Ordering of dimer vacancies on the Si(100) surface

We have investigated the ordering of dimer vacancies, in particular the formation of dimer-vacancy line defects, on the Si(100) surface using a tight-binding total-energy approach. We find that the dimer-vacancy line formed perpendicular to the direction of the surface dimer row is energetically favorable at low vacancy concentrations, whereas at higher vacancy concentrations the dimer-vacancy line is aligned parallel to the direction of the surface dimer row. The energetics and geometries of various dimer-vacancy configurations and the possible pathways to the line-defect formation through the diffusion of dimer vacancies are discussed. The calculated results are in good agreement with experiments and provide an explanation for the observed structural transition resulted from a temperature-driven random-ordered dimer-vacancy redistribution.