Double nonequivalent chain structure on a vicinal Si(557)-Au surface

We study electronic and topographic properties of the vicinal Si(557)-Au surface using scanning-tunneling microscopy (STM) and a reflection of high-energy electron diffraction technique. STM data reveal double wire structures along terraces. Moreover, the behavior of the voltage-dependent STM tip-surface distance is different in different chains. While the one chain shows oscillations of the distance which are sensitive to the sign of the voltage bias, the oscillations in the other chain remain unchanged with respect to the positive or negative biases. This suggests that one wire has metallic character while the other one has a semiconducting one. The experimental results are supplemented by theoretical calculations within tight binding model suggesting that the observed chains are made of different materials, one gold and the other silicon.