Structures and defects of atomic wires on Si(553)-Au: An STM and theoretical study

Room-temperature structure of the Au-induced atomic wire array on the stepped Si(553) surface, which exhibits an exotic double Peierls phase transition at low temperature [J. R. Ahn , Phys. Rev. Lett. 95, 196402 (2005)], is investigated by scanning tunneling microscopy (STM) and first-principles calculations. The energetics of various structure models proposed so far are calculated and compared systematically. The most energetically favorable structure is composed of a single Au chain on a terrace and a Si honeycomb chain on a step edge. This model reproduces excellently the high-resolution STM images observed. High-resolution STM images also reveal that there exist several different types of defects on the atomic wires, as categorized by their apparent bias-dependent shapes. The defect with a dominating population is found to be due to water adsorption on the step-edge Si chains. These defects have different effects on the wire lattice at room temperature, that is, only the specific types of defects with minor populations induce a long-range lattice (charge) distortion with a x2 period not on Si step-edge chains, but on Au terrace chains.