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Time-independent and -dependent Monte Carlo simulations of a two-dimensional lattice gas were performed to investigate the effect of fixed particles on periodic adatom arrangements on Si(111) 1x1 surfaces. In both the simulations introducing fixed particles, domains of the periodic structures were divided into small fragments around them. This can be explained by the fixed particles reducing the degree of freedom of the adatom configurations so the number of ways of reaching the uniform configuration is highly restricted. Based on the simulations, we predict that a large 1x1 region without any obstacle impurities is desirable to obtain a large periodic structure of Si adatoms.
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Figure Typical adatom configurations at the 10 000 000th MC step obtained by time-independent MC simulation. Solid and open circles indicate mobile Si adatoms and fixed particles, respectively. (a) Without fixed particles; (b) containing two fixed particles.