The structure of the chlorine induced reconstruction of Ag(111) has been studied by a combination of low-temperature scanning tunneling microscopy (STM), low-energy electron diffraction (LEED), and density-functional theory (DFT). We demonstrate that previously observed mysterious LEED pattern arises as a result of diffraction from a system of small $\left(15–30\text{Å}\right)$ triangular antiphase domains with a new $\left(3\times 3\right)$ superstructure. In our model supported by DFT calculations, within a $\left(3\times 3\right)$ unit cell the upper silver layer reconstructs forming a couple of three-atom triangles placed in fcc and hcp sites of the substrate. Chlorine atoms occupy fourfold hollow sites between these triangles. The corner holes, which look like depressions in the STM images, are also occupied by chlorine atoms.

• Received 6 May 2010

DOI:https://doi.org/10.1103/PhysRevB.81.205434