Electron microscopy
 
HAADF-STEM Contrast at Interface between Two Crystals
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In most cases, the interface between two crystals is not ideal. It is very common that the atomic number of the interface is lower than those of the crystalline bulks and there is chemical intermixing between them. For instance, nickel oxide (NiO) nanocrystals epitaxially grown on (001) strontium titanate (SrTiO3) single crystal substrates [1] had been characterized by aberration corrected high angle annular dark field scanning transmission electron microscopy (HAADF-STEM). The rough and irregular interface between the NiO and SrTiO3 crystals had a lower average atomic number than the two crystalline bulks as indicated by the dark layer at the interface shown in Figure 1352 (a) and (d). Figures 1352 (b) and (c) show EDS (for Ni and Sr) and EELS (for O and Ti) data, respectively, simultaneously acquired from a line scan across the NiO-SrTiO3 interface (marked as a yellow arrow in Figure 1352 (a)). Figure 1352 (c) suggests lack of a sharp interface in the O K profile and presence of oxygen vacancies at the NiO-SrTiO3 interface. Figures 1352 (b) and (c) show that there is intermixing between NiO and SrTiO3 near the interface. Figure 1352 (c) shows that the real interface, where the oxygen minimum locates, is not the same as the interface, represented by the minimum of HAADF contrast.

 

(a)
(b)
(c)
(d)
Figure 1352. (a) HAADF STEM image at low magnification, (b) EDS data along the yellow arrow in (a), (c) EELS data along the yellow arrow in (a), and (d) HAADF STEM image at atomic resolution. Adapted from [1]

 

 

 

 

 

 


[1] Xuan Cheng, Jivika Sullaphen, Matthew Weyland, Hongwei Liu, and Nagarajan Valanoor, Role of interface structure and chemistry in resistive switching of NiO nanocrystals on SrTiO3, APL Materials 2, 032109 (2014).

 

 

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