Search

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.

Electron energy-loss spectroscopy (EELS) has been used to determine the valence state of manganese for all the samples at low temperature (93 K). EELS results indicate that the valence state of manganese keeps constant (∼3.5) for all the samples. The effects of the A-site cation size mismatch on the charge ordering (CO) behaviors in the manganites (La1−xYx)0.5(Ca1−ySry)0.5MnO3 are studied by transmission electron microscopy (TEM). TEM images show that the size mismatch and disorder of A-site cations have a suppression effect on the CO transition. The schematic models are proposed for the incommensurate CO modulation in the samples with size mismatch σ2⩽0.003. The disappearance of the CO transition in the sample with the largest mismatch (σ2=0.005) is explained by the random arrangements of Mn3+ and Mn4+ ions.

Ultrathin films (

The ferroelectric switching mechanism in strontium bismuth tantalate [SrBi2Ta2O9 (SBT)] has been studied using in situ transmission electron microscopy observations of the nucleation and growth of polarization domains, such as 180° and 90° domains. Thank to this high density of the antiphase boundary (APB), a switching mechanism in SBT based on the nucleation of new polarization domains at APBs as well as the electrode interfaces put forward and the fatigue-free behavior of SBT with a platinum electrode is explained.

Aberration corrected scanning transmission electron microscopy revealed that Bi0.85Nd0.15Fe0.9Ti0.1O3 ceramics contain coherent Nd-rich precipitates distributed throughout the perovskite lattice, implying charge compensation is obtained by the creation of VNd/// and not VBi///. At low concentrations, therefore, Ti4+ replace Fe2+ with the creation of 2/3VNd///, and at higher concentrations (when Fe2+ have been eliminated and the conductivity suppressed), Fe3+ with the creation of 1/3VNd///. The switch in ionic compensation mechanism from 2/3VNd/// at low Ti concentrations (∼1%) to 1/3VNd/// at higher concentrations (>1%) results in a decrease in the magnitude of ΔTC/Δx, as the disruption of long range anti-polar coupling declines.

A low temperature nickel process has been developed that produces Ohmic contacts to n-type germanium with specific contact resistivities down to (2.3 ± 1.8) x10-7 Ω-cm2 for anneal temperatures of 340 degC. The low contact resistivity is attributed to the low resistivity NiGe phase which was identified using electron diffraction in a transmission electron microscope. Electrical results indicate that the linear Ohmic behaviour of the contact is attributed to quantum mechanical tunnelling through the Schottky barrier formed between the NiGe alloy and the heavily doped n-Ge.

Low optical and mechanical loss Ta2O5 amorphous coatings have a growing number of applications in precision optical measurements systems. Transmission electron microscopy is a promising way to probe the atomic structure of these coatings in an effort to better understand the causes of the observed mechanical and optical losses. Analysis of the experimental reduced density functions using a combination of reverse Monte Carlo refinements and density functional theory molecular dynamics simulations reveals that the structure of amorphous Ta2O5 consists of clusters with increased contribution from a Ta2O2 ring fragment.

The details of the domain structure of the incommensurate antiferroelectric structure in La-doped zirconium-rich lead zirconate titanate have been revealed in detail for the first time. The structure is dominated by 60° domain boundaries close to {101} planes of the primitive perovskite cell; and tilts of the perovskite sublattice of about 0.5° are also noted at such boundaries consistent with a small tetragonal distortion of the primitive cell. Within each domain a streaked nanostructure is revealed under weak diffraction conditions perpendicular to the long b-axis of the incommensurate supercell, which appears to be a consequence of planar faulting perpendicular to this b-axis. 90° domain boundaries are also observed but are less frequent than 60° boundaries and in contrast to previous reports, these often have rather curved and irregular boundary planes. The close similarity of all these features, with the one exception of the streaked nanostructure, to the domain structure of the commensurate antiferroelectric PbZrO3, demonstrates the close relationship of the two phases and leads one to speculate that the atomic structures of the phases are also closely related.

We present results of the magnetic, structural and chemical characterizations of Mn+-implanted Si displaying n-type semiconducting behavior and ferromagnetic ordering with Curie temperature,TC well above room temperature. The temperature-dependent magnetization measured by superconducting quantum device interference (SQUID) from 5 K to 800 K was characterized by three different critical temperatures (T*C~45 K, TC1~630-650 K and TC2~805-825 K). Their origins were investigated using dynamic secondary mass ion spectroscopy (SIMS) and transmission electron microscopy (TEM) techniques, including electron energy loss spectroscopy (EELS), Z-contrast STEM (scanning TEM) imaging and electron diffraction. We provided direct evidences of the presence of a small amount of Fe and Cr impurities which were unintentionally doped into the samples together with the Mn+ ions, as well as the formation of Mn-rich precipitates embedded in a Mn-poor matrix. The observed T*C is attributed to the Mn4Si7 precipitates identified by electron diffraction. Possible origins of and are also discussed. Our findings raise questions regarding the origin of the high ferromagnetism reported in many material systems without a careful chemical analysis.

Herringbone domain structures have been mapped using electron backscatter diffraction in two tetragonal piezoelectrics: lead zirconate titanate [Pb(Zr,Ti)O3] and bismuth ferrite–lead titanate [(PbTi)0.5(BiFe)0.5O3]. Analysis of the domain misorientations across the band junctions shows that the structures correspond very well to crystallographic models. High resolution mapping with a 20nm step size allowed the crystal rotation across one of these band junctions in lead zirconate titanate to be studied in detail and allowed an improved estimation of the peak strain at the junction, of 0.56GPa. The significance of this for crack nucleation and propagation in such materials is discussed.