Abstract
Although scanning transmission electron microscopy (STEM) images of individual heavy atoms were reported 50 years ago, the applications of atomic-resolution STEM imaging became wide spread only after the practical realization of aberration correctors on field-emission STEM/TEM instruments to form sub-Ångstrom electron probes. The innovative designs and advances of electron optical systems, the fundamental understanding of electron–specimen interaction processes, and the advances in detector technology all played a major role in achieving the goal of atomic-resolution STEM imaging of practical materials. It is clear that tremendous advances in computer technology and electronics, image acquisition and processing algorithms, image simulations, and precision machining synergistically made atomic-resolution STEM imaging routinely accessible. It is anticipated that further hardware/software development is needed to achieve three-dimensional atomic-resolution STEM imaging with single-atom chemical sensitivity, even for electron-beam-sensitive materials. Artificial intelligence, machine learning, and big-data science are expected to significantly enhance the impact of STEM and associated techniques on many research fields such as materials science and engineering, quantum and nanoscale science, physics and chemistry, and biology and medicine. This review focuses on advances of STEM imaging from the invention of the field-emission electron gun to the realization of aberration-corrected and monochromated atomic-resolution STEM and its broad applications.
Highlights
Human beings have long been, and will continue to be, fascinated by Nature and how it works
The use of an field-emission gun (FEG) for scanning transmission electron microscopy (STEM) imaging had been unambiguously proved successful, especially for applications in imaging biological systems stained with heavy metal atoms or clusters
Krivanek et al (2003) described a new design of a quadrupole/octupole corrector to correct all fifth-order aberrations while still keeping a small CC value. They proposed that when such a corrector is coupled to an optimized STEM column, sub-Ångstrom probe sizes would be obtainable at 100 kV and sub-0.5 Å probes would be achievable at higher operating voltages
Summary
Human beings have long been, and will continue to be, fascinated by Nature and how it works. The continuous improvement in telescopes has vastly expanded our knowledge of the Universe, while the development of various types of microscopes has enabled us to directly observe bacteria, viruses, molecules, and even individual atoms The invention of both the telescope and the microscope has unlocked countless mysteries of Nature and enabled numerous discoveries that have positively impacted our daily life. The practical realization of the correction of lens aberrations to routinely achieve sub-Ångstrom image resolution with picometer precision and high chemical sensitivity greatly enhanced the impact of STEM and associated techniques on many research frontiers Such an accomplishment has revolutionized how we understand matter at the atomic level and will have a tremendous impact on how we understand Nature. The requirement of maintaining a high vacuum within an electron microscope, in contrast to light microscopes, and the strong interaction between charged particles and matter impose significant limitations on practical applications of the various types of electron microscopes
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