Type of presentation: Oral

MS-9-O-2442 Atomic Structure of antiphase nanodomains in Fe-doped SrTiO3 films used for resistive switching memory (ReRAM) applications

Du H.1, 2, Jia C.1, 3, Mayer J.1, 2, Lenser C.3
1Ernst Ruska-Centrum für Mikroskopie und Spektroskopie mit Elektronen, Forschungszentrum Jülich GmbH, Jülich, 52425, Germany, 2Gemeinschaftslabor für Elektronenmikroskopie (GFE), RWTH Aachen, Aachen, 52074, Germany, 3Peter Grünberg Institut, Forschungszentrum Jülich GmbH, Jülich, 52425, Germany
h.du@fz-juelich.de

Strontium titanate (SrTiO3) has been used as a model material to understand the underlying mechanism of resistive switching phenomena for ReRAM applications.[1,2] It has been widely accepted that lattice defects play an essential role in the resistive switching processes in SrTiO3.[2,3] Therefore, a profound knowledge of the microstructures of a large variety of defects is a prerequisite for thoroughly understanding the microscopic switching mechanism. In this study, we have investigated antiphase nanodomains in Fe-doped SrTiO3 films by high resolution scanning transmission electron microscopy (STEM).

Randomly distributed dark contrast features with size up to about a few nanometers were observed in both the cross-section and plan-view bright field images of the Fe-doped SrTiO3 film (Fig. 1). High-resolution cross-section HAADF images recorded along [100] and [110] zone axes reveal that these dark contrast features are antiphase nanodomains formed by half unit cell shifting along the [011] direction with respect to the surrounding film (Fig. 2). Plan-view HAADF imaging shows that the antiphase boundaries appear to be composed of edge-shared TiO6 octahedra with a local Ti enrichment (Fig. 3). The edge-shared TiO6 octahedra are commonly seen in TiO2, such as anatase and rutile. The observed antiphase boundaries therefore differ from those of the Ruddlesden-Popper phases,[4] which are with an A-site atom enrichment.

Since antiphase nanodomains were not observed in Fe-doped SrTiO3 single crystals, Fe-doping alone is not sufficient for the formation of antiphase nanodomains. A reasonable explanation for the formation of the antiphase nanodomains appears to be atomic scale chemical inhomogeneities or fluctuations during the film growth causing local Ti-enrichments, which in turn induce the formation of antiphase nanodomains.

The identified defect structures offer great potential for tailoring the electronic properties of SrTiO3. By deliberately controllable chemical fluctuations, a similar formation of Antiphase nanodomains in other perovskite oxides is conceivable.

References

[1] Waser, R.; Aono, M. Nat. Mater. 2007, 6, 833.

[2] Waser, R.; Dittmann, R.; Staikov, G.; Szot, K. Adv. Mater. 2009, 21, 2632.

[3] Szot, K.; Speier, W.; Bihlmayer, G.; Waser, R. Nat. Mater. 2006, 5, 312.

[4] Ruddlesden, S. N.; Popper, P. Acta Cryst. 1958, 11, 54.

This work has been supported by the DFG (SFB 917, Project Z2). The authors thank Cong Zhang for providing the single crystal samples, Doris Meertens, Wilma Sybertz, and Maximilian Kruth for preparing the TEM lamellae, Juri Barthel for permitting to use the Dr. Probe software for STEM simulation, and Lothar Houben and Chris Boothroyd for training in operating the FEI Titan-PICO microscope.

Fig. 1: Cross-section a) and plan view b) BF-TEM images of a Fe-doped SrTiO3 film grown on a Nb-doped SrTiO3 substrate.

Fig. 2: Cross section HAADF images recorded along a) the [100] and b) the [110] zone axes. Defect areas were marked by rectangles. Solid circles: matrix lattice; open circles: antiphase lattice (green: Sr, yellow: Ti). Scale bar: 1.0 nm.

Fig. 3: Plan view HAADF image of an antiphase nanodomain imaged aong the [001] zone axis. Edge-on areas were marked by rectangles, which was used for modeling and simulation. Structure models of the marked antiphase boundary and anatase are shown for comparison (green: Sr, yellow: Ti, red: O). Scale bar: 1.0 nm.