One-dimensional character of the dimer structure of S_B terrace on a Si(001) surface

We studied the influence of the finite width of S_B terrace on the structure of a Si(001) surface by using Monte Carlo simulations (MCSs) based on the asymmetric dimer model. Coupling constants among the buckling of the dimers are given by the first-principles calculation: We consider a narrow S_B terrace and treat the S_A and the S_B step edges by the free boundary condition for the buckling of the dimers. We find that the system reveals the feature of a one-dimensional Ising spin system at low temperature. As long as the temperature is finite, there is no long-range order and the structure of the system fluctuates. We calculated STM images and show that the images change in accordance with the scale of the observation time. LEED intensity reflects short-range order nearly independently of the scale of the observation time. It is indicated by the present MCSs that information about scanning speed of the STM is very important for interpreting the results of experimental STM images observed on the narrow terrace on the Si(001) surface.