ABSTRACT
At the end of 20th century, solving the problem of spherical aberration correction and realizing its potential in transmission electron microscopy (TEM) instrumentation caused a revolution in the field of EM. Such aberration-corrected microscopes made possible a great step toward the theoretical resolution limit for EM and are able to get point resolution of 50 pm (0.5 Å) in TEM mode. Also, in scanning transmission EM (STEM) the electron beam is focused to a fine probe (probe-corrected microscope) of less than 10 pm (<1 Å) and scanned over the sample having similar resolution (0.6 Å) in scanning mode. Combining the high-angle annular dark-field STEM (HAADF-STEM) and annular bright-field STEM (ABF-STEM) techniques together with simultaneously acquired spectroscopic techniques (EDX, EELS) made advanced TEM one of the most powerful, significant, and irreplaceable methods for materials characterization at an atomic level. In this chapter we are going to show examples of advanced TEM techniques to solve, discover new structures, and establish structure-property relationships in materials. A few examples of solving the structure of novel two-dimensional (2D) channels within Bi2-yVyV8O16 cubic hollandite and structure of CuInSe hexagonal flat nanoparticles by HAADF-STEM technique will be presented. Examples of complementary EDX and EELS elemental mapping in clathrate complex materials and complex perovskites also will be shown. The ability of two of these spectroscopic techniques will be discussed with an example of complex oxide structures. Discovery of new types of materials structures, such as quintuple perovskite, was possible thanks to applying HAADF-STEM, ABF-STEM, and EELS-STEM techniques. These techniques helped to establish chemical nanoscale ordering of Ln cations in quintuple perovskites Ln2Ba3Fe5-xCoxO15-δ, resulting in unconventional magnetism. Exceptional layered ordering of cobalt and iron in Y-Ba-Fe-Co-O complex perovskites was also discovered and is discussed in detail.
