In order to achieve reliable structural characterization by transmission electron microscopy, beam-induced structural changes should be clarified for any target material system. As an example, the movement of heavy adatoms on a thin carbon support has been repeatedly reported under the electron beam while the underlying reason for such motion is still in debate. By applying statistical analysis to the group behavior of gold adatoms, we investigated their motion under different beam conditions and detected features corresponding to beam-induced motion, under typical scanning transmission electron microscopy observation conditions. Our results are consistent with the theoretical prediction proposed by Egerton (2013).

To unambiguously evaluate the indium and nitrogen concentrations in InxGa1−xNyAs1−y, two independent sources of information must be obtained experimentally. Based on high-resolution scanning transmission electron microscopy (STEM) images taken with a high-angle annular dark-field (HAADF) detector the strain state of the InGaNAs quantum well is determined as well as its characteristic HAADF-scattering intensity. The strain state is evaluated by applying elasticity theory and the HAADF intensity is used for a comparison with multislice simulations. The combination of both allows for determination of the chemical composition where the results are in accordance with X-ray diffraction measurements, three-dimensional atom probe tomography, and further transmission electron microscopy analysis. The HAADF-STEM evaluation was used to investigate the influence of As-stabilized annealing on the InGaNAs/GaAs sample. Photoluminescence measurements show an annealing-induced blue shift of the emission wavelength. The chemical analysis precludes an elemental diffusion as origin of the energy shift—instead the results are in agreement with a model based on an annealing-induced redistribution of the atomic next-neighbor configuration.

In an earlier publication Rosenauer et al. introduced a method for determination of composition in AlGaN/GaN heterostructures from high-angle annular dark field (HAADF) images. Static atomic displacements (SADs) were neglected during simulation of reference data because of the similar covalent radii of Al and Ga. However, SADs have been shown (Grillo et al.) to influence the intensity in HAADF images and therefore could be the reason for an observed slight discrepancy between measured and nominal concentrations. In the present study parameters of the Stillinger–Weber potential were varied in order to fit computed elastic constants, lattice parameters and bonding energies to experimental ones. A reference data set of HAADF images was simulated, in which the new parameterization was used to account for SADs. Two reference samples containing AlGaN layers with different Al concentrations were investigated and Al concentrations in the layers determined based on the new data set. We found that these concentrations were in good agreement with nominal concentrations as well as concentrations determined using alternative techniques such as strain state analysis and energy dispersive X-ray spectroscopy.

Ultrathin ferroelectric heterostructures (SrTiO3/BaTiO3/BaRuO3/SrRuO3) were studied by scanning transmission electron microscopy (STEM) in terms of structural distortions and atomic displacements. The TiO2-termination at the top interface of the BaTiO3 layer was changed into a BaO-termination by adding an additional BaRuO3 layer. High-angle annular dark-field (HAADF) imaging by aberration-corrected STEM revealed that an artificially introduced BaO-termination can be achieved by this interface engineering. By using fast sequential imaging and frame-by-frame drift correction, the effect of the specimen drift was significantly reduced and the signal-to-noise ratio of the HAADF images was improved. Thus, a quantitative analysis of the HAADF images was feasible, and an in-plane and out-of-plane lattice spacing of the BaTiO3 layer of 3.90 and 4.22 Å were determined. A 25 pm shift of the Ti columns from the center of the unit cell of BaTiO3 along the c-axis was observed. By spatially resolved electron energy-loss spectroscopy studies, a reduction of the crystal field splitting (CFS, ΔL3=1.93 eV) and an asymmetric broadening of the eg peak were observed in the BaTiO3 film. These results verify the presence of a ferroelectric polarization in the ultrathin BaTiO3 film.

Recombinant ferritin is an excellent template for the synthesis of magnetic nanoparticles. This paper describes carefully performed experiments both to identify ironoxides within nanoparticles and to measure the number of iron atoms in the cores of recombinant human H-chain ferritin (HFn), based on spectroscopy techniques. Using electron energy-loss spectroscopy (EELS) analysis, magnetite (Fe3O4) has been unequivocally identified as the ironoxide formed within HFn cores under special preparation conditions. Atom counting analysis by EELS and high-angle annular dark-field imaging further allowed the correlation of the particle sizes to the real Fe atom numbers in a quantitative manner. These results help clarify some structural confusion between magnetite and maghemite (γ-Fe2O3), and also provide standard data for the number of Fe atoms within Fe3O4 particles of a given size, whose use is not limited to cases of magnetite synthesized in the cores of recombinant human ferritin.

