodine forms three phases on silver (111) depending on coverage. The phases were classified according to their LEED appearance. The R and likely the H phase have been observed before in STM. However, to our knowledge no prior STM measurements of the Tphase exist. The results and analytical methods used will be described in detail.