Reversible phase transitions in the pseudomorphic 7×3 -hex in layer on Si(111)

Using scanning tunneling microscopy, reversible phase transitions have been detected in the modulated pseudomorphic In monolayer on the Si(111) surface. It has been found that the room-temperature quasihexagonal $\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{3}$ structure is transformed into the $\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$ structure during cooling in the temperature range from $265\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}225\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Further cooling results in developing long-range modulations in the In layer, including formation of the chevron-type structure with $6\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$ periodicity, the ordered arrays with regular antiphase domain boundaries with local $3\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$, and $2\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{7}$ periodicity and the chained-ring structure with $\frac{10}{3}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\frac{40}{3}\sqrt{3}$ periodicity, which is believed to originate from the $\frac{5}{3}\sqrt{3}\ifmmode\times\else\texttimes\fi{}\frac{5}{3}\sqrt{3}$ structure occurring at room temperature near surface defects and at domain boundaries of the original $\sqrt{7}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\text{\ensuremath{-}}\mathrm{In}$ phase.