Au-induced reconstructions of the Si(111) surface with ordered and disordered domain walls

Scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) observa- tions combined with the density functional theory (DFT) calculations were used to elucidate atomic arrangement of Au/Si(111) reconstructions forming at Au coverage around one monolayer. They include the Si(111)6 x 6-Au with ordered domain walls, the Si(111)alpha -root 3 x root 3-Au and the Si(111)beta - root 3 x root 3-Au surfaces with disordered domain walls of various density, and the Si(111)2 root 21 x 2 root 21-Au surface which structure is relevant to those of other reconstructions, albeit cannot be ascribed solely to the domain walls. Using detailed comparison of the STM and ARPES data with the results of DFT calculations, we explicitly proved the atomic model of Si(111)6 x 6-Au surface proposed by Grozea et al. [Surf. Sci. 418, 32 (1998)]. This model provided us a hint for constructing an atomic model of domain walls which demonstrates a proper coincidence between experimental and simulated STM images. The model contains five Au atoms per 2 x root 3 unit cell, i.e., 1.25 monolayers of Au. For the alpha root 3 x root 3-Au and beta - x root 3 x root 3-Au surfaces, this finding allows an overall description of their atomic arrangement and, hence, accurate determination of their Au coverages. Knowledge on the atomic arrangement of the Si(111)6 x 6-Au surface and domain walls also allowed us to construct an atomic model of the Si(111)2 root 21 x 2 root 21 surface. The obtained data were unified in the refined formation phase diagram for the Au/Si(111) system.