Surface diffusion of single vacancies on Ge(111)-c(2x8) studied by variable temperature scanning tunneling microscopy -: art. no. 165410

The dynamics of single vacancies on Ge(111)-c(2x8) 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 (1) over bar0] direction is E-dy=0.83+/-0.03 eV, while along [(1) over bar(1) over bar2] it is E-dx=0.95+/-0.04 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 Ge(111)-c(2x8) 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 K.