Reexamination of the $\mathrm{Si}\mathrm{}\left(111\right)3\times 1-\mathrm{Na}$ reconstruction on the basis of Si atom density and unit cluster determination

Using scanning tunneling microscopy, features of the $\mathrm{Si}\mathrm{}\left(111\right)3\times 1-\mathrm{Na}$ reconstruction have been found, namely, Si atom density of 4/3 ML and a unit cluster that shows up in STM images as a group of four protrusions forming a $(\sqrt{3}a\times 1a)$ rectangle. These findings led to the reexamination of the atomic arrangement of a $\mathrm{Si}\mathrm{}\left(111\right)3\times 1$ phase. As a result, a double-$\pi$-bonded chain model is proposed. The model incorporates two Si $\pi$-bonded chains in faulted-unfaulted orientations connected through Na atoms.