Order-disorder phase transition on the Si(001) surface: Critical role of dimer defects

There is some experimental evidence that the c(4×{}2) structure is the low-temperature phase of the Si(001) surface. The critical temperature for the order-disorder transition was experimentally determined as about 200 K. This structural phase transition was studied by using a two-dimensional Ising spin model whose interaction parameters were estimated by first-principles total-energy calculations. Monte Carlo simulations were then performed. The effects of dimer defects on the nature of the phase transition are discussed.