STM observation and first-principles determination of Ge nanoscale structures on Si(111)

Abstract

Scanning tunneling microscopy observations and first-principles quantum mechanical calculations were employed to investigate the nanoscale structures formed on Si(111) surfaces upon germanium deposition at a coverage of $\ensuremath{\sim}0.3$ monolayer. At room temperature, Ge atoms form nanoclusters with sizes of $1.5--6\phantom{\rule{0.3em}{0ex}}\text{nanometers}$ in width. After annealing, the nanoclusters become two-dimensional islands with typical size of $\ensuremath{\sim}10$ nanometers in width. We propose that the annealing or high-$T$ deposition results in a partial transformation of $(7\ifmmode\times\else\texttimes\fi{}7)$ reconstructed unit cells to unreconstructed Si(111) configurations on which the Ge adatoms reside at the ${T}_{4}$ sites and form a $(\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3})R30\ifmmode^\circ\else\textdegree\fi{}$ reconstruction.