Development of Electronic and Topographic Structure of the Vacuum-cleaved SrTiO$_{3}$ (001) Surface as a Function of Annealing

A progressive disappearance of the conductance stripes along with emergence of new surface electronic states were observed at a vacuum-cleaved SrTiO$_{3}$ (001) surface upon annealing at $150-375^{\circ}C$. This disappearance started with an expansion of the TiO$_{2}$ stripe, as seen in conductance mapping of scanning tunneling microscopy, and progressed as the annealing time increases until the TiO$_{2}$ stripes dominate most of the surface. Such development can be associated with a topographic evolution from the initial alternating TiO$_{2}$/SrO surface termination into a step-terrace structure with mainly TiO$_{2}$ termination, which is more thermodynamically favorable during ultra-high vacuum annealing. The completeness of the TiO$_{2}$ terrace after the annealing was found to depend significantly on the original surface structure and, thus, vary across the surface. This different degree of TiO$_{2}$ coverage resulted in different emerging electronic states, in which several were found within the range of 0.6-1.7 eV above the Fermi level on both TiO$_{2}$ and the remaining SrO terminated surface. Interestingly, it was found that a short annealing at $150^{\circ}C$ could produce a significant change in electronic structure where states can be found within 1 eV above and below the Fermi level.