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A STM study of surface reconstructions on Si(111):B

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Physical Review B



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The scanning tunneling microscope is used to study the boron-doped Si(111)surface as a function of annealing times and temperatures. The surface structure is found to be determined by the concentration of B. When the substitutional B concentration is less than 1% of the top 1 X 1 bilayer atoms, the surface is largely 7X7 but surrounded by adatom-covered 1X1 regions (which have higher B concentration). When the B concentration is more than 3', the whole surface will be adatom-covered 1X1 regions including (v 3 Xv 3)R30' structures. The (&3Xv 3)R30' domains will increase with the B concentration. Because 7 X7 can only exist in the region with low B concentration, the growth of 7 X7 is slowed down. Further annealing at 560'C can convert 2X2, c(4X2) into 7X7 and 9X9. Sides of the 7X7 domain preferentially grow along the three equivalent [112]directions. The adatom-covered 1 X 1 regions are bounded by faulted halves of the 7 X7 domains. The dark sites of 7 X7 are observed and counted. They are further interpreted in terms of a B substitution model. The pattern of bright and dark atoms in (V 3 X&3)R30' domains is analyzed and a criterion for a B stabilized Si-1&3X v 3)R30' structure is obtained.