HAADF image (left) and the respective elemental EELS maps of a LNO/LAO superlattice with 4 u.c. thick single layers grown on SrTiO3 substrate. The right image is an overlay of the La, Ni, and Al maps. The horizontal image width is 1.8 nm. The aluminium and nickel atoms are arranged in layers while the lanthanum pattern is continuous.
HAADF images of an LNO/LAO superlattice with 4 u.c. thick single layers: (a) overview, (b) white rectangular in (a) at higher magnification. The brightest spots are the La columns, in between weaker Ni and Al columns are visible. (c) Integrated EELS linescan over the horizontal width of image (b) from the bottom (A) to the top (B). The profiles of the normalized intensities of the Ni L2 (blue) and Al K (red) edges are plotted.
HRTEM image of the planar RP faults which are marked by arrows.
(a) HAADF image of a planar RP fault (marked by the upper arrow) near the interface to the substrate. The unit cells of LSAO and LNO are overlaid: La blue, Ni yellow, O grey, (La,Sr) green, and Al red. The termination of the substrate differs on the two sides of the RP fault. On the left, the substrate is terminated by a (La,Sr)O plane, on the right by a AlO2 plane. This results in a surface step of the substrate which is the origin of the RP fault. The unit cells of LNO show that the atomic planes from the both sides are shifted against each other and that one NiO2 plane is missing. Elemental EELS maps (2.56 × 2.56 nm2) are shown in (b) and (c) (low pass filtered). The dashed line in (c) shows the position of the RP fault.
(a) HAADF image showing several blocks (marked by dotted rectangles). (b) Enlarged image from the area within the solid rectangle in (a) showing a single block which consists of columns with similar brightness. (c) 3D atomic model of the white rectangle in (b) La blue, Ni yellow, and Al red. The blocks are surrounded by RP faults (marked by dotted lines). In the perfect superlattice, there are pure La, Ni, and Al columns along the viewing direction (black arrow). In contrary, the columns are mixed in the upper left part resulting in the similar intensity of all columns within the block.
Atomic model showing the normal growth of a superlattice on the left side and the growth of a 3D RP fault on the right. La blue, Al red, and Ni yellow; O is not shown for simplicity. The starting point is in both cases a perfectly flat LaO plane (a). On top of it an AlO2 plane is deposited in the case of perfect growth, in contrary LaO is locally deposited (surrounded by AlO2) in the case of the growth of a 3D RP fault (b). This is followed by normal growth: LaO on top of AlO2 and AlO2 on top of LaO (c). The cross-sections whose position is marked by the arrow in (c) show the perfect superlattice and the 3D block after further deposition steps (d).
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