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Intermediate Structures Appearing in the Phase Transition of Si(111)7×7 to (/3×/3)R30º Induced by HBO2 Molecular Irradiation

Abstract 　We have investigated the breakdown process of the 7×7 structure during its transition to the (/3×/3)R30 phase induced by HBO2 irradiation. The 7×7 structure was destroyed over the wide area before the nucleation of the (/3×/3)R30 phase. Even when the (/3×/3)R30 structure nucleated in the disordered area, disordered structure existed between the domains of the 7×7 and (/3×/3)R30 structural phases. The observed results are completely different from the (/3×/3)R30 formation processes induced by other group III atoms, where (/3×/3)R30 phases are formed as adjacent to the 7 × 7 structural domains. The surface B atom concentration in the 7×7, disordered, and (/3×/3)R30 regions were estimated to be about one, three, and six per 7×7 unit cell. The disordered structure remained on the surface even after annealing the sample at 750 and 900C. And the B concentration in the disordered region did not change. These results indicate that the disordered structure is an intrinsic nature of the B-induced reconstruction, and suggest the existence of the relationship between the B atom concentration and the stability of the 7×7 structure.

Results

・Characteristic phase transition observed on the breakdown process of the 7×7 structure during its transition to the (/3×/3)R30º phase induced by HBO2 irradiation. STM images of the surface formed by 3, 5, 20, 50 min. of HBO2 irradiation. 3 min.: Characteristic site preference of boron atoms 5 min.: Appearance of the disordered structure 20 min.: Ordering of the (/3×/3)R30º phase 50 min.: Completion of the (/3×/3)R30º phase

・Relationship between the surface B concentrations and the surface reconstructed structures STM: Magunified image of the boundary between 7×7 and disordered structures. Graph: The surface boron concentration (atoms per 7×7 unit cell size) in the 7×7, disordered, and (/3×/3)R30º regions.

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