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(a) and (b). It revealed that the bright feature in SEM is due to the height change about 10 µ m in a lateral scale of ∼ 10 µ m, which is about 45 degree incline. The fractured Nb:STO surfaces were found scannable by STM in most of the smooth regions seen in SEM image. 

Figure 3 shows the spatial evolution of the topographies measured by STM along the [001] direction within the red square region indicated in fig. 2 (b). Figure 3 (a)-(f) show the topographies with 300 nm × 300 nm dimensions. Each image was measured ∼ 5 µ m apart along one line toward sample edge ([001] direction), as indicated in fig. 3 (g). Note that since the SEM image was measured ex-situ , the arrows in fig. 3 (g) only indicate relative positions of the STM images in (a)-(f). In this case, it can be seen that the topography changes when moving toward the sample edge. In fig. 3 (a), the region furthest from the sample edge, large ( ∼ 100 nm) atomically flat terraces were observed. While moving toward the sample edge (fig. 3 (b)-(f)), the terrace width decreases. In addition, wide and narrow terraces appear alternatively along [100] direction. This alternative-terrace behavior was observed in our previous study [10], which corresponded to alternate surfaces terminations - SrO vs. TiO 2 . This demonstrates that the atomically flat fractured Nb:STO surfaces extended all the way to the sample edge, indicating the study of the interfaces between a thin oxide film and STO is plausible. 

In addition to the observations mentioned above, dislocations were also observed in both the STM and SEM images. Figure 4 (a) shows a fine scale SEM image with observation 

