Atomic imaging using secondary electrons in a scanning transmission electron microscope: Experimental observations and possible mechanisms

Abstract

We report detailed investigation of high-resolution imaging using secondary electrons (SE) with a sub-nanometer probe in an aberration-corrected transmission electron microscope, Hitachi HD2700C. This instrument also allows us to acquire the corresponding annular dark-field (ADF) images both simultaneously and separately. We demonstrate that atomic SE imaging is achievable for a wide range of elements, from uranium to carbon. Using the ADF images as a reference, we studied the SE image intensity and contrast as functions of applied bias, atomic number, crystal tilt, and thickness to shed light on the origin of the unexpected ultrahigh resolution in SE imaging. We have also demonstrated that the SE signal is sensitive to the terminating species at a crystal surface. A possible mechanism for atomic-scale SE imaging is proposed. The ability to image both the surface and bulk of a sample at atomic-scale is unprecedented, and can have important applications in the field of electron microscopy and materials characterization.

The correction of electron lens aberrations

“…Electron holography continues to benefit from aberration correction (for which Dennis Gabor originally invented it) and the realisation that an aberration corrector can be thought of as a phase plate [40] is having repercussions on, for example, electron vortex beam studies. Zhu et al [212] and Inada et al [75] have succeeded in obtaining high-resolution secondary electron images in a corrected STEM equipped with a suitable detector; the latter paper includes a very clear diagram of the microscope column (see too Inada and Zhu [72]). …”

High Speed and Sensitive X-ray Analysis System with Automated Aberration Correction Scanning Transmission Electron Microscope

“…EV3000 has two kinds of detector, one is for spectrum and another is three-channel photo-multipliers for direct element observation using an electro-magnetic prism (Kaji et al, 2001;Isakozawa et al, 2008). In addition to STEM imaging, the HD-2700 including an aberration-correction device performs SE imaging with atomic-level resolution, and also elemental analysis, mapping of the chemical bond statuses, etc., it can collect information from specimens in a versatile manner, and it dramatically improves analysis performance (Zhu et al, 2009;Inada et al, 2011aInada et al, , 2011bInada & Zhu, 2014).…”

“…We have developed as a product an electron microscope the performance of which is dramatically increased by inclusion of a sphericalaberration-correction function (Inada et al, 2009a(Inada et al, , 2009b. In addition, the application of new aberration-correction techniques, such as atomic-resolution secondary-electron (SE) imaging, is now being investigated (Zhu et al, 2009;Inada et al, 2011aInada et al, , 2011bInada & Zhu, 2014). Scherzer (1947) proved that combinations of rotationally symmetrical electromagnetic lenses had convex lens effects only, and the spherical aberration coefficients were always positive.…”

TEM Characterization of Metallic Nanocatalysts

“…A STEM-SEM image has a comparable spatial resolution with the simultaneously taken ADF-STEM images, although it has high noise. A possible mechanism for atomic-scale SEM imaging is proposed [74]. Although the technique is still under development, the ultrahigh-resolution SEM technique potentially could be important for identifying the surface structure of nanoparticles.…”