Scanning tunneling microscopy of the $7\times 7$ to $3\times 1$ transformation induced on the Si(111) surface by Na adsorption

Using scanning tunneling microscopy (STM), the process of the $\mathrm{Si}\mathrm{}\left(111\right)3\times 1-\mathrm{Na}$ phase formation induced by Na adsorption on the $\mathrm{Si}\mathrm{}\left(111\right)7\times 7$ samples with a terrace width of 3000–6000 Å has been studied. The STM monitoring of the successive stages of the $7\times 7$ to $3\times 1$ transformation enables us to elucidate its main regularities. The redistribution of Si atoms in a top Si(111) layer has been found to play a critical role in the $\mathrm{Si}\mathrm{}\left(111\right)3\times 1-\mathrm{Na}$ growth mode. As a result of the Si redistribution, initially flat $\mathrm{Si}\mathrm{}\left(111\right)7\times 7$ terrace converts into the two-level system of the $3\times 1-\mathrm{Na}$ islands on the $3\times 1-\mathrm{Na}$ terrace. From the quantitative consideration of the Si mass transport balance, the top Si atom density of the $\mathrm{Si}\mathrm{}\left(111\right)3\times 1-\mathrm{Na}$ phase has been determined to be 4/3 monolayer.