√7 x √3 surface with a double layer of In on Si(111) exhibiting both hexagonal and rectangular features

Using a scanning tunneling microscope (STM), we demonstrate that the In-induced hexagonal (root 7 x root 3-hex) and rectangular (root 7 x root 3-rect) root 7 x root 3 phases on Si(111) are from the same surface with a double layer of In. The double-layer In thickness was derived from observations that a root 7 x root 3-hex island was formed on the root 7 x root 3-'striped' phase, which is believed to have a single layer of In atoms. Bias-dependent STM images were obtained from the same root 7 x root 3 domain and exhibited both root 7 x root 3-hex and root 7 x root 3-rect features, which led to the conclusion that both root 7 x root 3 STM features originate from the same structure. These findings are in stark contrast to the prevailing idea that there are two root 7 x root 3 surfaces with different structures and In coverage. We also observed a long-range Moire-like superstructure in the root 7 x root 3 surface and attribute it to the mismatch of the lattices of the surface layer of In and the Si(1 1 1) substrate.