In the scanning transmission electron microscope, multiple signals can be simultaneously collected, including the transmitted and scattered electron signals (bright field and annular dark field or Z-contrast images), along with spectroscopic signals such as inelastically scattered electrons and emitted photons. In the last few years, the successful development of aberration correctors for the electron microscope has transformed the field of electron microscopy, opening up new possibilities for correlating structure to functionality. Aberration correction not only allows for enhanced structural resolution with incident probes into the sub-Ångstrom range, but can also provide greater probe currents to facilitate mapping of intrinsically weak spectroscopic signals at the nanoscale or even the atomic level. In this issue of MRS Bulletin, we illustrate the power of the new generation of electron microscopes with a combination of imaging and spectroscopy. We show the mapping of elemental distributions at atomic resolution and also the mapping of electronic and optical properties at unprecedented spatial resolution, with applications ranging from graphene to plasmonic nanostructures, and oxide interfaces to biology.

By measuring the energy losses of high-energy electrons transmitted through a thin sample, electron energy-loss spectroscopy provides information on the local electronic structure in materials. Using electron beams smaller than 0.1 nm, the technique provides exquisite sensitivity to changes in valence and coordination of the excited atoms such that local changes in the bonding environment are probed with a resolution approaching the Ångstrøm level, with an energy resolution competitive with complementary techniques such as x-ray absorption spectroscopy. With the development of spectroscopic imaging in the scanning transmission electron microscope, this technique can be used to map, at the atomic level, the composition of atomic columns and the valence of atoms at defects, interfaces, and surfaces. Recent applications of this technique are provided as examples showing the potential of the method for materials research.

The success of the correction of spherical aberration in the electron microscope has revolutionized our view of oxides. This is a very important class of materials that is promising for future applications of some of the most intriguing phenomena in condensed matter physics: colossal magnetoresistance, colossal ionic conductivity, high Tc superconductivity, and ferroelectricity. Understanding the physics underlying such phenomena, especially in low dimensional systems (thin films, interfaces, nanowires, nanoparticles), relies on the availability of techniques capable of looking at these systems in real space and with atomic resolution and even beyond, with single atom sensitivity; in many cases, the system properties depend on minuscule amounts of point defects that alter the material’s properties dramatically. Atomic resolution spectroscopy in the aberration-corrected electron microscope is one of the most powerful techniques available to materials scientists today. This article will briefly review some state-of-the-art applications to oxide materials: from atomic resolution elemental mapping and single atom imaging to applications to real systems, including oxide interfaces and mapping of physical properties such as the spin state of magnetic atoms.

Identifying constituent atoms in materials is the ultimate goal for all analytical techniques. Here, we describe the successful achievement of single atom spectroscopy in nanostructured carbon-based materials using a scanning transmission electron microscope equipped with electron energy-loss spectroscopy. The chemical analyis of individual metallofullerene molecules can be successfully performed without massive beam damage. Atom-by-atom spectroscopy of the edge carbon atoms in single layer graphene is also discussed.

The possibility has recently been reported of using spatially resolved electron energy loss spectroscopy and cathodoluminescence in scanning (transmission) electron microscopes to probe optical excitations—plasmons, photons, excitons—at a scale that could not have been considered only a few years ago. This allows these excitations to be studied at the relevant scale for the characterization of novel materials with potential applications in nanophotonics and nanoplasmonics. This review aims at describing the state-of-the art experimental and theoretical techniques of this emerging field and its major uses and applications.

We review the recently introduced technique of atomic-resolution chemical mapping in scanning transmission electron microscopy (STEM) based on energy-dispersive x-ray spectroscopy. Working at the atomic level is facilitated by ultrasensitive energy-dispersive x-ray detectors in combination with Cs-correction of the STEM probe. Details of the experimental implementation are discussed, and a theoretical framework within which the measured results can be understood is described. Three case studies are presented: the analysis of specimens of GaAs and SrTiO3, as well as examination of an interface between SrTiO3 and PbTiO3. Detailed theoretical simulations of the imaging process show that the projected positions of elements in atomic columns can be directly deduced from the chemical maps. For the core shells used, the effective ionization interaction is local and generally localized in the vicinity of the atoms being ionized. The local nature of the effective ionization potential means that this is an incoherent mode of imaging, akin to Z-contrast imaging but with additional chemical information.

The high sensitivity of electron energy-loss spectroscopy (EELS) for detecting light elements at the nanoscale makes it a valuable technique for application to biological systems. In particular, EELS provides quantitative information about elemental distributions within subcellular compartments, specific atoms bound to individual macromolecular assemblies, and the composition of bionanoparticles. EELS data can be acquired either in the fixed beam energy-filtered transmission electron microscope (EFTEM) or in the scanning transmission electron microscope, and recent progress in the development of both approaches has greatly expanded the range of applications for EELS analysis. Near single atom sensitivity is now achievable for certain elements bound to isolated macromolecules, and it becomes possible to obtain three-dimensional compositional distributions from sectioned cells through EFTEM tomography.

Colloidal nanocrystals can combine the benefits of inorganic semiconductors with size-tunable electronic structure and inexpensive solution-based device fabrication. Single- and multicomponent nanocrystal assemblies, also known as superlattices, provide a powerful general platform for designing two- and three-dimensional solids with tailored electronic, magnetic, and optical properties. Such assemblies built of “designer atoms” can be considered as a novel type of condensed matter, whose behavior depends both on the properties of individual building blocks and on the interactions between them. Efficient charge transport is crucial for applications of nanocrystal-based materials in various electronic and optoelectronic devices. For a long time, nanocrystals were considered poor electronic conductors. To facilitate charge transport, we developed novel surface chemistry using all-inorganic ligands, namely metal chalcogenide complexes that transformed colloidal nanomaterials into a very competitive class of solution-processed semiconductors for electronic, thermoelectric, and photovoltaic applications.