Structure of the quasi-one-dimensional Si(553)-Au surface: Gold dimer row and silicon honeycomb chain

The Si(553)-Au surface consists of a periodic array of single steps and (111) terraces with a quasi-one-dimensional electronic structure. In this paper, the determination of the atomic structure of this surface with x-ray diffraction is reported. The gold coverage of the surface was measured to be 0.5 monolayer using x-ray fluorescence spectroscopy, i.e., two gold atoms per primitive unit cell. A structural model was constructed directly from the x-ray diffraction intensities with a step-by-step approach. First, the relative positions of the gold atoms were obtained from the Patterson map. Using the positions of the gold atoms, the deconvolution of the Patterson map was calculated and the positions of the gold atoms relative to the substrate were determined. Finally, the positions of the silicon atoms at the surface were obtained from a reconstruction of the electron density with an iterative phase and amplitude recovery algorithm. The main features of the structural model obtained in this way are a row of gold dimers on the (111) terraces in the topmost layer of the surface, and a honeycomb chain of silicon atoms near the step edge. Structural refinement of this model with the experimental diffraction data gave reasonable atomic positions and a ² value of 3.35, better than previous models. The model is related to the ×2  m1 model recently proposed by Krawiec [Phys. Rev. B 81, 115436 (2010)] but without the strong ×2 modulation. ©2010 The American Physical Society