III-V nitride (AlGa)N distributed Bragg reflector devices are characterized by combined high-angle annular dark-field (HAADF) and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope. Besides the complete structural characterization of the AlN and GaN layers, the formation of AlGaN transient layers is revealed using Vegard law on profiles of the position of the bulk plasmon peak maximum. This result is confirmed by comparison of experimental and simulated HAADF intensities. In addition, we present an advantageous method for the characterization of nano-feature structures using low-loss EELS spectrum image (EEL-SI) analysis. Information from the materials in the sample is extracted from these EEL-SI at high spatial resolution.The log-ratio formula is used to calculate the relative thickness, related to the electron inelastic mean free path. Fitting of the bulk plasmon is performed using a damped plasmon model (DPM) equation. The maximum of this peak is related to the chemical composition variation using the previous Vegard law analysis. In addition, within the context of the DPM, information regarding the structural properties of the material can be obtained from the lifetime of the oscillation. Three anomalous segregation regions are characterized, revealing formation of metallic Al islands.

In this study the nanomorphology of P3HT:PC61BM absorber layers of organic solar cells was studied as a function of the processing parameters and for P3HT with different molecular weight. For this purpose we apply scanning transmission electron microscopy (STEM) at low electron energies in a scanning electron microscope. This method exhibits sensitive material contrast in the high-angle annular dark-field (HAADF) mode, which is well suited to distinguish materials with similar densities and mean atomic numbers. The images taken with low-energy HAADF STEM are compared with conventional transmission electron microscopy and atomic force microscopy images to illustrate the capabilities of the different techniques. For the interpretation of the low-energy HAADF STEM images, a semiempirical equation is used to calculate the image intensities. The experiments show that the nanomorphology of the P3HT:PC61BM blends depends strongly on the molecular weight of the P3HT. Low-molecular-weight P3HT forms rod-like domains during annealing. In contrast, only small globular features are visible in samples containing high-molecular-weight P3HT, which do not change significantly after annealing at 150°C up to 30 min.

Aberration correction, after a 50 year incubation period of developing ideas and techniques while awaiting enabling technology, has transformed electron microscopy during the first dozen years of the 21st century. Some of the conditions that accompanied this transformation, the required complexity and its effect on the way microscopy is pursued, recent results that promise to change the field, and directions for the future are briefly described.

A simple parameterization is presented for the elastic electron scattering cross sections from single atoms into the annular dark-field (ADF) detector of a scanning transmission electron microscope (STEM). The dependence on atomic number, Z, and inner reciprocal radius of the annular detector, q0, of the cross section σ(Z,q0) is expressed by the empirical relation

where A(q0) is the cross section for hydrogen (Z = 1), and the detector is assumed to have a large outer reciprocal radius. Using electron elastic scattering factors determined from relativistic Hartree-Fock simulations of the atomic electron charge density, values of the exponent n(Z,q0) are tabulated as a function of Z and q0, for STEM probe sizes of 1.0 and 2.0 Å.

Comparison with recently published experimental data for single-atom scattering [Krivanek et al. (2010). Nature464, 571–574] suggests that experimentally measured exponent values are systematically lower than the values predicted for elastic scattering from low-Z atoms. It is proposed that this discrepancy arises from the inelastic scattering contribution to the ADF signal. A simple expression is proposed that corrects the exponent n(Z,q0) for inelastic scattering into the annular detector.

The aberration-corrected scanning transmission electron microscope can provide information on nanostructures with sub-Ångström image resolution. The relatively intuitive interpretation of high-angle annular dark-field (HAADF) imaging technique makes it a popular tool to image a variety of samples and finds broad applications to characterizing nanostructures, especially when combined with electron energy-loss spectroscopy and X-ray energy-dispersive spectroscopy techniques. To quantitatively interpret HAADF images, however, requires full understanding of the various types of signals that contribute to the HAADF image contrast. We have observed significant intensity enhancement in HAADF images, and large expansion of lattice spacings, of surface atoms of atomically flat ZnO surfaces. The surface-resonance channeling effect, one of the electron-beam channeling phenomena in crystalline nanostructures, was invoked to explain the observed image intensity enhancement. A better understanding of the effect of electron beam channeling along surfaces or interfaces on HAADF image contrast may have implications for quantifying HAADF images and may provide new routes to utilize the channeling phenomenon to study surface structures with sub-Ångström spatial resolution.

