Surface diffusion of single vacancies onGe(111)−c(2×8)studied by variable temperature scanning tunneling microscopy

Abstract

The dynamics of single vacancies on $\mathrm{Ge}(111)\text{\ensuremath{-}}c(2\ifmmode\times\else\texttimes\fi{}8)$ surfaces have been investigated by means of variable temperature scanning tunneling microscopy (STM). These vacancies were deliberately created with the STM at different sample temperatures by slight tip-sample contacts. The activation energies and the preexponential factors for the surface diffusion of the created vacancies have been measured, finding that it is a thermally activated motion that presents a slight anisotropic behavior. The activation energy barrier obtained along the $[1\overline{1}0]$ direction is ${E}_{dy}=0.83\ifmmode\pm\else\textpm\fi{}0.03\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, while along $[\overline{1}\overline{1}2]$ it is ${E}_{dx}=0.95\ifmmode\pm\else\textpm\fi{}0.04\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$. The origin of such anisotropy is discussed in terms of previous experimental results measured only at room temperature as well as previous first-principle calculations of the pristine $\mathrm{Ge}(111)\text{\ensuremath{-}}c(2\ifmmode\times\else\texttimes\fi{}8)$ surface. Finally, the vacancy extraction procedure has been investigated in a wide temperature range and it is shown for the first time that it is possible to create single vacancies at temperatures as low as $40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$.