In situ electron microscopy methods

‘‘Seeing is believing’’ is perhaps the mantra of every in situ microscopist. The ability to observe the evolution of material microstructure and properties in real time provides insight into material processes and mechanisms often unobtainable by other means. Instead of performing experiments outside the microscope and then observing the samples post-mortem, in situ microscopy allows for direct observation of the dynamic behavior of materials under a variety of conditions. With advancements in spatial and temporal resolution, in situ experiments are increasingly able to provide fundamental information that can be correlated with models, used to develop and verify theories, and incorporated into new models to predict the microand macroscopic behavior of materials. Part of the magic of in situ microscopy is the shear breadth of experiments possible. To begin, electrons can be used to advantage for a variety of length scales, and can provide imaging, diffraction, and chemical information, from internal structures as well as surfaces, with very high resolution. Instruments such as transmission electron microscopes (TEM), scanning transmission electron microscopes (STEM), scanning electron microscopes (SEM), and low-energy electron microscopes (LEEM) are frequently chosen for in situ experiments. To expand their capabilities, these electron microscopes can be modified to introduce external variables such as magnetic fields, gaseous environments, laser pulses, or direct irradiation. Special sample holders or stages, which are truly small ‘‘laboratories,’’ provide further possibilities such as heating, cooling, straining, nanoindentation, applied electrical and magnetic fields, and liquid environments. Together, these elements combine to create the potential for studying almost any dynamic material event. The capabilities of the in situ field continue to grow, as microscope systems, stages, sample preparation methods, image processing techniques, and recording devices advance. For example, microand nano-electromechanical systems (MEMS and NEMS, respectively) and nanodevices have aided in the miniaturization of components, allowing for in situ stages to accommodate increasingly complex experiments, often with the ability to simultaneously collect quantitative data. In addition, techniques such as microand nano-lithography and the focused ion beam (FIB) have expanded the range of sample preparation methods and increased the number of approachable systems. Innovations such as these offer new opportunities for the scientific community to study the behavior of materials under specific processing and experimental conditions. This special issue of Microscopy Research and Technique features a collection of 17 papers, representing many of the recent advances and exciting new results at the frontier of in situ electron microscopy. Although not every application is represented here, we have strived to include papers over a wide range of topics to highlight the variety of experiments and quality of science emanating from the field today.