High-angle annular dark-field and annular bright-field imaging experiments were carried out on an aberration-corrected transmission electron microscope. These techniques have been demonstrated on thin films of complex oxides Ba3.25La0.75Ti3O12 and on LaB6. The results show good agreement between theory and experiments, and for the case of LaB6 they demonstrate the detection of contrast from the B atoms in the annular bright-field images. Elemental mapping with electron-energy-loss spectroscopy has been used to deduce the distribution of Cr and Fe in a thin film of the complex oxide Bi2(Fe1/2Cr3/2)O6 at the unit cell level and the changes in the near-edge structure within the inequivalent regions in the crystalline unit cell. Energy-filtered images in the low-loss region of the energy-loss spectrum show contrast and resolution consistent with the modulation of the signals from elastic scattering. High-resolution contrast, mediated by phonon scattering, is observed for interband transitions. The limitations in terms of detection and signal are discussed.

The recent advent of a novel design of in situ heating technology for electron microscopes has permitted unprecedented control of elevated temperature studies of catalytic materials, particularly when coupled with the sub-Ångström imaging performance of a modern aberration-corrected scanning transmission electron microscope (STEM). Using micro-electro-mechanical-systems (MEMS)-based Aduro™ heating chips from Protochips, Inc. (Raleigh, NC, USA) allows nearly instantaneous heating and cooling of catalyst powders, avoiding effects of temperature ramping as experienced with standard heating stages. The heating technology also provides stable operation limited only by the inherent drift in the microscope stage, thus allowing full image resolution to be achieved even at elevated temperatures. The present study details the use of both the high X-Y spatial resolution in both dark-field and simultaneous bright-field imaging, along with the high resolution in Z (depth sectioning) provided by the large probe incidence semiangle in the aberration-corrected instrument, to characterize the evolution of microstructure in a commercial Au/Fe2O3 water-gas shift catalyst during elevated temperature treatment. The phenomenon of Au diffusion to the surface of hematite support particles to form discrete crystalline Au nanoparticles in the 1–2 nm size range, after a prior leaching treatment to remove surface Au species has been characterized.

The movement of heavy atoms on a thin carbon substrate is readily observed using a sub-Ångstrom electron probe. The observed movement is consistent with an electron beam activation mechanism whereby atoms are occasionally detached from bonding sites, allowing rapid diffusion to new sites that may be quite far from the original. The bonding sites are most often observed to lie at defects, steps, and other asperities in the substrate. Formation of three-dimensional clusters can occur during diffusion of several isolated atoms. Coalescence and dissolution of larger clusters and islands both occur under varying observation conditions, but island coalescence appears most probable for islands that are greater than 2 nm in size.

A systematic distortion in high-angle annular dark-field scanning transmission electron microscope (HAADF-STEM) images, which may be caused by residual electrical interference, has been evaluated. Strain mapping, using the geometric phase methodology, has been applied to images acquired in an aberration-corrected STEM. This allows this distortion to be removed and so quantitative analysis of HAADF-STEM images was enabled. The distortion is quantified by applying this technique to structurally perfect and strain-free material. As an example, the correction is used to analyse an InAs/GaAs dot-in-quantum well heterostructure grown by molecular beam epitaxy. The result is a quantitative measure of internal strain on an atomic scale. The measured internal strain field of the heterostructure can be interpreted as being due to variations of indium concentration in the quantum dot.

The first paper on the FFT multislice method was published in 1977, a quarter of a century ago. The formula was extended in 1982 to include a large tilt of an incident beam relative to the specimen surface. Since then, with advances of computing power, the FFT multislice method has been successfully applied to coherent CBED and HAADF-STEM simulations. However, because the multislice formula is built on some physical approximations and approximations in numerical procedure, there seem to be controversial conclusions in the literature on the multislice method. In this report, the physical implication of the multislice method is reviewed based on the formula for the tilted illumination. Then, some results on the coherent CBED and the HAADF-STEM simulations are presented.