The articles in this issue of MRS Bulletin provide a sample of what is novel and unique in the field of in situ transmission electron microscopy (TEM). The advent of improved cameras and continued developments in electron optics and stage designs have enabled scientists and engineers to enhance the capabilities of previous TEM analyses. Currently, novel in situ experiments observe and record the behavior of materials in various heating, cooling, straining, or growth environments. In situ TEM techniques are invaluable for understanding and characterizing dynamic microstructural changes. They can validate static TEM experiments and inspire new experimental approaches and new theories.

Temperature is one of the most important factors affecting the state and behavior of materials. In situ heating transmission electron microscopy (TEM) is a powerful tool for understanding such temperature effects, and recently in situ heating TEM has made significant progress in terms of temperature available and resolution attained. This article briefly describes newly developed specimen-heating holders, which are useful in carrying out in situ heating TEM experiments. It then focuses on three main applications of these specimen holders: solid–solid reactions, solid–liquid reactions (including highresolution observation of a solid–liquid interface, size dependence of the melting temperatures of one-, two- and three-dimensionally reduced systems, size dependence of the contact angle of fine metal liquid, and wetting of Si with liquid Au or Al) and solid–gas reactions. These results illustrate the benefit of in situ heating TEM for providing fundamental information on temperature effects on materials.

There is a wide array of technologically significant materials whose response to electric and magnetic fields can make or break their utility for specific applications. Often, these electrical and magnetic properties are determined by nanoscale features that can be most effectively understood through electron microscopy studies. Here, we present an overview of the capabilities for transmission electron microscopy for uncovering information about electric and magnetic properties of materials in the context of operational devices. When devices are operated during microscope observations, a wealth of information is available about dynamics, including metastable and transitional states. Additionally, because the imaging beam is electrically charged, it can directly capture information about the electric and magnetic fields in and around devices of interest. This is perhaps most relevant to the growing areas of nanomaterials and nanodevice research. Several specific examples are presented of materials systems that have been explored with these techniques. We also provide a view of the future directions for research.

We review the development of time-resolved, high-resolution environmental scanning/ transmission electron microscopy [E(S)TEM] for directly probing dynamic gas–solid, liquid–solid, and gas–liquid–solid interactions at the atomic level. Unlike a regular TEM, such a microscope allows us to use high gas pressures (up to 40 mbars) in the sample region. The unique information available from experiments performed using E(S)TEM has enabled visualization of the dynamic nature of nanostructures during reactions. Such information can be directly applied to the development of advanced nanomaterials such as carbon nanotubes, silicon nanowires and processes, including the design of novel routes to polymers synthesis, and has aided in the identification of important phenomena during catalysis, chemical vapor deposition, and electrochemical deposition.

This article introduces the use of in situ high-resolution transmission electron microscopy (HRTEM) techniques for the study and development of nanomaterials and their properties. Specifically, it shows how in situ HRTEM (and TEM) can be used to understand diverse phenomena at the nanoscale, such as the behavior of alloy phase formation in isolated nanometer-sized particles, the mechanical and transport properties of carbon nanotubes and nanowires, and the dynamic behavior of interphase boundaries at the atomic level. Current limitations and future potential advances in in situ HRTEM of nanomaterials are also discussed.

The spatial resolution of the transmission electron microscope makes it an ideal environment in which to continuously track the real-time response of a system to an external stimulus and to discover and quantify the rate-limiting fundamental microscopic processes and mechanisms governing the macroscopic properties. Advances in instrumentation, stage design, recording media, computational power, and image manipulation software are providing new opportunities for not only observing the microscopic mechanisms but also measuring concurrently the macroscopic response. In this article, the capability of this technique as applied to mechanical properties of materials is highlighted.