Advances and Applications of Atomic-Resolution Scanning Transmission Electron Microscopy

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.

Phase Formation and Exchange Bias in LuFeO3–CoxFe3–xO4 Nanocomposite Films

“…Figure a and b show STEM images of the C1F2(90)–LF14(90) and C3(90)–LF06(90) nanocomposites, revealing a pillar and matrix geometry in the cross-section. As the contrast in the HAADF STEM images is approximately proportional to the atomic number, Z 1.7 , LFO appears brighter than CFO because of the heavy rare earth element Lu ( Z = 71) compared to Co ( Z = 27). The vertical microstructures revealed in cross-section are typical of vertically aligned nanostructures with a range of thicknesses. ,, …”

Accelerating Quantum Materials Development with Advances in Transmission Electron Microscopy

“…67−69 The three proposed pathways to circumvent the aberrations of static rotationally symmetric lenses include: (i) incorporating noncircular or multipole lenses that can cancel the positive C s aberration of the round lens by generating a negative C s value, (ii) deploying time-varying fields and (iii) inserting a charge on-axis. 67,70 In the 1990s, multipole correctors based on two designs of octupole/quadrupole and hexapole (sextupole) assemblies were successfully implemented and the first prototypes of C s aberration corrected EM were developed. 68,71−75 The invention of aberration correctors is considered a revolutionary step toward atomic-resolution imaging.…”

“…The aberrations, mainly spherical aberration ( C s ), chromatic aberrations ( C c ), in rotationally symmetric lenses are unavoidable (Scherzer’s theorem). In 1947, Scherzer proposed three major schemes to compensate for the aberrations, serving as a roadmap toward developing aberration corrected S/TEMs. − The three proposed pathways to circumvent the aberrations of static rotationally symmetric lenses include: (i) incorporating noncircular or multipole lenses that can cancel the positive C s aberration of the round lens by generating a negative C s value, (ii) deploying time-varying fields and (iii) inserting a charge on-axis. , In the 1990s, multipole correctors based on two designs of octupole/quadrupole and hexapole (sextupole) assemblies were successfully implemented and the first prototypes of C s aberration corrected EM were developed. ,− …”

Disentangling multiple scattering with deep learning: application to strain mapping from electron diffraction patterns

“…Scanning transmission electron microscopy (STEM) has emerged as one of the primary nanoscale materials characterization tools 1 . A STEM experiment focuses an electron beam on to a sample, with the probe dimensions ranging from tens of nanometers down to the atomic scale, which is made possible by hardware aberration correction 2,3 .…”