Dimer buckling dynamics in the vicinity of missing dimers on Si(100) surfaces

The Si(100) surfaces undergo an order-disorder phase transition from the 2 x 1 to the c(4 x 2) structure below the critical temperature T-e, which is strongly influenced near T-e by surface defects. We study the missing dimer effects on both the phase transition and the dimer buckling dynamics in th e vicinity of missing dimers, based on the Ising spin model Hamiltonian. Te mperature dependence of the apparent "order parameter" corresponding to the normalized (1/4 1/2) low energy electron diffraction spot intensity was ca lculated by the Metropolis method and the buckling dynamics was calculated by the kinetic Monte-Carlo simulation. The "order parameter" is strongly su ppressed near T-e as missing dimer concentration increases, while the suppr ession is relaxed with lowering temperature. The suppression of the "order parameter" near T-e is caused by formation of out-of-phase domain boundarie s induced by missing dimers, while the out-of-phase domain boundaries are d iminished as temperature decreases. From the time evolution of dimer buckli ng near T-e, the time averaged buckling configuration over duration Deltat was calculated in the vicinity of missing dimers. It suggests strong depend ence on the scanning velocity of the scanning tunneling microscope image in the vicinity of missing dimers. (C) 2001 Elsevier Science B.V. All rights reserved.