Present status and future prospects of spherical aberration corrected TEM/STEM for study of nanomaterials^∗

Abstract

The present status of Cs-corrected TEM/STEM is described from the viewpoint of the observation of nanomaterials. Characteristic features in TEM and STEM are explained using the experimental data obtained by our group and other research groups. Cs correction up to the 3rd-order aberration of an objective lens has already been established and research interest is focused on correcting the 5th-order spherical aberration and the chromatic aberration in combination with the development of a monochromator below an electron gun for smaller point-to-point resolution in optics. Another fundamental area of interest is the limitation of TEM and STEM resolution from the viewpoint of the scattering of electrons in crystals. The minimum size of the exit-wave function below samples undergoing TEM imaging is determined from the calculation of scattering around related atomic columns in the crystals. STEM does not have this limitation because the resolution is, in principle, determined by the probe size. One of the future prospects of Cs-corrected TEM/STEM is the possibility of extending the space around the sample holder by correcting the chromatic and spherical aberrations. This wider space will contribute to the ease of performing in situ experiments and various combinations of TEM and other analysis methods. High-resolution, in situ dynamic and 3D observations/analysis are the most important keywords in the next decade of high-resolution electron microscopy.

Study of PtPd Bimetallic Nanoparticles for Fuel Cell Applications

“…The correction of Cs is achieved by incorporating a separate aberration corrector, containing non-round elements, into the electron optical system to eliminate the Cs of the round objective lens. The Cs-correction allows the lens to be used with wider convergence angles of electron waves; thus, the probe size can be decreased according to the principle of Fourier transform, and probe current becomes larger than that in conventional STEM 28 . Using Cs-correction in a STEM instrument, it is possible to obtain atomic resolution of high-angle annular dark field (HAADF)-STEM images with high spatial resolution that can be used in the qualitative and quantitative Z-contrast analysis.…”

Efficient diffractive phase optics for electrons

“…Scanning transmission electron microscopy (STEM) has recently offered a large number of critical insights into the structure and behavior of materials at the atomic scale [1][2][3]. As a result of several decades of advancements in electron optics, modern STEM instruments use precisely controlled electric and magnetic fields to prepare angstrom-sized 60-300 keV electron probe beams with currents on the order of nano-amperes [4,5].…”

Image registration of low signal-to-noise cryo-STEM data

“…Imaging atomic structures with sub-angstrom resolution and sub-picometer precision is now possible in modern scanning transmission electron microscopes (STEMs). While advances in aberration correction have enabled subangstrom electron probes [1,2,3], making full use of these narrow electron beams has required optimizing the stability of the microscope, sample stage, and room environment [4]. To minimize the effect of any remaining mechanical, electromagnetic, thermal, and acoustic instabilities and to improve the signal-to-noise ratio (SNR) of the final image, a variety of post-processing algorithms have been developed, and have proven essential for high precision, quantitative STEM analysis [5,6,7,8].…”