FIG. 2: (a) OM picture; (b) SEM image of one fractured surface of Nb:SrTiO 3 . (c) the profilometer data of the same surface. Constant height contour plot according to the profilometer data was added in (a) and (b). The numbers shown in contour plot are in the unit of µ m. (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 4