The ability to modify the stacking sequence of ultrathin films offers a unique way to change either the interaction strength or the doping, but demands a careful control of each atomic monolayer. Progress is hampered by the lack of a direct method that allows differentiation on a local scale between the various terminating layers of a crystal. Here, the combination of a vacuum annealing process and friction force microscopy reveals this local distinction on aSrTiO3surface. Using the friction contrast, we find how the terminating layer of a single crystal profoundly influences the terrace edge structure. ©1998 American Institute of Physics.