Studies of Mo/Si multilayers with coherent electron beams

Advances and Applications of Atomic-Resolution Scanning Transmission Electron Microscopy

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.

Measuring electrostatic potential profiles across amorphous intergranular films by electron diffraction

Amorphous 1-2-nm-wide intergranular films in ceramics dictate many of their properties. The detailed investigation of structure and chemistry of these films pushes the limits of today's transmission electron microscopy. We report on the reconstruction of the one-dimensional potential profile across the film from an experimentally acquired tilt series of energy-filtered electron diffraction patterns. Along with the potential profile, the specimen thickness, film orientation with respect to the grain lattice and specimen surface, and the absolute specimen orientation with respect to the laboratory frame of reference are retrieved.

Electron nanodiffraction

Electron nanodiffraction, particularly as performed in a dedicated STEM instrument with coherent illumination, provides, in principle, a means for obtaining information on structural detail in the range between that of STEM image resolution, about 0.2 nm, and the limits of information possible from elastic scattering from atoms, about 0. 03 nm. In practice, most nanodiffraction work has been concerned with finding the crystal structure, crystal defects, and sometimes crystal shapes for nanoparticles in the size range of 1-2 nm or for regions of thin crystalline films of about these dimensions. Available equipment allows for the recording of nanodiffraction patterns at the rate of 30 per second, or faster, providing means for detailed study of extended areas or of dynamical processes.