Dimer buckling dynamics in the vicinity of missing dimers on Si(1 0 0) surfaces

The Si(1 0 0) surfaces undergo an order–disorder phase transition from the 2×1 to the c(4×2) structure below the critical temperature Tc, which is strongly influenced near Tc by surface defects. We study the missing dimer effects on both the phase transition and the dimer buckling dynamics in the vicinity of missing dimers, based on the Ising spin model Hamiltonian. Temperature dependence of the apparent “order parameter” corresponding to the normalized (1412) low energy electron diffraction spot intensity was calculated by the Metropolis method and the buckling dynamics was calculated by the kinetic Monte-Carlo simulation. The “order parameter” is strongly suppressed near Tc as missing dimer concentration increases, while the suppression is relaxed with lowering temperature. The suppression of the “order parameter” near Tc is caused by formation of out-of-phase domain boundaries induced by missing dimers, while the out-of-phase domain boundaries are diminished as temperature decreases. From the time evolution of dimer buckling near Tc, the time averaged buckling configuration over duration Δt was calculated in the vicinity of missing dimers. It suggests strong dependence on the scanning velocity of the scanning tunneling microscope image in the vicinity of missing dimers.