  Room-temperature and low-temperature (77 K) scanning tunneling spectroscopy
(STS) and voltage-dependent scanning tunneling microscopy (STM) data are used
to study the local electronic properties of the quasi-one-dimensional
Si(557)-Au surface in real space. A gapped local electron density of states
near the Gamma-point is observed at different positions of the surface, i.e.,
at protrusions arising from Si adatoms and step-edge atoms. Within the gap
region, two distinct peaks are observed on the chain of localized protrusions
attributed to Si adatoms. The energy gap widens on both types of protrusions
after cooling from room temperature to T = 77 K. The temperature dependence of
the local electronic properties can therefore not be attributed to a Peierls
transition occurring for the step edge only. We suggest that more attention
should be paid to finite-size effects on the one-dimensional segments.
