STRAIN FIELD AROUND A SINGLE-DIMER VACANCY OF SI(100) SURFACE STUDIEDBY A MONTE-CARLO SIMULATION

We have investigated effects of the Vacancies on the order-disorder ph ase transition by a Monte Carlo simulation using an Ising system, wher e two states of a buckled dimer were regarded as spins up and down. Fi rst, we calculated the correlation length in the model. In the followi ng, we introduced single-dimer vacancies into the model. As a result, a new local structure appeared in the vicinity of an isolated vacancy near a critical temperature T-c(MC) (approximate to 320 K) due to a st rain field. The strain was considered to be a local next nearest neigh bor (n.n.n.) antiferromagnetic (AF) one, where the strain energy (A) w as deduced to be about 20 meV. Since our model without any vacancies s hows the nearest neighbor (n.n.) AF structure to be the ordered state, we concluded that competition between the overall n.n. AF coupling an d the local n.n.n. AF coupling induced by the defect occurred near T-c , which agreed with the STM experiment (T. Yokoyama, K. Takayanagi, Ph ys. Rev. B 56 (1997) 10483). (C) 1998 Elsevier Science B.V. All rights reserved.