  Antiphase domain boundaries (APDBs) in the ($n \times 1$)($n=4,5$)
reconstructions of the SrTiO$_3$(110) surface were studied with scanning
tunneling microscopy, x-ray photoemission spectroscopy, and density functional
theory (DFT) calculations. Two types of APDBs form on each reconstruction; they
consist of Ti$_x$O$_y$ vacancy clusters with a specific stoichiometry. The
presence of these clusters is controlled by the oxygen pressure during
annealing. The structural models of the vacancy clusters are resolved with DFT,
which also shows that their relative stability depends on the chemical
potential of oxygen. The surface band bending can be tuned by controlling the
vacancy clusters at the domain boundaries.
