√7  ×  √3 surface with a double layer of In on Si(1 1 1) exhibiting both hexagonal and rectangular features

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