STM observation of the 2×3 and c(2×6) structures on Ba/Si(1 0 0)

Barium induced 2×3 and c(2×6) structures on Si(1 0 0), which appear at the Ba coverage below 1/3 ML, have been studied by scanning tunneling microscopy (STM). It is revealed that the 2×3 structure has only one adsorption phase, being independent of Ba coverage. Based on high resolution filled-state STM images where four protrusions are resolved in a unit cell, a model of 2×3 structure is proposed where the building unit consists of a Ba dimer and two Si dimers. It is also found that the c(2×6) structure always coexists with the 2×3 structure and has the same building block. The c(2×6) is realized when adjacent rows of building blocks are out of phase.