Dimers at Ge/Si(001) surfaces: Ge coverage dependent quenching, reactivation of flip-flop motion, and interaction with dimer vacancy lines

Abstract

We studied Ge coverage $({\ensuremath{\theta}}_{\mathrm{Ge}})$ dependent quenching, reactivation of the flip-flop motion, and interaction with dimer vacancy lines (DVLs) of dimers on Ge/Si(001) surfaces using a scanning tunneling microscope (STM) combined with a molecular beam epitaxy apparatus. Deposition of $\ensuremath{\sim}0.3\mathrm{ML}$ (monolayer) Ge quenched the flip-flop motion, making all dimers asymmetric. Further deposition introduced DVLs at ${\ensuremath{\theta}}_{\mathrm{Ge}}>~\ensuremath{\sim}0.5\mathrm{ML},$ and symmetric dimer domains appeared again locally at $\ensuremath{\theta}>~1.5\mathrm{ML}.$ High-resolution STM images indicated that asymmetric dimer rows always invert their phase in alternation with buckled dimer's up-end at the DVLs. Low-temperature STM images indicated that the symmetric dimer domains were due to flip-flopping of asymmetric dimers activated by large ${\ensuremath{\theta}}_{\mathrm{Ge}}$ at room temperature. The symmetric dimer domains extended along the dimer rows over the DVLs due to the phase correlation.