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Detectors are revolutionizing possibilities in scanning transmission electron microscopy because of the advent of direct electron detectors that record at a high quantum efficiency and with a high frame rate. This allows the whole back focal plane to be captured for each pixel in a scan and the dataset to be processed to reveal whichever features are of interest. There are many possible uses for this advance of direct relevance to understanding the nano- and atomic-scale structure of materials and heterostructures. This article gives our perspective of the current state of the field and some of the directions where it is likely to go next. First, a wider overview of the recent work in this area is given before two specific examples of its application are given: one is imaging strain in thin films and the other one is imaging changes in periodicity along the beam direction as a result of the formation of an ordered structure in an epitaxial thin film. This is followed by an outlook that presents future possible directions in this rapidly expanding field.

The improper ferroelectric CsNbW2O9 has recently been highlighted as the first material outside the manganite family to exhibit a similar meandering, sixfold domain structure to that responsible for enhanced and diminished conduction at charged domain walls in the rare earth manganites. While there is no current evidence for variation in domain wall conduction relative to bulk in CsNbW2O9, the similarities in microstructure strongly suggest that charged domain walls are present in this material. Herein, we report a comprehensive study of the domain microstructure of CsNbW2O9 by both piezoresponse force microscopy and transmission electron microscopy to reveal that there are, in fact, clear distinctions in the domain structure of the two systems. Constraints arising from the crystal structure of CsNbW2O9, namely, the connectivity of the BO6 polyhedra and atomic displacements occurring purely along the c axis, mean that domain walls preferentially run parallel to the c direction (the polar axis of the material) and thus remain uncharged. The characteristic cloverleaf domain structure reminiscent of the manganites is still present; however, the structure meanders predominantly in the ab plane and, therefore, appears differently depending on the projection direction from which it is viewed. As a result of this microstructural constraint, charged domain walls are not prevalent in this material.

Amorphous tantala (a-Ta2O5) is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta2O5 coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta2O5 and other a-T2O5 studies.

Stepped antiphase boundaries are frequently observed in Ti-doped Bi0.85Nd0.15FeO3, related to the novel planar antiphase boundaries reported recently. The atomic structure and chemistry of these steps are determined by a combination of high angle annular dark field and bright field scanning transmission electron microscopy imaging, together with electron energy loss spectroscopy. The core of these steps is found to consist of 4 edge-sharing FeO6 octahedra. The structure is confirmed by image simulations using a frozen phonon multislice approach. The steps are also found to be negatively charged and, like the planar boundaries studied previously, result in polarisation of the surrounding perovskite matrix.

Observation of an unusual, negatively-charged antiphase boundary in (Bi0.85Nd0.15)(Ti0.1Fe0.9)O3 is reported. Aberration corrected scanning transmission electron microscopy is used to establish the full three dimensional structure of this boundary including O-ion positions to ∼±10 pm. The charged antiphase boundary stabilises tetragonally distorted regions with a strong polar ordering to either side of the boundary, with a characteristic length scale determined by the excess charge trapped at the boundary. Far away from the boundary the crystal relaxes into the well-known Nd-stabilised antiferroelectric phase.