Force microscopy study of SrTiO₃(001) surfaces with single atomic-layer steps

An atomically flat SrTiO₃(001) surface was successfully obtained by combining ultrasonic agitation and subsequent annealing at 1000 °C in air. The topographic images taken using an atomic force microscope revealed that the surface was composed of clear atomic-steps and atomically smooth terraces. The steps were 0.2 nm in height corresponding to half of the unit cell height of SrTiO₃, or the single atomic-layer height. The terraces were categorized into two types; wide and narrow terraces appear alternately. Surface composition analyzed by coaxial impact collision ion scattering spectroscopy indicated that the topmost surface was covered by domains of the SrO and TiO₂ layers, where the latter domain was dominant. The result suggests that the topmost surface of the narrow terrace was terminated by SrO and the wide terrace by TiO₂. This was further examined by the use of a friction force microscopy technique with which we were able to distinguish the different surface terminations.