be sensed by STM. In fig. 4 (d), sub-micron wide terraces were observed; while alternating terminated terraces were found in fig. 4 (e). Unit cell height steps were found near the edge of terraces in fig. 4 (d), indicating the a mixed termination surfaces on the adjacent large terraces, as previously reported by Chien et al. [11]. On the other hand, terraces a few tens of nm wide were found in the region shown to be textured in the SEM images. In this region, two different terminated surfaces were found. In those narrow terrace regions, relatively wider ( ∼ 20 nm) and narrower ( ∼ 10 nm) terraces were revealed. As reported in our previous study by Guisinger et al. [10], the wide terraces have smoother surfaces (smaller than half unit cell, 0.2 nm) and were assigned to be TiO 2 terminated surfaces; while the relative narrow terraces have rougher surfaces (about half unit cell), were assigned to be SrO terminated surfaces. 

There are many factors that affect the resulting fractured surfaces. For examples, the speed of the fracturing; the sample temperature; the torque during the fracturing etc. The speed of the fracturing in all of our experiments was controlled with the use of a precision motion manipulator mounted in the ultra high vacuum chamber. The samples were sitting on the end of the manipulator and moved with steady speed of about 1 mm/sec. The torque experienced by the samples during the fracturing were minimized by controlling the sample positions, so that the forces applied to the samples were normal to the sample surfaces. We examined the effect of the fracturing temperature at RT and at 50 K. It is found that for RT fractured samples, statistically, narrow and alternating-terminated terraces are the most likely surface; while the samples fractured at 50 K have larger (sub-micron) terrace regions. As discussed above, large and narrow terraces can be found simultaneously on the same fractured surfaces. From this we conclude that the low temperature fracturing must create relatively larger smooth regions with larger terraces than the high temperature fracturing. This is a similar behavior to that observed in layered oxides [13], in which low temperature fracturing created lower defect-density surfaces. In the sense that steps are one kind of defects, our temperature-dependent fracturing on perovskite oxides exhibits similar conclusions. We also note that to we have fractured 14 samples to be examined with XSTM and only two of them were not scannable by STM. This illustrates that even in a complex fracturing process for a non-cleavable material, we can reliably generate atomically flat surfaces to study. 

In summary, in-situ fracturing was utilized to routinely create atomically flat surfaces 

