Transmission Electron Microscopy

Abstract

Abstract Transmission electron microscopy (TEM) is the premier tool for understanding the internal microstructure of materials at the nanometer level. It allows one to obtain real‐space images of materials with resolutions on the order of a few tenths to a few nanometers, depending on the imaging conditions, and simultaneously obtain diffraction information from specific regions in the images (e.g., small precipitates). Variations in the intensity of electron scattering across a thin specimen can be used to image strain fields, defects such as dislocations and second‐phase particles, and even atomic columns in materials under certain imaging conditions. In addition to diffraction and imaging, the high‐energy electrons (usually in the range of 100 to 400 keV of kinetic energy) in TEM cause electronic excitations of the atoms in the specimen. Two important spectroscopic techniques make use of these excitations by incorporating suitable detectors into the transmission electron microscope, energy‐dispersive x‐ray spectroscopy (EDS), and electron energy loss spectroscopy (EELS). Nanometer‐scale chemical compositional analysis can be performed by using a focused electron probe. Spatial distribution of elements can be obtained by scanning the probe over the specimen, or by energy‐filtered imaging, a special mode in advanced EELS spectrometer. The recent advancements in aberration‐correction technologies have improved the image resolution and probe size to sub‐Ångstrom level, and current density in the probe is increased by an order, which catalyze the emergence of new contrast theories and microanalysis techniques. Many other analyses are also possible in TEM with the development of novel detectors.