  We study electronic and topographic properties of the vicinal Si(557)-Au
surface using scanning tunneling microscopy and reflection of high energy
electron diffraction technique. STM data reveal double wire structures along
terraces. Moreover 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/negative
biases. This suggests that one wire has metallic character while the other one
- semiconducting. The experimental results are supplemented by theoretical
calculations within tight binding model suggesting that the observed chains are
made of different materials, one is gold and the other one is silicon chain.
