Surface termination effect of SrTiO3 substrate on ultrathin SrRuO3

A well-defined substrate surface is crucial for the epitaxy of complex materials, especially for revealing intrinsic properties of films in ultrathin limit. Here by atomically precise growth and characterization, the origin for the lateral inhomogeneity of ultrathin SrRuO${}_{3}$ films due to the step effects of SrTiO${}_{3}$ (001) is revealed. Two distinct types of step propagation along the [011] and $[\overline{01}1]$ crystallographic direction is identified, respectively. In particular, the type-II $[\overline{01}1]$ step results in lateral discontinuity of monolayer SrRuO${}_{3}$ and originates from the SrO-terminated regions along the TiO${}_{2}$-terminated step edge, responsible for the distinct electronic and magnetic properties of monolayer SrRuO${}_{3}$.