Instrumental requirements for the detection of electron beam-induced object excitations at the single atom level in high-resolution transmission electron microscopy

Abstract

This contribution touches on essential requirements for instrument stability and resolution that allows operating advanced electron microscopes at the edge to technological capabilities. They enable the detection of single atoms and their dynamic behavior on a length scale of picometers in real time. It is understood that the observed atom dynamic is intimately linked to the relaxation and thermalization of electron beam-induced sample excitation. Resulting contrast fluctuations are beam current dependent and largely contribute to a contrast mismatch between experiments and theory if not considered. If explored, they open the possibility to study functional behavior of nanocrystals and single molecules at the atomic level in real time.

Observing Atoms at Work by Controlling Beam–Sample Interactions

“…Indeed, an electron-beam-induced amorphization of small particles occurs commonly, even if moderate beam currents are used, because the energy deposited by the electron beam easily exceeds the total binding energies of nanoparticles 3-4 nm in size. [ 11 ] Finally, the electron exit wave function is available, which allows single images to be recalculated at any focus value (Figure 2 g) that can be directly compared with the initial recording in Figure 2 a. This comparison also indicates the large contrast enhancement obtained by reconstructing the electron exit wave function from 50 images, which not only maintains the targeted resolution and single-atom sensitivity, but also helps to preserve the genuine structure of radiation-sensitive objects.…”

“…It is available at the Molecular Foundry, which houses the two TEAM microscopes that allow a Nelsonian illumination scheme to be set up using Wien fi lter monochromators for imaging. [ 11 ] First, benefi ts are described by contrasting the new approach with traditional practices using nanoparticles. Consider gold particles of various sizes that are dispersed on an amorphous carbon support, as shown in Figure 2 .…”

“…[ 11,12 ] Our approach addresses this shortcoming by using a Nelsonian illumination scheme that eliminates any uncontrolled sample irradiation in broadbeam mode [ 11 ] and allows dose rates as low as attoamperes per square-Ångstrom to be worked with, which were found to delay sample degradation and improve image contrast. [ 15 ] Its effect on image contrast is depicted in Figure 2 d-g, which show a second set of previously unexposed gold particles on the carbon support.…”

“…Post-acquisition, the images were aligned with sub-pixel accuracy and reconstructed to obtain the complex electron exit wave function, which is a smart averaging scheme that boosts image contrast, solves the phase problem, and creates an in-line hologram. [ 11 ] Atom column positions are marked by contrast maxima in the phase image of the in-line hologram. In addition, it is straightforward to probe for …”

“…0.5 Å) with electron beams of voltages in the range between 20 kV and 300 kV. [ 10,11 ] Clearly, the majority of advanced applications already benefi ts greatly from aberration-corrected electron microscopy by decoding the electronic and atomic structure of matter together with its chemical composition at the level of single atoms in broad-beam and scanning electron microscopy (see for example ref. [ 12 ] , and they will steadily grow.…”