  Surfaces of homoepitaxially grown TiO2-terminated SrTiO3(001) were studied in
situ with scanning tunneling microscopy and spectroscopy. By controlling the
Ti/Sr ratio, two-dimensional domains of highly ordered linear nanostructures,
so-called "nanolines", are found to form on the surface. To further study how
the surface structure affects the band structure, spectroscopic studies of
these surfaces were performed. Our results reveal significantly more band
bending for surfaces with the nanolines, indicative of an acceptor state
associated with these features. Additionally, an in-gap state is observed on
nanoline surfaces grown under high oxygen deficient conditions. This state
appears to be the same as that observed previously, arising from the (++/+)
transition level of surface oxygen vacancies.
